Waste heat recovery

Reduced steam temperature

Many plants can cut energy costs considerably by replacing their shell-and-tube reboilers or steam heaters with compact heat exchangers. The higher thermal efficiency of compact heat exchangers often allows you to use a lower temperature heating medium compared to shell-and-tubes. Switching to lower grade steam will cut energy costs in most cases.

Example

Sour water stripper unit

A refinery asked Alfa Laval to evaluate the possibilities of using lower grade steam in their sour water stripper unit.

Exchanging the existing shell-and-tube for a Compabloc allowed the refinery to switch heating medium from medium-pressure steam at 180°C (356°F) to low-pressure steam at 138°C (280°F).

The stripper column operates at 127°C (261°F) and Compablocs are capable of handling temperature approaches as close as 3°C (5.4°F). This means the steam temperature in this example could have been as low as 130°C (266°F).

As well as cutting energy costs, the new Compabloc also had a much smaller installation footprint.

 

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Using a more efficient heat exchanger as a reboiler allows you to use steam of a lower grade. 

Assumptions

  • Initial steam consumption = 14.15 metric tons/hour
  • Operating hours per year = 8,400
  • Low-pressure steam at 3.5 bar(a) available and possible to use as heating medium in the reboiler
  • Cost for heat exchanger = €568,000
  • Installation factor = 3
  • Installed cost of heat exchanger = €1,704,000

Payback period

Reduced utility temperature

Payback period when switching from medium-pressure steam at 180°C (356°F) to low-pressure steam at 138°C (280°F)

Payback period (years)

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