LPG Reticulated System design.

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MSDBD
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LPG Reticulated System design.

#1 Post by MSDBD » Sat Nov 28, 2020 8:15 pm

Dear Experts,

Please help me to get the solution for LPG reticulated system of my Building.

We are going to install a 900/1000 Liter LPG storage Tank in our apartment. It’s a 7 storied Building having 28 nos. of residential Flats. We are going to supply the gases 9only for cooking purpose) to each flat through piping network from the storage tank.

1) Each Flat use a double burner LPG stove of rating = 3.6KW / 3.6KW. Consider all flats use same brand & same rating stoves.
2) LPG tank capacity 900 to 1000-liter liquid LPG. Inner diameter of the tank = 1.2meter, Height = 1.8 meter.
3) Our LPG is 30% Propane and 70% Butane. Consider the Ambient Temperature is = 25 degree centigrade.

My Question:
If all the 28 flats start using their LPG stove at the same time (say for 1 hour), Is it possible for the tank to supply the required gases to all those 28 stoves by using its natural vaporizing capacity? Or we have to use an extra vaporizer to supply the gases to all stoves simultaneously without any trouble.


Please provide calculations if there any.

Brian_H
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Re: LPG Reticulated System design.

#2 Post by Brian_H » Sat Nov 28, 2020 8:19 pm

I'm not too sure your going to get the answer to what your asking here, this forum is mostly concerned with LPG use on vehicles rather than domestic use. That may not be too clear from the forum name though.

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Re: LPG Reticulated System design.

#3 Post by Gilbertd » Sat Nov 28, 2020 8:20 pm

You're probably asking in the wrong place as this forum is for people running motor vehicles on LPG. However, someone may have an answer for you. I would have thought the only thing you would need to take into account would be the size of the outlet and pipe from the tank so it can deliver sufficient vapour when needed but that is only a guess I'm afraid.
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MSDBD
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Re: LPG Reticulated System design.

#4 Post by MSDBD » Sun Nov 29, 2020 10:22 am

Please suggest me related discussion forum to get my answers.

Dear Gilbertd, thanks for your comment -"the size of the outlet and pipe from the tank" might be the the solution.

Pinger
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Re: LPG Reticulated System design.

#5 Post by Pinger » Sun Nov 29, 2020 11:53 am

Work back from how much gas is required for each stove (research calorific value of propane/butane mix and calculate quantity required to support 3.6kW) then multiply by 28. That should then give a start point in mass wrt to unit time eg, kg/s which can be converted to litres (or cubic metres) per unit time (minutes or seconds) if appropriate.

Take that and dig into latent heat of evaporation data at specific temperatures for intended gas mix. The geometry of the tank will be a factor (re surface area of liquid gas exposed to heat). With the consumption of all 28 burners known though it should be possible (I'd have thought) for your tank supplier to advise if it can vaporise sufficiently quickly to supply demand.
If you have at any point to refer to domestic mains gas pressure, in the UK it is 21 mbar (0.021 bar).

Incidentally, in India 125cc motorcycles (circa 7.5kW) can be made to run from vapour alone from 15kg (or smaller) gas bottles. Forklifts (in very cold warehouses) as far as I know run straight from vapour.
28 x 3.6kW = 100kW (134hp). Given an engine has circa 25% efficiency, the flow rate you require is the same as a 25kW (34hp) engine would need. Intuitively - given the relative tank sizes - I'd wager what you propose is viable.
Intuitively, I might imagine the gas supply pressure to vary over the height of the building - unless each stove has its own pressure regulator and you can feed at a higher pressure. This may be necessary to achieve the required flow rate anyway. As Gilbert.d alluded - pipe diameters will have an effect - more so with low pressure.

Pursuing research along the lines of the above will likely lead you to forum/discussion groups that can help. They will be quite specific so narrowing down specific questions will help. Once you have established the flow rate - ask your tank supplier before going any further. The answer may be there already.

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Re: LPG Reticulated System design.

#6 Post by LPGC » Sun Nov 29, 2020 3:28 pm

This is the wrong place to be asking, as others have said this is a vehicle LPG conversion forum....

Coming from a vehicle LPG conversion background I'd approach this question in a way related to vehicles that I'm familiar with:

3.6kw is around 4.8bhp. 28 x 4.8bhp = 134.4bhp. Even a much smaller tank (vehicle size tank, say 80 litres capacity) could maintain tank pressure in 25degC conditions if supplying a constant 134.4bhp.

The difference between vehicle tanks and vapour tanks is that on vehicle tanks liquid gas is drawn, whereas in vapour tanks vapour is drawn. Drawing vapour from the tank will have twice as much cooling effect on the tank as drawing liquid, so that 134.4bhp becomes the equivalent of 268.8bhp but the tank is many times larger than the example 80L tank I mentioned above - the bigger the tank the bigger the heat sink so bigger tanks don't get as cold for same gas output. Twice the cooling effect on vapour tanks because on vapour tanks all the gas that is used has to boil in the tank and as the level of liquid gas goes down even more gas (the same amount as that which is used) has to boil in the tank to maintain tank pressure. it's the boiling that has the cooling effect on the tank and it's the cooling effect that lowers tank pressure. On liquid gas take off tanks there's only half the cooling effect of drawing vapour because the gas that is used cools something other than the tank down, the only cooling effect on the tank from drawing liquid is that as liquid level in the tank falls the headroom of vapour space increases so some of the liquid in the tank has to be boil to maintain tank pressure.
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Re: LPG Reticulated System design.

#7 Post by Pinger » Sun Nov 29, 2020 3:56 pm

EDIT: REVISED.

Thrown this across a calculator and the rough figures are:

To fuel 28 x 3.6kW stoves requires a gas mass flow of 0.002kg/s.
The latent heat of evaporation for your 30:70 propane: butane mix is 398.6kJ/kg.
Thus, 0.8kJ/s of heat is required to evaporate the liquid to gas to meet the stoves' requirements.
This is as far as I can take this. From here you are in the realm of heat transference from surroundings to the bulk liquid. Unless your tank supplier has appropriate data.

If you intend using the above figures I strongly recommend that you check them for errors. The energy density values for propane and butane (in MJ/kg form) can be found online, ditto the latent heat of evaporation values (in J/kg form).

EDIT.
Note revised figures since first posting (the above is now for 28 x stoves, not just one as previously).

NB: '0.8kJ/s of heat' is 0.8kW.

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