production of acrylonitrile
TRANSCRIPT
1. INTRODUCTION
1.1 HISTORY
Acrylonitrile was first synthesized in 1893 by Charles Moureu. It did not become
important until the 1930s, when industry began using it in new applications such as
acrylic fibers for textiles and synthetic rubber.
Although by the late 1940s the utility of Acrylonitrile was unquestioned, existing
manufacturing methods were expensive, multistep processes. They seemed reserved for
the world’s largest and wealthiest principal manufacturers. At such high production costs,
Acrylonitrile could well have remained little more than an interesting, low-volume
specialty chemical with limited applications.
However, in the late 1950’s, Sohio’s research into selective catalytic oxidation led
to a breakthrough in Acrylonitrile manufacture. The people who invented, developed, and
commercialized the process showed as much skill in marketing as in chemistry. The
result was a dramatic lowering of process costs. All other methods of producing
Acrylonitrile used till then have become obsolete.
Commercially, Acrylonitrile is manufactured today mainly by a single-step direct
method from propylene, ammonia and air over a fluidized bed catalyst. The process is
discovered and developed in the 1950s by scientists and engineers at The Standard Oil
Company, or Sohio which became part of British Petroleum (BP) in 1987.
Acrylonitrile (AN) is one of the leading chemicals with a worldwide production
of about 6 million tons in 2003. The most important applications are acrylic fibers,
thermoplastics (SAN, ABS), technical rubbers, adiponitrile, as well as speciality
polymers.
IPCL Vadodara produces Acrylonitrile of 84000 tons per annum in India. RIL
produces 70000 tons per annum of Acrylonitrile. Haldia Petrochemicals produces 40000
tons of Acrylonitrile per annum. Saudi Petrochemicals is one of the most famous plants
that produces Acrylonitrile in the World.
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2. PHYSICAL AND CHEMICAL PROPERTIES AND USES
2.1 Physical Properties
Acrylonitrile (C3H3N, mol.wt = 53.064) is an unsaturated molecule having a
carbon–carbon double bond conjugated with a Nitrile group. It is a colorless liquid, with
the faintly pungent odor of peach pits. Acrylonitrile is miscible with most organic
solvents, including acetone, benzene, carbon tetrachloride, ether, ethanol, ethyl acetate,
ethylene Cyanohydrin, liquid carbon dioxide, methanol, petroleum ether, toluene, xylene,
and some kerosene’s.
Table 2.1 Physical Properties of Acrylonitrile
Property Value
Molecular weight 53.06
Boiling point, 0C
At 101.3 kPa 77.3
At 66.65 kPa 64.7
At 33.33 kPa 45.5
At 13.33 kPa 23.6
At 6.665 kPa 8.7
Critical pressure, kPa 3.535 × 105
Critical temperature, 0C 246.0
Cryoscopic constant, mol%0C 2.7
Density, g/L
At 200C 806.0
At 250C 800.4
At 410C 783.9
Flash point (tag open cup), 0C −5
Freezing point, 0C −83.55 ± 0.05
Viscosity at 250C, mPa·s (= cP) 0.34
Heat of combustion, liquid at 250C, kJ/mol −1.7615 × 103
Heat of formation at 250C, kJ/mol
2
Vapor 189.83
Liquid 151.46
Heat of polymerization, kJ/mol −72.4 ± 2.1
Ignition temperature, 0C 481.0
Solubility in/of water at 20 0C 7.3%/3.08%
2.2 Chemical properties
The presence of both a double bond and an electron-accepting nitrile group permits
acrylonitrile to participate in a large number of addition reactions and polymerizations.
2.2.1 Reactions of the Nitrile Group:
Hydration and Hydrolysis:
In concentrated 85% sulfuric acid, partial hydrolysis of the nitrile group produces
acrylamide sulfate, which upon neutralization yields acrylamide; this is the basis for acryl
amide’s commercial production. In dilute acid or alkali, complete hydrolysis occurs to
yield acrylic acid.
Alcoholysis:
Reactions with primary alcohols, catalyzed by sulfuric acid and convert
acrylonitrile to acrylic esters. In the presence of alcohol and anhydrous halides, imido
ethers are formed.
2.2.2 Reactions with Olefins and Alcohols:
The Ritter reaction occurs with compounds such as olefins and secondary and
tertiary alcohols which form carbonium ions in acid, and N-substituted acrylamide’s are
formed.
2.2.3 Reactions with Aldehydes and Methylol Compounds:
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Catalyzed by sulfuric acid, formaldehyde and acrylonitrile react to form either
1,3,5-triacrylylhexahydro-s-triazine or N,N-methylenebisacrylamide, depending on the
conditions. Similarly, in the presence of sulfuric acid, N-methylolbenzamide reacts to
yield mixed bisamides. N- Ethylolphthalimide reacts to give N-
phthalimidomethylacrylamide. Reactions of the Double bond.
2.2.4 Diels-Alder Reactions:
Acrylonitrile acts as a dienophile with conjugated carbon–carbon double bonds to
form cyclic compounds. On the other hand, acrylonitrile can act as a diene. For example,
with tetrafluoroethylene 2,2,3,3- tetrafluorocyclobutanecarbonitrile forms; and with itself,
dimers of cis and trans cyclobutanedicarbonitriles form at high temperatures and
pressure. The activation energy for acrylonitrile cyclodimerization has been reported to
be 90.4 kJ/mol.
2.2.5 Hydrogenation:
With metal catalysts, an excellent yield of Propionitrile is attained, which can be
further hydrogenated to propylamine.
2.2.6 Halogenation:
At low temperatures, halogenation proceeds slowly to produce 2,3-
dihalopropionitriles. In the presence of pyridine, addition of chlorine forms 2,3-
dichloropropionitrile quantitatively. At elevated temperatures, without UV light, 2,2,3-
trihalopropionitrile is obtained; with UV light, both 2,2,3- and 2,3,3-isomers are formed.
Simultaneous chlorination and alcholysis occur to give 2,3-dichloropropionic acid esters.
2.2.7 Hydroformylation:
In a process also known as the Oxo-synthesis, acrylonitrile reacts with a mixture
of hydrogen and carbon monoxide, catalyzed by cobalt octacarbonyl, to give β-
cyanopropionaldehyde. This reacts with hydrogen cyanide and ammonia, and then
hydrolysis produces glutamic acid on a large commercial scale.
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2.2.8 Hydrodimerization:
The reductive dimerization of acrylonitrile can be done either chemically or
electrochemically to form adiponitrile. Hydrodimerization with its derivatives also takes
place.
2.2.9 Reactions with Azo Compounds:
Meerwein reactions of diazonium halides with acrylonitrile take place at low
temperatures, catalyzed by cupric chloride, to yield 2-halo-3-arylpropionitriles. Reactions
with diazomethane compounds lead to pyrazolines and finally cyclopropanes. Reactions
with 9-diazofluorene produce a cyanocyclopropane derivative, with the generation of
nitrogen. Phenyl azide reacts with acrylonitrile to yield a heterocyclic nitrile at room
temperature or an open-chain nitrile at elevated temperature.
2.3 Uses:
a) Acrylonitrile (ACN) is used principally as a monomer or co-monomer for
synthetic fibers, plastics, and elastomers. CAN contributes heat, chemical,
solvent, and weathering resistance to polymers. In addition to its use in acrylic
and mod acrylic fibers, acrylonitrile is used to produce adiponitrile, a nylon
intermediate, by electrolytic reduction and dimerization. Adiponitrile is then
hydrogenated to hexamethylenediamine, a comonomer with adipic acid in the
manufacture of nylon 66 polymers used in fibers and plastics.
b) Acrylonitrile is an important constituent of high impact strength resins such as
Acrylonitrile/butadiene/styrene (ABS) and styrene/acrylonitrile (SAN). ABS
contains about 25 percent acrylonitrile, and SAN contains about 30 percent
acrylonitrile. ABS is used in appliances, business machines, telephones,
transportation and recreation equipment, luggage, and construction. SAN is used
in appliances, packaging, house wares, and automotive applications.
c) Nitrile rubbers, made by copolymerization of acrylonitrile with butadiene, have
good resistance to abrasion, heat aging, lubricating oils, and gasoline. They are
chiefly used in automotive applications such as fuel lines.
d) Catalytic hydrolysis of acrylonitrile yields acrylamide, which forms a variety of
homo polymers and copolymers. These polymers are used as flocculants in water
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and waste treatment, as mobility control agents in crude oil recovery, as retention
aids in paper making, and in froth floatation process.
e) Polyacrylonitrile (PAN) is the precursor for carbon fiber for high strength
applications ranging from aircraft parts to sporting equipment. PAN-based carbon
fiber is still a low volume specialty material due to its relatively high cost to
produce.
f) Other applications for acrylonitrile include adhesives, corrosion inhibitors, and
comonomer with vinyl chloride, vinylidene chloride, vinyl acetate, and/or
acrylates in resins for paints and coatings.
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3. LITERATURE SURVEY FOR DIFFERENT PROCESSES
3.1 Production of Acrylonitrile from different Feed stocks
3.1.1 From Propionitrile
Propionitrile is subject to oxidative dehydrogenation at high temperatures in the presence
of a stoichiometric excess of a metal oxide oxygen donor to produce acrylonitrile at a
high rate of conversion and selectivity.
Process Description:
Propionitrile is oxidatively dehydrogenated to form acrylonitrile in the presence of an
excess of at least 15% of
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ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff
ffffffffffffffffffffffffffffffffffffffffffffffffff metal oxide donor over the amount of the metal
oxide stochiometrically required to furnish the oxygen necessary for the oxidative
reaction at temperatures of 725-900 0C. The metal oxide donor is selected from the group
consisting of stannic oxide, lead oxide, zinc oxide and antimony oxide. Stannic oxide is
preferred and it is preferably supported on an alumina carrier. Feed rate is adjusted so as
to provide the best conversion rate of propionitrile and selectivity of acrylonitrile.
CH3 – CH2 – CN → CH2 = CH – CN + H2 (3.1)
3.1.2 From Acetylene
Addition of Hydrogen cyanide to Acetylene
Process Description:
This is highly exothermic reaction:
C2H2 + HCN → CH2 = CH-CN + 175 kJ/mol at 298 K (3.2)
This is conducted industrially in the liquid phase in the presence of a catalyst consisting
of cuprous chloride and ammonium chloride in hydrochloric acid solution. A large excess
of acetylene is used (6-15 mol/mol of HCN) at a pressure slightly above 105 Pa and a
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temperature of 80-90 0C. The molar yield is up to 90% in relation to hydrogen cyanide
and 75-80% in relation to acetylene. The main byproducts are acetaldehyde,
vinylacetylene, divinylacetylene and vinylchloride etc.
The same reaction can be conducted in the vapor phase around 500-600 0C on charcoal
impregnated with caustic soda and cyanides.
3.1.3 From Acetaldehyde
Process Description:
The raw material is acetaldehyde converted in two steps to acrylonitrile:
In the first step lacto nitrile is formed by the addition of hydrogen cyanide to
acetaldehyde.
CH3-CHO + HCN → CH3-CHOH-CN (3.3)
The reaction which is highly exothermic and very fast takes place between10-200C and at
pH between 7-7.5 with a molar yield of 97-98 %.
In the second step, the lacto nitrile is dehydrated to acrylonitrile.
CH3-CHOH-CN → CH2 = CH - CN + H20 (3.4)
To prevent redecomposition into acetaldehyde and hydrogen cyanide, the reaction takes
place with a large excess of phosphoric acid by spraying at 600-700 0C in a reactor in
which the lacto nitrile is placed in contact with a hot, oxygen free inert gas during an
interval shorter than 3 s. The total molar yields are about 90 % in relation to acetaldehyde
and 92 % in relation to hydrogen cyanide.
3.1.4 From propylene with Nitric oxide
Process Description:
This involves the following Conversion
4CH2 = CH - CH3 + 6NO → 4CH2 = CH - CN + 6H2O + N2 (3.5)
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It takes place at atmospheric pressure, between 450-550 0C in presence of a silver oxide
based catalyst deposited on silica or of alkali earth metal oxides, thallium and lead, and
with excess propylene. An inert is used as a diluent, in order to absorb the heat generated
during the conversion, whose molar yield is 70 % in relation to propylene.
3.1.5 From Propylene by Ammoxidation Process
This involves the following Conversion
CH2 = CH - CH3 + NH3 + 3/2O2 → CH2 = CH – CN + 3H2O (3.6)
Process Description:
The reaction is highly exothermal which releases 123 kcal/mol and takes place in gaseous
phase over a suitable catalyst at temperatures of 300-500 0C and pressures of 1.5-3 bar in
fluid bed or fixed bed reactors with efficient cooling.
3.2 Different technologies employed for Ammoxidation
3.2.1 Tandem Process
The indirect ammoxidation of glycerol to acrylonitrile via intermediate formation of
acrolein was studied using a tandem reactor coupling a dehydration step with an
ammoxidation step. For the first step of dehydration of glycerol to acrolein, we used a
previously optimized WO3/TiO2 catalyst, while Sb-V-O or Sb-Fe-O catalysts were
developed and used for the subsequent ammoxidation step. Especially, the Sb-Fe-O
catalysts were found highly selective and thus were more-deeply investigated. The
corresponding catalysts were characterized by nitrogen physisorption, X-ray powder
diffraction, thermo gravimetric analysis, X-ray photoelectron spectroscopy, and
temperature-programmed reduction in the presence ofH2. We found that the presence of a
FeSbO4 mixed phase on the synthesized samples was correlated to a high selectivity to
acrylonitrile. Further, we observed an increase in selectivity to acrylonitrile with the
reaction time, which was explained by the progressive formation of additional amounts of
FeSbO4 on the catalysts during the reaction. Finally, the reaction parameters
(temperature, catalyst amount, molarNH3/AC ratio and molar O2/AC ratio) for the
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catalyst with an Sb/Fe molar ratio of 0.6 were optimized, whereby a maximum yield in
acrylonitrile of 40% (based on glycerol) could be achieved.
Figure 3.1 Flow Diagram for Tandem Process
3.2.2 DuPont Technology ( Licensor Kellogg Brown and Root):
This technology is used in Beaumont, Texas (200,000 MMTPA). Propylene, ammonia
and air are fed to a fluidized bed reactor to produce acrylonitrile using DuPont’s
proprietary catalyst system. Other useful products are HCN and Acetonitrile. The
reaction is highly exothermic and heat is recovered from reactor by producing high
pressure steam. The reactor effluent is quenched and neutralized with sulfuric acid
solution to remove excess ammonia.
The product gas from the quench is absorbed with water to recover the Acrylonitrile,
Acetonitrile and HCN. The aqueous solution of Acrylonitrile, Acetonitrile and HCN is
then fractionated and purified into high quality products. The products recovery and
purification is highly efficient and low energy consumption process. The acrylonitrile
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P1
P2
O2
NH3
O2
N2
gylcerol feed
acidic solution
dehydrationammoxidation
off-gas
sample
technology minimizes the amount of aqueous effluent, a major considerations for all
acrylonitrile producers.
The acrylonitrile is based on high activity, high throughput catalyst. The propylene
conversion is 99 % and with a selectivity of 85 % to useful products of Acrylonitrile,
Acetonitrile and HCN. The DuPont catalyst is mechanically superior catalyst, resulting in
low catalyst loss. DuPont has developed a Catalyst Bed Management Program (CBMP)
to maintain the properties of the catalyst bed inside the reactor at optimal performance
throughout the operation. The catalyst properties, CBMP and proprietary reactor internals
provide an optimal performance of acrylonitrile reactor, resulting in high yields.
With over 30 years of experience, DuPont has developed know-how to increase the on-
stream factor of the plant. This know-how includes the effective use of inhibitors to
reduce the formation of cyanide and nitrile polymers and effective application of an
antifouling system to increase on-stream time for equipment.
Figure 3.2 Flow Diagram for DuPont Process
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4. SELECTION OF A PROCESS
4.1 Selection of Sohio Process
We here select the Sohio process that is direct ammoxidation of propylene by considering
all the below mentioned factors:
The manufacturing of acrylonitrile by Sohio process is selected because of the high
performance achieved with the modern catalysts based on molybdenum/antimonium
oxides. The conversion of propene is practically complete, while the ammonia and
oxygen are used in amounts close to stoichiometry. Fluid-bed-reactor technology allows
short reaction times and very high heat-transfer coefficients to be achieved, by preserving
safety despite the potential explosive reaction mixture and very high exothermic effect.
Maximum conversion is achieved in the Sohio process that is fluidized bed reactor
technology. This is the current technology that is mostly employed, more economical,
commercial process and production costs are less when compared to the other
technologies. Sohio technology is invented when the existing dupont and other
technologies are insufficient to satisfy the demand of Acrylonitrile. High Capacity plant
can be achieved using the technology.
4.2 Process description:
The process for the manufacture of acrylonitrile (99% pure) is accomplished in
various sections. Primarily the reactants are charged into the reactor at required
proportions where they convert into various products. The separation and purification of
the products are the later steps in the process. The detailed process in various equipments
is as follows.
4.2.1 Reactor
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Reactor is the heart of the entire process. The production of acrylonitrile from
propylene, ammonia and air is accomplished catalytically in a fluidized bed reactor,
forming some other by products. The reactions are highly exothermic.
1). Acrylonitrile
C3H6 +32 O2 + NH3 → CH2 = CH - CN + 3H2O
2). Acetonitrile formation
C3H6 + 3/2 O2+ NH3 → 3/2 CH2CN + 3H2O
3). Acrolein formation
C3H6 + O2 → CH2 = CHCHO + H2O
4). Acrylic acid
C3H6 + 32O2 → CH2 = CHCOOH + H2O
5). Hydrocyanic acid
C3H6 + 3O2 + 3NH3 → 3HCN + 6H20
6). Propylene burning to carbon dioxide
C3H6 + 92O2 → 3CO2 + 3H2O
7) Propylene burning to carbon monoxide
C3H6 + 3O2 → 3CO + 3H2O
The process air compressor provides reaction air. The reacting gases rising
through catalyst bed will not only cause the bed to ride and expand, but will cause it to
flow and turn over in the reactor. Too low flow of gases through the reactor will not give
good contacting, but will allow the gas to merely bubble through or channel through the
catalyst bed. On the other hand, too high a flow of gases will cause the catalyst to be
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carried over in the reactor and a loss of catalyst will result. The catalyst is a finely divided
solid. As the reactions that take place are exothermic in nature, cooling is necessary. Heat
from the reaction is transferred to the circulating water in the steam coils producing
steam.
The gas stream, leaving the reactor passes through the cyclones. These cyclones
retain most of the entrained catalyst and return it to the catalyst bed. During normal
operation, catalyst fines are produced in the reactor due to attrition. Fines that are too
small to be retained by the cyclones pass out of the reactor with the effluent gases.
Reactor effluent gases pass through the cooler where they give up heat to boiler feed
water. From there, the partially cooled effluent gases flow to the hot quench. It is always
desirable to keep the temperature of gases from cooler outlet above 2320C to limit
condensation of heavy polymers and avoid fouling. The effluent from the reactor must be
continuously monitored for oxygen content. Zero oxygen in the reactor causes reduction
of the catalyst. On the other hand, high oxygen contents forms explosive mixture and
increases the risk of fire hazards.
4.2.2 Quench column
Partially cooled reactor effluent gases at a temperature not less than 2320C are
introduced to the bottom of the quench column. The quench column is made of two
stages. Adiabatic cooling to 85 – 900C takes place in the column depending upon the load
and cooler outlet temperature. Catalyst fines and polymers will be caught by the lower
stage spray and removed from quench column bottom.
Unreacted ammonia entering the quench upper stage is neutralized by sulphuric
acid distributed by spray spargers. Ammonium sulphate solution, collected in the
collection tray sump and ammonium sulphate recovered as by-product. DM water on
stripper bottom can be used to charge the quench system. The outlet stream from upper
section will have a minimum of 33wt% (NH4)2SO4. The effluent gas comes out of the
quench at around 850C. The gaseous stream later enters coolers. Here, the effluent gases
will be cooled from 850C to about 350C using cooling water and partial recycle of the
condensed steam before it enters the absorber.
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4.2.3 Separation column
The cooled reactor effluent gases leaving the quench column are scrubbed counter
currently using lean water in the absorber, used to recover the Acrylonitrile and other
organic reaction products. Carbon monoxide, carbon dioxide, nitrogen, unreacted oxygen,
unreacted propylene and hydrocarbons, which are not absorbed come out from the top
and sent to the incinerator.
The Absorber water flows downward to the absorber bottom absorbing the
acrylonitrile and other organics from the reactor effluent gases. The absorber is designed
to recover 99% of Acrylonitrile in the feed gases. A portion of the bottom stream is
cooled the water then passes through the propylene vaporizer. This cold water is then
returned to the absorber bottom cooler. The rich water leaving the bottom of the absorber
is heated by exchanging heat with solvent water in a heat exchanger and then enters the
recovery column separates the Acetonitrile from the acrylonitrile by extractive
distillation.
Water is used as the solvent in the separation of acrylonitrile from Acetonitrile.
The acrylonitrile goes overhead, preferably as an acrylonitrile water azeotrope. The
Acetonitrile goes out at the bottom of the column in dilute water solution. The hydrogen
cyanide in the feed splits; most of the hydrogen cyanide goes overhead with acrylonitrile
and some goes out the bottom with the Acetonitrile. A stripper is employed to remove the
Acetonitrile and hydrogen cyanide from the bulk of circulating water, so that the water
can b reused in the absorber and recovery column. On the other hand, head drying
column removes hydrogen cyanide and water from acrylonitrile. The feed to this column
is crude acrylonitrile from the recovery column.
The net overload stream from the heads column will be primarily hydrogen
cyanide with a little acrylonitrile, which will be taken to hydrogen cyanide purification.
4.2.4 Product column
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The product column operates under vacuum which separates heavier and lighter
fractions from the acrylonitrile. The column is equipped with an overhead condenser and
a vent condenser for removing non-condensable.
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17
Fluidized bed reactor
VaporizerVaporizer
Compressor
Propylene
Ammonia
Air
Steam
BFWCatalyst settling pit
Uppersection
Lowersection
Cooler
Water
Sulphuric acid
(NH4)2SO2
condenser
Quench column
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In process bottom s storage
19
Reco
very
col
umn
Crude Aceto nitrile
CrudeAcrylonitrile
strip
per
Aqueous residue to treatment
Figure 4.1 Flow Diagram for Sohio Process
5. PROCESS DETAILS INCLUDING CHEMISTRY AND
THERMODYNAMICS
5.1 Chemistry issues
The ammoxidation of propene to acrylonitrile described by the global equation actually
involves a very complex reaction mechanism. More generally, the reaction of
ammoxidation refers to the interaction of ammonia with a hydrocarbon partner (alkene,
alkane or aromatic) in the presence of oxygen and suitable catalyst. An ammoxidation
catalyst must fulfill two conditions: possess redox properties and be multifunctional. The
major steps in a catalytic cycle. Firstly, ammonia interacts with the bi-functional active
centers, generating an extended “ammoxidation site”. The first active species forms from
ammonia as = NH, then on this site the alkene inserts as an “allylic complex” byα -
hydrogen abstraction. After the rearrangement of atoms the surface complex is
transformed in the product H2C = CH - CN, which further desorbs from the surface. The
result of this process is a reduced surface site whose regeneration takes place by the
oxygen (O2-) coming exclusively from the catalyst lattice. Subsequently, the lattice has to
be filled - in with oxygen coming from the gas phase. Thus, the overall reaction takes
place via a common solid - state lattice capable of exchanging electrons, anion vacancies
and oxygen transmission. The above mechanism is consistent with the concept of “site
isolation” proposed by Grasselli and Callahan the inventors of the SOHIO catalyst, which
states that an ammoxidation catalyst becomes selective when the reacting oxygen species
at the active centers are spatially isolated from each other. The knowledge of the reaction
mechanism is important for process design. Firstly, only olefins with activated methyl
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groups may undergo ammoxidation reactions to nitriles. Otherwise, oxidative
dehydrogenation takes place preferentially. For example, from the isomers = C 4 only
isobutene can give methacrylicnitrile. Toluene and xylenes can be converted to the
corresponding nitriles too. Secondly, the role of ammonia as chemisorbed species = NH
is primordial in reaction, because they start the catalytic cycle before propene. Therefore,
sufficient ammonia has to be present in the reaction mixture, slightly above the
stoichiometric amount. Otherwise, the sites are occupied by oxygen and the combustion
prevails. The oxygen should be fed so as to replace only the amount consumed in the
lattice, in slight excess above the stoichiometry. As a result, the reaction mechanism
suggests that propane and ammonia should be mixed and fed together, while the oxygen
should enter the reaction space independently in order to fill the lattice. This principle is
applied in the reactor technology. Among secondary reactions the most important losses
are by oxidations, namely by propene combustion:
CH2=CH-CH3 + 32O2 → 3CO2 + 3H2O
CH2 = CH-CH3 + 3 O2 → 3CO + 3H2O
As a consequence, the overall exothermic effect rises to about 160 kcal/mol propene. In
the absence of ammonia the active sites are oxidic leading to Acrolein:
CH2 = CH-CH3 +12O2 → CH2 = CH-CHO + H2O
Partially, the oxidation may progress to alylic alcohol. Other byproducts of significance
are HCN and Acetonitrile, whose formation may be expressed by the overall reactions:
CH2 = CH-CH3 + 3NH3 + 3O2 → 3HCN + 6H2O
2CH2 = CH-CH3 + 3NH3 + 32O2 → 3CH3-CN + 3H2O
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The stoichiometry indicates a complex reaction mechanism. The amount of HCN is
generally larger than that of acetonitrile, the ratio depending on the catalyst formulation
and reaction conditions. Both reactions are favored by higher temperature and pressure,
as well as by longer residence time. It is interesting to note that supplementary reactions
leading to impurities may takesplace outside the reaction space, mostly in the aqueous
phase during the first separation steps of quench and absorption in water. Typical
examples are the formation of propion- cyanhydrine and dinitrile - succinate favored by a
basic pH.
CH2 = CH – CHO + HCN → NC-CH2-CH2-CHO
CH2 = CH – CN + HCN → NC – CH2-CH2-CN
The reaction may be exploited to convert acrolein, which is difficult to remove, into
heavier species. Reaction may take place during the distillation of acrylonitrile. More
generally, the separation/purification of acrylonitrile is complicated by secondary
chemical reactions in which the pH of liquid phase plays an important role. These aspects
will be examined later. In addition, undesired species may originate from reactions with
impurities present in the fresh feed, such as ethylene giving acetaldehyde and acetic acid,
or butenes leading to heavies. For this reason the concentration of non - C3 alkene in the
fresh propylene feed has to be limited to a maximum of 0.5%.
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6. FLOW DIAGRAM
6.1 Block diagram for the process:
Figure 6.1 Block diagram
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s
Reactor
Quench column
Absorber
Recovery column
Heads column
Product column
Product
stripper
Crude acetonir
ile
feed
7. MATERIAL AND ENERGY BALANCES
7.1 Introduction
In any chemical industry material balances is very important factor to produce any
product. Using the material balance calculation one can design equipment for desired
product in a steady state or unsteady state, continuous or batch or semi batch operations.
On the basis of material balances a design engineer can design the sizes of pipelines,
reactor, distillation, columns, pumps etc. In this project material balances are done based
on 200MT per day of acrylonitrile produced. Energy balance calculations are important
to calculate the heat duties and the heat requirements to achieve a desired degree of
separation. A process design starts with the development of a process flow diagram, for
development of such diagram, material balance calculations and energy balance
calculations are necessary for each individual equipment.
7.2 Raw Materials
7.2.1 Description of raw materials
Propylene:
Propylene is commercially available at a concentration of 93% propylene and 7%
propane and other gases. For calculations pure propylene of 100% concentration is
considered. It is usually stored in spheres.
Ammonia:
Ammonia is commercially available at above 95% concentration. Anhydrous ammonia is
taken for calculations purpose. It is usually stored in spheres or atmospheric storage tanks
at -33°C.
Air:
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Atmospheric air is the usual source of oxygen in the ammoxidation process. Besides
serving as the raw material, air is also required for actuating the control instruments like
pneumatic control valves as instrument air.
Sulphuric acid:
Sulphuric acid is available at 98% commercially and is used to neutralize the unreacted
ammonia from the reactor to form ammonium sulphate.
Water:
Water can be obtained from the nearby water resources or reservoirs or underground
water. The water must be treated in ion exchanger to make it fit for raising steam in
boilers.
7.3 Assumption taken in material and energy balance calculation:
In this process Propylene is limiting component and NH3 is excess component
Steady state operation is incurred
All raw materials are 100% pure. Sulphuric acid is 98% pure.
Heat of mixing is neglected in columns
Uniform temperature in the reactor
Table 7.1 Components’ names and their molecular weights:
ComponentMol.wt
.Name Component Mol.wt. Name
C3H3N 53.064 Acrylonitrile C3H4O 56.002 Acrolein
CH3CN 41.054 Acetonitrile C3H6 42.078 Propene
HCN 27.028 Hydrogen cyanide NH3 17.034 Ammonia
C3H4O2 72.062 acrylic acid O2 32 Oxygen
CO2 44.01 Carbondioxide H2O 18.016 Water
CO 28.01 Carbon monoxide H2SO4 98.0795 Sulphuric acid
N2 28.02 Nitrogen (NH4)2SO4 132.1405 Ammonium Sulphate
C4H5NO 83 Acrolein Cyanohydrin
26
7.4 Materials balances
Basis selection according to the trend:
So we selected 120000 tons per annum as basis
7.4.1 Basis calculation for raw material requirement:
Plant capacity: 120000 MTPA
Consider 300 working days/annum
Therefore output/day = 120000 tons/ 300 days = 400 tons/day
= 16,666.67 kg/hr = 314.08 kmol/hr
Acrylonitrile formation reaction
C3H6+32O2+N H 3→CH2=CHCN+3 H2O(7.1)
27
Assume 3% losses due to polymerization
Molar flow rate of acrylonitrile into the reactor = 1.03 × 314.08 = 323.504 kmol/hr
The propylene required to produce 323.504 kmol/hr of acrylonitrile (1kmol C3H6=1 kmol
C3H3N) = 323.504 kmol/hr
But only 80% is being converted to acrylonitrile;
Therefore actual C3H6supplied = 323.504 /0.8 = 404.378 kmol/hr
The optimum operating pressure = 2 × 105Pa
The operating pressure should be as low as possible to prevent the formation of by
products
At 2 × 105Pa, the conversion of C3H6is good, around 98.3 %
On the other side higher pressure would be preferable for quenching and scrubbing.
Assume, the feed propane is pure = 100% C3H6
Propane and ammonia should be mixed and fed together while O2 should enter the
reaction space independently.
The better feed composition for 80% conversion = propylene/ ammonia/ air = 1/ 1.2/ 9.5
C3H6supplied = 404.378 kmol/hr
NH3 supplied = 1.2 × 404.378 kmol/hr = 485.25 kmol/hr
Air supplied = 9.5 × 404.378 kmol/hr = 3841.591 kmol/hr
Summary for Raw material required:
Product capacity : 400 tons/day of ACRYLONITRILE
Propylene : 16983.876 kg/hr (404.378kmol/hr × 42.078)
Ammonia : 8249.25 kg/hr (485.25 kmol/hr × 17)
28
Air : 110831.43 kg/hr (3841.591 kmol/hr × 28.85)
Propylene/ammonia/air : 1/1.2/9.5 (Mole ratio)
7.4.2 Reactor
The reactions that place in the fluidized bed reactor along with percentage conversion are
as follows:
Acrylonitrile formation
R1¿C 3H 6+32O2+N H3→CH2=CN+H2O 80 %(7.2)
Acetonitrile formation
R2) C3H6+32O2+
32N H 3→
32CH 2CN+3 H2O2.3 %(7.3)
Acrolein formation
R3)C3H6+O2→CH 2=CHCHO+H 2O 0.7%(7.4)
Acrylic Acid formation
29
R4)C3H6+32O2→CH2=CHCOOH+H 2O1.5 %(7.5)
Hydrocyanic acid formation
R5) C3H6 + 3NH3 + 3O2 → 3HCN + 6H2O
5.9% (7.6)
Propylene burning to carbon dioxide
R6) C3H6 + 92 O2→ 3CO2 + 3H2O
5.1% (7.7)
Propylene burning to carbon monoxide
R7) C3H6 + 3O2→ 3CO + 3H2O
2.9% (7.8)
The reactions mentioned above occur according to their conversions at 420°C and 2 bar.
BASIS: Conversion per hour
R1¿C3H 6+32O2+N H 3→CH 2=CHCN+3 H2O(7.9)
Reactants: Products:
C3H6 = 404.378 × 0.8 (conversion 80%) C3H3N = 1×323.5024
= 323.5024 kmol = 323.5024 kmol
NH3 = 1× 323.5024 = 323.5024 kmol H2O = 3×323.5024 =
970.5072 kmol
O2 = 1.5 × 323.5024 kmol = 485.25kmol
R2) C3H6+32O2+
32N H3→
32C H2CN+3 H 2O(7.10)
30
Reactants: Products:
C3H6 = 0.023 × 404.378 (2.3 % conversion) C H2CN = 1.5 × 9.3 = 13.95
kmol
= 9.3 kmol
NH3 = 1.5 × 9.3 = 13.95 kmol H2O = 3× 9.3 = 27.9 kmol
O2 = 1.5 × 9.3 = 13.95 kmol
R3) C3H6+O2→CH2=CHCHO+H 2O(7.11)
Reactants: Products:
C3H6 = 0.007 × 404.378 (0.7% conversion) C3H4O = 1 × 2.83 = 2.83
kmol
= 2.83 kmol
O2 = 1 × 2.83 = 2.83 kmol H2O = 1 × 2.83 = 2.83 kmol
R4) C3H6+32O2→CH2=CHCOOH+H 2O (7.12)
Reactants: Products:
C3H6 = 0.015 × 404.378 (1.5% conversion) C3H4O2 = 1 × 6.065 = 6.065
kmol
= 6.065 kmol
O2 = 1.5 × 6.065 = 9.0975 kmol H 2O = 1 × 6.065 = 6.065
kmol
R5) C3H6 + 3NH3 + 3O2 → 3HCN + 6H2O (7.13)
31
Reactants: Products:
C3H6 = 0.059 × 404.378 (5.9% conversion) HCN = 3 × 23.85 = 71.57
kmol
= 23.85 kmol
NH3 = 3 × 23.85 = 71.57 kmol H 2O = 6 × 23.85 = 143.14
kmol
O2 = 3 × 23.85 = 71.57 kmol
R6) C3H6 + 9/2 O2→ 3CO2 + 3H2O (7.14)
Reactants: Products:
C3H6 = 0.051 × 404.378 (5.1% conversion) CO2 = 3 × 20.623 = 61.869
kmol
= 20.623 kmol
O2 = 4.5 × 20.623 = 92.804 kmol H2O = 3 × 20.623 = 61.869
kmol
R7) C3H6 + 3O2 → 3CO + 3H2O (7.15)
Reactants: Products:
C3H6 = 0.029 × 404.378 (2.9% conversion) CO = 3 × 11.72 = 35.16
kmol
= 11.72 kmol
O2 = 3 × 11.72 = 35.16 kmol H2O = 3 × 11.72 = 35.16
kmol
Unconverted propylene = 1.6 / (100 × 404.378) = 0.000039566 kmol
O2 balance:
32
Converted: 485.25 + 13.95 + 2.83 + 9.0975 + 71.57 + 92.804 + 35.16 =710.66 kmol
Oxygen taken as feed = 0.21 × 3841.59 = 806.7339 kmol
Unconverted oxygen = 806.7339 – 710.66
= 96.0739 kmol
NH3 balance:
Converted: 323.5024 + 13.95+71.57 = 409.0224 kmol
NH3 taken as feed = 485.25 kmol
Unconverted ammonia: 485.25 – 409.0224 kmol = 76.2276 kmol
Table 7.2 Showing Components’ Mol.Wt. and Inlet, Outlet Flow rates
Component Mol. Wt Input
Kmol/hr
Output
Kmol/hr
Input
Kg/hr
Output
Kg/hr
C3H3N 53.064 0 323.508 0 17,166.6
CH2CN 41.054 0 13.940 0 572.736
HCN 27.028 0 71.576 0 1934.39
C3H4O2` 72.062 0 6.0656 0 437.122
CO2 44.01 0 61.871 0 2722.92
CO 28.01 0 35.18 0 985.448
N2 28.02 3034.916 3034.916 85038.346 85038.346
C3H4O 56.002 0 2.83 0 158.52
C3H6 42.078 404.378 6.47 17015.749 272.2518
NH3 17.034 485.26 76.22 8265.97 1298.44
O2 32 806.7498 96.041 25815.99 3073.32
H2O 18.016 0 1247.5304 0 22475.55
Total 47313.314 4976.17 136136.0612 136135.894
7.4.3 Material balance for Quench Tower:
33
The quench tower consists of two sections i.e. upper and lower. The gases from
the outlet of reactor pass through the effluent gas cooler. The gases are then sent to the
quench lower section. In this section, water is added in order to remove the catalyst
particles which could not be recovered through the cyclones in the reactor. Polymerized
compounds also get separated in the section 2% of acrylonitrile is lost with this stream.
All the water added to the quench comes out from the bottom. In the quench upper
section ammonia is being removed in the form of ammonium sulfate using sulfuric acid
(98%). Ammonium sulfate leaves as a side stream from the quench upper sections as
33% solution. Water is added to the upper section in order to maintain 33% solution
concentration.
Quench lower section:
Catalyst waste = 0.3-0.7 kg/ton of acrylonitrile.
Mass flow rate of acrylonitrile = 17166.524 kg/hr
Catalyst waste = 0.7 × 17166.524 = 12.01656 kg/hr
Assuming 0.5 % (wt) of acrylonitrile is converted to polymers.
Total polymers formed = 0.5 × 17166.524/100 = 85.832 kg
Assuming acetonitrile loss as 2% = 2/100 × 571.95 = 11.439 kg/hr
The amount of water required to flush the catalyst and polymers is given as:
Water input for 36954 kg/hr of inlet gases = 5445 kg/hr
Therefore, water input for 136114.708 kg/hr of inlet gas = 136114.708 × 5445/36954
= 20,055.869 kg/hr
Quench upper section
The following reaction occurs in the upper section
2NH3 + H2SO4 → (NH4)2SO4
34
NH3 present in gas (unconverted) = 76.2276 kmol/hr
H2SO4 required = 76.2276/2 = 38.1138 kmol/hr = 38.1138 × 98.076 = 3738.04 kg/hr
But 98% H2SO4 includes 2% water = 0.02/0.98 × 3738.04 = 76.286 kg/hr
(NH4)2SO4 formed = 76.2276/2 = 38.1133 × 132.144 = 5036.4439 kg/hr
For 33% (NH4)2SO4 solution, the amount of water added = 5036.4439/0.33- 5036.4439
= 15261.95121-5036.4439
= 10,225.51 kg/hr
7.4.4 Summary of material balances for Quench Tower
Table 7.3 Lower section Material balance:Stream 2 Input
Kg/hr
Output
Kg/hr
Water 20,034.18 20034.18
Catalyst 12.01656 12.01656
C3H3N 0 85.832
CH3CN 0 11.454
Total 20,046.2 20142.65056
Table 7.4 Lower Section Material balance:Component Input
Kg/hr
Output
Kg/hr
C3H3N 17166.5236 17,080.69
CH3CN 572.736 561.282
HCN 1934.39 1934.39
C3H4O2 437.122 437.122
CO2 2722.92 2722.92
CO 985.448 985.448
N2 85018.558 85018.558
C3H4O 158.7 158.7
35
C3H6 272.26 272.26
NH3 1298.182 1298.182
O2 3073.216 3073.216
H2O 22474.6102 22474.6102
Total 136114.7044 136017.416
Table 7.5 Upper Section Material balance:
Stream 2 Input
Kg/hr
Output
Kg/hr
Water 10225.49 10225.49
H2SO4 3738.002 0
(NH4)2SO4 0 5036.434
Total 13963.492 15261.92
Table 7.6 Upper Section Material balance:
Component Input
Kg/hr
Outlet
Kg/hr
C3H3N 17080.69 17080.69
CH3CN 561.2824 561.2824
HCN 1934.398 1934.398
C3H4O2 437.122 437.122
CO2 2722.932 2722.932
CO 985.44 985.44
N2 85018.5598 85018.5598
C3H4O 158.7 158.7
C3H6 272.268 272.268
NH3 1298.182 0
O2 3073.216 3073.216
H2O 22474.16 22474.16
Total 136017.416 134719.22
36
7.4.5 Material balance of knock out pot
After the quench column there is a condenser in which only the water gets
condensed. The rest of the components remain in the vapor phase. After the condenser,
there is a knock out pot in which all remaining water will be condensed.
Water removed in knock out pot = 22474.61 kg/hr
7.4.6 Summary of material balance in knock pot
Table 7.7 Material balance in knock pot:
Component Input
Kg/hr
Output
Kg/hr
C3H3N 17080.69 17080.69
CH3CN 561.2824 561.2824
HCN 1934.398 1934.398
C3H4O2 437.122 437.122
CO2 2722.932 2722.932
CO 985.44 985.44
N2 85018.5598 85018.5598
C3H4O 158.7 158.7
C3H6 272.268 272.268
O2 3073.216 3073.216
H2O 22474.56 0
Total 134719.24 112244.624
Stream 2 Inlet Outlet
Water 0 22474.61
7.4.7 Absorber
37
Water is used to absorb Acrylonitrile, HCN and other organic components in the
gas phase. The unabsorbed gases leave the absorber from top. These gases are then sent
to the incinerator, where all hydrocarbons and others combustible are brunt and flue gases
can be released to the atmosphere. In this, 1% of acrylonitrile is lost to the off gases.
Absorber is maintained at 21°C at bottom. Gases enter at 35°C. The unabsorbed gas
mainly contains CO2, CO, O2, N2,C3H6 small HCN, Acrylonitrile.
1% loss of Acrylonitrile in off gases = 0.01 × 17080.692 = 170.806 kg lost
The basic design of the absorber is about 3.7 mole of water per mole of gas entering the
absorber.
Flow of gas entering = 3650 kmol/hr
Moles of water entering = 3.7 × 3650 = 243090 kg/hr
Acetonitrile HCN, C3H4O, C3H4O2 are having good solubility in water at 25°C.
The C3H4O is lighter, and is difficult to separate from the system. And it is converted to
propion-cyanhydrin in the bottom of the absorber. This product formed is heavier and
easy to separate from the mixture.
C3H4O + HCN → C4H5NO (7.17)
The amount of C3H4O present in the bottom = 158.7 kg
Amount of HCN converted = 158.7 × 27.028/56.062 = 76.51 kg/hr
Amount of C4H5NO formed = 76.51 + 158.7 = 235.21 kg/hr
Amount of HCN present in bottom = 1934.398-79.35 = 1855.048 kg/hr
7.4.8 Summary of material balance absorber:
Table 7.8 Material balance of Absorber:
Stream 2 Input
kg/hr
38
Water 243090 kg/hr
Component
sInlet Top Bottom Bottom (after Rxn)
Kg/hr Kg/hr Kg/hr Kg/hr
C3H3N 17080.69 170.8062 16909.88 16909.88
CH3CN 561.2824 0 561.2824 561.2824
HCN 1934.398 0 1934.398 1857.8874
C3H4O2 437.122 0 437.122 437.122
CO2 2722.932 2722.932 0 0
CO 985.44 985.44 0 0
N2 85018.5598 85018.5598 0 0
C3H4O 158.7 0 158.7 0
C3H6 272.268 272.268 0 0
O2 3073.216 3073.216 0 0
H2O 0 0 243090 243090
C4H5NO 0 0 0 235.21
Total 112244.624 92243.24 263125.8 263125.8
7.4.9 Material balance in recovery column
The recovery column is a extractive distillation column. The bottoms from the
absorber are first preheated and then sent to the recovery column. Water is used as a
solvent for the purpose of extractive distillation.
The feed to the water recycle ratio in weight is 1.2:1
The feed to recovery column = 263125.848 kg/hr
Water needed for extractive distillation = 263125.848/1.2 = 219271.54
Feed = 219271.54 + 263125.848 = 482397.388 kg/hr
39
Top:
99.1% of acrylonitrile in feed comes out in the distillate.
Acrylonitrile in distillate = 0.991 × 16909.88 = 16757.69 kg/hr
And 97.5% of HCN in feed comes out in distillate = 0.975 × 1857.88 = 1811.440 kg/hr
(Acetonitrile present in distillate is in traces and is not considered in the top)
2.3% of H2O comes out in distillate.
H2O in distillate = 2.3/100 × (243124+219271.44) = 10635.09512 kg/hr
Bottom:
Acrylonitrile in bottom = Feed – Top = 16909.88 – 16757.69 = 152.1846 kg/hr
HCN in bottom = HCN in Feed – Top = 1857.88 – 1811.44 = 46.44 kg/hr
Acetonitrile= 561.28 kg/hr
Acrylic acid = 437.122 kg/hr
C4H5NO = 235.2107 kg/hr
H2O = 219271.54 + 243124 – 10635.09 = 451760.45 kg/hr
7.4.10 Summary of material balance for recovery column
Table 7.9 Material balance for Recovery column:
Stream 2 Input
Kg/hr
Water 219271.54
Component InputKg/hr
TopKg/hr
BottomKg/hr
C3H3N 16909.884 16757.696 152.189
40
CH3CN 561.2824 0 561.2824
HCN 1857.886 1811.44 46.4473
C3H4O2 437.122 0 437.122
H2O 243124.4602 10635.098 451760.4
C4H5NO 235.2106 0 235.2106
Total 263125.8478 29204.24 453192.6
7.4.11 Decanter:
Assuming 95% separation of water and organic phase in the decanter the
following material balance can be achieved.
Therefore 95% of water = 95/100 × 10635.098 = 10103.34 kg/hr
7.4.12 Summary of material balance in decanter
Table 7.10 Material balance in decanter:
Component Organic phase
Kg/hr
Water
Kg/hr
C3H3N 16757.68 0
HCN 1811.44 0
H2O 531.754 10103.342
Total 19100.874 10103.342
7.4.13 Material balance for stripper
Feed = 453192.69 kg/hr
Top:
41
90% of acrylonitrile is removed to distillate = 0.9 × 561.282 = 505.1358 kg/hr
50% of HCN in feed goes to top = 0.5 × 46.4473 = 23.22 kg.hr
0.2 % H2O present in feed is removed to distillate = 0.002 × 451760.94 = 903.52 kg/hr
Bottom:
Acrylonitrile in bottom = 561.28 – 505.15 = 56.125 kg/hr
HCN = 23.22 kg/hr
Acrylic acid = 437.122 kg/hr
C4H5NO = 235.21 kg/hr
H2O = 451760 + 903.52 = 4580856.92 kg/hr
Acrylonitrile = 152.18 kg/hr
7.4.14 Summary for material balance stripper
Table 7.11 Material balance for stripper:
Component Feed(Kg/hr)
Top(Kg/hr)
Bottom(Kg/hr)
C3H3N 152.189 0 152.18
CH3CN 561.28 505.15 56.12
HCN 46.446 23.22366 23.22366
C3H4O2 437.122 0 437.122
H2O 451760.4 903.5208 450857
C4H5NO 235.2108 0 235.210
TOTAL 453192.6 1431.89 450936.2
7.4.15 Material balance for head drying column
42
The organic phase from the recovery column decanter enters the heads drying column. In
this, most of the HCN is recovered from the top and acrylonitrile is obtained from the
bottom.
Feed = 19100.88 kg/hr
Top:
HCN = 100% = 1811.44 kg/hr
Bottom:
Total = 19100.88 – 1811.44 = 17289.44 kg/hr
7.4.16 Summary for the material balance of head columns
Table 7.12 Material balance for head columns:
Component Input
Kg/hr
Top
Kg/hr
Bottom
Kg/hr
C3H3N 16757.695 0 16757.695
HCN 1811.44 1811.44 0
H2O 531.754 0 531.754
Total 19100.88 1811.44 17289.45
7.4.17 Material balance for product column
Vacuum condition applied.
The column pressure is at 500 mm Hg and bottom temp is at 60°C
Feed = 17289.44 kg/hr
Top = 99% acrylonitrile = 16926.964 [16757.68 / (x + 16757.68) = 0.99, solve for x]
Bottom = 362.486 kg/hr
43
7.4.18 Summary for material balance of product column
Table 7.13 Material balance for product column:
Component Inlet
Kg/hr
Top
Kg/hr
Bottom
Kg/hr
C3H3N 16757.68 16757.68 0
H2O 531.754 169.26 362.486
Total 17289.448 16926.954 362.486
7.5 ENERGY BALANCE
Cp = A + BT + CT2 + DT3 +ET4kJ/kmol.k, T in k
Table 7.14 Gas specific heat constants of compounds
Compound A B C D E
Propylene 17.9051 1.48 × 10-01 6.88 × 10-05 -1.38 × 10-07 4.84 ×10-11
Ammonia 34.236 -2.21 × 10-02 1.21 × 10-04 -1.09 × 10-07 3.20 ×10-11
HCN 21.86 6.06 ×10-02 -4.96 × 10-05 1.82 ×10-08 0
CO2 29.268 -2.24 × 10-02 2.65 × 10-04 -4.15 × 10-07 2.01 × 10-10
CO 29.7 -6.50 × 10-03 1.83 × 10-05 -9.39 × 10-09 1.08 × 10-12
Water 33.7634 -5.95 × 10-03 2.24 × 10-05 -9.96 × 10-09 1.10 × 10-12
O2 29.7045 -9.90 × 10-03 3.39 × 10-05 -3.39 ×10-08 9.18 × 10-12
Acrolein 11.97 2.11 × 10-01 -1.07 × 10-04 1.91 × 10-08 0
Acrylonitrile 10.69 2.21 × 10-01 -1.57 × 10-04 4.60 × 10-08 0
Acetonitrile 20.48 1.20 × 10-01 -4.49 × 10-05 3.20 × 10-09 0
Acrylic acid 1.742 3.19 × 10-01 -2.35 × 10-04 6.98 × 10-08 0
Nitrogen 29.8018 -7.02 × 10-03 1.74 × 10-05 -8.48 × 10-09 9.34 × 10-13
Table 7.15 Liquid heat capacities constants:
Component A B C D
Acrylic acid -18.242 1.22 -3.12 × 10-03 3.14 × 10-06
44
Acrolein 48.243 5.82 × 10-01 -1.93 × 10-03 2.69 × 10-06
HCN 252.13 -1.4144 3.06 × 10-03 -1.18 × 10-06
Acrylonitrile 33.362 5.86 × 10-01 -1.86 × 10-03 2.50 × 10-06
Acetonitrile 4.296 6.94 × 10-01 -2.09 × 10-03 2.50 × 10-06
Water 92.053 -4.00 × 10-02 -2.11 × 10-04 5.35 × 10-07
Ammonium
sulphate
39.861 5.13 × 10-01 -1.30 × 10-02 3.79 × 10-09
Table 7.16 Standard heat of formation of compounds
Compound ∆Hf , heat of formation at 298 K
( kJ/kmol)
Propylene 2.04 × 10+04
Ammonia -45720
HCN 1.31 × 10+5
CO2 -393800
CO -110600
Water -242000
O2 0
Acrolein -70920
Acrylonitrile 1.85 × 10+05
Acetonitrile 8.79 × 10+04
Acrylic acid -336500
Nitrogen 0
The reference temperature for calculations is taken as To = 298K
∆ H = enthalpy change
∆T = temperature change
45
Cp = specific heat
7.5.1 Enthalpy balance for reactor
The input temperature of air is at 523 K and both NH3 and C3H6 enters at 338 K.
The operating condition of reactor is 4200C
The reaction products leave at 4200C
The reaction takes place in the fluidized bed reactor are mentioned
∆ H=∆ H°reactants + ∆ H °reaction + ∆ H °products
Reactants: ∆ H=n∫T 1
T 2
CpdT
Products: ∆ H=n∫T 1
T 2
CpdT
∆ H=∆ H fof products - ∆H fof reactants
Table 7.18 Reactants and their temperatures, enthalpies:
Reactor
Reactants T1,k T2,k Kmol/hr ∆ H ,kJ/mol
O2 523 298 806.7339 -5501845.088
N2 523 298 3034.91 -200292705
C3H6 338 298 404.378 -1098373.987
NH3 338 298 485.25 -704392.729
Total -27333882.3
Table 7.19 Reactions and their enthalpies:
Reactions ∆H , kJ/mol Kmol/hr ∆H ,kJ/hr
R1 -520600 323.508 -168418264.8
R2 -545970 9.3008 -5077521.776
46
R3 -333350 2.830 -9436130.845
R4 -598930 6.0656 -3632687.808
R5 -942240 23.8586 -22509873.34
R6 -1927800 20.6236 -39758176.79
R7 -1078200 11.727 -12644256.61
Total -251351393.6
Table 7.20 Products and their temperatures, enthalpies:
Product T1, k T2, k ∆ H , kJ/hr
Propylene 298 693 238386.2
Ammonia 298 693 1259257.6
HCN 298 693 1177011.2
CO2 298 693 1080279.4
CO 298 693 415928
Water 298 693 173851306.2
O2 298 693 164221.52
Acrolein 298 693 102109.2
Acrylonitrile 298 693 11005472
Acetonitrile 298 693 377931.4
Acrylic acid 298 693 260887.4
Nitrogen 298 693 35616936
Total 69083548
The amount of heat removed in the reactor = -27333882.3-251351393.6+69083548
= -209601727.9 kJ/hr
7.5.2 Enthalpy balance for effluent gas cooler
47
∆ H=n∫T 1
T 2
CpdT
Table 7.21 Components in Effluent gas cooler and their Inlet, Outlet Flow rates:
Component Inlet = 693 K
Kmol/hr
Outlet = 505 K
∆ H ,kJ/hr
C3H3N 323.5088 -4067134.19
CH3CN 13.9513 -235120.24
HCN 71.5762 -595064.48
C3H4O2 6.0656 -35495.8912
CO2 61.8710 -482464.18
CO 35.18 -201498.4638
N2 3034.916 -17211923.37
C3H4O 2.8306 -4902.8335
C3H6 6.4701 -6126.018
NH3 76.2272 -647695.7204
O2 96.04166 -577360.9146
H2O 1247.5304 -8500503.704
Total -32565289.81
The heat to be removed from the effluent gas cooler =-32565289.81 kJ/hr
= -9045.91 KW
7.5.3 Enthalpy balance in quench tower
Table 7.22 Lower Section in quench tower Enthalpy balance:
Quench tower Input = 505 K Output = 358 K
Component Kmol/hr ∆ H ,KJ
C3H3N 323.5088 -427106.023
CH3CN 13.9513 -130820.0845
48
HCN 71.5762 -422884.0182
C3H4O2 6.0656 -90047.759
CO2 61.8710 -386613.1054
CO 35.18 -152849.072
N2 3034.916 -13109910.06
C3H4O 2.8306 -35063.6514
C3H6 6.4701 -80795.69168
NH3 76.2272 -444334.64
O2 96.04166 -430124.9066
H2O 1247.5304 -6348580.242
Total -22059128.99
Quench upper section:
The following reaction occurs
2NH3 + H2SO4 → (NH4)2SO4
NH3 present in the gas = 76.22664 kmol
H2SO4 required = 76.22664/2 = 38.1133 kmol = 38.1133 × 98.076 = 3738.0 kg/hr
∆ H=∆ H°reactants + ∆ H °reaction + ∆ H °products
∆ H=n∫T 1
T 2
CpdT
Reactants:
T1,k T2,k Kmol/hr kJ/hr
NH3 358 298 76.226 -160303.278
Reaction:
49
∆ H=∆ H f of products - ∆ H f of reactants
= -268071 kJ/mol ammonium sulphate formed
= -268071× 76.2266/2 = 10217077.09 kJ
∆ Hof dilution:
H2SO4 enters at a concentration of 98% at 35˚C
Its enthalpy = -840 kJ/kg of solution
Water flow into the system = 10225.49 kg/hr
H2SO4 flow rate = 3738.0024 kg/hr
Thus the concentration after dilution = 3738/ (3738+10225.49) = 26.769811% (wt)
Its enthalpy = 275 kJ/kg solution
∆ Hof dilution = ∆ H of solution at 27% - ∆H of solution at 98% at 35˚C
= (-275×13963.4) - (-840×3814.28) = -635939.8 kJ/hr
Specific heat of H2SO4 = 3.3kJ/kg.K at 27%
Enthalpy change of 27% H2SO4 at 25˚C = 3.3 × (35-25) × 13963.4 = 460792 kJ
Ammonium sulfate solution of conc. 33% comes out at 80˚C
So, the enthalpy change = 2265.112 MJ = 264513.26 kJ
Total heat change in upper section = -635939.8+264513.26-460792-10217077.09-
160303.278
= -11738625.43 kJ
This heat must be removed.
7.5.4 Enthalpy balance in cooler:
50
The mole fraction of water vapor = 0.255
The partial pressure = 344.27 mm Hg
From the vapor pressure data, the dew point of water is 79˚C at 1.8 bar
∆ Hof water = ∆ H specific in vapour +∆ H condensation + ∆ H specific in liquid
∆ HVaporization at 79˚C = 41750 kJ
Table 7.23 Water balance in cooler:
Cooler T1,K T2,K KJ/kmol
H2O vapor 358 352 -200
condensation 358 352 -41750
H2O liquid 358 308 -4082.979
n = 1247.53 kmol/hr Total -46032.97
∆ Hof Water = 1247.53 × -46032.97 = -57427522.9 kJ
Table 7.24 Gas phase balance in cooler:
Cooler Input = 358K Output = 308K
Component Kmol/hr ∆ H kJ/hr
C3H3N 323.5088 -1108632.964
CH3CN 13.9513 -38671.6292
HCN 71.5762 -133163.233
C3H4O2 6.0656 -25617.42
CO2 61.8710 -118677.7446
CO 35.18 -51343.268
N2 3034.916 -4415681.03
C3H4O 2.8306 -10033.63
C3H6 6.4701 -22719.316
O2 96.041 -142601.848
Total -6067142.084
Total heat change in cooler = -6067142.084 - 57427522.9 = -63494664.98 kJ/hr
51
Table 7.25 Enthalpy changes in absorber:
Absorber T1 = 308K T2 =298K
Component Kmol/hr ∆ H kJ/hr
C3H3N 321.888 -207628.7624
CH3CN 13.6718 -7202.7962
HCN 71.57 -25892.53552
C3H4O2 6.065918 -4778.3161
CO2 68.8707 -22881.4427
CO 35.18206 -10242.2188
N2 3034.209842 -881395.917
C3H4O 2.833842 -1883.897
C3H6 6.47058 -4242.344
O2 96.038 -28333.675
Total -1194481.907
Table 7.26 Absorber components and their flow rates:
Component λ, cond 298K
kJ/mol
Kmol/hr kJ/hr
C3H3N -31418.2596 318.6696 -10012044.22
CH3CN -34403.6 13.6718 -470359.1385
HCN -26375.3 71.57014 -1887690.771
C3H4O2 -42094 6.0659 -255337.99
C3H4O -29216.925 2.83384 -82796.0907
Total -12708223.94
The following reaction occurs in the bottom
C3H4O + HCN → C4H5NO (7.18)
C3H4O present in the bottom is 158.7 kg
So, HCN converted = 158.7× 27.028/56.062 = 76.5107 kg/hr
52
The heat of reaction = -49133.418 kJ/kmol
= -49133.418 × 2.83384 = -139236.2453 kJ/kmol
The net heat change in the absorber = -139236.2453 + -1194481.907+-12708223.94
= -14041942.09 kJ/hr
7.5.6 Enthalpy balance for recovery column
Feed enters at 100˚C and top is maintained at 800C and bottom is at 1050C
Table 7.27 Enthalpy balance for recovery column:
Recovery column Top Output temp = 353 K
Component kmol/hr ∆ H ,kJ/hr
C3H3N 315.8 -764866
HCN 67.0208 -126669.312
H2O 590.314 -932696.12
Total -1824231.432
In rectifying section net enthalpy change is = -912115.716 kJ/hr
Table 7.28 Recovery column Outlet flow rate and Enthalpy:
Recovery column Bottom Output temp = 378K
kmol/hr ∆ H ,kJ/hr
C3H3N 3.044 1798.2534
HCN 2.2746 843.76
H2O 25075.512 10280960.34
C3H4O2 6.0659 2669.0038
C4H5NO 2.83386 2513.8296
CH3CN 13.6718 8115.05
Total 10296900.25
In stripping section the net enthalpy added = 10296900.25 kJ/mol
53
In addition to those above both values, the latent heat is added to components of distillate
in the reboiler and removed in the condenser.
7.5.7 Enthalpy balance in heads drying column:
Feed enters at 800C, top is maintained at 250C and bottom temperature is at 840C.
Table 7.29 Enthalpy balance in heads drying column:
Heads drying column Top Output temp = 298K
kmol/hr ∆H ,kJ/hr
HCN 67.02 -284771.665
In the rectifying section the net enthalpy change = -284771.665 kJ/hr
Heads drying column Bottom Outlet temp = 357K
kmol/hr ∆H ,kJ/hr
C3H3N 315.8 133899.86
H2O 29.5157 8264.396
Total 142164.256
In the stripping section the net enthalpy added = 142164.256 kJ/hr
In addition to values above, the latent heat is added to components of distillate in the
reboiler and removed in the condenser.
7.5.8 Enthalpy balance in the product column
The feed enters at 357 K
Top temperature is 323 K
Table 7.30 Enthalpy balance in product column:
54
Product column Top Output temp = 323K
kmol/hr ∆ H ,kJ/hr
C3H3N 315.8014 -73787.19
H2O 4.67414 -5382.36
Total -79153.55
In the rectifying section the net enthalpy change = -79153.55 kJ/hr
Product column Bottom Output temp=333K
kmol/hr ∆ H ,kJ/hr
H2O 24.84 -55189.6
In the stripping section the net enthalpy added = -55189.6 kJ/hr
55
8. SPECIFIC EQUIPMENT DESIGN
8.1 Process design & mechanical design of fluidized bed reactor
8.1.1 Kunii-levenspiel (KL) bubbling-bed model:-
Ref :- 1. Chemical engineering, J kingsauduniv, Vol 4, Eng.sci.(2),page. 127-142
2. Introduction to chemical reaction engineering and kinetics, Ronald W. Missen,
Charles A.Mims,bradly A. Saville, john wiley& sons
8.1.2 Assumptions: (fine particles)
a. It is the first order reaction
b. The reactor operates isothermally at constant density and at a steady state.
c. The fluidizing (reactant) gas is in convective flow through the bed only via the bubble gas region (with associated clouds and wakes); that is, there is no convective flow of gas through the emulsion region.
d. The bubble region is in PF (upward through the bed).
e. Gas exchange occurs 1. Between bubbles and clouds, characterized by exchange coefficient Kbc and 2. Between clouds and emulsions, characterized by Kce
f. Bubbles are same size and distributed evenly throughout the bed rising through it.
g. Gas within a bubble essentially remains in bubble, but recirculates internally and penetrates slightly into the emulsion to form a transitional cloud region around bubble; all parameters involved are functions of the size of bubble.
i. The emulsion is at mf conditions.
8.1.3 Reactor design
umf = Minimum fluidization velocity
ut = Terminal velocity
56
ufl = Fluidization velocity
ubr = the rise velocity of bubbles in fluidised bed models for single bubble
D = Bed diameter
ubr = 0.711(gdb)1/2 (db/D) < 0.125
ubr = [0.711(gdb)1/2]1.2e-1.49db/D 0.125 < (db/D) < 0.6
absolute rise velocity of bubbles in the bed (ub)
ub = ubr + ufl - umf
fb = the volume fraction of bubbles, fb, m3 bubbles/ m3bed
εb = 1
the volume avgvoidage in the fluidized bed
εfl = fb (εb) + (1- fb) εmf
fb = (εfl−εmf )(1−εmf )
fb = ufl/ub
fc = the ratio of cloud volume to bubble volume
fc = 3 umf f b
εmf ubf −umf
The ratio of wake volume to bubble volume (fw)
fw = αfb (α = 0.2 to 0.6)
The bed fraction in the emulsion (fe)
fb + fc + fw + fe = 1
γb = m3 solid in bubbles / m3 bubbles
γcw = m3 solids in cloud + wakes/m3 bubbles
γe = m3 solid in emulsion /m3bubbles
γb + γcw + γe = m3 total solids/ m3 bubbles = (1-εmf)(1-fb)/fb
γb = 0.01 to 0.001
57
Usually taken as γb = 0.005
γcw = (1-εmf)(fc + fw)/ fb
Dm = the molecular diffusion co efficient of the gas
Data:-
γb = 0.005
umf = 0.0533 m/sec
εmf = 0.367
α = 0.34
db = 0.1 m
dp = 50 µm
ρP = 80 lb/ft3= 1281.7 kg/m3
µf =1.44 kg/hr.m
T = 420 0C
P = 2 bar = 200000 N/m2
kA = rate constant = 1.964 sec -1
conversion fA = 0.985
Dm at 400˚C = 0.14 m2/hr
D α T3 /2
P
Dm at 420 ˚C = 0.14623 m2/hr
Wcat = ρq p (1−εmf )ubr ln(CAO
C A)
koverall .u fl
FAO = 404.384 kmol/hr (propylene)
Fto = 4731.314 kmol/hr
58
The total volumetric feed rate in
Qo = F¿ RTP
= 4731.314 × 1000 ×8.314 × 693/3600 ×200000
= 37.861 m3/sec
ubr = 0.711(gdb)1/2
= 0.711(9.81×0.1)1/2 = 0.70421 m/sec
ub = ubr + ufl - umf = 0.4977-0.0533+0.704213 = 1.1486 m/sec
Kbc = 4.5(umf/db) + 5.85(Dm1/2g1/4/db
5/4)
= 4.5(0.0533/0.1) + 5.85[(0.14628/3600)1/2(9.8)1/4/(0.1)5/4]
= 3.57208 sec-1
Kce = 6.77( εmf Dmubr
db3 )
12
= 6.77[0.37×(0.14628/3600)×0.704213/(0.1)3]0.5= 0.696598 sec-1
fb = ufl/ub = 0.4977/1.1486 = 0.43331
fc = 3×ubr f b
(εmf ubf−umf ) = 3 × 0.0533×0.43331/(0.37×0.704213-0.0533)
= 0.3342983
fw = αfb = 0.37×0.4331 = 0.160324
fc = 1-0.4331-0.3342983-0.1603247 = 0.072067
γc = ( ((1−εmf ))(1−f b )
f b) - γb - γcw
= (1-0.37)(1-0.4333)/0.4331-0.005-0.07191
= 0.0997799
γcw = (1-εmf) (fc + fw)/ fb
= (1-0.37)(0.3342+0.16032)/0.4331
59
= 0.7191446
κ overall = γbκ A +
11κbc
+ 1
γ cw κA+1κce
+ 1γe κA
= 1.098211 sec-1
The bed depth (Lfl)
Lfl = - (ln (1−f A )ub )koverall
= -[ln(1-0.985)]1.1486/1.098211
= 4.392396 m
Wcat = ρq p (1−εmf )ubr ln(CAO
C A)
koverall .u fl
= (1218.7)(37.861)(1-0.37)(0.704213)/(1.098211×0.4977)
= 165420 kg
q = uflAc = ufl πD2/4
D = (4q/ufl π)1/2 = 9.84413 m
Reactor volume = (πD2/4) Ln = π(9.84413)2(4.3923)/4 = 328.9350 m3
Volumetric flow rate = 37.861 m3/sec
Residence time = 328.9350/37.861 = 8.6879 sec
Cyclones design: ( Ref: Coulson and Richardson, 6th volume, page 448.)
Cyclone type: high gas rate cyclone (stairmand)
The available height for the cyclone ≤ 4.3 (reactor height)
For standard cyclone, height = 4 diameter of cyclone
Let the cyclone length = 4 m = 4 Dc so, diameter of cyclone = 1 m
60
Then the volume of 1 cyclone = πDc2/4 = 3.1415 m3 roughly
The optimum inlet velocity = 15 m/s
Particle size of catalyst = 50 µm (at this efficiency is 1)
Volumetric flow rate of outlet gas = 39.828 m3/sec
Catalyst circulation rate = ( total catalyst weight)/(time required to travel 1 reactor length × density) = 165420/(8.69×1281.7) = 14.851 m3/sec
(Assumption: catalyst travel at fluidizing velocity)
Stream flow rate to cyclones = Gas velocity + Catalyst flow rate = 39.28 +14.851
= 54.13 m3/sec
Area required to flow into cyclones = 54.13 / 15 = 3.6 m2
But, Duct area available for 1 cyclone of ( Dc =1m) = 0.28125 m2
So, No of cyclones required = 3.113 / 0.28125 = 12.8 = 13 cyclones approx.
Flow rate to each cyclone = 46.7/13 = 3.59 m3/sec
Total volume required to accommodate 13 cyclones = 13× 3.14 = 40.82 m3
The reactor height needed extra = volume/Ac of reactor = 40.82 /76.071 = 0.5366 m
Therefore the total height of the reactor = 4.392 + 0.5366 = 4.928 m
8.1.4 Calculation for number of tubes required to remove the heat:
Reactor heat duty = -209601727.9 kJ/hr (From energy balance of reactor)
Let BFW at 230 0C and 41.5 kg/cm2g enters into the reactor and comes out at 370 0C,
41.5 kg/cm2g.
The ΔH enthalpy change for this 2 conditions = 39031 kJ/kmol
Q = n × ΔH
n = 209601727.9/39031 = 5370.13 kmol/hr = 96785.99 kg/hr water .
Q = U × A × ΔTlm
61
For gas water system U= 20-300 W/m2.0C U is taken as 270 W/m2.0C
ΔTlm = (T 2−t 2 )−(T 1−t 1)
ln (T 2−t 2)(T 1−t 1)
ΔTlm = ((420-230)-(420-370)/ln((420-230)/(420-370)) = 104.8688
A = Q
U .ΔT lm = 209601727.9 × 103/( 260× 104.8688×3600)
= 2135.36 m2surface area
Let us take length of the tubes of Dt = 50 mm dia and length, lt = 8m
Surface area per tube = π × Dt × lt = 1.256637 m2
Total no of tubes = 2135.36m2/1.256637 m3 = 1699.26 tubes = 1700 tubes
Volume of compensation in the reactor for this tube = 1700× π × Dt2 × lt/4 = 26.702 m3
The length to be added = 26.702/ π × 9.844132/4 = 0.2710 m
Now, the total height of the reactor = 4.928 +0.2710 = 5.2 m
8.1.5 Reactor mechanical design:
Data:
Reactor length = 5.2 m
Diameter of reactor Di = 9.84413 m
Material of construction = SS321L
Design stress f = 120 N/mm2
Insulation thickness = 50 mm
Pressure = 2×105 N/m2= 0.2 N/mm2
Temperature = 420 0C
62
Shell thickness:
For calculation, take design pressure 20 % more than operating pressure
Pi = 0.2 + 0.2 × 0.2 = 0.24 N/mm2
ts = Pi×Di / (2f – Pi) = 0.24 × 9844.13/(2×120-0.24) = 9.85 mm = 10 mm
but to withstand the weight and overload, partial thickness would be
For Di > 3.5 m, ts = 12 mm
So, the thickness of the shell = 12 mm
Weight of the vesse = Wl = π × 9.8413 × 5.2 × 8000 × 0.012 = 15433.9 kg
= 151252.65 N
Sm= density of SS321L material.
Weight of the top and bottom heads = W2
= 2×1.2×Di2×π×(t-c)×Sm/ 4
= 2×1.2× 9.852×π×(12-6)×8000 / 4
= 8778.38 kg = 86028.124 N
Weight of catalyst = W3 = 165420 kg = 1621116 N
Insulation weight = W4 = 7540 N
Cyclones weight = 54241 N
Wtot = 151252.65 + 86028.12 + 1621116 + 7540 + 54241 = 1920177.77 N
Analysis of stresses:
Primary stresses: due to pressure
Circumferential σh = P ×Di2t = 0.24× 9844.13 / 2 × 12 = 98.4413 N/mm2
63
Longitudinal σL= P×Di4 t = 0.24× 9844.13 / 4 × 12 = 49.2206 N/mm2
The direct stress (σw) = W tot
(π× (Di+t )×t ) = 1920177.77/(3.14×(9844.13+12)×12)
= 5.17 N/mm2
Bending stress:
σb = ±Mx(Di/2+t)/Iv
Iv = π(Do4-Di
4)/4 = 3.14 (9868.134-9844.134)/4 = 7.215E13
Mv = total bending moment = Wx2/2 = 9066×5.2×5.2/2 = 122572.32 Nm
σb = ± 122572.32 × (9844.13/2+12)/7.215E13 = ± 0.0083822 N/mm2
wind loading:
Dynamic wind pressure = 1280 N/mm2
Mean diameter including insulation = 9.84413 + 2(12+50) × 0.001 = 9.968 m
Loading per linear meter Fw = 1280×9.968 = 12759.04 N/m
σz = σL + σW + σb = 49.2206 -2.990 + 0.0083822 = 46.238 N/mm2
Upwind = 46.238 N/mm2
Downwind = 49.2206 -2.990 -0.0083822 = 46.222 N/mm2
The greatest difference between the principal stresses will be
= σh – 46.222 = 98.4413– 46.222 = 52.219 N/mm2
Is well below the maximum allowable design stress.
Check for elastic stability (buckling):
σW = 2.990 N/mm2
σb = 0.0083822 N/mm2
64
σW + σb = 2.9983822 N/mm2,well below σc
Head calculation:
Type: Torispherical head
ho (Excluding straight flange) = Ro- [ (Ro−Do )×( Ro+Do
2−2r o)]
12
ro = 0.06×9.844 = 0.59064
D = 9.844 + 12 × 10-3 = 9.856 m
Ro = Do = 9.856 m
ho = 9.856-[(9.856-(9.856/2))×(9.856+(9.856/2)) – 2×0.59064)]1/2
= 1.355 m
Sf = 40 mm
The length of straight flange = 3 × 12 = 36 mm
Total height = 1.355 + 0.036 = 1.3917 m
Total height of the column = 5.2 + (2×1.3917) = 7.983 m
Support:
Bracket support: bracket support is chosen for this vessel in consideration with the height of the column.
Data:
Diameter of the vessel = 9.844 m
Height of the vessel = 5.2 m
Clearance from the vessel bottom = F = 3 m
Weight of the vessel with contents = 1920177.77 N
Wind pressure = 1285 N/mm2
no of brackets = n = 8
Dia of anchor bolt circle = 10.0143 m
65
Permissible stress for structural steel
Tension = 140 N/mm2
Compression = 123.3 N/mm2
Bending = 157.5 N/mm2
Maximum compressive load:
Wind pressure
Pw = k × p × h × Do
= 0.7 × 1285×5.2×9.8443
= 46045.72 N
Px = 4Pw(H−F )(n×Db ) +
W tot
n
= 4 ×46045.72×(5.2-3)/(8×7.109)+1920177.77/8
= 247148.4263 N
Bracket:
Base plate: a = 140 mm B = 200 mm
C = 10.0143-9.844 = 0.17 m
Paw = 247148.4263 / (140×200) = 8.826 N/mm2
f = 0.7Paw×B2
T12 × [ a4
(B4+a4 ) ] = 0.7× 8.826 × 202/T1
2 × (142/(202+142))
= 812.702/T12 (take f=157.5 N/mm2)
T1 = 22 mm
Web plate:
Bending moment of each plate = px × C/2 = 247148.4263 N(10.0143-9.844) ×100/(2×2)
= 1050380.12 Ncm
66
Stresses at the edge = f
f = 3×Px×C/(T2×a×cosɵ)
Take ɵ = 450
=3×247148.4263× (10.0143-9.844)×10/(T2×142×2×0.707)
T2 = 15.044 mm
8.1.6 Cyclone dimensions:
Cyclone dimensions were calculated from the stairmand standard High gas rate cyclone
Ref: Coulson and Richardson Vol.6, page 449 refer to figure 4.2
Figure 8.1 Equipment Diagram of Reactor
8.1.7 Summary of the process design of the reactor
67
Table 8.1 Process design of reactor:
Process design of the FBRS.No Description Specification Unit1 Design model K-L model2 Type Fluidized bed -3 Shape Vertical cylinder -4 Height 5.2 M5 Diameter 9.8446 M6 Catalyst Bismuth molybdate7 Temperature 420 ˚C8 Pressure 2 Bar9 Weight of catalyst 82710.117 Kg10 Residence time 8.687911 Flow rate of feed 37.861 m3/sec12 No of cyclones 1313 No of cooling tubes 1700
8.1.8 Summary of the mechanical design of the reactor
Table 8.2 Mechanical design of reactor:
S.No Description Specification Unit1 Material of constructions SS321L2 Inside diameter 9.8446 M3 Shell thickness 12 mm4 Outside diameter 9.8686 M5 Insulation Mineral wool6 Insulation thickness 50 Mm7 No of heads 28 Thickness of heads 12 mm9 Height of head 1.355 m10 Reactor height including heads 7.983 m11 Type of support Bracket12 Feed location Bottom through spurgers13 No of brackets 814 Tube diameter 50 mm15 Tube length 8 m
68
9. SAFETY, HEALTH AND ENVIRONMENTAL ASPECTS
A chemical manufacturing process is described as inherently safer if it reduces or
eliminates hazards associated with materials and operations used in the process, and this
reduction or elimination is a permanent and inseparable part of the process technology. A
hazard is defined as a physical or chemical characteristic that has the potential for causing
harm to people, the environment. These hazards are basic properties of the materials and
the conditions of usage, and cannot be changed. An inherently safer process reduces or
eliminates the hazard by reducing the quantity of hazardous material or energy, or by
completely eliminating the hazardous agent. A traditional approach to managing the risk
associated with a chemical process is by providing layers of protection between the
hazardous agent and the people, environment, or property which is potentially impacted.
The layers of protection are intended to reduce risk by reducing either the likelihood of
potential incidents resulting in an impact on people, the environment, or property, or by
reducing the magnitude of the impact should an incident occur.
The protective layers may include one or more of the following:
a. The process design
b. Basic controls, alarms, and operator control
c. Critical alarms, operator control, and manual intervention
69
d. Automatic actions- emergency shutdown systems and safety interlock
systems
e. Physical protection equipment such as pressure relief devices
f. Physical mitigation systems such as spill containment dikes
g. Emergency response systems – for example, fire fighting
h. Community emergency response – for example, notification and evacuation
The acrylonitrile plant like any chemical plant or Petroleum refinery is a place
where safety is of prime importance. The best procedure for achieving accident free
operation is to have personnel conscious of safety and potential hazards at all times. The
extreme toxic and flammable nature of some of the chemicals involved should be given
special attention. Personnel should be familiar with the properties, and consideration of
these properties should be given importance in all job’s planning’s. The table below
demonstrates the properties health hazards and remedies that ought to be followed when
exposed to the handled chemicals above hazardous limits. Additional caution must be
paid to leak detection.
To facilitate the quick removal of acrylonitrile, Acetonitrile, hydrogen cyanide and other
harmful chemicals from the body, safety showers and washing facilities must be provided
at strategic locations throughout the plant. When working around hydrogen cyanide
handling equipments, it should be required that people carry a suitable emergency
breathing apparatus. Off gases must be continuously monitored to ensure the emission
levels of various components are within the norms dictated by the pollution board.
9.1 Plant Safety
1. Plant safety through design features
a). Temperature control of a highly exothermic reaction mixture is always a concern,
especially in large reactors that often have less heat transfer area per volume of reactants.
Improper design and/or operation of batch reactors and auxiliary equipment on several
occasions have contributed to serious accidents. Ammoxidation reaction is designed to be
carried out at a little higher temperature but at very short residence times in a fluidized
bed reactor. Continuous flow reactor has been chosen for the production of Acrylonitrile
70
since they offer important advantages as compared to batch processes in terms of safer
operation and better-controlled condition.
b). A Cooling coil in which BFW flows is chosen which provides excellent heat-transfer
characteristics. The velocities of the BFW in the tubes are high in order to provide
sufficient turbulence so that the proper amount of heat is transferred in the tubes.
c). The designer must be careful to assure that no stagnant areas exist inside the reactor.
High finishes on the interior surfaces of the reactor with complete freedom from surface
pits or pockets which could trap product are to be specified.
d). Precautions should also be taken to prevent formation of explosive gaseous mixtures.
The gases after the reactor contain unreacted propylene and oxygen. These conditions
favor the chances of explosion. It is recommended that inert gas blanketing in such a
situation. Hence, only a slight excess of hydrocarbon is used and the reactor was designed
to operate at such a temperature and pressure to prevent any accidents.
2. Plant safety through operating procedures
a). It is required that continuous observation of the ammoxidation temperature is
maintained. By properly controlling the BFW and feed rates of the feed streams the
reactors can be operated safely.
b).upon shutdown of the equipment, it is required to displace the entire product from the
apparatus. Only if the apparatus is completely free traps or pockets can this displacement
procedure be carried out with assurance that no ammoxidation product will be trapped
and remain behind in the reactor.
3. Plant safety through process control
Ammoxidation reactions must be considered potentially hazardous. This is because the
heat of ammoxidation is exothermic. Great care has to be taken to properly design the
control system for Acrylonitrile plant.
a). Continuous ammoxidation demands accurate metering and control equipment.
71
b). Temperature in the reactor is controlled by throttling the boiler feed water flow rate to
the reactor. Automatic stopping of the feed material in the event of an undue temperature
rise in the reactor, a failure of the boiler feed water. Solenoid-operated controls which are
“fail-safe” are also commonly used. The expression “fail-safe” generally implies that the
operation can be carried out only when all necessary services such as power,
refrigeration, or agitation are functioning. High temperature switches will shut off the
feeds and open the boiler feed water valve wide.
9.2 Personnel Safety
Hazards in Ammoxidation plants include handling and recovery of acids, flammability of
the hydrocarbon feeds and products, side reactions including undesired oxidations, and
the toxicity of some hydrocarbons. Consequently, care must be exercised to protect plant
personnel.
9.3 Pollution abatement
Major polluting substances from this ammoxidation process are ammonia, HCN,
unreacted propylene, CO2, CO and all other Organic compounds involved. The efficient
operation of plant is must to minimize the emission of these compounds. Two major
sources of polluting the environment are air emissions and water emissions.
Control measures to be taken to reduce the emissions:
a. The vent streams from the absorber top should be flared. (provided combustion
efficiency can be ensured)
b. Catalytic Oxidation facilities of off gases are recommended.
c. Emission from storage, loading, and handling should be prevented using internal
floating screens in place of fixed roof tanks as well as wet scrubbers.
d. Biological treatment system with at least 90 percent abatement of waste water
from the quench tower, stripper and columns is needed.
72
9.3.1 Hazardous emissions:
HCN, Acrylonitrile, Acetonitrile, Ammonium sulphate are considered to be
hazardous. Due to its reactive and toxic nature, hydrogen cyanide cannot be stored for
periods longer than a few days. If the material cannot be sold or used, it must be burnt.
The capability to destroy all of the hydrogen cyanide produced should therefore be
ensured.
The following measures should be implemented:
a. Gas detectors should be installed in hazard areas, wherever possible.
b. All spills should be avoided and precautions should be taken to control and
minimize them.
c. Adequate ventilation should be provided in all areas where hazardous and toxic
products are handled.
d. Air extraction and filtration should be provided in all indoor areas where
emissions and dust can be generated.
Table 9.1 Material Safety Data Sheet (MSDS)
Component Properties Explosive
limit
(vol)
Hazardou
s limit
(ppm)
Health
Hazards
And remedies
Propylene Heavier than air
Colorless, odorless 2.4-11.1% 4000
Personnel
exposed to
these chemicals
should be
removed to
fresh air.
Hydro-
cynamic acid
Colorless liquid
with odor of bitter
almonds
6.0-41.0% 100 Headache, eye
irritation are
signs. Must be
73
shifted to fresh
air.
Ammonia Colorlesscompoun
d with a very
pungent odor
16-25% Irritation of the
skin or mucous
membranes. Be
washed with
water.
Acrylonitrile Colorless liquid,
odorless, highly
flammable, very
reactive, toxic.
3-17% 2 Mild exposure
causes nausea,
vomiting,
diarrhea.
Acetonitrile Colorless liquid
with an aromatic
odor, toxic and
flammable
4.2-13.5% In case of
contact with
skin, must be
washed with
water.
Acrolein Slightly yellowish
liquid. Very toxic,
highly reactive and
flammable.
0.5 Burns and
irritations
caused by this
chemical should
be treated to
caustic
Carbon
monoxide
Highly poisonous,
odorless and
tasteless
100
Sulphuric acid Strong affinity for
water
In the splashed
area wash with
large quantities
of water.
74
10. INSTRUMENTATION AND PROCESS CONTROL
10.1 Introduction
Process control is defined as maintenance of desired set of variables under optimum
conditions suitable for efficient production of a process product. The decreasingly
tentativeness of process parameters, cost, competitiveness and quality consciousness have
made it imperative to opt for Automotive process control in place of manual control.
Process may be controlled more precisely to give uniform and higher quality
products by the application of automatic control, often leading to higher profits. In
addition to this, process that responds too rapidly can be better controlled by automatic
control systems. Automatic control is also beneficial in certain remote, hazardous or
routine operations. After a period of experimentation, computers are now being used to
operate and automatically control processing systems.
Since process profit is usually the most important benefit to be obtained by
automatic control, the quality control and its cost should be compared with the economic
return expected and the process technical objections. The economic return includes
reduced operating costs, maintenance and off-specification product along with imported
process operability and increased through-put. Automation, of course, requires close
interaction between designers and control system designers.
75
Coming to acrylonitrile production by vapour phase catalytic propylene
ammoxidation, process control plays a vital role in this plant, since the product is highly
flammable with wide explosive limits. The reaction is highly exothermic and there are
chances that runaway reaction may take place leading to fire accidents. To control the
parameters of important equipments, to monitor and control the concentration of various
components at various locations throughout the plant automatic control is must. It brings
about better control over final product quality.
10.2 The different instrumentation aspects and control loops for the Reactor are as
follows:
Reactor is the Heart of the process. Because of exothermic reaction, even the slight
changes in conversion of reactants can induce considerable and adverse effects on heat
transfer in the reactor. These changes eventually lead to fire accidents. And also
performance of reactor is the deciding factor in the rate of production of Acrylonitrile
from the plant. Any change in operating conditions in the reactor changes most of the
other conditions. Therefore, the total effect of any change is difficult to predict. For
instance, an increase in pressure in the reactor reduces the volume of the gases in the
reactor, and therefore reduces the velocity of the gases through the catalyst bed.
The important parameters that must be measured and controlled maintained in
the reactor are:
1. Temperature in reactor
2. Pressure in the reactor
3. Density of the fluidized bed
4. Concentrations of various components
10.2.1 Temperature measurement and control:
Since the reaction is exothermic, heat is evolved during the reaction. To maintain a
constant temperature in the reactor, the evolved heat must be continuously removed. Heat
from the reaction is transferred to the circulating water in the steam coils producing
76
steam. Temperature control can also be accomplished by adjusting the feed rates of
reactants to the reactor. The steam is generated in the reactor cooling coils in the process
for removing the exothermic heat of reaction. A thermocouple is placed in the Thermo
well which is submerged in the reacting liquid in the reactor. The indication from this
thermocouple will be sent to temperature controller (TIC). This TIC will be cascaded
with the FCV on cooling water outlet line from the reactor. Bypassing of steam can be
employed to ensure required degree of superheat. Usually PID controllers are preferred
for temperature control. An alarm is also installed to indicate high temperature. A control
loop is provided in case off increase in temperature. As the shell side water flow rate
increases the temperature can controlled.
10.2.2 Pressure measurement and Control:
A pressure-recording controller controls the pressure in the reactor. This control valve
fixes the top pressure in the reactor at the level necessary to obtain the proper velocity in
the reactor. Under any conditions, velocity in the reactor should not be allowed to cross
0.9 m/sec, as it will result in excessive loss of expensive catalyst. PID controllers
provides better control in this aspect.
The pressure in the Reactor is maintained at 2 bar. This is achieved by providing
one Pressure Control Valve (PCV) on the reactor. The pressure transmitter measurers the
pressure of the reactor and will send signals to PCV which will vent out the excess gas
from the reactor maintaining the value within the desired range.
The process air compressor provides reaction air at 2.5 Kg./cm g. Flow of air to the
reactor is controlled by the flow-recording controller. Minimum compressor flow is
maintained by venting air to the atmosphere by antisurge flow, which is controlled by
flow controller.
10.2.3 Flow Control:
Propylene and ammonia vapor flow to the reactor are controlled by flow Recording
Controllers. Orifices, or mass flow meters can be used but for sophisticated control FRC
77
(Flow control valves) are used. Feed must be controlled to ensure that the correct ratios of
the various components are fed to the reactor. This usually has a very significant effect on
the process economics and it may cause serious operation problem, if cross the safe
operating region. Flow of boiler feed water into the steam tubes must also be equipped
with proper flow controlling and recording device. A bypass stream to the superheated
steam line can be used to control the degree of superheat by a proper control valve. The
catalyst can also be reduced if the ammonia to propylene ratio becomes too low. The
ammonia to propylene ration should be maintained between 1.20-1.22. The reactor feed
streams of propylene and Ammonia are controlled by flow or ratio controller and using
other suitable flow control device.
10.2.4 Measurement of concentration of Important Components in Reactor:
The oxygen content of the reactor effluent is an important variable and is continuously
monitored in the overhead stream before entering into the absorber. Typical range is 0.5-
1.2%. Oxygen in the reactor outlet should never be allowed to cross upper alarm limit of
2.0% because it can create explosive mixture in the reactor. Zero oxygen in the reactor
causes reduction of the catalyst, which should be avoided.
The catalyst is severally reduced under such conditions. When the catalyst is
reduced, Propylene conversion to acrylonitrile goes down. Zirconia oxygen analyzer is an
electrochemical method for measuring oxygen. The zirconia oxygen analyzer does not
require sampler, it has fast response, accurate for the low concentration down to 1 to 100
ppm. For gas analysis, chromatography is a relatively simple physical process of
separating, isolating, identifying and quantifying components of the complex mixture.
Detectors of suitable types located at the outlet point would measure the amount of
components and the results recorded as what is known as chromatogram, from which the
constituents and their percentages are evaluated.
10.2.5 Bed density a measure for fluidization:
78
One means of checking whether or not the bed has good fluidization is to measure the
amplitude of the level trace on the level density recorder. The narrower the band the
better the fluidization will be. This method, is however, not very reliable. Poor particle
size distribution may be the cause of high catalyst losses if the catalyst is too fine. Highly
excessively coarse catalyst may result in low yield of acrylonitrile. Catalyst losses may be
expected to increase as reactor velocity increase. Reactor velocity must be frequently
checked and reduced to more acceptable levels by suitable pressure controller.
Density can be measured by various methods. Mechanical method and the
electrical method are the two major classes that are in practice. The average density of the
bed can be calculated from the internal pressure drop inside the fluidized bed and the
porosity of the fluidized bed. Bed pressure drop can be measured directly by a pressure
tap placed right above the gas distributor such as vertical pressure probe, a wall pressure
tap and/or a distributor buried type. To prevent particles entering, filtering material must
be used. To avoid gas dynamic pressure, the hole of a pressure tap must face parallel to
the main gas flow. The porosity does not change significantly with variations in operating
conditions. The porosity value can be calculated from the density of the fluidized bed,
which can be measured with a pycnometer by regularly taking a bed sample. A tight
control over the feed rates is achieved by a combination of an online measurement of
reactant streams with online pressure drop measurements.
79
11. PLANT LAYOUT
11.1 Introduction:
A plant layout is that arrangement of machines, so that such operation is performed at the
point of greatest convenience.
Definition:
Plant layout is placing of the right equipment, coupled with right method, in the
right place to permit the processing of a product is the most effective manner through the
shortest possible distance and the shortest possible time.
The importance of a good layout is better pronounced is operating effective, such
as economics in the cost of materials handling, minimization of production delays and
avoiding bottlenecks etc., one of the preliminary task of a good layout is the selection of a
proper site.
11.2 Site Selection:
A site may be selected considering the following features.
1. Soil and topography: If heavy machinery is to be installed, soil strength should
be high enough. Ground must be of equal level otherwise it needs land
development which increases total cost.
2. Disposal of waste: The site selected for location of the plant should have a
provision for disposal of waste particularly for sugar steel and leather industries.
80
3. Transport facilities: This site should be well connected by rail road and if
possible sea transport.
4. Civic amenities: When large number of workers is needed, industry should be
located where civic amenities like banks, educational institutions, recreation
facilities are available.
5. Land: If industry required large area, it should be located at a place, where land is
cheap and the land should be free from all encumbrances.
6. Local laws or Government Policy: In the name of balanced regional
development, many backward regions in India have been selected for the location
of new industries. So the factory should be located in such places where
government gives facilities and concessions in the form of reduction in sales tax,
electricity policy, freight policy, institutional finance with least percentage interest
etc.,
7. Availability of labor: It should be located in a place where skilled, unskilled and
semi skilled labor are available.
8. Water: Depending upon the nature of the process, the industry should be located
where abundant water is made available.
11.3 Objectives of good layout:
1. To produce better quality product with minimum cost.
2. To use maximum utilization of floor space horizontal and vertical as well as cubical
most effectively.
3. To minimize internal transportation and improved material handling.
4. To minimize accidents.
5. To minimize production delays and to have proper production control.
6. To have a space for the future expansion.
7. To eliminate waste effort and speeding of production.
81
8. To have better working conditions and neatness.
9. To avoid unnecessary charges.
10. To have minimum equipment investment.
11. To have imported quality control.
12. To minimize back trading of materials.
13. To maintain flexibility of arrangement and operations.
14. To promote effective utilization of man power.
15. To provide adequate gangways, and aisles for the movement of men and materials.
11.4 Factors considered while planning layout:
The different factors that contribute to the evolution of final layout are as
follows:
1. Materials factor: This includes raw materials, materials in process, finished
products, shop tools etc., The main considerations are type of product,
characteristics of various materials, quantity and variety of products.
2. Machine factor: This includes various machines and equipment. The main
considerations are type of machinery, tools and equipment, machine utilization
and maintenance and replacement of their parts.
3. Main factor: The main considerations are man power requirements, safety and
working conditions, utilization of men.
4. Movement factor: It mainly deals with movement of materials and men namely
inter departmental movements and short movements. The considerations are flow
patterns, movement of men, incoming and outgoing material reducing
unnecessary and uneconomical handlings.
5. Waiting factor: Whenever man stops work, waiting occurs which costs money
such as money tiled up with idle materials handling cost in waiting area etc., the
82
main considerations are storage or delay points, designing of material waiting
space, method of storage and its safe guards.
6. Service factor: This includes employee facilities fire protection lightening and
ventilation.
7. Expansion factor: Choice of expansion must always be kept in mind. The
proposed layout must exercise flexibility for expansion. However this requires
sound engineering judgment. Nevertheless the cost of change must be borne, for
the economic viability of larger units, if it asks for replacement or revamp.
8. Building factor: This includes outside and inside building features and types of
building and height building which can economically accommodate the required
machinery.
9. Analysis of Handling Methods: The handling method depends upon the
characteristics of material, quantity and place of movement and type of handling
equipment, condition of route, frequency of movement etc.,
11.5 Rail and Roads:
Existing or possible future rail road and highways adjacent to the plant must be known in
order to plan rail sidings and access roads with in the plant.
The ideal procedure for any plant is to build the layout around the product and then
design the building around the layout. However this is ideal method and cannot always be
followed.
Good layout today is based on principle of flow. Such evidences of steady flow as
regular movement of production, absence of bottle neck operation, all contribute shorten
the manufacturing cycle and reduce the amount of material in progress. There also the
matter of flow of the people, the arrangement of employee facilities, assist, plant
entrances and parking areas for uncontested traffic. A systematic layout for this
incorporating all the fore said principles is presented in the figure 11.1
83
Figure 11.1 Plant Layout
11.6 Plant Location
Considering all the above factors and the plant layout conditions, we are choosing to
construct our plant in the “Industrial area of Visakhapatnam.”
The advantages of locating the plant in Industrial area of Visakhapatnam are:
1. Existence of sea port.
2. Well connection to the road and rails.
3. Soil strength is good.
4. Existence of industries to get raw materials like propylene from HPCL.
5. Ammonia can be obtained from the nearby fertilizer Industry.
6. Waste water disposal into the Sea.
84
12. MATERIALS OF CONSTRUCTION
12.1 Characteristics
The most important characteristics to be considered when selecting a materials of
construction are:
1. Mechanical properties:
a. Strength- tensile strength.
b. Stiffness-elastic modulus (young’s modulus)
c. Toughness-fracture resistance.
d. Hardness-ware resistance.
e. Fatigue resistance.
f. Creep resistance.
2. The effect of high temperature, low temperature and thermal cycling on
mechanical properties.
3. Corrosion resistance.
4. Any special properties such as thermal conductivity, electrical resistance,
magnetic properties.
5. Ease of fabrication-forming, welding, casting.
6. Availability in standard sizes-plates, sections, tubes.
7. Cost
Table 12.1 Mechanical properties of common metals and alloys
Metal & alloys Machining Cold
Working
Hot working Casting Welding Annealing
Temperature ºC
Mild steel S S S D S 750
Low alloy steel S D S D S 750
Cast iron S U U S D/U -
Stainless S S S D S 1050
Nickel S S S S S 1150
Monel S S S S S 1100
Copper D S S S D 800
85
S - Satisfactory, D – difficulty, special techniques needed, U - unsatisfactory
12.2 Selection for corrosion resistance
In order to select the correct material of construction, the process environment to which
the material will be exposed must be clearly defined. In addition to the main corrosive
chemicals present, the following factors must be considered:
1. Temperature-affects corrosion rate and mechanical properties.
2. Pressure.
3. pH
4. Presence of trace impurities-stress corrosion.
5. The amount of aeration-differential oxidation cells.
6. Stream velocity and agitation-erosion-corrosion.
7. Heat transfer rates-differential temperatures.
The conditions that may arise during abnormal operation, such as at startup and
shutdown, must be considered, in addition to normal, steady state operation.
12.3 Materials used in Reactor
Red mud is produced during the Bayer process for alumina production. It is the insoluble
product after bauxite digestion with sodium hydroxide at elevated temperature and
pressure. It is a mixture of components originally present in the parent mineral, bauxite
and of compounds formed or introduced during the Bayer cycle. It is disposed as a slurry
having a solid concentration in the range of 10-30%, pH in the range of 13 and high ionic
strength.
Red mud is a very fine material in terms of particle size distribution. Typical values
would account for 90 volume % below 75µm. The specific surface (BET) of red mud is
around 10m2/g. A chemical analysis would reveal that red mud contains silica,
aluminium, iron, calcium, titanium as well as an array of minor constituents, namely Na,
K, Cr, V, Ni, Ba, Cu, Mn, Pb, Zn etc, The variation in chemical composition between
different Red mud world wide is high. Typical values would account
86
Table 12.2 Composition in Red mud
Component Weight %
Fe2O3 30 – 60
Al2O3 10 – 20
SiO2 3 – 50
Na2O 2 – 10
CaO 2 – 8
TiO2 Trace – 25
87
13. COST ESTIMATION
The cost estimation for the proposed project is based on multiple factor method. In
this method, individual factors are chosen to estimate the expenses of equipment, labor,
piping, instrumentation etc., in consultation with the experienced personnel. The accuracy
and factors used of this method would depend on the type of process, material of
construction, location of plant and past experience.
13.1 Fixed Cost Estimation:
Instrumentation and controls cost:
Instrumentation costs, installation, labor costs, and expenses for auxiliary equipment and
materials constitute the major position of capital investment required for instrumentation.
Total instrumentation cost depends on the amount of controls required and may amount
to 6 to 30% of the purchased cost.
Unit costs:
Availability of unit cost data, however does not assure a good estimate. Changing
work forces, geographical locations, weather, labor efficiency, inflation and specified job
conditions effectively rule out use of unit installation costs for other than guide lines.
Piping estimation:
The cost of piping covers fittings, pipe supports, labor and other items involved in
the complete erection of all piping used directly in the process. Process plant piping can
run as high as 80% of process equipment cost.
Auxiliaries Estimation:
The definition of auxiliaries includes all structures, equipment and services, which do not
enter directly in to chemical process. Typical chemical auxiliaries include buildings,
storage, substation, steam and electric distribution fire protections communications etc.,
88
Land Cost:
The cost of land depends on the size of the proposed plant, its location with the
cost being very high if located in the industrial area. As a rough appropriate land cost of
industrial plants amount to 4-8% of purchased equipments.
Contingencies:
The contingency allowance is reserved for unpredictable items of cost not known at the
time of the estimate. These unpredictable may include floods, strikes, price charges, etc.
contingency estimate may range from 8-20% of direct and indirect plant cost.
13.2 Manufacturing cost estimation:
The checklist of different manufacturing cost items is as follows:
1. The cost of raw materials, catalyst, and chemical depends on their volume,
their proximity to the place of purchase and type of purchase and quality
etc.,
2. The cost of utilities include steam, cooling water, DM water electricity
refrigeration, compressed air, instrument air and effluent treatment etc.,
3. Labor cost includes direct and indirect costs like labor, the cost of
supervision, fringe benefits, shift premium and overtime wage rates, and
scheduling of working hours.
4. Maintenance cost is built up of three components material required
manpower to install them and overhead for supervision and scheduling.
5. Insurance coverage, property fares plant overhead like security, janitors,
administrative offices, cafeterias, charge house and same of other factors to
be considered while estimating the working capital.
89
13.3 Estimation of Cost of Reactor
Volume of reactor = 328.935 m3
Cost of the reaction vessel Cv (16*) = Rs 15, 70,391
Cost of insulation (17*) = Rs 650/kg
Total weight of insulation = 7450 kg
Total cost of insulation, Ci = 650 x 7450
= Rs 4901000
Weight of the catalyst = 165420 kg
Cost of the catalyst (18*) = Rs 1250
Cost of the catalyst, Cc = Rs206775000
Boiler and its accessories Cb = Rs 50, 00,000
Number of Cyclone separators = 13
Cost of Cyclone = Rs 58,000
Total cost of cyclones, Cs = Rs 754000
Total cost of the reactor = CV + Ci + Cc + Cs + Cb
= Rs 17, 31, 45,391
90*- refer to bibliography
13.4 Total Equipment cost:
Table 13.1 Quantity of each Equipment and their cost:
Equipment Quantity (No’s) Cost in lakhs
Reactors 1 1731
Columns 5 250
Heaters 2 15
Coolers 5 25
Refrigeration system 1 100
Reboilers 2 12
Condensers 3 15
Tanks 3 287
Pumps 12 36
Total equipment cost
(TEC)
2471
13.5 Cost Estimation:
Table 13.2 Values of Direct costs:
Direct costs Cost in lakhs
Total equipment cost (TEC) 2471
Installation of equipment (30% TEC) 741.3
Instrumentation (13% TEC) 321.23
Piping costs (50% TEC) 1235.5
Buildings & services cost (30% TEC) 741.3
Land cost (8% TEC) 197.68
Insulation cost (5% TEC) 123.55
Electrical facilities (12% TEC) 296.52
Auxiliaries (60% TEC) 1482.6
Total Direct Costs 7610.68
91
Table 13.3 Values of Indirect costs:
Indirect Costs Cost in lakhs
Engineering and supervision (33% TEC) 815.43
Construction Expenses (41% TEC) 1013.11
Total direct and Indirect Costs 9439.22
Contingency (10% of total plant cost) 943.922
Contractor fees (5% TPC) 471.96
Total estimated project cost 10855.103
13.6 Profit and Pay Off period:
Manufacturing Cost = Direct production cost + Fixed charges + Plant over head costs
Table 13.4 Estimation of manufacturing cost per year:
1. Direct Production cost In crores
a. Raw material (60% of total production cost = S.P
= 839.69)
503.814
b. Operating Labor (10%) 83.9
c. Direct supervisory and electrical labor (10%) 9.0
d. Utilities (15%) 125.9
e. Maintenance and repairs (5%) 4.98
f. Labor charges (10%) 9.0
g. Patents and royalties (0.5%) 5.42
Total 742.02
2. Fixed charges
a. Depreciation (10% of total project cost) 10.85
b. Local taxes (1%) 1.08
c. Insurance (1%) 1.08
Total 13.01
3. Plant overhead costs: (5% of total production
cost)
41.9845
92
Manufacturing Cost (MC) = Direct production cost + fixed charges + plant overhead cost
= 742.02+13.01+41.9845
= 797.8195
Total plant investment = Rs 108.55 crores
Cost of Acrylonitrile per ton (19*) = Rs 94, 940
Cost of Acetonitrile per ton (20*) = Rs 94, 000
Cost of Hydrogen cyanide per ton (21*) = Rs 12,625
Cost of Ammonium Sulphate per ton (22*) = Rs 19,000
Selling price of Acrylonitrile/year = 120000 x 74,940
= Rs 726.2crores
Selling price of Acetonitrile/year = 3617.31 x 94,000
= Rs 34.0crores
Selling price of Hydrogen cyanide/yr = 12971.3 x 12,625
= 16.37crores
Selling price of Ammonium sulphate / yr = 36064.89 x 19000 = Rs 68.52crores
Total Selling price = 6852 + 16.37 + 28.8 + 726 = 839.69 crores
Gross profit Earned/year = Selling price – Manufacturing Cost
= 839.69 –797.8195
= Rs 41.8705 crores
Amount of Taxes to be paid = Rs 12.56crores
93
*- refer to bibliography
(30% of Grossprofit)
Net profit earned/year = Gross profit – taxes paid
= Rs 29.309 crores
Pay Off period = total plant investment
Net profityear
= 108.5529.309
= 3.703 years
The estimated pay off period is 3.7 years.
94
95
