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Coal-fired power plants with semi-dry flue gas desulfurization (semi-dry FGD) system produce daily tones of ashes contaminated with calcium sulphite. To turn this solid waste useful (e.g. to the cement industry) and avoid landfill disposal, the present study suggests a semi-dry FGD solid waste treatment unit, that promotes the dry oxidation of calcium sulfite to calcium sulfate. Sizing of main equipment using pilot-plant and patents data allows economic evaluation of capital expenditure, operational and maintenance costs, and sale of the treated residue, which permits estimation of levelized cost of energy to assess the impact of the technology on the electricity price of a power plant using the proposed solid waste treatment unit. As base case, a Brazilian coal-fired power plant facing decision making process on semi-dry FGD waste destination is selected. Results demonstrate that the semi-dry FGD, without the solid treatment unit, has total levelized cost of energy increased in 0.56% (from 94.44 to 94.97 $/MWh) resulting from solids waste disposal. If the treated semi-dry FGD waste was transferred (at zero revenue) as additive to a cement industry, the levelized cost of energy of the power plant would remain approximately unchanged. This is because the increase of 0.51$/MWh resulting from the investment and operation and maintenance cost of the treatment unit is compensated by the decrease of 0.53$/MWh, in virtue of the avoided waste disposal costs. However, if the commercialization as raw material of the treated semi-dry FGD waste is considered, a reduction of 2.83 $/MWh (∼3%) on the levelized cost of energy (to 92.14 $/MWh) would occur. In both cases, the proposed treatment unit shows small impact on the total power plant levelized cost of energy, besides solving the solid management problems of landfill saturation, land use and costs related to landfill maintenance. Thus, it is adequate to implement the semi-dry FGD waste treatment unit on the power plant in question. The conclusion can be extended to plants with similar design and economic parameters. [ABSTRACT FROM AUTHOR]

Coal-fired power plants with semi-dry flue gas desulfurization produce several metric tons per day of residues with 10–18%w/w of hemi-hydrated calcium sulfite. The rest of the 90–80%w/w of such residues contains silica, aluminium-silicates and calcium/magnesium carbonates, sulfates and hydroxides. This material could be added to cement, but sulfites degrade the cement quality and lead to costs of landfill disposal. To test upgrading desulfurization residues to turn it into an acceptable cement feedstock, a pilot plant was built to oxidize residues with hot air converting sulfites to sulfates. This pilot comprehends a fluidized bed reactor, an air heater, a cyclone and a heat recovery exchanger. Its operation showed that residues react favorably under fluidization. The effect of independent variables, residence time and temperature, was investigated and sulfite conversions up to 89.4% were observed. With statistical treatment of pilot experimental data, response surface of conversion of sulfites to sulfates was developed, allowing to estimate the effect of independent coordinates on conversion and the optimal oxidation conditions. Experimental data and model predictions showed agreement leading to low estimated variance. [ABSTRACT FROM AUTHOR]