外文文獻(xiàn)翻譯--選煤廠介耗分析

1、<p><b>　　中文4300字</b></p><p><b>　　專業(yè)英文翻譯</b></p><p><b>　　畢業(yè)設(shè)計(jì)英語(yǔ)翻譯</b></p><p>　　姓 名： 學(xué) 號(hào)： </p>

2、<p>　　學(xué) 院： 應(yīng)用技術(shù)學(xué)院 </p><p>　　專 業(yè)： 礦物加工工程 　 </p><p>　　翻譯題目： 選煤廠介耗分析 </p><p>　　指導(dǎo)教師：

3、 職 稱： 講 師 </p><p>　　2011年6月 </p><p><b>　　英文原文</b></p><p>　　An analysis of medium losses in coal washing plants</p><p><b>　　

4、Abstract</b></p><p>　　A major operating cost in dense-medium separation is in replacement of lost medium solids. The loss of medium solids, being costly, plays a crucial role in determining the economi

5、cs of any preparation operation. Coal washeries that employ dense-medium cyclones often attempt optimization of the processes by varying the vortex or the spigot diameter and the feed relative density. While these change

6、s help in closer control of the separation process, they also result in medium losses due to changes </p><p>　　A systematic study through laboratory tests and a detailed plant sampling campaign helped in ide

7、ntifying the causes of magnetite loss. Upon implementation of the recommendations, the magnetite losses decreased, resulting in a saving of approximately US$27,500 per annum. The study also helped in evolving some checkp

8、oints for plant operators for identifying magnetite losses. </p><p>　　Keywords: dense-medium cyclone; magnetite losses; drain-and-rinse screens; magnetic separators </p><p>　　1. Introduction<

9、/p><p>　　Dense-medium (magnetite in the case of coal), a slurry/suspension having a relative density intermediate to that of valuable mineral and gangue, is generally used as the medium of separation in most co

10、al preparation plants. The medium, being costly, plays a crucial role in determining the economics of any preparation operation. Dardis (1987) quotes figures of 20–40% of dense-medium plant operating cost being attributa

11、ble to medium loss for plants engaged in mineral separations employing ferrosil</p><p>　　2. Causes of medium loss in dense-medium plants</p><p>　　There are normally only two possible routes by w

12、hich medium can be lost from the plant: </p><p>　　? adhered to the products of separation, after draining and washing on screens; and</p><p>　　? present in the final effluent from the medium reg

13、eneration process, usually magnetic separators, settling cones or other solid–liquid separation devices.</p><p>　　The causes of loss from these sources are as follows: </p><p>　　? forces of attr

14、action between the ore and medium particles, ore porosity, and inefficient washing;</p><p>　　? magnetic separation and classification inefficiencies;</p><p>　　? corrosion and abrasion of the med

15、ium, reported for ferro-silicon medium;</p><p>　　? excessive circuit loadings during the addition of fresh medium;</p><p>　　? housekeeping (when the floors are being cleaned and washed off);<

16、/p><p>　　? plant downtime (associated with housekeeping);</p><p>　　? medium properties (size, shape, magnetic susceptibility).</p><p>　　There has been much work done over the years, us

17、ually by operating plants, to identify and quantify the sources of medium loss and to minimize consumption. The task, however, is complicated by the difficulty of determining an unequivocal medium balance across the plan

18、t by sampling process streams. It is rare that a balance thus established, for a relatively short operating duration, reflects quantitatively the actual consumption recorded by the plant over normal reporting periods suc

19、h as a month</p><p>　　2.1. Factors affecting losses through drain-and-rinse screens</p><p>　　Napier-Munn et al. (1995), during their investigations of the iron ore washing plants at Mount Newman

20、 and Tom Price, found that adhesion loss increases with screen loading. The effect was quite strong, and even moderately loaded screens showed a significant increase in loss (expressed in g/t/m of screen width) over ligh

21、tly loaded screens. </p><p>　　An increase in operating relative density also led to significant increases in losses. Most of the increase in loss was attributed to the poor drainage characteristics of the hi

22、gher viscosity medium (Kittel et al., 1987). A small increase in relative density led to a large increase in viscosity and thus poorer drainage characteristics. </p><p>　　The washing arrangement was also fou

23、nd to affect medium losses significantly through drain-and-rinse screens. Of the various washing arrangements, screens with weirs and a vigorous tumbling action reduced the magnetite losses considerably compared to slott

24、ed spray bars and screens with flood boxes. </p><p>　　2.2. Losses through the magnetic separators</p><p>　　There is no consensus in the literature as to the contribution which magnetic separator

25、 losses make to total medium loss in dense-medium plants. Dardis (1987), for example, claims that magnetic separators account for more than 75% of losses, whereas Mulder (1985) attributes only 18% to this source for the

26、Sishen iron ore dense-medium cyclones. Kittel et al. (1987) reported magnetic separator losses between 2.4% and 24% of the total for the Mt. Newman dense-medium cyclone plant. However, on occas</p><p>　　Adhe

27、sion to coal and the losses in the magnetic separator are the two main routes through which magnetite gets lost in a coal washing plant. In general, magnetic separators seem to contribute 20–40% of this loss, though this

28、 proportion will fall where adhesion losses are abnormally high, for example, with porous ores. Magnetic separators are therefore an important, though, not necessarily, a dominant source of medium loss. Since their perfo

29、rmance can deteriorate markedly if not operated correctl</p><p>　　Analysis of losses in magnetic separators collected in plant surveys by Rayner (1994) suggests that this could be due to the separator being

30、overloaded, in terms of either its volumetric capacity or, less often, its dry solids capacity. Hawker (1971) and Sealy and Howell (1977) gave loading limits in terms of dry solids feed rate of magnetics and volumetric f

31、low rate of feed slurry, which could not be exceeded without loss of performance. </p><p>　　Dardis (1987) confirmed that the operating variables, which affect magnetic separator performance, include pulp hei

32、ght, magnet position (angle), separation and discharge zone gaps, drum speed, and magnetics to non-magnetics ratio. Lantto (1977), writing from the perspective of a hard rock ilmenite concentrator, explained that the rec

33、overy in a magnetic separator was feed quality dependent. He also gave recommendations for various separator parameters. </p><p>　　Based on operating experience at the Iscor iron ore mines, De Villiers (1983

34、) observed that overloading of the magnetic separators was the main cause of magnetic losses. He also gave the separator settings used at the Iscor plants. </p><p>　　3. Investigations at Tata Steel's coa

35、l washeries</p><p>　　Tata Steel at Jamshedpur, Jharkhand, India owns captive coal washeries, which supply 60% of coking coal requirements for its integrated steelmaking operations. In the washeries, the ROM

36、coal after being crushed and screened at 0.5 mm, the + 0.5 mm fraction is treated in dense-medium cyclones (called the coarse circuit) and the ? 0.5 mm in a flotation circuit (called the fines ci

37、rcuit). The + 0.5 mm coal is fed to the primary cyclones, which produce clean coal at a lower relative density of separ</p><p>　　Fig. 1. Schematic medium recovery circuit and the sampling poin

38、ts. </p><p>　　The dense-medium and clean coal (middlings or rejects, as the case may be) is laundered to sieve bends and one set of drain-and-rinse screens. The sieve bends and the first section of each drai

39、n-and-rinse screen are used to drain medium from the coal; the medium is collected in screen under-pans and returned to the primary cyclone sump via the primary cyclone medium distribution box. The second section of the

40、screens is used to rinse and drain the coal free of adhering medium. The spray water co</p><p>　　The dilute medium thus collected in the dilute medium sump is pumped to magnetic separators, which produce the

41、 recovered magnetite as over-dense medium and a reject tailings circuit. The over-dense medium is returned to the over-dense medium sump and distributed to the dense-medium washing circuits as make up. Magnetic separator

42、 tailings are used as product rinsing water. </p><p>　　Considering the overall economics of steel-making, it was thought to reduce the composite clean coal ash at the washeries from 17% to 16% starting April

43、 2003. With a view to achieving 16% clean coal ash, the following changes were made in the coal washing plants: </p><p>　　(a) The relative density of medium in the primary cyclone circuit was reduced from 1.

44、36 to 1.3–1.33</p><p>　　(b) The spigot diameter of the secondary cyclones was reduced from 140 mm to 125 mm.</p><p>　　These changes would have an effect on the medium split ratio (rati

45、o of the medium flow rate in overflow to underflow) and hence an effect on magnetite recovery. </p><p>　　3.1. Effect of reduction of primary relative density on the magnetite recovery circuit</p><

46、p>　　He and Laskowski (1995) studied the changes in medium split ratio by changing the vortex finder diameter and spigot diameter and cyclone inlet pressure at two different medium densities. A total of 27 different vo

47、rtex finders versus spigot diameter combinations were studied. The tests were carried out with four different magnetite compositions. The studies showed that at a fixed inlet pressure, the relationship between medium spl

48、it ratio and cone ratio was independent of medium properties. Exten</p><p>　　3.2. Effect of reducing the spigot diameter in the secondary circuit</p><p>　　Reducing the spigot diameter of the cyc

49、lones would indirectly increase the cone ratio, i.e., the ratio of the diameter of vortex finder to the spigot thus affecting the medium split. The flow rate of medium through the overflow would increase and that through

50、 the underflow decrease, thus increasing the overall medium split. </p><p>　　Changes in the cone ratio would result in either lower/higher pulp relative density and higher/lower flow rates through the cyclon

51、e outlets. Lower pulp relative density will have a negligible effect on the performance of the drain-and-rinse screens. However, lower pulp relative density in the feed to the magnetic separator will inhibit the formatio

52、n of flocs, which has been identified as the main process step for magnetic separation. According to the “conceptual collection mechanism” model devel</p><p>　　Similarly higher pulp relative density would in

53、crease the viscosity of the medium coming out through the outlets of the dense-medium cyclone. This in turn would reduce drainage through the drain screens and increase adherence of the medium to the coal samples. This i

54、ncreased adherence of magnetite to coal would directly increase the magnetite loss after rinsing. </p><p>　　Within the capacity of the screens, increase/decrease in medium flow rate would not affect the perf

55、ormance of the drain-and-rinse screens. However, increased medium flow rate to the magnetic separator would reduce the residence time and hence the recovery of magnetics. </p><p>　　Decreased/increased medium

56、 flow rate to the magnetic separator would also affect its performance. The pool depth in the magnetic separator needs to be maintained at an optimum for an efficient magnetic separation. This can be done by adjusting th

57、e tailings discharge in the magnetic separator. </p><p>　　4. Experimentation</p><p>　　Detailed sampling campaigns were carried out in the magnetite recovery circuit. Samples of clean coal, middl

58、ings and rejects, and overflow, underflow and feed to the primary magnetic separator and one secondary separator were collected. These samples were collected in fifteen increments over a period of about 1 min using

59、standard samplers. Each sample was collected from all parts of each flow stream, and all material in the stream had the same probability of being collected. About 15 kg of taili</p><p>　　The major opera

60、ting variables of a medium recovery screen that influence its performance are (i) the adhesion of the medium prior to washing, (ii) quantity of wash water, (iii) screen-ore conveying velocity, (iv) screen-ore bed depth,

61、(v) screening duration, (vi) ore size, (vii) ore porosity and (viii) properties of the medium pulp. For any washing plant, the ore size remains constant, and the rank of coal treated also remains unchanged. Hence the fac

62、tors that were considered for the laboratory </p><p><b>　　Table 1. </b></p><p>　　Results of simulation of drain-and-rinse screen tests carried out in the lab </p><p>　　F

63、igures show percentage of magnetite lost after rinsing.The levels of the variables are coded and mentioned as 1, 2 and 3. “Wash water 1” is the quantity of wash water which was coded as level 1, etc.</p><p>

64、　　A simple test procedure was adopted to simulate the drain-and-rinse screen section of the medium recovery circuit in the laboratory. Media with three different relative densities were manually prepared using magnetite

65、(size: 90%, ? 0.045 mm and 90% magnetics) collected from the washery. The coal had a size range of ? 13 +0.5 mm, and 50 g of sample was taken for each test. </p><p>　　In this wo

66、rk, the experimental procedure was to initially contact the ore with the medium so as to allow the medium adhesion to occur. The ore to be contacted was placed inside a wire basket and lowered into the re-circulating med

67、ium for about 30 s and then taken out. The 30-s contact time is much more than the normal 4–5 s contact time observed in a cyclone. </p><p>　　The contacted ore was then taken out of the wire basket

68、 and placed on a laboratory screen mounted on a sieve shaker to simulate the medium recovery step across a vibrating medium recovery screen. The sieve shaker was operated without wash water for 15 s to allow the exc

69、ess medium to drain free from the ore. A sample of the drained ore was taken to determine the mass of the medium adhering to the ore prior to the washing step. The sample was then taken in an open bucket filled with wate

70、r, the vol</p><p>　　The rest of the ore on the screen was further shaken for about 5–15 s with wash water to wash off the adhered medium. Particles that were still adhered to the ore after the washing s

71、tep were recovered from the ore by scrubbing, as mentioned above. </p><p>　　The tests were carried out using statistical design of experiments and the results analysed using the analysis of variance (ANOVA)

72、technique. The variables were studied at different levels, and the percentage of magnetite lost was calculated for each test. The sum of squares, the mean sum of squares, the ‘F’ ratio and the ‘p’ values were calculated.

73、 Those variables having a ‘p’ value of more than 0.05 were taken as significant factors. </p><p><b>　　中文譯文</b></p><p><b>　　選煤廠介耗分析</b></p><p><b>　　摘要&l

74、t;/b></p><p>　　在重介質(zhì)分選中主要的操作損失是介耗。昂貴的介耗在決定介質(zhì)準(zhǔn)備中起著關(guān)鍵性的作用。選煤人員常常試圖通過改變渦流或者套管直徑和給料密度來優(yōu)化選煤過程。雖然這些變化有利于更好控制分離過程，但導(dǎo)致介質(zhì)流失是由于對(duì)介質(zhì)分離比率的改變（從溢流至底流的介質(zhì)比率）。由于介質(zhì)會(huì)黏附在產(chǎn)品上并且會(huì)隨磁選機(jī)流出，因此需要改進(jìn)磁選流程。印度jharkhand塔塔鋼鐵公司的選煤人員，使用一段和二段重介

75、質(zhì)旋流器生產(chǎn)精煤，中礦和矸石。降低介質(zhì)的相對(duì)密度在介質(zhì)分離比率中起著一定的作用。另一方面，錐比的改變（溢流直徑與底流直徑之比）改變了相對(duì)密度和旋流器出口的流量，從而影響磁選機(jī)磁選的性能。</p><p>　　通過實(shí)驗(yàn)室試驗(yàn)和機(jī)械設(shè)備采樣運(yùn)動(dòng)的系統(tǒng)研究有助于查明磁鐵礦損失的原因。經(jīng)研究表明，選煤廠介耗降低后每半年可節(jié)省美國(guó)大約27500美元。這項(xiàng)研究還有助于為正在擴(kuò)建中的選煤廠操作人員提供磁鐵礦損失的原因。 <

76、;/p><p>　　關(guān)鍵字：重介質(zhì)旋流器；磁鐵礦損失；脫水篩；磁選機(jī)</p><p><b>　　1、引言</b></p><p>　　水煤漿懸浮液中有用的固體和煤矸石的重物（對(duì)煤炭中的磁鐵礦）在大多數(shù)選煤廠被普遍分離。昂貴的介質(zhì)在選煤廠決定經(jīng)濟(jì)成本時(shí)起著關(guān)鍵的作用。達(dá)迪斯（ 1987年）的報(bào)價(jià)數(shù)字中20-40 ％的重介質(zhì)選煤廠生成成本是由于選煤廠

77、使用硅介質(zhì)而造成的介耗，對(duì)磁鐵礦則是10–20%。通過較小的投資改進(jìn)工作流程和改變?cè)O(shè)備型號(hào)能很好地減少這方面的損失。文章鼓勵(lì)以印度jharkhand塔塔鋼鐵公司賈姆謝普爾的經(jīng)驗(yàn)確定選煤廠影響介耗的因素。</p><p>　　2 、重介質(zhì)選煤廠介耗分析</p><p>　　一般情況下，選煤設(shè)備中的介耗有兩種途徑：</p><p>　　?排水和清洗工作后依然進(jìn)行產(chǎn)品分離

78、；</p><p>　　?介耗通常是因磁選機(jī)沉降錐或固液分離器受損引起。</p><p>　　介耗的原因列舉如下：</p><p>　　?礦石和介質(zhì)顆粒之間由于礦石空隙而產(chǎn)生的吸附作用；</p><p>　　?磁選和分離效率低；</p><p>　　?用硅做介質(zhì)造成的介質(zhì)腐蝕和磨損；</p><p&

79、gt;　　?在補(bǔ)加新介質(zhì)時(shí)管路太多；</p><p>　　?廠房清洗（樓層清理和清洗）；</p><p>　　?設(shè)備停機(jī)檢修（與廠房清洗有關(guān)）；</p><p>　　?介質(zhì)特性（大小，形狀，磁化率）。</p><p>　　多年來選煤廠做了很多工作以確定介耗的數(shù)量并將介耗降到最低。然而，這種工作由于在礦漿中決定介質(zhì)平衡而存在的困難顯得很復(fù)雜。在

80、相對(duì)較短的運(yùn)行期間這種固定的平衡是很難的，只能通過分選設(shè)備在一個(gè)月或一年的報(bào)導(dǎo)期反映數(shù)量上的消耗。</p><p>　　2.1通過沖洗篩面等影響因素造成的損失</p><p>　　皮爾-文基賢等人（1995年）在摩紐曼和湯姆選煤廠對(duì)鐵礦石的研究發(fā)現(xiàn)黏附損失會(huì)因篩面裝填而增加。負(fù)載篩面顯示超輕負(fù)載篩面的損失（以克/噸/米，篩面寬度表示）有明顯的增長(zhǎng)。</p><p>

81、　　操作時(shí)的相對(duì)密度加大也導(dǎo)致介耗明顯的增加。大多數(shù)的介耗增加是由于高粘度介質(zhì)的低水流特性（kittel等人，1987年）。相對(duì)密度小幅度的增加會(huì)導(dǎo)致粘性而且更低水流特性介質(zhì)較大的增長(zhǎng)。</p><p>　　通過選煤流程發(fā)現(xiàn)排水管和沖洗篩面也會(huì)在介耗方面有加大的影響。各種選煤流程表明篩堰和劇烈的篩分與橫向開槽給水管和有溢流堰的篩子相比能明顯地減少磁鐵礦的損失。</p><p>　　2.2

82、磁選設(shè)備介耗</p><p>　　在文獻(xiàn)里關(guān)于選煤廠磁選設(shè)備介耗對(duì)總的介耗的影響沒有一致的觀點(diǎn)。例如，達(dá)迪斯（1987）認(rèn)為磁選設(shè)備的介耗多達(dá)75%以上，而穆德（1985）認(rèn)為對(duì)于選礦用重介質(zhì)旋流器只有18%的介耗。kittel等人（1987）則稱在紐曼重介質(zhì)選煤廠磁選設(shè)備介耗在總的介質(zhì)的2.4%~24%之間。然而當(dāng)使用高粘度的介質(zhì)時(shí)就會(huì)觀察到大量介耗。</p><p>　　介質(zhì)黏附到煤塊

83、上和在磁選設(shè)備中的損失是選煤廠磁鐵礦損失的兩個(gè)主要原因。一般情況下磁選設(shè)備的介質(zhì)消耗占20%~40%，但這個(gè)比率會(huì)由于粘度損失異常高而下降，例如孔隙多的礦石。因此磁選設(shè)備雖不是必然但是重要突出的介耗設(shè)備。所以這些設(shè)備的性能會(huì)因不正確的操作或維修而明顯的惡化，因此應(yīng)對(duì)其進(jìn)行密切的關(guān)注。</p><p>　　Rayner (1994)通過分析選煤廠磁選機(jī)中介耗后指出這種現(xiàn)象可能是由于磁選機(jī)所裝物料就其額定容積或?qū)嶋H容

84、積而言超過了其處理范圍。Hawker (1971) 、Sealy 和Howell (1977)從固液比和（）給出了磁選機(jī)的裝填極限，這些介質(zhì)損失因素都不能超出范圍。</p><p>　　Dardis (1987)指出影響磁選機(jī)分離性能的操作因素有pulp height、磁鐵方位（角度）、separation and discharge zone gaps, drum speed以及磁性物與非磁性物的比率。Lant

85、to (1977)從鈦鐵礦收集器得出觀點(diǎn)認(rèn)為磁選機(jī)介質(zhì)回收率與介質(zhì)入料質(zhì)量有關(guān)。他還給出不同分選設(shè)備性能參數(shù)推薦數(shù)據(jù)。DeVilliers (1983)根據(jù)Iscor鐵礦礦井實(shí)際運(yùn)作經(jīng)驗(yàn)發(fā)現(xiàn)磁選機(jī)容積超載是磁介質(zhì)損失的主要原因。他同時(shí)列出了在該礦廠使用的分離設(shè)備。</p><p>　　3 、塔塔鋼鐵公司選煤廠調(diào)查</p><p>　　印度jharkhand賈姆謝普爾塔塔鋼鐵公司擁有提供其煉

86、鋼所需焦煤60%的煉焦選煤廠。在選煤廠ROM coal經(jīng)過破碎后以0.5mm粒度界限篩分，大于0.5mm的煤經(jīng)過重介質(zhì)旋流器分選（初選），小于0.5mm的煤通過浮選流程分選（精選）。大于0.5mm的煤經(jīng)過旋流器一段產(chǎn)生相對(duì)密度低的（1.3-1.5）精煤，一段底流作為二段的入料產(chǎn)生相選密度高的中煤和矸石（1.6-1.9）。該廠的磁鐵礦回收循環(huán)是在每個(gè)選煤廠都有的循環(huán)。見圖一</p><p>　　圖一 磁鐵礦回

87、收循環(huán)及采樣點(diǎn)圖</p><p>　　重介質(zhì)和精煤（中煤或矸石）通過弧形篩和脫介篩脫介。弧形篩和第一組脫介篩用于從煤中脫除介質(zhì)，介質(zhì)在篩下收集后通過一段旋流器介質(zhì)桶又返回一段旋流器。第二組篩子是用來沖洗黏附在煤表面的介質(zhì)并將煤脫水。沖洗煤之后含重介質(zhì)的沖水被收集在二段脫介篩篩下并返回稀介質(zhì)桶用于之后的介質(zhì)回收?？梢酝ㄟ^PID介質(zhì)循環(huán)改變稀介質(zhì)桶中的磁鐵礦礦漿濃度。當(dāng)介質(zhì)桶中磁鐵礦濃度增加時(shí)，會(huì)減少介質(zhì)系統(tǒng)中的介質(zhì)

88、以保持介質(zhì)系統(tǒng)的平衡。循環(huán)特征也導(dǎo)致介質(zhì)控制系統(tǒng)中介質(zhì)濃度的高低變化。</p><p>　　稀介質(zhì)桶中的介質(zhì)通過泵打到磁選機(jī)中與里面的高濃度介質(zhì)混合產(chǎn)生循環(huán)介質(zhì)。高濃度介質(zhì)返回到高濃度介質(zhì)桶中以補(bǔ)償介質(zhì)密度。磁選機(jī)殘?jiān)魑驳V處理。</p><p>　　考慮到煉鋼的經(jīng)濟(jì)效益，該廠曾從2003年4月起將精煤灰分從17%降到16%。為了將精煤灰分降為16%，選煤廠做了如下的改進(jìn)：</p&g

89、t;<p>　　一段旋流器中介質(zhì)相對(duì)密度從1.36降為1.3-1.33；</p><p>　　二段旋流器入料口直徑從140mm降為125mm。</p><p>　　這些改變對(duì)介質(zhì)分離比率（從溢流至底流的介質(zhì)比率）有影響因此也將對(duì)介質(zhì)回收產(chǎn)生作用。</p><p>　　3.1減少一段介質(zhì)相對(duì)密度對(duì)磁鐵礦回收的影響</p><p>

90、　　Laskowski (1995)在兩種不同密度介質(zhì)中通過改變旋流器溢流管管路直徑以及旋流器入料口壓力研究介質(zhì)分離比率的變化，總共研究了27組不同旋流器入料管直徑，這項(xiàng)測(cè)試用了四種不同的磁鐵礦。研究表明在入料口壓力不變的情況下，介質(zhì)分離比率和旋流器錐比對(duì)介質(zhì)特性是不變的。通過對(duì)改變一段介質(zhì)相對(duì)密度的爭(zhēng)論后得出結(jié)論認(rèn)為將相對(duì)密度從1.36降至1.3-1.33對(duì)介質(zhì)分離比率沒有影響，因此可以忽略對(duì)介耗造成的影響。</p>&

91、lt;p>　　3.2降低二段旋流器入料管直徑的影響</p><p>　　降低旋流器入料管直徑會(huì)間接增加錐比，也就是說旋流器溢流管直徑與管路直徑之比會(huì)影響介質(zhì)分離。通過溢流的介質(zhì)流量會(huì)增加而底流減少，從而影響總體介質(zhì)分離。</p><p>　　改變錐比會(huì)導(dǎo)致旋流器出料礦漿相對(duì)密度低/高或高/低的變化。密度較低的礦漿對(duì)脫介篩影響很小，可以忽略。但是低密度的礦漿給入磁選機(jī)時(shí)將抑制磁選機(jī)中重

92、要成分絮凝劑的性能。通過Rayner和Napier-Munn (2000)“conceptual collection mechanism”模式發(fā)展，磁選機(jī)快速形成的絮凝劑或者礦漿給料所帶來的經(jīng)濟(jì)效益很快就在磁選應(yīng)用領(lǐng)域流傳開來。當(dāng)?shù)V漿通過磁選機(jī)的介質(zhì)收集區(qū)時(shí)剩余的磁性顆粒被排出。當(dāng)單一介質(zhì)顆粒黏附在絮凝劑表面上時(shí)顆粒就會(huì)被排出。礦漿相對(duì)密度低時(shí)，絮凝作用對(duì)絮凝劑與礦漿發(fā)生絮凝形成太慢了，因此絮凝作用就在單一介質(zhì)顆粒中進(jìn)行，這對(duì)易流失的

93、細(xì)小顆粒產(chǎn)生明顯的負(fù)面影響。</p><p>　　與此類似相對(duì)密度更高的礦漿會(huì)增加重介質(zhì)旋流器出口介質(zhì)的粘度，這種變化將減少脫水篩的排水量而增加煤樣中介質(zhì)的粘性。這將直接增加沖洗磁鐵礦損失。在篩子的處理能力范圍內(nèi)增加或減少介質(zhì)循環(huán)比率不會(huì)影響脫介篩的性能，但是在磁選機(jī)中增加介質(zhì)循環(huán)比率將減少停留時(shí)間因此影響磁性介質(zhì)的回收率。</p><p>　　減少或增加介質(zhì)循環(huán)比率也會(huì)影響磁選機(jī)的性能，

94、磁選機(jī)水槽深度應(yīng)保持在最佳液面高度以保證高效的介質(zhì)分離。這可以通過調(diào)整磁選機(jī)中介質(zhì)排放量來調(diào)整。</p><p><b>　　4.實(shí)驗(yàn)</b></p><p>　　研究人員在磁鐵礦回收系統(tǒng)中進(jìn)行了詳細(xì)的抽樣實(shí)驗(yàn)，選取了精煤、中煤和矸石，以及溢流、底流、磁選一段入料和二段入料作為樣本。這些樣本通過一分鐘標(biāo)準(zhǔn)樣本增量的15%來收集，每個(gè)樣本在所有流體中抽取，流體中所有成分

95、被采集的概率是一樣的。在一分鐘抽樣過程中大約有15kg尾礦和1kg精礦被收集。干濕樣本的重量用適當(dāng)?shù)膶?shí)驗(yàn)技術(shù)(Rayner, 1999)測(cè)量，計(jì)算礦漿的相對(duì)密度（質(zhì)量/體積）和固體濃度。少數(shù)的精礦和尾礦磁性物樣本用Davis Tube回收。樣本資料的收集要花一個(gè)月的時(shí)間，應(yīng)注意避免選煤廠有反?，F(xiàn)象時(shí)抽樣。這些資料反應(yīng)精礦固體含量和每個(gè)試驗(yàn)的磁性物回收量。</p><p>　　影響脫介篩性能的主要因素有：1、介質(zhì)在

96、潤(rùn)濕之前的粘度；2、洗選用水量；3、篩上物移動(dòng)速度；4、床層厚度；5、篩分時(shí)間；6、礦物粒度；7、礦物的孔隙度；8、礦漿特性。選煤廠的煤粒度是固定的，牌號(hào)也不會(huì)改變。因此實(shí)驗(yàn)室研究的影響因素就是介質(zhì)在潤(rùn)濕之前的粘度、篩分時(shí)間、篩分速度和介質(zhì)的相對(duì)密度以及洗選用水量。實(shí)驗(yàn)所用煤為從洗選設(shè)備中選取的精煤（1號(hào)）和矸石（2號(hào)）。洗煤用水和煤的牌號(hào)分為兩個(gè)等級(jí)，其它因素作為第三等級(jí)。實(shí)驗(yàn)總共做了108組，實(shí)驗(yàn)結(jié)果見表一。</p>

97、<p>　　表一 脫水脫介篩模擬實(shí)驗(yàn)結(jié)果表</p><p>　　表中數(shù)據(jù)顯示洗選之后磁鐵礦損失的百分含量。影響因素分為1、2、3等級(jí)，“洗選用水量1”指一級(jí)洗選用水量。</p><p>　　在實(shí)驗(yàn)室中可以用簡(jiǎn)單的實(shí)驗(yàn)步驟模仿介質(zhì)在脫介篩中的回收流程。在選煤廠用三種不同相對(duì)密度的介質(zhì)（粒度：90% ?0.045 mm，磁性物含量：90%）收集磁鐵礦。每個(gè)實(shí)驗(yàn)用50g粒

98、級(jí)在13-0.5mm之間的煤樣。</p><p>　　在這個(gè)實(shí)驗(yàn)中第一步是將礦物與介質(zhì)接觸以使其粘附在一起，被粘附的礦物被帶入篩籃后進(jìn)入介質(zhì)循環(huán)系統(tǒng)30s后排出，這一時(shí)間比在旋流器里的4-5s要多。礦物被排出篩籃后又進(jìn)入振動(dòng)篩篩面通過脫介篩篩面震動(dòng)模擬介質(zhì)回收過程，振動(dòng)篩在沒有噴水的情況下運(yùn)行15s以使多余的介質(zhì)從礦物中排出。通過排出礦樣的多少推測(cè)出在洗選過程中介質(zhì)粘附礦物的量。然后將礦樣裝入盛有水的桶中，其體積

99、是礦樣的兩倍。用葉輪攪拌裝置攪拌大約2min，之后取出礦樣，干燥，稱重。通過對(duì)礦物的沖洗就可以回收礦物中粘附的介質(zhì)。篩面上的礦物通過大約5-15s的進(jìn)一步篩分、噴水以沖出被粘附的介質(zhì)，仍被粘附在礦物中的細(xì)小顆粒用上面所用的沖洗礦物的方法回收。</p><p>　　實(shí)驗(yàn)采用統(tǒng)計(jì)方法設(shè)計(jì)實(shí)驗(yàn)，試驗(yàn)結(jié)果用方差分析方法(ANOVA)分析。從不同層次研究實(shí)驗(yàn)影響因素，磁鐵礦損失在每個(gè)實(shí)驗(yàn)中都進(jìn)行了計(jì)算。方差之和、“F”比率