PROCESS SIMULATION FOR CO2 AND SO2 CAPTURE BY USING FLY ASH AS SOLID SORBENT

Abstract

Fly ash, a waste material from coal fired power plants, becomes an interesting solid sorbent due to their low cost and their applications after CO2 capture. The performance of fly ash as a solid sorbent material for CO2 capture via surface adsorption and carbonation reaction were evaluated using gas chromatogram analysis and EDTA titration respectively. At 30 oC, 1 atm and 5 wt% moisture content, fly ash exhibited a total CO2 capture capacity of 208 µmol/g sorbent. A scaled-up reactor system comprising of two tubular reactors in series by employing the annual quantity of qualified fly ash (1,800 ktonne/year) was proposed using Aspen plus process simulation software, which can capture a total amount of 16.48 ktonne CO2/year equivalent to 0.09% of the annual CO2 emission from Mae Moh coal fired power plant of the Electricity Generating Authority of Thailand (EGAT). Fly ash was suggested to be used as an admixture in cement after the CO2 capture.Unqualified fly ash can also serve as a solid sorbent to lower the load of the desulfurization unit in coal fired power plants at low temperatures. The SO2 capture of fly ash via adsorption and sulfation reaction were evaluated using mass spectrometry and EDTA titration, respectively. The reversible SO2 adsorption at low temperatures is not desirable for SO2 capture. However, the reaction of irreversible SO2 sulfation with fly ash boosts up at high temperatures and the highest yield of SO2 capture was observed at 400 oC. A scaled-up reactor system equipped with two tubular reactors in parallel was simulated in Aspen plus process simulation software using the annual intake of unqualified fly ash (200 ktonne/year), which can capture 4.882 ktonne SO2/year equivalent to 0.37% of the annual SO2 emission from Mae Moh coal fired power plant, Thailand. The effect of different parameters on this system will be discussed.