外文翻譯--選煤概述和煤的可選性

1、<p>　　The outline of coal preparation and Economics of Coal Cleaning</p><p><b>　　Abstract</b></p><p>　　Coal preparation, simply put, is the conversion of run-of-mine (ROM) coal

2、(or coal as it leaves the mine complete with impurities and prior to any processing) into a marketable product. Originally, coal preparation began as a line of equipment-crushers, feeders, screens, etc.-to control the si

3、ze of the mined coal. Perhaps the easiest way to understand the evolution of coal cleaning and to understand the evolution of coal cleaning and to understand the variations found within the industry is to b</p>&l

4、t;p>　　Level 0 processing is the mining and shipping of ROM coal.</p><p>　　The product of Level 1 processing is commonly termed raw coal.</p><p>　　Level 2 processing involves the cleaning of t

5、he coarser sizes of raw coal (or coal which is larger than 1/2”).The coal finer than 1/2” would be added to the cleaned coal (the plus 1/2mm coal) or sent elsewhere.</p><p>　　Level 3 processing extends the c

6、leaning of the raw coal to the intermediate size raw coal-1/2” by 1/2mm.The minus 1/2mm material is added to the cleaned coal (the plus 1/2mm coal) or sent elsewhere.</p><p>　　Level 4 processing extends the

7、cleaning to include the minus 1/2mm raw coal.</p><p>　　The feed to the coal preparation plant is then raw coal from Level 1 processing. Coal’s impurities are numerous, but by far the largest have specific we

8、ights greater than coal. The raw coal is thus characterized by partitioning the very heterogeneous coal into relatively homogeneous subpopulations on the basis of size and specific gravity.</p><p>　　The sepa

9、ration unit operations normally process water/raw coal slurries, thus the term’ Coal Washing.’ Coal preparation is the quality control arm of the coal industry. It is an integral part of the coal business. </p>&l

10、t;p>　　2. The Cumulative Float Curve-a plot of the cumulative float weight percent versus the cumulative float ash percent.</p><p>　　The outline of coal preparation</p><p>　　Coal preparation,

11、simply put, is the conversion of run-of-mine (ROM) coal (or coal as it leaves the mine complete with impurities and prior to any processing) into a marketable product. (A quality-controlled substance whose composition me

12、ets the ever-increasing specifications required for its use whether it’s combustion, liquefaction, gasification or carbonization.)</p><p>　　The coal we mine today represents the deposition of phytogenic mate

13、rial 50 to 350 million years ago. The resulting horizontal strata, what we call coal seams, will vary in thickness from several inches to several hundred feet. They are usually separated by varying thicknesses of sedimen

14、tary rocks such as shales, clays, sandstones and, sometimes, even limestone, OR-when combined with coal-what are known as impurities in terms of preparation.</p><p>　　Originally, coal preparation began as a

15、line of equipment-crushers, feeders, screens, etc.-to control the size of the mined coal. Among the product line was the conveying picking table which was used to visually inspect the ROM coal so that obvious impurities

16、could be removed manually. Thousands of men, women and children performed this unfulfilling work until mechanization replaced it withmore modern coal cleaning equipment.</p><p>　　Generally speaking, this coa

17、l cleaning equipment was developed for British and European mines because their coal was of much greater value per ton than in the U.S. Its value reflected its cost of mining-which was high –because the seams were more d

18、ifficult to mine compared with American coal seams.</p><p>　　However, although U.S. seams are among the easiest in the world to mine, preparation took on a new significance with the unionization of mines dur

19、ing the New Deal. A rapidly rising demand for machines to mine coal both underground and above ground was created; machines which were not and are not selective and which mine whole seams, including partings and some roo

20、f and floor mater ials.</p><p>　　Mechanical mining meant mechanical cleaning.</p><p>　　Perhaps the easiest way to understand the evolution of coal cleaning and to understand the evolution of coa

21、l cleaning and to understand the variations found within the industry is to become familiar with the levels of coal preparation.</p><p>　　Each level is indicative of the intensity of the work performed on ru

22、n-of-mine coal and each is an extension of the previous level.</p><p>　　Level 0 processing is the mining and shipping of ROM coal.</p><p>　　Level 1 processing combines top-size control by crushi

23、ng, with some removal of undesirable constituents such as tramp iron, timber and perhaps strong rocks. The product of Level 1 processing is commonly termed raw coal.</p><p>　　Level 2 processing involves the

24、cleaning of the coarser sizes of raw coal (or coal which is larger than 1/2”).The coal finer than 1/2” would be added to the cleaned coal (the plus 1/2mm coal) or sent elsewhere.</p><p>　　Level 3 processing

25、extends the cleaning of the raw coal to the intermediate size raw coal-1/2” by 1/2mm.The minus 1/2mm material is added to the cleaned coal (the plus 1/2mm coal) or sent elsewhere.</p><p>　　Level 4 processing

26、 extends the cleaning to include the minus 1/2mm raw coal.</p><p>　　Developing the appropriate circuitry for processing raw coals at Levels 2,3 and 4 involves four areas-characterization, liberation, separat

27、ion and disposition.</p><p>　　Characterization is the systematic examination of the ROM coal in order to determine the make up of the feed to the coal preparation plant. A coal processing engineer will devel

28、op a flowsheet of the unit operations required to achieve the desired preparation level.</p><p>　　Liberation is the creation of individual particles whose composition are predominantly coal or refuse. This i

29、s achieved by size reduction or the crushing of the justmined coal to a particular top size as determined by the characterization study. The feed to the coal preparation plant is then raw coal from Level 1 processing. Un

30、fortunately, particles containing both coal and refuse－known as middlings-are also created</p><p>　　Separation is, simply, the dividing of the particles into their appropriate groups-coal, refuse and middlin

31、gs. Coal’s impurities are numerous, but by far the largest have specific weights greater than coal. The dominant method for separating the liberated coal is by gravity concentration which relies on two physical property

32、differences-size and specific gravity. The raw coal is thus characterized by partitioning the very heterogeneous coal into relatively homogeneous subpopulations on the basis</p><p>　　Disposition is the clean

33、ing up of the various streams.</p><p>　　The separation unit operations normally process water/raw coal slurries, thus the term’ Coal Washing.’ The predominant disposition operation is the dewatering (separat

34、ing the liquid and the solis ) of the various atre ams after the separations have been made. The second most important disposition operation is refuse disposal, followed by other environmental control operations.</p&g

35、t;<p>　　Coal preparation is the quality control arm of the coal industry. It is an integral part of the coal business. </p><p>　　Washability</p><p>　　Washability studies are conducted pri

36、marily to determine how much coal can be produced at a given specific gravity and at what separation difficulty and size.</p><p>　　The importance of the size analysis is perhaps more clear if you think of th

37、e cleaning process as removing impurities form individual pieces of coal, rather than in terms of tons of coal.</p><p>　　As the individual pieces get smaller they become harder—and more costly—to clean.</

38、p><p>　　Generally , the testing procedures of a washability study begin by obtaining a representative sample of the material already reduced to a designated top size, Next, the sample is sized at several diff

39、erent screen apertures, with each fraction held separately for further evaluation. A typical size analysis for a feed material is shown in Table 1.</p><p>　　The table presents the percent of total weight, as

40、 well as an analysis of ash, sulfur content and Btu of each fraction, both individually and cumulatively.</p><p>　　Then the material of each size fraction undergoes a float-sink test in liquids of pre-select

41、ed, carefully controlled specific gravities, beginning with the lowest.</p><p>　　The float material from each specific gravity bath is then weighed and sink material is tested in the next heavier bath.</p

42、><p>　　The procedure is repeated until the desired number of float-sink result for the fraction in Table1 is given in Table 2.</p><p>　　Since wider ranges are treated commercially, composite r

43、esults are usually made by properly combining the individual size fraction results. A typical composite result of the material (Level 3 processing)in Table 1 is shown in Table3.</p><p>　　This type of data i

44、s then used to develop washability curves-curves as unique to the coal as fingerprints to a hand-which describe the various characteristics of the coal.</p><p>　　For example, Figure 1 shows three curves, gen

45、erated from the data in Table 3, which are generally employed:</p><p>　　1. The Yield Curve-a plot of the cumulative float weight percent versus specific gravity;</p><p>　　2. The Cumulative Float

46、 Curve-a plot of the cumulative float weight percent versus the cumulative float ash percent;</p><p>　　3. The Cumulative Sink Curve-a plot of the cumulative sink weight percent versus the cumulative sink ash

47、 percent.</p><p>　　The theoretical cleaning capability can be determined from the curves. For example, if it is desired to produce a 28m product of 10% ash, the theoretical product quantity will be 75.8% of

48、the feed. The separation must be made at a specific gravity of 1.665 and the rejects should analyze 82.1% ash.</p><p>　　Economics of Coal Cleaning</p><p><b>　　Abstract</b></p>

49、<p>　　A second stage of evaluation is then based on user costs deriving from coal properties. Losses of yield in cleaning represent the biggest item contributing to total cleaning costs because the size, and hence

50、the capital cost of a cleaning plant, is based on the throughput capacity for raw coal .It is generally accepted that capital costs reduce with increases in plant size, although not all the items comprising a cleaning pl

51、ant are directly units .For example ,the sizes of raw coal storage and h</p><p>　　Economic analysis is also greatly influenced by the relationship of the coal producer to the coal user .At least three differ

52、ent considerations may arise:(1) cleaned coal is produced for sale under comparatively short term contracts (1 to 3 years) in a competitive market, (2) coal is produced on long-term (7years and more) supply contracts, an

53、d (3) coal production and cleaning forms part of a totally integrated operation in which coal is mined and used by a single industrial undertaking. The ele</p><p>　　For a given annual production, capital cos

54、ts are highly dependent upon raw coal quality as determined by ash content and size consist. The former determines the yield of clean coal, and since plant capacities are dictated by raw coal throughputs, this factor has

55、 the major influence on capital requirements. The average yield of current American coal cleaning plants is 71%. </p><p>　　Economics of Coal Cleaning</p><p>　　In recent times modern wash plants

56、in the United States has been standing idle because the premium on price necessary to cover cleaning costs could not be recovered in a slack coal market tend to evaluate their coal purchases by methods that indicate mini

57、mum costs in energy terms (i.e., delivered cost per million Btu). A second stage of evaluation is then based on user costs deriving from coal properties. These can be complex and include such items as ash content, ash co

58、mposition and fusion temp</p><p>　　However, calorific value is not a primary control function in coal cleaning .It has an approximately linear relationship to ash and moisture contents. But after gross rock

59、dilution in a raw coal has been removed, the yield in terms of thermal efficiency of recovery with ash content becomes nonlinear and an increasing penalty in thermal recovery for unit decreasing in ash content becomes th

60、e rule. Losses of yield in cleaning represent the biggest item contributing to total cleaning costs because </p><p>　　Economic analysis is also greatly influenced by the relationship of the coal producer to

61、the coal user .At least three different considerations may arise:(1) cleaned coal is produced for sale under comparatively short term contracts (1 to 3 years) in a competitive market, (2) coal is produced on long-term (7

62、years and more) supply contracts, and (3) coal production and cleaning forms part of a totally integrated operation in which coal is mined and used by a single industrial undertaking. Types </p><p>　　Additi

63、onal complexity arises from tougher environmental regulation in which coal cleaning is only one aspect of control technology available for limited emissions of sulfur oxides and particulates, including hazardous trace el

64、ements. It has already been noted that environmental regulation relating to the operation of cleaning plants –liquid effluents, fugitive dust, and noise—have resulted in significant increases in capital and operating cos

65、ts. </p><p>　　The future growth of coal cleaning in the United States will be largely determined by the attitude of the electric utilities industry and the extent to which utilities companies enter into full

66、 or joint ownership of the means of coal production. This may result in decisive changes in the way in which economic evaluation of new coal projects, including cleaning, are made .The financial yardsticks applied, until

67、 very recent times, for determining the economic worth of coal cleaning were relatively</p><p>　　The utilities employ different accounting principles from the DCF-ROI type of evaluation and they employ diffe

68、rent funding methods, particularly as regards debt/equity ratios. Traditionally, their payback periods are substantially longer, 3o to 40 years for fossil-fired plant. These differences can result in substantial changes

69、in the fixed capital largest element in coal cleaning costs, being greater than 50% at all levels of preparation. Although a number of cost studies are in progress, the f</p><p>　　The elements of the cost of

70、 coal cleaning comprise fixed costs arising from capital charges, and fixed or variable costs arising from plant operation. </p><p>　　Capital charges are determined by the depreciation of costs incurred in l

71、and acquisition and preparation; design procurement and construction; provision of utilities and transportation and communications facilities; taxes; working capital; and interest charges. They are a fixed-cost burden un

72、affected by actual plant throughputs. </p><p>　　Operating expenses include salaries, wages, power costs, water costs, and productive supplies, including fuels, refuse, and waste disposal. This category may i

73、nclude fixed costs independent of plant throughput (e. g., salaries) or variable costs tied directly to throughput (e. g., productive supplies).</p><p>　　For a given annual production, capital costs are high

74、ly dependent upon raw coal quality as determined by ash content and size consist. The former determines the yield of clean coal, and since plant capacities are dictated by raw coal throughputs, this factor has the major

75、influence on capital requirements. The average yield of current American coal cleaning plants is 71%. The most expensive items of capital equipment to provide and operate are required for handling fine and ultrafine coal

76、 sizes </p><p>　　Capital and operating costs are also sensitive to plant utilization and the system of working. Plant practices vary from single-shift, 5-day-week operation to continuous-shift, 7-day operati

77、on. The latter normally allows one to three shifts per week downtime planned maintenance. It is clear that, for a given annual production, plant sizes and hence capital costs are related to the working practice adopted.&

78、lt;/p><p>　　選煤概述和煤的可選性</p><p><b>　　摘要</b></p><p>　　煤炭加工選煤概述簡單說來，選煤就是把原煤（即開采后未經(jīng)加工含有各種雜質(zhì)的煤）。商品煤是具有一定質(zhì)量規(guī)格的產(chǎn)品，它能滿足燃燒，液化氣化等方面所不斷提高的技術(shù)要求。現(xiàn)在開采的煤是五千萬到三億五千萬年前的植物沉積而成，所形成的水平層狀物稱之為煤層，

79、厚度不一，從數(shù)英寸到數(shù)百英尺。煤層中經(jīng)常夾雜著厚度不等的頁巖，粘土砂巖，有時(shí)還夾雜石灰?guī)r等沉積巖。從選煤的角度來說，這些和煤結(jié)合在一起的夾雜物稱之為雜質(zhì)。三級(jí)加工——選別中等粒度（1/2英寸×1/2毫米）的原料煤，小于1/2毫米粒級(jí)的則歸入精煤（大于1/2毫米）或送往他處。</p><p>　　原煤可選性的研究主要是為了決定在某一比重下可能獲得的產(chǎn)品數(shù)量和洗選的難以程度，并確定入洗煤的粒度。如果把選煤看

80、成是從一塊塊的煤中除區(qū)雜質(zhì)，而不是根據(jù)成噸的煤去考慮問題，就能比較清楚的理解粒度分析的重要性。粒度越小，選煤難度越大，成本越高。在可選性研究的試驗(yàn)程序開始之前，通常是先取出經(jīng)破碎達(dá)到規(guī)定粒度上限的煤樣，然后用各種篩子進(jìn)行篩分。各粒級(jí)產(chǎn)物要分別存放，以便進(jìn)行可選性評(píng)定。表1所示為入料粒度的典型分析。表中列出了各粒級(jí)產(chǎn)物的重量百分?jǐn)?shù)灰分硫分和發(fā)熱量，分本級(jí)和累計(jì)兩項(xiàng)。先配好重液，準(zhǔn)確調(diào)節(jié)其比重，然后對(duì)各粒級(jí)產(chǎn)物進(jìn)行浮沉試驗(yàn)，從比重最小的重液

81、開始。每一級(jí)重液中的浮起物要稱記重量，下沉物移入較高比重的重液，依次進(jìn)行，直到獲得個(gè)級(jí)比重物為止。表2為表1中產(chǎn)物的浮沉實(shí)驗(yàn)結(jié)果。由于工業(yè)上處理的粒級(jí)范圍較廣，經(jīng)常把某些粒級(jí)浮沉試驗(yàn)結(jié)果加以適當(dāng)組合，形成綜合結(jié)果。</p><p>　　近年來，由于支付選煤成本所需的額外費(fèi)用不能在蕭條的煤炭市場上回收，美國的現(xiàn)代化選煤廠一直處于停產(chǎn)狀態(tài)。在競爭性的市場上，用戶往往首先根據(jù)按能量計(jì)算最低價(jià)格（即每百萬英熱單位包括交貨

82、費(fèi)用在內(nèi)的價(jià)格）的方法判斷他們是否要購買。其次是判斷按煤的性質(zhì)決定的使用價(jià)值。煤的性質(zhì)比較復(fù)雜，它包括灰分，灰的組成及熔點(diǎn)，固定碳，硫分，破碎和磨碎特性等各項(xiàng)因素?？紤]了這些因素以后，還會(huì)改變最初的判斷，但按一般規(guī)律來說，只有在使用中如能明顯地節(jié)約費(fèi)用，才能認(rèn)為選煤這項(xiàng)額外費(fèi)用是合算的。</p><p>　　然而，熱值并不是選煤中應(yīng)加以控制的主要方面。它與灰分和水分呈近似的線性關(guān)系，但是在原煤中大塊巖石被揀除后，

83、產(chǎn)率和灰分之間變成非線性關(guān)系，一般的規(guī)律是降低灰分就要增加熱值回收率的損失。選煤中的產(chǎn)率損失是影響選煤總成本的最大項(xiàng)。由于選煤廠的規(guī)模乃至基建投資是以處理原煤的能力為基礎(chǔ)的，因此產(chǎn)率損失對(duì)投資費(fèi)產(chǎn)生最直接的影響。雖然構(gòu)成選煤廠的各個(gè)項(xiàng)目并非全部都直接涉及選煤設(shè)備的處理能力，但通常人們認(rèn)為隨著工廠規(guī)模增大，投資費(fèi)反而減少。按慣例，還本期很長，一個(gè)燃煤的廠的還本期為30-40年。</p><p>　　關(guān)鍵詞：煤炭加工

84、 選煤 原煤可選性</p><p>　　簡單說來，選煤就是把原煤（即開采后未經(jīng)加工含有各種雜質(zhì)的煤）。商品煤是具有一定質(zhì)量規(guī)格的產(chǎn)品，它能滿足燃燒，液化氣化等方面所不斷提高的技術(shù)要求。</p><p>　　現(xiàn)在開采的煤是五千萬到三億五千萬年前的植物沉積而成，所形成的水平層狀物稱之為煤層，厚度不一，從數(shù)英寸到數(shù)百英尺。煤層中經(jīng)常夾雜著厚度不等的頁巖，粘土砂巖，有時(shí)還夾雜石灰?guī)r等沉積巖。

85、從選煤的角度來說，這些和煤結(jié)合在一起的夾雜物稱之為雜質(zhì)。</p><p>　　最初，選煤是用一系列設(shè)備如破碎機(jī)給料機(jī)篩分機(jī)等來控制煤的粒度。其中手選皮帶是靠視力檢查原煤，利用人工揀除那些明顯的矸石。在手選帶被較現(xiàn)代化的洗選設(shè)備取代之前，揀矸工作是靠成千上萬的成人和兒童來完成。</p><p>　　一般說來，比較現(xiàn)代化的選煤設(shè)備是為英國等歐洲國家的煤礦研制的，因?yàn)檫@些國家每噸煤的價(jià)格大大地高

86、于美國。煤價(jià)反映了采煤成本。在英國和歐洲，煤層的難采度大于美國的，成本較高，因而煤價(jià)較高。</p><p>　　雖然美國的煤層屬于世界上最容易開采的煤層之列，在新政策（譯注：這是美國在二十世紀(jì)三十年代為緩解經(jīng)濟(jì)危機(jī)指定的一系列政策）時(shí)期，由于煤礦成立了工會(huì)，為了符合工會(huì)會(huì)章，選煤有了新的意義。人們對(duì)于無論是井下，露天用的或至今還沒有被淘汰的，以及開采全煤層（包括夾層，一些頂板和底板在內(nèi)的煤層）用的各種采煤機(jī)的需求

87、都有迅速增長。</p><p>　　機(jī)械化開采意味著機(jī)械化選煤。下面熟悉一下選煤等級(jí)，這也許是了解選煤發(fā)展和變化的一條捷徑。</p><p>　　每一等級(jí)都表示出毛煤加工的程度，同時(shí)又是前一級(jí)的延續(xù)。</p><p>　　零級(jí)加工——原煤的開采和運(yùn)輸。</p><p>　　一級(jí)加工——用破碎方法控制粒度上限，并除去某些雜物，如混入的鐵塊，坑木

88、和硬巖石等。該級(jí)產(chǎn)品常稱為入選原煤。</p><p>　　二級(jí)加工——選別粗粒級(jí)（大于1/2英寸）的入選原煤，而小于1/2英寸粒級(jí)的則歸入粗精煤或送往他處。</p><p>　　三級(jí)加工——選別中等粒度（1/2英寸×1/2毫米）的原料煤，小于1/2毫米粒級(jí)的則歸入精煤（大于1/2毫米）或送往他處。</p><p>　　四級(jí)加工——選別包括小于1/2毫米在內(nèi)

89、的入選原煤。</p><p>　　適合于二，三，四級(jí)加工的選煤流程的制定必須包括煤質(zhì)特性鑒定，解離，分選和選后處理等四個(gè)方面的內(nèi)容。</p><p>　　煤質(zhì)鑒定是有系統(tǒng)地測(cè)定毛煤，以便確定入廠原煤的組成。選煤工程師制定機(jī)組操作所需流程圖，以求出所需要的分選等級(jí)。</p><p>　　解離主要是使煤和矸石單體分離。其方法是減小粒度，即把剛采出的煤破碎到煤質(zhì)研究所確定

90、的粒度上限。入廠原煤是一級(jí)加工的產(chǎn)品。在解離過程中還有中煤即含煤和矸石的顆粒產(chǎn)生。</p><p>　　分選，簡而言之，是把入洗原煤分組，分成精煤，矸石和中煤。煤中的雜質(zhì)很多，但絕大多數(shù)雜質(zhì)的比重大于煤。選別單體解離的煤的主要方法是重力選，該方法以粒度和比重兩種物理特性的差異為基礎(chǔ)，把各部分極不勻質(zhì)的入選原煤分成相對(duì)勻質(zhì)的產(chǎn)品。</p><p>　　選后處理是指清除各種水分。分選作業(yè)過程通

91、常在水或原生煤泥水中進(jìn)行，因而叫做洗煤。選后處理作業(yè)最主要是選后產(chǎn)品的脫水（即把液體和固體分離），其次是廢渣處理和其它的環(huán)境保護(hù)措施。</p><p>　　選煤是煤炭工業(yè)中控制質(zhì)量的一個(gè)環(huán)節(jié)，是煤炭事業(yè)不可分割的一部分工作。</p><p>　　原煤可選性的研究主要是為了決定在某一比重下可能獲得的產(chǎn)品數(shù)量和洗選的難以程度，并確定入洗煤的粒度。</p><p>　　如

92、果把選煤看成是從一塊塊的煤中除區(qū)雜質(zhì)，而不是根據(jù)成噸的煤去考慮問題，就能比較清楚的理解粒度分析的重要性。粒度越小，選煤難度越大，成本越高。</p><p>　　在可選性研究的試驗(yàn)程序開始之前，通常是先取出經(jīng)破碎達(dá)到規(guī)定粒度上限的煤樣，然后用各種篩子進(jìn)行篩分。各粒級(jí)產(chǎn)物要分別存放，以便進(jìn)行可選性評(píng)定。表1所示為入料粒度的典型分析。表中列出了各粒級(jí)產(chǎn)物的重量百分?jǐn)?shù)灰分硫分和發(fā)熱量，分本級(jí)和累計(jì)兩項(xiàng)。</p>

93、;<p>　　先配好重液，準(zhǔn)確調(diào)節(jié)其比重，然后對(duì)各粒級(jí)產(chǎn)物進(jìn)行浮沉試驗(yàn)，從比重最小的重液開始。每一級(jí)重液中的浮起物要稱記重量，下沉物移入較高比重的重液，依次進(jìn)行，直到獲得個(gè)級(jí)比重物為止。表2為表1中 級(jí)產(chǎn)物的浮沉實(shí)驗(yàn)結(jié)果。</p><p>　　由于工業(yè)上處理的粒級(jí)范圍較廣，經(jīng)常把某些粒級(jí)浮沉試驗(yàn)結(jié)果加以適當(dāng)組合，形成綜合結(jié)果。表3所示是表1中 級(jí)產(chǎn)物的典型綜合結(jié)果。</p>&

94、lt;p>　　根據(jù)上列數(shù)據(jù)就可以繪制可選性曲線以顯示煤的不同特性。這些曲線象指紋一樣互不相同。</p><p>　　例如，圖1即為根據(jù)表3中的數(shù)據(jù)繪制的三條常用曲線：</p><p>　　近年來，由于支付選煤成本所需的額外費(fèi)用不能在蕭條的煤炭市場上回收，美國的現(xiàn)代化選煤廠一直處于停產(chǎn)狀態(tài)。在競爭性的市場上，用戶往往首先根據(jù)按能量計(jì)算最低價(jià)格（即每百萬英熱單位包括交貨費(fèi)用在內(nèi)的價(jià)格）的

95、方法判斷他們是否要購買。其次是判斷按煤的性質(zhì)決定的使用價(jià)值。煤的性質(zhì)比較復(fù)雜，它包括灰分，灰的組成及熔點(diǎn)，固定碳，硫分，破碎和磨碎特性等各項(xiàng)因素。考慮了這些因素以后，還會(huì)改變最初的判斷，但按一般規(guī)律來說，只有在使用中如能明顯地節(jié)約費(fèi)用，才能認(rèn)為選煤這項(xiàng)額外費(fèi)用是合算的。</p><p>　　然而，熱值并不是選煤中應(yīng)加以控制的主要方面。它與灰分和水分呈近似的線性關(guān)系，但是在原煤中大塊巖石被揀除后，產(chǎn)率和灰分之間變成

96、非線性關(guān)系，一般的規(guī)律是降低灰分就要增加熱值回收率的損失。選煤中的產(chǎn)率損失是影響選煤總成本的最大項(xiàng)。由于選煤廠的規(guī)模乃至基建投資是以處理原煤的能力為基礎(chǔ)的，因此產(chǎn)率損失對(duì)投資費(fèi)產(chǎn)生最直接的影響。雖然構(gòu)成選煤廠的各個(gè)項(xiàng)目并非全部都直接涉及選煤設(shè)備的處理能力，但通常人們認(rèn)為隨著工廠規(guī)模增大，投資費(fèi)反而減少。例如，原煤貯煤倉和處理設(shè)備的規(guī)格以及精煤倉和裝卸裝備的規(guī)格往往是根據(jù)所設(shè)計(jì)的貯運(yùn)系統(tǒng)的需要而定的。</p><p&g

97、t;　　經(jīng)濟(jì)分析在很大程度上取決于煤的生產(chǎn)者和消費(fèi)者之間的關(guān)系。至少有三種不同的考慮：（1）生產(chǎn)的精煤能在較短的銷售合同期限內(nèi)（1-3年）在競爭性市場上銷售；（2）煤炭生產(chǎn)的供應(yīng)合同期較長（7年或7年以上）；（3）煤炭生產(chǎn)和洗選構(gòu)成不可分割的整體作業(yè)中的一個(gè)部分，而煤的開采和使用則由一個(gè)工業(yè)企業(yè)負(fù)責(zé)。（1）和（2）兩類情況代表了冶金用煤和熱力用煤的過去和現(xiàn)狀。第（3）類狀況在目前煤炭工業(yè)重新組織和調(diào)整以及大型煤炭轉(zhuǎn)化廠和井口發(fā)電站增長后

98、可能適合。</p><p>　　比較難于對(duì)付的環(huán)境保護(hù)問題又增加了問題的復(fù)雜性。在環(huán)境保護(hù)法中，選煤控制氧化硫以及各種有害的微量元素的顆粒散發(fā)出去的唯一可行的方法。人們已經(jīng)注意到，解決選煤廠造成的污染——排出的污水，飛揚(yáng)的煤塵和噪聲——已使投資和運(yùn)轉(zhuǎn)費(fèi)用顯著提高。</p><p>　　在美國，今后選煤的發(fā)展主要取決于電力工業(yè)的狀況，也取決于電力事業(yè)公司擁有煤炭生產(chǎn)手段的程度，即全部擁有還是

99、共同擁有。這會(huì)引起對(duì)新的煤炭工程項(xiàng)目包括選煤工程項(xiàng)目在內(nèi)所作的經(jīng)濟(jì)估計(jì)發(fā)生決定性的變化。直到最近為止，用來確定選煤經(jīng)濟(jì)價(jià)值的財(cái)政尺度比較簡單。原煤的質(zhì)量，噸產(chǎn)量和預(yù)測(cè)的市場價(jià)格與精煤的相同參數(shù)相比較，然后估計(jì)出選煤的投資費(fèi)和運(yùn)轉(zhuǎn)費(fèi)，把它加到毛煤的基本生產(chǎn)費(fèi)中去。預(yù)計(jì)的生產(chǎn)費(fèi)用和銷售價(jià)格之間的差別成為使用各種計(jì)算工具來確定經(jīng)濟(jì)收益之間平衡的基礎(chǔ)。通常，通過現(xiàn)金貼現(xiàn)率分析能計(jì)算出10—15年期間各種不同方案的投資回收原則。因?yàn)槊禾可a(chǎn)公司對(duì)