Need advice on R-22 flooded system

[clliew]

Hello All,

I have recently "inherited" a continous ice cream freezer (Soren) with a flooded type barrel. Basically the system runs smoothly during operation. However, during start-up the condenser safety valve will blow due to high pressure at 24 bars (condenser rating is at 30 bars design pressure). FYI, the condenser water pump is switched on even when the unit is in shutdown.

On operation side, during flavour change (prior to start-up), hot water is allowed to flow through the barrel (flooded evaporator) for CIP (clean in place). Could this cause the liquid to evaporate and create a pressure build up at the condenser?

Will pumping down the system prior to CIP completely eliminate the problem or are there other recommended modifications to the system. Previous experience in pumping down the system causes oil to accumulate at the condenser.

Thanks in advance for any advice/help/suggestions.

PS: Normally we relieve the gas, start up the system, and recharge the system again which I find quite baffling .

[gregd1401]

Do you have a crankcase pressure regullator fitted to the system?

[chemi-cool]

You did not mention what is the pressure after you charge the system.
Is it one compressor or a few?
You need an oil separator if you loose oil.

Pump down is vital if you wash the barrel with hot water. There is liquid refrigerant insideand the pressure is too high.

Its the same method in DX milk tanks, always pump down before washing with hot water [ 80°C]

[clliew]

The system is charged to:

Discharge pressure: 240 psig
Suction pressure: 0 psig

According to the user manual, 50 kgs of R-22 is required.

A back pressure regulator is installed right after the cooling barrel, before the suction accumulator.

We have recently replaced the old oil seperator with one size up and solved the low oil pressure problem. However, yesterday we had a safety valve blow out again and we had been running at 200 psig discharge and 0 psig suction. However, this causes the compressor to frequently trip on low oil pressure.

[clliew]

Forgot to mention that this is a single compressor system (Bitzer S6H 20.2 compressor).

[taz24]

.

You need to think about what could cause this,
I know you already have but I mean at a very basic level.

What is different now to when it was ok?

What would cause the discharge pressure to high on start
up when it is not on normal running.

The first thing that comes to mind is back pressure
(suction pressure). The suction pressure is too high
initially untill the comp gets hold of the pressures??

Or could there be air in the system. If the back pressure
is 0 then it could have pulled air in and maybe that is a problem..

all the best

taz

.

[clliew]

Thanks for the advice Taz. Perhaps I HAD overlooked the most basic of refrigeration (leak test) since we've been discharging and recharging so often, it is not obvious if we have a leak problem.

Will keep you guys updated once I can arrange for proper leak test.

[clliew]

Hello again everyone, just an update, completed leak testing and re-modifying the system. Following are what went wrong:

1) System was previously modified so as the system's receiver tank inlet to be located AFTER the solenoid valve, effectively disabling it during pump down (thus causing the condenser to blow its safety valve). This have been rectified.

2) The receiver tank was "blamed" for the slow startup after CIP. It has been found that the inlet and outlet of the receiver tanks were swapped around (liquid in connected to bottom of the tank while outlet was on top of the tank) during previous modifications. This was rectified as well.

Currently putting the system to test after modification works.

Thanks for everyone's help so far.

[Magoo]

The compressos are loading too fast. Slow and easy is recommended. Hence why system operates OK at design, but not during pulldown. Tell the production ****heads to wait until system has stabilized and ready to operate.
magoo

[clliew]

Thank all for the help offered so far. After modifying, the system (Figure 2 as per attached) is running stable for 5 days so far .

However, prior to modifying, we also considered to go for an alternate arrangement (Figure 1: Proposed System as per attached). The reason is that the system as per proposed in Figure 1 would keep all the liquid in the receiver tank and then from the receiver goes to the intercooler/expansion valve.

Which would be the proper configuration?

Thanks in advance.

Figure01.jpg
Figure02.jpg