毕业论文外文翻译生物质混烧方案的减排和燃煤发电厂的发电成本

1、外文文献：Biomass co-firing options on the emission reduction and electricity generation costs in coal-fired power plantsAbstractCo-firing offers a near-term solution for reducing CO2 emissions from conventional fossil fuel power plants. Viable alternatives to long-term CO2 reduction technologies such as

2、 CO2 sequestration, oxy-firing and carbon loop combustion are being discussed, but all of them remain in the early to mid stages of development. Co-firing, on the other hand, is a well-proven technology and is in regular use though does not eliminate CO2 emissions entirely. An incremental gain in CO

3、2 reduction can be achieved by immediate implementation of biomass co-firing in nearly all coal-fired power plants with minimum modifications and moderate investment, making co-firing a near-term solution for the greenhouse gas emission problem. If a majority of coal-fired boilers operating around t

4、he world adopt co-firing systems, the total reduction in CO2 emissions would be substantial. It is the most efficient means of power generation from biomass, and it thus offers CO2 avoidance cost lower than that for CO2 sequestration from existing power plants. The present analysis examines several

5、co-firing options including a novel option external (indirect) firing using combustion or gasification in an existing coal or oil fired plant. Capital and operating costs of such external units are calculated to determine the return on investment. Two of these indirect co-firing options are analyzed

6、 along with the option of direct co-firing of biomass in pulverizing mills to compare their operational merits and cost advantages with the gasification option.1. Introduction The evidence of the effects of anthropogenic emission on global climate is overwhelming 1. The threat of increasing global t

7、emperatures has subjected the use of fossil fuels to increasing scrutiny in terms of greenhouse gas (GHG) and pollutant emissions. The issue of global warming needs to be addressed on an urgent basis to avoid catastrophic consequences for humanity as a whole. Socolow and Pacala 2 introduced the wedg

8、e concept of reducing CO2 emissions through several initiatives involving existing technologies, instead of a single future technology or action that may take longer to develop and stronger willpower to implement. A wedge represents a carbon-cutting strategy that has the potential to grow from zero

9、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, man

10、y 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 emissions-free power sector, but they

11、 will take years to come 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 elec

12、tricity 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 agri

13、cultural 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 l

14、and in Canada, which were earlier farmed, are no longer farmed. These lands could be planted withfast-growing energy crops, like switch-grass offering potentially large quantities of biomass for energy production 6. Living biomass plants absorb CO2 from the atmosphere. So, its combustion/gasificatio

15、n 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 bioma

16、ss co-firing has a lower net CO2 contribution over conventional coal-fired plants. Biomass co-firing is one technology that can be implemented immediately in nearly all coal-fired power plants in a relatively short period of time and without the need for huge investments. It has thus evolved to be a

17、 near-term alternative to reducing the environmental impact of electricity generation from coal. Biomass co-firing offers the least cost among the several technologies/ options available for greenhouse gas reduction 7. Principally, co-firing operations are not implemented to save energy but to reduc

18、e cost, and greenhouse gas emissions (in some cases). In a typical co-firing 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 coal-fired plant. The primary savings f

19、rom co-firing 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 prov

20、ide the cost savings needed 8. Apart from direct savings in fuel cost, other financial benefits that can be expected from co-firing include the following:·Various pollution-reduction incentives: As co-firing, through synergetic effects, reduces the net SOx, NOx and heavy metal emissions, the pl

21、ant could claim the applicable pollutionreduction incentives offered by government agencies.· Financial incentives for plant greenhouse gas (GHG) emission reduction: A co-firing plant that uses biomass to replace an amount of coal in an existing boiler will reduce almost an equal amount of net

22、CO2 emission from the plant.· On-demand power production: Unlike other renewable energy technologies (e.g.: solar, wind), biomass-based 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

23、.· An option towards meeting a renewable energy portfolio: Cofiring offers a fast track, low-cost opportunity to add renewable energy capacity economically as it can be added to any coalfired plant immediately, with minimum investment.· Earning of renewable energy tax credits: The use of b

24、iomass as an energy source to displace fossil fuel can be eligible for special tax credits from many governments.· Fuel flexibility: Biomass as a fuel provides a hedge against price increases and supply shortages of coal ore. In co-firing, biomass can be viewed as an opportunity fuel, used only

25、 when the price is favorable.·biomass fuels are generally sourced from the areas in the immediate vicinity of the plant (to save on transportation costs), the local communities benefit economically from the production of biomass fuels. All these potential benefits are, however, complex function

26、s 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 co-firing. The present paper discusses the effect of these factors on the viability of differen

27、t technical co-firing options in coal-fired power plants. To illustrate these effects, an analysis of the economic aspects of different co-firing options is performed by considering the case of a 150 MW pulverized coal (PC) fired power plant in Canada.2. Co-firing options Biomass co-firing has been

28、successfully demonstrated in over 150 installations worldwide for a combination of fuels and boiler types 9. The co-firing technologies employed in these units may be broadly classified under three types: i. Direct co-firing, ii. indirect co-firing, and iii. gasification co-firing. In all three opti

29、ons, 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 co-firing option depends on a number of fuel and site specific factors. The objective of this an

30、alysis is to determine and compare the economics of the different co-firing options. Brief descriptions of the three co-firing options are presented here.2.1. Direct co-firing Direct co-firing involves feeding biomass into coal going into the mills, that pulverize the biomass along with coal in the

31、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

32、incorporate biomass cofiring in pulverized coal power plants 10. In the first option, the pre-processed biomass is mixed with coal upstream of the existing coal feeders. The fuel mixture is fed into the existing coal mills that pulverize coal and biomass together, and distribute it across the existi

33、ng coal burners, based on the required co-firing rate. This is the simplest option, involving the lowest least capital costs, but has a highest risk of interference with the coal firing capability of the boiler unit. Alkali or other agglomeration/corrosion-causing agents in the biomass can build-up

34、on heating surfaces of the boiler reducing output and operational time 11. Furthermore, different combustion characteristics of coal and biomass may affect the stability and heat transfer characteristics of the flame 12. Thus, this direct co-firing option is applicable to a limited range of biomass

35、types and at very low biomass-to-coal co-firing ratios. The second option involves separate handling, metering, and pulverization of the biomass, but injection of the pulverized biomass into the existing pulverized fuel pipe-work upstream of the burners or at the burners. This option requires only m

36、odifications external to the boiler. One disadvantage would be the requirement of additional equipment around the boiler, which may already be congested. It may also be difficult to control and to maintain the burner operating characteristics over the normal boiler load curve. The third option invol

37、ves the separate handling and pulverizationof the biomass fuel with combustion through a number of burners located in the lower furnace, dedicated to the burning of the biomass alone. This demands a highest capital cost, but involves the least risk to normal boiler operation as the burners are speci

38、fically designed for biomass burning and would not interfere with the coal burners. The final option involves the use of biomass as a reburn fuel for NOx emission control. This option involves separate biomass handling and pulverization, with installation of separate biomass fired burners at the exi

39、t of the furnace. As with the previous option, the capital cost is high, but risk to boiler operation is minimal.2.2. Indirect or external co-firingIndirect co-firing involves the installation of a completely separate biomass boiler to produce low-grade steam for utilization in the coal-fired power

40、plant prior to being upgraded, resulting in higher conversion efficiencies. An example of this option is the Avedore Unit 2 project in Copenhagen, Denmark. In Canada, Greenfield Research Inc. has developed a similar CFB boiler design that utilizes a number of units of the existing power plant system

41、s like ID fan etc. to reduce the capital cost. In this system, a subcompact circulating fluidized bed boiler is designed specifically to have a piggy-back ride on an existing power plant boiler. Since it is not a stand-alone boiler it does not need many of the equipment or component of a separate bo

42、iler. This unit releases flue gas at relatively high temperature and joins the existing flow stream of the parent coal-fired boiler after air heater. Thus, the flue gas from the co-firing unit does not come in contact with any heating elements of the existing boiler, thus avoiding the biomass relate

43、d fouling or corrosion problem, which is the largest concern of biomass cofiring. This boiler is totally independent of the parent unit, and as such, any outage in the co-firing unit does not affect the generation of the parent plant. Thus this indirect combustion-based option offers high reliabilit

44、y. The piggy-back boiler produces low pressure steam feeding into the process steam header of the power plant. Fig. 1 shows the photograph of one such unit built by Greenfield Research Inc., for a 220MWe Pulverized coal-fired boiler in India. In this specific case, the piggy-back boiler fired waste

45、fuel from the parent boiler as that was the need of the plant. 2.3. Gasification co-firing Co-firing through gasification involves the gasification of solid biomass and combustion of the product fuel gas in the furnace of the coal-fired boiler. This approach offers a high degree of fuel flexibility.

46、 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

47、contains highly corrosive elements like chlorine, alkali etc., a certain amount of gas cleaning may be needed prior to its combustion in the furnace.Another important benefit of injection of gas in the furnace is that it serves as a gas-over firing designed to minimize NOx. Although less popular, in

48、direct 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 make these two options more attractive to utility companies in

49、 some cases.3. Current status of biomass co-firingThere are a number of co-firing 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 co-firing, mainly because it is the simples

50、t and least cost option. Examples include the 635 MWe EPON Project of Gelderland Power Station in Holland which uses direct co-firing with waste wood and the 150 MWe Studstrup Power Plant, Unit 1, near Aarhus, Denmark co-firing straw. Gasification co-firing is also an attractive option. Three exampl

51、es of the plants operating on this type of co-firing 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 co-firing installat

52、ions is operated at biomass: coal co-firing ratios of less than 10%, on a heat input basis. The successful operation of these plants shows that co-firing at low ratios does not pose any threat or major problems to the boiler operation. Fig. 2. Worldwide co-firing plant locationsFor higher co-firing

53、ratios, however, it might be necessary to use an indirect co-firing method.4. Case study methodology The present analysis of co-firing options considers only the economic and emissive effects of co-firing biomass within the plant facility and does not include changes in fuel transportation requireme

54、nts. 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 b

55、iomass 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 co-firing because especially in direct firing, the boiler furnace designed for a specific fossil fu

56、el may not respond favorably as there is a major departure in combustion and flame radiation characteristics when some other fuels in used. If co-firing 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 plan

57、t located in Eastern Canada. As such, only 10% biomass co-firing rate is considered in all the three different co-firing options examined here. Engineering design of the indirect co-firing system, its capital cost estimation, including fuel requirements for all three options, was carried out through

58、 a computer-based 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 th

59、e 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 co-firing options, the energy input remains the same, and was determined using the overall plant