6 replies to this topic

[tsrc8204]

Dear all,

Now I am designing a vaporizing process for process purging. For cost saving, I would like to apply the gravity flow for fluid flow between the liquefied propylene receiver and vaporizer. But I don't know What is the velocity for the gravity flow? if the demand of vaporized gas is 600kg/hr. Also, if I rate a 3" piping for liquid charge, is it enough for process demand?? please give some comments thank you.

Process data: receiver pressure 16kg/cm2.G @ 25 degree C (liquid)
vaporizer (kettle type) pressure 15kg/cm2.G @ 55 degree C (gas)
height difference between receiver and vaporizer is 1.5~2.0M


tsrc8204.

[Art Montemayor]

tsrc8204:

Please provide us with a clear and detailed sketch of what your vaporizer process looks like. It is difficult to visualize exactly what you intend to pipe up. A "receiver" is usually not a feed tank for a vaporizer.

How do you intend to feed the vaporizer by gravity? Do you intend to employ a self-venting pipe? Or do you intend to equalize both vessels? Please be specific.

[tsrc8204]

Dear Art,

Good to hear your response again. Attached is the simple shetch for my design case in my plant, for you further review.

Sorry, I can't unload this word file to forum, I will send it to your message box later.

tsrc8204

Edited by tsrc8204, 16 November 2009 - 09:14 PM.

[tsrc8204]

Dear all,

The drawing was unloaded and attached.

tsrc8204.

Attached Files

•  Simple PFD.doc   372.5KB   106 downloads

[Art Montemayor]

tsrc8204:

Thank you for process sketch. Now what you are trying to do starts to make more sense.

However, you still fail to be specific and detailed. You state that you are vaporizing Propylene (Propene). Your sketch shows what appears to be a total Propylene condenser (E-3701A) feeding a Receiver (D-3352) by gravity flow with an equalizer line. However, you fail to show the inlet stream (vapor?) into the total condenser. I have to assume that the condensed Propylene is saturated at the pressure you cite for the receiver, 16 kg/cm2G. Without knowing the true conditions, I have to assume that you are producing saturated, condensed Propylene. If that is the case (which I suspect is true), then the Propylene in the receiver has to be at 11.8 kg/cm2A if it has a temperature of 25 oC. Yet you state that the receiver pressure is 16 kg/cm2.G. That may mean that the Propylene is not “pure”. What I am searching for is the density of the liquid fluid in the receiver in order to identify the height required for gravity flow. The temperature and pressure you cite for the vaporizer also does not match Propylene properties.

Your process sketch does not make logical sense for pure Propylene. You cannot use gravity flow and produce a superheated vapor in the vaporizer. A vaporizer is simply just that: a heating element that VAPORIZES. It produces a saturated vapor, not a superheated vapor. It only supplies latent heat of vaporization. Because it does that, it is usually supplied by gravity feed from a receiver vessel, with which it is connected by an equalization line. The pressure in the vaporizer is the same as the pressure in the receiver.

You should not worry or bother about the liquid velocity in the vaporizer supply line. Simply make that line big enough so that it does not create a restriction to easy flow. Yours is a very short line and you should keep the velocity down to a value of 3 to 5 ft/sec – maybe less.

My concern is that your process DOES NOT WORK as described by you and by your sketch. Perhaps you have a language problem and you mean to say “superheated” vapor, but still the process does not work the manner that you have depicted it. If you simply require saturated vapor, the process is very simple and straight-forward.

Check out your thermodynamic properties.

[tsrc8204]

Dear Art,



Thanks for your identification and comments. As you mentioned some fail points, I checked the drawing again and found that feed stream (noted as 7 on sketch) was lost; so I would try to describe more detailed in this vaporizing process even my English skill is not well. Now on details.



Firstly, we collected the vented gaseous mixtures from process area and its composition is 96% propylene, 2.5% propane, 1% (ethylene + CH4) and 0.5% hydrogen, so you are right it is not a pure propylene condition. Then this mixture will feed to partial condenser E-3701A (operating pressure is 16kg/cm2.G) for cooling/liquefying all C3 fraction under 2~6 degree C with chill water. Of course, ethylene and hydrogen will be vented from top through a control valve (see noted as 8 stream).

Due to the liquefied C3 mixture can be treated as LPG, so I designed a high pressure receiver D-3752 for liquid C3 storage temporarily. That is why I shown that condenser E-3701A located on top of D-3752 and liquid flow through the piping by gravity; and also added an equalizer line between these 2 devices. Here, my first concern is 2 inch piping for gravity flow is enough to 300kg (assume density is 500kg/m3) per hour? Do we need to add an equalizer line (1 or 2 inch) to ensure the gravity flow is smoothly in operation??



As the C3 vaporizing process, I thought if the liquefied process cab be work we will recover more vented gas, so my idea is to install a vaporizer or reboiler to heat the liquid C3 from 15kg/cm2 @25℃ to 15kg/cm2 @55℃ and then reducing the C3 vapor pressure to 1kg/cm2 for boiler burning. Of course, the heating source is low pressure steam (2.3~2.5kg/cm2.A). Here, my second concern is 2 or 3inch piping for liquid charge into reboiler via gravity flow is enough to 600~1000kg per hour(assume density is 500kg/m3)?? Or we need to install a pump for feeding??



Above is the process concept, I want to realize this design due to it has some benefit whether energy saves or CO2 reducing in chemical plant.

Please comment again!

tsrc8204

[Art Montemayor]

tsrc8204:

I would place an equalizer between any two vessel subjected to gravity flow.

What you are now telling us is that your feed to the receiver is really a mixture of propylene and propane. Therefore, we don’t know the real, actual vapor pressure properties of the mixture. You still fail to account for my basic question(s) regarding whether you have a saturated liquid or not.

You also have failed to state what is the pressure downstream of the vaporizer. Presumably, it is less than the 15 kg/cm2(g) and is being reduced down to 1.0 kg/cm2(g). If that is the case, then you should have a very simple application where you equalize the vaporizer with the receiver and allow the vapor formed in the vaporizer to be regulated down to 1.0 kg/cm2(g). One thing that you may have to confront is that there may be a concentration of propane in the vaporizer due to the lighter end (propylene) having a propensity for vaporizing out first.

I would not use a pump in the vaporizer system, unless I was forced to. This basic proposal should work very well with only gravity flow. But you should furnish ALL of the basic data involved, in order for us to furnish accurate, and detailed comments.