Compressor Suction Throttle

[technologist]

A gas loop is operating with a centrfugal compressor.

Compressor is oversized and is having constant speed.
Compressor suction is 14 Kg abs. Discharge - 19 Kg abs.
After compressor there is pressure killing device to reduce the
pressure to 17 kg as plant requires only 17 kg. Now system drop is 3 kg

making it 14 kg at suction.

It is proposed to use suction throttling after removing discharge side
pressure killing device to save power.

Will there be any power saving in the proposed system

[Abhisek Chowdhary]

There may be some savings in term of power, but it will strongly depend on the nature of the compressor operating curve (corrected curve at the given operating speed). Normally throttling outside compressor (i.e. at suction) will cause some PD at the inlet valve and thus reduce the compressor discharge power. The compressor will still pump the required volume, but the operating region will change, this can help in some power savings. However, it is a strong function of the operating efficiency and in case the new region falls in bad efficiency region, the savings can be upset by this loss.

 

There are some other options also worth considering here. The compressor vendor can be contacted for looking into the possibility of providing inlet guide vanes / or similar device. This is a better option as the vendor will be aware of the nature of curve and can design a optimized guide vane / louver type of device. The second option is to look into impeller trimming. This option is very well proved for centrifugal pumps, but will have to be looked cautiously for compressors (as the compressor stability, leak / bypass, efficiency can be greatly affected). Here also the vendor can give his advice for feasibility of the option.

 

Finally, some advantage can be gained if some type of speed variation is possible in the compressor. In case it motor driven; a VSD can be considered. In case of steam / gas driven feasibility of using a governer to reduce the operating speed can be looked into. This option will reduce the compressor efficiency, but will give the best power savings (if feasible) without doing a lot of change irreversible changes in the system.

 

[Elias ElHossari]

technologist <p_bi...@yahoo.com> wrote:

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[Elias ElHossari]

Flow is directly related to HP for centrifugal compressors.

 

The higer the flow, the higher the HP requirement that leads to higher fuel cost or electric power. To answer your question: yes, you do save power by installing a suction controller valve. Ensure that you are operating within the flow curve of the compressor.

 

You should confirm the above by obtaining a copy of the compressor flow curves.

 

.By the way: Pressure should be expressed in Kg/sq.cm abs. Cheers.

technologist <p_bi...@yahoo.com> wrote:

[technologist]

Thanks Mr Abhishek,
However, my question still remains.

This is not a question on saving by suction throttle or guide vane.
Its a question on Dischrge throttle Vs suction throttle.

Compressor is fixed speed. Curve is available.

[Elias ElHossari]

I am assuming throttling the suction or discharge line keeps the compressor on the compressor's operating curve, I think you should control the suction to avoid waisting fuel and energy.

 

Cheers,

technologist <p_bi...@yahoo.com> wrote:

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[Abhisek Chowdhary]

Yes, I also agree to go ahead with suction throttling. The operating curve should however be consulted before the modification is carried out (the changes in inlet conditions of T, P should be taken into account to account for density corrections, if any in the curve).