METHOD AND SLURRY TREATMENT PLANT FOR REDUCING METHANE EMISSION FROM SLURRY

Abstract

Disclosed is a method for reducing methane emission from slurry produced in a livestock farm. The method comprising the steps of guiding unheated slurry from the livestock farm to a slurry heat exchanger, raising the temperature of the unheated slurry in the slurry heat exchanger to at least 65# Celsius, guiding the at least 65# Celsius hot slurry to an intermediate slurry tank, raising the temperature of the heated slurry to at least 75# Celsius in the intermediate slurry tank, guiding the at least 75# Celsius hot slurry through the slurry heat exchanger to exchange heat with the unheated slurry to raise the temperature of the unheated slurry to the at least 65# Celsius and to cool the at least 75# Celsius hot slurry to at least below 40# Celsius, and guiding the at least below 40# Celsius cold slurry to a slurry reservoir. Furthermore, a slurry treatment plant for reducing methane emission from slurry is disclosed.

Claims

1. A method for reducing methane emission from slurry produced in a livestock farm, said method comprising the steps of: guiding unheated slurry from said livestock farm to a slurry heat exchanger, raising the temperature of said unheated slurry in said slurry heat exchanger to at least 65° C., guiding said at least 65° C. hot slurry to an intermediate slurry tank, raising the temperature of said heated slurry to at least 75° C. in said intermediate slurry tank, guiding said at least 75° C. hot slurry through said slurry heat exchanger to exchange heat with said unheated slurry to raise the temperature of said unheated slurry to said at least 65° C. and to cool said at least 75° C. hot slurry to at least below 40° C., and guiding said at least below 40° C. cold slurry to a slurry reservoir.

2. The method according to claim 1, wherein the temperature of said at least 65° C. hot slurry is raised to a temperature in the range from 70° C. to 100° C., preferably in the range from 80° C. to 95° C., in said intermediate slurry tank.

3. The method according to claim 1, wherein the temperature of said unheated slurry is raised to a temperature in the range from 65° C. to 80° C. in said slurry heat exchanger.

4. The method according to claim 1, wherein said method comprises a further step of cooling said at least below 40° C. cold slurry to at least below 30° C. in a cooling unit.

5. The method according to claim 1, wherein said method comprises a further step of cooling said at least below 40° C. cold slurry to a temperature in the range from 10° C. to 30° C., such as in the range from 15° C. to 25° C., for example 20° C.

6. The method according to claim 1, wherein ammonia produced in said slurry heat exchanger and/or said intermediate slurry tank is collected and guided to a mixing unit in which said ammonia is dissolved in at least a portion of said at least below 40° C. cold slurry.

7. (canceled)

8. The method according to claims 1, wherein said at least 65° C. hot slurry is guided through an auxiliary slurry heat exchanger for further heating of said hot slurry before said step of guiding said hot slurry to said intermediate slurry tank.

9. The method according to claim 8, wherein ammonia produced in said slurry heat exchanger and/or said intermediate slurry tank is collected and guided to a combustion chamber for combustion of said ammonia, and wherein exhaust gases of said combustion is guided to said auxiliary slurry heat exchanger to exchange heat with said at least 65° C. hot slurry to raise the temperature of said at least 65° C. hot slurry.

10. The method according to claim 8, wherein the temperature of said at least 65° C. hot slurry is raised to at least 80° C. in said auxiliary slurry heat exchanger.

11. (canceled)

12. (canceled)

13. (canceled)

14. The method according to claim 1, wherein at least a portion of said at least below 40° C. cold slurry is guided back to said livestock farm and into said slurry heat exchanger.

15. (canceled)

16. The method according to claim 1, wherein said hot slurry guided to said intermediate slurry tank is kept in said intermediate slurry tank for at least 10 minutes.

17. A slurry treatment plant for reduction of methane emission from slurry produced in a livestock farm, said slurry treatment plant comprising: a slurry receiving tank, a slurry pump, a slurry heat exchanger arranged to receive unheated slurry from said livestock farm and raise the temperature of said unheated slurry to at least 65° C., an intermediate slurry tank arranged to receive said at least 65° C. hot slurry from said slurry heat exchanger and raise the temperature of said heated slurry to at least 75° C., wherein said slurry heat exchanger is further arranged to receive said at least 75° C. hot slurry and exchange heat with said unheated slurry to raise the temperature of said unheated slurry to said at least 65° C. and to cool said at least 75° C. hot slurry to at least below 40° C., and a slurry reservoir arranged to receive and store said at least below 40° C. cold slurry.

18. (canceled)

19. (canceled)

20. The slurry treatment plant according to claim 12, wherein said slurry treatment plant comprises an auxiliary slurry heat exchanger arranged for further heating of at least 65° C. hot slurry.

21. (canceled)

22. The slurry treatment plant according to claim 12, wherein said slurry treatment plant comprises a cooling unit arranged to cool said at least below 40° C. cold slurry to a temperature below at least 30° C.

23. TheA slurry treatment plant according to claim 12, wherein said slurry treatment plant comprises a mixing unit and a first gas conduit, wherein said first gas conduit is arranged to guide ammonia from said slurry heat exchanger and/or said intermediate slurry tank to said mixing unit, and wherein said mixing unit is arranged to dissolve ammonia received from said first gas conduit in at least a portion of said at least below 40° C. cold slurry.

24. The slurry treatment plant according to claim 12, wherein said slurry treatment plant comprises an auxiliary slurry heat exchanger arranged to raise the temperature of said at least 65° C. hot slurry.

25. (canceled)

26. The slurry treatment plant according to claim 12, wherein said slurry treatment plant comprises a second gas conduit, a combustion chamber, and an exhaust gas conduit, wherein said second gas conduit is configured to guide ammonia from said slurry heat exchanger and/or said intermediate slurry tank to said combustion chamber for combustion of said ammonia, and wherein said exhaust gas conduit is configured to guide exhaust gases of said combustion to said auxiliary slurry heat exchanger.

27. The slurry treatment plant according to claim 12, wherein said slurry treatment plant comprises a ventilation air conduit configured to guide ventilation air from said livestock farm to said combustion chamber for combustion of said ventilation air.

28. The slurry treatment plant according to claim 12, wherein said intermediate slurry tank comprises at least one heating element arranged to raise the temperature of said at least 65° C. hot slurry to at least 75° C. in said intermediate slurry tank.

29. The slurry treatment plant according to claim 12, wherein said slurry treatment plant comprises a heat pump arranged to provide heat to said intermediate slurry tank by transfer of heat from said at least below 30° C. cold slurry to said intermediate slurry tank.

30. (canceled)

Description

FIGURES

[0083] The invention will be described in the following with reference to the figures in which FIG. 1 illustrates a method of and a slurry treatment plant for reducing methane emission from slurry produced in a livestock farm according to an embodiment of the invention,

[0084] FIG. 2 illustrates an embodiment of the invention wherein heat-treated slurry is further cooled by a cooling unit,

[0085] FIG. 3 illustrates an embodiment of the invention wherein ammonia produced by heating of slurry is dissolved in slurry in a mixing unit,

[0086] FIG. 4 illustrates an alternative embodiment of the invention wherein two slurry products are stored in respective slurry reservoirs,

[0087] FIG. 5 illustrates an embodiment of the invention wherein slurry is further heated in an auxiliary slurry heat exchanger,

[0088] FIG. 6 illustrates an embodiment of the invention wherein slurry is heated in an intermediate slurry tank by a heat pump, and

[0089] FIG. 7 illustrates an embodiment of the invention wherein at least a portion of heat-treated slurry is fed back to the livestock farm and the slurry heat exchanger of the slurry treatment plant.

DETAILED DESCRIPTION

[0090] FIG. 1 illustrates a method for reducing methane emission from slurry produced in a livestock farm 1 according to an embodiment of the invention. As shown in the exemplary embodiment of FIG. 1, the method is carried out by a slurry treatment plant 19. For sake of simplicity of the drawing, the livestock farm 1 is represented as a single animal (a pig in this example), however by a livestock farm is naturally understood a farm which houses several livestock.

[0091] The livestock of the livestock farm 1 contributes, through their release of urine and faeces, to the production of slurry. The slurry is captured in a slurry receiving tank 20 which is a reservoir/tank underneath the livestock where untreated slurry 2 from the livestock is initially received. The slurry receiving tank 20 shown in this embodiment is a reservoir which spans the entire area underneath the livestock in the livestock farm, however in other embodiments of the invention, the slurry receiving tank 20 may be a distributed receiving tank comprising one or more receiving areas which are joined together by tubing/piping to form a larger effective receiving tank. The untreated slurry 2 is pumped by a slurry pump 21 to a slurry heat exchanger 3. The slurry pump 21 of this embodiment of the invention is shown as a centrifugal pump, however, in other embodiments of the invention the slurry pump 21 may be of different pump designs such as a positive displacement pump or rotary pump.

[0092] The untreated slurry 2 which has been pumped into the slurry heat exchanger 3 is next heated by exchange of heat with already heated slurry in the slurry heat exchanger to a temperature of at least 65° C. The now at least above 65° C. hot slurry 4 is guided by a first slurry conduit 23 into an intermediate slurry tank 5 for further heating. The intermediate slurry tank 5, which is a tank configured for receiving and heating slurry, is used to heat the at least 65° C. hot slurry to a temperature of at least 75° C. The slurry 4 received in the intermediate slurry tank 5 is kept within the intermediate slurry tank 5 for at least 10 minutes, however in other embodiments of the invention the slurry 4 may be kept in the intermediate slurry tank 5 for a greater time duration, and in yet other embodiments of the invention, the slurry 4 may be kept in the intermediate slurry tank 5 for less than 10 minutes.

[0093] Once heated in the intermediate slurry tank, the now at least above 75° C. hot slurry 6 is guided by a second slurry conduit 24 into the slurry heat exchanger 3 where an exchange of heat (heat energy) with the unheated slurry 2 occurs such that the temperature of the unheated slurry 2 increases while the temperature of the at least 75° C. hot slurry decreases accordingly. It is naturally understood that a reference to the at least 75° C. hot slurry is to be understood as a reference to the slurry which have passed through the intermediate slurry tank 5 and thus a heat transfer from this slurry to the unheated slurry 2 may naturally also occur at temperatures below 75° C.

[0094] Once the at least 75° C. hot slurry 6 which entered the slurry heat exchanger 3 has passed through the slurry heat exchanger 3 its temperature is reduced to at least below 40° C. The cooling of the slurry after its heat treatment is advantageous since then evaporation of methane and ammonia may be reduced.

[0095] The now at least below 40° C. cold slurry 7 is finally guided to a slurry reservoir 8 for storage. In this embodiment of the invention the slurry reservoir takes the form of a silo, however according other embodiments of the invention the slurry reservoir may take other forms such as a container or a tank, or any other kind of reservoir or storage unit configured to store slurry.

[0096] It should be understood from FIG. 1 that lines comprising arrows which indicate directions in which slurry is guided according to the method, equally well indicates appropriate piping, tubing, conduits, or gutters of the slurry treatment plant 19 by means of which slurry is guided through the slurry treatment plant 19.

[0097] FIG. 2 illustrates a method for reducing methane emission from slurry produced in a livestock farm 1 according to another embodiment of the invention. As shown in the exemplary embodiment of FIG. 2, the method is carried out by a slurry treatment plant 19. The embodiment of the invention as represented by FIG. 2 is like the embodiment of the invention as shown in FIG. 1 with the exception that the embodiment of FIG. 2 shows a cooling unit 9. The cooling unit 9 is configured to reduce the temperature of the at least below 40° C. cold slurry 7 to a temperature below at least 30° C. The at least below 30° C. cold slurry 29 is guided to the slurry tank 8 for storage.

[0098] As further shown in the embodiment of FIG. 2, the intermediate slurry tank 5 comprises a heating element 22 arranged to increase the temperature of the at least 65° C. hot slurry 4 which is guided to the intermediate slurry tank 5. As shown in this embodiment of the invention, the intermediate slurry tank comprises a single heating element 22, however in other embodiments of the invention, the intermediate slurry tank 5 may comprise more than one heating element 22 such as two or more heating elements 22. In yet other embodiments of the invention, the heating of the slurry in the intermediate slurry tank 5 is ensured by heat energy supplied to the intermediate slurry tank 5 by a heat pump 18.

[0099] FIG. 3 illustrates a method for reducing methane emission from slurry produced in a livestock farm 1 according to an embodiment of the invention. As shown in the exemplary embodiment of FIG. 3, the method is carried out by a slurry treatment plant 19. The embodiment of the invention as represented by FIG. 3 is like the embodiment of the invention as shown in FIG. 1 with the exception that ammonia is dissolved into the slurry after the heat treatment of slurry.

[0100] As the slurry is heated in the slurry heat exchanger 3 and the intermediate slurry tank 5 ammonia is released from the slurry since the solubility of ammonia in slurry decreases with increasing temperature of the slurry. The ammonia produced 10 from the heating of slurry is collected and guided by a first gas conduit 25 to a mixing unit 11. The mixing unit 11 of the present embodiment is a mixing tank, however according to other embodiments of the invention the mixing unit 11 may be a mixing vessel. The mixing tank 11 takes as input the at least below 40° C. cold slurry 7 as well as the ammonia 10 guided by the first gas conduit 25. Within the mixing tank 11 ammonia 10 is dissolved into the at least below 40° C. cold slurry. Hereby the slurry may regain its nutritional properties. The at least below 40° C. cold slurry 7 in which ammonia 10 is dissolved is guided to a slurry reservoir 8.

[0101] FIG. 4 illustrates an embodiment of the invention which is an alternative to the embodiment of the invention illustrated in FIG. 3.

[0102] The at least below 40° C. cold slurry 7 is divided into two streams, where a first portion of the slurry is guided to a mixing unit 11, which in this embodiment of the invention is a mixing tank, where ammonia 10 produced from the heating of slurry in the slurry heat exchanger 3 and/or the intermediate slurry tank 5 is dissolved in the slurry. The portion of the at least below 40° C. cold slurry 7 into which ammonia 10 dissolved in the mixing tank 10 is guided to an auxiliary slurry reservoir 12 for storage. The other portion of the at least below 40° C. cold slurry is guided to a slurry reservoir 8 for storage. The slurry treatment plant 19 of the present embodiment is thus able to produce two different final slurry products from the same unheated slurry 2.

[0103] FIG. 5 illustrates a method for reducing methane emission from slurry produced in a livestock farm 1 according to an embodiment of the invention. As shown in the exemplary embodiment of FIG. 5, the method is carried out by a slurry treatment plant 19. Unheated slurry 2 produced at a livestock farm 1 is pumped using a slurry pump 21 into a slurry heat exchanger 3 where the temperature of the slurry is increased to a temperature of at least 65° C. The now at least 65° C. hot slurry 4 is next guided by a first slurry conduit 23 to an intermediate slurry tank 5. The first slurry conduit 23 of this embodiment comprises a path which runs through an auxiliary slurry heat exchanger 13. The auxiliary slurry heat exchanger 13 is arranged to further increase the temperature of the at least 65° C. hot slurry by exchange of heat with another heat source. After heating in the auxiliary slurry heat exchanger 13, the slurry is guided to the intermediate slurry tank for further heating. The auxiliary slurry heat exchanger 13 is arranged to heat slurry by exchange of heat with exhaust gases from a combustion chamber 14.

[0104] The combustion chamber 14 is arranged to combust ammonia produced from the heating of slurry in the slurry heat exchanger 3 and/or the intermediate slurry tank 5. In this embodiment of the invention is shown that ammonia 10 is collected from the intermediate slurry tank 5 and guided to the combustion chamber 14 by a second gas conduit 26. The combustion chamber 14 of the present embodiment takes as input in addition to ammonia 10 also a fuel gas 30 in the form of biogas. However, in other embodiments of the invention the fuel gas may be other types of gases such as methane, propane, or other flammable gases. Furthermore, the combustion chamber 14 of the present embodiment of the invention takes ventilation air from the livestock farm 1 as input. The ventilation air of the livestock farm 1 is guided by a ventilation air conduit 28 to the combustion chamber. In this embodiment of the invention, the ventilation air conduit 28 is configured to be attached to an already existing ventilation air system of the livestock farm 1, however, in other embodiments of the invention the ventilation air conduit 28 may also comprise a collecting unit which independently of an already existing ventilation air system may collect ventilation air from the livestock farm 1.

[0105] The at least below 40° C. cold slurry 7 is guided to a cooling unit 9 for cooling of the slurry to a temperature below at least 30° C. The now at least below 30° C. cold slurry 29 is guided to a slurry reservoir 8 for storage.

[0106] Although not shown in this embodiment of the invention, ammonia from the intermediate slurry tank may also be collected and guided by a first gas conduit 25 and be dissolved into at least a portion, or all, of the at least below 40° C. cold slurry, such as at least below 30° C. cold slurry in a mixing unit 11 as also described in relation to various other embodiments of the invention.

[0107] FIG. 6 illustrates a method for reducing methane emission from slurry produced in a livestock farm 1 according to an embodiment of the invention. As shown in the exemplary embodiment of FIG. 6, the method is carried out by a slurry treatment plant 19. The embodiment of the invention as represented by FIG. 6 is similar to the embodiment of the invention as shown in FIG. 2 with the exception that the embodiment of FIG. 6 further features a heat pump 18. The heat pump 18 further reduces the temperature of the at least below 30° C. cold slurry 29 to a temperature below at least 20° C. and in this example the temperature is reduced to between 10° C. to 15° C. before the slurry is guided into the slurry reservoir 8. The heat pump 18 thus takes heat energy from the at least below 30° C. and transfers heat to the intermediate slurry tank 5 for heating of slurry to a temperature of at least 75° C. in the intermediate slurry tank 5.

[0108] Although the heat pump 18 is shown together with a cooling unit 9 in the embodiment of the invention of the invention as shown in FIG. 6, it is noted that according to other embodiments of the invention, the slurry treatment plant 19 may feature just the heat pump 18 for additional cooling of slurry and thereby not also rely on the cooling unit 9. It should further be noted that according to other embodiments of the invention, the slurry treatment plant 19 may also feature combinations of the heat pump 18 with the mixing unit 11 and/or the auxiliary slurry heat exchanger 13 and combustion chamber 14.

[0109] FIG. 7 illustrates a method for reducing methane emission from slurry produced in a livestock farm 1 according to another embodiment of the invention. As shown in the exemplary embodiment of FIG. 7, the method is carried out by a slurry treatment plant 19. The embodiment of the invention as represented by FIG. 7 is like the embodiment of the invention as shown in FIG. 1 with the exception that a portion of the at least below 40° C. cold slurry 7 is guided back to the livestock farm 1 and into the slurry heat exchanger 3 by a slurry feedback conduit 31. Hereby is achieved that any conduits, piping, tubing, or gutters between the livestock farm 1 and the slurry treatment plant 19 is flushed which results in further reductions in methane emission from slurry.

[0110] Although specific embodiments of the invention have been shown in the drawings accompanying these embodiments, various components/units shown in these specific embodiments may be combined in different configurations in other embodiments of the invention. As an example, the cooling unit 9 disclosed in relation to the embodiments represented by FIGS. 2 and 5 may also be included in the slurry treatment plant 19 of the embodiments of the invention comprising a mixing unit 11, e.g. in the embodiments shown on FIGS. 3 and 4. Cooling the at least below 40° C. cold slurry 7 prior to dissolving ammonia 10 in the slurry in the mixing unit 11 is advantageous in that a greater amount of ammonia 10 may be dissolved in the slurry.

TABLE-US-00001 List: 1 Livestock farm 2 Unheated slurry 3 Slurry heat exchanger 4 Hot slurry (at least 65° C.) 5 Intermediate slurry tank 6 Hot slurry (at least 75° C.) 7 Cold slurry (at least below 40° C.) 8 Slurry reservoir 9 Cooling unit 10 Ammonia 11 Mixing unit 12 Auxiliary slurry reservoir 13 Auxiliary slurry heat exchanger 14 Combustion chamber 15 Exhaust gases 16 Ventilation air 17 Fuel gas 18 Heat pump 19 Slurry treatment plant 20 Slurry receiving tank 21 Slurry pump 22 Heating element 23 First slurry conduit 24 Second slurry conduit 25 First gas conduit 26 Second gas conduit 27 Exhaust gas conduit 28 Ventilation air conduit 29 Cold slurry (at least below 30° C.) 30 Fuel gas 31 Slurry feedback conduit