Waste heat recovery is being more used more and more often today as it is becoming more effective, due to increasing energy prices, technological developments and a decrease in equipment costs. Heat recovery can be classified into three main strategies: recycling energy back into the process, recovering the energy for other onsite use and using it to generate electricity in combined heat and power systems. Once the system has been made as efficient as possible before using waste heat recovery, passive strategies are used. These have no significant input for operation except for auxiliary equipment such as pumps and fans. The last case is active strategies, which require some input of energy to upgrade the heat to a higher temperature or electricity. These need industrial heat pumps and a combined heat and power system.
High temperature energy recovery options
Heat exchangers are commonly used to transfer heat from combustion exhaust gases to air entering the furnace. By increasing the temperature of the gases entering less work is required by the fuel, the saves fuel that also means a decrease in combustion air. Below are some common heat exchanger devices.
Recuperators are used to recover exhaust gas heat in medium to high temperature applications such as annealing ovens and melting furnaces. They can be made of metal (below 1000ºC) or ceramic (900-1500ºC) tubing and can be based on radiation, convection or a hybrid. The most basic is the simple radiation recuperator, which consists of two concentric tubes one carrying exhaust one carrying combustion gases. Although it would be more efficient to run them counter flow they are commonly parallel flow, this is because it helps cool the ducts carrying gases away increasing service life. The convective one passes the hot gases through a series of relatively small diameter tubes contained in a large shell. This increases the contact area and as the incoming