4 replies to this topic

[mykid]

Hi all, would like to know if anyone has experience in starting up TEG contactor with a reciprocating compressor.

On the existing FPSO, there was a reciprocating compressor designed for 165 barh discharge pressure. New client requested for a gas dehydration unit to dry the gas lift to 7Mlb h2O/MMscf.

Vendor has subsequently designed and installed a GDU suitable for this high operating pressure downstream of the contactor.


Downstream of the TEG contactor, a moisture analyser will flare the gas when it is offspec and close the SDV going to the gas lift riser.

My question is with regards to startup operation.

Given that reciprocating compressor works against back pressure, the gas lift riser will have to be pressurised prior to the startup. In this application there is no pressure control valve downstream of the contactor to maintain its operating pressure. Therefore the only way to pressurise will be using wet gas with TEG contactor bypassed. To avoid hydrate formation, methanol will be injected to the wet gas. Once the pressure increased to 165barg TEG can be introduced to the contactor for drying the gas.

Will the above works on startup? Or anyone has a better suggestion?
Issue with the reciprocating compressor is if we want to pressurise the gas lift riser with dry gas, we can pressurise the contactor with the onspec SDV closed and stop flaring once the gas is on spec. However the moment SDV valve opens , the pressure will equalise and probably trip the recip compressor on low low. Unless there is a PCV this scheme wont work. PCV is not normally recommended for reciprocating compressor. Therefore i am interested to find out what other alternative is available.

The other solution is probably to pressurise the riser with nitrogen. This will avoid the hydrate problem.

I will upload a simple schematic later as i am using my phone to post the topic.

[Bobby Strain]

There is no reason that you can't start your compressor with the discharge pressure the same as the suction pressure. So, just start it whenever you want.

 

Bobby

[mykid]

Hi Attached is the schematic for the process flow for your understanding.

 

My concern is mainly to send wet gas with methanol injection for every startup/restart when the riser is empty.

Would like to know if there is a better way to start the system.

Attached Files

•  20160603_095706_resized.jpg   43.37KB   4 downloads

[Papps]

Start TEG circulation and start the Gas Compressor.

Once you load the compressor fully discharge pressure starts to raise. If you want to raise pressure quickly increase the Gas flow to the compressor which subsequently increase the discharge pressure. Once you attain your desired discharge pressure reduce the inlet flow rate according to the pressure control system available.

[Papps]

Start TEG circulation and start the Gas Compressor.

Once you load the compressor fully discharge pressure starts to raise. If you want to raise pressure quickly increase the Gas flow to the compressor which subsequently increase the discharge pressure. Once you attain your desired discharge pressure reduce the inlet flow rate according to the pressure control system available.