4 replies to this topic

[kimsun74]

Hi All,

I have a high pour point(33degC) crude oil sitting in ship's tank for about one month and maintained at temperature of 50degC. May i know,

1. Will paraffins wax precipitate/formed thruout the time?
2. How can i determine whether wax started to form?

Your advice are appreciate!

[Himanshu Sharma]

sir,

First,May i know the name of the crude !

Paraffin solubility in crude oil depends on the chemical composition of the crude oil, pressure, and temperature. Paraffin will begin to crystallize out of solution as soon as the equilibrium temperature and pressure is reached cloud point. The paraffin deposits will often begin on surfaces cooler than the liquid. The viscosity of the crude oil is increased by the presence of the paraffin crystals and, if the temperature is reduced sufficiently, the crude will become very viscous pour point

High molecular weight paraffins (waxes) precipitate out of the crude oil when the temperature of the oil drops below the theoretical value of the cloud point temperature (determined thermodynamically), which is the solubility limit. It is to be noted that the experimentally determined value of theroup cloud point, or the wax appearance temperature (WAT), is usually lower than the theoretical value because a finite amount of precipitate is required for detection. Under conditions of equilibrium cooling, wherein the cooling rate applied on the waxy oil is lower than the rate of precipitation, the experimentally determined cloud point could compare closely to the theoretical value.

However, the WAT is not an equilibrium point; wax appearance is a kinetically-controlled nucleation process, and as such can be influenced by many factors, including temperature, temperature gradients (e.g. wall cooling), cooling rates and availability of nucleation sites (e.g. small particles). This means that quite different WATs may be observed for the same oil depending on experimental procedure.

Having explained that ,i can give a politically correct answer that "It depends" but i'll prefer a rather friendly answer that if difference between your cloud point and storage temperature is greater than 10 Deg C practically there will not any crystallisation.This 10 Deg C figure i got from my Pipeline Process Engineering Group,may be just on experience !

[kimsun74]

Hi Sharma,

Is Nile blend Crude.

Your opinion is so long we maintance 10degC higher then WAT the crytalization of wax should be minimise?

[Himanshu Sharma]

i checked and could not find any actual pipeline design data for this crude blend .

what i told you is a thumbrule that is commonly observed during design of high wax crude pipeline.

Since this has worked for so many people over the years ,i hope this should work for you too !

[micass]

Hi Sharma,

Is Nile blend Crude.

Your opinion is so long we maintance 10degC higher then WAT the crytalization of wax should be minimise?

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