heating an oil tank.. not boiler related

[sxturbo]

hey all, so at work we have a contract to maintain some containerised gensets for an unmanned oil rig, with the contract we've inherited some design flaws as well, which we have overcome the majority now, however we had another one rear it's ugly head which we didn't think would be an issue.

from new and as designed, the gensets have there own 800 ltr oil tank, this is fabricated into the subframe of the containerised unit, in the tank is 2x 0.5 kw heaters, the heaters have a thermostat installed to switch off at 50 degrees c.

these gensets run an unmanned oil rig in the middle of the north sea and so there is 3x of them in total, and they run 24/7 for 3 weeks each on a rotational basis.

anyway, the oil is currently not getting up to temperature and is causing issues with the starting of the machines and they had a total blackout yesterday as 1 went down due to an air flap failure and the other 2x both failed to start due to them being so cold.

the heaters are on, however i believe they aren't powerful enough to counter the heat dissipation that 800 ltrs of oil in a steel uninsulated container has.

The heaters are always on, and there is no problem with that, but how do i calculate a larger heater (with the required associated upgrades to the wiring and MCB) to take into account the heat loss

 

[Terrywookfit]

Contact the manufacturer who designed the unit.

 

[sxturbo]

Contact the manufacturer who designed the unit.

the genset you mean?

went bust 15 years ago

it was a bespoke design specific to the rig owners requirements.

 

[Terrywookfit]

Insulating the tank would be the obvious solution. Is it fuel or coolant.

 

[SFK]

SXTurbo,
Following is in imperial units, but this has heat loss details for a tank and its walls
.
As yours is oil (not water) I think you might also have to consider 'specific heating capacity'.
https://industrialheatingsystems.com/How-calculate-heat-loss.html
and
https://www.engineeringtoolbox.com/heat-loss-open-water-tanks-d_286.html
and
https://www.spiraxsarco.com/learn-a...transfer/energy-consumption-of-tanks-and-vats
SFK

 

[sxturbo]

this is the tank, its the width of the skid.

this pic is with the canopy and engine HVAC system removed (engine is air cooled), this all covers the tank and is stainless steel.

the skid sits in a recess on the oil rig, so it is not possible to insulate the tank.

the tank is filled with engine oil and is part of the dry sump system for the engine

 

[sxturbo]

SXTurbo,
Following is in imperial units, but this has heat loss details for a tank and its walls
.
As yours is oil (not water) I think you might also have to consider 'specific heating capacity'.
https://industrialheatingsystems.com/How-calculate-heat-loss.html
and
https://www.engineeringtoolbox.com/heat-loss-open-water-tanks-d_286.html
and
https://www.spiraxsarco.com/learn-a...transfer/energy-consumption-of-tanks-and-vats
SFK

perfect thats great thanks,

i know has half the heat loss than water supposedly

 

[SFK]

SXTurbo
Those skids are going to act as very efficient heat sinks.
I provides some maths above.

BUT I would consider (esp as it is cold at the moment), heating the oil to a know temp in your wearhouse.
Put in several computer monitored thermo couples (in teh oil, on teh frame and in the air).
Put the whole structure outside in the cold and monitor rate of cooling, both with and without heat being applied.

If possible do this with full, 3/4, 1/2 and 1/4 full tanks.

SFK

 

[sxturbo]

SXTurbo
Those skids are going to act as very efficient heat sinks.
I provides some maths above.

BUT I would consider (esp as it is cold at the moment), heating the oil to a know temp in your wearhouse.
Put in several computer monitored thermo couples (in teh oil, on teh frame and in the air).
Put the whole structure outside in the cold and monitor rate of cooling, both with and without heat being applied.

If possible do this with full, 3/4, 1/2 and 1/4 full tanks.

SFK

would it be ok to do it as full only? when in use the tank stays full and re-circulates the oil between the engine and tank (tank is the engines remote sump)

 

[SFK]

i know has half the heat loss than water supposedly

https://www.engineeringtoolbox.com/specific-heat-fluids-d_151.html

Oil has a SHeat of about 2 kJ/(Kg.°C)
typo Corrected>> Water has a SHeat of about 4 kJ/(Kg.°C)

Informally, it is the amount of energy (heat) that must be added, to one Kg of the substance, in order to cause an increase of one °C.

So less energy is need to heat oil over water.

BUT this means that it cools at lot quicker than water.
And worse, steel has a SHeat of about 0.5 /(Kg.°C), so all that connected steel will suck the heat out of oil.

 

[sxturbo]

https://www.engineeringtoolbox.com/specific-heat-fluids-d_151.html

Oil has a SHeat of about 2 kJ/(Kg.°C)
Oil has a SHeat of about 4 kJ/(Kg.°C)

Informally, it is the amount of energy (heat) that must be added, to one Kg of the substance, in order to cause an increase of one °C.

So less energy is need to heat oil over water.

BUT this means that it cools at lot quicker than water.
And worse, steel has a SHeat of about 0.5 /(Kg.°C), so all that connected steel will suck the heat out of oil.

i'm just working out how to install the sensors and monitor them witht he skid outside and not get robbed by pi keys, or vandalised by youth's

 

[SFK]

would it be ok to do it as full only

My suggestion of different volumes was because I was worried that 1/2 a tank might be cooled quicker by environmental temp (but also heated quicker by your heater).

As normally full then no point doing smaller tank levels.

 

[SFK]

As an aside -
Are you warming the pipes from the tanks to the delivery points?
Could you be having warm oil in the tanks near the heater, but cold oil in cold pipe lines?

Thinking of aircraft (and perhaps lorries in Canada????) with heated fuel lines and carbs.

 

[Lower]

I presume that the gensets have operated for the last 15 years, so the oil heating is marginal rather that fundamentally underpowered.

As the elements are thermostatically controlled, i'd just replace both elements with 1kw units and just double the capacity.

Calculating the heat loss out of that tank and heat sink will be difficult.

 

[sxturbo]

no the pipes aren't warmed, there is no way of warming them, but they are all triple walled rubber.

ideally i would like to install a pumped oil heater, so that the engine is being primed of oil ready for starting and its started on hot oil, with the engine kept warm it will also improve the cold staring of the engine. unfortunately this means a design change for which the customer has to fill in an obscene amount of paperwork (for which we have just completed on one engine for a controls upgrade).

for the past 20 years this hasnt been a problem but a few one off scenarios have amalgamated to cause a flag on this issue