GB2027603A

GB2027603A - System for mixing dissimilar liquids

Info

Publication number: GB2027603A
Application number: GB7928136A
Authority: GB
Original assignee: PLATON Ltd G
Current assignee: PLATON Ltd G
Priority date: 1978-05-11
Filing date: 1979-08-13
Publication date: 1980-02-27

Abstract

Dissimilar liquids A and B are mixed in a substantially fixed proportion at varying flow rates, using a constant displacement device 3 with a return line 5 which incorporates a control device 6. The second liquid B is mixed with the first liquid A downstream of the return line 5 but upstream of the constant displacement device 3, and the rate of flow of the second liquid B is controlled by a second flow control device 12. Both control devices 6 and 12 are adjusted by a delivery modulating device 7 so that as the delivery rate is altered by altering the flow through the return line 5, the proportions remain substantially the same. <IMAGE>

Description

SPECIFICATION System for mixing dissimilar liquids BACKGROUND OF THE INVENTION The invention relates to a system for mixing dissimilar liquids in a substantially fixed proportion, at varying flow rates, i.e. irrespective of the demand flow rate for the mixture over the range for which the whole installation is designed.

One particular use of the system of the invention is in oil-burning heater installations. It is modern practice to include relatively large quantities of water in the fuel for the heater; for instance, a small heater burner may be modulated from a minimum consumption of 3 gallons/hour to a maximum consumption of 1 0 gallons/hour of oil, with the addition of 20% of water to the oil throughout the whole range. However, the invention is not limited to systems for such use, and systems of the invention can be used for instance in making cream cake fillings (including edible oil and water) or for making emulsions in the pharmaceutical industry, and the liquids can be miscible or immiscible and in any suitable proportions.

Often, one or both of the liquids are pre-heated.

For instance, with a heater burning heavy fuel oil, the oil and the water may be pre-heated to about 1250C.

THE INVENTION The present invention provides a system as set forth in Claim 1 and an installation as set forth in Claim 5.

In order to reduce the delivery of the mixture, the first flow control device allows the flow in the return line to increase while at the same time the second flow control device reduces the flow in the second supply line. The invention can give good modulation of the delivery rate of the mixture whilst maintaining the liquids in the same proportion to a reasonable extent.

If one or both of the liquids is pre-heated upstream.

df the mixing point, the invention can reduce the cooling which occurs because energy is imparted by the recirculation around the return line; this can avoid for instance gelling or loss of emulsion.

Claims 2 and 3 set forth preferred features of the invention.

DESCRIPTION OF PREFERRED EMBODIMENT The invention is hereinafter described, by way of example, with reference to the accompanying drawing, which is a schematic diagram of a system in accordance with the invention.

For convenience, it is indicated by way of example how the system can be applied to an oilburning heater installation, but the system can be incorporated in any other suitable installation.

The drawing shows a liquid A, which may be highly viscous (e.g. a heavy fuel oil), in a container 1 from which a first delivery line 2 leads via a constant displacement device 3 to a delivery point 4 (e.g. the injection nozzle of a burner). The constant displacement device may be a sliding vane pump, or a gear pump as indicated. Around the pump 3 is a return line 5 which incorporates a first flow control device in the form of a control valve 6. This control valve 6 is adjusted by an outside demand modulating device 7 (e.g.

responsive to the temperature of a fluid heated by a burner). In this way, the rate of delivery of mixed liquids at the delivery point 4 can be modulated or altered.

A second liquid B, which will usually be of lower viscosity than liquid A (e.g. being water), is in a container 8 from which a second supply line 9 extends to the first supply line 2, which it enters upstream of the constant delivery device 3 and downstream of the return line 5; the second supply line 9 includes a pump 10 and a second flow control device in the form of a constant flow regulating device 11 and a control valve 12. The pump 10 should permit some slip (i.e. not be strictly of constant displacement), but a gear-type pump is satisfactory. If conditions were suitable, for instance if there was a sufficient head of liquid B, the pump 10 could be omitted completely. The control valve 1 2 is also adjusted by the demand modulating device 7.

The control valves 6 and 1 2 may have a linear lift:flow ratio, and are arranged so that as the valve 6 is open, the valve 12 is closed i.e. as the return around the pump 3 is increased, the additive flow of liquid B is reduced. It is preferred to have some return around the return line 5, for instance 1 0% of the total flow, even when the system is providing maximum delivery. The valves 6 and 12 and their mechanisms are so matched for size and characteristics as to produce a constant ratio at the delivery 4. The valves 6 and 12 can be needle valves, for instance of the type which we sell as "M-Valves".

The flow regulating device 11 includes a valve controlled by a balanced spring and diaphragm, as indicated in a conventional manner; the device 11 ensures that there is a constant pressure drop across the valve 1 2 and hence a constant flow for any setting of the valve 12. Altering the setting of the valve 1 2 changes the set point of the device 11. Thus the device 11 substantially prevents pressure changes at the input to the constant displacement device 3 altering the rate of flow of the liquid B. The device 11 can be for instance that which we sell under the registered Trade Mark "Flostat".

The modulating device 7 can take several forms. One form is to have pneumaticallyoperated valves 6 and 1 2 having follow-up servo devices. Alternatively, the valves 6 and 12 can S electrically motorised and have position feedsensors. A simple mechanical arrangement can also be used, with the valves 6 and 12 connected by a suitable linkage. The modulating device 7 could operate digitally.

If pre-heating is required, conventional preheaters can be associated with the containers 1 and 8, or with the supply lines 2 and 9 upstream of the point where the liquids A and B are mixed.

The system of the invention is particularly suitable where the two liquids are not normally miscible as the action of the positive displacement device 3 churns the two liquids together.

Instead of mixing two liquids, the system could, with suitable modification, be used for mixing a liquid and a gas, or two gases, i.e. in general for mixing two fluids.

Claims

1. A system for mixing dissimilar liquids in a substantially fixed proportion, at varying flow rates, the system comprising: a first supply line for a first liquid; a constant displacement device in that supply line; a return line in parallel with the constant displacement device, for returning liquid from the delivery' side to the input side of the constant displacement device; a first flow control device in the return line; a second supply line for a second and different liquid, the second supply line being connected to the input side of the constant displacement device, downstream of the return line; a second flow control device in the second supply line; and a delivery modulating device for altering the rate of delivery of the mixed liquids from the system, the delivery modulating device being arranged to adjust both the first and second flow control devices so that as the delivery rate is altered, the liquids remain in substantially the same proportion.

2. The system of Claim 1 , wherein the second supply line has a pump therein and is connected to the first supply line upstream of the constant displacement device, and also incorporates a constant flow regulating device.

3. The system of Claim 1 or 2, wherein means are incorporated for pre-heating at least one of the liquids upstream of the point where the first and second liquids are mixed.

4. A system for mixing dissimilar liquids, substantially as herein described with reference to, and as shown in, the accompanying drawing.

5. A heater installation, comprising an oilburning heater to which the system of any one of the preceding Claims is connected, for supplying an oil/water mixture to the heater.