Heat exchange ammonia cracker for ammonia cracking

Abstract

The present invention relates to a combined heat exchange and ammonia cracker system said combined cracker system comprising a heat exchange ammonia cracker arranged in parallel or series with a primary ammonia cracker. At least a portion of the cracked stream from the primary ammonia cracker is fed as heat supply to the heat exchange ammonia cracker. A process for cracking a first feed comprising ammonia is also provided.

Description

[0001] HEAT EXCHANGE AMMONIA CRACKER FOR AMMONIA CRACKING

[0002] TECHNICAL FIELD

[0003] The present invention relates to a combined heat exchange and ammonia cracker system said combined cracker system comprising a heat exchange ammonia cracker arranged in parallel or series with a primary ammonia cracker. At least a portion of the cracked stream from the primary ammonia cracker is fed as heat supply to the heat exchange ammonia cracker.

[0004] BACKGROUND

[0005] Liquid ammonia is an important source of hydrogen because it is an important energy carrier, for instance in situations or locations having limited hydrocarbon fuel sources. The advantage of ammonia as energy carrier is that liquid ammonia is easier to transport and to store than for instance natural gas or hydrogen gas. Additionally, storing energy in ammonia is less expensive than e.g . in hydrogen or batteries.

[0006] Ammonia cracking involves the catalyst-promoted conversion of ammonia to hydrogen. An ammonia cracker is a catalytic cracking furnace in which the ammonia synthesis reaction is reversed at elevated temperatures. The resulting cracked gas consists mainly of hydrogen and nitrogen. After a subsequent separation step, purified hydrogen is obtained .

[0007] The cracked ammonia can be fed to a gas turbine or hydrogen can be recovered for fuel cells or other use. All tubular reformer crackers have a maximum size and this limits the possible cracking capacity.

[0008] It is an object of embodiments of the invention to provide better utilization of waste heat from a primary ammonia cracker and lower fuel consumption. Another object is to enable the use of a smaller main ammonia cracker.

[0009] SUMMARY

[0010] It has been found that, by utilizing the cracked gas outlet from the primary ammonia cracker (which typically has a temperature of 700°C - 900°C) as heat source in a heat exchange ammonia cracker, the heat exchange ammonia cracker will carry out part of the cracking process, and thereby lighten the load on the primary ammonia cracker resulting in a larger maximum possible capacity. The heat exchange ammonia cracker will - at the same time - simplify the process, enabling lower CAPEX and OPEX.

[0011] So, in a first aspect a combined heat exchange and ammonia cracker system is provided. The combined cracker system comprises: a first feed comprising ammonia, a heat exchange ammonia cracker (HEAC) arranged to receive at least a portion of the first feed and to output a first cracked stream, a primary ammonia cracker arranged to receive at least a portion of said first feed and / or at least a portion of the first cracked stream, and output a second cracked stream and wherein, at least a portion of the second cracked stream from the primary ammonia cracker is fed as heat supply to the heat exchange ammonia cracker.

[0012] A process is also described for cracking a first feed comprising ammonia, in the system provided herein.

[0013] Further details of the technology are provided in the enclosed dependent claims, figures and examples.

[0014] LEGENDS

[0015] The invention is illustrated by means of the following schematic illustrations, in which:

[0016] Fig. 1 shows a series arrangement of heat exchange ammonia cracker 10 and primary ammonia cracker 20, in which the primary ammonia cracker is arranged to receive at least a portion of the first cracked stream from the HEAC.

[0017] Fig. 2 shows a parallel arrangement of heat exchange ammonia cracker 10 and primary ammonia cracker 20, in which the primary ammonia cracker is arranged to receive at least a portion of said first feed.

[0018] DETAILED DISCLOSURE combined heat exchange and ammonia cracker system is provided, as illustrated generally in Figures 1 and 2. Generally, the system converts a feed comprising ammonia, and optionally steam, to a cracked stream comprising hydrogen and nitrogen. The cracked stream may be further purified to provide a hydrogen-rich product stream.

[0019] According to the invention, the cracker system comprises a heat exchange ammonia cracker and a primary ammonia cracker. The heat exchange ammonia cracker may be arranged in parallel or series with the primary ammonia cracker, although a series arrangement is more preferred.

[0020] First Feed

[0021] The first feed comprises ammonia. Suitably, the first feed comprises at least 50% v / v ammonia, more preferably at least 75% ammonia, more preferably at least 90% v / v ammonia. The first feed is gaseous.

[0022] The first feed may additionally comprise steam. The presence of steam decreases the catalyst activity. Suitably first feed comprises 0.2 - 0.5 wt% steam.

[0023] The first feed is suitably supplied at a temperature of between 400-700 °C, and a pressure between 10-60 bar.

[0024] At least a portion of the first feed is arranged to be fed to the inlet of the heat exchange ammonia cracker. Optionally, a first portion of the first feed is arranged to be fed to the inlet of the heat exchange ammonia cracker, and a second portion of the first feed is arranged to be fed to the inlet of the primary ammonia cracker.

[0025] In the "parallel" embodiment, in which at least a portion of the first cracked stream is fed to the primary ammonia cracker, a portion of the first feed may be combined with the first cracked stream, upstream the inlet of the primary ammonia cracker.

[0026] Second feed

[0027] A second feed may be optionally present. If present, this feed may be arranged to be fed to the inlet of the primary ammonia cracker or the inlet of the heat exchange ammonia cracker. In one aspect, the second feed has the same composition, the same temperature and / or the same pressure as the first feed. In other aspects, the second feed may comprise more steam, or less steam than the first feed. The second feed may also contain recycled H2 or an H2-rich mixture of H2 / N2, also recycled. The presence of H2 decreases the nitriding potential and thereby the demand on the materials of construction The second feed is gaseous. The second feed may - in some embodiments - be mixed with the first feed, and the combined feeds may be fed to the inlet of the primary ammonia cracker or the inlet of the heat exchange ammonia cracker.

[0028] The second feed is suitably supplied at a temperature of between 400-700 °C, and a pressure between 10-60 bar.

[0029] Heat exchange ammonia cracker, HEAC

[0030] As set out above, the heat exchange ammonia cracker is arranged to receive at least a portion of the first feed and to output a first cracked stream.

[0031] The first cracked stream is gaseous. Typically, the first cracked stream has the following composition NH3: 70 - 50 vol%, H2 and N2 according to stoichiometry. Water less than 0.5 vol.%

[0032] The first cracked stream is suitably outputted at a temperature of between 500-700 °C, and a pressure between 10-60 bar.

[0033] The heat exchange ammonia cracker comprises an ammonia cracking catalyst, over which the first feed is converted into a first cracked stream. The cracking catalyst of the HEAC may be the same active metal catalyst which is present in the primary ammonia cracker or a different active metal catalyst.

[0034] The heat exchange ammonia cracker suitably operates in the temperature range 400-700°C in the presence of an ammonia decomposition catalyst, such as any of: a Fe, Co, Ru or Ni based catalyst, preferably a Ni-based catalyst, a bimetallic Ni-containing catalyst, or an alloy of Fe, Co, Ru or Ni, preferably an alloy of Fe with Ni and / or Co.

[0035] In one aspect, the heat exchange ammonia cracker is a shell-and-tube heat exchanger, in which reactor tube(s) comprise an ammonia cracking catalyst and is / are arranged to receive at least a portion of the first feed at a first end of said reactor tube(s) and to output a first cracked stream from a second end of said reactor tube(s). A shell is arranged to receive at least a portion of the second cracked stream from the primary ammonia cracker and to output a cooled second cracked stream, and wherein heat exchange takes place from said shell to said reactor tube(s). The heat exchange ammonia cracker may be using bayonet type tubes for cracking the first feed, wherein the first cracked feed will deliver part of its sensitive heat to the cracking process before leaving the HEAC reactor.

[0036] As an alternative, the catalyst might be loaded in between the tubes and the cooling gas fed through the tubes. This solution can only be used for parallel arrangement. Shell-and-tube reactors provide effective heat transfer between gases.

[0037] In one aspect, the heat exchange ammonia cracker is arranged to receive heat from the portion of the second cracked stream from the primary ammonia cracker and to output a cooled second cracked stream.

[0038] Primary Ammonia Cracker

[0039] The primary ammonia cracker is arranged to receive at least a portion of said first feed (in the parallel layout) and / or at least a portion of the first cracked stream (in the series layout), and output a second cracked stream.

[0040] Of the two layouts, the series layout is preferred, i.e., wherein the primary ammonia cracker is arranged to receive at least a portion of the first cracked stream from the heat exchange ammonia cracker.

[0041] The ammonia cracking reactor may be a reactor comprising one or more catalyst-filled tubes. The catalytic fixed-bed and catalyst-filled tubes contain a catalyst active in ammonia cracking. The catalyst is suitably an ammonia decomposition catalyst. Hence, the ammonia cracking reactor suitably operates in the temperature range 300-900°C in the presence of an ammonia decomposition catalyst, such as any of: Fe, Co, Ru or Ni based catalyst, preferably a Fe-based catalyst.

[0042] In an embodiment, the ammonia cracking reactor operates in the temperature range 450- 900°C, for instance 650-800°C, 550-675°C or 600-750°C.

[0043] The primary ammonia cracker may be selected from an electrical ammonia cracker, a fired ammonia cracker, or an autothermal ammonia cracker, preferably an electrical or a fired ammonia cracker. When an autothermal ammonia cracker is used, a feed comprising oxygen is required. The primary ammonia cracker may be a fired heated reactor comprising one or more catalyst-filled tubes. This reactor is the same as a tubular reformer i.e. conventional steam methane reformer (SMR), where the heat for catalytic dissociation of ammonia is transferred chiefly by radiation in a radiant furnace, and where now instead of using typical feed stream such as natural gas or pre-reformed natural gas, the feed stream is the first cracked stream.

[0044] In another embodiment, the primary ammonia cracker is an electrically heated reactor, where electrical resistance is used for generating the heat for catalytic dissociation of ammonia. This is for instance suitable where electricity is readily available, particularly when available from green source such as by power generated from solar or wind sources. This reactor can operate at high temperatures and pressures, for instance at 1000°C or more, as well as pressures of 100 barg or higher, such as 500 barg or even higher, which can be relevant for certain downstream applications requiring hydrogen product being recovered or delivered at high pressures, such as at about 700 barg. Despite the high pressure, the higher temperature in the reactor enables also a lower ammonia slip in the effluent gas stream of the reactor.

[0045] In another embodiment, the primary ammonia cracker is an induction heated reactor, where a tube heat exchange ammonia cracker includes the use of an induction coil in order to generate an alternating magnetic field within at least a part of an inner tube comprising a bed of catalyst material susceptible for induction heating. This is for instance also suitable where electricity is readily available, particularly when available from green source such as by power generated from solar or wind sources.

[0046] Combinations of such reactors are also envisaged.

[0047] The catalyst in the heat exchange ammonia cracker and the catalyst in the primary ammonia cracker, may be in the form of pellets or a monolith.

[0048] The second cracked stream suitably has the following composition: NH3: 0.2 - 6.0 vol.%, stoichiometric H2 and N2. The water content will depend on the feed concentration and is normally less than 0.3% v / v.

[0049] The second cracked stream is suitably outputted at a temperature of between 600-900 °C, and a pressure between 10-60 bar.

[0050] In the ammonia cracking process, either in the HEAC or the primary ammonia cracker, gaseous ammonia is dissociated into a mixture of hydrogen and nitrogen gases in the reversible reaction: 2 NH3 (g) N2 (g) + 3 H2 (g) (1). This reaction is endothermic, requiring heat for maintaining the ammonia cracking reaction, and hence the temperature will decrease across the reactor.

[0051] When performed under the conditions of the present invention, catalysts are preferably Ni- based or Ni / Co based and the process is performed at lower temperatures in the range 400- 800°C, as recited above. Particularly for the fired primary ammonia cracker, this reactor is for instance operated at temperatures in the range 600-700°C, which increases conversion to hydrogen. The higher temperatures may in some instances require the use of catalysts capable of operating at such temperatures, such as Ni catalysts. For instance, the temperature of a first cracked stream, corresponding to the inlet temperature of the primary ammonia cracker, is suitably about 600°C, such as 580 or 590°C, while the temperature of the second cracked stream, corresponding to the outlet temperature of the primary ammonia cracker, is about 800°C such as 810, 815, 790 or 780°C.

[0052] As set out above, at least a portion of the second cracked stream from the primary ammonia cracker is fed as heat supply to the heat exchange ammonia cracker. By this, is meant that the second cracked stream carries out heat exchange with the first ammonia feed. By carrying out heat exchange with the first ammonia feed, the second cracked stream is not combusted in the HEAC, thus avoiding impurities, and maintaining the yield of hydrogen.

[0053] Process

[0054] A process is also provided for cracking a first feed comprising ammonia, said process comprising the steps of: providing the cracker system as described herein, feeding at least a portion of said first feed comprising ammonia, to the heat exchange ammonia cracker and outputting a first cracked stream, feeding at least a portion of said first feed and / or at least a portion of the first cracked stream to the primary ammonia cracker and outputting a second cracked stream, and feeding at least a portion of the second cracked stream from the primary ammonia cracker as heat supply to the heat exchange ammonia cracker. Again, in the process described herein, the series layout is preferred, i.e. wherein the process comprises the step of feeding at least a portion of the first cracked stream to the primary ammonia cracker and outputting a second cracked stream.

[0055] All details relating to the system described herein are relevant for the process, mutatis mutandis.

[0056] Specific embodiments

[0057] Fig. 1 shows a combined heat exchange and ammonia cracker system 100 having a series arrangement of heat exchange ammonia cracker and primary ammonia cracker. A first feed 1 comprising ammonia is fed to the heat exchange ammonia cracker 10 and a first cracked stream 11 is outputted. Additionally, as shown by the dotted line in figure 1, a portion of the first feed 1 may be fed to the primary ammonia cracker 20.

[0058] At least a portion of the first cracked stream 11 is fed to primary ammonia cracker 20 and a second cracked stream 21 is outputted. The second cracked stream 21 from the primary ammonia cracker 20 is fed as heat supply to the heat exchange ammonia cracker 10. A cooled second cracked stream 21A is outputted from the HEAC 10.

[0059] When an autothermal ammonia cracker is used, a feed 5 comprising oxygen is required.

[0060] Figure 1 also shows optional second feed 2 comprising ammonia, said second feed being arranged to be fed to the inlet of the primary ammonia cracker 20, suitably in admixture with first cracked stream 11.

[0061] Fig. 2 shows a combined heat exchange and ammonia cracker system 100 having a parallel arrangement of heat exchange ammonia cracker and primary ammonia cracker. Components of figure 2 are as in figure 1.

[0062] First feed 1 comprising ammonia is fed both to the heat exchange ammonia cracker 10 and the primary ammonia cracker 20. A first cracked stream 11 is outputted from the heat exchange ammonia cracker 10. A second cracked stream 21 is outputted from the primary ammonia cracker 20.

[0063] The second cracked stream 21 from the primary ammonia cracker 20 is fed as heat supply to the heat exchange ammonia cracker 10, in admixture with the first cracked stream 11. A cooled second cracked stream 21A is outputted from the HEAC 10. When an autothermal ammonia cracker is used, a feed 5 comprising oxygen is required.

[0064] Figure 2 also shows optional second feed 2 comprising ammonia, said second feed being arranged to be fed to the inlet of the heat exchange ammonia cracker 10, suitably in admixture with first feed 1 comprising ammonia. EXAMPLE

[0065] A comparison was made between (A) a stand-alone fired tubular cracker, (B) an adiabatic pre-converter followed in series with a fired tubular cracker and (C) a heat exchange precracker in series with a fired tubular cracker. In the three cases the feed to the ammonia decomposition system (either stand-alone fired cracker or pre-converter in series with fired cracker) consists of pure ammonia at 650 °C. The outlet from the fired cracker is at 800 °C and 34 bar g in the three cases. The results are shown in Table 1 :

[0066] A = Tubular fired-cracker, stand-alone

[0067] B = Adiabatic pre-converter + Tubular fired-cracker, series

[0068] C = Heat exchange pre-converter + Tubular fired-cracker, series (effluent from tubular cracker used as heating medium in pre-converter)

[0069] Table 1

[0070] In the two cases in series, the inlet to the fired cracker consists of 100% of the first cracked gas. This first cracked gas is reheated to 600 degC before entering the fired cracker: in the case of an adiabatic preconverter this is done in a heat exchanger, and in the case of the heat exchange pre-cracker this is done by heat exchange with the hot second cracked gas.

[0071] Pre-conversion, either in an adiabatic or a heat-exchange cracker reduces the firing duty (i.e. the fuel consumption) in the tubular cracker. Higher pre-conversions can be obtained in a heat-exchange cracker because the average temperatures of the catalyst bed are higher than in an adiabatic converter. The required duty for a tubular Cracker is equivalent to the required size of the tubular cracker. The example illustrates that the invention enables a larger single line ammonia cracking capacity when using a tubular cracker

[0072] The present invention has been described with reference to a number of Figures and embodiments. However, the skilled person may combine embodiments and features from the text as required. All cited references are incorporated by reference.

Claims

CLAIMS1. A combined heat exchange and ammonia cracker system (100) said combined cracker system (100) comprising : a first feed (1) comprising ammonia, a heat exchange ammonia cracker (10) arranged to receive at least a portion of the first feed (1) and to output a first cracked stream (11), a primary ammonia cracker (20) arranged to receive at least a portion of said first feed (1) and / or at least a portion of the first cracked stream (11), and output a second cracked stream (21) and wherein, at least a portion of the second cracked stream (21) from the primary ammonia cracker (20) is fed as heat supply to the heat exchange ammonia cracker (10).

2. The system according to claim 1, wherein the first feed further comprises steam.

3. The system (100) according to any one of the preceding claims, wherein the primary ammonia cracker (20) is arranged to receive at least a portion of the first cracked stream (11) from the heat exchange ammonia cracker (10).

4. The system (100) according to any one of the preceding claims, further comprising a second feed (2) comprising ammonia, said second feed being arranged to be fed to the inlet of the primary ammonia cracker (20) or the inlet of the heat exchange ammonia cracker (10).

5. The system (100) according to any one of the preceding claims, wherein at least a portion of the first cracked stream (11) is arranged to be mixed with the second cracked stream (21) from the primary ammonia cracker (20), and the combined stream is fed as heat supply to the heat exchange ammonia cracker (10).

6. The system (100) according to any one of the preceding claims, wherein the catalyst in the heat exchange ammonia cracker comprises the same active metal catalyst as the catalyst in the primary ammonia cracker.

7. The system (100) according to any one of the preceding claims, wherein the catalyst in the heat exchange ammonia cracker comprises a different active metal catalyst to the catalyst in the primary ammonia cracker.

8. The system (100) according to any one of the preceding claims, wherein the catalyst in the heat exchange ammonia cracker and the catalyst in the primary ammonia cracker, are in the form of pellets or a monolith.

9. The system (100) according to any one of the preceding claims, wherein the heat exchange ammonia cracker (10) is arranged to receive heat from said portion of the second cracked stream (21) from the primary ammonia cracker (20) and to output a cooled second cracked stream (21A).

10. The system (100) according to any one of the preceding claims, wherein the heat exchange ammonia cracker (10) is a shell-and-tube heat exchanger, in which reactor tube(s) comprise an ammonia cracking catalyst and are arranged to receive at least a portion of the first feed (1) at a first end of said reactor tube(s) and to output a first cracked stream (11) from a second end of said reactor tube(s), and in which a shell is arranged to receive at least a portion of the second cracked stream (21) from the primary ammonia cracker (20) and to output a cooled second cracked stream (21A), and wherein heat exchange takes place from said shell to said reactor tube(s).

11. The system (100) according to any one of the preceding claims, wherein the heat exchange ammonia cracker (10), in which reactor tubes are bayonet tubes, wherein ammonia cracking catalyst is installed in the bayonet annulus, whereby the first feed (1) is arranged to enter the ammonia cracking catalyst in the anulus of the bayonet tube and the first cracked stream (11) outlet the annulus is cooled in the central part of the bayonet tube in counter-current flow to the annulus flow before it leaves the ammonia cracker.

12. The system (100) according to any one of the preceding claims, wherein the primary ammonia cracker (20) is selected from an electrical ammonia cracker, a fired ammonia cracker, or an autothermal ammonia cracker.

13. The system according to any one of the preceding claims, wherein the first feed further comprises hydrogen.

14. A process for cracking a first feed (1) comprising ammonia, said process comprising the steps of: providing the cracker system (100) according to any one of the preceding claims, feeding at least a portion of said first feed (1) comprising ammonia, to the heat exchange ammonia cracker (10) and outputting a first cracked stream (11),feeding at least a portion of said first feed (1) and / or at least a portion of the first cracked stream (11) to the primary ammonia cracker (20) and outputting a second cracked stream (21), and feeding at least a portion of the second cracked stream (21) from the primary ammonia cracker (20) as heat supply to the heat exchange ammonia cracker (10).

15. The process according to claim 14, comprising the step of feeding at least a portion of the first cracked stream (11) to the primary ammonia cracker (20) and outputting a second cracked stream (21).