Study On The Effect Of Pretreatment Of Lignite On Microbial Gas Production

Existing natural gas resources are difficult to meet the growing demand.The development of unconventional natural gas is an important means to ensure energy security in China.China has abundant low-rank coal resources such as lignite.Based on its characteristics of easy weathering,high water content,difficult storage and easy pollution caused by combustion,a method of biodegradation of lignite to produce gas is put forward to solve the problem of efficient and clean utilization of lignite and alleviate the relative scarcity of natural gas resources.In this study,physical and chemical pretreatment methods are used to pretreat lignite,which has been used since then.The obtained microbial flora degraded lignite and enhanced biogas production through pretreatment.In this study,the effects of two pretreatments,crushing and ball milling,hydrogen peroxide,nitric acid and potassium permanganate,on biodegradation of lignite and microbial gas production were investigated.The results show that ball milling method is superior to crushing method in physical pretreatment,hydrogen peroxide pretreatment method is superior to nitric acid solution pretreatment method and potassium permanganate solution pretreatment method;chemical pretreatment method is based on physical pretreatment method,and the biogas production of lignite degradation is increased more obviously after chemical pretreatment.In the physical pretreatment method,the effects of particle size range of lignite after crushing and ball milling on the gas production after microbial degradation were investigated.The results showed that with the decrease of particle size range of lignite,the gas production increased first and then decreased.The gas production reached the highest when the particle size range was 400-500 mesh,and the gas production after ball milling was higher than that after crushing.In chemical pretreatment,the effects of hydrogen peroxide,potassium permanganate solution and nitric acid solution on the gas yield of lignite after microbial degradation were investigated.The results showed that the cumulative gas yield of lignite treated with hydrogen peroxide solution(mass fraction 5 %,solid-liquid ratio 1:1,treatment time 2 days)was 39.65 m L,which was 25.77 m L higher than that of original coal.The cumulative gas production of lignite was increased by 53.86 %;the cumulative gas production of lignite was 39.23 m L after treatment with potassium permanganate solution(mass fraction 2.5 %,solid-liquid ratio 1:2,treatment time 2 days),which was 17.30 % higher than that of original coal(gas production 33.47 m L);the cumulative gas production of lignite was 36.30 m L after treatment with nitric acid solution(mass fraction 2 %,solid-liquid ratio 1:2,treatment time 2 days).Compared with raw coal,the cumulative gas production increased by 29.64 %.Lignite treated by hydrogen peroxide,potassium permanganate solution and nitric acid,the gas production reached 39.65 m L,39.23 m L and 36.30 m L,respectively,which were 53.86 %,17.30 % and 29.64 % higher than raw coal.Under the same conditions,the gas production of lignite treated by hydrogen peroxide in different particle size ranges reached 43.50 m L.Oxygen-water pretreatment is superior to nitric acid solution pretreatment and potassium permanganate solution pretreatment.