Dry Scrubber involves the injection of a dry sorbent into a hot flue gases exiting a process to capture acid gases, metals and semi-volatile organic compounds. In most case, it involves the injection of sodium based or lime based minerals such as sodium bicarbonate or hydrated lime to capture acid gases such as HCl, HF, HBr, HI and SOx.
The capture of heavy metals and semi-volatile organic compounds can be carried on simultaneously with the acid gas capture or in a second stage by the injection of lignite coke or activated carbon.
Dry scrubbers are used mainly to remove acid gases from combustion sources. Generally, this is done by introducing a series of dry reactants to exhaust gas at high speeds. This neutralizes the pollutants in the gas. This task is done in three steps: gas cooling, reagent injection, and filtering.
First, gas cooling must be done to prepare exhaust gases. In the gas cooling system, emission gases are cooled to make it easier to remove pollutants and other toxins from the gas. The exhaust gas is diluted using an evaporative cooler. Once the gas has been significantly cooled the reagent injection can begin. It is in this step that the harmful components are actually removed from the gas.
Components of the dry reagent are generally chosen because of their neutralizing properties - thus sodium bicarbonate is frequently included. A variety of powders are mixed together and fired at high pressures into the exhaust gas.
Chemical reactions occur that reduce the acidity of the gas and remove harmful pollutants. The final step is using a dust collector to capture the used scrubbing powder as the cleaned gas exits the scrubbing chamber.
This spent powder can sometimes be cleansed and reused for dry scrubbing, but frequently it must be disposed of since it cannot be properly washed.