8 replies to this topic

[Burgoo]

I am looking for some advice on the design of a fuel storage system (Tank, Pump, Heater).  

 

This tank is a one day storage tank for a fuel oil being used in an industrial furnace.  Due to the viscosity of the oil it needs to be heated to flow well enough to be atomized in the furnace burner.  The client has requested that the fuel oil heater be external.  My current design is an insulated vessel with a pump that circulates oil through a steam heated shell and tube exchanger recalculating a majority of the flow back to the storage tank with the rest being sent to the furnace under flow control.  The vessel will use a nitrogen blanket to ensure an inert vapour space and a PCV will control the pressure inside the vessel to slightly above atmospheric (~5 mbar).

 

My questions are as follow:

1. Do the overflows on storage tanks typically have a rupture disk to reduce the wasting of nitrogen
2. As this system has an external heater it is dependent on the pump running in order to keep the contents of the vessel warm is this common in the industry?  Do these systems have some sort of emergency steam tracing on the lower portion of the vessel?
3. Are radar level instruments the norm for level measurement?
4. I currently plan to specify the pump to be able to turn over the contents of the vessel every six hours, is this a reasonable value?
5. At 4 bar(g) the steam temperature is ~ 150 for a fairly heavy oil am I at risk of auto ignition?
6. Was planning on having the oil the tube side, any issues with this?
7. Is there anything else I should think about or are there an huge mistakes in my design?

Additional Information Below:

Fuel Oil

Pour Point = 24 C

Flash Point = 66 C

Viscosity = 180 cSt

B/L Supply Temp = 120 C

 

Fuel Oil Tank

Atmospheric Vertical Cylindrical Tank 

Volume = 100 m3

Storage Temp = 100 C

 

Heater

Shell and Tube 

Steam Pressure 4 bar(g)

[mansari]

It is a common practice to use external heaters for fuel oil. Internal heating coils have their own disadvantages in case they develop leakeage. Steam pressure is higher, so steam/condensate will be mixed with fuel oil causing problems at the burner.

 

Set point of fuel oil heating is defined by the required viscosity as specified by the burner vendor. Higher the viscosity, higher the line pressure drop. Therefore fuel oil lines are normally insulated and steam traced.

 

If your tanks are nitrogen blanketed, yes then overflow line should be provided with an RD, essentially set at a pressure equal or lower than the tank design pressure. Since API-650 tanks have a maximum design pressure of 2.5 psig, RD set pressure may be defined between the maximum set pressure of nitrogen pressure control set point and the tank design pressure.

[fallah]

 

Burgoo,

 

Be careful using RD in overflow line as follows:

 

Because you have to put the RD in bottom end of the overflow line to burst in tank overflow condition, be ensure condensation wouldn't occur inside the tank otherwise it can accumulate above the RD and might cause the RD would burst when not needed.

 

If you would face to such problem it is better using seal leg instead RD.

[mansari]

Yes very good suggestion from Fallah. Since pressure of the tank is not high, a suitable water loop seal can be designed and installed.

[Burgoo]

Thank you everyone for their replies they have been very helpful.  Are non contacting radar or ultrasonic level transmitters a good choice for level indication?

[breizh]

Go for radar and Consider to contact Vega ,to me the best in the class!

 

http://www.vega.com/...measurement.htm

 

http://www.saab.tank...icle_lowres.pdf

 

You may consider :E&H , Rosemount or others 

 

Hope this helps.

 

Breizh

Edited by breizh, 10 July 2013 - 01:15 AM.

[JMW]

Fuel oil heater control is relatively easy these days.

At one time the only way to control heating for burners was to take frequent samples for lab analysis, then find the EVT (Equi-Viscous Temperature) i.e. the temperature at which the viscosity is the optimum for the burners (as indicated above, the burner manufacturer will provide the optimum viscosity) and then combine excess Oxygen and frequent flame inspections to adjust the set point as necessary.

Fuel oils to burners do not receive the same treatment as fuel oil to engines where they filter, centrifuge etc prior to the injectors. Hence when the fuel oil heater viscometer for engines was the twin capillary as standard, there was nothing suitable for burners. I recall that at PREPA (Puerto Rico) they were required to use viscometers and had to have an online viscometer and a standby in parallel and would have to switch over every one-two weeks to clean the viscometer.

PFA or PTFE coated vibrating element viscometers are suitable for burners and make life simpler.

The pioneer for burners was the Emerson 7827, then the 7829 but now there is also the Lemis DC 52.

 

For a 180cSt fuel oil the the viscosity will be around 21cst at 100degC and around 6.5cst at 150degC.

In the installations I have seen, the oil is usually maintained in storage at lower temperatures, around 50-60 Deg C where the viscosity is around 100-180cst, and only the flow to the burners heated separately to achieve the target viscosity for the burners.

I think this is more energy efficient but I'll bow to superior judgement on this. I can only really advise on the viscometers.

 

 

(see here for some useful spreadsheets: http://www.cheresour...nloads&mid=987)

[Burgoo]

Once again thank you for all the answers.  One more questions Is there a specific kind of insulation recommended to limit the chance the insulation absorbs any spilled fuel oil creating a fire risk?

[breizh]

Burgoo ,

 

Consider this link , it might helps.

 

http://www.industry....n/applications/

 

Breizh