Dear All
I appreciate the effort you all put into supporting young engineers who are new to the industrial world.
My company recently had a client who produces natural gas and exports via a 8" line to a recipient who utilize the gas for other purposes.
It has been observed that whenever the gas recipient temporarily shutoffs their reception of gas due to a temporary maintenance or for any reason whatsoever, there is usually a back pressure build up to the gas scrubber.
I have attached a sketch of the gas supply system below.
Although, the system was initially designed to flare once the export line is shutoff, but it seems the flare line and Control Valve system is not able to do this. The pressure builds up from the shuf off hand valve (shown in the diagram) backwards to the scrubber.
The pressure downstream the scrubber (production separator) is 930psi, PCV is set to open at 1000psi, flare is atmospheric (1 atm), temperature downstream scrubber is 90 deg C. Gas flow rate is 0-30 MMSCFD.
I have been assigned by my boss to propose a possible rsolution to prevent the back pressure.
Some of my observation during my discussions with the client at the concluded site visit are as follows:
1. The export tie in point is a simple tee joint (I am surprised at this) which I believe should have been a valve manifold arrangement.
2. PCV installation on the flare line might have not been the best judgement (my thought), I prefer to take my PCV reading just before the shut off hand valve where the pressure is expected to build up, but however this does not stop the back pressure.
3. There is also a massive hydrate formation buildup downstream the PCV bypass hand valve. (I am not sure why this has happened considering that the operating temperature of the gas is above the hydrate formation temperature)
I had earlier suggested installing a valve manifold at the export gas tie in point to check mate the back pressure. I felt a single check valve on the export line (upstream the hand valve) would be catastrophic due to pressure buildup in two direction.
However, I am not sure that installing the valve manifold would be the best option in terms of cost and performance. Please could I get support as to other possible solutions / configurations that will checkmate the back flow to the scrubber..
Any form of support would be appreciated.
Please note that the attached picture represents the current configuration of the supply point at the gas production facility.
Thank you.