ADDITIVE BLENDING SYSTEM AND METHOD

Abstract: 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.

Description: Additive Blending System and Method 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. Oleaginous materials such as crude oils, lubricating oils, heating oils and other distillate petroleum fuels, for example diesel fuels, contain al anes 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°C to about 500°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. 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, beinq 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 aspect 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. The invention will now be further and more particularly described by way of example only and with reference to the accompanying drawing which shows a diagrammatic view of an additive blending system. 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 -- - 7 - 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.

Claims: Claims 1. 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. 2. A system as claimed in Claim 1 comprising a common injection means for simultaneous injection of the additive compositions. 3. A system as claimed in Claim 1 or Claim 2 comprising control means to operate the adjustment means in accordance with input data representing the measured characteristics of the liquid prior to the injection of additives, input data representing the desired specification of the blended liquid, and a database relating to the effect of the different additive compositions. 4. A system as claimed in Claim 3 also comprising sensor means for measuring characteristics of the liquid prior to the injection of additives, and for providing signals representing those characteristics as input data to the control means. 5. A system as claimed in Claim 3 or Claim 4 also comprising sensor means for measuring characteristics of the liquid after injection of the additives, and for providing signals representing those characteristics as input data to the control means. 6. 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. 7. A method as claimed in claim 6 wherein the liquid is a fuel oil. 8. A method as claimed in claim 7 wherein the fuel oil is a middle distillate fuel oil.

Inventors: BARACCHINI FRANSCESO L, DAVIES BRIAN WILLIAM, TAN GERARD B H, BARACCHINI, FRANSCESO, L., DAVIES, BRIAN, WILLIAM, TAN, GERARD, B., H.
Applicants: BARACCHINI FRANSCESO L, DAVIES BRIAN WILLIAM, EXXON CHEMICAL PATENTS INC, TAN GERARD B H, BARACCHINI, FRANSCESO, L., DAVIES, BRIAN, WILLIAM, EXXON CHEMICAL PATENTS INC., TAN, GERARD, B., H.
Application year: 1995
Main classification: B01F15
IPC codes: B01F3, B01F15, G05D11