The present invention relates to the control of the ratio of liquid to gas in a fluid being conveyed through a pipe.

The amount of liquid condensate in a fluid that is at or near its boiling point depends upon the amount of energy supplied to and the pressure applied to the fluid. Assuming that no energy is supplied to or taken from the fluid, the liquid/gas ratio can be adjusted by changing the applied pressure. Alternatively, assuming the pressure of the fluid is maintained constant, the liquid/gas ratio can be adjusted by supplying energy to or taking energy from the fluid. The magnitude of the change in the liquid/gas ratio will of course depend upon the latent heat of vapourisation of the fluid and the thermal capacity of the systems.

There are many circumstances in which it is necessary to convey boilable liquids through pipes.

For example, butane is pumped through pipes to gas burners incorporated in boilers. Such burners cannot operate if they receive any liquid butane, and accordingly the pumping system must be set up so that even if there is liquid butane in the system the butane reaching the burner is all in the gaseous phase. This can be achieved by supplying energy to the butane so that it remains gaseous at the burner inlet pressure. Ideally only just enough energy should be supplied to maintain the butane in the gaseous phase but in practice it is difficult to

' determine precisely how much energy is required as even if the temperature and pressure of the fluid ? approaching the burner is known the proportion of liquid in the fluid is not. The energy required to

vapourise large volumes of butane is considerable and therefore it is conventional practice to ensure that the fluid reaching the burner is normally at a temperature well above boiling point so that any liqui _^ is boiled off before it can reach the burner. This approach requires a continuous energy consumption appropriate to "worst case" conditions which in most circumstances do not apply, and thus the energy consumed considerably exceeds what is actually,necessary.

It is an object of the present invention to obviate or mitigate the above problems.

According to the present invention, there is provided an apparatus for controlling the liquid/gas ratio in a fluid flowing through a pipe, comprising a weighing tube flexibly connected in the pipe, means for emulsifying fluid within the tube, means for supporting and weighing the tube and its contents, means for calculating the ratio of liquid to gas in the emulsified fluid within the tube by reference to the weight of the tube and its contents, and means for supplying energy to or removing energy from the fluid to maintain the ratio of liquid to gas within predetermined limits.

The invention also provides a method for controlling the liquid/gas ratio in a fluid flowing through a pipe, wherein a weighing tube is flexibly connected in the pipe, fluid within the tube is emulsified, the tube and its contents is supported and weighed, the ratio of liquid to gas in the emulsified fluid within the tube is calculated by reference to the weight of the tube and its contents, and energy is supplied to or removed from the fluid to maintain the liquid to gas ratio within predetermined limits.

The tube is weighed empty and this "tare" weight is deducted from the monitored weight of the tube and its contents. The resultant weight is the weight of any liquid within the tube. From this weight, a measure of the fluid temperature, and the known latent heat of vapourisation of the liquid the energy required to vapourise all the liquid can be calculated. In some circumstances, it may not be necessary to vapourise all the liquid within the pipe but merely to ensure that the ratio of liquid to gas is within desired limits appropriate to particular delivery pressure and temperature conditions which can themselves be monitored.

The tube is preferably in coil form to provide a large volume of fluid within a relatively limited region of the pipe.

The emulsifying means may comprise for example conventional static and/or dynamic mixers located within or upstream of the tube. In some circumstances, the fluid, pumping rates and pipe dimensions will be such that e ulsification occurs without the intervention of specific mixer components, the "emulsifying means" in such circumstances being the pump and pipe.

Preferably the coil and the pipe are thermally insulated to limit extraneous energy transfers.

An embodiment of the present invention will now be described, with reference to the accompanying drawings, in which :-

Fig. 1 is a side view of a weighing tube assembly for use in accordance with the present invention; and

Fig. 2 is a view on the lines II-II of Fig. 1. Referring to the drawings, the illustrated assembly comprises a coil weighing tube 1 which is

connected by flexible tubes 2 to an inlet 3 and an outlet 4. The coil is suspended from a framework 5 on a link rod 6 the upper end of which is connected to a load cell 7. The output of the load cell 7 (not shown) is connected to an input of a microcomputer 8. The microcomputer is also provided with inputs from temperature and pressure sensors (not shown? arranged to sense the temperature and pressure within the coiled weighing tube 1.

The inlet tube 3 is connected to a static mixer (not shown) incorporating appropriate baffle plates such that fluid pumped therethrough is emulsified. The emulsified fluid is then pumped through the weighing tube 1 and out of the outlet 4.

The output of the load cell 7 when the weighing tube is empty is recorded in the microcomputer. Fluid is then pumped through the coil and the weight of material within the coil is determined by deducting the stored output of the load cell when the coil is empty from the output of the load cell as fluid is pumped through the weighing tube 1. The microcomputer also monitors the temperature and pressure within the weighing tube 1.

The outlet 4 delivers fluid to an appliance such as a burner and the temperature and pressure within the burner is also monitored by appropriate transducers which provide respective inputs to the microcomputer. The microcomputer then calculates in accordance with known principles the maximum liquid content of fluid within the weighing tube 1 which will result in the fluid issuing from the outlet 4 having desired characteristics. In the case of a butane burner the output should deliver fluid which is 100% gas. A heater (not shown) is provided in the outlet 4 and energy is supplied to it sufficient to

vapourise any excess liquid the presence of which is detected within the weighing coil 1 by monitoring of the output of the load cell 7. The arrangement thus supplies the minimum amount G ^" ϊ energy required to provide the desired liquid/gas ratio in the fluid delivered through the outlet 4.

Although it is -not shown in the drawings, the • inlet, outlet and weighing coil 1 will all be thermally insulated to limit any heat transfer between the fluid and the surrounding atmosphere.

It will be appreciated that the fluid tubes 2 do not restrain the displacement of the weighing tube 1 in the vertical direction and accordingly the weight registered by the load cell 7 is a true reflection of the weight of the contents of the weighing tube 1 and the weight of the weighing tube itself. Knowledge of the density of the liquid phase of the fluid then enables the volume of liquid within the weighing tube 1 to be calculated. The latent heat of vapourisation of the fluid is also known and therefore the energy required to vapourise the liquid within the weighing tube 1 can be calculated in accordance with conventional principles.