【正文】 of reducing CO2 emissions through several initiatives involving existing technologies, instead of a single future technology or action 外文文獻(xiàn) 及譯文 2 that may take longer to develop and stronger willpower to implement. A wedge represents a carboncutting strategy that has the potential to grow from zero today to avoiding 1 billion tons of carbon emissions per year by 2055. It has been estimated [3] that at least 15 strategies are currently available that, with scaling up, could represent a wedge of emissions reduction. Although a number of emission reduction options are available to the industry, many of them still face financial penalties for immediate implementation. Some measures are very site/location specific while others are still in an early stage of development. Carbon dioxide sequestration or zero emission power plants represent the future of a CO2 emissionsfree power sector, but they will take years to e to the mainstream market. The cost of CO2 capture and sequestration is in the range of 40e60 US$/ton of CO2, depending on the type of plant and where the CO2 is stored [4,5]. This is a significant economic burden on the industry, and could potentially escalate the cost of electricity produced by as much as 60%. Canada has vast amounts of biomass in its millions of hectares of managed forests, most of which remain untapped for energy purposes. Currently, large quantities of the residues from the wood products industry are sent to landfill or are incinerated [6]. In the agricultural sector, grain crops produce an estimated 32 million tons of straw residue per year. Allowing for a straw residue of 85% remaining in the fields to maintain soil fertility, 5 million tons would still be available for energy use. Due to an increase in land productivity, significant areas of land in Canada, which were earlier farmed, are no longer farmed. These lands could be planted withfastgrowing energy crops, like switchgrass offering potentially large quantities of biomass for energy production [6]. Living biomass plants absorb CO2 from the atmosphere. So, its bustion/gasification for energy production is considered carbon neutral. Thus if a certain amount of biomass is fired in an existing fossil (coal, coke or oil) fuel fired plant generating some energy, the plant could reduce firing the corresponding amount of fossil fuel in it. Thus, a power plant with integrated biomass cofiring has a lower CO2 contribution over conventional coalfired plants. Biomass cofiring is one technology that can be implemented immediately in nearly all coalfired power plants in a relatively short period of time and without the need for huge investments. It has thus evolved to be a nearterm alternative to reducing the environmental impact of electricity generation from coal. Biomass cofiring offers the least cost among the 外文文獻(xiàn) 及譯文 3 several technologies/ options available for greenhouse gas reduction [7]. Principally, cofiring operations are not implemented to save energy but to reduce cost, and greenhouse gas emissions (in some cases). In a typical cofiring plant, the boiler energy usage will be the same as it is operated at the same steam load conditions (for heating or power generation), with the same heat input as that in the existing coalfired plant. The primary savings from cofiring result from reduced fuel costs when the cost of biomass fuel is lower than that of fossil fuel, and avoiding landfill tipping fees or other costs that would otherwise be required to dispose of unwanted biomass. Biomass fuel at prices 20% or more below the coal prices would usually provide the cost savings needed [8]. Apart from direct savings in fuel cost, other financial benefits that can be expected from cofiring include the following: 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. Ondemand power production: Unlike other renewable energy technologies (.: solar, wind), biomassbased power generation can be made available whenever it is needed. This helps to accelerate the capital investment payoff rate by utilizing a higher capacity factor. 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. 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