Vapor degreaser

[Nereferman]

I am about to start a new project for our customer. They have changed solvents in a large vapor degreaser. This caused drastic load changes on the system and since this change was made, they have been loosing components. Valve plates and wral valves mostly.

I think this question needs some context. This is a large Barron and Blakeslee unit that is built into the floor of a very large factory. It is not getting replaced. When the solvent change was made we had slugging issues and lost a compressor. It is a 7.5 hp Copeland discuss. I was not involved with the project at the time and from what I understand the unit was converted from r22 to r407c. Well we lost another one 6 months later. This is when I got involved. The valves failed and damaged the compressor internals. A brand new comp was installed, along with a wral that I had made up, a sporran Kelvin 2 controller and valve kit. This system only did the cold trap, and the freeboard coil was ran with a 3/4 hp semi on 404. The unit ran for about a year but was running high discharge superheat and made it much longer than I thought it would. This time we lost a valve plate. New plate was installed and we made some adjustments to de superheating valve and slowed up pid curve on exv controller. It has been running good for a little over a year and then we lost hot gas valve. This was fixed and two weeks later we lossy the freeboard compressor. My thought is to run the freeboard off my main cold trap compressor and give that thing some load. What do you guys think about running a -20 evap temp freeboard coil and a 35 deg cold trap coil with r407c. I am still working out the details, but I am thinking adding eprs, along with a suction line accumulator heat exchanger at the very least. My 7.5 hp skid is water cooled and I cold add some form of external compressor cooling.

[seanf]

Does the comp have any capacity control?

Whats a wral valve?

[Nereferman]

There is no capacity control on the compressor itself, but the wral valve acts as one. It is essentially a hot gas bypass valve, with a de superheating valve feeding into a mix chamber that ties into the suction header for compressor. So hot gas bypass unloading.

[Nereferman]

Sorry it is spelt rawal valve

[seanf]

There is no capacity control on the compressor itself, but the wral valve acts as one. It is essentially a hot gas bypass valve, with a de superheating valve feeding into a mix chamber that ties into the suction header for compressor. So hot gas bypass unloading.

Is the TXV(s) on the Rawal valve the correct one for the refrigerant in the system?
Was it liquid refrigerant or oil slugging?

[Nereferman]

Yes txv is sized correctly. Before we added rawal valve set up it was liquid slugging. Once the hot gas bypass was installed and set up that went away. We did run really high discharge superheat with this set up at first because it was hot gassing so much. I ended up lowering head pressure with my head pressure control valve and playing with the charge. We had 90 lbs of 407c at first and currently as it sits we are at 74 lbs with half way decent superheats. The rawal set up is by passing at its max capacity. When I pulled the valve plate the nickel coating on it had been washed off and it was down to the copper plating. At first I though it was due to velocity being high in the suction line from the hot gas, but now my thoughts are that it is due to just hot gassing so much it’s cooking up the compressor. I am concerned that when we add the low temp coil to this circuit that the compression ratio is going to be to high and we will be running those high discharge superheats. I looked into going 407a but I struggle to understand what that gives me. On pt chart they are slinky 2psi apart at -20 and 200 deg. I have not found a glide chart yet for both to compare glides yet. But is the 407 family of gas my best option. Should I go to 404a at this point?

[seanf]

Yes txv is sized correctly. Before we added rawal valve set up it was liquid slugging. Once the hot gas bypass was installed and set up that went away. We did run really high discharge superheat with this set up at first because it was hot gassing so much. I ended up lowering head pressure with my head pressure control valve and playing with the charge. We had 90 lbs of 407c at first and currently as it sits we are at 74 lbs with half way decent superheats. The rawal set up is by passing at its max capacity. When I pulled the valve plate the nickel coating on it had been washed off and it was down to the copper plating. At first I though it was due to velocity being high in the suction line from the hot gas, but now my thoughts are that it is due to just hot gassing so much it’s cooking up the compressor. I am concerned that when we add the low temp coil to this circuit that the compression ratio is going to be to high and we will be running those high discharge superheats. I looked into going 407a but I struggle to understand what that gives me. On pt chart they are slinky 2psi apart at -20 and 200 deg. I have not found a glide chart yet for both to compare glides yet. But is the 407 family of gas my best option. Should I go to 404a at this point?

Sorry I meant, is the TXV head/power element for the correct refrigerant?

I've only ever come across 407C and 407A on medium and high temp equipment. R404a may be the better option.

For me, I think I would be looking at what capacity I really need. Sort of sounds like even if you put an EPR on and run the -20 and +35 on the same comp, you may still be recirculating a lot of hot gas.
If comp capacity still works out to be way too high and you dont have the option of changing the comp size, maybe an alternative capacity control method should be looked at.

Keep an eye on your thread, others may post better advise.