AU2004201950A1

AU2004201950A1 - Process and device for biological treatment of a suspension in a bioreactor with integrated hydraulic top scum treatment

Info

Publication number: AU2004201950A1
Application number: AU2004201950A
Authority: AU
Inventors: Thomas Buchner; Matthias Herms; Gerhard Langhans
Original assignee: Linde KCA Dresden GmbH
Current assignee: Linde Engineering Dresden GmbH
Priority date: 2003-12-11
Filing date: 2004-05-07
Publication date: 2005-06-30
Also published as: CN1626457A; ATE358655T1; CN100431980C; JP2005169375A; KR20050058181A; DE10358399A1; PT1553057E; ES2286553T3; DE502004003386D1; EP1553057B1; EP1553057A1

Abstract

Biological treatment of suspension, comprises circulating the suspension, where some are routed through vertically aligned guide zone so that vertical flow of portion of suspension is produced, which flow proceeds into area of suspension fill level or from area of suspension fill level; and feeding fluid in area of suspension fill level to cause rotary flow of surface of suspension and/or of top scum floating on surface of suspension. An independent claim is also included for a bioreactor for biological treatment of a suspension comprising in the interior of the bioreactor, a guide with a vertical alignment for circulating the suspension, and at least one nozzle (11, 13) for feeding a fluid into the bioreactor in the area of the suspension fill level.

Description

AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION NAME OF APPLICANT(S):: Linde-KCA- Dresden GmbH ADDRESS FOR SERVICE: DAVIES COLLISON CAVE Patent Attorneys 1 Nicholson Street, Melbourne, 3000, Australia INVENTION TITLE: Process and device for biological treatment of a suspension in a bioreactor with integrated hydraulic top scum treatment The following statement is a full description of this invention, including the best method of performing it known to me/us:- 5102 Cross Reference To Related Application This application is related to a concurrently filed application entitled "Process And Device For Biological Treatment Of A Suspension In A Bioreactor With r Integrated Hydraulic Bottom Layer Removal" (Attorney Docket No. LINDE-0615) by the identical inventors. Priority is claimed of German Application 10358399.8.

The invention relates to a process for biological treatment of asuspension in a bioreactor in which to circulate the suspension, at least some of the suspension is routed through a vertically aligned guide zone so that a vertical flow of at least a portion of the suspension is produced, which flow extends into the area of the suspension fill level or proceeds from this area, as well as a device for carrying out the process.

Processes for biological treatment of suspensions are, aerobic or anaerobic processes for biological treatment of waste water, sewage sludge or waste, in which the biodegradable substances that are contained in the suspension are decomposed by microorganisms.

Processes for biogas recovery are defined below as the anaerobic treatment of suspensions containing biodegradable materials, especially the fermentation of waste or sludge digestion in the treatment of sewage sludge. Here, the biodegradable materials that are also called fermentation media are fermented into biogas in a bioreactor called a fermentation reactor with the exclusion of air. Often mechanical stirring systems or hydraulic recirculation systems are used to thoroughly mix the fermentation medium in the fermentation reactor. Injecting gas into the vicinity of the bottom of the fermentation reactor is also used in various ways.

In so-called loop reactors, a gas is injected into the central guide pipe that is located within the fermentation reactor, by which.the fermentation medium is drawn into the guide pipe. In this way, the fermentation medium can be conveyed by the guide pipe from the vicinity of the bottom of the fermentation reactor to the surface of the fermentation medium that is contained in the fermentation reactor. Thus, at least most of the fermentation medium can be circulated in the fermentation reactor. Such a system is described in, DE 197 25 823 Al. In addition to the important feature that there are no moving parts in the fermentation reactor, this system offers still other advantages. For example, low-gradient, thorough mixing is achieved via the vertical loop. Moreover, the possibility of integrating a heat exchanger into the fermentation reactor in the form of a double-jacketed pipe through which hot water flows is offered.

By blowing gas into the loop flow and the associated surface surge formation and turbulent bcottom mixing, in the surface flow that is pointed radially outward, moreover, the formation of surface scum is controlled. As a result of the defined flow conditions near the bottom for sediment transport in the direction of the central bottom outlet, finally the formation of sediment deposits is also prevented.

In practical operation, however, it has been shown that for special sludge and waste qualities that are supplied to the fermentation reactor in a system-specific manner, surface layer and sediment problems can occur that require additional control measures.

This relates, on the one hand, to sludges with a higher content of detergents and fine-fibrous plastic and cellulose particles, as they result from community waste water treatment or special commercial organic residues, as well as more highly viscous sludges; the mass proportions that are larger depending on origin contain glass fragments and other irregularly shaped inert particles.

For the initial materials, flotational skimming can take place with collection in the outer area of the fermentation surface in the reactor, where the radially decaying turbulence is no longer sufficient for bottom mixing. For sediments that are dissimilar to sand (rounded quartz grains), entanglement of the particles by their irregular fracture edges can occur; this means increased resistance to hydraulic transport to the center bottom discharge point.

Accordingly, objects of the invention are to configure a process and apparatus of the initially mentioned type such that the top scum problems are reliably ameliorated.

Upon further study of the specification and appended claims, further objects and advantages of this invention will become apparent to those skilled in the art.

According to the process aspect of a invention a fluid is passed in the area of the suspension fill level, so that the surface of the suspension and/or the top scum floating on the surface of the suspension is forced into rotary flow. Here, the fluid is fed into the bioreactor via a nozzle preferably as a free liquid jet.

The basic idea of the invention therefore comprises superimposing a hydraulic jet system on the gas-induced loop reactor principle. In this way, the processengineering advantages of a loop reactor with a guide pipe and gas injection can be used and at the same time problem cases that occur depending on the media are controlled without significantly increasing the addition of energy to the bioreactor system.

A free liquid jet injected into the bioreactor in the area of the suspension fill level causes rotation of the liquid mass near the surface. Rotary flow around the reactor center is formed from liquid jets emerging from nozzles placed substantially tangentially around the periphery of the bioreactor in the area of the fill level.

According to the invention, intensified top scum treatment takes place via nozzle systems that are located near the surface on the periphery of the tank. Here, the fluid that is suctioned off from the bioreactor is fed into the bioreactor in part or in a time sequence via at least one nozzle that is provided in the area of the suspension fill level such that the surface of the suspension and/or the top scum floating on the surface of the suspension is forced into rotary flow.

Preferably, the fluid is fed into the bioreactor via nozzles that are located tangentially on the periphery of the tank. Here, advantageously, a portion of the suspension that is suctioned off from the bioreactor is used as a fluid. The nozzles are preferably supplied with fluid at different times. Especially preferably the nozzles are operated with a common pump and successively supplied from the latter by means of cyclic switching of the series.

The top scum and foam particles that accumulate in the vicinity of the periphery of the tank have the tendency to stick together and compact over the longer term. They must therefore be continually wetted and kept slippery, must be agitated when they combine, and adhesively adhering gas bubbles must be eliminated in order to reduce the buoyancy. Optionally, deflection into the vicinity of the surface must be possible.

Complete control over the entire reactor periphery is not technologically feasible since especially steel fermentation reactors are generally not designed for a fill level in the area of the roof slope in terms of strength. Thus, the free liquid surface corresponds to the cross-sectional area of the cylindrical reactor part.

According to an especially preferred embodiment of the invention, the problem is solved in that the top scum that has been pushed together externally into a ring by the radial surface flow from the guide zone to the edge of the tank is exposed hydraulically to free liquid jets by preferably at least two nozzles located tangentially on the periphery of the tank and is forced into rotation by means of the transferred pulses. In doing so, the top scum ring runs through the jet zones and is wetted and agitated here in the desired manner.

The top scum outlet attached radially to the inside wall of the tank with a drop pipe that can be pushed away at the level of the liquid surface feasibly enables removal of floating material that can no longer be stirred into the suspension as necessary. The conditions can be adjusted by a change in the fill level in the bioreactor such that either the top scum rotates over the outlet or the material is pushed into the outlet box in batches.

To do this, preferably a nozzle is located at a distance in front of the top scum outlet such that it washes. the material into the outlet box with sufficient momentum.

Preferably, there is a second nozzle opposite that provides for movement and wetting.

Advantageously, operation of the two nozzles likewise takes place cyclically.

Preferably, the fluid is fed into the bioreactor with a flow velocity of 10 to m/s and a volumetric flow rate of from 300 to 600 m/h.

In addition to the biogas recovery process, the invention also relates to a device for biological treatment of a suspension with a bioreactor for receiving the suspension, in the interior of the bioreactor there being a guide means that extends into the area of the suspension fill level with a vertical alignment for circulating the suspension.

The apparatus according to the invention comprises at least one nozzle for feeding a fluid into the bioreactor in the area of the suspension fill level.

The nozzle can advantageously be supplied with the suspension via a feed line that is connected to the interior of the bioreactor and via a pump. Preferably, there are several nozzles distributed in the vicinity of the surface on the periphery of the bioreactor, advantageously with a tangential alignment. Here, the nozzles are preferably connected to a common pump. The nozzle advantageously has a diameter of from 50 to 120 mm.

Without further elaboration, it is believed that one skilled in the art can, using the preceding description, utilize the present invention to its fullest extent. The following preferred specific embodiments are, therefore, to be construed as merely illustrative, and not limitative of the remainder of the disclosure in any way whatsoever.

Brief Description of the Drawings The invention will be explained in more detail based on an embodiment that is shown diagrammatically in the figure.

The figure shows, for example, a plant for fermentation of wet garbage. The wet garbage is processed in pretreatment steps that are not shown in the figure such that pulp-or hydrolysate is formed. The pulp or the hydrolysate is supplied to the bioreactor labeled as the fermentation reactor 2 via a line 1 as a suspension that is called the fermentation medium. In the fermentation reactor 2, methanation of the pulp or the hydrolysate is carried out. To do this, the fermentation reactor 2 is kept under anaerobic conditions, and the contents of the fermentation reactor are circulated.

The anaerobic biomass contained in the fermenting pulp and the hydrolysate converts the organic substances partially into carbon dioxide and methane. The resulting biogas is drawn off from the fermentation reactor 2 via the line 3.

Since the pulp or the hydrolysate also contains sulfur compounds, H 2 S would also be formed without further measures and would be found again ultimately in the biogas. In order to minimize the undesirable H 2 S portions in the biogas, the entire contents of the fermentation reactor defined by an oxygen-containing zone are transported with adequate contact time betwveen the oxygen-containing gas and fermentation medium. For this purpose, the fermentation reactor 2 is made as a loop reactor with an inside loop in the form of a centrally and vertically arranged guide pipe that acts as the oxygen-containing zone. Here, the biogas that is pumped into the lower part of the interior of the guide pipe and that is branched off from the biogas discharge line 3 via the biogas branch line 6 is used as a propellant gas. As a result of the decrease in the density of the mixture in the guide pipe 5 and the gas buoyancy force, the fermentation medium is conveyed from bottom to top through the guide pipe In doing so, the hydraulic conditions are set by choosing the guide pipe geometry and the injected biogas flow, such that the entire contents of the fermentation reactor are pumped at least twice per hour through the guide pipe 5. Air is. metered into the inner ascending flow of the guide pipe 5 by means of an air feed line 7 in quantitative ratios such that the fermentation medium adequately acquires oxygen contact during passage through the guide pipe 5 in order to limit H 2 S formation in its metabolic processes in the desired manner. At the same time, the oxygen is decomposed biochemically to such an extent that there are no longer any oxygen portions that adversely affect the process in the biogas. The air demand can thus be minimized such that the nitrogen in the biogas does not lead to a significant diminishment of gas quality for further caloric use. To maintain an operating temperature that is optimum for biological treatment of the fermentation medium, the guide pipe 5 is made to be heated. To do this, the guide pipe 5 is provided with a double-walled jacket that has a feed 8 and discharge 9 for the heating water. In addition, the contents of the fermentation reactor can be temperature-treated by means of an outside heat exchanger 19 through which heating water flows.

To control the problem cases that occur specific to the media, especially sediment problems that arise for special sludge and waste qualities, a hydraulic jet system is superimposed on the gas-induced loop reactor principle. In this way, the process-engineering advantages of the loop reactor with a guide pipe 5 and gas injection 7 can be used and at the same time problems that arise specific to the media are solved without significantly increasing the addition of energy into the fermentation system. For this purpose, the fermentation medium is drawn off from the fermentation reactor 2 via line 15 and pump 16 and supplied to a nozzle 11 via line 12.

The fermentation medium as a free liquid jet is fed into the fermentation reactor 2 via the nozzle 11 with a nozzle velocity of from 10 to 15 m/s and a volumetric flow rate of from 300 to 600 m 3 /h in the area near the bottom. In fermentation reactors with up to 8000 inm 3 of reaction volume and diameters of up to 24 m, the necessary pulsed flow is produced in this way in order to have the liquid mass near the bottom rotate at roughly 0.5 m/s near the tank wall. Here, the nozzle 11 that has a diameter of from to 120 mm, depending on the tank size and the process parameters, is offset by 400 to 600 to radial flow in order to induce torque. A tilt angle of the nozzle 11 to the horizontal of between 0 and 100 compensates for the media-induced buoyancy forces in the jet field. In practice, between two and five nozzles are arranged at corresponding distances on the periphery over the entire fermentation reactor tank circumference, depending on the reactor size. For the sake of clarity, the figure shows only one nozzle 1 1. All of the installed nozzles are connected to a single pump, specifically the pump 16, and are successively supplied from the latter by means of cyclic switching of the series. This makes possible an efficient and low-maintenance mode of operation.

In order to control top scum problems, a branch line 14 leads from the pump 16 to a nozzle 13 that is located on the fermentation reactor tank circumference near the surface. The hydraulic connection of this nozzle 13 takes place via the pump 16 when the on cycles are evaluated as too little and one or two additional operating cycles can be assigned to the bottom system. When the nozzle 13 is working frequently because of the nature of the media, a separate pump should be preferred. As with the nozzles 11 located in the vicinity of the bottom, it is also recommended with respect to the i nozzle 13 located near the surface that there be several nozzles. Also nozzles 13 are preferably offset in a similar manner to nozzles 11. For the sake of clarity, however, only one nozzle 13 is shown in the figure.

In the above description, the "area of the suspension fill levels includes the suspension surface and generally some centimeters above and below the surface, for example, above and below 30 or 20 or 10 or 5 or 3 centimeters from the surface, depending on the size of the vessel.

The entire disclosures of all applications, patents and publications, cited herein are incorporated by reference herein.

From the foregoing description, one skilled in the art can easily ascertain the essential characteristics of this invention and, without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions.

Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

The reference to any prior art in this specification is not, and should not be taken as, an acknowledgement or any form of suggestion that that prior art forms part of the common general knowledge in Australia.

Claims

1. In a process for biological treatment of a suspension in a bioreactor in which to circulatethe suspension, at least some of the suspension is routed through a vertically aligned guide zone so that a vertical flow of at least a portion of the suspension is produced, which flow proceeds into the area of the suspension fill level or from the area of the suspension fil! level, the improvement comprising passing a fluid in the area of the suspension fill level so as to cause rotary flow of the surface of the suspension and/or the top scum floating on the surface of the suspension.

2. Process according to claim 1, wherein the fluid is fed into the bioreactor via nozzles that are mounted tangentially on the periphery of the tank.

3. Process according to claim 1 and 2, wherein the suspension that is suctioned off from the bioreactor is used as a fluid.

4. Process according to claim 2 and 3, wherein the nozzles are supplied with fluid at different times.

Process according to one of claims 2 to 4, wherein the nozzles are operated with a cornion pump and are successively supplied from the latter by means of cyclic switching of the series.

6. Process according to one of claims 1 to 5, wherein at least a portion of the top scum floating on the surface of the suspension in the rotary flow is removed via at least one top scum outlet on the inside wall of the bioreactor in the area of the suspension fill level.

7. Process according to claim 6, wherein the top scum is washed into the top scum outlet by means of a fluid supplied in the vicinity of the top scum outlet.

8. Process according to claim 7, wherein a fluid that keeps the top scum in motion and wets it is delivered opposite the top scum outlet.

9. Process according to claim 8, wherein the fluid is delivered via a nozzle that is provided in the vicinity of the top scum outlet with a momentum such that the top scum is conveyed into the top scum outlet.

Process according to one of claims 1 to 9, wherein the fluid is delivered with a flow velocity of from 10 to 15 m/s.

11. Process according to one of claims 1 to 10, wherein the fluid is delivered with a volumetric flow rate of from 300 to 600 m3/h.

12. Device for biological treatment of a suspension with a bioreactor for receiving the suspension, in the interior of the bioreactor there being a guide means that extends into the area of the suspension fill level with a vertical alignment for circulating the suspension, wherein there is at least one nozzle for feeding a fluid into the bioreactor in the area of the suspension fill level.

13. Device according to claim 12, wherein the nozzle can be supplied with the suspension via a feed line that is connected to the interior of the bioreactor via a pump.

14. Device according to claims 12 and 13, wherein there are several nozzles distributed in the area of the suspension fill level on the periphery of the bioreactor.

Device according to claims 12 to 14, wherein there is a top scum outlet that is attached radially to the inside wall of the bioreactor in the area of the suspension fill level.

16. Device according to claim 15, wherein there is a nozzle for feeding a fluid in the vicinity of the top scum outlet. 2

17. Device according to claims 15 and 16, wherein there is a nozzle for feeding a fluid on the side of the bioreactor opposite the top scum outlet.

18. Device according to one of claims 12 to 17, wherein the nozzle has a diameter of 50 120 mm.

19. Process and/or device for biological treatment of a suspension and/or a bioreactor, substantially as hereinbefore described with reference to the drawings. The steps, features, compositions and compounds disclosed herein or referred to or indicated in the specification and/or claims of this application, individually or collectively, and any and all combinations of any two or more of said steps or features. DATED this SEVENTH day of MAY 2004 Linde-KCA- Dresden GmbH by DAVIES COLLISON CAVE Patent Attorneys for the applicant(s) 5108