MASTER. Livingston, New Jersey Conference Sponsor: Integrated' CarbonizerKPFBC Pilot Plant. Authors: Contractor: Contract Number :

Transcription

1 ntegrated' CarbonizerKPFBC Pilot Plant Authors: A. Robertson J. Van Hook Contractor: Foster Wheeler Development Corporation 12 Peach Tree Hill Road Livingston, New Jersey Contract Number : DE-AC21-86MC21023 Conference Title: 12th Annual nternational Pittsburgh Coal Conference Conference Location: Pittsburgh, Pennsylvania Conference Dates: September 11-15, 1995 Conference Sponsor: University of Pittsburgh and American Coal Foundation MASTER

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4 NTEGRATED CARBONZEWCPFBC PLOT PLANT A. ROBERTSON AND J. VAN HOOK Foster Wheeler Development Corporation 12 Peach Tree Hill Road Livingston, New Jersey ABSTRACT The key components of second-generation or advanced pressurized fluidized bed combustion (APFBC) plants have been successfully tested separately at the pilot plant scale. The tests involved a 254-mm (10-inch)-diameter bubbling bed carbonizer, a 203-mm (84nch)-diameter circulating bed carbonizer, and a 203-mm (8-inch)diameter circulating pressurized fluidized bed combustor (CPFBC) operating at 1.42-Mpa (14-atm) pressure. n these tests, particle-capturing ceramic barrier filters were incorporated to investigate g a s compatibility issues. The next step in the development of APFBC plant technology is to integrate a carbonizer and a CPFBC with their ceramic barrier filters, then operate the subsystem to investigate integration characteristics. These tests will involve load following and transfer of the char from the reducing atmosphere of the carbonizer to the oxidizing atmosphere of the CPFBC at steady and controlled rates. This paper describes the integrated carbonizer/cpfbc pilot plant being constructed to perform these tests at the John Blizard Research Center of Foster Wheeler Development Corporation (FWDC) in Livingston, New Jersey. Construction and comissioning progress are presented with a n overview of the technological development program. NTRODUCTON FWDC is leading a team of companies in a program aimed a t developing advanced or second-generation pressurized fluidized bed (PFB) combustion technology for coal-fired electrical power generation. Our team members are Foster Wheeler Energy Corporation; Foster Wheeler USA; GilberUCommonwealth, nc.; nstitute of Gas Technology; Westinghouse Power Generation Business Unit (PGBU); and Westinghouse Science and Technology Center (STC). The work is being done under USDOE Contract DE-AC29-86MC Figure 1 is a flow diagram of the proposed

5 plant. t will enable utilities to generate electrical power at higher efficiencies, lower costs of electricity and reduced emissions when firing high-sulfur coal. n the plant coal is fed to a pressurized carbonizer that produces a low-btu fuel gas and char. After passing through a cyclone and ceramic barrier filter to remove gasentrained particulates and a bed of ematkelite pellets to remove alkali vapors, the fuel g a s is burned in a topping combusfor 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 CPFBC and a n external fluidized bed heat exchanger (FBHE). The carbonizer char is burned in the CPFBC with high excess air. The vitiated air from the CPFBC passes through its own cyclone, ceramic-barrier filter and alkali-getter and supports combustion of the fuel g a s in the g a s turbine 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 pyrolysis/mild 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 sulfur-containing tarllight 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 g a s is fired hot. Thus the expensive, complex, fuel gas heat exchangers and chemical or sulfur-capturing bed clean-up systems that a r e 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 a r e captured by high-temperature filters, rendering the fuel g a s essentially free of particulates and able to meet New Source Performance Standards (NSPS). The captured material, with carbonizer bed drains, is collected and injected into the CPFBC where the burning char heats the high-excess-air flue gas to 871"C (1600 F); surplus heat is transferred to the FBHE by sorbent recirculation between the two units. The high percentage of excess air in the combustor transforms the calcium sulfide to sulfate, allowing its disposal with the normal CPFBC spent sorbent. 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. n 1987 a conceptual design of a 3;percent-sulfur Pittsburgh No. 8 coal-fired APFBC plant with a conventional 16.5 MPa/538OC/538OC/63.5-mm Hg (2400 psig/l OOO"F/ 1000 F/2-1/2 inch Hg) steam cycle was prepared, and its economics were determined. When operated with a 1.42-MPd871 OC (14-atm/6OOaF) carbonizer, the plant efficiency was 44.9 percent (based on the higher heating value of the coal),

6 and its cost of electricity was 21.8 percent lower than that of a conventional pulverized coal-fired plant. Based on pilot plant carbonizer test results, plant efficiency is now expected to be 46.2 percent []. The R&D needs of this new type plant and an ntegrated Program Plan for meeting the needs have been presented [2,3]. n accordance with that plan, the key components of this new plant have been tested separately in P h a s e 2 to ascertain their individual performance characteristics. A series of topping combustor tests has already been conducted at the University of Tennessee Space nstitute (UTS) under the direction of Westinghouse PGBU [4]. These tests were successful in proving the topping combustor concept. PHASE 2 PLOT PLANT n November, 1991, FWDC began operating a PFB pilot plant at its John Blizard Research Center in Livingston, New Jersey. The plant was equipped with a multipurpose reactor and a ceramic barrier filter. The reactor was designed to test a second-generation plant carbonizer first, then, after modification, a CPFBCFBHE. Ceramic barrier filters provided by Westinghouse STC were used with both units to demonstrate particulate control capabilities. The carbonizer had a 5.8-m- (19-foot)deep jetting fluidized bed and a 2.92-m (9-foot, 5 3/4-inch)-tall freeboard. The D was 254 mm (10 inches) for the first 1.40 m (4 feet, 7 inches) of bed height, 305 mm (12 inches) to the top of the bed, and 356 mm (14 inches) in the freeboard. The carbonizer test program was very successful. Eight bubbling fluidized bed test runs were completed encompassing 37 setpoints and 533 hours of operation. Portions of the collected data have been discussed in other publications [5-71. Although highly caking Pittsburgh No. 8 coal and Ohio Plum Run dolomite were most frequently used, llinois No. 6 and Wyoming Eagle Butte coals, petroleum coke and Alabama Longview limestone were also tested. The Pittsburgh coal typically had a 3.5-percent sulfur content and a Free Swelling ndex of 6.5;the Eagle Butte coal contained 0.7-percent sulfur and 27-percent moisture. The CPFBC was refractory-lined to yield a 203-mm (8-inch) D, and its primary and secondary zones were 3.8 m (12 foot, 6 inches) and 4.9 m (16 feet) tall, respectively. The CPFBC test program was also very successful; it consisted of five test runs entailing 23 test points and 413 hours of operation. The fuels and sorbents tested in the carbonizer program together with their charkorbent residues, were all burned in the CPFBC. Test results have been presented 181. The CPFBC exhibited combustion efficiencies greater than 99.5 percent and sulfur-capture efficiencies with highsulfur coal greater than 96 percent at calcium-to-sulfur molar feed ratios ranging from 1.25 to 2.0, depending upon the solids circulation rate. PHASE 3 PLOT PLANT With Phase 2 tests having successfully demonstrated carbonizer and CPFBC operations and since the test data support an even higher commercial plant efficiency (46.2 vs percent), the project has moved to its third and final phase. n January, 1994, we began constructing an addition to the Phase 2 pilot plant The multipurpose reactor was returned to

7 its original bubbling bed carbniizer configuration, but with a Sdot-tall spool piece added that lengthem the unit and allows it to operate with a commerdal-scale 24-footCleep bed (see Figure 2). A new,larger CPFBC, with its m i t a n t equipment (Le., FBHE, m i c harrier filter and ash drain lod<hoppers), has been added.as shown in Figure 2, the new CPFBC has a 33(knm (134~41)D and is 11.7 m (38.25feet) tall. The.increased secondary zone height and, hence, gas residence time provided by the larger CPFBC should further improve CombllsfOT performance. The c a r t x x i and CPFBC have been interccxnected to demonstrslte c a h m i i - b CPFBC chartransfer, and Figure 3 is a sd7ematicofthe expanded pilot plant The coal-fired pilot plant operates with a maximum heat input of 3.6 MWt. The coal flow is proportioned between the carbonizer and CPFBC in varying amounts, as dictated by test conditions. The coal and limestone sorbent can be fed into the units via a lock-hopper-type pneumatic transport feed system or mixed with water and pumped in as a paste. The fuel gas generated in the carbonizer and the flue gas generated in the CPFBC contain particulate matter (char, sorbent, fly ash) elutriated from their fluidized beds. Each 871 C (1600 F) gas stream is provided with a cyclone separator and a ceramic candle filter that removes the particulate. The cleaned gases then pass through separate stellite-coated orifice plates that reduce their pressure (typically 14 bara) to ambient, and water is sprayed into the gas streams to cool them to 177 C (350 F). Demisters remove any liquid droplets remaining in the gases before they enter baghouse filters. The carbonizer and CPFBC gases then proceed to a stack, with the carbonizer gas first being burned in a natural-gas-fired incinerator. The char-sorbent residue generated in the carbonizer is collected in a centrally located hopper. Nuclear level indicators monitor the char level in the hopper, and a screw feeder a t its base withdraws char as required to maintain a constant char level. A nitrogen-aerated riser picks up the char at the screw feeder outlet and transports and injects the char into the CPFBC. Combustion of the char and coal fed directly to the CPFBC release heat that is absorbed by a sorbent fly ash stream continuously circulated between the CPFBC and an external FBHE. The FBHE contains a water-cooled tube bundle that cools the 871"C (1600 F) circulating sol- ids to 649OC (1200 F) before their return to the CPFBC. Nonmechanical J valves are provided on the CPFBC cyclone dipleg and in the FBHE solids return line to provide the necessary pressure seals between t h e CPFBC and FBHE. As of June, 1995, a series of cold and hot shakedown runs have been completed, and the pilot plant is ready for testing. REFERENCES A. Robertson, et ai Second-Generation PFBC Systems Research and Development-Phase 2, Best Efficiency Approach in Light of Current Data. Proceedings of the Coal-Fired Power Sysfems 9SAdvances in GCC and PFBC Review Meeting, Don Bonk (ed.), DOWMETC 93/6131. A. Robertson, et al Second-Generation Pressurized Fluidized Bed Combustion Plant: Research and Development Needs. Foster Wheeler Development Corporation, Livingston, NJ. Phase 1 Task 2 Report FWC/FWDC-TR-89/06 to the USDOE under Contract DE-AC21-86MC21023.

8 3. A. Robertson, et al Second-Generation Pressurized Fluidized Bed Com- bustion Plant: ntegrated R&D Program Plan. Foster Wheeler Development Corporation, Livingston, NJ. Phase 1 Task 3 Report FWCFWDC-TR to the USDOE under Contract DE-AC21-86MC W. Domeracki, et ai Second-Generation PFBC Systems Research and Development, Proceedings of fhe Ninfh Annual Coal-Fueled Heat Engines, Advanced Pressurized Fluidized Bed Combusfion, and Gas Sfream Cleanup Sysfems Contractors Review Meeting, DOUMETC 93/ A. Robertson, et al Second-Generation PFBC Systems Research and Development, Proceedings of fhe Twelffh Annual Gasification and Gas Stream Cleanup Sysfems ConfracforsReview Meefing, Vol. 1, DOEMETC 92/ A. Robertson, et al nitial Second-Generation PFB Carbonizer Pilot Plant Test Results. Proceedings of fhe Ninfh Annual nfernafional Piffsburgh Coal Conference, University of Pittsburgh. 7. J. Van Hook, A. Robertson and D. Bonk, Carbon Conversions Measured in a Second-Generation PFB Pilot Plant Carbonizer, Proceedings of fhe 72fh lnfernafional Conference on Fluidized Bed Combusfion, Vol. 2, L. N. Rubow (ed.), ASME, New York. 8. A. Robertson, et al Second-Generation PFBC Systems Research and Development-Proceedings of fhe Coal-Fired Power Sysfems 96Advances in GCC and PFBC Review Meefing, DOUMETC... Second Generation r. 8 ALKAL REMOVAL REMOVAL PARTCULATE REMOVAL FUEL GAS FLUE GAS CARBONZATON (CARBONZER) t C1 R SORBENT... STEAM GENERATON STACK TURBNE ASH SORBENT (FBHE) A + (HRSG) REMOVAL b-sorbent GAS TURBNE m TOPPNG COMBUSTON COA First Generation SORBENT COMPRESSOR AR Fig. 1. Simplified Process Block Diagram-Second-generation PFB Combustion Plant

9 4' UL MaLE Carbon izer CPFBC Fig. 2. Phase 3 Test Units \..&.[.".. NfL... : La....* ELCClRlC HEATER Fig. 3. Phase 3 Pilot Plant Schematic