Aerosol Formation during the Combustion of Straw with Addition of Sorbents

The influence of six sorbents on aerosol formation during the combustion of straw in a 100 MW boiler on a Danish power plant has been studied in full-scale. The following sorbents were studied: ammonium sulfate, monocalcium phosphate, Bentonite, ICA5000, clay, and chalk. Bentonite and ICA5000 are mixtures of clay minerals and consist mainly of the oxides from Fe, Al, and Si.

The straw used was Danish wheat and seed grass. Measurements were also made with increased flow of primary air. The experiments showed between 46% and 70% reduction in particle mass concentrations when adding ammonium sulfate, calcium phosphate, Bentonite, ICA5000, and clay. The addition of chalk increased the aerosol mass concentration by 24%.

Experiments in a laminar flow aerosol condenser with the six sorbents were carried out in the laboratory using a synthetic flue gas to avoid fluctuations in the alkali feeding. These experiments showed similar reductions to the ones found in full-scale. When feeding ammonium sulfate, the aerosol mass concentration increased as a result of the feeding method.

The chemical compositions of the fine particles suggest that there is chemical equilibrium in the gas for the sulfation reaction at temperatures above 812 degrees C.