Gasification Technology
Hydrogen production
Workshop on CCS
Mexico City, Thursday, March 29th, 2012
Jon Gibbins
Professor of Power Plant Engineering and Carbon Capture
School of Engineering
University of Edinburgh
High temperature entrained flow gasifiers (vs. other gasifiers)
for turning complex solids (and liquids) into simple gases
• Pressure and fuel feeding
• Feeding – solids vs liquids, making solids into liquids
• Mineral matter/Ash – just get hot!
• Tar – just get hot!
•Temperature – getting it and containing it – refractory vs. membrane wall
• Oxygen consumption (slurry/dry feed)
• Char conversion – mixing – axial or opposed burners
Chemical equilibrium – water gas shift reaction
Adiabatic reactor modelling – GASEQ
Water gas shift for hydrogen production
Acid gas removal – CO2 purity
GASIFIER TYPES
(Modified (in red), from Tavoulareas and Charpentier, 1995)
E. Rensfelt & D. Everard, Update on Project ARBRE, Seminar on Power Prod’n from Biomass , Espoo, 1998
(also see www.tps.se)
Rensfelt, 1998
E. Rensfelt, Atmospheric CFB gasification, Int. Conf. On Gasification and Pyrolysis of Biomass, Stuttgart, 1997
Rensfelt, 1998
Rensfelt, 1998
GE gasifier Coal slurry feed
SHELL
GASIFICATION
PROCESS (Shell Brochure, 1989)
http://www.powergeneration.siemens.com/products-solutions-services/products-packages/fuel-gasifiers/
Siemens Fuel Gasifier
http://www.powergeneration.siemens.com/products-solutions-services/products-packages/fuel-gasifiers/
Siemens Fuel
Gasifier
ECUST Gasifier
http://www.chinainvestsinamerica.com/files/China-US%20Clean%20Energy%20Seminar/Coal%20Gasification%20Technology%20in%20China(en).pdf
CHEMICAL ENERGY AND THE SECOND LAW
Criterion for chemical equilibrium
If all reaction rates are fast compared to the time available then after
a period of time the composition of an isolated system of reacting
species would reach some constant value for a given pressure and
temperature- it would be in chemical equilibrium (and pressure and
thermal equilibrium).
Reaction rates at elevated temperatures (say >1000K) are often high
enough for a close approach to chemical equilibrium in many
engineering applications.
What would affect the equilibrium composition?
Conservation of mass / elements
First Law (displacement work only) dQ - P.dV = dU
Second Law ?
Second Law criterion for equilibrium of adiabatic system dSsys ≥ dQ / T ANY system must always obey the Clausius inequality
as its composition changes For an adiabatic system: dQ = 0 dSsys ≥ 0 Reactions proceed as far as they can in direction of increasing entropy. Chemical equilibrium for an adiabatic system when dS = 0 (or 100% conversion).
Second Law constraints on
composition for chemical reactions in
an adiabatic system (from C&B, Fig. 15-2, pg 678)
(but not all systems are adiabatic…..)
Chemical equilibrium for system at specified P & T ANY system must always obey the Clausius
inequality as its composition changes dS ≥ dQ / T AND the First Law dQ – dW = dU or dQ - P.dV = dU
hence dQ = dU + P.dV Combining and rearranging: dU + P.dV - T.dS 0 Can calculate all system properties above if P, T and composition known.
Define Gibbs function G = H - T.S
(combination of properties so also property) dG = dH - T.dS - S.dT (but H = U + PV by definition): = dU + P.dV + V.dP - T.dS - S.dT but if P & T specified, dP and dT are zero: dG = dU + P.dV - T.dS (see above)
Second Law criterion for any process: dG 0 at specified P & T
At specified temperature and pressure reactions proceed as far as they can
in direction of decreasing Gibbs function.
Chemical equilibrium when dG = 0 (or may look like 100% conversion).
Chemical equilibrium for system at specified P & T
Equilibrium composition depends only on system properties
P, T, G
so independent of reaction pathways
Second Law constraints on
composition for chemical equilibrium
in a system at specified pressure and
temperature
(from C&B, Fig. 15-4, pg 679)
GASEQ BYCHRIS MORLEY http://www.arcl02.dsl.pipex.com/
IPCC Special Report on CCS
Hydrocarbon fuels
Types of Carbon Capture Technology
and hydrocarbon
production
PRE-COMBUSTION CAPTURE (IEA GHG www.ieagreen.co.uk)
Extra steam
(or water quench)
Jon Gibbins, Imperial College London, New Europe, New Energy. Oxford, 27 Sep 2006
+ Sulphur
removal CO + H2O CO2 + H2
Water gas shift reaction
http://www.topsoe.com/Business_areas/Gasification-based/Processes/Sour_shift.aspx
Topsoe's sulphur tolerant water gas shift technology (sour shift) is used after the
gasifier to convert part of the CO to H2. The shift conversion is adjusted to match
the required CO/H2 ratio, depending on the end product.
The sour shift catalyst requires a certain minimum of sulphur in the feed gas to
maintain its high activity.
Features
The features of the sour shift reaction include:
flexible layout of the sour shift section due to a broad range of temperature
and steam to carbon monoxide ratios
the sour shift catalyst allows operation at lower steam to carbon monoxide
ratios than conventional high temperature shift catalysts resulting in lower
steam consumption
high catalyst flexibility allows the use of adiabatic beds which are easy to
operate and cost-efficient
Example of a commercial sour shift catalyst
High temperature and low temperature shift
Gasifier or
Autothermal
Reformer
HTS
Heat out
LTS
Heat out
Additional
steam / water
H2 product to
final separation
Fuel Steam
Oxygen
The Selexol process uses a physical solvent to remove acid gas from streams of
synthetic or natural gas. The process may be regenerated either thermally, by
flashing, or by stripping gas. The Selexol process is ideally suited for the selective
removal of H2S and other sulfur compounds, or for the bulk removal of CO2.
The Selexol process uses Union Carbide’s Selexol solvent, a physical solvent made
of a dimethyl ether of polyethylene glycol. The Selexol solvent is chemically inert and
is not subject to degradation.
The Selexol process also removes COS, mercaptans, ammonia, HCN and metal
carbonyls. A variety of flow schemes permit process optimization and energy
reduction.
The Selexol process allows for construction of mostly carbon steel due to its non-
aqueous nature and inert chemical characteristics.
Acid gas partial pressure is the key driving force for the Selexol process. Typical feed
conditions range between 300 and 2000 psia with acid gas composition (CO2 + H2S)
from 5% to more than 60% by volume. The product specifications achievable depend
on the application and can be anywhere from ppmv up to percent levels of acid gas.
SELEXOLTM PROCESS (UOP 2000)
http://www.uop.com/objects/97%20Selexol.pdf
http://www.uop.com/objects/97%20Selexol.pdf
Cleaned gas
CASE Gasifer CO2 Shift
CO2 Capture
AGR Process
(3) CO2 CO N2 H2 H2S
Others (mainly CO, N2)
%vol (molar), dry
A.1 Shell NO NO MDEA
A.2 Shell NO NO MDEA
B.1 Shell Sour YES Selexol 97.98 0.16 1.70 0.01 0.16
B.2 Shell Clean YES Selexol 97.56 0.67 1.60 0.01 0.16
B.3 Shell Sour YES (1) MDEA 98.70 0.72 0.53 0.05
B.4 Shell Sour YES Selexol 97.51 0.17 2.00 0.01 0.31
C.1 Texaco NO NO Selexol
C.2 Texaco Sour NO Selexol
C.3 Texaco NO NO MDEA +
AGE
D.1 Texaco Sour YES Selexol 97.40 0.47 1.80 0.01 0.31
D.2 Texaco Sour YES (1) Selexol 97.34 1.70 0.65 0.31
D.3 Texaco Sour YES (2) Selexol 98.05 0.63 1.25 0.00 0.07
D.4 Texaco Sour YES Selexol 98.07 1.60 0.01 0.31
Estimated CO2 impurity levels from IGCC plants, based on IEA GHG Report PH4/19, Potential for improvement in gasification combined cycle power generation with CO2 capture
(see www.ieagreen.org.uk for further details).
Notes (1) Combined removal of CO2 and H2S , (2) Lower Capture rate
(3) AGR is acid gas (CO2, H2S) removal, MDEA is MethylDiEthanolAmine (chemical solvent); Selexol is
polyethylene glycol dimethylether (physical solvent), AGE is Acid Gas Enrichment (installation downstream
AGR of another MDEA washing)
IEA GHG (2006), CO2 capture as a factor in power station investment decisions, Report No. 2006/8, May 2006
Costs include compression to 110 bar but not storage and transport costs.
These are very site-specific, but indicative aquifer storage costs of
$10/tonne CO2 would increase electricity costs for natural gas plants by
about 0.4 c/kWh and for coal plants by about 0.8 c/kWh.
Natural gas plants Coal/solid fuel plants
IEA GHG: ELECTRICITY
COSTS FOR CAPTURE PLANTS
Note high fuel component for gas
Consistent costs here, but lots of variation for actual projects
0.00% 5.00% 10.00% 15.00% 20.00% 25.00%
75% to 85% load factor
95% to 98% fuel conversion
Two stage gasification
Wet to dry feed
FB advanced gas turbine (vs F)
Advanced gas cleaning
Ion Transfer Membrane vs Cryogenic Oxygen Plant
85% to 90% load factor
H ultra-advanced gas turbine (vs. FB)
SOFC+turbine hybrid cycle
Cost reduction
Efficiency improvement
David Gray, Salvatore Salerno, Glen Tomlinson, Current and Future IGCC Technologies: Bituminous
Coal to Power. Mitretek Technical Report MTR-2004-05, August 2004
COST REDUCTIONS NOT THE SAME
AS EFFICIENCY IMPROVEMENTS
0.00% 5.00% 10.00% 15.00% 20.00% 25.00%
75% to 85% load factor
95% to 98% fuel conversion
Two stage gasification
Wet to dry feed
FB advanced gas turbine (vs F)
Advanced gas cleaning
Ion Transfer Membrane vs Cryogenic Oxygen Plant
85% to 90% load factor
H ultra-advanced gas turbine (vs. FB)
SOFC+turbine hybrid cycle
Cost reduction
Efficiency improvement
David Gray, Salvatore Salerno, Glen Tomlinson, Current and Future IGCC Technologies: Bituminous
Coal to Power. Mitretek Technical Report MTR-2004-05, August 2004
COST REDUCTIONS NOT THE SAME
AS EFFICIENCY IMPROVEMENTS
EXAMPLE IS GASIFICATION BUT
RELIABILITY
AVAILABILITY
MAINTAINABILITY
OPERABILITY
ARE WHAT MATTER FOR
ALL POWER PLANTS
CONCLUSIONS
• Entrained flow gasifiers use temperature to tackle tar and
ash removal problems
• Many variations of entrained flow gasifier, and still
developing
• Variety of fuels, tradeoff between cost and performance
• Chemical equilibrium gives a good idea of gasifier
performance (but quench complicates final composition)
• Sour shift coming into use for IGCC + CCS
• Extra steam needed for shift (or can get clever – combined
membrane/shift or intermediate CO2 removal)
• Physical solvents for acid gas removal, combined or
separate – geological storage and regulations decide
• No clear winner for coal with CCS (yet)
• Cost improvements not necessarily efficiency improvements
• Reliability, Availability, Maintainability, Operability
