A System And Method For Recovering Ammonia From an Ammonia-Containing Liquid

Abstract

A system for recovering ammonia from an ammonia-containing liquid, which system comprises a waste tank (10) for receiving ammonia-containing liquid entering the system; a filtration unit (14) comprising an ultrafiltration unit for receiving the ammonia-containing liquid from the waste tank (10) and filtering the ammonia-containing liquid to remove solids; an ammonia concentrating unit comprising a reverse osmosis unit (18) for receiving ammonia-containing liquid from the filtration unit (14) and concentrating the ammonia within the liquid; and an ammonia-recovery unit (100) for receiving concentrated ammonia-containing liquid from the ammonia concentrating unit (18) and recovering ammonia therefrom, wherein the ammonia-recovery unit (100) comprises a rectifier (102) for separating ammonia from the concentrated ammonia-containing liquid and recovering the ammonia as ammonia-containing gas; and wherein the system does not comprise an ammonia stripper.

Claims

1-20. (canceled)

21. A system for recovering ammonia from an ammonia-containing wastewater, which system comprises: a waste tank for receiving ammonia-containing wastewater entering the system; a filtration unit comprising an ultrafiltration unit and/or microfiltration unit for receiving the ammonia-containing wastewater from the waste tank and filtering the ammonia-containing wastewater to remove solids; an ammonia concentrating unit for receiving ammonia-containing wastewater from the filtration unit and concentrating the ammonia within the wastewater; and an ammonia-recovery unit for receiving concentrated ammonia-containing wastewater from the ammonia concentrating unit and recovering ammonia therefrom; wherein the ammonia-recovery unit comprises a rectifier for separating ammonia from the concentrated ammonia-containing wastewater by heating the concentrated ammonia-containing wastewater to remove the ammonia as an ammonia-containing gas; and wherein the system does not comprise an ammonia stripper.

22. A system according to claim 21 configured to recirculate ammonia-containing wastewater through the filtration unit.

23. A system according to claim 21 wherein the ammonia concentrating unit comprises a reverse osmosis unit and/or a forward osmosis unit and/or an evaporator.

24. A system according to claim 21 wherein the ammonia concentrating unit comprises a reverse osmosis unit.

25. A system according to claim 24 configured such that in use ammonia-containing wastewater passes through the ammonia concentrating unit in a single pass, or is recycled through the ammonia concentrating unit for multiple passes.

26. A system according to claim 21 wherein the ammonia concentrating unit comprises an evaporator.

27. A system according to claim 26 comprising a thin film evaporator.

28. A system according to claim 26 wherein the evaporator operates under an at least partial vacuum.

29. A system according to claim 27 wherein the evaporator operates under an at least partial vacuum.

30. A system according to claim 21 comprising a heat exchanger for recovering heat from liquid leaving the rectifier and transferring it to the concentrated ammonia-containing wastewater entering the rectifier.

31. A system according to claim 30 wherein the ammonia recovery unit comprises a condenser, to condense ammonia contained within the ammonia-containing gas? into liquid.

32. A system according to claim 31 wherein the ammonia recovery unit further comprises a cooler, to cool the liquid, and/or a drier to remove water from the liquid.

33. A system according to claim 21 for recovering ammonia as anhydrous liquid ammonia, and/or as an ammonia compound.

34. A system according to claim 33 wherein the ammonia compound is ammonium hydroxide.

35. A method for recovering ammonia from ammonia-containing wastewater, which comprises the steps of: passing the ammonia-containing wastewater from a waste tank into a filtration unit for filtering the liquid to remove solids; passing the ammonia-containing wastewater from the filtration unit into an ammonia concentrating unit for concentrating the ammonia within the wastewater; and passing the concentrated ammonia-containing wastewater from the ammonia concentrating unit to an ammonia-recovery unit for recovering ammonia therefrom; wherein the ammonia-recovery unit comprises a rectifier for separating ammonia from the concentrated ammonia-containing wastewater, wherein the concentrated ammonia-containing wastewater is heated to remove ammonia as an ammonia-containing gas; and wherein the method does not comprise the use of an ammonia stripper.

36. A method according to claim 35 which is performed using a system according to claim 1.

37. A method according to claim 35 for recovering ammonia as anhydrous liquid ammonia and/or an ammonia compound.

38. A method according to claim 36 for recovering ammonia as anhydrous liquid ammonia and/or an ammonia compound.

39. A method according to claim 37 wherein the ammonia compound is ammonium hydroxide.

40. A method according to claim 38 wherein the ammonia compound is ammonium hydroxide.

Description

[0049] The present invention will now be described in detail with reference to the accompanying drawing, in which:

[0050] FIG. 1 shows a process flow diagram for the system and method of the first and second aspects of the invention.

[0051] Thus, referring to FIG. 1, an embodiment of a system for recovering ammonia from an ammonia-containing liquid according to the first aspect of the present invention is shown. For the sake of this embodiment, the ammonia-containing liquid is ammonia-containing wastewater, but the system and method of the present invention are not limited in this way, and may potentially be used to recover ammonia from any ammonia-containing liquid.

[0052] The embodiment of the system shown in FIG. 1 comprises a waste tank 10 for receiving ammonia-containing water entering the system as indicated by arrow A, for holding the ammonia-containing liquid and regulating flow. The waste tank 10 may help to remove larger particulate solids from the ammonia-containing water. Coagulation and/or flocculation reagents may be added before the ammonia-containing water enters the tank 10 to promote agglomeration of finely suspended particles into larger and denser particles, which settle more quickly than smaller less dense particles. However, it is preferred that the use of such reagents is avoided if possible.

[0053] The ammonia-containing water passes from the waste tank 10 into a filtration unit 14 via pump 12, for removal of solids. In the illustrated embodiment, the filtration unit 14 comprises an ultrafiltration unit, but a microfiltration unit may additionally or alternatively be used. In the ultrafiltration unit 14 the ammonia-containing water is forced under pressure across a partially permeable membrane (not shown). Suspended solids and higher molecular weight solutes are removed in the retentate (i.e. the fraction of the feed which does not pass through the membrane of the ultrafiltration unit), with water and lower molecular weight solutes, including ammonia, passing through the membrane in the permeate (i.e. the fraction of the feed containing the ammonia, which does pass through the membrane of the ultrafiltration unit). The permeate contains the ammonia, and is pumped to an ammonia concentrating unit, comprising a reverse osmosis unit 18 in the illustrated embodiment, via pump 16. The retentate is recycled back into the tank for further processing via return channel 15. The ammonia-containing water may be recycled via return channel 15 to pass through the filtration unit 14 multiple times.

[0054] Thus, in the illustrated embodiment, the permeate passes to a reverse osmosis unit 18 via pump 16, to concentrate the ammonia within the ammonia-containing water. In the reverse osmosis unit 18, pressure is applied to the ammonia-containing water (permeate) within the reverse osmosis unit 18, forcing water but not the ammonia through a partially permeable membrane. In this way, the concentration of ammonia in the ammonia-containing water is increased, through the removal of water.

[0055] It is to be noted that in the system and method of the first and second aspects of the present invention, the ammonia concentrating unit may additionally or alternatively comprise a forward osmosis unit and/or an evaporator (not shown in FIG. 1) as described herein.

[0056] The concentrated ammonia-containing water passes from the reverse osmosis unit 18, as indicated by arrow C, to an ammonia recovery unit, generally indicated by reference 100, to recover ammonia. The unwanted water may be recycled back into the ammonia concentrating unit 18 for further recovery of ammonia, as indicated by arrow D, and/or may be discharged to waste.

[0057] In the embodiment shown in FIG. 1, the ammonia recovery unit 100 comprises a rectifier 102 for removing ammonia from the concentrated ammonia-containing water. The concentrated ammonia-containing water passes from the reverse osmosis unit 18 into a heat exchanger 104, for recovering heat from water leaving the rectifier 102 and transferring it to the concentrated ammonia-containing liquid entering the rectifier 102. The concentrated ammonia-containing water then passes into a generator 106, which heats the concentrated ammonia-containing water to generate ammonia-water vapour. This vapour passes upwards within the rectifier 102 where the ammonia vapour becomes increasingly pure, through the removal of water vapour. As discussed above, condensed water leaving the rectifier 102 passes through heat exchanger 104 prior to discharge.

[0058] In the illustrated embodiment, the ammonia vapour then passes from the rectifier 102 into a condenser 108, to condense the ammonia-containing gas into liquid. Liquid ammonia exiting the condenser 108 may be recycled into rectifier 102 for further removal of any residual water. In the embodiment shown in FIG. 1, the liquid ammonia is then cooled in a cooler 110, dried in a drier 112 to remove any remaining water, for example using a gas drying agent, compressed in compressor 114, and stored in collection unit 116 as anhydrous liquid ammonia.

[0059] The system and method of the first and second aspects of the present invention may be used to recover ammonia as anhydrous liquid ammonia, or an ammonia compound, such as an ammonium salt, for example ammonium hydroxide.

[0060] It will be appreciated that the specific embodiments described herein are for illustrative purposes only, and that further modifications and variations of the embodiments are possible without departing from the scope of the present invention as defined by the appended claims.