Boiling water reactor with auxiliary heaters, reactor revamping method and methanol synthesis

Abstract

The present invention relates to boiling water reactors arranged to receive a synthesis gas for producing raw gas products, such as a raw methanol product, particularly for transient operation, such as where the synthesis gas is at least partly provided by producing hydrogen by electrolysis of water or steam. Embodiments of the invention include a boiling water reactor, a method of revamping an existing boiling water reactor, and a process for producing raw gas product, such as raw methanol product, utilizing the boiling water reactor.

Description

[0001] Title:

[0002] BOILING WATER REACTOR WITH AUXILIARY HEATERS, REACTOR REVAMPING METHOD AND METHANOL SYNTHESIS

[0003] The present invention relates to boiling water reactors arranged to receive a synthesis gas for producing raw gas products, such as a raw methanol product, particularly for transient operation, such as where the synthesis gas is at least partly provided by producing hydrogen by electrolysis of water or steam. Embodiments of the invention include a boiling water reactor, a method of revamping an existing boiling water reactor, and a process for producing raw gas product, such as raw methanol product, utilizing the boiling water reactor. Preferred embodiments are directed to methanol synthesis.

[0004] Synthesis gas (syngas) is a mixture of hydrogen and carbon oxides (carbon monoxide and carbon dioxide), typically produced from natural gas or a carbonaceous (renewable or fossil) feedstock via processes like steam reforming or gasification. Hydrogen and carbon monoxide in the syngas may also be produced by electrolysis of a water feedstock, i.e. water or steam, and / or electrolysis of CO2. The syngas is used as an intermediate in producing synthetic natural gas, ammonia, methanol, and other chemicals.

[0005] Particularly for methanol, herein also referred to as MeOH:

[0006] Methanol is an important chemical feedstock used in a variety of industries including plastics, adhesives, and solvents. Methanol is becoming a highly relevant chemical as it can be utilized as energy carrier, more specifically as hydrogen carrier and thus suitably used as green methanol for transportation where methanol can be produced by renewable sources. Methanol may also be further converted to gasoline or jet fuel, thus providing green transportation fuels.

[0007] Typically, the methanol reaction, i.e. the MeOH synthesis reaction, involves the catalytic conversion of carbon oxides and hydrogen gases. In the present invention, the methanol reaction is performed in a so-called boiling water reactor. The boiling water reactor design for methanol synthesis comprises a reactor vessel i.e. a pressure shell, containing a plurality of tubes loaded with catalyst active for the exotherm methanol synthesis reaction. In the reactor vessel catalyst tubes are installed. The catalyst is typically composed of copper and zinc oxide, which are known to be effective catalysts for the methanol synthesis reaction. The pressure shell is equipped with a cooling system that provides cooling to the catalyst tubes, thus to the catalyst bed. The cooling system is designed to maintain the temperature of the catalyst bed within a specified range for the methanol synthesis reaction. The cooling system is preferably a water-cooled system that uses boiling water which circulates through the pressure shell to remove excess heat.

[0008] In operation, the reactants carbon oxides and hydrogen gas are introduced into the pressure shell at a controlled rate. The reactants flow through the catalyst bed, where they are at least partially converted into methanol. The remaining part may for instance be recycled back to the reactor forming a methanol synthesis loop.

[0009] The boiling water reactor design for methanol synthesis provides several advantages over traditional methanol production methods. A main advantage of using boiling water reactor is the efficient removal of reaction energy maintaining the temperature close to equilibrium being more effective.

[0010] The production of green methanol, which is methanol that is produced using renewable carbon source and / or hydrogen generated through electrolysis with a renewable energy source such as wind, solar, nuclear, hydro, geothermal, faces several challenges that need to be addressed to enable large-scale production and adoption.

[0011] During normal operation, the boiling water reactor provides the necessary cooling for the exotherm methanol synthesis reaction. However, due the nature of renewable electricity disruptions in the process, i.e. its inherent intermittency, insufficient supply of renewable electricity and thereby of hydrogen feed can cause a decrease in the methanol product yields. In some cases, this may even lead to a complete shutdown of the plant and process for producing methanol until the renewable electricity is available again. If the development of reaction heat in the methanol boiling water reactor stops, the reactor temperature gradually reduces because of heat loss eventually requiring a complete shutdown of the methanol synthesis. In such so-called eMeOH plants with hydrogen being produced from electrolysis generated by power, preferably renewable power i.e. renewable electricity, there is no frontend generating steam which can be used to heat-up the boiling water of the reactor. The plant is often isolated from other infrastructure (island mode) or close to combined heat power (CHP) plant where steam level available is not sufficient. Furthermore, downstream the methanol boiling water reactor, the methanol product produced is purified by removing water also produced during the methanol synthesis. The water removal is performed in typically large distillation columns requiring the use of the available steam.

[0012] The methanol boiling water reactor could be maintained hot by its start-up steam ejector using an auxiliary steam supply during hot standby i.e. hot idle operation. The steam ejectors are used for heating up the methanol reactor during start-up from cold conditions and same system could also be applied for maintaining it hot, for instance providing steam ejectors with medium pressure steam as the motive fluid. However, it would require the start-up steam system to be online all the time.

[0013] Applicant’s WO 2020 / 254121 discloses a process for the preparation of methanol in which hydrogen in the frontend is produced by electrolysis. WO 2010 / 144547 discloses a fuel synthesis system including a multiple methanol reactor train, operated in parallel from a common input of synthesis gas from a solar driven chemical reactor, and synthesis gas from a storage tank. Applicant’s co-pending patent applications PA 2023 30073 (DK202330073) and PA 2023 30091 (DK202330091) disclose a process for the preparation of methanol by using auxiliary heaters.

[0014] There is a need for a reliable and effective auxiliary heating that can be used in the event of disruptions in the methanol synthesis process, to ensure the efficient and continuous operation of the process.

[0015] To prevent such disruptions from impacting the methanol synthesis process, it is necessary to maintain the temperature of the reactor coolant at a constant level.

[0016] More generally, to prevent disruptions from impacting a process utilizing a synthesis gas, such as any of: a methanol process, a water gas shift conversion (WGS, herein referred to as shift) process, a methanation process, an ammonia process, it is necessary to maintain the temperature of the reactor coolant at a constant level. This is achieved by providing auxiliary heating to the reactor coolant, in addition to the heat provided by the boiling water reactor, as set out in the appended claims and corresponding embodiments recited herein.

[0017] Accordingly, in a first general embodiment of a first aspect of the invention, there is provided a boiling water reactor (BWR) arranged to receive a synthesis gas 101 and provide a raw gas product 103, in which the boiling water reactor 100 comprises: a pressure shell 102, the pressure shell 102 comprises a tube side 104 and a boiling water side 106; the tube side 104 comprises a plurality of tubes 104’ and a fixed bed of catalyst 104” arranged within the plurality of tubes 104’; the boiling water reactor 100 is further arranged to receive boiling water 105 and circulate the boiling water 105 within the water side 106 for removing excess heat generated in the tube side 104; the boiling water reactor 100 further comprises a steam drum 108 arranged in fluid communication with the pressure shell 102 for providing the boiling water 105; wherein the pressure shell 102 defines an inner surface and an outer surface along the pressure shell length 102 L, and wherein the pressure shell 102 further comprises one or more auxiliary heaters 110 which are arranged along a portion 110 L of said outer surface of the pressure shell 102 and in direct contact thereto; and wherein the boiling water reactor is any of: i) a methanol boiling water reactor in which the synthesis gas is methanol synthesis gas, the catalyst is a methanol synthesis catalyst, and the raw gas product is a raw methanol product; ii) a shift boiling water reactor in which the synthesis gas is pre-shifted synthesis gas, in which the catalyst is a shift catalyst, such as any of a high temperature shift (HTS) catalyst, a medium temperature shift (MTS) catalyst and a low temperature shift (LTS) catalyst, and the raw gas product is a shifted synthesis gas i.e. a gas having a higher hydrogen and CO2 content than the pre-shifted synthesis gas; iii) a methanation boiling water reactor, in which the synthesis gas is methanation synthesis gas, in which the catalyst is a methanation catalyst and the raw gas product is a raw methane-rich gas, such as a raw substitute natural gas (SNG) or a raw renewable natural gas (RNG); iv) an ammonia boiling water reactor in which the synthesis gas is ammonia synthesis gas, the catalyst is an ammonia synthesis catalyst, and the raw gas product is a raw ammonia product. Hence, for instance, in a first aspect of the invention, there is provided a methanol boiling water reactor arranged to receive a methanol synthesis gas and provide a methanol product, in which the methanol boiling water reactor comprises: a pressure shell, the pressure shell comprises a tube side and a boiling water side; the tube side comprises a plurality of tubes and a fixed bed of methanol synthesis catalyst arranged within the plurality of tubes; the methanol boiling water reactor is further arranged to receive boiling water and circulate the boiling water within the water side for removing excess heat generated in the tube side; the methanol boiling water reactor further comprises a steam drum arranged in fluid communication with pressure shell for providing the boiling water; wherein the pressure shell defines an inner surface and an outer surface along the pressure shell length, and wherein the pressure shell further comprises one or more auxiliary heaters which are arranged along a portion of said outer surface of the pressure shell and in direct contact thereto.

[0018] For the purposes of the present application:

[0019] The term “first aspect of the invention” means embodiments associated with a boiling water reactor, such as a methanol boiling water reactor. The term “second aspect of the invention” means embodiments associated with a method of revamping an existing boiling water reactor, such as a methanol boiling water reactor. The term “third aspect of the invention” means embodiments associated with a process for producing a raw gas product, such as a raw methanol product.

[0020] The term “present invention” or simply “invention” may be used interchangeably with the terms “present application” or simply “application”, respectively.

[0021] The term “and / or” means in connection with a given embodiment any of three options. The term “and / or” may be used interchangeably with the term “at least one of” the three options.

[0022] The term “boiling water reactor (BWR)” may be used interchangeably with the term “boiling water reactor (BWR) arrangement”.

[0023] The term “comprising” includes “comprising only” i.e. “consisting of”. The term “suitably” means “optionally”, i.e. an optional embodiment. The term “synthesis gas” may be used interchangeably with the term “syngas” and means any of: “methanol synthesis gas”, “pre-shifted synthesis gas”, “methanation synthesis gas”, “ammonia synthesis gas”. The term “methanol synthesis gas” means a gas mixture of hydrogen and carbon oxides (carbon monoxide and carbon dioxide), preferably having a module “M” defined in molar terms: M=(H2-CC>2) / (CO+CO) of 1.9-2.2, more preferably of 2.

[0024] The term “pre-shifted synthesis gas” means a gas mixture comprising hydrogen and carbon oxides prior to being shifted, i.e. prior to being subjected to water gas shift (WGS), by which carbon monoxide reacts with water to increase the content of hydrogen and carbon dioxide. It is thus understood that the shifted synthesis gas is a gas having a higher hydrogen and CO2 content than the pre-shifted synthesis gas. As is well-known in the art, the shift (WGS) is any of: high temperature shift (HTS), medium temperature shift (MTS) catalyst, low temperature shift (LTS) catalyst, and combinations thereof.

[0025] The term “methanation synthesis gas” means a gas mixture comprising hydrogen and carbon oxides which reacts to produce a methane-rich gas. The raw product gas from the methanation BWR may thus be regarded as a raw substitute natural gas (SNG) or raw renewable natural gas (RNG). RNG results where the methanation synthesis gas is produced upstream from renewable sources, for instance by renewable electricity driving an electrolysis unit and / or renewable carbonaceous feed fed to a thermal decomposition unit such as a gasifier.

[0026] The term “ammonia synthesis gas” means a gas mixture of hydrogen and nitrogen, preferably with the molar ratio 3H2:N2.

[0027] The term “pressure shell length (102 L)”, as shown in the appended figure, means the distance extending along the length direction of the pressure shell 102 from a first boundary 102 L’ to a second boundary 102 L”, in which the first boundary 102 L’ defines the inlet position of the plurality of tubes 104’ and the second boundary 102 L” defines the outlet position of the plurality of tubes 104’.

[0028] The term “at least a portion of” a certain item means the entire item or a portion (fraction) of the item. For instance, the term “at least a portion” of a certain process stream, such as a gas stream, means that the entire gas stream or a portion (fraction) of the stream is used. The gas stream may simply be split into fractions of identical composition. It is not meant to refer to a separation of the components of the gas.

[0029] The use of the article “a” or “an” means “at least one”, or alternatively “one or more”. For instance, the term “a methanol boiling water reactor” means “at least one methanol boiling water reactor”, or “one or more methanol boiling water reactors”. The term “power” or “renewable power” may be used interchangeably with the term “electricity” or “renewable electricity”, respectively.

[0030] The term “fluid communication” means “direct or indirect fluid communication”. The term “direct fluid communication” means that there is no intermediate unit or step changing the composition of a process stream. Conversely, the term “indirect fluid communication” means that there is an intermediate unit or step changing the composition of a process stream.

[0031] Unless otherwise stated, percentages (%) or concentrations of a given process stream are provided as vol.%

[0032] The the term “hot standby” means “hot idle operation” which is a specific form of transient operation.

[0033] The term “transient operation” means non-continuous operation of the boiling water reactor, e.g. the methanol boiling water reactor, where the boiling reactor has not reached a steady state corresponding to normal operation, including the supply of a continuous feed of synthesis gas to the reactor. Thus, during the transient operation there is often no hydrogen feed or insufficient hydrogen feed being generated, for instance in upstream electrolysis. Transient operation corresponds therefore to, in an embodiment, periods without operating electrolysis upstream the boiling water reactor. The transient operation is any of start-up operation, hot-idle operation, and shut-down operation. The start-up operation may also comprise reducing of the catalyst in the boiling water reactor, thus a period in which the catalyst is transitioned into its active-reduced form.

[0034] Other definitions are provided in connection with one or more of above or below embodiments.

[0035] The invention provides integrated auxiliary heater(s) that enable maintaining the temperature of the boiling water reactor e.g. methanol boiling water reactor coolant at a safe level, ensuring the efficient and continuous operation of the e.g. the methanol synthesis process.

[0036] The invention enables uniform heating along the circumference (perimeter) of the pressure shell while also enabling a short time for reaching the required temperature. The auxiliary heater(s) are in direct contact with the surface of the pressure shell, thus ena- blina direct heat conduction with no need of including piping and pumping equipment as there is no associated pressure drop compared to e.g. a situation where the auxiliary heater is provided outside the pressure shell and connected thereto via piping and attendant pump(s). In other words, the auxiliary heater(s) are integrated with the pressure shell, which means that there is no piping connecting the auxiliary heater(s) with the pressure shell of the boiling water reactor, and the associated plot size is thereby reduced. The invention results therefore also in low operating expenses (OPEX) and capital expenses (CAPEX).

[0037] For instance, for methanol synthesis, the invention enables providing the pressure shell of the methanol boiling water reactor with e.g. electrical tracing to heat up the water and ensure boiling to start circulation in the reactor and thereby heat-up the tubes and catalyst. There is no need for steam to heat up the methanol reactor during a transient operation such as start-up or to maintain temperature during a transient operation such as idle mode operation when hydrogen production upstream is limited due to limited production of renewable electricity.

[0038] While an immediate approach would be in e.g. a methanol boiling water reactor to maintain it hot by means of its start-up steam ejector using an auxiliary steam supply during hot standby i.e. hot idle operation, the invention surprisingly provides a completely different solution. It will be understood that the steam ejectors, as earlier recited, are traditionally used for heating up the methanol boiling water reactor during start-up from cold conditions and thus the same system could also be applied for maintaining it hot, for instance providing steam ejectors with medium pressure steam as the motive fluid.

[0039] Any available steam is thus now utilized for driving downstream distillation columns for removal of water produced in the methanol synthesis. As is well-known in the art, the raw methanol product is produced by the exothermic reactions: CO+2H2=CH3OH and CC>2+3H2=CH3OH+H2O. AS power is the main feed input to a green methanol plant, i.e. eMethanol plant, and the required power to perform as herein intended is insignificant compared to the total power consumption including upstream electrolysis, the solution according to the present invention turns out to be an excellent fit for green methanol plants and thus for any downstream plants relying on green methanol as feed, such as in plants for producing gasoline and jet fuel. The jet fuel may thus be used as part of the supply chain of sustainable aviation fuels (SAF). There is no need for steam import to drive the downstream distillation while at the same time coping with the shortcomings of transient operation of the BWR.

[0040] The steam drum is in fluid communication and thereby connected with the pressure shell by a riser / downcomer system. The riser / downcomer system comprises a conduit, such as a pipe or channel, that runs alongside the pressure shell. The primary function of the riser / downcomer is to supply coolant water from the upper part of the pressure shell to the bottom part of the pressure shell by natural circulation.

[0041] The invention enables maintaining pressure and / or temperature on the shell side of the methanol boiling water reactor during a transient operation such as hot standby, which is also relevant at least for the following reasons: i) If e.g. the methanol catalyst is exposed to low temperatures, there will be risk of wax condensing inside the catalyst causing catalyst deactivation; ii) if the reactor cools down and is heated up again during restart and this procedure is carried out often, there will be risk of fatigue stress of the associated mechanical parts. By maintaining the boiling water pressure constant and thereby keeping the temperature variation for the reactor to a minimum during standby mode, fatigue stress need not to be considered for the mechanical design, thus providing the additional benefit of significantly simplifying the reactor design.

[0042] In an embodiment, said one or more auxiliary heaters 110 are powered by electricity 110’, such as electricity produced from renewable sources comprising at least one of wind, solar, nuclear, hydroelectric, geothermal. Thereby the carbon intensity and thereby also the carbon footprint of the associated methanol plant and process is significantly reduced.

[0043] In an embodiment, the one or more electric heaters 110 are of the induction type or resistance type. As is well known in the art, induction type heaters generate heat by magnetic fields inducing eddy currents in the material to be heated, which is thus directly heated. Resistance type heaters generate heat by passing an electric current through a resistive material, causing it to heat up due to electrical resistance. Preferably, the one or more electric heaters 110 are of the resistance type. By the invention, as already recited, the pressure shell further comprises one or more auxiliary heaters which are arranged along a portion of said outer surface of the pressure shell and in direct contact thereto. In an embodiment, said portion 110 L of the outer surface of the pressure shell 102 is between 0.1 and 100% of the outer surface of the pressure shell 102 L. In a particular embodiment, said portion 110 L of the outer surface of the pressure shell 102 is less than 2 / 3 of the outer surface of the pressure shell 102 L; preferably less than 1 / 2, such as between 1 / 10 and 1 / 3 of the outer surface of the pressure shell 102 L. For instance, said one or more auxiliary heaters define an inner surface and an outer surface, and the inner surface of the one or more integrated auxiliary heaters is in direct contact with said portion of the outer surface of the pressure shell.

[0044] Suitably, as shown in the appended figure, a horizontal central axis “A” running across the pressure shell defines an upper part of the pressure shell and a bottom part of the pressure shell. The pressure shell defines also a radius “R” as also shown in the figure. Hence, a horizontal direction is defined by central axis “A” or by radius “R”, as so is a length direction perpendicular to the horizontal direction. The length direction is thus here a vertical direction which refers to the direction along which the gravity force acts. The one or more auxiliary heaters are arranged along such length direction and along the circumference of the pressure shell, as also shown in the appended figure.

[0045] Suitably, the one or more auxiliary heaters are arranged symmetrically with respect to central horizontal axis “A” defining the upper portion of the pressure shell and the lower portion of the pressure shell, as also illustrated in the appended figure.

[0046] In an embodiment, the one or more auxiliary heaters 110 are provided as one or more metal and / or ceramic sheets and the curvature of the outer surface of the pressure shell 102 L corresponds to the curvature of inner surface 110 L of the one or more metal and / or ceramic sheets.

[0047] The inner surface of the one or more metal and / or ceramic sheets is in direct contact with the pressure shell.

[0048] The auxiliary heaters may for instance be provided as a single auxiliary heater, thereby as a substantially continuous belt around the pressure shell. The curvature of the outer surface of the pressure shell and the inner surface of the metal and / or ceramic sheet is then their circumferences, thus the total curvatures i.e. perimeters.

[0049] The auxiliary heaters may for instance be provided as a plurality of auxiliary heaters being arranged as discrete, i.e. distinct, metal and / or ceramic sheets, thereby as a substantially discontinuous belt around the pressure shell. The total curvature of the plurality of auxiliary heaters is then less than the total curvature, i.e. the perimeter, of the outer surface of the pressure shell.

[0050] The integrated auxiliary heaters may for instance be provided as discrete continuous belts. For instance, a discrete continuous belt may be provided as a metal sheet and another discrete continuous belt may be provided as a ceramic sheet.

[0051] Combinations of the above embodiments are also envisaged.

[0052] Any of these embodiments also enables uniform heating along the perimeter of the pressure shell while also enabling a short time for reaching the required temperature in the boiling water reactor.

[0053] In an embodiment, at least one of the metal sheets comprises one or more heating elements selected from a sheathed heating cable, a heat tape, or combinations thereof. A single or a plurality of metal sheets are suitably arranged to provide a continuous or discontinuous belt around the pressure shell. The pressure shell of the boiling water reactor is thereby provided with electrical tracing to heat up the water and ensure boiling to start circulation in the reactor and thereby heat-up the tubes and catalyst.

[0054] In an embodiment, at least one of the ceramic sheets comprises one or more flexible ceramic pads. A single or a plurality of flexible ceramic pads are suitably arranged to provide a continuous or discontinuous belt around the pressure shell. For instance, with flexible ceramic pads, electric resistance heating is enabled by connecting to a power supply providing alternating current. Flexible ceramic pads (FCP’s) have been in use in the industry for decades, but the purpose has been to perform so-called local post weld heat treatment (PWHT) of welds, thus for mitigation of welding-induced residual stresses in pressure vessels and pipes. For instance, in connection with process gas waste heat boilers (PGWHB), in case of a leak, which is a common failure mechanism for PGWHBs after many years of service, the tubes must be plugged at the tube sheets. In order to carry out this plugging in a long-term reliable manner, plugging by welding is required. Due to the presence of hydrogen in the process gas, a subsequent Post Weld Heat Treatment (PWHT) is conducted. Now surprisingly, FCPs are utilized to actively supply heat across the pressure shell of the boiling water reactor and to control the temperature therein. Traditionally, steam jacketing is used where a certain temperature is required to be maintained around the pressure shell. Further, as earlier explained, this enables also to divert the steam available to other units or sections of the plant, such as distillation in connection with the production of methanol.

[0055] Preferably, the auxiliary heaters are arranged to provide a continuous belt, as shown in the appended figure. This enables the best utilization of the available surface and uniform heating at least across the region of the pressure shell associated with that continuous belt.

[0056] In an embodiment, the one or more metal and / or ceramic sheets comprises one or more sheathed heating cables, the one or more sheathed heating cables comprising: an outer stainless-steel sheath and an inner conductor, such as a nichrome (nickelchromium) conductor, optionally also an intermediate insulation separating the steel sheath from the inner conductor. The electrical heating element, for instance here a sheathed heating cable, is directly attached to the pressure shell. The heat generated by the electrical current passing through the element is then transferred to pressure shell and thus to its interior, thereby quickly and efficiently maintaining or raising its temperature to the desired level for performing the methanol synthesis reaction.

[0057] In an embodiment, the metal and / or ceramic sheet, such as the one or more sheathed heating cables of a metal and / or ceramic sheet, comprise a circuit which is provided with a thermistor controlling power based on the temperature measured on water in the steam drum. The associated circuit may therefore include a thermistor controlling power, e.g. power ON / OFF, based on the temperature measured on water in the steam drum.

[0058] A thermistor is a type of resistor whose resistance changes significantly with temperature. As is well-known in the art, the term "thermistor" combines the terms "thermal" and "resistor". As used herein, the thermistor is a temperature sensor which is integrated into the heating system to monitor the temperature of the water in the steam drum of the boiling water reactor.

[0059] Suitably, the thermistor is attached to the steam drum and as the temperature of the water of the steam drum changes, so does the resistance of the thermistor. The change in resistance is then measured and converted into a temperature reading, which is then used to control the heat output of the heat tracing system of the metal and / or ceramic sheet(s) provided as the auxiliary heater(s) of the boiling water reactor. When the water temperature drops below a set point, there is an increase of the heat output to compensate for the temperature drop, and vice versa. This enables precise temperature control and thereby also better energy efficiency of the auxiliary heater(s) precisely meeting the limited power being available. Hence, the heat is only provided exactly when and where it is needed. Furthermore, a short time for reaching the required temperature is achieved.

[0060] In an embodiment, the boiling water reactor is arranged to operate as a loop reactor. For instance, a methanol boiling water reactor or ammonia boiling water reactor are arranged to operate as a loop reactor.

[0061] In operation, for methanol synthesis, the reactants carbon oxides and hydrogen gas in the methanol synthesis gas are introduced into the reactor at a controlled rate. The reactants flow through the catalyst bed, where they are partially converted into the raw methanol product. The remaining part is recycled back via a recycle compressor to the reactor forming a methanol synthesis loop. In another embodiment, the methanol boiling water reactor is arranged to operate as a once-through reactor. Thereby there is no need for a recycle loop and associated recycle compressor.

[0062] In operation, for ammonia synthesis, the reactants nitrogen and hydrogen in the ammonia synthesis gas are introduced into the reactor at a controlled rate. The reactants flow through the catalyst bed, where they are partially converted to the raw ammonia product. The remaining part is recycled back via a recycle compressor to the reactor forming an ammonia synthesis loop.

[0063] For a shift boiling water reactor, the shifted synthesis gas is suitably further supplied to a water separation unit, e.g. a process condensation unit, and the thus water-depleted shifted synthesis gas may be further supplied to: carbon dioxide removal, e.g. in an amine absorber or a cryogenic unit; and / or hydrogen purification e.g. in a pressure swing adsorption (PSA) unit.

[0064] For a methanation boiling water reactor, the raw substitute natural gas (SNG) or raw renewable natural gas (RNG) is further purified for separating methane from any other gases. The SNG or RNG, which then is similar to natural gas (NG), can be used for the same purposes as NG.

[0065] In a second aspect of the invention, there is provided a method of revamping an existing boiling water reactor.

[0066] Accordingly, there is provided a method of revamping a boiling water reactor 100, in which the boiling water reactor 100 is any of: a shift boiling water reactor, a methanation boiling water reactor, a methanol boiling water reactor, an ammonia boiling water reactor; the boiling water reactor 100 comprising: a pressure shell 102 comprising a tube side 104 and a boiling water side 106, the tube side 104 comprising a plurality of tubes 104’ and a fixed bed of catalyst 104” arranged within the plurality of tubes 104’, the boiling water reactor 110 being further arranged to receive boiling water 105 and circulate the boiling water 105 within the water side 106 for removing excess heat generated in the tube side 104, the boiling water reactor 110 further comprising a steam drum 108 arranged in fluid communication with the pressure shell 102 for providing said boiling water 105; the pressure shell 102 defining an inner surface and an outer surface along the pressure shell length 102 L; the method of revamping comprising:

[0067] - installing one or more auxiliary heaters 110 along a portion 110 L of the outer surface 102 L of the pressure shell 102 and in direct contact thereto.

[0068] The revamping provides a simple solution with surprisingly high associated benefits, as recited in connection with the first aspect of the invention. Further, the solution is provided without increasing plot size of the plant as the auxiliary heater(s) are integrated with the methanol boiling water reactor, as well as requiring fewest modifications to the existing reactor. Any of the embodiments and associated benefits of the first aspect of the invention (boiling water reactor) may be used in connection with the second aspect of the invention (method of revamping), or vice versa.

[0069] In a third aspect of the invention, there is provided a process for producing any of said raw gas products.

[0070] Accordingly, there is provided a process for producing a raw gas product, in which the raw gas product is any of: a shifted synthesis gas, a raw methane-rich gas, a raw methanol product, a raw ammonia product; the process comprising the steps of:

[0071] - providing a boiling water reactor 100 according to any of the preceding embodiments according to the first aspect of the invention;

[0072] - providing a synthesis gas 101 ;

[0073] - converting the synthesis gas 101 in boiling water reactor 100 to the raw gas product 103; the process further comprising in transient operation, thus in transient periods such as in periods without operating with upstream electrolysis:

[0074] - interrupting the provision of said synthesis gas 101 resulting in stop of the provision of the raw gas product 103 in the boiling water reactor 100;

[0075] - supplying power 110’ to the one or more auxiliary heaters 110 for providing heat to the boiling water reactor 110 by maintaining the boiling of the water in the water side 106 of the boiling water reactor 100.

[0076] In an embodiment, the raw gas product is a raw methanol product, the process comprising the steps of:

[0077] - providing a methanol boiling water reactor 100;

[0078] - providing a hydrogen feed, optionally by electrolysis of a water feedstock;

[0079] - providing a carbon oxide feed comprising CO and / or CO2, optionally in periods of operating said electrolysis;

[0080] - mixing at least a portion of the hydrogen feed and the carbon oxide feed into a methanol synthesis gas 101 ;

[0081] - adjusting the molar content of hydrogen, carbon monoxide and / or carbon dioxide of the methanol synthesis gas 101 to a module “M” of (H2-CO2) / (CC>2+CO) to between 1.9 and 2.2; - converting the methanol synthesis gas 101 in the methanol boiling water reactor 100 to a raw methanol product 103.

[0082] Hence, the process further comprises in transient operation, such as in periods without operating said electrolysis:

[0083] - interrupting the provision of said hydrogen feed and / or said carbon oxide feed resulting in a stop of the provision of the raw methanol product in the methanol boiling water reactor;

[0084] - supplying power to the one or more auxiliary heaters for providing heat to the methanol boiling water reactor by maintaining the boiling of the water in the water side of the methanol boiling water reactor.

[0085] The term “water feedstock” means any of liquid water or steam. It is understood that liquid water is provided in low temperature electrolysis, thus alkaline and / or PEM (proton exchange membrane) electrolysis. It is understood that steam is provided in high temperature electrolysis, thus solid oxide electrolysis (SOE). These technologies are well-known in the art.

[0086] In an embodiment, the transient operation, such as in periods without operating said optional electrolysis, is: during start-up or hot-idle operation. The start-up may include a period for replacement of catalyst in the BWR and / or for reducing the catalyst into its active form. This catalyst replacement and / or activation of catalyst may be conducted in e.g. MeOH plants without electrolysis, for instance existing MeOH plants in which the MeOH synthesis gas is produced by conventional means including steam methane reforming (SMR) and / or autothermal reforming (ATR).

[0087] In an embodiment, the one or more auxiliary heaters 110 are one or more electric heaters, and the heat input of the one or more electrical heaters is controlled by adjusting the power input 110’ for maintaining the pressure in the water side 106 of the boiling water reactor 100.

[0088] In an embodiment, the process further comprises at least one of: - the optional electrolysis being powered by electricity, said electricity optionally being produced from renewable sources comprising at least one of: wind, solar, nuclear, hydroelectric, geothermal;

[0089] - the optional electrolysis being performed in a solid oxide electrolysis (SOE) unit;

[0090] - the process further comprises partially converting CO2 to CO by electrolysis, such as by electrolysis of CO2 in a separate SOE unit;

[0091] - the carbon oxide feed consisting of a carbon monoxide feed and / or carbon dioxide feed, has a concentration of >95% CO2, more preferably >99% CO2.

[0092] In an embodiment, the carbon dioxide is biogenic and / or anthropogenic.

[0093] Biogenic carbon dioxide refers to carbon dioxide (CO2) that is released into the atmosphere through natural biological processes and the burning of biomass, such as wood or agricultural residues.

[0094] Anthropogenic carbon dioxide refers to the release of carbon dioxide (CO2) into the atmosphere as a result of human activities. This release and thus emissions primarily stem from the burning of fossil fuels, such as coal, oil, and natural gas, for energy production, transportation, and industrial processes.

[0095] In an embodiment, the raw gas product 103 is a raw methanol product, and the process further comprises converting at least a portion of the raw methanol product to gasoline as renewable gasoline or to jet fuel as renewable jet fuel, suitable for use as sustainable aviation fuel. Suitably, a diesel product is also produced.

[0096] Any of the embodiments and associated benefits of the first aspect (boiling water reactor) and second aspect (method of revamping) of the invention may be used in connection with the third aspect (process) of the invention, or vice versa.

[0097] The sole appended figure shows a schematic of a methanol boiling water reactor in accordance with an embodiment of the invention.

[0098] With reference to the figure, a methanol boiling water reactor 100 is shown, which is arranged to receive a methanol synthesis gas 101 and provide a raw methanol product 103. The methanol product 103 is further purified by removal of water produced in the methanol synthesis in a distillation column arranged downstream (not shown). The methanol boiling water reactor 100 comprises a pressure shell 102, itself comprising a tube side 104 and a boiling water side 106. The tube side 104 comprises a plurality of tubes 104’, here schematically illustrated with four tubes and a fixed bed of methanol synthesis catalyst 104” arranged within the tubes. The methanol boiling water reactor 100 is further arranged to receive boiling water 105 and circulate the boiling water 105 within the water side 106 for removing excess heat generated in the tube side 104. The water is withdrawn as saturated steam 107. As part of the methanol boiling water reactor 100, a steam drum 108 is arranged in fluid communication with the pressure shell 102 for providing the boiling water 105 via downcomer line 105 and further to receive saturated steam 107 exiting the pressure shell 102 via a riser line 107. The pressure shell 102 defines an inner surface and an outer surface, the latter depicted as 102 L, which sweeps the total curvature, thus the circumference (perimeter) of the pressure shell 102. 102 L defines also the pressure shell length as the distance extending along the length direction of the pressure shell 102 from a first boundary 102 L’ to a second boundary 102 L”, in which the first boundary 102 L’ defines the inlet position of the plurality of tubes 104’ and the second boundary 102 L” defines the outlet position of the plurality of tubes 104’. A horizontal central axis “A” running across the pressure shell defines an upper part of the pressure shell 102 and a bottom part of the pressure shell 102. The pressure shell 102 defines also a radius “R” as also shown in the figure. Hence, a horizontal direction is defined by central axis “A” or by radius “R”, as so is a length direction perpendicular to the horizontal direction. The length direction is along the pressure shell length 102 L, i.e. along the length direction of the pressure shell, thus here a vertical direction which refers to the direction along which the gravity force acts. The one or more auxiliary heaters 110 are arranged along such length direction and along the circumference of the pressure shell, as also shown in the figure. The length direction of the steam drum 108 runs along the horizontal direction defined herein. The pressure shell 102 comprises the one or more auxiliary heaters 110 arranged along a portion 110 L of said outer surface 102 L of the pressure shell 102 and in direct contact thereto. For instance, revamping of an existing BWR comprises installing one or more auxiliary heaters 110 along a portion 110 L of the outer surface 102 L of the pressure shell 102 and in direct contact thereto. The auxiliary heater 110 is powered by electricity 110’, suitably generated from a renewable source. Suitably also, the one or more integrated auxiliary heaters 110 are arranged symmetrically with respect to the central horizontal axis “A” defining an upper portion of the pressure shell and a lower portion of the pressure shell.

Claims

CLAIMS1. Boiling water reactor (BWR) arranged to receive a synthesis gas (101) and provide a raw gas product (103), in which the boiling water reactor (100) comprises: a pressure shell (102), the pressure shell (102) comprises a tube side (104) and a boiling water side (106); the tube side (104) comprises a plurality of tubes (104’) and a fixed bed of catalyst (104”) arranged within the plurality of tubes (104’); the boiling water reactor (100) is further arranged to receive boiling water (105) and circulate the boiling water (105) within the water side (106) for removing excess heat generated in the tube side (104); the boiling water reactor (100) further comprises a steam drum (108) arranged in fluid communication with the pressure shell (102) for providing the boiling water (105); wherein the pressure shell (102) defines an inner surface and an outer surface along the pressure shell length (102 L), and wherein the pressure shell (102) further comprises one or more auxiliary heaters (110) which are arranged along a portion (110 L) of said outer surface of the pressure shell (102) and in direct contact thereto; and wherein the boiling water reactor is any of: i) a methanol boiling water reactor in which the synthesis gas is methanol synthesis gas, the catalyst is a methanol synthesis catalyst, and the raw gas product is a raw methanol product; ii) a shift boiling water reactor in which the synthesis gas is pre-shifted synthesis gas, in which the catalyst is a shift catalyst, such as any of a high temperature shift (HTS) catalyst, a medium temperature shift (MTS) catalyst and a low temperature shift (LTS) catalyst, and the raw gas product is a shifted synthesis gas; iii) a methanation boiling water reactor, in which the synthesis gas is methanation synthesis gas, in which the catalyst is a methanation catalyst and the raw gas product is a raw methane-rich gas, such as a raw substitute natural gas (SNG) or a raw renewable natural gas (RNG); iv) an ammonia boiling water reactor in which the synthesis gas is ammonia synthesis gas, the catalyst is an ammonia synthesis catalyst, and the raw gas product is a raw ammonia product.

2. Boiling water reactor (100) according to claim 1 , wherein said one or more auxiliary heaters (110) are powered by electricity (110’), such as electricity produced fromrenewable sources comprising at least one of wind, solar, nuclear, hydroelectric, geothermal.

3. Boiling water reactor (100) according to claim 2, wherein the one or more electric heaters (110) are of the induction type or resistance type.

4. Boiling water reactor (100) according to any preceding claim, wherein said portion(110 L) of the outer surface of the pressure shell (102) is between 0.1 and 100% of the outer surface of the pressure shell (102 L).

5. Boiling water reactor (100) according to claim 4, wherein said portion (110 L) of the outer surface of the pressure shell (102) is less than 2 / 3 of the outer surface of the pressure shell (102 L); preferably less than 1 / 2, such as between 1 / 10 and 1 / 3 of the outer surface of the pressure shell (102 L).

6. Boiling water reactor (100) according to any preceding claim, wherein the one or more auxiliary heaters (110) are provided as one or more metal and / or ceramic sheets and the curvature of the outer surface of the pressure shell (102 L) corresponds to the curvature of inner surface (110 L) of the one or more metal and / or ceramic sheets.

7. Boiling water reactor (110) according to claim 6, wherein:- at least one of the metal sheets comprises one or more heating elements selected from: a sheathed heating cable, a heat tape, or combinations thereof; and / or- at least one of the ceramic sheets comprises one or more flexible ceramic pads.

8. Boiling water reactor (110) according to any of claims 6-7, wherein the one or more metal and / or ceramic sheets comprise one or more sheathed heating cables, the one or more sheathed heating cables comprising: an outer stainless-steel sheath and an inner conductor, such as a nichrome (nickel-chromium) conductor, optionally also an intermediate insulation separating the steel sheath from the inner conductor.

9. Boiling water reactor (110) according to any of claims 6-7, wherein the one or more metal and / or ceramic sheets comprise a circuit which is provided with a thermistor controlling power based on the temperature measured on water in the steam drum.

10. A method of revamping a boiling water reactor (100), in which the boiling water reactor (100) is any of: a shift boiling water reactor, a methanation boiling water reactor, a methanol boiling water reactor, an ammonia boiling water reactor; the boiling water reactor (100) comprising: a pressure shell (102) comprising a tube side (104) and a boiling water side (106), the tube side (104) comprising a plurality of tubes (104’) and a fixed bed of catalyst (104”) arranged within the plurality of tubes (104’), the boiling water reactor (110) being further arranged to receive boiling water (105) and circulate the boiling water (105) within the water side (106) for removing excess heat generated in the tube side (104), the boiling water reactor (110) further comprising a steam drum (108) arranged in fluid communication with the pressure shell (102) for providing said boiling water (105); the pressure shell (102) defining an inner surface and an outer surface along the pressure shell length (102 L); the method of revamping comprising:- installing one or more auxiliary heaters (110) along a portion (110 L) of the outer surface (102 L) of the pressure shell (102) and in direct contact thereto.

11. A process for producing a raw gas product, in which the raw gas product is any of: a shifted synthesis gas, a raw methane-rich gas, a raw methanol product, a raw ammonia product; the process comprising the steps of:- providing a boiling water reactor (100) according to any of claims 1-9;- providing a synthesis gas (101);- converting the synthesis gas (101) in boiling water reactor (100) to the raw gas product (103); the process further comprising in transient operation:- interrupting the provision of said synthesis gas (101) resulting in stop of the provision of the raw gas product (103) in the boiling water reactor (100);- supplying power (110’) to the one or more auxiliary heaters (110) for providing heat to the boiling water reactor (110) by maintaining the boiling of the water in the water side (106) of the boiling water reactor (100).

12. Process according to claim 11 , in which the raw gas product is a raw methanol product, the process comprising the steps of:- providing a methanol boiling water reactor (100);- providing a hydrogen feed, optionally by electrolysis of a water feedstock;- providing a carbon oxide feed comprising CO and / or CO2, optionally in periods of operating said electrolysis;- mixing at least a portion of the hydrogen feed and the carbon oxide feed into a methanol synthesis gas (101);- adjusting the molar content of hydrogen, carbon monoxide and / or carbon dioxide of the methanol synthesis gas (101) to a module “M” of (H2-CO2) / (CC>2+CO) to between 1.9 and 2.2;- converting the methanol synthesis gas (101) in the methanol boiling water reactor (100) to a raw methanol product (103).

13. Process according to claim 12, wherein the transient operation, such as in periods without operating said optional electrolysis, is: during start-up or hot-idle operation.

14. Process according to any of claims 11-13, wherein the one or more auxiliary heaters (110) are one or more electric heaters, and the heat input of the one or more electrical heaters is controlled by adjusting the power input (110’) for maintaining the pressure in the water side (106) of the boiling water reactor (100).

15. Process according to any of claims 11-14, wherein the process further comprises at least one of:- the optional electrolysis being powered by electricity, said electricity optionally being produced from renewable sources comprising at least one of: wind, solar, nuclear, hydroelectric, geothermal;- the optional electrolysis being performed in a solid oxide electrolysis (SOE) unit;- the process further comprising partially converting CO2 to CO by electrolysis, such as by electrolysis of CO2 in a separate SOE unit;- the carbon oxide feed consisting of a carbon monoxide feed and / or carbon dioxide feed, has a concentration of >95% CO2, more preferably >99% CO2.

16. Process according to any of claims 12-15, wherein the carbon dioxide is biogenic and / or anthropogenic.

17. Process according to any of claims 12-16, wherein the raw gas product (103) is a raw methanol product, and wherein the process further comprises converting at least a portion of the raw methanol product to gasoline as renewable gasoline or to jet fuel as renewable jet fuel, suitable for use as sustainable aviation fuel.

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