DOE/MC/2 1023-96/C0559

Second Generation PFB for Advanced Power Generation

Authors:

A. Robertson J. Van Hook

Con tractor:

Foster Wheeler Development Corporation 12 Peach Tree Hill Road Livingston, New Jersey 07039

Contract Number:

DE-AC2 1 -86MC2 1 023

Conference Title:

1 1 th U.S .-Korea Joint Workshop

Conference Location:

Pittsburgh, Pennsylvania

Conference Dates:

October 1-6, 1995

Conference Sponsor:

Pittsburgh Energy Technology Center

DISCLAIMER

This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manu- facturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.

This report has been reproduced directly from the best available COPY.

Available to DOE and DOE contractors from the Office of Scientific and Technical Information, 175 Oak Ridge Turnpike, Oak Ridge, TN 37831; prices available at (615) 576-8401.

Available to the public from the National Technical Information Service, U.S. Department of Commerce, 5285 Port Royal Road, Springfield, VA 22161; phone orders accepted at (703) 487-4650.

DISCLAIMER

Portions of this document may be illegible electronic image products. Images are produced from the best available original document.

SECOND-GENERATION PFB FOR ADVANCED POWER GENERATION

A. Robertson J. Van Hook

Foster Wheeler D eve1 o prn ent Corporation Livingston, New Jersey, USA

Abstract

Research is being conducted under a United States Department of Energy (USDOE) contract to develop a new type of coal-fueled plant for electric power generation. This new type of plant-called an advanced or second-generation pressurized fluidized bed combustion (APFBC) plant4ffers the promise of 45-percent efficiency (HHV), with emissions and a cost of electricity that are sigdicantly lower than

APFBC Technology

Foster Wheeler Development Corporation (FWDC) is leading a team of companies in the development of advanced or second-generation pressurized fluidized bed combustion (APFBC) technology. The work is being conducted under United States Department of Energy (USDOE) Contract DE-AC2 1-86MC21023 by Foster Wheeler Development Corporation; Foster Wheeler Energy Corporation; Foster Wheeler USA Corporation; GilbertKommonwealth, Inc.; Institute of Gas Technology; Westinghouse Power Generation Business Unit; and Westinghouse Science and Technology Center.

APFBC Technology will enable coal-fired power plants to generate electricity with an efficiency greater than 45 percent, based on the higher heating value of the coal. Compared with

conventional pulverized-coal-fired plants with scrubbers. This paper summarizes the pilot plant R&D work being conducted to develop this new type of plant. Although pilot plant testing is still underway, preliminary estimates indicate the commercial plant will perform better than originally envisioned. Efficiencies greater than 46 percent are now being predicted.

conventional pulverized-coal-fired plants incorporating wet flue gas desulfurization, APFBC plants are projected to have a 20- percent-lower cost of electricity and lower stack gas emissions. Figure 1 is a simplified process block diagram of an APFBC plant.

In the plant coal is fed to a pressurized carbonizer that produces a low-Btu &el gas and char. After passing through a cyclone and ceramic candle filter to remove gas-entrained particulates and a packed bed of emathelite pellets to remove alkali vapors, the fuel gas is burned in a topping combustor to produce the energy required to drive a gas turbine. The gas turbine drives a generator and a compressor that feeds air to the carbonizer, a circulating pressurized fluidized bed combustor (CPFBC)

and a fluidized bed heat exchanger (FBHE). The carbonizer char is burned in the CPFBC with high excess air.

The vitiated air from the CPFBC supports combustion of the fuel gas in the topping combustor. Steam generated in a heat-recovery steam generator (HRSG) downstream of the gas turbine and in the FBHE associated with the CPFBC drives the steam turbine generator that furnishes the balance of electric power delivered by the plant.

The low-Btu gas is produced in the carbonizer by pyrolysishild devolatilization of coal in a fluidized bed reactor. Because this unit operates at temperatures much lower than gasifiers currently under development, it also produces a char residue. Left untreated, the fuel gas will contain hydrogen sulfide and sufircontaining tar/light oil vapors. Therefore, lime-based sorbents are injected into the carbonizer to catalytically enhance tar cracking and to capture sulfur as calcium sulfide. Sulfur is captured in situ, and the raw fuel gas is fired hot. Thus the expensive, complex fuel gas heat exchangers and chemical or sulfurcapturing cleanup systems that are part of the coal-gasification, combined- cycle plants now being developed are eliminated.

The char and calcium sulfide produced in the carbonizer and contained in the fuel gas as elutriated particles are captured by high- temperature ceramic candle filters, rendering the fuel gas essentially particulate-free and able to meet New Source Performance Standards (NSPS). The captured material, with carbonizer bed drains, is collected in a central hopper and injected into the CPFBC through a nitrogen- aerated, nonmechanical valve. The high excess air in the combustor transforms the calcium sulfide to sulfate, allowing its disposai with the normal CPFBC spent sorbent.

In the CPFBC the burning char heats the high- excess-air flue gas to 1600OF; any surplus heat is transferred to the FBHE by the recirculation of solids (sorbent and coal fly ash) between the units. Controlled recirculation is accomplished

with cyclone separators and nonmechanical valves. The FBHE contains tube surfaces that cool the circulating solids. As a result of the low fluidizing velocity in the FBHE ( ?4 Ns), the risk of tube erosion is virtually eliminated.

The exhaust gases leaving the carbonizer and the CPFBC contain sorbent and fly-ash particles-both of which can erode and foul downstream equipment. A hot-gas cleanup (HGCU) system, consisting of ceramic barrier filters preceded by cyclone separators, cleans the gases to e20 ppm solids loading before they enter the fuel-gas topping combustor and the gas turbine, preventing erosion and fouling. Ceramic cross-flow filters, screenless granular-bed filters and others are candidate alternatives for the candle filters, should their performance and economics be found superior. All these devices are currently under development for first- generation PFB combustion plants. They should also be applicable to the APFBC plant.

The topping combustor, which consists of metallic-wall multiannular swirl burners (MASBs), will be provided in two external combustion assemblies (topping combustors) on opposite sides of the gas turbine. Each MASB contains a series of swirlers that aerodynamically create fuel-rich, quickquench and fuel-lean zones to minimize NO, formation during the topping combustion process. The swirlers also provide a thick layer of air at the wall boundary to control the temperature of the metallic walls.

Our USDOE contract is divided into three phases, the first two of which are essentially complete. In Phase 1 we prepared a conceptual design of an APFBC plant, determined its economics and formulated an R&D program plan for the development of this new technology. In Phase 2 the key components of this new plant were tested separately at the pilot-plant scale to determine their individual performance characteristics. In Phase 3, which is underway, key components of this plant are being operated as an integrated subsystem to investigate, at a slightly larger pilot-plant scale, performance and integration characteristics.

The move to commercialization of this new type of plant involves the five steps shown in Figure 2. Starting from the left and moving to the right, each succeeding step involves increased integration of components and increased plant size/complexi~. In the first stepphase 2 of our USDOE contract-the key components of this new type of plant were tested separately. These Phase 2 tests involved testing (1) a 10-inch- diameter carbonLzer (Figure 3) with a cyclone and ceramic barrier filter; (2) an 8-inchdiameter CPFBC (Figure 4) with a cyclone and ceramic barrier filter and (3) 12-inch- , 14-inch- and 18- inch-diameter MASBs (Figure 5).

The first two test programs were conducted by FWDC at its John Blizard Research Center in Livingston, New Jersey. These programs were successful, and test reports have been released to the National Technical Information Services (NTIS) for publication. The MASB tests were conducted at the University of Tennessee Space Institute at Tullahoma, Tennessee, under the direction of the Westinghouse Power Generation Business Unit. Although a final report has not yet been issued (two additional tests are planned), test results have been presented at previous meetings [1][2][3].

In 1987 we prepared a conceptual design of a 3- percent-sulfur Pittsburgh No. 8 coal-fired, second-generation PFB plant with a conventional 2400 psig/1000"F/1000"F/2-%-in. Hg steam cycle and determined its economics [4]. We estimated that, when operated with a 14- atm/l600"F carbonizer, the plant efficiency would be 44.9 percent (based on the higher heating value of the coal), and its cost of electricity would be 2 1.8 percent lower than that of a conventional pulverized-coal-fired plant. The tests conducted in our Phase 2 pilot-scale carbonizer yielded performance superior to that estimated in 1987. As a result, we now expect a more energetic fuel gas and a plant efficiency of 46.2 percent with a 1600°F carbonizer [5 ] (see Figure 6).

In the second step to commercialization-Phase 3 of our USDOE contract-a carbonizer and

CPFBC, with their respective cyclones and ceramic candle filters, are being interconnected and operated as an integrated subsystem. The FWDC pressurized fluidized bed pilot plant in Livingston, New Jersey, was expanded in 1994 to permit this integrated operation. The new and previously tested units are compared in Figures 3 and 4. The new CPFBC is 13 inches in diameter by 38.3 feet tall and operates at a 2 1R-times- higher throughput than the previous Phase 2 unit. The new carbonizer is actually the previous unit lengthened by a 5-foot-tall spool piece that allows operation with a commercial-scale, 24- footdeep bed height. The hot shakedown of the expanded integrated carbonizer/CPFBC pilot plant is underway.

In Step 3 of Figure 2 a MASB and a gas turbine will be integrated with a carbonizer and CPFBC. This will be the first either has operated with carbonizer fuel gas, as all previous MASB tests used gas mixtures synthesized to the composition predicted by FWDC for a commercial plant. This integration will occur at the Southern Company Services Power Systems Development Facility (PSDF) at Wilsonville, Alabama. This facility is being funded for advanced coal-based power system R&D by the USDOE, the Electric Power Research Institute (EPRI) and industry.

The APFBC process will be tested at the PSDF, and a process-flow diagram is presented in Figure 7. The plant will incorporate a 37-inch- ID CPFBC, an FBHE with two tube-bundle- containing fluidized beds, cyclones and ceramic candle filters, an 18-inch MASB, and an =3MWe gas turbine. For cost savings no steam turbine will be provided, and the FBHE heat absorption will be exhausted to atmosphere via cooling towers, The 18-inch MASB will combust = 1700°F carbonizer fuel gas to raise the = 1600°F CPFBC flue gadvitiated air to 2300°F. The gas turbine, being a relatively small unit, operates with a 1975°F turbine inlet temperature. Compressor discharge air will be injected into the 2300°F MASB exhaust to cool it to 1975"F, allowing commercial plant MASB operation to be demonstrated.

The PSDF will be operated with Illiois No. 6 bituminous and Eagle Butte subbituminous coals. Limestone from Lonpiew, Alabama, will be injected into the APFBC fluidized beds to capture sulfur in situ. Each of these feedstocks has already been successfully tested in the Livingston Phase 2 carbonizer and CPFBC pilot plants. Based on these tests, the 1700°F Wilsonville carbonizer is expected to produce a fuel gas with a 124-Btu/SCF heating value when operating with Illinois No. 6 coal. A gas yield of 3.2 1bAb of coal is expected, and the limestone sulhr- capture efficiency is projected to be 94 percent at a calcium-to-sulfur molar feed ration of 1.75. The detailed performance of the carbonizer is presented in Figure 8. The char-sorbent residue from the carbonizer will be transferred to and burned in the CPFBC. Livingston pilot plant test data shown in Figures 9 and 10 indicate the CPFBC will operate with at least a 99-percent combustion and a 97-percent sulfk-capture efficiency, respectively. The Phase 2 CPFBC was operated with a 12 ft/s gas velocity, and the effectiveness of staged combustion for controlling NO, emissions was investigated. As a result of the low height of the unit (28.5 feet), the gas residence time in the oxidizing zone was less than 1 1/2 seconds. The Phase 3 CPFBC is 38.3 feet tall and, with its higher oxidizing zone residence time, we anticipate NOx emissions will be substantially less than the levels shown in Figure 11.

The Wilsonville APFBC will be commissioned in stages. Beginning in early 1996, the plant will be operated as a first-generation PFB (no carbonizer or topping combustor), with coal being fired in the CPFBC. When the topping combustor is delivered in the second quarter of 1996,

integrated carbonizer/CPFBC operation will begin. With proposed feedstocks and operating conditions having already been tested in Phase 2 and with Wilsonville personnel having witnessed Phase 2 testing and Phase 3 integrated carbonizerKPFBC pilot plant commissioning runs, we anticipate a successful two-year test program.

Step 4 of Figure 2 involves the construction and operation of a complete APFBC plant as the first large-scale demonstration of this technology. Under the USDOE Clean Coal V Demonstration Plant Program, an award has been made to Air Products and Chemicals Inc. to construct and operate such a plant. The plant, entitled The Four Rivers Energy Modernization Project, will be constructed at an Air Products chemicals manufacturing facility in Calvert City, Kentucky. The plant will be a cogeneration facility that will produce 72MWe of electrical power and 190 psia, 420°F process steam at a rate of 3 10,000 Ibsh for use by the manufacturing facility. A Westinghouse 25 1 B 12 combustion turbine, incorporating MASB topping combustion burners, will be used to generate 38MWe of power; the 34MWe balance will be supplied by a steam turbine. The steam load will vary from approximately 250,000 lbsh in the summer to 400,000 lbsh in the winter. If all the steam were expanded through the steam turbine, the plant would generate approximately 95MWe (gross) of power. The plant will be fueled by Kentucky No. 9 bituminous coal injected into the unit as a 75-percent-coaY25-percent-water paste. A dry lockhopper-type feed system will pneumatically inject limestone into the unit to capture the coal's 3 percent sulfkr as calcium sulfate. Figure 12 is a schematic of the plant.

I REFERENCES

1. W. Domeracki, et al. 1994. Development Topping Combustor for Advanced Concept Pressurized Fluidzed Bed Combustion. Proceedings of the Coal-Fired Power Systems 94, M. McDaniel, R. Staubly and V. Venkatarman (ed.), DOE/METC 94/1008.

2. W. Domeracki, et al. 1993. Second-Generation PFBC Systems Research and Development. Proceedings of the Coal-Fired Paver Systems 93, Don Bonk (ed.), DOE/METC 93/6 13 1.

3. W. Domeracki, et al. 1992. Second-Generation PFBC Systems Research and Development. Proceedings of the Ninth Annual Coal-Fueled Heut Engines, Advanced Pressurized Fluidized Combustion and Gas Stream Cleanup Systems Contractors' Review Meeting, DOE/METC

4.

5 .

9316 129.

A. Robertson, et al. 1988. Second-Generation PFB Combustion Plant Performance and Economics. 1988 Seminar on Fluidized-bed Combustion Technology for Utility Applications, Palo Alto, CA.

A. Robertson, et al. 1993. Second-Generation PFBC Systems Research and Development Phase 2, Best Efficiency Approach in Light of Current Data. Proceedings of the Coal-Fired Power Systems 93-Adiances in IGCC and PFBC Review Meeting, Don Bonk (ed.), D O E M T C 93/6 13 1.

GAS TURBINE ' *

ALKALI REMOVAL

STEAM GENERATION

(HRSG)

t PARTICULATE REMOVAL

COAL 111_)) SORBENT

FUEL GAS

:ARBONEATION

I

REMOVAL TURBINE

I I I

PARTICULATE REMOVAL

C I ASH I

FLUE GAS

Fk- COMBUSTION

(CPFBC) ZHAR (CARBONIZER) e n n n m - a n - 3UKDICN I 4

SORBENT I I

AIR ASH

+ I ASH) STEAM

GENERATION (FBHE)

COMPRE~SOR AIR

Figure 1 : Simplified Process Block Diagram-APFBC Combustion Plant ARS6062.PPT

7 Under Way - Future

1 .I -MWe PHASE 3

7-MWe WILSONVILLE

75-MWe DEMONSTRATION

250-MWe COMMERCIAL

1 .I-MWe PHASE 2 I Carbonher/ I

HGCU Car bo n ize r/ I HGCU I

+ I Carbonizerl I

HGCU + +

+ + +

I Top pi n g 1 Combustor I Topping I Combustor + + + I Gas Turbine I I Gas Turbine I

+ +

+ +

I Steam Turbine (L. P./L. T. ) I I Steam Turbine I (H.P./H.T.)

q25 37 q25 45 AR95050.PPT Figure 2: APFBC Plant Development Plan

3 0 O.D. x 39'4'' TALLVESSEL

3 0 O.D. x 34'4" TALLVESSEL

FUEL

GAslI 9'4 3/4

TOP OF BED ! t 19-0"

TOP OF

3 '4 1/4

- 141.D. 'REEBOARD

12" I.D.

IO" I.D.

rEil AIR AND STEAM

COAL, SORBENT t AND AIR

PHASE 2

4 I.D. NOZZLE

ED OVERFLOW

SORBENTANDAIR

PHASE 3

AR95050A.PPT

Figure 3: Carbonizer Comparison

36" D.D. x 44'"" TALL VESSEL

28'-

1

30" OIDI x 34'-6" TALL VESSEL

8' I.D,

SECONDARY AIR

TOP OF DENSE BED

R

I COAL, SORBENT AND AIR

PHASE 2

38'-

CARBONIZER

A J R -

I

I FROM

r- AIR

PASTE u-l 3d:rIR SPARGER

7 ) BED DRAIN , I .

I SURBENT & AIR

PHASE 3

Figure 4: CPFBC Comparison

AR95050B.PPT

Primary Air --, Quen h nd ilution Air F l y

Natural .-.... .........._ Gas “......IU

Low Btu Syngas T Lean Zone Swirler

Cooling A i d

Figure 5: 18-inch-diameter Westinghouse MASB Test Unit

Diffuser

AR95050C.PPT

489 'I CONDENSRTE

265.5 P 9286 u

AR95050D. PPT

............. e.2.- TO ASH I I m.owmwm 75529 I

467.749 I

2682.7 ? 930.8 F 140126 H

4 R 4 l H 5,116.53E Y

AIR IN

1 A

Figure 6: Phase 2-APFBC Commercial Plant Update (46.2% BEP) 1Catml1600"F Carbonizer

38dd 9NllWl

W

)a -4 2127 1930

HHV (Btu/lb) (wet) LHV (Btu/lb) (wot) Moloeulrr Wolght (wet) 24.388 LHV (Btulofia) (wot) 124

LHV (Btu/lb) 10,263 LHV (Btullb) 2386 PFB Release' 10,393 PF6 Release* 2575 . CH, 2.051 1.349

AR95050F. PPT

Skln Heat Loaser = 3665 Btulh

Figure 8: Wilsonville 1700°F Carbonizer Performance with Illinois No. 6 Coal

.Sulfur Caplurrd .I 94.0% 88a8Od On 8UlfUf IOlOO8Od, CrlS 2.29 e---- -- -----__ ---

100

99.5 . o 0'

>; t w 0 lL

0 99

- - 98.5

z 0 F u) 98 3 rn 2 0

97.5

97 1500

AR95050G.PPT

1550 1600 1650 BED TEMPERATURE, "F

Figure 9: Phase 2 CPFBC Combustion Efficiencies

1700 1750

AR95050H.PPT

I O 0

98

96

94

92

90 0 1

0 0

2 3 4

CALCIUM -TO-S U LFU R FEED RATIO

Figure 10: Phase 2 CPFBC Sulfur Capture Efficiencies

5

0 w 0

0 c3 0

n1SlNWSa-i 'SNOISSIW3 'ON

0 Q,

0 QD

0 r-

0 CD

0 v)

0 v

0 0

Lu z 0 N - K a m

0" z

2

ii 3 w

FIGURE 12: FOUR RIVERS ENERGY MODERNIZATION PROJECT I ’

Coal Limestone

ALKALI GETTER

ALKALI GETTER ....................

- CYCLONE - BFW

A d I - 1

CONDITIONER

Bottom Ash

SILO

Condensate ~ T O R GENERATOR

CONDENSER

Water J.PPT Figure 12

CONDITIONER

Disposal

AR95050.