Liberation Law Of Caking Coal From Ma Lan And Technical And Economic Evaluation Of Its Middlings

In this paper,on the basis of exploring the liberation laws of coking raw coal and pure middlings,three characteristic parameters: liberation degree,particle size and theoretical separability were proposed,thus the re-separability of coking middlings can be evaluated.In addition,basing on experiments,the primary separation of coking coalmiddlings re-separation combined process was built,and a math model was deduced to evaluate the combined process.The experiments were carried out to analyze fundamental properties of coking raw coal and pure middlings,the results were as follows: The XRD analysis showed that the mineral in raw coal was mainly clay mineral while the mineral in middlings were primarily composed of silicon and clay mineral;The particle size analysis indicated that there are a large amount of fine products in raw coal and middlings while the latter had more coarse products than the former;The density analysis suggested that the raw coal was relatively difficult to separate.The liberation laws of raw coal and middlings were explored and the results were as follows:(1)The distribution characteristics of pure middlings in different particle size of raw coal were analyzed,and the results showed that the yield of pure middlings was highest in 50-25 mm particle size of raw coal while the content of pure middlings in this particle size was lowest,the yield of pure middlings in other particle sizes were relatively similar.(2)The liberation law of raw coal and pure middlings at different upper limit of crushing were explored and the results were as follows: the analysis on yield and ash content showed: with the decrease of upper limit of crushing,the-0.5mm fine products of raw coal largely increased and the difference between fine and coarse products was significant;and for pure middlings,the increase of-0.5mm products was not as much apparent as raw coal,and the ash content of fine and coarse products barely changed with the decrease of upper limit of crushing.The density analysis showed: For raw coal,the cumulative yield gradually increased with the decrease of upper limit of crushing,but the three cumulative yields were all lower than that of raw coal before crushing.And for pure middlings,the cumulative yield of its crushing products increased with the decrease of upper limit of crushing.The analysis on maceral groups showed: For raw coal and pure middlings,products with low density mainly consisted of organic macerals including vitrinite and inertinite while products with high density mainly consisted of minerals.Compared to raw coal,maceral composition of float-sink products of pure middlings presented characteristic of low vitrinite content in products with low density and high vitrinite content in products with high density.(3)The liberation laws of products in different particle sizes of pure middlings and 1.45-1.7 products of raw coal were explored.The results showed: For pure middlings,the yield of coarse products gradually increased with the decrease of particle size,and the ash content of coarse products was generally higher than that of fine products,And the density analysis showed the yield of crushing products presented a characteristic that the yield of low density and high density products were low while the yield of medium density products were relatively high,and the ash content of products in different particle sizes were similar.For 1.45-1.7 g/cm~3 products of raw coal,the +0.5mm coarse products increased with the decrease of particle size,and the ash content of coarse products were generally higher than that of-0.5mm fine particles.Relatively,the liberation effect of products in 50-25 mm was the best while the liberation effect of products in 13-6mm was the worst.The coking properties of-1.45 g/cm~3 products liberated during crushing process were studied.The results showed:(1)The caking property of products liberated from pure middlings was worse than that of products liberated from raw coal.And the caking property of products liberated from pure middlings decrease with the decrease of the particle size.For 1.45-1.7 g/cm~3 products of raw coal,the caking property of its crushing products showed no regular change.(2)At different upper limit of crushing,the volatile matter content of crushing products of raw coal was higher than that of pure middlings.And the volatile matter content of crushing products liberated from raw coal and pure middlings at different upper limit of crushing showed no significant difference.With the decrease of particle,the products barely changed.(3)The maximum reflectance of vitrinite of-1.45 g/cm~3 products liberated during crushing process showed no regular change with the decrease of upper limit of crushing and particle size.On the basis of experiment,to establish separability of re-separation of middlings,characteristic parameters of liberation degree L and particle size S were put forward.Combining the two characteristic parameters,characteristic parameters of theoretical separability Re of coking middlings re-separation was established finally.To recycle middlings,primary separation of coking coal-middlings re-separation combined process was proposed.According to two aspects of “re-separation process of middlings for maximum yield of clean coal” and “re-separation process of middlings for minimum ash content of clean coal”,two combined process were built.Basing on this,a a model for evaluation of economic efficiency of primary separation of coking coal-reseparation of middlings combined process was built.Equations of coal preparation benefit,economic efficiency of primary separation of coking coal-re-separation of middlings combined process were deduced,respectively.According to this,breakeven point of primary separation of coking coal-re-separation of middlings combined process was predicted.And products price at breakeven point of economic efficiency was calculated.Additionally,economic efficiency of primary separation and re-separation of middlings was apportioned.