System and method

Abstract

An ozone sterilisation system 2 comprising a mixer 4 comprising a mixing chamber for receiving material to be sterilised and an ozone generator 8 configured to generate a supply gas comprising ozone a

Description

The present disclosure relates to ozone sterilisation systems and methods particularly, but not exclusively, for treating animal feed. Microorganisms can form on food which produce chemical compounds that are harmful to human and animal health. Sterilisation by heat is the most widely used means to increase food safety by destroying harmful substances from telluric origin or resulting from contamination during storage. Contaminants include microbes, bacteria, pesticide residues, mycotoxins and various spores. The use of heat may cause an alteration of the nutritional properties of the food. Therefore, other techniques exist which do not involve heating, such as physical treatment by ionization and chemical treatments. However, these two techniques have serious disadvantages. In particular, the needed control of these treatments (especially ionization) might lead to increased transportation costs to ad-hoc facilities and are in general incompatible with a normal setting where animal feed is produced. Chemical agents might include hydrogen peroxide, chlorine or peracetic acid, which might be difficult to control, or harmful to health or the environment by the creation of further chemical compounds. An alternative approach to cold sterilisation which is very promising in destroying contaminants without affecting organoleptic characteristics is the use of ozone. Ozone has a natural tendency to break down into dioxygen (O2) and atomic oxygen (0) or to react with other compounds. This ability to easily give up an oxygen atom gives it a very strong oxidizing power (E° = 2.07 V) compared to chlorine (E° = 1.36 V) and oxygen (E° = 1.23 V). As a result, ozone is highly reactive with biological matter, degrading the cellular walls of harmful substances. However, current ozone sterilisation systems and methods are not well optimised, particularly for use with animal feed, and suffer from high energy requirements. It is therefore desirable to provide improved ozone sterilisation systems and methods. In accordance with an aspect, there is provided an ozone sterilisation system comprising: a mixer comprising a mixing chamber for receiving material to be sterilised; an ozone generator configured to generate a supply gas comprising ozone and oxygen; a storage tank having an inlet which is fluidly connected to the ozone generator and an outlet which is fluidly connected via a valve to an ozone inlet provided on the mixer which opens into the mixing chamber; wherein the mixer is configured to operate in a batchwise manner with the material being loaded, treated and then unloaded and wherein the ozone generator is configured to fill the storage tank with the valve in a closed position while the material to be sterilised is loaded into and / or unloaded from the mixing chamber. In some examples, the storage tank is expandable. In some examples, the storage tank comprises a bladder, diaphragm or other movable barrier. In some examples, the mixer further comprises an outlet vent which expels an exhaust gas from the mixing chamber. In some examples, the ozone sterilisation system further comprises a control system, wherein the control system comprises one or more sensors which detect the presence and / or concentration of components in the exhaust gas from the mixing chamber. In some examples, the control system is configured to identify a change in one or more of the components in the exhaust gas which indicates that sterilisation is complete. In some examples, the control system is configured to detect the presence and / or concentration of components in the supply gas and to compare this to the exhaust gas to determine the change. In some examples, when the control system detects that sterilisation is complete, the control system is configured to stop the mixer and / or evacuate the mixing chamber. In some examples, the control system comprises one or more of an ozone sensor, an oxygen sensor and a CO2 sensor. In some examples, the outlet vent is fluidly connected to an extraction fan or pump. In some examples, the extraction fan or pump is configured to maintain a negative pressure in the mixing chamber. In some examples, the ozone sterilisation system further comprises a control system, wherein the control system comprises a pressure sensor which is configured to sense the pressure within the mixing chamber and to actively control the extraction fan or pump to maintain the negative pressure in the mixing chamber. In some examples, the outlet vent is connected to a return line which returns the exhaust gas to the ozone generator. In some examples, one or more of a CO2 scrubber, a dryer and one or more storage tanks are provided along the return line. In some examples, the outlet vent is connected to a return circuit which recycles the exhaust gas such that it passes through the mixer multiple times. In some examples, the ozone sterilisation system further comprising an oxygen concentrator which is fluidly connected to the ozone generator and is configured to supply oxygen to the ozone generator. In some examples, the supply gas comprises 10-20% ozone. In some examples, the material is treated with ozone at an ozone to material weight ratio of 2kg / T - 4kg / T. In some examples, the mixer further comprises water injectors which supply water to the material to be sterilised. In some examples, the water injectors are configured to supply water having a weight which is 5-10% of the weight of the material to be sterilised, preferably 7-9% and more preferably 8%. In some examples, the ozone generator operates continuously while the material is being loaded, treated and unloaded. In some examples, the mixer is a plough mixer. In accordance with an aspect, there is provided an ozone sterilisation method comprising: loading a mixing chamber of a mixer with material to be sterilised; while the mixing chamber is being loaded, filling a storage tank with a supply gas comprising ozone and oxygen from an ozone generator; introducing the supply gas from the storage tank to the mixing chamber; mixing the material in the mixing chamber in the presence of the supply gas in order to sterilise the material; unloading the material from the mixing chamber; and while the material is being mixed and unloaded, refilling the storage tank with supply gas from the ozone generator. In accordance with an aspect, there is provided an ozone sterilisation system comprising: a mixer comprising a mixing chamber for receiving material to be sterilised; an ozone generator configured to generate a supply gas comprising ozone and oxygen which is fed to an ozone inlet provided on the mixer which opens into the mixing chamber; wherein the mixer comprises an outlet vent which is configured to expel an exhaust gas from the mixing chamber; and wherein the outlet vent is connected to a return line which returns the exhaust gas to the ozone generator. In some examples, one or more of a CO2 scrubber, a dryer and one or more storage tanks are provided along the return line. In accordance with an aspect, there is provided an ozone sterilisation method comprising: generating a supply gas comprising ozone and oxygen using an ozone generator; introducing the supply gas to a mixing chamber of a mixer containing material to be sterilised; mixing the material in the mixing chamber in the presence of the supply gas in order to sterilise the material; expelling exhaust gas from an outlet vent of the mixer; and recycling the exhaust gas to the ozone generator for reuse in generating supply gas. In accordance with an aspect, there is provided an ozone sterilisation system comprising: a mixer comprising a mixing chamber for receiving material to be sterilised; an ozone generator configured to generate a supply gas comprising ozone and oxygen which is fed to an ozone inlet provided on the mixer which opens into the mixing chamber; wherein the mixer comprises an outlet vent which is configured to expel an exhaust gas from the mixing chamber; and wherein the outlet vent is fluidly connected to an extraction fan or pump; wherein the extraction fan or pump is configured to maintain a negative pressure in the mixing chamber. In some examples, the ozone sterilisation system further comprises a control system, wherein the control system comprises a pressure sensor which is configured to sense the pressure within the mixing chamber and to actively control the extraction fan or pump to maintain the negative pressure in the mixing chamber. In accordance with an aspect, there is provided an ozone sterilisation method comprising: generating a supply gas comprising ozone and oxygen using an ozone generator; introducing the supply gas to a mixing chamber of a mixer containing material to be sterilised; mixing the material in the mixing chamber in the presence of the supply gas in order to sterilise the material; expelling exhaust gas from an outlet vent of the mixer; and maintaining a negative pressure in the mixing chamber using an extraction fan or pump fluidly connected to the outlet vent. In accordance with an aspect, there is provided an ozone sterilisation system comprising: a mixer comprising a mixing chamber for receiving material to be sterilised; an ozone generator configured to generate a supply gas comprising ozone and oxygen which is fed to an ozone inlet provided on the mixer which opens into the mixing chamber; wherein the mixer comprises an outlet vent which is configured to expel an exhaust gas from the mixing chamber; and wherein the ozone sterilisation system further comprises a control system, wherein the control system comprises one or more sensors which detect the presence and / or concentration of components in the exhaust gas from the mixing chamber. In some examples, the control system is configured to identify a change in one or more of the components in the exhaust gas which indicates that sterilisation is complete. In some examples, the control system is configured to detect the presence and / or concentration of components in the supply gas and to compare this to the exhaust gas to determine the change. In some examples, when the control system detects that sterilisation is complete, the control system is configured to stop the mixer and / or evacuate the mixing chamber. In some examples, the control system comprises one or more of an ozone sensor, an oxygen sensor and a CO2 sensor. In accordance with an aspect, there is provided an ozone sterilisation method comprising: generating a supply gas comprising ozone and oxygen using an ozone generator; introducing the supply gas to a mixing chamber of a mixer containing material to be sterilised; mixing the material in the mixing chamber in the presence of the supply gas in order to sterilise the material; expelling exhaust gas from an outlet vent of the mixer; and analysing the exhaust gas using one or more sensors to detect the presence and / or concentration of components in the exhaust gas from the mixing chamber. It will be appreciated that any of the aspects described above may include features from any of the other aspects. For a better understanding of the invention, and to show more clearly how it may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which: Figure 1 is a schematic diagram of an ozone sterilisation apparatus according to an embodiment of the disclosure; Figure 2 is a schematic diagram of an another embodiment of the disclosure; Figure 3 is a schematic diagram of an another embodiment of the disclosure; Figure 4 is a schematic diagram of an another embodiment of the disclosure; and ozone sterilisation apparatus according to ozone sterilisation apparatus according to ozone sterilisation apparatus according to Figure 5 is a schematic diagram of an ozone sterilisation apparatus according to another embodiment of the disclosure. Figure 1 shows a schematic diagram of an ozone sterilisation system 2 according to an embodiment. The ozone sterilisation system 2 comprises a feed mixer 4. In this example, the mixer 4 is a plough mixer (also referred to as a plough shear mixer, ploughshare mixer, plow mixer). The plough mixer comprises a cylindrical drum which defines a mixing chamber. A rotatable shaft extends axially within the cylindrical drum. A plurality of mixing elements (e.g., plough elements) extend radially from the shaft at positions which are spaced circumferentially and axially along the shaft. The shaft is connected to a drive motor which rotates the shaft and thus the mixing elements within the mixing chamber. The cylindrical drum comprises an inlet and an outlet. In this example, the plough mixer is a batch (discontinuous) mixer and so the inlet and outlet are selectively closable. The inlet may therefore be opened and a batch of material (e.g., animal feed) introduced to the cylindrical drum through the inlet. The inlet can then be closed during operation of the mixer 4. Once the material has been sufficiently mixed (e.g., after a predetermined time), the outlet can be opened to remove the mixed material from the cylindrical drum. The process can then be repeated to mix another batch of material. The ozone sterilisation system 2 further comprises an oxygen concentrator 6. The oxygen concentrator 6 is configured to remove nitrogen from air to provide a supply of oxygen. The oxygen concentrator 6 provides the supply of oxygen to an ozone generator 8 which is configured to generate ozone gas. Specifically, the ozone generator 8 splits apart some of the dioxygen molecules (O2) into individual oxygen atoms (0) which recombine with the dioxygen to form ozone (O3). A proportion of the oxygen atoms will also combine with other oxygen atoms to again form dioxygen. Accordingly, the gas supplied by the ozone generator is a mix of ozone and dioxygen (referred to simply as oxygen below). In other examples, the oxygen concentrator 6 may be integrated into the ozone generator 8 such that the ozone generator 8 utilises air, rather than oxygen. The ozone generator 8 is connected to an inlet port 10 of a storage tank 12 via a valve 14. The storage tank 12 has an outlet port 16 which is connected to an ozone inlet 20 provided on the mixer 4 (e.g., in the cylindrical drum and opening into the mixing chamber) via a valve 18. The mixer 4 is also provided with an outlet vent 22. As shown in Figure 1, the outlet vent 22 is connected to an extraction fan 24. A filter 26 may be disposed between the outlet vent 22 and the extraction fan 24. The extraction fan 24 is connected to an exhaust chimney 28 which vents to atmosphere. The ozone sterilisation system 2 can be used to sterilise animal feed. The animal feed (e.g., feed mash or the constituent ingredients of the animal feed) can be loaded into the mixer 4 via the inlet. As described previously, the mixer 4 is a batch mixer and thus a batch of animal feed is loaded into the mixing chamber whilst the mixing elements are stationary. While the batch of animal feed is being loaded into the mixer 4, the oxygen concentrator 6 and ozone generator 8 are operational, with the valve 14 upstream of the storage tank 12 open and the valve 18 downstream of the storage tank 12 closed. Accordingly, the ozone generator 8 supplies ozone gas (along with oxygen) to the storage tank 12 while the mixer 4 is being loaded. The way ozone decomposes in oxygen at room temperature means that the ozone generation has a maximum capacity of 20% (by weight) ozone concentration in oxygen. Ozone sterilisation systems typically use much lower concentrations of ozone for treatment. However, it has been found that using higher concentrations is not only more effective for sterilisation but also minimises the quantity of oxygen required, thereby improving efficiency. In particular, it has been found that concentrations of between 10-20% (150-300g / Nm3) are particularly effective, with 20% preferred. It has also been found that an ozone to animal feed ratio of 2kg / T - 4kg / T provides optimum results, with potentially a log reduction of 3 or higher. The storage tank 12 may be expandable (i.e., has a variable capacity / volume) such that it is initially empty, and its volume increases with the volume of ozone and oxygen provided by the ozone generator 8. This arrangement minimises the volume of air in the storage tank 12 prior to and after filling with ozone and oxygen. For example, the storage tank 12 may comprise a bladder, diaphragm or other movable barrier. Once the mixer 4 has been filled with the batch of animal feed, the valve 18 downstream of the storage tank 12 can be opened in order to release the ozone and oxygen stored in the storage tank 12 which is then fed into the mixer 4 via the ozone inlet 20. This acts to displace the air within the mixer 4 out of the outlet vent 22. The expandable nature of the storage tank 12 may be beneficial in that it generates a biasing force which drives the ozone and oxygen mix out of the outlet port 16 and into the mixer 4. It will be appreciated that the storage tank 12 is able to provide a high volume and flow rate of ozone to the mixer 4. In particular, the storage tank 12 may provide a higher volume and flow rate of ozone than can be supplied directly by the ozone generator 8 and this arrangement therefore allows a smaller, less expensive and more efficient ozone generator 8 to be used. The mixer 4 can be operated to rotate the shaft and thus mixing elements, thereby mixing the animal feed in the presence of ozone. The ozone quickly reacts with biological matter present in the animal feed and thus removes pathogens and other contaminants from the animal feed. The extraction fan 24 can be operated to remove gas from within the mixer 4. The extraction fan 24 may be activated (e.g., continuously or intermittently) while the mixer 4 is being operated or only after a predetermined time. The operation of the extraction fan 24 may be configured so as to ensure that a negative pressure (i e., below ambient pressure) is maintained within the mixing chamber of the mixer 4. The mixing chamber of the mixer 4 is not intended to be hermetically sealed. This is beneficial since the reaction of ozone with organic material is exothermic and thus would lead to a pressure increase in a completely sealed chamber. Therefore, creating a negative pressure ensures that, if there is a leak, ambient air will leak in rather than ozone leaking out from the mixing chamber which would be hazardous. It will be appreciated that the operation of the extraction fan 24 is configured to balance the requirement for negative pressure against ensuring sufficient residence time of the ozone within the mixing chamber to provide efficient usage of ozone. Once sufficient time has elapsed to ensure proper mixing and sterilisation, the animal feed can be emptied from the mixer 4. While the mixer 4 is being emptied, the valve 18 downstream of the storage tank 12 is closed. The oxygen concentrator 6 and ozone generator 8 can continue to operate with the valve 14 upstream of the storage tank 12 open so that the storage tank 12 is refilled prior to treatment of a subsequent batch of animal feed. It will be appreciated that, while the animal feed is treated in batches, the ozone can be generated continuously. It has been found that it is more efficient to operate the ozone generator 8 continuously instead of intermittently (i.e., only during treatment of the animal feed) and so the temporary storage of ozone leads to an overall reduction in energy consumption. The continuous operation of the ozone generator 8 has also been found to provide a more consistent supply of ozone and oxygen with smaller variation in the concentration of ozone. In some examples, it may take 4-6 minutes to fill the mixer 4, 6 minutes to treat the animal feed and a further 4-6 minutes to empty the mixer 4. It can be seen that the ozone / oxygen flow is only required for approximately one third of the time during the process. The ozone generator 8 can therefore be sized to be sufficient for the time averaged ozone consumption when combined with the ozone / oxygen storage system that can store the ozone / oxygen while the feed ingredients are being loaded / unload into the mixer 4. Figure 2 shows another embodiment of an ozone sterilisation system 102. The ozone sterilisation system 102 is similar to the ozone sterilisation system 2 and corresponding features are identified by the same reference numerals. The ozone sterilisation system 102 further comprises a control system 130. The control system 130 receives a sample of the exhaust gas removed from within the mixer 4. In this example, the sample is taken after the filter 26, although in other examples, the sample may be taken from upstream of the filter 26. The control system 130 comprises one or more sensors which detect the presence and / or concentration of certain components within the gas removed from within the mixer 4. In particular, the control system 130 may comprise an ozone sensor which determines the concentration of ozone in the exhaust gas. The composition of the exhaust gas may differ from that introduced from the storage tank 12 and the composition may differ over time. In particular, initially the ozone may react strongly with the material in the mixer 4 thus oxidising into dioxygen. As a result, the exhaust gas may initially contain a relatively low concentration of ozone. However, once the ozone has successfully destroyed contaminants in the animal feed, a greater proportion of ozone may reach the outlet vent 22 without oxidising such that a higher concentration of ozone is present in the exhaust gas. The control system 130 can detect this increase in ozone which signifies that the reaction is complete and can then take action to stop the mixer 4 and / or close the valve 18. The control system 130 may also activate or increase the speed of the extraction fan 24 to evacuate the mixer 4. Alternatively or in addition, the control system 130 may comprise an oxygen sensor which may be used to monitor the converse trend in the oxygen concentration. Specifically, the exhaust gas may initially contain a relatively high concentration of oxygen which reduces over time once the reaction is complete. The control system 130 may also comprise sensors which monitor products, such as carbon dioxide, associated with the reaction of the ozone with contaminants. Again, this may serve as a proxy to determine the progress of the reaction and when the mixer 4 and / or ozone supply can be stopped. The control system 130 may actively sense the composition of the gas supplied to the mixer 4 and use this to compare against the exhaust gas. Accordingly, additional sensor(s) may be provided for this purpose, or the same sensors may be used at different times for the analysis of the supply and exhaust gases. Figure 3 shows another embodiment of an ozone sterilisation system 202. The ozone sterilisation system 202 is similar to the ozone sterilisation systems 2, 102 and corresponding features are identified by the same reference numerals. The ozone sterilisation system 202 further comprises a control system 130. The control system 230 comprises a pressure sensor which detects the pressure in the mixing chamber of the mixer 4. The control system 230 controls the operation of the extraction fan 24 in response to the current pressure in the mixing chamber so as to maintain a negative pressure within the mixing chamber. The control system 230 may comprise an additional pressure sensor that detects the external pressure which can then be compared to the internal pressure within the chamber to determine the pressure difference. Alternatively, or in addition, the control system 230 may include flow sensors which measure the flow rate into and out of the mixing chamber which can be used to ensure a net outflow. As described previously, maintaining a negative pressure within the mixing chamber ensures that hazardous ozone is not able to leak out from the mixing chamber. By actively monitoring the pressure and / or flow rates, it is possible to minimise the usage of the extraction fan 24 thus reducing energy consumption and ensuring efficient usage of ozone. If, for some reason, the extraction fan 24 is unable to maintain a negative pressure within the mixing chamber, then the control system 230 may be configured to immediately close the valve 18 to cut off the supply of ozone. The control system 230 may also comprise an alert, such as a visual and / or audible alarm, which indicates to users that there is a problem and that the area should be evacuated. It will be appreciated that the control system 230 may also incorporate the functionality of the control system 130 used in the ozone sterilisation system 102. Figure 4 shows another embodiment of an ozone sterilisation system 302. The ozone sterilisation system 302 is similar to the ozone sterilisation systems 2 and corresponding features are identified by the same reference numerals. Unlike the ozone sterilisation system 2, the ozone sterilisation system 302 does not have exhaust chimney 28 which vents to atmosphere but instead has a return line 328. The return line 328 is connected at a position between the oxygen concentrator 6 and the ozone generator 8 (or via a separate inlet to the ozone generator 8) and recycles the exhaust gas to the ozone generator 8. The exhaust gas is predominantly dioxygen (around 80% oxygen by volume) and so recycling the exhaust gas to the ozone generator 8 reduces the energy consumption of the ozone generator 8. Figure 5 shows another embodiment of an ozone sterilisation system 402. As per the previous examples, the ozone sterilisation system 402 comprises a mixer 4, an oxygen concentrator 6 and an ozone generator 8. The ozone generator 8 is connected to an inlet port 10 of a storage tank 12 via a valve 14. In this example, the outlet port 16 of the storage tank 12 is connected to a 3-way valve 440. Two further ports of the 3-way valve 440 are connected to a pump 442 and a bypass line 444 which are provided between the 3-way valve 440 and a 2-way valve 446. A filter 448 and a manifold 450 are provided between the 2-way valve 446 and the ozone inlet 20 of the mixer 4. A further storage tank 464 (which may correspond to the storage tank 12 described previously) is also provided on the outlet side of the mixer 4. Disposed between the outlet vent 22 of the mixer 4 and the storage tank 464 is a manifold 452, a filter 454, a 2-way valve 456 and a 3-way valve 462, with a bypass line 458 and a pump provided between the 2-way valve 456 and the 3-way valve 462. A further valve 466 is also provided on the downstream side of the storage tank 464. To release the supply gas from the storage tank 12, the 3-way valve is configured to communicate with the pump 442 which directs the supply gas to the mixer 4. The supply gas passes through the mixer 4 and out of the outlet vent 22 as exhaust gas. The exhaust gas passes through the 2-way valve 456 and the bypass line 458 and to the 3-way valve 462. Initially, the exhaust gas may contain a significant volume of ozone which has not been used and so the 3-way valve 462 can direct the exhaust gas to the pump 460 which drives the exhaust gas back to the mixer 4. The exhaust gas again passes through the mixer 4 in a reverse direction and out of the ozone inlet 20. With the 2-way valve 446 and the 3-way valve 440 appropriately configured, the exhaust gas then passes along the bypass line 444 and is pumped back to the mixer 4 by the pump 442. It will be appreciated that this arrangement can be used to recirculate the supply gas through the mixer 4 several times in order to fully utilise the ozone content for sterilisation. After an appropriate number of cycles or time, the 3-way valve 462 can be configured to allow the spent exhaust gas to enter and intermittently fill the storage tank 464, in a similar manner to the supply of ozone and oxygen to the mixer 4. It will be appreciated that alternative return circuits may be used to recycle the exhaust gas back through the mixer 4 in either a reverse direction or in the same direction in order to fully utilise the ozone content for sterilisation. A control system which actively detects the composition of the exhaust gas, such as the control system 130, may be used to monitor the exhaust gas and determine whether (further) recycling is needed. Like the ozone sterilisation system 302, the ozone sterilisation system comprises a return line 428. Disposed along the return line is a pump 468 which pumps the exhaust gas through a dryer 470 and a CO2 scrubber 472 which condition the exhaust gas. The dryer 470 removes any water from the exhaust gas which may have been introduced in the mixer 4 and the CO2 scrubber 472 removes CO2 generated through the reaction of the ozone with contaminants. A further storage tank 476 (which may correspond to the storage tank 12 described previously) is provided along the return line 428 with valves 474, 478 on either side. The storage tank 476 stores the conditioned exhaust gas (oxygen and some ozone) before supplying it to the ozone generator 8. In other examples, the storage tanks 464 and / or 476 may be omitted and the conditioned exhaust gas may be returned directly to the oxygen concentrator 6 or ozone generator 8. It will be appreciated that the ozone sterilisation systems 302, 402 may also comprise control systems such as those described in relation to the ozone sterilisation systems 102, 202. The mixer 4 of any of the ozone sterilisation systems described herein may be provided with one of more water injectors for introducing moisture to the animal feed within the mixing chamber. For example, the water injectors may deliver atomized water or steam (which may be deionised or ozonated). It has been found that the addition of water increases the rate of deactivation of pathogenic bio-organisms during ozone treatment. For example, it was observed that a 5% increase in feed moisture content, would give greater than a 1 log reduction in measured pathogens. The addition of water therefore potentially allows the amount of ozone required for sterilisation to be reduced. For example, it has been found that introducing water in the quantity of 8% reduces the amount of ozone required by up to half. The addition of moisture has also been found to be beneficial for the subsequent pelletisation of the animal feed since it prevents pellets from disintegrating. The addition water has been found to increase the total water content of the animal feed to an optimum level for pelletisation which is considered to be around 18%. The optimum amount of water has been found to be between 5-10% of the weight of the animal feed to be treated, depending on the type of animal feed and its initial moisture content. Based on experiments with representative samples of animal feed, the optimum amount of water has been found to be between 7-9% and more preferably 8%. The ozone sterilisation systems described herein may be retrofitted to existing mixers used in the preparation of animal feed, for example. Although the invention has been described with reference to a plough mixer, the mixer may instead be any form of mixer including a conditioner used prior to pelletisation or the like. While the storage of supply gas may be beneficial in mixers operating in a batchwise manner, it will be appreciated that other aspects described herein may be used with continuous mixers. To avoid unnecessary duplication of effort and repetition of text in the specification, certain features are described in relation to only one or several aspects or embodiments of the invention. However, it is to be understood that, where it is technically possible, features described in relation to any aspect or embodiment of the invention may also be used with any other aspect or embodiment of the invention. The invention is not limited to the embodiments described herein, and may be modified or adapted without departing from the scope of the present invention.

Claims

1. An ozone sterilisation system comprising:a mixer comprising a mixing chamber for receiving material to be sterilised;an ozone generator configured to generate a supply gas comprising ozone and oxygen;a storage tank having an inlet which is fluidly connected to the ozone generator and an outlet which is fluidly connected via a valve to an ozone inlet provided on the mixer which opens into the mixing chamber;wherein the mixer is configured to operate in a batchwise manner with the material being loaded, treated and then unloaded and wherein the ozone generator is configured to fill the storage tank with the valve in a closed position while the material to be sterilised is loaded into and / or unloaded from the mixing chamber.

2. An ozone sterilisation system as claimed in claim 1, wherein the storage tank is expandable.

3. An ozone sterilisation system as claimed in claim 2, wherein the storage tank comprises a bladder, diaphragm or other movable barrier.

4. An ozone sterilisation system as claimed in any one of the preceding claims, wherein the mixer further comprises an outlet vent which expels an exhaust gas from the mixing chamber.

5. An ozone sterilisation system as claimed in claim 4, wherein the ozone sterilisation system further comprises a control system, wherein the control system comprises one or more sensors which detect the presence and / or concentration of components in the exhaust gas from the mixing chamber.

6. An ozone sterilisation system as claimed in claim 5, wherein the control system is configured to identify a change in one or more of the components in the exhaust gas which indicates that sterilisation is complete.

7. An ozone sterilisation system as claimed in claim 6, wherein the control system is configured to detect the presence and / or concentration of components in the supply gas and to compare this to the exhaust gas to determine the change.

8. An ozone sterilisation system as claimed in claim 6 or 7, wherein, when the control system detects that sterilisation is complete, the control system is configured to stop the mixer and / or evacuate the mixing chamber.

9. An ozone sterilisation system as claimed in any of claims 6 to 8, wherein the control system comprises one or more of an ozone sensor, an oxygen sensor and a CO2 sensor.

10. An ozone sterilisation system as claimed in any one of the claims 4 to 8, wherein the outlet vent is fluidly connected to an extraction fan or pump.

11. An ozone sterilisation system as claimed in claim 10, wherein the extraction fan or pump is configured to maintain a negative pressure in the mixing chamber.

12. An ozone sterilisation system as claimed in claim 11, wherein the ozone sterilisation system further comprises a control system, wherein the control system comprises a pressure sensor which is configured to sense the pressure within the mixing chamber and to actively control the extraction fan or pump to maintain the negative pressure in the mixing chamber.

13. An ozone sterilisation system as claimed in any one of claims 4 to 12, wherein the outlet vent is connected to a return line which returns the exhaust gas to the ozone generator.

14. An ozone sterilisation system as claimed in claim 13, wherein one or more of a CO2 scrubber, a dryer and one or more storage tanks are provided along the return line.

15. An ozone sterilisation system as claimed in any one of claims 4 to 14, wherein the outlet vent is connected to a return circuit which recycles the exhaust gas such that it passes through the mixer multiple times.

16. An ozone sterilisation system as claimed in any one of the preceding claims, further comprising an oxygen concentrator which is fluidly connected to the ozone generator and is configured to supply oxygen to the ozone generator.

17. An ozone sterilisation system as claimed in any one of the preceding claims, wherein the supply gas comprises 10-20% ozone.

18. An ozone sterilisation system as claimed in any one of the preceding claims, wherein the material is treated with ozone at an ozone to material weight ratio of2kg / T - 4kg / T.

19. An ozone sterilisation system as claimed in any one of the preceding claims, wherein the mixer further comprises water injectors which supply water to the material to be sterilised.

20. An ozone sterilisation system as claimed in claim 19, wherein the water injectors are configured to supply water having a weight which is 5-10% of the weight of the material to be sterilised, preferably 7-9% and more preferably 8%.

21. An ozone sterilisation system as claimed in any one of the preceding claims, wherein the ozone generator operates continuously while the material is being loaded, treated and unloaded.

22. An ozone sterilisation system as claimed in any one of the preceding claims, wherein the mixer is a plough mixer.

23. An ozone sterilisation method comprising:loading a mixing chamber of a mixer with material to be sterilised;while the mixing chamber is being loaded, filling a storage tank with a supply gas comprising ozone and oxygen from an ozone generator;introducing the supply gas from the storage tank to the mixing chamber;mixing the material in the mixing chamber in the presence of the supply gas in order to sterilise the material;unloading the material from the mixing chamber; andwhile the material is being mixed and unloaded, refilling the storage tank with supply gas from the ozone generator.

24. An ozone sterilisation system comprising:a mixer comprising a mixing chamber for receiving material to be sterilised;an ozone generator configured to generate a supply gas comprising ozone and oxygen which is fed to an ozone inlet provided on the mixer which opens into the mixing chamber;wherein the mixer comprises an outlet vent which is configured to expel an exhaust gas from the mixing chamber; andwherein the outlet vent is connected to a return line which returns the exhaust gas to the ozone generator.

25. An ozone sterilisation system as claimed in claim 24, wherein one or more of a CO2 scrubber, a dryer and one or more storage tanks are provided along the return line.

26. An ozone sterilisation method comprising:generating a supply gas comprising ozone and oxygen using an ozone generator;introducing the supply gas to a mixing chamber of a mixer containing material to be sterilised;mixing the material in the mixing chamber in the presence of the supply gas in order to sterilise the material;expelling exhaust gas from an outlet vent of the mixer; andrecycling the exhaust gas to the ozone generator for reuse in generating supply ydo.

27. An ozone sterilisation system comprising:a mixer comprising a mixing chamber for receiving material to be sterilised;an ozone generator configured to generate a supply gas comprising ozone and oxygen which is fed to an ozone inlet provided on the mixer which opens into the mixing chamber;wherein the mixer comprises an outlet vent which is configured to expel an exhaust gas from the mixing chamber; andwherein the outlet vent is fluidly connected to an extraction fan or pump;wherein the extraction fan or pump is configured to maintain a negative pressure in the mixing chamber.

28. An ozone sterilisation system as claimed in claim 27, wherein the ozone sterilisation system further comprises a control system, wherein the control systemcomprises a pressure sensor which is configured to sense the pressure within the mixing chamber and to actively control the extraction fan or pump to maintain the negative pressure in the mixing chamber.

29. An ozone sterilisation method comprising:generating a supply gas comprising ozone and oxygen using an ozone generator;introducing the supply gas to a mixing chamber of a mixer containing material to be sterilised;mixing the material in the mixing chamber in the presence of the supply gas in order to sterilise the material;expelling exhaust gas from an outlet vent of the mixer; andmaintaining a negative pressure in the mixing chamber using an extraction fan or pump fluidly connected to the outlet vent.

30. An ozone sterilisation system comprising:a mixer comprising a mixing chamber for receiving material to be sterilised;an ozone generator configured to generate a supply gas comprising ozone and oxygen which is fed to an ozone inlet provided on the mixer which opens into the mixing chamber;wherein the mixer comprises an outlet vent which is configured to expel an exhaust gas from the mixing chamber; andwherein the ozone sterilisation system further comprises a control system, wherein the control system comprises one or more sensors which detect the presence and / or concentration of components in the exhaust gas from the mixing chamber.

31. An ozone sterilisation system as claimed in claim 30, wherein the control system is configured to identify a change in one or more of the components in the exhaust gas which indicates that sterilisation is complete.

32. An ozone sterilisation system as claimed in claim 31, wherein the control system is configured to detect the presence and / or concentration of components in the supply gas and to compare this to the exhaust gas to determine the change.

33. An ozone sterilisation system as claimed in claim 31 or 32, wherein, when the control system detects that sterilisation is complete, the control system is configured to stop the mixer and / or evacuate the mixing chamber.5 34. An ozone sterilisation system as claimed in any of claims 30 to 33, wherein thecontrol system comprises one or more of an ozone sensor, an oxygen sensor and a CO2 sensor.

35. An ozone sterilisation method comprising:10 generating a supply gas comprising ozone and oxygen using an ozone generator;introducing the supply gas to a mixing chamber of a mixer containing material to be sterilised;mixing the material in the mixing chamber in the presence of the supply gas in15 order to sterilise the material;expelling exhaust gas from an outlet vent of the mixer; andanalysing the exhaust gas using one or more sensors to detect the presence and / or concentration of components in the exhaust gas from the mixing chamber.

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