A study on utilization of wastes from the semi-dry FGD installations for sulfite and anhydrite binders production

In Poland the power industry is the major source of pollution into the atmosphere resulting largest changes in environment. In 1994 as a result of signing by Polish Republic's Government document called "second Sulfur Protocol" the limit values of SO(2) in 2010 were settled. In order to achieve this target the investment program for flue gas desulfurization (FGD) installations in polish power industry was initiated. Sustainable development of FGD installations as well as implementation of fluidized bed combustion furnaces in electric and thermal power plants led to the production of new type of wastes. After wet lime/limestone flue gas desulfarization with gypsum as and product, the semi-dry FGD process using lime as sorbent is the most used FGD technology in industry. While for the wet FGD process there already existed a market demand for gypsum and the FGD by-product could gradually replace the use of natural gypsum, the establishment of recycling and utilization of semi-dry FGD product has been more difficult. For each installation in the semi-dry method depending on the existing dust removal system, operation conditions of desulfurization installation and SO(2) concentration variations in a stream of gases the chemical and mineralogical composition of desulfurization products change. In this paper the examination results of chemical and phase composition, microstructure, specific surface as well as wastes grain size composition from the semi-dry flue gas desulfurization (Siersza power plant, Lodz power and heat station) have been presented. Wastes are fine-grained like a fly ash and contain mainly CaSO(3).0.5H(2)O, Ca(OH)(2) (unreacted sorbent), CaCO(3) (carbonizated sorbent), CaSO(4) and CaCl(2)-2H(2)O. Basing on the chemical, mineralogical and physical characterization of wastes, the possibilities of utilization in building materials production arc proposed. Wastes were subjected to calcination at the temperature of 350 and 600 degrees C in order to assess the opportunity to obtain sulfite and anhydrite binders. The phase composition and microstructure changes after thermal treatment of the samples have been determined. The setting time and compressive strength of the standard wastes slurries, unmodified and modified with fly ash, were carried out. The laboratory tests on the waste from Siersza with an addition of fly ash have given 5 MPa compression strength after 7 days of hardening. The semi-dry FGD by-product after thermal treatment at the temperature of 350 degrees C can be used to manufacture the sulfite binders of properties similar to properties of gypsum binders used in finishing construction works. As a result of thermal oxidizing of the calcium sulfite to form calcium sulfate, e.g. at 500 to 600 degrees C, one obtains product with properties similar to natural anhydrite.