Study Of The Crushing Effect Of Coal Middlings From Dense Medium Separation Based On The Different Crushing Modes

Fat coal and prime coking coal is the basic materials of metallurgical coke. Although our China is the world’s largest coal producing country, the materials of this will be insufficient with consumption of coking coals. So many experts focus on coal middlings which is the production of coal separation to achieve some clean coals. How to liberate some clean coal from coal middlings and avoid overcrushing are difficult problems based on the characteristic of it. This paper has been studied crushing effects of the coal which is the middling of Malan Mining District, Xi Shan Coal Electricity Group Co., Ltd by different comminuting process.By the density composition and size composition of the middling coal, the coal middlings slime is little, so we can igore it. Size distribution of coal middlings is uniform except slime. The ratios of low density and high density are low, namely they are main centering on middle density. Theoretical yield of clean coal is about 7.00% when the theoretical ash is 12.00%, the content of δ±0.1 is about 80%, which shows the coal is extremely difficult to separate.This paper have been studied crushing effects of the coal by different comminuting process from differert crushing, different opertating frequency, different feed size, feed proportionality and different moisture content. The main conclusions are as follows:(1) The size of crushing product by impact foce relative to this by extrusion force to crush is smaller and more regular and the roundness, the fractal dimension is more approximate to “1”, pore volume and specific surface is bigger. The ration of-0.5mm in the crushing product obviously increased with crushing upper limit decline from 3mm to 1mm. The yield of-0.5mm in the crushing product by impact foce to crush is almost 60.00% while which is just 40.00% by extrusion force to crush when the crushing upper limit is 1mm. Cumulative float curves of +0.5mm and-0.5mm are almost coincidence. This shows the liberation of the coal is bad though the crushing upper limit is 1mm. Luckily, the effects of liberation by impact foce to crush is inherently better than that by extrusion force to crush. The energy consumption will increase with the crushing upper limit decline, but the energy consumption of hammer crusher is bigger than that by roll crusher.(2) Cumulative float of crushing product which results from hammer crusher will increae with the operating frequency increase, but cumulative float of crushing product which results from roll crusher is almost at the same with the operating frequency increase. The crushing energy consumption of hammer crusher increases while that of roll crusher declines with the the operating frequency increase.(3) The size distribution of crushing product which results from hammer crusher is almost at the same. This reason is that mesh size decide the size of crushing product by impact foce. The size distribution of crushing product which results from roll crusher is almost at the same, but the ration of +0.5mm increase and-0.5mm decline compared with 50-0mm feed. This may be due to mixed feed along with optimized force.(4) Feed Proportionality has little effect on the crushing of hammer crusher, which shows hammer crusher has adaptability. Feed Proportionality has much effect on the crushing of roll crusher, which shows roll crusher has bad adaptability. Crushing product size of inhomogeneous feed is large and the ratio of over crushing decline.(5) The ration of 1-0.5mm and-0.074 mm in crushing produc which results from hammer crusher increase when the feed is moist. Cumulative float of crushing product is almost at the same, but the screen is easy to blocking and the capacity is smaller. The ration of 1-0.5mmin crushing produc which result from hammer crusher increase, but the ration of-0.074 mm decline when the feed is moist. This shows moist coal middlings has effect on its liberation and deteriorate it.(6) The paper explores and compares different crushing craft based on characteristic of different crushing process. The two stagy crushing craft that hammer crusher at the first stage, roll crusher at the second stage and closed hydrocyclones may achieve theoretical yield of clean coal is 6.73% when the theoretical ash is 12.00% and the ratio of +0.5mm in crushing product is 53.02%.