CLEANING OF CONDUITS, ESPECIALLY OF A PHOTOBIOREACTOR

Abstract: Apparatus for cleaning internal walls of at least one conduit (10), for example of a photobioreactor, comprises mobile cleaning means, such as a pig (4) or a bead, within the conduit (10), at least one inlet valve (2) for introducing liquid into the conduit (10) such that said liquid can propel said cleaning means (4) along said conduit (10), at least one aperture (6) in said conduit (10) arranged to permit part of the liquid in said conduit (10) to pass from said conduit into a collection vessel (7), and to prevent passage of said cleaning means (4) through said aperture (6), and pump means (9) to pump liquid passing through the aperture back to the inlet valve (2).

Description: CLEANING OF CONDUITS, ESPECIALLY OF A PHOTOBIOREACTOR The present invention relates to method and apparatus for cleaning at least one conduit of, for example, an automotive radiator or a photobioreactor . A common problem when fluid flows through a conduit is that there is an accumulation of debris on the internal walls. This is a particular problem with photobioreactors, and the following background to the invention is given in the context of photobioreactors . Typically, photobioreactors comprise substantially optically transparent tubes in which photosynthetic microorganisms, such as algae or the like, dispersed within a culture medium in such tubes, can utilise light to undergo photosynthetic reactions . Generally, after a period of time in the photobioreactor, micro-organisms accumulate on the internal walls of the tube to which they adhere. Adhesion of the microorganisms to the internal tube walls leads to a reduction in the volume of culture within the tube which may be exposed to light, and consequently to less efficient biomass production. It is therefore desirable for a photobioreactor system to incorporate a cleaning mechanism which prevents adhesion of the microorganisms to the internal walls of the tube. It is desirable for any such cleaning mechanism to be automatic in order to optimise biomass production by obviating the need to shut the reactor down. Many cleaning systems have been previously proposed for photobioreactors. An example of such a cleaning system comprises pockets at each end of the photobioreactor. Periodic reversal of the flow of liquid culture medium in the tube instigates movement of a cleaning element in the direction of the flow in the photobioreactor tube, which cleaning element removes micro- organis s adhering to the internal walls of the tube. Such pocket-type cleaning systems can be expensive to use, therefore increasing the production costs of the photobioreactors. Similar problems arise with accumulation of debris on the internal walls of other closed liquid circulation systems, such as, for example, automotive radiators or the like. Thus, it is the purpose of one aspect of the present invention to alleviate such difficulties and to provide a substantially improved and more cost effective apparatus for cleaning internal walls of a liquid circulation system. Therefore, according to one aspect of the present invention there is provided apparatus for cleaning internal walls of at least one conduit, the apparatus comprising: mobile cleaning means within the conduit; at least one inlet valve connectable to the conduit for introducing liquid into the conduit, wherein the liquid entering the conduit is arranged to propel the cleaning means along the conduit; at least one aperture in the conduit arranged to permit a substantial portion of the liquid in the conduit to pass from the conduit into a collection vessel, and to prevent passage of the cleaning means through the aperture; and pump means to pumping liquid passing through the aperture to the inlet valve. Preferably the apparatus includes a plurality of the above-mentioned apertures arranged to permit liquid from the conduit to pass to a collection vessel. Thus, advantageously, when the conduit is part of a photobioreactor, the introduction of a culture medium into the conduit may cause the cleaning means to be circulated around a photobioreactor circuit without the need to reverse the flow of the culture medium. Thus, in this embodiment, the culture medium may be pumped under pressure into a respective tube from the collection vessel, the culture medium being then recycled to the photobioreactor tube, the cleaning means being maintained within the closed photobioreactor circuit. New culture medium may advantageously be introduced into the collection vessel when required so as to replenish depleted nutrients in the culture medium. Preferably the inlet valve is provided substantially downstream relative to flow of the liquid from the or each such aperture. Thus, advantageously, when the conduit is part of a photobioreactor, and culture medium is pumped back into the respective tube from the collection vessel, the medium is under pressure and induces a flow in the medium already present in the photobioreactor tube downstream of the or each aperture. The flow of the culture medium between the inlet valve and the respective aperture (s) is substantially reduced by the flow of a substantial portion of the culture medium into the collection vessel. The flow of culture medium downstream of the respective aperture (s) advantageously induces an increase in the flow rate in the culture medium in the tube between the apertures and the inlet valve, which increased flow advantageously allows the cleaning means to pass along the photobioreactor tube containing the apertures. Typically, the inlet valve is arranged to introduce the liquid substantially adjacent the conduit. In a preferred embodiment of the invention, approximately 40-70% of a culture medium may be passed through the aperture or apertures to the collection vessel. Preferably, the collection vessel is fitted with a gas valve, which advantageously allows gaseous by-products of photosynthesis which have accumulated in the culture medium to be released therefrom. Therefore, the apparatus has the further advantage of permitting removal of gaseous waste by-products of photosynthesis, such as oxygen, from the medium, in addition to permitting cleaning of the photobioreactor tube. The de-gassed culture medium may then be re-introduced into the photobioreactor tube by a pump mechanism as described above. In one embodiment of the invention, the cleaning means comprises a plurality of granules or beads which can be passed within the liquid along the conduit. Thus, advantageously, such beads may clean the internal walls of the conduit by contacting the internal walls when the beads are dispersed in the flowing culture medium. In this embodiment, the culture medium is propelled around the photobioreactor circuit directly by a pump mechanism which in turn propels the beads or granules around the photobioreactor circuit. Preferably a centrifugal pump is used, and where such a pump is used, the algae used in the culture medium may have relatively thick cell walls. Thus, advantageously, when thick walled algae are used, it is possible to use granules or beads to clean the internal walls of the photobioreactor, which beads or granules are easily propelled around the photobioreactor circuit by a simple pump mechanism. Preferably such beads are substantially cylindrical. Typically, the beads have an average major dimension of 1 to 3mm (typically both the axis of the cylinder, and the diameter, have averages values in this range) . Desirably, the beads are of polystyrene, polypropylene, nylon, PVC or polyvinylacetate. Preferably the liquid is propelled along the conduit directly by a pump mechanism which in turn propels the beads or granules along the conduit. In an alternative embodiment of the first aspect of the invention, the cleaning means comprises a pipeline pig. Advantageously the pig may be of sufficient size that it can clean substantially the entire surface of the internal walls of the conduit. Preferably, the pig has a density substantially equal to that of water. The pig is also preferably compressibly resilient, such that it may pass through the conduit in a slightly compressed condition. Sometimes however, it is not possible to use a photobioreactor which is in the form of a closed circuit. Therefore, it may be necessary to have a cleaning system which can reciprocate through the photobioreactor circuit from one end of the tube to the other (that is, to travel alternately in one direction and then in the other) . In this embodiment of the invention, the at least one photobioreactor tube having the aperture (s) preferably has a length substantially equal to or (preferably) less than the length of the pig. Preferably the inlet valve is arranged to introduce the culture medium substantially adjacent the photobioreactor tube having the aperture (s) . Thus, advantageously, the pressure drop of the culture medium in the photobioreactor tube having the apertures is kept to a minimum. According to a second aspect of the present invention there is provided a method of cleaning one or more conduits in a closed circuit, which method comprises introducing a liquid medium into a selected conduit of a circuit via an inlet valve, the medium being propelled by a pump from a collection vessel to the inlet valve, said medium collecting in the collection vessel following passage through an aperture provided in at least one of the conduits, the introduction of the medium into the conduits being arranged to propel cleaning means around the circuit. Preferred aspects of the method according to the invention are as described above with reference to the apparatus. The method preferably further comprises releasing accumulated gaseous products of photosynthesis by a gas valve provided in the collection vessel. Thus the method has the dual advantage of not only cleaning the tubes but permitting removal of gaseous products of photosynthesis. The invention may be more clearly understood from the following description given by way of example only, with reference to the accompanying drawings, wherein: Figure 1 is a sectional view of an apparatus for cleaning conduits such as photobioreactor tubes according to a first aspect of the present invention; Figure 2 is a sectional view of an apparatus at one end of a conduit for cleaning such a conduit in a non-closed photobioreactor circuit according to a fourth aspect of the present invention; and Figure 3 is a schematic view of the complete apparatus for cleaning a conduit in a non-closed photobioreactor circuit. Referring to Figure 1, there is illustrated apparatus for cleaning photobioreactor conduits in a closed photobioreactor circuit generally indicated by the reference numeral 1. The apparatus comprises an ejector tube 2 which connects a collection vessel 7 to a photobioreactor conduit 3. Several conduits 3 are connected together to form a photobioreactor (not shown in full) . Within the photobioreactor is a pipeline pig 4 which is propelled within the conduit 3 around the photobioreactor circuit by movement of a culture medium 5 within the conduit 3. A further photobioreactor conduit 10 comprises a plurality of apertures 6 therein which allow approximately 40 to 70% of the culture medium 5 to flow into a collection vessel 7 when the culture medium reaches the tube 10. The apertures 6 are dimensioned to prevent passage of the pig 4 therethrough. Collection vessel 7 comprises a gas valve 8 which allows oxygen or other gaseous products accumulated within the culture medium by virtue of photosynthesis, to be released. A further inlet (not shown) may be provided to introduce fresh culture medium into the photobioreactor to replenish the culture medium. In use, liquid culture medium 5 circulates around the photobioreactor 1 and enters the tube 10. A substantial portion of the culture medium 5 enters the collection vessel 7 by flowing through apertures 6 whilst the remainder of the culture medium 5 continues to circulate around the photobioreactor tubes. The culture medium 5 accumulating in the collection vessel 7 is pumped by a pump 9 from the collection vessel 7 to the tube 3 via the ejector tube 2. When the culture medium 5 enters the tube 3 via the ejector tube 2 the medium 5 is under a greater pressure than the culture medium 5 already in the tube 3 , thereby inducing a flow of the medium 5 in the tube 3 , in the direction of arrow A, around the photobioreactor circuit. Any culture medium 5 which does not enter the collection vessel 7 remains in the tube 10 and is at a greatly reduced pressure compared to the culture medium 5 which enters the tube 3 downstream of the apertures 6. The culture medium 5 flowing in the direction of arrow A induces the culture medium 5 in tube 10 to flow in the direction of arrow A, thus pulling the cleaning pig 4 through the tube 10. Once the pig 4 has passed the ejector tube 2 it is pushed by the incoming culture medium 5 to begin its journey through the photobioreactor tube 3 until it reaches tube 10 once again. Therefore a continuous flow circuit is provided in one direction in the photobioreactor. Referring to Figures 2 and 3, there is illustrated apparatus for cleaning photobioreactor tubes in a non-closed photobioreactor circuit generally indicated by the reference numeral 31. The apparatus comprises culture medium reception vessels 32 and 33 and manifolds 34 and 35, at both ends of a photobioreactor tube 36. Within the photobioreactor tube 36 is a pipeline pig 37 (shown in Figure 2) which is propelled from end to end of the photobioreactor tube 36 by movement of the culture medium 38. In use, the culture medium flowing in the direction of arrow A (as shown in Figure 3) is received in the reception vessel 32 by passing through a section of photobioreactor tube 36 having apertures 39 therein. The cleaning pig 37 has a greater length than the dimensions of the apertures 39 and therefore passes through the photobioreactor tube having the apertures 39 (as shown in Figure 2) and then comes to rest adjacent the manifold 34, there being insufficient flow to carry the pig 37 any further. The reception vessels 32 and 33 are connected to a collection tank 40 by conduits 45 and 46 and the culture medium 38 passes through conduit 45 from reception vessel 32 and accumulates in the tank 40 when the valve 41 is open. The culture medium is then pumped under pressure by a centrifugal pump 50 to the manifold 35, when the valve 42 is also open. Valves 41 and 42 are opened and closed simultaneously. The culture medium then flows in the direction of arrow A from the manifold 35 past reception vessel 33, which is sealed by closing of valve 44. The culture medium 38 flows around the photobioreactor tube until it once again reaches vessel 32 and the cycle begins again. When it is necessary to clean the tubes, the pig 37 is moved from its rest position adjacent manifold 34, around the tube 36 in the direction of arrow B (which is opposite in direction to arrow A) . To do this, the flow of the culture medium 38 must be reversed. Valves 41 and 42 are then simultaneously closed and valves 43 and 44 opened. The culture medium 38 is then pumped under pressure from the collection tank 40 by the pump 50, to the manifold 34. The culture medium 38 then enters the photobioreactor tube 36 from the manifold 34 and flows in the direction of arrow B. This results in a reversal of the flow of culture medium 38 and forces the pig 37 from its rest position adjacent manifold 34 around the photobioreactor tube 36 until the culture medium 38 eventually passes the reception vessel 33 to come to rest adjacent manifold 35 (as shown in Figure 2) . The culture medium 38 then enters reception vessel 33, via the apparatus 39 and begins the cycle once more by entering the tank 40 via conduit 46. Therefore, the valves 41 to 44 can be opened and closed as appropriate to change the direction of the culture flow and hence the direction of the pig 37. An oxygen release valve 47 is provided on the reception vessels 32 and 33 which allows accumulated oxygen from the photosynthetic reaction to be released from the photobioreactor circuit 1.

Claims: CLAIMS : 1. Apparatus for cleaning at least one conduit, said apparatus comprising: mobile cleaning means within said conduit; at least one inlet valve connectable to said conduit for introducing liquid into the conduit, such that said liquid entering the conduit via said inlet valve can propel said cleaning means along said conduit; at least one aperture in said conduit arranged to permit part of the liquid in said conduit to pass from said conduit into a collection vessel, and to prevent passage of said cleaning means through said aperture; and pump means for pumping liquid passing through said aperture to said inlet valve. 2. Apparatus according to claim 1, which includes a plurality of said apertures. 3. Apparatus according to claim 1 or 2 , wherein said inlet valve is provided substantially downstream relative to flow of said liquid from said aperture. 4. Apparatus according to any of claims 1 to 3 , wherein said inlet valve is arranged to introduce said liquid substantially adjacent the at least one tube. 5. Apparatus according to any of claims 1 to 4 , wherein said collection vessel has a gas valve. 6. Apparatus according to any of claims 1 to 5, wherein said cleaning means, comprises a plurality of granules or beads which can be passed within the liquid along the conduit. 7. Apparatus according to claim 6, wherein said beads are cylindrical. 8. Apparatus according to claim 6 or 7, wherein said liquid is propelled along said conduit directly by a pump mechanism which in turn propels the beads or granules along the conduit. 9. Apparatus according to any of claims 6 to 8, wherein said beads have an average major dimension of 1 to 3mm. 10. Apparatus according to any of claims 6 to 9, wherein said beads are of polystyrene, polypropylene, nylon, PVC or polyvinylacetate. 11. Apparatus according to any of claims 1 to 5, wherein said cleaning means comprises a pipeline pig. 12. Apparatus according to claim 11, wherein said pig has a density substantially equal to that of water. 13. Apparatus according to claim 11 or 12, wherein said pig is compressibly resilient. 14. Apparatus according to any of claims 1 to 13, wherein said conduit is a photobioreactor. 15. Apparatus according to claim 14, wherein said conduit comprises an acrylic plastics material or glass. 16. Apparatus according to claim 14 or 15, wherein said liquid comprises a culture medium. 17. A method of cleaning one or more conduits in a closed circuit, which method comprises introducing a liquid into a selected conduit of a circuit via an inlet valve, said liquid being propelled by a pump from a collection vessel to said inlet valve, said medium collecting in a collection vessel following passage through an aperture provided in at least one of said conduits, said introduction of said medium into said conduits being arranged to propel cleaning means around the circuit. 18. A method according to claim 17, wherein said conduit comprises photobioreactor tubes. 19. A method according to claim 18, which further comprises releasing accumulated gaseous products of photosynthesis by a gas valve provided in the collection vessel. 20. A method according to any of claims 17 to 19, wherein said cleaning means comprises a plurality of granules or beads which can be passed within the liquid along the conduit. 21. A method according to claim 20, wherein said beads are substantially cylindrical. 22. A method according to claim 20 or 21, wherein said beads have a major dimension of 1 to 3mm. 23. A method according to any of claims 20 to 22, wherein said beads are of polystyrene, polypropylene, nylon, PVC or polyvinylacetate. 24. A method according to any of claims 20 to 23, wherein said liquid is propelled along said conduit directly by a pump mechanism which in turn propels the beads or granules along the conduit. 25. A method according to claim 17 or 18, wherein said cleaning means comprises a pipeline pig. 26. A method according to claim 25, wherein said pig has a density substantially equal to that of water. 27. A method according to claim 25 or 26, wherein said pig is compressibly resilient. 28. A method according to any of claims 17 to 27, wherein said conduit comprises unplasticised PVC. 29. A method according to any of claims 17 to 28, wherein said liquid comprises a culture medium.

Inventors: JENKINS DAVID PAUL DI, JENKINS, DAVID, PAUL +DI
Applicants: APPLIED PHOTOSYNTHETICS LIMITE, JENKINS GWYN & LM, APPLIED PHOTOSYNTHETICS LIMITED, JENKINS, GWYN +LM
Application year: 1997
Main classification: B08B9
IPC codes: B08B9, F28G1