Indian Coal to Chemicals New Rev8

8/12/2019 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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i

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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iii

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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v

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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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