Numerical Simulation Of Heat Transfer Characteristics Of Denitration Air Preheater

Selective catalytic reduction(SCR)denitration devices are widely used in thermal power plants to reduce the nitrogen oxide pollution caused by coal combustion.The installation of SCR devices can negatively impact the overall performance of boilers,as the gas flues need to be reconstructed to compensate for the lowered boiler exits after SCR installation.Therefore,a denitration air preheater was designed in this study that could also be used as an SCR reactor.The catalysts with different temperature-dependent catalytic activities were selected according to thermal distribution of the heat transfer element in the air preheater for optimal denitration efficiency and air preheating.The denitration air preheater can decrease the investment of new denitration devices and potential modification of existing boilers.Moreover,the corrosion-resistant heat transfer element on the preheater can reduce corrosion near the boiler exit,and thus lower the risks associated with power plant operation.This project aimed to investigate the impact of installing a denitration air preheater on heat transfer performance,and to optimize the design of the preheater to enhance system performance.This project focused primarily on the following aspects.(1)A rotary air preheater was selected to model the denitration air preheater.The temperatures of the heat transfer element at hot,middle and cold section of the preheater were set to be 300-400,220-300 and 100-220 ?,respectively.The internal temperature field in the original air preheater was simulated with the Fluent software based on the porous media model.The simulation results suggested that the lengths of the hot,middle and cold sections of the preheater were 586,675 and 989 mm,respectively,and that the total height of the preheater was 2250 mm.(2)The heat transfer element in the rotary air preheater was re-designed for denitration.The heat transfer element in the hot section was designed to be model DU24 plates made with a commercially available vanadium-titanium(V/Ti)catalyst.The middle section heat transfer element was DU24 carbon steel plates coated with the Mn0.4-Ce0.07/TiO2 catalyst(0.1 mm in thickness).The heat transfer element in cold section was the carbon steel enamel-coated NF6 plates.All the plates were 1.15 mm in thickness.(3)A three-dimensional model of the performance of the newly installed heat transfer element,as described earlier,was constructed with Fluent software.The results indicated that the heat transfer performance at either the hot or the middle section was decreased after installation of new plates.Besides,the temperatures of flue gas and the wall temperatures were found increased.However,the overall changes in wall temperatures were not significant,and only minor adjustments of preheater height were needed to enable heat transfer in the preheater and catalytic reactions for denitration.(4)The dimensions of the denitration air preheater were re-designed.The hot section was lengthened from 586 to 765 mm(30.5%increase),and middle section from 675 to 791 mm(17.2%increase).The length of the cold section remained unchanged(989 mm).The overall height of the preheater was changed from 2250 to 2545 mm(13.1%increase).Further simulation of the performance of this preheater showed expected flue gas temperatures and wall temperatures,and suggested that this preheater was capable of simultaneous air preheating and denitration.