Case Study: Pumping power reduction at chilled water System

Area of Improvement:
500TR Chilled water system was having primary and secondary circuits for circulation of chilled water through Chiller and plant.


Observation:
In a typical chilled water/ brine system, Primary circuits are used circulate water/ brine though chiller and reduce temperature of chilled water / brin., further this chilled water is transferred to the plan for process cooling as shown below.

Plant return pipe was having pressure which was lost at tank inlet, the pressure loss at hot well tank inlet was from two sources:-

  1. Excess pressure supplied from plant circulating pump (Secondary pump) for circulation at different heat exchangers.
  2. Gravity pressure because of plant height.
    Energy Conservation Measure:
  3. The energy conservation measure was taken in two steps :-
  4. Step -1
    In step-1 Chiller circulating pump was eliminated with the use of plant return line flow and pressure as shown below :-

Energy Conservation Measure:

The energy conservation measure was taken in two steps :-

Step -1

In step-1 Chiller circulating pump was eliminated with the use of plant return line flow and pressure as shown below :-

Hot well tank and chilled water circulation pump was eliminated, With the elimination of chilled water pump, pumping power of 25Kwhr was saved.

Step – 2
Further in step-2, the pressure loss post chiller circulation was used as suction of plant circulation pump along with VFD to control pressure and flow at plant. A pressure relief valve is necessary to be used post circulation pump to avoid higher pressure generation at circulation.

Circulation pump power was reduced from 65 KWhr to 23 KWhr with the use of VFD as differential head required for the pump was reduced from 45 Mtr to 20 Mtr. (20mtr head was required to overcome pressure loss from pipe and heat exchangers)
Overall saving through the system was 67KW/hr with investment payback of just 3-4 months.

Limitation:
Pump flow of primery and secondary to be confirmed in step 1, there should not be more than 10% variation of flow, if the flow is very high at secondary ( Plant circulation) pump one bypass pipeline arrangement needs to be done. While going to step 2 both the flow must be balanced, if not balance flow balanced to be done with the help of contol valve.

Please contact info@energypurse.com for more info if you are facing any difficulty in reducing power from chilled/ brine circulation pumps.

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