Coal Gasification and Purification of Synthesis gas

Subgroup I:

Members• Sahil Aggarwal (Subgroup leader)• Mohd. Wasil• Mradul Raj Jain• Harshit Sinha• Tarun Singh• Suresh Sharma• Kritesh Patel• Mohit Meena

Coal Gasification and Reactor Assembly

Process Flow Diagram for coal gasification:

Coal feed preparation ( i) crushing ii) washing iii) drying iv) buffer stock) Coal gasification Removal of solid particulates (fine and coarse solids) Syngas purification (heavy metal removal and acid gas removal) Claus Treatment plant.

CRUSHERDesign Parameters [1]

Jaw Crusher : Capacity = 150nbsdµγ , n =

Double Roller Crusher : Capacity = 50LDndγ

Specifications :

References:1. Coarse Size Reduction of Raw materials, Heidelberg Cement India Limited2. DSMAC ZSW Series Vibrating Feeder, http://www.dcrusher.com/v3/products/feeder-screen/zsw-vibrating-feeder.html3. DSMAC PE Series Jaw Crusher, http://www.dscrusher.com/v3/products/crushing-equipments/jaw-crusher.html4. DSMAC 2PG Series Double Roller Crusher, http://www.dscrusher.com/v3/products/crushing-equipments/2pg-roller-crusher.html

Equipment 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 dia)

Motor Power 15KW 110KW 90KW

Coarse Coal Washing – Heavy Media Vessel

Heavy media vessel capacity [5]

Size 30-50mm

Feed rate(C) 147ton/hr

Heavy-Media rate(M)

441ton/hr (M:C=3:1) [5]

%Ash Content 38%

• For Average Grain Size 40mm,Vessel Capacity is 40 ton/hr ft weir width

• η = 70% 102.9 ton/hr is the amount in float• Weir Width = 102.9/40 = 2.57ft = 0.78m• Assuming a retention time of 40 min and L/D = 3 [6]• Volume of Vessel = 249.08 m3

• L = 13.96m , D = 4.65 m

References:5. Smart Dog Mining, An Introduction to Dense Media Vessels http://www.smartdogmining.com/tools/Notebook/Process/MineralProcess.html6. Separator Vessel Selection and Sizing, http://www.klmtechgroup.com/Engineering%20Design%20Guildelines.htm

ton/

hr ft

wei

r wid

thaverage grain size(mm)

Media Recovery Screen

• Media Recovered [7] = = 5.68ton/hr

• D- Average Grain Size = 40mm, SG- Specific Gravity of refuse = 2.2

Coal Recovered 102.9ton/hr

Media recovered 5.68ton/hr

%Yield 70%

% Ash in Washed Coal 30%

Model 2YK1235

Slope Screen 150

Screen Area 4.2m2

Handling Capacity 20-150m3/hr

Power 7.5kW

Dimension 3705*2393*2339mm

Design Specifications [8]:

Washing in Heavy Media Vessel

References :7. Smart Dog Mining, Vibrating Screens, http://www.smartdogmining.com/tools/Notebook/Process/MineralProcess.html8. DSMAC YK Series Vibrating Screen, http://www.dscrusher.com/v3/products/feeder-screen/yk-circular-vibrating-screen.html

Fine Coal Washing-Heavy 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)

%Ash Content 30%

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

Input :Density, Feed Rate, Feed Pressure = 100kPa, Cyclone Capacity = 235m3/hr,No. of Cyclones= 1, Cone Angle = 200

Coal Recovered 74ton/hr

%Yield 80%

% Ash in Washed Coal 25%

References:9. Smart Dog Mining, SDM Cyclone Sizing, http://www.smartdogmining.com/tools/Software.html

Counter-Current Rotary DryerLength and Diameter

• Volume occupied by coal = 0.15*Volume of Dryer [10] • Feed rate of coal to dryer = 74ton/hr = 49.33 m3/hr• Volume of Coal fed (tres = 20min) = 49.33 m3/3 = 16.44m3

• Volume of Dryer = 109.6m3 , *D2*L = 109.6 D2*L = 139.62 m3 ……(i)• tres = *F [11]• tres=20min,p =30,n = 3rpm, = 360,F=2

• L/D = 8.47…….(ii), L = 21.35m D= 2.52m

Heat-Duty of Dryer : Heat for evaporation of moisture + Other Losses• Heat duty of dryer = mS*(XA-XB)* λ, (η = 50%) [10]• mS = 20.55Kg/s , XA = 0.077 , XB =0.0116, λ = 2260KJ/Kg• Heat Duty = 3037.5kW, Actual Heat Duty = 6075kW

References:10. Arun S. Mujumdar ,Drying: Principles and Practice, Albright’s Chemical Engineering Handbook11. Drying of Raw Materials, Heidelberg Cement India Limited

Lifting Flights

Air Separation: Ion Transport membrane• Membrane : Perovskite Hollow Fibre Membranes of the Chemical

Composition BaZrxCoyFezO3−δ (BCFZ)

• Specification :Temperature - 9000C, Outer Diameter = 0.88mm , Wall thickness = 0.175mm,Inner Diameter = 0.705mm,Length = 330mm [20]

• Calculation for Membrane Area :

• O2 permeation flux = 7.6 mL min−1 cm−2 [20]

• Density of O2 = 1.43g/L, Molecular Weight = 32

• O2 permeation flux = 5.66*10-6 mol cm−2s-1

• Feed rate of O2 = 0.781lbmol/hr = 0.098mol/s

• Area of membrane = 0.098/5.66*10-6 = 1.73 m2

• Cost of Pervoskite membrane = 1000 €/m2 = 71330 Rs/m2

• Total membrane Cost = Rs 1,23,400

BCFZ Fibre after sintering

References:20. 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

• SILO• For constant supply of feed coal for continuous production• Protection of coal from environmental variations • Uniform mixing and normalization of variations in composition of coal• Spare silos are required in case of non-functioning of the working silos

References:12. Anudhyan Mishra (10505028), Assembly of coal quality of some Indian coals, National Institute of Technology, 200913. Dr. J. Y. Ooi, Arching propensity in coal bunkers with non-symmetrical geometries, School of Civil and Environmental Engineering, University of Edinburgh, September 200514. Physical properties of agricultural materials and food products, friction of solids and flow of granular solids, page 246http://bioen.okstate.edu/home/jcarol/Class_Notes/BAE2023_Spring2011/FrictionNotes.pdf

Coal bulk density, ρb 1550 kg/cum [12]

Internal friction angle 30° [13]

Friction coefficient, µ 0.58 [14]

Discharge rate 69 tonnes/hr

Design ParametersAssuming a max storage capacity for 2 weeks,

Total capacity = 69 X 24 X 14 = 23184 tonnes ≈ 24000 tonnes / week

• Silos of capacity up to 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 = πr2L = 3πD3/4D = 10.3 mL = 3D = 30.9 m

Coal particle size range = 5mm-10mmOutlet diameter (B)= 10 X (max particle size) [16]

Outlet diameter (B)= 10 X 10 mm = 100 mm = 0.1 m

References:15. Ralph Foiles, Dust explosion venting of silos http://www.processprotection.net/pdf/1.pdf16. Karl Jacob, Bin and Hopper Design, The Dow Chemical Company, Solid Processing Lab, March 2000.

• Problems: arching, flushing, rat-holing, insufficient flow, inadequate emptying etc. In case of non-functioning condition of working silo, 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 Johannson Equation,

[16]

Where,W = discharge rate in kg/sӨ c = angle of hopper from vertical

= 69 X 1000/ (4 X 3600) = 1550 X π/4 X (9.8/4.tanӨc)0.5 X 0.12.5

Өc = 32.33°For height of hopper, H,

= [10.3/2 - 0.1/2]/HH = 8 m

A rotary valve will be used for discharging coal from hopper. [16]

References:16. Karl Jacob, Bin and Hopper Design, The Dow Chemical Company, Solid Processing Lab, March 2000.

Fig 2: Design of silo

Concrete for SiloAssuming a thickness of wall = 10 inch = 0.254 m [17]

Inner diameter, D1 = 10.3 mOuter diameter, D2 = 10.3 + 0.254 = 10.554 m Total volume of concrete for a silo = Vol. of silo wall + Vol. of hopper wall= π (r1

2 – r22)L + 1/3.π(r1

2 – r22)H ≈ 140 m3

Density of concrete = 2400 kg/m3 [18]

Mass of concrete for 6 silos = 2016 tonnes.

Belt Conveyor

• Transport coal from one unit operation to other • From one unit operation to other, coal quantity varies.• Belt specification varies from one location to other.

Surcharge angle for coal = 25° [19]

Assuming troughing angle = 20°References:17. Mostafa H. Mohmaud, Standard Practice for Design and Construction of Concrete Silos and Stacking Tubes for Storing Granular Materials (ACI 313-97), ACI Committee 313, January 199718. Density of concrete, The Physics Factbook, Glenn Elert (McGraw-Hill Encyclopedia of Science and Technology) http://hypertextbook.com/facts/1999/KatrinaJones.shtml19. Masons engineers (NZ) ltd. http://www.masons.co.nz/quick-reference-charts#fourth

Table 1: Belt specificationsBelt Capacity (Coal)

Tonnes per hourAssumed belt

width, mmCross section area

(CSA), m2Velocity, 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 83Dryer to silo 69 450 0.016 77

Fig.2: Values of cross section angle for trough and surcharge angle at different belt width. [19]

References:19. Masons engineers (NZ) ltd. http://www.masons.co.nz/quick-reference-charts#fourth

Mass balance (using Aspen Plus):• Deliverables: 500 tonnes per day of synthesis gas (H2 +CO) (tolerance 100 lb/hr

~ 0.2%), CO2/(CO2+CO) mole ratio = 0.3

• Constraints: H2/CO ratio = 3 (tolerance 0.1 ~ 3.3 %);

• Optimisation: Minimal consumption of input resources i.e. mass inflow of Coal + Steam + O2

• Determine the composition of product synthesis gas and its physical properties.

• I made the following assumptions:

1. Process is steady state and isothermal.

2. The ash rejected out of the system contains only carbon and inerts.

3. Carbon conversion achieved is 90% as opposed to 97% as cited in literature [2].

Under these assumptions and constraints, I have used RGibbs reactor in Aspen plus [1] to simulate the fluidised bed reactor.

References:1. 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_Process2. Lori Allison Simpson, The suitability of coal gasification in India’s energy sector, Massachusetts Institute of Technology, September 2006:

http://dspace.mit.edu/bitstream/handle/1721.1/38569/154723366.pdf?sequence=1

500 TPD H2 and CO COAL OXYGEN PRODUCT STEAMMole Flow kmol/s C 76.7 *10-2 0 0 0O2 26.2*10-3 9.84*10-5 2.17*10-23 0CO 0 0 16.99*10-2 0CO2 0 0 36.17*10-2 0H2 14.2*10-2 0 50.97*10-2 0H2O 70.9*10-3 0 54.7*10-2 1.32C2H4 0 0 4.5*10-7 0C2H6 0 0 1*10-5 0C3H8 0 0 1.9*10-9 0C3H6 0 0 7.310-10 0H2S 0 0 2.2*10-3 0COS 0 0 3.7*10-5 0CH4 0 0 23.55*10-2 0S 2.2*10-3 0 2.97*10-15 0Total Flow kmol/s 1.01 9.84*10-5 1.83 1.32Total Flow kg/s 11.69 3.1*10-3 35.41 23.72Total Flow m3/s 4.16 2.4*10-3 17.41 51.11Temperature K 300 300 930 445Pressure bar 8.1 8.1 8.1 8.1Density kg/m3 1550 1.3 2.03 4.21

Average MW gm/mole NA 32 19.39 18.02

Composition of coal after washingAsh 30%Moisture 6.82%Carbon 49.18H 3.06N2 1.62Sulphur 0.38Oxygen 8.94

Total coal required 19 kg/sTotal ash generated 5.7 kg/s

Simulation results from Aspen Plus:

Previous PresentationPoints from the previous presentation:-

•Reactor Decision – Fluidized Bed Reactor.

•Feed to the reactor by multiple units of MULTICORE – S160 by manufactured by Schenck Process (multiple units to ensure continuity).

•Reaction time for a single coal particle came out to be 34.6 minutes (revised to account the change in flow rates).

Mean Residence Time• Assuming conversion 97%.• Using relation

[1]• t* =• t* came out to be .1558.• Using this and 34.6 min as reaction time the MRT came out to

be 133 mins.

Bed Height• From the MRT and the area value bed height came out to

be approximately 11m.

References:1. Levenspiel Textbook by Ocatave Lavenspie

Steam GenerationDivided the unit into 2 sub units

• Water preheating: Using the sensible heat of syngas and latent heat of water in the out let gas to preheat normal water to a mixture of water and steam at 100 degrees and 1 atm (integration).

• Basic boiler: Actual Boiling of the preheated mixture to get the steam at 8 atm and 700 degrees(this steam goes to the reactor).

Water Preheating

Shell and tube type heat exchanger used.

Parameters :-• U = 150 W/m2K, Tavg = 211.289K, FT = 1 [1]

• Heat transfer area needed = 71.88 m2.

References:[1] Kern Handbook (used in class)

Water PreheaterConfiguration :-•OD 1.9 schedule 80 tubes in a 39 inch shell(160 schedule), 17/8 inch square pitch [2]. •Tube count is 252. •Length of tubes = 5.2m.•Water inside the tube and syngas on the shell side (for pressure drop reasons).•2.6m baffle spacing.

Pressure Drop :-•ΔP came out to be 232.27 Pa for steam. So suitable for our case since we need less pressure pressure drop.• ΔP came out to be 6.9 bar for syngas(due to the high flow rate in small dia).

Boiler

Parameter Inlet condition

Outlet condition

Mass flow rate of water 6.82kg/s 25kg/s

Mass flow rate of steam 16.876kg/s -

Pressure 1 bar 8 bar

Temperature 373k 973k

Parameter initial and required

We have to convert preheated water to steam. Gasifier inlet have both steam and water so we are using burner for generating steam.

Required capacity of boilerQ/t=ṁ1*(λ2-λ1)+ṁ2*(λ4-λ3)65486 kJ/s

Burner for 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 (1.11mx1.11mx1.11m).• We have to install five burner .• Assumption thickness of wall of container 15cm.• Each one has capacity of 13000 KJ/S (MEGAFIRE® Industrial Burner).• Total required power is 65486 kw. • Container is made up of stainless steel.

References:[1] Introduction to Transport Phenomena book appendix.[2] INTRODUCTION TO CHEMICAL ENGINEERING THERMODYNAMICS Sixth Edition by Je M. Smith H. C. Van Ness M. M. Abbott.[3] Maxon corporation megafire gas/oil burners.

Steam and O2 InletSteam generated from steam generator is inserted into gasifier from bottom section. O2 is supplied through distributor of holes sizes 2-4 mm.

References:[1] Y.J. Kim et al. / Fuel 79 (2000) 69–77.[2] American Journal of Engineering and Applied Sciences, 2012, 5 (2), 170-183.

Fig.1. Distributor Fig.2. Conical plate in annulus section

Reactor Area:Area will be total inlet O2 and steam flow rate divided by inlet velocity which we are taking twice of umin.

Minimum Fluidization Velocity:

The Ergun equation can be used to describe the behaviour of a fluidized bed at the minimum fluidization velocity correctly. At minimum fluidization condition u becomes umin.

Assumptions and parameter values:Inlet pressure 8 atm

Temperature 700 C

Assuming spherical particles, so sphericity 1

Assuming bed void fraction at umin is min 0.5

Average particle diameter(dp) 0.0075 m

Bed density 800 kg/m3

References:[1] Powder Technology, 75 (1993) 67-78.[2] Calculation of the viscosity of the gas mixtures by F. J. Krieger RM-649 13 July 1951.

Calculation of Reactor Dimensions

Mixture viscosity 3.5714x10-5 Pas

From steam table specific volume of steam at inlet condition

0.55 m3/kg

Steam+Oxygen Density 1.78 kg/m3

umin 2.79 m/s

uin = 2umin 5.58 m/s

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

References:[1] Energy Vol. 23, No. 6, pp. 475–488, 1998.[2] Kerns handbook.

Reactor Wall Layout

Ash RemovalGasification Ash/Coarse Ash is a ‘clinker’ ash with heterogeneous texture varying from fine material to large irregularly shaped aggregates.

•Coal Ash Density = 0.650 gm/cc (Various Sources [1])•This means around 8769 cc of ash•5.7 kg/hr of both fly and settles ash.•Why Overdesign so much?•We use hopper+ Schedule 40 – 8 inches pipe

References:[1] http://www.aqua-calc.com/page/density-table/substance/cinders-coma-and-blank-coal-blank-ash

SYNGAS EXIT

62673 m3/hr 17.4m3/s ~ 2m/s

Chapter 1B: Syngas Purification and Conditioning

Cyclone Separator

Cyclone a/D b/D De/D H/D h/D S/D B/DRatio 0.618 0.236 0.622 4.236 1.618 0.62 0.382

Figure 1: Ratio analysis of dimensions for cyclone separator

References:[1] Analysis and Optimization of Cyclone Separators Geometry Using RANS and LES Methodologies by Khairy Elsayed Submitted to the Department of Mechanical Engineering, in partial fulfillment of the requirements for the degree of Doctor in Engineering Vrije Universiteit Brussel October 2011 Advisor: Prof. Dr. Ir. Chris Lacor[2] Elemental Characterization of Particle Size-Density Separated Coal Fly Ash by Spectrophotometry, Inductively Coupled Plasma Emission Spectrometry, and Scanning Electron Microscopy-Energy Dispersive X-ray Analysis Kellchl Furuya, * Yoshlhiro Miyajlma, Tohru Chiba, and Tadashl Klkuchl Department of Applied Chemistry, Faculty of Science, Science University of Tokyo, 1-3 Kagurazaka, Shinjuku-ku, Tokyo 162, Japan

Feed conditions and Cyclone dimensions

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 dia De 1.29 m

Dust outlet dia B 0.79 m

Flow rate G 35.41 kg/sec

gas density ρparticle 650 kg/m3

particle density ρsyngas 2.03 kg/m3

viscosity µsyngas 0.03 cP

inlet velocity v 27.19 m/s

References:[1] Coulson and Richardson’s CHEMICAL ENGINEERING VOLUME 2 FIFTH EDITION Particle Technology and Separation Processes.[2] Alex C. Hoffmann and Louis E.. Stein’s Gas Cyclones and Swirl Tubes: Principles, Design and Operation

Pressure drop is calculated by the following equation [2]

ESPThe design of electrostatic precipitator is taken same as used for Hequ Power Plant [1] which is used for ash of same composition as of Indian coal. Some of the specifications are

Number of chambers 2

Number of fields 5

Channel per chamber 38

Height of plate 15.24

Length of plate 19.725

Spacing 400mm

Efficiency >99%

References: [1] GUO LING, WANG LIQIAN, DING JINWU AND MICHAEL ZHU, SIZING AND DESIGN EXPERIENCES OF THE ELECTROSTATIC PRECIPITATORS FOR TWO 600 MW POWER GENERATING UNITS

Pneumatic Conveying of Ash:• Total ash 45217.5 lb/h• Bottom ash 9043 lb/h• Fly ash 36173 lb/h

Pneumatic Conveying of Ash

•Conveying pressure is directly proportional to conveying distance •Conveying capacity is inversely proportional to conveying distance

CalculationConveying distance 150meterMinimum conveying velocity of Ash 400fpm (from source) Conveying velocity 480fpmSystem capacityMaterial flow rate 236tphMass flow rate of air 18.3 lb/minBulk density of fly ash 30lb/cub. ft Solid loading ratio 428 Pipe line is cross section area .545 ft²Pressure across 150 meter pipe 186.11 psig

Pressure Pneumatic Conveying System operates on batch/continuous operating concept and can also convey the much coarser particles of bottom ash

Reference•Pneumatic Conveying Systems by A.Bhatia Continuing Education and Development, Inc.9 Greyridge Farm Court .•Pneumatic Conveying Design Guide Second Edition by David Mills 2004.

Ash Silo

Bottom Ash silo

3 days storage capacity. [1]Bottom ash produced in 3 days = 295.2 tons L/D = 3. [2]Material balance gives the dimension of silo asD = 5.8 mL = 17.4 mCone opening diameter = 70 mmAssuming mass flow, and using Johannson Equation [1]

W = discharge rate in kg/s, Θc = angle of hopper from verticalΘc = 40.3o m Height of hopper, H ≈ 3.4 m

References:[1] Bernard H. Schonbach, Director of engineering Allen-Sherman Hoff company, Operation and Maintenance Guidelines for Silo Unloading Equipment[2] Marietta silos http://www.mariettasilos.com/59

Fig - Ash silo

Fly ash silo

Fly ash produced in 3 days = 1180.8 tonsD = 5m L = 15m No. of silos = 4Using Jenike’s equation [1]

Dmin = (fc,crit X H(θ)) / (ρ X g)

fc,crit = critical yield stress in N/m2 Dmin = minimum hopper diameter to prevent arching

H(θ) = 2.2 for conical hoppersfc,crit = 1152 N/m2 [1]Dmin = 22.7 cmΘc = 20o

H = 6.9 mReferences:

[1] S. Behera and S. Das, Characterisation of Bulk Materials Flowability for Design of Hopper using Jenike Shear Cell, Regional Research Laboratory, Bhubaneswar - 751013

Ash disposalAsh will be disposed from the silo using PD trucks (28 m3 volume) .

No. of trucks required = 27 trucks

Minimum flow rate of ash = 36.4 tons/hour

Ash will be disposed in different areas such as land filling

Cement industry etc.

Land fill design approach [1]

• A 1 mm layer linear low density polyethylene

(LLDPE) geo membrane will be placed over the

entire landfill site as the barrier layer component.

• A 12-inch layer of sand will be placed over the

LLDPE geo membrane.References:[1] Conestoga-Rovers & Associates 651 Colby Drive Waterloo, Ontario Canada N2V 1C2FINAL CLOSURE AND POST CLOSURE PLAN COAL ASH LANDFILL COVER SYSTEM ASH LANDFILL PERMIT SW-09/01 INVISTA SITE SEAFORD, DELAWARE

Fig - Percent disposal of ash in different areas

A 6-inch layer of topsoil will be placed layer to support a vegetative growth over the entire landfill cover system.

Addition of bauxite reduces the pH value and the toxicity and also reduce effectively both the arsenic and boron content. [1]

Wind barrier [1]

Reforestation of disposal site will improve the ecosystem.

References:[1] Reintegration of coal ash disposal sites and mitigation of pollution in the West Balkan Area Handbook on treatment of coal ash disposal sites FR, BOKU, BTUC

Fig – Tree distribution for wind barrier

Heavy Metal Removal: Mercury and Trace Elements• Emission laws more stringent than ever.• India fetched 2nd rank in global mercury emissions after China [1].• Mercury concentration of Indian coal 0.272 ppm [2]• Use of Calgon Type-HGR carbon bed loaded with sulphur• Sulfur reacts with Hg to form HgS which is stable• Removal of Hg to below detectable levels by using activated

carbon bed (less than 0.01 µg/Nm3) [3].• Bed discarded after its economic life is over to hazardous

chemical disposal site

References:1. Lesley Sloss, “Mercury emissions from India and South East Asia”, funded by US Dept. of State, United Nations Environment Programme report, October 2012,

CCC208 ISBN 978-92-9029-528-02. United Nations Environment Programme, A report on hazardous substances and coal combustion in India: http://

www.unep.org/hazardoussubstances/Portals/9/Mercury/Documents/para29submissions/India-Response%20to%20questionnaire-COAL.pdf3. Product Bulletin, HGR for mercury removal, Granular Activated Carbon,

http://www.calgoncarbon.com/media/images/site_library/84_HGR_MercuryRemoval_0108R.pdf.

Activated Carbon Bed Design Principles:

Parameters for Ergun equation:Bulk density of bed 593 kg/m3

Viscosity of syngas (assumed) 5*10-5 kg/m.s

Sphericity of granular particles (assumed)

1

Porosity of bed 0.4

U.S. Sieve series No. 4 [1] 4.76mm

U.S. Sieve series No. 10 [1] 2mm

Size of particles assumed 4mm

Density of syngas 2 kg/m3

Residence time (calculated) [2]

15 seconds

Final design of the activated bed and economic runtime.Minimum fluidisation velocity

0.8 m/s

Diameter of bed 5.18 m

Length of bed 11.8 m

Amount of carbon granules required

147.5 tonnes

Hg removal rate 9.54*10-6 kg/s

Hg adsorbed on bed 5.66 tonnes

Saturation time /Economic life

18.8 years

Expected pressure drop 0.675 atm

References:1. Sigma Aldrich conversion tables, particle size conversion: http://

www.sigmaaldrich.com/chemistry/stockroom-reagents/learning-center/technical-library/particle-size-conversion.html2. Nick Korens, Dale R. Simbeck, Donald J. Wilhelm, SFA Pacific, Inc., Engineering and Economic consultants, “Process Screening Analysis Of Alternative Gas Treating And

Sulfur Removal For Gasification”, prepared for US Dept. of Energy.

Acid gas removal: Choice of solvent• Solubility in physical solvents obeys Henry’s Law,

hence “usually” occurs at higher pressures [1]• Chemical solvents are more effective for low acid gas

partial pressure applications than physical solvents [2].• MDEA has become popular with the natural gas

industry • MDEA content can be higher as it is less corrosive,

reducing circulation rates and hence smaller trays.• Effectiveness of MDEA: 4ppm H2S, upto 20% COS while

allowing CO2 slip [3]References:1. Nick Korens, Dale R. Simbeck, Donald J. Wilhelm, SFA Pacific, Inc., Engineering and Economic consultants, “Process Screening Analysis Of Alternative Gas

Treating And Sulfur Removal For Gasification”, prepared for US Dept. of Energy.2. U.S. Department of Energy, Gasifipedia, Acid Gas removal.3. W.I. Echt,”Chemical Solvent-based Processes For Acid Gas Removal In Gasification Applications”, Union Carbide Corporation, DOW Chemical Industry.

Acid gas removal: activated MDEA

• To maintain CO2/(CO+CO2) = 0.3, we need to get rid of 80% CO2, i.e. 20% CO2 slip ~ 200,000 ppmv of CO2 in treated gas.

• Approx. 80% of COS will be removed 4ppmv of COS in treated gas

References:1. Nick Korens, Dale R. Simbeck, Donald J. Wilhelm, SFA Pacific, Inc., Engineering and Economic consultants, “Process Screening Analysis Of Alternative Gas Treating And Sulfur

Removal For Gasification”, prepared for US Dept. of Energy.2. R. Scott Alvis, Nathan A. Hatcher & Ralph H. Weiland. “CO2 Removal from Syngas Using Piperazine Activated MDEA and Potassium Dimethyl Glycinate”, Optimized Gas ‐

Treating, Inc.

Design specifications for tray tower/absorption column:• Followed procedure given in Mass Transfer Operations, Robert E. Treybal, 3rd

Edition, pages 158 - 176

Table of values used to design tray towerDensity of MDEA solvent 1000kg/m3

Density of syngas (1atm, 373K)

0.652 kg/m3

Vapour flow rate 1.28 kmol/s

Q (vapour rate) (1atm, 373K)

39.2 m3/s

q(liquid rate) 0.168 m3/s

do (hole diameter) 4.5mm

Pitch (p’) 12mm

Surface tension of liquid 0.04 N/m

f friction factor [17] 0.0045

Results and dimension specifications for the design of actual tray tower.W/T 0.7 hw (height of weir) 190 mm

Steel Plate thickness

1.935 mm how (height of liquid over weir)

105.6 mm

Tray spacing (t) 1m h3 (downcomer backup)

122.3 mm

VF (flooding velocity)

5.05 m/s Check on flooding condition

417.3 < 500

V (Velocity of liquid) (0.8VF)

4.04 m/s T (tower diameter) 1.385m

Vow (weeping velocity)

7.49 m/s Distance of weir from centre

1.3126 m

Vo (velocity of vapour)

44.82 m/s Expected pressure drop for gas

9600 Pa ~ 9.5%

Calculation of number of stages reqd: Composition of synthesis gas exiting

from the top of the tray tower500 TPD H2 and CO PRODUCT

Mole Flow kmol/s

CO 16.99*10-2 Total Flow kmol/s 98*10-2

CO2 7.27*10-2 Total Flow kg/s 12.74

H2 50.97*10-2 Total Flow m3/s 17.41

CH4 23.55*10-2 Temperature K 373

Density kg/m3 0.53 Pressure atm 0.92

Average MW gm/mole 13 Density kg/m3 0.53

• The number of stages comes out to be 8. With a tray spacing of 1 metre, the height of the tower comes out to be 8 metres.

• The expected pressure drop for gas is about 9600 Pa ~ 9.5% of initial gas pressure.

References:1. R. Scott Alvis, Nathan A. Hatcher & Ralph H. Weiland. “CO2 Removal from Syngas Using Piperazine‐

Activated MDEA and Potassium Dimethyl Glycinate”, Optimized Gas Treating, Inc.

Design of Buffer Tank for activated MDEA solution and pump:

Density of fluid 1000 kg/m3 Vopt = 12 ṁ0.1/ρ0.36 (fps units) 1.5 m/sVolume flow rate 0.168 m3/s Diameter of pipe 0.38 mVolume of tank (assuming 2 hours buffer) 1210 m3 Reynolds number 5644Diameter of tank (assumed) 15 m f friction factor 0.036Length of tank 6.9 m Length of pipe (assume) 10 mṁ (SI units) 168 kg/sec Hf head due to friction 0.11 mHead generated 6.94 m

Figure : Pump arrangement and layout

Design Specifications for Pump:

For constant Diameter P/Q3 = constt.

Assuming efficiency 65%

Power required (assumed efficiency of 0.65) 77.53 hp

Q1 0.168 m3 /s = 2662.8 US gpm

Shaft Diameter 4 in

For constant rpm H/D2 = constt.

Head 6.94 m

Motor RPM 700 rpm

Due to limited data in pump-head discharge curve, affinity laws areused to calculate rpm and impeller diameter.

References:[1] Lecture slides .[2] McCabe, Smith handbook.

CLAUS TREATMENT PLANT:

• Thermal reactor – 1.• Catalytic Reactors – 2.• Possible Results

INPUT OUTPUT

H2S17.57 kmol/hr

O2 8 kmol/hr

H2S 12.23 kmol/hr

SO2 5.33 kmol/hr

H2O 5.33 kmol/hr

S -----

2H2S + 3 O2

2SO2 + 2H2O

THERMAL REACTOR• Modeled as RGIBBS in Aspen HYSIS.• Rule of Thumb: 1/3rd * (weight of Hydrogen Sulphide)

= Weight of Oxygen.• Temperature : 1000 degrees Celsius• Pressure: 1.5 barg.• Idea is to provide stoichiometry for next reaction.

References:[1] (2010) Abedini et al. Modeling and Simulation of Condensed Sulphur in catalytic beds of Claus Process: Rapid Estimation, Chemical Engineering Research Bulletin 14 (2010) 100-114.[2] Chemical Engineering Research Bulletin 14 (2010) 110-114.

Physical Design

Catalytic Reactor• It is expected that in this reactor, the remainder of the Hydrogen Sulphide

gets transformed into yellow sulphur.

• Temperatures (about 470-620 K) over an alumina- or titanium dioxide-based catalyst.

• 2H2S + SO2 -> 3S + 2H2O ∆Hr = -108 kJ moL-1

• Clogging: Increase in viscosity of Sulfur around 430 K.

• The Claus process is equilibrium-limited, adequate residence time has to be provided in order to allow this reaction.

References:[1] American Journal of Environmental Sciences 4 (5): 502-511, 2008.

Other gases