EXHAUST GAS TREATMENT SYSTEM

Abstract

There is provided an exhaust system for the treatment of a humid exhaust gas comprising ammonia in an amount of up to 250 ppm, the system comprising: a dehumidifier system comprising a humid air inlet for providing a flow of humid exhaust gas; an exhaust gas inlet for providing a flow of dehumidified exhaust gas; an ammonia storage material arranged to receive the dehumidified exhaust gas from the exhaust gas inlet; an ammonia oxidation catalyst arranged downstream of a selected portion of the ammonia storage material; and a heating device for heating gas before it passes through the selected portion of the ammonia storage material to release ammonia stored therein for treatment on the ammonia oxidation catalyst; wherein the system is configured so that the selected portion of the ammonia storage material changes over time; and wherein the flow of dehumidified exhaust gas provided by the exhaust gas inlet is received from the dehumidifier system.

Claims

1. An exhaust system for the treatment of a humid exhaust gas comprising ammonia in an amount of up to 250 ppm, the system comprising: a dehumidifier system comprising a humid air inlet for providing a flow of humid exhaust gas; an exhaust gas inlet for providing a flow of dehumidified exhaust gas; an ammonia storage material arranged to receive the dehumidified exhaust gas from the exhaust gas inlet; an ammonia oxidation catalyst arranged downstream of a selected portion of the ammonia storage material; and a heating device for heating gas before it passes through the selected portion of the ammonia storage material to release ammonia stored therein for treatment on the ammonia oxidation catalyst; wherein the system is configured so that the selected portion of the ammonia storage material changes over time; and wherein the flow of dehumidified exhaust gas provided by the exhaust gas inlet is received from the dehumidifier system.

2. The exhaust system according to claim 1, wherein the dehumidifier system comprises: a humid air inlet for providing a flow of humid exhaust gas; a further gas inlet for providing a further flow of heated gas; a plurality of water-sorbent beds, comprising a water storage material, for releasably storing water; a further gas outlet in fluid communication with the exhaust gas inlet; an external gas outlet; and a dehumidifier valve system configured to establish independently for each water-sorbent bed fluid communication in a first or second configuration, wherein: i) in the first configuration the flow of the humid exhaust gas from the humid air inlet contacts a water-sorbent bed for storing water and then passes to the further gas outlet; and ii) in the second configuration the further flow of heated gas from the further gas inlet contacts a water-sorbent bed for releasing the water to form a heated humidified gas which then passes to the external gas outlet; wherein the dehumidifier valve system is configured to ensure that at least one water-sorbent bed is in the first configuration and, at least one other water-sorbent bed is in the second configuration.

3. The exhaust system according to claim 1, wherein the dehumidifier system comprises: a humid air inlet for providing a flow of humid exhaust gas; a water storage material arranged to receive the humid exhaust gas from the humid air inlet; a further gas outlet for receiving dehumidified exhaust gas passing through the water storage material, which is in fluid communication with the exhaust gas inlet, an external gas outlet, arranged downstream of a selected portion of the water storage material; and a further gas inlet for providing a further flow of heated gas arranged to pass through the selected portion of the water storage material to release water stored therein and to form a heated humidified gas which passes through the external gas outlet; wherein the dehumidifier system is configured so that the selected portion of the water storage material changes over time.

4. The exhaust system according to claim 1, wherein the humid exhaust gas comprises from 1 to 50 ppm ammonia. ammonia.

5. The exhaust system according to claim 1, wherein the heating device is configured to heat the gas before it passes through the selected portion of the ammonia storage material to a temperature of from 50 to 300° C.

6. The exhaust system according to claim 1, wherein the system further comprises one or more material filters between the exhaust gas inlet and the ammonia storage material.

7. The exhaust system according to claim 1, wherein the system comprises an H.sub.2S sorbent material and/or an As sorbent material upstream of the ammonia storage material.

8. The exhaust system according to claim 1, the system comprising means for cooling a previously-heated portion of the ammonia storage material with a supply of ambient air.

9. The exhaust system according to claim 1, the system comprising means for ducting gas from a previously-heated portion of the ammonia storage material to pre-heat a soon-to-be heated portion of the ammonia storage material.

10. The exhaust system according to claim 1, wherein the ammonia storage material is provided within a sorbent bed which is arranged to rotate so that, in use, portions of the ammonia storage material are each contacted with a heated gas in turn.

11. (canceled)

12. The exhaust system according to claim 10, wherein the sorbent bed is configured to rotate stepwise.

13. (canceled)

14. (canceled)

15. The exhaust system according to claim 10, wherein the sorbent bed comprises a plurality of inserts comprising the ammonia storage material.

16. The exhaust system according to claim 1, wherein the heating device is located between the exhaust gas inlet and the ammonia storage material.

17. The exhaust system according to claim 1, wherein the heating device is located between the ammonia storage material and the ammonia oxidation catalyst and wherein the system further comprises a duct for recycling at least a portion of the gas from the ammonia oxidation catalyst upstream of the selected portion of the ammonia storage material.

18. The exhaust system according to claim 1, wherein the heating device is a heat exchanger arranged to recover heat from gas downstream of the ammonia oxidation catalyst.

19. The exhaust system according to claim 18, further comprising a second heating device located between the ammonia storage material and the ammonia oxidation catalyst, wherein the second heating device is configured to heat gas passing to the ammonia oxidation catalyst to 200 to 300° C.

20. The exhaust system according to claim 1, wherein the heating device is supplied with heat obtained from the catalytic treatment of the ammonia, whereby the system can be maintained in an autothermal condition.

21. (canceled)

22. The exhaust system according to claim 2, wherein the dehumidifier system further comprises means for recovering heat from the heated humidified gas.

23. (canceled)

24. A livestock house comprising the exhaust-gas system according to claim 1.

25. A method of treating a humid ammonia-containing exhaust gas, the method comprising passing the humid ammonia-containing exhaust gas through the exhaust-gas system according to claim 1.

Description

[0145] The invention will now be described in relation to the following non-limiting figures, in which:

[0146] FIG. 1 shows a schematic of an exhaust gas system as described herein.

[0147] FIG. 2 shows a schematic of a sorbent bed wheel as described herein.

[0148] FIG. 1 shows a poultry house 1 provided with an exhaust gas system as described herein. The poultry house 1 provides a source of humid exhaust gas 5 which will typically contain about 20 ppm of ammonia. The humid exhaust gas 5 is passed to a material filter 10 to ensure that any undesirable physical contaminants, such as poultry feathers are removed. The exhaust gas 5 then passes to an H.sub.2S sorbent 15 to ensure that H.sub.2S is removed and does not poison the downstream components of the system.

[0149] The humid exhaust gas 5 then passes to a dehumidifier system 16 which comprises a water storage material. The majority of the humid exhaust gas 5 passes directly through the dehumidifier system 16 to provide a flow of dehumidifier exhaust gas 17 which is then directed to a sorbent wheel 20 which comprises ammonia storage material. The majority of the dehumidified exhaust gas 17 passes directly out of the sorbent wheel 20 to the atmosphere 25 as an ammonia-depleted exhaust gas 30, with the ammonia having been stored on the ammonia storage material. The ammonia-depleted exhaust gas 30 typically comprises less than 1 ppm ammonia and preferably essentially no ammonia. A minority of the dehumidified exhaust gas 17 passes through a heater 35, such as a propane burner or a resistive heater coil, to provide a heated dehumidified exhaust gas 40 (around 150° C.).

[0150] The heated dehumidified exhaust gas 40 passes through a selected portion 45 of the sorbent wheel 20. Because of the heated dehumidified exhaust gas 40, ammonia absorbed on the sorbent wheel 20 is desorbed. This forms an ammonia-rich gas 50 containing at least 250 ppm ammonia and preferably at least 1000 ppm ammonia. The ammonia-rich gas 50 leaving the selected portion 45 of the sorbent wheel 20 is directed to a further heater 55 and then to an oxidation catalyst 60 for decomposing the ammonia to nitrogen and water before this is released to the atmosphere 25 with levels of ammonia of less than 1 ppm and preferably essentially no ammonia.

[0151] The gases released to the atmosphere 25 may instead be returned to the poultry house 1. This allows the heat to be retained in the atmosphere when the ambient temperature in the poultry house 1 is below the outside ambient temperature, reducing heating costs.

[0152] Instead or in addition to the heater 35, a heat exchanger 65 can be used to provide the heated exhaust gas 40. Instead or in addition to using a minority of the dehumidified exhaust gas 17 to desorb the ammonia, a source of fresh gas 70, such as fresh air, can be used.

[0153] A further heater 36 provides a flow of heated fresh air 37 to the dehumidifier system 16 for releasing water stored on a portion of the water storage material thereby regenerating the water storage material. The heated fresh air 37 produces a heated humidified exhaust gas which is then passed to the atmosphere 25.

[0154] Gas recycle routes and some alternatives or optional features/ are shown with dashed lines.

[0155] FIG. 2 shows a sorbent wheel 20 and in particular the selected portion 45 which receives the minority of heated exhaust gas 40. As further shown, due to the direction of rotation (R) there will also be a cooling portion 46 and there may be a pre-heating portion 47.

[0156] In order to minimise ammonia slip, the cooling portion 46 is desirably cooled with a source of fresh air 70, optionally flowing in a counter-current direction. After passing through the cooling portion 46 the gas may then be allowed to pass freely through the selected portion 45, the pre-heating portion 47 or the remainder portion 48. Alternatively the gas can be directed specifically to the pre-heating portion 47 for energy efficiency. After passing through the pre-heating portion 47, the gases can be further heated with the heat exchanger 65 to then be ducted upstream of the selected portion 45 to provide hot gas for desorbing ammonia. All of this gas flow can be controlled with suitable ducting and, where necessary with driving fans.

[0157] Although preferred embodiments of the invention have been described herein in detail, it will be understood by those skilled in the art that variations may be made thereto without departing from the scope of the invention or of the appended claims.