propane refrigeration discharge pressure

[Tylamontagne]

During hot summer months, throughput through the plant is limited by the discharge pressure of our refriges. Unless we flare some inlet, the refriges go down on high discharge pressure. Evaporative condensers are not an option due to lack of water. any tips to lower the ambiant air temp? We are currently running h2o on our discharge piping but this is scaling pipes up fast.

 

[Montemayor]

Tyla:

Since you can’t consider Evaporative condensers, cooling water towers are an obvious rejection. Without cooling water – and not knowing other basic data: location, type and size of compressors, loads, etc. – its almost impossible to point to an alternative to what you describe as your overheating problem.

Why (& how) are you venting “inlet” (suction propane refrigerant?) ? Have you considered the possibilities of non-condensables as the problem?

The scarcity of basic data once more handcuffs our ability to help out. All we can do is generalize and the general answers are:

1) Look at a change-out of refrigerant. A refrigerant with a lower discharge temperature may work.
2) Scrap your present compressors. Design new ones for the specific application.
3) Look at creating a self-cooling cycle; this is very inefficient and reduces the net refrigeration effect, but you describe your site as an oven, so you’ve got to pay the price for being there.

If you can’t get cooling water, you’re tied to atmospheric air-cooling and the climate you find yourself in. This should have been designed into the facilities from the outset.

You describe your problems as lack of cooling, but it could be something else. I’ll assume you know what you’re talking about and have correctly identified the cooling (or lack of it) as the culprit.

 

[Tylamontagne]

sorry about that. We work at a gas plant and I meant flaring inlet gas into the plant to reduce load on our chillers. Non- condensables could very well be a possability but we think we've come to the conclusion of ambiant air as we have no problems other than when its really hot. The reduction in volume from a gas to a liquid in the condenser causes the pressure drop, is it not? Mabe we dont have large enough condensers. What about the option of a pre-cooler before the condensers?(same idea as running water over the piping)
I've also heard of running refrigerant coils through the condenser(basically turning it into a air conditioner). I'd like to hear what you think

 

[Montemayor]

Tyla:

What you bringing up now is exactly what I referred to in the previous post. You should know what dischargre temperature you should be having on your refrigerant out of the compressor and into your condenser. You should also know the temperature and condensing load of the refrigerant in the condenser's receiver. The highest the temperature in the receiver should be is approx. 2-5 degrees below the refrigerant's saturated temperature at the condenser's pressure. You don't furnish those data nor do we know the ambient air temperature you're facing - so we can't ever guess where you are at in trying to condense the refrigerant.

Yes, you can cool the hot refrigerant discharge out of the compressor's last stage, prior to entering the condenser. All that is is making it easier for your existing condenser to do its job. And, as I previously stated, you can dedicate a portion of your refrigeration cycle to cooling the discharge out of the compressor - but it lowers the overall net refrigeration load that you obtain from the refrigeration cycle. We need a lot more basic data before we can really be of any help. Sorry.

We don't even know if your refrigerant is a pure, refrigeration-grade Propane. Do you have a non-condensable auto-purge unit?

 

[TXiceman]

If by venting some gas, you manage to lower the discharge pressure, you may have non-condnesables in the system. If you do not refrigerant grade of propane, for recharging, you will have some light ends in the gas (I believe HD-5 grade propane can have up to 5% impurities). These light ends tend to concentrate in the condenser and will change the partial pressure and raise the discharge pressure. You can install a purger and vent and reclaim the refrigerant. Take a pressure reading in the receiver and convert this to the equavalent saturation temperature. If you are reading a pressure of 227.5 PSIG, this has an saturation temperature of 120 dF. Measure the liquid temperature of the liquid leaving the condenser. It should be about 118 dF up to about 120 dF. Any lower and you have some inerts or non-condensables in the unit. This is presuming you have no subcoling surface in the system.

The best place to purge on the condenser/receiver system is a quiet area and purge slowly.

If inerts are not the problem, you may need more condenser surface to cure the problem.

I do not know what kind of system you are running, but your best bet may be to get a qualified refrigeration technician out to help with the system.

Ken

TXiceman

http://www.rae-corp.com