选煤厂介耗分析论文.docx

1、选煤厂介耗分析论文 专业英文翻译中 国 矿 业 大 学毕业设计英语翻译姓 名： 学 号： 学 院： 应用技术学院 专 业： 矿物加工工程 翻译题目： 选煤厂介耗分析 指导教师： 职 称： 讲 师 英文原文An analysis of medium losses in coal washing plants AbstractA major operating cost in dense-medium separation is in replacement of lost medium solids. The loss of medium solids, being costly, plays

2、a crucial role in determining the economics 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 changes help in closer control of the separat

3、ion process, they also result in medium losses due to changes in the medium split ratio (ratio of the medium flow rate in overflow to underflow). Since medium solids are lost by adhesion to products and as magnetic separator effluent, the effect of the change in medium split ratio on the drain-and-r

4、inse screens and, hence, the magnetic separator circuit needs to be studied. In Tata Steels coal washeries, at Jharkhand India, which employs primary and secondary dense-medium cyclones in series to produce clean coal, middlings and rejects, reducing the relative density of feed medium, had an insig

5、nificant effect on the medium split ratio. On the other hand, changing the cone ratio (ratio of the overflow diameter to the underflow diameter) changed the relative density and the flow rates through the cyclone outlets, thus affecting the performance of the magnetite recovery circuit. A systematic

6、 study through laboratory tests and a detailed plant sampling campaign helped in identifying 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 ch

7、eckpoints for plant operators for identifying magnetite losses. Keywords: dense-medium cyclone; magnetite losses; drain-and-rinse screens; magnetic separators 1. IntroductionDense-medium (magnetite in the case of coal), a slurry/suspension having a relative density intermediate to that of valuable m

8、ineral and gangue, is generally used as the medium of separation in most coal preparation plants. The medium, being costly, plays a crucial role in determining the economics of any preparation operation. Dardis (1987) quotes figures of 2040% of dense-medium plant operating cost being attributable to

9、 medium loss for plants engaged in mineral separations employing ferrosilicon as the medium. The figure is 1020% in the case of magnetite. There are clearly incentives to reduce this loss, and it is often possible to do so with minimal capital expenditure through improved operating procedures and mi

10、nor changes to plant configuration. This paper draws on the experience from one such study carried out by R&D Tata Steel, Jamshedpur, Jharkhand, India to identify some important operating issues in medium loss in coal washing plants and the factors influencing the loss. 2. Causes of medium loss in d

11、ense-medium plantsThere are normally only two possible routes by which medium can be lost from the plant: adhered to the products of separation, after draining and washing on screens; and present in the final effluent from the medium regeneration process, usually magnetic separators, settling cones

12、or other solidliquid separation devices.The causes of loss from these sources are as follows: forces of attraction between the ore and medium particles, ore porosity, and inefficient washing; magnetic separation and classification inefficiencies; corrosion and abrasion of the medium, reported for fe

13、rro-silicon medium; excessive circuit loadings during the addition of fresh medium; housekeeping (when the floors are being cleaned and washed off); plant downtime (associated with housekeeping); medium properties (size, shape, magnetic susceptibility).There has been much work done over the years, u

14、sually 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 plant by sampling process streams. It is rare that a balance thus established, for

15、a relatively short operating duration, reflects quantitatively the actual consumption recorded by the plant over normal reporting periods such as a month or a year. 2.1. Factors affecting losses through drain-and-rinse screensNapier-Munn et al. (1995), during their investigations of the iron ore was

16、hing plants at Mount Newman 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 lightly loaded screens. An increase in operating relative

17、 density also led to significant increases in losses. Most of the increase in loss was attributed to the poor drainage characteristics of the higher viscosity medium (Kittel et al., 1987). A small increase in relative density led to a large increase in viscosity and thus poorer drainage characterist

18、ics. The washing arrangement was also found 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 slotted spray bars and screens with flood bo

19、xes. 2.2. Losses through the magnetic separatorsThere is no consensus in the literature as to the contribution which magnetic separator 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 Mu

20、lder (1985) attributes only 18% to this source for the 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 occasions, when very high viscosity media were used, subs

21、tantial elevation of the adhesion losses was observed. Adhesion 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 2040% of this loss, though this proportion will fall

22、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 performance can deteriorate markedly if not operated correctly or properly maintained, they deserve close a

23、ttention. Analysis of losses in magnetic separators collected in plant surveys by Rayner (1994) suggests that this could be due to the separator being overloaded, in terms of either its volumetric capacity or, less often, its dry solids capacity. Hawker (1971) and Sealy and Howell (1977) gave loadin

24、g limits in terms of dry solids feed rate of magnetics and volumetric flow rate of feed slurry, which could not be exceeded without loss of performance. Dardis (1987) confirmed that the operating variables, which affect magnetic separator performance, include pulp height, magnet position (angle), se

25、paration 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 recovery in a magnetic separator was feed quality dependent. He also gave recommendations for various separator par

26、ameters. Based on operating experience at the Iscor iron ore mines, De Villiers (1983) 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. 3. Investigations at Tata Steels coal washeriesTata Steel a

27、t Jamshedpur, Jharkhand, India owns captive coal washeries, which supply 60% of coking coal requirements for its integrated steelmaking operations. In the washeries, the ROM coal after being crushed and screened at 0.5mm, the +0.5mm fraction is treated in dense-medium cyclones (called the coarse cir

28、cuit) and the 0.5mm in a flotation circuit (called the fines circuit). The +0.5mm coal is fed to the primary cyclones, which produce clean coal at a lower relative density of separation (1.31.5). The underflow from the primary cyclones form the feed to the secondary cyclones which in turn produce mi

29、ddlings and rejects at a higher relative density of separation (1.61.9). The magnetite recovery circuit is a typical circuit that exists in any coal washing plant and is shown in Fig. 1. Fig. 1.Schematic medium recovery circuit and the sampling points. The dense-medium and clean coal (middlings or r

30、ejects, 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 drain-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 p

31、rimary cyclone medium distribution box. The second section of the screens is used to rinse and drain the coal free of adhering medium. The spray water containing the dense-medium rinsed from the coal is collected in the second section of the screen under-pans and returned to the dilute medium sump f

32、or subsequent magnetite recovery. The level of magnetite water slurry in the dilute medium sump can be adjusted using the PID (Proportional, Integral, Derivative 3-term controller) loop provided for level control and the modulating splitter actuator. When the slurry levels in the sump rises, the splitter actuator would divert the flow away from the system to maintain balance. The indication loop also generates high and low alarm levels within the control system. The dilute medium thus collected in the dilute medium sump is pumped