Method of making pozzolands and cementitious materials from coal combustion by-products

Abstract

Ash produced by many coal-fired utilities has little or no commercial value as a cement additive or as a component in building materials because of its chemical or mineralogical composition. This condition is especially common with ash materials produced by Fluidized Bed Combustion boilers (FBC) or Circulating Fluidized Bed Combustion boilers (CFBC) fired with bituminous coal or waste coals (gob) reclaimed from inactive coal mine sites. The present invention describes a novel process that converts otherwise low-value materials such as bottom and fly ashes produced by a FBC or CFBC boilers, for example, into materials that have desirable physical, chemical and mineralogical compositions that can be used as a valuable cement additive or component in building materials. The novel process closely integrates the boiler (steam generator) that produces the ash with a new high-temperature process, such as a kiln. The ash is mixed with limestone or other bulk materials to provide a feed for the kiln of the desired chemical composition. The mixture is treated at elevated temperatures in the kiln to produce a product, that in combination with further processing, exhibits desirable pozzolanic properties. Integrating boiler and kiln operations provides economic and environmental benefits. Waste heat produced by the kiln that would otherwise be released into the atmosphere is made available to the steam or turbine cycle, thus improving the overall boiler heat rate. Effluents and gases produced by the kiln may be efficiently treated by the boiler environmental control systems or independent environmental control systems. Novel production methods and feed materials will be claimed.

Dependencies are inferred from the claim text.