Effect of Calcium Sulfate Addition on the Activity of the Absorbent for Dry Flue Gas Desulfurization

Abstract

The addition of calcium sulfate in the procedures of preparing flue gas desulfurization absorbent from calcium oxide and coal fly ash causes a negative effect in the slaking step and a positive effect in the following hydrothermal treatment step. The role of calcium sulfate added in each step was investigated. For the slaking step, XRD, XAFS, and Raman spectroscopic studies revealed that the addition of calcium sulfate in the step of slaking CaO with coal fly ash resulted in the coverage of calcium hydroxide with calcium sulfate to decrease the reactivity of the calcium hydroxide toward coal fly ash to form calcium silicate. For the hydrothermal treatment step, measurements of XRD, surface area, and Raman spectrum revealed that the addition of calcium sulfate promotes the formation of calcium silicate by suppressing crystal growth of calcium hydroxide to keep the reactivity of the calcium hydroxide toward coal fly ash.

Preparation and characterization of sorbents prepared from ash (waste material) for sulfur dioxide (SO2) removal

“…5). The positive effect of CaSO 4 on the surface area of sorbent prepared from coal fly ash was also reported by Ishizuka et al 3 However, in his work, Ca(OH) 2 is used as the raw material instead of CaO. It was reported that this phenomenon is due to the role played by CaSO 4 , since it promotes the formation of calcium silicate by suppressing the crystal growth of Ca(OH) 2 , and thus forces the reactivity of the Ca(OH) 2 to produce hydrated products.…”

“…It has also been shown that the addition of calcium sulfate (CaSO 4 ) to the preparation mixture can further promote the formation of the hydrated products. 3 This phenomena is because of the role played by CaSO 4 , which promotes the formation of hydrated products by suppressing the crystal growth of Ca(OH) 2 to force the reactivity of the Ca(OH) 2 to produce hydrated products.…”

Kinetics of pozzolanic reaction for preparation of flue gas desulfurizer from fly ash and Ca(OH)2

“…Time of initial stage was reduced to 2 h, but time of balanced stage was increased to 12 h because new hydrated productions (such as ettringite) generated breaking of the resultant layer. At the same time, SO 4 2− in slurry permeated into the resultant layer and thus improving its permeability [11]. As a result, pozzolanic reaction easily took place and the reaction time was longer.…”

Removal of Sulfur Dioxide From Flue Gas Using Absorbent Prepared by Water and Steam Hydration

“…The SO 2 formed is then released to the environment through the boiler's flue gas. The concentration of SO 2 released could easily reach 2500 ppm 1 , whereas the permissible concentration allowed by most environment control regulation around the world is only about 500 ppm 2 . Therefore, in order to reduce the emission of SO 2 , flue gas from the boiler has to be treated with appropriate yet affordable desulfurization technology before being emitted from the chimney to the environment.…”

“…The influence of the absorbent micro-structural properties such as the BET specific surface area, which is one of the major parameters affecting the efficiency of the absorbent in removing SO 2 , has been mentioned by a number of researchers 1,3,[5][6][7][8][9][10] . Recently, Ishizuka et.…”