Waste heat recovery unit (WHRU) is an energy recovery heat exchanger system that recovers heat from hot streams with potential high energy content, such as hot flue gases from a diesel generator or steam from cooling towers or even waste water from different cooling processes such as in steel cooling. Waste heat recovery units help to recollect and combine all the waste heat from different sources, for recycling waste heat energy. Various types of waste heat recovery units are Recuperators, Regenerators, Heat pipe exchanger, Thermal Wheel, Heat Economizer, and Heat pumps.

Waste heat found in the exhaust gas of various processes or even from the exhaust stream of a conditioning unit can be used to preheat the incoming gas. This is one of the basic methods for recovery of waste heat. Many steel making plants use this process as an economic method to increase the production of the plant with lower fuel demand. There are many different commercial recovery units for the transferring of energy from hot medium space to lower one.

Advantages of Waste Heat Recovery

  • Increase in Industrial Process Efficiency: Waste heat recovery process will add to the efficiency of the process and thus decrease the costs of fuel and energy consumption needed for that process
  • Reduction in Pollution: Thermal and air pollution will dramatically decrease since less flue gases of high temperature are emitted from the plant since most of the energy is recycled.
  • Reduction in the equipment sizes: As Fuel consumption reduces so the control and security equipment for handling the fuel decreases. Also, filtering equipment for the gas is no longer needed in large sizes.
  • Reduction in auxiliary energy consumption: Reduction in equipment sizes means another reduction in the energy fed to those systems like pumps, filters, fans,…etc

Waste Heat Recovery Systems

  • Heat Recuperators: This name is given to different types of heat exchanger that the exhaust gases are passed through, consisting of metal tubes that carry the inlet gas and thus preheating the gas before entering the process. The heat wheel is an example which operates on the same principle as a solar air conditioning unit.
  • Regenerators: This is an industrial unit that reuses the same stream after processing. In this type of heat recovery, the heat is regenerated and reused in the process.
  • Heat Pipe Exchanger: Heat pipes are one of the best thermal conductors. They have the ability to transfer heat hundred times more than copper. Heat pipes are mainly known in renewable energy technology as being used in evacuated tube collectors. The heat pipe is mainly used in space, process or air heating, in waste heat from a process is being transferred to the surrounding due to its transfer mechanism.
  • Thermal Wheel or Rotary Heat Exchanger: consists of a circular honeycomb matrix of heat absorbing material, which is slowly rotated within the supply and exhaust air streams of an air handling system.
  • Heat Economizer: In case of process boilers, waste heat in the exhaust gas is passed along a recuperator that carries the inlet fluid for the boiler and thus decreases thermal energy intake of the inlet fluid.
  • Heat Pumps: Using an organic fluid that boils at a low temperature means that energy could be regenerated from waste fluids.