METHODS AND SYSTEMS FOR PRODUCING AMMONIA AND FOR LONG-TERM DEPOSITING OF CARBON DIOXIDE

Abstract

Methods and systems for producing ammonia and for long-term depositing of carbon dioxide are disclosed, wherein off-site produced cold carbon dioxide received at the plant from a road vehicle, railway car, or vessel is used for cooling locally produced ammonia from a local ammonia production plant, such as a blue ammonia production plant.

Claims

1. A method of producing ammonia at an ammonia production plant generating CO.sub.2 as a by-product, comprising the following steps: A generation of CO.sub.2 in the plant; B generation of NH.sub.3 in the plant; C separating the CO.sub.2 generated in step A; D injecting the separated CO.sub.2 obtained in step C into an underground storage; F cooling the NH.sub.3 produced in step B having a first temperature (T.sub.1) to a second lower temperature (T.sub.2); additionally comprising the following step: E importing to the plant from a road vehicle, railway car, or vessel off-site produced CO.sub.2 having a temperature (T) lower than the second lower temperature (T.sub.2) carried by the road vehicle, railway car, or vessel, and, wherein, in step F, at least part of the cooling is carried out using the imported off-site produced CO.sub.2 from step E.

2. The method of claim 1, additionally comprising a step H, wherein the heated off-site produced imported CO.sub.2 resulting from step F is injected into an underground storage.

3. The method of claim 2, wherein, in steps D and H, the heated imported CO.sub.2 obtained from step F, and the CO.sub.2 obtained in step C, respectively, are co-injected into one and the same underground storage.

4. The method of claim 1, additionally comprising a step G, in which step separated CO.sub.2 obtained from step C is cooled using off-site produced imported CO.sub.2 obtained from step E.

5. The method of claim 1, wherein the underground storage is located under the seabed.

6. A system for producing ammonia and depositing carbon dioxide generated as a by-product during the ammonia production comprising: a NH.sub.3 producing plant generating carbon dioxide as a by-product; means for separating CO.sub.2 generated in the plant; means for cooling the NH.sub.3 produced in the plant; piping means for conveying the separated CO.sub.2 to an underground storage; wherein the system is configured to receive from a road vehicle, railway car, or vessel off-site produced carbon dioxide carried by the road vehicle, railway car, or vessel, and wherein the means for cooling the NH.sub.3 comprises a heat exchanger having an inlet for the off-site produced carbon dioxide as a cooling medium.

7. The system of claim 6, additionally comprising piping means for conveying heated CO.sub.2 exiting the heat exchanger to an underground storage.

8. The system of claim 7, wherein the piping means for conveying the heated CO.sub.2, and the piping means for conveying the separated CO.sub.2 lead to, and, are connected to, one and the underground storage.

9. The system of claim 6, additionally comprising a heat exchanger for cooling CO.sub.2 separated in the plant having an inlet for the off-site produced carbon dioxide as a cooling medium.

10. A method of producing ammonia at an ammonia production plant, comprising the following steps: B generation of NH.sub.3 in the plant; F cooling the NH.sub.3 produced in step B having a first temperature (T.sub.1) to a second lower temperature (T.sub.2); additionally comprising the following two steps: E importing to the plant from a road vehicle, railway car, or vessel off-site produced CO.sub.2 having a temperature (T) lower than the second lower temperature (T.sub.2) carried by the road vehicle, railway car, or vessel, and, H injecting the heated off-site produced imported CO.sub.2 resulting from step F into an underground storage, and wherein, in step F, at least part of the cooling is carried out using the imported off-site produced CO.sub.2 from step E.

11. A system for producing ammonia and depositing carbon dioxide comprising: an NH.sub.3 producing plant; means for cooling the NH.sub.3 produced in the plant; wherein the system is configured to receive from a road vehicle, railway car, or vessel off-site produced carbon dioxide carried by the road vehicle, railway car, or vessel, and wherein the means for cooling the NH.sub.3 comprises a heat exchanger having an inlet for the off-site produced carbon dioxide as a cooling medium, and wherein an outlet from said heat exchanger is connected to an underground storage.

12. The system of claim 11, wherein the means for cooling the NH.sub.3 is the heat exchanger having an inlet for the off-site produced carbon dioxide as a cooling medium, which heat exchanger also has an inlet for NH.sub.3 to be cooled therein.

13. The system of claim 11, wherein the means for cooling the NH.sub.3 additionally comprises an additional heat exchanger having an inlet for NH.sub.3 to be cooled in the additional heat exchanger, and an intermediate working fluid loop, wherein the intermediate working fluid loop is configured to thermally connect said two heat exchangers.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0024] Captured carbon dioxide is typically pressurized and cooled before being transported, such as by ship, to a location of long-term underground storage. Such long-term underground storage may be located under the seabed. The temperature of carbon dioxide being transported to a destination for long-term storage is typically 47 C. or lower. Before being injected into a long-term underground storage, the cold carbon dioxide typically needs to be heated to higher temperature. The required heating is dependent i.a. on the specific construction and arrangement of the pipeline system leading to the underground storage. Typically, the cold carbon dioxide will preferably be heated to at least 10 C. in order to be able to allow for the use of economical pipeline materials and minimise seawater freezing when being injected into the long-term storage. The present invention is based on using such cold carbon dioxide obtained from another site for cooling purposes on an ammonia production site, especially for cooling purposes beyond ambient cooling, i.e. to a temperature below ambient, of the ammonia produced.

[0025] The ammonia production plant is connected to a long-term underground storage for carbon dioxide, into which storage by-product carbon dioxide generated at the ammonia production plant is injected.

[0026] For use as feedstock in the ammonia synthesis, it is necessary to generate hydrogen and nitrogen. The ammonia production plant envisaged by the invention therefore typically includes also a system configured to produce hydrogen, and also a system configured to produce nitrogen. The hydrogen is typically obtained at least partly from a carbonaceous feedstock (such as natural gas), in which case CO.sub.2 is produced in the plant, or alternatively only from the electrolysis of water, in which case no CO.sub.2 is produced. The nitrogen is typically obtained from the separation of air.

[0027] In the inventive method, the off-site produced CO.sub.2 is preferably heated to a temperature suitable for injection thereof into an underground storage via a pipeline, such as about 10 C. Accordingly, the claimed method allows for receiving at the ammonia production plant off-site produced CO.sub.2 and injecting same into a long-term storage. The long-term storage is preferably the same long-term storage as used for the on-site produced CO.sub.2. The heated off-site produced CO.sub.2 and the cooled on-site produced CO.sub.2 may preferably be co-injected into the long-term storage.

[0028] The ammonia is preferably cooled to a temperature T.sub.2 at which the ammonia is in a liquid state at the prevailing pressure, i.e. below the dew point at the prevailing pressure, such as 5 C. at 180 barg.

[0029] For an efficient cooling to be obtained according to the invention (in step F), the temperature of the resulting heated CO.sub.2 (from step F) should preferably be at least 5 C. lower than the temperature T.sub.2 of the resulting cooled NH.sub.3.

[0030] In the inventive method, the on-site produced CO.sub.2 is preferably at least partly cooled using the cold imported off-site produced CO.sub.2. In a more preferred embodiment the on-site produced CO.sub.2 is cooled using the cold imported off-site produced CO.sub.2.

[0031] The inventive system for long-term CO.sub.2 storage comprises an ammonia production plant, which plant also generates, as a by-product, CO.sub.2. The ammonia production plant is typically located by the sea, i.e. by coast or near the coastline or seashore. It is also conceivable that the ammonia production plant is located off-shore. In an embodiment of the system configured for direct cooling of NH.sub.3, the ammonia production plant includes a heat exchanger for cooling the NH.sub.3 produced in the plant, which heat exchanger has an inlet for CO.sub.2 as cooling medium into which inlet imported cold CO.sub.2 is fed. In the heat exchanger, NH.sub.3 having a first temperature T.sub.1 entering the heat exchanger is cooled to a second lower temperature T.sub.2. For a more effective transfer of heat from the ammonia to the cold carbon dioxide, it is preferred that the newly synthesized ammonia is under a high pressure when being cooled by the carbon dioxide. Accordingly, the newly synthesized ammonia, preferably after ambient cooling, may for example be fed to the heat exchanger at a pressure of about 180 barg and a temperature T.sub.1 of about 5 C. Accordingly, in one embodiment T.sub.1 is about 5 C. Similar conditions are preferably also used in embodiments configured for indirect cooling of NH.sub.3, wherein the NH.sub.3 and CO.sub.2, respectively, are fed into different heat exchangers thermally connected by a working fluid loop, as will be described below.

[0032] Preferably the system additionally comprises piping means for conveying imported heated CO.sub.2, exiting the heat exchanger, to an underground storage, preferably to same underground storage as the on-site produced CO.sub.2 is conveyed to.

[0033] In a preferred embodiment the system additionally comprises a heat exchanger for cooling CO.sub.2 separated in the plant, which heat exchanger has an inlet to receive CO.sub.2 as cooling medium into which inlet imported cold CO.sub.2 is fed. In the heat exchanger, on-site produced CO.sub.2 entering the heat exchanger is cooled.

[0034] The piping means for conveying CO.sub.2 preferably connects the plant with the underground storage. For example, a first end of the piping means may be connected to a long-term deposit, which is preferably located underground, and more preferably under the seabed outside the ammonia production plant, and a second end of the piping means may be configured to receive heated off-site produced CO.sub.2 exiting the NH.sub.3/CO.sub.2 heat exchanger, and preferably also heated off-site produced CO.sub.2 exiting the CO.sub.2/CO.sub.2 heat exchanger.

[0035] The inventive system is configured to receive off-site produced carbon dioxide. To this end the system may be configured to be connected to a container, e.g. a canister, containing off-site produced CO.sub.2, which container has been transported to the system. The means of transport is not critical, and could e.g. be by road, railway, air, or sea, depending of the local geography and location of the ammonia production plant and infrastructure. Transport by sea is generally preferred. The system could include an intermediate storage tank for holding cold off-site produced CO.sub.2 received at the system from a means of transport. From said tank cold CO.sub.2 could be conveyed via a conduit to the NH.sub.3/CO.sub.2 heat exchanger, and, optionally, also to the CO.sub.2/CO.sub.2 heat exchanger.

[0036] While described hereinabove with reference to an ammonia production plant generating carbon dioxide as a by-product, the inventive cooling using off-site produced carbon dioxide could also be used in an ammonia production plant not generating carbon dioxide as a by-product. Such embodiments of the invention principally take advantage of the cooling requirement during ammonia production, and the heating requirement for cold carbon dioxide to be able to be injected into a long-term storage, which storage is located nearby the ammonia production plant. Such embodiments of the invention also principally take advantage of locating an ammonia production plant nearby an underground storage.

[0037] In an alternative embodiment, the ammonia production plant does not produce carbon dioxide as a by-product, and is located nearby a long-term underground storage for carbon dioxide, into which storage off-site produced carbon dioxide is injected.

[0038] In the inventive methods and systems, part of the imported off-site produced cold carbon dioxide could also be used for transferring gaseous ammonia into liquid ammonia, which phase transition would not necessarily involve a change of temperature of the ammonia, especially in a case where the ammonia is very pure. Such phase transition could for example be provided for after a compressor further downstream in the process.

[0039] Accordingly, the inventive methods could include an additional step J, wherein gaseous ammonia is transferred into liquid ammonia using the imported off-site produced CO.sub.2 from step E by heat transfer from the ammonia to the imported off-site produced CO.sub.2.

[0040] Analogously, the inventive systems could include an additional heat exchanger or a condenser having an inlet for gaseous ammonia and an outlet for liquid ammonia, and having an inlet for the off-site produced carbon dioxide as a cooling medium, and an outlet for carbon dioxide from said heat exchanger connected to an underground storage.

[0041] For thermodynamical reasons it is preferred to use cold imported off-site produced CO.sub.2 to provide cooling (refrigeration) to the NH.sub.3 directly in a heat exchanger. However, in case of a leak or rupture in said heat exchanger, either the CO.sub.2 or the NH.sub.3 may become contaminated with the other, depending on which side of the heat exchanger is at higher pressure. Typically, this would mean the CO.sub.2 being contaminated with NH.sub.3; this carries the potential for formation of solids, such as ammonium carbamate. Formation of solids would present a maintenance challenge and would be disruptive to operations. To avoid this potential problem, it is also possible to use the CO.sub.2 to still provide the cooling duty to the NH.sub.3, but indirectly, via an intermediate working fluid loop, e.g. a water-ethylene glycol mixture. Such a loop would preferably be operated at a lower pressure than either the CO.sub.2 or the NH.sub.3, such that a heat exchanger leak could not contaminate either the CO.sub.2 or the NH.sub.3.

[0042] Accordingly, in one embodiment of the respective inventive methods, the cooling in step F is direct, such as using a heat exchanger, where the hot side is NH.sub.3 and the cold side is CO.sub.2. In another embodiment of the respective inventive methods, the cooling in step F is indirect, such as via an intermediate working fluid loop and two heat exchangers, (i.e. one for imported off-site produced CO.sub.2 and one for NH.sub.3, respectively) wherein the working fluid loop thermally connects the two heat exchangers.

[0043] Analogously, in one embodiment of the respective inventive systems, the means for cooling the NH.sub.3 is a heat exchanger having an inlet for the off-site produced carbon dioxide as a cooling medium. In another embodiment of the respective inventive systems, the means for cooling the NH.sub.3 comprises the heat exchanger having an inlet for the off-site produced carbon dioxide as a cooling medium, and, additionally, an intermediate working fluid loop, and an additional heat exchanger having an inlet for NH.sub.3 to be cooled in the additional heat exchanger, wherein the intermediate working fluid loop is configured to thermally connect said two heat exchangers.