Ammonia Stripper Apparatus and Method

Abstract

An ammonia stripper (32) and method for stripping ammonia from ammonia-containing water is described, comprising an ammonia-containing water inlet (56), a steam inlet (70), and a forced air inlet (82), and an ammonia-containing gas outlet (36) and a wastewater outlet (72). The steam and air contact the ammonia-containing water in counter-flow to release ammonia from the ammonia-containing water. The ammonia stripper further comprises a steam and air mixing duct (200) shaped to create turbulence in the steam and air flow to promote mixing of the steam and air flow prior to contacting the ammonia-containing water. Also described is an ammonia stripper and method comprising a precipitation unit for precipitating solids from the ammonia-containing water prior to the inlet, and an ammonia stripper and method comprising a steam flash vessel for generating steam from the wastewater produced by the ammonia stripper for recycling into the ammonia stripper. Further described are thermal destructors for destroying ammonia in ammonia-containing gas from an ammonia stripper; and a method of removing ammonia from ammonia-containing gas wherein ammonia-containing gas is drawn from the ammonia-containing gas outlet and returned into the ammonia stripper to mix with the forced air entering the ammonia stripper.

Claims

1.-21. (canceled)

22. An ammonia stripper for stripping ammonia from ammonia-containing water, the ammonia stripper comprising an ammonia-containing water inlet, a steam inlet, and a forced air inlet; and an ammonia-containing gas outlet and a wastewater outlet; wherein, in use, the steam and air contact the ammonia-containing water in counter-flow to thereby release ammonia from the ammonia-containing water; and wherein the ammonia stripper further comprises an apparatus selected from the group consisting of: a steam and air mixing duct having a spiral shape and/or internal baffles to create turbulence in the steam and air flow by diverting the steam-air mixture through an extended turning flow path to promote mixing of the steam and air flow prior to contacting the ammonia-containing water, the mixing duct being positioned between the steam and air inlets and the location within the ammonia stripper where the steam and air contact the ammonia-containing water, a precipitation unit upstream of the ammonia-containing water inlet, for precipitating solids from the ammonia-containing water prior to the inlet, and a steam flash vessel downstream of the wastewater outlet, for generating steam from the wastewater produced by the ammonia stripper for recycling into the ammonia stripper.

23. The ammonia stripper according to claim 22, wherein the apparatus is the precipitation unit, which is adapted for precipitating carbonates.

24. The ammonia stripper according to claim 23, wherein the carbonates comprise calcium and/or magnesium carbonate.

25. The ammonia stripper according to claim 23, wherein the precipitation unit is located at ground level.

26. The ammonia stripper according to claim 23, wherein the precipitation unit includes an acid for reaction with the ammonia-containing water.

27. The ammonia stripper according to claim 26 wherein the acid comprises sulphuric acid.

28. An ammonia stripper according to claim 22, wherein the apparatus is the precipitation unit, and wherein conditions within the precipitation unit include hot incoming wastewater containing carbonates interacting with ammonia-containing gas exiting the ammonia stripper.

29. A method for removing ammonia from ammonia-containing water which comprises the steps of: providing an ammonia stripper according to claim 22, wherein the apparatus is the precipitation unit; and contacting steam and air with the ammonia-containing water in counter-flow within the ammonia stripper to thereby release ammonia from the ammonia-containing water; wherein the ammonia-containing water is pre-treated in the precipitation unit prior to entering the inlet, to precipitate solids from the ammonia-containing water.

30. The ammonia stripper according to claim 22, wherein the apparatus is the steam flash vessel, and wherein the steam flash vessel provides steam for the ammonia stripping process.

31. The ammonia stripper according to claim 22, wherein the apparatus is the steam flash vessel, and wherein the steam flash vessel comprises a heater for heating the wastewater under pressure prior to it generating steam for recycling into the ammonia stripping process.

32. The ammonia stripper according to claim 22, wherein the apparatus is the steam flash vessel, and wherein a range of between about 1 and 20 wt % of the wastewater is converted to steam by the steam flash vessel.

33. A method for removing ammonia from ammonia-containing water which comprises the steps of: providing the ammonia stripper according to claim 22, wherein the apparatus is the steam flash vessel; and contacting steam and air with the ammonia-containing water in counter-flow within the ammonia stripper to thereby release ammonia from the ammonia-containing water; wherein the wastewater passes from the wastewater outlet to the steam flash vessel downstream of the wastewater outlet, where it is at least partially converted to steam and recycled into the ammonia stripper.

34. A thermal destructor for destroying ammonia in ammonia-containing gas from an ammonia stripper, wherein the thermal destructor comprises a feature selected from the group consisting of: an exhaust gas recycler for recycling exhaust gasses from the thermal destructor back into the thermal destructor for further combustion; and a sealed upper end and exhaust gasses are vented via an economiser for heat transfer from the exhaust gases to liquid entering the ammonia stripper.

35. A method for destroying ammonia in ammonia-containing gas, which method comprises passing the ammonia-containing gas through the thermal destructor according to claim 34 to decompose the ammonia therein, and recycling exhaust gasses from the thermal destructor back into the thermal destructor for further combustion.

36. The thermal destructor according to claim 34 wherein the economiser is adapted for heat transfer to high pressure hot water for use in ammonia stripping.

37. A method for removing ammonia from ammonia-containing water which comprises the steps of: providing an ammonia stripper comprising an ammonia-containing water inlet, a steam inlet, and a forced air inlet; and an ammonia-containing gas outlet and a wastewater outlet; and contacting steam and air with the ammonia-containing water in counter-flow within the ammonia stripper to thereby release ammonia from the ammonia-containing water; wherein the method comprises a further step selected from: at least partially pre-humidifying the forced air in a pre-humidifier prior to mixing with the steam; and drawing ammonia-containing gas from the ammonia-containing gas outlet and returning it into the ammonia stripper to mix with the forced air entering the ammonia stripper.

38. The method according to claim 37 wherein a cooling tower is used as the pre-humidifier, wherein air enters the ammonia stripper through an air inlet towards or at the base of the cooling tower and is heated and saturated with water within the cooling tower prior to mixing with steam.

Description

[0043] An example of a known system for removing ammonia from ammonia-containing water will now be described with reference to the following drawings in which:

[0044] FIG. 1 shows a process flow diagram for a system and method for removing ammonia from ammonia-containing water as known in the art;

[0045] FIG. 2 shows a schematic of an ammonia stripper used in the system shown in FIG. 1;

[0046] FIG. 3 shows a schematic: of a thermal destructor used in the system shown in FIG. 1.

[0047] Referring to FIG. 1, landfill gas 10, comprised substantially of methane is fed into burners 12, 14 located within a thermal destructor 16 via a buffer vessel 18. Hot exhaust gas from the thermal destructor is circulated via a conduit 20 through an economiser 22. High pressure water is circulated through a high pressure water conduit 24 and heat is exchanged between the hot exhaust gases and the water in the economiser 22 to raise the temperature and pressure of the water to approximately 140° C. at 10 bar. The high pressure hot water passes through a boiler 26 in the form of a kettle wherein water is heated by heat exchange with the hot water to create steam. Downstream of the boiler 26 the hot water passes through a first heat exchanger 28. The heat exchanger 28 has a hot water flow path therethrough and an ammonia-containing water flow path therethrough so that passage of the two fluids causes heat transfer from the hot water to the ammonia-containing water to raise its temperature.

[0048] The ammonia-containing water exiting the first heat exchanger 28 passes through a conduit 30 into the top of an ammonia stripper 32 that is described in more detail with reference to FIG. 2. Steam from the boiler 26 enters towards the bottom of the stripper 32. Also at the lower end of the stripper 32 is an inlet for a forced air flow created by blower 34. Within the stripper 32 an ammonia-containing water flows in a generally downwards direction under the influence of gravity and the mixture of steam and forced air flow in the opposite direction. The flow of the wet air over the ammonia-containing water thermally releases ammonia therefrom. The ammonia is carried out of the stripper 32 via an outlet 36 at its upper end. By the time the ammonia-containing water has passed through the stripper it is substantially free of ammonia and exits towards a lower end thereof as wastewater. The temperature of the wastewater is above ambient temperature and accordingly carries with it energy from the process. A further heat exchanger 38 is provided in the wastewater flow path 40 in which heat is exchanged between incoming ammonia-containing water 42 and outgoing wastewater so as to recover some of the energy from the wastewater and preheat the incoming ammonia-containing water.

[0049] An anti foaming agent 44 may be added to the incoming ammonia-containing water that prevents foaming of the ammonia-containing water in the system, in particular in the thermal stripper.

[0050] Ammonia-containing gas exits the stripper 32 via outlet 36 and passes therefrom into a thermal destructor 16 described in more detail in relation to FIG. 3 below. The thermal destructor heats the ammonia-containing gas by passing it over burners that are combusting landfill gas so as to destroy the ammonia therein. As the ammonia-containing gas contains a large amount of water a significant amount of energy from the burners 12, 14 is consumed in heating the water.

[0051] A condenser 48 is provided in the ammonia-containing gas flow path 46 between the stripper 32 and the thermal destructor 16. The condenser 46 is cooled by passing a flow of incoming ammonia-containing water therethrough. As the incoming ammonia-containing water is below the condensation point of water, moisture within the ammonia-containing gas will condense in the condenser and heat will be transferred from the ammonia-containing gas to the incoming ammonia-containing water, thereby raising its temperature. The condenser 48 is placed in the ammonia-containing water flow path between the first heat exchanger 28 and the further heat exchanger 38. A further cooling circuit 50 may also pass through the condenser 48 to provide additional cooling if required. Condensate from the condenser is accumulated at a low point of the circuit and is pumped by a pump 52 to the top of the stripper 32 so that it may pass therethrough to release any ammonia that may have become dissolved therein as it condensed.

[0052] Located below the stripper is a cooling tower 54 that cools the wastewater exiting the stripper 32. The wastewater is fed into the top of the cooling tower 54 and the forced air is fed into the bottom of the cooling tower. The forced air and the wastewater pass in counter flow over one another so that heat is exchanged between the wastewater and the forced air thereby cooling the wastewater and preheating the forced air. The forced air exits the cooling tower and enters the stripper 32. The forced air may mix with the steam either before it enters the stripper 32 or within the stripper 32.

[0053] A controller (omitted for clarity) controls the flow of air and steam to obtain a temperature of approximately 80° C. for the incoming saturated heated air. The controller also controls the amount of landfill gas being burned and the fluid flow through the heat exchangers, in particular through the first heat exchanger 28 to obtain an ammonia-containing water temperature of approximately 75° C. at the point of entry of the ammonia-containing water into the stripper 32. In this way the temperature of the ammonia-containing water passing through the stripper 32 can be maintained at a temperature at which thermal release of ammonia from the ammonia-containing water is effective.

[0054] Referring now to FIG. 2, a combined ammonia stripper 32 and cooling tower 54 is shown. The stripper 32 has an inlet 56 at its upper end at which ammonia-containing water is introduced into the stripper 32. The ammonia-containing water flows through a distributor 58 so that it is distributed evenly over the upper surface of a first packed bed 60 which is supported on a first packing support 62. The packed bed 60 may comprise any suitable packing material, for example pall rings.

[0055] Below the first packing support 62 is a liquid re-distributor 63 that redistributes the ammonia-containing water evenly over the upper surface of a second packed bed 64 supported on a second packing support 66.

[0056] An inlet 68 for ambient air and steam is provided below the second packing support 66. The steam mixes with the air to saturate it and to raise its temperature. In use the steam and air pass upwardly through the packed beds 64, 60 as the ammonia-containing water passes in the opposite direction under the influence of gravity. The packed beds 64, 60 ensure a large surface area of ammonia-containing water is exposed to the saturated hot air. The ammonia is released from the ammonia-containing water in the stripper 32 and passes out of an ammonia-containing gas outlet 36 at the top of the stripper 32. At the bottom of the stripper 32 is an outlet 72 for the treated ammonia-containing water (wastewater).

[0057] Situated immediately below the stripper 32 is a cooling tower 54 in which the wastewater is cooled. A conduit 74 transfers the wastewater from the outlet 72 to a fluid distributor 76 from where it passes over a further packed bed 78 supported on a further packing support 80, under the influence of gravity.

[0058] Below the further packing support 80 is an ambient air inlet 82 through which forced air enters the cooling tower 54. The forced air and the wastewater pass in counter flow over the packed bed and the forced air exits the cooling tower at an outlet 84 at its upper end. Counter flow of the wastewater and the forced air cools the wastewater and raises the temperature of the air so that it is already preheated before it mixes with the steam.

[0059] A discharge outlet 86 is located at the bottom of the cooling tower 54 through which wastewater exits the combined cooling tower/stripper assembly.

[0060] A conduit 88 transfers the preheated air from the cooling tower 54 to the ammonia stripper 32. The conduit 88 has a steam inlet 70 through which steam is injected into the air flow passing therethrough to saturate it and further heat it.

[0061] Although shown as a combined unit, the stripper 32 and the cooling tower 54 may be provided as two separate components, which could be placed adjacent one another rather than on top of one another.

[0062] Referring now to FIG. 3, a thermal destructor 16 for use in the system is shown. The thermal destructor 16 comprises a combustion area towards its lower end and a large chimney-like structure 90 extending vertically therefrom. The chimney-like structure 90 is capped at an upper end and has a vent (not shown) through which gasses can be vented, however it will be appreciated that the chimney-like structure 90 could also open to vent at its upper end.

[0063] The chimney-like structure 90 has an exhaust gas outlet 92 and a return exhaust gas inlet 94. Hot exhaust gas taken from the outlet 92 and returned to the inlet 94 passes through a heat exchanger to drive heat fluid in the high pressure hot water circuit.

[0064] Referring now to the combustion area, this is split into a primary combustion area and a secondary combustion area. An ammonia-containing gas manifold 96 feeds ammonia-containing gas to a primary inlet 98 located at the bottom of the combustion zone. A baffle plate may be provided above the inlet 98 and have a central outlet therethrough so that ammonia-containing gas is fed substantially up the centre of the primary combustion area. A plurality of primary combustion burners 100 are fed via a manifold with landfill gas. The landfill gas is burned in the burners 100 and the ammonia-containing gas passes thereover as it rises through the primary combustion area. A plurality of louvers 102 allow air to be drawn into the thermal destructor 16 to pass with the ammonia-containing gas through the primary burners 100.

[0065] The ammonia-containing gas manifold 96 also feeds ammonia-containing gas to a second inlet 104 from where it enters a circumferential plenum chamber 108 inside the thermal destructor 16. The plenum chamber 108 has at least one outlet around its upper edge through which the ammonia-containing gas can exit the plenum chamber 108 into the second combustion area. Situated circumferentially around the interior of the thermal destructor 16 at a position above the plenum chamber 108 outlet is a second plurality of burners 106. In use ammonia-containing gas passing out of the plenum chamber 108 is directed over the second plurality of burners 106 so that it becomes heated.

[0066] It is an object of the present invention to provide improved ammonia stripper apparatus and methods, in particular ammonia stripper apparatus and methods for the thermal stripping of ammonia from ammonia-containing water.

[0067] Thus, according to the present invention in a first aspect there is provided an ammonia stripper for stripping ammonia from ammonia-containing water, the ammonia stripper comprising an ammonia-containing water inlet, a steam inlet, and a forced air inlet; and

[0068] an ammonia-containing gas outlet and a wastewater outlet;

[0069] wherein, in use, the steam and air contact the ammonia-containing water in counter-flow to thereby release ammonia from the ammonia-containing water;

[0070] and wherein the ammonia stripper further comprises a steam and air mixing duct shaped to create turbulence in the steam and air flow to promote mixing of the steam and air flow prior to contacting the ammonia-containing water.

[0071] Thorough mixing of the steam and air prior to ammonia stripping in the stripper improves the efficiency of the stripping process.

[0072] The steam and air mixing duct is shaped to create turbulence in the steam and air flow to promote mixing of the steam and air flow. The mixing duct may thus be shaped so as to divert the steam-air mixture through an extended, turning flow path. The mixing duct may thus contain curves, for example have a spiral (e.g. circular or helicoidal) shape. The mixing duct may include other features to promote turbulence, such as corners or internal baffles.

[0073] The steam and air mixing duct is positioned within the ammonia stripper so as to mix the steam and air prior to contacting the ammonia-containing water. Thus, for example, the mixing duct may be positioned between the steam and air inlets and the location within the ammonia stripper where the steam and air contact the ammonia-containing water, for example the packed bed in the ammonia stripper described hereinabove.

[0074] A schematic of an embodiment of a steam and air mixing duct for use in the ammonia stripper of the first aspect of the present invention is shown in FIG. 4. Like reference numerals as used in FIGS. 1 to 3 are used in FIG. 4 as appropriate.

[0075] Thus, referring to FIG. 4, forced air passes into the ammonia stripper 32 (shown in FIG. 2 and partially in FIG. 4) from cooling tower outlet 84 (shown in FIG. 2), via the mixing duct 200. Steam also enters the mixing duct 200 via steam inlet 70. The mixing duct 200 is shaped so as to divert the steam-air mixture through an extended, turning flow path. The mixing duct 200 shown schematically in FIG. 4 has a spiral helicoidal shape, but other arrangements may be used. The steam and air mixture then passes through the inlet 68 (shown in FIG. 2), for use in the ammonia stripper as described hereinabove.

[0076] According to a second aspect of the present invention there is provided a method for removing ammonia from ammonia-containing water which comprises the steps of:

[0077] providing an ammonia stripper comprising an ammonia-containing water inlet, a steam inlet, and a forced air inlet; and an ammonia-containing gas outlet and a wastewater outlet; and

[0078] contacting steam and air with the ammonia-containing water in counter-flow within the ammonia stripper to thereby release ammonia from the ammonia-containing water;

[0079] wherein the forced air is at least partially pre-humidified in a pre-humidifier prior to mixing with the steam.

[0080] Pre-humidifying the forced air per the method of the second aspect of the present invention reduces the steam requirement for raising the temperature of the air to operational levels for ammonia stripping.

[0081] In systems for removing ammonia from ammonia-containing water as described hereinabove, a cooling tower, such as that described with reference to FIG. 2, may be used as the pre-humidifier. In such ammonia strippers, forced air entering the ammonia stripper through the forced air inlet towards or at the base of the cooling tower may be heated and saturated with water within the cooling tower prior to mixing with steam.

[0082] According to a third aspect of the present invention there is provided an ammonia stripper for stripping ammonia from ammonia-containing water, the ammonia stripper comprising an ammonia-containing water inlet, a steam inlet, and a forced air inlet; and

[0083] an ammonia-containing gas outlet and a wastewater outlet;

[0084] wherein, in use, the steam and air contact the ammonia-containing water in counter-flow to thereby release ammonia from the ammonia-containing water;

[0085] and wherein the ammonia stripper further comprises a precipitation unit upstream of the ammonia-containing water inlet, for precipitating solids from the ammonia-containing water prior to the inlet.

[0086] Whilst the ammonia-containing water may be filtered to remove solids prior to entering the ammonia stripper, solids can nevertheless build up within the stripper, in particular carbonates (for example, calcium and/or magnesium carbonate) and cause blockages, thus reducing the efficiency of the stripper. Removal of the material causing the blockage can be expensive and time-consuming. For example, in embodiments such as those described with reference to FIG. 2, it can require removal, cleaning, and replacement of the packing from the stripper. The use of a precipitation unit for precipitating solids from the ammonia-containing water prior to the inlet can reduce or eliminate such blockages.

[0087] The ammonia-containing water is pre-treated within the precipitation unit to precipitate solids from the water prior to the ammonia stripper inlet. Precipitation of solids within the precipitation unit is encouraged by adjusting the conditions within the unit to maximise precipitate formation. For example, within the precipitation unit hot incoming wastewater containing carbonates can interact with ammonia-containing gas exiting the ammonia stripper, which contains high concentrations of ammonia and carbon dioxide. The interaction of these two streams leads to the precipitation of carbonates in the precipitation unit, this avoiding their precipitation in the ammonia stripping column. The precipitation unit may additionally or alternatively include an acid for reaction with the ammonia-containing water. For example, sulphuric acid may be used to preferentially react with and precipitate out carbonates, such as calcium and/or magnesium carbonate, within the ammonia-containing water. Sulphuric acid may be available on many sites as the effluent from a hydrogen sulphide bioscrubber.

[0088] The precipitation unit is preferably located at ground level so as to be readily accessible.

[0089] According to the third aspect of the present invention there is also provided a method for removing ammonia from ammonia-containing water which comprises the steps of:

[0090] providing an ammonia stripper comprising an ammonia-containing water inlet, a steam inlet, and a forced air inlet; and an ammonia-containing gas outlet and a wastewater outlet; and

[0091] contacting steam and air with the ammonia-containing water in counter-flow within the ammonia stripper to thereby release ammonia from the ammonia-containing water;

[0092] wherein the ammonia-containing water is pre-treated in a precipitation unit prior to entering the inlet, to precipitate solids from the ammonia-containing water.

[0093] According to a fourth aspect of the present invention there is provided a thermal destructor for destroying ammonia in ammonia-containing gas from an ammonia stripper, wherein the thermal destructor comprises an exhaust gas recycler for recycling exhaust gasses from the thermal destructor back into the thermal destructor for further combustion.

[0094] Recycling of the exhaust gasses back into the thermal destructor for further combustion permits the control of both ammonia gas release and the formation of nitrogen oxides (NOx), both to very low concentrations.

[0095] The thermal destructor may comprise features as described hereinabove, for example as described with reference to FIG. 3. Thus, the thermal destructor of the fourth aspect of the present invention may further comprise one or more of the following features:

[0096] a tower for retaining heated gasses for a dwell time;

[0097] a circumferential plenum chamber extending around the tower towards the lower end thereof and having a first ammonia-containing gas inlet and at least one plenum outlet;

[0098] a first plurality of landfill gas burners disposed around the circumference of the tower above the at least one plenum outlet;

[0099] a second plurality of landfill gas burners, substantially centrally located in the tower and disposed vertically below the at least one plenum outlet;

[0100] a second ammonia-containing gas inlet located at the bottom of the thermal destructor; and

[0101] a plurality of air inlet louvers disposed in the exterior surface of the tower vertically between the second ammonia-containing gas inlet and the second plurality of landfill gas burners.

[0102] According to the fourth aspect of the present invention there is also provided a method for destroying ammonia in ammonia-containing gas, which method comprises passing the ammonia-containing gas through a thermal destructor to decompose the ammonia therein, and recycling the exhaust gasses from the thermal destructor back into the thermal destructor for further combustion.

[0103] A schematic of an embodiment of a thermal destructor according to the fourth aspect of the present invention is shown in FIG. 5. Like reference numerals as used in the previous Figures are used in FIG. 5 as appropriate.

[0104] Thus, turning to FIG. 5, as described in more detail above with reference to FIG. 3, a thermal destructor 16 comprises a chimney like structure 90, primary 100 and secondary 106 burners fed by fuel and air as indicated, an exhaust gas outlet 92 and a return exhaust gas inlet 94. The thermal destructor 16 also comprises an exhaust gas recycler 210 for recycling exhaust gasses back into the thermal destructor for further combustion. Other features and functions of the thermal destructor 16 are as described hereinabove with reference to FIG. 3.

[0105] According to a fifth aspect of the present invention there is provided a thermal destructor for destroying ammonia in ammonia-containing gas from an ammonia stripper, wherein the thermal destructor comprises a sealed upper end and exhaust gasses are vented via an economiser for heat transfer from the exhaust gases to liquid entering the ammonia stripper.

[0106] In contrast to the thermal destructor described hereinabove with reference to FIG. 3, from which exhaust gasses are either vented via a vent at the upper end or is open at the upper end, the thermal destructor of the fifth aspect of the present invention is sealed at the upper end, for example by a lid, to increase energy recovery and control of energy within the thermal destructor. In the thermal destructor of the fifth aspect of the present invention, the exhaust gasses are vented via an economiser, for example as described hereinabove with reference to FIG. 1, for heat transfer to liquid entering the ammonia stripper, for example high pressure hot water for use in ammonia stripping. The economiser may form part of the thermal destructor itself, or may form part of an ammonia stripper to which the thermal destructor is operationally connected or which it forms a part.

[0107] The thermal destructor of the fifth aspect of the present invention may comprise one or more of the features described above with reference to the fourth aspect of the present invention.

[0108] A schematic of an embodiment of a thermal destructor according to the fifth aspect of the present invention is shown in FIG. 6. Like reference numerals as used in the previous Figures are used in FIG. 6 as appropriate.

[0109] Thus, turning to FIG. 6, as described in more detail above with reference to FIGS. 3 and 5, a thermal destructor 16 comprises a chimney like structure 90, primary 100 and secondary 106 burners fed by fuel and air as indicated, and an exhaust gas recycler 210 for recycling exhaust gasses back into the thermal destructor for further combustion. In the embodiment shown in FIG. 6, the thermal destructor 16 also comprises a sealed upper end 220 and exhaust gasses are vented via an economiser 230 for heat transfer from the exhaust gases to liquid entering the ammonia stripper, for example high pressure hot water for use in ammonia stripping, as indicated. Other features and functions of the thermal destructor 16 are as described hereinabove with reference to FIGS. 3 and 5.

[0110] According to a sixth aspect of the present invention there is provided an ammonia stripper for stripping ammonia from ammonia-containing water, the ammonia stripper comprising an ammonia-containing water inlet, a steam inlet, and a forced air inlet; and

[0111] an ammonia-containing gas outlet and a wastewater outlet;

[0112] wherein, in use, the steam and air contact the ammonia-containing water in counter-flow to thereby release ammonia from the ammonia-containing water;

[0113] and wherein the ammonia stripper further comprises a steam flash vessel downstream of the wastewater outlet, for generating steam from the wastewater produced by the ammonia stripper for recycling into the ammonia stripper.

[0114] The steam flash vessel used in the ammonia stripper of the sixth aspect of the present invention thus provides steam for the ammonia stripping process, i.e. at least some of the water required for the stripping process is produced by the process itself.

[0115] The steam flash vessel may comprise a heater for heating the wastewater under pressure prior to it generating steam for recycling into the ammonia stripping process. The amount of wastewater which is converted to steam by the steam flash vessel may be, for example, from 1 to 20 wt %, for example approximately 10 wt %.

[0116] According to the sixth aspect of the present invention there is also provided a method for removing ammonia from ammonia-containing water which comprises the steps of:

[0117] providing an ammonia stripper comprising an ammonia-containing water inlet, a steam inlet, and a forced air inlet; and an ammonia-containing gas outlet and a wastewater outlet; and

[0118] contacting steam and air with the ammonia-containing water in counter-flow within the ammonia stripper to thereby release ammonia from the ammonia-containing water;

[0119] wherein the wastewater passes from the wastewater outlet to a steam flash vessel downstream of the wastewater outlet, where it is at least partially converted to steam and recycled into the ammonia stripper.

[0120] According to a seventh aspect of the present invention there is provided a method for removing ammonia from ammonia-containing water which comprises the steps of:

[0121] providing an ammonia stripper comprising an ammonia-containing water inlet, a steam inlet, and a forced air inlet; and an ammonia-containing gas outlet and a wastewater outlet; and

[0122] contacting steam and air with the ammonia-containing water in counter-flow within the ammonia stripper to thereby release ammonia from the ammonia-containing water;

[0123] wherein ammonia-containing gas is drawn from the ammonia-containing gas outlet and returned into the ammonia stripper to mix with the forced air entering the ammonia stripper.

[0124] It has been unexpectedly found that by “seeding” the incoming forced air with ammonia-containing gas exiting the ammonia stripper, the performance of the ammonia stripper is enhanced. The combination of carbon dioxide gas and ammonia in air from the ammonia stripper results in adjustments within the column, for example alkalinity, which are favourable to improved removal of ammonia from the wastewater.

[0125] It is to be noted that each of the different aspects of the present invention may be used in combination with one or more of the other aspects of the invention. Thus, for example, the ammonia stripper of the first aspect may be used with one or more of the method of the second aspect, the ammonia stripper and method of the third aspect, the thermal destructor and method of the fourth aspect, the thermal destructor of the fifth aspect, the ammonia stripper and method of the sixth aspect, and the method of the seventh aspect, and so forth for the other aspects of the invention. It is also to be noted that each of the aspects of the present invention may be used in combination with any of the features of the system, ammonia stripper, cooling tower and thermal destructor as known the art and described herein.