A study of ash deposition from a cleaned bituminous and conventional bituminous coal is presented. An electrically heated drop tube furnace is used to burn the coal and provide deposition conditions representative of proposed coal-fired gas turbines. Variations in the combustion temperature and deposit surface temperature demonstrate that surface cooling may significantly reduce ash deposition, or may provide little benefit, depending on the combustion conditions. Lower temperature combustion produced larger ash particles, with a greater fraction of ash adhering to the deposition test surface. Although the sticking coefficient was higher at the lower combustion temperature, the deposits were readily removed. A modest numerical simulation suggests that the smallest ash particles can experience significant boundary layer cooling and may account for the reduction in sticking observed at some conditions.

No abstract

In order to acquire real-time transient alkali data on coal-derived gaseous fuel and combustion streams often at low ppb levels, an extractive, total (vapor and particle-bound) sodium and potassium monitor has been designed, constructed, and tested. This fiber-optic alkali monitor (FOAM) utilizes state-of-the-art fiber-optic light transfer, a novel light-filtering background correction method, and high sensitivity photodiode signal detection. The sample enters the monitor's high-temperature flame, which supplies energy to both decompose and excite the sample. The flame then emits light at the characteristic wavelengths of sodium and potassium. The resulting emissions are transferred by the fiber-optic bundle to the detection system, where the signal is filtered, background corrected, and transferred to the data system. The FOAM has advantages over previous instrumentation in being rugged, portable, and compact. Laboratory testing of the FOAM has been completed. The FOAM was determined to be highly sensitive (mid-ppt detection limits) with a wide linear dynamic range (four orders of magnitude). The results of field monitoring of alkali levels in the exhaust strea.m of a pressurized combustor using the FOAM indicated that the monitor was capable of real-time, fast tracking of transient alkali behavior in a high-temperature/high-pressure process stream.

The combustion of coal and coal-derived fuels in heat engines poses significant technical challenges in terms of establishing high combustion rates and efficiencies, controlling emissions, and minimizing the impact of fuel contaminants on engine components. An entrained reactor has been designed and constructed to study coal particle combustion, the tendency of coal ash to form deposits on heat engine components, and the effects of fuel additives on residual ash composition. The reactor is designed for high temperature/pressure conditions similar to those of a coal-fired gas turbine. Optical access ports and advanced instrumentation allow the in situ measurement of gas and particle temperatures, and vapor phase alkali concentrations. The reactor has been used to study the deposition potential of several coals as a function of process conditions, and to determine the effects of selected additives on the deposition rate.