Does anybody have any experience with these? Got a shot at a job, passed assessment and will be given an extensive amount of training, all on full pay .
Just to satisfy my own curiosity exactly how does it work, obviously itâs not a simple vent system, even I can grasp that.
As far as I can imagine youâve got liquefied gas sat in the bottom of the tank, with gas filling your ullage (spelling?) space, and as the tank is emptied something is pushed through? Fresh air? Inert gas? To balance out what your removing so it doesnât fold.
Would appreciate any knowledge some of you may have, having a chat with the TM he said it took him a while to actually wrap his head around it, but thereâs heaps of classroom and practical training before they even consider letting you loose.
Alant:
It will depend which gas you will be dealing with ie flammable are totally different to cryogenic etc
Flamables, no cryogenic work. The load I had on was a butane mix, couldnât tell you what it was mixed with, regret not writing down the UN number now. A lot of work will be in to aresol factorys, deodorant and similar apparently.
fridger:
Does anybody have any experience with these? Got a shot at a job, passed assessment and will be given an extensive amount of training, all on full pay .
Just to satisfy my own curiosity exactly how does it work, obviously itâs not a simple vent system, even I can grasp that.
As far as I can imagine youâve got liquefied gas sat in the bottom of the tank, with gas filling your ullage (spelling?) space, and as the tank is emptied something is pushed through? Fresh air? Inert gas? To balance out what your removing so it doesnât fold.
Would appreciate any knowledge some of you may have, having a chat with the TM he said it took him a while to actually wrap his head around it, but thereâs heaps of classroom and practical training before they even consider letting you loose.
Apologies for the amount of waffle!
Hi fridger,
Without the name of the actual gas involved and going from your mention of âliquefied gasâ my guessed answer is that the system used will probably be the vapour balance system that you learned on your ADR course.
If my guess is correct, the idea of that is that the pressure in the two tanks is balanced by a vapour balance system, so the pressure in the two vessels is the same during discharge. Iâll get you to imaging two snorkels that reach from high in the vapour space of both vessels to the outside, then simply connecting them together using a vapour (pressure) balance pipe.
Product is then pumped from the delivery vessel to the receiving vessel, whilst the slight drop in pressure in the delivering vessel is balanced out by the slight raise in pressure in the receiving vessel swopping places with each other.
Mystic Dave says⌠The answer to your next question is that the liquefied gas gets into the pump by gravity.
Alant:
It will depend which gas you will be dealing with ie flammable are totally different to cryogenic etc
Flamables, no cryogenic work. The load I had on was a butane mix, couldnât tell you what it was mixed with, regret not writing down the UN number now. A lot of work will be in to aresol factorys, deodorant and similar apparently.
Hi fridger,
It seems that Alant had the same wonderment that I did.
Now that youâve given a substance name, my next guess is that what you were carrying wasâŚ
UN 1965 HYDROCARBON GAS MIXTURE, LIQUEFIED, N.O.S., (PROPANE and BUTANE), 2.1
However, there are other aerosol propellant gases and mixtures of gases.
In this situation, is the aim not to equalise the pressure in each tank so as not to cause a vacuum implosion? So it is not the ullage room as such that is important, but as the new product is piped into storage it is replaced with residual vapour piped back from storage tank?
When it does not go to planâŚyoutu.be/6hP0L1hqnPM
Thanks for that Dave, only done liquid before, so the idea of tipping gas sounds a bit like witch craft to me.
I was pleasantly surprised in the difference between how a trailer full of gas handles compared to liquid, Iâm guessing the pressure involved slows some of the motion.
A lot of âliquified â gas is actually pumped off.
If the gas is liquified with pressure, than the liquid will actually expand while the pressure reduce, turning liquid into gas.
The creation of a vacuum will never occur as the pump cannot pump gas, only liquid.
It can be either off loaded by a vehicle mounted pump (as LPG) or a factory side pump.
( a bit how you fuel a car LPG tank up)
A lot of nitrogen can get off loaded by balancing the pressure in the receiver tank, with the delivery tank. ( a bit how you fill a gas lighter from a can)
Assume that the receiver tank is empty and atmospheric, and your delivery tank is 100 bar, the product would go to the atmospheric tank until the pressure balance out, than you start the pump and empty the remainder out.
You will never go below atmospheric pressure as the liquid in the delivery tank turn to gas by the lower pressure and your pump stops working.
Depends on the liquid gas but a lot of tanks are transferred by pressure. Higher pressure in the tanker and a lower pressure in the receiver tank, the two pressures will equalise and when this happens the liquid gas is in a vapour, to get the vapour out which can be a lot of product, you use a compressor to pump the vapour into a liquid. A compressor cannot compress a liquid only a vapour. The vapour is then transferred from the tanker into the receiver. Your pressure gauges then tell you when your empty. It is called vapour recovery. A procedure I have carried out many times. A pump is of no use with gas.
Janos:
In this situation, is the aim not to equalise the pressure in each tank so as not to cause a vacuum implosion? So it is not the ullage room as such that is important, but as the new product is piped into storage it is replaced with residual vapour piped back from storage tank?
When it does not go to planâŚyoutu.be/6hP0L1hqnPM
Hi Janos,
Yes, the blue part is exactly what I described, youâve just said it differently, but equally correct.
With the substance in question, pressures are equalised first (leaving the vapour balance pipe connected) then setting the pump to work.
The part you wrote about implosion normally applies more to liquids when both tanks are at atmospheric pressure, because an implosion would happen much sooner in the process than when compared to shifting a liquefied pressurised gas. The principle is broadly similar though.
Thatâs why you pump liquified gas out, LPG tankers donât do vapour recovery, as they reload with the same product.
You are correct that you canât pump gas, but you can certainly liquified gas, what is just a liquid.
Thatâs why you pump liquified gas out, LPG tankers donât do vapour recovery, as they reload with the same product.
You are correct that you canât pump gas, but you can certainly liquified gas, what is just a liquid.
Yes if your reloading with the same liquid gas then you can leave the vapour as you say. I have some videos showing this process, liquid transfer under pressure then vapour recovery to empty the tank. We transfer mainly refrigerant gases but was doing cyanide hydrogen with same process. We vapour recover purely to get every drop out as it is expensive to leave.
Regarding compressors, you wouldnât really want to pump air = Oxygen into a flammable gas, would you?
Also on inert gasses you would contaminate the product by blowing compressed air into the tank.
The problem with gas, even in liquid form, it mixes very easy with other gasses, like oxygen, and there is always gas above the liquid, regardless how high the pressure is, or how cold it is to turn into a liquid.
Alant:
It will depend which gas you will be dealing with ie flammable are totally different to cryogenic etc
Flamables, no cryogenic work. The load I had on was a butane mix, couldnât tell you what it was mixed with, regret not writing down the UN number now. A lot of work will be in to aresol factorys, deodorant and similar apparently.
Hi fridger,
How was my guess at UN 1965 (above,) does that sound familiar?
Anyway and just to avoid any confusion, the process being discussed by UKtramp and caledoniandream, is also correct, but doesnât apply in your case.
Thatâs not to knock either of them BTW, itâs just so you donât end up befuddled with lots of extra info thatâs not applicable to the job you described.
caledoniandream:
Regarding compressors, you wouldnât really want to pump air = Oxygen into a flammable gas, would you?
Also on inert gasses you would contaminate the product by blowing compressed air into the tank.
The problem with gas, even in liquid form, it mixes very easy with other gasses, like oxygen, and there is always gas above the liquid, regardless how high the pressure is, or how cold it is to turn into a liquid.
The compressor doesnât introduce air, it compresses the vapour and pumps it as a high pressure gas, no air involved. Its how refrigerant gasses are pumped, they are special compressors not ordinary types, they are sealed units, air in a refrigeration system would cause havoc with both moisture and high discharge pressures. However when we pump cyanide gas we always pump nitrogen through the system to purge all of this gas. Gas turns into liquid at pressure, for example if you keep ammonia under pressure it stays as a liquid, as soon as you get an air leak and it hits atmospheric pressure it comes out of solution and immediately gases. I transfer various gases on a daily basis and by keeping them pure is the only way to do the job properly. You do not cross contaminate or introduce air in any circumstances.
Alant:
It will depend which gas you will be dealing with ie flammable are totally different to cryogenic etc
Flamables, no cryogenic work. The load I had on was a butane mix, couldnât tell you what it was mixed with, regret not writing down the UN number now. A lot of work will be in to aresol factorys, deodorant and similar apparently.
Hi fridger,
How was my guess at UN 1965 (above,) does that sound familiar?
Anyway and just to avoid any confusion, the process being discussed by UKtramp and caledoniandream, is also correct, but doesnât apply in your case.
Thatâs not to knock either of them BTW, itâs just so you donât end up befuddled with lots of extra info thatâs not applicable to the job you described.
as already said it really does depend on which gases your dealing with. My cases are either refrigerants or toxic pharmaceutical industrial gases. I would be interested to know what gas your dealing with and how it is transferred though. I enjoy threads like this as it is educational and interesting.
fridger:
Thanks for that Dave, only done liquid before, so the idea of tipping gas sounds a bit like witch craft to me.
I was pleasantly surprised in the difference between how a trailer full of gas handles compared to liquid, Iâm guessing the pressure involved slows some of the motion.
Sounds like youâre confusing yourself fella . You should get comprehensive training which will explain everything , follow the rules and donât cut corners , youâll be fine . Who are you on with ?
Thanks for the insight chaps/ladies, itâs the kind of thing that never crossed my mind before, gas that is, and how it all works. Even if itâs not specific to my job still interesting to read about your own experiences uktramp and caladonin.
Diesel dave I would love to say I recognise the UN number but I would just be nodding and smiling.
So if Iâm beginning to understand, because a loaded trailer is pressurised, and your using a vapour recapture system, as product is moved from one tank to another the product is expanding in to a gas as your tipping, as well as vapour coming back in to the trailer via recapture system, all while stay above atmospheric pressure untill pretty much empty, save any remaining vapour.
So my original question about what is replacing the gas as you tip a load is redundant, because itâs nothing like tipping a regular liquid tank eg. Milk water or something not requiring vapour recapture.
Unless iv completely missed the point and should have tried harder in schoolâŚ
.
Thatâs not to knock either of them BTW, itâs just so you donât end up befuddled with lots of extra info thatâs not applicable to the job you described.