7 replies to this topic

[Sridhar P]

Does water freeze in tanks where the ambient temperature(Dry bulb) goes below 0 deg C.(wet bulb definitely will go below 0 deg C)

But, I have seen plants in Jordan, where water tanks are not provided with heater arrangment and where ambient temperature goes below 0 deg C Dry bulb.

Is that water freezing in tanks is not that much easier.

Pl. share your experience.

[gvdlans]

Of course water will freeze if it is subject to temperatures below 0°C, BUT the time required to freeze a large volume of water may exceed the time span that the ambient temperatures are below 0°C.

Especially in Jordan I would expect that freezing temperatures only occur for a short period of time (e.g. a few hours during the night).

Even in Norway it is not required to provide heat tracing or even insulation on pipes containing stagnant water if the line size is more than 10 inch (see NORSOK P-001 standard, chapter 7).

Edited by gvdlans, 05 November 2009 - 08:21 AM.

[Sridhar P]

Dear Sir,

NORSOK P-001 standard gives clearly the heat tracing requirment. Thanks.

However for stagnant water in small pipe lines can you provide some reference on the calculation for the time required for water to freeze.

[Qalander (Chem)]

Truly it is the

surface area 'exposed to' or 'remains in-contact' with below 0 C temperature and

rate of heat transfer, U across that surface area

including the 'time required to affect the freezing' of water bulk

Hence the outcome varies at times greatly and a general consensus observation becomes difficult.

Just to somewhat elaborate on the guidoo's above post. Hope proves useful!

[kkala]

I agree with gvdlans that "the time required to freeze a large volume of water may exceed the time span that the ambient temperatures are below 0°C". A good parameter for checking risk of water freezing is the "average one day mean temperature", often found (or estimated) in local climatic data. Of course a strictly quantitative approach would require rather complex heat tranfer analysis (see note by Qualander).
If water partially freezes in a tank, it will go to the surface with probably no damage, more risk is involved in the water piping that can be broken by internal ice formation.
In Greece average ambient temperature is about 15 C, and very rarely "average one day mean temperature" gets about 0 C or lower. During this cold time above ground water pipes to departments can be broken, if water is stagnant. The risk is practically eliminated by letting some water flow out of a tap.
I was working in the Salonica Fertilizer Plant in winter 1979-80, when such cold time lasted unexpectedly long (that is few days). The plant had installed no winterizing measures, so only water purging (small continuous rate) to sewers was applied. No relevant "accident" occurred.

[Qalander (Chem)]

I agree with gvdlans that "the time required to freeze a large volume of water may exceed the time span that the ambient temperatures are below 0°C". A good parameter for checking risk of water freezing is the "average one day mean temperature", often found (or estimated) in local climatic data. Of course a strictly quantitative approach would require rather complex heat tranfer analysis (see note by Qualander).
If water partially freezes in a tank, it will go to the surface with probably no damage, more risk is involved in the water piping that can be broken by internal ice formation.
In Greece average ambient temperature is about 15 C, and very rarely "average one day mean temperature" gets about 0 C or lower. During this cold time above ground water pipes to departments can be broken, if water is stagnant. The risk is practically eliminated by letting some water flow out of a tap.
I was working in the Salonica Fertilizer Plant in winter 1979-80, when such cold time lasted unexpectedly long (that is few days). The plant had installed no winterizing measures, so only water purging (small continuous rate) to sewers was applied. No relevant "accident" occurred.

Thanks Dear kkala, For this valuable practical update indeed.

However as regards frozen water(Ice) behaviour inside petroleaum storage tanks,

I feel the raising to surface of formed Ice May or May not take place as per stored product

(1) specific gravity in comparision to the ice ,

(2)Viscosity of the stored product permitting it to raise,

(3)any waxy materials getting solidified and also raising to the surface& getting co-mingled.

If such a situation does occur and no internal bed coil heating etc.,Exterior insulation is available.

We might be leading towards a complicated& Challenging situation indeed.

Other experienced forum colleagues who might have witnessed such circumstance physically may throw light in even better way,I believe.

Hope it is not cosidered as 'spewing of rubbish' by some colleagues and proves helpful.

[djack77494]

Under severe weather, water in tanks can freeze. The more mass present, the more difficult it is to get freezing. When freezing does occur, however, I would say that the water at the surface begins freezing first. This is followed by water near the tank walls freezing. To actually freeze the entire contents of anything but a very small tank will take a lot of time at subfreezing conditions. Even if the air temperature is below freezing, solar radiation emanating from the warmed walls will act to impede freezing. Finally consider that the floor of the tank is probably near the annual average temperature. Unless you're in an Artic climate, that is typically very far from freezing. During cold weather conditions, heat would be continuously flowing from the ground into the tank contents.

[kkala]

In the discussion of 6th Dec 09, I considered tanks full of water. Oil tanks usually contain a small amount of water under normal conditions (say 0.1% or 0.2% w/w), which can substantially increase if they accept products of washing, slops, etc. Tank liquid temperature has a big inertia, eliminating upper and low peaks of ambient temperature and approaching a smoothed "average", smoother than average one day mean temperature (tanks of 5000 - 100000 m3, info from operators, seems logical).
Concerning water in suspension, it is quite improbable to freeze, even if ambient temperature is below zero for one day or more. Wax solidification is a more probable event, I think.
Concerning water having settled in the tank bottom items and being stagnant (boot, drain, suction line), the risk of freeze is higher. There are measures against it (probably described in mentioned Norsok standards). I cannot remember such measures in Southern Greece, they are probably applicable at colder regions.