AMMONIA CRACKING PROCESS INTEGRATED WITH RENEWABLE ELECTRICITY FOR REDUCED OPEX AND INCREASED FLEXIBILITY

Abstract

In the present invention, energy efficiency measures within the ammonia cracking process go beyond achieving a zero steam export configuration. A process flowsheet including all energy efficiency measures associated with better heat integration is targeted, where external energy from the NPO can be used to reduce ammonia consumption. This external energy is preferably cheaper than the NH3 feed, only then a reduction in H2 TCO is expected. Intermittently, renewable energy is available in abundance and at very low prices (lower than NH3 on a per MJ basis). The approach described in the present invention is to integrate electricity into the ammonia cracking without reducing the overall efficiency (NH3 PCS + Electricity for specific H2 production). Abstract Figure: Fig. 2

Description

Title of the invention: AMMONIA CRACKING PROCESS INTEGRATED WITH RENEWABLE ELECTRICITY FOR REDUCED OPEX AND INCREASED FLEXIBILITY

[0001] The present invention relates to a method for producing hydrogen using non-hydrocarbon raw materials. More specifically, embodiments of the present invention relate to the use of ammonia as a raw material in a hydrogen production plant instead of hydrocarbons, in particular natural gas.

[0002] In order to reduce the effects of carbon dioxide emissions, new energy carriers are becoming increasingly important. Hydrogen is one of the main energy carriers; however, due to its small molecular size, high pressure requirements and very low boiling point, the transportation of elemental hydrogen is difficult and expensive.

[0003] Ammonia (NH3) has received some attention in the literature, since existing infrastructure can be used for storage and transportation (e.g., LPG - liquefied petroleum gas) infrastructure. Thus, hydrogen production from ammonia, rather than natural gas, is expected to play a major role in the future of hydrogen as a key molecule in the low-carbon energy transition.

[0004] Cracking of ammonia to produce hydrogen is well reported and published. Reference is made herein to a tubular combustor ammonia cracker in which ammonia is cracked to H2+N2 over a catalyst. The thermal reaction for cracking ammonia is supplied externally via fuel combustion. Several process schemes are published in which the combustion load can be reduced by preheating / superheating the ammonia feed, preheating the combustion air used for combustion, partially cracking the ammonia (upstream) outside the main firebox type cracker (firebox in this disclosure) in an adiabatic / heated pre-cracker. Using appropriate thermal integration of the process stream and flue gases can result in a system in which steam co-production can be zero.

[0005] It is proposed to use electricity in the ammonia cracking process to drive motors for fans, pumps and instruments, etc.

[0006] Some of the problems associated with the separation methods known so far are as follows: Ammonia cracking heat is required at different temperature levels. The heat is usually supplied via the combustion of an external fuel. Although with good thermal integration and pre-cracking steps, a process flowsheet without steam co-production can be achieved, the ammonia-to-H2 efficiency is still low.

[0007] Therefore, it would be advantageous to provide a solution enabling efficient production of hydrogen from an ammonia feed gas without suffering from the aforementioned drawbacks.

[0008] Furthermore, in typical steam turbine generators (STGs), the gaseous fuel is burned under pressure in a combustion chamber and introduced into the gas turbine. The exhaust gases at the outlet of the gas turbine still contain a significant amount of energy. These hot flue gases are used to generate high-pressure superheated steam. The remaining heat is used to preheat the air for combustion and the BFW for steam generation. The remaining heat in the flue gases, which is about 130°C, is lost to the atmosphere via the flue gas stack. The high-pressure superheated steam is then used to generate electricity in steam turbines. The exhaust steam from the STG is drawn through a vacuum system where the pressure is defined by the available coolant / condensate fluid, which is typically cooling water.Typically, steam conditions at the condenser inlet are approx. 60°C and 0.3 bara.

[0009] One of the problems with this configuration is that in the electricity generation scheme described above, the condensation of steam releases a lot of energy to the atmosphere via a cooling water system. Thus, in a stand-alone electricity generation system, there is no offtake for low temperature / quality heat, as it is lost to the atmosphere as explained previously.

[0010] The present invention relates to an apparatus and method that satisfy at least one of these needs. In some embodiments of the invention, an ammonia feed gas may be cracked to form hydrogen, and then unreacted NH3 is separated from a cracked gas downstream of the cracker, before the recovered ammonia is recycled for use as fuel or raw material.

[0011] In the present invention, the energy efficiency measures within the ammonia cracking process go beyond achieving a configuration without steam export. A process flowsheet including all energy efficiency measures associated with better heat integration is targeted, where external energy from the NPO can be used to reduce ammonia consumption. This external energy must be less expensive than the supply of NH3, only then is a reduction in H2 TCO expected. Intermittently, renewable energies are available in abundance and at very low prices (below NH3 per MJ). The approach described in the present invention is to integrate electricity into ammonia cracking without reducing overall efficiency (NH3 LHV + electricity for a specific H2 production).

[0012] In another embodiment, since a future use of hydrogen produced by ammonia cracking is for electricity generation, it is anticipated that such hydrogen-producing ammonia cracking units will be located close to the end use, namely hydrogen fuel-based power plants. Therefore, in some embodiments of the present invention, it may be useful to recover waste heat from a hydrogen-based power plant, which can be used in ammonia cracking units, thereby increasing the overall efficiency of ammonia in electricity generation.

[0013] A method for producing hydrogen using a feed stream comprising ammonia is provided. The method may include the steps of: preheating an ammonia feed stream; vaporizing the ammonia feed stream to form a gaseous ammonia feed; cracking the gaseous ammonia feed in an ammonia cracker to produce a cracked gas stream comprising hydrogen, nitrogen, and unreacted ammonia; cooling the cracked gas stream to a first temperature that is sufficient to condense at least a portion of the unreacted ammonia to form a two-phase fluid; separating the two-phase fluid in an ammonia separator to produce a liquid ammonia stream and an overhead gas stream composed primarily of hydrogen and nitrogen;and recycling the liquid ammonia stream produced by the ammonia splitter, or a stream derived therefrom, to a point upstream of the ammonia cracker, the upstream point possibly comprising a fuel inlet and / or an ammonia feed inlet, the process parameters being selected such that the NH3 cracking process is in an energy deficit state, the energy deficit being compensated by additional energy supplied from outside the facility (OSBL) and / or a power plant operating on hydrogen produced by an ammonia cracking plant. ;

[0014] In optional embodiments of the method of the invention: • the additional energy is in the form of electricity; • additional energy is provided to heat the combustion air used to burn the fuel; • additional energy is provided to heat the combustion air used to burn the fuel and preheat / vaporize the NH.3 feed the process. additional energy is provided to heat the combustion air used for fuel combustion and preheat / vaporize the NH3 feed to the process; an inlet temperature of a precracking stage is between 200 and 650°C, preferably between 350 and 500°C; an inlet temperature of a hot cracking gas providing heat to the feed gas is between 500 and 750 °C, preferably between 600 and 700 °C a hot cracking gas comes from a hearth-type cracker (or combustion chamber) equipped with catalytic tubes to carry out the ammonia cracking reaction; the hot cracking gas from said hearth-type cracker is at a temperature of 650 to 850°C, preferably between 700 and 800°C; The said hearth-type cracker is also equipped with an internal heat recovery mechanism (SMR-X). said hearth-type cracker is supplied with combustion air at a temperature between 500 and 700°C, preferably between 530 and 650°C; the hearth-type cracker comprises the absence of an internal heat recovery mechanism; the flue gases from the NH3 cracking plant are cooled to a temperature of 400 to 600 °C by supplying heat to the combustion air and to the NH3 feed and / or to the partially cracked ammonia in the pre-cracking stage; additional energy includes renewable electricity; additional energy includes non-renewable electricity; heat from the power plant arrives in the form of low-pressure steam; the flue gases from the gas turbine are cooled to a temperature of 500 to 800°C, preferably 650 to 750°C, providing heat to the high-pressure steam boiler and the high-pressure steam superheater; the cold flue gases from the NH3 cracking plant and the cold flue gases from the gas turbine plant are mixed; and / or The cooler mixed flue gases are then cooled by supplying heat to the combustion air, producing and superheating medium pressure steam and preheating the feed water to the boiler.

[0015] These and other features, aspects and advantages of the present invention will be better understood in light of the following description, claims and accompanying drawings. It should be noted, however, that the drawings illustrate only several embodiments of the invention and should therefore not be considered as limiting the scope of the invention since it may admit other equally effective embodiments.

[0016] [Fig. 1] shows an embodiment of a hydrogen production plant using ammonia as feedstock in accordance with a prior art embodiment.

[0017] [Fig.2] shows an embodiment of a hydrogen production plant using ammonia as a feedstock that includes the integration of external electrical power in accordance with an embodiment of the present invention.

[0018] [Fig.3] shows a second embodiment of a hydrogen production plant using ammonia as a raw material which includes the integration of external electrical energy in accordance with an embodiment of the present invention.

[0019] [Fig.4] represents an embodiment of a hydrogen production plant using ammonia as feedstock in accordance with an embodiment of the prior art.

[0020] [Fig.5] shows a third embodiment of a hydrogen production plant using ammonia as a feedstock which includes the integration of external electrical energy in accordance with an embodiment of the present invention.

[0021] [Fig.6] shows a fourth embodiment of a hydrogen production plant using ammonia as a raw material which comprises the integration of external electrical energy in accordance with an embodiment of the present invention.

[0022] Although the invention is described in connection with several embodiments, it will be understood that it is not intended to limit the invention to these embodiments. Rather, it is intended to cover all alternatives, modifications, and equivalents that may be included within the spirit and scope of the invention defined by the appended claims.

[0023] A reference base case is provided in [Fig. 1], based on the cracking of ammonia to produce hydrogen. Liquid ammonia is pumped to the required pressure which is defined by the required H2 pressure at the end use out of the plant. The ammonia is preheated, vaporized and superheated up to 400 °C using the heat supplied by cracking gas, flue gas, and LPG steam. The superheated ammonia steam passes through a suitable catalyst bed inside tubes with heat supplied to the gas flowing in the tubes. The catalyst-filled tubes are suitably arranged in a pressure shell. The partially converted NH3 along with H2+N2 is fed into the hearth-type main cracker. The cracking temperature is selected to achieve >95% of the NH3 feed. The cracked gas (after supplying heat to the feed gas in the tubes using HLX tubes) is cooled by supplying heat to the feed gas and steam boilers. The cracked gas cooled to 20 °C is sent to the scrubbing and recovery section where the unconverted ammonia is recovered and used as fuel in the ammonia cracking process.

[0024] Compared to [Fig.2], the combustion air is preheated in an electrically heated air preheater. For optimal heat integration, said electrical air preheater is located between the hot air preheater and the cold air preheater using flue gas as a heat transfer fluid. In this electrically heated air, the combustion air is preheated from 280°C to 435°C. The energy saved in the FG by this implementation makes it possible to superheat the main charge of the cracker up to a temperature of 520°C. The increase in the superheat temperature of the feed reduces the ignition load in the main cracker and thus the overall ammonia consumption.

[0025] In a second embodiment of the present invention, shown in [Fig. 3], in addition to (partial) preheating of the combustion air using green electricity, a portion of the total ammonia entering the process is preheated and vaporized using green electricity. Alternatively, energy via renewable electricity can also be supplied directly to the steam drum to generate additional steam, which is then used to preheat and superheat the ammonia introduced into the process. [Tables 1] figure. 1 figure. 2 figure. 3 Parameter Base case Integrated 1 Integrated 2 Total ammonia feed kg / h 64734 63892 63138 Excess steam in the NH3 cracking part kg / h 0 0 0 Ammonia consumption kg NH3 / kg H2 7.18 7.09 7.01 Pre-cracker inlet temperature °C 400 400 400 Pre-cracker outlet temperature °C 403 416 416 Main cracker feed superheat temperature °C 452 518 565 Combustion air preheat temperature. °C 650 650 650 Renewable electricity for an ammonia cracking plant MW 0 3.83 7.19 Total cost of ownership H2 (1) € / kg H2 3.36 3.33 15h30 H2 TCO (with 50% of the operating time with renewable electricity) € / kg H2 3.36 3.34 3.34 NH3 to H2 efficiency (PCI basis) H2*PCT / (NH3*PCT+renewable energy) % 89.1 89.2 89.4

[0026] Compared to [Fig.4], a reference scenario is provided. This embodiment is based on cracking ammonia to produce hydrogen and the same hydrogen is used in a power plant to produce electricity. Liquid ammonia is pumped to the required pressure, which is defined by the inlet pressure of the gas turbine (assumed 45 barg in the comparison below). The ammonia is preheated, vaporized and superheated up to 400 °C using the heat provided by the cracking gas, the flue gas and the LPG steam. The superheated ammonia steam passes through a suitable catalyst bed inside tubes with heat supplied to the gas flowing in the tubes. The catalyst-filled tubes are suitably arranged in a pressure shell. Partially converted NH3 with H2+N2 is fed into the hearth-type main cracker.The cracking temperature is selected to achieve >95% of the NH3 feed. The cracked gas (after providing heat to the feed gas in the tubes using HLX tubes) is cooled by providing heat to the feed gas and steam boilers. The cracked gas cooled to 20 °C is sent to the scrubbing and recovery section where the unconverted ammonia is . recovered and used as fuel in the ammonia cracking process.

[0027] AH2+N2 mixture with -75 mol% H2 is sent to the gas turbine where it is burned using preheated combustion air. In the comparison below, the flue gases leaving the turbine are approx. 950 °C which is then used in the steam cycle to generate high pressure steam, HP (110 barg) and medium pressure steam, MP (45 barg). The HP steam is superheated to 510 °C and expanded to the MP level in the first stage of the steam turbine. The MP steam from the MP steam boiler in FG and the HP steam expanded to the MP level are mixed and then superheated to 410 °C. The superheated MP steam is then sent to the 2nd stage of the steam turbine. Finally, the steam is expanded to 0.3 bara (corresponds to -65 °C). The gas turbine and steam turbine spin the generator to produce electricity. The vacuum-expanded steam is then condensed using cooling water.

[0028] In the embodiment shown in [Fig.5], the partially cracked Nh3 feed stream is further superheated to a higher temperature by utilizing the waste heat of the flue gases up to a temperature of 570°C. This will reduce the steam production in the flue gas boiler of the NH3 cracking portion by two times - (1) a higher feed temperature of the combustor type cracker results in lower heating, lower flue gas flow rate, and (2) higher heat absorbed by the flue gases in the feed. The superheater results in less heat available for steam generation. As the base case was a balanced steam configuration, meaning that the steam required in the NH3 cracking portion was produced internally and there is no steam export or import.However, the increase in charge superheat and combustion air temperature results in a steam deficit for the Nh3 cracking part. The power / steam required for the Nh3 cracking part is provided by a nearby power plant, which operates on H2 fuel produced by the NH3 cracking plant.

[0029] In the embodiment shown in [Fig.6], the flue gases from the Nh3 cracker are only used to preheat the air and superheat the Nh3 feed streams and then mixed with the flue gases from the gas turbine at a suitable temperature level. This could result in investment savings for the WHRS with the NH3 cracking unit after the feed and combustion air preheater. A combined flue within the power plant efficiently extracts heat from the mixed flue gases with a common stack and flue gas fan. [Tables 2] figure. 4 figure. 5 figure. 6 Parameter Base case Integrated 1 Integrated 2 Total ammonia requirement kg / h 65582 62253 61780 Excess steam in the cracking part NH3 kg / h 0 0 0 Ammonia consumption kg NH3 / kgH2 7.29 6.92 6.87 Pre-cracker inlet temperature Ôc 400 400 400 Pre-cracker outlet temperature Ôc 429 425 426 Main cracker feed superheat temperature Ôc 429 570 600 Combustion air preheating temperature. ok 468 650 650 Heat supplied from power plant to ammonia cracking plant kW 0 14934 18783 Hydrogen from Nh3 cracking plant to gas turbine kg / h 8993.8 8993.8 8993.8 Net power produced by power plant kW 167049 165016 160561 NH3 to H2 efficiency (LHV basis) H2*PCS / (NH3*PCS+power plant energy) % 87.7 88.3 88.0 H2 to energy efficiency (LHV basis) Electricity produced / (H2*TCG) % 56.2 55.5 54.0 NH3 to energy efficiency (LHV basis) Electricity produced / (NH3 *BT) % 49.3 51.3 50.3 .

[0030] With reference to the figures, unless otherwise indicated, the dotted and dotted lines between two pieces of equipment are intended to indicate that the equipment is, at a minimum, thermally integrated. In some cases, dotted lines originating from "electricity" indicate that the equipment receives electrical power, preferably from an external NPO source.

[0031] Although the invention has been described in conjunction with specific embodiments thereof, it is apparent that numerous alternatives, modifications, and variations will occur to those skilled in the art in light of the foregoing description. Accordingly, it is intended to encompass all such alternatives, modifications, and variations as fall within the spirit and broad scope of the appended claims. The present invention may suitably comprise, consist of, or consist essentially of the elements disclosed and may be practiced in the absence of any undisclosed element. In addition, language referring to order, such as first and second, is to be understood in an exemplary and not a limiting sense. For example, those skilled in the art may recognize that certain steps or devices may be combined into a single step / device.

[0032] The singular forms "a," "a," and "the" include plural referents, unless the context clearly indicates otherwise. Terms about / approximately a particular value include that particular value plus or minus 10%, unless the context clearly dictates otherwise.

[0033] Optional or elective means that the event or circumstance described later may or may not occur. The description includes cases where the event or circumstance occurs and cases where it does not.

[0034] Ranges may be expressed herein 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 ranges from one particular value and / or to the other particular value, as well as all combinations within said range.

Claims

[Claim 1] Claims A method of producing hydrogen using a feed stream comprising ammonia, the method comprising the steps of: preheating an ammonia feed stream; vaporizing the ammonia feed stream to form a gaseous ammonia feed; a cracking process comprising cracking the gaseous ammonia feed in an ammonia cracker to produce a cracked gas stream comprising hydrogen, nitrogen and unreacted ammonia; cooling the cracked gas stream to a first temperature that is sufficient to condense at least a portion of the unreacted ammonia to form a two-phase fluid; separating the two-phase fluid in an ammonia separator to produce a liquid ammonia stream and an overhead gas stream composed primarily of hydrogen and nitrogen; and recycling the liquid ammonia stream produced by the ammonia splitter, or a stream derived therefrom, to a point upstream of the ammonia cracker, the upstream point possibly comprising a fuel inlet and / or an ammonia feed inlet, wherein the process parameters are selected such that the cracking process is in an energy deficit state, the energy deficit being compensated by additional energy supplied by a power plant which operates on hydrogen fuel produced by an ammonia cracking plant.

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