机械专业外文资料及翻译-选煤

1、COAL PREPARATIONTABLE 7-14. Effect of Geometry and Concentration of Feed Solids on throughput for a 1/6-in, diam hydro cyclone cleaning 1/4-inVarying the distance between the bottom of the vortex finder and the hydro cyclone cone bottom. For example, the washed coal ash can be reduced by decreasing

2、the diameter of the vortex finder, decreasing the length of the vortex finder, or increasing the diameter of the underflow orifice. Increasing feed-Solids content increases the specific gravity of separation and, therefore, washed coal yield and ash, which indicates the importance of maintaining a c

3、onstant feed-solids content to preserve washed coal quality.Capacity is influenced by cyclone geometry, i.e., the sizes of the overflow, underflow, and inlet openings, and by feed-solids content. The effects of these parameters is given in Table 7- 14.Increasing inlet pressure is a simple method of

4、increasing capacity without changing hydro cyclone geometry, and washed yield and ash are not significantly affected. However, the penalty is increased pumping cost, and degradation of the coal. Flow sheetsSoon after the hydro cyclone was developed, it became evident that performance was inferior to

5、 nearly all other cleaning devices. Consequently, in an effort to improve performance, three two stage circuits, shown in Fig. 764, were developed. In the earliest two-stage circuit, called two-stage relearn or TSR, the refuse from a primary hydro cyclone is simply relearned in a secondary hydro cyc

6、lone, The overflows from the two hydro cyclones are recombined as the washed coal product, and the underflows from the secondary hydro clone contains the final refuse. In more recent installations, one of the products from the secondary hydro cyclone is recirculated to the feed of the primary hydro

7、cyclone. In the two-stage overflow recirculation circuit, TSOR, the primary or first-stage hydro cyclone is adjusted to produce an acceptable clean coal and the secondary hydro cyclone is adjusted to produce a refuse essentially free of misplaced coal. The overflow from the secondary hydro cyclone,

8、which contains the misplaced coal in the underflows of the primary hydro cyclone, is returned to the feed of the primary hydro cyclone for reprocessing. In the two-stage underflow recirculation circuit, TSUR, and the overflow is relearned in the secondary hydro cyclone. The underflow from the second

9、ary hydro clone is recalculated to the feed of the primary hydro cyclone. The overflow from the secondary hydro cyclone contains the washed coal.Each of these circuits has advantages that depend upon the size and specific gravity compositions of the feed, as well as the required washed coal quality.

10、 The TSOR circuit is more effective in recovering washed coal whereas the TSUR circuit is more effective in rejecting heavy impurity. The TSR circuit is most effective when the specific gravity of separation of the two hydro cyclones is similar. Conversely, the performance of TSOR and TSUR is improv

11、ed by diverging the specific gravity of separation of the two cyclones. At the present time, the TSOR is the most common circuit. A variation of the TSR circuit has been proposed whereby underflow from the primary cyclone is relearned on a concentrating table rather than a secondary hydro cyclone.So

12、me plants using jigs to clean the coarse coal utilize hydro cyclones to improve performance on the finer sizes. One method is to relearn the underflow of the washed coal screen, commonly the 1/4-in.material, with hydro cyclones. Another method is to screen the raw coal at about this size and clean t

13、he undersize with hydro cyclones.Hydro cyclones have been used ahead of dense-medium cyclones to remove some of the low specific gravity coal and thereby reduce the amount of material sent to the dense-medium plant. The hydro cyclones are adjusted to separate at a specific gravity of about 1.35 to 1

14、.40. The advantage is that the capacity of the dense-medium cyclone plant can be smaller, thus reducing capital and operating costs.Hydro cyclone PerformanceAs mentioned previously, the quality of the washed coal and refuse products can be regulated by changing the diameters of the overflow and unde

15、rflow orifices. However from a performance standpoint, a ratio of overflow diameter to underflow diameter in a range of about 1.7 to 2 gives the best results. Performance at lower ratios is inferior. Also, the solids content in the feed to primary and secondary hydro cyclones should range from 8 to

16、15 % (by weight). Outside this range, either above or below, performance is adversely affected.Separations obtained in a single hydro cyclone and two-stage circuits (TSR) are shown by the distribution curves in Fig. 7-65. The sharpness of separation of the two-stage circuit is significantly superior

17、 to that of a single hydro cyclone. Also, the sharpness of separation of the two-stage circuit is not nearly as sharp as the separations characteristic of a dense-medium cyclone. It follows then that hydro cyclones are not applicable for difficult-to-clean coal or separations at low specific gravity

18、 unless followed by a more effective relearning process. Also, they are not suitable for friable coal or where the refuse particles are platy. Table 7-15 gives detailed performance data for two-stage (TSR) hydro cyclones. These data indicate that in general the specific gravity of separation increas

19、es and the sharpness of separation decreases with decreasing particle size.Hydro cyclones may be especially applicable for cleaning -30-mesh (0.6- mm) coal if the coal is not amenable to flotation. However, the Majority of US coals are easily cleaned by flotation. But if the coal is not amenable to

20、flotation because of a slime-coating problem or the coal is oxidized, then hydro cyclones may be a viable alternative. Also if fine pyrite is present in the feed, hydro cyclones are reported to be superior to flotation for lowering the sulfur content of the washed coal.The coarser particles of an ea

21、sy-to-clean coal with a top size of 1/4 or 3/8 in.(6.3 or 9.5 mm) can be cleaned about as efficiently in a two-stage hydro cyclone circuit as on a concentrating table, but not as efficiently as in a feldspar jig. However, the concentrating table cleans the finer particles much more efficiently than

22、the hydro cyclone. The distribution curves for a two-stage hydro cyclone circuit (TSR) and a concentrating table cleaning a 1/4-in (6.3mm*0) feed are shown in Fig. 7-66. A major advantage of hydro cyclones is that the space requirement is much less than for concentrating tables and jigs, but much mo

23、re power and water are required. Spiral concentrators are also used to clean-14-mesh (1.2-mm) coal.A relatively new separator, called the air-spared hydro cyclone, has been developed and can be used to clean opal. It is essentially a porous cylinder without the usual conical section. Feed enters tan

24、gentially at the top and spirals downward. Air is introduced through the porous cylinder, and the air bubbles and flotation reagents along with the vortex effect the separation. Coal particles attach to the rising air bubbles and exit the top through a vortex.选煤表7-14，给出了影响入料分选密度和粒度的处理量。旋流器直径为1/4-in.

25、表7-14入料%底流口直径,in溢流口直径,in入料口直径,in处理量t/h10.20.751.501.231.89.81.753.001.232.99.81.753.003.004.517.31.753.003.008.9改变旋流器溢流口和底流口的距离。例如，要降低分选精煤的灰分可以减小旋流器溢流口的距离，减小溢流管的长度，或者增大底流口的直径。增大入料量会降低分选效率，因此，分选精煤的产率和灰分的关系表明了保证恒定的入料量才能保证洗选精煤的质量。处理量影响着旋流器的几何尺寸，包括溢流口的尺寸，底流口的尺寸，入料口的尺寸和入料量。这些参数的影响如表7 14。改变入料压力是一个改变旋流器参数的

26、简单方法，然而对改变精煤的产率和灰分的影响不显著，况且会增加抽水成本，还会增加煤的泥化现象。流程图随着旋流器的发展，很明显它毫不逊色于其他所有的洗选设备。因此，为了提高性能，两段分选的旋流器（如图7-64）被开发了出来。最早的两段分选旋流器叫第二段再选或者叫TSR，从第一段旋流器出来的产品只是简单的在第二段再选，从两段旋流器溢流口出来的煤被混合当作洗选精煤产品。从第二段旋流器底流出来的物料被视为洗选尾矿作为矸石。最近的有一种设备，一种从旋流器第二段出来的产品被循环作为第一段的入料。在两段旋流器的溢流循环，TSOR，这种从旋流器的第一段被作为调节产品所要求精煤，第二段作为调节尾矿中保证没有错配物

27、。从旋流器第二段的溢流出来的物料包含本该进入到第二段旋流器底流的错配物，所以返回到第一段旋流器进行再次循环洗选。在两段旋流器底流循环，TSUR，这种从第一段旋流器的底流出来的物料被作为最终的尾矿矸石，第二段的底流出来的物料再次进入到第一段作为第一段的入料。从第二段溢流出来的产品被作为最终的洗选精煤产品。上述的其中每个流程都有优点，取决于入料的粒度组成，和所要求的精煤产品质量。TSOR流程能更有效地回收分选精煤，而TSUR流程更有效地排除重产物。当两段旋流器分选的比重类似时TSR流程是最有效的流程。相反，TSOR和TSU的性能取决于两段旋流器的分流量。在目前，TSOR是应用的最为普遍的一种流程。

28、有人提出一种改进的TSR流程是从第一段主选底流出来的物料被再次分选浓缩代替第二段旋流器分选。有一些厂用跳汰机分选块煤，利用旋流器分选细粒的煤。一种方法是用煤用振动筛筛分的筛下物（通常1/4英寸）的煤用旋流器分选，另一种方法是用煤用振动筛筛分出粗粒煤，细粒度的煤用旋流器分选。旋流器也被运用到重介质分选中去分选出一些含煤少的贫矿，以降低选煤厂重介质的消耗。旋流器可以调节的分选密度大概在1.351.40之间。这样的优点是大大的降低了分选过程中所需重介质的体积，节约了资金和运营的成本。水力旋流器性能正如上文以前，对洗精煤产品质量和垃圾，可通过改变调节溢出和下溢口的直径。但是从性能的角度来看，溢流直径到

29、底流直径的比例范围为约1.7至2为最好，较低的比率性能为低劣产品。此外，在原料中固体物含量，一段和二段水力旋流器应定为8至15（重量）。此范围以外，高于或低于，性能将产生不利影响。分离获得的水力旋流器和一个两阶段的电路（TSR）是由图所示的分布曲线，两个阶段的电路分离清晰度明显优于单一的水力旋流器，另外，这两个阶段的电路分离清晰度几乎没有像重介质旋流器特点鲜明，由此得出结论，水力旋流器应用于难以清洁煤或低比重的适用，除非更，有效的再分选过程。此外，他们没有合适的煤或者易碎的煤矸石颗粒板状。表7-15给出了详细的两个阶段（TSR）的水力旋流器的性能数据。这些数据表明，在一般的分离增加，分离小颗粒的清晰度的减少。水力旋流器可能会适合分选- 30目（0.6毫米）的煤，如果煤不浮选。然而，美国多数煤浮选煤很容