In-Boiler Beneficiation of Coal Combustion Products for Enhanced Cementitious Value

摘要

A novel and cost effective method for in-boiler beneficiation of coal combustion products (CCP) was developed to substantially improve cementitious value in terms of strength development of the resulting supplementary cementitious material (SCM). This process used an existing coal fired boiler with minor modifications as the source for CCP. The improved strength development characteristics enables much higher Portland cement clinker replacement levels in cement and concrete than today’s typical 15-25%, thereby reducing the environmental footprint of the cementitious end product and providing an environmentally sound alternative to current wet or dry disposal methods employed for CCP. This paper presents new research and results related to strength development, durability and workability of cementitious products based on in-boiler beneficiation of CCP. The results highlight the potential benefit of using a customized, multiple input materials approach when compared to the effect of sole limestone addition as a common scrubber to control SOx emissions. In particular, the customized approach enables a selection of additions to contribute to superior strength development, durability and rheology compared to simple limestone addition. The results further indicate the possibility to produce a blended cement with the current ASTM C595 maximum 40% replacement level at similar or improved performance relative to today’s typical 20% clinker replacement, or even higher replacement levels in concrete. Furthermore, since the improved strength development characteristics of the modified CCP enable higher substitution levels, many high calcium ashes that normally would not be considered ASR or sulfate friendly at 20-30% replacement may be considered ASR and sulfate durable at higher replacement levels when properly modified to offset the negative effect of elevated calcium in the parent coal.