Mix crude oil and diesel

  • Thread starter EC-Wilfredo Gonzalez Vidal
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Thread Starter

EC-Wilfredo Gonzalez Vidal

Hi everybody,

In my process, Diesel is add to Crude Oil in order to reduce the crude viscosity. The mixture takes place in the suction of the pumps. These pumps are pumping the crude oil until the following section of the process. I need to measure the crude viscosity in a common collector at the end of these pumps, in order to develop a control loop to controlling this parameter.

The exact question is:
What distance of the pumps I should put the viscosity meter in order to ensure a real reading of this parameter ?
Does anybody know of any practical experience ?

Any suggest will be of great utility.

Best Regard

Wilfredo Gonz=E1lez Vidal
Empresa de Computaci=F3n del MINBAS
Especialista en Automatizaci=F3n
Tel=E9fono: (537)62-4533 Directo, (537)62-9015 al 19 Piz.
Email: [email protected]
You don't say what type of viscometer you have chosen and i suspect you should look carefully at your choice if they are not able to provide the advice you need (i assume you are looking at a process measurement for closed loop feedback control, not sample taking for laboratory measurements).
However, the actual question you ask is not directly related to the viscometer instrument at all but to the best place in a pipeline to obtain a representative sample for a control measurement, whether by process instrument or laboratory sample evaluation.
API 555 is a very good source of advice.
The simple answer is to decide what conditions you need for a representative measurement and then find how close you can get to the mixing point and find these conditions. The closer you can get the faster the control response. The faster the control response the more accurate the control. At the measurement point you need a fully homogenous flow where the mixing is complete.
No matter how fast you want the response you should not try to measure closer to the mixing point than where the fluid is fully homogeneous. (Assume you need the fastest response possible. If you do not need fast response do not assume you can go further downstream. Conditions may no longer be representative; use the best position for fast response then ajust [slow] the response time through the controller you use.)
If you are using a jet mixer system (eg by Jiskoot)or static mixers (e.g. by Chemineer, Vortab or Koch)then this point will be close to the diesel injection point or not far down stream from the pump outlet. If you have neither and are relying on pipeline mixing you may never achieve suitable homogenous blend, at least, not where you can measure a representative sample for closed loop control purposes.
You will need to consult the pump or static mixer suppliers for a calculation of this distance i.e. how close to the injection point you can approach and be sure of homogeneous flow. Ideally you may need to be where laminar flow has just been re-established for good sample extraction.
The viscosity instrument supplier (process measurement) should give you very good advice about the installation requirements as they affect the viscosity instrument itself. Be sure they can deliver what you need which is the kinematic viscosity at the reference temperature (e.g cSt at 100degC), which they have to be able to determine from the measurement they make which might be either dynamic (cP)or kinematic (cSt)viscosity at the mixing temperature (e.g. viscosity measured at 85degC say).
If the viscometer instrument manufacturer you are considering is not giving you this information or the support and advice you need (the agent may not be fully knowledgable) then you should suspect the capability of the instrument to do what you what it to do.
The information above is true for any measurement in any system. It is about finding the best place for a representative measurement. That is the value of API 555.
However, you need to be sure that the supplier you are considering has the knowledge and skills to support the instrument in your application. Some of these problems may be technology specific i.e. due to the measurement instrument. Some may be application specific.
For example: the proceding comments are true if one ignores two important features; what happens when distilate and heavy oils are freshly mixed together and how particular technologies will respond.
When diesel/distilate is blended with crude oil (or with visbreaker outflow, vacuum tar residuals, heavy fuel oils or any heavy oil) asphaltene recipitation is possible (Fuel Field Manual by Kim B Peyton, Mc Graw and Hill).
Experience in the Canadian pipe lines has shown us that close to the mixing point the crude oil and diesel tend to behave as if they are still a mixture and precipitation is evident. Further downstream behaviour is more nearly that of a blend and further asphaltene precipitation does not occur (so far as the viscometer is concerned). This is very important to viscosity measurement. Some technologies will be very sensitive to the asphaltene precipitation. I assume you will not want to have to shut down and remove the sensor for cleaning every week or two. Others will be immune. The closer you get to the mixing point the better the response. In pipe line applications the finacial benefits of controlliong distilate use are very significant indeed. In refineries the cost benefits and accuracy targets may be substantially different. Be sure you can choose an appropriate solution.
Traditionally any kind of blending has had to depend on volumetric flow rate ratios calculated using ASTM D341 and reliant upon laboratory viscosity evaluation.
In some critical applications the laboratory evaluation is suplimented or replaced by the use of process capillary viscometers which control the temperature of the sample to the reference temperature (+/-1degF and +/-1%FSD on dynamic viscosity... a density meter is required to convert to kinematic viscosity).
You really need to identify appropriate viscosity instrument manufacturers and obtain evidence that they have experience in this application and, if possible, can provide independent end user references.
Viscosity measurement has made rapid advances in the last 7-8years so you can confidently set quite tough objectives about accuracy, speed of response, maintenance and cleaning.
Some sites to visit (including our own) include:
http://www.viscosity.com (Norcross)
http://www.viscometer.com (Brunswick.. mass flow based)