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LPG Reticulated System

11/18/2020 3:53 AM

Dear Experts,

We are going to install a 450 Kg (846 Liter) LPG storage Tank in our apartment. Its a 7 storied Building having 28 nos. of residential Flats. Each flat use double burner cooking stove. We are going to construct a piping network using required valves, regulators, gauges, etc. to supply the gases to each flat with individual meter.

I'm not a Mechanical engineer and have little knowledge about the reticulated system.

Usually the household cylinders vaporize the gas naturally by utilizing ambient temperature and the natural vaporization has its own limit. In our case, we are going to use a 450 Kg tank for 28 nos. of flats and as per my understanding, natural vaporization of our tank (Inner diameter=1 meter) would not be enough to supply the gases to all 28 flats simultaneously. My questions is:

1) Do we need to use extra vaporizer with the tank ? If yes, how to select a cost effective solution ? What would be the ratings of the vaporizer ?

2) If we don't use extra vaporizer, In how many flats we can supply the gas depending on natural vaporization of 450 kg tank ? ( Our LPG is 30 % Propane and 70% Butane) considering the ambient temperature 30 to 35 degree centigrade.

Please provide the calculations if there any for my 2nd question.

Thanks in advance.

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#1

Re: LPG Reticulated System

11/18/2020 4:06 AM

This forum is not the route to carrying out a detailed design. It is better to engage a local Process Engineer into the <...We...> to size the <...vaporizer...>, as this individual will have familiarity with practices, standards and in particular the safety features applicable at this particular location. This individual will need to have pressures and temperatures to hand as these are fundamental to its sizing, as are the rates of consumption of the <...LPG...> in answer to the second question.

The source of heat for the <...vaporizer...> is also fundamental to the selection and sizing; this has been withheld from the forum.

The intended supplier(s) of the <...LPG...> is/are (a) good sources of information, assuming their telephone numbers are to hand. Make some calls.

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#3
In reply to #1

Re: LPG Reticulated System

11/19/2020 12:13 AM

I've done zero calculations, but if his ambient temperatures are in the 30-35°C range, I'd think ambient heat would be pretty adequate. With the fuel already that warm, it shouldn't take much energy to vaporize it. That's obviously in the tropics.

On the other hand, with 56 burners all running at once, that could consume quite a bit of fuel, and the evaporation of that fuel will cool the remaining liquid. I've seen a similar size tank with pure propane where the level of liquid was really obvious, because of frost forming on the part of the tank in contact with the liquid. Of course this was certainly NOT with an ambient temperature in the 30's. A 450kg tank sounds a bit small to me.

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#4
In reply to #3

Re: LPG Reticulated System

11/19/2020 4:12 AM

It's always good practice to talk to someone who has done it before, and learn from that individual's experiences. It's certainly cheaper than making one's own mistakes.

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#5
In reply to #4

Re: LPG Reticulated System

11/19/2020 11:28 AM

Absolutely!

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#6
In reply to #3

Re: LPG Reticulated System

11/22/2020 4:28 PM

Dear dkwarner,

Would you please help me to get clear idea about the requirement of extra vaporizer? Or the calculations if there any?

As I said total 28 flats in the building and each flat use double burner stove with a rating 3.4KW/3.4KW (all are of same brand & model). Our proposed tank's internal diameter is 1.2 meter.

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#7
In reply to #6

Re: LPG Reticulated System

11/23/2020 12:25 AM

I'll try...

When any liquid evaporates, those atoms/molecules that leave the liquid to become vapor are some of the higher energy ones. Higher energy implies higher temperature and higher velocity, which is why they are able to escape from the liquid. Thus those molecules that have yet to evaporate (the remaining liquid) are effectively cooled by the loss of the hotter molecules that left as vapor.

In my climate (Northern California, 600m above sea level), it's common for the ambient temperature to be near freezing. Of course when the outside temperature is near freezing, people are heating their houses. The least expensive form of heat here is LPG, usually just propane (No natural gas available in our small foothills community). so propane tanks are very common. If people are using propane (or any LPG) to heat and/or cook, they are removing the vapor from the top of the tank, thus removing the warmer vapor molecules, and the remaining liquid is cooled.

Since the propane was initially at ambient near freezing, the remaining liaquid is cooled below freezing, so frost forms on the outside of the tank, but only where there is liquid in contact with the metal. This frost is quite visible, showing white frost below the liquid surface, and the tank's painted color above that surface.

In your climate, you will probably never see this phenomenon, but the cooling still occurs. As the liquid cools, the remaining liquid consists of the slower moving molecules, which don't evaporate as easily as the faster ones did, leading to a lowered vapor pressure. When many people try to use the fuel at the same time, they lower the pressure further, cooling the remaining liquid even further, and that fiurther cooling makes it even slower for the liquid to evaporate. If enough people try to use the fuel at the same time, the pressure will fall so low that the vapor can't flow fast enough to the various burners, and they can't cook or heat.

If that happens, then the cold liquid in the tank must somehow be warmed enough for it to be able to evaporate at the needed rate. With an ambient temperature in the 30's(°C) I presume no one is trying to heat their living spaces, so the only gas that would be needed would be for cooking, as implied by your 2 burners per household, and possibly for water heating.

I have no knowledge of the amount of flow required by the 56 burners, so I really don't know whether the ambient air would provide enough heat to vaporize the required amount of fuel.

There will also be some variation depending on the size, shape, and orientation of the tank. In our home, we use propane for space and water heating, but use electricity (Induction) for cooking. We also burn wood for a significant portion of our space heating, which of course reduces the amount of propane required. Our propane tank, serving nothing but our home, has a capacity of 760 liters, so a 450 liter tank for 28 units sounds terribly small to me. On the other hand, we have our tank filled between 3 and 4 times a year; your little tank is going to require filling much more frequently.

The common fixed propane tank here is a cylinder with hemispherical ends, usually mounted with the tank axis horizontal. I have seen a few with the tank axis vertical, but a vertical orientation will have a smaller liquid surface area, so less evaporation, and should be avoided.

I hope this helps!

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#2

Re: LPG Reticulated System

11/18/2020 4:12 PM
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