gas to liquid process with heat integration

Gas To Liquid Technology

-A Simulation Case Study in Hysis with heat integration

Subhasish MitraM.TechDepartment of Chemical EngineeringIIT Kanpur

Brief Introduction:

� Of late, serious need is felt for producing cleaner fuel on sustainable basis.

� Natural gas : Natural choice over depleting oil resources being more green however most of the natural gas reserves are economically stranded.

� GTL technology:

The key concept is chemical conversion of natural gas to longer chain hydrocarbons that typically remain in the range of middle distillate i.e. transportation fuel.

Process steps:

GTL process consists of four basic steps:

• Treatment of natural gas to remove water and impurities if required.

• Reforming of the natural gas to produce syn-gas.

• Fischer-Tropsch conversion to produce desired long chain hydrocarbon liquids.

• Upgrading to produce finished products.

Process Flow Diagram

-Main Process Sections: [1]

[1] US patent US6,172,124B1, Wolflick et al, Jan 9, 2001

GTG

Separator section

Furnace

Synthesis gas reactor

Air Compr

FT reactor

Process Flow Diagram

-Main Process Sections: [1]

[1] US patent US6,172,124B1, Wolflick et al, Jan 9, 2001

GTG

Separator section

Furnace

Synthesis gas reactor

Air Compr

FT reactor

Process Flow Diagram

-Energy Integration Sections: [1]

[1] US patent US6,172,124B1, Wolflick et al, Jan 9, 2001

Integration loop-2

Integration loop -1

Integration loop-3

Integration loop-4

Novelty in the invention:[1]

� Substantial amount of heat generated in the process is recovered through an efficient heat integration system for use in generating steam required for the process or for conversion into mechanical energy.

� Tail gas produced by the process is used internally as fuel gas for combustion purpses.

� Air is used instead of pure oxygen which eliminates requirement of Air-Separation plant.

[1] US patent US6,172,124B1, Wolflick et al, Jan 9, 2001

Typical Reactions:

Auto-thermal Reaction:

� 2CH4 + H2O + 0.5O2 � 5H2 + 2CO

� 2CH4 + 2H2O + O2 � 6H2 + 2CO2

Water Gas Shift Reaction (HTS & LTS)

� CO + H2O � H2 + CO2

Combustion Reaction:

� CxHy + z(x+y/4)O2 � xCO2 + (y/2)H2O

� CxHy + z(x/2+y/4)O2 � zxCO + (z.y/2)H2O

FT reaction product distribution: [2]

[2] www.fischer-tropsch.org/primary_documents/presentations/acs2001_chicago/chic_slide04.htm

FT reaction product distribution: [3]

[3] Simulation, integration and economic analysis of gas-to-liquid process. Buping Bao, M.M.El-Halwagi, Nimir.O.Elbashir, Fuel Processing Technology, 2010 (in press)

Chain growth probability factor Alpha = 0.95

Modeling Strategy:

Process Simulator:

Hysys Version: V7

Thermodynamic models:

Vapor phase : Peng-Robinson EOS

Unit operations:

Turbine driven compressor : Compressor + Gibbs reactor + expander

Simulation strategy (Contd):

� Sulfur removal bed : Component Splitter

� Furnace : Fired heater

� ATR : Gibbs reactor

� Heater/Cooler : 2 stream heat exchanger

� FT reactor : Conversion Reactor along with 3 phase separator.

Chain growth probability factor : 0.95, Carbon chain length : C1 – C30. No of Rxn : 30

Simulation Process Flow Diagram – Gas Turbine Section

CompressorCombustor

Turbine

Power generation

Simulation Process Flow Diagram – Air Compression Section

Process Simulation Flow sheet – Overall Plant:

Heat integration primary loop

Heat integration secondary loop

Simulation Figures:

� Natural Gas Feed Rate : 100 MMSCFD

� Product rate : 9845 bbl/day

� Gasoline fraction (C5 – C12): 23.6 wt%

� Diesel fraction (C13 – C18): 19.2 wt%

� Wax fraction (C19 – C30): 57.3 wt%

� Water out from the process : 10190 kmol/hr ~ 185m3/hr

Simulation Figures (Contd.)

� Natural gas to Air Ratio : 0.85

� Natural gas to steam ratio : 2.12

� Sulfur content in natural gas: 982 ppm

� ATR reaction condition: 18050F & 535 psi, H2/CO : 3.48

� FT reaction condition : 4150F & 34 psi

� Fired heater furnace :

Flue gas temp : 90 – 100 deg C

CO content in flue gas : Nil

Energy Recovery Summary - Power:

Power generation source Available Heat Content MW

Power generated (MW)

GT exhaust heat stream 9.65 3.1

FT product stream 178.5 94.96

Tail gas recovery from FT product 117 15.45

Heat extracted from GT exhaust, ATR and FTR product stream utilized through heat integrated system to generate steam and power.

Steam generation source kmol/hr

E-31 10910

Energy Recovery Summary – Tail gas:

Tail gas consumers Kmol/hr

GT combustor 482

Fired heater FH-26 894

Steam Boiler - 64 3600

Steam Super-heater - 65 1100

Tail Gas Source Generation rate (Kmol/hr)

Internal consumption(Kmol/hr)

LHV (MJ/m3)

SEP 42A,B,E 10580 6071 7.68

SEP 42C,D,F,G 12 0 13.1

Tail gas recovery : 57.4%

Balance tail gas can be sold out to adjacent facility.

Cooling duty requirement:

Cooling consumers

MW

GTG Condenser E-101

12.98

Process Air Compressor inter-stage coolers

5.81

FT product cooler (C-41)

58.33

K66 turbine exhaust cooler

271.2

Total CW duty requirement

348.32 MW

Summary:

� A GTL plant simulation study is carried out based on the flow scheme obtained from Ref 1.

� The simulation is done for 100 mmscfd natural gas feed rate which produces 9845 bbl/day syn-fuel.

� Heat integration results into 113.5 MW power generation along with complete steam requirement for the process.

� ~57% tail gas utilized as fuel gas in the process itself. Balance gas can be sold out to any adjacent facility.

� Water generated by the process can be used for cooling water make up in the process itself.

Thanks

for

your attention!