Boilers fuel characteristics

Boiler Design Issues Boiler design involves the interaction of many variables water-steam circulation, fuel characteristics, firing systems and heat input, and heat transfer. The furnace enclosure is one of the most critical components of a steam generator and must be conservatively designed to assure high boiler availability. The furnace... 

Fuel Characteristics Fuel choice has a major impact on boiler design and sizing. Because of the heat transfer resistance offered by ash deposits in the furnace chamber in a coal-fired boiler, the mean absorbed heat flux is lower than in gas- or oil-fired boilers, so a greater surface area must be provided. Figure 27-42 shows a size comparison between a coal-fired and an oil-fired boiler for the same duty. 

The characteristic distribntion in the pyrolysis oil is a low yield of medinm oil, for diesel or boiler fuel, but a high yield of light oil. The light oil has similar properties to naphtha from crude oil. If this is used in the recycling process as fnel, no volatile oil tax (gasoline tax) is imposed. However, in the case of external sale, the nser has to pay the tax. As a resnlt of regulation by the volatile oil tax law, the light oil is not appropriate for ontside sale at all. 

EUREKA pitch is quality pulverized fuel as its characteristics shown in Table 3. The conventional boiler designed for fuel oil can be used for pitch burning as it is. Several Japanese manufacturers had employed EUREKA pitch as boiler fuel. 

Tillman, D.A. 2(K)3. Fundamental Fuel Characteristics of Woody Biomass Implications for Cofiring in Coal-Fired Boilers. International Confq-ence on Co-Utilization of Domestic Fuels. Gainsville, FL. Feb. 5-6. 

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. 

The remaining sections of this chapter focus on the fuel characteristics of TDF including some comparisons to other types of fossil fuels. The bulk of the chapter focuses on case studies where TDF has been utilized in industrial and utility boilers. These studies are highlighted to provide information on successes and concerns experienced by the various users. 

Characteristics of various atomizers are given in Table 24.1. Primary considerations are selecting the best principle for the type of fuel, the size of the burner/boiler and the type of application. Other important characteristics are ability to operate with the minimum of excess air, turndown ratio and questions of durability and maintenance. 

However, this is not likely to be the case. In this example, the two boilers might have different fuels, with different fuel costs and different efficiencies, and the gas turbine (perhaps, with supplementary firing) will have completely different characteristics from the steam boilers. Thus, there are degrees of freedom created by multiple steam generation devices with different costs of fuels, different boiler efficiencies and different power generation potential. Individual steam boilers and HRSGs will have minimum and maximum flows. 

FIG. 24-59 Characteristic curves for boiler thermal efficiency as a function of flue gas effluent temperature and flue gas water dew points. Based on the LHV of a fuel, and stoichiometric reaction, 100 percent efficiency would be achieved if sufficient combustion heat were recovered and removed, so that the temperature of the effluent flue gas was reduced to 25°C. For a flue gas with a 55°C dew point, recovering additional heat via condensation by cooling from 175 to 35°C (as shown) would increase the overall efficiency by more than 13 percent. Courtesy Combustion b- Energy Systems, Ltd. www.condexenergy.com.)... 

Fuel viscosity directly influences the pumping and atomization characteristics of the fuel. High-viscosity fuel may be difficult to efficiently pump through lines and filters unless it is heated. Also, high-viscosity fuels may not atomize and finely disperse when injected into the combustion chamber of an engine or into the firebox of a boiler. Incomplete atomization results in poor fuel efficiency and high hydrocarbon emission values. 

Rankine Cycle. The sleam-Rankine cycle employing steam turbines has been the mainstay of utility thermal electric power generation for many years. The cycle, as developed over the years, is sophisticated and efficient. The equipment is dependable and readily available. A typical cycle (Fig. 21) uses superheat, reheat, and regeneration. Heat exchange between flue gas and inlet air adds several percentage points to boiler efficiency in fossil-fueled plants. Modern steam Rankine systems operate at a cycle top temperature of about 800 K with efficiencies of about 40%. All characteristics of this cycle are well suited to use in solar plants. 

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