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畢業(yè)設(shè)計(jì)（外文翻譯）
題 目：標(biāo)準(zhǔn)篩振篩機(jī)的總體及夾緊裝置的設(shè)計(jì)
系 別 航空工程系
專業(yè)名稱 機(jī)械設(shè)計(jì)制造及其自動(dòng)化
班級(jí)學(xué)號(hào) 078105332
學(xué)生姓名 徐立軒
指導(dǎo)教師 羅海泉
二O一一 年三月
COAL PREPARATION
TABLE 7-14. Effect of Geometry and Concentration of Feed Solids on throughput for a 1/6-in, diam hydro cyclone cleaning 1/4-in
Varying 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 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 constant 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 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 sheets
Soon after the hydro cyclone was developed, it became evident that performance was inferior to nearly all other cleaning devices. Consequently, in an effort to improve performance, three two stage circuits, shown in Fig. 7~64, 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 cyclone, 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 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, 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 secondary 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. 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 improved 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.
Some 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 the 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 1.40. The advantage is that the capacity of the dense-medium cyclone plant can be smaller, thus reducing capital and operating costs.
Hydro cyclone Performance
As mentioned previously, the quality of the washed coal and refuse products can be regulated by changing the diameters of the overflow and underflow 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 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 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 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 increases 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 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 easy-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 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 more 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 tangentially 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.
選煤
表7-14，給出了影響入料分選密度和粒度的處理量。旋流器直徑為1/4-in.
表7-14
入料%
底流口
直徑,in
溢流口
直徑,in
入料口
直徑,in
處理量
t/h
10.2
0.75
1.50
1.23
1.8
9.8
1.75
3.00
1.23
2.9
9.8
1.75
3.00
3.00
4.5
17.3
1.75
3.00
3.00
8.9
改變旋流器溢流口和底流口的距離。例如，要降低分選精煤的灰分可以減小旋流器溢流口的距離，減小溢流管的長度，或者增大底流口的直徑。增大入料量會(huì)降低分選效率，因此，分選精煤的產(chǎn)率和灰分的關(guān)系表明了保證恒定的入料量才能保證洗選精煤的質(zhì)量。
處理量影響著旋流器的幾何尺寸，包括溢流口的尺寸，底流口的尺寸，入料口的尺寸和入料量。這些參數(shù)的影響如表7 – 14。改變?nèi)肓蠅毫κ且粋€(gè)改變旋流器參數(shù)的簡單方法，然而對(duì)改變精煤的產(chǎn)率和灰分的影響不顯著，況且會(huì)增加抽水成本，還會(huì)增加煤的泥化現(xiàn)象。
流程圖
隨著旋流器的發(fā)展，很明顯它毫不遜色于其他所有的洗選設(shè)備。因此，為了提高性能，兩段分選的旋流器（如圖7-64）被開發(fā)了出來。最早的兩段分選旋流器叫第二段再選或者叫TSR，從第一段旋流器出來的產(chǎn)品只是簡單的在第二段再選，從兩段旋流器溢流口出來的煤被混合當(dāng)作洗選精煤產(chǎn)品。從第二段旋流器底流出來的物料被視為洗選尾礦作為矸石。最近的有一種設(shè)備，一種從旋流器第二段出來的產(chǎn)品被循環(huán)作為第一段的入料。在兩段旋流器的溢流循環(huán)，TSOR，這種從旋流器的第一段被作為調(diào)節(jié)產(chǎn)品所要求精煤，第二段作為調(diào)節(jié)尾礦中保證沒有錯(cuò)配物。從旋流器第二段的溢流出來的物料包含本該進(jìn)入到第二段旋流器底流的錯(cuò)配物，所以返回到第一段旋流器進(jìn)行再次循環(huán)洗選。在兩段旋流器底流循環(huán)，TSUR，這種從第一段旋流器的底流出來的物料被作為最終的尾礦矸石，第二段的底流出來的物料再次進(jìn)入到第一段作為第一段的入料。從第二段溢流出來的產(chǎn)品被作為最終的洗選精煤產(chǎn)品。
上述的其中每個(gè)流程都有優(yōu)點(diǎn)，取決于入料的粒度組成，和所要求的精煤產(chǎn)品質(zhì)量。TSOR流程能更有效地回收分選精煤，而TSUR流程更有效地排除重產(chǎn)物。當(dāng)兩段旋流器分選的比重類似時(shí)TSR流程是最有效的流程。相反，TSOR和TSU
的性能取決于兩段旋流器的分流量。在目前，TSOR是應(yīng)用的最為普遍的一種流程。有人提出一種改進(jìn)的TSR流程是從第一段主選底流出來的物料被再次分選濃縮代替第二段旋流器分選。
有一些廠用跳汰機(jī)分選塊煤，利用旋流器分選細(xì)粒的煤。一種方法是用煤用振動(dòng)篩篩分的篩下物（通常1/4英寸）的煤用旋流器分選，另一種方法是用煤用振動(dòng)篩篩分出粗粒煤，細(xì)粒度的煤用旋流器分選。
旋流器也被運(yùn)用到重介質(zhì)分選中去分選出一些含煤少的貧礦，以降低選煤廠重介質(zhì)的消耗。旋流器可以調(diào)節(jié)的分選密度大概在1.35～1.40之間。這樣的優(yōu)點(diǎn)是大大的降低了分選過程中所需重介質(zhì)的體積，節(jié)約了資金和運(yùn)營的成本。
水力旋流器性能
正如上文以前，對(duì)洗精煤產(chǎn)品質(zhì)量和垃圾，可通過改變調(diào)節(jié)溢出和下溢口的直徑。但是從性能的角度來看，溢流直徑到底流直徑的比例范圍為約1.7至2為最好，較低的比率性能為低劣產(chǎn)品。此外，在原料中固體物含量，一段和二段水力旋流器應(yīng)定為8至15％（重量）。此范圍以外，高于或低于，性能將產(chǎn)生不利影響。分離獲得的水力旋流器和一個(gè)兩階段的電路（TSR）是由圖所示的分布曲線，兩個(gè)階段的電路分離清晰度明顯優(yōu)于單一的水力旋流器，另外，這兩個(gè)階段的電路分離清晰度幾乎沒有像重介質(zhì)旋流器特點(diǎn)鮮明，由此得出結(jié)論，水力旋流器應(yīng)用于難以清潔煤或低比重的適用，除非更，有效的再分選過程。此外，他們沒有合適的煤或者易碎的煤矸石顆粒板狀。
表7-15給出了詳細(xì)的兩個(gè)階段（TSR）的水力旋流器的性能數(shù)據(jù)。這些數(shù)據(jù)表明，在一般的分離增加，分離小顆粒的清晰度的減少。水力旋流器可能會(huì)適合分選- 30目（0.6毫米）的煤，如果煤不浮選。然而，美國多數(shù)煤浮選煤很容易分選通過浮選。但是，如果煤炭，不受外界因?yàn)轲ね繉訂栴}浮選或煤被氧化，然后水力旋流器可能是一種可行的選擇。另外，如果細(xì)粒黃鐵礦是目前的原料，據(jù)報(bào)道水力旋流器，對(duì)于降低洗精煤的硫含量優(yōu)于浮選。一個(gè)易于清潔粗顆粒煤，有1 / 4或3 / 8英寸（6.3或9.5毫米大小的粗顆粒頂部）可以被兩階段水力旋流器有效地清理，作為一個(gè)選礦臺(tái)，但沒有有效的長石跳臺(tái)。但是，集中清理的細(xì)小顆粒表比水力旋流器更有效。如圖7-66.所示：
一種相對(duì)較新的名為空氣旋流器的分選設(shè)備被研制出來并可用于分選蛋白石。它本質(zhì)上是一個(gè)沒有通常錐形部分多孔圓筒。入料進(jìn)入切向頂部并螺旋下降，空氣是透過多孔圓筒，氣泡和浮選劑隨著漩渦影響分選。煤顆粒附著在氣泡上升到漩渦的頂部。
圖 7-56 旋流器典型分布圖
表7-15 旋流器的性能
尺寸，網(wǎng)目（mm）
3*200
（6.3*0.075）
3*200
（6.3*0.075）
3*200
（6.3*0.075）
3*200
（6.3*0.075）
30*200
（0.6*0.075）
30*200
（0.6*0.075）
篩分分析
原煤
93.9
94.8
91.0
95.4
84.4
86.6
精煤
92.2
94.3
88.1
93.1
80.7
85.7
矸石
97.4
97.9
97.8
97
97.5
84.0
灰分含量
原煤
17.5
16.1
29.8
17.9
21.1
16.1
精煤
7.0
10.3
13.1
8.7
9.6
11.8
矸石
50.3
51.4
64.8
64.4
55.4
65.1
洗選出精煤的產(chǎn)率
75.8
86.0
67.7
83.5
74.8
91.9
理論產(chǎn)率
84.7
90.8
75.5
88.2
82.5
93.8
分選效率
89.5
94.7
89.7
94.7
90.7
98.0
-1.30
93.1
97.1
94.5
96.9
96.0
99.2
1.30～1.40
86.0
94.6
88.8
95.5
89.4
98.4
1.40～1.50
68.4
81.2
75.6
88.8
75.8
94.8
1.50～1.60
47.4
56.4
61.8
83.7
59.7
89.5
1.60～1.70
25.1
37.4
40.3
71.9
53.0
79.6
1.70～1.80
13.7
29.8
32.5
62.4
36.9
72.5
+1.80
5.2
14.5
7.0
15.4
12.5
36.7
分選密度
1.54
1.58
1.61
1.88
1.62
1.96
錯(cuò)配率
78
105
120
123
118
-
可能性偏差
0.12
0.18
0.22
0.24
0.23
-