Information for Storage Tank Manufacturers – Fuel Oil Information

INFORMATION FOR
STORAGE TANK MANUFACTURERS
AND FUEL OIL USERS

Relevant Standards : BS799 / BS5410

 

Fuel Oils – Information

Delivery, Handling and Storage

1) Fuel oils need to be heated for handling and storage purposes. Heavy fuel oil is normally delivered at a temperature of 50C or higher, and should be kept and transferred at the recommended temperatures given in the Table shown below. Medium and light fuels will be delivered at minimum handling temperatures. Heating oil in tanks and pipes above the temperature needed for storage and handling should be avoided as this wastes energy.

Steam traps on the tank and outflow heaters should be regularly maintained. It is advisable not to return hot fuel oil from a ring main system back to the fuel storage tank as this can give rise to excessively high and uncontrolled storage temperatures. In addition it wastes energy and can seriously degrade the fuel causing combustion problems. It is recommended that such fuel is recirculated back to the suction side of the pump.

 

Gas Oil

Light Fuel Oil

Medium Fuel Oil

Heavy Fuel Oil

BS2869 Class

D

E

F

G

Density, kg/litre @ 15C

0.84

0.93

0.94

0.96+

Litres / tonne @ 15C

1190

1075

1064

1041

Gross Calorific Value

MJ/ kg-1

45.4

43.7

43.0

42.8

Btu/lb-1

19500

18800

18500

18400

kWh/l-1

10.6

11.2

11.3

11.4

Therms/gal-1

1.64

1.74

1.75

1.77

Sulphur content (% mass)

0.5

3.2

3.5

3.5

Water content (% vol)

0.05

0.1

0.2

0.3

Sediment (% mass)

0.01

0.02

0.03

0.04

Ash (% mass)

0.01

0.02

0.03

0.04

Mean specific heat (0-100 C)

kJ/kg-1 C-1

2.05

1.93

1.90

1.89

Btu/lb-1 F-1

0.490

0.461

0.454

.0452

Volume correction factor

C-1

0.00083

0.00072

0.00070

0.00068

F-1

0.00046

0.00040

0.00039

0.00038

Storage Temperatures

 

 

 

 

Minimum Storage

10 C

25 C

40 C

Minimum Handling

10 C

30 C

50 C

Old Name

220 Sec. Redwood No.1

950 Sec. Redwood No.1

3500 Sec. Redwood No.1

2) Tanks and oil pipes in the open should be insulated and weather-proofed and steam or electric tracing applied to oil pipes to maintain the minimum handling temperatures.
On vertical tanks insulation should not reach ground level : 300mm (12in.) clearance will prevent standing water soaking into the insulation and destroying its insulating properties.Storage temperatures should remain at the recommended levels if 50mm (2in) of insulation is used on oil storage tanks, with very little, if any, heating required. Increasing the storage temperature above that recommended will result in unnecessary heat loss. The outflow heater should provide the extra heat necessary to raise the oil to the minimum handling temperature.Oil line steam tracing needs to be checked regularly for leaks and damage, and electric tracing checked for continuity.
British Standards as above state the normal storage conditions for Oil Fuels, and these are noted below. It is our experience, however, that few users actually adhere to the Standards and allow their oil, especially the heavier grades, to go cold.

This is not a good idea for a number of reasons, the least of which is that one could end up with a tankful of immovable oil – all for the lack of a small amount of money spent keeping it liquid. Furthermore, it is very well known that the change of Standard viscosity measurement from Seconds Redwood No. 1 (SR1) to the “Class” system has broadened the band within which a refinery is allowed to produce a certain grade.

For Example : Suppose we have 3500 SR1 oil (Class G) to hand. Because the grade is directly stated it is a simple matter to say that it will be close to that viscosity or at worst, at some lower viscosity. If however we have Class G oil, then the viscosity of this may range from, say 3000 SR1 to 4000 SR1, and here lies the potential problem.

When at some point in the future the oil producers begin to provide oil at the upper limit of the band, then this oil will naturally require a quite different set of storage conditions than those prevailing at present. In other words, it will always require to be kept ‘hot’. There will be no option available. A.K. Waugh Limited therefore presents you with an integrated range of Outflow Heaters – completely upgradeable if necessary – which surpass the present requirements by a useful margin, thus allowing oil quality to vary substantially before necessitating a change of heater.

The temperature of the oil exiting the Outflow Heater is controlled by a thermostatic device.

In an electric heater this control is achieved by a thermostat or sensing device mounted on the tubeplate, with the sensor directly in the path of oil flowing from the heater. The control set point is set at the oil burning temperature and the required Safety thermostat is set approximately 20 C higher to compensate for the differentials between the two instruments. Should the control system fail while in the “ON” position, the Safety thermostat acts as a master cut-out and switches the heater off. When the fault has been rectified the reset button on the safety thermostat is depressed and the circuit is re-established.

For Steam or HPHW heaters a thermostatic regulator and Steam Control valve are incorporated for fully automatic control. Optionally an electronic version of this system is available, however it is often preferable to have the mechanical system since this does not – obviously – rely on the presence of electrical power. It should be noted that where such heaters are used it is advisable to have the control device situated inside the heater shell in the same manner as for electric thermostats to ensure a steady oil temperature under flow and standby conditions. Where the controls are sited away from the heater, say in a branch pipe, this can give good results under flow conditions, but does not react well to uncontrolled shut-down.

Basic Electronic control via thermocouple and relay is achievable in much the same way as described above except that control differentials are minimised. Thyristor control is also suitable for electric heaters, this mode providing a stepless variation in input load as commanded by a temperature sensor or sensors. We still insist on the provision of a Safety Thermostat for these devices.

Split loads are available on standard controls, generally using heating elements linked in groups of 3 (star connection) to provide a balanced load.

For the purposes of standardisation of outputs, and to smoothly interface with our Line Heater Catalogue, all heaters are shown with an outlet oil temperature of 55 C, the recommended handling temperature for Class G oil.

 

OTHER SOURCES OF INFORMATION :

Combustion Engineering Association (CEA)
Health & Safety Executive
Department of the Environment

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