System and method for continuously and simultaneously injecting two or more additives into a main stream of oleaginous liquid

Additives are blended with a stream of liquid, for example of diesel fuel, by injecting at least two different additive compositions into the stream, and adjusting the rates of injection and the relative proportions of the injected additive compositions. This enables the consumption of additives to be minimized while enabling desired fuel characteristics to be maintained despite variations in the characteristics of the untreated liquid. The rates of injection may be adjusted by an automatic controller (32) in response to signals from sensors (28, 30) representing characteristics of the liquid before and after treatment.

FIELD OF THE INVENTION 
The present invention relates to a system and to a method for blending 
additives with a main stream of a liquid, particularly but not exclusively 
where the liquid is an oleaginous liquid. 
BACKGROUND OF THE INVENTION 
Oleaginous materials such as crude oils, lubricating oils, heating oils and 
other distillate petroleum fuels, for example diesel fuels, contain 
alkanes that at low temperature tend to precipitate as large crystals of 
wax forming a gel structure so that the fuel or oil loses its ability to 
flow. The lowest temperature at which the crude oil, lubricating oil or 
fuel oil will still flow is known as the pour point. In the case of fuels 
as the temperature of the fuel falls and approaches the pour point, 
difficulties arise in transporting the fuel through lines and pumps. 
Further, the wax crystals tend to plug fuel lines, screens and filters at 
temperatures above the pour point. These problems are well recognized in 
the art, and various additives have been proposed, many of which are in 
commercial use, for depressing the pour point of fuel oils. Similarly, 
other additives have been proposed and are in commercial use, for reducing 
the size and changing the shape of the wax crystals that do form. Other 
additives may also retain wax crystals in suspension, and may be referred 
to as anti-settling aids. Additives may also be added to improve other 
properties of the fuel oil, for example to act as corrosion inhibitors, or 
detergents or to inhibit sediment formation. 
The invention is relevant but not restricted to fuel oils, including those 
boiling in the gasoline range, but is particularly relevant to those 
liquids referred to as middle distillate fuel oils. These fuel oils 
typically boil in the range of about 120.degree. C. to about 500.degree. 
C., and may comprise atmospheric distillate or vacuum distillate, or 
cracked gas oil, or a mixture of straight-run and cracked distillates. The 
most common petroleum distillate fuel oils are kerosene, jet fuels, diesel 
fuels, and heating oils. In any event it is almost always necessary to add 
a small proportion, for example between 10 and 2,000 ppm by weight, of 
additives to the liquid as produced by a refinery, in order to produce a 
fuel or oil which is suitable for sale and meets desired specifications. 
Typically a refiner would use one additive composition for all fuels or 
might, in some cases, use one additive composition (A) if producing diesel 
fuel, or a different additive composition (B) if producing heating oil; 
each additive composition (A or B) comprising a mixture of the 
chemically-different types of additive discussed above, chosen to ensure 
the desired specification is met. Where the characteristics of the 
untreated fuel oil vary (due for example to changes in refinery operation 
or changes in crude oil), the refiner ensures that the desired 
specification continues to be met by adjusting the proportion of the 
additive composition (say A) which is added. In the same way the refiner 
can produce fuel oils which meet different specifications, for example for 
use in different climates, by adjusting the proportion of the additive 
composition (say A) which is added. 
SUMMARY OF THE INVENTION 
According to the present invention there is provided a system for blending 
additives with a main stream of liquid, the system comprising a plurality 
of containers for different additive compositions, means to inject into 
the main stream of liquid at least two additive compositions from the 
containers, and means to adjust, during operation, the rates of injection 
and the relative proportions of the different additive compositions which 
are injected. 
Each additive composition may comprise one or more chemically-different 
additives as discussed above, for example a selection of pour-point 
depressants, wax anti-settling agents, wax crystallization modifiers, 
corrosion inhibitors etc. and may contain co-additives which improve the 
effectiveness of one or other of the additives. These components may be in 
admixture with a carrier liquid, e.g. dissolved or dispersed in an 
inactive oleaginous solvent. Some of the additive compositions may contain 
a single additive; others may comprise several different additives. 
Preferably the injected additive compositions are injected simultaneously, 
and through a common injector, into the liquid stream. Alternatively they 
may be injected through different injectors, which injectors may be spaced 
apart either in the direction of the liquid flow or transverse to that 
direction. 
The adjustment means may comprise separate adjustable pumps to pump the 
different additive compositions to the injector means, or may comprise 
separate flow restrictor valves to control the flow rates of the different 
additive compositions. 
Desirably the system is automated, and includes computerised control means 
to operate the adjustment means in accordance with input data representing 
measured or measured and computed characteristics of the untreated liquid 
or fuel components and input data representing the desired specification 
of the blended liquid, and a database relating to the effect of the 
different additive compositions on the different liquids. 
By adjusting the relative proportions of the different additive 
compositions the overall consumption of additives can be reduced, saving 
unnecessary expense. This is because the composition of what is injected, 
being made up of adjustable proportions of the different additive 
compositions, can be optimised: 
a) to accommodate variations in the characteristics of the untreated 
liquid, for example due to changes in distillation cut-point, or the type 
of crude oil; and 
b) to achieve a variety of different product specifications, for example 
different fuel grades, or different requirements between summer and 
winter, or different product types. 
These aims can be achieved while avoiding the waste involved in injecting a 
particular additive as part of a standard additive composition at higher 
injection rates than are required in a particular situation, merely 
because that injection rate is necessary in relation to another component 
of that standard additive composition. In particular, additive 
compositions in the present invention may not be discrete additives 
optimised for different fuels but sub-assemblies of additives that, when 
admixed in situ, provide the minimum overall additive consumption. 
Desirably, in an automated system, the control means is also responsive to 
input data representing measured characteristics of the treated liquid. 
The system preferably includes measuring means to determine 
characteristics of the untreated liquid, and of the treated liquid, and to 
supply the requisite input data to the control means. 
In a second a spect the invention provides a method for blending additives 
with a main stream of liquid, the method comprising injecting into the 
main stream of liquid a plurality of different additive compositions, and 
adjusting, during operation, the rates of injection and the relative 
proportions of the different additive compositions to provide a blended 
liquid having desired characteristics.

DETAILED DESCRIPTION OF THE INVENTION 
Referring to the drawing, an additive blending system 10 is shown for 
injecting additives into a flow of oil/fuel flowing in the direction shown 
by arrows along a pipe 12 from a production unit (not shown) to a storage 
tank (not shown). Typically the production unit would be an oil refinery 
and the flowing liquid might be intended as heating oil or diesel fuel. 
Four containers 14 are arranged near the pipe 12, each with an outlet tube 
16 incorporating an electrically adjustable valve 18, all the tubes 16 
communicating via a common manifold 20 to an outflow tube 22. The outflow 
tube 22 incorporates an electric pump 24, and communicates with the pipe 
12. 
A sensor 28 communicates with the pipe 12 upstream of the tube 22, and a 
sensor 30 communicates with the pipe 12 well downstream of the tube 22. 
The sensors 28, 30 measure characteristics of the oil/fuel in the tube 12 
before and after the injection of additives, and provide the results of 
these measurements as input data to a computerised controller 32. For 
example the sensor 28 might measure the density, the distillation 
temperature, and the cloud point of the oil/fuel, and the sensor 30 might 
measure the cold filter plugging point (CFPP) of the treated oil/fuel. The 
controller 32 provides output electrical signals to control operation of 
the pump 24 and of each of the valves 18. 
In use of the system 10 each of the containers 14 contains a different 
additive composition. The controller 32, in response to the input data 
from the sensor 28 and in accordance with the specification of the 
oil/fuel which is required (this data being provided by an operator to the 
controller 32 by means of a keyboard (not shown)), determines what rate of 
injection of each of the different additive compositions is required. The 
controller 32 then supplies appropriate signals to the pump 24 and to the 
valves 18 so that the required quantities of the additive compositions are 
injected via the outflow tube 22 into the oil/fuel in the pipe 12. From 
the input data received from the downstream sensor 30 the controller 32 
can ascertain whether or not the desired specification is being achieved; 
and if not, the controller 32 can adjust the injection rates of one or 
more of the additive compositions accordingly. 
The blending system 10 thus operates automatically, blending with the 
untreated oil/fuel the necessary combination of additives to provide the 
desired specification. It will be appreciated that the operator can at any 
stage alter the desired specification, for example to change from 
producing winter diesel fuel to summer diesel fuel, and the system 10 will 
automatically make the necessary changes in the additives by selecting a 
different combination of the additive compositions (or different relative 
proportions of the additive compositions) from the containers 14. 
As shown in the drawing the additives are injected into the flowing 
oil/fuel through the mouth of the outflow tube 22, which therefore 
constitutes the injector. It will be appreciated that the injector may 
take a different form, for example a jet eductor as described in WO 
93/18848. The system 10 is shown as including four containers 14, but it 
will be appreciated that it might have a different number, desirably 
between two and eight; the number is merely equal to the number of 
different additive compositions which are to be provided. All the 
containers 14 are shown as being the same size, but it may be preferable 
to store in larger containers those additive compositions of which larger 
quantities are expected to be used. The system 10 might additionally be 
provided with meters (not shown) to measure the volume of oil/fuel which 
flows along the pipe 12, and to measure the volumes of the different 
additive compositions which are injected; these metered volumes might also 
be supplied as data to the controller 32, and may be recorded so that 
operation of the system 10 can be monitored. 
The mode of operation of the controller 32 may rely on empirical 
calculations to relate the characteristics of the untreated oil/fuel to 
the necessary additions of the additive compositions, or may rely on an 
expert system, or a neural network. In any event because the need for 
additives may differ considerably for oil/fuels of only slightly different 
characteristics, and because the characteristics of the untreated oil/fuel 
from the production unit may be expected to vary continuously, it is 
desirable to monitor the treated oil/fuel and hence modify the treatment. 
That is the purpose of the sensor 30. It is also desirable to monitor the 
characteristics of the oil/fuel in the storage tank supplied by the pipe 
12, to ensure that it meets the specifications. It is therefore desirable 
to provide a further sensor unit (not shown) for this purpose, whose 
measurements may also be supplied as input data to the controller 32. 
A preferred embodiment of the invention has been described above, and it 
will be apparent that the system 10 can be modified in a wide variety of 
ways while remaining with the scope of the invention.