Printable View
Dear Friends:
I don' know what can i do???
If I have a system working with 06 air coolers (DX) and a spray chiller, tell me what is the right capacity that I should take to design the suction accumulator vessel to avoid liquid inlet to the compressor, knowing that the spray chiller doesn´t need this vessel. Is that correct the schematic I attach in order to make the design of this vessel?
I hope somone help me.
Thanks....
Luis.
The capacity of the accumulator should be based on the maximum capacity you would want to add to this vessel. In your drawing you have a suction line extending beyond that required for the DX coils. How much more capacity would you add to this line (in addition to the DX coils shown)?
Dear US Iceman:
The total capacity of 6 DX coils will be 210741 kcal/h i don't sure if this capacity is right for design the suction line accumulator or i have to take the compressor's capacity ( 970000 Kcal/h)
If the vapor volume flow from the spray chiller does not flow through the accumulator then the accumulator is sized only for the DX coils. However, I have to warn you it is less expensive to provide a larger accumulator than you need right now. When you add more coils or compressors the accumulator would need to be larger. It is cheaper to install a larger vessel now, than wait until later and install a second accumulator.
If you provide a larger accumulator then I would install a larger suction line which would be sized for the operating conditions based on the larger accumulator capacity.
I am assuming the compressor is sized for the total cooling load (coils + spray chiller).
Hi Luis:
I find unusual your facility design, which is a direct expansion ammonia (NH3-dx). These facilities often have problems of excessive heating and very high (dangerous) temperature on return gas.
Typically, the six evaporators should be fed by a pump from a recirculation station that includes a suction accumulator.
Hi Luis:
Encuentro inusual que su proyecto de instalacion, sea expansion directa con amoniaco (dx-nh3). Estas instalaciones suelen presentar problemas de excesivo recalentamiento y altisimas temperaturas del gas de retorno.
Comunmente , los evaporadores debieran ser alimentados por una bomba desde una estacion de recirculacion que incluye un acumulador de succion.
This reminded me of something...If you use an accumulator in your system design, why not add some pumps and change the coils to liquid overfeed?Quote:
I find unusual your facility design, which is a direct expansion ammonia (NH3-dx). These facilities often have problems of excessive heating and very high (dangerous) temperature on return gas.
Typically, the six evaporators should be fed by a pump from a recirculation station that includes a suction accumulator.
Six evaporators is not very many and a lot of people would do exactly what Luis is doing. However, if you size the accumulator & pumps for the spray chiller + evaporators + some additional capacity you have a very nice system.;)
Thanks guys.
Your comments are very important for me but now i need to know how do i compute the accumulator (dimensions)?? somebody has some file or guide for that?????
Best regards.
Luis Sandoval.
Accumulator sizing is an art based on some science. ;)
You have to know what the actual volume flow of the suction vapor is first (Total compressor displacement is safe).
Then you need to know what the maximum allowable separation velocity is. This velocity is based on the maximum velocity at which a specific liquid particle will separate by gravity for a given diameter (& mass). This velocity will be valid for a narrow range of separating distances (flow distance from the liquid to the vessel outlet).
Volume flow / max. allowable velocity = vessel diameter
Then you need to calculate the vessel volume to ensure it will hold all of the liquid you think it will need to contain during any operational condition. The liquid holding volume will be below the separation distance for the particles to fall by gravity back down to the liquid.
Dear US Iceman
you said "Total compresor displacement is safe" but in this case i can't use this value because the accumulator only works with the coils ( 210741 kcal/h) but the compresor is sized for the total cooling load (coils + spray chiller 970000 Kcal/h) so i understand that volume flow of the suction vapor for size the accumulator will be of the coils. is this correct???
Yes you can. Using the compressor displacement will only make the vessel somewhat larger in diameter, than if you use only the evaporator coil capacity. This will make the vessel cost a little more, but it will not make any difference. In fact, the accumulator would have a little extra capacity to ensure the liquid does separate from the vapor.Quote:
Originally Posted by luissandoval
Concider a horizontal accumulator, as this will increase surface area and reduce surging and possilble carryover to compressor, base vessel volume to safely contain 50>70 % of system liquid charge, add a high level alarm as protection, oil drain and safety releif fittings, keep pipe loses in suction to compressor to 1'C or less, to ensure low velocity and reduce carryover.
magoo
That would work also. Just make sure the liquid level does not rise above 50% of the vessel diameter (with the surge volume) since the separation height decreases rapidly with an increase in liquid level.Quote:
Originally Posted by Magoo
Estas en lo cierto Luis. No hay que inventar la rueda.Quote:
Originally Posted by luissandoval
Usando tablas de diseño Mycom llegue estos datos para su Acumulador de Succion:
Using tables of data Mycom for Suction Accumulator:
- Only Evaporators> M3/HR: 270 > 406 Dia x 1200 mm H > You could use 20 "Dia size.
- Entire system> M3/HR: 1200 > 812Dia x 2000 mm H >W´d be 2 times diameter higher.
Dimensions in milimeter except where shown inches
Thanks Josei, could you send your tables of mycom please?? i want to see more specificactions like Height and connections. I hope that you can help me.
Best Regards
Luis Sandoval.