Air emission from the co-combustion of alternative derived fuels within cement plants: Gaseous pollutants
Cement manufacturing is a resource- and energy-intensive industry, utilizing 9% of global industrial energy use while releasing more than 5% of global carbon dioxide (CO2) emissions. With an increasing demand of production set to double by 2050, so too will be its carbon footprint. However, Australian cement plants have great potential for energy savings and emission reductions through the substitution of combustion fuels with a proportion of alternative derived fuels (ADFs), namely, fuels derived from wastes. This paper presents the environmental emissions monitoring of 10 cement batching plants while under baseline and ADF operating conditions, and an assessment of parameters influencing combustion. The experiential runs included the varied substitution rates of seven waste streams and the monitoring of seven target pollutants. The co-combustion tests of waste oil, wood chips, wood chips and plastic, waste solvents, and shredded tires were shown to have the minimal influence when compared to baseline runs, or had significantly reduced the unit mass emission factor of pollutants. With an increasing ADF% substitution, monitoring identified there to be no subsequent emission effects and that key process parameters contributing to contaminant suppression include (1) precalciner and kiln fuel firing rate and residence time; (2) preheater and precalciner gas and material temperature; (3) rotary kiln flame temperature; (4) fuel–air ratio and percentage of excess oxygen; and (5) the rate of meal feed and rate of clinker produced.
Implications: Monitoring of gaseous air emission from 10 rotary kilns used in cement industry showed that full compliance to site and international obligations can be achieved while providing the required energy demands. Benefits specifically related to reduction of materials to landfill, safe destruction of hazardous wastes, cost savings of waste handling, and reduction of fossil fuel extraction are achievable and look promising from both environmental and economic perspectives.