System and method for removing ammonia from an ammonia containing effluent

Abstract

A method of forming an ammonia product and / or ammonium product includes - Feeding a feed stream containing ammonia to a stripper (2) at temperatures below the boiling point of water, - Introducing a stripper gas into the stripper at a stripper gas inlet (16), contacting the feed stream with the stripper gas, and removing the stripper gas at a stripper outlet (17), - Forming a condensate from the stripper gas in a condenser (20), - Feeding the condensate to a process unit (25), - Forming an ammonia and / or ammonium product in the process unit (25), and - Feeding an outlet (34,48) of the process unit (25) to the stripper gas inlet (16) of the stripper (2). Also a system (1) for removing ammonia from an ammonia containing effluent is described.

Description

[0001] System and method for removing ammonia from an ammonia containing effluent

[0002] Field of the invention

[0003] The invention relates to a system for removing ammonia from an ammonia containing effluent comprising a stripper having a reactor volume, with at a first side a feed inlet connected to an inlet duct for receiving a feed stream containing ammonia, and a gas outlet, and with at a second side a stripping gas inlet for receiving a gas stream and feeding the gas stream through the reactor volume in counter current to the feed stream, and an effluent outlet that is connected to a processing unit.

[0004] The invention also relates to method for removing ammonia from an ammonia containing effluent and for producing ammonia products .

[0005] Background art

[0006] Ammonia is common in nature and is widely used industrially, such as for cleaning, as a refrigerant in cooling systems or in agricultural applications such as fertilizers to provide the nitrogen source required to increase crop yields. Large concentrations of ammonia may be damaging for human health and ecosystems.

[0007] One of the primary naturally occurring sources of ammonia is the decay of organic matter. Ammonia is also generated by human and agricultural waste. Various types of effluent contain high concentrations of ammonia and toxic compounds, such as those that are derived from secondary effluent of municipal wastewater treatment plant, animal manure, and landfill leachate. Consequently, ammonia is a commonly encountered water pollutant, which needs to be removed in order to prevent unsafe concentrations in both water and land and to provide drinking water that is safe for consumption.

[0008] It is known to remove ammonia from effluent by an ammonia stripping method, which is a fairly stable process allowing the ammonia to be recovered from the stripping process for reuse. Two principal methods of stripping ammonia from liquid are known, wherein the ammonia is removed as a gas. The first method is a chemical process that involves increasing the pH of the liquid, and the second is a thermal method that uses heat only. Both methods break the ionic bond that holds ammonia as NH and convert the ammonia to NH3, the free, gaseous, form. Increasing the pH usually involves the adding of a caustic agent such as lime or caustic soda.

[0009] A system for carrying out a thermal stripping method through steam stripping and subsequent rectification in a low-pressure stripping / rectification tower is known from WO 96 / 11732 A1. The tower overhead is condensed with a portion of the condensed overhead being returned as a reflux. The known system for removing ammonia from wastewater through steam stripping has as a downside that it uses a large amount of energy for heating, making it rather expensive.

[0010] It is an aim of the invention to provide an improved system and method for removing ammonia from ammonia-containing effluent, which is effective, utilizes reduced amounts of energy and can be carried out in an environmentally friendly and economic manner. It is a further object of the invention to provide a system and method for effectively and efficiently removing ammonia from effluent and providing ammonia products that can be utilized in processes such as the production of fertilizers, NOx removal processes or biological treatment processes.

[0011] Summary

[0012] According to the invention, the system for removing ammonia from an ammonia containing effluent comprises:

[0013] - a stripper having a reactor volume, with at a first side a feed inlet connected to an inlet duct, for receiving a feed stream containing ammonia, and a gas outlet, and with at a second side a stripping gas inlet for receiving a gas stream and feeding the gas stream through the reactor volume in counter current to the feed stream, and an effluent outlet,

[0014] - an inlet heater at the inlet duct, that is adapted for heating the feed stream in the inlet duct to a temperature that is below the boiling point of water,

[0015] -a condenser having an inlet connected to the gas outlet for forming a condensate stream and having a condensate outlet and a process gas outlet,

[0016] -a process unit having a condensate inlet that is connected to the condensate outlet of the condenser, and having an outlet port for an ammonia and / or ammonium product and a return outlet duct connected to the gas inlet of the stripper and adapted for supplying return gas at a temperature below 80°C, preferably below 60°C.

[0017] By using an air stripper that operates at temperatures below the boiling point of water, and by recycling the cleaned process gas from the process unit back to the stripper, an energy efficient and effective system for removal of ammonia from effluent streams is provided, yielding an ammonium and or ammonia product.

[0018] The system according to the invention results in a reduced use of sulfuric acid and hence reduced costs. Furthermore, difficulties that arise with seasonal sales of ammonium sulphate liquid (ASL) that is produced in known systems using sulfuric acid, can be avoided.

[0019] The concentrated ammonia that is produced in the system according to the invention can be applied for many purposes such as the production of an ammonium bicarbonate (ABC)- solution and other Nitrogen (N) containing fertilizer products.

[0020] The stripper in the system according to the invention preferably comprises a vertical air stripping column. In one embodiment the process unit comprises a CO2 (carbon dioxide) scrubber connected with its condensate inlet to the condenser, with the return outlet duct connected to the stripper gas inlet and comprising a gas inlet that is connected to a process gas outlet of the condenser, a CO2 inlet for CO2 and a product outlet for supplying an ammonium bicarbonate solution.

[0021] By production of ammonium bicarbonate according to the invention, CO2can be captured as a fertilizer so that it will be converted by the crops to biomass and oxygen. Concentrated ABC-water (e.g., 4-15wt% N) may be used in fertilizer products or as an intermediate for fertilizer products, such as KNOs / Nitric acid. The ABC produced according to the invention can be used as a substitute for urea and form an N-supplement in fertilizer products, it can be applied as a C / N feed for biological treatment plants or be applied in NOx removal (DeNOx).

[0022] In an embodiment of a system according to the invention, the condenser is adapted to set a temperature in the CO2 scrubber below a predetermined threshold temperature.

[0023] When producing an ABC-solution by contacting the ammonia-containing gas and condensate with CO2- water and / or CO2 gas it was found that the temperature of the washing step should be below 40°C, preferably below 35°C, most preferably below 33°C for a stable reaction of NH3and CO2. Above these temperatures, the ABC- solution was found to be unstable.

[0024] It will be understood that when stripping a digestate, CO2 is already present in the resulting stripping gas loop. CC>2-gas (e.g. obtained from biogas upgrading) can be added to the stripping gas, if the treated effluent does not contain enough CO2.

[0025] The process unit may comprise a water scrubber device having a gas inlet connected to the process gas outlet of the condenser, a water inlet, a gas outlet and a condensate outlet, the gas outlet being connected to the return duct, and a rectifier unit having a condensate inlet, a product outlet and a condensate outlet, the condensate inlet being connected to the condensate outlet of the water scrubber device and to the condensate outlet of the condenser.

[0026] The ammonia condensate production is improved by lowering the condenser temperature and adding cold scrubbing of the NH3 from the gas phase with (chilled) water. This could be carried out by a scrubber, e.g. either a full-size scrubber or a smaller diameter jet scrubber. The small ammonia condensate stream is rectified in order to produce concentrated ammonia water that can be applied for many purposes such as the production of an ABC- solution and other N-containing fertilizer products.

[0027] In an embodiment of a system according to the invention the system comprises a rectifier heat exchanger configured for thermally coupling the condensate inlet and the condensate outlet of the rectifier unit. According to an embodiment, a condenser heat exchanger may be provided configured in heat exchanging contact with the return duct and in heat exchanging contact with the condenser.

[0028] Recovery of thermal energy released in the condenser to the gas recycle entering the stripper (gas intercooler) including humidification with water vapor will reduce evaporation in the bottom part of the stripper column and leads to a better temperature profile in the stripper column improving the stripping performance and heat requirement.

[0029] An embodiment of a system according to the invention comprises an upstream heat exchanger thermally coupling the product inlet and the product outlet of the stripper.

[0030] Heat recovery of the outlet and inlet feed / digestate streams will reduce the heat demand of the system.

[0031] A method of forming an ammonia product and / or ammonium product according to the invention comprises:

[0032] Feeding a feed stream containing ammonia to a stripper at temperatures below the boiling point of water,

[0033] Introducing a stripper gas into the stripper at a stripper gas inlet, contacting the feed stream with the stripper gas, and removing the stripper gas at a stripper outlet, Forming a condensate from the stripper gas in a condenser, Feeding the condensate to a process unit,

[0034] Forming an ammonia and / or ammonium product in the process unit, and Feeding an outlet of the process unit to the stripper gas inlet of the stripper.

[0035] Advantageous embodiments are further defined by the dependent claims.

[0036] Brief description of the drawings

[0037] Some embodiments of a system according to the invention for the removal of ammonia from an ammonia containing effluent, will by way of non-limiting example, be described in detail with reference to the accompanying drawings. In the drawings:

[0038] Fig. 1 shows a schematic lay-out of a system according to the invention,

[0039] Fig. 2 shows an embodiment of the system of figure 1 , with a process unit comprising a CO2- water scrubber, and

[0040] Fig. 3 shows an embodiment of the system of figure 1 , with a process unit comprising a rectifier column.

[0041] Figures 4 - 8 show respective further embodiments of the system of figure 1.

[0042] Similar or corresponding elements, features or structures are indicated by the same reference signs. The drawings are not intended to be on scale. Detailed description

[0043] Figure 1 shows a schematic representation of a system 1 according to the invention, comprising a stripper 2, a condenser / scrubber unit 20 and an upgrading unit 25. The stripper 2 receives at its inlet 3 a feed stream containing ammonia. The feed stream may be a digestate and can be derived from chemical processes, agricultural activities or municipal wastewater treatment plants. In the stripper 2, which may be an air stripper, stripper gas is formed at a relatively low temperature, containing NH3, CC^and H2O at a temperature of about 80°C. The stripper gas is transported to the condenser / scrubber unit 20 in which ammonium bicarbonate (ABC) and ammonium water are produced with a nitrogen content of between 0,1 and 2,5% by weight and a temperature at the outlet 26 that is below 33°C or even below 25°C.

[0044] In the upgrading unit 25, a number of different products can be formed, such as pure ammonia water with 20-25wt% N, a solution of ABC / ammonia water with 4-15wt% N or crystalline ABC.

[0045] No (sulfuric) acid is needed in the system 1. The ABC / ammonia water solution may be used in the production of an organic fertilizer. The upgrading unit 25 may receive a liquid product at its input and can in that case comprise a rectifier or a reverse osmosis unit. In case the feed of the upgrading unit comprises a crystalline product, the unit 25 can involve a reverse osmosis and crystallization process.

[0046] Figure 2 shows the system 1 with a stripping column 2 that has at a top side an inlet 3 for receiving the feed stream containing ammonia. The feed stream is supplied to the stripping column 2 by a pump 5 through an inlet duct 4 with a feed of for instance 3 m3 / h containing 4.3 g / l N at a temperature of 37°C, and passes a heater 6 that is controlled by a controller 7 to raise the inlet temperature of the feed stream at the inlet 3 to about 80°C. In the reactor volume 8 of the column 2, the feed stream is transported to an outlet 9 and is contacted in counter current direction by a stripping gas, such as air. The stripped feed stream is removed from the column 2 via the outlet 9 at a temperature of for instance 53°C via a discharge pump 10 at a rate of for instance 2.6 m3 / h, containing 2.2 g / l of N. A recirculation pump 12 feeds part of the outlet stream back to the inlet 3 through a recirculation duct 11 at a rate of for instance 6m3 / h.

[0047] Stripping gas is supplied by a pump 15 to a gas intake16 near the bottom of the column 2. The temperature of the stripping gas at the intake16 may be about 53°C. The stripping gas flows upward, in countercurrent to the feed stream and exits the column 2 at a gas outlet 17. The ammonia containing process gas that is formed by the stripping gas and gaseous components that are stripped from the feed stream, pass through an outlet duct 18 to a condenser 20 at temperatures between 65°C and 70°C. The condenser 20 comprises a cooling member 21 to which a cooling medium such as water or glycol is supplied, cooling down the process gas to a temperature of about 30°C. The condensate that is formed in the condenser 20 is supplied to the process unit 25 through a condensate outlet duct 24. The cooled process gas is supplied to the process unit 25 via a pump 22 and duct 23.

[0048] In the process unit 25, an ammonia and / or ammonium product is formed, for instance by scrubbing the condensate and the ammonia containing process gas with CO2 and water, forming an ammonium bi-carbonate solution, or by rectification of the condensate in a rectifier. The ammonia and / or ammonium product is removed at a product outlet 26 of the process unit 25.

[0049] Through a return duct 27, cleaned process gas having a relatively low ammonia concentration, is recycled to the intake 16 of the stripping column 2. A part of the process gas flowing through the outlet duct 18 of the stripping column 2, may be fed to the intake 16 via a duct 28.

[0050] Figure 3 shows an embodiment in which the process unit 25 comprises a CC>2-water scrubber 30, receiving CO2 at a scrubbing gas inlet 31, cooled process gas at inlet 32 and condensate at inlet 33. The condensate that is formed in the condenser 20 and that is supplied through the condensate outlet duct 24 consists of a solution of ammonium bicarbonate and NH3. At the product outlet 26 of the scrubber 30, a watery ammonium bicarbonate solution is produced. Through the outlet 34 and the return duct 27, cleaned process gas is recycled from the CO2 treatment process in the scrubber 30.

[0051] The condenser 20 can for example comprise a water / glycol cooled gas cooler, or a dry cooler.

[0052] It was experimentally found that condensate water that was produced at the condensate outlet duct 24 consisted for a major part of ABC and for the remaining part of unreacted and dissolved NH4. Regarding the produced ABC-solution obtained by contacting the ammonia containing gas and condensate with CO2- water, it was found that the temperature of the washing step in the scrubber 30 must be kept below about 33°C for a stable reaction of NH3and CO2. Above 33°C the ABC- solution was found to be unstable.

[0053] Figure 4 shows an embodiment wherein the process unit 25 comprises a cold-waterjet scrubber 40 and a rectifier column 41. Water is fed to the scrubber 40 via a water supply duct 46 and via a return duct 47 that carries process water from a condensate outlet 48 of the rectifier column 41. Before entering the scrubber 40, the process water in the duct 47 is cooled in a cooling heat exchanger 49.

[0054] By lowering the operation temperature of the condenser 20 and by adding cold scrubbing of the NH3from the gas phase with (chilled) water in scrubber 40, the ammonia condensate production is improved. The scrubber 40 could be either a full scrubber or a smaller diameter jet scrubber. Process gas from the scrubber 40 is transported from the gas outlet 42’ to the return duct 27. Condensate is transported by a pump 44 from the outlet 43 of the jet scrubber 40, to the inlet 45 of the rectifier column 41. A heat exchanger 50 transfers heat from the process water at the outlet 48 of the column 41 to the condensate at the inlet 45.

[0055] In the rectifier column 41, a heater 51 heats the condensate such that the small ammonia concentrate stream (ABC+ ammonia solution (upto about 2 wt% N)) at the inlet 45 is rectified and concentrated ammonia water is produced at the outlet 26. Once concentrated ammonia has been produced, it can be applied for many purposes such as the production of an ABC- solution and other N-containing fertilizer products.

[0056] Heat exchanger 52 recovers heat from the release of thermal energy in the condenser 20, which heat is transferred to the gas recycle stream entering the stripper 2 (gas intercooler), including humidification with water vapor. The latter will reduce evaporation in the bottom part of the stripping tower 2 and leads to a better temperature profile in the stripper column improving the stripping performance and its heat requirement.

[0057] Via heat exchangers 53, 54, heat is recovered at the digestate outlet 9 and is transferred to the inlet digestate stream via heat exchanger 54. This reduces the heat demand of the system.

[0058] Figure 5 shows an embodiment with a scrubber 40, in which through a duct 60, a caustic solution of NaOH is supplied upstream of the inlet 45 of the rectifier column 41. This results in the production of a concentrated ammonia solution (e.g. 20-25wt% N) at the product outlet 26.

[0059] Figure 6 shows an embodiment in which no additional chemicals are added. At the inlet of the rectifier column 41 an ABC / ammonia solution containing 0,1-2,2wt% N is supplied.

[0060] Concentrated ammonia water and ABC solution are formed at the outlet 26, containing 4- 15wt% N.

[0061] Figure 7 shows an embodiment in which via an outlet duct 61 of the scrubber 40, ABC an ammonia solution (1-2wt% N) is supplied to a reverse osmosis unit 62 that provides at its outlet 26 an ABC solution that may be processed into a crystalline ABC product.

[0062] Figure 8 shows an embodiment in which the scrubber 41 is connected to an electrodialysis unit 63, while utilizing higher temperatures and lower pH values. The heat exchanger units 20, 52 may be omitted.

[0063] With the system of figures 2-8, stripping efficiencies can be achieved in the range of 50% to 99,9%.

[0064] In the embodiments as described above the rectifier or rectifier unit can be configured for atmospheric operation. Alternatively, the rectifier or rectifier unit can be configured for operation under reduced pressure or vacuum. Glossary

[0065] 1 system

[0066] 2 stripping column / stripper

[0067] 3 inlet for feed (digestate)

[0068] 4 inlet duct

[0069] 5 pump

[0070] 6 heater

[0071] 7 controller

[0072] 8 reactor volume

[0073] 9 (digestate) outlet

[0074] 10 discharge pump

[0075] 11 recirculation duct

[0076] 12 recirculation pump

[0077] 15 pump

[0078] 16 stripping gas intake

[0079] 17 process gas outlet 17

[0080] 18 outlet duct

[0081] 19 condenser inlet

[0082] 20 condenser

[0083] 21 cooling member

[0084] 22 pump

[0085] 23 process gas outlet / duct

[0086] 24 condensate outlet / duct

[0087] 25 process unit

[0088] 26 product outlet

[0089] 27 return outlet duct

[0090] 28 duct

[0091] 29 condensate inlet

[0092] 30 CC>2 / water scrubber

[0093] 31 scrubbing gas inlet

[0094] 32 inlet

[0095] 33 inlet

[0096] 34 outlet

[0097] 40 cold water jet scrubber

[0098] 41 rectifier column

[0099] 42 gas inlet of jet scrubber 42’ gas outlet of jet scrubber

[0100] 43 condensate outlet of scrubber

[0101] 44 pump

[0102] 45 inlet of rectifier column 46 water supply duct

[0103] 47 return duct

[0104] 48 condensate outlet

[0105] 49 cooling heat exchanger

[0106] 50 heat exchanger 52 heat exchanger

[0107] 53 heat exchanger

[0108] 54 heat exchanger

[0109] 60 duct

[0110] 61 outlet duct 62 reverse osmosis unit

[0111] 63 electrodialysis unit

Claims

Claims1. System (1) for removing ammonia from an ammonia containing effluent comprising:- a stripper (2) having a reactor volume (8), with at a first side a feed inlet (3) connected to an inlet duct (4), for receiving a feed stream containing ammonia, and a gas outlet (17), and with at a second side a stripping gas inlet (16) for receiving a gas stream and feeding the gas stream through the reactor volume (8) in counter current to the feed stream, and an effluent outlet (9) ,- an inlet heater (16) at the inlet duct (4), that is adapted for heating the feed stream in the inlet duct (4) to a temperature that is below the boiling point of water,-a condenser (20) having an inlet (19) connected to the gas outlet (17) for forming a condensate stream and having a condensate outlet (24) and a process gas (23) outlet, -a process unit (25) having a condensate inlet (29,33,45) that is connected to the condensate outlet (24) of the condenser (20), and having an outlet port (26) for an ammonia and / or ammonium product and a return outlet duct (27) connected to the gas inlet (16) of the stripper (2) and adapted for supplying return gas at a temperature below 80°C, preferably below 60°C.

2. System (1) according to claim 1, the stripper (2) comprising a vertical air stripping column.

3. System (1) according to claim 1 or 2, the process unit (25) comprising a CO2 scrubber connected with its condensate inlet (33) to the condenser (20), with the return outlet duct (27) connected to the stripper gas inlet (16) and comprising a gas inlet (32) that is connected to a process gas outlet (23) of the condenser (20), a CO2 inlet (31) for CO2 and a product outlet (34) for supplying an ammonium bicarbonate solution.

4. System (1) according to claim 3, the condenser (20) being adapted to set a temperature in the CO2 scrubber below a predetermined threshold temperature.

5. System (1) according to claim 1 or 2, the process unit (25) comprising:- a water scrubber device (40) having a gas inlet (42) connected to the process gas outlet (23) of the condenser (20), a water inlet (46), a gas outlet (42’) and a condensate outlet (43), the gas outlet (42’) being connected to the return duct (27), and- a rectifier unit (41) having a condensate inlet (45), a product outlet (26) and a condensate outlet (48), the condensate inlet (45) being connected to the condensate outlet (43) of the water scrubber device (40) and to the condensate outlet (24) of thecondenser (20).

6. System (1) according to claim 5, comprising a rectifier heat exchanger (50) configured for thermally coupling the condensate inlet (45) and the condensate outlet (48) of the rectifier unit (41).

7. System (1) according to claims 5 or 6, comprising a condenser heat exchanger (52) configured in heat exchanging contact with the return duct (27) and in heat exchanging contact with the condenser (20).

8. System (1) according to claims 5,6 or 7, comprising an upstream heat exchanger (53,54) thermally coupling the product inlet (4) and the product outlet (9) of the stripper (2).

9. System (1) according to any one of the preceding claims 5 - 8, wherein the rectifier unit (41) is configured for operation under atmospheric pressure.

10. System (1) according to any one of the preceding claims 5 - 8, wherein the rectifier unit (41) is configured for operation under vacuum or below atmospheric pressure11. Method of forming an ammonia product and / or ammonium product comprising: Feeding a feed stream containing ammonia to a stripper (2) at temperatures below the boiling point of water,Introducing a stripper gas into the stripper at a stripper gas inlet (16), contacting the feed stream with the stripper gas, and removing the stripper gas at a stripper outlet (17),Forming a condensate from the stripper gas in a condenser (20),Feeding the condensate to a process unit (25),Forming an ammonia and / or ammonium product in the process unit (25), and Feeding an outlet (34,48) of the process unit (25) to the stripper gas inlet (16) of the stripper (2).

12. Method according to claim 11 , comprising contacting in a scrubber (30), the stripper gas condensate and the stripper gas with CO2 and forming an ammonium bicarbonate solution, and feeding gas from the outlet (34) of the scrubber (30) to the stripper gas inlet (16) of the stripper (2).

13. Method according to claim 11 , comprising:feeding the stripper gas from the stripper outlet (17) to a cold-water scrubber (40), feeding condensate from the cold-water scrubber (40) to the process unit and feeding stripper gas from the water scrubber to the stripper gas inlet (16) of the stripper (2), the process unit (25) comprising a rectifier unit (41), and -feeding condensate from a condensate outlet (48) of the rectifier unit (41) to the stripper gas inlet (16) of the stripper (2).

14. Method according to claim 13, comprising heat transfer from the condenser (20) to the gas return stream flowing to the stripper gas inlet (16).

15. Method according to claim 13 or 14, comprising heat transfer from a processed feed stream leaving the stripper (2) to an unprocessed feed stream entering the stripper (2).

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