Evaluation of solid sorbents for acid flue gas emissions treatment

Removal of acid gases from exhaust emissions of industrial applications (SOx, HCl, HF) still represents a challenge for many sectors, in particular for waste to energy facilities. In dry absorption processes, the solid reagent (typically Ca(OH)2 or NaHCO3) is injected countercurrent to the gas in a reaction chamber that allows for optimal contact modes and times between the phases. Efficiency is influenced by the specific surface area of the solid (m2 kg-1 reagent), by the degree to which it is mixed with the gas, the concentration of the gas to be adsorbed, the temperature and humidity of the flow and the concentration of the reagent, usually expressed in terms of stoichiometric ratio. After reacting, solid sorbents can be separated from the flue gas together with the dust particles via a fabric filter. Recently, new formulation of calcium and sodium based sorbents have been investigated. Hence, the design and development of accurate systems for the experimental characterization of these material is important. The objective of the present study was to compare the absorption capacity of different types of solid sorbents against a gas stream containing HCl. A nitrogen/HCl gas mixture provided by an external laboratory was used for that purpose. Calcium and sodium-based sorbents were evaluated in an experimental installation consisting of a gas feed line, a gas flow meter and a reactor in which the absorption reaction took place. Unreacted chlorine was collected downstream with a bubbler filled with ultrapure water. The chlorine and water solution was finally tested in an ion chromatograph to determine the residual chlorine concentration.