Journal of Energy Engineering

Pulverized coal combustion (PCC) dry bottom ash is a by-product of coal combustion that originates from the burning of pulverized coal to produce electricity. Because of the increasing costs associated with the disposal of bottom ash and the environmental regulations in place, a significant need exists to develop alternate methods for profitable and environmentally safe uses of this waste material. The physical properties of bottom ash are similar to those of natural sand, with particle sizes ranging from fine gravel to fine sand with low percentages of silt and clay-sized particles. Bottom ash has been used in the past as a substitute for aggregates in concrete. However, not much effort has been made in examining the geotechnical engineering properties of bottom ash, and as a consequence its use in geotechnical engineering applications is still very limited. Characteristics of bottom ash depend on the type of coal burned and the type of furnace used to burn the coal. This paper presents the results of an experimental study conducted to obtain technical data on the geotechnical engineering properties of Illinois PCC dry bottom ash amended with bentonite, which data are needed to assess its use for geotechnical engineering applications. Bottom ash modified with up to 20% bentonite by weight of bottom ash was tested to determine the effects of bentonite on consistency, moisture-density relationships, shear strength, and hydraulic conductivity of the bottom ash-bentonite mixtures.

A 1-D transient model (RESHEAT), developed by the writers, was used to study the thermal performance of a highly reflective paint applied sequentially to the outer walls and roof of a simulated residence in a hot and arid region of the southwestern United States. The model uses climatological inputs from a file that includes hourly data on ambient temperatures, insolation, cloud cover, and so on, at the particular location. The model focuses particularly on the potential cooling load reduction due to the reduced heat pickup from the inside attic surfaces to the outer surfaces of the supply duct. This simulation showed that a reduction of 33.6% (cooling load) on the average is achieved over the base case where no reflective paint is used when the outer surface of the roof and walls are painted. Alternatively, only a 11% reduction would be achieved if the reflective paint is applied only to the roof. Savings of $42 per month are conservatively estimated from calculations made when applying this technology to a typical residence (roof and walls) equipped with a 4 ton refrigeration unit in the Southwest.