Research On Low Order Coalbed Methane Deoxidation Method Based On Coal Iron Deoxidizer

Low rank coalbed methane,as an important raw material for natural gas preparation in China,requires deoxygenation treatment before preparation to avoid safety issues beyond the explosion limit.In recent years,with the deoxidation of low rank coalbed methane becoming a research hotspot in the field of coal development,domestic and foreign scholars have increasingly explored the deoxidation of low rank coalbed methane with different components.In this paper,from the point of view of"treating coal with coal",deoxidizer prepared from coal and hematite is used to deoxidize low rank coalbed methane.The effects of different reactant particle sizes,reaction temperatures,coal iron molar ratios,and coal moisture content on the preparation results of deoxidizers were studied,as well as the effects of deoxidizers on the deoxidation results of coalbed methane under different filling volume ratios,gas flow rates,and p H environments.The specific research results and conclusions are as follows:（1）Under the conditions of different reactant particle sizes（10 mm,5mm,2 mm,1 mm,0.1 mm）,the smaller the reactant particles,the greater the amount of iron produced by coal reduction of hematite.Under the conditions of different reaction temperatures（200℃,500℃,800℃,1000℃,1100℃）,when the reaction temperature exceeds 700℃,the amount of iron produced by coal reduction of hematite increases with the increase of temperature.When the reaction temperature is below 500℃,there is basically no reduction of elemental iron.Under different coal molar ratios（1:2,3:4,3:2,3:1,9:2）,when the coal molar ratios are 3:1 and 9:2,i.e.when there is an excess of coal participating in the reaction,the reduction amount of iron gradually increases with the increase of carbon content.When the coal molar ratio is 1:2 and 3:4,that is,when the coal participating in the reaction is insufficient,the reduction amount of iron gradually decreases with the decrease of carbon content.The water content of coal has no effect on the reduction of hematite by coal at 1100℃,because in the reaction atmosphere where H₂O and CO₂ coexist,the competitive relationship between H₂O and CO₂ and coal reaction exists,and the reduction amount of iron will not increase significantly.（2）Under the conditions of different proportion of iron powder filling volume（1/5,2/5,3/5,4/5,5/5）,the larger the filling volume of iron powder,the higher the removal rate of oxygen.When the iron powder is completely filled,the maximum removal rate of oxygen is around 3.4%.Under the conditions of different gas flow rates（50 m L/min,100 m L/min,150m L/min,200 m L/min and 300 m L/min）,the iron powder suspension has the highest removal rate of oxygen when the air flow rate is kept at 100ml/min,while the removal rate under the condition of 50 ml/min is not as high as that under the condition of 100 m L/min.After 100 m L/min,the oxygen removal rate gradually decreases with the slow increase of the flow rate.Under the conditions of p H values（4.0,6.0,7.0,8.0,10.0）in different liquid environments,the suspension of iron has the best absorption effect on oxygen in a neutral liquid environment.At p H<7.0,the deoxygenation effect of oxygen gradually deteriorates with the decrease of p H.At p H>7.0,the deoxygenation effect of oxygen gradually deteriorates with the increase of p H.（3）Observation under a fluorescence microscope revealed that no intermediate products were generated during the oxygen absorption process,except for iron oxide.Moreover,iron powder and iron oxide exhibit aggregation and hardening to a certain extent,which may reduce the rate of oxygen absorption.（4）After response surface optimization analysis,the optimal process parameters obtained by the response surface regression model are coal iron molar ratio（A）of 4.42636,reaction temperature（B）of 1068.32℃,and coal iron mixed particle size（C）of 0.0822101 mm.Under these conditions,the maximum reduction amount of iron is achieved.The influence of various factors on the amount of iron reduction in the iron catalyzed reaction is:C>A>B.（5）After response surface optimization analysis,the optimal process parameters obtained by the response surface regression model are iron powder filling volume ratio（A）of 5/5,gas flow rate（B）of 123.546m L/min,and liquid environment p H value（C）of 6.48975.Under these conditions,the highest oxygen removal rate can reach 3.5%.The actual oxygen absorption rate of the validation experiment is 3.45%,and the influence of each factor on the oxygen absorption reaction of iron powder suspension is:A>B>C.To sum up,in the reduction process of coal to hematite,the molar ratio of coal to iron,reaction temperature and mixed particle size of coal to iron all have an impact on the deoxidizer’s reducibility.The impact of each factor on the iron reduction amount of the reaction of coal to iron is in the following order:mixed particle size of coal to iron,molar ratio of coal to iron,reaction temperature,while the water content of coal has a small impact on the deoxidizer’s reducibility.In the reaction of iron powder suspension absorbing oxygen,the proportion of iron powder filling volume,the gas flow rate and the p H value of the liquid environment all have an impact on the reaction process.The impact of each factor on the reaction of iron powder suspension absorbing oxygen is in the following order:the proportion of iron powder filling volume,the gas flow rate,and the p H value of the liquid environment.