Coal Gasification Research, Development andDemonstration - Needs and Opportunities

Neville Holt - EPRI

San Francisco, CaliforniaOctober 10, 2001

Coal Gasification RD&D Needs

Background

• Global climate is the key issue affecting energy strategy, policy and technology development.

• If CO2 emissions related legislation is enacted, there would be upward pressure on the price of natural gas and electricity produced from it.

• If CO2 removal is required, IGCC is the preferred coal technology and competes with NGCC at NG price > $4.50/MBtu.

• If the use of carbonaceous liquid transportation fuels is also to be curtailed, this implies power and hydrogen as the two energy carriers, and gasification as a key technology, if coal is to be retained in the energy portfolio.

Gasification RD&D NeedsIGCC Key Areas

• Air Separation Unit (ASU)

• Coal Feeding at High Pressure

• Entrained Gasifier Design

• Fluid Bed Gasification

• Syngas Coolers (SGC)

• Hot Gas Filters

• Desulfurization

• Gas Separation Membranes

• Mercury etc. Removal

• ATS Gas Turbines

• Advanced Power Cycles (FC etc.)

Air Separation Units - RD&D Needs

• Reduce auxiliary power consumption

- Coordinated control for partial ASU/GT integration

• HP O2 supply for IGCC with CO2 removal - HP O2 compressor + 100 bar ( 1450 psi)

- Liquid O2 pump (tradeoff with LOX production)

• ITM ASU preliminary estimate of IGCC cost reduction of 100 $/kW and heat rate reduction of 200 Btu/kWh

- What is the best use of the hot vitiated air?

Coal Feed to Gasification -RD&D Needs

• Coal Pump• Coal/Water slurry heating. Better atomization and vaporization

• Lock hopper systems problematic at HP

• New concepts using slurry pumping to achieve HP- Slurry flash with cyclone underflow to gasifier and flashed steam added to raw gas for shift

- Evaporate slurry with gasifier raw gas, cyclone and filter catch fed to gasifier. (See BI-GAS, HRL IDGCC and van der Burgt/KEMA/EPRI OGCC).

• Coal in liquid CO2 slurries either directly or with flash evaporation (EPRI/ADL): water quench for shift etc.

• Re-examine above concepts for IGCC with shift and CO2 removal and particularly for low cost low rank coals.

Coal/Water Slurry Heating,Flashing and Dry Coal Feed

Coal/WaterSlurry Flash

GasifierDryCoal

Filter

N2 or CO2

Slag

Syngas toShift

N2 or CO2

N2 or CO2

Water

Steam/O2

Steam

Coal Gasifier Feed SystemsRD&D Needs

• Texaco gasifier supplied to Olin in West Virginia (1950’s) used flashed slurry feed with fired heater and experienced hot spots, fouling, tar.

• BI-GAS (1980-3) also used flashed slurry with a spray dryer to feed dry.

• Coal should not be heated above plastic deformation temperature

• Can use flashed water for downstream shift, etc.

• OGCC and IDGCC result in high moisture syngas. If desulfurization is required, cooling condenses most water and the energy losses reduce efficiency. Warm gas clean up could avoid such losses.

However, if shift is required, then this moisture is an advantage, and these concepts should be re-examined.

Coal/Water Slurry, Evaporation withGasifier Raw Gas and Dry Coal Feed

Dry Coal

Filter

CO2 or N2

Moist Syngas to Shift etc.

Coal/WaterSlurry

Dry Coal/Char

Slag

CO2 or N2O2

Cyclone

Gasifier

Coal in Liquid CO2 SlurryGasifier Feed

Coal/CO2 Slurry02

Moist Syngasto Shift, etc.

(Alternatively, heat flash andcyclone underflow to gasifier)

Slag

Slag

02

Coal/CO2Slurry

H20

Moist Syngasto Shift, etc.

H20

CO2

Gasifier

Gasifier

Scrubber

Steam

Coal Gasifier Feed SystemsRD&D Needs

Coal/ CO2 Slurries:

• 1982-6 EPRI/ADL 2 inch diameter 280 foot long test loop. Slurry viscosity data up to 88% w/w solids with low rank coals. (Report AP 4849).

(Pipe loop also studied by Southwestern Public Service - now Exel).

• CO2 has latent heat of vaporization ~ 25% that of water.

• Using coal/ CO2 slurry as feed for Texaco gasifier with Texas lignite increases CGE from 67% with coal/water to ~ 83% with coal/ CO2 .

(Report AP 4509)

• However, syngas CO content increases to ~ 60%. If shift is needed for CO2 removal, then quench or partial quench can be used to supply steam.

Selected Data from TexacoIGCC Lignite Study withVarious Feed Systems

Dried LigniteCO2 Slurry Preheated

CaseDescription

Dried LigniteWater Slurry

Raw LigniteWater Slurry

50% Raw LigniteWater Slurry,Skimmed

Case Number 3 8 7 10

Feed Dry Solids %

Molar ratio O2/C

Cold Gas Efficiency % LHV Basis Raw GasCompositionMole%

H2COCO2H2O

66.7% withsteam

88% with CO2 60% 50%

0.417 0.416 0.518 0.589

81.3 83.1 70.0 67.1

31.538.511.417.4

26.559.8

5.96.4

24.130.814.929.0

20.121.217.939.7

Entrained Flow GasifiersRD&D Needs

• Highest cold gas efficiency (CGE) would be a two stage dry coal fed system e.g. O2 blown Mitsubishi or/2 stage Shell, Prenflo, Noell/GSP

• Vertical cylindrical shape preferred for minimum design complexity and for least cost HP design.

• Higher rank, low moisture and low ash coals are preferred by current designs. Higher moisture and ash contents results in lower CGE and high O2 usage, particularly for coal/water slurry fed gasifiers.

- Need to extend range of coals to include abundant low cost rank coals probably with innovative feed systems.

Entrained Flow GasifiersRD&D Needs

Candidate Improved Design FeaturesImprovement/Technology

HP Dry Feed System

Add 2nd Stage

Reduce Gas Recycle

Partial Quench

Fire Tube SGC

Continuous Slag Removal

High Pressure

Other

Shell/Prenflo Texaco Global E-Gas Mitsubishi Noell/GSP

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New Radiant

SGCCylindrical

DesignUseO2

If denominator 1.0 reaction rate 1st orderIf Kr Pr > 1 + Kp Pp reaction rate zero orderAt higher pressures, less likely to be first order.Gasifier sizing typically assumes first order. - Doubling gasifier pressure enables doubling throughput and same gas residence time, but solids residence time is halved.

- If 1st order, the reaction rate is doubled since partial pressure is doubled and compensates for halving the solids residence time.

- If < 1st order, more residence time needed to achieve comparable carbon conversion.

Gasifier Design - Kinetics

Gasification Reactions: C+ H2O CO + H2

C+ CO2 2 CO

Reaction Rate: 1+ Kp Pp + Kr Pr

Ks = KPr

Entrained Gasifer DesignRD&D Needs

• Actual reaction rates not known and size based on pilot experience.

• Slurry reactors need additional time to evaporate water.

• Reaction rate varies inversely with coal rank.

• Petroleum coke reactivity < most bituminous coals.

• Accords with experience e.g. Ube petroleum coke.

• Scale up Montebello Ruhrchemie Cool water satisfactory for bituminous coals. However at Tampa, lower carbon conversion per pass experienced for both Pittsburgh #8 and Illinois #6 coals, than at Cool water.

• Co-gasification of coal and petroleum coke may have advantages for petroleum coke carbon conversion.

Entrained Gasifier DesignRD & D Needs

Surface Area: Coarse slag flows down gasifier wall and is low C Fine slag follows gas path, does not contact wall and is higher C

Ratio: Surface Area ∝ 1 Gasifier Volume D(Diameter)

So at same L/D a 12 foot D gasifier has Surface/Volume ratio 25% that for a 3 foot D gasifer and less surface is available per unit of coal fed for slag flow.

Therefore, as diameter increases ratio of coarse slag to fine slag decreases and overallcarbon conversion per pass also decreases.

Solutions: Increase L/D Increase Volume } or both

Increase Temperature (trade off with Refractory Life)

Fluid Bed Gasification RD&D Needs

• China and India plan to use their domestic coals for power, however most of these are high ash content with ash fusion temperatures unsuitable for current commercial entrained gasifiers.

• Fluid beds can be designed for such coals and also for U.S. low cost low rank coals. They are also more suitable than entrained gasifiers for processing wood, biomass and wastes.

The world needs commercially viable fluid bed gasification.

• Bubbling bed designs (KRW, ‘U’ Gas) do not appear economically competitive, however, the ash-agglomeration aspect is desirable to obtain higher carbon conversion.

• Circulating fluid beds are being developed but have limited pilot scale experience (except HT Winkler).

• HT Winkler IGCC planned at Vresova, Czech Republic.

Fluid Bed Gasification RD&D Needs

• Existing lock hopper feed systems are seldom truly continuous, and for high pressure some of the previously described slurry systems could be used for high pressures.

• Circulating or fast fluid (transport) designs are preferred over bubbling bed to reduce vessel diameter and cost.

• KBR transport gasifier at DOE PSDF looks very promising. The fine grind and high circulation should give high carbon conversion at reasonable temperatures.

Needs: - Establish attainable carbon conversion for various feeds. Does it need unconverted char

combustion? - Develop scale-up plan (locate at existing coal plant?)

• Foster Wheeler GFBCC has circulating fluid bed partial gasifier with char burnt in AFBC that also acts as HRSG for the syngas fired gas turbine.

Small unit at Livingston, NJ under Vision 21.

Syngas Cooling - RD&D Needs

Syngas Cooling

• Fire tube much lower cost than water tube.

• Improved materials for superheated steam production in SGC’s would improve steam cycle.

• Alternatively higher temperature materials could enable hot raw gas/clean gas heat exchange to put more energy into the Brayton Cycle.

• If shift is required partial quench slurry feed evaporation can provide steamin situ.

Syngas Clean Up RD&D Needs

Hot Gas Filtration

• Temperature < 1200° F is necessary to avoid alkali vapor but probably < 1000° F would be preferred to eliminate unreliable refractory lined piping and to have a viable gas turbine fuel control valve.

• Current practice 600-700° F at Wabash and Berrenath.

• Need more higher temperature experience on candidate materials from the DOE PSDF test program.

Candle life, solids bridging, fouling and corrosion of metallic components are issues that need more development and exposure time.

• Hot gas filtration is the key enabling technology if hot gas separation membranes areto succeed.

Hot Gas Separation RD&D Needs

Hot Gas Desulfurization

• Despite considerable R&D low cost attrition resistant sorbent has yet to be identified.

• RTI membrane at 400-500° F, if successfully developed, could enable desulfurization of moist syngas from low cost quench gasification without loss of energy and mass through condensation.

• However, removal of other species also needs to be accomplished prior to gas turbine- Ammonia (SCO? SCR?)

- Chloride ( Carbonate? Quench OK?) - Mercury and other trace metals

Membrane Separations for H2

• Effect of trace components on membrane materials

• If H2 at atmospheric pressure this maybe ok for H2 as by-product, but is unlikely to be economic for H2 as fuel for IGCC.

Mercury and other PBT’s RD&DNeeds

• EPA plans Mercury regulations for coal plants.

• Eastman reports 90-95% mercury removal from syngas at Kingsport, TN, using pre-sulfided activated carbon beds at system pressure (~900 psi) and 30° C.

Should be fairly low cost effective method.

• Need additional information on Mercury and other trace element speciation.

- From different upstream syngas processing

- Different sorbents

- Measure capture of other potential Persistent Bio-accumulated Toxins (PBTs) such as As, Se, Col, Pb, etc.

Advanced Turbine Systems(ATS) RD&D Needs

• First models built for the natural gas application alone and when evaluated for IGCC only offer very modest improvements over current (F) designs.

• Need modifications to the compressor/turbine match to enable full advantage to be taken of the ATS high temperature high efficiency features for the IGCC application.

• Additional combustion and other system testing for syngas and H2 firing may be needed to achieve the ultra low NOx emission levels that are under consideration by some environmental jurisdictions.

Advanced Power SystemsRD&D Needs

• HAT type cycles integrate well with lower cost quench gasification, where low level heat can be used to provide additional energy to the gas turbine Brayton cycle.

The equipment uses standard type components. How can this be further developed?

• Siemens-Westinghouse propose Solid Oxide Fuel Cell (SOFC) with ITM type process on anode gas to complete fuel oxidation and yield CO2 + H2O. Can enable use of clean syngas (or natural gas) to produce pure CO2 without need for shift and prior CO2 removal and attendant energy losses.

• Clean Energy Systems proposed O2 fired rocket engine that could also use clean syngas to produce a pure CO2 stream. Challenges are the rocket engine development and materials for high temperature steam environment and high cost ofthe ASU.

Gasification Supporting Studies RD&D Needs

• Materials Development - SGC, filter candles, gasifier refractory, gas separation membranes.

• Computational Fluid Dynamic (CFD), modeling for new or proposed modifications to gasifier designs.

• Engineering Economic Evaluations of the competing alternativeIGCC improvements for RD&D planning.

Proposed New Coal Projects

•The EPRI Roadmap and DOE’s Vision 21 envisage future power plants or powerplexes based on the gasification of coal ( as the most abundant fossil fuel) and other carbonaceous feedstocks to produce electricity for the grid, hydrogen for transportation fuels and distributed generation and CO2 for use or sequestration. Three new projects are proposed:

– CO2 Capture and Sequestration Regional Test Centers

– Coal use in refineries

– Phased IGCC construction allowing for subsequent CO2 removal and hydrogen production.