The EERC has three sophisticated laminar-flow drop-tube furnaces (DTFs) which are used to investigate various aspects of fly ash formation, ash deposition, and reactivity associated with the combustion or partial combustion/gasification of pulverized coal, beneficiated coal fuels, coal char, coke, and various alternative fuels.

The DTF systems are relatively inexpensive to operate and can generate multiple data sets in a very short time. Of utmost importance is the ability of these systems to mimic key full-scale combustion conditions. Feed rates for the DTFs range from only 0.1 to 1.0 grams of coal per minute; therefore, it is difficult to mimic all aspects of full-scale combustion. However, the DTFs can be configured using key operational parameters to produce results similar to those observed in a full-scale boiler. Key parameters include gas temperature, gas velocity, particle residence time, excess air, gas-cooling rates, and deposit surface substrate temperatures.

Bench-Scale Combustors

Atmospheric Drop-Tube Furnace
The atmospheric drop-tube furnace (ADTF) is a laboratory-scale, electrically heated, entrained-flow tube furnace with the ability to combust coal and produce ash under closely controlled conditions. The furnace is capable of maintaining gas temperatures up to 1600°C.

Combustion parameters–such as initial hot-zone temperature, excess air, residence time, and gas-cooling rate–can be closely controlled and monitored. Chars and ash can be collected at various residence times to examine the transformations that occur during the combustion process.

Entrained ash can be collected in bulk or with size-segregating devices such as a University of Washington Mark 5 source test cascade impactor and a U.S. Environmental Protection Agency Southern Research Institute five-stage cyclone. Ash and slag deposits are collected on a water-cooled deposition probe inserted into the DTF to determine sticking coefficients, deposit strengths, and deposit compositions. Combustion gases are monitored for carbon dioxide, carbon monoxide, and oxygen.

Optical Drop-Tube Furnace
The optical drop-tube furnace (ODTF) facility is similar to the ADTF, with provision for an optical section that allows visual and video monitoring of deposit formation and in situ deposit adhesion strength measurements on the probe. The optical access section also allows in situ temperature measurements by optical pyrometry and entrained particle-size determinations made by near-forward-angle laser scattering, as well as the capacity to add additional nonintrusive optical diagnostics. The ODTF is specially designed to assess the fouling and slagging tendencies of coal. A cylindrical deposition probe with a controlled skin temperature can be inserted into a heated deposition zone, and the initial slagging temperature, deposit adhesion strength, and deposit growth rates can be determined. The heated zones in the furnace reactor tube can be customized to reflect temperature regimes in a real utility boiler. The maximum temperature that can be achieved is 1650°C.