METHOD AND DEVICE FOR THE TREATMENT OF ORGANIC MATTER, INVOLVING RECIRCULATION OF DIGESTED SLUDGE

Abstract

The present invention relates to a method for the treatment of organic matter, in particular sewage sludge, where the organic matter is first fed to a disintegration system. The organic matter is then subjected to thermal hydrolysis in the disintegration system to form disintegrated matter. The disintegrated matter is fed to a digester in which the disintegrated matter is at least partially digested such that digested sludge is formed, where at least part of the digested sludge obtained is recirculated via a recirculation line to a point upstream of the disintegration system. The invention further relates to a device for the treatment of organic matter, in particular sewage sludge, comprising a disintegration system, a digester downstream thereof, and a recirculation line for at least partially digested disintegrated matter, said recirculation line extending from a point downstream of the digester to a point upstream of the thermal disintegration system.

Claims

1. A method for treatment of organic matter, the method comprising: feeding the organic matter to a disintegration system, thermal hydrolysis of the organic matter in the disintegration system to form disintegrated matter, feeding the disintegrated matter to a digester in which the disintegrated matter is at least partially digested such that digested sludge is formed, and recirculating at least part of the obtained digested sludge to a point upstream of the disintegration system via a recirculation line.

2. The method according to claim 1 wherein the recirculation is controlled such that a predetermined flow rate is obtained in the disintegration system so that a static operating state is given in the disintegration system.

3. The method according to claim 1 wherein the flow rate in the disintegration system has a flow velocity of 0.4 meters per second to 1.5 meters per second.

4. The method according to claim 1 wherein high-thermal hydrolysis is conducted in the disintegration system at temperatures beyond 100° C.

5. The method according to claim 1 wherein a hydrolysate recirculation line is additionally provided, by way of which at least part of the disintegrated matter can be recirculated to a point upstream of the disintegration system, where the non-recirculated portion of the disintegrated material is fed to the digester.

6. The method according to claim 5 wherein cleaning liquid for cleaning the system is circulated through the hydrolysate recirculation line and the disintegration system.

7. The method according to claim 6 wherein the supply of fresh organic matter to the disintegration system is stopped prior to cleaning and the organic matter located in the disintegration system is discharged with water into the digester.

8. The method according to claim 7 wherein the cleaning liquid comprises a chemical cleaning agent, and wherein the concentration of the cleaning agent is monitored by way of conductivity measurement.

9. The method according to claim 1 wherein the recirculated digested sludge is intermixed with freshly fed organic matter.

10. The method according to claim 1 wherein freshly fed organic matter is via a bypass line passed past the disintegration system and fed downstream of the disintegration system to the disintegrated matter.

11. The method according to claim 1 wherein the digested sludge is removed from the digester by way of the recirculation line and mixed with freshly fed organic matter, and a part thereof is fed directly into a storage tank or the disintegration system, while the other part is via a circulation line delivered directly into the digester.

12. A device for treatment of organic matter, the device comprising: a disintegration system; a digester arranged downstream of the disintegration system; and a recirculation line for at least partially digested disintegrated matter, wherein the recirculation line extends from a point downstream of the digester to a point upstream of the thermal disintegration system.

13. The device according to claim 12 wherein the disintegration system comprises an indirect heat exchanger in which pipes for the organic matter are provided having a nominal width of DN 20 to DN 60.

14. The device according to claim 12 further comprising a storage tank arranged upstream of the disintegration system, wherein the recirculation line and a feed line for fresh organic matter each open into the storage tank.

15. The device according to claim 12 wherein the recirculation line is part of a circulation circuit, in which a feed line for fresh organic matter is arranged upstream of a removal line, and wherein the removal line is arranged upstream of the disintegration system.

16. The method according to claim 6 wherein the cleaning liquid comprises water.

17. The method according to claim 16 wherein the cleaning liquid comprises a chemical cleaning agent.

18. The method according to claim 16 wherein the cleaning liquid comprises acid and/or lye.

19. The device according to claim 13 wherein the pipes have a nominal width of DN 25 to DN 50.

Description

[0055] The invention shall now be further explained using embodiments that are illustrated in the following figures.

[0056] FIG. 1 shows a first embodiment of a device according to the invention for the treatment of organic matter.

[0057] FIG. 2 shows a second embodiment of a device according to the invention for the treatment of organic matter.

[0058] FIG. 1 shows an embodiment of a device according to the invention for the treatment of sewage sludge with which an embodiment of the method according to the invention can be implemented. The device comprises a feed line 1 for feeding organic matter in the form of fresh sludge to a storage tank 2. Wastewater or sludge treatment components such as, for example, a thickener can be provided upstream of feed line 1.

[0059] A mechanical thickener in the form of a solid-liquid separation unit can be provided as a thickener. Additionally or alternatively, polymers can in the thickener be added to the fresh sludge for increasing its viscosity. The sewage sludge is removed in particular as thin sludge from a secondary sedimentation basin of a sewage treatment plant and converted into thick sludge in at least one of said thickeners (not shown). In other embodiments, the device illustrated can also be connected directly to a secondary sedimentation basin of the sewage treatment plant, so that thin sludge is treated.

[0060] The organic matter is then via a feed pump 3 fed from storage tank 2 to a disintegration system 4 in which thermal hydrolysis is performed, in particular at temperatures beyond 100° C. The disintegration system comprises at least one indirect heat exchanger in which the organic matter is by way of thermal oil heated to hydrolysis temperature. A digester 5 is provided downstream of disintegration system 4, where the inflow of disintegrated matter, i.e. hydrolyzed organic matter, can be regulated via a digester valve 6. Digester valve 6 enables in particular interrupting the inflow to digester 5 when disintegration system 4 is cleaned. At least one heating element of a preheating stage can be provided upstream in disintegration system 4 and at least one cooling element of a cooling stage can be provided downstream of disintegration system 4. The heating and cooling elements can also be configured as indirect heat exchangers and be connected via a heating media circuit so that heat can be recovered in the cooling stage and can be used for preheating the organic matter in the preheating stage.

[0061] According to the invention, a recirculation line 7 is provided downstream of the digester and removes the digested sludge, i.e. the partially or completely digested organic matter, from digester 5 and recirculates it to a point upstream of thermal disintegration system 4. Recirculation line 7 can in particular be connected in a base region of digester 5. Recirculation line 7 is provided with a recirculation pump 8 which enables delivering the digested sludge to a point upstream of disintegration system 4. Recirculation pump 8 can be provided with a shut-off valve which makes it possible to close recirculation line 7. Alternatively, said shut-off valve can also be provided as a separate component upstream or downstream of recirculation pump 8.

[0062] Furthermore, in the embodiment according to FIG. 1, a hydrolysate recirculation line 9 is provided extending from a point between disintegration system 4 and digester valve 6 to a point upstream of disintegration system 4. Hydrolysate recirculation line 8 extends in particular up to storage tank 2. Hydrolysate recirculation line 9 is provided with a hydrolysate recirculation valve 10 which makes it possible to close hydrolysate recirculation line 9. In particular, hydrolysate recirculation valve 10 can be a controllable valve with which predetermined amounts of disintegrated matter can be recirculated. In addition to hydrolysate recirculation valve 10, a hydrolysate recirculation line (not shown) can also be provided.

[0063] The embodiment in FIG. 1 therefore by way of hydrolysate recirculation line 9 comprises an internal recirculation or circuit passage and by way of recirculation line 7 comprises an external recirculation or circuit passage.

[0064] The flow through recirculation lines 7 and 9 can be regulated such that a predetermined flow rate is obtained in disintegration system 4 which in particular enables a static operating state to be obtained in disintegration system 4. Advantageous conditions in the disintegration system can thereby be created so that, firstly, efficient hydrolysis can be performed and, secondly, the risk of burn-on and deposits can be reduced.

[0065] Furthermore, in the event of failure of devices upstream of the device according to the invention, operation of the disintegration system can nevertheless be upheld by way of a circuit, in particular via recirculation line 7, until the problem has been resolved or disintegration system 4 has been shut down in a controlled manner.

[0066] This circuit has the particular advantage that digester 5 and the organic matter contained therein form a temperature storage, so that overheating of the organic matter is prevented, which could lead, in particular, to damaging feed pump 3. For this circuit operation, in particular, valve 10 is closed, valve 6 is opened, and pumps 3 and 8 are set to the same delivery rate. During normal operation, recirculation of digested sludge via recirculation line 7 and renewed thermal hydrolysis thereof in disintegration system 4 can enable improved utilization of the organic matter and thus, for example, an increased biogas yield.

[0067] Furthermore, a bypass line 11 with a bypass valve 12 is provided in FIG. 1. Bypass valve 12 can in other embodiments of course, be replaced by or added a bypass pump. Bypass valve 12 enables passing freshly fed organic matter parallel to thermal disintegration system 4. For this, the bypass line extends from a point upstream of disintegration system 4 to a point downstream of disintegration system 4. Bypass line 9 in particular extends from a point upstream of storage container 2 to a point downstream of digester valve 6.

[0068] The device according to FIG. 1 enables water or cleaning liquid to be circulated via hydrolysate recirculation line 9 while digester 5 is closed by digester valve 6. Bypass line 11 enables disintegration system 4 to be decoupled during this cleaning operation so that the treatment components disposed upstream need not be halted. Otherwise, a correspondingly large-sized and cost-intensive storage container with an additional delivery pump would have to be installed in storage tank 2. According to the invention, however, the organic matter can initially be passed directly into digester 5 and then after completion of the cleaning via recirculation line 7 be recirculated and fed to disintegration system 4.

[0069] Recirculation lines 7 and 9 enable recirculation of disintegrated matter and digested sludge into storage tank 2, and operation of disintegration system 4 can thereby be optimized in particular in terms of the flow rate, the pressure losses occurring therein, the heat transfer, and the viscosity of the organic matter therein, even during normal operation without necessarily coupling the upstream treatment components, e.g. the mechanical thickener.

[0070] Feed pump 3 is, in particular, a cost-effective standard eccentric screw pump. Operation of this pump is usually monitored via pressure sensors on the output side as well as temperature sensors in the stator. An emergency shutdown of feed pump 3 occurs, in particular, at a temperature of more than 60° C. If, in the event of failure of the upstream system parts, only disintegrated matter were to be recirculated via hydrolysate recirculation line 9, then the temperature of the disintegrated matter would within a short time lead to an excessive temperature in feed pump 3 and thus to an emergency shutdown thereof.

[0071] Due to the high degree of automation, the device according to the invention is in municipal sewage treatment systems often operated only during a single shift with an emergency service on weekends and public holidays. The reaction time, for example, in the event of failure of the mechanical thickening upstream of the device according to the invention, is up to 12 hours. If feed pump 3 were now to shut down in an emergency, this would also lead to failure of disintegration system 4. However, it is time-consuming to restart the disintegration system, since a high heat recovery rate is realized during normal operation via the aforementioned preheating and cooling stages, so that renewed heating without heat recovery is time and energy-consuming, thereby causing long and expensive down-time of the device. A combination of internal and external recirculation for stable and reliable operation is for this reason advantageous.

[0072] The desired flow volume of the external recirculation via recirculation line 7 can, for example, be determined and controlled via the temperature in the storage tank.

[0073] FIG. 2 shows an alternative embodiment of the device according to the invention. Recirculation line 7 is there combined to a circulation line 13, the flow rate of which can be regulated by way of a circulation line valve 14. Feeding organic matter via feed line 1 is there effected into recirculation line 7. Downstream of feed line 1, the freshly fed organic matter, during operation of recirculation line 7 mixed with digested sludge, is by way of a removal line 15 fed to storage tank 2.

[0074] If circulation line valve 14 is now opened, at least part of the organic matter flows via circulation line 13 directly into digester 5. This in turn allows decoupling disintegration system 4, in particular for cleaning purposes. Otherwise, the organic matter is via removal line 15 fed to storage tank 2 where it is optionally intermixed with disintegrated matter recirculated via hydrolysate recirculation line 9 and is via feed pump 3 fed to thermal disintegration system 4 and thermally hydrolyzed therein. The disintegrated matter is then via a hydrolysate line 16 passed to digester 5.

[0075] For cleaning the thermal disintegration system, a hydrolysate line valve 17 is closed and hydrolysate recirculation valve 10 is opened, so that water or cleaning liquid can be circulated through storage tank 2, feed pump 3 and disintegration system 4. Simultaneously, fresh sludge fed to the device is passed via circulating line 13 directly into digester 5.

[0076] Recirculation pump 8 allows for intermixing in digester 5.

[0077] Furthermore, heating of the digested sludge can be effected by the circulation, where a heating element (not shown) can be provided in circulation line 13 and designed to heat the organic matter to 35° C. to 55° C., so that its temperature is in the mesophilic or thermophilic temperature range.

[0078] Recirculation pump 8 can in particular deliver at a constant delivery volume, so that, depending on the quantity of fresh sludge fed via feed line 1, a variable mixing ratio of fresh sludge and digested sludge arises in circulation line 13, which can then without any further regulation be introduced into storage tank 2 and be fed via feed pump 3 to disintegration system 4. The expenses for regulation of the external recirculation can thereby be significantly reduced.

[0079] The external recirculation through recirculation line 7 is regulated in particular in dependence of the filling level in storage tank 2. This means that the volume capacity of recirculation pump 8 can be adjusted in dependence of the filling level of storage tank 2. If no storage tank is provided, then it is also possible for the system to be self-regulating, namely that the flow in recirculation line 7 is regulated by the suction pressure upstream of feed pump 3.