Dry Injection of Trona Sorbent to Mitigate SO_x, NO_X and Hg Emissions

摘要

Boilers, furnaces, metals, ceramics manufacture and similar processes produce waste off-gasescontaining acidic species that, if released uncontrolled, are harmful to human health and theenvironment. The acid gases of primary concern are oxides of sulfur (SO_x), NO_x and hydrogenhalides (HX). SO_2 and NO_x are criteria pollutants that affect both public health and the naturalenvironment, and as such it has both primary and secondary National Ambient Air QualityStandards (NAAQS). Alkaline gas scrubbing is generally employed to reduce emissions ofthese acid gases. Various different scrubbing technologies have been well proven in operationbut the least expensive to implement and simplest to operate are the “dry scrubbing” or drysorbent injection (DSI) systems. In DSI systems, a dry powdered alkaline material is injectedinto the hot gas stream to neutralize the acidic species, and the resulting solid salts and remainingexcess alkaline material is collected by a downstream particulate capture device. These systemsare capable of high levels of acid gas reduction. Various alkaline materials, both chemicallyprocessed and naturally occurring, have seen application in dry scrubbing. Dry hydrated lime, acalcium based alkaline sorbent, is in wide use in dry scrubbing, largely because of its moderatecost and availability. However, sodium based alkaline sorbents such as sodium bicarbonate,nacholite, and trona can provide particular advantages that make them a superior choice incertain applications. More recently, mechanically refined fine trona powder is being usedthroughout the coal electric utility industry for SO_x mitigation. Recently more data accumulatedduring SO_x mitigation sheds more light on NO_x and Hg abatement by the trona sorbent. Thispaper will discuss the process data, important variables to insure optimal sorbent usage, thechemistry of the operation and data collected under various injection conditions – into Cold andHot Side ESPs as well as baghouse including the effect of milling on SO_x, NO_x and Hg removal.This paper summarizes the advantages of DSI systems and dry injection of sodium basedalkaline sorbents in particular.