CA1102019A - Fermentation zone mixing and heating apparatus - Google Patents

Abstract

FERMENTATION ZONE MIXING AND HEATING APPARATUS

Abstract of Disclosure A combined mixing and heating apparatus for an anaerobic fermentation zone which comprises means defining a substantially vertically extending conduit to heat the contents within the bounds of the conduit and means for moving the contents upwards through the conduit. The apparatus preferably also includes means capable of de-flecting the contents that have been passed up through the conduit outwardly onto the surface of the general contents of said fermentation zone.

Description

l~VZ~319 Background of the Invention Recently steps have been taken to use anaerobic fermentation as a means of disposing of a wide range of organic wastes, for example manures from cowsheds, hen houses, pigsties and the like, all of which have a substantial liquid content. The general principle involved is to provide a fermentation zone from which air is largely excluded. Of the various types of apparatus that have been used, the most commonly used zone-defining apparatus is one utilizing a flexible bag formed for example from butyl rubber. The flexible bag is normally bounded on its base by a foundation and on its sides by a peripheral constraining member which may be made up of a plurality of panels. No constraint is necessary above the bag as the bag is closed at that portion and there is much less pressure. Inlets for charging the zone with the organic materials to be fermented are provided and outlets are normally provided for drawing off the super-natant liquid and the sludge as required. A person skilled in the art will appreciate the various means whereby such inlets and outlets can be provided without allowing the entrance of air into the zone. The general background on apparatus of the kind with which the present invention is involved can be obtained from a perusal of British Patent Specification No. 1417194 the contents of which are herein incorporated by way of reference.

~1~2Qlg The operation of a biomass fermentation zone results in the generation of certain gases of which methane is the most important as it can be utilized as a source of energy externally of the fermentation zone, while a portion of it can also be used to maintain the biomass within the required temperature ranges of from 85F to 120F
(preferably 96F). To maintain a stable temperature, therometers and therometer controlled burners or the like are preferably utilized and the actual digester apparatus is preferably insulated.
A person skilled in the digester art, however, will realize that there is a level of content within the digester and a gaseous zone above that level consisting largely of methane. The methane gas is drawn off by an appropriate gas line to be stored or otherwise used.
Since the digester is fed with raw organic material periodically (preferably daily) provision is made for drawing off supernatant liquid as well as sludge from the bottom, both of which can be used as a manure.
In order to obtain the required degree of fermentation it is necessary to provide some sparging type apparatus which will have the effect of mixing the various layers of contents of the digester. Normally such a sparging apparatus takes the form of a stirring type apparatus (normally an Archimedes type screw). Often means is provided in addition to the sparging device adapted to spread contents from the centre of the digester to the ~32~19 periphery of the digester, e.g. a rotating boom.
Conventionally the heating apparatus for such a tank takes the form of a heating coil or the like located below the digester. Heat transference is thus through the bag in which the contents are obtained. Such a requirement for heat transfer through the bag is undesirable since it affects the life of the bag and also tends to cause the formation of a crust on the inside lining of the bag thus increasingly making the efficient conductance of heat more difficult. Similarly the alternative of having immersion heaters in the digester can be adversely affected by crusting. There is, therefore, some need to - provide apparatus which will provide the required heating and preferably which will also provide the required sparging.

Summary of the Invention In one aspect the present invention consists in a combined mixing andheating apparatus in an anaerobic fermentation zone comprising means defining a substantially vertically extending passageway, there being included for at least a portion of the passageway means to heat some of the contents within the bounds thereof and means for moving said contents upwards through said passageway.
Preferably said means for drawing the contents up through said passageway comprises an impeller within said passageway.

:

~2~1g Preferably also said means for defining said passageway comprises a conduit having an open top end and inlet means at or adjacent the lower end thereof, with said means to heat some of the contents within the bounds of the passageway preferably being defined by a heating jacket having interconnected therewith an inlet conduit and an outlet conduit respectively for a heating fluid. In other forms of the present invention, however, said means for defining a passageway could in itself com-prise a closely coiled conduit which is sufficiently closely coiled so as to define a passageway through which a semblance of ordered movement of the contents can be caused by said means for drawing the contents up through said passageway. With such an alternative construction the means for heating the contents could include the passing of a heating liquid through the coiled conduit.
In a further aspect the present invention consists in the combined mixing and heating apparatus previously defined wherein said impeller is a propeller or screw positioned to rotate about a substantially vertical rotational axis towards the top of said means defining said passageway but below the level of the contents of said fermentation zone. Preferably positioned about the level of contents within said fermentation zone is means de-fining a surface against which material raised by said impeller can impinge to thereby be deflected outwards and back onto the surface of the contents in said fermentation zone. Preferably said surface is defined by a splash plate.

2als In a further aspect, the present invention con-sists in a method of anaerobically fermenting organic waste material which comprises the steps of operatively mixing and maintaining the contents of the fermentation zone within required temperature ranges using apparatus in accordance with the present invention.
In still a further aspect the present invention consists in apparatus for installation in an anaerobic fermentation zone, comprising a substantially straight elongate conduit having open ends and having a jacket at least partly thereabout which has an inlet and an outlet, impeller means including a propeller or screw, a shaft therefor and means operative in use to rotate the same, and means to locate said conduit and impeller means in association with the propeller or screw within the conduit and rotatable relative thereto with the longitudinal axes of said conduit and the shaft being substantially coincident.
Preferably a plate normal to said shaft is mounted to said impeller means so that when assembled it will be outside of and spaced from one of the open ends of said conduit.

Brief Description of the Drawings The preferred embodiment of the present invention is shown in the accompanying drawings in which:

Figure 1 is an elevational view of the combined mixing and heating apparatus of the present invention when installed in an anaerobic fermentation ~one, Figure 2 is a side elevation view of the upper portion of the preferred passageway of the present invention showing the impeller assembly, splash plate and the jacket in relation thereto.

11~2~1~

Detailed Description of the Drawings Figure 1 shows the preferred and essential features of the apparatus for defining a fermentation zone in which organic wastes such as manures and the like can be anaerobically fermented in order to provide the required purification of the solids and the liquids contained in the manures or other wastes and to generate substantially 70% by volume methane and substantially 30% by volume carbon dioxide. When the biomass is fermenting sweetly substantially 1/4 of 1% by volume of the gas generated is hydrogen sulphide.
A person skilled in the art will appreciate the skills with which a fermentation zone must be established and it is not the function of this description to teach such methods. Reference however should be made to the aforementioned British Patent specification for some ~` indication as to the factors involved in such fermentation.
The preferred fermentation zone of the present invention has a concrete base foundation 1 and a sub-stantially circular insulated frame 2 adapted to constrain the butyl rubber or other suitable material bag which will provide the gas and liquid tight containment of the contents and gas of the fermentation zone. The side walls 2 are preferably formed by the bolting together of a plurality of prefabricated panels having appropriate flanges and apertures adapted to enable the same to be combined. Ideally also there are strengthening ribs ~1~32~1~

incorporated in such panels which pass around the cir-cumference of the circular or substantially circular wall 2. A person skilled in structural engineering will appreciate that ideally the spacing will be closer to-gether for such strengthening ribs near the lower portions of the side wall 2.
In order to hold the upper reaches of the wall

2 to the prearranged configuration, raker like members 3 formed preferably from a metal extend upwardly. These raker members extend in from almost every direction so as to provide a mounting for the mixing unit 4 which will be described hereafter in more detail. A person skilled in the art however will appreciate how a plurality of such raker members 3 can be combined to define a structure near the apex of the apparatus shown in Figure 1 which is capable of supporting the weight of a man. This is necessary so that the mixing unit 4 if required can be serviced or unbolted or the like for removal. Moreover such raker members 3 are adapted to provide some form of constraint on the over-inflation or deformation of the containment bag that is~bounded thereby and by the wall 2 and the base 1.
The bag is not specifically shown in Figure 1 although it should be appreciated that it does abut against members or regions 1, 2 and 3 and the same is adapted to provide an airtight and liquid tight seal with all inlets and outlets and ports into and out of the fermentation zone.

1102~9 For the ease of explanation the preferred level at which the contents are kept in the fermentation zone is to level 5. Above that space the gases are in use generated to some required pressure before they are led away from that region via the gas line 6 which has its inlet at 7. The gas line passes the mixture of methane, carbon dioxide and hydrogen sulphide to a purifier 8 down which the gas passes before being passed to an accumulation tank or to some reticulation system, e.g.
a heating system for example to maintain the warmth of the hen house from which the manure to charge the whole fermentation zone is obtained or to some electric generating plant or the like. Of course some proportion of the gas generated is ideally used to maintain the anaerobic fermentation zone at its preferred operating temperature which is preferably 96F but which to be economic should be above 85F and well below 140F.
~; The purifying column 8 shown in Figure 1 is preferably one of two. This is desirable so that when one purifier is being used the other can be regenerated.
Ideally the purifier is charged with iron swarf which in a rusted condition will form Fe203 which reacts with any of the odorous and poisonous hydrogen sulphide entrained in the generated gases and removes the same as a solid.
A period skilled in the art will appreciate the chemical changes involved. For an understanding of the claimed invention of the present specification it is not necessary to dwell on such ancilliary features.

1~2~19 A relief valve 9 is provided to ensure that the bag in which the fermentation zone operates is not over-pressurized. The pressure involved, of course, will depend upon the strength of the structure and the bag. No detailed description need be given thereof.
Also shown diagrammatically is a feed inlet pipe lO which preferably daily will inject communicated or substantially homogeneous organic wastes into the fer-mentation zone. As such organic wastes are fed into the tank the decanting outlet inlet 11 by virtue of the increased head or level of contents 5 passes the same out of the outlet 12 thereof into a supernatant tank 13.
Low odours are caused by such an arrangement as the supernatant liquid is adequately fermented in order to ~
deodorize the same. In fact when the biomass is operating optimally such supernatant decant liquid can be sprayed onto pastures and will be readily consumed by livestock which indicates the fact that the same has been adequately fermented.
Also disposed within the fermentation zone, but adjacent the bottom thereof is a sludge drain inlet 14 which again using a hydrostatic head allows the draining -this time sludge through a valved outlet 15 as required, an operation normally only necessary periodically.
Projecting into the fermentation zone is a temperature control thermometer 16 which is preferably adapted to provide a source of control for the heating system and which would be used in a controlled manner to 1~2~ig provide source signals to operate the heating system shown diagrammatically in Figure ~ and designated by 17.
The description of Figure 8 will now be given in order to understand the way in which this heating system is controllable by the therometer 16.
Mounted on the pipeline 19 is a circulating pump that is universally available. Mounted up the water lines is a temperature gauge which can be used for reg-ulating the temperature of the hot water passing into and out of the jacket which will be described hereafter.
It is important to ensure that the temperature does not exceed 140F as this may cause the scaling of pipelines inside the fermentation zone and may also minimize the overall efficiency of the fermentation. The temperature gauges may also be used to calculate the heat transfer efficiency so as to give an indication as to when servicing of the combined heater and mixing unit of the present invention will be necessary.
Linked to the hot water line is a header tank which acts as an expansion vessel and pressure relief vent as well as a constant water head. The header tank can be situated for automatic refilling of evaporation losses and would normally be hooked up to a mains water supply via a ball cock and float. A person skilled in the art will appreciate the requirements of such a system.
Ideally the thermometer is used to control the flow and the temperature of the flow of liquid (preferably water) through the hot line and back out of the cold line ~1~2~

so as to control the overall temperature of the contents of the fermentation zone. A more detailed description of this flow control system need not be given as a person skilled in the art will appreciate the requirements thereof. Moreover a person skilled in the art will appreciate the requirements of a heater in order that the same can burn a mixture of 70~ by volume only of com-~ bustible gas.
; In Figure 1 there is shown a substantially cylindrical conduit 24 which has its upper level below the level 5 of the contents of the fermentation zone.
This is preferably although not essential. It can be seen that the conduit 24 has an open and preferably flared top 25 end and an inlet 26 at the base thereof which is similarly open. However the lower region of course could instead include side entrances in the bottom reaches of the conduit 24. Disposed for a substantial distance around the conduit 25 is the substantially coaxial member 27 which with appropriate end pieces defines a water or heating liquid jacket which has previously been referred to. This jacket has an inlet adjacent the top thereof for the heating liquid passing through the pipeline 20 and has from the base thereof an outlet for drawing out the cooled heating liquid and passing the same back through the pipeline 19. Preferably the arrangement of the conduit 25 is such that good heat exchange will occur from the water jacket to any contents passing up there-through. Ideally the same is provided with a matt black P~

finish which will resist abrasion by and poisoning of the contents of the fermentation zone. For example a suitable epoxy resin. However, a person skilled in the art will appreciate suitable such coatings.
Preferably the lower end of the conduit 24 and its associated water jacket is supported on a skeletal framing stand 31 which is supported by a standing relation-ship on the inside wall of the bag constrained by the foundation 1. The mounting of the same is not all that important provided some vertical support is provided and some degree of lateral stability is provided. ' Additional lateral support is provided by the locating ring 32 (see Figure 2) which abuts against the inner surface of the conduit 24. The locating ring can best be seen with reference to Figure 2 where it can be seen that there is a central collar 33, a peripheral cylindrical rim 34 and three spokes 35. The collar 33 engages around a sleeve 36 which itself is located laterally by a mounting depending from the raker members 3 and which also obtains mutual lateral support with its association with the internal face (via the locating ring) of the conduit 24.
Located within the sleeve 36 is the shaft 37 which is rotatable by an electric motor 37A which is supported as a unit from a manhole lid type region 38 defined at the upper extremities of the raker members 3 (see Figure 1) and which itself is in an air and liquid tight relationship with the appropriate opening in the bag constrained as previously described.

l~V2~1g Disposed below the motor 37A is an appropriate power transmission train which need not be described in detail. It can be seen, however, that there is an approp-riate coupling 39, bearing 40, thrust washer 41 and a support and housing for the sleeve 36. The shaft 37, of course, extends down through the sleeve 36 in a lubricated manner. A person skilled in the art will ; appreciate the type of tolerances required. Ideally the shaft 37 is 1 1/4" diameter shaft and has attached at the end thereof on a reduced diameter of 1" a propeller or screw 42. Preferably the screw used is a 5hp x 1400rpm propeller.
Disposed above the opening 25 of the conduit 24 is a splash plate 43. This is a circular plate preferably 1/8" thick which has a collar 44 which is fixed in a nonrotating relationship on the sleeve 36. The splash plate is preferably 1'6" in diameter and is preferably disposed about 1 to 2 feet above a propeller 42. The propeller 42 is arranged to draw the contents of the fermentation zone up through the conduit 24 which in the art will be called an "eductor tube". The apparatus of the present invention therefore is an education heating system for a fermentation zone.
Previously we have described an alternative way whereby means could define a passageway e.g. a closely wound spiral. Such forms, however, are not as preferred as the preferred form bearing in mind the costs involved . ~
~lV2C~19 and also the relative flow efficiency. It can be seen by a person skilled in the art that by maintaining the level 5 and operating the apparatus as described, liquid is drawn in from all over the fermentation zone into the inlet 26 of the eductor tube and is heated during its passage therethrough by virtue of its heat transfer previously described. The same is drawn up by the propeller 42 and is lifted at considerable velocity so as to impinge against the deflector or splash plate 43 and thereby be spread outwards back onto the surface of the contents 5, thus effecting an efficient mixing and temperature stabilizing arrangement within the tank.
Such a system, a person skilled in the art will appreciate can be readily removed as required by virtue of an un-bolting of the mixing unit and a lifting of the same through the manhole region opening 38 as required. In order to effect such an arrangement, it is not necessary to empty the contents of the fermentation zone or to significantly empty the same. Moreover it can be seen that removable members only would ever require preventative maintenance and there is no damage occasioned by the use of the bag as a heat transfer medium. It is believed therefore that the combined unit of the present invention should find a widespread use in fermentation zones of the type contemplated as the use of the apparatus and the method of the present invention, would be favoured not only because of the costs thereof but also the efficiencies and maintenance free nature thereof.

Claims (11)

WHAT IS CLAIMED IS:

1. In an anerobic fermentation system for organic material a combined mixing and heating apparatus comprising means defining a substantially vertically extending passageway having included for at least a portion of the passageway means to heat the contents within the passageway and means for moving said contents upwardly through said passageway whereby the material is continuously circulated and maintained at an optimal fermentation temperature.

2. Apparatus as claimed in Claim 1, wherein said means for drawing the contents up through said passageway comprises an impeller mounted within said passageway.

3. Apparatus as claimed in Claim 2, wherein said means defining said passageway comprises a conduit having an open top end and inlet means at or adjacent the lower end thereof.

4. Apparatus as claimed in Claim 3, wherein said conduit has disposed about a portion thereof means defining a heating jacket to which leads and from which leads an inlet conduit and an outlet for a heating fluid, to thus provide said means to heat some of the contents within the bounds of the passageway.

5. Apparatus as claimed in claim 4, wherein said impeller is a propeller or screw positioned to rotate about a substantially vertical rotation-al axis proximate the top of said means defining said passageway but below the level of the contents of said fermentation zone.

6. Apparatus as claimed in claim 5, wherein the contents of such a fermentation zone when in use have thereabove a space filled with gases generated by such fermentation and there is there disposed a surface against which material raised by said impeller can impinge to thereby be deflected outwards and back onto the surface of the contents in said fermen-tation zone.

7. Apparatus as claimed in claim 6, wherein an electrical motor is coupled above said impeller and arranged to drive the same using a drive shaft, said drive shaft being passed down through a sleeve member which supports in a non-rotation manner said splash plate.

8. Apparatus as claimed in claim 7, wherein said fermentation zone is defined by a flexible bag member located within a frame and on a base adapted to provide a constraint thereof.

9. The apparatus of claim 8, wherein the combustion of gas which evolves from the fermentation zone is used to provide a heating source for said means to heat some of the contents within the bounds of said passageway.

10. Apparatus for use in an anaerobic fermentation system accord-ing to claim 1 comprising a substantially straight elongate conduit having open ends and having a jacket at least partly thereabout which has an inlet and an outlet, impeller means including a propeller or screw, a shaft there-for and means operative in use to rotate the same, and means to locate said conduit and impeller means in association with the propeller or screw within the conduit and rotatable relative thereto with the longitudinal axes of said conduit and the shaft being substantially coincident.

11. Apparatus as claimed in claim 10, wherein a plate normal to said shaft is mounted to said impeller means so that when assembled it will be outside of and spaced from one of the open ends of said conduit.