Title of Invention

DIGESTER

Abstract

A digester (10, 49) for composting biodegradable material has a plurality of treatment compartments (16-19, 21 a) one above the other with respective closable openings (26-29) in the floors thereof to allow material to pass through the digester compartments in a controlled manner. The uppermost compartment (16) has inlet means (20) for receiving a batch of material to be treated and means (36-40) are provided for transferring heat into the compartment (17) immediately below the uppermost compartment so as to heat the floor thereof and thus enhance digestion of material therein, the heat being transferred from one of the lower, hotter compartments (18, 19). Means (46) are also provided for spraying water in the chambers, the water being heated by means of heat from one of the compartments, and there are also means (50) for blowing air into the compartments. A transfer means, such as an elevating screw (50), can be provided to move material from a lower compartment into the uppermost compartment (16).

Full Text

This invention relates to a digester in which biodegradable material is composted, in use, so that treated material leaves the digester with a stable cyN ratio, and an object of the invention is to provide such a digester in an improved form. According to a first aspect of the Invention, there is provided a digester having a first treatment compartment for receiving a batch of biodegradable material to be composted in the digester, in use, a second treatment compartment arranged to receive material from the first compartment in a controlled manner, a third treatment compartment arranged to receive material from the second compartment in a controlled manner, and ducting means for the controlled transfer of heat from said third compartment to said second compartment. Preferably the second treatment compartment, in use, receives material directly from the first treatment compartment, and most preferably the third treatment compartment, in use, receives material directly from the second treatment compartment. According to a second aspect of the invention, there is provided a digester having a first treatment compartment for receiving a batch of biodegradable material to be composted in the digester, in use, a plurality of further treatment compartments arranged so as, in use, successively to transfer material from the first compartment, through the digester, to an outlet thereof, fluid reservoir means in one of said further compartments to provide fluid, in use, for spraying materia! in said first compartment or any one of said further compartments, and means for utilising heat ft"om another of said further treatment compartments to raise the temperature of fluid in said reservoir. According to a third aspect of the invention, there is provided a digester having a first treatment compartment for receiving a batch of biodegradable material to be composted in the digester, in use, a second treatment compartment arranged to receive material which has left said first compartment and is passing through the digester, transfer means for transferring material from the second compartment to the first compartment, and material moving means in the second compartment for moving material therein to said transfer means. Accordingly the present invention provides a digester having a first treatment compartment for receiving a batch of biodegradable material to be composted in the digester, in operation, a second treatment compartment arranged to receive material from the first compartment in a controlled manner, a third treatment compartment arranged to receive material from the second compartment in a controlled maimer, transfer of material between compartments, in operation, being via respective transfer openings in respecfive floors of the treatment compartments, with respective doors being provided for opening and closing said transfer openings, material moving means in each treatment compartment comprising a plurality of arms rotatable about an axis perpendicular to the floor of each treatment compartment, and ducting means for the controlled transfer of heat from said third compartment to said second compartment. The invention will now be described, by way of example, with reference to the accompanying drawings, inwhich:- Figure 1 is a schematic internal side view of a digester of one embodiment of the invention. Figure 2 is a schematic view on line A-A of Figure 1, Figure 3 is a schematic internal side view of a digester of a second embodiment of the invention. Figure 4 is a schematic view on both lines B-B and C-C of Figure 3, Figure 5 is a schematic diagrammatic view showing a spraying system of the digester, and Figure 6 is a schematic diagrammatic view showing an air flow system of the digester. Figures 1 and 2 show a first embodiment of a digester 10 of the present invention, this embodiment, in fact, incorporating two inventive concepts, as will be described, which can be used, as shown, together, or alternatively, independently. The digester is formed with an upright hollow cylindrical body or casing 11 which is divided vertically into a series of treatment compartments by respective vertically spaced horizontal floors 12-15 within the cylindrical body 11. In the example shown in Figure 1 there are four such compartments, the uppermost or first compartment being denoted by the numeral 16, the second compartment, immediately below the first compartment, being denoted by the numeral 17, and so on for the third and fourth compartments 18, 19 respectively. As can be seen from Figure 1, the top of the body 11 is closed, but is provided with an inlet 20 for supplying, at intervals, batches of biodegradable material which is to be composted by passage through the digester. At the bottom of the digester Is an outlet conveyor 21 within an outlet enclosure 21a which is defined at the bottom of the body 11 below the fourth compartment 19, i.e. beneath the floor 15. The conveyor transports treated material out of the digester. Although four compartments are shown in the embodiment of Figure 1, the number of compartments can be varied, both in relation to the embodiment illustrated in Figure 1, and also in relation to the useof the two inventive concepts, referred to above, independently of one another. However in the example Illustrated in Figure 1 there could be more than four compartments, with any additional compartments generally operating in the same manner as will be described in relation to compartments 18 and 19. In the floors 12 to 15 are respective self sealing transfer doors 22-25 which close or open respective transfer openings 26-29 respectively in the floors, (as shown for the door 22 and opening 26 of the floor 12 in Figure 2), the transfer doors moving between their respective open and closed positions in a horizontal plane immediately below their associated respective floors, or being hinged to move in a vertical plane. As will be described, the transfer openings are for allowing material in the digester to pass from one compartment to the compartment beneath it and thereby pass fully through the digester from the first compartment, successively through the other compartments and finally into the outlet enclosure. The inlet is provided with a slide door 30 for opening or closing the inlet, the door in its closed position preventing escape of fumes and heat upwardly out of the digester from the first compartment. The doors 22-25 and 30 can be operated by reciprocation of pneumatically controlled pistons in respective cylinders, with pressure operated piston location switches. In each compartment is a set of rotatable arms mounted on a rotational drive unit. The drive unit could possibly be a central axial shaft extending vertically upwardly through the casing and having the arms in each compartment extending therefrom. The arms can extend radially, or be somewhat offset, as shown, for example, in Figure 4. However the number and orientation of arms in each compartment is not critical provided they perform their desired function, which is to disturb the material and/or to move it to the transfer opening of its compartment. However alternatively separate drive means can be provided for each compartment as shown schematically in Figure 1, with the drive means being denoted by the numeral 31. Whatever the form of drive means, it can be arranged that the arms in each of the compartments are rotatable independently of one another. In Figure 1 the arms in the four compartments 16 to 19 respectively are denoted by the numerals 32-35. As with the doors 22-25 and 30, there could be pneumatically operated pistons to drive the arms. The digester has ducting to communicate various compartments with one another for the transference of heat, and also to take heated air from the digester to a biofilter unit disposed exteriorly of the digester, from which cleaned air is pumped. Accordingly it can be seen that in the embodiment of Figure 1 there are outlet ducts 36, 37 respectively from the compartments 18, 19, these ducts 36, 37 joining a common duct 38 which leads into the top of the second compartment 17. Appropriate valves 39, 40 respectively, for example pneumatically controlled, are contained in the ducts 36,37 for controlling flow of heated air into the common duct 38 as will be described. Further outlet ducts 41, 42 respectively extend from the first and second compartments, these ducts leading to a common duct 43 which itself extends to the biofilter referred to above. In the ducts 41, 42 are valves 44, 45 respectively, preferable of the same form as the valves 39, 40. All the valves may be remotely operated. The duct may communicate with the biofilter via an air scrubber, and an air humidifier, with a recirculation and dosing control unit being associated with the air scrubber. Operation of the digester of Figures 1 and 2 will now be described. After a commissioning period, the normal situation in the compartments prior to feeding a batch of material into the digester would be for the first compartment to be empty and all the other compartments 17, 18 and 19 to contain biodegradable material which is to be composted as it passes downwardly through the digester. At this time, the inlet slide door 30 would be open and at least the transfer door 22 would be closed. At the completion of the feeding of a batch of biodegradable material into the digester, the inlet slide door would closed. The further opening and closing of the inlet door and the transfer doors to allow transfer of material down through the compartments to the outlet conveyor, would be controlled by a timing regime which is outside the scope of this patent, but which could be of conventional form. It will be appreciated that material will fall through the transfer openings 26-29 respectively from one compartment to the one below it successively as the transfer doors are opened. The timing regime described would be such so that material would spend an appropriate time interval within a specific compartment before passing to the compartment below it and eventually finally to the outlet enclosure. It will be appreciated that the lowermost compartment is emptied before each downwards transfer of material through the digester once material has reached said compartment. Whilst the most convenient heat transference arrangement is heat being transferred by ducting from compartmentIS and/or 19 to compartment 17 which is directly below the uppermost compartment 16 to which material is initially fed, so that the floor of compartment 16 is heated, transference could as well or instead take place from a treatment compartment below compartment 18 into compartment 18 or a compartment below compartment 18, i.e. into a compartment which itself is not directly below compartment 16, purely to enhance the composting process therein. The transference need not be between compartments directly one above the other. Within the digester would be arranged a series of water sprays 46 (Figure 5) including at least one arranged to spray water onto material before or as it is transferred from at least compartment 17 to compartment 18. The positions and number of sprays can be varied as required. The operation of these sprays would be by means of a control system, based on a time-cycle with variations initiated by the temperature of the material detected by temperature probes 47, such as a thermocouple, in the various compartments, which time cycle is also outside the scope of this patent, but which again may be of known form. The numbers and positions of the probes 46 in each compartment can be varied as required. As previously mentioned, the example shown in Figure 1 is a digester which incorporates two inventive features which are shown used together. However, as also mentioned above, these two features can be used independently of one another. A preferred embodiment of one of the inventive features is the transference of heat from at least one of the compartments into the compartment immediately below the compartment into which material is initially fed. A preferred embodiment of the other Inventive feature relates to the provision of fluid, preferably water^ storage means, in one compartment, which storage means is heated by heat transferred from another compartment below the compartment in which the storage means is contained. specifically, in said one embodiment, the water to be delivered via the sprays 46 onto material as it is transferred from compartment 17 to compartment 18 will, prior to the spraying, be held in a water reservoir or tank 48 which is disposed in the compartment 17 immediately below the floor 12 of compartment 16. The water would normally be pumped to the digester. With the other inventive concept, it is specifically the case in the Figure 1 embodiment that heat is transferred from compartment 18 and possibly also lower compartments such as compartment 19, into and across the top of compartment 17 for three purposes, namely i) to impart hot air into compartment 17 to maintain and possibly increase the temperature of the material within that compartment, ii) to heat the underside of the floor 12 of compartment 16, thus imparting heat into the material in the first compartment, without any physical disturbance of that material, such as by movement of the arms 32. This lack of disturbance allows fungus in the material to develop and thus accomplish degradation and composting of the material, iii) to preheat the water in the tank before the water is used to spray material, e.g. as it is transferred between compartments 17 and 18. Clearly the arrangement could be such that only one of said objectives is provided for in any particular embodiment of the digester. To ensure that water In the tank does not shock-cool the material in a respective compartment, the water may be fed into the tank In small doses over a period of, for example 12 hours, starting after transfer of material from compartment 17 into compartment 18 (during which it has been sprayed from the tank supply) has been completed. A somewhat different spraying arrangement will be described later with reference to Figure 5. Probes 47 would normally be arranged to monitor the temperature of the material in each of the compartments, the probes being connected to a control system, which is outside the scope of this patent, but which again may be of known form. The control system would be such that when within a pre-set time scale the temperature in the compartment is low, the compartment arms will rotate with air blown through the arms to encourage microbiological action within the material. Any suitable means can be provided for blowing such air through the arms 32-35 as they rotate. When the temperature in the compartment Is high, the compartment arms will rotate without air blowing therethrough, so that there is release of excess heat into the top of the respective compartment. Again suitable means can be provided for rotation of the arms without the blowing of air therethrough into the compartment. A suitable air blowing system will be described later with reference to Figure 6. The air could be blown into the compartment(s) other than through the arms. With prior art digester arrangements, ducting from the compartments would normally all exit via a single duct atone side of the digester, direct to the biofilter unit. There would thus be no transference of heat, for whatever purpose, from one compartment to another. However with the present arrangement of ducting and valves, the hot air from compartment 18 and/or any lower treatment compartments, will pass into the top of compartment 17 before entering the duct leading to the biofilter unit. Due to the advancement of the decomposition in the lower compartments, the heat therein will be greater than in the upper compartments. To facilitate this transfer of heat when required, and to conserve heat at other times, the ducting valves 39, 40 and 44 and 45 relating to each compartment will be controlled as follows: Valve 44- normally closed, and fully opens only when the temperature in the material in compartment 16 rises above a pre-set temperature. Valve 45- normally closed. Opens fully when temperature in material in compartment 17 rises above a pre¬set temperature or when any of the valves associated with a lower compartment is fully open. Opens to a partial pre-set position when temperature of material in compartment 17 falls below a pre-set level or when one of the valves associated with a lower compartment partially opens. Will return to closed position when temperature falls below the pre-set level or when all lower compartment valves are closed. Valve 39, 40 {and, if applicable, similar valves associated with lower normally closed. Opens to a partial pre-set position when temperature in the respective compartment falls below a low pre-set level and to fully open position when the compartments) - temperature rises above a high pre-set level. Valves return to the closed position when temperature returns to between the low and high pre-set levels. A further inventive concept Is shown incorporated in the digester of Figures 3 and 4, this being utilisable independently of either of the inventive concepts described and illustrated with respect to Figure 1, but also being for use with one or both of said inventive concepts if desired. The basic form of digester 49 shown in Figures 3 and 4 is the same as that shown in Figures 1 and 2, but for clarity the water tank and the ducting for transference of heat between compartments and to the biofilter are not shown. Otherwise the construction and operation is of the same form as described for the digester 10, so that again the operation of the arms and transfer doors are controlled by a pre-set time sequence and also by a series of temperature probes set in each compartment. One of the intermittent operations controlled by the temperature probes 47 is that of rotating a set of arms just above the floor of a particular compartment when the material in the compartment rises in temperature above a pre-set level. At such periods of high temperature induced rotation, air is not passed through the arms. Identical reference numerals to those used in Figures 1 and 2 are used in Figures 3 and 4 for identifying identical items. The main difference with the digester 49 is that the floor of each compartment other than the uppermost one 12 may be extended at one side, as shown in Figure 4 for compartments 17 and 18. The extensions of these floors have fitted thereto a screw conveyor or an elevating screw 50 at the exterior of the main part of the body of the digester, the screw 50 extending vertically upwardly beyond the closed top of the digester 49. A chute 51 extends from the top of the elevating screw downwards into the first compartment 16. Instead of the elevating screw 50 shown, any other suitable transfer means can be provided for transferring material into the uppermost compartment from one or more other compartments therebelow, and means other than mechanical means may be used if appropriate. One alternative, for example, could be a conveyor belt, which may have buckets or other material receiving means thereon. In operation, as the arms in a chamber with an extended floor rotate, at any time whether induced by high temperature or otherwise, a small amount of material will be pushed into this extended floor area and will remain there unless the elevating screw 50 is operating. When any set of arms is rotating due to control by a high temperature reading in any compartment, the elevating screw will be actuated to operate. Material pushed into the elevating screw, via the floor extension, when the elevating screw is running, will be conveyed upwards by the screw and discharged, by the enclosed chute 51, into the compartment 16 which will normally already contain material for composting. The means for disturbing the material, i.e. the arms, could be different from the means moving material to the screw 50. As the high heat level in a compartment is due to the vigorous activity of the bacteria in the material, this means that active bacteria will be fed into the material in the uppermost compartment 16 and thus boost the activity of the bacteria in the material in that compartment. At some times while hot material is being transferred to the uppermost compartment, another compartment may also be transferring colder material if the arms In the other compartment are revolving for a reason other than high temperature. This will happen quite often, but will not be detrimental as a required hot bacteria will still remain active within the time scale envisaged. At other times material will be transferred from two or more compartments all due to high temperature and this will be advantageous. When the elevating screw comes to a stop, due to the respective set of compartment arms also stopping, then the arms in the uppermost compartment will rotate for a pre-set period. For this purpose of stopping the elevating screw, the one of the three set of arms which started rotating first, when more than one set of arms have rotated at the same time, will be used as the respective set of arms. Accordingly this inventive concept enables improved bacteriological composting in the uppermost compartment, which might otherwise be the coolest compartment of the digester and thus normally have reduced composting action therein. As described, water sprays can be provided in digester 10 and digester 49, with the water tank 48 in any of the compartments, except the uppermost one, being heated by transfer of heat Into that compartment from one or more of the other compartments. Moreover tanks could be provided in more than one compartment. Although normally heat would be transferred from a compartment to one or more compartments above it, this is not essential. Moreover heated water from a tank could be piped to an upper or lower compartment for spraying therein. Figure 5 shows a modified spraying arrangement with a boiler 52, outside of the digester, being fed at 53 with mains water and at 54 with rainwater, e.g. from the digester roof. The water in the boiler is heated by an immersion heater 55, heated water being fed from the boiler by way of a pump 56 through a flow meter S7 SLXxd flow contxaX ysAvQ 5b Xo a vextAcaS pipe 59 extending upwardly along the side of the digester, with branch pipes therefrom to the respective digester compartments. A fluid reservoir, namely the tank 48 is formed in compartment 17, and also, in the example illustrated, in compartment 18, by an enlargement of the branch pipe. Thus in this arrangement water heated by external means is further heated by heat generated naturally in the digester for two compartments. The arrangement could be modified so that the additionally heated water is sprayed in any number of compartments. In Figure 5, the ducting for supplying heat from one or more other digester compartments to the compartment or compartments having a water tank 48 is not shown. With the first and second aspects of the invention, the spray water could be heated in the boiler only, without heat being added in the digester. Figure 6 shows how air blowers 60 can introduce air to the compartments for blowing it through the arms 32 to 35. In this example the air is in each case introduced into the chamber below that containing the arms through which the air is to be blown^ and fed upwardly through pipework. The air can pass along a passage in the arms and exit through suitable outlet holes. In the example illustrated, air can pass from all the compartments to be led to the biofilter. Pneumatically operated valves 62 can control exhaust of air from the compartments. Each compartment can be provided with a weighted air inlet flap 61. Prior to waste material entering the digester through inlet 20, It can be fed to a shredder which Itself can be sprayed with mains water to treat material passing therethrough. WE CLAIM 1. A digester having a first treatment compartment for receiving a batch of biodegradable material to be composted in the digester, in operation, a second treatment compartment arranged to receive material from the first compartment in a controlled manner, a third treatment compartment arranged to receive material from the second compartment in a controlled manner, transfer of material between compartments, in operation, being via respective transfer openings in respective floors of the treatment compartments, with respective doors being provided for opening and closing said transfer openings, material moving means in each treatment compartment comprising a plurality of arms rotatable about an axis perpendicular to the floor of each treatment compartment, and ducting means for the controlled transfer of heat from said third compartment to said second compartment. 2. A digester as claimed in claim 1, wherein the second treatment compartment is arranged to receive material directly from the first treatment compartment. 3. A digester as claimed in claims 1 or 2, wherein a floor of said first treatment compartment is heated, in operation, by heat in said second treatment compartment. 4. A digester as claimed in any one of claims 1 to 3, wherein heat is also transferred to said second treatment compartment from one or more further treatment compartments. 5. A digester as claimed in any one of claims 1 to 3, wherein said third treatment chamber is arranged to receive material directly from the second treatment compartment. 6. A digester as claimed in any one of the claims 1 to 5, wherein the ducting means has valve means for controlling the flow of heat to the second compartment. 7. A digester as claimed in any one of the claims 1 to 6, wherein the first treatment compartment has an inlet thereinto which is opened or closed by a door. 8. A digester as claimed in any one of the claims 1 to 7, wherein a lowermost compartment receives treated material, in operation, and has an outlet conveyor therein for removing said treated material from the digester. 9. A digester as claimed in any one of the claims 1 to 8, wherein means are provided for blowing air into one or more of the treatment compartments, in operation. 10. A digester as claimed in any one of the claims 1 to 9, wherein means are provided for blowing air, in operation, into one or more of the treatment compartments through said rotatable arms. 11. A digester as claimed in claim 10, wherein the air is blown into one treatment compartment and is arranged to pass upwardly through the floor of the treatment compartment directly above to be distributed into said compartment through said rotatable arms. 12. A digester as claimed in any one of the claims 1 to 11, wherein in at least one treatment compartment fluid spray means are provided for spraying fluid, in operation onto material in the treatment compartment. 13. A digester as claimed in claim 12, wherein the sprayed fluid is heated by heat from a treatment compartm^ent. 14. A digester as claimed in claim 12, wherein the fluid is heated externally of the digester, 15. A digester as claimed in claim 14, wherein the fluid is heated in a boiler of a fluid supply system associated with the digester. 16. A digester as claimed in any one of the claims 1 to 15, wherein at least one temperature probe is associated with each treatment compartment to monitor the temperature therein, in operation. 17. A digester as claimed in any one of the claims 1 to 16, wherein it has valve means for conserving heat in, or transferring heat from, one or both of the first and second treatment compartments, in operation. 18. A digester substantially as hereinbefore described, with reference to, and as shown in Figures 1 and 2 of the accompanying drawings.

Documents:

2180-mas-1998 abstract.pdf

2180-mas-1998 claims duplicate.pdf

2180-mas-1998 claims.pdf

2180-mas-1998 correspondence-others.pdf

2180-mas-1998 correspondence-po.pdf

2180-mas-1998 description (complete) duplicate.pdf

2180-mas-1998 description (complete).pdf

2180-mas-1998 drawings duplicate.pdf

2180-mas-1998 drawings.pdf

2180-mas-1998 form-19.pdf

2180-mas-1998 form-2.pdf

2180-mas-1998 form-26.pdf

2180-mas-1998 form-4.pdf

2180-mas-1998 form-6.pdf

2180-mas-1998 petition.pdf