Waste heat recovery

Boosting compressor capacity

The superior heat transfer in compact heat exchangers make them just as suitable for cooling services as for heat recovery.

Efficient cooling is essential for compressor performance. The capacity of the compressor can be increased by cooling the incoming gas.

The high thermal efficiency of compact heat exchangers makes them very suitable for this service. The gas flowing into the compressor will be cooler compared to a shell-and-tube under the same conditions, and you get higher output.

Besides higher compressor capacity, improved cooling can also lead to lower energy consumption and less wear on the compressor.

Example

Sour water stripper unit

Alfa Laval performed a study on a syngas compressor in an ammonia plant. The plant experienced capacity limitations during 20% of the year due to high cooling-water temperatures in the summer. The existing shell-and-tube syngas cooler was not able to cool the gas sufficiently and compressor capacity dropped.

The study showed 3.2% more syngas could pass through the compressor during summer by exchanging the shell-and-tube syngas cooler for a compact heat exchanger just upstream of the compressor.

When the cooling water had a temperature of 30°C (86°F), the shell-and-tube cooled the gas to 46°C (115°F). The new compact heat exchanger lowered the temperature an additional 11°C (20°F) to 35°C (95°F).

 

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Boost compressor capacity by using a more efficient heat exchanger for cooling inlet gas.

Assumptions

  • 8,400 operating hours per year
  • Capacity limitation 20% of the year (2.4 months), when cooling water is at its hottest.
  • Syngas behaves as an ideal gas
  • Compressor capacity is directly proportional to inlet gas volume, and hence inversely related to gas temperature
  • Heat exchanger: Compabloc in Titanium
  • Installation factor: 3
  • Production capacity: 365,000 tons/year

Payback period

Compressor debottlenecking

Payback period for compressor-cooler revamp for different product gross margins.

Payback period (years)

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