Boiler and firing system

BOILERS AND FIRED SYSTEMS
INTRODUCTION
Boilers and other fi red systems are the most significant energy consumers. Almost two-thirds of the fossil-fuel energy consumed in the United States involves the use of a boiler, furnace, or other fi red system. Even most electric energy is produced using fuel-fi red boilers. Over 68% of the electricity generated in the United States is produced through the combustion of coal, fuel oil, and natural gas. (The remainder is produced through nuclear, 22%; hydroelectric, 10%; and geothermal and others, <1%.) Unlike many electric systems, boilers and fi red systems are not
inherently energy efficient
ANALYSIS OF BOILERS AND FIRED SYSTEMS
Boiler Energy Consumption
Boiler and other fired systems, such as furnaces and ovens, combust fuel with air for the purpose of releasing the chemical heat energy. The purpose of the heat energy may be to raise the temperature of an industrial product as part of a manufacturing process, it may be to generate high-temperature high-pressure steam in order to power a turbine, or it may simply be to heat a space so the occupants will be comfortable. The energy consumption of boilers, furnaces, and other fi re systems can be determined simply as a function of load and effi ciency as expressed in the equation:
Energy consumption =
? (load) × (1/efficiency) dt 5.1
Similarly, the cost of operating a boiler or fi red system can
be determined as:
Energy cost =
? (load) × (1/efficiency) × (fuel cost) dt (5.2)
As such, the opportunities for reducing the energy consumption or energy cost of a boiler or fi red system can be put into a few categories. In order to reduce boiler energy consumption, one can either reduce the load, increase the operating efficiency, reduce the unit fuel energy cost, or combinations thereof. Of course equations 5.1 and 5.2 are not always that simple because the variables are not always constant. The load varies as a function of the process being supported. The efficiency varies as a function of the load and other functions, such as time or weather. In addition, the fuel cost may also vary as a function of time (such as in seasonal, time-of-use, or spot market rates) or as a function of load (such as declining block or spot market rates.) Therefore, solving the equation for the energy consumption or energy cost may not always be simplistic.