Simulation Of Coal Mine Ventilation Air Methane Preheat Catalytic Oxidation Flow Characteristics And Oxidation Characteristics

The amount of ventilation air methane caused by coal mining is huge in China every year,which has caused serious energy waste and environment pollution.It is difficult to be utilized by the way of traditional oxidation methods because of the characteristics of huge air flow,low methane concentration and wide range of concentration.Therefore,it is of great significance to effectively utilize the ventilation air methane to save the energy and reduce the emission.For the situation,a new type of preheat catalytic oxidation reactor of coal mine ventilation air methane with three chamber was designed based on preheating catalytic oxidation theory.The catalytic oxidation chamber was directly connected with the preheater.Catalytic oxidation chamber was divided into two areas by pressing plate and heat can be exchanged between the two areas by pressing plate.The catalytic oxidation bed was arranged in three directions,which made the ventilation air methane enter the oxidation bed to react from three directions.The structure size of catalytic oxidation bed was designed and the preheating system was selected.Based on the design plan,the structure of device was improved.The flow characteristics and oxidation characteristics of the reactor were simulated under different operating parameters.With the method of numerical simulation,the influence of diversion distribution system in primary air intake on the flow uniformity of oxidation bed was studied by optimizing the shape and installing of the deflector.The result showed that the non-uniformity coefficient of oxidation bed ahead reduced to 0.241 by using four bending plate and the left and right oxidation bed reduced to 0.381.Flow uniformity of the left and right oxidation bed was improved by installing deflectors on the left and right gas collection tank.The result showed that the non-uniformity coefficient of all the oxidation bed reduced below 0.25 by using three deflectors which radius is 140 millimeter and the relative height is 0.1-0.12.The structure optimization of catalytic oxidation bed was used to improve the velocity distribution of the oxidation bed.The non-uniformity coefficient of the left and right oxidation bed was the least and the non-uniformity coefficient of the oxidation bed ahead was less than 0.25 when the height of the oxidation bed is 1650 millimeter.When the distribution coefficient of oxidation bed ahead was 0.353,the flow distribution of oxidation bed was the best.The non-uniformity coefficient of the oxidation bed ahead reduced to0.218 and the non-uniformity coefficient of the left and right oxidation bed reduced to0.222.The influence of inlet temperature,inlet air volume flow and inlet methane concentration on the flow uniformity and oxidation uniformity of the device with optimum structure was simulated.The result showed that the velocity non-uniformity coefficient of the left(right)oxidation bed was first increased and then decreased when the inlet temperature increased from 400 degrees Celsius to 550 degrees Celsius and the velocity non-uniformity coefficient reduced to the minimum value at 450 degrees Celsius.The velocity non-uniformity coefficient of the oxidation bed ahead increased a little and the temperature non-uniformity coefficient of oxidation bed decreases gradually.The rate of methane conversion increased from 57%to 99.5%.The inlet temperature should not be below 440 degrees Celsius in this working condition to ensure the flow uniformity and oxidation uniformity.The velocity non-uniformity coefficient first increased and then decreased with air volume flow increasing which value all were less than 0.25.The temperature non-uniformity coefficient of oxidation bed ahead gradually increased and the left(right)oxidation bed first decreased and then increased.The temperature non-uniformity coefficient of left oxidation bed reduced into a minimum value and the methane conversion rate gradually decreased to 92%when the air volume flow is10000Nm~3/h.With the increase of methane concentration,the velocity non-uniformity coefficient decreased gradually,the temperature non-uniformity coefficient was gradually increased to 0.062,and the conversion rate of methane is increasing continuously.When the air volume was not higher than 15000Nm~3/h,the inlet temperature was not less than500,and the methane concentration within the range of 0.4%~1.2%,it can be guaranteed that the conversion rate of methane was higher than 90%.