Effective Removal of HCl and SO2 With Dry Injection of Sodium Bicarbonate or Trona

Abstract

The newly promulgated EPA MACT rules for solid waste incinerators require HCl to be mitigated to extremely low concentrations. Most existing air pollution control systems will probably not be able to satisfy these very low limits. To meet the new challenges, dry injection of sodium bicarbonate or trona is a low-cost solution that can be applied in the following situations: (1) Replace existing acid gas mitigation systems; (2) Supplement existing systems; (3) Install where no acid gas mitigation systems exist yet. In a dry sorbent injection system, sodium bicarbonate or trona is injected directly into hot flue gas. After injection, the sorbent is calcined into porous activated sodium carbonate. Its high surface area enables fast gas-solid reactions between acid gases (mainly HCl and SO2) and Na2CO3 to form NaCl and Na2SO4 which are collected by either electrostatic precipitators (ESP) or fabric filters. The dry injection systems with sodium bicarbonate have shown over 99% removal of HCl and 95% removal of SO2 at over 150 Waste-To-Energy plants in Europe. This paper will describe the concept of dry sorbent injection system with sodium bicarbonate or trona, provide performance data from several plants, and describe system design guidelines.