About Stripping Steam Temperature ?

[consilience1]

Dear All,

I got a simple question, as you know, stripping steam at side stripper in crude distillation unit make to derease a partial pressure of oil portion in the stripper. Normally, there is Low Pressure Steam (~4.5bar, 160~180'C) to be stripping steam.

Look, Question : is there any temperature range or limit of stripping steam in side stripper? I would like to know theorical expalain like preventing condensation in the stripper..

Thanks for reading.

 

[Milutin]

Steam should be superheated to prevent condensation. Slug of condensate in stripping steam will upset stripping trays in CDU column. Steam is usually superheated in CDU fired heater.

Regards,

Milutin

 

[25362]

Apart from the possible mechanical upset, if the steam is wet, stripping efficiency suffers, since its moisture would vaporize robbing sensible heat from the side-product, subcooling it, and reducing its flash point below specification. Therefore, the steam should, at least, be "freed" from condensate with suitably located traps on the supply line.

Following Milutin's remark let us add that stripping steam is ineffective with upset trays. The pressure drop should be about 30 cm water for a four-tray stripper. A much lower [Δ]P would serve to indicate the trays may be damaged.

 

[Milutin]

Another indication for upset trays, if you don't have ?P measurement, is atmospheric residue quality - flash point spec. and low IBP. It is necessary to be careful because similar symptoms in case of residue/crude oil heat exchanger leaking, although it can be checked by taking samples before and after HE.


Regards,

Milutin

 

[consilience1]

Dear All, esp, Milutin and 25362!

Truly appreciate your replies, and it's very benefit.
By the way, another point I want to know is how high temperature is allowable for stripping steam. Is there any high limitation on steam temperature. Why do we use normally LP-Steam for? Because the steam doesn't or need not give heat to the side-product, I think LP-steam could be enough. What do you think about this?

Best Regards,
S.Lion

 

[25362]

Equilibrium in the stripper is attained on a molar basis. Stripping efficiency in CDU's is affected by two factors:

(a) Cooling. Frequently by the steam itself, since the temperature of the stripping steam is frequently lower than that of the oil, and, of course, by the evaporation of lights.

(b) A drop in vapor pressure. Typical of a multicomponent mixture as the more volatile components are removed.

Therefore the removal of lights by stripping would be more effective when the steam temperature is high relative to the boiling point of the oil and when the boiling range of the oil is narrowed. In some places steam is superheated in the convection section of fired heaters.

The use of LP steam is dictated by economics. It usually is the cheapest steam in the refinery.

BTW, there are a variety of steam stripping applications in which the heat of the steam is actually used as when stripping water solutions.