Blending Petroleum Products and Petrochemicals.With what, how and where?
Blending
What does blending mean?
–‘blended -combined or mixed together so that the constituent parts are indistinguishable’
We blend things all the time:
Unfortunately blending petroleum products or petrochemicals in bulk is not as simple.
Blending has a long history.
This picture has relevance –as you will hear.
•What does blending achieve?
–To change a product so as to meet a specification
–To dilute a contamination to insignificance
–To make a ‘new product’
What is made by blending ?
All petroleum products.
For example:
All are made by blending different intermediate streams produced from the refining of crude oil.
Petrochemicals?
Most petrochemicals are first manufactured and shipped as near pure products. Clearly these cannot be produced by blending.
However off-specification petrochemicals can be blended back to specification.
Many marketed products are blends including petrochemicals.
Examples are paint, printing inks, chemical cleaners etc.
What are the components of a blend?
There are two main classes of components in a blend, blendstocks and additives.
Major components are referred to as blendstocks:
–They each make up a significant part of the blend, generally measured in percentage terms -perhaps 1%,10%,20 %, 50% or more.
–They assign the main characteristics to the blend.
As an example gas oil may be introduced as a blendstock into residual oil so as to reduce viscosity and create a product marketable as fuel oil.
Blendstocks -What must they provide.
Blendstocks contribute the following to the blend:
•They must, in mixture, produce the required specification across a variety of parameters of quality.
•They must be an economical choice for the production of the required product.
•They must be compatible, so that the mixture is stable.
Blendstocks –Producing the required specification.
•Some quality characteristics blend linearly
–Water content
–Sulphur content
–Lead content
•Some do not
–Flash point
–Vapour pressure
–Colour
–Octane rating
–Viscosity
•Design of blends must therefore be sophisticated
Blendstocks –Economics.
•There may be many different ways to mix available components and additives to produce a blend of the desired specification.
•Designing a blend which meets specification and is the most economical is therefore an iterative process.
•Most companies routinely involved in blending therefore use computer programmes which automatically assess available options.
Blendstocks –Compatibility and Stability.
Compatibility.
Some blendstocks are not compatible and give rise to problems when mixed.
Example.
When blending fuel oil from different components the mixture of oils with high aromatic content with paraffinic oils can lead to the precipitation of solid asphaltenes.
These can be so hard that they have to be manually dug out of the shore or ship’s tanks storing the blend.
Stability.
Some blendstocks are unstable and impart that instability to the blend.
Example.
Light cycle oil (LCO) is used as a blending component in blends of gas oil and diesel. It is colour unstable* and can impart that instability to the whole blend. This phenomena can be very concentration sensitive. For example a blend containing 12% LCO might be colour stable and one containing 13% colour unstable.
* This is much less of a problem now as LCO is often treated in a way that makes it more stable.
Additives -What they do.
Additives are substances which can be added to a blend to modify its performance. They are:
–Generally used in very small amounts, often measured in parts per million.
–Critical to final performance properties and often provide a ‘big bang for the bucks’.
Their introduction is sometimes referred to as additivation.
Additives are introduced in small concentrations but can have important effects on the blend.
•Examples
–Antioxidants, lubricants, flow improvers etc
–Pour and cloud point depressants.
–Hydrogen sulphide scavengers.
–Metal deactivators to restore thermal stability of jet fuel after copper/metal contamination.
–Combustion modifiers to control deposition of metal salts in boilers, allowing higher metal content fuel oils to be used.
–Lubricity improver into jet fuel, when used as dual purpose kerosine.
–Static dissipator additive into kerosine to allow compliance with jet fuel specifications.
Blending –Things that go wrong.
In our experience there are four main classes of problem that arise in making petroleum blends.
•Compatibility and stability issues as already discussed.
•Blend design, that is blends not performing as mathematically predicted.
•Blends not being properly mixed.
•Lack of quality reserve.
Blend design.
As indicated earlier blends can be designed by mathematical calculation. However in our experience no calculation method can be relied on to predict the characteristics of a blend.
For this reason, having designed a new blend, the prudent blender will conduct trial blends in a laboratory
before making the blend, using the planned components and additives in the intended proportions.
Lack of quality reserve.
When performing corrective blending, for example after a contamination, bslendstock brought in to correct the problem must better the required quality by a margin to result in an on specification blend
Example.
Consider a contaminated parcel of fuel oil has a water content of 2% against a specification of 1%. No amount of blending with a blendstock containing 1 % water will solve the problem.
This can cause some unexpected problems in the field!
How to mix the blend.
This depends on where and why you are making the blend. Alternatives are:
In refinery/ manufacturing plant. (Specialist facilities may be available).
-In line blend.
-In tank blend.
-Fly blend.
Downstream for value creation or contamination correction. Specialist facilities are unlikely to be available.
-In tank blend.
-In ship blend.
-Through a portable mixer.
ShoreTank blending techniques where facilities ‘built in’
•Mechanical agitation
–Usually top or more often side mounted agitator to mix the phases. Normally built in and used for viscous liquids
•Circulation
–Jet mix blending -Liquid out of tank,recirculated and returned to tank. The turbulence created mixes the fluids. A liquid jet mixer is more efficient as it entrains fluid in the motive jet.
•Gas Injection
–Can be used but is generally less efficient and particularly costly if using nitrogen. There is also the creation of an atmospheric emission.
Agitation
Jet Mixers –How they operate...
An example of Air (or nitrogen) blending
In –line blending
Mixing the blend without special facilities.
Corrective or creating blending is often done downstream from a refinery, perhaps without specialist facilities. The available techniques are:
•Blend in shore tanks. The tanks may have facilities for agitation in which case the possible procedures are as already discussed. Otherwise blending can be achieved by use of gravity or by pumping.
•Blend on board a ship, mixing by pumping.
•Blend in a portable mixer.
These options are illustrated on the following slides.
Gravity blending.
Re-circulation blending by shore tank
Ship re-circulation
In line blending –on shore
Portable blending
Ship board blending
Ship board blending
Issues
•Finite number of tanks available –perhaps all are full.
•Stability and stress (free surface effects)
•Difficult or impossible to circulate, dependent on cargo capacity used.
•Difficult to achieve cargo homogeneity, which is legally required.
•Load heavy cargo first due to fact that only bottom loading capability
•Legislation changes...
Restrictions -Where can blending take place?
Ships?????????
-International Maritime Agency to ban blending of cargoes on voyage!!!!!!!!!
Ships?????????
•Countries.
–Air/Nitrogen sparging not allowed in some due to environmental emissions.
–Differing regulations for blending on shore –customs regulations may preclude blending.
•Terminals
–Air/Nitrogen sparging not allowed at some due to environmental emissions.
–Non-standard practices, often not allowed by individual terminal management.
The new European Union chemical policy REACH (Registration, Evaluation and Authorisation of Chemicals) will require the blender to have evaluated the blending components and the final blended product for its properties, safety assessment and risk management.
