Waste heat recovery

Preheating in interchangers

Feed/effluent heat exchangers, lean/rich interchangers, in-and-out heat exchangers, and feed/bottoms heat exchangers are all different names for the same concept: preheating of an ingoing stream of a unit operation using heat from the outgoing stream.

This is commonly done in:

  • Reactors
  • Electrolytic cells
  • Absorption stripping systems
  • Leaching tanks
  • Stripper- or distillation columns
  • Evaporation systems

Changing to plate heat exchangers is a straightforward way to improve heat recovery levels. This reduces the heat/steam consumption, resulting in either fuel savings and reduced emissions, or increased electricity generation. Cooling needs are also often reduced, which is valuable in many situations.


Feed/effluent heat exchanger – condensate stripper

The following example is based on a heat exchanger specification from a condensate treatment stripper. An existing shell-and-tube heat exchanger is replaced with a Compabloc welded plate heat exchanger, which increases heat recovery by 3.8 MW (13 MMBtu/h).  It is assumed that 85% of the recovered heat translates into saved steam and, in turn, fuel savings or increased electricity generation.

Before                                                 After




  • 8,400 operating hours per year
  • Overall pressure drop increases by approximately 1 bar, but no new pump is needed only operating costs increase)
  • Physical properties on both sides are similar to water
  • Installation factor = 3, i.e. the heat exchanger represents 33 % of the total project cost
  • Cold side flow rate 75 m³/h and hot side 90 m³/h
  • Boiler efficiency 90% (boiler case)
  • Turbine isentropic efficiency 80% (electricity case) 

Preheating in interchangers

Payback period

Fuel savings in boiler

Payback period as a function of energy price when using the recovered energy for saving fuel. 

Payback period (years)

Increased electricity generation

Payback period as a function of energy price when using the recovered energy for electricity generation.

Payback period (years)