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RECOMMENDATIONS TO DESIGN HEAVY OIL FEEDING PLANTS
This paragraph is intended to give some suggestions to make feeding plants for heavy oil burners. To get a regular burner operation, it
is very important to design the supplying system properly. Here some suggestions will be mentioned to give a brief description.
The term "heavy oil" is generic and summarises several chemical-physical properties, above all viscosity. The excessive viscosity
makes the oil impossible to be pumped, so it must be heated to let it flow in the pipeline; because of the low-boiling hydrocarbons and
dissolved gases, the oil must be also pressurised. The pressurisation is also necessary to feed the burner pump avoiding its cavitation
because of the high suction at the inlet. The supplying system scope is to pump and heat oil.
The oil viscosity is referred in various unit measures; the most common are: °E, cSt, Saybolt and Redwood scales. Table 3 shows the-
various unit convertions (e.g.: 132 cSt viscosity corresponds to 17.5°E viscosity).
The diagram in Fig. 12 shows how the heavy oil viscosity changes according to its temperature.
Example: an oil with 22°E viscosity at 50°C once heated to 100°C gets a 3 °E viscosity.
As far as the pumping capability, it depends on the type of the pump that pushes the oil even if on diagram in Fig. 12 a generic limit is
quoted at about 100 °E, so it is recommended to refer to the specifications of the pump provided.
Usually the oil minimum temperature at the oil pump inlet increases as viscosity does, in order to make the oil easy to pump. Referring
to the diagram on Fig. 13, it is possible to realise that to pump an oil with 50°E viscosity at 50°C, it must be heated at about 80°C.
Pipe heating system
Pipe heating system must be provided, that is a system to heat pipes and plant components to mantain the viscosity in the pumping lim-
its. Higher the oil viscosity and lower the ambient temperature, more necessary the pipe heating system.
Inlet minimum pressure of the pump (both for supplying system and burner)
A very low pressure leads to cavitation (signalled by its peculiar noise): the pump manifacturer declares the minimum value. Therefore,
check the pump technical sheets.
By increasing the oil temperature, also the minimum inlet pressure at the pump must increase, to avoid the gassification of the oil low-
boiling products and the cavitation. The cavitation compromises the burner operation, it causes the pump to break too. The diagram on
Fig. 14 roughly shows the inlet pump pressure according to the oil temperature.
Pump operating maximum pressure (both for the supplying system and burner)
Remember that pumps and all the system components through which the oil circulates, feature an upper limit. Always read the techni-
cal documentation for each component. Schemes on Fig. 15 are taken from UNI 9248 "liquid fuel feeding lines from tank to burner"
standard and show how a feeding line should be designed. For other countries, see related laws in force. The pipe dimensioning, the
execution and the winding dimensioning and other construcitve details must be provided by the installer.
Adjusting the supplying oil ring
According to the heavy oil viscosity used, in the table below indicative temperature and pressure values to be set are shown.
Note: the temperature and pressure range allowed by the supplying ring components must be checked in the specifications table of the
components themselves.
ATTENTION: Atomizing air pressure is tipically set at 1 bar lower than oil pressure.
C.I.B. UNIGAS - M039126CE
HEAVY OIL VISCOSITY AT 50 °C
cSt (°E)
< 50 (7)
> 50 (7)
< 110 (15)
> 110 (15)
< 400 (50)
> 400 (50)
< 4000 (530)
Tab. 1 - Supply pipeline hydraulic scheme 3ID0024, pump n.4
PIPELINE
PIPELINE
PRESSURE
TEMPERATURE
bar
°C
1- 2
20
1- 2
50
1- 2
65
1- 2
100
14
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