6 replies to this topic

[AleAndrade]

Hi Friends,

I am new to this forum. Would appreciate if someone can advise me on the below mentioned case:

We are considering install a new compression station (centrifugal compressor) to transport low molecular natural gas (C1>90%). To meet gas specification (7 lb H2O/MMSCFD), a dehydration package is required. What is common in the gas industry, install the the dehydration package upstream or downstrean of the compressor. What is the typical arregement in natural gas plants??

Thanks,
Alex

[Padmakar Katre]

Hi Alex,

It is not clear form your post that what is actual requirement. If you can tell us the background of the problem, we can comment/suggest appropriately. The natural gas processing train consists the first unit as the acid gas recovery unit followed by the dehydration unit before it enters the cryogenics for liquid products recovery. Since the basis of the compressor station is not clear we can not comment. What is the sourcse of the gas? is that compressed from gas filed which reaches at the unit battery limit at lower pressure than required for further processing? Please tell us the brief about the facilty so that forum memebers can give their helpful comments.
Waiting for your inputs.

[vskumar]

Padmakar,
Dehydration plants are always downstream of Compression facilities. Sequence is compression - liquids knock out - dehydration - knock out - pipeline.
Dehydration at higher pressure has several advantages - You are sizing equipment at higher pressure - sizing is smaller - you have pretty conditioned the gas (removed condensables), therefore facilitates dehydration process. Dehydration is effective at high pressures and low temperatures.
Srinivas

[ankur2061]

AleAndrade,

Have a look at the following link for the sequence of natural gas processing in a majority of NG processing plants:

http://en.citizendiu..._gas_processing

Hope this helps.

Regards,
Ankur.

[AleAndrade]

Thank you all for your responses....

More information>
Gas is water saturated gas from fields. The gas is produced offshroe and then gathered in a onshore facilities. Gas needs to be compressed because of the low pressure and the trasported to the delivery point, where water content should be less than 7 lb H2O/MMSCFD. I would like to know the advantanges and disadvantages of dehydration the gas before compression or after compression. What is more convenient? cost effective

Regards, Alex

[Zauberberg]

Gas is usually compressed and then dehydrated, mainly for the following reasons:

- Dehydrating the gas does not affect material selection for the compressor, so there is no benefit from that point of view;
- If dehydration is performed at low pressure, it might be the case that you have very limited number of technologies capable of dehydrating the gas, or it could be the case when you cannot even dehydrate the gas down to such low water content you need. Water content of gas increases sharply as pressure is reduced.

Ideally, you need to do a small concept study, and compare size/cost of two dehydration units - one located upstream and the other one downstream of the compressor.

[Vimalesh Agnihotri]

Hi Dear,
Dehydration of natural gas is always advantageous at High Pressure and low temperature. however after compression , the temperature of gas will also rise which is not good for dehydration, so you have to see the available utilities for cooling also. basically you have to optimize the stages of compression between which you can put dehydration unit and able to provide a low temperature range for dehydration.