Cofiring with coal

McGowin, C. R. 1991. Alternate fuel cofiring with coal in utility boilers. Proceedings 1991 Conference on Waste Tires as a Utility Fuel. Electric Power Research Institute, Palo Alto, CA, EPRI GS-7538, 1/1-1/9. 

Zauderer B Coal Tech Corp Merion Station, PA Control of Dioxin Emissions from Waste Fuel Combustion by Cofiring with Coal U.S. Department of Energy... 

This chapter reviews the fuel characteristics of TDF, along with several commercial demonstrations of tire-derived fuel cofired with coal in industrial and utility furnaces. Included in the fuel characteristics section are discussions of fuel characteristics, preparation and handling systems of the tire-derived fuel, methods of utilization of the cofired fuel including appropriate combustion systems (e.g., cyclone boilers, stokers, fluidized bed boilers) and environmental results of the TDF cofiring programs. 

Several conclusions can be drawn regarding the use of TDF cofired with coal in industrial and utility boilers. These include ... 

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. 

Also, wood fuel is low in sulfur, ash, and trace toxic metals. Wood-fired power plants emit about 45% less nitrogen oxides, NO, than coal-fired units. Legislation intended to reduce sulfur oxides, SO, and NO emissions may therefore result in the encouragement of wood-burning or cofiring wood with coal. 

Most electricity from biofuels is generated by direct combustion. Wood fuels are burned in stoker boilers, and mill waste lignin is combusted in special burners. Plants are generally small, being less than 50 MW in capacity. There is considerable interest in combustion of biomass in a process called cofiring, when biomass is added to traditional fuels for electricity production. Cofiring is usually done by adding biomass to coal, but biomass also can be cofired with... 

Biomass sequestration, which has been embraced by coal companies as the least expensive way to start carbon management, relies on capture from air. Cofiring with biomass followed by sequestration also would lead to a net C02 reduction in the atmosphere (Keith, 2001). On a per ton basis, this option is quite cost effective, but the amount of land area that would be required is extremely large to be practical. Consequently, it is worthwhile to consider other options. Currently, studies that consider capture of C02 directly from the air by chemical means are under way. These processes will require good chemical sorbents that do not pose any environmental concerns in their own right and can be regenerated cost effectively. 

Demirbas, A., Sustainable cofiring of biomass with coal. Energy Conversion Manage 2003,44 (9), 1465-1479. 

Cofiring Biofuel with Coal in an Industrial Boiler... 

Tillman, D.A. 2001. Final Report EPRI-USDOE Cooperative Agreement Cofiring Biomass With Coal. Contract No. DE-FC22-96PC96252. EPRI, Palo Alto, CA. 

Hus, P.J. and D.A. Tillman. 2000. Cofiring multiple opportunity fuels with coal at Bailly Generating Station. Biomass and Bioenergy. 19(6) 385-394. 

Harding, N. S., 2002. Cofiring Tire-Derived Fuel With Coal, 27 International Technical Confoence on Coal Utilization and Fuel Systems, Clearwater, FL. 

The testing demonstrated that cofiring petroleum coke with coal at Paradise Fossil Plant reduced the concentrations of mercury, chromium, lead, zinc, and cadmium in the fuel fed to the boiler [28]. The only metals exhibiting a significant increase in concentration in the fuel blend were vanadium and nickel. Because of the increase in concentration of vanadiiun and nickel, attention was given to the consequent partitioning and speciation of these metals found in abundance in the petroleum coke. Vanadium and nickel concentrations... 

The technical and economic consequence of the improved boii efficiency—up to 1.25 percent when cofiring 25 percent petroleum coke on a mass basis or 29 percent petroleum coke on a heat input basis— included reduced fuel flow to the bunkers and boiler. This, in turn, reduced the load on conveyors, fans, and other related mechanical systems. The improved efficiency resulted in a slightly reduced house load as a function of firing petroleum coke with coal. 

The fates of vanadium and nickel w also examined during the BGS test pro am. Metal balances were conducted for the tests when cofiring petroleum coke with coal— with and without the addition of urban wood waste. On average, and with little deviation, the vanadium partitioned equally between flyash and slag only half of the vanadium ended up in the flyash. Only 25 percent of the nickel ended up in the flyash with 75 percent reporting to slag [15,29-31]. 

Cofiring petroleum coke with coal in I C boilers has the economic potential associated with reducing fuel costs id tified previously. However, there are certain limitations with PC boilers. Many of these units sell flyash as pozzolanic material under the American Society for Testing and Materials (ASTM) Specification C-618. ASTM C-618 limits the unbumed carbon content in the flyash [32]. About 25 percent of the flyash generated in the US is sold under ASTM Specification C-618. The ability to sell flyash—or the inability to sell flyash—can impact plant... 

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