A gas fired furnace operating at 1000C with conventional burners vents about 50% of the applied energy to atmosphere via the furnace flue. Only half of the energy going into the furnace goes into the load, the rest is wasted to the atmosphere and is paid for by the furnace owner.
There are a number of techniques we can use to recapture waste heat.
A plant's energy efficiency is improved when waste heat is used in the most efficient way. In an evaluation process known as PINCH analysis, high temperature flue gas from an industrial furnace is identified as a high grade heat source. The purpose of PINCH analysis is to define where heat exchangers can be used effectively. PINCH evaluation will provide a number of options and will determine if waste heat is better used directly, as in the case of load preheating, or should be returned to the process in the form of preheated combustion air.
A typical heat exchanger for a gas fired furnace will capture between 30% and 50% of the waste heat from the furnace. Typical regenerative heat recovery systems 70% to 80% of the waste heat. A high efficiency burner system returns this captured waste heat to the furnace.
The most convenient method of using energy captured by the heat exchanger is in the form of preheated air. Combustion air preheating provides some technical challenges due to the higher level of pollutants generated in hotter flames, however, modern technologies are available to address the environmental concerns of most air quality regulations. These techniques can be applied to all burner systems including oil fired regenerative system, gas fired furnaces, and even biomass dust systems.
Types of High Efficiency Burner Systems: