GB2214770A

GB2214770A - Irradiation of a continuously flowing fluid

Info

Publication number: GB2214770A
Application number: GB8802121A
Authority: GB
Inventors: Richard Austin Smith; Elizabeth Mary Bostock
Original assignee: Individual
Current assignee: Individual
Priority date: 1988-02-01
Filing date: 1988-02-01
Publication date: 1989-09-06
Also published as: GB8802121D0

Abstract

A continuously flowing fluid is irradiated by a radioactive source 6 operating on a transport passage through which the fluid passes at a rate dependent on the radioactive source output and the degree of irradiation required. The radioactive source may be contained in a central conduit 2 around which is a concentric conduit 8 for containing the fluid flow 4. The fluid may alternatively flow through a helical passage (Figure 4), a plurality of passages around the central conduit (Fig 2) or a vicusoidally convoluted passage (Figure 1). A plurality of sources may be located in a tank through which the fluid flows, the tank containing stirring means (Figure 5) or baffles (Figure 6). <IMAGE>

Description

Improvements in or relating to the irradiation of a continuously flowing fluid This invention relates to the irradiation of continuously flowing fluid and more particualarly, though not exclusively, to the irradiation of a continuously flowing stream of sewage sludge.

The requirement of stabilisation and/or treatment of sewage sludge prior to disposal to agricultural land or certain tips has, in the past, been overcome in several different ways such as:- by lime dosing; cold or heated digestion; or by air drying for periods of up to one year. The reason for stabilisation and/or treatment is the killing of pathogens which would otherwise render the sludge unacceptable, from many aspects of Environmental or Public Health legislation, for an agricultural fertiliser which is the main or principal disposal route.

Existing methods of stabilisation and/or treatment require large volumes of storage to be available either in the open air or in such as steel or concrete tanks. Such storage facilities for vast volumes is expensive to provide in restricted municipalities. A further problem with existing methods is that they are also very labour intensive and involves the handling and double handling of an instrinsically unpleasant substance. The present invention will substantially overcome, if not completely irradicate these problems.

G. B. Patent No. 2120510A describes an apparatus for irradiating a continuously flowing stream of fluid. However, this apparatus is only suitable for small sample irradiation and would not be suitable for large scale irradiation of waste in a municipality. Sewage sludge would not be successfully irradiated with such equipment.

It is therefore an object of this invention to provide a means of irradiating a continuously flowing fluid which will substantially overcome, if not completely irradicate previous problems and provide munucipalities with a more compact, less labour intensive and cheaper plant.

According to the invention we provide a means of irradiating a continuously flowing fluid, comprising:- a radioactive source means operable on a transport passage through which said continuously flowing fluid passes at a rate dependent on said radioactive source output and the degree of irradiation required.

The invention will now be described by way of example only, in conjunction with the accompanying diagrams in which: Figure 1 shows apparatus for providing an easily flowable fluid with maximum contact with minimum length radiation source.

Figure 2 shows apparatus for providing maximum volumetric flow in conjunction with maximum irradiation.

Figure 3 shows apparatus for providing maximum irradiation of a thick continuously flowing fluid e.g. sludge.

Figure 4 shows apparatus for providing maximum irradiation for the required sterilisation of a continuously flowing fluid within a confined longitudinal space.

Figure 5 shows a motor driven stirrer and irradiation source combined and, Figure 6 shows a tank, or silo in which irradiation means are fitted.

Referring now to figure 1, a source containment tube (1) is mounted on the longitudinal axis of a conduit (2) around which is wrapped a continuous, or series of continuous, pipes(s) (3) wherein the pipe or pipes is/are folded back on its/themselves at each end of the conduit (2) to form a zig zag path, for a continuously flowing fluid contained in the pipe or pipes (3) around the conduit (2).

Each continuous pipe or pipes has an inlet (4) and an outlet (5).

The source containment tube provides a housing for at least one radio active source element (6) which may be conveniently mounted on a source rod (7). The number of radioactive source elements required will vary with the type of continuously flowing fluid to be irradiated and the radiation source in use. Although drawn with the inlet and outlet in close proximity it may be more convenient for the outlet to be as far away as possible from the inlet thereby ensuring less chance of contaminating irradiated fluid.

Referring to figure 2 wherein the numerals used refer to like parts in figure 1 the tubes (3) are all laid paralled to each other along, and outside, the length of the conduit (2) with their inlets at one end and their outlets at the other. This configuration affords maximum exposure for the required sterilisation within a confined lateral space. It also provides maximum volumetric flow in conjunction with maximum irradiation.

Referring to figure (3) wherein the numerals used refer to like parts in figure 1 and 2 the source containment tube (1) is mounted on the longitudinal axis of the conduit (2) around which is fitted a further conduit (8) to form an annular conduit through which the continuously flowing fluid passes. The source containment tube (1) may be used to form the inner wall of the annulus but it is preferable that the source containment tube (1) and radioactive source element (6) and rod (7) are extractable as a complete unit without contact with the fluid. This configuration affords the fluid maximum exposure for the required sterilisation within a simple plant arrangement.

Referring to figure 4, a method similar to that shown in figure 1 is employed except that the tube (3) is spirally wound around the source containment tube (1). As with the configuration of figure 1 this provides maximum exposure for the required sterilisation within a confined longitudinal space.

The apparatus shown in figures 1,2, 3 and 4 may be operated in any dimensional plane with the fluid flow induced by gravity, or positive or negative pressure.

Referring to figure 5 a number of source containment tubes (1) are mounted on a gantry (9). The central axis (10) of which is a motor drive shaft, with a motor (11) mounted above. The complete arrangement may be located in a tank (12) containing fluid, such as sludge, charged and withdrawn by such as gravity, or positive or negative pressure. The gantry (9) operates as a support framework for the source containment tubes (1) housing the source elements and rods, (6) and (7) respectively, and also as a stirrer for the agitation of the fluid. It is also to be understood that adequate irradiation may be obtained by the continuous flow method with a low flow rate.

Referring to figure 6, the source containment tube (1) is located in a tank or silo (13) through which fluid, such as sludge, enters and is withdrawn under gravity or by positive or negative pressure. The irradiation zone (14) is divided laterally into concentric annular zones, with different retention times in each zone; or different flow rates in each zone. In this irradiator, control valves, not shown, mounted below the concentric annular zones are adjusted to provide periods increasing in duration from the central to the outer zone, thus compensating for the reduction in dose rates for increase in distances from the radio active source element (6). Baffles (15) may also be mounted within the annular zones in order to cause more turbulent fluid flow and homogenous fluid exposure within each zone.

It will be obvious to those skilled in the art that various materials may be used, for example, the two conduits (2) and (8) may be manufactured from such as iron, steel, plastic, asbestos cement, unreinforced or reinforced concrete dependent on requirement and the general situation and/or location in which the irradiation is to take place. The plant may be conveniently housed in a building suitable for providing security against unauthorised access and adequate safety precautions relating to the radio active source used, which may be one of many dependent on choice and circumstances, may be easily installed. With the equipment of figures 5 and 6 a free discharge outlet direct to open or closed storage, or to road, rail or sea tankers is made simple.

Claims

1. A means of irradiating a continuously flowing fluid, comprising:- a radioactive source means, operable on a transport passage through which said continuously flowing fluid passes at a rate dependent on said radioactive source output and the degree of irradiation required.

2. A means of irradiating a continuously flowing fluid as claimed in Claim 1 wherein the continuously flowing fluid is sewage sludge for treatment prior to dispersal to such as agricultural land.

3. A means of irradiating a continuously flowing fluid as claimed in Claim 1 or Claim 2 wherein the radioactive source is a radioactive atom.

4. A means of irradiating a continuously flowing fluid as claimed in Claim 1 or Claim 2 wherein the radioactive source is a radioactive isotope.

5. A means of irradiating a continuously flowing fluid as claimed in Claim 1 or Claim 2 wherein the radioactive source is a radioactive chain.

6. A means of irradiating a continuously flowing fluid as claimed in Claim 1 or Claim 2 wherein the radioactive source is electron bombardment.

7. A means of irradiating a continuously flowing fluid as claimed in Claim 1 or Claim 2 having an irradiation zone which is divided laterally into concentric annular zones.

8. A means of irradiating a continuously flowing fluid as claimed in Claim 7 wherein each zone has a different retention time.

9. A means of irradiating a continuously flowing fluid as claimed in Claim 7 wherein each zone has a different flow rate.

10. A means of irradiating a continuously flowing fluid substantially as described and illustrated in the specification.