R290 Suction Scrubber HI Level

[Knappyfro]

Hello all. I work at a NG processing plant. We have a Frick RWBII compressor running our r290 refrigeration system. The compressor is set up to control capacity based off of the suction pressure. Usually 4-4.5 psi. We have the following setup starting from compressor discharge:
1) Condenser Towers (fan speed based off discharge pressure, usually 195-215 setpoint)
2) Accumulator Vessel (never has a level, temp between 90 & 120)
3) Valve (controled by level in economizer vessel)
4) Economizer (when on, kept at 65-70 psi, wont keep a level unless suction scrubber is dry)
6)Expansion valve (controlled off suction temp leaving Process Exchanger)
6) Process Exchanger (chiller-tube & shell, gas inlet temp from 45-75F)
7)Suction Scrubber Vessel (has a habit of accumulating liquid propane, temperature can be between -20 and 50F)

My question is this...

What can I do to get the refrigerant out of the suction scrubber when it gets there, and why could the system run fine and all liquid propane in the economizer and other times all in the suction scrubber. I have watched the suction temperatures coming out of the process exchanger and they usually are right around 0 degrees. (Everyone else that has worked here sets the maximum valve opening right at what they guess to be optimum, and anytime the suction temp swings lower than another arbitrarily figured PID tuning setpoint, the PLC lowers the expansion valve to "prevent carryover." Obviously, we need a new method of control, but that's less perplexing issue to me at this point.)

I have installed a guage before the expansion valve, suspecting that when the suction scrubber has a high level, the process expansion valve is not getting full liquid propane. Just going off of the rapid and frequent "ticking" of nearly 20 psi, I'm going to assume that I'm not off-base there.

I'm a young little fart trying to be a good hand for a small company. I would be really appreciative of any information that could be sent my way.

Thanks!

Paul Sparkman

[Knappyfro]

This morning, there's a level in the suction scrubber. The suction temp never went below -5 last night, and shortly after I arrived, we lost cooling.
Right now here's the presses and temps:

Process Gas into Exchanger: 50
Gas Leaving: 3+
Pressure: 900psi

Propane Temp before Exp V: 45
Propance Temp after Exp V: 0 (+or- 10)
Propane Press Before Exp V: 67psi
Propane Press After Exp V: 4.0psi
Propane Temp Leaving Exchanger: 40+

Suction Scrubber Surface Temp: -50??
Suction Scrubber Gas Temp: 20F
Level: right below the kill switch

The expansion valve was getting about half and half gas and liquid when I arrived this morning, and the process gas leaving the chiller was -15F, but there's almost no liquid getting there now and the process gas leaving is 3+ now!!!
HOW CAN I GET THE PROPANE TO FLASH OUT OF THE SUCTION SCRUBBER????