Heavy Fuel Storage Temperature

[tomatge]

I operate a land based power station using slow speed marine diesel engines operating on heavy fuel oil (3500sec Redwood). We have about 11,000 tonnes of storage in steam heated tanks of capacity 1000 - 4500 tonnes. Historically, we have maintained the tank temperatures at about 50 degC. Additionally there are outflow heaters. Steam was produced from exhaust gas boilers, and hence effectively "free".

Now the power station runs intermittently, we have to generate steam using package boilers - steam is no longer free, in fact its quite an expensive commodity.

Hence my question ... is it necessary to maintain temperature at 50 degC, and how low can I allow the temperature to drop and still be able to start and run the power station in an emergency.

Naturally I could do various calculations etc. but I was also looking for some practical advice on what happens elsewhere.

 

[jmw]

One problem (there may be others) with letting the temperature drop is that the viscosity will increase significantly. This may cause severe pumpng problems.
If you visit

http://www.solartron.com

and follow the bunker monitor link you will find a spreadsheet which shows the temperature viscosity variation of a range of heavy fuel oils. Values are in cst and the spreadsheet uses the ASTM D341 equation to calculate the viscosity at various temperatures.
In many systems where heavy fuel oil is the primary fuel start up is using distillate fuels until the engine can provide suficient steam for heating purposes. I don't know what advise anyone else would give but i would think a small holding tank of HFO would be easier to heat up after a cold start on distillate and if HFO running persists then the main storage tanks could be more gradually heated to become available once the small ready use tank is in need of topping up.
However, i would suggest the engine manufactures probably would advise on an effective solution for you based on the fuel consumption etc.
Incidently, while you visit the above page, take a look at the fuel heater viscosity meter, Viscomaster.

 

[tomatge]

jmw

Thanks for your response, but maybe I wasn't clear enough in my original queation.
We do indeed have local (15 tonne) clean and uncleaned HFO tanks, typically stored at 90 degC. My question related to the main bulk storage tanks. As I said, I could calculate how long it would take to heat up the bulk tanks if they were allowed to cool, or how big an outflow heater I may require to draw off cooler oil.
Really, I just wondered what happens elsewhere, are we keeping the bulk tanks unnecessarily warm?
I am not familiar with the Viscomaster equipment, but measuring HFO density, and controlling fuel heaters reliably is a long standing problem. I'll check this one out.
Thanks
Tom

 

[volvo49]

as long as you keep the fuel above its pour point temperature by about 10C it will remain fluid. When you need to transfer refer to the viscosity of the fuel. You need to have a maximum viscosity of about 600cSt to allow pumping and good flow.
good luck

 

[Booth]

Hi,
Depending on your average ambient temp. it should not be neccessary to heat the contents of the tanks , only the amount drawn out via the outflow heater. The tanks should be painted black to optimise ambient heat absorption.
If the plant is not run 24hrs, electric heating elements in the outflow heater and electric tracing to piping will help with cold start up.
Regards,
Eric
This works well in South Africa where we have high ambient temps.