Beneficiation Technology Deep Dive: Manufactured Aggregates

Abstract Coal combustion products (CCPs) are the solid materials that remain after pulverized coal is burned to generate electricity. CCP includes coal ash and flue gas desulfurization (FGD) solids. About 60% of CCPs are beneficially used in the US. About 40% of CCPs are disposed, mainly due to lack of local market or non-conformance with market specifications. In addition, an estimated 2 billion tons of CCPs are stored in ponds and landfills in the US. New technologies could enable the productive use of unmarketable CCPs as well as CCPs contained in ponds and landfills. Multiple commercial and near commercial technologies exist that use coal ash as a raw material to produce aggregates. The technology developers most often describe their desired product as “lightweight” aggregate, but it is not clear the actual finished aggregate materials are suited to all lightweight aggregate uses. The aggregate production technologies are based on either thermal or chemical bonding of the particulate ash. Thermal bonding technologies include sintering processes such as Lytag, LSA/Certyd, Feeco) and plasma melting technologies. Chemical bonding processes include geopolymer systems such as Alkemy Environmental,Trung Hau, Nometrain, Polyagg and non- geopolymer systems such as Nu-Rock. The history of beneficial use includes several previous commercial technologies including Minergy’s sintered aggregate production operated at Oak Creek Power Plant in Wisconsin, Universal Aggregates Verslite production at Birchwood Power in King Georgia, Virginia. Publications reference also technologies called PyroGenesis, and Aardelite. The UK Department of Environment, Food and Rural Affairs reviewed manufactured aggregates in 2007. The project objective is to address the following questions: 1. What are the main markets for lightweight aggregates in the US? 1.1. How large are the markets, and what rate are they growing? 1.2. Are there important regional or local market considerations? 1.3. What are the specifications and other requirements for these markets? 2. What are commercial and near commercial aggregate manufacturing technologies are applicable to CCPs? 2.1. What are the limitations or feed specifications? 2.1.1. Is the technology especially suited to a particular CCP? 2.2. What is the capital cost to build an operation processing dry off-spec or ponded CCPs? 2.3. What is the operating cost for processing dry off-spec or ponded CCPs? 2.4. What are the permitting requirements? 2.5. What waste streams are generated? 3. Why did previous manufactured aggregate operations fail?