• Water Management

Solid Waste Production

As raw feed travels through the portland cement kiln system, particulates of the raw materials, partially processed feed, and components of the final product are entrained in the combustion gases flowing countercurrent to the feed. These particulates and combustion gas precipitates are collected in the particulate matter control device (PMCD)—electrostatic precipitators and fabric filters—and are collectively referred to as cement kiln dust (CKD).

In general, CKD is a very heterogeneous mix both by chemistry and particulate size, and these characteristics are dependent on the raw materials, fuels, kiln pyroprocessing type, overall equipment layout, and type of cement being manufactured. It is incorrect to label all dusts collected in the PMCD as waste. Many facilities return all or a major portion of the CKD to the kiln as a feedstock while other facilities sell the dust for numerous beneficial uses, such as soil consolidation, waste stabilization, and other uses. Recycling this byproduct reduces the need for limestone and other raw materials and helps conserve energy. The most common reasons for not returning CKD to the kiln system are equipment limitations for handling the dust and chemical constituents in the dust that would be detrimental to the final cement product. The fraction of CKD that is not returned to the kiln or otherwise beneficially used is placed in landfills.

Beginning in 1990, the Portland Cement Association has tracked the amount of CKD sent to landfills. Over that time period the amount of CKD placed in landfills has decreased dramatically and when compared to the clinker production, the amount of CKD per unit of clinker had decreased at an even greater rate.

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