Cyclone boilers

Cyclone boilers, like wet-bottom pulverized coal units, burn low ash fusion temperature coal, but the coal is crushed so that 95 percent is smaller than 1/4 inch.9 The coal is fed tangentially to the cyclone burners, which are mounted horizontally on the outside of the boiler and are cylindrical in shape.9 A typical cyclone burner is shown in 

Because most of the ash is removed as molten slag, addition of a bottom grate is not necessary.7 However, small TDF is required, because much of the combustion must occur in suspension.7 TDF that is too large to combust completely can get carried over into the boiler or dust collection system, and cause blockage problems.9 Therefore, particle size may inversely determine the amount of TDF that can be used in a cyclone boiler.11 Three cyclone-fired boilers at utilities have burned 1M x 1 TDF in test operation, one at the 2 percent, one at the 5 percent, and one at up to a 10 percent level.3,9,12 One pulp and paper mill plans the use of TDF in a cyclone-fired hog-fuel boiler.13 

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V. Nast, G. Ekschele, and W. Hutchinson, "TDE Co-firing Experience in a Cyclone Boiler," Proceedings, Strategic Benefits of Biomass and Waste Fuels Conference, EPRI, Washington, D.C., 1993. 

There has been increased interest in firing wood waste as a supplement to coal in either pulverized coal (PC) or cyclone boilers at 1—5% of heat input. This appHcation has been demonstrated by such electric utilities as Santee-Cooper, Tennessee Valley Authority, Georgia Power, Dehnarva, and Northern States Power. Cofiring wood waste with coal in higher percentages, eg, 10—15% of heat input, in PC and cyclone boilers is being carefully considered by the Electric Power Research Institute (EPRI) and Tennessee Valley Authority (TVA). This practice may have the potential to maximize the thermal efficiency of waste fuel combustion. If this practice becomes widespread, it will offer another avenue for use of fuels from waste. 

In 1991, Goodyear began working with Cadence Environmental Energy (Indiana) to market a whole tine feed system to supplement fuel for cement kilns. The system is used by several cement manufacturers. In 1992, Goodyear furnished tines for a Tennessee Valley Authority (TVA) test bum at a Memphis power plant. The electric utiUty used tine-derived fuel (TDE) to supplement coal fuel in a cyclone boiler. These tests were successflil. 

Industrial Uses. Large industrial faciUties, particularly those using cyclone boilers or fluidized-bed boilers, are potential markets. In addition, several vendors of small- and medium-sized industrial energy and steam faciUties are marketing units capable of using I DE. As the availabiUty of I DE expands with new producers entering the market, it is hoped that the industrial use of I DE will also expand (7). 

The WP L cyclone boiler will bum I DE continuously with coal, as about 5% of its fuel mix, with htfle or no modification. By contrast, pulverized-coal boilers, which account for about 80% of the coal-fired capacity in the United States, probably caimot bum tire chips without significant modifications. In these boilers, which bum very fine coal particles in suspension, the heavy chips will fall from the area where best combustion occurs. 

Another furnace that does not require fuel preparation is the stoker boiler, which was used by New York State Electric Gas Corporation (NYSEG) in its TDE tests. At NYSEG, the stoker boiler, which has a 1649°C (3000°E) flame temperature (as does the cyclone boiler), has routinely blended low quaUty coal, and more recently, wood chips with its standard coal to reduce fuel costs and improve combustion efficiency. In the tire-chip tests, NYSEG burned approximately 1100 t of tire chips (smaller than 5x5 cm) mixed with coal and monitored the emissions. The company determined that the emissions were similar to those from burning coal alone. In a second test-bum of 1900 t of TDE, magnetic separation equipment removed metal from the resulting ash, so that it could be recycled as a winter traction agent for roadways. 

Table 7 lists the results of test bums at two coal-combusting power plants a western Kentucky power plant, which burned pure Illinois Basin coal (Table 4) and two blends of this coal + TDF (99 wt% coal + 1 wt% TDF 97 wt% coal + 3 wt% TDF) in a cyclone boiler (Hower et al. 2001) and the Purdue University power plant, which used a stoker boiler to combust a comparable Illinois Basin coal as well as a blend containing 95 wt% of this coal and 5 wt% TDF (Table 4 this study). 

Mass balance measurements for 41 elements have been made around the Thomas A. Allen Steam Plant in Memphis, Tenn. For one of the three independent cyclone boilers at the plant, the concentration and flow rates of each element were determined for coal, slag tank effluent, fly ash in the precipitator inlet and outlet (collected isokinetically), and fly ash in the stack gases (collected isokinetically). Measurements by neutron activation analysis, spark source mass spectroscopy (with isotope dilution for some elements), and atomic adsorption spectroscopy yielded an approximate balance (closure to within 30% or less) for many elements. Exceptions were those elements such as mercury, which form volatile compounds. For most elements in the fly ash, the newly installed electrostatic precipitator was extremely efficient. 

Stopek, D.J., A.K. Millis, J.A. Stumbaugh, and D.J. Diewald. Testing of Tire-Derived Fuel at a 560 MW Cyclone Boiler. Presented at the EPRI Conference ... 

Tillman, D. A. and Stahl, R. W., Wood cofiring experience in cyclone boilers. Abstracts of Papers of the American Chemical Society 1995, 209, 31-FUEL. 

This was because in cyclone boilers the bulk of silicate ash is discharged as molten slag but the residual ash is relatively rich in sulphate. 

The plant has two 485 MW cyclone boilers and each boiler is approximately 138 feet high. During these tests, the LTS-100 launch and detector enclosures were mounted on flanges on fhe sides of the boiler approximately 103 feet above the bottom of the boiler. The pathlength of the LTS-100 measurement beam was 48 feet. The processing unit was located in the plant terminal room 122 feet below the measurement location. 

There are two types of wet-bottom boilers the slag-tap boiler and the cyclone boiler. The slag-tap boiler burns pulverized coal and the cyclone boiler burns crushed coal... 

Other commercial systems include cyclone boilers, fluidized-bed boilers, grate-based fiunaces, and fuel cells. 

Boiler slag A molten ash collected at the base of slag tap and cyclone boilers that is quenched with water and shatters into black, angular particles having a smooth glassy appearance. 

Liquid slag corrosion of cyclone boilers Fossil 120 1.02... 

Post-consumer materials provide the final category of opportunity fuels. Representative post-consumer materials include tire-derived fuel (TDF), commonly used in cyclone boilers, stoker boilers, and cement kilns. Other post-consumer materials used as opportunity fuels include waste oil and re-refined oil, wastewater treatment gas, landfill gas, paper-derived fuel (PDF), plastics-derived fuel, refuse-derived fuel (RDF), sewage sludge, wastewater treatntent gas, and selected hazardous wastes burned in industrial boilers and kilns. 

With all of these pressures, Letheby [4] concludes that the baseload coal-fired power plant is among the most promising ntarkets for opportunity fuels. These plants can utilize up to 400,000 tonnes/yr at blend rates up to 20 percent— which is the common limit for using opportunity fuels in existing PC and cyclone boilers. At 20 percent (heat input basis) the opportunity fuels can significantly impact fuel cost, environmental performance, and other technical and economic parameters of such units. 

Cyclone boilers, installed by electric utilities until about 1975 in order to utilize slagging coals typically found in the Midwestern US, are distinct combustion systems that are highly favorable to cofiring petroleum coke. Coal crushed typically to 6.35 mm x 0 mm (V4 x 0 ) is introduced into a barrel typically 2.4 - 3.0 m (8 - 10 ft) diameter and 3.0 m - 3.7 m (10 - 12 ft) long where combustion occurs in a highly intense environment. Normally 2-14 cyclone barrels are mounted horizontally for a given furnace the largest cyclone boiler has 23 cyclone barrels. 

Petroleum coke has been cofired in several such units [21, 27]. The impact of petroleum coke cofiring in cyclone boilers has been detailed in two such units Paradise Fossil Plant (PAF), owned by Tennessee Valley Authority (TVA), and Bailly Generating Station (BGS),... 

Petroleum coke was cofired in Paradise Fossil Plant (see Figure 2.7) Unit 1, a 700 MWe cyclone boiler equipped with 14 cyclone barrels, each 3.05 m (10 ft) in diameter. These cyclones are equipped with radial feeders. The boiler generates 611.6 kg/sec (4,850,000 Ib/hr) of 166.6 bar/565°C/538°C (2415 psig/1050T/1000 F) steam. The unit is equipped with a wet scrubber for SO2 emissions control. At the time of testing, the typical fuel burned at this installation was Western Kentucky high sulfur coal, with characteristics as shown in Table 2.10. Also shown in Table 2.10 is the analysis of the petroleum coke burned during the test period. 

The cofiring of petroleum coke at Paradise Fossil Plant demonstrated key benefits to the use of this opportunity fuel in cyclone boilers. Testing at the Bailly Generating Station of NIPSCO further reinforced and extended these findings. 

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