Criteria for the Selection of Microprocessor Combustion Controllers for Dual-Fuel Package Boilers

In a typical package boiler, flue gas losses can account for 15 to 20 percent of the total heat released, and 20 to 25 percent of the fuel entering the boiler is lost. Boiler efficiency can be improved by minimizing excess air requirements within the level of safe and reliable boiler operation. However, until recently, combustion control equipment was too costly for installation and use with small package boilers. This study surveyed manufacturers to identify combustion controllers appropriate for application to small package boilers. The survey revealed that 'oxygen trimming' is the most common control method. Six manufacturers were selected for the final evaluation of three types of systems: (1) an in situ O2 analyzer (2) an ex situ O2 and combustibles analyzer, and (3) an air and fuel flow-metering device. The systems were reviewed and compared on the basis of case of installation and maintenance, effectiveness, and cost. Three commercially available combustion control packages were identified, one from each category, for a later field test demonstration. Three sites were selected for that demonstration. The results of such a demonstration could quantify the effects of state-of-the-art combustion control systems on the efficiencies of small package boilers.