United States Environmental Protection Agency Industrial Environmental Research Laboratory Research Triangle Park NC 27711 Research and Development EPA-600/S7-84-031 Apr. 1984 v>ERA Project Summary Evaluation and Demonstration of the Chemically Active Fluid Bed R.E. Sommer, A.S. Werner, and Z. Kowszun Results are reported on the operation of a 17-MW Chemically Active Fluid Bed (CAFB) demonstration unit, retrofitted to a natural gas boiler. The CAFB pro- cess gasifies high-sulfur, high-metals- content liquid and solid fuels. Residual oil, lignite, and bituminous coal were gasified separately or together between November 1979 and June 1981. Oil was gasified for 540 hours. A maximum con- tinuous-rating test sustained 22 MW of electrical energy for 2 hours. Sulfur re- moval efficiencies of up to 90 percent were achieved during oil gasification. Lignite and bituminous coal were gas- ified for 42 hours: sulfur removal effi- ciencies of up to 70 percent were obtained. Design and operational areas which need to be upgraded were iden- tified. Continuous monitors were used to measure boiler flue gas emissions of SO,, nitrogen oxides (NOX), CO, oxy- gen, CO,, and opacity. Periodic manual emission tests were conducted for par- ticulate, SO,, and NOX, using EPA reference methods. Emissions of these three criteria pollutants were generally lower than New Source Performance Standards for utility boilers, although occasionally excessive particulate and SO, emissions were observed. NOX emissions were consistently lower than those from natural gas combustion. Po- tential multimedia impacts from the three major discharge streams from the CAFB (boiler flue gas, spent solids from the gasifier bed, and sulfur recovery system ash) were characterized using the phased approach to environmental assessments developed by EPA. Results of detailed chemical analyses and bio- logical assays are reported. This Project Summary was developed by EPA's Industrial Environmental Re- search Laboratory, Research Triangle Park, NC, to announce key findings of the research project that is fully documented in a separate report of the same title (see Project Report ordering information at back). Background The Chemically Active Fluid Bed (CAFB) process was developed in the late 1960's by the Esso Research Center, Abingdon (ERCA), England, as a way to generate elec- trical energy from high-sulfur, high-metal, heavy fuel oil. In the CAFB process, oil or coal is fed continuously into a fluidized bed of lime maintained at 870 °C. Air is preheated and fed to the gasifier in substoichiometric proportions. The fuel entering the gasifier is vaporized, oxidized, and cracked to produce a low-Btu low-sulfur gas which, after pass- ing through cyclones to remove particulate matter, is burned in a conventional gas boiler. Sulfur contained in the oil initially forms various gaseous compounds which then react with the bed lime to yield solid calcium sulfide. Some of the fuel-bound trace elements are also bound to the bed stone. The sulfided lime is cycled to a regeneration unit where it is oxidized to pro- duce calcium oxide (which is returned to the gasifier) and S02 (which is sent to a sulfur recovery unit). During the early and mid-1970's, the pro- cess was demonstrated at a 2.9 MW pilot plant to provide energy efficiently from both liquid and solid fuels while simultaneously limiting emissions of S02, NOX, vanadium, and nickel. Based on the successful pilot plant tests in England, the U.S. EPA and the Texas-based Central Power and Light Com- pany (CP&L) commissioned Foster Wheeler Energy Corporation (FWEC) to construct a 17-MW demonstration plant in San Benito, TX. The agreement with CP&L, signed in ------- May 1975, provided for construction and operation of the demonstration plant. The contract with EPA (68-02-2106) covered engineering design, labor for start-up, fuels and feedstocks, and environmental monitor- ing. Design of the unit, based on the ERCA design and operating experience, was ini- tiated in January 1975, and construction was completed in January 1979. The plant incor- porated FWEC's proprietary sulfur recovery system, RESOX™. More than 130 contrac- tors and subcontractors were employed dur- ing construction. A test program using heavy oil, lignite, and bituminous coal was con- ducted between October 1979 and June 1981. This report describes the design, opera- tion, and environmental aspects of the San Benito plant. Plant Operation Oil, lignite, and bituminous coal were gasified separately or together in the CAFB unit, which was retrofitted on the front end of a natural gas boiler, between November 1979 and June 1981. Eleven test runs were conducted during this period. Operating con- ditions and fuels employed for the runs are summarized in Table 1. Residual oil was gasified during the first four runs, totaling 343.5 hours of operation. The fifth gasifica- tion run was the longest and most suc- cessful. All three systems, the gasifier, regenerator, and RESOX™ reactor, were operational during the run. During the fifth run, oil (the primary feedstock) was gasified for 196 hours; however, lignite was intro- duced and gasified in combination with the oil for the final 3 hours of operation. During the second run, a maximum continuous- rating test sustained 22 MW of electrical energy on oil for 2 hours. Problems with the transfer of bed stone between the gasifier and regenerator limited regenerator opera- tion during oil gasification to 213 hours. The RESOX™ sulfur recovery system was operated during oil gasification for 115 hours. Sulfur removal efficiencies of up to 90 per- cent were obtained. West Texas lignite was gasified for 10.5 hours: problems with the coal feed system precluded additional operation. An eastern bituminous coal was gasified for 31.7 hours during the final four runs: again, coal feed problems caused premature termination of two of the runs. Throughout the final two runs, the boiler flames were strong and well- defined. A sulfur removal efficiency of 70 percent was achieved during the final run. The following alterations would improve operation: • More efficient cleanup of product gas entering the boiler. The single-stage cyclones at San Benito were, at times, inadequate. • A sturdier, more reliable coal feed system. The coal feed system was very sensitive to coal physical properties and was prone to plugging under some con- ditions. • A burnup cell for the carbon on the cyclone fines. • More reliable rotary seals, valves, dampers, augers, and filters, to better withstand the severe conditions of CAFB operation. Environmental Aspects The demonstration unit was evaluated to determine its capability to control flue gas criteria pollutant emissions and to estimate potential multimedia pollution impacts. Con- tinuous monitors were used by FWEC to measure S02, NOX, CO, oxygen, C02, and opacity. In addition, periodic manual emis- sion tests were conducted by FWEC for par- ticulate, S02, and NO using EPA Table 1. Summary of the 11 Gasification Runs Between December 1979 and June 1981 Hours of Fuels Regenerator RESOX™ Boiler load Run Dates gasification used operation operation product gas 1 2 • 3 4 5 6 7 8 9 10 11 12/19/79- 12/20/79 1/27/80- 1/31/80- 4/ 8/80- 4/14/80 7/29/80- 81 1/80 9/24/80- 101 1/80 11/20/80- 11/25/80 121 9/80- 12/12/80 2/81 3/11/83- 3/12/83 61 5-61 6/81 61 7-61 8/81 61 9-6/10/81 6/22/81- 6/23/81 32 77.5 144 90 196 79 5.5 4 10 19.5 17.5 19 16 Oil Oil Oil Oil Oil Lignite, 2 fir Oil Lignite Oil/lignite Oil Oil/lignite Lignite Lignite Oil, 3 hr Oil /coal, 3 hr Coal, 4 hr Oil Oil, Oil/coal Oil, Oil/coal Oil, 3 hr Oil/ coal, 5 hr Coal, 8 hr No No No 3hr Yes Yes No Yes Yes No Yes No No No No Yes 17 hr Yes No No No No No No 4MW- 6hrs 9-10MW-28hrs 9-11 MW 14-15 MW 20-22 MW- 3hrs 7.2-15 MW 10.5 MW 72 hrs product /natural gas 8.5 MW - product gas 2-hr coal provided 30% of 8.5 MW 5- 6 MW 9 MW 7.5 MW 8.7 MW 9.0 MW 4.8 MW - product gas 5.9 MW - natural gas Comments Maintained 22 MW for maximum continuous rating. First use of /V2 for material transfer between gasifers and regenerator. During this run GCA performed environmental assessment The gasifier bed appeared to be releasing S02. Run aborted. Approximately 4.5 MW was from product gas. The bed from run 10 was reused in this run. ------- reference methods 5, 6, and 7, respectively. Potential multimedia environmental impacts were determined under a separate contract (68-02-2695) by GCA/Technology Division. This program, which followed protocols developed by EPA, characterized in detail the chemical composition of the three major streams discharged from the CAFB: boiler flue gas, spent lime sorbent, and ash from the sulfur recovery system. The major environmental conclusions of the demonstration programs follow. • NOX emissions from the combustion of product gas generated by gasification of oil, lignite, or bituminous coal were con- sistently below 100 ng/J (0.233 lb/108 Btu) and were lower than NOX emis- sions from natural gas combustion. • During oil gasification, the sulfur removal efficiency (SRE) varied from 60 to 90 percent. The SRE decreased markedly as the gasifier bed temperature was raised above 870°C. Recycling of RESOX™ tail gas to the gasifier decreased SRE, probably as a conse- quence of steam and elemental sulfur entrained in the tail gas. • Particulate emissions during oil gasifica- tion averaged 31.3 ng/J (0.073 lb/10« Btu) based on the results of five EPA Method 5 tests. Opacity was generally below 20 percent. However, the higher than anticipated elutriation rate of bed material from the gasifier resulted in ex- cessive paniculate buildup in the boiler. Periodically this material would be blown off the boiler tubes by increasing the gas flow to the boiler, resulting in momen- tary jumps in opacity. • Particulate collected from the boiler flue gas showed neither appreciable toxici- ty nor any positive mutagenicity. • Some mutagenicity was indicated by an Ames test on extracts of XAD porous polymer resin used to collect samples of gaseous organic compounds from the flue gas. • Leachates collected from the spent stone and RESOX™ ash contained low metal and anion concentrations. Anion concentrations in both leachates were well below EPA Primary and Secondary Drinking Water Regulations. Rebecca E. Sommer and Arthur S. Werner are with GCA/Technology Division, Chapel Hill, NC 27514; Z. Kowszun is with Esso Research Centre, Abingdon, Oxfordshire, OX136AE. England. Samuel L. Rakes is the EPA Project Officer (see below). The complete report, entitled "Evaluation and Demonstration of the Chemically Active Fluid Bed," (Order No. PB84-159 243; Cost: $ 19.00, subject to change) will be available only from: National Technical Information Service 5285 Port Royal Road Springfield, VA 22161 Telephone: 703-487-4650 The EPA Project Officer can be contacted at: Industrial Environmental Research Laboratory U.S. Environmental Protection Agency Research Triangle Park, NC 27711 U.S GOVERNMENT PRINTING OFFICE, 1984 — 759-015/7640 ------- United States Environmental Protection Agency Center for Environmental Research Information Cincinnati OH 45268 Official Business Penalty for Private Use $300 ------- |