Sulphur Dioxide Emissions during the Firing of Ceramic Bodies Based on Class C Fly Ash

Abstract

Fluid fuel combustion technology in coal-fired power plants is very popular in the Czech Republic, resulting in a relatively high production of a specific by-product - fluidized fly ash (class C according to ASTM definition), which differs from the classical high-temperature fly ash in mineralogical composition with a high sulphur content of anhydrite CaSO4. Fluidized ash is not yet used in the production of fired building materials, where it could be used as a source of calcium oxide (for example, the production of porous ceramic tiles). However, high volume of sulphur dioxide emissions during the re-firing of fluidized fly ash in ceramic raw materials mixtures has been solved. The aim of the paper is definition of temperature ranges of anhydrite decomposition (formation of SO2 emission) from pure class C (fluidized) fly ashes from different sources (power plants) depending on granulometry of fly ash especially.

A Novel Process for the Containment of SO2 Emissions from Class C Fly Ash in the Fired Materials by Haüyne Formation

“…When the milled CCFA was used, the decomposition of anhydrite started at lower temperatures (about 1040 °C). Sulfur dioxide appears in the flue gases from low temperatures close to 940 °C (milled fly ashes) or 990 °C (unmilled fly ashes) due to the decomposition of anhydrite CaSO 4 in dry-pressed clay-fly ash bodies [ 24 , 25 ]. Haüyne Na 4 Ca(Si 3 Al 3 )O 12 (SO 4 ) = 2Na 2 O·CaO·3SiO 2 ·Al 2 O 3 (SO 4 ) [ 26 ] is a tectosilicate sulfate mineral from the sodalite group (feldspathoids).…”

“…Despite abundant laboratory research [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 ], there are no examples of a broad application of CCFA within the production of fired building materials because the decomposition of anhydrite and the resulting re-release of sulfur dioxide (SO 2 ) into the atmosphere has not been solved. The previous research only provides information about the temperature ranges of the SO 2 content in the flue gas during the firing of pure CCFA bodies or the mixtures containing CCFA [ 24 , 25 ]. The finding of new ways for the utilization of CCFA is important for the environment and sustainable development since the CCFA is produced in very large quantities all over the world, and this number is predicted to continue to grow due to the transition from conventional high-temperature coal burning to fluidized bed reactor coal burning due to the efforts to reduce emissions released into the air.…”