Method for treating a purge gas stream to remove ammonia

Abstract

A method for treating an ammonia-containing purge gas stream on board a marine vessel is described, the method comprising at least the steps of: (a) providing the ammonia-containing purge gas stream from an engine of the marine vessel, and (b) passing the ammonia-containing purge gas stream through a first tank containing water to provide an exhaust gas stream with reduced ammonia.

Description

[Technical field]

[0001] The present invention relates to a method for treating an ammonia-containing purge gas stream on board a ship, a system for such treatment and regeneration, and an apparatus therefor. [Background technology]

[0002] Following the 2018 International Maritime Organisation's commitment to reduce greenhouse gas emissions from international shipping, ammonia-fueled ships, or engines adapted to be powered by ammonia fuel, are increasingly being developed and built.

[0003] On the one hand, for ships and vessels having engines that run on low flash point fuels, regulations require that the engine and the piping between the fuel valve train be purged, typically with nitrogen, whenever the engine is shut down, either intentionally or due to a trip. During the purging process, some of the fuel may evaporate into the nitrogen purge stream and thus be exhausted from the vessel along with the nitrogen.

[0004] If the fuel is ammonia, it is desirable to minimize emissions of ammonia gas because ammonia is toxic, especially for the safety of the crew and in the event that the engine is shut down at an unplanned time (e.g., due to an engine trip).

[0005] The present invention seeks to help overcome such problems. [Brief description of the drawings]

[0006] [Figure 1] 1A-1D are schematic diagrams illustrating aspects and embodiments of the present invention, both individually and collectively. [Diagram 2] 4 is a graph of the molar composition of ammonia in the ammonia-reduced exhaust gas versus time. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0007] According to one aspect of the invention, there is provided a method for treating an ammonia-containing purge gas stream on a vessel, comprising at least: (a) providing said ammonia-containing purge gas stream from an engine of a marine vessel; (b) passing the ammonia-containing purge gas stream into a first tank containing water to provide an ammonia-depleted exhaust gas stream; A method is provided comprising:

[0008] Optionally, the treatment method is the first stage of a batch process or the first stage of a more general or overall process for treating an exhaust gas stream and regenerating the treatment process on board a ship.

[0009] According to a further or independent aspect of the invention, the method further comprises the steps of the method according to any one of the preceding claims, (e) providing a second tank containing a caustic solution; (f) passing the caustic solution from the second tank into the first tank to provide a resultant solution and a gaseous ammonia stream; (g) passing the gaseous ammonia stream to a storage tank or a reliquefaction unit; It further comprises:

[0010] Such a step may provide the second step in an overall process, or the first stage in a regeneration process. According to a further or independent aspect of the invention, the method comprises the steps of: (h) passing the resulting solution from the first tank into the second tank; (i) heating the resulting solution in the second tank to provide a steam flow and a rechargeable caustic solution; (j) condensing the water vapor stream to provide a liquid water stream; (k) directing said liquid water stream into said first tank to provide said water of step (b); It further comprises:

[0011] This provides the third stage of the overall treatment method, or the second stage of the regeneration process. Thus, according to a further aspect of the present invention there is provided a system for the treatment and regeneration of an ammonia-containing purge gas stream on board a ship, comprising at least (a) providing an ammonia-containing purge gas stream from an engine of a marine vessel; (b) passing the ammonia-containing purge gas stream through a first tank containing water to provide an ammonia-depleted exhaust gas stream; (c) optionally sparging the ammonia-containing purge gas stream into the water through a sparging device; (d) venting the ammonia-depleted exhaust gas stream to the atmosphere or further treating the ammonia-depleted exhaust gas stream; (e) providing a second tank containing a caustic solution; (f) if necessary, passing the caustic solution from the second tank into the first tank to provide a resultant solution and a gaseous ammonia stream; (g) passing the gaseous ammonia stream to a storage tank or a reliquefaction unit; (h) passing the resulting solution from the first tank into the second tank; (i) heating the resulting solution in the second tank to provide a water vapor flow; (j) condensing the water vapor stream to provide a liquid water stream; (k) directing said liquid water stream into said first tank to provide said water of step (b); A system is provided comprising:

[0012] According to a further aspect of the present invention, 1. An apparatus for reducing the ammonia content of an exhaust gas stream of an engine of a ship, comprising: a first tank containing water; a second tank containing a concentrated caustic solution; a transfer pump between the first tank and the second tank; - a condenser between the second tank and the first tank; an ammonia storage tank; An apparatus is provided comprising:

[0013] Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which: The use of ammonia as fuel in engines has been known for some time. Now, what is called "green ammonia" can be provided by reacting nitrogen separated from the air with hydrogen produced by water electrolysis using wind or solar energy. Green ammonia is considered potentially more environmentally friendly than fossil fuels, since it has no carbon emissions. Green ammonia is also a cheaper fuel than hydrogen for the shipping industry, since it is easier to store and can be burned in standard internal combustion engines.

[0014] However, ammonia is also considered to be relatively toxic, and therefore regulations requiring that the ship's or vessel's piping between the engine and the fuel valve train be purged with nitrogen whenever the engine is shut down, either intentionally or by trip, can cause a portion of the ammonia fuel to be evaporated into the nitrogen purge stream and thus vented along with the nitrogen. Venting ammonia is undesirable due to its toxicity.

[0015] According to one embodiment of the present invention, there is provided a method for treating an ammonia-containing purge gas stream on a ship, comprising at least: (a) providing an ammonia-containing purge gas stream from an engine of a marine vessel; (b) passing the ammonia-containing purge gas stream into a first tank containing water to provide an ammonia-reduced exhaust gas stream; A method is provided comprising:

[0016] The vessel may be any marine or seagoing vessel, including ships, carriers, and the like. The engine type may be an existing or standard internal combustion engine, or an engine further developed to use ammonia fuel. Some engines may also be capable of using a mixture of ammonia and additional fuels, and the present invention extends to all such engines. Purge gas streams are known in the art and generally contain one or more inert gases, including those that are inert to the engine fuel type. A purge gas stream is passed through the engine, lines, tanks, piping, etc. to purge gas or liquids from the engine, lines, tanks, piping, etc. for various reasons, including changing or cleaning the engine's fuel, or to prevent undesirable buildup. The most common gas used in the purge gas stream is nitrogen, but other gases may be used or mixed.

[0017] The method of the present invention involves passing a purge gas stream on board the vessel through the vessel's engine to be purged, and optionally also through associated piping networks and piping between the fuel valve trains, to provide a resultant ammonia-containing purge gas stream, i.e., containing the ammonia that needs to be evaporated and purged from the engine, etc.

[0018] In the present invention, such a gas stream is passed into a first tank containing water to provide an ammonia-reduced exhaust gas stream. Water is known to dissolve ammonia, and the resulting gas passed through and exiting the water may have a reduced ammonia content, referred to herein as an ammonia-reduced exhaust gas stream.

[0019] Optionally, the first tank contains water that is ammonia-free or that contains only a small amount (ie, a "trace amount") of ammonia. Optionally, the ammonia-containing purge gas stream is passed through the water of the first tank under some form of excitation or stimulation to increase the surface area between the ammonia-containing purge gas stream and the water. Various means and apparatus are known to achieve the stimulation of the gas stream through the liquid stream, including various sparging means. One common means of achieving stimulation in such a manner is aeration, which uses a sparging device, sparging means, or sparging "head" intended to create bubbles in the exhaust gas stream to create a high or higher surface area for ammonia absorption.

[0020] It is known that ammonia can be dissolved in ammonia-free water at ambient temperature and pressure in some cases. Absorption can be assisted using elevated conditions, such as above ambient pressure. Absorption provides an ammonia-reduced exhaust gas stream that is 90% or more free of its ammonia content, in some cases greater than 95% ammonia-free, and in some cases can be greater than 99% ammonia-free.

[0021] If the ammonia-reduced gas stream is greater than 99% ammonia-free, it may be possible to vent the ammonia-reduced exhaust gas stream directly to the atmosphere. Thus, by the method of the present invention, (d1) venting the ammonia-reduced exhaust gas stream to the atmosphere. may further be provided.

[0022] Additionally or alternatively, the ammonia-reduced exhaust gas stream is further treated by one or more additional treatment processes or steps. One known additional treatment step is the use of a scrubbing process intended to further capture or recover the ammonia in the exhaust gas stream, in particular the use of a scrubbing process as an acid scrubbing step. Thus, the method of the present invention provides: (d2) further treating the ammonia-reduced exhaust gas stream. may further be provided.

[0023] The steps outlined and described above provide the first stage of the process, and may be carried out for the time or duration required to treat the ammonia-containing exhaust gas stream (i.e., as a batch process).

[0024] The resulting ammonia-rich water remains in the first tank. According to the present invention, (e) providing a second tank containing a caustic solution; (f) passing the caustic solution from the second tank into the first tank to provide a resultant solution and a gaseous ammonia stream; (g) passing the gaseous ammonia stream to a storage tank or a reliquefaction unit; is further provided.

[0025] Caustic solutions are well known in the art and typically contain one or more alkalis. Concentrated forms of caustic solutions are preferred. The desired concentration of caustic solutions for ammonia release is well known in the art and will not be described further herein.

[0026] By providing a caustic solution in a second tank and passing the caustic solution from the second tank into the first tank to mix with the ammonia-rich water therein, the caustic solution provides a release of the ammonia dissolved in the first tank in gaseous form to provide a gaseous ammonia stream and a resultant solution that is generally a less concentrated caustic solution.

[0027] Passage of solution between the first and second tanks, and between the second and first tanks, may be provided by any suitable means including one or more pumps, etc., as known in the art. Optionally, using appropriate valves and piping, one pump can provide the means for pumping liquid between both tanks.

[0028] The gaseous ammonia stream can be directed back to a suitable storage tank, such as an ammonia fuel tank, or back to the ammonia reliquefaction unit, or both, as desired or required. In such a manner, ammonia that was previously vented with the exhaust gas stream is now recovered.

[0029] Recovery of ammonia provides the second stage of the method for treating an ammonia-containing exhaust gas stream, or alternatively, or additionally, forms the first stage of the regeneration process of the systems described herein.

[0030] According to the present invention, (h) passing the resulting solution from the first tank into a second tank; (i) heating the resulting solution in the second tank to provide a steam stream and a recharged caustic solution; (j) condensing the water vapor stream to provide a liquid water stream; (k) directing a liquid water stream into the first tank to provide the water of step (b); is further provided.

[0031] Heating of the resulting solution in the second tank may be provided by any suitable means, including electric, steam, and other heating means known in the art. Condensation of the water vapor stream may be provided by any suitable condenser, which generally has a condensate stream passing therethrough intended to reduce the temperature of the water vapor stream to provide a liquid water stream.

[0032] The liquid water stream is therefore now ammonia-free and ready to be returned to the first tank for reuse, while the caustic solution remaining in the second tank has also been recovered and is ready to be reused the next time it is needed.

[0033] Recovery of the ammonia-free water and caustic solution provides a third stage of the method for treating an ammonia-containing exhaust gas stream, or alternatively or additionally forms the second stage of the regeneration process of the system described herein.

[0034] Generally therefore, in accordance with the present invention there is provided a system for the treatment and regeneration of an ammonia-containing purge gas stream on board a marine vessel, comprising at least (a) providing an ammonia-containing purge gas stream from an engine of a marine vessel; (b) passing the ammonia-containing purge gas stream into a first tank containing water to provide an ammonia-reduced exhaust gas stream; (c) optionally sparging an ammonia-containing purge gas stream into the water through a sparging device; (d) venting the ammonia-reduced exhaust gas stream to the atmosphere or further treating the ammonia-reduced exhaust gas stream; (e) providing a second tank containing a caustic solution; (f) passing the caustic solution from the second tank into the first tank to provide a resultant solution and a gaseous ammonia stream; (g) passing the gaseous ammonia stream to a storage tank or a reliquefaction unit; (h) passing the resulting solution from the first tank into a second tank; (i) heating the resulting solution in the second tank to provide a water vapor flow; (j) condensing the water vapor stream to provide a liquid water stream; (k) directing a liquid water stream into the first tank to provide the water of step (b); A system may be provided comprising:

[0035] The use of sequential lettering for the steps described herein does not limit the order in which one or more of the steps may be performed in alternative sequences. One skilled in the art will appreciate that steps (a) through (k) of the system can be repeated such that a cycle is provided by the system.

[0036] Optionally, step (d) is replaced by a step of acid scrubbing the ammonia reduced exhaust gas stream. Optionally, the path from the first tank to atmospheric venting or further processing is closed once venting in step (d) is completed.

[0037] Optionally, the pathway from the first tank to the storage tank or reliquefaction unit is opened once evacuation in step (d) is completed. Referring to the drawings, FIG. 1 shows a method of treating an ammonia-containing purge gas stream 2 on board a marine vessel (not shown) comprising at least the steps of providing an ammonia-containing purge gas stream 2 from an engine (not shown) of the vessel being purged, and passing the ammonia-containing purge gas stream 2 into a first tank 4 containing water 6 to provide an ammonia-reduced exhaust gas stream.

[0038] Purging engines on marine vessels with a stream of purging gas, such as nitrogen, is well known in the art to remove gases from the engine when it is shut down, either intentionally or unintentionally. If the removed gas is not harmful or toxic, it may be vented directly to the atmosphere.

[0039] However, ammonia is relatively toxic, therefore the purge gas stream for engines that use ammonia should not be vented directly to the atmosphere. In one example of the present invention, the ammonia-containing purge gas stream 2 includes a purge gas nitrogen and ammonia. This gas stream 2 can be passed through ammonia-free water 6 in a first tank 4 so that the water 6 absorbs the ammonia content. The ammonia-containing purge gas stream 2 can be sparged through a suitable sparging device or sparging head 8 at or near the bottom of the first tank 4 to distribute the passage of the ammonia-containing purge gas stream 2 through the water 6 in a manner known in the art so that the ammonia is better dissolved in the water 6 and the exhaust gas is "cleaned" of its ammonia content.

[0040] The ammonia-reduced exhaust gas stream obtained from the water 6 is passed up through a first tank 4 which routes it into a suitable header pipe 10. Following the opening of exhaust valve 14, the resulting ammonia-reduced or optionally ammonia-free exhaust gas stream can be vented to the atmosphere along a pipeline 12 in a manner known in the art and not further described herein, or can be further treated, if required, such as by a subsequent acid scrubbing step.

[0041] A supply of ammonia-containing purge gas stream 2 that needs to be purified can be provided as a first stage, providing a process whereby a completely or nearly ammonia-free exhaust gas is vented to the atmosphere or, if required, to a subsequent acid scrubbing process.

[0042] Once the treatment of the ammonia-containing purge gas stream 2 has stopped or is complete, the exhaust valve 14 can be closed. Over time, the water 6 in the first tank 4 becomes ammonia rich and needs to be replaced or purified to allow it to absorb more ammonia. This is typically referred to as "regenerating" and can be the second stage of a treatment method or the first stage of a regeneration process to regenerate the water in the tank 4.

[0043] 1 shows a second tank 20 containing a caustic solution, optionally a concentrated caustic solution. If necessary, the caustic solution 22 can be pumped into the first tank 4 via a bottom pipeline 24, a pump valve 26, a pump 28, a next pump valve 30, and a pipeline 32. The caustic solution 22 then reacts with the ammonia-rich water 6 in the first tank 4 to release the absorbed ammonia and form ammonia gas in a manner known in the art. By opening the return valve 16, the gaseous ammonia stream thus produced in the first tank 4 is released through the header pipe 10 and the return valve 16, and by using an appropriate valve after the first return valve 16, it can then be returned to a storage tank or a fuel tank 52 and / or sent to re-liquefaction through a pipeline 54. In such a manner, the ammonia provided by the ammonia-containing purge gas stream 2 and absorbed by the water 6 is completely or nearly recovered.

[0044] In the third stage of the method of the present invention described herein, or the second stage of the regeneration process, the resulting solution in the first tank 4 can be returned into the second tank 20 via the transfer pump 28 by closing the pump valves 26 and 30 and opening the return valves 36 and 34 in the bypass pipelines 40 and 38.

[0045] Thus, the solution obtained from the first tank 4 is sent into the second tank 20. The solution obtained can in turn be heated by steam flow 42 through control valve 44 (and a steam condensate flow 46 exiting the second tank 20 is obtained). Heating of the solution obtained in the second tank 20 provides a water vapor flow, which is sent upwards, through a header pipe 60, through control valve 48, and into a suitable water condenser 50 for condensation. The ammonia-free and caustic-free liquid water flow 56 thus formed recovered in such a manner can be provided back into the first tank 4 to provide water for step (b) above (i.e., purified water capable of absorbing ammonia in the ammonia-containing purge gas flow 2) and provide an ammonia-reduced exhaust gas flow through lines 10 and 12.

[0046] Following the regeneration process, recovery and return of the ammonia-free water in the first tank 4 and the caustic solution 22 in the second tank 20 are provided, ready for further treatment of the ammonia-containing exhaust gas in another cycle than that described above.

[0047] Thus, once the process is complete, the cycle may begin again. Depending on the purge required and the amount of water selected, it is possible to approach 100% ammonia recovery, with greater than 99% expected. If a subsequent acid scrub finish is used instead of direct venting of the ammonia-reduced exhaust gas stream to the atmosphere, acid consumption is reduced proportionately.

[0048] Those skilled in the art will appreciate that the above-described methods and processes provide an overall system for the treatment and regeneration of an ammonia-containing purge gas stream on board a ship, comprising at least: (a) providing an ammonia-containing purge gas stream 2 from an engine; (b) passing the ammonia-containing purge gas stream 2 into and through a first tank 4 containing water 6 to provide an ammonia-reduced exhaust gas in a pipeline 10; (c) sparging the ammonia-containing purge gas stream 2 through a sparging device 8 into the water 6 to increase ammonia absorption; (d) venting the ammonia-reduced exhaust gas stream to the atmosphere via pipeline 12 or further processing the ammonia-reduced exhaust gas stream; (e) providing a second tank 20 containing a caustic solution 22; (f) if necessary, passing caustic solution 22 from second tank 20 into first tank 4 to provide a resultant solution and a gaseous ammonia stream; (g) delivering the gaseous ammonia stream to a storage tank 52 or a reliquefaction unit via a pipeline 54; (h) transferring the resulting solution from the first tank 4 into the second tank 20; (i) heating the resulting solution in the second tank to provide a water vapor flow; (j) condensing the water vapor stream in a pipeline 60 to provide a liquid water stream 56; (k) directing a liquid water stream 56 into the first tank 4 to provide the water 6 of step (b); It can be seen that a system is provided comprising:

[0049] One skilled in the art will appreciate that steps (a) through (k) of the system can be repeated such that a cycle is provided by the system. According to FIG. 1, there is also provided an apparatus for reducing the ammonia content of an exhaust gas stream of an engine of a ship, comprising: a first ammonia absorption tank containing water and a sparging device present in the first tank; a second regeneration tank containing a concentrated caustic solution; a transfer pump between the first tank and the second tank; a condenser between the second tank and the first tank; an ammonia storage tank; An apparatus comprising:

[0050] FIG. 2 is a graph of the molar composition of ammonia in the ammonia-reduced exhaust gas versus time. This is an example showing the reduction in the vented ammonia content during the first stage of the process described above. FIG. 2 can be interpreted in conjunction with FIG. 1 using the following parameters: Ammonia-containing purge gas stream 2 flows into first tank 4 at a rate of 1320 kg / h, with a composition of 44 mol % ammonia (the remainder being nitrogen). First tank 4 contains 5 m 2 of water 6. The ambient temperature, which is assumed to be the prevailing temperature in the system itself, is 25° C. The pressure in the first tank 4 is maintained at 0.2 MPa (gauge pressure) using a control valve 14. Figure 2 shows the ammonia content of the ammonia-depleted exhaust gas in pipeline 10 (and ultimately pipeline 12) as determined over time.

[0051] 2, a total of 117.23 kg of ammonia enters the first tank 4 as part of the ammonia-containing purge gas stream 2. After passing through the water 6, only 0.46 kg of ammonia is not absorbed by the water and therefore exits the first tank 4 (in pipeline 10 and ultimately pipeline 12) as part of the ammonia-reduced exhaust gas stream. Hence, 116.77 kg is captured in the water 6 in the first tank 4, representing an ammonia capture efficiency of 99.6%.

Claims

1. 1. A method for treating an ammonia-containing purge gas stream on a vessel, comprising at least (a) providing said ammonia-containing purge gas stream from an engine of a marine vessel; (b) passing the ammonia-containing purge gas stream through a first tank containing water to provide an ammonia-depleted exhaust gas stream; A method for providing the above.

2. (c) sparging the ammonia-containing purge gas stream into the water. The method of claim 1 further comprising:

3. (d1) venting the ammonia-depleted exhaust gas stream to the atmosphere. The method of claim 1 or 2, further comprising:

4. (d2) further treating the ammonia-depleted exhaust gas stream The method of claim 1 or 2, further comprising:

5. 3. A method according to claim 1 or 2 which forms the first stage of a batch process.

6. (e) providing a second tank containing a caustic solution; (f) passing the caustic solution from the second tank into the first tank to provide a resultant solution and a gaseous ammonia stream; (g) passing the gaseous ammonia stream to a storage tank or a reliquefaction unit; The method of claim 1 or 2, further comprising:

7. 7. The method of claim 6 forming the first stage of a regeneration process.

8. (h) transferring the resulting solution from the first tank into the second tank; (i) heating the resulting solution in the second tank to provide a steam flow and a rechargeable caustic solution; (j) condensing the water vapor stream to provide a liquid water stream; (k) directing said liquid water stream into said first tank to provide said water of step (b); The method of claim 6 further comprising:

9. 9. The method of claim 8 forming a second stage of a regeneration process.

10. 3. The method of claim 1 or 2, wherein the ammonia-containing purge gas stream comprises nitrogen and ammonia.

11. 3. The method of claim 1 or 2, wherein the ammonia-containing purge gas stream is provided from a nitrogen purge exhaust gas stream from an engine of the marine vessel.

12. 3. The method of claim 1 or 2, wherein the ammonia-depleted exhaust gas stream is substantially ammonia-free.

13. 1. A system for treating and regenerating an ammonia-containing purge gas stream on board a vessel, comprising at least (a) providing an ammonia-containing purge gas stream from an engine of a marine vessel; (b) passing the ammonia-containing purge gas stream through a first tank containing water to provide an ammonia-depleted exhaust gas stream; (c) optionally sparging the ammonia-containing purge gas stream into the water through a sparging device; (d) venting the ammonia-depleted exhaust gas stream to the atmosphere or further processing the ammonia-depleted exhaust gas stream; (e) providing a second tank containing a caustic solution; (f) if necessary, passing said caustic solution from said second tank into said first tank to provide a resultant solution and a gaseous ammonia stream; (g) passing the gaseous ammonia stream to a storage tank or a reliquefaction unit; (h) transferring the resulting solution from the first tank into the second tank; (i) heating the resulting solution in the second tank to provide a water vapor flow; (j) condensing the water vapor stream to provide a liquid water stream; (k) directing said liquid water stream into said first tank to provide said water of step (b); A system comprising:

14. 14. The system of claim 13, wherein steps (a) through (k) are repeated such that a cycle is provided by the system.

15. 15. The system of claim 13 or 14, wherein step (d) is replaced by an acid scrubbing of the ammonia-depleted exhaust gas stream.

16. 15. The system of claim 13 or 14, wherein the path from the first tank to atmospheric venting or further processing is closed upon completion of venting in step (d).

17. A system as described in claim 13 or 14, wherein the path from the first tank to the storage tank or the reliquefaction unit is opened when evacuation in step (d) is completed.

18. 1. An apparatus for reducing the ammonia content of an exhaust gas stream of an engine of a ship, comprising: a first tank containing water; a second tank containing a concentrated caustic solution; a transfer pump between said first tank and said second tank; - a condenser between said second tank and said first tank; - an ammonia storage tank; An apparatus comprising:

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