| As is known to all, the nitrogen oxides(NOX) is one of the pollutants in the atmosphere. It is not only one of the culprits of acid rain and photochemical smog, but also some scholars have pointed out that one of the main reasons for the formation of the haze weather are also the nitrogen oxides. Due to the limitation of energy consumption structure, the emission of nitrogen oxides in China is huge, which produced by combustion of coal-fired boiler NOX emissions accounted for 70% of total emissions. Therefore, the NOX emission control for coal-fired boiler flue gas in our country is more and more strict. At present, the most widely used and most efficient nitrogen oxide control technology is selective catalytic reduction(SCR) flue gas denitrification technology. And before the new SCR device put into operation, designers use CFD numerical simulation and a similar experimental model method of SCR device initial design optimization scheme, to achieve high denitration efficiency. A SCR denitration device of a 300 MW boiler unit of a coal-power plant is studied by CFD numerical simulation. The main research contents and conclusions are drawn:First of all, the SCR denitrification reactor of a 300 MW pulverized coal boiler is simulated by CFD. And the standard deviation of velocity and concentration of NH3 on the specific cross section of the SCR device is calculated, which includes the AIG upstream section, the AIG downstream section of and the cross section of the first layer catalyst. It is found that the reactor in the flow field and concentration field distribution is not uniform. The main reason for the large deviation of the velocity and the NH3 concentration of the SCR is that the SCR inlet is asymmetric, and the flue gas is affected by the centrifugal force at the turning point, and the abrupt expansion of the first layer of catalyst inlet. For these reasons and through in the CFD simulation in repeated careful design changes, eventually in the interior of the SCR reactor was established four groups of optimization and the deflector groups, establish the deflector groups where there is at the entrance to the SCR, spray ammonia upstream corner, downstream of the ammonia injection and first catalyst layer at the entrance of the 90 degree bend.Numerical simulation and cold test results show that the flow field uniformity in the reactor which was added guide plates has been greatly improved. With inlet section of the first layer catalyst as an example, before optimization, the speed standard deviation values of simulation and cold test were 25.69%, 28.91%, after optimization of 2.4% to 11.5%. However, the simulation and test results show that the installation of the guide plate does not improve the uniformity of the ammonia concentration in the reactor. The reason is caused by the original vortex mixed plate of ammonia injection system. Ammonia is sprayed into the reactor by six ammonia spraying pipe, the long time stay in the low pressure vortex area of back side of the mixed plate, resulting in ammonia in the cross section of lateral diffusion capacity is weak. In this paper, we try to replace the vortex mixing board with the ammonia grid for the spray system. The results show that the standard deviation value of the first layer of the first layer of SCR denitrification unit is 14.5%. And the system resistance loss reduce from 681 Pa to 657 Pa. |
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