Case Study - Energy Saving For Water Pump

Application : -

Transfer of hot return water from Reheating furnace to the cooling Tower fans.

Motors Employed : -

3-phase AC induction motors.

  1. 37 kw, 415 v, 1460 rpm = 2 nos
  2. 22 kw, 415 v, 1440 rpm = 1 no.

Previous System : -

  1. Star Delta starter for motor operation.
  2. Flange coupling for operating the centrifugal pumps.

Observations : -

  1. One centrifugal pump was being operated with 60% outlet valve opening.
  2. Cooling Tower Tank level was not maintained with the operation of single pump.
  3. Second pump was being operated to maintain to Tank level for short intervals. It was operated approx. 40times in 24 hrs.
  4. Sometimes, second pump was being operated with by-pass valve half open to drain tank to avoid the over flow of Cooling Tower Tank.

Observations : -

  1. Pump was operated at full capacity to realize the increased flow to cooling tower. Motor got overloaded.
  2. Observations were done physically about Tank levels with one pump in operation.
  3. Psychological fear of lower water level was taken and range of water level was given.
  4. It was observed that the standby pump needs to operated only 6 to 7 times in a day (24 hrs.)
  5. Further low & high level switch was installed with an Alarm & Indicator to take care of manual labour & manpower wastage.
  6. To utilize the motor power effectively a VFD was installed and operated at 30 Hz frequency. The pump RPM takes as 900 and outlet valve was operated fully.
  7. Power consumption reduced from 32 kw to 16 kw

Merits of New System : -

  1. Mechanical & Electrical stresses during starts of the motor reduced to negligible. Hence the life of the equipment increased.
  2. Presence of a supervisor or monitoring of the level got avoided. Hence the manpower cost reduced.
  3. System power consumption reduced.
  4. No churning of water in the pump & hence increases life of impeller.

Cost Benifit Analysis : -

  1. Previous System (Without Drive) -
  2. Present System (With Drive) -
  3. Energy Saving per year -
  4. Cost incurred in the installation of New VFD -
  5. Saving in Rupee Terms / Year -
  • Speed=50 Hz, Kw (Consumption)=32
  • Speed=30 Hz, Kw (Consumption)=16
  • 16 Kw X 20 X 300 = 96,000 KwH
  • 2 X 1,50,000 = Rs. 3,00,000 /-
  • 96,000 X 4 = 3,84,000 /-
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