| Thermal power generation is the most important form of power generation in China.Natural draft dry cooling tower(NDDCT)with flue gas injection is a new type of flue gas emission technology in coal-fired power plant,and it is of great significance to study the influence of the flue gas diffusion characteristics of NDDCT with flue gas injection on the corrosion protection and small-scale environment of cooling towers.In China,affected by meteorological conditions and other factors,the NDDCT with flue gas injection is mainly distributed in the north of the Qinling-Huaihe line.In this paper,the numerical simulation and wind tunnel experiment are used to study the flue gas diffusion characteristics of NDDCT with flue gas injection,and the improvement measures are put forward to solve the difficulty of flue gas exhaust of NDDCT with flue gas injection in winter heating in northern China.Based on Reynolds-Averaged Navier-Stokes(RANS)method,numerical simulation study of the flue gas emission from a NDDCT with flue gas injection is carried out and compared with that from traditional chimney.The results show that the pollutants in the downstream of the NDDCT with flue gas injection are horseshoe-shaped,and the maximum spatial concentration increases first and then decreases with the increase of the environmental wind speed.The distribution of pollutants discharged by chimney has no obvious characteristics,and the maximum spatial concentration decreases monotonously with the increase of the environmental wind speed,but it is all greater than the spatial concentration of the integrated smoke extraction method.In order to simulate the diffusion and propagation characteristics of pollutants more accurately,Large Eddy Simulation(LES)method is used to simulate the flow field and pollutant concentration field of the NDDCT with flue gas injection,and compared with RANS method.By comparing the difference of the two methods’equations and flow field characteristics,the difference of pollution diffusion characteristics is analyzed.The results the LES method can capture the flow field details and pulsations which cannot be captured by RANS when simulating the flue gas diffusion.Therefore,it is necessary to use LES method when it is necessary to accurately simulate the diffusion of pollutants.The diffusion of pollutants in the NDDCT with flue gas injection was studied through wind tunnel experiment.Relying on the atmospheric boundary layer wind tunnel of Guodian Environmental Protection Research Institute,the hot film anemometer,pollutant sampler and gas chromatograph are used to study the cavity area and downwind landing concentration of NDDCT with flue gas injection.For the studied NDDCT with flue gas injection project,the cavity area length,height and width are about 1.9,1.3 and 1.1 times the tower height,respectively.With the increase of environmental wind speed,the concentration of pollutants on the ground increased first and then decreased.Under the condition of 15 m/s ambient wind speed,the ground pollutant concentration reached the maximum value,the maximum hourly concentration of SO2 was 31.55 μg/m3.In the north of China,the temperature is relatively low in winter,the power plant needs to freeze the radiators while providing heat to the outside,and the air flow in the cooling tower is greatly reduced,which may lead to the difficulty of flue gas exhaust in the NDDCT with flue gas injection.To solve this problem,numerical simulation and wind tunnel experiments were carried out under the most unfavorable conditions.The results show that the flow field inside the cooling tower is disordered and the pollutant concentration is greatly increased due to the decrease of ventilation and heat exchange caused by the closure of louvers.Mixing air can prevent or reduce the flue gas from touching the wall.With the increase of stack height,the flue gas can resist the turbulence in the cooling tower by its initial kinetic energy and rush out of the tower,and the flue gas diffusion in the cooling tower gradually improves.In this paper,numerical simulation and wind tunnel experiments are used to study the NDDCT with flue gas injection in northern China.In the aspect of numerical simulation,RANS and LES methods are used to study the flue gas exhaust characteristics of the NDDCT with flue gas injection.In the aspect of wind tunnel experiment,the cavity area and ground concentration of the NDDCT with flue gas injection are studied.In addition,numerical simulation and wind tunnel experiment are used to study the flue exhaust characteristics of the NDDCT with flue gas injection under adverse conditions.The research results can provide reference for the feasibility analysis of the project. |
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