PDA

View Full Version : HP Receiver sizing in ammonia systems?







refrigeng
12-09-2014, 03:34 PM
hello
How can I calculate size (volume) of HP receiver in ammonia liquid overfeed(liquid circulation) systems,please? Is there any formula?

what is the optimum L/D(Length/Diameter) ratio for HP receiver?
thank you.

sterl
12-09-2014, 06:55 PM
The smallest it needs to be is sufficient to accomodate your swing charge....Which is the amount of refrigerant thats going to be in your evaporators and liquid lines and suction mains when all evaporators and condensers are working hard, compared to that which will be required when all units are encountering relative low real loads; plus the potential change in charge location as vessels are replenished. Much of that swing is related to how you are controlling things at low loads, and how coincidental in terms of high load-low load your collection of evaporators tends to be. There is also some swing associated with any heat reclaim, oil cooling, reheat and similar high side points deviations including HG defrost.....

The need for a "largest" versions is usually a "full pump down" vessel which means you have enough space for the entire liquid charge below the 85% line. Most complex systems don't use that number, the economics are simply prohibitive.

refrigeng
14-09-2014, 07:27 AM
thank you sterl
can you give me a formula or rule of thumb for calculation of required volume of HP receiver?

sterl
17-09-2014, 08:27 PM
Size of these purely driven by charge, and where potentially it could be located at any time: there are circuits that don't need them at all.....

As rule of thumb: the swing charge of you HPR should be:

1) At least as big as the sum of
a) maximum operating content of your biggest low side vessel.
b) the largest, by volume, low side coil you have...
c) 15% of your total condenser volume....
d) all of your liquid lines, including thermosyphon supply and return lines

2) If that does not come to exceed 30% of the circuit total charge: figure out 30% and buy that much....

For most industrial plants of large scale, the HPR is a lot like a spare bed you only unwrap for guests: It is stationed in a corner, it does not do much of anything most of the time, and the first time you know you didn't get enough is when its too full....

As to Proportions: Where the high side is a free draining arrangement (no in line discharge or liquid line pressure controls, check valves or similar....) the height of the condensers and their drain line piping may dictate a max height. Similarly for Thermosyphon Piping, may dictate a minimum height. Also the style of the receiver: a through type, surge type and so on.

Some "commercial guidlines": Most pinch rolls will handle 120 Inch plate; most plate as full portions comes 120 inches wide. So the cylindrical portion is most cost effective at 120 inches....That does vary some places in the world. In the US heads are reasonably proportional in price from 30" to 72" Diameter. An 84" head is about 160% of the price of a 72" Head. So: it is more economical overall to by a 60" by 20-foot long shell, plus about 18" for each semieliptical head; than it is to buy an 84" by 10-foot shell plus 24" each head: They are basically the same internal volume but the unit Head Price makes the latter more expensive. Above that size you will run headlong into some transport issues as well.

Small horizontals another topic...