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A new technology for the combined production ofcharcoal and electricity through cogeneration

Adriana de Oliveira Vilela a,*,1, Electo Silva Lora b,Quelbis Roman Quintero b, Ricardo Antonio Vicintin a,1,Thalis Pacceli da Silva e Souza a,1

a Rima Industrial S/A, Departamento de Pesquisa e Desenvolvimento, Anel Rodovi�ario, km 4,5,

Belo Horizonte 30622-910, MG, Brazilb NEST e Nucleo de Excelencia em Gerac~ao Termel�etrica e Distribuıda, Instituto de Engenharia Mecanica,

Universidade Federal de Itajub�a, Av. BPS 1303, CP 50, Itajub�a 37500-083, MG, Brazil

a r t i c l e i n f o

Article history:

Received 17 February 2014

Received in revised form

16 June 2014

Accepted 27 June 2014

Available online

Keywords:

Charcoal

Pyrolysis gas

Cogeneration

Electricity

Biomass energy

* Corresponding author. Tel.: þ55 31 3329 44E-mail addresses: adn@rima.com.br (A. d

1 Tel.: þ55 31 3329 4000.http://dx.doi.org/10.1016/j.biombioe.2014.06.00961-9534/© 2014 Elsevier Ltd. All rights rese

a b s t r a c t

This paper presents an historical approach on the development of the existing biomass

carbonization technologies in industrial operation in Brazil, the biggest charcoal producing

country in the world. The gravimetric yield of charcoal from wood does not usually surpass

25%; the time of each operation cycle is more than seven days; and less than 50% of the

energy contained in the feedstock is transformed into charcoal e the rest is discharged into

the environment. The electricity generation associated with charcoal production is

nowadays inexistent in Brazil. This paper presents the development of an industrial

technology of semi-continuous pyrolysis process, characterized by using metallic kilns

with forced exhaust system: the Rima Container Kiln (RCK). The results of the test runs are

related to 5 m3 and 40 m3 kilns, with a thermal power of 200 kW (pilot scale: 5 m3) and

3000 kW (industrial scale: 40 m3). The low heating value of the pyrolysis gases is 670 and

1470 kJ/m3, respectively.

The main results are: a 3 h carbonization time; an average productivity per kiln of 1 ton

of charcoal per hour; and a gravimetric yield of 35%. In this paper, four scenarios for the

conversion of exhaust gases and tar into electricity were evaluated: the Conventional

Rankine Cycle (CRC) and the Organic Rankine Cycle (ORC), each one with and without

forest residues utilization. It is shown that the best economic indicators correspond to the

scenario where ORC technology is used. The electricity generation cost is around U$30/

MWhe for ORC and US$40/MWhe for CRC.

© 2014 Elsevier Ltd. All rights reserved.

83.e Oliveira Vilela), electo@unifei.edu.br (E.S. Lora).

19rved.

Table 1 e Products of carbonization.

Products of carbonization % Dry base

Charcoal (80% fixed carbon) 33.0

Pyroligneous acid 35.5

(Acetic acid) (0.5)

(Methanol) (0.2)

(Soluble tar) (5.0)

(Water and others) (23.5)

Insoluble tar 6.5

Non condensable gases (NCG) 25.0

(Hydrogen e 0.63%) (0.16)

(CO e 34%) (8.5)

(CO2 e 62%) (15.5)

(Methane e 2.43%) (0.61)

(Ethane e 0.13%) (0.03)

(Others e 0.81%) (0.20)

Total 100

b i om a s s a n d b i o e n e r g y 6 9 ( 2 0 1 4 ) 2 2 2e2 4 0 223

1. Introduction

1.1. The relevance of charcoal production in brazil

Some reports indicate that around the year 500 A.C. the

Macedonians used wood to produce charcoal and tar. Even

before that, the carbonization ofwoodwas already known and

utilized by the Egyptians, the Persians and the Chinese. The

process used by these ancient civilizations remains almost

unchanged today, especially from the energy loss point of

view, which can reach more than 50% of the biomass energy

content.

Fig. 1 shows the share of the total energy produced from

charcoal and the respective energy loss in the State of Minas

Gerais, Brazil from 1978 to 2010 [1]. Energy losses reduction, as

observed in recent years, was only possible through process

improvement, leading to increase in charcoal yield and more

efficient forest handling.

According to the National Energy Balance [2], Brazil has

44% of its energy matrix supplied by renewable sources. From

this total, around 10% correspond to wood and charcoal, 15%

to hydraulic electric generation, 16% to sugarcane, and 3%

corresponds to wind and solar energy based generation.

Around 4% of the total installed capacity for electricity gen-

eration in Brazil corresponds to thermal power stations,

which burn coal, gas, oil and biomass (such as bagasse and

wood dust). Nevertheless, there is not a single thermal power

installation that uses exhaust energy from carbonization

processes.

1.2. Wood carbonization

Wood carbonization involves a complex phenomenon that

allows the generation of awide range of chemical compounds,

which can be grouped as: charcoal, tar, pyroligneous acid and

gases [3].

Table 1, adapted from Refs. [4] and [5], shows the mass

fraction content, dry basis, of the main products derived from

wood pyrolysis. These results were obtained at laboratory

scale without oxygen supply and by using external heating.

Fig. 1 e Share of the total energy produced from charcoal in

the Minas Gerais State, Brazil from 1978 to 2010, as

granulated charcoal, other products (dust, tar and losses

(smoke).

The phenomena that occur during carbonization are

grouped differently depending on the author. For example,

Refs. [3] and [6], divide them in four stages as follows:

� A: Up to 200 �C, there is production of gases, such as water

vapor, CO2, formic and acetic acid.

� B: from 200 to 280 �C, the same gases from zone A are

released; but the emission of CO begins and there is a

substantial decrease in water vapor emission. The re-

actions in this zone are endothermic.

� C: from 280 to 500 �C. Carbonization occurs through

exothermic reactions. The products obtained in this stage

are influenced by secondary reactions, including formation

of fuel gases, tar, CO and CH4.

� D: over 500 �C. All wood has been converted into charcoal.

Various secondary reactions take place, catalyzed by the

carbonization layer.

According to Ref. [7], sugarcane bagasse and wood pyroly-

sis can be divided by stages in a similar way based on thermal

analysis results. Stage B corresponds to hemicelluloses

destruction and stage C to cellulose and lignin conversion into

charcoal.

Table 2, shows the main products generated in each stage

of carbonization, according to the temperature evolution of

the process. The values found in Table 2 correspond to tests

performed at laboratory scale as show in Ref. [8].

Fig. 2 presents the photos of wood pieces at different

carbonizationstagesaspreviouslydescribed. Fromleft to right:

in the first stage, the wood is dried and the released gases

contain only water vapor. In the second stage, the product is a

partially carbonizedwood, or toastedwood. This toastedwood

has the highest energy content per weight and also a great

content of volatile matters. In the third stage, hydrocarbons

start to be released and carbonization pushes forward to the

center of the wood piece, reducing its volume in the radial di-

rection. Finally, in the last stage, when the temperature rea-

ches 500 �C in the center of thewood piece, carbonizationmay

be interrupted. The charcoal at this final temperature has a

fixed carbon content of around 75%. Above 500 �C, the charcoalstructure and composition continues changing and the fixed

carbon content can reach more than 90%.

Table

2e

Evolutionofca

rbonizationasafu

nctionoftem

pera

ture.

Carb

onizationstage

Waterrem

oval

Oxyge

natedgase

spro

duction

Beginningofhydro

carb

ons

release

Hydro

carb

ons

release

CnH

m

Disso

ciation

ofch

arcoal

Hydro

genphase

Temperatu

re[�C]

150e200

200e280

280e380

380e500

500e700

700e900

Carb

onco

ntent(%

ofth

ech

arcoal)

60

68

78

84

89

91

Non

conden

sable

gases(%

)

CO

268.0

66.5

35.5

31.5

12.2

0.5

CO

30.0

30.0

20.5

12.3

24.6

9.7

H2

0.0

0.2

6.5

7.5

42.7

80.9

Hydro

carb

ons

2.0

3.3

37.5

48.7

20.5

8.9

Heatingvalue[kJ/m

3]

4.61

5.07

16.41

20.01

15.20

13.23

Condensa

ble

constituents

inth

egas

Watervapor

Watervaporand

ace

ticacid

Ace

ticacidmeth

ylalcohol

Lots

ofheavytar

Tar

Low

condensa

tion

Amountofgas

Very

small

Small

Important

Important

Small

Very

small

b i om a s s a n d b i o e n e r g y 6 9 ( 2 0 1 4 ) 2 2 2e2 4 0224

1.3. Traditional wood carbonization technologies

The “Hot Tail” kilns are the most widespread kilns within

Brazil, due to its simplicity and low cost, especially for small

producers. They are recommended for flat sites and, in gen-

eral, are built with baked bricks, clay and sand mortar. Nor-

mally, more than one kiln is used and they are disposed as

batteries or tandems.

The operation of the kiln starts with the firewood loading,

followed by carbonization and unloading of charcoal. The use

of dry firewood is essential for good carbonization, because

the firewood moisture directly influences the yield of the kiln

as show in Ref. [9].

There is an ideal temperature, around 60 �C, for unloadingthe kiln because the contact of air and charcoal at superior

temperatures can lead to fires. A standard kiln operation

consists of three to six days for carbonization, five days for

cooling and one day to unload/load the kiln [9].

In addition to the “Hot Tail” kiln there are other carbon-

ization technologies in Brazil, with similar productivity,

gravimetric yield and energy efficiency, such as: slope kiln,

surface kiln, rectangular kiln, beehive kiln, JG kiln, all made of

hewn stone and without forced exhaust system. The names

presented on this paragraph are a free translation from Por-

tuguese to English.

Table 3 and Table 4 present the results of studies [10] about

charcoal production from the main types of kilns in Brazil.

To ensure the economic and operational viability of the

mechanized charcoaling process, it was necessary to build

rectangular kilns, which can reach a production capacity

equivalent to five (5) surface kilns [11]. Today it is possible to

find rectangular kilns in operation with and without external

combustion. Their firewood capacity is higher than 700 m3

and they possess equipment for tar recovering, which is

usually released into the atmosphere in conventional hewing

stone kilns [12].

Table 5 presents the main charcoal production technolo-

gies, now in operation in the world, visited in 2007, with the

indication of capacity.

Vital et al. [13], made a comparative analysis of the pres-

ently used carbonization technologies. The results are pre-

sented in Table 6.

There is a technology, under development at laboratory

scale, based on the conversion of wood into charcoal by mi-

crowaves. According to Ref. [14], it is possible to attain a high

productivity conversion, with a specific energy consumption

of around 1000 kWh/(ton of wood).

The constraints of the traditional technologies for charcoal

production include:

� Difficulty in the mechanization of firewood loading and

charcoal unloading.

� Fragmentation of charcoal during unloading.

� Difficulty in automation due to the lack of instrumentation,

in particular: weight, flow rates and temperature

monitoring.

� Impossibility to use wood chips, which favors the gravi-

metric yield and productivity e an exception is the

continuous retort.

Fig. 2 e Wood pieces at different stages of the carbonization process. Source: Author.

Table 3 e Performance of the carbonization kilns in Brazil.

Type of construction Operation cycle (hours) Capacity Volumetric yield (st/CMC)

Firewood (st) Charcoal (CMC)

Hewing stone with internal heat source

Slope 240 20 8.7 2.3

Hot tail 144e168 20 8.0 2.5

JG surface 144 10e11 4e5 2.2

Rectangular V&M 264e312 180e240 95e130 1.8

Rectangular ACESITA 264 110 65 1.8

Metallic with internal heat source

Semi-continuous JG NA NA NA NA

Metallic with external heat source

DPC semi-continuous 72 80 53.3 1.5

NA ¼ Not available.

st ¼ cubic meter of stacked wood.

CMC ¼ cubic meters of charcoal.

b i om a s s a n d b i o e n e r g y 6 9 ( 2 0 1 4 ) 2 2 2e2 4 0 225

� High heterogeneity in the drying, pre-pyrolysis and the

pyrolysis profiles inside the kiln.

� High rate of partially carbonized wood formation due to

heterogeneous thermal distribution in the kiln.

� Large operation time, with low productivity.

� Difficulty in gas collection and in sealing the kiln.

1.4. Constraints of by-products utilization forcogeneration in conventional carbonization kilns

According to Ref. [15], companies that produce charcoal have

been developing alternatives to use the energy from gases

generated during the carbonization process. Some trials, at

the beginning of the 80's decade of the 20th century, allowed

obtaining tar, which was successfully used as fuel in

Table 4 e Constructive and operational characteristics ofthe hewing stone kilns.

Kilns Slope(3 m)

Hot tail(3 m)

Beehive(5 m)

JG(3 m)

Diameter [m] 3.0e4.0 2.9e3.8 3.0e8.0 3.0

Maximum

height [m]

2.5e2.8 2.3 max. 3.2e5.0 2.3 max.

Loaded firewood 20.0 st 8 st 5.0e200.0 t 14 st

Charcoal

[m3/months]

24.0 16.0e20.0 50.0e60.0 22

Cycle [days] 7e8 5e7 8e9 5e6

Useful life [years] 3 2e3 3e5 2e3

substitution of oil. Recently, there has been an evident in-

crease of interest in the use of gases from charcoal produc-

tion in burners and kilns, thus reducing gas emissions and

possibly obtaining thermal energy in a first stage (gases

burners) and electricity in a more advanced phase of

development.

According to Ref. [15], it is also important to mention the

technological barriers linked to the quality of the gases, whose

composition and heating values are not homogeneous

throughout the phases of the carbonization process. Such

barriers are present in the highly variable heating values of

the gases; especially in the initial phase of wood drying, when

the produced gases are difficult to combust, due to their high

water vapor content.

Among themain barriers that limit the use of gases and tar

from charcoal production for thermal power generation are:

a) Low heating value of the gases.

b) Variable composition and temperature of the gases in

different carbonization stages.

c) Variable moisture content of the tar generated during the

carbonization process.

d) Difficulties in developing a project of an adequate burner

for the combustion of the pyrolysis gases with high and

variable content of particulates, moisture and condens-

ables, which would require the installation of pre-filters.

e) The dilution and partial burning of the gases due to

admission of undesired air.

Table 5 e Characteristics of the conventional carbonization kilns.

Technologies Photos Characteristics

Hot tail kiln Kilns with amaximum diameter of 3.8 m and 2.3 m high, producing no

more than 4 m3 of charcoal per load. It presents low yield; control is

done by the color of the smoke. There are smoke and tar emissions.

The process lasts from 10 to 12 days.

Surface kilns Kilns with 5.0 m diameter, producing a maximum of 20 m3 of charcoal

per cycle from 36 st of firewood; the process lasts from 10 to 12 days.

Rectangular kilns 13 m long, 4 m wide and 3.5 m high, with a capacity to process 200

e700 m3 of firewood in stalks; operation cycles of 15 days and a

capacity of 2000 t of charcoal/year.

Slope kilns Widely used in the State of Minas Gerais because of their low cost and

operation very similar to the “Hot tail” kilns, with yields that do not

surpass 25%.

DPC process The stalks of firewood are dried, then carbonized and the charcoal is

cooled inside cages that are inserted in the kilns. In this technology,

the gas flow is modified according to the stages of the carbonization

process. The gas from the carbonization is used as thermal fluid. The

cycles last 60 h.

b i om a s s a n d b i o e n e r g y 6 9 ( 2 0 1 4 ) 2 2 2e2 4 0226

Table 5 e (continued )

Technologies Photos Characteristics

CML France Batteries of 12 fixed kilns; a charcoal production of 2500 t/year, with a

yield of 20e25%. Each load of 5th residual firewood produces 2 m3 of

charcoal per cycle. The cycle lasts 24 h.

Continuous retort The carbonization is carried out by the hot gases from the combustion,

and part of the gases from the pyrolysis. The firewood is fed, in pieces,

with 20% humidity, at the top of the retort, the cold charcoal is

discharged at the bottom, with tar recovering. The capacity of the

equipment is from 2000 to 10,000 t/year.

b i om a s s a n d b i o e n e r g y 6 9 ( 2 0 1 4 ) 2 2 2e2 4 0 227

It should be emphasized that there is an emission of 50 kg

of methane for each ton of produced charcoal. This is the

main environmental impact of the charcoal industry: it is well

known that methane has 25 times more global warming po-

tential than CO2 in a 100 years timeframe [16]. As methane is

not captured during photosynthesis, it is necessary to find a

way to mitigate its emissions. A possible alternative is the

combustion of the gases generated during the carbonization

process for heat recovery and electricity production. Other

possibility is to increase the gravimetric yield of charcoal,

because it would imply in less gas emissions.

This article intends to present a technology that can solve

the above listed challenges, providing a possible true fruitful

association between the charcoal production and the elec-

tricity cogeneration through by-products utilization,

reducing altogether the environmental impact of wood

carbonization.

Table 6 e Comparison of the performance of the kilns at use to

Kiln Capacity per kiln Investment Grav

Hot Tail 5 ton per month R$14/ton.year

Circular 8 ton per month R$27/ton.year

Rectangular 42 ton per month R$237/ton.year

Continuous Retort 450 ton per month R$648/ton.year

DPC 57 ton per month R$250/ton.year

2. Material and methods

2.1. Materials

In this work, three reactors with different design, sizes and

operation, were tested and used to improve the industrial

container reactor project, or Rima Container Kiln (RCK). In

order to combine the slow pyrolysis furnace with electric

power generation, the following reactors or kilns were used:

� laboratory scale reactor (5 L)

� pilot scale reactor (5 m3)

� industrial scale reactor (40 m3)

All of those reactors were designed, manufactured, tested

and evaluated during this study. The lab scale reactor, with

day in Brazil.

imetric yield Bio-mass based carbochemicals production

25% Very low

25% Low

30% 70e120 kg/t of charcoal

33% 250 kg/t of charcoal

35% 250 kg/t of charcoal

Fig. 3 e Scheme of gases analyzer and thermocouples in RCK.

b i om a s s a n d b i o e n e r g y 6 9 ( 2 0 1 4 ) 2 2 2e2 4 0228

electrical heating, was used to obtain the reference results.

Next, the project, construction and operation of the pilot

container were the basis for the definition of drying, carbon-

ization and cooling behaviors. Finally, the industrial reactor

was projected maintaining the same structural proportions

from the pilot kiln, but with structural, mechanical and

operational improvements.

For modeling and geometric definition of the pyrolysis re-

actors (pilot and industrial ones), a finite volume softwarewas

used (Ansys CFX, R.13). Pressure gauge, flow meter, thermo-

couples, infra-red temperature sensor, gas analyzer, wind

speed meter, precise weighbridge scales, weighing load cell

system and anemometer were used as instrumentation. Fig. 3

is a scheme of the rig and its instrumentation.

The wood used in the experiment was urograndis, a hybrid

between eucalyptus grandis and eucalyptus urophylla. The wood

pieces tested in the experiments had the following di-

mensions: (100 ± 20) cm in length; (60 ± 20) cm in width and

(40 ± 10) cm in thickness.

2.2. Local and procedures

All experimental data were taken from the pilot plant in

operation in the RimaGroup Forest Unit, located in Buritizeiro,

Minas Gerais.

Rima Industrial S/A is a metallurgy enterprise founded in

1975, located in Belo Horizonte, with factories in the northern

part of the State of Minas Gerais, Brazil. The ferro-alloys,

silicon and magnesium production from Rima Industrial S/A

requires an average consumption of 50,000 m3 of charcoal per

month.

The initial input values for energetic, economic, environ-

mental and thermodynamic calculations were taken from

theoretical and real data, measured on a pilot plant.

The designed system is able to provide real-time, accurate

measurement of mass flow rate of themain gas stream on the

furnace exhaust. This value is obtained indirectly by

measuring temperature, pressure and gas content. The mea-

surement and calculation are based on the stoichiometric

definitions, given by Fig. 4.

A program was specifically developed in MS Excel Solver

for the calculation of physical and chemical properties. Fig. 5

provides a block diagram of this program with the specific

inputs and outputs:

The entries in the program are:

� Weight loss of loaded firewood, internal temperature of the

kiln, flow rate and composition of the gases generated in

carbonization.

And the outputs are:

� Composition, temperature, volumetric and mass flow of

the outlet gas

� Heating value of the outlet gas

� Thermal power of the process

b i om a s s a n d b i o e n e r g y 6 9 ( 2 0 1 4 ) 2 2 2e2 4 0 229

� Percentage of tar, pyroligneous acid, carbonization gas and

charcoal which must be burned to sustain the carboniza-

tion process.

� Oxygen excess content

� Air flow inlet

� Percentage or rate of complete combustion

� Heat losses by gases

� Heat loss from the kiln

The MS Excel Solver provides these responses when the

difference between the mass content of non-condensable gas

components measured and the theoretical values derived

from the reaction is less than 2%. The final results presented

in the next sections are derived from the conduction of 10

tests in industrial model Rima Container Kiln (RCK).

For the evaluation of the electricity generation potential,

the following scenarios were considered:

� 1A: a CRC (conventional Rankine Cycle) using only the

pyrolysis gas as fuel.

� 1B: an ORC (Organic Rankine Cycle) using only the pyrolysis

gas as fuel.

� 2A: a CRC using the pyrolysis gas and fines (forest residues)

as fuel.

� 2B: an ORC using the pyrolysis gas and (fine forest residues)

as fuel.

General data for all the considered scenarios are as follows:

� Gas flow from each kiln: 6500 m3/h

� Number of kilns: 6

� Gas heating value: 1470 kJ/m3

� Gas thermal power: 15.8 MW

� Boiler efficiency in CRC: 80%

� Steam turbine efficiency in CRC: 75%

� Boiler efficiency in ORC: 90%

� Turbine efficiency in ORC: 80%

� Pump efficiency: 75%

3. RCK tests results

3.1. Development of a semi-continuous kiln: theindustrial Rima container kiln (RCK)

Ferreira [5] developed a container kiln and evaluated its

performance. The results indicated that the container kilns

have some advantages such as a higher productivity, gravi-

metric yield and durability; faster cooling, loading and

unloading operations, which can also be mechanized [12].

The first patent referred to this technology was granted by

INPI, the agency for industrial property in Brazil, to Rima

Industrial S/A in 2011. The technology developed by Rima

consists in the use of firewood pieces in metallic cylindrical

kilns, with lateral fissures, connected to an exhaust system,

as shown in Fig. 6.

The carbonization process in the Pilot RCK has the

following parameters:

� Yield: 33% of charcoal, with 81% of fixed carbon.

� 25% of non condensable gases, with a mean composition

of: 8% CO2, 12% CO, 2% of CH4, 1.5% H2, 2.5% O2 e 74% N2.

� 35% of pyroligneous acid solution, with 88% water, 5% of

acetic acid, 5% of tar and 2% of methanol.

� 6% of tar.

The gases composition was determined by chemical anal-

ysis carried out during the monitoring of the carbonization

process in the Pilot RCK.

Based on the results from the pilot reactor and with the

expectation of achieving better results in an industrial scale

reactor, the company decided to project, install and operate

an industrial unit (Industrial RCK) for the production of

charcoal. A schematic picture of this technology can be seen

in Fig. 7, that also shows the firewood loading, the carbon-

ization process and the unloading of charcoal.

This project startedwith the operation of a single kiln, with

sequential test runs. The tests in this kiln (Fig. 8) supplied

necessary information to evaluate the viability of energy

cogeneration, based on the pyrolysis gases. The information

included:

� Thermal and fluid dynamic simulations using a finite vol-

ume software to optimize the geometry of the industrial

kiln, as well as the exhaust system and the flow of the

gases during carbonization.

� Evaluation of the carbonization gases' circulation pattern

inside the kiln, from the hottest to the coldest section, in

order to homogenize temperature distribution. This would

avoid firewood burning in the hot section and the forma-

tion of partially carbonizedwood in the cold section, which

result in a low gravimetric yield.

� The implementation of a continuous and on-line data

attainment system.

� Instrumentation and automation of the process.

� Improvement in the utilization factor of the kilns and the

increase of their productive capacity.

� Development of a project for energy recovery from

exhausted carbonization gases for wood drying and elec-

tricity generation.

3.2. RCK development through modeling

From the studies of existing technologies, it was possible to

elaborate flow profiles, which identify the pathways of

generated gases according to the process conditions. Table 7

shows the possible configurations of the gases pathways.

The ignition procedure consists in the introduction/injec-

tion of energy into the kiln through the addition of burning

pieces of charcoal in the ignition valves. Next, the carbon-

ization takes place by gradually opening and closing other

valves according to local thermal needs.

When the 40 m3 RCK was built and the tests were run with

type A ignition, as it can be seen in Table 7, different problems

aroused. Explosions were frequent due to accumulation of

gases inside the kiln, and also due to formation of reflux zones

and gas pockets. Different pathway effects were analyzed

with the help of finite elements software, as it can be seen in

Fig. 9. This studywas based in the following premises: the kiln

is unloaded, the valves are open, the pressure inside the kiln is

Fig. 4 e Block diagram for the gas LHV calculation.

b i om a s s a n d b i o e n e r g y 6 9 ( 2 0 1 4 ) 2 2 2e2 4 0230

Fig. 5 e Block diagram for calculation of physical and chemical properties.

Fig. 6 e Top and lateral view of the Pilot RCK.

Fig. 7 e Industrial RCK loading, c

b i om a s s a n d b i o e n e r g y 6 9 ( 2 0 1 4 ) 2 2 2e2 4 0 231

equal to the atmospheric pressure and the gas flow is

6.500 m3/hr.

The problems were eliminated by varying the ignition

procedure and the pathway of gases. A continuous carbon-

ization cycle was ensured, with a mean duration of 3 h,

without throttling and/or internal blows or explosions. The

developed RCK technology took in consideration that the best

configuration for the gases flow pattern was the one with

ignition at the bottom and with central and bottom forced

exhaustion (type E in Table 7), keeping a continuous gas flow

along the whole height of the kiln, vertically and radially, as

shown in Fig. 10 and Fig. 11.

Based on the flow pathway analysis, the ignition was

changed to type E, meaning amodification from top to bottom

ignition. This change leads to:

� Homogenization of the internal temperature inside the

kiln.

� Substitution of a linear carbonization front for a volumetric

one.

arbonization and unloading.

Fig. 8 e Industrial RCK kiln with a capacity of 40 m3 of

firewood.

Topignition,ce

ntralexhaustion

byth

etop

Topignition,lateralexhaustion

byth

etop

austion

Ignitionatth

ebottom,ce

ntralexhaustion

byth

etop

Ignitionatth

ebottom,lateralexhaustion

byth

etop

b i om a s s a n d b i o e n e r g y 6 9 ( 2 0 1 4 ) 2 2 2e2 4 0232

� Reduction in the theoretical carbonization time in an in-

dustrial kiln.

� Increase of pyroligneous vapor fraction.

� A partial process of gasification, with the formation of

synthesis gas (Syngas) composed by CO and H2.

� The elimination of dead zones (gas stagnation), specially in

the case of hydrogen.

� Safe runs, without the formation of static pockets, mini-

mizing the possibility of combustion that induces blows

and explosions.

� Optimization of the RCK productivity with individual ca-

pacities similar to the Continuous Retort.

� A charcoal gravimetric yield equals to (34 ± 1) %. This value

is similar to the theoretical gravimetric yield, which was

determined to be 35%.

Table 8 shows the calculation of the theoretical gravimetric

yield. The calculation was based on the average content of

wood [17] and the conversion of each component into char-

coal [18]. The sum of the individual yields leads to the esti-

mated total gravimetric yield of carbonization.

Table

7e

Poss

ible

path

waysofth

egase

sfrom

theca

rbonization.

Topignition,ce

ntralexhaustion

byth

ebottom

Topignition,lateralexhaustion

byth

ebottom

Ignitionatth

ebottom,ce

ntralexhaustion

byth

ebottom

Ignitionatth

ebottom,lateralexh

byth

ebottom

3.3. Temperature vs. time relationship for ignition at thetop of the kiln

By monitoring internal temperatures in the industrial 40 m3

RCK, it was possible to obtain a thermal profile of the kiln. The

temperature monitoring system includes 28 points of tem-

perature measurement near the wall of the kiln and 42 points

in its internal part, as it is shown in Fig. 3. Moreover, there are

4 thermocouples located on the conical section of the kiln (at

the very bottom of the kiln).

As results of a series of tests with top ignition, the behavior

of the mean temperatures along the height of the kiln was

obtained. Fig. 12 shows the mean temperature for each height

level, calculated from the values of 10 thermocouples in each

level: 6 of them located in the middle of the reactor and 4 near

the wall (Fig. 3). The mean temperature for the conical part of

the kiln was calculated from the values obtainedwith the four

thermocouples located in this section. The level sequence is

descendent, with Level A being the top of the kiln and Level H

being the bottom (conical section). Fig. 13 shows the three

dimensional temperature profile of the kiln in the beginning,

middle and end of carbonization.

It is possible to infer that when ignition is done at the top of

the kiln, there is a highly heterogeneous temperature profile

during the carbonization process. At certain time intervals, if

Fig. 9 e Gas flow simulation in the empty RCK using

computational fluid dynamics program.

Fig. 11 e Flow of gases in a set of RCK.

Table 8 e Calculation of theoretical gravimetric yield ofcarbonization.

b i om a s s a n d b i o e n e r g y 6 9 ( 2 0 1 4 ) 2 2 2e2 4 0 233

comparing the top and the bottom of the kiln on Fig. 12, the

temperature difference is as high as 500 �C. A carbonization

kiln with this temperature profile has a carbonization time

superior to 8 h. In addition, the very humid gases generated

during carbonization show a descending pattern, going from

the hot region to the cold region; leading the vapors, which

also contain tar and pyroligneous acid, to condensate over the

non carbonized wood, significantly limiting heat transfer.

Another problem with the ignition at the top is the low tem-

perature in the bottom part of the kiln, which prevents the

complete carbonization of the wood. This is also observed in

Fig. 13, which shows the regions of the kiln with temperatures

Fig. 10 e Gas flow pattern in the RCK.

above 200 �C. It is possible to see that the hot regions are

restricted to the superior part of the kiln, moving next to the

center and then returning to the top (passing briefly through

the bottom).

These problems are aggravated due to the low thermal

conductivities of wood, partially carbonized wood and char-

coal. In the individual wood pieces, as carbonization proceeds

from the outside to the center (Fig. 14), the very low thermal

conductivities are themselves responsible for blocking the

carbonization front in the core of the piece [19], especially if

this piece is impregnated with tar.

By using the top ignition, there is also formation of gas

pockets, corresponding to dead zones of stagnant gases and/

or reflux. Hydrogen, being lighter, concentrates in the angles

and edges of the kiln, where it remains, not able to follow the

turbulent flow of the gases. These regions are potentially

explosive and, with favorable conditions, may cause explo-

sions with pressure waves so powerful that could lift a 40 ton

kiln.

Component Average contentin wood

Conversion ofcomponentinto charcoal

Finalyield

Cellulose 50% 34% 17%

Hemicelluloses 20% 10% 2%

Lignin 30% 55% 16%

Total yield 35%

Fig. 12 e Distribution of the temperature along the RCK for

top ignition procedure.

Fig. 13 e Three dimensional temperature profile for ignition at the top of the kiln.

b i om a s s a n d b i o e n e r g y 6 9 ( 2 0 1 4 ) 2 2 2e2 4 0234

3.4. Temperature vs. time relationship for ignition at thebottom of the kiln

By using 74 thermocouples, it was possible to obtain a tem-

perature distribution along the height of the kiln for the

carbonization process with ignition at the bottom. The tem-

perature profile is shown in Fig. 15, in which the height level is

descendent, with Level A representing the top of the kiln and

Level H, the bottom (conical section) of the kiln. Fig. 16 shows

the Three Dimensional Temperature Profile for the kiln in

different moments of carbonization.

When ignition of the kiln is done at the bottom, it is

possible to obtain improvements in kiln's performance in

comparison to top ignition. The first improvement is the ho-

mogeneity of temperature distribution, verified on Fig. 15 by

temperature differences from top to bottom of the kiln not

superior to 250 �C. This guarantees that materials in different

levels of the kiln are undergoing the same carbonization step

Fig. 14 e Wood pyrolysis mechanism.

virtually at the same time. This thermal homogeneity of the

kiln also allowed reducing the carbonization time to 3 h in a

kiln with 40 m3 capacity. Another advantage of this system is

the temperature increase at the bottom of the kiln, which now

makes possible a complete carbonization of the entire load

inside the reactor. This is observable on Fig. 16, in which the

regions above 200 �C extend throughout the entire volume of

the kiln e a clear difference from Fig. 13.

3.5. Curves of weight loss for bottom and top kilnignition

The industrial 40 m3 RCK is equipped with a weighing system,

which continuously monitors the weight loss during the

carbonization process. This systemallowed the comparison of

effects from bottom ignition and top ignition in carbonization.

Fig. 17 shows the curves of average weight loss registered

for carbonization with bottom and top ignition. Each curve is

represented by the mean of 10 runs and the standard devia-

tion is represented by error bars.

It is possible to observe in Fig. 17 that, when carbonization

is conducted with bottom ignition, the weight loss proceeds

more rapidly and the end of carbonization happens 5 h earlier.

3.6. Mass and energy balance

The main results obtained with carbonization in the 40 m3

RCK can be summarized as follows:

Fig. 15 e Temperature distribution from top to bottom of

the container kiln with the ignition at the bottom.

Fig. 16 e Three dimensional temperature profile for ignition at the bottom of the kiln.

0

2000

4000

6000

8000

10000

12000

14000

0 100 200 300 400 500 600

Time [min]

Wei

ght [

kg]

Ignition done by the Top Ignition done by the Base

Fig. 17 e Comparison of the mean weight loss curves when

ignition for the cases of top and bottom ignition.

b i om a s s a n d b i o e n e r g y 6 9 ( 2 0 1 4 ) 2 2 2e2 4 0 235

� Average gravimetric yield of (34 ± 1)% (the gravimetric yield

is defined as the ratio between the weight of produced

charcoal and the weight of dry firewood fed to the kiln).

� Volumetric conversion index of around 1.5 (this index is

defined as the ratio between the volume of firewood loaded

into the kiln and the volume of charcoal, in m3).

� Carbonization time: fluctuating from 3 to 5 h, depending on

the moisture of the firewood and on the final properties of

the charcoal i.e., the fixed carbon content, the density and

the mechanical resistance.

Table 9 provides information on the charcoal quality from

the industrial kiln (40 m3 RCK) with ignition at the bottom.

Table 9 e Charcoal quality.

Spin testa Drop testb Chem

Mean Deviation Mean Deviation %H2O %

53% 9% 34% 10% 6% 1

a Done according to ABNT MB 1375-80.b Done according to ABNT 7416-84.c Done according to NBR 8112 ABNT-D176264.d Done according to ABNT NBR 9165.e Done according to ASTM D 167-73.

The evolution in time of heating value and total thermal

power of the released gases in the 40 m3 kiln with bottom

ignition are shown in Fig. 18 and Fig. 19. Each curve corre-

sponds to one of the 10 tests done with the industrial kiln.

When comparing the 10 runs, it is possible to infer that the

curves show a stable behavior and a relatively low standard

deviation, especially when it is considered that the tests pre-

sented variation in the initial properties. As already

mentioned, the size of the wood pieces was (100 ± 20) cm in

length; (60 ± 20) cm inwidth and (40 ± 10) cm in thickness. The

humidity of thesewood pieces varied in the range of (19 ± 5) %.

The oscillations in Figs. 18 and 19 are the result of the

process time scale. The measurement or analysis of the gas is

done at 5 Hz, recording a moving mean of 10 s, which makes

the sampling interval shorter than the plotting interval. The

oscillations are represented as plateaus in Fig. 19 because of

the reduced time scale (many points and small area).

The results obtained in the industrial kiln were different

from the results previously obtained in the pilot kiln, mainly

the composition of the produced gas, as shown in Table 10.

The mean values presented on Table 10 are the results from 3

replicates conducted with the pilot kiln and 10 replicates with

the industrial one.

The performance of the industrial kiln was better than the

5 m3 pilot one, considering that the released gas was less

diluted. Another significant difference is that tar and pyro-

ligneous acid remained in the gas flow of the industrial kiln,

without condensation, as occurred in the pilot kiln.

Table 11 shows average gas composition results of test

runs carried out with the pilot and industrial kilns. Fig. 20

shows the energy distribution in carbonization products

ical analysisc Density

VM %ash %FC Bulkd (kg/m3) Truee (kg/m3)

8% 2% 81% 280 1500

Fig. 18 e Low heating value LHV (kJ/kg) of the gas.

Fig. 19 e Thermal power (MW) of the gas.

Table 11 e Gas composition tests results e mean values(%v/v).

Gases Pilotkiln

Deviation Industrialkiln

Deviation

CO2 7.1% 0.1% 11.6% 0.2%

CO 0.05% 0.01% 11.9% 0.4%

CH4 0.99% 0.05% 0.50% 0.01%

C3H8 0.15% 0.01% 0.30% 0.01%

H2 e e 0.10% 0.01%

O2 13% 2% 4.9% 0.1%

N2 77% 2% 71% 2%

Total 100% 100%

Low heating

value [kJ/m3]

670 2% 1470 1%

Fig. 20 e Energy distribution of the carbonization products

in the Pilot and Industrial RCK.

b i om a s s a n d b i o e n e r g y 6 9 ( 2 0 1 4 ) 2 2 2e2 4 0236

from pilot and industrial scale. The differences are due,

mainly, to design improvements in the industrial kiln and in

the process of carbonization. There are higher energy density

and temperature homogeneity in the industrial kiln, which

lead to the production of a gas with higher heating value and

higher potential for energy recovery.

Fig. 21 is a chart that includes the final energy balance, as

well as the energy available for cogeneration.

Fig. 21 e The final energy balance for the RCK.

3.7. Electricity generation using carbonization by-products

Container kilns make it possible to keep carbonization gases

composition and heating value constant. These kilns also

allow an energy recovery without implementing a cluster of

various kilns operating sequentially in different stages, which

would be an expensive and operationally complex procedure.

Based on a 6 container kiln unit, with a charcoal yield of

35% and wood with 19% initial humidity, it is possible to

generate around 6.0 MWe of power from the carbonization

Table 10 e Mass fractions of the byproducts from firewood carbonization (wet base).

Comparative analysis %Mass e pilot 5 m3 Deviation %Mass -industrial 40 m3 Deviation

Charcoal 27.0% 0.3% 28% 1%

Firewood gas 37.0% 0.9% 49% 7%

Tar þ pyroligneous 17.0% 0.6% 5.0% 0.5%

Humidity 19.0% 0.4% 18.0% 0.4%

Fig. 22 e Flow of the productive process and energy

recovery of the Rima Container Kilns.

Fig. 23 e Scheme of a conventional Rankine cycle.

Fig. 24 e A CRC for pyrolysis gases mo

b i om a s s a n d b i o e n e r g y 6 9 ( 2 0 1 4 ) 2 2 2e2 4 0 237

gas. This calculation assumes that the carbonization gas has a

heating value of 1470 kJ/m3 and the efficiency of the electricity

generation unit is 20%. The use of tar and forest residues as

complementary fuel would make energy generation increase

notably. Fig. 22 shows the productive process and energy re-

covery of the RCK plant.

The calculation of the installed power, when using

commercially available generation technologies, must be

preceded by its selection. For the conversion of energy from

the carbonization gas into electricity, external combustion

technologies were selected, as the gas contains tar, particles

and other compounds that may affect the operation of inter-

nal combustion devices. External combustion technologies

also allow the use of forest residues as complementary fuel.

Among external combustion technologies, the only one at

commercial stage is the Conventional Rankine Cycle (CRC),

which uses water as working fluid. The Organic Rankine

Cycle, known as ORC, which uses an organic fluid instead of

water, is at the early stages of commercialization, with few

hundred units in operation, mainly in Europe. One option to

increase the efficiency of such systems is the use of prime

movers as alternative to axial turbines systems in Conven-

tional Rankine Cycles, such as screw expanders, steam en-

gines and radial turbines. However, all these technologies

are in developing stage and demand a high investment cost.

The available power in a charcoal unit is of a few MWs e in

this power range, Conventional Rankine Cycles are techni-

cally feasible, although their efficiency could be low and the

investment cost high due to the low efficiency of axial tur-

bines. ORC systems have a higher efficiency in this power

range.

For modeling studies, related to energy recovery in RCK,

both the Conventional Rankine and ORC technologies were

considered. It was also assumed that eucalyptus biomass is

deled using cycle Tempo software.

Pyrolysis gas

Pump

Electricgenerator

Turbine CoolingTower

BoilerCondenser

Thermal Oil

Pump

Condenser

Pump

Organic

Fig. 25 e Scheme of an ORC system using pyrolysis gases.

b i om a s s a n d b i o e n e r g y 6 9 ( 2 0 1 4 ) 2 2 2e2 4 0238

chopped in the field and fines, not feasible for charcoal pro-

duction, are separately transported to the charcoal unit. The

fraction of fines is considered to be 3e5% and the average

transport distance 5e10 km.

Schemes and results for the four (4) evaluated scenarios

are presented in Figs. 23e26 and Tables 12e15.

Scenario 1A: CRC using only pyrolysis gases:

Scenario 1B: an ORC cycle using only the pyrolysis gas as

fuel.

Scenario 2A: CRC using the pyrolysis gas and fines (forest

residues) as fuel.

For scenarios 2A and 2B, the available fuel's thermal power

must include both the pyrolysis gases from the 6 kilns and the

fine forest residues, achieving a final value of 21.42 MW.

Scenario 2B: Pyrolysis gases and fines utilization in an ORC

system.

3.8. Investment and electricity generation costscalculations

An economic evaluation of each scenario was carried out to

determine the generation cost and the minimum commer-

cialization cost. In this calculation, the life of the generation

Fig. 26 e A conventional Rankine cycle for scenario

unit was assumed to be 18 years and the operation and

maintenance costs assumed to be 5% of the total investment.

Table 16 shows the results of the economic evaluation. The

lowest generation cost corresponds to scenario 2B, which

reached a value of 29.71 USD/MWh. The greatest NPV (Net

Present Value) corresponds also to scenario 2A. Theminimum

commercialization price for attaining economic feasibility, for

a corresponding IRR (internal rate of return) of 14%, was also

calculated for each scenario.

In Brazil, renewable energy sources represent 44% of the

total energy source, while in the world this ratio is only 14%

and in developed economies it is 6%. From the renewable

energy sources in Brazil, 33% correspond to hydraulic energy

and 58% to biomass energy. Approximately 22% of renewable

energy are forest based (firewood and charcoal). When it

comes to the generation of electricity, the most important

energy source is hydraulic, which represents 81% of the total

generation (MME, 2012).

Considering an average production of charcoal in Brazil

equal to 10 million ton/year, and based on the results of the

present work, it is possible to generate more than 800 MWe of

electric energy in the country from the use of pyrolysis gases.

Nevertheless, today, this contribution is null due to the lack of

consolidated technology.

Therefore, the generation of energy from all charcoal units

in Brazil could supply 5% of the electric demand of the coun-

try, considering altogether the use of biomass residues,

generated during firewood cutting.

There is great heterogeneity of costs in the electric sector,

which range from R$84.58/MWh for large hydroelectric plants

and R$956.70/MWh for thermoelectric plants based on diesel

oil. It is then possible to infer that the estimated costs in this

work for the generation of electric energy from pyrolysis gases

are highly competitive, especially if considering the current

stage of energy recession in Brazil, fundamentally dependent

on the inconstant rainfall regime.

2A, modeled using the software cycle Tempo.

Table 12 e Main results obtained from the modeling ofscenario 1A.

Parameters Unit Value

Fuel thermal power MW 15.8

Work fluid e Water

Net power MW 2.10

Efficiency % 13.36

Table 13 e Main results obtained from scenario 1B.

Parameters Unit Value

Fuel thermal power MW 15.8

Work fluid e Benzene

Thermal oil e DyPhenyl C2

Net power MW 3.04

Efficiency % 18.1

Table 14 e Main results obtained from scenario 2A.

Parameters Unit Value

Fuel thermal power MW 21.425

Working fluid e Water

Net power MW 2.9

Efficiency % 13.37

Table 15 e Main results obtained from scenario 2B.

Parameters Unit Value

Fuel thermal power MW 21.45

Working fluid e Benzene

Thermal oil e DyPhenyl C2

Net power MW 4.1

Efficiency % 18.2

b i om a s s a n d b i o e n e r g y 6 9 ( 2 0 1 4 ) 2 2 2e2 4 0 239

4. Conclusions

There is an enormous potential in the State of Minas Gerais

and in the entire Brazil for electricity generation using pyrol-

ysis gases and other byproducts from wood carbonization.

The reduction of the environmental impact related to gases

released into atmosphere must be also considered. For con-

ventional carbonization technologies, the energy recovery

from exhaust gases is complex because of the variation in its

composition during the different carbonization stages. Some

Table 16 e Results of the economical evaluation of scenarios 1

Parameters CRC e gas O

Fuel cost, USD$/(5e10 km) 0

Electric power, MW 2.1

Investment, USD$ 5,813,234

Levelized cost, USD$/MWh electric 51.65

Specific investment, USD$/MWe 2768.2

NPV, USD$ 353115.6

TIR, % 14.0

Minimum commercialization price, USD$

MWh�1

108.6

solutions as operation in synchronized clusters of kilns and

the built-up of a system of ducts is required. Another solution

is the implementation of a technology of semi-continuous or

continuous kilns.

The project development and tests results of a continuous

kiln e The Rima Container Kiln (RCM) were described and

discussed. Also, a technical and economical evaluation of

cogeneration options, based on a charcoal unit using RCK, was

performed.

The pilot RCKwas improved and it resulted in an industrial

unit, with an increased capacity, an instrumentation

arrangement, a control system, a mechanized operation and

improved thermal capacity.

During the tests, the load, the gas flow, the gas composi-

tion, the pressure and temperature values, the inlet air flow,

the firewood temperature in 74 points and the volume of

generated pyroligneous acid were monitored parameters. All

the data were continuously registered in real time. The tests

lead to a stabilized operational regime with the following

characteristics: volumetric yield: 1.3 st of firewood per m3 of

firewood; gravimetric yield: 34%; carbonization time: 3 h; gas

generation: 6500 m3/h in each kiln, with a heating value of

1470 kJ/m3; thermal power in each kiln: 3 MW; pyroligneous

acid production: 150 kg in each cycle and approximately 1 ton

of charcoal per hour, per kiln.

The RCK semi-continuous kiln allows solving the problems

present in conventional kilns for cogeneration based on py-

rolysis gases and other carbonization products. The gas

composition and its heating value are constant in time. The

average gas composition in the industrial prototypewas: CO2 -

11.2%, CO - 11.9%, CH4 - 0.50, C3H 8- 0.3, H2 - 0.1%, O2 -4.90, N2 -

70.7%.

The industrial kilns present higher productivity and po-

tential for utilization of carbonization by-products because

the composition and heating value of the pyrolysis gases are

constant. This avoids the necessity of building up ducts for

gases transportation and synchronizing kilns operation in a

pre-defined sequence.

Conventional Rankine Cycle (CRC) and Organic Rankine

Cycle (ORC) are the most suitable technologies for cogenera-

tion, using RCK by-products.

Four scenarios were evaluated: CRC and ORC technologies

with and without utilization of forest fines residues. From the

point of view of the economic indicators used in the feasibility

study (generation costs and NPV), the best scenarios are 1B

and 2A respectively. The best result is: ORC technology, which

has an electricity generation cost of 29.71 and 29.50 US$/MWh,

A, 1B, 2A and 2B.

RC e gas CRC e gas þ fines ORC e gas þ fines

0 1.36 1.36

3.0 2.9 4.1

4,602,433 6,214,207 6,288,781

29.50 39.74 29.71

1534.2 2142.83 1533.9

184121.7 392895.9 249167.9

14.0 14.0 14.0

61.2 82.5 61.4

b i om a s s a n d b i o e n e r g y 6 9 ( 2 0 1 4 ) 2 2 2e2 4 0240

for the cases with and without use of the forest residues

respectively.

The results obtained in this study lead to the conclusion

that the RCK presents not only a better carbonization perfor-

mance but it may also be an efficient and easier way to use

exhaust gases, tars and forest residues for electricity genera-

tion in a cogeneration arrangement.

Acknowledgment

The authors would especially like to thank the company Rima

Industrial S/A for believing, investing and providing human,

technical and financial resources for development, contin-

uous improvement and completion of this project. Special

thanks are also given to FINEP (a Brazilian Public Agency for

the promotion of Science, Technology and Innovation in

companies, universities and research institutions) for

believing and investing in this Project.

r e f e r e n c e s

[1] BEEMG. 26o Balanco Energ�etico do Estado de Minas Gerais,Ano base 2011. CEMIG; 2011.

[2] EPE. Balanco Energ�etico Nacional. E. d. P. Energ�etica. Rio deJaneiro: Minist�erio de Minas e Energia e MME; 2011. 267,from, https://ben.epe.gov.br/BENRelatorioFinal2011.aspx.

[3] Medeiros CA, Rezende MEA. Alcatr~ao Vegetal: Perspectivasde uso e produc~ao. Fundac~ao Jo~ao Pinheiro 1983;13(9a10):42e8.

[4] Gomes PA, Oliveira JB. Teoria da carbonizac~ao da madeira.In: Penedo WR, editor. Uso da madeira para fins energ�eticos.Belo Horizonte: CETEC; 1980. p. 158 [S�erie Publicac~oesT�ecnicas, n. 1].

[5] Ferreira OC. O futuro do carv~ao vegetal na siderurgia:emiss~ao de gases de efeito estufa na produc~ao e consumo docarv~ao vegetal. Revista Economia & Energia 2000;4(21).

[6] Mendes MG, Gomes PA, Oliveira JB. Propriedades e controleda qualidade do carv~ao vegetal. In: Produc~ao e utilizac~ao de

carv~ao vegetal. Belo Horizonte: Fundac~ao Centro Tecnol�ogicode Minas Gerais e CETEC; 1982. p. 77e89.

[7] Silva E, Nogueira L. Dendroenergia, Fundamentos eAplicac~oes. 2nd ed. Interciencia; 2003.

[8] Brito JO, e Barrichelo LEG. Considerac~oes sobre a produc~ao decarv~ao vegetal com madeiras da Amazonia. IPEF-ESALQ.S�erie T�ecnica, vol. 2; 1981. p. 1e25. #5.

[9] Fundac~ao Centro Tecnol�ogico de Minas Gerais e CETEC.Produc~ao e utilizac~ao de Carv~ao Vegetal, 1 v. Belo Horizonte:CETEC; 1982 [S�erie de Publicac~oes T�ecnicas].

[10] Pinheiros PCC, Sampaio RS, Rezende MEA. A produc~ao decarv~ao vegetal: teoria e pr�atica. Belo Horizonte; 2006.

[11] Nogueira CP, Franca GAC, Souza Junior L. Otimizac~ao daproduc~ao de carv~ao vegetal em escala industrial. In:Semin�ario De Balancos Energ�eticos Globais E Utilidades, 21.,1999, Vit�oria. Anais. Vit�oria: ABM; 1999. p. 1e10[Mimeografado].

[12] Baer RF. Avaliac~ao Economica, Ambiental e T�ecnica deQuatro Fornos para produc~ao de Carv~ao Vegetal. Monografia.UFV; 2008.

[13] Vital MHF, Pinto MAC. Condic~oes para a Sustentabilidade daProduc~ao de Carv~ao Vegetal para Fabricac~ao de Ferro-Gusano Brasil. BNDES Setorial 2009;30:237e97.

[14] Leal TE. Produc~ao de Carv~ao Vegetal atrav�es de micro-ondas.Monografia. Universidade Federal de Ouro Preto; 2012.

[15] Moura LF, Brito JO, Silva Junior FG. Effect of thermaltreatment on the chemical characteristics of wood fromEucalyptus grandis W. Hill ex Maiden under differentatmospheric conditions. CERNE (UFLA) 2012;18:449e55.

[16] United States Environmental Protection Agency. Methaneand nitrous oxide emissions from natural sources; April2010.

[17] Santos ID. Influencia dos teores de lignina, holocelulose eextrativos na densidade b�asica e contrac~ao da madeira e nosrendimentos e densidade do carv~ao vegetal de cinco esp�ecieslenhosas do cerrado. Departamento de Engenharia Florestale Universidade de Brasılia; Fevereiro 2008.

[18] Sinha S, Jhalani A. Modeling of pyrolysis in wood: a review.New Delhi e 110016-India: Department of MechanicalEngineering. Indian Institute of Technology.

[19] Di Blasi C. Analysis of convection and secondary reactioneffects within porous solid fuels undergoing pyrolysis.Combust Sci Technol 1993;90:315e39.