The requirement to mix liquids in continuous chemical processing is widespread in all branches of chemical engineering, and consequently many mixing devices are commercially available to do this. Many of these mixing devices are specifically adapted to suit certain process needs.

Mixers used in continuous processing may be characterised either as dynamic mixers or as static mixers. In the case of dynamic mixers an external source of energy provides the work needed to thoroughly and intimately mix two or more liquids. Typically the work is done on the liquids by means of a rotor, or a series of rotors which are driven from an external source. In the case of static mixers it is the kinetic energy of the liquids themselves that provides the work needed to mix them.

A particular kind of static mixer, which is known in the prior art for mixing gases comprises a chamber with a mechanical device for damping out pressure fluctuations. One such device is described in :

EP117699, published on 5th September, 1984, which discloses a chamber for mixing gases (in particular anaesthetic gases for medical purposes) . The chamber has multiple inlets and a single outlet.

It is an aim of the present invention to provide an apparatus which acts as a static mixer, and which is specifically adapted for use to mix liquids.

It is a further aim of the present invention to provide an apparatus which acts simultaneously as a mixer and a pressure pulsation damper for liquids.

These aims are achieved by means of an apparatus comprising a mixing vessel with two or more inlets, and a single outlet. Each one of the liquids to be mixed is introduced into the mixing vessel through an inlet. The inlets may be oriented in a manner suitable to maximise the mixing effect.

The mixing vessel also acts as a pressure pulsation damper due to the presence of a gas pocket above the liquid surface.

Summary of the Invention

An apparatus for mixing two or more liquids comprising a mixing chamber, two or more liquid inlets, and a liquid outlet; wherein the mixing chamber further comprises a gas inlet, and a means for regulating the pressure of the gas at the gas inlet.

The lower section of the mixing chamber contains liquid or liquids, and the upper section of the mixing chamber contains gas. Preferably the liquid inlets are located in the lower section of the mixing chamber, and the gas inlet is located in the upper section of the mixing chamber.

In a preferred embodiment of the invention the mixing chamber is in the form of a cylinder, the axis of the cylinder being vertically oriented, said cylinder having a top wall and a bottom wall. The mouth of said liquid outlet is positioned closer to the top wall than the bottom wall within the cylindrical chamber.

In a more preferred embodiment two liquid inlets are oriented such that the mouths of said inlets are substantially opposed and aligned on substantially the same axis. The distance between the opposing mouths of the liquid inlets being not more than 5 times the diameter of the internal diameter largest liquid inlet.

Detailed Description of the Invention

The mixer of the present invention has a number of advantages. It is a static mixer (i.e. a mixer with no moving parts) which nevertheless has the effect of a dynamic mixer. It is therefore inexpensive to manufacture, operate and maintain. It also has a very high mixing efficiency and is equally effective for mixing very small amounts of liquid at low throughput rates and very high amounts of liquid at high throughput rates.

Unlike other static mixers, the mixer of the present invention presents little or no obstacle to the liquid flow and there is therefore no pressure drop between the inlet and outlet of the mixer (i.e. no "backpressure")

The mixer of the present invention can be used to mix liquids in the preparation of foodstuffs, detergents etc.

Furthermore the mixer can be used to intimately mix two or more components which are chemically reactive. The chemical reaction is then started (and may even be completed) in the chamber of the mixer itself.

The mixing chamber may be jacketed, either for heating or for cooling. Heating may be desirable if it is required to promote a chemical reaction in the mixer. Cooling may be desirable if an exothermic reaction is producing heat in the mixer.

The effectiveness of mixing will be influenced by many parameters including the inlet pressures, and the velocity of the liquids when they are introduced into the mixing chamber, as well as the dimensions of the chamber and the number and orientation of the liquid inlets .

The invention will now be described by way of example and with reference to the accompanying drawings in which :

Figure 1 is a sectional view of a mixer of the present invention viewed from the side.

Figure 2 shows a plan view of a preferred embodiment of the present invention, with the top of the chamber removed.

Figure 3 is a sectional view A-A, showing detail of a modified arrangement of liquid inlets of the preferred embodiment of figure 2.

The mixer 1 of figure 1 comprises a closed cylindrical chamber 2 having a height of 400mm and a diameter of 30mm. There are two liquid inlets to the chamber 20, 30, both of which are pipes having an internal diameter of 12mm, and both of which discharge into the chamber at a height of 50mm above the base of the chamber. A liquid outlet 40 from the chamber is also provided, also having an internal diameter of 12mm. The mouth 41 of the liquid outlet is positioned 300mm above the base of the chamber. The liquid outlet of the chamber effectively divides the chamber into a lower section 3 which is liquid filled, and an upper section 4 which is gas filled. The boundary between the upper and lower sections of the chamber is defined by the liquid surface, "S". The liquid surface is typically in the form of a vortex, the apex of the vortex being located at the mouth 41 of the liquid outlet 40. The upper section 4 of the chamber is filled with gas under pressure. A gas inlet 50 and a pressure gauge 60 are provided in the upper section of the chamber wall. Valves 22, 32 and 42 are provided on each of the liquid inlets 20, 30, and the liquid outlet 40 in order to be able to regulate the flow of liquids into and out of the mixer. A

valve 52 is provided on the gas inlet 50. This valve 52 will normally be closed in steady state operation in order to isolate the gas in the upper section 4 of the chamber from the gas supply. A pressure regulator (not shown) is also included in order to control (either automatically or manually) the gas pressure in the upper section of the mixing chamber.

Figures 2 and 3 show a similar mixer to figure 1, in which the orientation of the two. liquid inlets 20, 30 has been modified to improve the mixing effect. The mouths 121, 131 of the liquid inlets ensure that the flow of liquid from one of the inlets is directed towards the mouth of the other inlet. This orientation generates high relative velocity of one incoming liquid to the other thereby maximising the kinetic mixing effect. In figure 2, the mouths 121, 131 of the liquid inlets are positioned 30 mm apart.

The dimensions of the embodiment described above are those of one particular embodiment of the invention. However, the man skilled in the art will appreciate that the detailed design of any given mixer will require appropriate choice of overall size and relative dimensions of the mixing apparatus depending on the process parameters, such as throughput, number of liquids to be mixed, fluid flow properties of the liquids to be mixed etc.

Furthermore the mixing apparatus may be made from any suitable material of construction. The choice will be determined by the- liquids to be used (corrosivity considerations etc.), the operating temperature, required pressure etc. Some suitable materials of construction are carbon steel, stainless steel, aluminium, glass, perspex, and polymeric materials such as polyester etc.

Any gas may be used in the upper section of the chamber. Nitrogen and air are particularly suitable gasses.