Case Study: Heat pump for boiler feed water preheating

Representative picture of heat pump

Area of Improvement:

In a process plant 60% of condensate is recovered at approx 90 Deg C, remaining condensate was contaminated as it is being used in steam ejectors, direct heating in process and multi utility reactor therefore it was not recovered.

Observation:

40% of feed water of approx 12 KL/hr was fed to deareator as boiler feed water, Steam is applied to boiler feed water to elevate feed water temperature from 70 deg C to 105 Deg C.

As the fresh water consumption to the deaerator was 12 KL/hr at 30 deg C, it is considered as potential area for heat pump. also in same plant chilled water was also produced with vapour compression system for process requirement at 7 Deg C. the compressor power requirement for chilled water generator was 0.7KW/TR.

Energy Conservation Measure:

Heat Pump was explored to preheat boiler feed water, most economical temperature was observed as 60 Deg C, at 60 Deg C of hot water generation and 7 Deg C of chilled water generation heat pump was designed to consume 1.25KW/TR of power. Power increase at compressor was 0.55KW/TR.

Heat pump with chilling capacity of 100TR and heating capacity of 135 TR was selected for feed water preheating application. Motor connected load was 132KW.

Since both chilling and heating effect was utilized at heat pump, heat pump is generally named as water to water heat pump, Extra power consumed neglecting refrigeration requirement at 0.7KW/TR was 0.55KW/TR, Which means 0.41KW was being consumed for generation of 1 TR of heat energy at 60 Deg C,

Cost reduction for heating water from 30 to Deg C reduced by 35% considering steam generation by coal and power cost from grid.

Payback of the system was just 14 months

Limitation:

Limitation with heat pumps are it is not very efficient at higher temperature range. In our case heat pump was available even at 70 deg C output put the power consumption was very high and was not economical.

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