Tank Blending for Crude Oil

[imans]

Dear Readers,

Does anyone have experience with blending heavy crude oil and light crude oil in one tank? How effective is the blending? Is it true that the common practice is a blending light crude with light crude only and heavy crude with heavy crude only?

Thank you,

 

[reena1957]

Dear Imans,
Give more details like
1.you want to process both together for getting a good blended distillate or reduce the lights load, or other operational advantages?
2.ullage problem in tanks? lack of tanks for segregated operation, etc.?
In the meantime, here are my two bits:
3.Normally the LIFO (last in first out) principle is for heavy crudes.For lights, it may or may not be so. If you have tank mixers, it may be possible to to get a reasonably good blend.
4. Normally ratioed line blending while feeding to unit is a better option for mixing as well as to control the ratio.
best wishes

 

[jmw]

I have had experience of pipeline blending heavy Alberta Crude with distillates before it can be shipped via the pipeline. SInce the distillates were returned from the destination refineruy for the crude there was not a compatibility problem but asphaltene precipitation can be and this was noticed in some instalations. Since these blends were controlled using both density and viscosity, the viscometers initially suffered from coating but redesigning the viscometer installation and PFA coating them solved the problem. Noticably, the further downstream from the blend point, the less affected by precipitation.

Asphaltene precipitaion occurs as the resins that bind together the asphaltenes and maltenes are soluble in the light fractions.

As a general rule, the greater the difference in viscosity/density the more problems to be anticipated.

However, a concern when blending any crudes is compatability and stability.
Some crudes are not compatible with each other and the results are referred to as "Cocktails". They will separate out when you least want it.

Heavy fuel oils represent a similar situation and you may find good advise on the IBIA website, VISW labs site and others dealing with fuel oil blending.

One point to be sure of is to make sure the crudes are properly mixed. Too many problems occur through inadequately mixed blends that subsequently separate whether they are compatible or not.

As Reena 1957 states, inline blending is to be preferred. You might visit the

http://www.jiskoot.com

wbsite for details on crude blending. Their blenders use jet mixers to ensure a good blend. Some operators rely on pipeline blending but an example quoted is of a large bore pipeline into which well water and reservoir water were introduced (discriminated by their hardness values) and they were found to be flowing as separate streams in the same pipe some 500feet downstream.
These were almost identical fluids. Light and heavy crudes are not and they tend to laminar flows anyway. Using jetmixers or custody transfer static mixers is a must.

Inline blending is increasingly preferred because today we have the process instruments for density and viscosity which provide for very tight closed loop control. The refinery standard process capillary is less suitable due to its inability to handle the untreated product and slow response times.

Modern instruments make inline blending both practical, accurate and cost efficient.

I couldn't tell you how much the cost benefit was to the ALberta operation using a fiscal density meter and oonline digital viscometer for inline blend control but it was a huge saving in distilates.

JMW

http://www.ViscoAnalyser.com

 

[imans]

Our refinery was designed with 8o% heavy crude and 20% light crude. We have 4 heavy crude tank and 2 light-crude tank. After couple of years operation, we changed the ratio to 50:50. Due to limited amount of light-crude tank, we blend light crude with heavy crude in heavy-crude tank. Then the blended crude is mixed with crude from light-crude tank in line. The problem is the mixing in the tank is poor. It has big impact on the processing unit. I just wonder would it be necessary to build a new light crude tank to solve this problem or we can avoid that option by just modifiying something on the blending tank.

 

[reena1957]

Hi Imans,
What type of blending is done in the tanks?
Side entry mixers are good. Do you have them?
First take the heavy crude in the tank and then add Lights. You can get some natural convection blending.
If You can receive the Lights from the Ship tanker into the tank, that will do a wonderful blending.
Secony Jet Mixers are good for viscous liquids, rather than side jet nozzles.
Start the blending Mixers 24 hrs before the tank is scheduled to feed. Stop Mixers (after 24 hrs of mixing)when when U start feeding the mixed Tank.Did U do 24 hrs blending? Did U stop Mixers too early and allow layering?
Pl give the details of the blending and feeding procedure.
Hope there is not much sludge in the tanks.