Structure Design And Mixing Performance Of Gas Pre-Distributors For Flue Gas Denitrification Reactors

The Selective Catalytic Reduction (SCR) for the flue gas denitrification has been used widely due to its ripe technique. Many factors affect the performance of a SCR system. For example, the distribution of gas mixture in the reactor determines the slip rate of ammonia, the life of catalyst and the denitrification efficiency. The designed devices are installed in the SCR system to improve the gas velocity and concentration distribution. In this paper, the numerical simulations have been conducted to understand the flow characteristics of SCR system by the FLUENT software. Through orthogonal experiment design method, the influences of the guide plate, the static mixer and the porous plate on the gas distribution have been studied in the SCR system. A cold-model experimental setup has been established to verify the numerical results. The experience gained may therefore serve as valuable reference for design.First, numerical simulations have been adopted to study the sensitivity sequence of influence factors. The results indicate that the sensitivity sequence of influence factors for the y axis velocity distribution on the catalyst entrance section is the B4 guide plate＞the static mixer＞the B2 guide plate＞the B1 guide plate＞the porous plate＞the B3 guide plate; For the concentration distribution, the sensitivity sequence of influence factor is:the B1 guide plate＞the porous plate＞the B3 guide plate＞the B4 guide plate＞the static mixer＞the B2 guide plate.Second, both the optimization model obtained through orthogonal experiment design method and the blank model have been compared to study the impact of the static mixer, the porous plate and the guide plate. The results indicate that they achieve uniformity of velocity distribution in the optimization model. And they effectively improve the gas flow direction and reduce the area of back flow. Though the static mixer, the porous plate and the guide plate change flow of gas mixture in the SCR system, they do not achieve uniform distribution of concentration on the catalyst entrance section.Finally, the cold-model experimental results show that the sensitivity sequence of influence factors for the concentration distribution is the B1 guide plate＞the porous plate＞the B3 guide plate＞the B4 guide plate＞the static mixer＞the B2 guide plate. The excellent porosity of the porous plate is 22.4%, while the excellent number of the B1 guide plate is 2. And the concentration distribution of gas mixture is closely related to the structure of ammonia-injection grid. Because the porous plate and the B1 guide plate are located in upstream of ammonia-injection grid, the guide plates located downstream of ammonia injection grid little affect concentration distribution on the catalyst entrance section of the SCR system. And the section of ammonia injection grid corresponds to the catalyst entrance section, the more gas flow form the tube more close to the entrance of ammonia, the higher concentration in the corresponding region of the catalyst entrance section. Transforming the structure of ammonia-injection grid is important in the industry design for ammonia uniform distribution of SCR systems.