| China is a county with much more coal energy, and the methane discharged into atmosphere annually by the coal mine VAM not only is a huge waste of clean energy, but also pollute the atmospheric environment. Because of low concentration, wide fluctuation range, huge volume flow and other characteristics, the governance and utilization of VAM has been a major problem. Preheating catalytic monolithic reactor was studied by Shandong University of Technology to handle VAM. It is compact and has high mechanical strength.The reactor recover energy and reduce energy consumption by using the exhausted gas to preheat the fresh air, and improve the thermal utilization and temperature of inlet flow of catalytic oxidation bed.It eliminate the need for a heating device, and has energy-saving and environmentally friendly meaning.This paper studied the design of deflectors, investigated and simulated the effects on flow field by varying structure parameters of oxidation bed, operating parameters and ceramic parameters. The main contents include:Preheating catalytic monolithic reactor and numerical calculation model of1000m3/h was built to study the uniformity of velocity distribution of the reaction chamber inlet. The simulation results show that the distribution is consistent with the experimental results, and the velocity in the center is much higher than surrounding. The larger part of the top and bottom of the oxidation bed is at a lower speed zone, and the velocity is very unevenly distributed.The flow field of the reaction chamber inlet of preheating catalytic monolithic reactor was numerically simulated to determine the optimized design of deflectors and improve the flow uniformity. In the original model without deflectors the non-uniformity coefficient of the velocity distribution at the inlet cross section of the oxidation bed is0.8. By arranging the horizontal deflectors, the velocity vertical distribution in the reactor is improved to some extent, and the non-uniformity coefficient is reduced to0.5. After the combination of the vertical deflectors and horizontal ones, the uniformity of the velocity distribution is improved obviously and the non-uniformity coefficient is reduced to0.2.Analysis the effects on velocity distribution uniformity when the parameters of the oxidation bed change in cold flow field:arranging current sharing bed in front of the catalyst bed can significantly improve the velocity distribution uniformity at the inlet cross section of the oxidation bed; The velocity distribution uniformity is best when the spacing distance of current sharing bed and catalyst bed is10mm; The changes of oxidation bed length and porosity affects it slightly; When the apparatus structure size is given, the best cross-sectional side length of oxidation bed is between550mm and600mm.The impact on the flow field of the operating parameters and the catalyst parameters:the increase of flow velocity will reduce the dwell time of the methane molecules on the wall, make the temperature rise slowly and decrease the methane conversion rate. Raising the temperature and methane concentration appropriately is good for elementary reaction of adsorption, and has a promoting effect on surface catalytic reaction. With other conditions unchanged, increasing the specific surface area of ceramic bed can increase the touching frequency of methane molecule and active particles, and speed up the rate of some key elementary reaction. The appropriate increase in the amount of catalyst coated can increase the number of active sites, and is conducive to the catalytic reaction proceed.Deflectors on hot flow field:after installing deflectors in the expansion section of the reaction chamber, the non-uniformity coefficient of the velocity distribution at the inlet cross section of the oxidation bed is reduced from0.5to about0.18. The non-uniformity coefficient of the temperature field in the middle of the oxidation bed is almost zero and the temperature gradient is very small. The running security of the oxidation bed is greatly improved. The non-uniformity coefficient of the CH4concentration is reduced and the fluctuation phenomenon of the methane concentration is obviously improved. The reaction time and the distance is shortened. So we can save the cost of the device by reducing the length of the bed appropriately according to the amount of wind. |
