High efficiency SNCR denitration technology
First, the technical background
In recent years, with the rapid development of the domestic economy, the emission of nitrogen oxides (NOx) pollutants has increased rapidly, seriously polluting the ecological environment, and has become one of the important factors restricting social and economic development. The main sources of nitrogen oxides are thermal power generation, motor vehicle emissions and industrial boiler kiln emissions. Among them, thermal power plants have become the first choice for national control of NOx emissions due to their large and relatively concentrated emissions and easy control over other sources. China has promulgated and implemented five standards on the emission of atmospheric pollutants from thermal power plants, and the requirements for emission control standards for NOx emissions from coal-fired power plants are becoming stricter.
Shandong Zhongtian Technology Engineering Co., Ltd. has been committed to the research and development of environmental technology engineering. The company has introduced Germany's advanced flue gas SNCR denitration technology, which can effectively remove nitrogen oxides from flue gas.
Second, the technical brief
Selective Non-Catalytic Reduction (SNCR) denitration is a denitration method that uses a reducing agent to reduce NOX in flue gas to harmless nitrogen and water in the absence of a catalyst. The process is to spray a reducing agent (such as ammonia, urea) containing NHx groups into a furnace temperature of 800 to 1100 ° C, the reducing agent is rapidly decomposed into NH 3 and reacted with NOx in the flue gas to form N 2 and H 2 O. . The method uses a crucible furnace as a reactor, which can be realized by reforming the boiler.
The main reaction of ammonia water and urea as reducing agent:
4NH3 + 4NO + O2 = 4N2 + 6H2O
CO(NH2)2 + 2NO + 1/2O2= N2 + CO2 + 2H2O
The traditional SNCR has not been modeled and analyzed, and the setting of the spray gun in the furnace is relatively simple and single, and the control of ammonia slipping can be completed while ensuring the denitration efficiency.
The company introduces foreign advanced denitrification technology to model and analyze fluids, so as to choose the optimal in-furnace denitration solution. The company is responsible for treating each project seriously, and doing sufficient preliminary work before the project starts driving and testing. The first step is to analyze the load performance, fuel (burning coal), load temperature and nitrogen oxide content in the furnace. The second step is to apply fluid dynamics software (CFD) (Computational Fluid Dynamics) to mechanical and chemical fluids in the boiler. Dynamics modeling and establishment of the injection model; the third step, simulation experiments, generating a chemical dynamics-based temperature distribution map, based on CKM to determine the position of the spray gun, preliminary judgment of the injection results of the spray gun; fourth step, analysis of the injection expectations Performance, diagram of the injection position, and complete the simulation, analysis, and prediction process of the entire reaction according to the type of spray gun required. The application of CFD software has largely replaced the expensive fluid dynamics experimental equipment, which has important guiding significance for the reaction, the installation and spraying of the spray gun.
Third, the process flow chart
Figure 1 shows the SNCR flow chart combined with CFD software simulation.
The process is mainly divided into three modules (1) a reagent module for reducing reagents; (2) a transporting and metering module for reducing agents, and (3) a dispensing module for reducing agents. The reducing agent is injected, metered, and dispensed through a spray gun to a suitable furnace location and reacted with nitrogen oxides. The amount of reducing agent injected is adjusted by measuring the ammonia slip amount of the exhaust gas and the nitrogen oxide content. Removal of nitrogen oxides by SNCR flue gas denitration can reduce nitrogen oxides by 50%-70%.
Five, engineering examples
Shandong Zhongtian Technology Engineering Co., Ltd. introduced advanced denitration technology from abroad and applied it to the actual production process, and achieved good denitration effect.
Taking the project of “2×220t/h circulating fluidized bed boiler flue gas purification system-denitration device” of Shanxi Pinglu 800,000 tons/year alumina project thermoelectric unit as an example, the denitration technology and denitration results are briefly described.
The project of thermoelectric installation of this project is 2×220t/h high temperature and high pressure circulating fluidized bed boiler, which provides electricity and steam for the alumina production process. The boiler flue gas denitration device adopts SNCR flue gas denitrification, and the denitration utility system equipment is considered according to 2 furnaces, and the expansion position of 2 furnaces is reserved.
The process design of SNCR technology includes testing the basic working conditions before the boiler is reformed, using three-dimensional computational fluid dynamics to simulate the combustion before the boiler is reformed, comparing the simulation results with the basic working condition test data to correct the combustion model parameters, and simulating the denitration comprehensive transformation. The effect on the flow field and combustion conditions in the furnace to guide the placement of the SNCR spray gun. The numerical simulation confirmed the position of the SNCR temperature window (950-1050 °C) with the best out-of-stock effect, and the arrangement of 4-6 SNCR spray guns. The spray gun was set up in three layers for a total of 16 sets. The performance test results are shown in the table:
Single 220t/h boiler performance table