The invention relates to apparatus for separating a mixture of fluids, such as separating a minor proportion of a lighter fraction of a liquid, e.g. oil, from a major proportion of a heavier fraction of a liquid, e.g. water. One kind (hereinafter referred to as of the kind described) of such apparatus, is disclosed, for example, in WO 89/02312, and comprises a pressure vessel containing a plurality of hydrocyclones, each providing an elongate separating chamber extending from an upstream head, at which there is an inlet for a mixture to be separated and an overflow outlet for a lighter fraction, to a downstream end at which there is an underflow outlet for a heavier fraction, the hydrocyclones being supported by a transverse plate which is provided with an array of holes through which respective ones of the hydrocyclones extend, the upstream heads also being associated with a conduit system through which the overflow outlets lead to outside the vessel via a lighter fraction outlet or outlets of the vessel; the vessel being divided into a mixture chamber, to which the inlets of the hydrocyclones are open and which leads from outside the vessel via a mixture inlet of the vessel, and a heavier fraction chamber to which the underflow outlets of the hydrocyclones are open and which leads to outside the vessel via a heavier fraction outlet of the vessel.

One of the few problems that occurs with hydrocyclone separator apparatus of this type is that an individual cyclone may become blocked by contaminants, making the apparatus less efficient. In order to clear a blocked reject port, forming the overflow outlet of an individual hydrocyclone, it is necessary to shut down the apparatus and remove pipework and/or access plates from surrounding casings in order to rod-out the hydrocyclone. It would therefore clearly be advantageous if the overflow outlets of the hydrocyclones were readily accessible for rodding.

It is known, see for example WO 85/00759, to provide axially extending reject tubes which extend from the overflow outlet of each hydrocyclone to an end wall of the cyclone separator apparatus. The outlets from plural reject tubes are connected together into a manifold so that the lighter fraction of the mixture to be separated can be led away through a single pipe. However, connecting individual pipes between the manifold and the ends of the reject tubes means that pipework has to be disassembled in order to gain access to the reject tubes for rodding purposes.

In accordance with the present invention, in separating apparatus of the kind described, the conduit system through which the overflow outlets lead to the outside of the vessel, comprises a plurality of reject tubes, one for each hydrocyclone, extending in the longitudinal direction of the hydrocyclones, each tube passing through and being sealed to an end plate of the pressure vessel; a number of sleeves corresponding to the number of reject tubes, each sleeve being open only at one end and being disposed around the free end of a respective reject tube and releasably attached and sealed to the face of the end plate opposite the hydrocyclones at an aperture larger than the cross-section of the reject tube; and at least one cavity within the end plate in communication with a plurality of the apertures at which the sleeves are connected, the reject cavity having an outlet for the lighter fraction of the mixture.

By this apparatus, the end plate itself provides a simple manifold for collection of the lighter fractions ejected from the overflow outlets of the hydrocyclones, and the sleeves provide for ready access to the interior of the reject tubes, e.g. for rodding, in a manner which is simple and quick and which does not require the disassembly of plural pipe couplings or removal of the end plate.

A further advantage, from the operator's point of view, is that by sensing the temperature of each of the

sleeves, the operator can detect whether or not a blockage has occurred in the respective hydrocyclone, the temperature being relatively higher when fluid is flowing from the end of the reject tube and the inside of the sleeve than when the hydrocyclone is blocked and no fluid is flowing through the sleeve.

One example of hydrocyclone separating apparatus according to the present invention will now be described with reference to the accompanying drawings in which:- Figure 1 is a diagrammatic simplified axial section through the apparatus; and.

Figure 2 is an enlarged view of part of Figure 1. The illustrated apparatus comprises a substantially cylindrical pressure vessel formed in two sections 3,4, which are provided with flanges 5 and are sealed and secured together by means of bolts 6 passing through the flanges. A hydrocyclone-supporting plate 7 is sandwiched between the flanges 5 and divides the interior of the pressure vessel into a mixture chamber 8 having an inlet 9 in the wall of the vessel, and a heavier fraction chamber 10 having an outlet 11 in the wall of the vessel. The upper end of the pressure vessel is closed and sealed by an end plate 12 which is secured by a ring of bolts 13 to a flange 14 of the vessel. Mounted in the pressure vessel and extending through and seated on the supporting plate 7 are a plurality of, say, fifty-five hydrocyclones 15. Only one hydrocyclone is shown and clearly the drawings are not to scale. Each hydrocyclone extends through a respective hole 16 in the plate 7, the hydrocyclone being secured to the plate and the hole being sealed by a bolted flange 17. Each hydrocyclone has a head 18 provided with an inlet 19 exposed to the chamber 8 and an overflow outlet 20 connected to a reject tube 21. The interior of each hydrocyclone provides a conventional tapering, elongate separating chamber extending from the head to an underflow outlet 22 in communication with the chamber 10 at the

smaller end of the hydrocyclone. As shown more clearly in Figure 2 , each reject tube 21 is coupled and sealed to the overflow outlet of its respective hydrocyclone by means of a screw down gland nut 23 which clamps a flange at the lower end of the reject tube onto an end of the hydrocyclone head 18. The end plate 12 is provided by upper and lower parts 24 and 25, which are releasably secured together by means of a ring of bolts 26, and sealed together by means of a sealing ring 27, to define between the parts a reject cavity 28 having an external outlet 29. Each reject tube 21 extends up through a hole 30 in the lower end plate part 25, to which it is sealed by a sealing ring 31, and with an appreciable clearance, through a larger aperture 32 in the end plate part 24. The projecting end portion of the reject tube is surrounded with an appreciable clearance 33 by a sleeve 34 having a closed upper end 35. The sleeve is sealed and secured to the plate by means of a flange 36 on the sleeve, bolts 37 and sealing ring 38. During assembly, with the end plate 12 removed, the individual hydrocyclones are fitted through and bolted to the supporting plate 6. After the reject tubes 21 have been secured to their respective hydrocyclones, the end plate 12 is offered downwards over the reject tubes prior to being bolted to the rest of the pressure vessel. In order to guide the reject tubes through the holes 30 and apertures 32, guide funnels 39 are bolted to the bottom of the lower part 25 of the end plate. Furthermore, in order to accommodate any misalignment between individual hydrocyclones and their respective holes and apertures through the end plate, each reject tube is provided with two flexible portions 40. It may in some cases be necessary to provide a locating spider 41, which, particularly when the flexible portions 40 are provided, prevents the upper parts of the reject tubes from being displaced away from the vertical under their own weight.

In use, a mixture of, for example, water polluted with a small proportion of oil, is fed under pressure through the inlet 9 into the chamber 8 and hence into the hydrocyclones through their inlets 19. The water, at least partially depleted of oil, passes through the underflow outlets 22 into the chamber 10 and hence out of the vessel through the outlet 11. Meanwhile the small proportion of reject oil passes through the overflow outlets 20 and the respective reject pipes 21, and hence up within the sleeves 34, down through the annular clearance 33 and aperture 32 into the reject cavity 28, and hence out of the outlet 29, as indicated by the arrows.

During operation the warm oil will raise the temperature of the sleeves 34 and by touching the sleeves it can readily be determined whether one of the hydrocyclones or its overflow conduit system is blocked. If it is, after shutting down the apparatus, the appropriate sleeve 34 can be removed, and without dismantling any further parts of the apparatus, access is provided for rodding the reject tube, and possibly overflow outlet and even separating chamber of the offending hydrocyclone. The upper end of the reject tube may be flared to make it easier for a rod to be inserted.