DENSIFIED REFUSE DERIVED FUEL CO-FIRING EXPERIENCE IN U.S. AIR FORCE SPREADER STOKER BOILERS

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1 DENSIFIED REFUSE DERIVED FUEL CO-FIRING EXPERIENCE IN U.S. AIR FORCE SPREADER STOKER BOILERS ALFRED W. JOENSEN Department of Mechanical Engineering Iowa State University DOUGLAS FISCUS Midwest Research Institute Kansas City, Missouri Ames, Iowa PAUL VITUCCI and STEVE HATHAWAY USAF Engineering and Services Center Tyndall AFB, Florida ABSTRACT The thermal and environmental performance of cofiring densified refuse-de rived-fuel (pellets) with coal in two USAF spreader stoker boilers at Wright Patterson Air Force Base is documented. One boiler is for hot water heating and one is for steam heating. A summary analysis of fuel analysis, excess air, boiler efficiency, environmental emissions, ESP efficiency, boiler derating and general firing experience will be presented. INTRODUCTION From May 1979 through June 1982, the U.S. Air Force co-fired densified refuse-derived-fuel (drdf) with coal in two types of spreader stoker boilers at Wright Patterson Air Force Base (WPAFB), Ohio. The co-ruing was conducted as part of a test program to demonstrate and evaluate the use of drdf in military heating and power systems. This program was being managed by the U.S. Air Force Engineering and Services Laboratory (ESC) at Tyndall Air Force Base, Florida. The resulting co-firing experience will provide the information necessary in the design, operation, and maintenance for either new or converted solid fuel heating and power boilers at U.s. Air Force base facilities. The potential use of drdf as an alternate fuel is in accordance with Department of Defense programs in energy conservation. This report summarizes some of the results associated with the thermal and environmental testing of co-firing unit no. 3 spreader stoker in Building 1240 (hot water heating plant) and unit no. 4 spreader stoker in Building 770 (steam heating plant). Complete results of these tests have been documented in reports submitted to ESL [1, 2]. Test results of drdf co-ruing at the Maryland Correctional Institute (MCI, Hagerstown, Md.), and at the General Electric Company Power House (Erie, Pa.) also have been reported. DESCRIPTION OF BOILERS AND TEST The Building 1240 unit no. 3 is a Babcock and Wilcox high temperature hot water (HTHW) boiler equipped with a Detroit Stoker Rotograte Spreader and is rated at 100 X 106 Btu/hr ( X 106 kj/h) heat output. The design water flow is 582,000 lb/hr (263,991 kg/h) with the water entering at 250 F (l21.1 C) and leaving at 414 F (212.2 C). Because of existing heating demand loads, the unit was tested at heat outputs ranging from 25 X 106 to 35 X 106 Btu/hr (26.38 X 106 to X 106 kj/h). Thus, no test situation existed to determine the amount of boiler derating. Only coal and drdf tests were conducted. The Building 770 unit no. 4 is a Keeler steam boiler designed to generate 150,000 lb/hr (68,038.9 kg/h) of steam at 400 psig (2758 kpa) saturated vapor with feed water entering at 200 F (l04.4 C). This unit has a design boiler efficiency of 81.8 percent with 30 percent excess air at the boiler outlet. Both boilers utilize an air heater to preheat combustion air going to the stoker grate windbox. Three sets of coal, drdf, and 60 percent coal40 percent drdf (by dry weight) tests were run at Building 770. During March 1981 through April 1981, the Building 1240 tests were performed. The Building 770 tests were conducted in February All drdf used were pellets produced by Teledyne National in Cockeysville, Maryland. The pellets were mixed with the coal in the outside 264

2 silo and conveyor system prior to injection by the Detroit Spreader in the Building 770 tests. The outflow from a dedicated d-rdf storage silo was dumped on top of the coal in a partially-filled belt conveyor passing underneath. The fuel volume rate was controlled by visual observation. Final mixing was achieved due to multiple belt and drag conveyor transfer drop-off points as the fuel was dumped into the plant bunker. ing 770 [1] are summarized in Tables 6 and 7. The observed emissions are reported as an index which is the ratio of the observed value to the New Source Performance Standard (NSPS). For both installations, the NO x emissions were slightly higher for coal than drdf, attributable to the lower level of fuel bound nitrogen in the drdf. SO x emissions were less for drdf and blends than coal, as would be expected from the low sulfur content of drdf. Both installations were equipped with electrostatic precipitators and met NSPS particulate emission rates; TEST R ESU L TS The average values for the ultimate analysis of the fuels used in the tests at Buildings 1240 and 770 are shown in Tables 1 and 2, respectively. It is interesting to note the difference in ash softening temperatures of coal and drdf as listed in Table 2. The boiler test averages for Building 1240 are sum-. marized in Table 3. Since this unit was tested only at low load, it was impossible to determine boiler derating at maximum load. The boiler efficiency for drdf firing was 3.56 percent lower than that for coal firing even though the exit flue gas temperatures were about the same. The boiler performance for unit no. 4 at Building 770 is shown in Table 4. Boiler derating was experienced down to 64.5 percent of design steam load. This resulted from the limit on the volume fuel spreader injection due to the low heating value and density of the drdf. The unusually high efficiency of percent for coal/drdf firing mode cannot be explained. The boiler efficiency was calculated on a calculated heat input based on the F fuel factor, the duct dry standard volume flow rate, and percent O2 Both units have a mechanical dust collector installed the emission rates were somewhat less for drdf and blends than for coal. No data were reported for chloride and fluoride emissions. Trace hydrocarbons are of interest because of their smog forming potential. The amounts observed were below detection limits of the test method used; thus it Was concluded that trace hydrocarbon emissions were of little significance. In summary, the Building 1240 tests resulted in a 3.56 percent decrease in boiler efficiency. No conclusion was made regarding the Building 770 unit no. 4 boiler efficiency results. Ratholing was experienced in both of the heating plant parabolic fuel bunkers. Reduced fuel density resulted in unit no. 4 derating because of limited volume feed capacity of the spreader mechanism. ACKNOWLEDGMENT The data summarized in this paper currently is being correlated as part of a research project conducted by the Iowa State University Engineering Research Institute and is funded by the USAF Engineering Service Center, Tyndall AFB, Florida. upstream of the electrostatic precipitator (ESP). Available particulate sizing characterization is shown in Table 5 for both building tests. For Building 1240, the ESP efficiency, power input, and resistivity were percent, kw, and 2.70 X 105 ohm-cm for drdf firing and percent, kw, and 5.49 X 103 ohm-cm for coal firing, respectively. Resistivity measurements were made on samples taken from one field of the ESP hopper ash and were performed in accordance with ASME PTC 28. For the Building 770 tests, the ESP collector efficiency for coal/drdf (60 percent-40 percent dry weight), drdf, and coal firing were 97.0 percent, 97.4 percent, and 97.0 percent. For the same firing mode, the fly ash resistivities were 4.7 X 107,4.9 X 107, and 4.6 X 107 ohmcm, respectively (based on ASME PTC-28). The gas emission data for tests conducted at Wright Patterson Air Force Base at Building 1240 [2] and Build- REFERENCES [1] "Boiler Efficiency and Emissions Testing Using Refuse Derived Fuel and Coal, Wright-Patterson Air Force Base, Building 770, Boiler No. 4, Dayton, Ohio," report prepared for Research Triangle Institute and U.S. Air Force Occupational and Environmental Health Laboratory. Entropy Environmentalists Incorporated, Research Triangle Park, North Carolina. Feburary [2] Carpenter, P. F., and Kleinhenz, N. J., "A Field Test Using drdf in an Spreader Stoker Hot Water Generator," report prepared for U.S. Environmental Protection Agency under Contract No , Systems Technology Corporation, Xenia, Ohio, May [3] Degler, G. H., Rigo, H. G., and Riley, B. T. Jr., "A Field Test Using Coal: drdf Blends in Spreader Stoker-Fired Boilers," report prepared for U.S. Environmental Protection Agency under Control No , available from NTIS, PB , August

3 (4) Kleinhenz, N. 1., Coal: drdf Demonstration Test in an Industrial Spreader Stoker Boiler. Use of Coal: drdf Blends in Stoker-Fired Boilers, Volume I, report prepared for U.S. Environmental Protection Agency under Contract No , Systems Technology Corporation, Xenia, Ohio, March (5) Kleinhenz, N. J., Coal: drdf Demonstration Test in an Industrial Spreader Stoker Boiler. Use of Coal: drdf Blends in Stoker-Fired Boilers, Appendices A, B, C, and D, Volume II, report prepared for U.S. Environmental Protection Agency under Contract No , available from NTIS, PB , September Key Words: Boiler. Combustion. Electrostatic Precipitator. Fuel. Performance. Refuse Derived Fuel. Spreader Stoker TABLE 1 BUILDING 1240 FUEL ULTIMATE ANALYSIS, AS FIRED drdf Coal Date Sample Avg_l 2 Ultimate Analysis, Carbon Hydrogen Oxygen Nitrogen Sulfur Ash Free Moisture HHV, B/lb 7, , (kj/kg) 16, , samples 23 samples 266

TABLE 2 WPAFB BUILDING 770 FUEL ULTIMATE ANALYSIS, AS FIRED 100 Coal 100 drdf drdf-coal Mixture Moisture, 6.73 0.21 11. 76 0.37 8.51 1.05 Ash, 4.96 0.41 8.31 1.19 6.59 2.46 Sulfur, 0.70 0.03 0.13 0.

4 TABLE 2 WPAFB BUILDING 770 FUEL ULTIMATE ANALYSIS, AS FIRED 100 Coal 100 drdf drdf-coal Mixture Moisture, Ash, Sulfur, Carbon, Hydrogen Nitrogen Oxygen HHV Btu/lb 13, , , (kj/kg) 31, , , Ash Softening Temp. OF ,

TABLE 3 BUILDING 1240 BOILER TEST AVERAGES SUMMARY Fuel Boiler Load 1 Excess Air Flue Gas Exit Temperature Boiler 2 Efficiency 29.8 154.9 301.4 (149.7) 76.45 6.4 9.2 5.3 (2.

5 TABLE 3 BUILDING 1240 BOILER TEST AVERAGES SUMMARY Fuel Boiler Load 1 Excess Air Flue Gas Exit Temperature Boiler 2 Efficiency (149.7) (2.9) 0.79 Coa (151.0) (1. 8) on 100 x 10 Btu/hr (105.5 x 10 6 kj/hr) heat output 2 Heat loss method 38 test runs 4 3 test runs 268

6 TABLE 4 BUILDING 710 BOILER TEST AVERAGES - SUMMARY Fuel Boiler Load1 Excess Air Boiler Efficiency2 ESP Outlet Gas Temp. Coal/dRDF (255.6) (8.3) 100 RDF (258.3) (4.4) 100 Coal (275.6) (7.8) lboiler no. 4 rating = 150,000 lb/hr (68,039 kg/hr) 2Based on heat input calculated from duct dry standard volume flow, F fuel factor and 0 2 ; and heat output calculated from chart steam flow 360 coal - 40 drdf by dry weight 269

7 TABLE 5 PARTICULATE SIZING CHARACTERIZATION TABLE 5A BUILDING 170 Fuel dg IJm ESP Inlet a 1 IJIft ESP Outlet dg IJm Nominal Steam Flow lb/hr (kg/hr) Coal + drdf , , , , 699 drdf , , , , 091 Coal , , , , 771 TABLE 5B BUI LDI NG 1240 ESP Inlet Run dg IJm April 16, a.m. April 16, p.m IFor Log Normal Distribution, dg = geometric mean diameter, having a cumulative weight percentage equal to 50 a g = geometric standard deviation 270

8 TABLE 6 NOx, SOx AND PARTICULATE EMISSION INDEXES, BUI LDING 1240 Pollutant NSPS Max. 6 lbjl0 Btu drdf Emission Index a Coal NO x SO x Particulates a Ratio of reported emission to NSPS maximum. TABLE 7 NOx, SOx, AND PARTICULATE EMISSION INDEXES, BUILDING 770 Pollutant NSPS Max. 6 lb/l0 Btu drdf/coal Emission Index a drdf Coal NO x SO x Particulates a Ratio of reported emission to NSPS maximum. 271

MEETING TODAY'S EMISSION STANDARDS WITH 198WS COMBUSTION TECHNOLOGY

MEETING TODAY'S EMISSION STANDARDS WITH 198WS COMBUSTION TECHNOLOGY by Craig A. Penterson Senior Staff Engineer Fuel Equipment Design Riley Stoker Corporation Presented at the Council of Industrial Boiler