Refinery atmospheric pipestill with methanol stripping

In an atmospheric pipestill stripping process where steam is utilized as the stripping gas to strip bottoms and side stream products, the improvement comprising utilizing methanol or a methanol and steam mixture as said stripping gas. In a refinery atmospheric pipestill stripping process utilizing a stripping gas, said process comprising utilizing a gas selected from the group consisting of methanol and a mixture of methanol and steam as said stripping gas.

FIELD OF THE INVENTION 
This invention relates to reducing the corrosivity of corrosive crudes in a 
refinery pipestill while using decreased amounts of steam for atmospheric 
pipestill stripping. 
BACKGROUND OF THE INVENTION 
Crude oil refineries include an atmospheric pressure pipestill (APS) which 
fractionates the whole crude oil into various product fractions of 
different volatility, including gasoline, fuel oil gas oil and others. The 
lower boiling fractions, including naphtha, from which gasoline is 
derived, are recovered from the overhead fraction. The fractions with 
intermediate volatility are withdrawn from the tower as side streams. Side 
stream products include kerosene, jet fuel, diesel fuel, and gas oil. The 
higher up on the column the side stream is withdrawn, the more volatile 
the product. The heaviest components are withdrawn in the tower bottoms 
stream. 
Stripping with steam is employed in atmospheric pipestills to strip bottoms 
and all side stream products (kerosene, diesel, gas oil). Without 
stripping, the typical pipestill, at best would be a poor fractionator. 
Steam stripping is used to adjust the front end of each liquid product to 
optimize the load to downstream processing, meet product specifications, 
or avoid downgrading a more valuable lighter product. Steam has 
historically been utilized as a stripping gas because it is available, 
inert and condensable and, thus, easily separated from hydrocarbons. 
U.S. Pat. No. 5,169,598 discloses a corrosion inhibitor for refinery 
overhead streams. Example 1 includes methanol as a carrier for the 
corrosion inhibitor. 
RU 2,024,574 teaches the use of an alcohol-ketone mixture as a distillation 
improver in atmospheric petroleum stills. 68 to 85 wt. % methanol is 
contained in the mixture; however, only 0.1 to 0.5 vol. % of the mixture 
is employed.

SUMMARY OF THE INVENTION 
In an atmospheric pipestill stripping process where steam is utilized as 
the stripping gas to strip bottoms and side stream products, the 
improvement comprising utilizing methanol or a methanol and steam mixture 
as said stripping gas. 
In a refinery atmospheric pipestill stripping process utilizing a stripping 
gas, said process comprising utilizing a gas selected from the group 
consisting of methanol and a mixture of methanol and steam as said 
stripping gas. 
DETAILED DESCRIPTION OF THE INVENTION 
In the past, atmospheric pipestill stripping with steam has been utilized 
to strip bottoms and side stream products (e.g., kerosene, diesel, gas 
oil, etc.). Applicants have discovered that utilizing pure methanol in 
place of the steam as the stripping gas, or alternatively utilizing a 
methanol and steam mixture as the stripping gas, affords a much improved 
stripping process. 
Applicants believe that stripping with methanol offers several advantages. 
The methanol can react with corrosive acids present in the crude oils 
being introduced into the pipestill, particularly naphthenic acids forming 
non-corrosive methyl esters of the naphthenic acids. This is most 
beneficial since corrosion in pipestills is a major concern for the 
refinery. Likewise, reduction of acidity will allow for processing of 
low-cost acidic crudes in existing equipment. 
Additionally, use of methanol would back out an equivalent amount of steam 
thereby reducing the amount of sour water produced from the pipestill. 
Sour water is a refinery concern since it accounts for a significant 
portion of the load (approximately 55%) on the waste water treatment 
plant. In light of stricter environmental regulations, any lessening of 
waste loads is beneficial. 
In the refinery, crude oil is passed to a desalter and heat exchanger prior 
to entering the atmospheric pipestill. In the instant invention, the 
methanol would be introduced into the crude just after the desalter. This 
allows for methanol reaction with naphthenic acids in the crude during 
heat exchange. 
In the instant invention, methanol may be utilized as the sole stripping 
gas. Alternatively, a mixture of methanol and steam may be used as the 
stripping gas. In the case of a mixture, the ratio of methanol to steam 
will be about 0.1:1 to about 100:1, preferably about 1:1 to about 10:1. 
The methanol may be mixed with the petroleum oil following the desalting 
unit, if present, just prior to entering the heat exchanger. The heat of 
the heat exchanger will be sufficient to introduce the methanol as a gas 
or vapor into the atmospheric pipestill unit and to achieve esterification 
with the organic acids contained in the crude. Thus, the methanol and 
crude will be heated to a temperature of at least about 250.degree. C., 
more preferably at least about 350.degree. C. in the heat exchanger. In a 
typical refinery, petroleum oil is passed to a desalting unit and then a 
heat exchanger prior to entering the atmospheric pipestill. The methanol 
is preferably introduced after the desalting unit and before the heat 
exchanger or in the bottom of the atmospheric pipestill. The methanol may 
likewise be introduced along the pipestill. Two such ports are shown on 
the FIGURE. However, more or less ports along the pipestill can be 
employed. 
Any excess methanol utilized in the stripping process may be recovered if 
desired. Recovery is easily accomplished by the skilled artisan. 
In the instant invention, the refinery atmospheric pipestill is operated in 
the typical manner known to the skilled artisan. The only modification 
necessary to carry out the instant invention is that methanol or a 
methanol and steam mixture be utilized as the stripping gas in the 
atmospheric pipestill.