CFD Simulation of Pollutant Emission in a Natural Draft Dry Cooling Tower with Flue Gas Injection: Comparison between LES and RANS

Guangjun Yang,Jingxin Xu,Zhen Xu,Li Ding,Xiaoxiao Li,Sheng Wang,Fahua Zhu,Zhigang Wang,Pengxiang Qiu,Zhaobing Guo

doi:10.3390/en12193630

Abstract

Accurate prediction of pollutant dispersion is vital to the energy industry. This study investigated the Computational Fluid Dynamics (CFD) simulation of pollutant emission in a natural draft dry cooling tower (NDDCT) with flue gas injection. In order to predict the diffusion and distribution characteristics of the pollutant more accurately, Large Eddy Simulation (LES) was applied to predict the flow field and pollutant concentration field and compared with Reynolds Average Navier-Stokes (RANS) and Unsteady Reynolds Average Navier-Stokes (URANS). The relationship between pollutant concentration pulsation and velocity pulsation is emphatically analyzed. The results show that the flow field and concentration field simulated by RANS and URANS are very close, and the maximum value of LES is about 43 times that of RANS and URANS for the prediction of pollutant concentration in the inner shell of cooling tower. Pollutant concentration is closely related to local flow field velocity. RANS and URANS differ greatly from LES in flow field prediction, especially at the outlet and downwind of cooling tower. Compared with URANS, LES can simulate flow field pulsation with a smaller scale and higher frequency.

Highlights

With the high speed development of China’s economy, the demand for energy has increased rapidly
The air mass flow rate and heat rejection of the cooling tower predicted by Reynolds Average Navier-Stokes (RANS) may meet the engineering accuracy requirement
In terms of pollutant diffusion simulation, results obtained by Unsteady Reynolds Average Navier-Stokes (URANS) are still not ideal even if the unsteady algorithm is adopted

Summary

Introduction

With the high speed development of China’s economy, the demand for energy has increased rapidly. 2017, coal would still be the dominant source of energy in China for a long time due to the national energy security and economic security policies. The coal-dominated energy conversion structure has caused the total emission of air pollutants in the thermal power industry to remain high for a long time. The total emission of SO2 and NOx reaches about 60% of the national industrial emission every year, which makes the problem of air pollution become increasingly prominent [1,2,3,4]. In view of the strict environmental regulations issued by many countries, coal-fired waste gas must be treated by denitrification, dust removal and desulfurization before entering the atmosphere [3]. Limestone wet flue gas desulfurization (FGD) technology has been widely used in coal-fired power

Objectives

Methods

Discussion

Conclusion