7 replies to this topic

[dhirennaidoo1]

Hi guys

A friend of mine, as part of her practical training as a chemical engineer needs to reduce the power consumption of a centrifugal compressor which is used to compress syngas in a gas loop. Now I'm a computer engineer, and while I understand the basic workings of the compressor, she is expected to reduce the power consumption by reducing pressure drops along the discharge side of the compressor. The chem eng aspect of this is what I'm not too familiar with. I would appreciate some ideas or guidelines with respect to this.

As I've stated, the gas being compressed is syngas. The suction pressure on the compressor is 19bar and the discharge pressure is 25bar. The compressor is being driven by an electric motor. One idea she has is to look at a globe valve that's being used in the gas loop. Apaarently, the pressure drop across this valve is big, and she wants to split the gas stream and use a bypass over the globe valve. Is this a recommended approach?

I was also thinking about pressure drops due to elevation in the piping, or changes in temperature? I'm not sure though, as I've said, my expertise is in programming

If the compressor is being driven by an electric motor, could a gearbox or belt drive with a different ratio be introduced?

Any other suggestions welcome. or if you need any other information, I can obtain it for you.

Thanks in advance

Dhiren

[djack77494]

Dhiren,
Practically speaking, the best way to deal with a problem like this is to get in contact with the original supplier/manufacturer of the compressor. (This is, of course, AFTER current and future needs have been fully defined.) There are many ways to induce the compressor to perform according to your desires. Some save energy while others are wasteful, and some require easy-to-achieve adjustments while others require a capital investment. Looking at some simple possibilities, throttling back on the discharge side will increase the compressor's discharge pressure, forcing the machine back on its curve. That would typically save only a very small amount of energy. One could also throttle the suction side of the machine. Doing this would require increase head but lower gas density on the suction side. This approach can be effective in minor machine adjustments AND it can be effective in saving energy. Many other approaches are possible. These include variable speed drivers, which can be quite energy efficient, or gas recycle, which is generally wasteful of energy.

I would warn you and her that compressor control is complex. It is possible to drive the machine's operation into undesirable regions such as surge or even stonewall. That is why I would strongly recommend that you speak with he who is most knowledgable about the machine - its mnanufacturer.

[dhirennaidoo1]

Thanks jack...she's looking into the points you gave...

She also wants to know if increasing the pressure on the suction side of the compressor would help...or if changing the temp of the gas on the suction side would allow more efficient operation?

If the pipeline diameter is reduced on the suction side, would it cause an increase in pressure on the side? The problem is, I assume creating a restriction like this on the suction side would introduce back pressure on the discharge side as well...

Thank you for your help

[djack77494]

She also wants to know if increasing the pressure on the suction side of the compressor would help...or if changing the temp of the gas on the suction side would allow more efficient operation?

By itself, increasing the suction side pressure would increase energy consumption. This is due to the higher gas density (and therefore higher mass flowrate) entering the machine and also the higher discharge pressure that would be generated. Suction side temperature changes can be similar to pressure changes, but in the opposite direction. Thus, increasing the suction temperature decreases the gas density, the mass flowrate, and the discharge pressure. Suction side pipeline diameter changes would act to impose more or less of a hydraulic restriction on the gas entering your machine, and could therefore be thought of a similar to suction pressure changes.

I assume creating a restriction like this on the suction side would introduce back pressure on the discharge side as well.

Restrictions on the suction side would not introduce back pressure on the discharge side. I'm not sure what you're thinking about here.

[dhirennaidoo1]

Thanks ..She is going to speak to the manufacturer of the compressor today....

Restrictions on the suction side would not introduce back pressure on the discharge side. I'm not sure what you're thinking about here.

I was thinking that restrictions on the suction side would result in back pressure further upstream, since the compressor is used in a gas loop...but anyway, the idea of changing pressures has been abandoned, and I'm tired of learning about compressors and natural gas

Thanks once again, you've been a great help.

By itself, increasing the suction side pressure would increase energy consumption. This is due to the higher gas density (and therefore higher mass flowrate) entering the machine and also the higher discharge pressure that would be generated. Suction side temperature changes can be similar to pressure changes, but in the opposite direction. Thus, increasing the suction temperature decreases the gas density, the mass flowrate, and the discharge pressure. Suction side pipeline diameter changes would act to impose more or less of a hydraulic restriction on the gas entering your machine, and could therefore be thought of a similar to suction pressure changes.


Would you please support the indicated affects of the suction temperature and pressure by formula? I do not see how the increase in the temperature can reduce the mass flowrate since the volumetric flow is increasing while the density is decreasing.

Bye

[wil ma]

i think we need to know if the reduced power reduction of the compressor may be at the cost of lesser (Norm)flow in the syngasloop?
can you please, please give us a more detailed setup of the process (loop, feed, valve, compressor)?

Kind regards

[dhirennaidoo1]

i think we need to know if the reduced power reduction of the compressor may be at the cost of lesser (Norm)flow in the syngasloop?
can you please, please give us a more detailed setup of the process (loop, feed, valve, compressor)?

Kind regards

Hey wil ma. Sorry, but this problem was a while back. I can barely remember the details, but she did solve it. Thanks anyway