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关键词：: 车运原煤自动采样控制系统设计 cad图纸

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车运原煤自动采样控制系统设计

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车运原煤自动采样控制系统设计说明书.doc

车运原煤自动采样系统设计

（控制系统设计）

摘要

论文阐述了可编程控制器PLC在车运原煤自动采样系统中的应用。主要介绍了车运原煤自动采样的PLC控制系统总体方案设计，设计出了硬件控制电路、软件程序梯形图

及指令表，并给出了系统组成框图和程序流程图。

我设计的是对汽车所运原煤进行采样的自动小车控制系统，实现小车的横向、大车的纵向移动以及采样螺旋探头的上升、下降过程。系统采用可编程控制器控制。

采样工作过程如下：

当载运车辆到达采样点时，人工启动采样系统，采样小车先横向运行指定时间后停止，然后大车进行纵向运行，到指定位置时停止，螺旋采样筒旋转，采样头下降并旋转进入汽车煤层，到达一定深度后稍做停留，将车载原煤载入采样筒上方的采样斗中；然后采样头上升，大车小车后退回原位，采样头料门打开，煤样流入料斗，取样完成。

入厂原煤采制样装置是洗煤厂入厂原煤质量分析中的重要设备。利用可编程序控制器，实现对入厂原煤采制样装置的自动控制，不仅简化了操作，而且提高了系统的可靠性。

关键词∶ 可编程控制器；采样系统；自动控制

Abstract

The thesis elaborated the programmable controller PLC in car carry automatic sampling system of raw coal of application. The thesis mainly introduced the total project design of PLC control system that the car luck raw coal automatically sample, design the hardware control electric circuit, software procedure trapezoid chart

And the instruction gage, and give the system composition block diagram and the procedure flow chart.

What I design is an automatic and small car control system that samples to the autocar raw coal progress carry, carry out the small car of transversal and big car travel and sample the rising that screw stretch forward and descend the process lengthways. The system adopts the programmable controller control.

Sampled the process of operate as follows:

When transport the vehicle to arrive the sampling spot, the artificial start sampling system, sample the small car to traverse the running first to stop after specify time, then the big car progress circulates lengthways, while arriving to specify the place stop, the screw sampling tube revolution, sample the prinipal to descend and revolve into the coal seam, coalbed of autocar , make to stop over slightly after arriving the certain depth, carry car the sampling bucket that the raw coal loads in to sample on the above of the tube. Then sample the rising of prinipal, the small car of big car recoil to return to home position, sampling the prinipal to anticipate the door to open, the coal sample flows in to anticipate the bucket, the sampling complete.

Go into the raw coal of plant adopts to make the kind apparatus is important equipments that washes the coal plant to go into the plant raw coal mass analysis. Make use of the programmable preface controller, carry out to adopt the automatic control of make the kind apparatus towards going into the raw coal of plant, not only simplified the operation, but also raised the system reliability.

Key words: Programmable Logic Controller ；Sample system ；Automatic control

摘要………………………………………………………………………………… ⅰ

Abstract…………………………………………………………………………… ⅱ

目录………………………………………………………………………………… ⅲ

绪论………………………………………………………………………………… 1

第一章车运原煤自动采样系统总体方案设计 ………………………………… 2

一、总体方案确定…………………………………………………………… 2

二、设计采制样装置及其主要设备………………………………………… 7

第二章车运原煤自动采样控制系统设计 ……………………………………… 11

一、采制样装置的PLC控制系统组成 …………………………………… 11

二、PLC 的工作原理和结构组成…………………………………………… 11

三、PLC 的选择……………………………………………………………… 15

四、CPU 模块型式及电源模块型式规格选择……………………………… 20

五、变频器的选型…………………………………………………………… 22

第三章车运原煤自动采样软件系统的设计 …………………………………… 28

一、建立I/O地址分配表…………………………………………………… 28

二、端子接线图……………………………………………………………… 29

三、程序流程图……………………………………………………………… 29

四、PLC 程序设计 ………………………………………………………… 31

五、PLC 控制系统抗干扰能力……………………………………………… 38

结论………………………………………………………………………………… 41

致谢………………………………………………………………………………… 42

参考文献…………………………………………………………………………… 43

附录………………………………………………………………………………… 44

一、英文资料及中文翻译………………………………………………………… 44

二、梯形图………………………………………………………………………… 59

一、本论文研究的目的和意义

随着计算机技术的飞速发展，计算机在工业自动化领域中的应用越来越广泛。可编程控制器就是其中的佼佼者，它以其卓越的性能，高可靠性、能在恶劣环境下工作、维修使用方便、通讯、组网功能强和具有较高的性价比等特点，被广泛的应用于工业控制中。

火力发电厂、港口和煤矿等部门都要对出入煤的质量进行分析,分析检验结果作为生产成本核算、控制锅炉工况或作为商品煤结算的依据。煤的质量分析包括采集样品(采样) 、制备试样、分析。用少量的样品的分析结果代表一批煤的质量必然会有偏差。此偏差由采样偏差、制样偏差和分析偏差构成,其中采样偏差最大。因此,分析结果的精确度,很大程度上取决于所采样品的代表性。以前靠人工采样,很难保证样品的代表性。分析偏差太大时还可以重新分析,而样品无代表性时,则往往由于煤已运走或已入锅炉烧掉而无法重新采样。如果煤样品无代表性,则无论分析结果多么精确也毫无意义。国家标准GB474 规定了各种情况下煤的采样方法。在流动的煤(煤流) 中采样时,应将采样处煤流横截面上的煤全部采出。

　　汽车入厂煤采样机是针对运煤汽车采样而设计的机械化采样设备。该设备集采样、破碎、缩分、集样于一体、结构合理、运行可靠、操作方便。采样制样工艺过程符合GB474，GB475国家标准。适用于电厂、煤矿、煤码头等进行煤质检验采样的场合。

　　汽车入厂煤采样机主要由采样头、给料机、破碎机、缩分集样器、余煤处理系统组成。首先由钻取式螺旋采样头提取煤样，通过密闭式给料机送放破碎机、破碎后进入缩分集样器，通过缩分的煤样进入集样器，多余的煤样由余煤处理系统反排回汽车或直接排回煤场。

采用本采样系统的优点有：

(1).可实现全断面采样，保证煤样代表性；

(2).采用专利破碎机，水份适用范围广，减少堵煤可能性；

(3).一体化设计，结构紧凑，采样时间短；

(4).半封闭结构，减少人为与环境因素的影响；

(5).设备自动化程度高，维护简单。

通过本设计可以使整个系统不易堵煤、监测系统更加趋于完善，程控特性更好，且易于安装和维护。

二、论文研究的主要内容

设计对汽车所运原煤进行采样的自动小车控制系统，实现小车的横向、大车的纵向移动以及采样螺旋探头的上升、下降过程。系统采用可编程控制器进行控制。

具体内容如下：

1 车运原煤自动采样系统总体方案设计；

2 车运原煤自动采样控制系统设计；

3 设计控制系统硬件，包括控制器选型设计和控制接线图；

4 控制系统软件设计，包括程序流程图和系统控制软件。

第一章车运原煤自动采样系统总体方案设计

车运原煤自动采样系统总体方案的设计应包括以下内容：采制样装置结构型式的确定，采制样装置基本组成、采制样装置工作原理、采制样装置主要设备的技术参数及机构的选择等内容。

一般应根据设计任务和要求提出数个总体方案，进行综合分析、比较和论证，最后确定一个可行的总体方案。

一、总体方案确定

（一）概述

煤的计量及其机械自动采制样是火力发电厂实现计算煤耗的前提，电力部颁布的《火力发电厂按入炉煤量正平衡计算发电煤耗（试行）》中指出 “机械自动采样装置是目前唯一能够采到具有代表性样品的手段”。

入厂煤机械自动采制样装置中机械结构设计新型实用，整体结构布局通畅，选取的技术参数合理，工艺调节方便，适应范围广。适用于火力发电厂的入厂煤采样及其它类似场合。机械可长期稳定运转，不堵煤，采样后的子样代表性强，满足现场实际需要。该装置作为现代化采制样设备，可为电厂，煤矿等有关单位提供煤质检测和监督的可靠依据，并且有助于燃煤管理的科学化和规范化。

电气控制部分采用目前国际上流行的可编程控制器作为主控元件，在设计思想上力求与国际接轨。因此，可靠性显著增强，控制性能大为提高，而且具有智能化的优点。

该设备采样技术及工艺过程完全符合《GB475-96商品煤样采取方法》的规定，制样方案完全符合《GB474-96煤样的制备方法》

车运原煤自动采样控制系统设计.gif

内容简介：: The outline of coal preparation and Economics of Coal CleaningAbstractCoal preparation, 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. Originally, coal preparation began as a line of equipment-crushers, feeders, screens, etc.-to control the size 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 become familiar with the levels of coal preparation.Level 0 processing is the mining and shipping of ROM coal.The product of Level 1 processing is commonly termed raw coal.Level 2 processing involves the 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.Level 3 processing 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.Level 4 processing extends the cleaning to include the minus 1/2mm raw coal.The feed to the coal preparation plant is then raw coal from Level 1 processing. Coals impurities are numerous, but by far the largest have specific weights 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.The separation 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. 2. The Cumulative Float Curve-a plot of the cumulative float weight percent versus the cumulative float ash percent.The outline of coal preparationCoal preparation, 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 meets the ever-increasing specifications required for its use whether its combustion, liquefaction, gasification or carbonization.)The coal we mine today represents the deposition of phytogenic material 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 sedimentary rocks such as shales, clays, sandstones and, sometimes, even limestone, OR-when combined with coal-what are known as impurities in terms of preparation.Originally, coal preparation began as a 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 could be removed manually. Thousands of men, women and children performed this unfulfilling work until mechanization replaced it withmore modern coal cleaning equipment.Generally speaking, this coal 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 difficult to mine compared with American coal seams.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 during 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 roof and floor mater ials.Mechanical mining meant mechanical cleaning.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 become familiar with the levels of coal preparation.Each level is indicative of the intensity of the work performed on run-of-mine coal and each is an extension of the previous level.Level 0 processing is the mining and shipping of ROM coal.Level 1 processing combines top-size control by crushing, 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.Level 2 processing involves the 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.Level 3 processing 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.Level 4 processing extends the cleaning to include the minus 1/2mm raw coal.Developing the appropriate circuitry for processing raw coals at Levels 2,3 and 4 involves four areas-characterization, liberation, separation and disposition.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 develop a flowsheet of the unit operations required to achieve the desired preparation level.Liberation is the creation of individual particles whose composition are predominantly coal or refuse. This is 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. Unfortunately, particles containing both coal and refuseknown as middlings-are also createdSeparation is, simply, the dividing of the particles into their appropriate groups-coal, refuse and middlings. Coals 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 differences-size and specific gravity. The raw coal is thus characterized by partitioning the very heterogeneous coal into relatively homogeneous subpopulations on the basis of size and specific gravity.Disposition is the cleaning up of the various streams.The separation unit operations normally process water/raw coal slurries, thus the term Coal Washing. The predominant disposition operation is the dewatering (separating 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.Coal preparation is the quality control arm of the coal industry. It is an integral part of the coal business. WashabilityWashability studies are conducted primarily to determine how much coal can be produced at a given specific gravity and at what separation difficulty and size. The importance of the size analysis is perhaps more clear if you think of the cleaning process as removing impurities form individual pieces of coal, rather than in terms of tons of coal. As the individual pieces get smaller they become harderand more costlyto clean. 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 different screen apertures, with each fraction held separately for further evaluation. A typical size analysis for a feed material is shown in Table 1. The table presents the percent of total weight, as well as an analysis of ash, sulfur content and Btu of each fraction, both individually and cumulatively.Then the material of each size fraction undergoes a float-sink test in liquids of pre-selected, carefully controlled specific gravities, beginning with the lowest.The float material from each specific gravity bath is then weighed and sink material is tested in the next heavier bath.The procedure is repeated until the desired number of float-sink result for the fraction in Table1 is given in Table 2.Since wider ranges are treated commercially, composite results 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.This type of data is 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.For example, Figure 1 shows three curves, generated from the data in Table 3, which are generally employed:1. The Yield Curve-a plot of the cumulative float weight percent versus specific gravity;2. The Cumulative Float Curve-a plot of the cumulative float weight percent versus the cumulative float ash percent;3. The Cumulative Sink Curve-a plot of the cumulative sink weight percent versus the cumulative sink ash percent.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 the feed. The separation must be made at a specific gravity of 1.665 and the rejects should analyze 82.1% ash.Economics of Coal CleaningAbstractA 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 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 plant are directly units .For example ,the sizes of raw coal storage and handling units ,and the sizes of cleaned coal bunkers and loading facilities ,are often determined by the needs for strategic stockpiles or the requirements of the transportation system .Economic analysis is also greatly influenced by the relationship of the coal producer to 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 (7years 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. The elements of the cost of coal cleaning comprise fixed costs arising from capital charges, and fixed or variable costs arising from plant operation. For a given annual production, capital costs 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 the major influence on capital requirements. The average yield of current American coal cleaning plants is 71%. Economics of Coal CleaningIn recent times modern wash plants 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 minimum 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 composition and fusion temperatures, fixed carbon (coke making), sulfur, and crushing and pulverizing characteristics. Considerations of these factors may modify the primary evaluation ,but as a general rule will justify a premium for cleaning only if substantial cost savings in utilization will result .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 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 the rule. Losses of yield in cleaning represent the biggest item contributing to total cleaning costs because the size, and hence 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 plant are directly units .For example ,the sizes of raw coal storage and handling units ,and the sizes of cleaned coal bunkers and loading facilities ,are often determined by the needs for strategic stockpiles or the requirements of the transportation system .Economic analysis is also greatly influenced by the relationship of the coal producer to 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 (7years 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 (1) and (2) are most representative of past and present practices for metallurgical and thermal coals. Type (3) may apply following the current reorganization and restructuring of the coal industry and the growth of large coal conversion plants and mine-mouth generating stations.Additional 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 elements. It has already been noted that environmental regulation relating to the operation of cleaning plants liquid effluents, fugitive dust, and noisehave resulted in significant increases in capital and operating costs. 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 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 very recent times, for determining the economic worth of coal cleaning were relatively simple measures .The quality, tonnage, and expected market price of raw coal were compared with similar parameters for cleaning were then estimated and added to the basic production costs of ROM coal .The difference between anticipated gross productions costs and forecast selling prices because the basic for applying various accounting devices accounting devices to determine the balance of economic advantage .Usually , a discounted cash flow (DCF ) analysis enabled calculation of return on investment (ROI ) over periods of about 10 to 15 years for the different options. This exercise was principally of concern to coal-producing companies because they carried the fiscal responsibility for the decision to clean or not to clean. As a general rule of thumb, a decision to proceed with cleaning depended on a DCF-ROI of at least 15%per year, and more commonly, 20%. If the case for cleaning was a foregone necessity, because of the markets requirements, the analysis was used to calculate a selling price that would produce the necessary ROI. These rules had worked well in an industry that, although still important and substantial, had been declining.The utilities employ different accounting principles from the DCF-ROI type of evaluation and they employ different 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 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 full impact of these changes and their wider importance for coal cleaning cannot be assessed at the present time.The elements of the cost of coal cleaning comprise fixed costs arising from capital charges, and fixed or variable costs arising from plant operation. Capital charges are determined by the depreciation of costs incurred in land 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 unaffected by actual plant throughputs. Operating expenses include salaries, wages, power costs, water costs, and productive supplies, including fuels, refuse, and waste disposal. This category may include fixed costs independent of plant throughput (e. g., salaries) or variable costs tied directly to throughput (e. g., productive supplies).For a given annual production, capital costs 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 the major 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 sizes (i.e., froth flotation vacuum filters, centrifuges, water clarification, and thermal drying). Cleaning costs are therefore highly sensitive to the quantity of sizes smaller than 1/4 in. in the feed.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 operation. 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.选煤概述和煤的可选性摘要煤炭加工选煤概述简单说来，选煤就是把原煤（即开采后未经加工含有各种杂质的煤）。商品煤是具有一定质量规格的产品，它能满足燃烧，液化气化等方面所不断提高的技术要求。现在开采的煤是五千万到三亿五千万年前的植物沉积而成，所形成的水平层状物称之为煤层，厚度不一，从数英寸到数百英尺。煤层中经常夹杂着厚度不等的页岩，粘土砂岩，有时还夹杂石灰岩等沉积岩。从选煤的角度来说，这些和煤结合在一起的夹杂物称之为杂质。三级加工选别中等粒度（1/2英寸1/2毫米）的原料煤，小于1/2毫米粒级的则归入精煤（大于1/2毫米）或送往他处。原煤可选性的研究主要是为了决定在某一比重下可能获得的产品数量和洗选的难以程度，并确定入洗煤的粒度。如果把选煤看成是从一块块的煤中除区杂质，而不是根据成吨的煤去考虑问题，就能比较清楚的理解粒度分析的重要性。粒度越小，选煤难度越大，成本越高。在可选性研究的试验程序开始之前，通常是先取出经破碎达到规定粒度上限的煤样，然后用各种筛子进行筛分。各粒级产物要分别存放，以便进行可选性评定。表1所示为入料粒度的典型分析。表中列出了各粒级产物的重量百分数灰分硫分和发热量，分本级和累计两项。先配好重液，准确调节其比重，然后对各粒级产物进行浮沉试验，从比重最小的重液开始。每一级重液中的浮起物要称记重量，下沉物移入较高比重的重液，依次进行，直到获得个级比重物为止。表2为表1中产物的浮沉实验结果。由于工业上处理的粒级范围较广，经常把某些粒级浮沉试验结果加以适当组合，形成综合结果。近年来，由于支付选煤成本所需的额外费用不能在萧条的煤炭市场上回收，美国的现代化选煤厂一直处于停产状态。在竞争性的市场上，用户往往首先根据按能量计算最低价格（即每百万英热单位包括交货费用在内的价格）的方法判断他们是否要购买。其次是判断按煤的性质决定的使用价值。煤的性质比较复杂，它包括灰分，灰的组成及熔点，固定碳，硫分，破碎和磨碎特性等各项因素。考虑了这些因素以后，还会改变最初的判断，但按一般规律来说，只有在使用中如能明显地节约费用，才能认为选煤这项额外费用是合算的。然而，热值并不是选煤中应加以控制的主要方面。它与灰分和水分呈近似的线性关系，但是在原煤中大块岩石被拣除后，产率和灰分之间变成非线性关系，一般的规律是降低灰分就要增加热值回收率的损失。选煤中的产率损失是影响选煤总成本的最大项。由于选煤厂的规模乃至基建投资是以处理原煤的能力为基础的，因此产率损失对投资费产生最直接的影响。虽然构成选煤厂的各个项目并非全部都直接涉及选煤设备的处理能力，但通常人们认为随着工厂规模增大，投资费反而减少。按惯例，还本期很长，一个燃煤的厂的还本期为30-40年。关键词：煤炭加工选煤原煤可选性简单说来，选煤就是把原煤（即开采后未经加工含有各种杂质的煤）。商品煤是具有一定质量规格的产品，它能满足燃烧，液化气化等方面所不断提高的技术要求。现在开采的煤是五千万到三亿五千万年前的植物沉积而成，所形成的水平层状物称之为煤层，厚度不一，从数英寸到数百英尺。煤层中经常夹杂着厚度不等的页岩，粘土砂岩，有时还夹杂石灰岩等沉积岩。从选煤的角度来说，这些和煤结合在一起的夹杂物称之为杂质。最初，选煤是用一系列设备如破碎机给料机筛分机等来控制煤的粒度。其中手选皮带是靠视力检查原煤，利用人工拣除那些明显的矸石。在手选带被较现代化的洗选设备取代之前，拣矸工作是靠成千上万的成人和儿童来完成。一般说来，比较现代化的选煤设备是为英国等欧洲国家的煤矿研制的，因为这些国家每吨煤的价格大大地高于美国。煤价反映了采煤成本。在英国和欧洲，煤层的难采度大于美国的，成本较高，因而煤价较高。虽然美国的煤层属于世界上最容易开采的煤层之列，在新政策（译注：这是美国在二十世纪三十年代为缓解经济危机指定的一系列政策）时期，由于煤矿成立了工会，为了符合工会会章，选煤有了新的意义。人们对于无论是井下，露天用的或至今还没有被淘汰的，以及开采全煤层（包括夹层，一些顶板和底板在内的煤层）用的各种采煤机的需求都有迅速增长。机械化开采意味着机械化选煤。下面熟悉一下选煤等级，这也许是了解选煤发展和变化的一条捷径。每一等级都表示出毛煤加工的程度，同时又是前一级的延续。零级加工原煤的开采和运输。一级加工用破碎方法控制粒度上限，并除去某些杂物，如混入的铁块，坑木和硬岩石等。该级产品常称为入选原煤。二级加工选别粗粒级（大于1/2英寸）的入选原煤，而小于1/2英寸粒级的则归入粗精煤或送往他处。三级加工选别中等粒度（1/2英寸1/2毫米）的原料煤，小于1/2毫米粒级的则归入精煤（大于1/2毫米）或送往他处。四级加工选别包括小于1/2毫米在内的入选原煤。适合于二，三，四级加工的选煤流程的制定必须包括煤质特性鉴定，解离，分选和选后处理等四个方面的内容。煤质鉴定是有系统地测定毛煤，以便确定入厂原煤的组成。选煤工程师制定机组操作所需流程图，以求出所需要的分选等级。解离主要是使煤和矸石单体分离。其方法是减小粒度，即把刚采出的煤破碎到煤质研究所确定的粒度上限。入厂原煤是一级加工的产品。在解离过程中还有中煤即含煤和矸石的颗粒产生。分选，简而言之，是把入洗原煤分组，分成精煤，矸石和中煤。煤中的杂质很多，但绝大多数杂质的比重大于煤。选别单体解离的煤的主要方法是重力选，该方法以粒度和比重两种物理特性的差异为基础，把各部分极不匀质的入选原煤分成相对匀质的产品。选后处理是指清除各种水分。分选作业过程通常在水或原生煤泥水中进行，因而叫做洗煤。选后处理作业最主要是选后产品的脱水（即把液体和固体分离），其次是废渣处理和其它的环境保护措施。选煤是煤炭工业中控制质量的一个环节，是煤炭事业不可分割的一部分工作。原煤可选性的研究主要是为了决定在某一比重下可能获得的产品数量和洗选的难以程度，并确定入洗煤的粒度。如果把选煤看成是从一块块的煤中除区杂质，而不是根据成吨的煤去考虑问题，就能比较清楚的理解粒度分析的重要性。粒度越小，选煤难度越大，成本越高。在可选性研究的试验程序开始之前，通常是先取出经破碎达到规定粒度上限的煤样，然后用各种筛子进行筛分。各粒级产物要分别存放，以便进行可选性评定。表1所示为入料粒度

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