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nsc
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Propane Chiller

09/05/2011 8:26 AM

Hi Everyone,

I want to understand more about the temperature control by the Level of inlet propane to shell side of chiller. There is natural gas in tube side of chiller. When fluid outlet temperature will rise, what is happening? Propane level will increase or decrease and vice versa?

Best regards.
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PWSlack
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#1

Re: Propane Chiller

09/05/2011 9:46 AM

One sentece with no numbers and two follow-up questions isn't really enough to go on. Try the Process Description document at the facility instead.

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nsc
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#4
In reply to #1

Re: Propane Chiller

09/06/2011 1:11 AM
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nsc
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#5
In reply to #1

Re: Propane Chiller

09/06/2011 1:46 AM

Hi again!

propane as coolant is entered to shell side (its condition before Level control valve is 7.62 deg C and 20.18 barg) and is vaporized at outlet (at -17.2 deg C and 2.56 barg). Natural gas is entered to tube side (at -6 deg C and 48.9 barg) and is cooled at outlet ( -14.6 deg C and 47.83 barg). I whant to know that when Natural gas outlet temperature is raised Level control valve will be more open or more close? why?
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pritam
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#2

Re: Propane Chiller

09/05/2011 12:11 PM

I think propane is refrigerant and natural gas on tube side is to be cooled. Liquid propane may always flood tubes, so controlling its level to control outlet temp of natural gas is not a good idea, it can roughly control. Better way to control is compressor load to vary propane flow rate.
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pritam
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#6
In reply to #2

Re: Propane Chiller

09/06/2011 1:58 AM

When fluid outlet temperature will rise, what is happening? Propane level will increase or decrease and vice versa?

I missed to answer this question in my previous comment #2. When fluid outlet temperature will rise, propane level will decrease. In fact it is other way round, when propane level will decrease fluid outlet temperature will rise. Because here propane level is cause and effect is fluid outlet temperature. More level means more heat transfer surface, so more cooling.
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nsc
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#7
In reply to #6

Re: Propane Chiller

09/06/2011 2:24 AM

Hi paritam

thanks for your attention

what kind of heat transfer is your purpose? Latent heat of vaporization or sensible heat transfer? By increasing propane level, infact there is more surface area for sensible heat and so there is lower surface area for latent heat of vaporization. It seams by increasing the level of propane in shell side, heat transfer rate is decreased ( As you know, latent heat of vaporization is 10 times more than sensible heat). Is it true?
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pritam
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#8
In reply to #7

Re: Propane Chiller

09/06/2011 8:09 AM

"what kind of heat transfer is your purpose?"

Definitely I mean latent heat transfer. In refrigeration system at condenser and evaporator (or chiller) refrigerant fluid undergoes phase change, so it's mainly latent heat transfer.

"By increasing propane level, in fact there is more surface area for sensible heat and so there is lower surface area for latent heat of vaporization. It seams by increasing the level of propane in shell side, heat transfer rate is decreased. Is it true?"

No, it's not true. By increasing propane level, more number of rows of tubes will be submerged. Latent heat transfer is possible mainly on submerged tubes because liquid propane should receive heat from natural gas flowing through the tubes. More number of submerged tubes means more surface area for latent heat of vaporization. In fact sensible heat transfer is mainly taking place where tubes are not submerged with propane liquid and it is negligible compared to latent.
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nsc
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#9
In reply to #8

Re: Propane Chiller

09/06/2011 8:53 AM

What is your view about subcooling condition? Assume that a condenser that propane saturated vapor entered to shell side of condenser and saturated liquid is exited from other side. If level of produced propane condensate in shell be increased, latent heat of vaporization will be increased or decreased?
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pradeep44
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#10
In reply to #9

Re: Propane Chiller

09/06/2011 11:26 AM

"latent heat of vaporization will be increased or decreased?" Latent heat of vaporization is a property of fluid, and it will not change with level. The change will be rate of vaporization.Even in sub-cooled condition, if level of produced propane condensate in shell be increased, rate of vaporization will be increased until all the tubes are submerged. After all the tubes are submerged, latent heat transfer rate will not increase even though level is further increased.
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Tornado
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#3

Re: Propane Chiller

09/05/2011 2:39 PM

Lower level of liquid propane in the shell equals less heat exchange area equals less cooling of the natural gas in the tubes.

For a single compressor on a single chiller, Pritam's suggestion would probably work better. With multiple chillers, each chiller may need its own control. This could be done by liquid level, as nsc describes; a back-pressure regulator on the propane vapor leaving the chiller might be even better.

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betomachine
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#11

Re: Propane Chiller

09/06/2011 12:22 PM

Temperature should be controlled, if possible, by the load setting on the compressor(s). Your chiller tubes should operate always submerged by saturated propane and should operate on a local level control. As the flow rate of the natural gas increases (or inlet temperature increases), the compressor will load up and in turn drop the vapor pressure in the chiller, which will cause the propane to boil away, which will cause the level controller to open and feed more propane to the chiller. This will cascade up through the economizer (if present it should also be on level control and fed by the accumulator) and condenser.

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betomachine (1); nsc (4); pradeep44 (1); pritam (3); PWSlack (1); Tornado (1)

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