Where a fluid is to be injected through a port into a chamber containing another fluid chemical reactions may occur, and these may lead to problems such as blockage of the injection port. In some cases these problems can be overcome by injecting the fluid at a high pressure, but an injection port which could operate effectively without requiring high pressures would be desirable. One such situation is in a plant for injecting molten sodium into water or aqueous caustic soda, where the injection port may be blocked by a solid deposit of a sodium/sodium hydroxide mixture or amalgam even if it is at a temperature well above the melting point of sodium.

According to the present invention there is provided a port assembly for the injection of a first liquid into a chamber containing a second liquid with which the first fluid reacts, the port assembly comprising a duct assembly communicating at one end with the chamber &t such a position as to be occupied by gas during operation, the duct assembly decreasing in diameter away from the chamber, and at its other end being closed by a plate defining a narrow orifice for injection of the first liquid, and at least one aperture being provided for injection of gas into the duct assembly remote from the chamber.

Preferably the duct assembly defines a stepped bore, there being a step in the bore between at least one said gas injection aperture and the orifice plate. The preferred duct assembly comprises an open-ended generally

cylindrical first duct communicating at one end with the chamber at such a position as to be occupied by gas during operation, the other end of the first duct communicating via a tapering coupling to one end of a generally cylindrical second duct of narrower diameter than the first duct, the other end of the second duct being closed by the orifice plate.

Preferably the gas injection aperture or apertures are such as to inject gas uniformly around the wall of the first duct adjacent to the tapering coupling. An aperture may also be provided for injection of gas into the second duct. The injected gas thus flows continuously out of the ducts and into the chamber, so carrying out of the ducts any droplets or aerosols of reactive liquids which may be present in the chamber.

Preferably means are also provided to inject a cleaning liquid through the or each gas injection aperture if any solid deposits are formed on the walls of the ducts.

The step in the bore (which may be provided by the tapered coupling) suppresses the flow of any aerosols into the vicinity of the orifice plate.

Preferably means are provided to push a rod through the orifice when injection of the first liquid is not required, so any blockages in the orifice can be mechanically removed. The rod is desirably coupled to operation of a valve for cutting off flow of the first liquid to the orifice.

Such a port assembly is desirably connected to the lid or top of a reaction vessel which constitutes the chamber, so the first liquid is injected downwardly into the reaction vessel containing the second liquid, and there is preferably a gas space above the liquid in the

vessel so the injected liquid passes through gas in both the ducts and the upper part of the vessel before meeting the liquid with which it reacts.

The port assembly is particularly suited to enabling molten sodium to be injected into a reaction vessel containing aqueous caustic soda, so the invention also provides a method of reacting a molten alkali metal with an aqueous liquid using the port assembly, and also a plant for performing the method.

The plant also desirably contains means to stir the liquids in the reaction vessel vigorously, for example by injecting jets of the aqueous liquid. The reaction generates hydrogen, so it is desirable to provide means to extract gas from the reaction vessel. The gas extracted from the reaction vessel may be mixed with a large flow of air, desirably by injecting the gas into an air stream near to the throat of a water venturi nozzle so any hydrogen is safely diluted before being disposed of.

The port assembly in this case might have an orifice of diameter between 0.5 mm and 12 mm, preferably between 1.5 mm and 5.0 mm, for example 2.5 mm. This orifice enables molten sodium to be injected at a rate of about 100 kg/hour at a pressure of less than one atmosphere, say 30 kPa.

The invention will now be further and more particularly described, by way of example only, and with reference to the accompanying drawings in which: Figure 1 shows a longitudinal sectional view of an injector port assembly ;

Figure 2 shows a sectional view of part of the assembly of Figure 1 to a larger scale; and Figure 3 shows a diagrammatic sectional view of a sodium disposal plant including the injector port assembly of Figure 1.

Referring now to Figure 1 there is shown an injector port assembly 10 for injecting molten sodium at about 280°C into a reaction vessel 12 containing aqueous sodium hydroxide (caustic soda) at a concentration of about 10 molar. The top of the reaction vessel 12 is about 0.3 m above the level of the caustic soda 14 (shown in Figure 2), nitrogen gas fills the space above the liquid, and there is a hole 16 in the top of the vessel 12. The assembly 10 is fixed to the top of the reaction vessel 12 at the hole 16 by a clamp 18. The assembly 10 includes a stainless steel tube 20 open at each end, the lower end having a flange 21 onto which the clamp 18 bears, and the upper end being attached to a stainless steel conical coupling 22. The top end of the coupling 22 is welded to a stainless steel tubular hub 24 of bore about 25 mm, such hubs being sold under the name Graylok (trade mark).

At the top of the hub 24 is a stainless steel plate'26 with a 2.5 mm diameter orifice 28 at its centre, and with projecting annular flanges near its rim which locate in the bore of the hub 24, and the bore of another such hub 30 above the plate 26, respectively. The upper end of the hub 30 is welded to the outlet duct of a conventional sodium valve 32 whose inlet duct is at 90°. Another such tubular hub 33 is welded to the inlet duct, and at its other end is a 2 mm filter plate 34 with projecting annular flanges near its rim; the plate 34 locates between the hub 33 and another such hub 35. The adjacent ends of the pairs of hubs 24 and 30, and 33 and 35, have

external tapered flanges, which are engaged by external clamps (not shown); the clamps hold the pairs of hubs and the plates 26 and 34 securely and tightly together but enable the pairs of hubs to be disassembled for example to service the valve 32 or to change one of the plates 26 or 34.

In use liquid sodium at about 280°C is supplied via a pipe (not shown in Figure 1) to the hub 35, so when the valve 32 is open the sodium flows through the filter plate 34 and the valve 32 to emerge as a jet from the orifice 28, typically at a flow rate of about 100 kg/hour so the sodium in the jet travels at about 6 m/s. It will be appreciated that the entire assembly 10 must be kept at about 300°C ; and this is achieved by trace heating and thermal insulation (not shown).

A pipe 36 communicates with the bore of the hub 24, and four radial pipes 37 (only two are shown) communicate with an annular slot 38 around the top of the wall of the tube 20. In normal operation nitrogen gas at up to 450°C is supplied to all the pipes 36 and 37 so there is a steady flow of gas out of the hub 24 and out of the tube 20, which prevents caustic soda aerosol diffusing up to the orifice plate 26. However if any solid deposits are formed on the walls of the tube 20 or the hub 24, the gas flow can be temporarily replaced by a flow of aqueous caustic soda taken from the reaction vessel 12 which will thoroughly wash away any deposits, whether they are of sodium or caustic soda.

The valve 32 includes a conventional valve stem 39.

A prodder rod 40 is fixed to the end of the valve stem 39, projecting axially from it, passing through an axial hole in a three-legged guide block 41 (which locates in

the hub 30), so that as shown to a larger scale in Figure 2 the tip 42 of the prodder rod 40, which is of diameter 2.5 mm, projects through the orifice 28 when the valve 32 is closed (as shown). When the valve stem 39 is retracted to open the valve 32 the tip 42 of the prodder rod 40 is thereby withdrawn from the orifice 28. If during operation any solid deposits form in the orifice 28, these will be displaced by the tip 42 of the prodder rod 40 when the valve 32 is next closed.

Referring now to Figure 3, the injector port assembly 10 may be used as part of a plant 50 for disposing of slightly radioactive sodium. The sodium in this plant 50 is stored in molten form in a stainless steel tank 52 and can be transferred via a pipe 53 and the port assembly 10 to the reaction vessel 12, by supplying nitrogen gas to an inlet pipe 54. The reaction vessel 12 contains aqueous caustic soda at about 10 molar, with a nitrogen-filled space above the liquid level 14. The tank 52 and the pipe 53 are insulated, and heated electrically to about 300°C. A pump 56 recirculates caustic soda from the base of the vessel 12 via a heat exchanger 55 to four injector ports 58 around the top, so the liquid in the vessel 12 is turbulent ; the heat exchanger 55 ensures the temperature of the caustic soda does not exceed about 40°C. Since the sodium is slightly radioactive, both the storage tank 52 and the reaction vessel 12 are within a shielded enclosure 60 (indicated by a chain dotted line), and air is continuously extracted at 1 m/sec from the enclosure 60 via a duct 62 and a water scrubber 64 to a clean air outlet stack 65. The air flow is brought about by injecting water through a venturi into the scrubber 64.

Gases, in particular hydrogen, generated by the reactions within the reaction vessel 12 are carried by a pipe 66

and mixed with the air stream just before it reaches the scrubber 64.

Thus in operation the molten sodium is injected into the caustic soda 14 at a rate of for example 100 kg/hour, reacting to form slightly more concentrated caustic soda.

The pH of the caustic soda 14 is monitored, as is its level. A valve 68 enables the caustic soda to be drained off if necessary. If the pH gets as high as about 10.5 then water is added via a pump 70 from the base of the scrubber 64, and caustic soda overflows via a weir pipe 72. The caustic soda overflowing from the reaction vessel 12 can be neutralised by reacting it with hydrochloric acid, and passed through an ion exchange bed to remove many of the radioactive ions, so that the resulting output is substantially clean sodium chloride solution.