| Rapid economic development has caused the acceleration of urbanization in our country, which makes the generated rubbish become one of the serious problems that troubled our city.Incineration has got more and more people’s attention because of its advantages of reduction, innocuity and stabilization. But incineration will generate nitrogen oxide, which will pollute the environment. In order to reduce the emissions of nitrogen oxide to meet the national standard, the incineration power plants take the formation and removal of NO_x very seriously. Taking the cost and efficiency of all kinds of denitration technology into consideration, the application of SNCR is more and more popular currently in incineration and flue gas purification system. Therefore, the research on low nitrogen combustion in garbage burning furnace and SNCR removal efficiency is of great significance.By FLIC bed calculation program and CFD numerical simulation software ANSYS 14.0, this paper carries on a numerical simulation study on a 750 t/d large municipal solid waste incinerator in Guangzhou. Compared to the actual data of incinerator’s 100% load operation condition, every parameter is in engineering error range and the study conforms to the requirements of the simulation. Simulation results were consistent with the actual combustion conditions. Using the validated model of incinerator, the results of numerical simulation of the furnace under variable load were analyzed. The results showed that as the load of the incinerator decreases, overall temperature levels in the hearth dropped while the temperature in the hearth areas rose gradually and drew close to the central chamber of the furnace, which reduced high temperature corrosion on the back wall of the chamber of the furnace. The high concentration area of NO was mainly formed in the second half of the grate and in the high temperature area inside the furnace, which was formed mainly due to the generation of heat and fuel NO, and in cooperation with the inhibitory effect of reducing atmosphere. With the decrease of the load, the regional distribution of a high concentration of CO moved forward to the second-level grate, and the emission concentration of NO_X of tail flue shows an evident rising trend.By optimizing the waste incinerator in deep air grading distribution of MCR conditions and adjusting the air distribution ratio in incinerator’s secondary air and overfired air, it is shown that when the proportion of secondary air and burning air is SA: OFA = 0.65:0.35, the combustion condition inside the incinerator is good. The increasing of the proportion of overfired air is advantageous to the decrease of emissions of NO_X in the tail flue outlet.By studying the influence on the SNCR removal efficiency by different reductants——ammonia and urea, analyzing the temperature field and flue gas component inside the incinerator according to concentration field, and comparing the change of NO_x emission concentration before and after SNCR denitration while analyzing the rules of SNCR removal efficiency in garbage incinerator changing with the different load, the simulation results showed that the “ammonia solution” has an obvious advantage in the boiler efficiency and denitrification rate and safety factor. So it is the best reductant for SNCR injection. According to the results of numerical simulation in the MCR working condition, the first flue SNCR reaction effect is very obvious since the NO concentration in the tail flue outlet is 131.9 mg/Nm3(converted into 11% oxygen). Compared with the emission concentration of 273.1 mg/Nm3(converted into 11% oxygen) by not using SNCR denitration, its denitration rate has reached 51.7%, which was a relatively ideal denitration effect. Among the SNCR denitration effects under different loads(50%, 65%, 80%, 65%), in addition to the denitration effect under 50% load working conditions being not ideal, the denitration efficiencies under 65%, 80%, 100% load have reached 45.1%, 26.3% and 45.1% respectively.Under the incinerator MCR conditions, simulation research has been respectively carried on the denitration effect of SNCR affected by the position of nozzle, jet velocity and layered injection ratio. the results showed that the reducing agent injected from the lower part of the first flue SNCR nozzle made the NO removal effect good.And the ammonium hydroxide jetting near the upper area of first flue moved by the smoke airflow lead into the second flue and produced ammonia leakage phenomenon. The result of the study on nozzle flow rate showed according to the results of the original working condition of jet velocity(13.8 m/s) of the mixed flow effect was good, the reductive reaction was more fully conduct, the denitration rate was 51.7%. This working condition of jet velocity can be used as a suit of SNCR design reference. In addition, in the case of a certain flow-rate of reductant, increase the lower SNCR nozzle flow, was beneficial to the improvement of the SNCR denitration efficiency. When SNCR-1:SNCR-2:SNCR-3 = 6:3:1, waste incinerator denitration efficiency reached 53.3%, which was a relatively good parameters of SNCR design. |
PDF Full Text Request