【正文】 t cofiring and gasifier cofiring), for capital cost amortization, the Revenue Canada guideline of allowing half the rate in the first year was used. . Internal rate of return 外文文獻(xiàn) 及譯文 14 Internal rate of return (IRR) for this new investment is the discount rate that would make the present value (NPV) of the investment’s ine stream total to zero. It is an indicator of the efficiency or quality of an investment, as opposed to present value (NPV), which indicates value or magnitude. The present analysis is based on IRR. 6. Results . Fuel consumption The biomass consumption differs for each cofiring option due to the different efficiencies of the cofiring systems. The fuel required for direct cofiring is the lowest and represents the base amount of biomass required to provide 10% of the heat energy in the furnace of the PC boiler. The fuel requirement for the external CFB boiler is the highest of the three and was calculated based on the given turbine efficiency of 88% as well as the calculated efficiency of CFB boiler. This efficiency was found to be % and was based on the calculated losses from the boiler. Table 4 presents the breakdown of energy losses in the external CFB boiler. The biomass consumption rates and costs of the three cofiring options are given in Table 5. 外文文獻(xiàn) 及譯文 15 . Emission credits ine For the economic analysis, the main source of ine for the three cofiring options is the emissions credits earned through the reduction in coal usage. The yearly offset of coal, subsequent reductions in emissions and emission credit ine are presented in Table 6. IRR estimates for the three cofiring options are given in Table 7. The analysis indicates that direct cofiring can offer an internal rate of return of more than twice that of indirect cofiring. Direct cofiring however suffers from the largest uncertainty about fouling and corrosion of its superheater tubes, and resulting breakdown of the plant while handling biomass. This loss, conservatively estimated at 1%, could have signif。 Earning of renewable energy tax credits: The use of biomass as an energy source to displace fossil fuel can be eligible for special tax credits from many governments. Various pollutionreduction incentives: As cofiring, through synergetic effects, reduces the SOx, NOx and heavy metal emissions, the plant could claim the applicable pollutionreduction incentives offered by government agencies. M costs due to direct cofiring were estimated at $ 外文文獻(xiàn) 及譯文 10 Analysis of the external cofiring option required a preliminary design of a Circulating Fluidized Bed (CFB) boiler. The required thermal input for the steam generated by the biomass boiler was determined using a turbine efficiency of 88%. A thermal design of the boiler was done using CFBCAD in order to calculate the efficiency of the CFB boiler and used in conjunction with the turbine efficiency to calculate the required biomass fuel flow rate. The capital costs of the external cofiring were determined using a detailed cost assessment. This included the estimated costs of engineering design work, project management, boiler fabrication, civil footing, secondary ponents, controls and instrumentation, and erection and missioning. This cost estimate was based on previous work done by Greenfield Research Inc. on the feasibility of a subpact, biomassfired CFB boiler for placement within an existing PCfired plant. The capital cost of the CFB boiler worked out to $139/kWth. The Oamp。biomass fuels are generally sourced from the areas in the immediate vicinity of the plant (to save on transportation costs), the local munities benefit economically from the production of 外文文獻(xiàn) 及譯文 4 biomass fuels. All these potential benefits are, however, plex functions of local factors such as the price of coal and biomass, government policies, capital investment, and the carbon market in the evaluation of the cost effectiveness of electricity production using biomass cofiring. The present paper discusses the effect of these factors on the viability of different technical cofiring options in coalfired power plants. To illustrate these effects, an analysis of the economic aspects of different cofiring options is performed by considering the case of a 150 MW pulverized coal (PC) fired power plant in Canada. 2. Cofiring options Biomass cofiring has been successfully demonstrated in over 150 installations worldwide for a bination of fuels and boiler types [9]. The cofiring technologies employed in these units may be broadly classified under three types: i. Direct cofiring, ii. indirect cofiring, and iii. gasification cofiring. In all three options, the use of biomass displaces an equivalent amount of coal (on an energy basis), and hence results in the direct reduction of CO2 and NOx emissions to the atmosphere. The selection of the appropriate cofiring option depends on a number of fuel and site specific factors. The objective of this analysis is to determine and pare the economics of the different cofiring options. Brief descriptions of the three cofiring options are presented here. . Direct cofiring Direct cofiring involves feeding biomass into coal going into the mills, that pulverize the biomass along with coal in the same mill. Sometime separate mills may be used or biomass is injected directly into the boiler furnace through the coal burners, or in a separate system. The level of integration into the existing plant depends principally on the biomass fuel characteristics. Four different options are available to incorporate biomass cofiring in pulverized coal power plants [10]. In the first option, the preprocessed biomass is mixed with coal upstream of the existing coal feeders. The fuel mixture is fed into the