Research programs have been under way at the EERC for more than 28 years to study ash fouling of boiler heat-transfer surfaces in coal-fired utility boilers. A 550,000-Btu/hr pulverized-coal pilot plant test furnace was constructed in 1967 to evaluate the influence of variables, including ash composition, excess air, gas temperature, and tube wall temperatures on ash fouling. Results from this work have shown a strong correlation between ash characteristics, boiler operating parameters, and degree of fouling.

The research capabilities of the combustion test facility (CTF) have been enhanced over the years and expanded to provide information on a wide range of combustion-related issues. To achieve a wide range of operating conditions, the refractory-lined furnace may be fired at a rate (approx. 70 lb coal/hr) sufficient to achieve a furnace exit gas temperature as high as 2500°F. Most tests are performed with the furnace exit gas temperature maintained at approximately 2000°–2200°F.

Research Applications of the Pilot-Scale Combustion Equipment

• Determine ash-fouling rates and the strength, composition, and structure of fouling deposits for coals of all rank and also determine the effectiveness of ash-fouling additives.
• Apply sophisticated analytical methods to characterize input coal, ash, and deposits and to correlate coal and ash properties with deposit growth rates and strength development.
• Evaluate the combustion characteristics of coal–water and biomass fuels, municipal solid waste, and petroleum coke.
• Determine fly ash collection properties of various fuels by electrostatic precipitation (ESP) or fabric filtration using a pulse-jet baghouse, including high-temperature applications.
• Evaluate the slagging potential and slag corrosion in a simulated wet-bottom firing mode.
• Perform flame stability tests for comparing a particular fuel at full load and under turndown conditions.
• Evaluate fouling, slagging, and ESP performance for blends of bituminous and subbituminous coals.
• Evaluate the combustion properties of petroleum coke, alone and in blends with subbituminous and lignite coals.
• Evaluate sorbent injection for SO_x control and assess integrated particulate and SO_x/NO_x control.

The CTF is fully instrumented to provide online analysis of the flue gas. Three flue gas sampling ports are available, although only two are used on a regular basis. Flue gas concentrations of O₂, CO₂, and SO₂ are obtained simultaneously at the furnace exit and stack. Emissions of CO and NO_x are obtained at the furnace exit. System O₂, CO, and CO₂ analyzers are manufactured by Beckman; the SO₂ analyzers are manufactured by DuPont; and NO_x is measured with a ThermoElectron chemiluminescent analyzer. All system temperatures, pressures, and flue gas analyses are recorded continuously to chart recorders and the system's computer-controlled data acquisition system.

Coal is pulverized remotely in a hammer-mill pulverizer to a size of 70% less than 200 mesh (75 µm). The coal is then charged to a microprocessor-controlled weight loss feeder from a transport hopper. Combustion air is preheated by an electric air heater. The pulverized coal is screw-fed by the gravimetric feeder into the throat of a venturi section in the primary air line to the burner.

Heated secondary air is introduced through an annular section surrounding the burner. Heated tertiary air is added through two tangential ports located in the furnace wall about 1 ft above the burner cone. The percentages of the total air used as primary, secondary, and tertiary air are usually 10%, 30%, and 60%, respectively. An adjustable swirl burner, which uses only primary and secondary air with a distribution of approximately 15% and 85%, respectively, is used during flame stability testing. Flue gas passes out of the furnace into a 10-in.-square duct that is also refractory-lined. Located in the duct is a vertical probe bank designed to simulate superheater surfaces in a commercial boiler. The fouling probes are constructed of 1.66-in.-OD Type 304 stainless steel pipe cooled to a surface metal temperature of 1000°F (or other specified temperature) with steam. Deposit strength can be assessed by laboratory determinations using a drop impactor technique and by scanning electron microscopy (SEM). The drop impactor technique provides a calculated measurement of deposit strength, taking into account the conditions under which the test was performed. SEM point count provides a point-by-point analysis of the deposit. These data can be used to calculate the viscosity of each data point that can be related to deposit strength.

After leaving the probe bank duct, the flue gas passes through a series of water-cooled heat exchangers before being discharged through either an ESP or pulse-jet baghouse. The test furnace has numerous ports that permit observation of the probes and the furnace burner zone during the test run. These ports can also be used for installation of additional test probes, auxiliary measurements, photography, or injection of additives.