Cofiring

Fig. 9. Monolithic multilayer ceramics (MMCs) derived from multilayer capacitor, high temperature cofire, and thick film technologies.

W. A. Vitriol andj. I. Steiaberg, "Development of a Low Fire Cofired Multilayer Ceramic Technology," 1983, pp. 593—598. 

C. A. Myler and J. L. Maliannali, Enef Recovery Erom Waste Explosives and Propellants Through Cofiring in CPIA Publication 556, CPIA, Laurel, Md., Oct. 1990, p. 61. 

D. Tillman, E. Hughes, and B. Gold, "Cofiring of Biofuels in Coal Eked Boilers Results of Case Study Analysis," Proceedings First Biomass Conference... 

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... 

Cofiring biomass has environmental benefits in addition to lowering greenhouse gases. Since biomass has little or no sulfur, sulfur dioxide (SOj) emissions are less when biomass fuels are used. In the United States, power plants have allowable sulfur dioxide levels for each gigawatt of power produced. If they produce less than the allowable amount of sulfur dioxide, they receive credits with which they can trade on the open market. The price for these sulfur dioxide credits is about 70 to 200 per ton. 

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. 

The low concentration of sulfur in biomass offers potential advantages for some applications. In cofiring applications, for example, the cleaner combustion gases from biomass dilute those from coal, and the overall concentrations of sulfur per unit of combustion gas are reduced. In most applications... 

The microstructure, properties, and performance of Ni-YSZ anodes depend sensitively on the microscopic characteristics of the raw materials (e.g., particles size and morphology of NiO and YSZ powders). The particle sizes of the starting YSZ powders vary usually from 0.2 to 0.3 pm, whereas those for the NiO powders are 1 pm. The Ni to YSZ volume ratio usually varies from 35 65 to 55 45. For example, the reported Ni to YSZ volume ratios include 34 66 [20, 21], 40 60 [24], 43 57 [22], and 55 45 [23], For a bilayer anode, the functional anode layer in contact with the electrolyte contains 45 to 50 vol% Ni, whereas the anode support layer has 35 to 40 vol% Ni [25, 26], A pore former is usually added to tailor the shrinkage (for the cofiring) and to achieve sufficient porosity (>30 vol%) in the anode or the anode support layer. 

The presence of a small amount of water vapor (up to pH20/pH2 = -0.03) in fuel reduces anode overpotential. For anode-supported cells, the use of pore formers is important to tailor the shrinkage during cofiring and to create adequate porosity for better performance. The difference in cell power output could differ by as much as 100% for cells as porosity changes from -30 to -50%. 

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. 

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