July 22, 2008

Guaranteed Energy Saving in Vacuum System

Steam Ejectors are the widely used equipments for vacuum generation till the recent developments of liquid ring & dry pumps. Also, the reason for preferable use of ejectors was availability of steam at different levels, low maintenance, non availability of other systems etc. with major one being the only system suitable for very high vacuum.

However, the major disadvantage of using ejectors is - higher steam consumption. As we go for higher vacuum, the steam consumption goes up exponentially & since the cost of fuel is going up like a rocket in the recent past, the alternative solutions are more benefitial.

Here is a proven method which is used by us for sometime & is working fine.

Related References

The option is to use dry vacuum pumps which are capable of running dry e.g. Screw or Scroll. The picture of a typical pump from M/s. Kinny is given above. Here are the two main parts as photographed from an actual installation.

The other advantage of these pumps is to recover process fluids. These pumps discharge non-condensables & vapor load at ambient pressure so the benefit is that you can boil your fluid at low temperature under vacuum & can recover them at atmospheric pressure with probably cooling water.

Thus it can be used for multipurpose depending your system. I am using them for both. In one of my process I have to remove methanol under vacuum So I used dry screw pump there & then recovered methanol at the downstream with cooling water condensation. Boiling was done using low temperature hot water at 80°C. However, the vapor load should be low in such cases.

This example is given for a 1 torr vacuum in the system. Kindly do some financial calculation before making any decision in your plant.

Calculate following.

  • Steam Running Cost Including boiler efficiency

  • Cooling water cost.

  • Cooling water Pumping cost

  • Condensate Pumping cost

  • Any other direct & indirect cost

Now the installation cost for steam ejectors was ~Rs.12 Lac while the cost of vacuum pump was only Rs. 16 Lac, but the saving was Rs. 10 Lac/year which paid back my investment in less than 6 months.

So now you need to assess your current systems & implement this sure shot energy saving plan.

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