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Petrol Blending
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Petrol Blending- Greenergybackground paper 2
Greenergysells around 7 million litres of petrol per day to
supermarkets and other petrol retailers. All of this petrol is
manufactured in-house from a range of different petrol blend
components.
By blending its own petrol, Greenergyis able to maintain both cost
and quality control over its supply chain. Cost savings can bepassed on to the customer through lower pricing. Quality control
procedures enable the production of special grades such as Tesco
99 Octane petrol. They also ensure that every day grades of fuel
such as premium 95 octane petrol are produced efficiently with no
quality wastage. The efficiency of this process and the absence of
any waste (known to blenders as giveaway) bring whole of life
environmental benefits.
Through the process of blending Greenergyhas also managed to
stay at the forefront of biofuel developments in the UK.
Introduction
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1 Principles of petrol blending
The principle of petrol blending is to take a variety of raw materials, called components, of differing quality and price
and combine them to make a target petrol quality, called the specification.
The aim of blending is to ensure that the total cost of the components, the tankage, the laboratory work and other
infrastructure costs is less than the cost of buying pre made petrol on the open market. Blending is a significant
source of profit for Greenergy.
Blending has a specific language and terminology. There is a glossary of commonly used terms at the end of this
background paper.
Figure 1:The princples of blending
$ (sum of components) + $ (infrastructure) < $ (finished product)
20% low cost component
25% lower cost component
55% expensive and superquality component
100% finished product atmarket price and quality
Calculate
Mix
Test
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2 Key qualities of petrol
A measure of the ability of a petrol to resist detonation
(knocking or pinking). There are two measures of octane:
RONResearch Octane Number, a historic test method. In a
real world engine, RON is measurement of the anti knock
performance of petrol under part throttle.
MONMotor Octane Number, a modern, more severe test. In
a real world engine, MON is a measurement of the anti knock
performance of petrol under full throttle.
Reid Vapour Pressure, expressed in kPa. In the real world,
RVP determines whether the fuel is too volatile or not volatile
enough to start. The limits for RVP are different for winter and
summer specifications.
Expressed in volume % evaporated at specified degrees C.
In practice a smooth curve is required for easy burning.
Expressed in weight %. The sulphur content of a petrol
affects ifs emissions, the catalytic converter and the efficiency
of a car.
All expressed in volume %. All affect cleanliness and harmful
emissions.
Expressed in weight %. Oxygen has a positive effect on
emissions and also affects car tuning settings and economy.
Octane:
-
-
RVP:
Distillation:
Sulphur:
Benzene,olefinsand aromatics:
Oxygen:
We blend petrol to meet many quality specifications. Some of the most importantthe key measures of quality are:
Petrol quality in the UK changes four times per year in line with the weather. Summer petrol needs to be low volatility
so that it does not gas up the engine in hot weather. Winter petrol needs to be high volatility so that the fuel can be
gassy enough to start up on the coldest winter day. Spring and autumn specifications are mid way between the
winter and summer specifications.
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Table 1:Specification for winter petrol
Table 2:Specification for summer petrol
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3 Petrol blending components sources
Petrol blending components can be sourced from oil refineries, chemical plants, gas plants and increasingly the
agricultural supply chain.
Petrol is not naturally found in crude oil. Instead a low octane component called naphtha is found, but naphtha is
only around 60 octane and therefore unsuitable for running in a car engine.
The majority of naphtha distilled from oil refineries is catalytically upgraded to a high octane petrol component called
reformate.
Approximately 40% of crude oil is an unwanted heavy fuel oil that cannot be sold in its existing form. This fuel oil is
therefore chemically cracked into a gasoline component called cat cracked spirit and when this is combined with
reformate and other components, petrol is made.
Due to changing product specifications, individual production unit capacities, market demands for fuel oil etc, most
oil refineries are not in technical or commercial component balance and have to buy or sell components to deal with
surpluses or cover deficits. Greenergytrades in these component markets.
Butane
Naphtha
Isomerate
Reformate
Alkylate, MTBE orpolymerate
Cat CrackedSpirit (CCS)
Crude oilDistillation
Isomerisation
Reforming
Alky, MTBE orPolymerate
Fuel oil cracking(FCC or HC)
ButaneButaneButane
Fuel oil
L Naphtha
H Naphtha
Chemical Butane
Figure 2:Refinery component sources
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Butane
MTBE
(main source)
Synthetic alcohol
Pyrolysis gasoline(Pygas), MTBE,
Isopentane and otherpure chemicals
Bioethanol / ETBE
Crude oilproduction
MTBE
Alcohol
Plastic and
chemicals
Food andagriculture
Figure 3:Non refinery component sources
Natural Gas production
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4 Petrol blending component qualities
There are hundreds of petrol components traded in Europe, and dozens within each
category of components. For example, reformates alone can vary from 97 octane to
108 octane depending on which refinery they come from.
The following tables summarises the benefits and disbenefits of the main generic
types of components.
4.1. Reformate
Reformate is expensive, but has excellent octane and low RVP. The limiting blending
factor is its high level of aromatics.
4.2. Butane
Butane is attractive because it is clean and low cost. It is very volatile.
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4.3. Alkylate
Alkylate is clean and versatile but also expensive, which minimises its use. Where it
is used; it is added to meet aromatic limits. It is sometimes referred to as blenders
friend accountants foe.
4.4. Isomerate
Insomerate is clean and often low in price, but volatile and not often available.
4.5. Cat Cracked Spirit (CCS, LCCS)
CCS, is high in sulphur but low in cost. It can be a key to the profitability of the blend.
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4.6. MTBE
MTBE is an oxygenate and a useful blending component.
4.7. Bioethanol
Bioethanol is very often required by regulation. It is high cost but often taxsubsidised, which makes it an attractive component.
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5 Bioethanol blending
Bioethanol is becoming an important part of the overall petrol component pool. Governments
around the world are encouraging its use as it is part renewable and hence a good tool in the
quest to reduce carbon emissions.
All petrol produced by Greenergycontains up to 5% bioethanol. Most of the bioethanol we
use is made in Brazil from sugar cane as this form of bioethanol results in greater
greenhouse gas emission savings than bioethanol produced from other crops.
Bioethanol is a very interesting blend component as in general it has excellent blending
.properties; very high octane, sulphur free, zero aromatics etc. The only down side is that it ishigh RVP, and slightly more complex to calculate its blend characteristics.
On a free market, quality adjusted, basis the cost of bioethanol compared to petrol is higher
than a blender would normally be prepared to pay.
To encourage its use, and to compensate for its cost, governments around the world have de-
taxed bioethanol compared to petrol. In the UK for instance Greenergypays 20 pence per
litre less duty on bioethanol than for petrol. This is a direct subsidy the cover the extra cost of
making and using bioethanol.
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6 The practicalities of blending
Figure 4 summarises the blending process at a typical Greenergyblending location.
Petrol components are imported by ship into specialised blending tanks. Typical ship sizes are 8 to 20 million litres.
These blending tanks are able to mix the components together rapidly. The blends are tested in the laboratory for all
petrol qualities. If a blend is not perfect (either giveaway or off-grade) it is reblended and retested until quality targets
are met.
Once the quality of the blend meets the quality targets, it is pumped out from the blend tankage into specialised road
delivery tanks which are then connected to truck loading racks.
Trucks arrive 24 hours per day to collect the petrol and deliver it to customers in typical loads of 25,000 to 35,000
litres per load. All petrol made by Greenergyincludes performance additives. The additives, such as detergents that
help keep the engine clean, lubricity enhancers or combustion improvers, are injected directly into the petrol as it is
loaded onto a customers truck. In this way individual customers can have their own preferred additive formulations
added to the fuel they buy.
Depending on their size individual blends take between 24 and 48 hours to prepare and pump over to the delivery
tanks. A typical blend size for Greenergyis 15 million litres split over two tanks. This is a continuous process; whereas one blend is being pumped out to delivery tanks, another blend is being made up.
Any bioethanol brought into the terminal has to be denatured so that it is no longer potable. This denaturing involves
adding a bitter chemical called Bitrex and methanol. Only denatured bioethanol can be used in blends.
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Blended productroad delivery
tankage
Refinery,blend tankage
Bio-ethanoldenaturing
Truck
Racks
Ship Jetty
Figure 4:Blending terminal schematic
Finished producttransfers
Sales
Productimports
Butaneimports
Blendcomponentimports
Bioethanolimports
Blending
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Glossary of blending terminology
General blending terms:
Component(s): The petrol raw materials that make up the blend.
Bounds: The minimum or maximum amount of any component that can be added to blend. Limitations may be due
to market availability, size of tank and the amount of tanks etc. Bounds are an inputlimitation to the blending
process.
Constraints: Product specifications or other factors that the final product must meet. These are normally set by the
technical requirements of the product such as minimum octane or maximum volatility. Constraints are outputlimitations.
Target function: The driving force of the blending process comprises any numerical factor that the blender seeks to
maximise (e.g. profits), minimise (e.g. costs), or achieve (e.g. a target level of production or a minimum/maximum
specification point). There can only be one target function, which is normally maximum gross margin.
LP (Linear Program): A computer program that takes into account all the components, bounds and constraints to
create the optimum target function. Greenergyhas its own LP which it developed in-house to optimise its petrol
blending.
Solution: The combination ofcomponentsthat achieves thetarget functionwhilst meeting the boundsand
constraints. This is normally determined by using an LP.
Terms related to actual blending solutions:
Tight: When petrol is blended up to a specification limit that costs money to achieve, it is said to be tight. Typical
specification limits are octane, volatility and chemical composition. Because it costs more to make 96 octane petrol
than 95 for example, Greenergys target for standard grade petrol is for the octane to be tight at 95 octane.
Giveaway: When petrol is not blended up to a specification limit and when this costs money, it is said to be in
giveaway.
Slack: When petrol is not up to a specification limit but the limit does not cost any money, it is said to be slack. For
instance the maximum level of olefins permitted in petrol is 18%, but the components that Greenergybuys are
seldom above 12% on average so Greenergyis normally slack on olefins. This is a positive outcome as olefins are
reactive and can create pollution.
On-grade: When a petrol meets a specification it is on-grade.