Patent Application
20240400381
Ammonia production is currently associated with substantial CO2 emissions as the syngas for ammonia production is generated by reforming at multiple steps—one primary reforming step which takes place in a classical tubular steam methane reformer with a combustion furnace; followed by a secondary reforming step which takes place in a catalytic reactor vessel. In this reactor vessel, air (which contains N2 molecules) is introduced which helps in partial combustion of hydrocarbon molecules coming from the primary reforming step before the gas enters the catalyst layer of the reactor vessel. When the gas enters the catalyst layer, the secondary reforming takes place enhancing the conversion of hydrocarbon to CO and H2. As the combustion furnace is inevitable with the conventional tubular steam methane reformer, a considerable amount of flue gas is emitted through the furnace exit which contains a considerable amount of CO2 and thus makes the whole process significantly CO2-intensive.
Classical ammonia plant configurations intrinsically include one CO2 capture step before final conditioning of ammonia synthesis gas in order to protect the ammonia synthesis catalyst. This step can be considered as a “pre-combustion CO2 capture step” as the “capturable CO2” is generated only from reforming and shift reaction and not by combustion. Pre-combustion CO2 capture can achieve an overall CO2 capture of ˜ 50-60% with conventional tubular steam methane reforming (SMR) based syngas generation process.
However, with this configuration, the overall direct CO2 capture rate is poor as a significant amount of CO2 gets emitted via flue gas. To increase the overall capture rate, there are only two options as follows:
To avoid the inefficiency and cost penalty caused by either of the abovementioned two approaches, ammonia production can include only one autothermal reforming step instead of primary and secondary reforming steps (as described earlier). Instead of a big combustion furnace associated with a tubular reformer and high flow of flue gas, the Autothermal process is normally associated with a fired heater with much lower process heat duty requirements compared to SMR furnace and therefore resulting in much less flue gas flow and emissions. That is why, in an Autothermal reforming based process for generation of ammonia synthesis gas, intrinsic CO2 capture of 85-90% is achieved from produced syngas.
Main thermal duty exchanges in the fired heater in an autothermal reforming based ammonia synthesis gas generation configuration, correspond to some process heat exchange which may include preheating of gas entering the feedstock purification section (e.g. hydrogenation and/or desulfurization section) and/or preheating of gas entering different steps of reforming (e.g. pre-reformer or autothermal reformer reactor) and/or superheating of steam produced in the process. All these process thermal duty demands govern the firing required in the fired heater and thus govern the extent of CO2 emissions. This CO2 emission results in the intrinsic CO2 capture rate of 85-90%. The CO2 capture rate can be increased by firing a split stream of product H2 in the fired heater as fuel. This method reduces the hydrocarbon fuel consumption and thereby reduces the carbon emission through the fired heater leading to a direct carbon capture rate >95%.
However, to generate this additional H2 to be used as fuel, more hydrocarbon feed needs to be reformed and the carbon footprint of the process is increased by that resulting in higher Scope 3 emissions. Also, to reform more hydrocarbon feedstock, more oxygen intake is also required, which means higher power consumption by the Air Separation Unit. Hence, enhancing the CO2 capture is realized by increasing the Scope 2 (electricity import) and Scope 3 (hydrocarbon feedstock) emissions which is counter-productive in terms of overall emissions. Or in other words, direct emissions are minimized by increasing indirect emissions.
In one embodiment of the current invention, the proposed novel solution allows achieving a direct CO2 capture rate of >95% by the autothermal reforming based ammonia production process with one CO2 removal unit with an efficient thermal integration and a low duty fired heater ensuring minimum direct carbon emission.
Process and method to produce ammonia with high CO2 capture rate. The invention entails production of ammonia in an efficient and innovative way with minimum carbon emissions within the production unit by use of only one CO2 removal unit and a minimum process heat exchange duties provided by heat of combustion. The proposed novel solution allows achieving a direct CO2 capture rate of >95% by the autothermal reforming based ammonia production process with one CO2 removal unit with an efficient thermal integration and a low duty fired heater ensuring minimum direct carbon emission.
For a further understanding of the nature and objects for the present invention, reference should be made to the following detailed description, taken in conjunction with the accompanying drawings, in which like elements are given the same or analogous reference numbers and wherein:
Illustrative embodiments of the invention are described below. While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.
It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developer's specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure.
In one embodiment of the present invention, a method of producing low carbon ammonia is described wherein the direct carbon emissions are minimized without increasing any Scope 3 emissions and with a minimized impact on Scope 2 emissions, thus reducing the carbon intensity of the process.
Turning to
Preheated ATR feed stream 109 is combined with purge gas recycle stream 125, thereby forming combined ATR feed stream 110. Combined ATR feed stream 110 may then be introduced into optional pre-reformer 111, thereby optionally producing pre-reformed ATR feed stream 112. Combined ATR feed stream 110, or optional pre-reformed ATR feed stream 112, is then introduced into ATR 113 along with oxygen containing stream 115, thereby forming raw syngas stream 116. Raw syngas stream 116 is then introduced into water-gas shift reactor 117, thereby producing shifted syngas stream 118. Shifted syngas stream 118 is then introduced into hydrogen separation device 119. Hydrogen separation device 119 produces ammonia synthesis gas stream 120 and purge gas stream 123.
Ammonia synthesis gas stream 120 is introduced into ammonia synthesis reactor 121, thereby producing raw ammonia stream 122. Purge gas stream 123 is divided into purge gas fuel stream 124 and purge gas recycle stream 125. Purge gas fuel stream 123 is combined with hydrocarbon fuel stream 126 and introduced as fuel into fired heater 102. Second portion 125 is combined with preheated ATR feed stream 109 to produce combined ATR feed stream 110.
State of the art autothermal reforming technologies are associated with at least one fired heater including heat exchange coils providing sufficient process heat. The temperature required for the different process steps of the production unit is provided by these heat exchanges. The heat duty required for this heat exchange is provided by firing of hydrocarbon fuel that leads to CO2 emissions. Main thermal duty exchanges in the fired heater in an autothermal reforming based ammonia synthesis gas generation configuration, correspond to some process heat exchange which may include preheating of gas entering the feedstock purification section (e.g. hydrogenation and/or desulfurization section) and/or preheating of gas entering different steps of reforming (e.g. pre-reformer or autothermal reformer reactor) and superheating of steam produced in the process. All these process thermal duty demands govern the firing required in the fired heater and thus govern the extent of CO2 emissions. The more heat exchange happens in the fired heater, heat duty requirement by fuel increases, and so increases the CO2 emissions.
This CO2 emission results in the intrinsic CO2 capture rate of 85-90%. The CO2 capture rate can be increased by producing more hydrogen than required as product by additional feedstock processing (reforming, shift, CO2 removal, gas conditioning) and firing that additional H2 product in the fired heater. This method reduces the hydrocarbon fuel consumption and thereby reduces the carbon emission through the fired heater leading to a direct carbon capture rate >95%.
However, to generate this additional H2 to be used as fuel, more hydrocarbon feed needs to be reformed and the carbon footprint of the process is increased by that resulting in higher scope 3 emissions. Also, to reform more hydrocarbon feedstock, more oxygen intake is also required, which means higher power consumption by the Air Separation Unit. Hence, enhancing the CO2 capture is realized by increasing the Scope 2 (electricity import) and Scope 3 (hydrocarbon feedstock) emissions which is counter-productive in terms of overall emissions. Or in other words, direct emissions are minimized by increasing indirect emissions. Thus, additional processing of feedstock has a direct adverse impact on carbon intensity as well as both operating and capital cost. Additional feedstock consumption, therefore higher oxygen, power and other utility consumption increases the operating cost. On the other hand, due to higher effective material flow, all equipment gets oversized and therefore the capital investment goes higher.
The present invention describes a method of producing low carbon ammonia by autothermal reforming process where the direct carbon emissions are minimized without increasing any scope 3 emissions and with a minimized impact on scope 2 emissions, thus reducing the overall carbon intensity of the ammonia production process.
Turning to
Heated feedstock stream 246 is introduced into hydrogen desulfurization unit 202, thus producing desulfurized feed stream 203. Desulfurized feed stream 203 is combined with steam stream 204, thus generating ATR feed stream 205. ATR feed stream 205 is introduced into fired heater 206 thus producing preheated ATR feed stream 208, and flue gas stream 238. Heated ATR feed stream 208 is combined with purge gas recycle stream 236, thus forming combined ATR feed stream 209. Combined ATR feed stream 209 may then be introduced into optional pre-reformer 210, thereby optionally producing pre-reformed ATR feed stream 211. Combined ATR feed stream 209, or optional pre-reformed ATR feed stream 211, is then introduced into ATR 212 along with oxygen containing stream 214, thereby forming raw syngas stream 215.
Raw syngas stream 215 is introduced into water-gas shift reactor 216, thereby producing shifted syngas stream 217. Shifted syngas stream 217 is divided into first stream 218 and second stream 219. First shifted gas stream 218 is then introduced into first heat exchanger 220, thereby producing first cooled shifted syngas stream 226. The cooling of stream 218 may take place by providing heat to the saturated steam stream 221 produced in the steam generating device located downstream ATR 212 and/or from steam generating device located downstream ammonia synthesis reactor 231 resulting in superheated steam stream 222.
Second shifted gas stream 219 is then introduced into second heat exchanger 223 thereby producing second cooled shifted syngas stream 227. The cooling, as indicated by heat exchange lines 224 and 225, may come from feedstock preheater 243, thus providing heat to hydrocarbon feedstock stream 201. In this arrangement, heat exchange lines 224 and 225 are thermally connected to heat exchange lines 244 and 245.
First cooled shifted syngas stream 226 and second cooled shifted syngas stream 227 are combined, thus forming cooled shifted syngas stream 228. Cooled shifted syngas stream 228 is then introduced into CO2 capture unit and hydrogen separation device or synthesis gas preparation device 229. CO2 capture unit and hydrogen separation device or synthesis gas preparation device 229 produces hydrogen containing stream or ammonia synthesis gas stream 230 and purge gas stream 234. Nitrogen containing stream 240 may be added through mixing route alternative 1 to CO2 capture unit and synthesis gas preparation device 229 producing an ammonia synthesis gas stream 230/230a.
Alternatively, CO2 capture unit and hydrogen separation device 229 may generate a hydrogen-rich stream (>90 mole % H2) 230 and then gets mixed with Nitrogen containing stream 240 through mixing route alternative 2 producing an ammonia synthesis gas stream 230a. Mixing of Nitrogen containing stream 240 in both scenarios results in a hydrogen to nitrogen molar ratio of 3:1 in the ammonia synthesis gas stream 230a.
Ammonia synthesis gas stream 230a having hydrogen to nitrogen molar ratio of 3:1 is introduced into ammonia synthesis reactor 231, thereby producing raw ammonia stream 232.
Purge gas fuel stream 234 is divided into purge gas fuel stream 235 and purge gas recycle stream 236. Purge gas fuel stream 235 is combined with hydrocarbon fuel stream 237 and introduced as fuel into fired heater 206. Second portion 236 is combined with preheated ATR feed stream 208 to produce combined ATR feed stream 209.
Turning first to
Heated feedstock stream 346 is introduced into hydrogen desulfurization unit 302, thus producing desulfurized feed stream 303. Desulfurized feed stream 303 is combined with steam stream 304, thus forming ATR feed stream 305. ATR feed stream 305 is introduced into fired heater 306 thus producing preheated ATR feed stream 308, and flue gas stream 338. Heated ATR feed stream 308 is combined with purge gas recycle stream 336, thus forming combined ATR feed stream 309. Combined ATR feed stream 309 may then be introduced into optional pre-reformer 310, thereby optionally producing pre-reformed ATR feed stream 311. Combined ATR feed stream 309, or optional pre-reformed ATR feed stream 311, is then introduced into ATR 312 along with oxygen containing stream 314, thereby forming raw syngas stream 315.
Raw syngas stream 315 is then introduced into first heat exchanger 320, thereby producing further first cooled shifted syngas stream 326. The cooling for first heat exchanger 320, as indicated by heat transfer lines 321 and 322, may come from various internal sources, as discussed in detail below. Further cooled raw syngas stream 326 is introduced into water-gas shift reactor 316, thereby producing shifted syngas stream 317. Shifted syngas stream 317 is introduced into second heat exchanger 323, thereby producing cooled shifted syngas stream 327. The cooling for second heat exchanger 323, may take place by providing heat to the saturated steam stream 324 produced in the steam generating device located downstream ATR 312 and/or from steam generating device located downstream ammonia synthesis reactor 331 resulting in superheated steam stream 325.
Cooled shifted syngas stream 327 is then introduced into CO2 capture unit and hydrogen separation device or synthesis gas preparation device 329. CO2 capture unit and hydrogen separation device or synthesis gas preparation device 329 produces hydrogen-rich stream or ammonia synthesis gas stream 330 and purge gas stream 334. Nitrogen containing stream 340 may be added through mixing route alternative 1 to CO2 capture unit and synthesis gas preparation device 329 producing an ammonia synthesis gas stream 330/330a.
Alternatively, CO2 capture unit and hydrogen separation device 329 may generate a hydrogen-rich stream (>90 mole % H2) 330 and then gets mixed with Nitrogen containing stream 340 through mixing route alternative 2 producing an ammonia synthesis gas stream 330a. Mixing of Nitrogen containing stream 340 in both scenarios results in a hydrogen to nitrogen molar ratio of 3:1 in the ammonia synthesis gas stream 330a.
Ammonia synthesis gas stream 330a having hydrogen to nitrogen molar ratio of 3:1 is introduced into ammonia synthesis reactor 331, thereby producing raw ammonia stream 332.
Purge gas fuel stream 334 is divided into purge gas fuel stream 335 and purge gas recycle stream 336. Purge gas fuel stream 335 is combined with hydrocarbon fuel stream 337 and introduced as fuel into fired heater 306. Second portion 336 is combined with preheated ATR feed stream 308 to produce combined ATR feed stream 309.
Turning
Heated feedstock stream 346 is introduced into hydrogen desulfurization unit 302, thus producing desulfurized feed stream 303. Desulfurized feed stream 303 is combined with steam stream 304, thus forming ATR feed stream 305. ATR feed stream 305 is introduced into fired heater 306 thus producing preheated ATR feed stream 308, and flue gas stream 338. Heated ATR feed stream 308 is combined with purge gas recycle stream 336, thus forming combined ATR feed stream 309. Combined ATR feed stream 309 may then be introduced into optional pre-reformer 310, thereby optionally producing pre-reformed ATR feed stream 311. Combined ATR feed stream 309, or optional pre-reformed ATR feed stream 311, is then introduced into ATR 312 along with oxygen containing stream 314, thereby forming raw syngas stream 315.
Raw syngas stream 315 is then introduced into first heat exchanger 320, thereby producing further first cooled shifted syngas stream 326.
Further cooled raw syngas stream 326 is introduced into water-gas shift reactor 316, thereby producing shifted syngas stream 317. Shifted syngas stream 317 is introduced into second heat exchanger 323, thereby producing cooled shifted syngas stream 327.
The inventive solution allows a high intrinsic CO2 capture rate in decarbonized ammonia production units with an overall low carbon intensity based on autothermal reforming which principally is targeted to achieve by reduction of heating demand from fired heater/heat of combustion.
The inventive solution comprises:
The inventive solution also comprises:
With these inventive steps, it is possible to achieve a very high direct CO2 capture rate without compromising the indirect capture rate, especially Scope 3 capture rate attributing to hydrocarbon feedstock consumption. As the steam superheating is executed utilizing the process heat and not by the heat of combustion, hydrocarbon fuel demand and hence carbon footprint of the plant gets significantly reduced. Apart from higher capture rate, cost of operation as well as capital investment gets minimized.
This solution distinguishes itself from others for the following reasons:
It is to be noted that to produce low carbon ammonia, the essential step is to produce a low carbon hydrogen-rich stream (>90 mole % H2) or low carbon ammonia syngas with hydrogen to nitrogen molar ratio of 3:1. Hence, all the embodiments cited may be used to produce low carbon hydrogen-rich stream (>90 mole % H2) only and utilize that hydrogen-rich stream for different usage other than ammonia production.
It will be understood that many additional changes in the details, materials, steps and arrangement of parts, which have been herein described in order to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims. Thus, the present invention is not intended to be limited to the specific embodiments in the examples given above.
This application claims the benefit of priority under 35 U.S.C. § 119 (a) and (b) to U.S. Provisional Patent Application No. 63/469,839, filed May 31, 2023, the entire contents of which are incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 63469839 | May 2023 | US |
