Some classes of equipment have a disproportionate effect on overall energy efficiency. Foremost among these is fired equipment, which includes furnaces and boilers.
Furnaces and boilers are an integral part of most sites in the process industries. Furnaces are commonly used to heat and vaporize hydrocarbon feeds. Boilers, in contrast, produce only steam. However, the classification isn’t always clear-cut, as many furnaces incorporate convection banks that produce steam, in addition to their hydrocarbon heating duty. An important example of this is the pyrolysis furnace used in ethylene plants, where the furnace steam production is an important part of the overall process.
Energy efficiency (η) can be defined by a simple equation: η = (Useful energy)/(Energy supplied)