Workshop on CCS Mexico City, Thursday, March 29th, 2012

Gasification Technology Hydrogen production Jon Gibbins Professor of Power Plant Engineering and Carbon Capture School of Engineering University of Edinburgh [email protected]

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)

Siemens Fuel Gasifier 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/

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

Second Law criterion for any process:

dG  0

(see above)

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

Second Law constraints on composition for chemical equilibrium in a system at specified pressure and temperature (from C&B, Fig. 15-4, pg 679)

Equilibrium composition depends only on system properties P, T, G so independent of reaction pathways

GASEQ BYCHRIS MORLEY http://www.arcl02.dsl.pipex.com/

Types of Carbon Capture Technology

and hydrocarbon production Hydrocarbon fuels IPCC Special Report on CCS

PRE-COMBUSTION CAPTURE

(IEA GHG www.ieagreen.co.uk) + Sulphur removal

Water gas shift reaction

CO + H2O

CO2 + H2

Extra steam (or water quench)

Jon Gibbins, Imperial College London, New Europe, New Energy. Oxford, 27 Sep 2006

Example of a commercial sour shift catalyst 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

High temperature and low temperature shift

Heat out

Heat out Fuel Steam Oxygen

Gasifier or Autothermal Reformer

HTS

Additional steam / water

LTS

H2 product to final separation

SELEXOLTM PROCESS (UOP 2000) 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 nonaqueous 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. http://www.uop.com/objects/97%20Selexol.pdf

Cleaned gas

http://www.uop.com/objects/97%20Selexol.pdf

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).

CASE

Gasifer

CO2 Shift

CO2 Capture

AGR Process (3)

CO2

CO

N2

H2S

Others (mainly CO, N2)

1.70 1.60 0.72 2.00

0.01 0.01 0.53 0.01

0.16 0.16 0.05 0.31

1.80 1.70 1.25 1.60

0.01 0.65 0.00 0.01

0.31 0.31 0.07 0.31

H2

%vol (molar), dry

A.1 A.2 B.1 B.2 B.3 B.4 C.1 C.2

Shell Shell Shell Shell Shell Shell Texaco Texaco

NO NO Sour Clean Sour Sour NO Sour

NO NO YES YES YES (1) YES NO NO

C.3

Texaco

NO

NO

D.1 D.2 D.3 D.4

Texaco Texaco Texaco Texaco

Sour Sour Sour Sour

YES YES (1) YES (2) YES

Notes

MDEA MDEA Selexol Selexol MDEA Selexol Selexol Selexol MDEA + AGE Selexol Selexol Selexol Selexol

97.98 97.56 98.70 97.51

97.40 97.34 98.05 98.07

0.16 0.67 0.17

0.47 0.63

(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: ELECTRICITY COSTS FOR CAPTURE PLANTS Note high fuel component for gas

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.

Consistent costs here, but lots of variation for actual projects

Natural gas plants

Coal/solid fuel plants

IEA GHG (2006), CO2 capture as a factor in power station investment decisions, Report No. 2006/8, May 2006

COST REDUCTIONS NOT THE SAME AS EFFICIENCY IMPROVEMENTS Cost reduction Efficiency improvement 0.00%

5.00%

10.00%

15.00%

20.00%

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

David Gray, Salvatore Salerno, Glen Tomlinson, Current and Future IGCC Technologies: Bituminous Coal to Power. Mitretek Technical Report MTR-2004-05, August 2004

25.00%

COST REDUCTIONS NOT THE SAME AS EFFICIENCY IMPROVEMENTS Cost reduction Efficiency improvement

EXAMPLE IS GASIFICATION BUT 0.00% 5.00% 10.00% RELIABILITY 75% to 85% load factor AVAILABILITY 95% to 98% fuel conversion MAINTAINABILITY Two stage gasification OPERABILITY Wet to dry feed FB advanced gas turbine (vs F) ARE WHAT MATTER FOR ALL Advanced POWER PLANTS gas cleaning

15.00%

20.00%

Ion Transfer Membrane vs Cryogenic Oxygen Plant 85% to 90% load factor H ultra-advanced gas turbine (vs. FB) SOFC+turbine hybrid cycle

David Gray, Salvatore Salerno, Glen Tomlinson, Current and Future IGCC Technologies: Bituminous Coal to Power. Mitretek Technical Report MTR-2004-05, August 2004

25.00%

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