METHOD FOR INTEGRATING AMMONIA CRACKING IN A STEAM METHANE REFORMER

Abstract

A method for retrofitting an existing steam methane reformer (SMR) for ammonia cracking is provided. In this embodiment, the existing SMR can include a pre-reformer, a desulfurization unit, a furnace, waste heat recovery sections, a water gas shift reactor, a pressure swing adsorption (PSA) unit, wherein the furnace has a plurality of SMR tubes and a plurality of burners. In certain embodiments, the method can include the steps of: providing the existing SMR; taking the desulfurization unit offline such that no fluid flows through the desulfurization during operation; taking the pre-reformer offline such that no fluid flows through the pre-reformer during operation; and adding means for providing a gaseous ammonia stream to the SMR tubes.

Claims

1. A method for producing hydrogen in an existing steam methane reformer (SMR) via ammonia cracking, the SMR comprising a furnace and a pressure swing adsorption (PSA) unit, wherein the furnace has a plurality of SMR tubes and a plurality of burners, the method comprising the steps of: (a) providing a gaseous stream consisting essentially of ammonia at a temperature of at least 100? C.; (b) introducing the gaseous stream into the SMR tubes of the furnace under conditions effective for catalytically cracking the ammonia, thereby forming a crude stream comprising hydrogen, nitrogen, and unreacted ammonia; and (c) introducing the crude stream into the PSA unit to produce a hydrogen product stream and a PSA offgas.

2. The method as claimed in claim 1, wherein the existing SMR is revamped to further comprise an ammonia storage vessel and an ammonia feed pump.

3. The method as claimed in claim 2, wherein step (a) further comprises withdrawing ammonia from the ammonia storage vessel; pumping the ammonia in the ammonia feed pump to a pressure of 25-60 bar (g); and then vaporizing the ammonia to provide the gaseous stream.

4. The method as claimed in claim 3, wherein the existing SMR is revamped to further comprise an ammonia vaporizer, wherein the ammonia is vaporized in the ammonia vaporizer to form the gaseous stream, wherein the gaseous stream in step (a) is tied into feed piping or a feed distribution system of the existing SMR, wherein the feed piping and feed distribution system are located immediately upstream the SMR tubes.

5. The method as claimed in claim 3, wherein the existing SMR is revamped to further comprise new equipment selected from the group consisting of an ammonia vaporizer, an ammonia interchanger, an ammonia preheater, an ammonia pre-reactor, and combinations thereof, wherein the new equipment is disposed upstream of the SMR tubes and downstream the ammonia feed pump.

6. The method as claimed in claim 3, wherein the existing SMR comprises an existing feed superheating section that is located upstream of the SMR tubes, wherein the ammonia is vaporized in the existing feed superheating section.

7. The method as claimed in claim 3, wherein the ammonia is vaporized using heat provided by electricity, steam, the crude stream, and/or a flue gas stream.

8. The method as claimed in claim 3, wherein the ammonia is vaporized and preheated to below 450? C., preferably below 350? C., more preferably below 300? C.

9. The method as claimed in claim 1, wherein the crude stream contains less than 5.0 mol % unreacted ammonia

10. The method as claimed in claim 1, wherein the conditions effective for catalytically cracking the ammonia include a pressure between 15-80 bar, preferably 20-60 bar, and a temperature between 600-850? C., preferably 650-750? C.

11. The method as claimed in claim 1, wherein gaseous stream in step (a) is provided from a pressurized gaseous ammonia feed received from outside of the existing SMR.

12. A method for retrofitting an existing steam methane reformer (SMR) for ammonia cracking, the existing SMR comprising a pre-reformer, a desulfurization unit, a furnace, waste heat recovery sections, a water gas shift reactor, a pressure swing adsorption (PSA) unit, wherein the furnace has a plurality of SMR tubes and a plurality of burners, the method comprising the steps of: (a) providing the existing SMR; (b) taking the desulfurization unit offline such that no fluid flows through the desulfurization during operation; (c) taking the pre-reformer offline such that no fluid flows through the pre-reformer during operation; and (d) adding means for providing a gaseous ammonia stream to the SMR tubes.

13. The method as claimed in claim 12, wherein the means for providing the gaseous ammonia stream comprise an ammonia storage vessel, an ammonia feed pump, and means for vaporizing ammonia sourced from the ammonia storage vessel.

14. The method as claimed in claim 13, wherein the means for vaporizing ammonia further comprise new equipment selected from the group consisting of an ammonia vaporizer, an ammonia interchanger, an ammonia preheater, an ammonia pre-reactor, and combinations thereof, wherein the new equipment is disposed upstream of the SMR tubes and downstream ammonia feed pump.

15. The method as claimed in claim 13, wherein the means for vaporizing ammonia further comprise an existing feed superheating section that is located upstream of the SMR tubes, wherein the existing feed superheating section is revamped by treating inner surfaces of the existing feed superheating section to improve nitridation resistance.

16. The method as claimed in claim 13, wherein the step of treating the inner surfaces of the existing feed superheating section includes a process selected from the group consisting of (1) applying a protective liner material that is mechanically coupled to the inner surface, (2) applying an aluminization layer to the inner surface, and (3) applying a diffusion barrier layer in conjunction with the aluminization layer, wherein the diffusion barrier layer is disposed between the inner surface and the aluminization layer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0048] These and other features, aspects, and advantages of the present invention will become better understood with regard to the following description, claims, and accompanying drawings. It is to be noted, however, that the drawings illustrate only several embodiments of the invention and are therefore not to be considered limiting of the invention's scope as it can admit to other equally effective embodiments.

[0049] FIG. 1 provides an embodiment of a steam methane reformer facility in accordance with an embodiment of the prior art.

[0050] FIG. 2 provides a simplified schematic representation of an overall scheme for catalytic cracking of ammonia to produce hydrogen in accordance with an embodiment of the present invention.

[0051] FIG. 3 provides an embodiment of the present invention.

[0052] FIG. 4 provides equipment layouts for an embodiment of the present invention.

[0053] FIG. 5 provides another embodiment of the present invention.

[0054] FIG. 6 provides another embodiment of the present invention.

[0055] FIG. 7 provides another embodiment of the present invention.

[0056] FIG. 8 provides another embodiment of the present invention.

[0057] FIG. 9 provides another embodiment of the present invention.

[0058] FIG. 10 provides another embodiment of the present invention.

DETAILED DESCRIPTION

[0059] While the invention will be described in connection with several embodiments, it will be understood that it is not intended to limit the invention to those embodiments. On the contrary, it is intended to cover all the alternatives, modifications and equivalence as may be included within the spirit and scope of the invention defined by the appended claims.

[0060] 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.

[0061] While decarbonization of NG-based H.sub.2 production is neither simple nor straight forward for the above-mentioned reasons, it is preferred to operate with a full decarbonization of existing plants based on a replacement of fossil feedstocks by ammonia. Ammonia itself can be produced from various sources and it can be easily transported worldwide by ship, pipeline or truck. It does not contain any carbon atoms. Therefore using it within an SMR yields an intrinsic complete decarbonization of the process. However, a replacement of methane by NH.sub.3 is not straightforward, but instead the process requires modifications in order to run safely and reliably. The use of NH.sub.3 has several significant advantages compared to NG-based SMR and newly built NH.sub.3 crackers: [0062] CO.sub.2 emissions are fully or partly eliminated from the plant. [0063] No additional infrastructure for CCS, e.g. CC unit, steam supply, CO.sub.2 storage, CO.sub.2 pipelines, tanks, CO.sub.2 ships, sequestration site etc. are needed at the location of hydrogen use. [0064] No additional legislation is needed, since NH.sub.3 already is traded worldwide, and therefore its production and shipping are well known. [0065] Existing SMR assets can be utilized, which saves investment costs and allows a faster rollout compared to new greenfield plants. [0066] In existing basins, the existing infrastructure and connections to customers can be used. [0067] In the emerging markets, H.sub.2 is typically used in new applications that normally don't require steam. If NH.sub.3 is used in SMR, the production of steam as byproduct is reduced due to the lower required heat duty of the NH.sub.3 splitting reaction. This is beneficial and increases the overall efficiency of the plant compared to one being tailored to high steam export. [0068] Broader operation range of the plant due to mitigation of the typical challenges in SMR, i.e. coking and metal dusting corrosion.

[0069] In principle, methane and NH.sub.3 have some similarities and some differences. Ammonia can be decomposed into N.sub.2 and H.sub.2 in an endothermic reaction (see Reaction Formulas below). The same is valid for methane. However, here the splitting products are carbon and H.sub.2. The production of solid C leads to challenges (clogging, fouling, solids handling). Therefore methane is normally converted within a reforming reaction, i.e. including water as a reagent in order to suppress carbon formation. NH.sub.3 splitting with this respect is much easier and does not require steam addition.

##STR00001##

[0070] In a modified SMR process with 100% NH.sub.3 feed, a few process parts are no longer needed, e.g. the desulfurization, pre-reformer, water gas shift section and condensate systems (refer to scheme).

[0071] This leads to reduced OPEX and higher reliability since the respective catalyst-containing vessel can be bypassed and therefore don't need regular monitoring or catalyst replacement. This also can reduce overall pressure drops within the system.

[0072] On the other hand, the process can include a few additional units for NH.sub.3 handling. Some non-limiting examples may include NH.sub.3 storage, a feed supply (pump+vaporizer) and optionally an additional water scrubbing downstream the reactor.

[0073] The ammonia cracking reaction requires much less heat per hydrogen molecule than the steam methane reforming reaction. For the case of 100% ammonia as feedstock no process steam is required, because carbon formation of hydrocarbons at too high temperature or heat flux or because of lack of process steam is not an issue anymore. This reduces the required process heat further or alternatively allows to convert more ammonia to hydrogen and increase the hydrogen output of the existing unit.

[0074] In a standard steam reforming process, the addition of process steam provides significant waste heat on the process and firing side, both leading to a reduced thermal efficiency of the plant. Process steam is cooled and condensed in the syngas cooling train preheating the feedstock and other process streams.

[0075] In case of 100% ammonia feedstock, elimination and minimization of process steam is desired to maximize the thermal efficiency to maximize the hydrogen product to ammonia feed ratio. As a result, much less waste heat is available on the process side of the unit, which is insufficient for preheating and vaporizing the ammonia feedstock.

[0076] At the same time, less firing heat is required for cracking ammonia, so waste heat contained in the flue gas is less and is available only at lower temperatures

[0077] A flow scheme for purely NH.sub.3-based H.sub.2 production is shown in FIG. 1. Ammonia is stored in a suitable storage vessel 1, preferably either as refrigerated fluid at ?33? C. and ambient pressure or at elevated pressure and ambient temperature. The liquid NH.sub.3 feed is moved by means of a liquid pump 3 against the system pressure (5-40 bar) into the SMR system, where it is bypassing potentially existing feed-pretreatment units 20, 40 (hydrogenation, H.sub.2S adsorption, pre-reforming), preheated in the NH.sub.3 preheating section 10, 30 where NH.sub.3 is vaporized and heated to suitable inlet conditions of 300-650? C. A part of the NH.sub.3 stream may be used as fuel 45 in the SMR furnace 50 if the heating value of the waste gases from the PSA is not sufficient for heating the reaction. In addition, a part of the H.sub.2 or the Syngas stream can be used as fuel as well in order to debottleneck the existing heat exchangers. The preheating can be done using a hot stream within the waste heat recovery section 10, 30, 90. For example, flue gas 54 can provide the heat energy for waste heat recovery section 30. While this feature is not shown in an effort to not further complicate the figures, the invention should not be so limited to what is show explicitly in the figures.

[0078] The preheated NH.sub.3 feed 43 is directed into the SMR reactor 50, i.e. setup with a multitude of tubular reactors situated within a heated furnace. The tubes can be filled with standard reforming catalysts, e.g., based on Ni on Al.sub.2O.sub.3. In certain embodiments, the catalyst may be replaced by more active catalyst systems, especially for debottlenecking purposes. Within the SMR tubes, the NH.sub.3 feed is converted into the product mixture at temperatures of 500-900? C. The gas mixture 53 comprises N.sub.2 and H.sub.2 as well as traces of unconverted NH.sub.3 (e.g., up to about 5 vol %). The heat required for this reaction is provided indirectly through the SMR tube wall from the combustion in the firebox. The hot gas mixture 53 is cooled down in successive heat exchangers 10 and within the process gas boiler 90 by means of water vaporization. This generates steam as byproduct. The steam production can be adjusted by adjusting the load to the SMR firebox. For this purpose, additional NH.sub.3 may need to be combusted.

[0079] In the embodiment shown, the gas mixture 53 bypasses the existing water gas shift reactor 60 and is cooled down in a series of waste heat recovery sections. Following the cooling, condensate 96 is removed from the cooled gas mixture 95 with the resulting dry gas mixture 101 being then sent to a water wash column that is configured to remove unreacted ammonia gas from the dry gas mixture by using pressurized water 84, preferably sourced from the boiler feed water 70. In one embodiment, the treatment section 102 can is a dedicated vessel that would be added to the existing SMR system.

[0080] In one embodiment, the treatment section can include a wash column placed in the existing syngas cooling section between the BFW Preheater outlet and the PSA inlet, i.e., below the dew point of the process gas 101, preferably between the final cooler and the PSA inlet. High pressure boiler feed water 84 from the existing units 70 will preferably be used for water dosing.

[0081] The treatment section can be designed for an inlet ammonia content in the range 0.2 to 5 mol %. As ammonia is very soluble in water, the water wash column can be designed and will reduce the remaining ammonia content in the feed to the PSA to a level below 100 ppm, preferably below 20 ppm and allow feeding the hydrogen and nitrogen mixture to the existing PSA.

[0082] The product gas 103 is sent to the pressure swing adsorption (PSA), where the H.sub.2 is purified to typically >99.5% purity. The residual gas stream (off-gas) contains H.sub.2, N.sub.2 and NH.sub.3. Wash column effluent stream 104 is withdrawn from the water wash column. In an optional embodiment, at least a portion 88 can be combined with the flue gas 54 of the SMR reactor 50

[0083] In an embodiment not shown, the off-gas stream from the PSA can be sent to the burners of the SMR in order to provide the heat required for the NH.sub.3 decomposition reaction. The presence of a mixture of H.sub.2 and NH.sub.3 as combustible components is beneficial since the fast H.sub.2 combustion and the slow NH.sub.3 combustion balance each other and allow using state-of-the-art burners. In certain embodiments, at least 14% H.sub.2 is present in the off-gas. In literature it is mentioned, that already 7-10% of H.sub.2 are sufficient to allow a smooth co-combustion of NH.sub.3 and H.sub.2. This also allows additional combustion of NH3 fuel without suffering from slow NH.sub.3 combustion.

[0084] In another embodiment not shown, the off-gas can be sent back to the SMR reactor tubes in order to more fully convert any residual ammonia, while also recovering additional residual hydrogen.

[0085] As noted in the background section, ammonia, particularly at elevated temperatures can cause embrittlement issues within the system. Certain embodiments of the present invention attempt to minimize these issues by using advantageous tie-in points for an existing SMR facility that allows for reduced CAPEX during the retrofit procedure.

[0086] FIG. 3 provides a simplified schematic representation of an embodiment of the present invention. Ammonia 22 is withdrawn from ammonia source 1 and pressurized in ammonia pump 3, preferably to a pressure of (5-40 bar) before being heating in waste heat recovery sections 30 to form preheated ammonia 42. As before, the preheated ammonia is sent to the reactor tubes of the SMR using a feed header 47 to distribute the ammonia gas 42 to all of the associated reactor tubes. Those of ordinary skill in the art will also recognize that a second header can be used to distribute the preheated ammonia 42 to the plurality of burners within the SMR as well. This feature is not shown in an effort to not overburden the figures.

[0087] In certain embodiments, the feed header is directly above the plurality of tubes, preferably within 10 meters.

[0088] Following the catalytic conversion of ammonia, the resulting mixed gas 53 is collected from the reactor tubes and then sent off for further processing. FIG. 2 provides non-limiting examples of further processing.

[0089] The flue gas 54 (i.e., the combustion product) can be redirected from the combustion chamber into the waste heat recovery section 30 (i.e., a series of heat exchangers), in which the heat is used to preheat and superheat various streams (e.g., combustion air, fuel, and feed). The untreated flue gas, which can contain NOx, can optionally be sent to flue gas treatment section 5 to form treated flue gas. In certain embodiments, the treatment section 5 can include a DeNOx unit and/or a selective catalytic reformer (SCR). Ammonia 99 can be used in both the DeNOx unit and the SCR.

[0090] Lines 25 and 35 represent appropriate tie in points that are in conformance with certain embodiments of the invention. Both tie-in points 25, 35 allow for bypassing most of the existing units (e.g., desulfurizer 20, pre-reformer 40), which thus greatly reduces potential embrittlement issues.

[0091] First tie-in point 25 can be located upstream of the first or second superheater coils that are part of the waste heat recovery section 30. The second tie-in point 35 can be located at, or just upstream the feed cross header 47. By using either one of these tie-in points, very little piping or equipment will need to be revamped using appropriate surface treatments.

[0092] In an additional embodiment, the pressure and temperature in the reactor tubes can be chosen that downstream of the reactor tubes, the ammonia content in mixed gas 53 is less than 2.5 mol %, which greatly reduces the risk of nitride formation and embrittlement issues for the downstream equipment. Suitable pressures can be 15-40 bar (a), preferably 20-35 bar (a), while suitable temperatures can be 600-850? C., preferably 650-750? C.

[0093] In light of the above, in certain embodiments of the present invention, in order to retrofit an existing SMR, additional equipment such as an ammonia hold-up vessel or tank and ammonia feed pump can be included. This is particularly true in the event that the ammonia feed can be provided at sufficient pressures and in vaporized form. In the event tie-in point 35 is used, it is preferable to heat the ammonia stream at a point between the ammonia pump and the feed header 47.

[0094] FIG. 4 provides a schematic representation of additional equipment that can be included with the revamped SMR facility. This embodiment can include ammonia hold-up vessel 710, ammonia feed pump 3, ammonia pre-heater 715, ammonia interchanger 725, ammonia vaporizer 730, and pre-reactor 740.

[0095] The ammonia vaporizer 730 and preheater 715 can be electrically heated, steam heated or heated by a process stream downstream of the existing process gas boiler or heated by the flue gas stream downstream of the existing flue gas boiler. The temperature range of the hot medium for the preheating/vaporizing step can be below 400? C., preferably below 300? C. The ammonia interchanger 730 and/or pre-reactor 740 can be arranged as shown in FIG. 4.

[0096] In the embodiment shown, first portion of liquid ammonia 702 is introduced into ammonia hold-up vessel 710, before being sent to a DeNox unit via line 714. Second portion of liquid ammonia 704 is compressed in ammonia feed pump 3. Following compression, the compressed liquid ammonia can then be tied into the retroffited SMR plant via tie-in point 25 via line 713, or to tie-in point 35. As tie-in point 25 is upstream of the existing heaters, the pressurized liquid ammonia 713 does not separate means of heating from ammonia pre-heater 715, ammonia interchanger 725, or ammonia vaporizer 730.

[0097] In certain embodiments in which tie-in point 35 is desired (e.g., immediately upstream the SMR tubes), then the compressed liquid ammonia 712 can be heated in ammonia pre-heater 715, ammonia interchanger 725, and then vaporized in ammonia vaporizer 730 before undergoing a pre-reaction conversion in ammonia pre-reactor 740. The resulting pre-reacted ammonia stream 742 is used to provide pre-heating energy in ammonia interchanger 725, before being sent to tie-in point 35 via line 744.

[0098] Notwithstanding the above, those of ordinary skill in the art will recognize that the equipment shown in FIG. 4 is not required in certain embodiments of the invention. Specifically, all of the additional equipment can be omitted if the ammonia is supplied pressurized and in vapor form, which means that the process steps of pressurization and vaporization occur outside of the battery limits of the existing unit.

[0099] In certain embodiments, a nitridation protective layer can be applied to certain pieces of equipment. The nitridation protective layer can be selected from the group consisting of a protective liner material that is mechanically coupled to the inner surface, an aluminization layer applied to the inner surface, a diffusion barrier layer in conjunction with the aluminization layer applied to the inner surface, wherein the diffusion barrier layer is disposed between the inner surface and the aluminization layer, and a weld-overlay applied to the inner surface. A more detailed discussion of acceptable nitridation protective layers can be found in co-pending U.S. application Ser. No. 17/896,026, filed on Aug. 25, 2022, which is incorporated by reference in its entirety.

[0100] Cracking ammonia in an existing SMR poses several challenges: [0101] 1) the lower heating value of ammonia (18.6 MJ/kg) relative to natural gas (42-55 MJ/kg), that would result in considerably higher fuel and air flow rates in the furnace for a given duty; [0102] 2) the existing heat exchangers might not have the required heat exchange surface; [0103] 3) as reported in various studies, a temperature higher than 500? C. is required for catalytic NH.sub.3 decomposition (Wang et al., Ammonia as hydrogen carrier for transportation; investigation of the ammonia exhaust gas fuel reforming, p. 9908). It is thus desirable to reach this T at the inlet to the reformer/cracker. The switch from steam methane reforming to NH.sub.3 cracking entails lower duties and temperatures, and upends the heat integration, with the consequence that it can be challenging to reach this T threshold; [0104] 4) undesirable nitride formation is much more prevalent above temperatures of 600? C. In the high temperatures in an SMR reformer (typically more than 850? C. at the outlet) nitridation could become a major issue; [0105] 5) non-optimized layout of existing equipment could lead to over-consumption of ammonia; and [0106] 6) discrepancy between the SMR being optimized with respect to H.sub.2 and steam production and the NH.sub.3 cracking system that actually could be operated fully without steam.

[0107] The aforementioned challenges can be overcome by various alternative embodiments of the present invention. For example,

[0108] In one embodiment having a cracking T of 800? C., a part of the H.sub.2 production can be used as fuel (H.sub.2 fueling), so as to meet the original design flow rates in the furnace and flue gas system, and achieve a better fit with the existing heat exchangers (problems 1 and 2).

[0109] H.sub.2 fueling alone is insufficient, however, since reaching a T of at least 500? C. at the cracker inlet is difficult. To overcome this issue, an additional one or more heat exchangers can be added. In certain embodiments, the first heat exchanger is installed on the converted H.sub.2 upstream of the PSA, to make use of low grade heat (?140? C.) to vaporize the ammonia and simultaneously use liquid ammonia as a low temperature cooling medium for the final raw H.sub.2 cooling. This low grade heat is traditionally considered to be waste heat on an SMR. (problem 3)

[0110] Optionally, a second heat exchanger can be installed on one of the SMR steam systems, either directly downstream of an existing boiler, or downstream of a steam superheater. This second heat exchanger allows for optimizing of the heat integration on the SMR without perturbing the main process, resulting in an overall reduced NH.sub.3 consumption (problem 5).

[0111] The use of H.sub.2 as the main fuel is more challenging than natural gas combustion, but is in general well understood, in part due to the experience of the use of PSA off-gas as fuel in SMRs. In contrast to NH.sub.3 combustion, which is challenging due to its low flame speed, H.sub.2 combustion is not as critical in this respect since its combustion is much faster than for natural gas or NH.sub.3.

[0112] In another embodiment having a cracking T of 600? C., a similar configuration proves to be advantageous: a limited amount of H.sub.2 fueling allows for matching of the existing heat exchanger setup and to reduce the duty and space velocity in the NH.sub.3 cracker correspondingly; and the addition of a heat exchanger on the raw H.sub.2 upstream of the PSA, and a heat exchanger on the steam system allows us to reach the required cracker inlet T of 500? C. (problem 3), while reducing the ammonia consumption by 5-10% (problem 5).

[0113] In this embodiment, H.sub.2 is co-combusted with NH.sub.3 (roughly 50:50 by LHV), yielding a fuel mixture with combustion properties that are easier to handle than pure H.sub.2 or pure NH.sub.3 combustion. Moreover, the risks of nitridation-induced material degradation are reduced significantly at this lower cracking T (problem 4)

[0114] Finally, as an advantage of these aforementioned embodiments, the volume flow rates on the process line are lower than with an SMR. In the event that green ammonia is being used, and that the existing plant is connected to an H.sub.2 pipeline, the green H.sub.2 production could be increased beyond what was possible with steam methane reforming, and another SMR on the same pipeline could reduce its production, thereby improving the overall carbon intensity of the H.sub.2 on the pipeline.

[0115] The reference case of the SMR, Case 1a, is described in FIG. 5. The process natural gas 100 is pre-heated in heat exchanger 150, is desulfurized in 151, mixed with steam 103 before being heated to ?650? C. in the reformer feed pre-heater 152. The steam methane reforming reaction takes place in catalyst filled tubes of the reformer 153, at an outlet reforming temperature of 850-900? C. The hot syngas is used to vaporize steam in the process gas boiler 154/169, before being sent to a water gas shift reactor 155. The shifted syngas 107 is used to pre-heat the natural gas in 156/150, and is subsequently cooled in the boiler feed water heater 157/168 to a temperature of ?110? C. The syngas 109 is then cooled by air coolers and a final cooler in the heat exchange apparatus 158, before being sent to the PSA, from which an H.sub.2 stream with high purity (99.9%) 111 is recovered.

[0116] The PSA off-gas 112, composed of CO.sub.2, H.sub.2, as well as unreacted CO & CH.sub.4 is sent to the burners of the reformer furnace 162, where it is mixed and combusted with natural gas fuel 113, and hot combustion air 116. Part of the heat generated in the furnace is used in the endothermic reforming reaction in 153. The remaining heat in the flue gas 117 is then successively used to heat the reformer feed in 163/152, superheat steam in 164/170, heat the combustion air in 165/161, generate steam in the flue gas boiler 166/169, and pre-heat the combustion air in 167/160

[0117] In this specific SMR, for the sake of simplification, we consider a common steam system for the process gas and flue gas. The boiler feed water 123 is pre-heated by shifted syngas in 168, vaporized in the boiler 169 by the process gas 105 and flue gas 119, and superheated in 170 by the shifted syngas 108. The required amount of steam 127 is then mixed with the process natural gas 102, and the remaining steam 126 is exported as a co-product.

[0118] In Case 1b, which is shown in FIG. 6, NH.sub.3 is used as the process feedstock 200 and as the fuel 211. The desulfurizer 151 and water gas shift reactor 155 are no longer needed and therefore bypassed. A small amount of the steam generated may be used as process steam 225/202, to mitigate the risks or nitridation-induced corrosion downstream in the process. For the rest, the heat exchanger arrangement is similar to that of Case 1a.

[0119] The H.sub.2 production matches that of the SMR base case, and the steam production is similar to that of the base case, with the exception that here nearly all the steam produced is exported. The fit with the existing SMR is quite poor, however (see Table 1). Owing to the low LHV of NH.sub.3 as fuel compared to NG, the molar flow rate of NH.sub.3 is considerably higher, with the consequence that the combustion air flow rate and flue gas volume flow rate at the reformer outlet have increased by a factor of 2.5 and 2.4 respectively. The required heat exchange surfaces have more than doubled for heat exchangers E-F1 reformer feed heater, E-F4 hot air combustion heater, E-F5 flue gas boiler and E-F6 cold air combustion heater (Table 1).

[0120] In an alternative embodiment of Case 1c, we keep the same arrangement as in FIG. 6, but reduce the cracking temperature to 800? C., and increase the hot combustion air temperature to 480? C. in an attempt to reduce the required amount of NH.sub.3 as fuel. The increase in combustion air temperature leads to a stark drop in steam export relative to Case 1b, and the steam export flow rate is now in line with that of the base case. The molar flow rate of NH.sub.3 fuel, flue gas volume flow rate and combustion air mass flow rate drop significantly compared to Case 1b, but remain too high relative to the base case. While the required heat exchange surface now fits for E-F5 flue gas boiler, E-F1 and E-F6 remain undersized, and the fit with E-F4 has gotten worse.

[0121] In Case 1d (see FIG. 7), we keep the same setup as in Case 1b and 1c, but now divert part of the H.sub.2 product 326 to use as fuel. The combustion air and flue gas flow rate match the SMR base case much better. The hot combustion air temperature can now be reduced, with the consequence that E-F4 fits better with the base case. With the lower flue gas temperatures than on the SMR, however, E-F3 is now undersized, and in spite of a reduction in the cracker inlet T, E-F1 is also undersized. In FIG. 7, a part of the purified H.sub.2 product recovered from the PSA can be preferably sent to the fuel.

[0122] Alternatively, a similar H.sub.2 fueling effect can be obtained by taking part of the raw H.sub.2 upstream of the PSA, or modifying the PSA to degrade the H.sub.2 recovery, such that the required quantity of H.sub.2 for fuel is contained in the PSA off-gas 310. In Table 1, we provide the molar flow rate of H.sub.2 sent to the fuel (excluding the H.sub.2 molar flow rate already present in the PSA off-gas), corresponding to the setup described in FIG. 7. To account for the alternatives where the H.sub.2 contribution to the fuel is provided upstream of the PSA, or through the PSA off-gas, we also include an H.sub.2 fuel ratio in Table 1, ?H.sub.2f, defined as follows:

[00001]$\begin{array}{cc}\frac{\mathrm{sum}\mathrm{of}\mathrm{all}H2\mathrm{mole}\mathrm{flow}\mathrm{rates}\mathrm{to}\mathrm{fuel}\left(\mathrm{kmol}H2/h\right)}{H2\mathrm{mole}\mathrm{flow}\mathrm{rate}\mathrm{at}\mathrm{cracker}\mathrm{outlet}\left(\mathrm{kmol}\frac{H2}{h}\right)}& \left(1\right)\end{array}$

[0123] In Case 1e (see FIG. 8), we add a new heat exchanger 457 on the raw H.sub.2 upstream of the PSA and an extra NH.sub.3 heater 450, since what is traditionally considered to be waste heat on an SMR can now be used to vaporize the process NH.sub.3. The heat integration is further improved, the steam export increases, and E-F3 provides a better fit with the Base case. On the downside, E-F1 is still undersized, in spite of a low cracker inlet T of 400? C. At a cracker inlet T below 500? C., the kinetics of the cracking reaction could be poor in the first part of the reformer tubes, which would then effectively be used as a heat exchanger section rather than a reactor.

[0124] In Case 1f (see FIG. 9), we add another heat exchanger 571/552, which uses part of the steam production 529 to vaporize and pre-heat the NH.sub.3 feedstock further. The steam export is reduced, but the heat integration is improved significantly. The quantity of H.sub.2 required as fuel drops compared to Case 1e, and the overall NH.sub.3 consumption is reduced. The cracker inlet T has been increased beyond the threshold of 500? C., and the fit with the Base case is now satisfactory, as not a single heat exchanger is undersized.

[0125] Further, in the event of a desired increase in the H.sub.2 production capacity beyond that of the original SMR, the bottleneck on the heat exchangers would lie in E-F1. One can simply increase the duty on the new heat exchanger 571 on the steam system, however, to lower the duty on E-F1 correspondingly.

[0126] Another similar configuration is described in FIG. 10. On an SMR the flue gas at the stack (stream 122 in FIG. 5), has to be kept above the dew point of sulfuric acid to avoid corrosion, with the consequence that the flue gas is emitted at a T of ?140? C. With NH.sub.3 as feedstock and fuel this constraint would no longer be applicable, so that a heat exchanger 668/651 could be installed to make use of this low grade heat in the flue gas to vaporize the NH.sub.3 feed. The advantage here is that there would be no reduction in steam export, albeit without the flexibility provided by the heat exchanger on the steam system. In such a case, given the similar temperature levels of the raw H.sub.2 609 and flue gas 623, the heat exchangers/NH.sub.3 vaporizers 658/650 and 668/651 could be combined into a single piece of equipment.

[0127] One of the main uncertainties in the use of an existing SMR to crack NH.sub.3 would lie in the achievable flue gas temperature at the outlet of the cracker (the so-called bridge-wall temperature), which can affect the entire process heat integration and is mainly dominated by the overall heat transfer within the furnace and the SMR tubes. Cases 1g and 1h use the same setup as Case 1f, with variations in the bridge-wall temperature of ?50? C. or +50? C. respectively. As Table 1 illustrates, these variations are easily compensated by adjusting the portion of the H.sub.2 product that is used as fuel, and the rest of the key process parameters and required heat exchange surfaces are unaffected. This H.sub.2 fueling setup thus provides a robust control parameter with which to ensure the process parameters stay in acceptable ranges.

[0128] Formation of undesirable nitrides is much more prevalent above temperatures of 600? C. At cracking temperatures of 800? C., nitridation could become a major issue, requiring costly mitigation measures (e.g. as described supra). Furthermore, a high cracking temperature implies a higher duty on the reformer/cracker, and thus a higher overall consumption of NH.sub.3.

[0129] In Case 2b (see Table 2), we replicate the setup of FIG. 9, with H.sub.2 fueling, and the additional heat exchangers 558/550 on the raw H.sub.2 and 571/552 on the steam system to vaporize and pre-heat the NH3 feedstock. albeit at a cracking T of 600? C. A greater quantity of NH.sub.3 fuel is required compared to Case 1f, but the required portion of the H.sub.2 production sent to fuel drops drastically, with the consequence that the overall NH.sub.3 consumption is reduced. Once again, with this flexible setup, the requirements on the process parameters (Cracker inlet T>500? C.) and heat exchanger areas can be satisfied, in spite of the significantly lower cracking T relative to the SMR. Cases 2c and 2d, with bridge-wall temperature variations of ?50? C. and +50? C. respectively, show that once again any changes or uncertainties in the bridge-wall temperature can easily be compensated by the amount of H.sub.2 product used as fuel.

TABLE-US-00001 TABLE 1 SMR base case, and NH3 cracking cases at cracking T > 800? C. Case 1f NH3 Case 1e cracking NH3 T crck Case 1d cracking 800? C. - Case Case Case 1b Case 1c NH3 T crck H2 fueling - 1g = 1h = Case 1a NH3 NH3 cracking 800? C. - E-R4 for NH3 Case 1f Case 1f Base cracking cracking T crck H2 fueling - pre-heating - with with case - T crck T crck 800? C. - E-R4 for NH3 E-stm for NH3 lower higher SMR 850? C. 800? C. H2 fueling pre-heating pre-heating BWT BWT Products/feedstock/fuel H2 prod (Nm3/h) 100000 100000 100000 100000 100000 100000 100000 100000 Steam export (kg/h) 80541 172127 86257 87082 96023 56658 47761 68740 NG/NH3 feed (kmol/h) 1520 3517 3523 4608 4608 4254 4160 4340 NG/NH3 fuel (kmol/h) 361 1924 1131 162 162 121 125 153 NG/NH3 total (kmol/h) 1880 5441 4654 4770 4770 4375 4285 4494 Key process parameters T cracking (? C.) 900 850 800 800 800 800 800 800 dT-cracker (Bridge-wall T ? 150 150 150 150 150 150 100 200 cracking T) H2 fuel (kmol/h) 0 0 0 1615 1615 1089 948 1217 ?H2f ? as defined in (1) 12.5% 15.0% 15.0% 35.0% 35.0% 29.6% 28.0% 31.0% (in %) Cracker inlet T (? C.) 650 650 550 400 400 620 620 620 Vol flow rate at cracker inlet 17046 10104 9002 9545 9545 11821 11558 12060 (m3/h) Hot combustion air T (? C.) 380 380 480 320 320 380 380 380 Combustion air mass flow rate 224039 562627 358383 228596 228596 178223 168747 196251 (kg/h) Vol flow rate at E-F1 inlet 889932 2120976 1345699 979894 979894 791614 723665 891596 (m3/h) LHV of NG/NH3 fuel as % 45% 76% 64% 8% 8% 8% 8% 9% total LHV to furnace Heat exchanger areas (calculated) E-R1 process gas boiler (m2) 390 200 204 290 283 252 248 254 E-R3 BFW heater (m2) 360 86 103 171 161 135 134 133 E-F1 reformer/cracker feed heater (m2) E-F3 steam superheater (m2) 684 644 452 935 746 524 540 503 E-F4 hot air combustion heater (m2) E-F5 flue gas boiler (m2) 6619 15263 6802 3918 5044 5534 4987 6469 E-F6 cold air combustion heater (m2)

TABLE-US-00002 TABLE 2 SMR base case, and NH3 cracking cases at cracking T = 600? C. Case 2b NH3 cracking T crck 600? C. - H2 fueling - E-R4 for NH3 Case 2a pre-heating - Case 2c = Case 2d = Base case - E-stm for NH3 Case 2b with Case 2b with SMR pre-heating lower BWT higher BWT Products/feedstock/fuel H2 prod (Nm3/h) 100000 100000 100000 100000 Steam export (kg/h) 80541 28054 22089 36171 NG/NH3 feed (kmol/h) 1520 3603 3520 3690 NG/NH3 fuel (kmol/h) 361 456 477 450 NG/NH3 total (kmol/h) 1880 4059 3997 4140 Key process parameters T cracking (? C.) 900 600 600 600 dT-cracker (Bridge-wall T - cracking T) 150 150 100 200 H2 fuel (kmol/h) 0 150 29 276 ?H2f - as defined in (1) (in %) 12.5% 15.0% 13.0% 17.0% Cracker inlet T (? C.) 650 550 539 550 Vol flow rate at cracker inlet (m3/h) 17046 9209 8868 9431 Hot combustion air T (? C.) 380 320 320 320 Combustion air mass flow rate (kg/h) 224039 203679 199645 212360 Vol flow rate at E-F1 inlet (m3/h) 889932 696301 647789 760034 LHV of NG/NH3 fuel as % total LHV to furnace 45% 39% 44% 36% Heat exchanger areas (calculated) E-R1 process gas boiler (m2) 390 167 165 168 E-R3 BFW heater (m2) 360 124 125 121 E-F1 reformer/cracker feed heater (m2) 547 546 544 479 E-F3 steam superheater (m2) 684 515 544 486 E-F4 hot air combustion heater (m2) 865 492 537 447 E-F5 flue gas boiler (m2) 6619 5110 4699 5730 E-F6 cold air combustion heater (m2) 10623 9346 9189 9754

[0130] As used herein, immediately upstream the SMR tubes is meant to encompass a situation in which the feed distribution system is directly above the plurality of tubes, or within a maximum of 10 m above based on the pigtail length, connecting the distribution system (manifolds) with the SMR tubes.

[0131] While the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications, and variations that fall within the spirit and broad scope of the appended claims. The present invention may suitably comprise, consist or consist essentially of the elements disclosed and may be practiced in the absence of an element not disclosed. Furthermore, language referring to order, such as first and second, should be understood in an exemplary sense and not in a limiting sense. For example, it can be recognized by those skilled in the art that certain steps or devices can be combined into a single step/device.

[0132] The singular forms a, an, and the include plural referents, unless the context clearly dictates otherwise. The terms about/approximately a particular value include that particular value plus or minus 10%, unless the context clearly dictates otherwise.

[0133] Optional or optionally means that the subsequently described event or circumstances may or may not occur. The description includes instances where the event or circumstance occurs and instances where it does not occur.

[0134] Ranges may be expressed herein as from about one particular value, and/or to about another particular value. When such a range is expressed, it is to be understood that another embodiment is from the one particular value and/or to the other particular value, along with all combinations within said range.