Enhancement of selenium removal in coal-fired flue gas across wet flue gas desulfurization spray tower by internal components-part 1: Demister and wall ring

Abstract

Wet flue gas desulfurization (WFGD) device is a key piece of equipment used to control selenium, but its removal efficiency is highly variable (13%–95%). Adding internal components into WFGD can alter the gas-liquid flow pattern and is regarded as a promising technology for selenium removal. In this study, the demister and wall ring were adopted as internal components to investigate their feasibility on selenium removal and inherent mechanisms. Compared with the open tower (without internal components), the outlet selenium concentration was reduced by 52.2%–61.7% by installing a demister. This was because a liquid film was formed on the baffle plates of the demister after intercepting mists, which leaded a secondary absorption process for selenium. The lower plates of the demister made a major contribution to selenium removal, and increasing the plate area of the demister was beneficial to this process. The wall ring reduced the selenium emission by up to 56.5%, because it could force the flue gas and liquid column near/on the walls to flow towards the center, and significantly improve the gas-liquid contact. The enhanced method and mechanisms reported in this study can help to develop a low-cost technology to improve the selenium purification efficiency of existing WFGDs.