Bruce A. Dockter

Strength development at low temperatures in coal ash deposits

At temperatures below approximately 1900°F, ash particles formed in coal-fired energy systems are relatively hard and not prone to sticking to system surfaces. However, if the ash collects on a surface not exposed to a shearing gas flow such as the downstream side of a heat exchanger or the surface of a hot-gas filter, the deposit can develop enough strength over a period of minutes to days so that it becomes difficult to remove, in some cases growing to sizes that impede the flow of gas. This paper presents data from ongoing measurements of the significance of ash and gas composition, deposit temperature, and time on the rates of strength development in simulated low-temperature ash deposits. Preliminary results of surface composition and particle-size distribution analyses of the ash, including submicron material, are also presented to explain the possible mechanisms of strength development.

Comparison of Dry Scrubber and Class C Fly Ash in Controlled Low-Strength Material (CLSM) Applications

Controlled low-strength material (CLSM) is a cementitious material, commonly a blend of portland cement, fly ash, sand, and water, that is usually flowable and self-leveling at the time of placement. It is generally used in nonstructural applications below grade where low strengths are desired. In these cases, the mature strength of the CLSM is intended to be no stronger than that of the surrounding soils.

Evaluation of Penetrating Sealers for Reinforced Concrete Bridge Decks

An evaluation of sealers based on eight sets of laboratory tests was done. Five concrete sealer treatments were studied: D335, DCS, SS, R7, and CT40. These sealers were evaluated for three groups of concrete mixes: normal, fly ash, and old concrete. There were also control specimens that did not use any type of sealer for comparison purposes. The test data were used to determine which sealer and concrete mix combination was the most adequate in improving resistance to the deterioration of concrete properties.

Rates and Mechanisms of Strength Development in Low-Temperature Ash Deposits

At temperatures below approximately 1900°F, ash particles formed in coal-fired energy systems are relatively hard and not prone to sticking to system surfaces. However, if the ash collects on a surface not exposed to a shearing gas flow such as the downstream side of a heat exchanger or the surface of a hot-gas filter, the deposit can develop enough strength over periods of minutes to days so that it becomes difficult to remove, in some cases growing to sizes that impede the flow of gas. This paper presents data from ongoing measurements of the significance of ash and gas composition, deposit temperature, and time on the rates of strength development in simulated low-temperature ash deposits. Preliminary results of surface composition and particle-size distribution analyses of the ash, including submicron material, are also presented to explain the possible mechanisms of strength development.

Sticking Mechanisms in Hot-Gas Filter Ashes

Large-scale hot-gas filter testing over the past 10 years has revealed numerous cases of cake buildup on filter elements that has been difficult, if not impossible, to remove. At times, the cake can bridge between candle filters, leading to filter failure. Physical factors, including particle-size distribution, particle shape, the aerodynamics of deposition, and system temperature, contribute to the difficulty in removing the cake, but chemical factors such as surface composition and gas–solid reactions also play roles in helping to bond the ash to the filter and to itself. In order to develop methods to predict the formation of sticky ash in hot-gas filtration systems, the University of North Dakota Energy & Environmental Research Center (EERC) worked with EPRI and a consortium of companies in partnership with the U.S. Department of Energy (DOE) to determine the factors causing hot-gas cleanup filters to develop deposits that can bridge the filters and cause them to fail. The primary deliverable was the Filter Bridging Index Code, a graphics-driven computer code to tie all of the knowledge together and make possible the prediction of rates of filter bridging based on coal, sorbent, filter, and system parameters. The objectives of this project were threefold: