5 replies to this topic

[asaklsak]

I have simulated a Gas Processing plant with the output Gas dew pointed to 10 Deg C using a Propane refrigeration unit in HYSYS. The sales Gas is exported at 3825 Kpa


A general composition of my NG is as follows:
C1 : 0.6787
C2 : 0.0942
C3 : 0.0297
C4 : 0.0134
H2O : 0.1342
Rest is heavier components.

I need to change the dew point of my Outlet Sales gas to -3 Deg C. Can this be done without reducing the export sales gas Pressure, say by reducing the chiller Outlet temperature??

Kindly tell me how to proceed in HYSYS.

[Dmitry]

I have simulated a Gas Processing plant with the output Gas dew pointed to 10 Deg C using a Propane refrigeration unit in HYSYS. The sales Gas is exported at 3825 Kpa


A general composition of my NG is as follows:
C1 : 0.6787
C2 : 0.0942
C3 : 0.0297
C4 : 0.0134
H2O : 0.1342
Rest is heavier components.

I need to change the dew point of my Outlet Sales gas to -3 Deg C. Can this be done without reducing the export sales gas Pressure, say by reducing the chiller Outlet temperature??

Kindly tell me how to proceed in HYSYS.

Hello,


Dew point of your sales gas is 10 Deg C? It is very high dew point temperature for water, may be you mean -10 Deg C?
If you made a mistake it's ok. Yes you can decrease dew point temperature from -10 Deg C to -3 Deg C. You can increase refrigerant compressor suction pressure, as result less rate of refrigerant will boil in chiller. With lower refrigerant flow rate you will have less duty of chiller.

Dmitry

Dmitry

[asaklsak]

I have simulated a Gas Processing plant with the output Gas dew pointed to 10 Deg C using a Propane refrigeration unit in HYSYS. The sales Gas is exported at 3825 Kpa


A general composition of my NG is as follows:
C1 : 0.6787
C2 : 0.0942
C3 : 0.0297
C4 : 0.0134
H2O : 0.1342
Rest is heavier components.

I need to change the dew point of my Outlet Sales gas to -3 Deg C. Can this be done without reducing the export sales gas Pressure, say by reducing the chiller Outlet temperature??

Kindly tell me how to proceed in HYSYS.

Hello,


Dew point of your sales gas is 10 Deg C? It is very high dew point temperature for water, may be you mean -10 Deg C?
If you made a mistake it's ok. Yes you can decrease dew point temperature from -10 Deg C to -3 Deg C. You can increase refrigerant compressor suction pressure, as result less rate of refrigerant will boil in chiller. With lower refrigerant flow rate you will have less duty of chiller.

Dmitry

Dmitry

Hi Dmitry,

I know this is a high water dew point and that is why I want to reduce it to -3 DegC. Here are the specs for the Refrigeration unit currently simulated:

Mass flow of ProPane : 6000 kg/h
Compressor : Inlet P of 442 kPa and Outlet P of 1817 kPa
Propane gets heated from 18 Deg C to 84 Deg C
Air Cooler : Condenses Propane to 50 Deg C
Evaporator : cools it to 41 Deg C
Expansion Valve : Flashes Propane to 5 Deg C and P of 550 kPa
Chiller : Use the Liquid Propane to cool the sales gas from 25 Deg C to 10 Deg C
This is also the Dew Point of Gss.

Now I need to do some modification to bring Water Dew Point down to -3 Deg C. Due to the huge size of the simulation I am unable to attach the case. Please suggest any modification to be made viz.

a. Flow rate of Propane
b. Compressor Outlet Pressure
c. Chiller Temp.

which will help me lower the Water Dew Point to -3 Deg C. I hope i have clarified the problem enough

Regards,
Nikhil

[Bobby Strain]

Seems to be some confusion. If you want to lower the dew point then you can use more glycol and/or reduce the chiller temperature. This, of course, will require greater duty on the propane system. And you can increase exchange between the inlet gas and chiller outlet gas.

Bobby

[Dmitry]

Hello Nikhil,

Is it design stage? Do you have compressors, condenser data?

1. If you have minimum suction pressure for compressor (from data sheet ) you can keep propane vapours pressure a little higher than this value (additional 3 psig for pressure drop will be ok). On our plant we operate chiller with pressure 200 kPa (shell side). I think you can play with it. As you know with lower propane pressure more liquid propane will evaporate and as Bobby hass wrote it can increase exchange between the inlet gas and chiller outlet gas. In a real life you need to have LCV upstream chiller on propane line. This valve will control flow rate of propane inside chiller to keep level of liquid propane enough to cover tube side with gas stream.

2. You can increase flow rate of propane, and it will increase exchange between the inlet gas and chiller outlet gas. In this case compressor will required more duty.

3. You can put additional glycol upstream chiller. Do you have glycol injection? Try to add ethylen glycol and check water dew point changes. Note: additional flow rate of glycol will required more duty of compressor because total mass flow of feed (gas glycol) will increase . But it can make an effect only for water dew point not for HC.

4. If you will increase compressor outlet pressure you have hotter outlet gas and propane condenser will required more duty. No effects on cooling gas.

5. Do you have gas/gas exchanger upstream your chiller. On out plant such exchanger (upstream chiller) reduces gas temperature from 30 to 1 C. It is the good option to reduce size of refrigerant loop.

Hope you will find useful this.

Regards,
Dmitry

[asaklsak]

Thanks Dmitry and Bobby,

Yes it is a desigN Problem and I have been racking my brain over it.Finally after a lot of studies and datasheet analysis, my simulation gives the result that a Chiller outlet temp. of -1 Deg C gives the water dew point as desired.
I need to either change the chiller or gas gas exchanger to give me the desired outlet temp.
Increasing the flow rate of Propane doest help since a huge quantity would be required.
Your first option sounds promising. Need to adjust the pressure. Maybe that ll reduce some load on the chiller.

Anyways Thanks again for your suggestion

Nikhil