studies on barrel type carbonizer
TRANSCRIPT
STUDIES ON BARREL TYPE CARBONIZER
FOR CARBONAIZATION
OF
SUGAR CANE TRASH
Introduction
Energy is a key factor in terms of both economic development and climate
change. Integrated energy supply systems involving the use of all renewable forms of
energy like solar, wind, biomass, biogas, geothermal, etc. have to be developed. Other
opportunities like hydrogen and nuclear energy will have to be integrated into an overall
sustainable energy security system.
The adverse impact of the steep rise in energy cost has multiple dimensions. First,
land and crops are being diverted from food to fuel production in many countries. For
example one forth of total maize production and 20 % of soybean oil production now go
for ethanol and bio-fuel manufacture in the United States. The bio diesel industry used
last year 60 % .of the rapeseed output in European Union. Because of the use of maize
for ethanol production, larger quantities of wheat are being diverted for feeding animals.
The export price of wheat which stood at$381 per tones in January 2008, climbed to$449
per tones in Feb 2008.
Agriculture produces not only economically useful products but also a lot of
waste material. In the case of grain crops, be it cereals, oilseeds or pulses, only about 30
to 40 % of the total biomass is in the form of grain, while the rest, called Stover, is
basically useless. Stalks of some cereals are used as cattle fodder, but they serve more as
fillers rather than as nutrition. Woody material such as stalks of cotton or pigeon pea is
burned directly in a cook stove, but that too is a very low quality fuel, producing a lot of
soot and smoke.
About 20 years ago, a briquette process was introduced into India, for
compressing light biomass into fuel pellets or briquettes, which could substitute wood.
Agricultural waste consists of highly lignified material. When such material is
compressed, the compression generates heat, which melts the lignin, which in turn holds
the particles of biomass together. The briquettes produced by the process burn just like
wood, and therefore the users were not willing to pay a higher price for them than that of
wood. But because the pressure required in this process was very high, use was made of
very heavy machinery and high energy. The raw material required for this process,
Agricultural waste, is scattered all over the countryside. Its low density and wide
distribution made it very costly to collect and transport it to a central briquette unit. As a
result of the high cost of machinery high energy requirement of the process and high cost
of collection and transport of the raw material the process turned out to be uneconomical
and it was therefore abandoned.
The scientists used the same raw material but instead of compressing the
unprocessed agricultural waste into briquettes they first converted the material into
charcoal and made briquettes out of the charcoal. The key to this process was the charring
kiln. In a traditional charcoaling kiln the entire material to be charred is enclosed in the
kiln and ignited. The air supply to the burning material is regulated in such a manner that
only a part of it burns and the heat generated by the burning material chars the rest of the
material. Most materials of the plant origin consist of about 70% volatile material. When
heated to temperatures above 2500C this volatile material escapes from the biomass. The
non-volatile part that remains behind is the charcoal. This separation of the biomass into
volatile and non- volatile parts is called pyrolysis.
When wood or woody biomass is used as household fuel part of the volatile
material burns producing the typical yellow flame but the volatile do not burn completely
so that a part of them also produce smoke which contains tar benzapyrenes, acetone etc.
some of the volatiles also condense on the walls and on the vessels as soot. If the smoke
is inhaled it can cause cancer because of the tar and the benzapyrenes in them therefore
wood fire is considered to be environmentally polluting. Charcoal on the other hand
consists mainly of carbon. When charcoal burns it just glows but it does not produce a
flame because it does not have any volatile in it. The combustion product of charcoal is
carbon dioxide and ash neither of which is harmful.
The traditional charcoaling kiln could not however be used for producing
charcoal from low density biomass because the charcoal from such material crumbles
under moderate pressure and once it gets mixed with ash it becomes very difficult to
separate the ash from the coal powder. In addition the conventional charcoaling process is
environmentally polluting because the volatiles produced in the process are released into
the atmosphere. The biomass is filled into metallic barrels with tightly fitting lids. The
lids have one hole each. These barrels are loaded upside down into upper compartment of
the kiln and a small fire is built in the lower compartment underneath the barrels. The
heat of the fire gasifies the volatile part of the biomass and the gas escapes from the holes
in the lid and burns underneath the barrels adding heat to complete the process of
pyrolysis. Because the biomass is enclosed in barrels it does not come in contact with
oxygen and therefore it does not burn and also des not produce any ash. One can thus get
pure charcoal without admixture of ash. Also because the volatiles are burned in the kiln
itself this process of charcoal is less polluting than the traditional charcoaling process.
Technically this type of kiln is called an oven-and-retort kiln. This required
standardization of the size of the barrels as well as of the height of the kiln so that the
barrels could be easily loaded and unloaded manually by a single person. The kiln
accommodated 7 barrels at a time. In order to save time between consecutive batches one
uses 14 barrels so tar while one set of the barrels is being pyrolysed another set is filled
with fresh biomass and kept ready it takes about 40 min. to pyrolyse one load and each
load produces about 7kg charcoal. Thus a team of two or three workers working from
sunrise to sunset can complete about 15 batches and produce about 100 kg charcoal daily.
Survey of the world
1.1 Sugarcane trash as raw material :-
Although this process can be used for charring any biomass the most abundantly
available agricultural residue in Maharashtra is represented by dry leaves of sugarcane
called sugarcane trash. This is the material that is left behind in the field after sugarcane
has been harvested. The leaves are highly lignified and rich in silica. Therefore they are
useless as cattle fodder the leaves are about a meter long and because they interfere with
all subsequent agricultural operations in the field the farmer just burn them in the field
itself. Each hectare of sugarcane produces about 10 tones of trash. Maharashtra has
450,000 hectares under sugarcane cultivation and therefore one can estimate that about
4.5 million tones of trash are just burned in the field every year. By using the process
described above it is possible to convert this trash into charcoal. Taking into
consideration the small amount of trash that would be burned as fuel in kiln sugarcane
trash has the potential of producing annually 900,000 tones of charcoal in Maharashtra.
As stated above this charcoal crumbles into powder under moderate pressure. The
powder is mixed with a binder such as starch paste and extruded into briquettes. The
briquettes have a calorific value of about 5000 to 5500 kcal/kg and they burn cleanly just
like charcoal.
1.2 Economic Considerations :-
The sugarcane harvesting period in Maharashtra extends over about 25 weeks .A
family can produce about 15 tones of charcoal in this period. The work of charring is
carried on for 6 days in a week. On the seventh day they operate the extruder and convert
the char into briquettes which are spread on the ground to dry under open sky. It takes the
next 6 days for the briquettes to dry during which period the next lot of charcoal is
produced. One kiln would require the trash from about 7 hectares which would be easily
available in any village in the sugarcane growing region. The process is economically
viable. Only if it is operated on a family scale by a farmer. Farmers do not take any salary
for themselves. Also at this scale there are no overheads like salaries of watchmen,
managers or accountants. There is also no expenditure on insurance.
The raw material is free of cost. Therefore whatever price the farmer gets for his
briquettes represents net profit for him. We have recommended a price of rs.5 per kg for
the briquettes based on which a family operating a single kiln can earn about us. 75,000
during this period which is a very good income for a rural family.
1.3 Marketing the briquettes:-
About 60 years ago charcoal was the preferred domestic fuel in the cities. But
about because charcoal is made from tree trunks and branches. Government of India
made kerosene available to the citizens at a very low cost in order to save trees. But about
2 years ago the subsidy on kerosene was withdrawn so that kerosene that used to cost
about Rs. 4 /liter now costs about Rs. 13 per liter. The urban poor, who were dependent
on kerosene’s their domestic fuel have now reverted back to using charcoal and wood.
The briquettes manufactured by our process can be used as domestic fuel because they
burn cleanly without producing smoke or soot. To use this fuel more rationally, The Sarai
system today costs about Rs. 550 but the price would come down to about Rs.300/ piece,
if the system is mass produced. It is estimated that a family would required about 400 g
of briquettes per day costing about Rs. 750 to 1000. Those families that use kerosene told
us that they required one liter per day.
1.4 Benefits of using char briquettes:-
This process uses a raw material that has no other use and which is traditionally
just burned in the field itself. The raw material is renewable. The charring process is
environmentally cleaner than the traditional charcoaling process. The process has the
potential of generating annually Rs. 45 billion in the rural areas of Maharashtra. It
provides the urban poor with a cleanly burning, renewable and cheap domestic fuel. The
use of fuel would reduce the pressure on wood charcoal, which in turn would save our
forest wealth.
1.5 Fuel briquettes from light Agro waste:-
Because most agricultural species are herbaceous agricultural waste is generally
in the form of leaves and thin stems. The act of threshing also results in generating
powdery agro waste. Agro waste in these forms cannot be used as fuel in a wood burning
stove but it can be converted into charcoal briquettes by using a charring kiln based on
the oven and retort system. The charcoal produced in this kiln is powdered mixed with a
suitable binder and extruded into char briquettes.
Sarai stove-cooker system:-
User friendly biogas technology and the traditional biogas technology based on
cattle dung are useful only to families having at least 6 to 8 heads of cattle. Because of
the low rate of gas generation /unit mass of dung and long retention time of about 40 days
the smallest domestic digester has a volume of about 2000litres. Feeding daily about
40kg cattle dung into the digester and disposing of daily about 80kg of effluent slurry is a
great bother. The new biogas plant developed by ARTI is much more users friendly.
Having a capacity of 1000litres it uses daily just 2kg of starchy agro waste( e.g. rhizomes
of banana , cannas, nut grass), non-edible seeds (e.g. Luciana, Sesbainia , tamarind,
mango, kernels, spoilt grain) oilcake of no edible oilseeds (pongamia, madhuka, castor)
or leftover food. Its reaction time is fast just a few hours. It produces just a couple of
liters of watery effluent that is easy to dispose of.
CHAPTER - II
EXPERIMENTAL WORK
BIOMASS POTENTIOAL AND CONVERSION
The reason for utilizing biomass and bio-wastes as energy sources are
numerous. Some of the obvious ones are,
1. Non fossil forms of fixed carbon are not deplete able in contrast to fossil
fuels such as oil, natural gas and coal.
2. Biomass is available in large quantities and in large quantities and
provides a raw material for conversion to synfuels.
3. Combining agro-waste disposal and energy recovery, process offers
recycling opportunities as well as improved disposal technology often at lower cost.
4. The synthetic fuel industry based on biomass is independent of foreign
price controls and regulations.
5. Technological breakthrough is not required for developing commercial
systems and processes.
6. Biomass can be regenerated.
2 .1 : BIOMASS POTENTIAL:
Biomass can be classified into three groups:
1. Land Based Biomass : Trees, Plants and Grass.
2. Water Based Biomass : Single Cell algae, multi-cell algae and aquatic
plants.
3. Bio-Residue : Agricultural residue, manure, urban refuse, wood
waste from Industries, industrial and municipal sewage etc.
Forests are often in remote or inaccessible location making it uneconomical to
extract wood purely for energy purpose unless retail value is high. This economical
difficulty could be substantially decreased by combining the harvesting of wood for
timber and for energy purpose. Logging operations produce large quantities of residues
(branches, stumps, thinning and diseased wood) which can account for up to one- third of
the total timber that is cut. Much of this residue is currently wasted, but if converted to
charcoal or producer gas, for example, could provide a substantial quantity of energy. It
is estimated that the worlds annual use of energy is only 1/10 th of the annual
photosynthesis energy storage
2 .2 : CROP RESIDUES AND WASTES :
Wastes are materials for which no application has yet been found, whereas
residues are often of value for a number of applications. For example, agricultural
residues and manure are often returned to the soil as fertilizer and to omprove soil
structure. About 0.3 – 0.8 tonnes/acre of residue is essential for supplying nutrients and
organic matter [ 2 ] for development of plant.
In agricultural production there are residues which could be utilized in several
ways : as fodder, land supplements, fibre and fuel. The potential of these residues has not
been systematically analysed so quantity is calculated via. Estimates of the ratio of by-
product to main crop yield for each crop type from the relation between main crop and
by-product . Table – I shows relation of main product to by-product for different
agricultural [ 3 ].
TABLE -I : RELATION OF MAIN PRODUCT TO BY-PRODUCT
FOR DIFFERENT AGRICULTURAL CROPS
Product Main Product By-Product Ratio of
Main product
to By-Product
Rice Grain Straw 1:1.4
Sorghum Grain Straw 1:1.4
Barley Grain Straw 1:1.2
Wheat Grain Straw 1:1.3
Maize Grain Straw 1:1.0
Bean Grain Straw 1:2.1
Peanut Nut Stalk 1:1.0
Sugarcane Sugar Bagasse 1:1.16
Table –II shows the potential of the Bio-residue for generating energy [4]. Table –
II shows that 31, 33745 x 10 tones of agricultural residue is available for energy
production in the world. Asia has an annual residue potential of 1.4 Gt which is about
44% of the total agricultural residue in the world. Africa and Latin America produce far
less residue.
Table - II: AGRICULTURAL RESIDUES IN WORLD
(10 3 TONNES/YEAR)
Product/
Country
Africa Asia Latin
America
North
America
Europe USSR Oceania World
Wheat 12047 229085 27195 124970 167970 98800 24538 678187
Rice 12015 6064476 23586 11929 2743 10 921 657943
Maze 22201 10157 51742 218437 60264 13000 549 449225
Sorghum 12603 30502 22793 41083 770 280 2639 100377
Sugar-cane 9592 48835 64746 25280 49 ---- 4226 131008
Barley 4398 19182 1482 28651 95342 5460 7271 205962
Peanut 3832 13840 846 2196 24 2 60 20611
Other
Residues
85672 318834 85482 136753 137345 19609 6882 890402
About 32.5 x 1010 J useful energy can be obtained from the biomass residues. All
residues shown in Table – II can be best utilized for heat generation since that is the
application for which conversion efficiency is highest.
There are various estimates of the total quantum of biomass available in our
country. Table – III shows the potential of the annual agricultural waste in INDIA [5]
TABLE – III: AGRICULTURAL RESIDUES IN INDIA
Statistical Data of Total Biomass available in Million tons:-
Type of Crop Agricultural Waste Estimated
Rice Husk 9.00
Timber Saw Dust 0.12
Maize Cobs 1.80
Groundnut Shell 1.80
Cotton Stalk 0.50
Pulses Stalk 1.00
Sugarcane Bagasse 14.50
Toppings 14.50
TOTAL 43.22
Approximately about 40 million tones of biomass can be used for energy
conversion. The study focuses attention on two of these biomass residues namely
sugarcane trash and sawdust.
Sugarcane growing countries produce a considerable amount of biomass residue
in the form of sugarcane trash green tops leaves, and bagasse. With depletion of resources
of fossil origin, the importance of these materials is growing especially because of their
renewable nature.
In developed countries, dry sawdust is used as heat insulator in walls and attics of
buildings and as absorptive material in floor sweeping compounds. As a source of
energy, this waste material has been traditionally used for domestic cooking and as fuel
in boilers. On account of their extremely small particle size, they need special types of
stoves and burners for effective and efficient utilization.
In sawmilling operation, sawdust accounts for 16% of the total gross volume of
logs processed. The study therefore concerns the design, development and fabrication of
low cost and efficient equipment and a process of continuously converting sawdust into
useful fuel gas.
2 -3 : BIOMASS CONVERSION :
Process for conversion of biomass to useful energy is divided generally into two
categories.
1. Biochemical
2. Thermochemical
2.3.1 : BIOCHEMICAL CONVERSION :
The complex structure of biomass can be
exploited by the use of living biological systems. The use of bacteria and yeasts in
aqueous suspension called fermentation is the principle technique. Ethyl alcohol, citric
acid from molasses and antibiotics from various nutrients are examples of chemicals
produced by fermentation. Among other product, gases from anaerobic digestion and
caustic or iron sponge digestion. The major environmental problem with anaerobic
digestion is the effluent form the digester. The digestion process removes carbon,
hydrogen and oxygen preserving the lignin and lignin protected organics, microbial
organics and mainly soluble in organics.
Anaerobic digestion requires wither temperature of 30 to 37 deg. C for
mesophillic bacterial or temperature of 49-51 deg C for thermophillic bacterial [ 6 ].
Product gases are methane (60%) and carbon dioxide (40%). Due to presence of CO2, the
BTU value of the gas is low which can be increased by removing CO2.
Anaerobic digesters are capital intensive and require considerable advancements
in crop quality and conversion using low cost biotechnologies includes to meet bio-
energy industry requirements. Anaerobic digestion includes a complex biological process
that requires sophisticated controls, safety precautions and care in end use adaptations.
Fermentation technique is most suitable for the product containing low percentage
of lignin.
2.3.2: THERMOCHEMICAL CONVERSION
There are four different ways of thermo-chemical conversion.
a. Pyrolysis
b. Gasification
c. Liquidification
d. Direct Combustion.
PYROLYSIS:-
This process occurs along a continuum of controlled oxygen supply,
temperature and time of reaction. The products from these processes are various mixtures
of solids, liquids and gases. Pyrolysis is nothing but a thermal decomposition of organic
matter in vacuum or in an inert atmosphere. Pyrolysis of biomass readily occurs at
temperatures above 250o C. For biomass having size greater than 1 cm, the rate of
pyrolysis is controlled by the rate at which heat is conducted through the biomass. The
various by-products of the biomass are:
1) Char about 30-35 %
2) Gases about 15-20 %
3) Pyroligeneous liquids about 35650 %
On a short term basis, pyrolysis can only be envisaged a basic reaction for
processes leading to energy products such as natural gas and fuel oil substitutes and
charcoal. Quality of charcoal products depends on its chemical and physical properties.
These are highly related to the raw material, tree species and operating condition of the
pyrolysis process.
GASIFICATION: -
The aim of gasification is to transfer the combustion value of the
solid fuel to a gaseous energy carrier preferably in the form of chemical energy.
Gasification is performed because of the advantage of a gas over a solid fuel. Gases arer
easy to clean, transport and combust with a low excess o air and there is little resulting
pollution.
Char gasification is relatively slow at temperatures below about 8000 C. Reactions
between char and H2O or CO2 are strongly endothermic hence energy requirement are
usually met b injecting O2 and sacrificing reactants. Gas solid surface reactions are
important in the operating range of 750o C to 1000 o C.
The gas consists of mainly CO, H2, N2, CO2, steam and hydrocarbons. The
combustion of the gas varies widely with the properties of the biomass, gasifying agent
and the process conditions. Heating value of gas vary between 3 and 33 MJ/Nm3. when
the biomass contains more water, more gasifying agent (air or O2) is necessary because
water must be heated up and evaporated. A producer gas from biomasses contains
relatively high quantities of steam, hydrogen and nitrogen compared to a producer gas
from dry biomass.
If a reasonable gas quality is to be produced, depending on the reactor type,
moisture content upto 30-50 % on a wet basis is admissible. If air is the gasifying agent,
the producer gas contains 40-60 % of N2. This can be decreased by using O2 or
O2enriched air.
LIQUIFICATION :-
The liquid product is obtained after gasification is done under
high pressure and low temperature. Relatively high yields of liquids are obtained. The
liquid fraction resulting from the process is a complex mixture of hydrocarbons. Many of
these are known to be carcinogenic which are otherwise serious pollutants. The liquid
produced in large scale gasifiers are injected into the boilers system and combusted.
DIRECT COMBUSTION:-
Direct combustion is highly desirable conversion process
for biomass. Currently this process applied mainly to wood, straw and municipal solid
waste. This is a complex chemical process which is governed by fuel properties such as
proximate and ultimate analysis, higher heating value, moisture content, and specific
gravity. Process involves at a gross level, fuel particle heating and drying, pyrolysis, gas
phase reactions and gas solid reactions.
Biomass combustion can be reasonably efficient. With first thermodynamic law,
system efficiencies of 68-79 % can be achieved depending upon fuel moisture content,
combustor design, and combustor operation.
Flame temperature of 1100-1480o C can be achieved when combustion is
accomplished with low levels of excess air.
2.4 THERMOCHEMICAL ROUTE FOR SUGAR CANE TRASH
AND SAWDUST
2.4.1: PYROLYSIS OF SUGAR CANE TRASH
Sugar cane trash is generally left in the
field except for a minor amount collected as folder for ruminants. The ratio of sugar cane
trash to cane stalk depends heavily on cane variety and may be roughly estimated as 0.30
+/- 0.05. Since sugar cane trash contains about 75% of volatile matter, thermo-chemical
method is most suitable for utilization of trash.
Barrel type continuous carbonizer, a laboratory model is designed and fabricated
for carbonization of pulverized trash. Capacity of this unit is 1 kg/hr. Yields are volatiles
and powered charcoal. Volatile can be burned to sustain the process.
2.4.2: GASIFICATION OF SAW DUST
Numbers of agricultural residues have thickness less than 1.mm can be reduced in
size with simple pulverizes. These are termed as light biomass and are found suitable for
fast pyrolysis.
A laboratory, compact and economical, unit heated tube gasfier, is designed and
developed. The unit consists of a vertical ceramic tube and hopper for feeding saw dust at
the upper end of ceramic tube. Sawdust is fed through the ceramic tube which passes
closely to the wall of ceramic tube. Air required for the gasification is passed in the
ceramic tube at the upper end. Saw dust is controlled by feeder passes through a ceramic
tube and gets rapidly pyrolysed gasified.
CHAPTER – III
PYROLYSIS AND GASIFICATION
Pyrolysis means decomposition of organic matter in vacuum or in an inert
atmosphere. Pyrolysis products are charcoal, a condensable liquid or pyroligeneous liquid
and gaseous products. The relative propositions of these products depend on the chemical
composition of biomass used and on the operational conditions. Pyrolysis process can be
explained by considering the chemical composition of wood.
3.1 : CHEMICAL COMPOSITION OF WOOD.
Wood is vegetal organic matter which can be represented by the empirical
formulae CH1.44 O 0.66. Considering the structure, wood is composed of dead and living
plant cells, the structure and composition of which depend on the different parts and
species of the plant. The green leaves consisting of living cells contain some proteins,
considerable water and less cellulogic cell wall materials. The woody tissues are
essentially composed of dead cells. The main components of the cell wall are cellulogic,
micro fibrils embedded in a matrix of hemicelluloses and lignin. Other minor components
such as lipids, hydrocarbons soluble in either and various phenolic compounds soluble in
benzene, alcohol or water can also be found, but they are more abundant in leaves than in
wood tissues.
In addition to these organic components wood also contains inorganic substances
which as residues (Ash) after ignition at high temperature. Ash composition is mainly
CaO (50%), K2O (20%), MgO, Fe2O3, P2O5 and these compounds play a catalytic role in
some reactions.
Wood is constituted mainly of cellulose component is the same in all type of
biomass, except for the degree of polymerization which can also vary slightly even in the
most uniform sample. The average molecular weight is 1, 00,000 AMU. Hemi cellulose
is mixtures of polysaccharides composed almost, 4-0 methyl glucose acid. Generally they
are of much lower molecular weight (30,000 AMU) than cellulose and some are
branched. In contrast to cellulose, the hemicelluloses are amorphous.
Lignin is a randomly linked, amorphous, high molecular weight phenolic
compound. It is more abundant and has a higher degree of polymerization in soft woods.
The content of these three components is variable and depends mainly on the tree
species. The cellulose content for most deciduous and coniferous trees varies between 40
% and 45 % but each can reach 55% for some. For the deciduous trees, hemicelluloses
represent 20 % to 35 % of total mass. For the coniferous trees, there is 20 % to 35 % of
total mass. For the coniferous trees there is 20 5 to 40 5 hemicelluloses. The ligin content
is 24 % to 30 % for coniferous trees and 17 % to 24 % for deciduous trees.
3.1.1.: INFLUENCE OF SPACIES ON PYROLYSIS PRODUCT YIELD .
The yield of the different reaction products varies with the species, which can be
seen in Table –I. Table shows the average values and their range obtained for about 20
different dexciduous tree samples pyrolysed under the same operational conditions.
TABLE – I YEILD IN PYROLYSIS PRODUCTS FOR 20
DECIDUOUS TREE SPECIES.
____
PRODUCT AVERAGE RANGE YEILD %
CHARCOAL 42.70 37.0 – 50.4 TAR 9.4 4.2 – 11.4 PYROLIGENEOUS 33.7 30.7 – 36.5 -ACID
The differences are greater between deciduous and coniferous trees, as shown in
TABLE – II
TABLE-II: YEILD ACCORDING TO WOOD SPECIES, DECIDUOUS AND CONIFEROUS
PRODUCT CONIFEROUS TREES DECIDUOUS TREES PINE SPURCE BIRTH
BEECH
CHARCOAL 37.8 37.8 31.8 35.0TAR 11.8 8.1 7.9 8.1GAS 14.7 14.9 14.0 15.8CH3COOH 3.5 3.2 7.1 6.0CH3OH 1.0 0.9 1.6 2.1H2O 22.3 25.7 27.8 26.7
Thus pyrolysis can be considered as a chemical pretreatment of biomass leading
to intermediate compounds to be separated or redefined.
3.2: EFFECT OF OPERATING PARAMETERS ON PYROLYSIS
PRODUCTS:-
The operational conditions acting on the yeold of the process products are,
heating rate, residence time of the reaction products, temperature used and pressure.
A rise in temperature increases the intrinsic rate of all chemical and physical
phenomena considered. The operating temperature also determines the equilibrium
composition of the gas [1]. In general temperature is determined by the quality of the
fuel, the ratio of the actual carbon supply of that required for combustion, and the heat
losses from reactor.
Pressure is also a major variable; it favorably influences the absolute rate of
reaction heat and mass transfer and modifies the equilibrium relation ships in favor of
CH4 and O2.
Residence time is a major parameter in thermal cracking reactions in the free
board zone of fluidized bed reactor. The residence time of the solids is normally
controlled by the flow rate of the air. The residence time can be decreased however, by
enhancing the ash extraction rate. But at cost of higher carbon losses in the residue. Joint
production of gas and charcoal is possible by this method.
Figure –I shows the product distribution as a function of heating rate, residence
time and reaction temperature. The yield of volatiles increases with the heating rate, but
for the highest temperatures, the condensations (tar) are cracked and the gas content is
increased. The char yield is maximum for low heating rates, low temperature and long
residence time.
Figure-I also shows the influence of pressure on the three main reaction products.
The decreasing pressure leads to decreasing residence, time of the volatile products.
Increase in the tar yield at medium temperatrure with low pressures has been
experimentally confirmed [2].
3.4.2: BASIC PRINCIPLE :-
Pyrolysis is the basic reaction of all thermal conversions of biomass. A good
knowledge of its mechanism should allow improvements in the yields and selectivity of
the carbonization process. Basically this is a thermal decomposition of biomass.
Initially at temperatures less than 300 oC the dominant processes are; the
reduction of molecular weight., the appearance of free radicals, the elimination of water
and formation of carbonyl and carbonyl groups which are assumed to give rise to out
gassing of carbon monoxide and carbon dioxide. The final product is a charred residue.
The structure of which is mainly that of crystalline cellulose. When wood is pyrolysed at
a low heating rate, the following sequence of events occurs [3].
1) At around 160 oC removal of moisture occurs the rate peaks at around 130
oC and drops to negligible levels by 200-280 oC.
2) Over the temperature range 200-280o C, all of the hemicellulose
decomposes yielding predominantly volatile products (CO, CO2 an condensable vapors)
3) From 280 – 500 o C cellulose which has already undergone through some
chemical transformation, decomposes at an increasing rate which reaches at maximum
around 320o C. The first and second steps are endothermic while the third is exothermic.
Thus when the pyrolysis process has entered the exothermic phase, no more outside
heating is required and the temperature slowly climbs until it reaches between 400-450 o
C.
11.4.1 : CHEMICAL REACTIONS :-
The two main chemical reactions occurs in the pyrolysis process are as follows:-
Cn Hm = CH4 + C + H + TARS
C + 2H2 = CH4
Although the overall process of pyrolysis appears simple, the sequence of
reactions is complex and involves both endothermic and exothermic processes, whose
thermodynamics and kinetics are not well understood. Pyrolysis of biomass readily
occurs at temperatures above 250o C. With particle greater than about 1 cm in size, heat
conduction is the rate controlling step and char production is about 40%. The process is
mildly endothermic.
Heat is transferred to the solid from the gaseous surrounding by conduction,
radiation and convection. Initial main mechanism to transfer the heat to the interior of the
solid is conduction. Once decomposition starts, volatile give rise to convection heat
transfer from the hotter solid, closer to the surface [4]. The porous structure of the solid
plays a fundamental role in determining the extent of heat transfer between gas and solid
within the particle. It has been suggested that primary pyrolysis has a very low enthalpy
of reaction, whereas the major part of the heat released by the reactions is due secondary
pyrolysis [5].
11.5 : REACTOR DESIGN:-
In practice, it is relatively easy to monitor the temperature, pressure and even
residence time, but it is more difficult to control the heating rate. It depends on two main
factors viz, the type of reactor and the biomass particle size. For a given reactor, with
increasing particle size, the conductivity of wood being low, the heating rate inside the
particle decreases and changes the yield of the three major products. For a given particle
size, the reactor type will determine the mode of heat transfer since radiation. Convection
and conduction vary according to the type of reactor.
Radioactive heat transfer has a lesser role than convective and conductive
transfer, in the range of 20-1000o C used in the majority of pyrolysis processes. In
addition, a given reactor can not pyrolysis particles of random size, for example, fluidized
bed reactor cannot treat large particles. Villermux [6] performed a systematic study of gas
and solid reactions, which can also be to categorize the pyrolysis process.
There are three main types of reactors usable for pyrolysis process, viz.
1) Liquid is best produced using a transported bed reactor with low
temperature, high heating rate and short residence time.
2) Charcoal is produced by using stacking kilns], multiple hearths knils,
rotary kilns with low temperature, low heating rate and more residence time.
3) Gas is produced by means of fluidized bed, circulating bed and even
cyclonic reactors, with high temperature and high heating rate.
In general design involves,
i) The estimation and selection of processing system to convert specified raw
materials into desired products.
ii) Size of the processing system based on analysis of rate process and on
experimental work.
iii) The detailed engineering specification of selected processing systems.
11.5 : GASIFICATION PROCESS
11.5.1 : BASIC PRINCIPLE
The aim of gasification process is to transfer the combustion value of the solid
fuel to a gaseous energy carrier preferably in the form of chemical energy and not in the
form of sensible heat.
Gasification is performed because of the advantages of gas over a solid fuel.
Gases are easy to clean, easy to transport and to combust with a low excess of air and
there is a little resulting pollution. Further more, gases can be burnt in the internal
combustion engine (turbine) and can be easily applied in combined cycles.
Biomass gasification can also be carried out via. Biological gas conversion.
Thermochemical route have the advantage of compact equipment due to the relatively
short residence time required (1-10 sec), easy start up, stable operation and there are no
requirements on the nutrient value of the feedstock.
Thermochemical route consists of following steps,
1) Partial oxidation of biomass by a gasifying agent, usually air or O2. Part of the
biomass is combusted to CO2 and steam.
2) Heating up of the biomass and evaporation of water.
3) Pyrolysis via further increase in temperature of the biomass. This decomposition
process takes between 150 o C and 500 o C, and results in the formation of char and gaseous
products. The most important components of the gas are water vapors, CO, CO2, H2,
hydrocarbons and acetic acid.
11.5.2 : CHEMICAL REACTIONS:-
The reaction mechanism is dependent on the process conditions [ 7 ]. Reduction
of gaseous components produced during process, by strong endothermic reactions. Char
is converted in to carbon monoxide and also reduced to CH4.
C + CO2 = 2 CO
C + H2O = CO + H2
C + 2H2 = CH4
The result is a gas consisting mainly of CO, H2, N2, and CO2, steam and
hydrocarbons. The composition of this gas varies widely with properties of biomass, the
gasifying agent and the process conditions. Heating values may be different vary between
3- 33 MJ/Nm3. If air is the gasifying agent, the producer gas contains 40-60 % volume of
N2 – this can be decreased by using O2 or O2 enriched air – Differences in the process
conditions are mainly dependent on the reactor type.
11.6 : THE ROLE OF CATALYIST IN GASIFICATION.
The catalytic gasification
is attractive because of the following reasons,
1) Increase in conversion rates giving higher throughputs.
2) Lower reaction temperatures giving greater efficiency and requiring
cheaper materials of construction, especially if indirect heat transfer is applied.
3) Cracking of tars which often simplifies gas treatment and improves
efficiency.
4) Realizing a product composition that is more suitable for a particular
application, such as methane rich, hydrogen rich, optimal for methanol synthesis or for
ammonia synthesis.
Catalysts that increase the rate of solid gasification are called primary catalysts.
Catalysts that affect product gas composition are called secondary catalysts. Primary
catalysts are particularly important in low temperature gasification if methane is the
desired product. The most challenging application for catalyst for biomass gasification is
probably in steam gasification for methanol production. The steam gasification is
relatively attractive because of the opportunity to avoid an expensive plant but it
normally produces a gas of un-favorable composition for methanol, being rich in CH2. and
tars. Generally oxygen and steam are used for high CO, high H2 gases with low nitrogen.
Fig: BRIQUETTED FROM SUGER CANE TRASH CHARCOAL
Briquetted Charcoal from Sugarcane Trash
Dry leaves, left in field after harvest of sugarcane, are called trash. On an average,
a hectare of sugarcane generates about 10 tonnes of trash. Because it has no value as
cattle fodder, and because it also r in this process. Each batch, taking about 40 min to
complete,
esists decomposition, the trash is burnt in situ, in order to clear the field for the
next crop. It is estimated that in the state of Maharashtra, more than 4,000,000 tonnes of
trash are destroyed in this way. Pyrolysing the trash and converting it into fuel briquettes,
can be a very profitable, small scale, rural business.
The Process:
The charring kiln, a portable cylindrical structure, about 150 cm wide and
100 cm tall) made out of sheet iron is placed in the field where sugarcane harvest is in
progress.
The trash is filled into cylindrical metal containers 37.5cm wide and 60 cm tall.
The kiln takes 7 such containers at a time. All containers together accommodate
21 kg trash.
After loading the containers into the kiln, the top of the kiln is closed with sheet
metal lid, which is provided with a chimney.
About 10 kg trash are burnt underneath the containers (in the kiln) to start the
process of pyrolysis. The heat of the trash burning underneath the containers pyrolyses
the trash in the container. Pyrolysis gas generated in the process leaves the containers
through holes in their bottom, and it too burns, to serve as additional fuel produces about
7 kg char (30% of the trash filled in the barrels).Three workers can simultaneously
operate
two kilns to produce about 80-100 kg char daily .The char is powdered, mixed
with a suitable binder ,and shaped, with the help of a mold into briquettes. Our mold
allows one person to produce daily about100 kg briquettes .The briquettes are laid out in
the sun for drying.
Economic considerations
For a family-owned enterprise:
The capital cost of two kilns with a set of 28 containers, and a small briquetting
machine is about Rs.50,000 (USD 1250).
A family unit of 3 persons can produce daily 100 kg briquettes. The briquettes
have a ready market in towns, where a cheap and cleanly burning fuel is in demand. An
NGO, SHG or a cooperative has to arrange the marketing of the briquettes in the
neighbouring townships. The family making the briquettes can thus earn daily Rs.800-
1000 (USD 20-25), which is equivalent to the income of an urban middle class family.
Use can be made of other agricultural waste material such as stems of cotton, pigeonpea,
safflower,
wheat and rice straw, maize cobs, or leaf litter from any plantation crop like
rubber, cashew, mango, papaya, palms, etc. Wood can also be converted into charcoal
using this unit. If wood is used as the raw material, there is no need for converting into
briquettes.
If the 16 weeks of the rainy (monsoon) season are excluded, such a unit can work
for about 36 weeks in a year, earning about Rs.200,000 (USD 5000). The metallic kilns
and barrels would however eventually burn out. Even assuming total replacement of
these items every year, the profit from this operation would be annually Rs.150,000 or
more than Rs.10,000 per month, which is a very good income by Indian rural standards.
For mass production:
This business can also be conducted by an entrepreneur, who invests about
Rs.500,000 in 20 kilns, a large capacity extruder and a shed. He gives two kilns each to
10 families, who make charcoal from whatever waste biomass that is locally available.
The entrepreneur buys the char from them at a price of Rs.3 per kg. Within a working
period of 200 days a year, the entrepreneur can get about 200 tonnes of char, which, after
converting into briquettes, can be sold at a wholesale price of Rs.2,000,000 (USD 50000)
After deducting depreciation on the equipment, bank charges, operating expenses and
overheads, the entrepreneur is left with a net annual profit of about Rs.1,000,000 (USD
25000).
Note: This profit has been calculated on the assumption that the briquettes would
be sold by the operators at Rs.10 per kg. The retail price in Pune is Rs.15 per kg. have
burnt themselves out and the fire has extinguished itself.
The cooking system is so designed that the food remains warm upto two hours, if
the vessel is not opened. The cost of Sarai Cooking System is Rs.500 (about USD 12).
The convenience of use and the low cost of fuel are the main attractions for the users.
Fig:A handy kiln for making charcoal.
There are about 5000 families in Pune who use the Sarai cooking system on a
daily basis and this has generated a monthly demand for about 5 tonnes of char briquettes
in Pune city alone.
Fig:A small Briquatting Machine
Fig:Sarai cooker for cooking system
Fig:Briquettes from agricultural waste
Product Cost:
1. Charring Kiln (ex factory, transport charges extra): Rs 20,000
2. Briquetting Machine (ex factory, transport charges extra): Rs 10,000
3. Briquetting Molds Pair (ex factory, transport charges extra): Rs 500
4. Char Briquettes: In Pune - Rs. 15 per kg
Elsewhere in India (M.R.P. inclusive of taxes and transport) - Rs. 20 per kg
5. Sarai Cooking System (M.R.P. inclusive of taxes and transport anywhere in
India)
For 8 lit capacity: Rs. 800
For 12 lit capacity: Rs. 1000
CHAPTER – III
PYROLYSIS STUDIES
INTRODUCTION:-
Although the overall pyrolysis process simple the sequence of reaction is complex
and involves both endothermic and exothermic process. The overall process can be
broadly classified in to primary and secondary stages [1]. The quantity of the charcoal
produced by carbonization depends on its chemical and physical properties. These are
highly related to the raw material, type of biomass, and operating conditions of pyrolysis
process.
Among the properties which characterize charcoal, the most significant seem to
be –
a. Yield : Expressed as a percentage, as a ratio of the weight of charcoal to
that of the dry material.
b. Content of volatiles: The weight loss per unit weight of charcoal when
charcoal is heated at 900o C under vacuum or in an inert atmosphere.
c. Fixed Carbon Content: The dry charcoal weight minus weight of volatiles
and ash per weight of charcoal.
Carbonizers currently available are either small or batch type for distributed
residues. Other designs which aim at large out puts are stationary plants. Sugar cane trash
poses a peculiar problem: it is very light, bulky and difficult to transport. However, it is
available in very large quantity ( 18 million tones) distributed over thousand of hectors.
So neither small batch type nor large stationary plants meet the requirements of
carbonization of sugarcane trash (S.C.T).
It is an established fact that a continuous process is always more economical than
a batch process. In order to design BARREL TYPE CONTINUOUS CARBONIZER
FOR carbonization of S.C.T, first pyrolysis parameters such as temperature, heating rate,
residence time and pyrolysis ambient were changed systematically and yield was
measured. From these data, carbonization parameters were selected for designing of
carbonizer.
111.1 : OPTIMIZATION OF PROCESS PARAMETERS .
The par meters which control the yield recovery in the pyrolysis process are –
I The heating rate (thermal flux)
II Residence time of the reaction products.
III The highest temperature used for the pyrolysis and
IV The pressure of the air /ambient.
The experimental set up used to determine process parameters for pyrolysis of
S.C.T is shown in the figure-I. it consists of a muffle furnace fitted with the stainless steel
tube of 100 cm length and 4.5 cm diameter. Both the ends of this tube are closed. The
sample is placed in a cylindrical box which can be opened on one side. For measuring
temperature of a opened on one side. For measuring temperature of a sample, chromel-
alumel thermocouple is fitted at the centre of the sample holder. The holder is mounted
on a movable rod so that sample can be shifted from cold zone to hot zone by pushing
this rod inside. A gas inlet is provided on one side and exhaust volatile matter is provided
on the other side.
About 2-3 gms of S.C.T is placed in a sample holder. Initially the sample is kept
in a cold zone, then the furnace is heated to desired temperature. The temperature of the
furnace is controlled with the help of dimmer stat. When the desired temperature is
reached, the sample is inserted into hot zone for specified time. The sample is again
moved back to the cold zone. After cooling, it is moved from the holder. After each step
of carbonization, the yield recovery and higher heating value (HHV) were measured.
The energy is defined as the energy which can be derived from the char after
carbonization. It is given as
Energy recovered= Energy obtained from Char
Energy obtained from trash
= Yield X HHV of Char
HHV of trash
When the oven is dried biomass is heated with constant temperature rise, the
volatile matters are removed. The rate of devolatization depends on the type of biomass,
rate of heating and the ambient. In order to choose temperature range over which
carbonization could be carried out, devolatization rate was studied as follows.
A weighed sample was kept in the pan was enclosed in a furnace. The
temperature of the furnace was raised at a constant rate (40 C/min). The furnace was
flushed with nitrogen. The rate of flow of nitrogen was kept 300 ml/min. The loss of
weight was continuously recorded as thermal decomposition/pyrolysis of the S.C.T took
place. Figure-2 shows the loss of weight with temperature. It is observed from this figure
that.
i. Weight loss is slow upto 3000 C.
ii. Weight loss increase at faster rate between temperature 300 to 4500 C.
iii. After 4500 C, the area of the weight loss reduces and after the temperature
6500 C weight remains constant.
These observations imply that most of the volatile matter goes out in the
temperature range 300 – 5000 C. Initial weight loss is only due to the moisture
evaporated form the sample. Hence we have varied the temperature of carbonization form
300 to 4500 C.
Figure – 3 shows the Coper mountain pyrolysis model. The dotted line indicates
the process path of carbonization of S.C.T. From the experimental results following
conclusions can be drawn.
1) The yield in general decreases as the carbonization temperatures as well as
residence time increases. The observation in valid for carbonization in ambient
temperature. Time-temperature variation of yield for ambient air is shown in figure -4.
2) The energy recovery also decreases with temperatures and time. These
observations are summarized in figure – 5.
However the energy recovery more strongly depend on the temperature than time.
We can from the figure – 5 that recovery decreases faster when temperature increased.
This is due to the fact that certain volatile matters especially liginin do not decompose at
low temperature.
3) The HHV of the char, though higher then the trash, does not change
appreciably with time or temperature. The HHV of S.C.T is 16.46 MJ/Kg where as the
average HHV of char is 21.09 MJ/Kg.
S.C.T contains about 73% volatile matter. The carbonization process is complex
when the decomposition of cellulise, hemi cellulise and liginin has began in such a way
that the initial atomic arrangement is totally change giving out some volatile matter. Thus
when yield in 45%, the carbonization process is complete. Further heating will remove
some of the carbon, reducing carbon content, in the char as well energy recovery. Hence
carbonization in the air ambient can be done under following conditions for maximum
energy recovery and quality.
AMBIENT TEMPERATURE RANGE RESIDENCE TIME
AIR 315-3650 C 2 – 6 min
Time temperature regions over which carbonization can be done efficiently are
shown in the figure -4 by shaded region.
Thus for The Continuous Carbonizer, temperature and residence eime must be
maintained in the above region in order to complete pyrilysis of S.C.T. The average yield
and recovery in this region are 45% and 57% respectively for air ambient.
III.2: DESIGN OF THE CARBONIZER :-
Salient features and some important dimensions of the laboratory modle are
shown in figure- . Essentially it is a vertical barrel of 20 cm diameter x 20 cm height
with a rotating cone inside the barrel. Vertical barrel is closed by cover plate of 7 mm
thickness. Polished shaft ( 25 mm dia.) is held in bearing and is rotated by level gear by
hand crank shaft.
At the lower end of the shaft, a cone of height 200 mm and 5 mm thickness is
fixed. For inside heating of/ barrel and igniting trash, a laboratory burner is used. It is
important to keep continuous ignition of trash inside the barrel. Asbestos cloth is used to
cover outer wall of barrel to minimize heat losses. After a number of variations and trials,
the essential requirements for continuous carbonization are well understood. For
example,
i. Size of the trash should be reduced to 2-3 cm.
ii. For continuous feeding of trash, screw feeder did not work satisfactorily. So feed
was intermittently pushed with a ram.
iii. Vertical flow of trash in barrel for effective carbonization is slowed down and
arrested with horizontal platforms made from perforated MS sheet.
iv. The trash is also required to be distributed by vertical rake on rotating cone. These
devices have proved useful for obtaining good carbonization.
For removal of char at the lower end of barrel, a ring is provided at the bottom of
the barrel which controls the width of passage for char. Projections on cone, by rotation,
force the char through the gap between ring and cone. Volatiles are required to be
removed rapidly out of the barrel to prevent volatile leakages at bottom. External air is
essential for partial combustion inside the barrel.
III.3 : WORKING OF THE CARBONIZER :-
In order to carbonize char continuously the essential steps required are as follows,
Trash is required to be pulverized so that length is conveniently small for
continuous feeding. Pulverized trash is intermittently fed by hand with a ram. This
pulverized trash which fed in to the barrel form top falls on the perforated horizontal
platform of rotating cone. The trash gets ignited due to the flame maintained by LPG
inside the barrel. The cone is rotated manually.
Partial burning of trash produces enough heat to maintain the temperature around
3000 C which requires for carbonizing the trash. The partly carbonized trash is agitated by
vertical rake. The carbonized trash being brittle breaks and falls on the second perforated
sheet through the holes in the top platform. The final char force in to the narrow space
between walls of barrel and rotating cone. Projections on rotating cone, steel balls help to
force the trash down the gap between adjustable ring at the bottom and rotating cone.
In the process of carbonization, volatiles are released in large quantities. Some
external air is also required, to partly burn the trash, so as to generate enough heat for
carbonization. An electric air blower is used to provide air as well as remove volatiles
from barrel.
Char coming out at the bottom is non-sticking and is free flowing. Due the high
temperature maintained inside the barrel, there is no sticky tar deposition on any parts of
the carbonizer.
III-4 : EXPERIMENTAL
Initial stage of carbonization is shown in figure-6. it depicts the burner for
maintaining the ignition is kept in a MS pipe which is having 50 mm bore and inclined
through an angle of 30o to the vertical. Outlet for volatiles is provided through a pipe of
20 mm bore which is located at 135 mm from bottom.
Idea behind this design was that, pulverized S.C.T fed by screw feeder will be
distributed by rotating the cone and the charcoal powder can be obtained at the bottom of
the barrel. A thin M.S circular disc is fitted at the upper end of inclined pipe to keep
continuous ignition inside the barrel.
Some of the problems faced while operating this carbonizer are
1) It s difficult to keep continuous ignition because of the failing of little biomass on
the burner.
2) Volatiles come out from the bottom instead of coming through pipe.
3) Vertical flow of biomass is not under control.
4) Screw feeder does not work satisfactory.
RESULTS:-
After conducting several experiments we found that:-
i) Residue obtained was, unburned biomass of smaller size.
ii) Burning of volatile is possible.
iii) Creation of suction, inside the barrel is necessary.
Modifications were done, to minimize the problems occurred:-
a) A vertical MS pipe is fitted to the top of barrel as an outlet for volatiles.
b) Position of flame and outgasing pipe were interchanged.
c) Air required for partial combustion is provided through an additional pipe of 20
mm bore which is fitted at the same level that of previous volatile outlet.
d) Four MS rods of helical shape are welded at different level on cone to control
vertical flow of S.C.T
OBSERVATIONS:-
i) Poor quality, charcoal powder was observed.
ii) Weight of the residue was about 75% that of biomass.
Some of the difficulties, while performing the experiments, were as follows.
1) Volatiles were coming through top vertical pipe as well as through bottom
of the barrel.
2) Vertical flow control was not satisfactory.
MODIFICATIONS :-
Design was modified to get rid of the above problem. Figure-7 shows the
modified design of carbonizer. Blower is used to suck volatiles, so that volatiles will not
come through the bottom. Welded rods are removed and two perforated sheets are fitted
on the cone. One more pipe of 20 mm bore, at the location of 50 mm form bottom of the
barrel, is fitted for one more burner flame to have a better carbonization rate.
Doing several experiments on this design by interchanging the position of air inlet
and gas flame. We got some considerable results, are tabulated in Table-I.
TABLE -1: QUALITY OF CHARCOAL AT DIFFERENT FEED RATE.
Sr No Weight of
biomass gm
Time required in
minutes
Weight of
charcoal in gms
Quality of
charcoal
1 450 60 200 Good
2 470 60 256 Slightly brown
3 667 60 325 Good
4 715 60 352 Good
5 1000 60 554 Slghtly brown
It is found that, quality of the charcoal depends on the velocity of air which is
used for suction. Vertical flow of S.C.T is well controlled by the perforated sheets.
Vertical rake is used to control the flow as well as to distribute trash properly. A ring is
provided at the bottom of the barrel to control the width of the passage for charcoal.
CHAPTER-IV
HEAT TUBE GASIFIER
INTRODUCTION
Thermochemical gasification is the conversation of biomass in to a gaseous
energy carrier by means of partial oxidation at high (=1000o C) temperatures. The gases
produced are applied mainly as a fuel gas for electricity generation and direct heating.
They can also be used as synthesis gas in the process industry to produce methanol or
ammonia. There are many cases in which gasification of biomass has advantages over
direct combustion of biomass or fossil fuel. For example small scale generation of
electricity can be done without the necessity of a steam cycle, simply by combustion of
the gas in a reciprocating engine. Another advantage is that the producer gas can be
cleaned in relatively compact units prior to combustion.
Biomass having an ash content less than 02% by weight and a moisture content
upto 30% by weight is generally suited for gasification [1]. The most widely applied
reactors for gasification of biomass are the Moving bed types and the fludized bed types.
Three sub types of moving types are Down- Draft, Up-Draft, and Cross-Draft reactors.
The fludized bed applied mainly for biomass having dimensions of 1-10 mm and ten
moving bed for 10-100 mm. the choice of a certain type is depended on many factors
such as biomass properties, desired gas composition, scale of operation and local
circumstances. For the design and operation, it is essential to know that the gasifier is a
thermal reactor, filled with combustible gases and is some times pressurized.
It is ideal to have all forms of biomass in a convenient and uniform physical
dimension so that design of any combustion device is simplified. Therefore obvious
choice would be to either briquette biomass in to ideal pallets of fixed dimension and
consistent density or to pulverize it in to a powdery form. Experiments conducted on this
line have shown that pulverization of the biomass would form an essential component for
achieving uniform pellets [2]. A preliminary economic evaluation of the process of
briquetting shows that it would be economically sensible to develop gasifier systems
which can directly use powdery biomass. This would not only eliminate the cost of
briquetting but would ensure the product versatility in terms of variety of inputs.
At the same time wood is a scare national resource and therefore it has to be
conserved to the maximum extant possible. However apart from the hard woody biomass,
there is abundance of other form of biomass. These includes site specific biomass like
saw dust, coir, pith etc or in general like rice husk, parthenium, leaves, grass etc.
Therefore if it is possible to make an efficient process, to utilize such biomass it would
also save fossil, fuel consumption like diesel.
A large number of light agricultural residues cannot be gasified in conventional
gasifiers due to material flow problem. All such material could be directly gasified with a
Heated tube. This is the principle used in tube gasfier.
IV.I : HEATED TUBE GASIFIER
IV.I.I : BASIC CONCEPT :-
The development of a successful fast pyrolysis technology for biomass offers a
product and process with the best features of conventional pyrolysis and air / oxygen
gasification. A major consideration for air gasification product applications is their
limitation to close coupled combustion related processes. Fast pyrolysis differentiates
from other processes with respect to temperature vapour residence times and end product.
Extremely rapid heating rates (200 to 10000 o C/s) high temperatures than 0.5 s are
required to maximize the production of high quality gases [3].
Number of laboratories abroad has conducted work on fast pyrolysis of biomass
in a heated tube, mostly directed to production of synthetic fuels.
In conclusion, the following general statements about fast pyrolysis in a heated
tube are offered for consideration and critical evaluation.
1. Fast pyrolysis in a heated tube promises high yields of concentrated high
quality intermediates, petrochemical syngas and fuel gas products from biomass. These
gases include olefins and other hydrocarbons.
2. Fast pyrolysis incorporates some of the best features associated with
conventional pyrolysis, flash pyrolysis and gasification without many of the related
advantages.
3. Fast pyrolysis of biomass is accompanied by-
i. Rapid heating rates,
ii. High temperature.
iii. Short vapour residence times.
iv. And rapid product quenching
It is found that at 1000 o C and a moderate pressure of 50 psi and residence times
of less than 3 s, mainly methane and carbon monoxide are formed in the almost
equimolar yields with almost all the carbon in the wood converted to product [4]. For the
future development of gasification following points are to be considered.
a) Necessity to utilize agricultural residues for gasification as wood would not be
available.
b) Requirements of small gasifiers for thermal applications for large kitchens,
bakeries etc to save wood.
c) Requirement of gasifiers to utilize industrial waste in paper, rice and similar
industries for thermal applications.
From the above requirements two conclusions are drawn-
1. Work on heated tube gasifiers for powdery biomass (or soft fibrous
) may have greater field applications tha use of char.
2. Gasification for thermal applications would also be an important
area of use.
Fast pyrolysis of biomass and gasification of volatiles effectively becomes more
rapid as temperature increases beyond 850 o C. With electrical heating temperature of the
order of 1000O C can be easily maintained than with normal combustion. Ceramic or
stainless steel components can withstand a temperature beyond 1000O C withouit
corrosion problem.
If HTG is used for thermal applications, electrical supply must invariably be
available for electric heating. When HTG is used for IC engines, a small alternator would
be necessary as an auxiliary on IC engines.
The main advantages of HTG are as follows-
1) It is possible to utilize a large number of agricultural residues for
gasification for which it is difficult to design conventional gasifiers.
2) HTG due to its small size is expected to cost much less than conventional
gasifiers.
3) With HTG it would be possible to meet large numbers of thermal power
applications in the range of 20-500 kw thermal.
Capacity of HTG would depend upon following two factors –
1) Rate at which fuel could be introduced in the tube.
2) Rate at which it could be pyrolysised.
Agricultural residues can be divided in two classes.
a) Hard biomass such as stalks, pine needles etc.
b) Other residues such as sawdust, sugar cane trash, ground nut shell, straw etc.
These are termed as LIGHT BIOMASS. The light biomass is particularly suitable
for fast pyrolysis with HTG. It is seen that out of 18 important agricultural residues, 14
can be termed as light biomass and can be conveniently reduced in size fir HTG with a
simple pulverizer.
The unit comprises s vertical ceramic tube with 205 cm bore and 30 cm long. The
external surface of the ceramic tube is electrically heated to 1000O C temperature. A
central tube of diameter 1.4 cm is kept inside the ceramic tube. Air provision is made at
upper end of the ceramic tube. Sawdust is fed from the hopper fixed at the upper end of
the ceramic tube. Biomass gets rapidly pyrolysed and gasified. At the bottom end of the
ceramic tube a cavity is provided through pyrolysis products pass to outlet. Due to the
additional heating coil maintained at around 1000O C the gum foaming volatiles would be
cracked. Gas obtained is passed through a water cooled heat exchanger and fed to blower.
The gas emerging out of the blower burns nicely-
IV.1.2: DESIGN OF HTG
The primary is to design and fabricate a working laboratory model of HTG to
achieve gasification. Figure-1 shows schematic diagram of HTG, the unit consists of
following components.
a) Ceramic tube.
b) Cavit at the bottom.
c) Hopper.
d) Cleaner / Cooler
e) Burner.
DESCRIPTION OF THE COMPONANTS:-
a) CERAMIC TUBE :- Ceramic tube is the heart of the Heated Tube Gasifier
Quarts tube normally used for high temperatures was not easily available. Function of the
ceramic tube is to create a hot zone of around 10000 C for fast pyrolysis of biomass. Figure-2
shows the ceramic tube used for HTG system. Dimensions and material of ceramic tube are
selected by following facts.
a. The material and dimensions are selected by the maximum temperature
required for fast pyrolysis of biomass and residence time respectively. The maximum
temperature of hot zone may go up to 13000 C hence tube should withstand upto this
temperature. Ceramic tube of 3 cm length, 2.5 cm diameter and 0.7 cm thickness is found
to be most suitable.
The residence time of the pyriolysis process depends on the velocity of biomass
and the length of the hot zone. Since the biomass is allowed to fall through a vertical
heated tube under the gravitational force, the velocity of the biomass is constant. Hence
the residence time of the fuel depends only on the length of the hot zone. X.Deglise and
P.Mange [1] have shown that to obtain maximum gasification of biomass at 10000 C
temperature, the residence time should be less than 0.5 sec seconds. The residence time
of HTG can be worked by making following assumptions.
i) Biomass falls due to the gravity only with initial velocity zero.
ii) The length of the heating zone is 24 cm.
iii) Up draft of the hot air is balanced by the downward flow of air flow of air
supplied externally.
With these assumptions and by using expression
S= ut + ½ a t 2
The residence time in the hot zone comes ot to be 0.25 seconds. This time is
sufficient to achieve maximum gasification.
The ceramic tube is electrically heated by winding kanthol wire on under surface
of the tube. The heat for pyrolysis is mainly obtained from combustion of fuel while
passing through the tube is not enough to maintain the temperature of hot zone. Hence
when external heating is employed the temperature of the hot zone is boosted up to
required value. Maximum capacity of HTG is mainly controlled by the rate at which fuel
could be introduced at the upper end of the tube.
This is worked out for 2.5 cm bore on some simplifying assumptions for saw dust
as a fuel.
i) At entry of HTG, saw dust particles occupy 30% of space.
ii) Initial velocity of saw dust particles is 5 cm/sec.
Rate of fuel flow = Cross sectional area of tube X Velocity of biomass X 0.3 X Density
of the fuel. = 4.9 X 5 X 0.3 X 0.5 = 3.6 gm / sec.
Fuel value of saw dust is 21 MJ/Kg, itmeans that 1 Kg of sawdust after burning
gives 21 MJ energy. For 3.6 gm/sec fuel flow rate,
Thermal input power will be 75.6 Kw.
In most of the gasifier systems fuel conversion efficiency varies between 70% to
85 % considering 75 fuel conversion efficency.
Thermal output power of system will be 56.7 Kw. Thus maximum thermal
capacity output of unit with 75 effeciency and 3.6 gm/sec feeding rate would give 56.7
Kw thermal.
CAVITY AT THE BOTTOM.
The purpose of cavity at the bottom is to crack the gum foaming volatiles and to
collect the ash at lower end. As outlet temperature is high , fitting metal components to
ceramic tube was difficult.
Passages for the output gases are now carved in the insulating bricks of 56 cm
bore diameter. Additional heating, for cracking of the gum forming volatiles, is
maintained in the carved brick. Electrically heated ceramic pipe of 10 cm length and 3.6
cm diameter is used to maintain the additional heating.
The figure-3 shows the cavity which is used for additional heating and collecting
the ash. Figure also shows the 6 mm width circular passage in which biomass gets
additional heating. A stainless steel made hollow cone is fitted at the lower end of the
brick for collection of the ash. Removal of ash arrangement is made at the lower most
end of the zone.
HOPPER
Hopper is used to feed the biomass for gasification. Figure -4 shows the
schematic diagram of hopper. Feeding mechanism for fuel is related to the following
properties of fuel.
1) Particle size.
2) Moisture content
3) Physical parameters
4) Mouldity characteristics.
It was decided to use charcoal powder and saw dust as fuels. Figure-4 shows a
metal cone of height 10 cm and upper diameter of 18 cm. A screw feeder is fixed at the
centre of the cone to control the feeding rate.
CLEANER/COOLER
The temperature of the outlet gas is more than 400 O C. also it contains small
particles of charcoal powder, hence gas needs to be cooled and cleaned to get better
quality of gas.
A schematic diagram of the system is shown in the figure-5. A metal vessel of
height 22 cm and 10 cm inner diameter is fixed in container. The temperature of the gas
inside the vessel is decreased to ambient temperature due inside heat exchanger with
continuous water flow. A small quantity of the glass wool is kept in the vessel for
filtration of the gas.
BURNER
The easiest test of good gasification is to burn it. A burner made of mild steel
which provides primary and secondary air is built and tested.
IV.2 : EXPERIMENTAL
Sawdust reduced in a size to 0.03-1.0 mm is fed by gravity at he top of te reactor
in a free fall mode. The air feed is pre-heated with electrical resistance and entrance the
wood particles which then flow con-currently down to the tube. The wood particles used
in the experiments consist of seasoned sawdust. The wood particles are dried for six
hours at approximately 60 o C. Feed rate of 40 gm/min is used. A char / ash trap separates
the residual solids from the gas. This is followed by water cooled condenser which
separates the lighter and heavier liquids. Sawdust is gasified in a serious of experiments
conducted at temperatures varying from 800 – 10000 C. The residence time of 0.25 sec is
kept constant. Experimental arrangement is shown in the figure-1.
The gas formed is collected in a small glass bottle which is having inlet and
outlet. The bottle inlet is joined in between blower and burner with rubber tube. Gas is
allowed to fill the bottle by opening the inlet and outlet of the bottle. After filling the
bottle i.e when burning of the gas at the outlet is observed, both the ends are closed by
straight bore cocks. Thus the gas sample is collected in bottle for analysis. This gas is
analyzed by a gas chromatograph (Chemito & Omega ) with H2 and N2 as carrier gases.
CHAPTER-V
RESULTS AND DISCUSSION
V.1: CARBONIZATION PROCESS :-
The quality of a charcoal depends on its chemical and physical properties. These
are highly related to the raw biomass material, tree species and the operating conditions
of the pyrolysis process. They will also determine the possibility of the charcoal to
undergo further treatment in order to provide more convenient final products such as char
bricks and pellets.
Among the properties which characterize charcoal more significant are [1]
a) Yield:- The yield is defined as the ratio of the weight of charcoal to that of
the dry material.
b) Volatile Contents:- The weight loss per unit weight of residue essential
hydrocarbons and carbon oxides) when charcoal is heated at 9000 C under vacuum or in
inner atmosphere and –
c) Fixed carbon content :- The dry charcoal weight minus the weight of
volatiles and in-combustible (ashes) per unit weight of charcoal.
The variation of these three properties with the terminal pyrolysis temperature can
be deduced from figure-1.
1) Ash content:- it is composed of the natural minerals contained in the raw
material. The ash content an the composition of these ashes often determined the choice
of a given charcoal for a given special utilization.
2) Specific heat :- it varies according to the specific weight of the raw
material . it is also influenced within a narrow range by the terminal temperature and the
heating rate.
3) Hardness: - it is very important for industries because of its abrasive
capacity.
4) Heating value :- it depends on the fixed carbon and range from 27 MJ/Kg
to 30 MJ/Kg.
5) Active surface :- the oxidation with steam or chemicals can increase the
surface area of charcoal (activated charcoal) which may measure 1500 m/g.
V.2 : EFFECT OF PROCESS PARAMETERS ON CHARCOAL.
V.2.1 : TEMPERATURE :- The reaction products of biomass pyrolysis are a
linear combination of the products expected from the separate pyrolysis of the three
major components. It is generally agreed that when biomass is pyrolysed at a low heating
rate the following sequence of events occurs [2].
i) AT around 1600 C removal of moisture occurs, the rate peaks at
around 1300 C and drops to negligible levels by 2000 C.
ii) Over the temperature range 200 – 2800 C all of the hemicellulose
decomposes, yielding pcedominantly volatile products (CO, CO2 and
condensable vapours)
iv) From 280 – 5000 C cellulose, which has already undergone some chemical
transformation, decomposes at an increasing rate which reaches a maximum at around
3200 C.
Figure-2 shows the variation of yield recovery and HHV of charcoal with
temperature at constant residence time of 2 min. We can see from the figure that at
temperature 3250 C, yield is 44.12 %. It increases up to 46.24 % at 3500 C. After 3500 C
yield decrease to 32.88 % at 4000 C a small increase in yield is seen at 4250 C which is
36.10 %.
Maximum energy recovery about 62 % can be seen at 3500 C temperature. Energy
recovery starts decreasing, minima occurs at 4500 C which is 35.86 %. Figure-2 also
shows the variation of HHV of charcoal. Maximum HHV can be seen at 3500 C which is
58MJ/kg. a reasonable HHV around 56 mg/kg can be seen at 4500 C temperature.
Figure-3-7 shows the variation of the yield, energy recovery and HHV of charcoal
for residence time of 5 min, 7.5 min, 10 min, 12.5 min and 15 min respectively.
V.2.2:-RESIDENCE TIME:- Figure -8-14 shows the variation of yield, energy
recovery and HHV of charcoal. For example figure-10 shows the maximum of yield,
energy recovery and HHV curves at 2.5 min and 3500 C, minimum of these three curves
can be seen at residence time of 10 min.
From these curves following conclusions can be drawn.
i) The yield is in general decreases as the carbonization temperature as well as
time increases. This observation is valid for carbonization in ambient atmosphere.
ii) The energy recovery also decreases with temperature and time. However the
energy recovery more strongly depend on the temperature than time. We can see from
figure-2 that the recovery decreases faster when temperature is increased, this due to the
fact that certain volatile matters, especially lignin does not decompose at lower
temperature.
iii) The HHV of the char though higher than the trash, does not change
appreciably with time or temperature. The HHV of S.C.T is 16.46 MJ/Kg, where as the
average HHV of char is 21.09 MJ/Kg obtained in he optimized area for air S.C.T contains
about 73 % volatile matter. The carbonization process is complete when the
decomposition of cellulose, hemicellulose and lignin has begun in such a way that the
initial atomic arrangement is totally changed giving out volatile matter. Thus when yield
is 45 % the carbonization process is complete, further heating remove some of the carbon
reducing carbon content in the char as well as energy recovery. Hence for carbonization
in the air can be done under following conditions for maximum energy recovery and
quality.
---------------------------------------------------------------------------------------
Temperature range Residence Time
_______________________________________________________________
315 – 365oC 2 – 6 min
_______________________________________________________________
Time temperature reasons over which carbonization can be done efficiently are
shown in the figure-15 & 16 by shaded region. Thus for the carbonizer temperature of
carbonization and residence time should be maintained in these regions in order to
complete the pyrolysis of S.C.T
The average yield and reviver in this region are 45 % and 57 % respectively. For
better understanding bachground of carbonization process can be tabulated as follows.
TABLE-1: QUALITY OF CHRCOAL AND CARBON CONTENT AT
DIFFERENT TEMPERATURES OF CARBONIZER.
CARBONIZATION TEMP oC CARBON CONTENT % QUALITY OF CHARCOAL
150 47 Not properly carbonized
200 51
275 70 Readly combustible brown
charcoal
350 76 Black charcoal of good
quality. Easy to ignite
500 80 Very black, dense and solid
charcoal, very difficult to
ignite.
The performance of “ THE BARREL TYPE CONTINUOUS CARBONOZER” is
evaluated in terms of charcoal production rate, charcoal yield and quality. Table -2 shows
the comparative performance of the new equipment.
TABLE -2: COMPARATATIVE PERFORMANCE OF THE EQUIPMENT.
Carbonization
method
Raw material Charcoal yield% Production rate
kg/hr
HHV MJ/kg
Modified drum Coconut husk 24.60 1.89 24.70
FPRDI sawdust
carbonizer
Sawdust 22.5 6.00 14.75
Barrel Type
continuous
carbonizer
Pulverized S.C.T 40.45 1.00 21.00
V.3: STRUCTURAL STUDIES :-
Charcoal is not just another form of carbon, such as graphite or diamond. It
consists of a complex mixture of organic chemical substances containing carbon,
hydrogen and oxygen in chemical combination, together with smaller amounts of
nitrogen and sulphur, coalification is the name given to the development of the series of
substances peat, lignite or brown coal, bituminaous coal and finally anthracite. The
degree of coalification or rank of the coal increases progressively from lignite through
low rank coal to anthracite. The carbon content increases and the oxygen and hydrogen
contents decrease throughout the series, while the reactivity decreases.
Coal can be analyzed chemically to determine the percentages of the main
elements present, namely carbon, hydrogen, oxygen and nitrogen. Typical analysis of
coals of different ranks are given in Table-III, with comparative values for wood, peat
and lignite [3].
TABLE-3: CHEMICAL COMPOSITIONS OF WOOD, PEAT AND VARIOUS
COALS.
% C % H % O % N
Wool 50.0 6.3 42.7 1.0
Peat 57.0 5.2 36.8 1.0
Lignite 65.0 4.0 30.0 1.0
Low-Rank coal 79.0 5.5 14.0 1.5
Med Rank coal 88.0 5.3 5.0 1.7
Anthracite 91.0 2.9 1.9 1.2
The charcoal obtained from “CONTINUOUS CARBONIZER” has a 76% of
carbon at 350oC, can be put in a low-rank coal.
The chemical structure of coal involves a carbon skeleton, and X-ray analysis has
provided very useful information on the arrangement of the carbon atoms. The diffraction
patterns derived from charcoal are very diffuse but examination shows that there are
board peaks present in diffraction at positions shown in figure-15. When the carbon
content in the coal is more than 85 % the diffraction pattern of coal and graphite are
similar but show broad peaks indicating smaller crystallite size [4].
Figure-16 also shows the X-ray diffraction patterns of sugar cane trash (SCT)
wood charcoal and graphite [200-plane]. For SCT, X-ray diffraction pattern of mid-vain
show semicrystalline structure whereas leaves show amorphous structure. X-ray
diffraction pattern of wood charcoal also shows semicrystalline structure butit is more
like a graphite.
Figure-16 shows the diffraction patterns of charcoal, pyrolysed under different
temperature and constant residence time. The structure shows high degree of crystallnity
specially at higher temperature of carbonizer. The diffraction pattern at higher
temperature is more sharp than diffraction patterns of char pyrolysed under different
temperatures.
When the diffraction patterns of char are compared with the diffraction pattern of
SCT, it can be concluded that:
1) The board peaks appearing between 13O – 20O become intense and sharp
after carbonization of SCT.
2) The diffuse peak appearing between 20O – 24O vanixhes after
carbonization.
3) New sharp peaks appear at 26O when processed at higher temperature.
Hemicellulose and lignin present in the biomass have amorphous structure and
low molecular weight. Both these give rise tovolatile when heated at 200-4000C.
Hemicellulose degrade at lower temperature ( 200-2600 C ) while lignin decomposes at
higher temperature (300 – 4000C). The diffuse peak appearing at 220 is due to
hemicellulose and lignin. This peak disappears when SCT is pyrolysed.
Thus our X-ray diffraction studies indicate that cellulose provides basic carbon
skeleton for forming crystalline char. Since carbon content in the char is 76% it’s
structure does not match with the graphite which contents more than 85% carbon.
V.4: HEATED TUBE GASIFIER :-
In applications requiring maximum conversion of feedstock to gas, the tubular
reactor has several advantages over other conversion technologies. The tubular reactor
subjects the feedstock to very rapid heating rates, of the order of 100000 C /s thereby
minimizing char and tar production and maximizing gas production especially the
valuable unsaturated hydrocarbons.
Because heat is generated external to the reactor tube, pyrolysis gases are not
contaminated by products of combustion or nitrogen, yielding a gas with a HHV of 6
MJ/m3 and with considerable quantities of hydrogen, carbon-monoxide, and the
unsaturated hydrocarbon species. External heating of the reactor tube also allows use of a
wide varity of heating methods including combustion of feedstock, process of gas, natural
gas or use of solar energy. The tubular reactor is operated in a continuous mode, has a
high throughput capability, and can be configured in a compact furnace.
The purpose of this study is to develop the process chemistry for the rapid
pyrolysis of biomass which include agricultural products with both reactive (H2, CO,
CO2, CH4, C2H4, & C2H6 ) and not reactive (N2 ) gases for the production of gaseous
hydrocarbon fuels and feedstock.
A versatile, compact and economical down flow entrained tubular reactor is
designed and developed for these studies. The wood particles used in the experiment
consists of a seasoned sawdust. Feed rate of 40 gm/min is used. The elemental analysis
and characterization of the feed and effluent products are made.
V.5 : GAS ANALYSIS : -
The powder gas mainly consists of the following gases when air is introduced into
the reactor. These are N2, H2, CO, CO2, CH4, C2H4, C2H6 and H2O. Normally N2 and H2
gases are used as carrier gases in gas chromatograph. When N2 is used as a carrier gas, all
gases can be analyzed except N2 gas from the sample. Same is true for H2 gas. Gas
chromatograph gives the percentage of the different gases by volume. Producer gas has to
be analyzed with N2 and H2 carrier gases.
V.5.1 : DETAILS OF THE GAS CHROMATOGRAPH :-
1) Gas chromatograph : Toshinal (CHEMITO -3800)
2) Carrier gas : i) N2 ( IOLAR – 95% )
ii) H2 (95%)
3) Column : i) Porapak – Q ( 3 M x 3 mm)
ii) Spherocarb ( 3 M x 3 mm
4) Temperature : i) Detector – 2000C
ii) Oven - 500C
iii) Injector - 1000C
5) Detectors : i) Thermal conductivity detector (TCD)
ii) Hot wire detector (HWD)
iii) Flame ionization detector (FID)
6) Gas flow : 30 – 40 ml /min ( Souk gas flow meter)
PORAPAK –Q :- This column is used for analysis of CO/N2, CO2, CH4, C2H4,
C2H6, & H2 O gases with H2 as carrier gas.
SPHEROCARB :-This column is sued for separation of N2 and CO gases with H2
as a carrier gas.
V:6 : RESULTS :-
The volume percentage of the product gases are tabulated in TABLE-4 , TABLE-
5, and TABLE VI for the system temperature of 8000C and 10000C respectively. The
percentage of the product gases by weight and by mole are also tabulated in the following
TABLES. Densities of the different product gases are taken from the standard book “
CHEMICAL ENGINEERS HANDBOOK” ( 4 )
TABLE-IV : WEIGHT OF THE PRODUCT GASES AND PERCENTAGE OF
THE PRODUCT GASES BY MOLE & VOLUME AT 8000C.
Sr.
No.
Substances Percentage by
volume
Density
gm/lit
Weight gm MOLE
number
%
1 N2 55.30 1.18 5.52 2.34 55.30
2 H2 15.30 0.08 1.30 0.65 15.30
3 CO 11.15 1.18 13.20 0.47 11.12
4 CO2 9.64 1.87 18.05 0.41 9.68
5 CH4 2.13 0.68 1.44 0.09 2.13
6 C2H4 1.18 1.19 1.40 0.05 1.18
7 C2H6 0.17 1.28 0.22 0.01 0.16
8 H2O 5.13 0.76 3.90 0.22 4
100.00 105.03 4.23 100.00
TABLE-V : WEIGHT OF THE PRODUCT GASES AND PERCENTAGE OF
THE PRODUCT GASES BY MOLE & VOLUME AT SYSTEM
TEMPERATURE 9000C.
Sr.
No.
Substances Percentage by
volume
Density
gm/lit
Weight gm MOLE
number
%
1 N2 58.14 1.18 68.89 2.46 58.10
2 H2 15.93 0.08 1.36 0.68 16.00
3 CO 11.54 1.18 13.66 0.49 11.55
4 CO2 9.59 1.87 17.96 0.41 9.60
5 CH4 2.39 0.68 1.62 0.10 2.36
6 C2H4 0.95 1.19 1.13 0.04 0.94
7 C2H6 0.17 1.28 0.22 0.01 0.16
8 H2O 1.29 0.76 0.98 0.06 1.29
100.00 105.82 4.24 100.00
TABLE-VI : WEIGHT AND PERCENTAGE OF THE PRODUCT GASES BY
MOLE & VOLUME AT SYSTEM TEMPERATURE 10000C.
Sr.
No.
Substances Percentage by
volume
Density
gm/lit
Weight gm MOLE
number
%
1 N2 57.12 1.18 67.68 2.42 57.19
2 H2 16.05 0.08 1.37 0.68 16.20
3 CO 12.32 1.18 14.59 0.51 12.09
4 CO2 9.15 1.87 17.14 0.39 9.20
5 CH4 2.85 0.68 1.93 0.12 2.84
6 C2H4 1.12 1.19 1.33 0.05 1.12
7 C2H6 0.37 1.28 0.47 0.01 0.35
8 H2O 1.02 0.76 0.77 0.04 1.01
100.00 105.28 4.23 100.00
V.7 : CARBON BALANCE IN FEED RATE AND GASESOUS PRODUCTS :-
The system has the advantage that complete carbon by weight can be balanced
and quantity of gas formed can be estimated. This can be done by calculating the carbon
content in feed rate which has to be balanced with carbon content in the gas produced.
V.7.1 : CARBON CONTENT IN FEED RATE :-
Wood is vegetal organic matter which has the composition, carbon 50% ,
hydrogen 6% and oxygen 44%. It can be represented by the empirical formula C H
1.44 0 0.66.
Feeding rate of sawdust/wood particles is 40 gm/min. Carbon content in 40gm of
sawdust is 20gm but it is difficult to convert 100 % carbon in gaseous form. In this
system 20 % residues observed at 9000C which contents mainly ash and unburned wood
particles. Thus net carbon in feeding is 16 gm i.e. 16 gm/min carbon is converted in to
gaseous form.
V.7.2 : CARBON CONTENT IN THE PRODUCT GASES :-
The carbon content in the product gases is estimated by considering 100 lit of the
gas sample. For example consider a 100 litre of gas at system temperature 900OC. The
weight of the product gases is given in the table-5
e.g. carbon content in CO2
C + O2 --------------> CO2
12g 32g 44 gm
i.e. 44 gms f CO2 contains 12 gms of carbon. The 100 lit of gas contains by
weight 17.96 gms of CO2 Then carbon content in the 17.96 gm of CO2 is,
Carbon content X = 12/44 x 17.96
= 4.90 gm.
Similarly carbon content, by weight in 100 lit of producer gas is calculated and is
tabulated in TABLE-4.
Table –VII: CARBON CONTENT IN 100 LITRE OF PRODUCER GAS AT
SYSTEM TEMPERATURE 9000C.
Sr No Substance Weight of gas in 100
lit gam
Carbon Content gm
1 N2 68.69 -
2 H2 1.36 -
3 CO 13.66 -
4 CO2 17.96 5.85
5 CH4 1.62 4.90
6 C2H4 1.13 1.22
7 C2H6 0.22 1.04
8 H2O 0.98 0.18
105.82 13.19
It is conducted from the TABLE-VII that 13.19 gm of carbon can be converted in
to 100 lit of producer gas. From section V:5.1, the net carbon available for conversion is
16 gm, so total producer gas formed will be 120 lit. Thus 40 gm of sawdust can produce
120 litres of producer gas.
V.8 : ENERGY CALCULATIONS:-
V.8.1 : INPUT ENERGY:-
The energy from sawdust and external electrical energy used, combines the total
input energy.
i) Energy from sawdust:-
The calorific value of the saw dust is determined by burning athe sawdust and
transferring the heat to a material of known specific heat, such as water or air after that
the temperature rise of the heat absorbing material is measured. The calorific value of the
sawdust is determined with the help of BOMP CALORIMETER. The calorific value of
the sawdust is 16 MJ/Kg, which means that 1 g of saw dust is 16 MJ/Kg, which means
that 1 kg of saw dust gives 16 MJ energy.
Since our sawdust feed rate is 40 gm/min which gives net input energy 64000 J.
ii) External electrical energy applied:-
The hot zone of HTG is created by applying external electrical energy. The
temperature of the zone is mentioned by adjusting the voltage across the heater coil. For
example to get 900OC system temperature the electrical energy required is
a) For heating ceramic tube
current flowing through the coil = 4.35 amp
resistance of the wire = 40 ohm
Power (IR) = 756.9 watt
b) For heating air and lower heating zone
power = 250.1 watt
Total external electrical power = 1007.0 watt
i.e. Total external energy = 60420 J
Thus total input energy (i+ii) = 700240 J
V.8.2 : OUTPUT ENERGY:-
Output energy is sum of the energies from combustible product gases. TABLE-
VIII shows the energy obtained from 120 lit of produced gas. The calorific values of the
product gases are taken from “Chemical Engineer’s Hand Book”
TABLE –VIII :-ENERGY OBTAINED FROM 120 LITRE OF PRODUCER
GAS AT SYSTEM TEMPERATURE 9000C.
Sr No Substance Std. Calorific values
J/Lit
Product gas Lit Energy J
1 N2 - 69.76 -
2 H2 10361.6 19.12 198113.79
3 CO 12134.6 13.85 167925.71
4 CO2 - 11.51 -
5 CH4 34404.2 2.87 98740.05
6 C2H4 57015.1 1.14 64997.21
7 C2H6 61830.4 0.20 12366.08
8 H2O - 1.55 -
120.00 542142.84
Thus total output energy obtained per min = 542142.34 J
V.9: EFFICIENCY
V.9.1 : CONVERSION EFFECIENCY
The conversion efficiency defines, amount of biomass is converted in to gaseous
form. For 9000C system temperature it comes out to be,
Efficiency = energy from product gases per min / energy from sawdust
per min.
= 542142.84/640000.0
= 0.847
Or = 84.70 %
V.9.2 : OVERALL EFFICIENCY OF THE SYSTEM :-
To calculate the system efficiency, the external applied energy should also be
taken in to consideration. For 9000C the system temperature it comes out to be,
Total input energy per minute = 700420.00
Total output energy per minute = 542142.84
Overall system efficiency = 542142.84 / 700420.00
= 0.774
Or = 77.40 %
Similarly conversion efficiency and system efficiency can be calculated for 8000C
and 10000C system temperatures. Table-7 shows the conversion efficiency and system
efficiency at different temperatures.
TABLE –IX : CONVERSION EFFECIENCY AND SYSTEM EFFECIENCY
AT DIFFERENT TEMPERATURES
Sr No Temperature 0C Conversion effi % System effi %
1 800 82.08 75.76
2 900 84.70 77.40
3 1000 88.83 78.52
V.10: SUMMARY OF EXPERIMENTAL OBSERVATIONS:-
The following observations can be drawn from the experimental work.
i) The main combustible gaseous products from the fast pyrolysis (air catalyst)
of wood biomass are hydrogen and carbon monoxide.
ii) Approximately 80 % of the carbon in the sawdust can be converted
to the gaseous products, mainly hudrogen and carbon monoxide in the temperature range
800 – 10000 C.
iii) Significant amounts of methane, ethane and ethylene are also formed
in the temperature range 800 – 10000 C.
iv) Even though conversion efficiency an overall system is
comparatively more at 10000 C it recommended to operate the system at 9000 C. AT
10000C breakages of different parts of the system are observed.
v) The quality of the gas obtained is in the category of Low Joule value
(L.J.V) gas. Calorific values, 4.45, 4.63 and 4.89 MJ/m3 are observed at the system
temperatures 800, 900 and 10000C respectively.
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Daud and Ali, 2004 W.A.W. Daud and W.S.W. Ali, Comparison on pore
development of activated carbon produced from palm shell and coconut shell,
Bioresource Technology 93 (2004), pp. 63–69. Article | PDF (288 K) | View Record in
Scopus | Cited By in Scopus (23)
Fernandez et al., 2001 E. Fernandez, T.A. Centeno and F. Stoeckli, Chars and
activated carbons prepared from Asturian apple pulp, Adsorption Science and Technology
19 (2001), pp. 645–653. Full Text via CrossRef
Font et al., 1991 R. Font, A. Marcilla, E. Verdu and J. Devesa,
Thermogravimetric kinetic study of the pyrolysis of almond shells and almond shells
impregnated with CoCl2, Journal of Analytical and Applied Pyrolysis 21 (1991), pp. 249–
264. Abstract | PDF (889 K) | View Record in Scopus | Cited By in Scopus (36)
Gergova et al., 1993 K. Gergova, N. Petrov and V. Minkova, A comparison of
adsorption characteristics of various activated carbons, Journal of Chemical
Biotechnology 56 (1993), pp. 77–82. View Record in Scopus | Cited By in Scopus (49)
Gonzalez et al., 1997 M.T. Gonzalez, F. Rodriguez-Reinoso, A.N. Garcia and A.
Marcilla, CO2 activation of olive stones carbonized under different experimental
conditions, Carbon 35 (1997), pp. 159–162. Abstract | Article | PDF (429 K) | View
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Guillot et al., 2000 A. Guillot, F. Stoeckli and Y. Bauguil, The microporosity of
activated carbon fibre KF1500 assessed by combined CO2 adsorption and calorimetry
techniques and by immersion calorimetry, Adsorption Science and Technology 18 (2000),
pp. 1–14. Full Text via CrossRef | View Record in Scopus | Cited By in Scopus (10)
Kifani-Sahban et al., 1996 F. Kifani-Sahban, L. Belkbir and A. Zoulalian, Etude
de la pyrolyse lente de l’eucalyptus marocain par analyse thermique, Thermochimica
Acta 284 (1996), pp. 341–349. Abstract | PDF (418 K) | View Record in Scopus | Cited
By in Scopus (3)
Mackay and Roberts, 1982a D.M. Mackay and P.V. Roberts, The influence of
pyrolysis conditions on the subsequent gasification of lignocellulosic chars, Carbon 20
(1982), pp. 105–111. Abstract | PDF (746 K) | View Record in Scopus | Cited By in
Scopus (9)
Mackay and Roberts, 1982b D.M. Mackay and P.V. Roberts, The dependence of
char and carbon yield on lignocellulosic precursor composition, Carbon 20 (1982), pp.
87–94. Abstract | PDF (795 K) | View Record in Scopus | Cited By in Scopus (21)
Marcilla et al., 2000 A. Marcilla, S. Garcia-Garcia, M. Asensio and J.A. Conesa,
Influence of thermal treatment regime on the density and reactivity of activated carbons
from almond shells, Carbon 38 (2000), pp. 429–440. Abstract | Article | PDF (1357 K) |
View Record in Scopus | Cited By in Scopus (15)
Molina-Sabio et al., 1995 M. Molina-Sabio, F. Caturla and F. Rodriguez-Reinoso,
Influence of the atmosphere used in the carbonization of phosphoric acid impregnated
peach stones, Carbon 33 (1995), pp. 1180–1182. Abstract | PDF (298 K) | View Record
in Scopus | Cited By in Scopus (17)
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carbons from materials of varying morphological structure, Thermochimica Acta 129
(1988), pp. 173–186. Abstract | PDF (907 K) | View Record in Scopus | Cited By in
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kinetics of lignocellulosics materials – three independent reactions model, Fuel 78
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dependence of char yield on the amounts of components in precursors for pyrolysed
tropical fruit stones and seeds, Microporous and Mesoporous Materials 59 (2003), pp.
85–91. Abstract | Article | PDF (654 K) | View Record in Scopus | Cited By in Scopus (9)
Rodriguez-Reinoso et al., 1982 F. Rodriguez-Reinoso, J.deD. Lopez-Gonzalez
and C. Berenguer, Activated carbon from almond shells 1 – Preparation and
characterisation by nitrogen adsorption, Carbon 20 (1982), pp. 513–518. Abstract | PDF
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Rodriguez-Reinoso et al., 1984 F. Rodriguez-Reinoso, J.deD. Lopez-Gonzalez
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structure, Carbon 22 (1984), pp. 13–18. Abstract | PDF (533 K) | View Record in Scopus
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size distributions of active carbons assessed by different techniques, Carbon 38 (2000),
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Activated carbon from olive kernels in a two-stage process: Industrial improvement,
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Caballero et al., 1997 J.A. Caballero, A. Marcilla and J.A. Conesa,
Thermogravimetric analysis of olive stones with sulphuric acid treatment, Journal of
Analytical and Applied Pyrolysis 44 (1997), pp. 75–88. Article | PDF (159 K) | View
Record in Scopus | Cited By in Scopus (35)
Cagnon et al., 2003 B. Cagnon, X. Py, A. Guillot and F. Stoeckli, The effect of
carbonization/activation procedure on the microporous texture of the subsequent chars
and active carbons, Microporous and Mesoporous Materials 57 (2003), pp. 273–282.
Abstract | Article | PDF (161 K) | View Record in Scopus | Cited By in Scopus (11)
Daud and Ali, 2004 W.A.W. Daud and W.S.W. Ali, Comparison on pore
development of activated carbon produced from palm shell and coconut shell,
Bioresource Technology 93 (2004), pp. 63–69. Article | PDF (288 K) | View Record in
Scopus | Cited By in Scopus (23)
Fernandez et al., 2001 E. Fernandez, T.A. Centeno and F. Stoeckli, Chars and
activated carbons prepared from Asturian apple pulp, Adsorption Science and
Technology 19 (2001), pp. 645–653. Full Text via CrossRef
Font et al., 1991 R. Font, A. Marcilla, E. Verdu and J. Devesa,
Thermogravimetric kinetic study of the pyrolysis of almond shells and almond shells
impregnated with CoCl2, Journal of Analytical and Applied Pyrolysis 21 (1991), pp.
249–264. Abstract | PDF (889 K) | View Record in Scopus | Cited By in Scopus (36)
Gergova et al., 1993 K. Gergova, N. Petrov and V. Minkova, A comparison of
adsorption characteristics of various activated carbons, Journal of Chemical
Biotechnology 56 (1993), pp. 77–82. View Record in Scopus | Cited By in Scopus (49)
Gonzalez et al., 1997 M.T. Gonzalez, F. Rodriguez-Reinoso, A.N. Garcia and A.
Marcilla, CO2 activation of olive stones carbonized under different experimental
conditions, Carbon 35 (1997), pp. 159–162. Abstract | Article | PDF (429 K) | View
Record in Scopus | Cited By in Scopus (52)
Guillot et al., 2000 A. Guillot, F. Stoeckli and Y. Bauguil, The microporosity of
activated carbon fibre KF1500 assessed by combined CO2 adsorption and calorimetry
techniques and by immersion calorimetry, Adsorption Science and Technology 18
(2000), pp. 1–14. Full Text via CrossRef | View Record in Scopus | Cited By in Scopus
(10)
Kifani-Sahban et al., 1996 F. Kifani-Sahban, L. Belkbir and A. Zoulalian, Etude
de la pyrolyse lente de l’eucalyptus marocain par analyse thermique, Thermochimica
Acta 284 (1996), pp. 341–349. Abstract | PDF (418 K) | View Record in Scopus | Cited
By in Scopus (3)
Mackay and Roberts, 1982a D.M. Mackay and P.V. Roberts, The influence of
pyrolysis conditions on the subsequent gasification of lignocellulosic chars, Carbon 20
(1982), pp. 105–111. Abstract | PDF (746 K) | View Record in Scopus | Cited By in
Scopus (9)
Mackay and Roberts, 1982b D.M. Mackay and P.V. Roberts, The dependence of
char and carbon yield on lignocellulosic precursor composition, Carbon 20 (1982), pp.
87–94. Abstract | PDF (795 K) | View Record in Scopus | Cited By in Scopus (21)
Marcilla et al., 2000 A. Marcilla, S. Garcia-Garcia, M. Asensio and J.A. Conesa,
Influence of thermal treatment regime on the density and reactivity of activated carbons
from almond shells, Carbon 38 (2000), pp. 429–440. Abstract | Article | PDF (1357 K) |
View Record in Scopus | Cited By in Scopus (15)
Molina-Sabio et al., 1995 M. Molina-Sabio, F. Caturla and F. Rodriguez-Reinoso,
Influence of the atmosphere used in the carbonization of phosphoric acid impregnated
peach stones, Carbon 33 (1995), pp. 1180–1182. Abstract | PDF (298 K) | View Record
in Scopus | Cited By in Scopus (17)
Mortley et al., 1988 Q. Mortley, W.A. Mellowes and S. Thomas, Activated
carbons from materials of varying morphological structure, Thermochimica Acta 129
(1988), pp. 173–186. Abstract | PDF (907 K) | View Record in Scopus | Cited By in
Scopus (7)
Orfao et al., 1999 J.J.M. Orfao, F.J.A. Antunes and J.L. Figueiredo, Pyrolysis
kinetics of lignocellulosics materials – three independent reactions model, Fuel 78
(1999), pp. 349–358. Article | PDF (244 K) | View Record in Scopus | Cited By in Scopus
(148)
Ouensanga et al., 2003 A. Ouensanga, L. Largitte and M.A. Arsene, The
dependence of char yield on the amounts of components in precursors for pyrolysed
tropical fruit stones and seeds, Microporous and Mesoporous Materials 59 (2003), pp.
85–91. Abstract | Article | PDF (654 K) | View Record in Scopus | Cited By in Scopus (9)
Rodriguez-Reinoso et al., 1982 F. Rodriguez-Reinoso, J.deD. Lopez-Gonzalez
and C. Berenguer, Activated carbon from almond shells 1 – Preparation and
characterisation by nitrogen adsorption, Carbon 20 (1982), pp. 513–518. Abstract | PDF
(498 K) | View Record in Scopus | Cited By in Scopus (58)
Rodriguez-Reinoso et al., 1984 F. Rodriguez-Reinoso, J.deD. Lopez-Gonzalez
and C. Berenguer, Activated carbons from almond shells-II : Characterization of the pore
structure, Carbon 22 (1984), pp. 13–18. Abstract | PDF (533 K) | View Record in Scopus
| Cited By in Scopus (12)
Rodriguez-Reinoso et al., 1985 F. Rodriguez-Reinoso, J.M. Martin-Martinez and
M. Molina-Sabio, A comparison of the porous texture of two CO2 activated botanic
materials, Carbon 23 (1985), pp. 19–24. Abstract | PDF (558 K) | View Record in Scopus
| Cited By in Scopus (29)
Saeman et al., 1954 J.F. Saeman, W.E. Moore, R.L. Mitchell and M.A. Millett,
Techniques for the determination of pulp constituents by quantitative paper
chromatography, Tappi 37 (1954), pp. 336–343.
Sarwardeker et al., 1965 J.S. Sarwardeker, J.H. Sloneker and A. Jeanes,
Quantitative determination of monosaccharides as their alditol acetates by gas liquid
chromatography, Analytical Chemistry 37 (1965), pp. 1602–1604.
Shafizadeh and Chin, 1977 Shafizadeh, F., Chin, P.P.S., 1977. Wood technology:
chemical aspect. In: Goldstein, I.S., (Ed.), ACS Symposium Series 43.
Stoeckli, 1995 F. Stoeckli, Characterization of microporous carbons by adsorption
and immersion techniques. In: J. Patrick, Editor, Porosity in Carbons – Characterization
and Applications, Arnold, London (1995), pp. 67–92.
Stoeckli et al., 1999 F. Stoeckli, E. Daguerre and A. Guillot, The development of
micropore volumes and widths during physical activation of various precursors, Carbon
37 (1999), pp. 2075–2077. View Record in Scopus | Cited By in Scopus (19)
Stoeckli et al., 2000 F. Stoeckli, A. Guillot, D. Hugi-Cleary and A. Slasi, Pore
size distributions of active carbons assessed by different techniques, Carbon 38 (2000),
pp. 938–941. Abstract | Article | PDF (77 K)
Stoeckli et al., 2002 F. Stoeckli, A. Guillot, D. Hugi-Cleary and A. Slasi, The
comparison of experimental and calculated pore size distributions of activated carbons,
Carbon 40 (2002), pp. 383–388. Abstract | Article | PDF (129 K) | View Record in
Scopus | Cited By in Scopus (32)
Suarez-Garcia et al., 2002 F. Suarez-Garcia, A. Martinez-Alonso and J.M.D.
Tascon, Pyrolysis of apple pulp: effect of operation conditions and chemical additives,
Journal of Analytical and Applied Pyrolysis 62 (2002), pp. 93–109. Article | PDF (365 K)
| View Record in Scopus | Cited By in Scopus (20)
Zabaniotou et al., 2008 A. Zabaniotou, G. Stavropoulos and V. Skoulou,
Activated carbon from olive kernels in a two-stage process: Industrial improvement,
Bioresource Technology 99 (2008), pp. 320–326. Article | PDF (413 K) | View Record in
Scopus | Cited By in Scopus (3)