METHOD FOR HEATING A FEED OF NATURAL GAS TO A STEAM REFORMER AND SYSTEM AND USE THEREOF

Abstract

A method for heating a feed of natural gas, used as feed for a steam reformer of an ammonia production system, wherein the system comprises a steam reformer, operably connected to a heat recovery unit comprising at least two heating coils maintained at a different temperature, wherein the feed of natural gas passes through the at least two heating coils, the method comprising: a) recovering heat in the heat recovery unit from the ammonia production system and b) exchanging at least part of the heat recovered in step a) with at least a portion of the feed of natural gas, thereby obtaining a heated feed of natural gas, wherein the feed of natural gas does not comprise steam.

Claims

1. A method for heating a feed of natural gas, used as feed for a steam reformer of an ammonia production system, wherein the system comprises a steam reformer operably connected to a heat recovery unit comprising at least two heating coils maintained at a different temperature, wherein the feed of natural gas passes through the at least two heating coils, comprising the steps of: a) recovering heat in the heat recovery unit from the ammonia production system; and b) exchanging at least part of the heat recovered in step a) with at least a portion of the feed of natural gas, thereby obtaining a heated feed of natural gas; wherein the feed of natural gas does not comprise steam; the method being characterised in that: the heat recovered in step a) is heat recovered from flue gas produced in the steam reformer and; step b) comprises the consecutive steps of: b1) heating the feed of natural gas from a temperature ranging from 10° C. to 40° C. to a temperature ranging from 180° C. to 210° C. upon contacting the feed with a first heating coil of the heat recovery unit, thereby obtaining a pre-heated feed of natural gas; and b2) subsequently further heating the pre-heated feed of natural gas from step b1) to a temperature ranging from 360° C. to 380° C. upon contacting the feed with a second heating coil of the heat recovery unit, thereby obtaining the heated feed of natural gas; step c) splitting the pre-heated feed of natural gas obtained in step b1) into a pre-heated feed stream fed to the second heating coil of the heat recovery unit and a gas stream having a temperature ranging from 180° C. to 210° C. used as fuel in the steam reformer, wherein the gas stream, having a temperature ranging from 180° C. to 210° C., used as fuel in the steam reformer obtained from step c) is further mixed with natural gas.

2. (canceled)

3. (canceled)

4. The method according to claim 1, further comprising the steps of: d) supplying the heated feed of natural gas to a sulfur removal unit, thereby obtaining sulfur-depleted natural gas; e) mixing the sulfur-depleted natural gas obtained in step d) with steam in a steaming unit, thereby obtaining a natural gas/steam mixture; f) heating the natural gas/steam mixture obtained in step e) from a temperature ranging 360° C. to 380° C. to a temperature ranging from 590° C. to 610° C. in a heating unit, thereby obtaining a heated natural gas/steam mixture; and g) supplying the heated natural gas/steam mixture obtained in step f) to the steam reformer, thereby forming a reformed gas, comprising at least hydrogen and carbon monoxide.

5. The method according to claim 4, further comprising the steps of: h) reacting the reformed gas, reformed in the steam reformer in a shift conversion unit, thereby producing a mixture of carbon dioxide and hydrogen; i) reacting the gas obtained from the reaction in the shift conversion unit in a carbon dioxide removal unit, thereby separating hydrogen from carbon dioxide; j) reacting the gas obtained from the carbon dioxide removal unit in a methanation unit, thereby converting remaining amounts of carbon monoxide and carbon dioxide in the hydrogen into methane, thereby producing hydrogen gas essentially free in carbon monoxide and carbon dioxide; and k) reacting the gas obtained from the reaction in the methanation unit in an ammonia synthesis unit, thereby producing ammonia.

6. A system for heating a feed of natural gas, used as feed for a steam reformer of an ammonia production system, comprising: a heat recovery system for recovering heat, comprising an inlet and an outlet and at least two heating coils maintained at a different temperature for 1), thereby providing a heated feed of natural gases; a steaming unit, comprising an inlet in fluid communication with the heated feed of natural gas and an outlet; and a steam reformer, comprising an inlet for the heated feed of natural gas in fluid communication with the heated feed of natural gas, and an outlet for a flue gas; wherein the heat recovery unit is positioned upstream the steaming unit; the system being characterized in that: the flue gas outlet of the steam reformer is in fluid communication with the heating coils of the heat recovery system, such that heat is recovered from the flue gas produced in the steam reformer and; a first heating coil is configured for heating the feed of natural gas from a temperature ranging from 10° C. to 40° C. to a temperature ranging from 180° C. to 210° C., thereby providing a pre-heated feed of natural gas, and a second heating coil is configured for heating the pre-heated feed of natural gas from a temperature ranging from 180° C. to 210° C. to a temperature ranging from 360° C. to 380° C., thereby providing a heated feed of natural gas, and the first heating coil is located upstream the second heating coil; means for splitting the pre-heated feed of natural gas into a pre-heated feed stream fed to the second heating coil of the heat recovery unit and a gas stream having a temperature ranging from 180° C. to 210° C. used as fuel in the steam reformer; and means for mixing the gas stream having a temperature ranging from 180° C. to 210° C. used as fuel in the steam reformer with natural gas.

7. (canceled)

8. (canceled)

9. The system according to claim 6, further comprising: a sulfur removal unit for removing sulfur from the feed of natural gas heated by the second heating coil, comprising an inlet and an outlet; a steaming unit, having an inlet and an outlet; and a heating unit for a natural gas/steam mixture from a temperature ranging from 360° C. to 380° C. to a temperature ranging from 590° C. to 610° C., and comprising an inlet and an outlet; wherein the inlet of the sulfur removal unit is in fluid communication with the outlet of the heat recovery unit, and wherein the inlet of the steaming unit is in fluid communication with the outlet of the sulfur removal unit, and wherein the outlet of the steaming unit is in fluid communication with the inlet of the heating unit, and wherein the outlet for the heating unit is in fluid communication with the inlet for the heated feed of natural gas of the steam reformer.

10. The system according to claim 6, further comprising: a shift conversion unit for reacting carbon monoxide gas produced in the steam reformer with water, thereby producing a mixture of carbon dioxide and hydrogen, in direct fluid communication with the steam reformer; a carbon dioxide removal unit in direct fluid communication with the shift conversion unit, for separating hydrogen from carbon dioxide in the mixture of carbon dioxide and hydrogen formed in the shift conversion unit; a methanation unit in direct fluid communication with the carbon dioxide removal unit for converting amounts of carbon monoxide gas formed in the steam reformer and of carbon dioxide formed in the shift conversion unit remaining in the hydrogen gas into methane, thereby providing hydrogen gas essentially free in carbon monoxide and carbon dioxide; and an ammonia synthesis unit for reacting the hydrogen gas provided by the methanation unit with nitrogen gas, thereby forming ammonia, in direct fluid communication with the methanation unit.

11. (canceled)

Description

LIST OF FIGURES

[0074] FIG. 1 shows a schematic representation of one embodiment of the system of the disclosure for heating a feed of natural gas (1)

[0075] FIG. 2 shows a flow diagram representation of the method of the disclosure for processing a heated feed of natural gas (10, 40) in an ammonia production system (39)

[0076] FIG. 3 shows a schematic representation of a primary reformer (19)

[0077] FIG. 4 shows a schematic representation of another embodiment of the system of the disclosure for heating a feed of natural gas (1)

LIST OF NUMERALS IN FIGURES

[0078]

TABLE-US-00001 1 feed of natural gas 2 flue gas 3 heat recovery unit 4 first heating coil 5 second heating coil 6 gas stream having a temperature ranging from 180° C. to 210° C. 7 means for splitting a heated feed of natural gas 8 means for mixing a heated gas stream with natural gas 9 pre-heated feed of natural gas 10 heated feed of natural gas 11 sulfur removal unit 12 inlet of sulfur removal unit 13 outlet of sulfur removal unit 14 sulfur-depleted natural gas 15 steaming unit 16 inlet of steaming unit 17 outlet of steaming unit 18 natural gas/steam mixture 19 steam reformer 20 inlet for natural gas of steam reformer 21 outlet for flue gas from steam reformer 22 reformed gas 23 outlet for reformed gas from steam reformer 24 shift conversion unit 25 inlet of shift conversion unit 26 outlet of shift conversion unit 27 gas mixture of carbon dioxide and hydrogen 28 carbon dioxide removal unit 29 inlet of carbon dioxide removal unit 30 outlet for carbon dioxide removal unit 31 Hydrogen 32 methanation unit 33 inlet for methanation unit 34 outlet for methanation unit 35 hydrogen gas essentially free in carbon monoxide and carbon dioxide 36 ammonia synthesis unit 37 inlet of ammonia synthesis unit 38 flue gas to stack of steam reformer 39 ammonia production system 40 second heated gas stream 41 heating unit 42 heated natural gas/steam mixture 43 inlet of heating unit 44 outlet of heating unit 45 Ammonia 46 inlet of heat recovery system 47 outlet of heat recovery system 48 Water 49 nitrogen gas 50 tube section of steam reformer 51 fuel section of steam reformer 52 stack of steam reformer 53 secondary reformer 54 Air

DETAILED DESCRIPTION

[0079] Throughout the description and claims of this specification, the words “comprise” and variations of them mean “including but not limited to”, and they are not intended to (and do not) exclude other moieties, additives, components, integers or steps. Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

[0080] Features, integers, characteristics, compounds, chemical moieties, or groups described in conjunction with a particular aspect, embodiment or example of the disclosure are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. The disclosure is not restricted to the details of any foregoing embodiments. The disclosure extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

[0081] The enumeration of numeric values by means of ranges of figures comprises all values and fractions in these ranges, as well as the cited end points. The term “from . . . to” as used when referring to a range for a measurable value, such as a parameter, an amount, a time period, and the like, is intended to include the limits associated to the range that is disclosed.

[0082] Reference is made to FIGS. 1 to 3. In a first aspect of the disclosure, a method is disclosed for heating a feed of natural gas 1 that does not comprise steam and is used as feed for a steam reformer 19 of an ammonia production system 39. The system comprises a steam reformer 19 operably connected to a heat recovery unit 3 comprising at least two heating coils 4 and 5 maintained at a different temperature, wherein the feed of natural gas passes through the at least two heating coils 4 and 5. The method comprises the steps of: [0083] a) recovering heat in the heat recovery unit 3 from the ammonia production system 39; and [0084] b) exchanging at least part of the heat recovered in step a) with at least a portion of the feed of natural gas 1, thereby obtaining a heated feed of natural gas 10. Since the feed of natural gas 1 does not comprise steam, in the method of the disclosure, at least a portion of the feed of natural gas 1 is heated in a heat recovery unit 3, before being mixed with steam in the steaming unit 15, typically positioned downstream of the heat recovery unit comprising the at least two heating coils (4,5) and being reacted in the steam reformer 19. As a result of this heat exchange step, a heated feed of natural gas 10 is obtained. This heated feed of natural gas 10 can then in turn be used as a source of energy such as the supply of heat in a heat exchange, thereby distributing in turn the heat in the ammonia production system 39. Alternatively, the heated feed of natural gas 10 can be mixed with natural gas at a different temperature, such that a feed at a pre-determined temperature can be obtained downstream the steaming unit 15, such that, in turn, a natural gas/steam mixture 42 at an optimal temperature is obtained before the reaction in the steam reformer 19. When the temperature of a mixture comprising the heated feed of natural gas is measured, it is possible to regulate, for example through a valve system, the amount of the initial feed of natural gas that goes through the heat exchange step b). Said otherwise, the method of the disclosure not only allows an optimal distribution of the heat recovered in the ammonia production system 39, it also ensures that the feed of the natural gas 1 is at an optimal temperature when reacted in the steam reformer 19. Such optimal temperature not only is necessary to ensure proper conversion of the natural gas 1 into a reformed gas, that is a mixture of carbon monoxide and hydrogen 22, it further optimizes the lifetime of the steam reformer 19 by minimizing the damages when the gases is at a too low or too high temperatures. Indeed, when the feed of natural gas 10 or 42 to the steam reformer 19 is at a too low temperature, additional heat may have to be provided by the furnace chamber 51, resulting in additional energy consumption and potential damages of the furnace chamber 51 when working at higher temperatures. In the event that the feed of natural gas to the steam reformer 10 or 42 is at a too high temperature, heating by the furnace chamber 51 may result in the natural gas in the tube section 50 reaching a temperature that is higher than that the design temperature of the tubes of the tube section 50, resulting in tubes damages and leakages between the furnace chamber 51 and the tube 50 sections.

[0085] In order to maximize the surface area and, hence, the exchange of heat in the heat exchange system 2, the heat exchange system 2 of the disclosure comprises at least two heating coils 4 and 5. The heating coils 4 and 5 afford a good surface area. In addition, the presence of multiple heating coils 4 and 5 allows for the multiple step, serial heating of the feed of natural gas 1 and, thereby, enhances the control of the temperature of the feed of natural gas 10.

Furthermore, the heat recovered in step a) is heat recovered from flue gas 2 coming out of the steam reformer 19 (FIG. 1). The flue gas is thus in thermal communication with all of the at least two heating coils 4 and 5.

[0086] As the temperature of the flue gas 2 in the furnace chamber 51 of the steam reformer 19 is as high as 1000° C., this flue gas 2 is a particularly suitable source of heat to be provided to the heat exchange system 3, in order for heat to be provided to the feed of natural gas 1. In addition, the stack 52 of the steam reformer 19 may be designed to handle temperatures not higher than 150° C. This means that it may be, in any event, necessary to recover the heat of the flue gas 2 before it is sent to the stack 52, through the use of fan (not shown) typically located at the bottom of the steam reformer 19 due to its weight. Therefore, the use of the flue gas 2 for recovering heat in the heat recovering system 3 presents the benefit of ensuring that the temperature of the flue gas 38 going to the stack 52 is not higher than the temperature that the stack 52 has been designed for.

[0087] In addition, the step b) of the method comprises the consecutive steps of (FIG. 1): [0088] b1) heating the feed of natural gas 1, particularly containing no steam, from a temperature ranging from 10° C. to 40° C. to a temperature ranging from 180° C. to 210° C. upon contacting the feed 1 with a first heating coil 4 of the heat recovery unit 3, particularly using heat recovered from the flue gas, thereby obtaining a pre-heated feed of natural gas 9; and [0089] b2) subsequently further heating the pre-heated feed of natural gas 9, particularly containing no steam, from step b1) to a temperature ranging from 360° C. to 380° C. upon contacting the feed 9 with a second heating coil 5 of the heat recovery unit 3, particularly using heat recovered from the flue gas, thereby obtaining the heated feed of natural gas 10.

[0090] As described above, heating of the natural feed gas 1 in several steps presents the advantage of enhanced control on the temperature of the feed of natural gas 10 or 42 entering the steam reformer 19. In addition, the pre-heated feed of natural gas 9 can be used as a source of energy supply, for example through heat exchange or mixing with other gases, as will be illustrated in the next embodiment. Hence, the multiple step heating process of the feed of natural gas 1 one also offers the benefit of optimal heat distribution throughout the entire ammonia production system 39.

[0091] Reference is made to FIGS. 1, 2 and 4. According to one embodiment of the method of the disclosure, the method further comprises the step of: [0092] c) splitting the pre-heated feed of natural gas 9 obtained in step b1) into a pre-heated feed stream fed to the second heating coil 5 of the heat recovery unit 3 and a gas stream 6 having a temperature ranging from 180° C. to 210° C. used as fuel in the steam reformer 19.

[0093] As described above, it is possible to use the pre-heated feed of natural gas 9 as a source of energy supply. By splitting the pre-heated feed of natural gas 9, a gas stream 6 at a temperature ranging from 180° C. to 210° C. can be obtained which is suitable for feeding to the furnace chamber 51 of the steam reformer 19. Consequently, no separate heating device is required for heating the gas fed as fuel 6 to the furnace chamber 51 of the steam reformer 19. Moreover, the method of the disclosure not only allows for controlling the temperature of the feed gas 10 or 42 to the steam reformer 19, it further allows to obtain a gas stream 6 at a temperature ranging from 180° C. to 210° C. suitable as fuel in the furnace chamber 51 of the steam reformer 19, as well as the control of the temperature of the gas stream 6, at a temperature ranging from 180° C. to 210° C. and used as fuel gas. This may be of particular importance in ammonia production systems 39, comprising steam reformers 19 made of multiple parallel units (not shown), each unit comprising a furnace chamber 51 and a tube section 50: in such systems, a problem that may be faced is the unequal heat distribution between the different units of the steam reformer. Controlling both temperatures of the heated feed of natural gas 10 and of the gas stream 6 and of the gas stream 40 brings a solution for controlling this problem.

[0094] Reference is made to FIG. 4. According to one embodiment of the method of the disclosure, the gas stream having a temperature ranging from 180° C. to 210° C. used as fuel 6 in the steam reformer 19 obtained from step c) is further mixed with natural gas. As an extension to the previous embodiment, the method of the disclosure allows for further control of the temperature and of the volume of gas 40 to fed as fuel to the furnace chamber 51 of the steam reformer 19.

[0095] Reference is made to FIG. 2. According to one embodiment of the method of the disclosure, the method further comprises the steps of: [0096] d) supplying the heated feed of natural gas 10 to a sulfur removal unit 11, thereby obtaining sulfur-depleted natural gas 14; [0097] e) mixing the sulfur-depleted natural gas 14 obtained in step d) with steam in a steaming unit 15, thereby obtaining a natural gas/steam mixture 18; [0098] f) heating the natural gas/steam mixture 18 obtained in step e) from a temperature ranging 360° C. to 380° C. to a temperature ranging from 590° C. to 610° C. in a heating unit 41, thereby obtaining a heated natural gas/steam mixture 42; and [0099] g) supplying the heated natural gas/steam mixture 42 obtained in step f) to the steam reformer 19, thereby forming a reformed gas 22, comprising at least hydrogen and carbon monoxide.

[0100] This embodiment of the method will enable the person skilled in the art to use the heated feed of natural gas 1 to produce a reformed gas, comprising a mixture of carbon monoxide and hydrogen 22. It will be evident to the person skilled in the art that, optionally, an additional step before step d) can be conducted and in which the heated feed of natural gas 10 is reacted with air 54, as a source of oxygen, in a secondary reformer 53, in order to further increase the conversion of the natural gas into the reformed gas 22, comprising hydrogen and carbon monoxide. The gas leaving the secondary reformer 53 can then be fed to the shift conversion unit 24.

[0101] Reference is made to FIG. 2. According to one embodiment of the method of the disclosure, the method further comprises the steps of: [0102] h) reacting the reformed gas 22, reformed in the steam reformer 19 in a shift conversion unit 24, thereby producing a mixture of carbon dioxide and hydrogen 27; [0103] i) reacting the gas 27 obtained from the reaction in the shift conversion unit 24 in a carbon dioxide removal unit 28, thereby separating hydrogen 31 from carbon dioxide; [0104] j) reacting the gas 31 obtained from the carbon dioxide removal unit 28 in a methanation unit 32, thereby converting remaining amounts of carbon monoxide and carbon dioxide in the hydrogen 31 into methane, thereby producing hydrogen gas essentially free in carbon monoxide and carbon dioxide 35; and [0105] k) reacting the gas 35 obtained from the reaction in the methanation unit in an ammonia synthesis unit 36, thereby producing ammonia 45.

[0106] This embodiment of the method will enable the person skilled in the art to use the heated feed of natural gas 1 to produce ammonia 45. The supply of nitrogen gas 49 to the ammonia synthesis unit 36, also commonly known as the Haber Bosch synthesis, is necessary in order for the hydrogen gas essentially free in carbon monoxide and carbon dioxide 35 to react with nitrogen 49 in the ammonia synthesis unit 36, thereby producing ammonia 45. Nitrogen gas 49 can be supplied to the ammonia synthesis unit 36 for example through an air separation unit (not shown) that splits or separates the oxygen in the air from nitrogen gas 49. Alternatively, if as described in relation to the previous embodiment, an additional step before step d) is conducted in which the heated feed of natural gas 10 is reacted with air 54, in a secondary reformer 53, nitrogen gas 49 is then supplied to the ammonia synthesis through the air 54 supplied to the secondary reformer 53.

[0107] Reference is made to FIGS. 1 to 3. In a second aspect of the disclosure, a system is disclosed for heating a feed of natural gas 1, used as feed for a steam reformer 19 of an ammonia production system 39. The system for heating comprises: [0108] a heat recovery system 3 for recovering heat, comprising an inlet 46 and an outlet 47 and at least two heating coils 4 and 5 maintained at a different temperature for exchanging part of the recovered heat with at least a portion of the feed of natural gas 1, thereby providing a heated feed of natural gas 10; [0109] a steaming unit 15, comprising an inlet 16 in fluid communication with the heated feed of natural gas 10 and an outlet 17; and [0110] a steam reformer 19, comprising an inlet for the heated feed of natural gas 20 in fluid communication with the heated feed of natural gas 10, and an outlet for a flue gas 21; wherein the heat recovery unit 3 is positioned upstream the steaming unit 15.

[0111] Since the heat recovery unit 3 is positioned upstream the steaming unit 15, at least a portion of the feed of natural 1 is heated in this heat recovery unit 3, before being mixed with steam in the steaming unit 15 and being reacted in the steam reformer 19. As a result of this heat exchange step, a heated feed of natural gas 10 is obtained, downstream of the steaming unit. This heated feed of natural gas 10 can then in turn be used as a source of energy such as the supply of heat in a heat exchange, thereby distributing in turn the heat in the ammonia production system 39. Alternatively, the heated feed of natural gas 10 can be mixed with natural gas at a different temperature, such that a feed at a pre-determined temperature can be obtained upstream the steaming unit 15, such that, in turn, a natural gas/steam mixture 42 at an optimal temperature is obtained before the reaction in the steam reformer 19. When the system comprises means for measuring the temperature (not shown) of a mixture comprising the heated feed of natural gas, it is possible to regulate, for example through a valve system, the amount of the initial feed of natural gas that goes through the heat exchange step b). Said otherwise, the system of the disclosure not only allows an optimal distribution of the heat recovered in the ammonia production system 39, it also ensures that the feed of the natural gas 1 is at an optimal temperature when reacted in the steam reformer 19. Such optimal temperature not only is necessary to ensure proper conversion of the natural gas 1 into a reformed gas, that is a mixture of carbon monoxide and hydrogen 22, it further optimizes the lifetime of the steam reformer 19 by minimizing the damages when the gases is at a too low or too high temperatures. Indeed, when the feed of natural gas 10 or 42 to the steam reformer 19 is at a too low temperature, additional heat may have to be provided by the furnace chamber 51, resulting in additional energy consumption and potential damages of the furnace chamber 51 when working at higher temperatures. In the event that the feed of natural gas to the steam reformer 10 or 42 is at a too high temperature, heating by the furnace chamber 51 may result in the natural gas in the tube section 50 reaching a temperature that is higher than that the design temperature of the tubes of the tube section 50, resulting in tubes damages and leakages between the furnace chamber 51 and the tube 50 sections.

[0112] In order to maximize the surface area and, hence, the exchange of heat in the heat exchange system 2, the heat exchange system 2 of the disclosure comprises at least two heating coils 4 and 5. The heating coils 4 and 5 afford a good surface area. In addition, the presence of multiple heating coils 4 and 5 allows for the multiple step heating of the feed of natural gas 1 and, thereby, enhances the control of the temperature of the feed of natural gas 10.

[0113] Furthermore, the flue gas outlet 21 of the steam reformer 19 is in fluid or thermal communication with the heating coils 4 and 5 of the heat recovery system 3, such that heat is recovered from the flue gas 2 produced in the steam reformer 19 (FIG. 1).

[0114] As the temperature of the flue gas 2 in the furnace chamber 51 of the steam reformer 19 is as high as 1000° C., this flue gas 2 is a particularly suitable source of heat to be provided to the heat exchange system 3, in order for heat to be provided to the feed of natural gas 1. In addition, the stack 52 of the steam reformer 19 may be designed to handle temperatures not higher than 150° C. This means that it may be, in any event, necessary to recover the heat of the flue gas 2 before it is sent to the stack 52, through the use of fan (not shown) typically located at the bottom of the steam reformer 19 due to its weight. Therefore, the use of the flue gas 2 for recovering heat in the heat recovering system 3 presents the benefit of ensuring that the temperature of the flue gas 38 going to the stack 52 is not higher than the temperature that the stack 52 has been designed for.

[0115] In addition a first heating coil 4 (FIG. 1), is configured for heating the feed of natural gas 1 from a temperature ranging from 10° C. to 40° C. to a temperature ranging from 180° C. to 210° C., thereby providing a pre-heated feed of natural gas 9, and a second heating coil 5 is configured for heating the pre-heated feed of natural gas 9 from a temperature ranging from 180° C. to 210° C. to a temperature ranging from 360° C. to 380° C., thereby providing a heated feed of natural gas 10. The first heating coil 4 is located upstream the second coil 5.

[0116] As described above, the presence of multiple heating coils 4 and 5 presents the advantage of enhanced control on the temperature of the feed of natural gas 10 or 42 entering the steam reformer 19. In addition, the pre-heated feed of natural gas 9 can be used as a source of energy supply, for example through heat exchange or mixing with other gases, as will be illustrated in the next embodiment. Hence, the presence of multiple heating coils 4 and 5 also offers the benefit of optimal heat distribution throughout the entire ammonia production system 39.

[0117] Reference is made to FIGS. 1, 2 and 4. According to one embodiment of the system of the disclosure, the system further comprises means for splitting 7 the pre-heated feed of natural gas 9 heated by a first heating coil 4 into a pre-heated stream 9 fed to the second heating coil 5 of the heat recovery unit 3 and a gas stream 6 having a temperature ranging from 180° C. to 210° C. used as fuel in the steam reformer 19.

[0118] As described above, this is possible to use the pre-heated feed of natural gas 9 as a source of energy supply. By splitting the pre-heated feed of natural gas 9, a gas stream 6 having a temperature ranging from 180° C. to 210° C. can be obtained and that is suitable for feeding to the furnace chamber 51 of the steam reformer 19. Consequently, no separate heating device is required for heating the gas fed as fuel 6 to the furnace chamber 51 of the steam reformer 19. Moreover, the system of the disclosure not only allows for controlling the temperature of the feed gas 10 or 42 to the steam reformer 19, it further allows to obtain a gas stream 6 having a temperature ranging from 180° C. to 210° C. suitable as fuel in the furnace chamber 51 of the steam reformer 19, as well as the control of the temperature of this gas stream 6 having a temperature ranging from 180° C. to 210° C. and used as fuel gas. This may be of particular importance in ammonia production systems 39, comprising steam reformers 19 made of multiple parallel units (not shown), each unit comprising a furnace chamber 51 and a tube section 50: in such systems, a problem that may be faced is the unequal heat distribution between the different units of the steam reformer. Controlling both temperatures of the heated feed of natural gas 10 and of the low temperature gas stream 6 and of the gas stream 40 brings a solution for controlling this problem.

[0119] Reference is made to FIG. 4. According to one embodiment of the system of the disclosure, the system further comprises means for mixing 8 the gas stream having a temperature ranging from 180° C. to 210° C. used as fuel 6 in the steam reformer 19 with natural gas. As an extension to the previous embodiment, the system of the disclosure allows for further control of the temperature and of the volume of gas 40 to fed as fuel to the furnace chamber 51 of the steam reformer 19.

[0120] Reference is made to FIG. 2. According to one embodiment of the system of the disclosure, the system further comprises: [0121] a sulfur removal unit 11 for removing sulfur from the feed of natural gas 10 heated by the second heating coil 5, comprising an inlet 12 and an outlet 13; [0122] a steaming unit 15, having an inlet 16 and outlet 17; and [0123] a heating unit 41 for heating a natural gas/steam mixture from a temperature ranging from 360° C. to 380° C. to a temperature ranging from 590° C. to 610° C., and comprising an inlet 43 and an outlet 44;
wherein the inlet 12 of the sulfur removal unit 11 is in fluid communication with the outlet 47 of the heat recovery unit, and wherein the inlet 16 of the steaming unit 15 is in fluid communication with the outlet 13 of the sulfur removal unit, and wherein the outlet 17 of the steaming unit 15 is in fluid communication with the inlet of the heating unit 41, and wherein the outlet 44 for the heating unit 41 is in fluid communication with the inlet for the heated feed of natural gas 20 of the steam reformer 19.

[0124] This embodiment of the system will enable the person skilled in the art to use the heated feed of natural gas 1 to produce a reformed gas, comprising a mixture of carbon monoxide and hydrogen 22. It will be evident to the person skilled in the art that, optionally, a secondary reformer 53 can be placed incorporated downstream the steam reforming unit 19 and upstream the shift conversion unit 24, for reacting the heated feed of natural gas 10 is reacted with air 54, as a source of oxygen, and thereby further increasing the conversion of the natural gas into the reformed gas 22, comprising hydrogen and carbon monoxide. The gas leaving the secondary reformer 53 can then be fed to the shift conversion unit 24.

[0125] Reference is made to FIG. 2. According to one embodiment of the system of the disclosure, the system further comprises: [0126] a shift conversion unit 24 for reacting carbon monoxide gas produced in the steam reformer 19 with water 48, thereby producing a mixture of carbon dioxide and hydrogen 27, in direct fluid communication with the steam reformer 19; [0127] a carbon dioxide removal unit 28 in direct fluid communication with the shift conversion unit 27, for separating hydrogen 31 from carbon dioxide in the mixture of carbon dioxide and hydrogen 27 formed in the shift conversion unit 24; [0128] a methanation unit 32 in direct fluid communication with the carbon dioxide removal unit 28 for converting amounts of carbon monoxide gas formed in the steam reformer 19 and of carbon dioxide formed in the shift conversion unit 24 remaining in the hydrogen gas 31 into methane, thereby providing hydrogen gas 35 essentially free in carbon monoxide and carbon dioxide; and [0129] an ammonia synthesis unit 36 for reacting the hydrogen gas provided by the methanation unit 32 with nitrogen gas 49, thereby forming ammonia 45, in direct fluid communication with the methanation unit.

[0130] This embodiment of the method will enable the person skilled in the art to use the heated feed of natural gas 1 to produce ammonia 45. The supply of nitrogen gas 49 to the ammonia synthesis unit 36, also commonly known as the Haber Bosch synthesis, is necessary in order for the hydrogen gas essentially free in carbon monoxide and carbon dioxide 35 to react with nitrogen 49 in the ammonia synthesis unit 36, thereby producing ammonia 45. Nitrogen gas 49 can be supplied to the ammonia synthesis unit 36 through, for example, an air separation unit (not shown) that splits the oxygen in the air from nitrogen gas 49. Alternatively, if as described in relation to the previous embodiment, a secondary reformer 53 is located downstream the steam reformer 19 and upstream the shift conversion unit 24, nitrogen gas 49 is then supplied to the ammonia synthesis through the air 54 supplied to the secondary reformer 53.

[0131] In a third aspect of the disclosure is disclosed the use of the system of the disclosure for heating, according to the method of the disclosure, a feed of natural gas used as feed for a steam reformer of an ammonia production system.

Example

[0132] Reference is made to FIGS. 1 to 4.

[0133] Heat from the flue gas 2 was recovered in the heat recovery system 3. The feed of natural gas 1 was contacted with the first coil 4 and pre-heated to 210° C. to produce the pre-heated feed of natural gas 9. This pre-heated gas stream 9 then was splitted into a gas stream 6 having a temperature ranging from 180° C. to 210° C. used as fuel and a remaining portion of the pre-heated gas stream 9. The pre-heated feed of natural gas 9 then was further heated upon feeding to the second coil 5, thereby yielding a heated feed of natural gas 10 having a temperature of 370° C. The heated feed of natural gas 10 was treated in the sulfur removal unit 11 and subsequently mixed with steam (in a steaming unit) prior to being reacted in the tube section 50 of the steam methane reformer 19, into carbon monoxide and hydrogen, comprised in the reformed gas 22. The fuel gas in the furnace chamber 51 was produced by mixing the gas stream 6 with a portion of the heated feed of natural gas 10, thereby producing the gas stream 40 having a temperature ranging from 150 to 170° C. The reformed gas 22 produced from the steam reformer 19 then was reacted in a secondary reformer 53, in order to produce additional carbon monoxide and hydrogen in the reformed gas 22. The reformed gas 22 was consecutively treated in the shift conversion unit 24, producing a mixture of carbon monoxide and hydrogen 27, in the carbon dioxide removal unit 28, producing the hydrogen gas flow 31, in the methanation unit 32, producing the hydrogen gas stream 35, essentially free in carbon monoxide and carbon dioxide, and in the ammonia synthesis unit 36, thereby producing ammonia 45.