熱能與動(dòng)力工程畢業(yè)論文外文翻譯

1、熱能與動(dòng)力工程畢業(yè)論文外文翻譯外文文獻(xiàn)：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 c02 emissions from conventional fossil fuel power plants. viable alternatives to long-term c02 reduction techn

2、ologies such as c02 sequestration, oxy-firing and carb on loop combustion are being discussed, but all of them rema in in the early to mid stages of development. co-firing, on the other hand, is a wel1-proven technology and is in regular use though does not eliminate c02 emissions entirely. an incre

3、mental gain in c02 reduction can be achieved by immediate implementation of biomass co-firing in nearly all coal-fired power plants with minimum modifications and modcratc investment, making co-firing a near-term solution for the greenhouse gas emission problem. if a majority of coal-fired boilers o

4、perating around the world adopt co-firing systeins， the total reduction in c02 emissions would be substantial. it is the most efficient means of power generation from biomass, and it thus offers c02 avoidance cost lower than that forc02 sequestration from existing power plants. the present analysis

5、examines several co-firing options including a novel option external indirect firing using com bustion or gasif ica tion in an existing coal or oil fired plant. capital and operating costs of such external units are calculated to dctcrminc the return on investment. two of these indircct co-firing op

6、tions are analyzed along with the option of direct co-firing of biomass in pulverizing mills to compare their operational merits eind cost advantages with the gasification option.1. introductionthe evidence of the effeets of anthropogenic emission on global climate is overwhelming 1. the threat of i

7、ncreasing global temperatures 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 avoi d catastrophic consequences for humanity as a whole.socolow and pacala 2 int

8、roduced the wedge concept of reducing c02 emissions through several initiatives involving cxisting 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

9、 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 currcntly available that, with scaling up, could represent a wedge of emissions reduction.although ci number of emission reduction options are available to t

10、he 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 developmcnt. carbon dioxide sequestration or zero emission power plants represent the future of a c02 emissions-free power

11、sector, but they will take years to come to the mainstream market. the cost of 002 capture and sequestration is in the range of 40e60 us$/ton of c02, depending on the type of plant and where the c02 is storeel 4, 5 this is a significant economic burdcn on the industry, and could potenti ally escalat

12、e the cost of elec trie ity 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 in dustry are sent to lan df ill or are inci

13、 negated 6. in the agricu ltu ral sec tor, gra in crops produce an estimated 32 mill ion tons of st raw residue per year. allowing for a straw residue of 85% remaining in the fields to maintain soi 1 fertility, 5 mil1 ion tons would still be available for energy use. due to an increase in land produ

14、ctivity, significant areas of land in canada, which were earlier farmed, are no longer farmed. these lands could be plan ted withfast-growing cncrgy crops, like switch-grass offering potentially large quantities of biomass for energy production6living biomass plants absorb c02 from the atmosphere. s

15、o, its combustion/gasificat ion for energy production i s consi dered carbon neutral. thus if a ccrtain 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 cimount of foss訂 fuel in it. thus, a pow

16、er plant with integrated biomass co-firing has a lower net c02 contribution over conventional coal-fired plants.biomass co-firing is one technology that can be implemcnted immediately in nearly all coal-fired power plants in a relatively short period of time and without the need for huge investments

17、. it has thus evolved to be a near-term alternative to reducing the environmental impact of elec trie ity gen erati on from coal. biomass co_f ir ing offers the 1 east cost among the several technologies/ options available for greenhouse gas reduction 7. principally, co-firing operations are not imp

18、lemented to save energy but to reduce 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 con di t i ons for hea ting or power generation , with the same heat input as that in the existing co

19、al-fired plant. the primary savings from 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 unweinted biomass. biomass fuel at prices 20% or more be

20、low the coal prices would usually provide the cost savings needed 8.apar t ftom clircc t savings in fuel cos t, other financial bene fits that can be expected from co-firing include the following:?various pollution-reduction incentives: as co-firing, through synergetic effects, reduces the net sox,

21、nox and heavy metal emissions, the plant could claim the applicable pollutionreduct ion incentives offered by government agencies.? financial incentives for plant greenhouse gas ghg emission reduction: a co-firing plant that uses biomeiss to replace an eimount of coal in an existing boiler will redu

22、ce almost an equal amount of net c02 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 nccdcd. this helps to accelerate the capital investment payoff rate by utiliz

23、ing a higher capacity factor.? an option towards meeting a tenewable 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 cre

24、dits: the use of biomass as an energy source to displcice fossil fuel can be eligible for special tax credits from many governments.? fuel flexibi 1 ity: biomass as a fuel provides a hedge against price increases and supply shortages of coal orc. in co-firing, biomass can be viewed as an opportunity

25、 fuel, used only when the price is favorable.?biomass fuels are genereilly sourced from the areas in the immediate vicinity of the plant to save on transportdtion costs , the local communi ties benefit economically from the production of biomass fuels.all these potential benefits arc, however, compl

26、ex functions of local factors such as the price of coal and biomass, government policies, capital investment, and the carbon market in the eveiluation of the cost effectiveness of electricity production using biomass co-firing. the present paper di scusses the effect of these factors on the viabilit

27、y of different 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. cofiring optionsbiomass co-firing

28、has been successfully demonstrated in over 150 installations worldwide for a combination of fuels and boiler types 9 the co-firing technologics employed in those units may be broadly classified under three types:i. direct co-firing,ii. indirect co-firing, andiii. gasification cofiring.in all three o

29、ptions, the use of biomass displaces an equivalent amount of coal on an energy basis , and hence results in the direct reduction of c02 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

30、analysis is to detenuine 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-firingdirect co-firing involves feeding biomass into coal going into the mi 11 s, that pulverize the biomass along with coal in t

31、he same mill. sometime separate mills may be used or biomass is injected directly into the boiler furn ace t hrough the coal bur nets, or in a separate system. the level of intcgration into the cxisting plant depends principally on the biomass fuel characteristics.four different options are availabl

32、e to 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 mixturc is fed into the existing coal mills that pulverize coal and biomass together, and distribute it across the ex

33、isting coal bur nets, based on the required cof ir ing rate. this is the simplest option, involving the lowest least capital costs, but has a highest risk of interferenee with the coal firing capability of the boiler unit. alkal i or other agglomcration/corrosion-causing agents in the biomass can bu

34、ild-up on heating surfaces of the boiler reducing output and operational time 11. furthermore, different combustion characteristics of coeil and biomass may affect the stability and heat transfer characteristics of the flame 12 thus, this direct co-firing option is appl icable to a limited range of

35、biomass types and at very low biomass-to-coal co-firing rati os.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 upstteam of the burners or at the bur ners. this opt ion requi

36、res only modifications external to the boi 1 er. one disadvantage would be the requirement of additional equipment around the boiler, which may already be congested. it may also be difficuit to control and to maintain the burner operating charactcristics over the normal boiler load curve.the third o

37、ption invoives the separate hemdling and pulverizationof the biomass fuel with combustion through a number of burners located in the lower furneicc, dcdicated to the burning of the biomass alone.this demands a highest capital cost, but involves the least risk to nomial boiler operation as the burner

38、s are specifically designed for biomass burning and wou1d not interfere with the coal burners.the final option invoives 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 a

39、t the exit 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 installa,tion of a completely separate biomass bo訂er to produce low-grade steam for utilization in the coal-fi

40、red power plant prior to being upgraded, resulting in higher conversion efficiencies. an example of this option is the avedore unit 2 project in copenhagen, denmark. tn canada, greenfield research tnc. has developed a similar cfb boiler design that utilizes a number of units of the existing power pl

41、ant systems 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 boi 1 er. since i t is not a stand-al one boi 1 er i t does not need many of the equipment or component

42、 of a separate boiler. this unit releases flue gas at relatively high temperature and joins the existi ng flow st ream of the parent coal-fired boiler after air hcater. thus, the flue gas from the co-firing unit does not come in contact with any heating elements of the existing boiler, thus avoiding

43、 the biomass relcited 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 off

44、ers high reliability. the piggy-back boiler produces low pressure steeim feeding into the process steam header of the power plant. fig. 1 shows the photograph of one such unit bui 11 by greenfield research tnc.、 for a 220mwe pulverized coal-fired boiler in india. in this specific case, the piggy_bac

45、k boiler fired waste fuel from the parent boiler as that was the need of the plant.fig. 12.3. gasification co-firingco-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 de

46、gree of fuel flexibility. since the gas cam be injeeted 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 ef

47、ficiency. if the biomass contains highly corrosive elements like chlorine, alkali etc., a certain amount of gas clcaning may be nceded 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.

48、al though less popular, indi reel or external and gasif ication cofiring options have certain adva nt ages, such as the possibil ity to use a wide range of fuels and easy removal of ash. despite the significantly higher capital investment requirement，these adveintages meike these two options more at

49、tractive to utility companies in 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. 29, 13, most of these installations employdirect co-firing, mai

50、nly because it is the simplest and least cost option. examples include the 635 mwe epon projec t of ge ider land 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

51、attractivc option. three examples of the plants operating on this type of co-firing are: the 137 mwe zeltweg power pla nt in sty ria in austria, the amergas biomass gasif icati on project at the amer power plant in geertruidenberg, holland, and the kymiarvi power station at lathi in finland.the majo

52、rity of biomass co-firing installations 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 pla

53、nt locationsfor higher co-firing ratios， however, it might be necessary to use an indirect co-firing method.4. case study methodologythe present analysis of co-firing options considers only the economic and emissive effects of co-firing biomass with in the pla nt facility and docs not include change

54、s in fuel transportation requirements. in nor th 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 transporteition of fuel. tn area

55、s 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 environmentai costs.the amount of fuel replaccmcnt with biomass is generally very low in co-firing because especially in direct firing, the boiler furnac

56、e designed for a specific fossil fuel 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 lim it may not be t hat strin gent. the presen t economic analysis is

57、 based on a 150 mw pulverized coal plant 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 cofiring system, its capital cost estimation, inc 1 liding fuel requirements for a

58、ll three options, was carried out through a computer-based analysis.table 1 lis ts the inp uts of the thermodyncimic design. the proper ties 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 discar

59、ded 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 boilets. 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 generation an