indian coal to chemicals new rev8
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Indian Institute of Technology Delhi
Indian Coal to ChemicalsGroup 5CHL471: Process Equipment
Design and Economics
IIndSemester 2012-13
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Executive Summary
The rate at which Indian coal is used today for thermal power generation purposes is low. It is
estimated to last over 200 years at the current consumption values and the reserves available.
Production of industrially and commercially useful chemicals from Indian coal involvesgasification of the coal to syngas as the first step. Indian coal has about 40% ash content
which reduces its usefulness unless very sophisticated techniques for coal gasification and
ash handling are used. Coal gasification produces 500 tonnes per day of syngas containing H2
and CO in mole ratio of 3:1 to be processed downstream for production of chemicals.
Gasification of Indian coal requires extensive feed preparation operations because of the
washing operations employed to reduce ash content. Feed preparation starts with crushing
large chunks of coal obtained from mines using jaw crusher. With the help of washing
operations, the ash content significantly reduces to about 25-30%. In the current plant,
528,000 kg of grade E Indian coal is processed per day. The feed preparation unit takes in
approximately 40 kg/s of coal and delivers 19 kg/s of coal with an overall efficiency of about
50%. The prepared coal then passes through pressure feeder which injects the coal at 8atm in
the gasifier. The fluidised bed reactor operates at 670 oC and 8 atm under optimum
conditions. Steam from steam generator and oxygen from air separation unit is also fed to the
gasifier from the bottom assembly. The syngas is purified before being sent downstream for
further processing. Since Indian coal has substantial quantities of sulphur content, the syngas
produced has huge acidic content. The impure syngas from the top of the reactor goes
through various cleaning and cooling operations. Solid impurities are removed with the help
of cyclone separators and the heat of the gas is used to preheater water for steam generation.
The gas is then treated for heavy metal removal and acid gas removal. Activated carbon bed
is used to get rid of mercury and other trace heavy metals. Activated MDEA solvent with a
hint of piperazine is used to absorb excess CO2 and other acid and residual gases from thesyngas. The treated syngas with required composition is sent to downstream operations for
methanol production. The solvent is regenerated by application of heat. The flue gas from the
top of regenerator is subjected to Claus Treatment reactors where sulphur is converted to
elemental form eventually and extracted out of the system for other commercial purposes of
economic value.
Methanol production starts after the syngas is purified by removal of catalyst poisons and
unwanted carbon dioxide. The incoming feed of 2600 kgmol/hour is first passed through a
guard bed to reduce the poison concentration to ppb levels, this is necessary to avoid excess
of deactivation of catalyst in the reactor. This feed is then compressed using reciprocating
compressors to get feed at a pressure of 70 bars and a temperature of 1100 degrees Celsius.The incoming feed is mixed with recycled feed, which is at a lower temperature of 115oC to
get mixed feed for the reactor at 237oC. This feed is then passed through a heat exchanger
also called economizer to heat up the feed to 250oC, which is the operating temperature of
the reactor. This operation ensures that additional operational costs are not incurred and heat
is optimally utilized. The reactor is 2.8 meters in diameter and 23 meters in height and
operates at a pressure of 70 bar and has the following zones:
1. A zone for gaseous feed to distribute properly [height = 1 m]2. Oil zonefilled with oil and catalyst this is where majority of the reaction takes place
[height = 18 m]
3. A disengagement zone for the oil rising with gaseous product to settle down within
the reactor [height = 4m]
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The exit gases from the reactor are sent to a cyclone, which separates out the catalyst
particles from the gaseous product. The gases are then cooled to extract out water and
methanol from them by the process of condensation. The final temperature of cooled gases is
64 oC. The gaseous mixture now consists of only CO, CO2and H2. 46% of these gases are
recycled and the rest purged. The product, which is in the form of liquid, comes out of the
condenser at a rate of 755 kgmol/hr. This is then sent to an atmospheric distillation column,which separated water from methanol and produces AA grade methanol at a rate of 453
MTPD.
Methyl acetate is produced using a combined technique of reactive distillation column which
incorporates both the reaction as well as purification in one. The reactive distillation column
has a double-feed design having a total of 35 trays. The reactants, methanol and acetic acid
are fed from the bottom at the 13th tray and the top at the 31st tray, respectively. Methanol
flows at a rate of 1860 kg/hr and acetic acid at 3500 kg/hr in a counter current fashion. The
reactive section lies between these two trays. The stripping section is at the bottom of the
tower (first 13 trays) and rectifying section is from tray 32 to 35. The product, 95% pure
methyl acetate, is produced at a rate of 173.5 MTPD.
Presently demand of acetic acid globally is 6.5 MMTPA. In India presently there 20
companies producing acetic acid with a total installed capacity of 150,000 MTPA. Our design
produces 63,000 MTPA of market grade (99% pure) acetic acid. Our plant aims to capture
15% of total Indian market of acetic acid. The mass balance on the reactor system was done
using ASPENplus software. The whole process plant is divided into two parts: one is
carbonylation unit and other is the purification unit. Carbonylation unit consists of the
reactor, gas absorber and few ancillary units like compressor, pump and heat exchanger. Feed
preparation is an important step. The pressure of carbon monoxide from the coal gasification
plant is increased from 1 atm to 42 atm and is also raised for methanol depending on the
reactor requirement. We are using a slurry bubble column reactor in order to carry out the
heterogeneous catalytic reaction between CO and MeOH. The reactor operates at 42 atm and
180oC. The purification unit consists of the liquid effluent column, distillation column,
refining column and end stripper. A heavy incinerator column is designed in order to absorb
the heavy by products from the bottom of the refining column. Part of the acetic acid
produced is sold to the market and part is sent for production of methyl acetate.
Acetic anhydride is produced by the carbonylation reaction of methyl acetate. Feed of methyl
acetate enters at 35.3 mol/s, which when throttled in a flash tank from a high pressure of 75
psig to 20 psig results in the vaporisation of methyl acetate at 16.4 mol/s. Methyl acetate and
CO are then passed into packed bed reactor, experiencing a pressure drop of 82 kPa. In thepacked bed reactor, CO reacts with Ru catalyst to form a coordinated complex which then
reacts with methyl acetate to produce acetic anhydride. A stream containing 86.1% acetic
anhydride, methyl acetate and CO is then passed through a distillation column where acetic
anhydride is obtained as bottom product in liquid form with 99% purity.
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Table of Contents
Executive Summary i
Project Team v
List of Tables vi
List of Figures viii
Nomenclature x
Introduction 1
Relevance of the Project 1
Chapter 1A: Coal Gasification Plant 2Coal Feed Preparation and Pulverisation operations
Jaw crusherDouble roller crusherCoarse Coal WashingHeavy Media vesselMedia Recovery ScreenFine Coal Washing - Heavy Media Cyclone
DryerAir Separation: Ion Transport MembraneSilo
Coal GasificationDesign of reactorTechniques for coal gasificationModelling and Simulation of Fluidised Bed Reactor using Aspen PlusConstraints and Variables involved in optimising reactor performance
Assumptions for simulationSensitivity Analysis- Variation of reactor and temperatureDesign options adopted
Gasifier assembly
Coal FeedMULTICORES160
Steam FeedWater pre-heater (Heat Exchanger)BoilerCalculation and specification of burnerSteam and Oxygen InletMinimum Fluidization VelocityResidence Time
AssumptionsReaction Time for a particleMean residence TimeReactor WallOutput of GasesOutput of Settled Ash From The Bottom Of The Reactor
Chapter 1B: Syn-gas Purification Plant 26Introduction
Solid Particle and Fine Particle Removal
Cyclone SeparatorElectrostatic Precipitator
Ash handlingHeavy Metal Removal: Mercury and Trace Elements
Activated carbon bedActivated Carbon Bed Design PrinciplesEconomic Life of the Activated Carbon Bed
Acid Gas Removal
Choice of Chemical Solvent: Activated MDEA
CO2 Removal
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Strength of Amine (MDEA) solutionDesign of Tray towerCalculation of number of trays required
Treatment of H2S gas: The Claus Treatment plant
Claus Process
Chapter 2: Methanol Production Plant 49
Removal of Methane from Syn GasProcess Flow DiagramMass balances
Preparation of Feed & Catalyst
Reactor Design
Choice of ReactorSparger DesignHydrodynamic ConsiderationsDetermination of Rate Law and Mass Transfer Coefficient
Product Purification/ Reactant Removal
Distillation ColumnHydrocyclone
Ancillary Units
Heat ExchangerPumps & Compressors
Chapter 3: Methyl Acetate Production Plant 81Introduction
ASPEN simulation
Mass balance
Feed PreparationStorage
Pump Design
Heat ExchangerTower Design
Reboiler and Condensor Design
Chapter 4: Acetic Acid Production Plant 107Mass balancesProcess Flow DiagramCarbonylation Unit
Feed PreparationPumpsCompressorsReactor DesignGas Absorber
Product PurificationCrude Fractionating ColumnRefining ColumnStorageEffluent Column
Ancillary UnitsHeat ExchangerEnd Stripping Column
Chapter 5: Acetic Anhydride Production Plant 143Process Flow Diagram
Design of Flashing Tank
Kinetics of ProcessDesign for Packed Bed Reactor
Pressure Drop
Costing of catalystDesign of Distillation Column
Conclusions 156
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Project Team
Team Leader: Rishabh Arora
Subgroup 1: Coal Gasification and Purification of Syn-GasMembers: Sahil Aggarwal (leader), Mradul Raj Jain, Mohd Wasil, Harshit Sinha, Tarun
Singh, Suresh Sharma, Kritesh Patel, Mohit Meena
Subgroup 2: Methanol ProductionMembers: Sarthak Nigam (leader), Aryanshi Kumar, Priya Meena, Mayuri Chowdhary,
Palash Agarwal, Seema Chouhan, Vipin Yadav, Rishabh Arora
Subgroup 3: Methyl Acetate ProductionMembers: Akash Sood (leader), Tapan Jain, Nishant Kumar, Raman Kumar*, Priya Ranjan*,
Nitesh Vijay, Vipul Garg
Subgroup 4: Acetic Acid ProductionMembers: Swarnim Raj (leader), Anshul Bang, Ravindra Verma*, Manish, Satyadeep Roat,
Sateesh Meena, Deepak Bonal, Jayesh Meena, Awadhesh Ranjan
Subgroup X: Acetic Anhydride Production
Members: Raman Kumar, Priya Ranjan, Ravindra Verma
*These members later shifted to a new subgroup, subgroup X, formed after the second progress report
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List of TablesTable 1: Specifications For Feeder and Crushers 3
Table 2: Coal Output from various units 3
Table 3: Feed to Heavy Media Vessel 4
Table 4: Washing in Heavy Media Vessel 4
Table 5: Feed to Heavy Media Cyclone 5
Table 6: Cyclone Dimensions 5
Table 7: Washed Coal in Heavy Media Cyclone 6
Table 8: Belt Specifications 10
Table 9: Constraints to be followed while simulating RGibbs block in Aspen Plus 11
Table 10: Composition of synthesis gas exiting from the top of the FBR 11
Table 11: Composition of coal after washing % weight 12
Table 12: Specifications of Multi core M-S160 based of operating conditions 15
Table 13: Parameter initial and required 17
Table 14: Assumptions and parameters values 19
Table 15: Calculations for dimensions of FBR 20
Table 16: Power cost of various units 23Table 17: Ratio analysis for the design of cyclone separator 27
Table 18: Dimensions for the design of cyclone separator 28
Table 19: Design of the Electrostatic Precipitator 29
Table 20: Specifications of activated carbon bed loaded with sulphur. 36
Table 21: Values to solve Ergun equation to calculate minimum fluidization velocity 36
Table 22: Final design of the activated bed and economic runtime 36
Table 23: Table of values used to design tray tower 40
Table 24: Results and dimension specifications for the design of actual tray tower. 40
Table 25: Experimental data for desorption of solution CO2 from activated MDEA 41
Table 26: Operating Line mass balance 42
Table 27: Composition of synthesis gas exiting from the top of the tray tower 43Table 28: Specifications of design of pump 44
Table 29: Aspen plus results of RGibbs reactor 45
Table 30: Mass balance results on streams 51
Table 31: Apparent maximum poison concentrations for methanol synthesis catalyst 53
Table 32: Parameter values for calculation of breakthrough time 54
Table 33: Breakthrough time through various adsorbent layers 54
Table 34: Comparison of type of reactors for Methanol Synthesis 55
Table 35: Design details of the sparger 57
Table 36: Stream Table 69
Table 37: Tray Sizing results 70
Table 38: Composition of specific heat capacities of inlet streams 75
Table 39: Composition of specific heat capacities of outlet streams 76
Table 40: Design Parameters 82
Table 41: Composition of Inlet Stream 84
Table 42: Composition of Outlet Stream 84
Table 43: Flow Rates 85
Table 44: Pipe Diameter 86
Table 45 86
Table 46 86
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Table 47: NPSHa 87
Table 48: Fluid Temperatures 89
Table 49: Overall heat transfer coefficient 91
Table 50: Feed composition 94
Table 51: Specific volume components 94
Table 52: Wilson Parameters 94
Table 53 95
Table 54: Activity Coefficients 95
Table 55: KATAPAK catalyst packing 96
Table 56: Saturation Pressure 97
Table 57: General Conditions and dimensions for tray towers 99
Table 58: General conditions and dimensions of sieve tray towers 100
Table 59: Pump Design 108
Table 60: Advantages and disadvantages of reciprocating compressors 110
Table 61: Specifications of reactor 115Table 62: bubble specification for the reactor 116
Table 63: Temperature and pressure condition for gas absorber 117
Table 64: Composition of Gases entering the absorber 117
Table 65: Dimension of Packed Tower 119
Table 66: Composition for Crude Fractionating column 121
Table 67: Composition for Refining Column 124
Table 68: Dimension for column material of Refining column 125
Table 69: Different Area of Tray 126
Table 70: Dry Pressure drop and different factors 127
Table 71: Hydraulic Head and its factors 127
Table 72: After reactor it is entering into effluent column 129
Table 73: Temperature pressure condition for effluent column 129
Table 74: Storage Data 130
Table 75: Storageof Methanol 132
Table 76: Composition in heat exchanger 133
Table 77: Column Diameter for Stripping Column 136
Table 78: Packing Properties 137
Table 79: Summary of data 145
Table 80: Reactor operating conditions 146
Table 81: Catalyst particle properties and other physical parameters 148
Table 82: Cost estimation 148
Table 83: Feed parameters in distillation column 149
Table 84: Distillate data 150
Table 85: Bottom product 150
Table 86: Calculation of k values and relative volatilities for top product 151
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List of FiguresFigure 1: Process flow diagram of coal gasification unit 2
Figure 2: Heavy media vessel capacity 4
Figure 3: Cyclone Dimensions 5
Figure 4: Lifting Flights 6
Figure 5: BCFZ Fib 7
Figure 6: Design of Silo and belt width 9
Figure 7: Values of cross section angle for trough and surchange angle at diff belt width 9
Figure 8: Variation of syngas composition 13
Figure 9: Diagrammatic view of the exchanger 16
Figure 10: Burner for the boiler 18
Figure 11: Distributor 19
Figure 12: Conical plate in annulus section 19
Figure 13: Ash exit mechanism and hopper configuration 22
Figure 14: Basic model of the reacor 22
Figure 15: Ratio analysis of dimensions for cyclone separator 27
Figure 16: Layout for handling fly ash 30
Figure 17: Treaa distribution for wind barrier 35
Figure 18: COS removal with CO2 removal with new aMDEA formulation 38
Figure 19: Effect of Piperazine concentration in MDEA on CO2 Level in Treated Syngas 39
Figure 20: Effect of Total Amine Strength on CO2 Level in Treated Syngas 39
Figure 21: Counter current multistage cascade, solute transfer from phase R to phase E 41
Figure 22: flow of liquid solvent (MDEA solution) and syngas (vapour phase) in tray tower 42
Figure 23: Manual construction to calculate number of stages in tray tower 43
Figure 24: Pump arangement and layout 44
Figure 25: Clause thermal reactor desing 46
Figure 26: Pore types in nanoporous graphine 49
Figure 27: Enersy barrier for pore A 49
Figure 28: Energy barrier for pore B 50
Figure 29: Process Flow Diagram 50
Figure 30: Homogeneous and churn-turbulent regimes in a column 58
Figure 31: Different models predicting rate law for Liquid Phase Methanol Synthesis 61
Figure 32: Different resistances involved in three phase reactor 62
Figure 33: Variation of concentration of Hydrogen with residence time 64
Figure 34: Variation of H2concentration in liquid phase with reactor height 65
Figure 35: Plot of concentration of H2with reactor volume 65
Figure 36: A typical Stairmand cyclone 68
Figure 37: Conventional processing schemes for esterification reaction 81
Figure 38: The Eastman reactive distillation process for methyl acetate manufacture 81Figure 39: Process Flow Diagram 82
Figure 40: Composition at different trays 83
Figure 41: Temperature Profile 83
Figure 42: Vapor and Liquid flow rates at different trays 83
Figure 43: Methanol storage tanks 85
Figure 44: Relation between Total head and capacity 87
Figure 45: LMTD correction factor 92
Figure 46: Tube side heat transfer factor 92
Figure 47: Shell side heat transfer factor 93
Figure 48: KATAPAK S250 Y catalyst 96
Figure 49: Thermosyphon Reboiler 101
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Figure 50: Process flow sheet for acetic acid production plant with help of aspen Plus 107
Figure 51: Schematic of SBCR auxiliarily setup 108
Figure 52: Reciprocating compressor interior view. 110
Figure 53: Working of Reciprocating compressor 111
Figure 54: Stages required for compressor at each stage 112
Figure 55: Slurry bubble column reactor 113Figure 56: Mass balance on slurry bubble column reactor 115
Figure 57: Material Balance For counter current flow absorber 116
Figure 58: Generalised flooding and pressure drop correlation 118
Figure 59: Crude Fractionating Column 120
Figure 60: McCabe method for stage calculation 128
Figure 61: Storage tank interior design 130
Figure 62: storage tank 132
Figure 63: Examples of Random Packings 136
Figure 64: Material Balance done in Aspen One using CHAO-SEA property 137
Figure 65: Generalised Pressure Drop Correlation 139
Figure 66: A gas injection type packing support 140Figure 67: A Pan type liquid distributor with bottom holes 141
Figure 68: Process flow diagram for acetic anhydride production 143
Figure 69: Flash tank design 144
Figure 70: Longitudnal catalytic Packed bed reactor 145
Figure 71: Distillation column flow diagram 149
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Nomenclature
T- temperature
t- time
C- specific heat capacity
G- mass flow rateU- average heat transfer coefficient
FT- correction factor for LMTD
Re- reynolds number
di- inner diameter
do- outer diameter
- viscosity
- density
e- wall roughness
- reaction time
Dgl - diffusivity
v- velocityV- volume
X - weight fraction vapourized
HuL- Upstream liquid enthalpy
HdV-Flashed vapor enthalpy
HdL- residual liquid enthalpy
cp - liquid specific heat
Tu - upstream liquid temperature, C
Td - liquid saturation temperature, C
Hv- liquid heat of vaporization
DP - pressure drop
G - mass velocity of the gas
Us- superficial velocity of gas in reactor
- porosity in packed bed
L - length of reactor
D - diameter of reactor
Dp- diameter of catalyst particle
dt- diameter of tube of the packed bed
F - feed to distillation column
Xf- mole fraction in feed
W- Total moles in bottom product
Xb- mole fraction in bottom product
D -Total moles in top product
Xd- mole fraction in top productKi - distribution coefficient for i component
i- relative volatilities of i component
N min - minimum no of plate
NR- number of plates of rectifying section
Ns- number of plates of stripping section
RD min - minimum reflux ratioRD actual -actual reflux ratio
Dc - diameter of column
H - height of column
- Fraction of gas, gas hold up
- Interfacial surface tension, N/m
- Activity coefficient of species i
- Bubble diameter- Orifice diameter, m
- Volumetric gas flow rate through each
orifice, m3/s
- Rate of consumption of Hydrogen
- Overall gas-liquid mass transfer
coefficient
- Gas-liquid interfacial area
- Liquid-particle mass transfer coefficient
- External surface area of the catalyst
pellets / particles per unit volume of reactor- Effectiveness factor based on pore
diffusional limitation
- Intrinsic reaction rate constant per unit
mass of catalyst per sec
- Catalyst mass per unit volume of reactor
- Saturation concentration of Hydrogen
(interfacial gas phase concentration)
- Equilibrium concentration of
Hydrogen
C - Discharge coefficient
f - friction factor
- Superficial gas velocity
HL- height of liquid in the column
- Liquid volume
- Tank diameter
dp- diameter of the sparger pipe
- Bubble rise velocity
No- number of holes in the sparger
Np- number of arms in the sparger
Larm - length of each arm of the sparger
- Free volume of molecules per mole- Time to initial breakthrough
-Time to midpoint of breakthrough
-Bulk denstiy of adsorbent (lbs/ft3)
- Henrys Law constant (lb moles/lb)
L - length of reaction zone
X - A factor accounting for initial and final
impurity concentration
d0= pitch of the sparger
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IntroductionThe semester long project taken up by our group aims at developing a commercially and
technologically viable process for production of industrially useful and high market value
chemicals from Indian coal. The aim of the project is to develop a process plant which
converts goal to synthesis gas while handling large amount of ash content and subsequentlyproducing methanol, methyl acetate, acetic acid and acetic anhydride. This involves first the
conversion of syn-gas to methanol via the Liquid Phase Methanol (LPMeOH) process. Next it
involves the production of methyl acetate from chemical grade methanol using a reactive
distillation process and finally to acetic acid and anhydride by the Acetica and Codec
processes respectively.
Relevance of the ProjectIndia has abundant geological reserves of coal, having the fifth largest coal reserves in the
world. The total estimated reserves by the Geological Survey of India as on April 1, 2011 are
285.86 billion tonnes, of which 114 billion tonnes are proven. The production of coal during
the period April, 2010 - March, 2011 as reported was 424.50 million tonnes. Going by the
current usage, the current proven reserves would last another 268 years. Apart from that,
currently over 70% coal is used in thermal power plants (TPPs) to produce electricity.
However, the coal available in India (mostly D, E and F grades) consists of a large amount of
undesirable materials like ash (38%), Sulphur (0.41%) and heavy metals like Hg, As, etc. As
other more renewable energy sources like wind, hydroelectricity, solar are being developed
to meet ever growing energy requirements, it is very unlikely that we will use the large
reserves of coal that India has for energy generation.
Moreover, methanol, acetic acid and acetic anhydride, each chemical has a number of uses.
Methanolis one of the most versatile compounds developed and is the basis for hundreds
of chemicals and is second in the world in amount shipped and transported around the
globe every year.
Acetic acid is an excellent polar protic solvent. It is frequently used as a solvent for
recrystallization to purify organic compounds. Acetic acid is used as a solvent in the
production of terephthalic acid (TPA), the raw material for the polymer PET.
Acetic anhydride finds its greatest application in the production of cellulose acetate from
cellulose, which is a component of photographic films. Also, it is used for the synthesis of
heroin from the diacetylation of morphine as well as aspirin and paracetamol, making it a
globally desired chemical.
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Chapter 1A: Coal Gasification Plant
Coal Feed Preparation and Pulverisation operations
Overall Process flow diagram for coal gasification and purification:
Fig1: Process flow diagram of coal gasification unit
The various unit operations and processes involved along the spectrum has been described below.
1. Coal feed preparation and pulverisation operations: Crushing and washing operations
2. Storage of coal in silo: Buffer stock for gasifier/design of silo.
3. Coal gasification: Prediction of syngas composition using Aspen Plus and optimizing
performance
4. Design of Fluidised Bed Reactor using CAD tools: Gasifier Assembly.
5. Removal of Solid impurities coarse/fine: cyclone separator
6. Syngas cooling: Preheating water for steam generation
7. Steam generator
8. Air separation unit: Ion exchange membrane
9. Syngas purification: Heavy metal removal in activated carbon bed
10.Syngas purification: Acid gas removal/Choice of solvent/Design of tray tower
11.Number of stages in a tray tower: Operating line and equilibrium curve
12.H2S treatment: Claus Treatment Reactors
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CRUSHERS : (Contributed by: Mohd Wasil)
Jaw Crusher : Primary Size reduction of Coal from 50cm to 30-50mm
Design Parameters [1]:
Crusher Capacity(Q) = 150nbsdn- rpm of drive shaft, b- width of swing Jaw, s- amplitude of swing jaw, d- mean size ofcrushed coal, D- mean size of crusher feed, -loading factor of crushed coal, -Specific
Gravity of Crushed Feed
where s is way length of swing jaw(jaw crusher angle = 200)
Drive Power of Jaw Crusher = nb( - )/0.34
Double Roller Crusher : Size Reduction from 30-50mm to 5-10mm
Design Parameters [1]:
Roller Capacity (Q) = 50LDndL-length of rolls, D- Diameter of rolls, n- speed of rotation of rolls, d- width of slots between
rolls, - bulk density of crushed material
Vibrating Feeder [2] Jaw Crusher [3] Double Roller Crusher [4]
Model ZSW-200 PE750*1060 2PG1008
Max feed
size
600mm 630mm 30mm
Capacity --------- 50-180ton/hr 40-120ton/hr
Spindle
Speed
--------- 250rpm 70-100rpm
Dimensions 4953*2200*2331mm 2660*2430*2800
mm
1000*800mm (roll
diameter)
Motor
Power
15KW 110KW 90KW
Table 1: Specifications for Feeder and Crushers
Jaw
Crusher
Heavy Media
vessel
Roller Crusher Heavy Media
Cyclone
Dryer
Output rate
(ton/hr)
147 ton/hr 102.9 92.5 74 69
Table 2: Coal Outputfrom various units
Coarse Coal Washing: Heavy Media vessel (Contributed by: Mohd Wasil)
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Fine Coal Washing - Heavy Media Cyclone (Contributed by: Mohd Wasil)Table 5: Feed toHeavy Media Cyclone
Size Range 5-10mm
Feed Rate of Coal(C) 92.5 ton/hr
Heavy-Media rate(M) 277.5 ton/hr (M:C= 3:1)
Total Feed rate 370ton/hr
%Ash Content 30%
Figure 3: Cyclone
dimensions
Input to SDM Cyclone Sizing Software :Density,Feed Rate,Feed Pressure = 100kPa,Cyclone Capacity =
235m3/hr,No. of Cyclones= 1, Cone Angle = 20
0
Table 6: Cyclone Dimensions
Dimensions(mm) [9] High Efficiency High Capacity
Cyclone Diameter 666.93 403.63
Feed Inlet Diameter 149.39 139.91
Inlet height 162.15 214.76
Inlet Width 108.1 71.59
Vortex Diameter 149.39 159.52
Cylinder height 367.54 350.77
Cone height 778.77 415.86
Spigot Diameter 100.04 100.91
Pressure drop(kPa) 350.98 356.05
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Table 7: Washed Coal in Heavy Media Cyclone
Coal Recovered 74ton/hr
%Yield 80%
% Ash in Washed Coal 25%
Dryer:(Contributed by: Mohd Wasil)
Counter-Current Rotary Dryer is used to dry coal. The drying medium (air, flue gases, steam) flows
counter-current to moist coal to minimize the chances of ignition of coal. Lifters and Flights areinserted in the shell to increase residence time of coal particles and hence ensuring high heat
transfer. Thermal Efficiency of Dryer varies from 30-60%. [10]
Design:
1. Calculation of Length and Diameter
Volume occupied by coal = 0.15*Volume of Dryer [11]
Feed rate of coal to dryer = 74ton/hr, Density of coal = 1500kg/m3
Volumetric Feed rate of Coal = 49.33 m
3
/hrFigure 4: Lifting Flights
Volume of Coal fed = 49.33 m3/3 = 16.44m
3
(Assuming Residence time of 20 min)
Volume of Dryer = 109.6 m3
*D2*L = 109.6 D
2*L = 139.62 m
3(i)
t = [12]
t-residence time(min), L-length(m), D-Diameter(m),p-slope of dryer, degrees n-revolution per minute
F-Constriction Factor in Dryer due to lifters and flights - angle of repose of coal
t =20min, p =30, n = 3rpm, = 360, F=2
Solving L/D from eq. (i), we get L/D = 8.47..(ii)
Solving (i) and (ii), L = 21.35m D= 2.52m
2. Calculation of Heat-Duty of Rotary Dryer:
Heat Duty of Dryer = Heat for evaporation of moisture + Other Losses
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Generally only 50% of heat supplied is converted to useful work ( = 50%). [12]
Hence, heat duty of dryer = 2mS (XA-XB)
mSmass flow rate of coal, XAand XBare initial and final mass of liquid per unit mass of coal, -
latent heat of vaporization
mS = 20.55kg/s = 19.33 Kg/s , XA= 0.077 , XB=0.0116, = 2260KJ/Kg
Calculating, Heat Duty =6075kW
Air Separation (Contributed by: Mohd Wasil)
Ion Transport Membrane (ITM) is used to obtain pure oxygen. The process is economic, produces
pure oxygen contrary to Cryogenic Distillation which is very expensive. The basic principle is that the
membrane selectively allows only Oxygen permeate through it, driving force being partial pressure
of oxygen across the membrane.
Membrane:
Perovskite Hollow Fibre membranes of the chemical composition BaZrxCoyFezO3(BCFZ) is selected
because of its high Oxygen Permeation Flux and Mechanical Stability
Specification:
Temperature - 9000C, Outer Diameter = 0.88mm, Wall thickness = 0.175mm,Inner Diameter =
0.705,Length = 33cm [46]
Calculation for Membrane Area :
O2 permeation flux = 7.6 mL min1
cm2
[46]
Density of O2= 1.43g/L,Molecular Weight = 32
O2 permeation flux = 5.66*10-6mol cm
2s-1
Feed rate of O2 = 0.781lbmol/hr = 0.098mol/s
Hence Area of membrane = 0.098/5.66*10
-6
= 1.73 m
2
Cost of Pervoskite membrane = 1000/m2 = 71330 Rs/m2 Figure 5: BFCZ fibre
Total membrane Cost = Rs 1,23,400
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Silo:(Contributed by: Mradul Raj Jain)
For the preparation of required syngas, a constant supply of 69 tph coal feed is required. This
constant supply is ensured by silo which also serves the purpose of protecting coal from
environmental conditions and ensuring uniform mixing and normalising any variation in composition
of coal. Spare silos are required in case of non-functioning of any of the working silos.
Coal bulk density, b= 1550 kg/cum [12]
Internal friction angle = 30 [13]
Friction coefficient, = tan 30 = 0.58 [14]
Discharge rate = 69 tonnes/hr
Silo should contain sufficient amount of coal so as to sustain production even in case of non-supply
of raw coal from mines or any disturbance in any unit operation before it or during their regular
maintenance.
Assuming a max storage capacity for 2 weeks, total capacity for silo =69 X 24 X 14 = 23184 tonnes 24000 tonnes / week
Silos have a widely varying capacity. Silos of capacity upto 5000 tonnes are easily constructed and do
not require special support. Choosing the capacity of silo as 4000 tonnes, 6 silos will be required.
Taking L/D=3 [15]
Volume of silo = (4000 X 1000)/1550 = r2L = 3D3/4
D = 10.3 m
L = 3D = 30.9 m
Coal particle size range = 5mm-10mmOutlet diameter (B)= 10 X (max particle size) [16]
= 10 X 10 mm = 100 mm = 0.1 m
Silos can suffer from various problems like arching, flushing, rat-holing, insufficient flow, inadequate
emptying etc. In such cases silos are repaired and become non-functional. In such case, to avoid any
effect on the feed rate of coal, spare silos can be utilised.
Using 4 silos at a time and keeping other 2 silos spare.
Assuming mass flow, and using Johanson Equation,
W = bX /4 X B2
X ( g.B/4.tanc)0.5
[16]
Where,
W = discharge rate in kg/s
c= angle of hopper from vertical
69 X 1000/ (4 X 3600) = 1550 X /4 X (9.8/4.tanc)0.5X 0.12.5
c= 32.33
For height of hopper, H,
Tan c= [10.3/2 - 0.1/2]/H
H = 8 m
A rotary valve will be used for discharging coal from hopper. [16]
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Concrete for Silo
Assuming a thickness of wall = 10 inch = 0.254 m [17]
Inner diameter, D1= 10.3 m
Outer diameter, D2= 10.3 + 0.254 = 10.554 m
Total volume of concrete required = volume of silo wall + volume of hopper wall
= (r12r2
2)L + 1/3.(r12r2
2)H
= /4 X 30.9 X (10.554210.32) + 1/3 X /4 X 8 X (10.554210.32)
140 m3
Density of concrete = 2400 kg/m3 [18]
Mass of concrete = 2400 X 140 X 6 = 2016 tonnes.
Figure 6 : Design of Silo & belt width
Belt Conveying
Belt conveyors transport coal from one unit operation to other. As coal moves from one unit
operation to other, its quantity decreases owing to the feed preparation processes done on it. Thus
the capacity and type of belt also varies from one location to other.
Fig.7: Values of cross section angle for trough and surchange angle at different belt width. [47]
Surcharge angle for coal = 25 [47]
Assuming troughing angle = 20
[47]
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Where,
CSA = cross section area in m2
Table 8: Belt specifications
Belt Capacity(Coal)
Tonnes
per hour
Assumed belt width,mm
Cross section area(CSA), m2
Velocity, cm/s
Crusher to heavy media
separator
146.83 600 0.031 85
Heavy media separator to roller
press
102.77 500 0.020 92
Roller press to cyclone 92.5 500 0.020 83
Cyclone to dryer 74 450 0.016 83
Dryer to silo 69 450 0.016 77
Coal GasificationDesign of reactor: (Contributed by: Sub-Group Contribution)
After feed preparation and pulverisation of coal to appropriate size, we move to next operation inproduction line i.e. coal gasification. The target is to produce about 500 meteric tonnes per day
(MTPD) of hydrogen (H2) and carbon monoxide (CO), the main ingredients of syngas, in molar ration
3:1.
Techniques for coal gasification:Extensive literature survey lead to the conclusion that there are largely three conventional
techniques used for coal gasification today [22]. They are:
1) Moving bed reactor
2) Entrained flow reactor
3) Fluidised bed reactor.Out of the three reactors used in conventional coal gasification above, we chose FBR (Fluidised Bed
Reactor) as most of the literature pointed out that it was the type of reactor to be used for ash
content coals. Entrained flow reactors posed a problem of slagging due to high operating
temperatures [19]. Moving bed gasifiers have non uniform temperature profiles (along radial
direction) hence results in high temperatures zones with slagging [19].
Under the light of concerns highlighted previously, FBR offers lucrative solutions to most of the
problems. It is important to note that the temperatures within the bed are less than the initial ash
fusion temperature of the coal to avoid particle agglomeration [20]. It has operating temperatures in
the range (900-1100oC) hence no slagging [19], residence times of the order of minutes (0.5-3 mins)
[19], carbon conversion of about 97% [19].
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Modelling and Simulation of Fluidised Bed Reactor using Aspen Plus:
(Contributed by: Sahil Aggarwal)
Coal from after pulverisation is fed to FBR using centrifugal system (MulticoreS160) made by
Schenck Process. Steam from steam generator and pure O2 is obtained from ASU (air separation
unit). The composition of synthesis gas and implementation of mass balance on the FBR has been
done with the help of Aspen Plus. Over the years the experiments conducted on the analysis of the
exit streams from coal gasification units have revealed that the gas composition can be well
predicted by minimisation of Gibbs free energy of the product stream while maintaining the phase
equilibrium. The block RGibbs in Aspen Plus provides exactly the type of reactor we can be used to
simulate the process as it satisfies all the above conditions [21].
Constraints and Variables involved in optimising reactor performance:
We have imposed several constraints on RGibss reactor while calculating the final gas composition of
synthesis gas. These have been tabulated below.
H2/CO mole ratio 3 Tolerance = 0.1
(H2+ CO) mass ( tonnes/day) 500 tpd ~ 500,000 kg/day Tolerance = 100 lb/day ~ 45 kg/day
Table 9: Constraints to be followed while simulating RGibbs block in Aspen Plus.
Note: These constraints have been dictated by the optimised conditions required for methanol
production unit.
Another limit to which we have to adhere is CO2/(CO+CO2) (mole ratio) = 0.3 which we have dealt
with later by absorbing excess CO2produced in MDEA solvent in gas purification operation.
While imposing the above constraints on the RGibbs block we have minimised the consumption of
input resources which can also be quantified in terms of sum of mass input of steam, coal and
oxygen by using optimisation function in Model Analysis Tools in Aspen Plus.
The variables involved in the simulation process is mass flow rates of steam, coal & oxygen;
temperature of the FBR.
With the above constraints and optimisation variables, the material and energy balance for the
fluidised bed reactor as predicted by Aspen Plus (RGibbs block) is as follows:
500 TPD H2and CO COAL OXYGEN PRODUCT STEAM
Mole Flow kmol/s
C 76.7 *10-2 0 0 0
O2 26.2*10-3 9.84*10-5 2.17*10-23 0
CO 0 0 16.99*10-2 0
CO2 0 0 36.17*10-2 0
H2 14.2*10-2 0 50.97*10-2 0
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H2O 70.9*10-3
0 54.66*10-2
1.32
C2H4 0 0 4.5*10-7 0
C2H6 0 0 1*10-5 0
C3H8 0 0 1.9*10-9
0
C3H6 0 0 7.310-10 0
H2S 0 0 2.2*10-3
0
COS 0 0 3.7*10-5 0
CH4 0 0 23.55*10-2 0
S 2.2*10-3 0 2.97*10-15 0
Total Flow kmol/s 1.01 9.84*10-5 1.83 1.32
Total Flow kg/s 11.69 3.1*10-3 35.41 23.72
Total Flow m3/s 4.16 2.4*10-3 17.41 51.11
Temperature K 300 300 930 445
Pressure bar 8.1 8.1 8.1 8.1
Density kg/m3 1550 1.3 2.03 4.21
Average MW gm/mole NA 32 19.39 18.02
Table 10: Composition of synthesis gas exiting from the top of the FBR.
Note: Column COAL essentially refers to quantities of elements present in Indian coal (composition
has been tabulated below). These elements amount to 68.4% by weight of coal. Hence the actual
coal requirement i.e. including ash and inerts is obtained by dividing the total flow (kg/sec) in
Column COAL by a factor of 0.684 and again by 0.9 to account for residence time calculations and
carbon conversion (explained in assumptions below).
A superficial analysis of the product synthesis gas shows that the concentration of H 2S comes out to
be around 1215 ppmv. The main ingredients of the syngas obtained are 19.8% by vol. of CO 2, 9.3%
CO, 27.9% H2, 29.9% H2O and finally 12.9% methane.
We have used the following composition of coal after feed preparation and washing & drying
operations [23]:
Ash 30% Oxygen 8.94
Moisture 6.82% N2 1.62
carbon 49.18 Sulphur 0.38
H 3.06
Table 11: Composition of coal after washing %wt
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Assumptions for simulation:
There are three main underlying assumptions that we have made while simulating the reactor
environment which are as follows:
1. Process occurs at steady state and isothermal;
2. The ash recycled out of the system can contain unreacted carbon and inerts (which
otherwise would not react with either steam or O2under any condition);
3. We have also assumed 90% conversion of carbon present in coal as opposed to 97% [19]
cited in literature to accommodate for errors in residence time experienced by individual
particles of coal on a probability basis.
This works out to 1010 tpd (tonnes per day) of coal; 2050 tpd of steam and about 268 kilograms per
day of pure oxygen which is a pretty decent value.
Sensitivity Analysis- Variation of reactor and temperature:(Contributed by: Sahil Aggarwal)
We also studied the sensitivity analysis, again using the Model Analysis Tools in Aspen Plus. This
feature allows to study the composition of syngas with respect to changing variable of choice. Hence
it can exploited to study the effect of temperature and pressure on fluidised bed reactor modelled
by RGibbs block. The results of varying temperature and pressure on the composition of syngas
while keeping other variables constant have been plotted below:
Figure 8(a): Variation of syngas composition with temperature (at 1 atm).
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Figure 8 (b): Variation of syngas composition with pressure (at 943K).
Using the conditions imposed on the FBR the optimum temperature is 930 K. We have chosen the
reactor pressure to be at 8 atm keeping in view the volumetric flow of product gas.
Design methods adopted:
Some of the key innovations which we learnt while doing literature survey and implemented in our
setup are as follows:
1) Instead of feeding in more conventional slurry form directly after washing operations (i.e.
without drying water) we have dried it before conveying it to the FBR. This decision intuitively
comes from cost estimation. Since water in coal will have to be evaporated so that coal can
reach reactor conditions, this would mean that well have to burn some of the syngas to
provide for sensible and latent heat of water. This would mean that product synthesis gas would
have had more CO2, hence higher separation costs in downstream gas purification operations
since we do not intend to produce CO2as our prime product. Though this would have been the
case for IGCC applications where we syngas is used to produce mechanical energy in turbines,
hence more volume is required.2) On similar arguments of economics, we have decided to use pure O 2rather than ambient air as
a source of oxidiser. Because the nitrogen in air must be heated to the gasifier exit temperature
by burning some of the syngas. Also because of the dilution effect of the nitrogen, the partial
pressure of CO2 in air-blown gasifier syngas will be one-third of that from an oxygen-blown
gasifier. This increases the cost and decreases the effectiveness of the CO2removal equipment
downstream [20].
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Reactor (Gasifier) assembly:
The main assembly of Gasifier has been discussed step by step from feed to product. Design
specification of each subunit is presented.
Coal Feed:(Contributed by: Tarun Singh)
After the feed gets piled up in the silos it is fed to the main gasifier for conversion from coal to
syngas. For feeding the coal feed to the reactor MULTICORE S160 would be used which is a
centrifugal system for pressure feed.
MULTICORES160: (Contributed by: Tarun Singh)
Manufactured by Schenck Process [36].
2 such units used (in case one malfunctions, itll keep the process continuous).
Accuracy upto +- .5% of flow rate.
Make use of centrifugal force to pressurize and pump the coal feed, provided with a pre-feeder to take the feed from silo before pressurizing it.
Automated control system for pressure and flow rate.
Property Multi Core Specs Our Requirement
Flow Rate 60 - 120 t/hr 64 t/hr
Pressure Withstand and generate up to 30 bar feed
pressure.
We would use 2 such units at 8
bar each.
Moisture Max 10% allowed. Assuming feed to be moisture
free.
Flow Properties
Needed
Free flow to slightly sluggish, pulverized
to granular (8mm).
Pulverized to 5 mm.
Table 12: Specifications of Multi core M-S160 based of operating conditions.
Steam Feed:(Contributed by: Tarun SIngh)
Steam to the gasifier is generated in 2 units:-
1 Water Preheater - Would use the heat in syngas to preheat water at room temperature to a
steam plus water mixture at 100 degrees celsius.
2 Boiler - Would take the steam plus water mixture from preheater to final conditions
required in the gasifier.
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Water preheater(Heat Exchanger):(Contributed by: Tarun Singh)
A typical shell and tube heat exchanger.
Inlet Conditions-
Water at 27 degrees Kelvin and 1 bar pressure.
Syngas at 700 degrees Celsius and 8 bar pressure (density = 2.232kg/m3and specific heat =1.02 KJ/Kg*K).
Total Heat available = G*C*(T) = 22748.04 KJ/sec.
Outlet Conditions-
Water + Steam at 100 degrees 1 bar pressure.
Syngas at 70 degrees and some bar.
After balancing the configuration (mostly data for pipes and coefficients from [5])-
Heat transfer needed 22748.04 KJ/sec.
U = 150 W/m2K, Tavg=211.289, FT= 1 [7].
Area for this heat transfer came out to be 71.88 m 2.
OD 1.9 schedule 80 tubes in a 39 inch shell(160 schedule being on the safer side as pressuredrop is quite high), 17/8 inch square pitch [7] were opted for the exchanger(after doing
iterations on the tube count and dia. of both shell and tube sides).
Tube count is 252.
Length of tubes = 5.2m.
Water inside the tube and syngas on the shell side (for pressure drop reasons as pressuredrop on the shell side would be higher and we need pressure drop on shell side).
2.6m baffle spacing (large space for lesser pressure drop we dont need too much of it).
Figure 9: Diagrammatic view of the exchanger
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Burner for boiler :-
Figure 10: Burner for the boiler
Calculation and specification of burner
Heat releases up to 13000 kJ/s.
High turndown capabilities.
10:1 on 2 oil.
15:1 on natural gas
Nine different styles and three different sizes
Heating surface area using( Q/t=(k*A*T)/x )1.23 m2
Dimension of heating chamber (1.11x1.11x1.11)
We have to install five burner. Each one has capacity of 13000 KJ/S (MEGAFIRE Burner).
Total required power is 65486 kWatt. Container is made up of stainless steel.
Steam And OxygenInlet:(Contributed by: Suresh Sharma)
Steam generated from steam generator is inserted into gasifier from bottom. The bottom plenum is
divided into two parts to supply O2 into the draught section and steam into the annulus sections
separately [29].
O2is supplied through distributor of holes sizes 2-4 mm. A typical distributor plate is shown in Fig. 1
[30].
Steam is supplied through conical plate into annulus section as shown in Fig. 2.
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Figure 11: Distributor Figure 12: Conical plate in annulus section
Minimum Fluidization Velocity:
The Ergun equation, the well-established relation for the pressure drop over packed beds of
spherical particles, can be used to describe the behaviour of a fluidized bed at the minimum
fluidization velocity correctly. At minimum fluidization condition u becomes umin[25].
The mixture gas viscosity can be calculated from this correlation [26].
Table 14: Assumptions and parameters values
Inlet pressure 8 atm
Temperature 700 C
Assuming spherical particles, so sphericity 1
Assuming bed void fraction at uminis 0.5 [27]
Average particle diameter(dp) 0.0075 m
Bed density( ) 800 kg/m3
gravity(g) 9.8 m/s2
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Table 15: Calculations for dimensions of FBR
Mixture viscosity( ) 3.5714x10-5
Pas
From steam table specific volume of steam at
inlet condition
0.55 m3/kg [28]
Steam+Oxygen Density( ) 1.78 kg/m3
umin 2.79 m/s
uin= 2umin 5.58 m/s [27]
Volume flow rate of steam+O2 51.11 m3/s
Reactor area(A) = (volume flow rate)/uin 9.14 m2
Reactor diameter(D) 3.41 m
Delta P per unit length taking =0.8 at uin ( ) 1.03*104Pa/m
Residence Time:(Contributed by: Tarun Singh)
For design of the actual bed mean residence time of a particle in the bed is needed. For average
residence time Shrinking Core Model was used assuming the diffusion to be the controlling step for
the reaction [31] .
Assumptions-
Diffusion through the ash layer is the slowest step. SCM is chosen for residence time [31].
Feed gas composition taken same throughout the bed [31].
Mixed flow assumed [31]
Effect of pressure on diffusivity is neglected [32].
Reaction Time for a particle-
Diffusivity of steam for complete diffusion inside a particle (micro as well as macro pores) is
Dsteam 5.2x10-8 m2/sec (700oC) [33].
Max average diffusivity when diffusion only through macropores 10-6 m2/sec [32].
Now, = (bulk*R2)/(6*b*Dsteam*Cbulk) for reaction time range (2 diffusivities) [31].
b=1, bulk = 1550 kg/m3, R = 5mm, Cbulkfrom aspen results.
On calculating 607 min > > 34.60 mins.
We choose to continue with lower limit i.e. 34.60 mins as complete conversion is not
practical plus would ask for an infinite bed.
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Mean residence Time-
Since the residence time for each coal particle would be different so residence time cannot be taken
equal to the reaction time. An average mean residence time is needed which can be used for further
design. For this, RTD technique for a mixed flow with diffusion controlled SCM model is used [31].
For a mixed flow following DSCM, (1-X) = 1/5(t*) 19/420(t*)2 where t* = (/tavg) and tavgis
the required mean residence time.
Assuming 95% conversion.
t* came out to be .26.
So the MRT is 133 mins.
Reactor Height:(Contributed by: Tarun Singh)
From the obtained fluid velocity, Area and MRT values reactor height is estimated. The results are
v=2*vmf(Previous knowledge of fluidization).
Area of Reactor G(vol. flow rate)/V = 9 m2
.
Bed Volume = MRT*G = 98 m3.
Bed Height 11m.
Reactor Wall:(Contributed by: Tarun Singh)
After the estimation of height the issue in hand is what should be the material used to design such a
structure. Used here is typical layout with three layers [41-43]:-
1 The inner hot face layer(100mm) is a high-quality brick (87% chromium oxide, marketed as
Zirchrom900, patented by saint gobain) suitable for temperatures up to about 1600C.
2 The intermediate layer(20mm) is castable bubble alumina(Alumina-chromeChromcor 12).
3 The outer cold face(40mm) is a silica firebrick lining (Bubble alumina RI34 or Alundum
AN599) with good thermal insulation properties.
This three-layer design combines the properties of high temperature-resistance and good insulation.
At the same time, it hinders the propagation of cracks that may arise in the hot face through to the
vessel shell.
Output Of Gases:(Contributed by: Harshit Sinha)
The gases escape from the gasifier at 62,673.32 m3/hr, which is equal to 17.4 m3/s. Since the area of
the reactor is roughly 9 m2, and our gas flow rate nearly 18 m3/s, we have a 2m/s exit velocity from
the gasifier, which is a reasonable value. From here, the gases are sent to a heat exchanger, before
going to the cyclone separator unit.
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Figure 13: Ash exit mechanism and hopper configuration
Output Of Settled Ash From The Bottom Of The Reactor:
Ash settles both at the bottom of the reactor and goes out as fly-ash. At the bottom, we have a fine
grate, on which a lot of the ash settles. There is a hopper on this grate, and using a scraper (manual
or automated) we can make the ash fall into the hopper, from where it goes into the pipe and then
the ash treatment unit. The density of settled ash is around 0.65 gm/cc[8]. 20,510.3 kg/hr (or 5.7
kg/s of ash in total) is exiting as both fly and settled ash. Weve designed the bottom pipes and
hopper for the total ash, so as to be on the safe-side. There are no potential harms on the
overdesign of pipes when it comes to ash-exit at the bottom. This means we need the pipe to handle
~8769 cc/s, which can be done using an 8 inch Schedule 40 pipe quite well.
Basic Google Sketup Model:(Contributed by: Harshit Sinha and Tarun Singh)
Figure 14: Basic Model of the reactor (done in google sketchup)
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Raw material and resource requirement of the units till this point:(Contributed
by: Harshit Sinha and Tarun Singh)
Following are estimates of the raw materials needed for the plant operation upto this point.
1 Coal feed
We are using 3528 tonnes of grade E (3400-4200 GCV) coal per day for gasification. The
prices of Coal as per Coal India notification (1/1/2012)[48] are:
GCV Price per tonne (INR)
4000-4300 640
3700-4000 600
3400-3700 550
Table 16a: Cost of different grades of carbon used.
We take an average of these (assuming an equal mix) , i.e. INR 21,05,040 per day.
2 Daily Water Costs
Shadow price is the maximum price that a firm is willing to pay for an extra unit of water. For
the Chemicals Industry this is equal to Rs. 3.164 for 1000 litres[49]. We need 4.4*10^9 litres
per day. The cost of water comes out to be an astonishing 1,39,72,000 INR.
3 Power Requirement
The cost of Industrial power is 3.3 INR per unit of electricity [50]. 1 unit is 0.01 kW
Utility Requirement (kWh) Price(INR)
Air Separation Unit 38609 127412
Feeder and Crusher 756000 2494800
Multicor S160 72000 237600
Total 866609 2859812
Table16b : Power(Electricity) cost of various units.
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22. Sheida Saeidi, Josh McElfresh and Joyce Stillman, Final Design for Coal-to-Methanol Process,University of California, La Jolla, California 92037, USA Department of Mechanical Engineering,
Chemical Engineering:http://www.academia.edu/333252/Final_Design_for_Coal-to-
Methanol_Process23. National Energy Technology Laboratory (NETL), U.S. Department of Energy (DOE), Gasifipedia:
http://www.netl.doe.gov/technologies/coalpower/gasification/gasifipedia/4-gasifiers/4-1_types.html
24. Properties of Coal, Coal gasification:http://www.productivity.in/knowledgebase/Energy%20Management/c.%20Thermal%20Energy%20sy
stems/4.1%20Fuels%20and%20Combustion/4.1.3%20Properties%20of%20Coals.pdf
25. A.K. Singh, B.N. Prasad and A.V. Sahay, Potential for underground coal gasification in India, CentralMine Planning and Design Institute, India.www.cmpdi.co.in/docfiles/coal_gasification.pdf
26. Powder Technology, 75 (1993) 67-78.27. Calculation of the viscosity of the gas mixtures by F. J. Krieger RM-649 13 July 1951.28. Energy Vol. 23, No. 6, pp. 475488, 1998.29. Kerns handbook.
30. Y.J. Kim et al. / Fuel 79 (2000) 6977.
http://www.dcrusher.com/v3/products/feeder-screen/zsw-vibrating-feeder.htmlhttp://www.dcrusher.com/v3/products/feeder-screen/zsw-vibrating-feeder.htmlhttp://www.dcrusher.com/v3/products/feeder-screen/zsw-vibrating-feeder.htmlhttp://www.dcrusher.com/v3/products/feeder-screen/zsw-vibrating-feeder.htmlhttp://www.dscrusher.com/v3/products/crushing-equipments/jaw-crusher.htmlhttp://www.dscrusher.com/v3/products/crushing-equipments/jaw-crusher.htmlhttp://www.dscrusher.com/v3/products/crushing-equipments/jaw-crusher.htmlhttp://www.dscrusher.com/v3/products/crushing-equipments/jaw-crusher.htmlhttp://www.dscrusher.com/v3/products/crushing-equipments/2pg-roller-crusher.htmlhttp://www.dscrusher.com/v3/products/crushing-equipments/2pg-roller-crusher.htmlhttp://www.dscrusher.com/v3/products/crushing-equipments/2pg-roller-crusher.htmlhttp://www.dscrusher.com/v3/products/crushing-equipments/2pg-roller-crusher.htmlhttp://www.smartdogmining.com/tools/Notebook/Process/MineralProcess.htmlhttp://www.smartdogmining.com/tools/Notebook/Process/MineralProcess.htmlhttp://www.dscrusher.com/v3/products/feeder-screen/yk-circular-vibrating-screen.htmlhttp://www.dscrusher.com/v3/products/feeder-screen/yk-circular-vibrating-screen.htmlhttp://www.dscrusher.com/v3/products/feeder-screen/yk-circular-vibrating-screen.htmlhttp://www.dscrusher.com/v3/products/feeder-screen/yk-circular-vibrating-screen.htmlhttp://www.smartdogmining.com/tools/Software.htmlhttp://www.smartdogmining.com/tools/Software.htmlhttp://www.smartdogmining.com/tools/Software.htmlhttp://bioen.okstate.edu/home/jcarol/Class_Notes/BAE2023_Spring2011/FrictionNotes.pdfhttp://bioen.okstate.edu/home/jcarol/Class_Notes/BAE2023_Spring2011/FrictionNotes.pdfhttp://www.processprotection.net/pdf/1.pdfhttp://www.processprotection.net/pdf/1.pdfhttp://www.processprotection.net/pdf/1.pdfhttp://hypertextbook.com/facts/1999/KatrinaJones.shtmlhttp://hypertextbook.com/facts/1999/KatrinaJones.shtmlhttp://hypertextbook.com/facts/1999/KatrinaJones.shtmlhttp://dspace.mit.edu/bitstream/handle/1721.1/38569/154723366.pdf?sequence=1http://dspace.mit.edu/bitstream/handle/1721.1/38569/154723366.pdf?sequence=1http://www.netl.doe.gov/technologies/coalpower/turbines/refshelf/handbook/1.2.1.pdfhttp://www.netl.doe.gov/technologies/coalpower/turbines/refshelf/handbook/1.2.1.pdfhttp://www.academia.edu/333252/Final_Design_for_Coal-to-Methanol_Processhttp://www.academia.edu/333252/Final_Design_for_Coal-to-Methanol_Processhttp://www.academia.edu/333252/Final_Design_for_Coal-to-Methanol_Processhttp://www.academia.edu/333252/Final_Design_for_Coal-to-Methanol_Processhttp://www.netl.doe.gov/technologies/coalpower/gasification/gasifipedia/4-gasifiers/4-1_types.htmlhttp://www.netl.doe.gov/technologies/coalpower/gasification/gasifipedia/4-gasifiers/4-1_types.htmlhttp://www.productivity.in/knowledgebase/Energy%20Management/c.%20Thermal%20Energy%20systems/4.1%20Fuels%20and%20Combustion/4.1.3%20Properties%20of%20Coals.pdfhttp://www.productivity.in/knowledgebase/Energy%20Management/c.%20Thermal%20Energy%20systems/4.1%20Fuels%20and%20Combustion/4.1.3%20Properties%20of%20Coals.pdfhttp://www.productivity.in/knowledgebase/Energy%20Management/c.%20Thermal%20Energy%20systems/4.1%20Fuels%20and%20Combustion/4.1.3%20Properties%20of%20Coals.pdfhttp://www.cmpdi.co.in/docfiles/coal_gasification.pdfhttp://www.cmpdi.co.in/docfiles/coal_gasification.pdfhttp://www.cmpdi.co.in/docfiles/coal_gasification.pdfhttp://www.cmpdi.co.in/docfiles/coal_gasification.pdfhttp://www.cmpdi.co.in/docfiles/coal_gasification.pdfhttp://www.cmpdi.co.in/docfiles/coal_gasification.pdfhttp://www.cmpdi.co.in/docfiles/coal_gasification.pdfhttp://www.cmpdi.co.in/docfiles/coal_gasification.pdfhttp://www.productivity.in/knowledgebase/Energy%20Management/c.%20Thermal%20Energy%20systems/4.1%20Fuels%20and%20Combustion/4.1.3%20Properties%20of%20Coals.pdfhttp://www.productivity.in/knowledgebase/Energy%20Management/c.%20Thermal%20Energy%20systems/4.1%20Fuels%20and%20Combustion/4.1.3%20Properties%20of%20Coals.pdfhttp://www.netl.doe.gov/technologies/coalpower/gasification/gasifipedia/4-gasifiers/4-1_types.htmlhttp://www.academia.edu/333252/Final_Design_for_Coal-to-Methanol_Processhttp://www.academia.edu/333252/Final_Design_for_Coal-to-Methanol_Processhttp://www.netl.doe.gov/technologies/coalpower/turbines/refshelf/handbook/1.2.1.pdfhttp://dspace.mit.edu/bitstream/handle/1721.1/38569/154723366.pdf?sequence=1http://hypertextbook.com/facts/1999/KatrinaJones.shtmlhttp://www.processprotection.net/pdf/1.pdfhttp://bioen.okstate.edu/home/jcarol/Class_Notes/BAE2023_Spring2011/FrictionNotes.pdfhttp://www.smartdogmining.com/tools/Software.htmlhttp://www.dscrusher.com/v3/products/feeder-screen/yk-circular-vibrating-screen.htmlhttp://www.dscrusher.com/v3/products/feeder-screen/yk-circular-vibrating-screen.htmlhttp://www.smartdogmining.com/tools/Notebook/Process/MineralProcess.htmlhttp://www.dscrusher.com/v3/products/crushing-equipments/2pg-roller-crusher.htmlhttp://www.dscrusher.com/v3/products/crushing-equipments/2pg-roller-crusher.htmlhttp://www.dscrusher.com/v3/products/crushing-equipments/jaw-crusher.htmlhttp://www.dscrusher.com/v3/products/crushing-equipments/jaw-crusher.htmlhttp://www.dcrusher.com/v3/products/feeder-screen/zsw-vibrating-feeder.htmlhttp://www.dcrusher.com/v3/products/feeder-screen/zsw-vibrating-feeder.html 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31. American Journal of Engineering and Applied Sciences, 2012, 5 (2), 170-183.32. Levenspiel Handbook.33. Perrys Handbook.34. Effective diffusivity of moisture in low rank coal during superheated steam drying at atmospheric
pressure by Zdzisaw Pakowski*, Robert Adamski, Sawomir Kwapisz, Chemical and Process
Engineering 2011, 33 (1), 43-51.
35. Wasteless combined aggregate-coal-fired steam generator/melting converter by L.S.Pioro, Volume23, Issue 4, 2003, Pages 333337, Waste management, Sciencedirect.
36. Binders, R.C. (1973), Fluid Mechanics, Prentice Hall, Inc. (Engle Wood Cliffs, NJ).37. Schenck Process and Manjunatha Varambally.38. Binders, R.C. (1973), Fluid Mechanics, Prentice Hall, Inc. (Engle Wood Cliffs, NJ).39. Kerns handbook.40. Various sources. For example: http://www.aqua-calc.com/page/density-table/substance/cinders-
coma-and-blank-coal-blank-ash.
41. Refractory wall structure and damper device. US patent no. US 20040094078 A1.42. Gasification by Christopher Higgins and Martin Van Der Burdt.43. http://www.refractories.saint-gobain.com/Gasification.aspx website for the Saint gobain
gasification refractories information and their uses.
44. Introduction to Transport Phenomena book appendix45. www.maxoncorp.com/Files/pdf/B-lt-megafire.pdf46. T.Schiestel,M.Kilgus,S.Peter,K.J.Caspary,H.Wang,J.Caro.Hollow Fibre Perovskite Membranes for
Oxygen Separation,Journal of Membrane Science,Volume 258
47. Masons Engineers(NZ) Ltd.http://www.masons.co.nz/quick-reference-charts#fourth48. New Pricing of non-coking coal based on GCV with effect from (1/1/2012):
http://www.coalindia.in/Documents/Revised_2nd_Ver_Coal_Price_for_uploading_310112.pdf
49. Suresh Chand Agarwal and Surender Kumar, Industrial Water Demand in India, Challenges andImplications for water pricing. Available on :http://www.idfc.com/pdf/report/2011/Chp-18-
Industrial-Water-Demand-in-India-Challenges.pdf
50. Industrial Power Tarrifs: www.indiastat.com/power/26/powertariff
http://www.maxoncorp.com/Files/pdf/B-lt-megafire.pdfhttp://www.maxoncorp.com/Files/pdf/B-lt-megafire.pdfhttp://www.masons.co.nz/quick-reference-charts#fourthhttp://www.masons.co.nz/quick-reference-charts#fourthhttp://www.masons.co.nz/quick-reference-charts#fourthhttp://www.coalindia.in/Documents/Revised_2nd_Ver_Coal_Price_for_uploading_310112.pdfhttp://www.coalindia.in/Documents/Revised_2nd_Ver_Coal_Price_for_uploading_310112.pdfhttp://www.idfc.com/pdf/report/2011/Chp-18-Industrial-Water-Demand-in-India-Challenges.pdfhttp://www.idfc.com/pdf/report/2011/Chp-18-Industrial-Water-Demand-in-India-Challenges.pdfhttp://www.idfc.com/pdf/report/2011/Chp-18-Industrial-Water-Demand-in-India-Challenges.pdfhttp://www.idfc.com/pdf/report/2011/Chp-18-Industrial-Water-Demand-in-India-Challenges.pdfhttp://www.idfc.com/pdf/report/2011/Chp-18-Industrial-Water-Demand-in-India-Challenges.pdfhttp://www.idfc.com/pdf/report/2011/Chp-18-Industrial-Water-Demand-in-India-Challenges.pdfhttp://www.coalindia.in/Documents/Revised_2nd_Ver_Coal_Price_for_uploading_310112.pdfhttp://www.masons.co.nz/quick-reference-charts#fourthhttp://www.maxoncorp.com/Files/pdf/B-lt-megafire.pdf -
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Chapter 1B: Syn-gas Purification Plant
Treatment and Conditioning of syngas - Purification of syngas
Introduction: (Contributed by: Sahil Aggarwal)
The syngas produced in the fluidised bed reactor contains a lot of impurities in the form of fly ash
which gets entrained out of the reactor owing to high gas velocities; gases like H 2S, COS which are
acidic in nature; heavy metals like Hg, etc. which are toxic in nature and lastly by products like heavy
hydrocarbons, excess CO2, steam etc.
In the context of Indian coal, syngas purification has more value attached to it because of the use
low grade coal having high sulphur and heavy metal impurities. This leads to huge expenses which
have to be incurred in the form of infrastructure required to remove impurities, hence the cost at
which a desired (set by emission laws) degree of purification is obtained becomes important.
In the era of environmental crisis, where a significant amount of air pollution worldwide is caused by
chemical industries, laws have become more stringent regarding the emission levels of hazardous
substances, in particular acid and greenhouse gases. However, while it is easier for developed
countries to follow these set limits at the expense of lower profits, it is not the case with developing
countries like India where the industries are still struggling to meet costs of production and generate
whatever meagre profits they manage to by competing with giant chemical manufacturers who are
virtually monopoly holders of the entire chemical market. Keeping this imbalance in mind, the
emission regulations vary from country to country, but a more critical review of the environmental
report and rising political tension points out to the possibility that one day these emission standardswill be made uniform for all.
So, Indian industries need to come up with more innovative techniques for purification that are
cheaper and more cost effective for syngas purification. We have tried to use the best and the latest
techniques available in literature to model the purification setup.
The arrangement includes cyclone separator to remove solid impurities, electrostatic precipitation
to remove finer solid impurities, heat exchanger to tap heat energy of hot syngas to preheat water
to generate steam to be later fed to FBR, activated carbon bed to get rid of heavy metal impurities,
tray tower to remove H2S, COS, CO2and other trace heavy hydrocarbons, regeneration of loaded
solvent, treating flue gas from regenerator column to remove CO2and get H2S rich gas which goes
for processing to Claus Reactors.
Cyclone Separator:(Contributed by: Kritesh Patel)
The flue gas coming from the gasifier contains ash along with it. To separate the dust from the gas
we are using cyclone separator. The gas enters the cyclone and is guided around a central pipe. The
heavy dust particles are not able to follow the air path around the pipe due to higher inertia. The
dust particles impacts the cyclone wall and drop at the bottom of the cyclone. As the cyclone
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becomes narrow at the bottom, as a result of this the smaller dust particles not able to follow the air
path (which spirals around in smaller diameter now) become separated and also fall at the bottom
of the cyclone. The base of the cyclone is submerged in water to form water seal which prevents gas
from escaping. There are different models correlating the cyclone diameter to the other parameters
of the cyclone. My calculation is based on the new design which is obtained by optimization of
Muschelknautz method [1].
Figure 15: Ratio analysis of dimensions for cyclone separator
a/D 0.618
b/D 0.236
/D 0.622
H/D 4.236
h/D 1.618
S/D 0.620
B/D 0.382
Table 17: Ratio analysis for the design of cyclone separator
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Feed:
Flow rate, G = 281019.39 lb/hr = 35.41 kg/sec
= 0.127 lb/ = 2.035 kg/
= 650 kg/
= 3.5 * Pa s
A cut point diameter (d) of 10 we can calculate the cyclone diameter by equating the terminal
velocity attained by the particle by Stokes law and by the cyclone design [2].
By cyclone
Terminal velocity, =
By Stokes Law
Terminal velocity, = g is gravity
Equating both the equation we get the following dimension
Dimension Symbol Value Unit
Diameter D 2.08 M
Inlet height A 1.28 M
Inlet width B 0.49 M
Overall height H 8.81 M
Cylinder height H 3.36 M
Outlet diameter 1.29 M
Dust outlet diameter B 0.79 M
Outlet length S 1.29 M
Table 18: Dimensions for the design of cyclone separator
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Now the entering velocity of the gas,
Now calculating the pressure drop across the cyclone based on the equations [3]
where q =
+
By putting all values and G=0.005 (Wall friction factor) we get
Now the syngas which still has some ash particles is sent to the heat exchanger and then to ESP for
the removal of remaining ash particles
Electrostatic Precipitator (contributed by: Kritesh Patel):The gas after cooling is sent to electrostatic precipitator which consists of series of vertically
negatively charged wires running through positively charged pipes. The electric field within these
pipes ionizes the tar particles which are negatively charged and are attracted to inner surface of pipe
where they condense and fall in drops to the slanted base. The gas from here is further sent to the
other units (e.g. to remove further impurities in the solid free syngas). It is known that Electrostatic
precipitators can achieve over 99% cleaning efficiency (White 1963). Now the syngas is at a lower
temperature which will increase the efficiency of the electrostatic precipitator. The design of
electrostatic precipitator is taken same as used for Hequ Power Plant [4] which is used for ash of
same composition as of Indian coal. Some of the specifications are
No. of chambers 2
No. of fields 5
Channel per chamber 38
Height of plate 15.24 m
Length of plate 19.725 m
Spacing 400 mm
Gas pressure drop 200 Pa
Efficiency 99.85 %
Table 19: Design of the Electrostatic Precipitator
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The ash particles are collected from the bottom and the solid free syngas is sent to furtherpurification.
Ash handling:(Contributed by: Mohit Meena)
Total ash 42500 lb/h
Bottom ash 8460 lb/h
Fly ash 33960 lb/h
Fly ash:
Particle of fly much finer and the particles of ash are carried away with the flue gases and get
collected at various locations along the flue gas by Esp. Particle of fly ash is very small so it can come
with flow
Bottom Ash:
When a sufficient amount of bottom ash drops into the hopper, it is removed by means of high-pressure water jets and conveyed by sluiceways either to a disposal pond or to a decant basin for
dewatering, crushing, and stockpiling for disposal or use. In this system, the ash slag discharged from
the furnace is collected in water impounded scraper installed below bottom ash hopper. The ash
collected is transported to clinkers by chain conveyors.
Pneumatic conveying of fly ash:
Assumption and calculation
Conveying distance 150 m
Minimum conveying velocity of Ash 400 fpm (from source) Conveying velocity 480 fpm
System capacity
Material flow rate 236 tph
Mass flow rate of air 18.3 lb/min
Bulk density of fly ash 30lb/cub. ft
Solid loading ratio 428
Pipe line is cross section area .545 ft
Pressure across 150 meter pipe 186.11 psig
Figure 16: Layout for handling fly ash
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Pressure Pneumatic Conveying System operates on batch/continuous operating concept and can
also convey the much coarser particles of bottom ash
Pipelines: - fly ash conveyed through a normal mild steel pipeline would probably wear a hole
through a 90bend within one day of operation. Thick walled spun alloy cast iron is a normal
specification for pipeline. In extreme cases is may be necessary to line the pipeline with basalt.
Ash silo:(Contributed by: Kritesh Patel)
The ash from the ESP is sent to the silo using pneumatic system to store ash and for further use. The
silo is usually design with the storage capacity of 3 days. [32] The design of the silo is discussed
below
Calculation
For bottom ash [6]
Mass flow rate of ash= 4.1 tonnes/ hour (assuming 20% bottom ash)
Density of bottom ash = 650 kg/
Angle of repose of ash =
Friction coefficient,
Storage capacity for 3 days storage = 4.1 *24*3 = 295.2 tonnes
For silo taking the L/D ratio to be 3 [33]
Equating the dimension of the silo based on the volume
LD2 / 4 = 295.2 X 1000/650
D = 5.78 m
L = 17.34 m
Now the size of coal is ranging from few micro meter to 10 mm
Outlet diameter (B) > 6 X (max particle size) > 6 X 10 mm (no arching condition)
So, taking hopper outlet diameter to be 70 mm
Assuming mass flow, and using Johanson Equation,
W = bX /4 X B2X ( gXB/4Xtan c)
0.5
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W = discharge rate in kg/s, c= angle of hopper from vertical
4.1*1000/3600=650* *
c= 40.3o
Now calculating the height of the hopper
tan
H = 3.4 m
For fly ash
To design fly ash silo we have to look into the flow patterns that the fly ash shows and the stresses
that will be acting. Now we will design fly ash silo of diameter 5 m as flow characteristics for that is
available [34]
Density of fly ash, flyash= 1141 kg/m3[34]
D = 5m
L = 15m
Volume that will be stored in on silo = 294.4 m3
Mass of ash that will be stored = 1141 X 294.4 = 335.9 tonnes
Mass flow rate of ash= 16.4 tonnes/ hour (assuming 80% fly ash)
Storage capacity for 3 days storage = 16.4 *24*3 = 1180.8 tonnes
Number of silos required = 1180.8/335.9 = 4
Using Jenikes equation, [34]
Dmin = (fc,critX H()) / ( X g)
fc,crit= critical yield stress in N/m2, Dmin= minimum hopper diameter to prevent arching
Now H () = 2.2 for conical hoppers
fc,crit= 1152 N/m2[31]
Dmin = 22.7 cm
c= 20o
Now calculating the height of the hopper
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tan
H = 6.9 m
Concrete that will be needed to build silo=
Assuming a thickness of 10 inch
Inner diameter = 5 m (fly ash silo)
Outer diameter 5.25m (fly ash silo)
Volume of concrete for silo = X [ X 17.4 X ((6)2- (5.78)2) + /3 X 3.4 X ((6)2- (5.78)2] + X [4 X X
15 X ((5.25)2- (5)
2) + 4 X /3 X 6.9 X ((5.25)
2- (5)
2)]
= 179.05
Mass of concrete needed= 2400 X 179.05 429.7 tons
Ash Disposal:(Contributed by: Kritesh Patel)
Now, once the ash is stored in the silo we have to dispose it properly. It will be transported to the
land filling site, cement industry and at other places with the help of trucks of around 1000 ( 28
) capacity. The truck is a pneumatic truck having one or more compartments, with each
compartment having a hatch on the top and an air circulating device, such as an air pad, an air stone,
or a cyclone at the bottom of each compartment, together with a compartment exit pipe. As is well
known in the art, the trucks are constructed so that with all hatches and appurtenances closed, the
truck is air tight avoiding ash particle to be disposed to environment [7] .A 4 inch diameter pipe
ASTM 40 steel pipe air discharge hose from trailer outlet was connected to a pipe which terminates
at dry ash storage. Ash will be removed from the silo on a daily basis.
Ash generated in one day= 756.9
No. of trucks required per day = 756.9/28 27 trucks
Now assuming the process of ash removal to be continuous.
Max time required to load a truck = (24*60)/27 min = 53.33
We have to load a truck in approximately half an hour as some time will be needed to attach the
pipe to the truck and other activities.
So the flow rate of ash needed to fill the truck in minimum 0.5 hour = 28/0.5 = 56
= 36.4 tonnes/hour
Since we are using a pipe of 4 inch diameter pipe
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Thus, the velocity at which the ash should flow > 56 / (3.14*10.16*10.16* ) > 1.91 m/s
The trucks will be sent to the sites for ash disposal. The landfilling operation involve a lot of
problems like ash disposal to environment, ground water contamination due to leaching, destruction
of local vegetation. To check these landfilling should be done as discussed in next part.
Landfill design[8](Contributed by: Kritesh Patel)
The design of the landfill is required in order to minimize need for further maintenance, prevent the
post-closure escape/release of solid waste constituents, leachate, and landfill gases to the surface
water, groundwater, or atmosphere, prevent direct contact with ash materials, minimize infiltration
to groundwater, mitigate soil erosion and runoff, promote establishment of vegetative cover.
Firstly the ash will be mixed with bauxite which reduces the pH value and the toxicity and also
reduce effectively both the arsenic and boron content. [9] After that ash will be disposed to the land
and for dust control during disposition, a water truck will be used, at the discretion of the field
oversight personnel, to apply a fine mist of water over the placed ash to control airborne emissions.
A 40-mil linear low density polyethylene (LLDPE) geo membrane will be placed over theentire landfill site as the barrier layer component of the Coal Ash Landfill cover system.
A 12-inch layer of sand will be placed over the 40-mil LLDPE geo membrane. The sand layerprovides physical protection for the geo membrane, but more importantly allows subsurface
drainage of accumulated water over the geo membrane.
A 6-inch layer of general fill will be placed over the subsurface sand drainage layer such that
there is a total of 18 inches of barrier protection soil cover over the geo membrane.
A 6-inch layer of topsoil will be placed over the general fill layer to support a vegetativegrowth over the entire landfill cover system.
Wind barrier design [9](Contributed by: Kritesh Patel)
Wind barriers are an effective method to prevent the dispersion of dust from the disposal sites.
Poplar trees will be planted in four rows. The rows should be perpendicular to the dominant wind
direction. The distance between each row and between trees should be six metres. Every second
line will be shifted three metres, so that the trees stand in triangles, providing a better coverage.
Hazel will be planted on the wind coming side, in two rows, also shifted and separated by 6 metres.
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Fig 17Tree distribution for wind barrier
Heavy Metal Removal: Mercury and Trace Elements
(Contributed by: Sahil Aggarwal)
Activated carbon bed:
Mercurys presence in air and water has increased dramatically in the past century owing to
emission from thermal power plants. The total mercury pollution potential from coal in India is
estimated to be 77.91 tonnes per annum [11].
The mercury emission study carried out by NTPC in some thermal power plants indicate that the
mean values of mercury concentration in coals of Indian origin are close to average concentration of
0.272 ppm [10], major portion of mercury gets emitted through stack and also remains associated
with fly ash whereas, only a small portion is found to retain with the bottom ash. Hence it is
conservative to assume that all the mercury partitions into the gas phase.
It is convenient to remove mercury with carbon activated beds as most of the literature survey
pointed out and the experience at coal gasification units worldwide reinforce this theory.
The Calgon Type-HGR carbon has been used for low-pre
top related