The Influence Of Thermal Modification Of Yuanbaoshan Lignite On The Flotation

Although the natural abundance and comfortable mining, the pratical exploitation and utilization of lignite is still limited by the disadvantages of low calorific value, high moisture, high ash content and high volatile. Consideration the fact that the major lignite will be used as fuel of the coal-fired power plant, the research centred on exploring the comprehensive application, which will retard the energy crisis, received widespread attention. Coal washing is a critical section in the comprehensive application of the lignite, which can reduced the mineral content substantially.It is difficult to get satisfied effect using traditional floation method due to the inferior floatability of the sample. Herein, we describe a new method referred to as "two step washing process"for the washing and ash reducing of lignite that involved pretreatment through low temperature pyrolysis and washing of the resulted char. The effect of impact factors such as collector dosage, former dosage, pulp density, revolving speed and aeration quantity on the char characteristic calcined at500℃have been investigated. Then, we conduct the flotation experiments of chars at different temperatures. The results give clear evidence that the thermal modification would increase the floatability of the lignite dramatically. The optimum conditions are kerosene3.5kg/t, octanol0.462kg/t, pulp density60g/L, revolving speed2100r/min, inflating volume300L/h, particle size<0.5mm. Then we conduct the flotation experiments of chars at different temperatures, comparing with the flotation under500℃condition. According to the comparation, the optimum thermal modification temperature is600℃.After screening, the flotation kinetics of600℃char of different particle size ranges are studied. The flotation rate of crude-graded char is lower than the fine-graded char, the particle size range of0.125-0.075mm presents the biggest flotation rate. We study the two processes of flotation of600℃char separately, after a rougher flotation, the cleans ash reduces from23.98%to12.10%, and the ash reducing rate reaches49.54%; we get coarse products when the600℃char was rougher flotated for once, after ore grinding we can get a10.30%char cleans ash.The ash reducing rate is55.22%, and we also inspect a process that adding a selection on the base of coarse products ore grinding flotation, after this mixing process, we get a cleans ash reduced to9.28,the ash reducing rate is59.65%, the ash decrease obviously, but it only decreases2.82%compared with a one time selection, and only decreases1.02%compared with the second selection of coarse product process, so it is not suitable to choose this process for flotation.We measure part of the properties of600℃char both before and after the flotation. And the experiment found that the ash percentage and the content of quartz of char cleans decreases while the content of volatile and calorific value increase. The kinetics study of char before and after flotation at different heating rate refers that:as the increasing of heating rate, the ignition point, the combustion rate temperaturn and burnout temperature have a rising trend. The activity energy and pre-exponential factor decreases gradually, and the activity energy is lower after flotation.