Ammonia Refrigeration Systems Interconnection

It is difficult to assist without a view of the P&ID for this plant.

In addition to the P&ID, which is important, can you describe the following:

Do the three systems operate at approximately equal evaporating and condensing pressures?

If the systems are interconnected, will this add up to enough total ammonia to require a more stringent safety classification, as based on the maximum possible release in the event of leak or accident?

If these considerations pose no problems, a general approach that could work is this:

Add a solenoid valve in the liquid outlet line from each receiver. Tie the outlets from each solenoid valve into a common liquid header to feed to the surge drums. Add a liquid level switch to each receiver (if there are a gauge columns available) so that if the liquid level in the receiver drops to say 25%, the switch deenergizes its respective solenoid valve. This is to ensure that no receiver runs empty.

I have connected 3 plants to 1 successfully but here are many things to take into consideration. i.e.

1. Each surge drum is designed to only handle a certain amount of kWR. If you combine your plants and the total kWR of the running compressers is higher than that of the surge drum, your chances of liquid down the throat of the compressor is high.
2. Any dry suction line longer than 50m poses a threat that when you experience a fluctuation in suction pressure, the NH3 will condense and liquid to your compressors.

There are many more dangers and usually it is NOT advisable to do so unless the layout gets evaluated by a designer/engineer.

If I had more info I would be glad to be of assisstance.

Regards

Even if all systems are operating at slightly different pressures it can still be done. Most often (but not always) accomplished by pumping high pressure NH3 liquid past all evaporators in a loop and returning excess liquid to a receiver vessel. Ammonia is excellent for this because of its very high latent heat. You can pump it for miles and only lose a couple of tons of capacity.

At each point of use, a hot tap off the liquid line takes what is needed from the liquid header and gets flashed via an expansion valve to the evaporator pressure. Vapor is returned via existing insulated piping to your compressor room. Your controls to prevent condensing at the compressor inlet header are very important or you can ruin your compressors.

You must select an operating pressure for the liquid line and the compressor suction lines that are A) sufficiently high enough to handle pressure drop across the worst case valve/evaporator for the liquid line, and B) sufficiently low enough to properly maintain your evap temps at all usage points, and to return all gas to the compressor room without creating liquid droplets at the inlet of the farthest compressor. As long as all compressor controls are tied in together to provide sufficient volumetric flow for each compressor while maintaining the liquid inventory in the receiver you should be OK. Hope this helps, but its about the best we can do without a P&ID of your process.

Also, make darn sure you include isolation valves at each evap to take them out of service if they are only used intermittently.