熱能與動力工程專業畢業論文外文文獻及翻譯(存儲版)

　　

【正文】 ws the photograph of one such unit built by Greenfield Research Inc., for a 220MWe Pulverized coalfired boiler in India. In this specific case, the piggyback boiler fired waste fuel from the parent boiler as that was the need of the plant. . Gasification cofiring Cofiring through gasification involves the gasification of solid biomass and bustion of the product fuel gas in the furnace of the coalfired boiler. This approach offers a high degree of fuel flexibility. Since the gas can be injected directly into the furnace for burning, the plant can avoid expensive flue gas cleaning as one would need for syngas or fuel gas for diesel engines. As the enthalpy of the product gas is retained, this results in a very high energy conversion efficiency. If the biomass contains highly corrosive elements like chlorine, alkali etc., a certain amount of gas cleaning may be needed prior to its bustion in the important benefit of injection of gas in the furnace is that it 外文文獻 及譯文 7 serves as a gasover firing designed to minimize NOx. Although less popular, indirect or external and gasification cofiring options have certain advantages, such as the possibility to use a wide range of fuels and easy removal of ash. Despite the significantly higher capital investment requirement, these advantages ma ke these two options more attractive to utility panies in some cases. 3. Current status of biomass cofiring There are a number of cofiring installations worldwide, with approximately a hundred in Europe, 40 in the US and the remainder in Australia and Asia (Fig. 2) [9,13]. Most of these installations employ direct cofiring, mainly because it is the simplest and least cost option. Examples include the 635 MWe EPON Project of Gelderland Power Station in Holland which uses direct cofiring with waste wood and the 150 MWe Studstrup Power Plant, Unit 1, near Aarhus, Denmark cofiring straw. Gasification cofiring is also an attractive option. Three examples of the plants operating on this type of cofiring are: the 137 MWe Zeltweg Power Plant in Styria in Austria, the AMERGAS biomass gasification project at the Amer Power Plant in Geertruidenberg, Holland, and the Kymiarvi power station at Lathi in Finland. The majority of biomass cofiring installations is operated at biomass: coal cofiring ratios of less than 10%, on a heat input basis. The successful operation of these plants shows that cofiring at low ratios does not pose any threat or major problems to the boiler operation. Fig. 2. Worldwide cofiring plant locations 外文文獻 及譯文 8 For higher cofiring ratios, however, it might be necessary to use an indirect cofiring method. 4. Case study methodology The present analysis of cofiring options considers only the economic and emissive effects of cofiring biomass within the plant facility and does not include changes in fuel transportation requirements. In North America, many local sources of biomass are available, and the use of a locally available source of biomass could have benefits beyond those discussed in this paper, in terms of reduced costs and emission generated from transportation of fuel. In areas where the supply of high quality biomass is limited transportation of biomass to the plant would likely be an important part of the economic and environmental costs. The amount of fuel replacement with biomass is generally very low in cofiring because especially in direct firing, the boiler furnace designed for a specific fossil fuel may not respond favorably as there is a major departure in bustion and flame radiation characteristics when some other fuels in used. If cofiring is applied to a fluidized bed boiler, this limit may not be that stringent. The present economic analysis is based on a 150 MW pulverized coal plant located in Eastern Canada. As such, only 10% biomass cofiring rate is considered in all the three different cofiring options examined here. Engineering design of the indirect cofiring system, its capital cost estimation, including fuel requirements for all three options, was carried out through a puterbased analysis. Table 1 lists the inputs of the thermodynamic design. The properties of the biomass fuel used in the analysis were taken as that of the hardwood maple. Hardwood species are widely available in Eastern Canada and are often discarded when harvesting of softwood trees for the pulp and paper industry takes place, making hardwood very cost effective. For coal, a low ash bituminous type coal was considered, typical of the fuel type used in the specific pulverized coal boilers. Table 2 presents the results of the ultimate analysis of coal and biomass. For all three cofiring options, the energy input remains the same, and was determined using the overall plant generation and heat rate: where, Qplant is the plant heat input (MJ), Pplant is plant electrical generation (MWh) and 外文文獻 及譯文 9 HRplant is the plant heat rate (MJ/MWh). The heat input required from the biomass was calculated at 10% of the overall heat required by the plant. The amount of coal that would be offset through the cofiring of biomass, in a year, was found through the following equation: where, mco is the mass of coal offset by cofiring (tons/year), fbf is the biomass cofiring fraction, HHVcoal is the higher heating value of coal (MJ/ton), and CF is the plant capacity factor. The capacity factor specifies as to what extent the installed capacity of the plant is utilized, either for technical reasons, or for operational reasons. Technical reasons, leading to technical availability of the plant, may be less than 100% due to forced shutdown or routine maintenance. The higher the reliability of the cofiring option, the higher is this factor. Dir