Energy efficiency tip of the day (waste heat recovery)

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Energy efficiency tip of the day (waste heat recovery)

Background

  • Heat recovery is the return of energy that would normally be wasted (i.e. exhaust gas) back to the process heating system.
  • The most common use of waste heat is to transfer it to the combustion air or process feed stream; this reduces the amount of fuel required to establish the necessary temperature of the air or feed stream.

How to implement:

  1. The first step should be to identify sources of waste heat and inspect and maintain equipment to minimize the production of waste heat.
  2. Evaluate the potential for waste heat recovery.
  3. Some low-cost opportunities may be feasible, such as:
    – capture waste heat from a clean waste stream that normally goes into the atmosphere or down the drain, and pipe the stream to where it can used.
    – use waste-process water as a heat source for a heat pump
    – re-use hot exhaust air for drying.
  4. Larger scale retrofits include:
    – install waste-heat reclamation equipment (i.e. replace a cooling tower circulation loop with a shell-and-tube heat exchanger)
    – use a low-grade chiller, which can convert low-grade heat to spare cooling
    – integrate a compact heat exchanger with other processes
  5. The wasted heat could be used to decrease the cooling load for air conditioning unit as it could be used to generate chilled water that decreases the AC unit refrigeration unit load and save more power.

Expected savings:

  • Savings vary depending on the source of the waste heat (and therefore quantity of waste heat).
  • A typical range is 5 to 30% savings.

 

Typical applications with related energy savings:

  1. Combustion air preheating: 10 to 30%
  2. Fluid or load preheating: 5 to 20%
  3. Heat cascading: 5 to 20%
  4. Fluid heating or steam generation: 5 to 20%

Magdy Aly

Energy manager, Energy efficiency consultant Passionate to help others to save Energy and Environment.

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