Beginners guide to crude oil blending?

[Dan877]

Where can I find basic information about blending sweet and sour crudes, sort of a "Crude Oil Blending for Dummies" kind of thing?

Thanks for any help
Dan

 

[Ashereng]

Are you looking more for information on what properties to blend to, or the tools of actually doing the blending?

Your current question is a bit vague, and you may not get the answers to the question you have in your mind.

"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?

 

[Dan877]

Here's the situation:

We have a small crude oil storage and pipeline system, handling about 30,000 bbls per week of high quality sweet crude. A local producer has drilled a well that is making sour crude and wants us to ship it for them. We know we're going to have to blend their sour with our sweet, but we don't want to degrade our sweet to the point that the refiner won't take it.

We've never blended crude before, so we're trying to understand the mechanics of it, both physical and analytical, that is, physically how do we blend, do we need to have special mixing valves or tanks or other mechanical means, and how do we determine the percentages to blend to get a desired result?

I'm not an engineer, I'm just the technician/computer geek. Our pipeline manager asked me to try to find basic information about what is needed to blend the sour and sweet crudes. I know this is to some extent rather vague, but it's all the information I've been given. We're just trying to find the starting point.

Any help would be greatly appreciated.
Dan

 

[21121956]

Hello everybody:

Dan, I would suggest to post this subject in "Petroleum engineering other topics" of these Forums.

In the meantime, you can search in the following threads:
thread483-198846; thread481-201471; thread481-140148 and thread378-49923.

I think you will need the help of an Engineer or someone that can make some little mathematical work to make you understand how does it work.

Good luck !

 

[Ashereng]

Dan,

For the physical equipment required to blend crude, it is pretty straight forward.

A PLC to do all the smarts.
A flow meter per line in the blend.
A flow control valve per line in the blend.
Pumps as needed.

Most blending is done on ratio: one part this to two parts that. It's not rocket science - more like making a drink.

You can blend one of two ways: into a tank, or into a pipeline direct.

The benefit of blending into the tank is that it is batched. If you make a mistake, empty the tank and reblend or correct. You can also mix the tank, and take a sample to check for sour content, and then ship to P/L once all is good. The downside is that you need a lot of tanks potentially.

The benefit of blending into P/L direct is that you save on tanks. The downside is that if you make a mistake, the refinery may downgrade or refuse it and then what do you do?

If you are trying to on-line blend out the sourness in "sourish" crude, you will need an on-line analyser for sulfur content. These you can get from various manufactureres. Like I said above, there is no room for error since the blended product goes directly to P/L.

I would recommend you blend to tankage - once you are comfortable doing that, then to P/L.

Many companies have "packaged" blending solutions that they offer, from the PLC right down to the flow meters and such. Honeywell is one of them. Depending on the volumne and size of your blending needs, they may or may not be too big. I have worked with them on jobs for Exxon and Shell (fairly large refineries), but I don't know how small they can scale their offering - doesn't hurt to give them a call.

"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?

 

[Dan877]

Thanks for the pointers, and I do apologize, I'd have sworn that I was in the Petroleum Engineer's forum when I started this thread. One day I'm going to learn to read.

Thanks
Dan

 

[jmw]

When blending just two components you can only optimise the blend quality for one property and all the other properties will then be a consequence of that optimisation.

For example, when blending/cutting Alberta crude for pipeline transport, the pipeline company imposes a density limit and a viscosity limit.
So long as the blend (crude plus distillate) is below the density limit the blend can be optimised for viscosity.
Very precise control of viscosity can deliver very significant cost benefits. That does not mean that the blend is at the viscosity limit, it is a high as the density limit allows.

However, what it means is that because of the two parameters, the blending operation requires only density and viscosity to be measured online. The other properties can be determined by calculation or by lab testing.

Except for viscosity and perhaps one or two other properties, most properties are additive. This includes sulphur.
One of the problems with sulphur measurement online is the repeatability and reproducibility which are both significant. This would make blending control using sulphur as an online feedback control parameter a bit difficult.

If the properties of the crudes to be blended are known then the blend ratio can often be better controlled by using another more accurately measured parameter as the control parameter. This might be density, if the density of the components is significantly different, or it might be viscosity. This is "indirect" measurement and is commonly used for process control.

Much depends on the objective for blending the crudes. When blending fuel oils sulphur measurement online is sometimes considered but it is allowed to use the fuel blend properties calculation to determine the blend properties and to use viscosity as a control parameter.

The difficulties come with multi-stream blending and especially when blending very similar components that differ significantly only in the sulphur content. The approach her would be to use one of the mass or volumetric blending methods such as batch blending described by Ashereng, (much frowned on in bunker fuel markets but mainly because of the lack of information about the original component qualities and the poor equipment often used)or meter blending.

Mechanical blenders are used where the viscosity is a good control parameter.

However, it is not always simp,y a case of optimising the blend for a parameter but to determine a blend which even though less than ideal, produces the greatest sustained yield for which some form of linear programming is often required. This link makes interesting reading and I did have another somewhere but finding it among the bookmarks is a bit difficult. If I find it, I will post it.

http://www.aspentech.com/brochures/Aspen_Blend.pdf

The bunker fuel calculators freely available may help determine some of the properties you are interested in but obviously the calculators concentrate ont he properties of bunker fuels. This link will take you to the shell calculations:

http://www.shell.com/static/marine-.../marine_fuels/library_shell_bunkercalc_pc.pdf

and you may find other useful calculation in their global resources pages, and from other oil companies also, witha bit of searching.


JMW

http://www.ViscoAnalyser.com