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LECTURE–6: FUEL AND INDUSTRIAL GASES
CHEMICAL TECHNOLOGY (CH-206)
Dr. Vimal KumarDepartment of Chemical Engineering
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INTRODUCTION The chemical industry depends to a major extent on
gases composed of one or more of the chemical elements of Carbon (C) Hydrogen (H2) Oxygen (O2), and Nitrogen (N2).
These gases are used for fuel and for the synthesis of organic and inorganic chemical compounds.
The raw material for these gases are Water, Air, Coal, Natural gas, and Petroleum.In India the manufacture of fuel gas is limited to coal as a source of carbon with vary low
production.
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FUEL GASES: CLASSIFICATION
Type Kcal/cu m Principal use
Producer gas (CO, N2, H2 with steam added to reduce Hnet to zero)
12001600 Steel industry’s heating requirements (heat treat, coke oven)
Water gas (CO, H2) 25002700 Heating, Chemical synthesis
Coke oven gas (CO2, CH4, H2)
45008000 Heating, Chemical synthesis
Carburetted or Oil gas (water gas and pyrolyzed oil)
40009000 Heating
Natural gas and LPG (Liquified Petroleum gas)
600014000 Heating, Chemical synthesis
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PERCENT COMPOSITION AND HEATING VALUES OF VARIOUS FUEL GASES
Fuel gas NG (mid continent)
NG (Pennysylvania)
Coke oven gas
Blue water gas
Carburated water gas
Bituminous producer gas
CO 6.3 42.8 33.4 27.0
CO2 0.8 1.8 3.0 3.9 4.5
H2 53.0 49.9 34.6 14.0
N2 3.2 1.1 3.4 3.3 7.9 50.9
O2 0.2 0.5 0.9 0.6
CH4 96.0 67.6 316 0.5 10.4 3.0
Ethane 31.3
Illuminants 3.7 8.9
Gross (Mj/m3)
36 46 21 11 20 5.5
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HEATS OF COMBUSTION OF COMMON NATURAL GASES
Substance MJ/m3 Btu/ft3
Methane 37.56 1000
Ethane 65.80 1763
Propane 93.65 2510
Butane 121.18 3248
Pentane 149.00 3752
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FUEL GASESPRODUCER (SUCTION) GAS: RAW MATERIAL
Raw material Coal or blast furnace coke Air Steam
Reaction (exothermic)2C + O2 + 3.73 N2 → 2CO+ 3.73 N2
Quantitative requirements Basis: 100 Nm3 of producer gas
Coke 2025 kgor coal 2530 kgAir 6080 Nm3
Steam 810 kg Typical plant capacities: 25,000250,000 cubic meter/day
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FUEL GASESPRODUCER GAS: PROCESS
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FUEL GASESPRODUCER GAS: PROCESS
Steam and air mixture injected in bottom of a watercooled jacketed steel furnace.
The steel furnace is equipped with a rotating grate to remove fusible ash.
Solid fuel is added from hopper valve on top of furnace.
Producer gas is cooled by passing through a waster heat boiler.
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FUEL GASESPRODUCER GAS: MAJOR ENGINEERING ISSUES
Design of suitable gas producer furnace to: Keep uniform fuel surface Provide adequate gasfuel contact time at high
temperature Avoid clinkering and provide for proper fused ash
removal Addition of correct steam quantities to supply
net heat of reaction near zero on a continuous oncethrough process.
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FUEL GASESWATER (SYNTHESIS) GAS: RAW MATERIAL Water gas is comprised of carbon monoxide and hydrogen. The gas is made by passing steam over a red-hot carbon fuel such
as coke:H2O + C → H2 + CO (ΔH = +131 kJ/mol)
The reaction is endothermic so the fuel must be continually re-heated to keep the reaction going.
In order to do this, an air stream, which alternates with the vapor stream, is introduced for the combustion of carbon to take place.
O2 + C → CO2 (ΔH = −393.5 kJ/mol) (Theoretically, for 6 L of water gas, 5 L of air is required.)
Alternatively to prevent contamination with nitrogen, energy can be provided by using pure oxygen to burn carbon into carbon monoxide.
O2 + 2 C → 2 CO (ΔH = −221 kJ/mol)(Theoretically 1 L of oxygen produces 5.3 L of pure water gas.)
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FUEL GASESWATER (SYNTHESIS) GAS: RAW MATERIAL
Raw material Bituminous, anthracite coal or coke Air Steam
Quantitative requirements Basis: 100 cu m of water gas from Carbon (C)
Coke (C) 55 kgor coal (C) 58 kgAir 220 Nm3
Steam 80 kg Typical plant capacities: 250,0001,500,000
Nm3/day
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FUEL GASESWATER GAS: PROCESS – REGENERATIVE PROCESS
It is comprising of two reactors One operates on blow period which heat carbon as follows:
C(s) + O2 (g) CO2 (g) HO = 96.5 Kcal
Other operates on run period where endothermic reaction takes place
C(s) + CO2 (g) 2CO (g) HO = +38.9 Kcal
The process cycle of 46 min is divided as: Blow or heat–up: 35% Downrun: 33% Uprun:30% Short purge uprun: 2%
The steel reactor is equipped with refractor lining. If higher BTU gas is required, an additional high – temperature
carburetor section is required for pyrolyzing oil spray and mixing.
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FUEL GASESWATER GAS: PROCESS – REGENERATIVE PROCESS
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FUEL GASESWATER GAS: PROCESS – CONTINUOUS PROCESS
The process was developed in 1940s based on use of tonnage or low purity grade oxygen made by air separation procedure.
The correct ratio of steam, oxygen, and coal is added to the reactor to yield a self sustaining reaction of approximately zero heat release.
Subsequent innovation allow for ash content > 30%. Therefore, Indian coal can also be used.
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FUEL GASESWATER GAS: PROCESS – CONTINUOUS PROCESS
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FUEL GASESWATER GAS: MAJOR ENGINEERING ISSUES
Designing suitable ash removal systems for various grades of coal in continuous processing.
Optimizing cycle for regenerative process.
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FUEL GASESCOKE OVEN GAS: RAW MATERIAL
Raw material Coking coal Air Producer gas
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FUEL GASESCOKE OVEN GAS: PROCESS
Upgraded coal for coking purpose is fed to a by product coke oven furnace.
The producer gas is fed for heating the chamber to 1000 0C for 12–20 hours.
The gas is removed continuously and put through a series of purification steps.
If specifically NH3 synthesis gas is required further purification operations are needed: scrubbing with alkali to remove CO2, liquefaction to remove light hydrocarbons, and scrubbing with liquid N2 to take out CO.
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FUEL GASESCOKE OVEN GAS: PROCESS
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FUEL GASESCOKE OVEN GAS: MAJOR ENGINEERING ISSUES
Suitable grade of coking coal in India. Before coking typically washing, preroasting, and solvent extraction are some of the pretreatments are needed.
Choice of scrubbing liquors for CO2 and CO are needed.
Process Economy – Indian Scenario500 tons of NH3 per day at Rourkela is produced using 1.8 x 106 m3 of coke oven gas in an ammonia synthesis plant.
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CONTINUE……….Natural gas processing
Liquefied Petroleum gas
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FUEL GASESNATURAL GAS
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FUEL GASESNATURAL GAS- COMPOSITION
Components of Natural Gas (NG)
Heats of Combustion of common Natural Gases
Substance MJ/m3 Btu/ft3
Methane 37.56 1000
Ethane 65.80 1763
Propane 93.65 2510
Butane 121.18 3248
Pentane 149.00 3752
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NG AND LPG TREATMENT PROCESSDrying Heavy end removal Purification
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FUEL GASESNATURAL GAS PROCESSING
Remove excess water Remove acid gas Dehydrate Remove mercury Remove nitrogen Separate NGL (ethane, and heavier
hydrocarbons)
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FUEL GASESNATURAL GAS PROCESSING
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FUEL GASESNATURAL GAS PROCESSING
Water removal Removes free liquid water and condensate gas Sends the gas to a refinery The water goes to waste
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FUEL GASESNATURAL GAS PROCESSING
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FUEL GASESNATURAL GAS PROCESSING
Acid Gases Hydrogen sulfide Mercaptans Carbon dioxide
Acid gas removal processes Amine treating (Monoethanolamine,
Diethanolamine, Diisopropylyamine, Methylethanolamine)
Benfield process Sulfinol process others
Hydrogen sulfide goes through a Claus process
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FUEL GASESNATURAL GAS PROCESSING: AMINE TREATMENT
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FUEL GASESNATURAL GAS PROCESSING: SULFINOL PROCESS
Used to reduce H2S, CO2, and mercaptans from gases Great for treating large quantities of gas Solvent absorbs the sour gas Sulfolane is used
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FUEL GASESNATURAL GAS PROCESSING: DEHYDRATION
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FUEL GASESNATURAL GAS PROCESSING: GLYCOL DEHYDRATION
Method for removing the water vapor from the gas
Usable glycols Triethylene glycol (most commonly used) Diethylene glycol Ethylene glycol Tetraethylene glycol
Absorption of water with glycol
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FUEL GASESNATURAL GAS PROCESSING: GLYCOL DEHYDRATION
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FUEL GASESNATURAL GAS PROCESSING: PRESSURE SWING ADSORPTION
Adsorbent material is used Gas and material go under high pressure Material adsorbs the gas ( H2S, mercaptans,
CO2)
Disadvantages Requires high pressures Slow cycle times
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FUEL GASESNATURAL GAS PROCESSING: MERCURY REMOVAL
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FUEL GASESNATURAL GAS PROCESSING: MERCURY REMOVAL
Current Processes Activated carbon – through chemisorption.
Activated has extremely high surface area
Mercury can damages aluminum heat exchangers Those used in cryogenic processing plants Those use in liquefaction plants
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FUEL GASESNATURAL GAS PROCESSING: NITROGEN REJECTION
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FUEL GASESNATURAL GAS PROCESSING: NITROGEN REJECTION
Cryogenic process Common refrigerants used Most common method for removal of impurities
such as nitrogen Disadvantages
Must reach extremely low temperatures Only useful for large scale production
Absorption process (using lean oil or solvent) Lean oil is fed countercurrent with the wet gas Temperature and pressure are set to allow for the
greatest absorption of unwanted gases Membrane separation Adsorption process (activated carbon)
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FUEL GASESNATURAL GAS PROCESSING: DEMETHANIZER
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FUEL GASESNATURAL GAS PROCESSING: DEMETHANIZER
The next step is to recover the NGL’s
Process Cryogenics using a turbo-expander can be used
This is the most common Lean oil adsorption can be used here
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FUEL GASESNATURAL GAS PROCESSING: CRYOGENIC PROCESS
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FUEL GASESNATURAL GAS PROCESSING: NGL RECOVERY
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FUEL GASESNATURAL GAS PROCESSING: NGL RECOVERY
The rest of the liquid is fed to three units Deethanizer Debutanizer Depropanizer
Process Separation using distillation column
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FUEL GASESNATURAL GAS PROCESSING: NGL SWEETENING
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FUEL GASESNATURAL GAS PROCESSING: NGL SWEETENING
Merox Processes Mercaptan oxidation Removes mercaptans from
Propane Butane Larger hydrocarbons
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FUEL GASESNATURAL GAS PROCESSING: NGL SWEETENING
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LPG PROCESSING
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SYNTHESIS GASES
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FUEL GASES: SYNTHESIS GAS INTRODUCTION
Synthesis Process
CO/H2 ratio
Catalysts Temp. OC Pres., atms.
Products
Methane Ni 205500 1 CH4
Fischer–Tropsch 0.50.2 Co, Ni, Fe 180300 130 Paraffinic & olifinic hydrocarbons varying from methane to waxes and small quantities of oxygenated products
Synol 0.30.5 Fe 185225 1530 Straight chain normal alcohol
Methanol 0.3 ZnO, CuO, Cr2O3
250350 100 300
Methanol
Higher alcohol synthesis
Fe + alkali 400500 100 300
Alcohols from C1 to Cn
Isosynthesis 0.5 ThO2, ZnO, Al2O3
400450 100 300
Saturated branched hydrocarbons
Oxosynthesis (uses olefins as additional starting material)
1.2 Cobalt [Co(CO)4]2
150200 150 200
Oxygenated hydrocarbons, aldehydes and alcohols
It is generally considered as a variable mixture of CO and H2 for synthesis of organic compounds. In some applications CO is not needed, such as: ammonia synthesis gas (3H2 + 1N2) and hydrogenation of alcohols (H2 only)
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FUEL GASESSYNTHESIS GAS: PROCESSES
From petroleum hydrocarbons Reforming (ICI steam–naphtha reforming
process) Partial combustion
From coal or coke Water gas Coke oven gas
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FUEL GASESSYNTHESIS GAS: REFORMING (ICI STEAM–NAPHTHA REFORMING PROCESS)
Reforming reaction (endothermic and exothermic reaction)
Kcal 52.0- H O;H CH 3H CO (b)
6n for Kcal 382 H
1n for Kcal 52 H ;1)H(2n OnH HC (a)
o242
o
o2222nn
Ni
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FUEL GASESSYNTHESIS GAS: REFORMING (ICI STEAM–NAPHTHA REFORMING PROCESS)
Raw material Refinery naphtha or off–gases Air (optional) Steam Catalysts (nickel and promoted iron oxide) Solvents (ethanolamine, and ammoniacal cuprous formate)
Quantitative requirements Basis: 100 Nm3 of hydrogen of 99.0 % purity
Naphtha 21.9 kgSteam 560 kgFuel (as naphtha) 22.3 kg
Cooling water 6.5 tonsElectricity 1.4 KWH
Typical plant capacities: 10 – 200 tons/day of H2
80,0001,680,000 Nm3/day of synthesis gas
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FUEL GASESSYNTHESIS GAS: REFORMING (ICI STEAM–NAPHTHA REFORMING PROCESS)
Reforming for preparation of synthesis gas containing H2 with or without CO.
Ammonia Gas
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FUEL GASESSYNTHESIS GAS: REFORMING (ICI STEAM–NAPHTHA REFORMING PROCESS)
Reforming for preparation of ammonia synthesis gas.
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FUEL GASESSYNTHESIS GAS: REFORMING (ICI STEAM–NAPHTHA REFORMING PROCESS)
The hydrocarbon is mixed with steam and fed to the reforming furnace.
The nickel catalyst is packed in vertical tubes of 3–4 inches in diameter and about 20–25 feet long.
Heat for the endothermic reaction is supplied by combustion gas.
The reaction temperature is maintained in the range of 700–1000 OC; high temperature alloy steel is used for the tubes and the steel wall of the furnace is refractory lined.
A space velocity of 500–600 /hr is maintained. Depending on the required product there are three
alternate processes after the reformer.
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FUEL GASESSYNTHESIS GAS: REFORMING (ICI STEAM–NAPHTHA REFORMING PROCESS)
For CO–H2 synthesis: The effluent reformer gas is cooled to 35 OC and pumped
to a hot potassium carbonate scrubbing system to remove CO2.
For H2 gas: Stream is mixed with product gas and fed to shift converter to
produce more H2 from CO. Reformer gas is quenched with steam to give 350 OC input gas to
a catalytic converter using iron oxide catalyst promoted with chromium oxide.
A space velocity of 100–200 /hr is maintained. CO2 is scrubbed using amine absorption process and traces of CO
are removed by methanation reaction. For high purity hydrogen, one or two additional stages of the shift
converter, CO2 absorption combination are added with either ammonical cuprous formate or molecular sieves used added to remove residual CO and CO2 down to 10 ppm or less.
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FUEL GASESSYNTHESIS GAS: REFORMING (ICI STEAM–NAPHTHA REFORMING PROCESS)
For NH3 synthesis: The correct amount of nitrogen is added via air
and the oxygen is burned out by hydrogen in a Ni catalyzed combustion chamber inserted immediately following the reformer.
Gases are cooled to 350 OC using water quenching tower and then passed to the shift converter.
Except for additional N2 which passes through, the remainder of the process is same as for hydrogen preparation.
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FUEL GASESSYNTHESIS GAS: MAJOR ENGINEERING ISSUES
Sulfur contamination of reforming catalyst (sulfur content in the naphtha should be 5 ppm)
Design of an efficient reformer furnace to economically supply endothermic heat of reaction.
Avoid carbon formation on catalyst by use of highly specific catalyst.
Removal of CO2 and CO. The bulk of the CO2 is removed by the absorption
process using either potassium carbonate or monoethanolamine (MEA).
Final traces of CO and CO2 can be removed by methanation process (reverse refoming process):
O;H CH 3H CO (b)
atm 10-8 C, 400-003 O;2H CH 4H CO (a)
24Ni
2
O24
Ni22
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FUEL GASESSYNTHESIS GAS: PARTIAL COMBUSTION
Chemical reactions
0H ;5H OH 3CO 2O 3CH :reactionNet
2H 2CO CO CH (c)
3H CO OH CH (b)
O2H CO 2O CH (a)
2224
224
224
2224
The CO:H2 ratio can be lowered by adding extra steam to give the water gas shift reaction:
222 H CO OH CO
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FUEL GASESSYNTHESIS GAS: PARTIAL COMBUSTION
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FUEL GASESSYNTHESIS GAS: PARTIAL COMBUSTION
Raw material Low purity natural gas or cheap liquid hydrocarbons Tonnage oxygen (low purity grade) Steam Catalysts (promoted iron oxide shift converter catalyst) Solvents (ethanolamine, and ammoniacal cuprous formate)
Quantitative requirements Basis: 100 Nm3 of hydrogen of 99.0 % purity
Naphtha 29.2 kgSteam 104 kgOxygen 26 Nm3
Cooling water 8 tonsElectricity 0.7 KWH
Typical plant capacities: 10 – 200 tons/day of H2
100,0001,600,000 Nm3/day of synthesis gas
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FUEL GASESSYNTHESIS GAS: PARTIAL COMBUSTION
The process feed and oxygen are preheated separately. The preheated feed and oxygen are mixed at 550 OC and
fed to a burner in a refractory lined furnace labeled gas generator.
After wash quench the product gas is routed for different routes depending upon the required products:
H2 route Steam is mixed with product gas and fed to shift converter to
produce more H2 from CO. Amine absorption of CO2 is followed by caustic scrubbing. Traces of CO and CO2 can be removed by either ammonical
cuprous formate or liquid nitrogen scrubbing. The purified H2 after mixing with N2 can be used for further
production of NH3.
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FUEL GASESSYNTHESIS GAS: PARTIAL COMBUSTION
CO + H2 route: The shift converter is by passed and scrubbed
with amine to remove CO2.
Acetylene route: The product gas is treated with dimethyl
formamide to remove acetylene and polymer before further CO–H2 processing.
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FUEL GASESSYNTHESIS GAS: MAJOR ENGINEERING ISSUES
Proper design of burner for flame stabilization in gas generator
Removal of trace impurities of CO and CO2. Handling of deposited carbon on the catalyst.
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AMMONIA SYNTHESIS
Sulfur Removal
Steam–Methane Catalytic
Reforming
Carbon Dioxide Removal
Shift Conversion
MethanationAmmonia Synthesis
Feed Steam
Ammonical Product
Operating pressure for: The steam reforming, shift conversion, carbon dioxide removal and methanation:
25 to 35 bar, The ammonia synthesis loop 60 to 180 bar (depending upon the
proprietary design used)
Steam reforming
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AMMONIA SYNTHESISSULFUR REMOVAL
Sulfur compounds are removed from the feedstock because sulfur deactivates the catalysts used in the synthesis of ammonia.
Catalytic hydrogenation is carried out to convert sulfur compounds in the feedstocks to gaseous hydrogen sulfide:
H2 + RSH → RH + H2S(gas)
The gaseous hydrogen sulfide is then adsorbed and removed by passing it through beds of zinc oxide where it is converted to solid zinc sulfide:
H2S + ZnO → ZnS + H2O
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AMMONIA SYNTHESISCATALYTIC STEAM REFORMING, SHIFT CONVERSION & CO2 REMOVAL
The sulfur – free feedstock is then passed into a catalytic steam reformer to produce hydrogen plus carbon monoxide (synthesis gas):
CH4 + H2O → CO + 3H2
The mixture of CO and H2 is then proceeds to the catalytic shift converter to convert the carbon monoxide to carbon dioxide and more hydrogen:
CO + H2O → CO2 + H2
The carbon dioxide is then removed either by absorption in aqueous ethanolamine solutions or by adsorption in pressure swing adsorbers (PSA).
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AMMONIA SYNTHESISCATALYTIC METHANATION
Further the catalytic methanation is carried out to remove any small residual amounts of carbon monoxide or carbon dioxide from the hydrogen:
CO + 3H2 → CH4 + H2O
CO2 + 4H2 → CH4 +2H2O
To produce ammonia, the hydrogen is then catalytically reacted with nitrogen (derived from process air) to form anhydrous liquid ammonia (ammonia synthesis loop also referred to as the Haber-Bosch process):
3H2 + N2 → 2NH3
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AMMONIA SYNTHESISCATALYTIC METHANATION Due to the nature of the (typically multi-
promoted magnetite) catalyst used in the ammonia synthesis reaction, only very low levels of oxygen-containing (especially CO, CO2 and H2O) compounds can be tolerated in the synthesis (hydrogen and nitrogen mixture) gas.
Relatively pure nitrogen can be obtained by Air separation, but additional oxygen removal may be required.
Since relatively low single pass conversion rates (typically less than 20%), a large recycle stream is required. This can lead to the accumulation of inerts in the loop gas.
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ACKNOWLEDGEMENT
Slides are developed from the following references: Austin G. T., "Shreve’s Chemical Process Industries",
Fifth edition, Tata McGraw Hill, NY. Kent J.A., "Riegel's Handbook of Industrial
Chemistry,” CBS Publishers. Gopala Rao M. & Marshall Sittig, "Dryden’s Outlines
of Chemical Technology for the 21st Century", Affiliated East –West Press, New Delhi.
Mall I. D., "Petrochemical Process Technology", Macmillan India Ltd., New Delhi.
NPTEL (online) http://encyclopedia.che.engin.umich.edu/Pages/
SeparationsChemical/Adsorbers/Adsorbers.html
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SUBSTITUTE NATURAL GAS
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FUEL GASES: SUBSTITUTE NATURAL GAS
CO + H2 mixture from coal and steam by gasification process Low–heat content (3.7 to 7.5 MJ/m3, having 50%
N2) Medium–heat content
The low–heat content gas is used mainly as an onsite Industrial fuels, and Intermediate in the production of formaldehyde
and ammonia The medium–heat content gas is used to
produce substitute natural gas after methanation.
COAL GASIFICATION PROCESS TECHNOLOGIESGasifier Technology Coal Feed,
t/dayLocation
Fixed bed Lurgi–dry ash British Gas/Lurgi Slagging
ATC/Wellman
1st generation2nd generation
2nd generation
600–800 3800200
WorldwideWestfield, ScotlandNoble County OhioYork, Pa.
Fluidized Bed Hygas U–gas
2nd generation2nd generation
752800
Chicago, Ill.Memphis, Tenn.
Entrained Bed Kopper – Totzek Texaco
1st generation2nd generation
1501000200
WorldwideGermanyBarstow, Cailf.Muscle Shoals, Ala.
Shell - Koppers 2nd generation
150 W. Germany
Combustion Engineering 2nd generation
150 Windsor, Conn.
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Status–1981
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LURGI PRESSURE GASIFIER (PROCESS) It has a pressurised moving bed (~2800 kPa) system, therefore it
cannot use caking coals and operated with either air or oxygen.
80
Devolatilization takes places as the coke flow downward due to gravityDevolatilization and gasification of the resulting char takes place at 620 OC – 760 OC temperatures.
The crude gas leaves the gasifier at temperatures between 370 OC and 595 OC, depending upon the type of coal.The crude gas contains tar, oil,
naphtha, phenols, ammonia, and traces of coal and ash dust.
The crude gas is passed to a scrubber and washed with a circulating gas liquor and then cooled to a temperature at which the gas is saturated. The gas leaving the gasifier after
scrubbing are CO2, CO, CH4, H2, and H2O.
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PROCESS FLOWSHEET OF SASOL–LURGI GASIFICATION PROCESS
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WINKLER GENERATOR FLUIDIZED BED GASIFIER
It has the advantage of uniform temperature distribution and excellent solid gas contact.
It can handle wide variety of coals without a significant loss of efficiency.
Crushed and fine coal is fed into the top and oxygen and steam into the bottom of the reactor.
The exit gas have high dust contents and it must be removed before further processing
The oeprating temperature is higher, 800 OC – 1000 OC.
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KOPPER – TOTZEK ENTRAINED BED GASIFIER
It has the advantage of higher capacity and gas production as compared to other processes.
It can handle wide variety of coals and produce a gas free of tars and phenols.
The Pulvarised coke, steam and oxygen are fed together and the coal is gasified in suspension.
No pretreatment is needed as the flowing gas separates the particles and they are gasified so rapidly that they cannot agglomerate.
The operating temperature is very higher 1900 OC. Further it needs high amount of oxygen.
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COMPOSITION OF TYPICAL PRODUCT GASES(DRY BASIS – MOLE %)
Component Lurgi Kopper-Totzek Winkler
H2 38.0 36.7 41.8
CO 20.2 55.8 33.3
CO2 28.6 6.2 20.5
CH4 11.4 0.0 3.0
C2H6 1.0 0.0 0.0
H2S or COS 0.5 0.3 0.4
N2 0.3 1.0 1.0
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TEXACO GASIFICATION PROCESS It also uses entrained flow technology for gasification of coal. It gasifies coal under relatively high pressure (20–85 atm) by
injection of oxygen (or air) and steam with concurrent gas/solid flow.
Fluidized coal is mixed with either oil or water to make it into pumpable slurry.
This slurry is pumped under pressure into a vertical gasifier, which is basically a pressure vessel lined inside with refractory walls.
The slurry reacts with either air or oxygen at high temperature. The product gas contains primarily CO, CO2, and H2 with some
quantity of methane. Because of high temperature, oil or tar is not produced. This process is basically used to manufacture CO-rich
synthesis gas.
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TEXACO GASIFICATION PROCESS
The gasifier operates at around 1100–1370°C and a pressure of 20–85 atm.
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COAL GASIFICATION: SUMMARY The low and medium – heat syngas produced from coal can be
converted to a high heat content gas (30 – 37 MJ/m3) by the following reactions:
(1) C + H2O CO + H2 (gasification)
(2) CO + H2O CO2 + H2 (water gas shift reaction controlled to give CO:H2 = 1:3)
(3) C + CO2 2CO (Boudouard reaction)
At sufficiently high pressure the hydrogen from reactions (1) and (2) will hydrogenate some of the carbon to yield methane:
(4) C + 2H2 CH4
(5) CO + 3H2 CH4 + H2O (methanation)
Before methanation the sulfur and CO2 are removed from the gas
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COAL GASIFICATION: SUMMARY Operating pressure: atmospheric to 6.9 MPa Operating temperature:800 OC to 1650 OC The higher pressure and lower temperature result in the
formation of large amount of methane.
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COAL GASIFICATION: SUMMARY
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IN-SITU COAL GASIFICATION (UCG)
In situ gasification, or underground gasification, is a technology for recovering the energy content of coal deposits that cannot be exploited either economically or technically by conventional mining (or ex situ) processes.
Coal reserves that are suitable for in situ gasification have low heating values, thin seam thickness, great depth, high ash or excessive moisture content, large seam dip angle, or undesirable overburden properties.
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IN-SITU COAL GASIFICATION
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CLAUS PROCESS
The Claus process is a catalytic chemical process that is used for converting gaseous hydrogen sulfide (H2S) into elemental sulfur (S).
The process is commonly referred to as a sulfur recovery unit (SRU) and is very widely used to produce sulfur from the hydrogen sulfide found in: raw natural gas, and the by-product sour gases containing hydrogen
sulfide derived from refining petroleum crude oil and other industrial facilities.
In 2010, the world wide production of by-product sulfur was 68 M metric tons, majorly from petroleum refining and natural gas processing plants.
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CLAUS PROCESS: HISTORY In nineteenth century, there were many alkali manufacturing
plants in England producing sodium carbonate (Na2CO3) by the Leblanc process.
The original Claus process was developed by Carl Friedrich Claus, a chemist working in England, for the purpose of recovering sulfur from the waste calcium sulfide (CaS) generated by the Leblanc process.
As a catalyst, he chose a bog iron ore and later bauxite (a mineral with a high alumina content).
In 1883, Claus was granted a British patent for the process. During the next 53 years, the Claus process underwent
several minor modifications. In 1936, I.G. Farbenindustrie a (German conglomerate of
chemical companies) introduced a modification of the process that utilized a thermal conversion step followed by catalytic conversion steps, which is the basically the concept currently used in modern Claus sulfur recovery units.
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CLAUS PROCESS: FEED GAS COMPOSITION
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CLAUS PROCESS: REACTION MECHANISM
The Claus reaction to convert H2S into elemental sulfur requires the presence of one mole of SO2 for each two moles of H2S:
2H2S + SO2 → 3S + 2H2O
To provide that ratio of components, the first step in the Claus process is the combustion of one-third of the H2S in the feed gas:
H2S + 1.5 O2 → SO2 + H2O
The overall process reaction, combining reactions (1) and (2), is:
2H2S + O2 → 2S + 2H2O
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CLAUS PROCESS: PROCESS DESCRIPTION The feed gas to a is burned in a reaction furnace using sufficient
combustion air to burn only one-third of the H2S it contains. The furnace temperature and pressure is maintained at about
1000 OC and 1.5 bar gauge (barg). At those conditions, the Claus reaction occurs thermally in the
reaction furnace (i.e., without requiring any catalyst). About 70% of the H2S in the feed gas is thermally converted
into elemental sulfur in the reaction furnace. The hot reaction product gas, containing gaseous sulfur, is used
to produce steam in a waste heat boiler (or boiler) which results in cooling the gases.
The gas is then further cooled and condensed in a heat exchanger while producing additional steam.
The condensed liquid sulfur is separated from the remaining unreacted gas in the outlet end of the condenser and sent to product storage.
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CLAUS PROCESS: PROCESS DESCRIPTION
The separated gas is then reheated and enters the first catalytic reactor maintained at an average temperature of about 305 °C, where about 20% of the H2S in the feed gas is converted into elemental sulfur.
The outlet product gas from the first reactor is cooled in another condenser while also producing steam.
The condensed liquid sulfur is separated from the remaining unreacted gas in the outlet end of the condenser and sent to product storage.
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CLAUS PROCESS: PROCESS DESCRIPTION The separated gas from the second condenser is sent to
another reheater and the sequence of gas reheat, catalytic reaction, condensation and separation of liquid sulfur from unreacted gas is repeated for the second and third reactors at successively lower reactor temperatures. About 5% and 3% of the H2S in the feed gas is thermally converted
into elemental sulfur in the second reactor and third reactors, respectively.
The remaining gas (or tail gas) separated from the last condenser is either burned in an incinerator or further desulfurized in a "tail gas treatment unit" (TGTU).
In a Claus sulfur recovery plant having three catalytic reactors, an overall conversion of at least 98% can be achieved.
In fact, the latest modern designs can achieve up to 99.8% conversion of hydrogen sulfide into product sulfur that is 99+% saleable "bright yellow sulfur".
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CLAUS PROCESS: PROCESS FLOW DIAGRAM
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CLAUS PROCESS: REHEAT METHODS
The various methods used for the reheating required upstream of each catalytic reactor include: Direct gas-fired heaters using fuel gas and
designed to operate at sub-stoichiometric conditions to prevent any oxygen (O2) from getting into the reactors which can damage the catalyst.
Gas-to-gas heat exchangers in which cooled gas from a condenser exhanges heat with the hot gas from the upstream reactor.
Steam-to gas heat exchangers in which the cooled gas from a condenser is heated with high-pressure steam.
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CLAUS PROCESS: OTHER DESIGN FEATRUES Older Claus sulfur recovery units were designed using only two
catalytic reactors. Such units will typically convert only about 97% of the H2S in the
feed gas. Because of stringent environmental regulatory requirements in
the United States as well as many other nations, many of those older units have been upgraded to include three reactors.
The tail gas from those that have not been upgraded is very probably desulfurized further in a tail gas treatment unit.
When the feed gas to a Claus unit includes ammonia and hydrocarbons (such as in the overhead gas from a petroleum refinery sour water stripper), special designs of the reaction furnace burner are available to provide complete combustion of those feed gas components.
To obtain higher reaction furnace temperatures and/or reduce the gas volume to be processed, pure oxygen may be used to enrich the reaction furnace combustion air.
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CLAUS PROCESS: CATALYST The catalytic reactors each contain a bed of catalyst (porous
aluminum oxide (Al2O3) or also referred as alumina) with a depth of about 90 to 120 cm.
The catalyst not only increases the kinetics (i.e., the rate of reaction) of the Claus reaction equation (1), but it also hydrolyzes the carbonyl sulfide (COS) and carbon disulfide (CS2) that is formed in the reaction furnace:
COS + H20 → H2S + CO2 (4)
CS2 + 2H20 → 2H2S + CO2 (5)
The H2S formed as per the hydrolysis equations (4) and (5) is then converted into elemental sulfur as per the Claus reaction (1).
Most of the hydrolysis occurs in the first Claus reactor.
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CLAUS PROCESS: CATALYST
Other Claus catalysts based on titanium dioxide (TiO2) are also used.
The titanium dioxide catalysts are produced from anatase, one of the three naturally occurring mineral forms of titanium dioxide.
Titania catalysts and are said to be more resistant to thermal aging than the alumina catalysts.
They are also said to have a higher activity for the hydrolysis of COS and CS2 which allows the first Claus reactor to operate at lower temperatures compared to alumina catalysts.
However, they are significantly more expensive than the alumina catalysts.
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CLAUS PROCESS: REFERENCES J.H. Gary and G.E. Handwerk(1984), Petroleum Refining Technology
and Economics, 2nd Edition, Marcel Dekker, ISBN 0-8247-7150-8. Fundamental and Practical Aspects of the Claus Sulfur Recovery Proce
ss P.D. Clark, N.I. Dowling and M. Huang, Alberta Sulfur Research Ltd., Calgary, Alberta, Canada
The SuperClaus process Sulfur production report by the United States Geological Survey Gas Processors Suppliers Association(GPSA) (1987), Gas Processors
Suppliers Association Engineering Data Book, 10th Edition, Gas Processors Suppliers Association. (See Volume II, Section 22)
The Role of Claus Catalyst in Sulfur Recovery Unit Performance Terry McHugh, Ed Luinstra and Peter Clark,presented at Sulphur 98 conference in Tucson, Arizona, November 1998.
Arthur Kohl and Richard Nielson (1997), Gas Purification, 5th Edition, Gulf Professional Publishing, ISBN 0-88415-220-0.
Howard F. Rase (2000), Handbook of Commercial Catalysts:Heterogeneous Catalysts, 1st Edition, CRC Press, pp. 240 - 242, ISBN 0-8493-9417-1.
British patent 5,958 (1883)
