Plasma based thermal reactor with consecutive expansion and quenching

Abstract

The invention relates to a thermal reactor arrangement and a corresponding method of operation, designed for high-temperature chemical reactions such as the synthesis of nitrogen oxides (NOx). The reactor incorporates a plasma chamber and a downstream expansion chamber configured to facilitate controlled reaction dynamics, efficient product formation, and rapid quenching of reactive gases.

Description

[0001] Thermal reactor with consecutive expansion and quenching

[0002] Technical field

[0003]

[0001] The present disclosure relates to thermal reactors and thermal reactor arrangements using a plasma jet for performing desired chemical reactions, such as but not limited to the synthesis of nitrogen oxides (NOx) and in particular reactors for plasma synthesis of NO, NO2 and HNO3, as well as to methods of operating such reactors and arrangements.

[0004] Background

[0005]

[0002] Plasma technology has wide application in both industrial and research applications, as the high temperatures and the presence of highly active radicals make it possible to decompose unwanted compounds, or to synthesize desired compounds. Plasma technology can for example be used to dissociate nitrogen and oxygen molecules, allowing them to recombine into reactive nitrogen species like nitrogen monoxide (NO), a precursor to nitrogen oxides (NOX) that can be further processed into nitric acid (HNO3). Plasma-based nitrogen fixation using thermal reactors presents an alternative and sustainable approach to ammonia production that circumvents the need for traditional high-pressure fossil fuel-based processes, such as the Haber-Bosch process.

[0006]

[0003] The major advantage of plasma-based nitrogen fixation is its reliance on electrical energy, which can be sourced from renewable energy systems, making the process entirely CCh-free if green electricity, for example geothermal energy, wind power or photovoltaics, is used. This offers a possibility of decentralized, small-scale ammonia production, particularly suited for areas with abundant renewable resources but limited infrastructure. Transition to plasma-based nitrogen fixation would significantly reduce the carbon emission footprint of agriculture.

[0007]

[0004] There are also initiatives to reduce and eventually eliminate the carbon footprint of the Haber-Bosch process by utilizing renewable energy sources to

[0008] 240060PC_251217_FINAL power the reaction and to produce hydrogen via electrolysis. This approach maintains the scalability and efficiency of the traditional method while addressing its environmental drawbacks. This green transition depends heavily on the availability of low-cost, renewable electricity and large amounts of hydrogen produced in cost-effective electrolyzers. Despite being more sustainable, the Green Haber-Bosch process remains capital-intensive and primarily suited for centralized, large-scale production facilities. Unlike the large-scale Green Haber-Bosch process, plasma-based systems can be highly modular and adaptable to varying production scales. Plasma technology is however associated with other challenges, and there is a need for developing energy efficient, safe and scalable processes.

[0009]

[0005] WO 2024 / 151883 discloses a plasma reactor system that includes a gasflow-engineered reactor for producing fixed nitrogen products. In some instances, the reactor may include a vortex-inducing input mechanism and / or a quenching mechanism. According to WO 2024 / 151883 said vortex-inducing input mechanism and / or quenching mechanism are both integrated in the plasma chamber.

[0010]

[0006] WO 98 / 09753 discloses a process and apparatus for the synthesis of submicron particles. In particular, the WO 98 / 09753 relates to a novel approach utilizing vaporization and ultra-rapid thermal quenching based on adiabatic expansion of the vapor through a boundary layer converging-diverging nozzle to produce submicron particles under controlled operating conditions.

[0011]

[0007] US 5,749,937 discloses a reactor and method intended for high temperature reactions that require rapid cooling to freeze the reaction products to prevent back reactions or decompositions to undesirable products. Nitrogen is mentioned as an input gas needed to achieve the correct chemical environment for synthesis of nitride, boride, and carbide ceramic materials. An additional reactant, such as hydrogen at ambient temperatures, can be tangentially injected into the diverging section of a converging-diverging nozzle to complete the reactions or prevent back reactions as the gases are cooled.

[0012]

[0008] WO 2023 / 248165 discloses in broad and unspecific terms a method and system where plasma is generated and directly injected into a fluid, such as water,

[0013] 240060PC_251217_FINAL conceptually different and impossible to reconcile with the presently claimed high- temperature, high-pressure plasma-generated nitrogen fixation process.

[0014]

[0009] WO 2024 / 228659 relates to relates to a method and a system for producing high-purity silicon or other metal or metalloids involving the use of plasma providing activated species for reduction. In WO 2024 / 228659, a nozzle is employed, dimensioned according to equations from rocketry nozzle design.

[0015]

[0010] There remains a need for further improvements, inter alia to improve the energy efficiency and to better control the reaction kinetics as well as the course and endpoints of the chemical reactions involved in plasma-based chemical processes. Further aspects and their associated advantages will be evident from the detailed description and examples.

[0016] Summary

[0017] [Oil] The present inventors have made it possible to operate thermal reactors with increased yield, safely and economically, by controlling the expansion and quenching of the process gases with greater precision, enhanced, and separated in time and space, as outlined in the attached claims and as described in further detail in the following summary, description, and drawings.

[0018]

[0012] The invention is as defined in the appended claims. One aspect relates to a thermal reactor arrangement comprising a plasma chamber (3) having a gas inlet (31) configured to introduce a gas mixture, a heater (33) configured to heat said gas mixture to generate a plasma in a plasma-generation zone (32), a reaction zone (34) downstream of said plasma-generation zone (32), and a gas outlet (36) configured to release gas from said reaction zone (34); wherein a separate expansion chamber (4) is arranged in fluid connection with said gas outlet (36), and wherein at least one inlet (301, 302, 303) is arranged in said plasma chamber (3), configured to introduce a quenching medium, said at least one inlet configured to introduce the quenching medium tangentially, parallel to the inner surface of the plasma chamber (3), creating a vortex in the plasma chamber (3)

[0019] 240060PC_251217_FINAL that travels downstream, toward the gas outlet (36), wherein said expansion chamber (4) further comprises an outlet (42) configured to release expanded and quenched gas.

[0020]

[0013] According to an embodiment said at least one inlet (301, 302, 303) is / are configured to create a vortex which passes through the gas outlet (36) into the expansion chamber (4), and preferably also maintaining a swirling flow in the expansion chamber (4).

[0021]

[0014] According to another embodiment, freely combinable with the above, at least one inlet (411, 412, 413) is arranged in the expansion chamber (4) and configured to cause at least a portion of the quenching medium to flow tangentially along the inner surface of said expansion chamber (4) in a direction towards the outlet (42) of the expansion chamber.

[0022]

[0015] According to another embodiment, freely combinable with the above, at least one inlet (411, 412, 413) is arranged in the expansion chamber (4) and configured to cause at least a portion of the quenching medium to initially flow in a direction substantially opposite to the gas entering the expansion chamber (4) creating turbulence.

[0023]

[0016] According to yet another embodiment, also freely combinable with the above, least one dimension of said expansion chamber (4), such as diameter or length, is selected in relation to the corresponding dimension of the plasma chamber (3) to create a pressure drop.

[0024]

[0017] Preferably the pressure is reduced to a pressure in the expansion chamber (4) which is about 30 to 70 % of the pressure in the plasma chamber (3), preferably about 30 to 60 %, more preferably about 50 %, and most preferably about 40 % or less of the pressure in the plasma chamber (3).

[0025]

[0018] According to an embodiment, freely combinable with any of the above, the pressure in the expansion chamber (4) is at least 1 bar (100 kPa) absolute pressure.

[0026] 240060PC_251217_FINAL

[0019] According to an embodiment, freely combinable with any of the above, a diameter (D) of the expansion chamber (4) is greater than a diameter (d) of the plasma chamber (3), preferably at least two times, more preferably 3 times the diameter (d) of the plasma chamber (3).

[0027]

[0020] According to an embodiment, freely combinable with any of the above, said reaction zone (34) and said expansion chamber (4) both are rotationally symmetric about their longitudinal axis, and wherein the diameter (D) of said expansion chamber (4) is at least two times, preferably at least three times the diameter (d) of said reaction zone (34).

[0028]

[0021] According to an embodiment of the first aspect, the quenching medium is selected from nitrogen, oxygen, air, and water, or mixture thereof, wherein the quenching medium is introduced as a liquid, gas, or mixture thereof.

[0029]

[0022] According to another embodiment, freely combinable with any of the above, said heater (33) is chosen from a microwave generator, a radio wave generator, a laser generator, an inductively coupled plasma (ICP), a transformer coupled plasma (TCP), or an electric discharge generator.

[0030]

[0023] According to another embodiment, freely combinable with any of the above, said thermal reactor arrangement is configured for the synthesis of nitrogen oxides (NOx) wherein the plasma (P) is held in the reaction zone (34) at a temperature and pressure sufficient to dissociate nitrogen and oxygen molecules.

[0031]

[0024] A second aspect relates to a method for operating a thermal reactor for performing a desired chemical reaction, comprising the following steps: providing a gas mixture; and heating said gas mixture in a plasma chamber to form a plasma at a temperature and pressure at which the desired chemical reaction takes place, forming a mix of reaction products and unreacted gas, wherein the resulting mixture of reaction products and unreacted gas is transferred to an expansion chamber and expanded to form an expanded gas mixture of a pressure which is about 70 % of the pressure at which nitrogen and

[0032] 240060PC_251217_FINAL oxygen molecules dissociate, preferably about 60 %, more preferably about 50 %, and most preferably about 40 % or less of the pressure at which nitrogen and oxygen molecules dissociate, and wherein a quenching medium is introduced tangentially, parallel to the inner surface of the plasma chamber creating a vortex which travels downstream, toward an outlet leading into said expansion chamber.

[0033]

[0025] According to an embodiment of the second aspect, said tangential vortex flow is maintained through the outlet of said plasma chamber into said expansion chamber.

[0034]

[0026] According to another embodiment, quenching medium is introduced in said expansion chamber to further reduce the temperature of the expanded gas mixture.

[0035]

[0027] According to an embodiment, freely combinable with the above, quenching medium is introduced in said expansion chamber causing at least a portion of the quenching medium to initially flow in a direction substantially opposite to the gas entering the expansion chamber (4) creating turbulence.

[0036]

[0028] According to a further embodiment, said quenching medium is chosen from nitrogen, oxygen, air, and water, or mixture thereof, and wherein said quenching medium is introduced in the form of a liquid, a gas, or a mixture thereof.

[0037]

[0029] According to an embodiment, said thermal reactor is operated to form nitrogen oxides (NOx), wherein said gas mixture comprises oxygen and nitrogen and a plasma (P) is generated and held in said reaction zone at a temperature and a pressure at which nitrogen and oxygen molecules dissociate.

[0038]

[0030] According to an embodiment of the above, a gas mixture comprising oxygen and nitrogen is heated to a temperature of at least 2300 K and held at a pressure of 2 - 100 bar, such as 5 - 100 bar, or a pressure of 10-100 bar, forming a gas mixture comprising NOx.

[0039]

[0031] In an embodiment of the above method, said gas mixture is expanded to form a gas mixture at a pressure of at least about 1 bar (100 kPa), preferably a

[0040] 240060PC_251217_FINAL pressure of 1 - 50 bar (100 - 5000 kPa), such as 1 - 30 bar (100 - 1000 kPa), such as 1 - 10 bar (100 - 1000 kPa).

[0041]

[0032] Further aspects and embodiments, as well as their advantages, will be apparent from the attached drawings and the detailed description.

[0042] Short description of the drawings

[0043]

[0033] The invention is now described, by way of example, with reference to the accompanying drawings, in which:

[0044]

[0034] Figure 1 schematically shows a single-pressure plasma-based nitrogen fixation process as a model of a plasma-driven chemical process, here shown as starting with a booster compressor (1) compressing a gas mixture, typically 50 % O2 and 50 % N2 to a desired pressure. The compressed gas mixture is fed into a plasma reactor (3) equipped with a heater (33) for generating a plasma. Said heater is chosen from a microwave generator, a radio wave generator, a laser generator, an inductively coupled plasma (ICP) heater or a transformer coupled plasma (TCP) heater, and an electric discharge generator. Following the plasma reactor (3), the gas mixture is led into an expansion chamber (4) where it is subsequently quenched. The gas mixture is then led to a downstream treatment equipment (7), for example comprising but not limited to an adsorption column (70) where the gas mixture reacts with water or dilute HNO3 to form HNO3 which is led to further processing (8) depending on the intended end-product. Unreacted gas is recirculated, and fresh gases (9) fed into the process to maintain a constant feed into the reactor.

[0045]

[0035] Figure 2 schematically shows an alternative single-pressure plasma-based nitrogen fixation process similar to that shown in Fig. 1, but where the gas mixture exiting the expansion chamber (4) is led (6) to a heat exchanger (2) where process heat is recovered and used to heat a compressed gas mixture before it enters the plasma reactor (3). After passing the heat exchanger, the gas mixture is led to downstream treatment equipment (7), comprising but not limited to an adsorption column (70) as in Fig. 1. Unreacted gas can be recirculated from the downstream

[0046] 240060PC_251217_FINAL treatment (7), pressurized in a second booster compressor (not shown) and introduced into the plasma reactor (3) or expansion chamber (4), and fresh gases (9) fed into the process to maintain a constant feed into the reactor.

[0047]

[0036] Figure 3 schematically shows a dual-pressure high-temperature plasmabased nitrogen fixation process, where gas leaving the expansion chamber (4) is led into one or more turbines (5) to improve energy recovery. The process thus features two primary pressure levels, a high-pressure level at the reactor (3) inlet and a lower pressure in the heat exchanger (2) as well as upstream of the downstream treatment equipment (7) comprising but not limited to an absorption column (70). The turbines, placed directly in the gas flow, expand the high- temperature, high-pressure gas, converting excess thermal energy into mechanical energy, which can be further converted into electricity. This results in a net energy gain, despite the increased work required for recompression. Also here, unreacted gas can be recirculated from the downstream treatment equipment (7), pressurized in a second booster compressor (not shown) and introduced into the plasma reactor (3) or expansion chamber (4), and fresh gases (9) fed into the process to maintain a constant feed into the reactor.

[0048]

[0037] Fig. 4 schematically shows a dual-pressure low-temperature plasma-based nitrogen fixation process, where gas leaving the expansion chamber (4) is first led to a heat-exchanger (2) before entering one or more turbines (5). In this set-up, the turbine operates under milder conditions, as the gases have transferred part of their thermal energy to the compressed gas in the heat exchanger (2), preheating it before it enters the plasma reactor (3). This set-up optimizes preheating efficiency, as the temperature is not constrained by the turbine's inlet temperature limit. Also here, unreacted gas can be recirculated from the downstream treatment equipment (7), pressurized in a second booster compressor (not shown) and introduced into the plasma reactor (3) or expansion chamber (4), and fresh gases (9) fed into the process to maintain a constant feed into the reactor.

[0049]

[0038] Fig. 5 shows a schematical cross-section of a plasma chamber (3) configured to hold a plasma (P) at a temperature and a pressure at which nitrogen and oxygen

[0050] 240060PC_251217_FINAL molecules dissociate, said plasma chamber (3) having a gas inlet (31) configured to introduce a gas mixture, a heater (33) configured to heat said gas mixture to generate a plasma in a plasma-generation zone (32), a reaction zone (34) downstream of said plasma-generation zone (32), and a gas outlet (36) configured to release gas from said reaction zone (34) into a separate expansion chamber (4) arranged in fluid connection with said gas outlet (36), and at least one port (41), configured to introduce a quenching medium into said expansion chamber (4), and an outlet (42) configured to release expanded and quenched gas.

[0051]

[0039] Fig. 6 illustrates, for a set-up as shown schematically in Fig. 5, how the plasma chamber (3) and in particular the reaction zone (34) has one dimension, here a diameter (d), and the adjacent but separate expansion chamber (4) has another dimension, here a diameter (D) which is larger than the diameter of the plasma chamber (3). The gas mixture thus passes from a chamber with a first cross-section into a chamber with a second cross-section larger than said first cross-section. In one embodiment, this transition is immediate, in that the chamber with a first diameter and a first pressure opens to a chamber with a second diameter larger than said first, and a second pressure, lower than said first pressure. In one embodiment, not shown, this transition from one dimension, e.g. one diameter to another, takes place through a converging opening (36), where a cross-section of said opening, in the direction of the flow, is shaped as a cone, an hourglass, has a bell-shape or similar. This transition is preferably smooth and continuous.

[0052]

[0040] In a preferred embodiment, the said reaction zone and said expansion chamber exhibit rotational symmetry around their length axis, and most preferably the diameter (D) of said expansion chamber is then at least two times, preferably at least three times the diameter (d) of said reaction zone. The dimensional change when going from the plasma chamber (3) to the expansion chamber (4) is crucial for achieving a rapid expansion and pressure drop when gas passes through the outlet (36). This can be achieved by designing the upstream (37) and downstream (38) dimensions of the outlet (36) so that outlet is first converging and then diverging in the direction of the flow into the expansion chamber.

[0053] 240060PC_251217_FINAL

[0041] Fig. 7 schematically shows how a quenching medium is introduced into the expanded gas in the expansion chamber (4) through inlets (41), wherein the inlets (41) are arranged so that the quenching medium at least in part moves in a direction substantially opposite to the direction of the expanded gas, and flows substantially counter-current therewith before adjusting to the flow of expanding gas. This is a result inter alia of the Venturi effect and this helps to create a flow of colder gas along the inner walls of the expansion chamber in the part of the expansion chamber where the hot gas first enters. This cools the inner walls, increases the efficiency of the quenching, and additionally helps to center and stabilize the gas flow within the expansion chamber. A further advantage is that this flow helps to break up the fast and hot jet from the outlet of the reactor, rapidly cooling it down and reducing its velocity. This helps to avoid or minimize the occurrence of shock waves. This also significantly reduces the noise, and other problems associated with shock waves, such as vibrations, temperature variations including a temporary increase in temperature, risking backward reactions and damage to the reactor components.

[0054]

[0042] Fig. 7 also illustrates how inlets (301, 303) can be arranged in the walls of the plasma chamber, configured to introduce a cooling medium, such as a gas selected from nitrogen, oxygen, air, and water, or mixture thereof, wherein this medium is introduced as a liquid, gas, or mixture thereof. The positioning of inlets (301) and (303) indicates schematically how one inlet (301) can be placed in the upstream section of the plasma chamber (3) and another inlet (303) downstream, closer to the outlet (36) leading into the expansion chamber.

[0055]

[0043] Fig. 8 illustrates how the outlet (36) indicated in Figs 5 - 7 preferably comprises a converging portion (37) and an opening (38) into the expansion chamber (4). It is also shown how one or more inlets for quenching medium, e.g. recycled gas, here designated (301, 302, 303) can be arranged in the plasma chamber (3) to introduce a cooling or quenching medium, e.g. recycled gas, already upstream, before the converging portion (37) leading into the expansion chamber (4). In Fig. 8, the positions are indicated as (301, 302, 303) and in each position, a number of two, three or more inlets are preferably positioned symmetrically along

[0056] 240060PC_251217_FINAL the periphery of the opening (31), or around the periphery of the wall of the plasma chamber (3). Through a symmetric arrangement of the inlets (301, 302, 303), as shown in Fig. 12A 1 and 2 below, the flow of quenching medium can center and stabilize the incoming plasma.

[0057]

[0044] Fig. 9 illustrates how one or more inlets for quenching medium, here designated (411) can be integrated in the end wall of the expansion chamber (4) and thus feeding quenching medium into the expanded gas at an early phase of expansion. In Fig. 9, the positions are indicated as (411) but preferably three or more inlets are positioned symmetrically along the periphery of the opening (38), or around the periphery of the wall of the expansion chamber (4). Through a symmetric arrangement of the inlets (411, 412, 413), as shown in Fig. 12B 1 and 2 below, the flow of quenching medium can center and stabilize the incoming plasma and the expanded gas. Also here, the early introduction of quenching media increases the efficiency of the expansion quenching and additionally allows controlling the gas flow pattern within the expansion chamber, and also to protect the inner walls of the expansion chamber.

[0058]

[0045] Fig. 10 illustrates how one or more inlets for quenching medium, here designated (412) can be arranged in the side walls of the expansion chamber (40) to feed quenching medium into the expanded gas. Also here, a symmetric arrangement of the inlets (411), as shown in Fig. 12B 1 and 3, creates a flow of quenching medium that centers and stabilizes the plasma and expanded gas. The inlets are preferably configured to create a tangential flow of quenching medium, creating a swirl or vortex in the expansion chamber (4).

[0059]

[0046] Fig. 11 illustrates an embodiment where at least two sets of inlets (413) and (414) are arranged to introduce quenching medium into the expansion chamber, but in different locations. Here, a first set of inlets are exemplified by the inlets (413) introduce quenching medium in a direction at least partially coinciding with the direction of the gas entering the expansion chamber (4) through the downstream portion (38) of the converging outlet (37) from the reaction chamber (3). A second set of inlets, here exemplified by the inlets (414) are arranged to

[0060] 240060PC_251217_FINAL introduce quenching medium in the expansion chamber (4) and configured to cause at least a portion of the quenching medium to initially flow in a direction substantially opposite to the gas entering the expansion chamber (4). This increases turbulence, increases mixing and significantly enhances the rate of cooling the expanded gas.

[0061]

[0047] Fig. 12A shows two schematic views, 1 and 2, wherein Fig. 12A 1 shows a cross section of the plasma chamber (3) with an inlet (31) for feed gas, and inlets (301, 302, 303) here shown as three separate inlets, preferably symmetrically arranged in the end wall of the plasma chamber, for introducing recycled gas between the inlet (31) and the walls of the plasma chamber (3). Fig. 12A 2 shows an alternative embodiment where three separate inlets (301, 302, 303) are arranged in the walls of the plasma chamber (3) for tangentially introducing recycled gas, creating a flow of gas along the inner walls of said plasma chamber. Both arrangements are configured to create a swirling flow or vortex along the inner wall of the plasma chamber 3, moving longitudinally with the flow towards the outlet (36). Preferably said swirl or vortex continues into the converging portion (37) of the outlet (36), forming a layer of colder gas protecting the walls of the outlet.

[0062]

[0048] Fig. 12B also shows two schematic views, 1 and 2, but here Fig. 12B 1 shows a cross section of the expansion chamber (4), with the outlet (38), and three inlets (411) for introducing quenching medium arranged in the end wall of the expansion chamber (4) symmetrically positioned around the outlet (38) through which the hot gas enters from the plasma chamber (3). Fig. 12B 2 shows how four inlets (412, 413) are arranged in the side wall of the reaction chamber (4) introducing quenching medium tangentially along the side walls. In combination with the incoming gas entering the expansion chamber through the opening (38), the flow of quenching medium here can be configured to either create turbulence and effective mixing, or to form a swirl or vortex traveling along the length of the expansion chamber. This protects the walls of the expansion chamber from the high temperatures of the expanded gas, and allows the use of less expensive materials, and / or reduced material thickness and / or cooling arrangements.

[0063] 240060PC_251217_FINAL

[0049] Fig. 13 is a graph showing an axial plot of the static temperature (Kelvin) as a function of the distance the flow of gas travels in an expansion chamber in a setup as shown in the figure - the geometry of the flow part shown in bold, and the direction of flow indicated by an arrow.

[0064]

[0050] Fig. 14 is a graph showing an axial plot of the velocity (m / s) as a function of the distance in the same set-up as shown in Fig. 13.

[0065]

[0051] Fig. 15 is a graph showing an axial plot of the static pressure (Pa) as a function of the distance in the same set-up as shown in Fig. 13.

[0066]

[0052] Fig. 16 is a graph showing an axial plot of the static temperature (Kelvin) as a function of distance in a geometry as in Fig. 13 but with the introduction of quenching media and the formation of a turbulent flow, schematically indicated with arrows.

[0067]

[0053] Fig. 17 is a graph showing an axial plot of the velocity (m / s) as a function of the distance in the same set-up as shown in Fig. 16.

[0068]

[0054] Fig. 18 is a graph showing an axial plot of the static pressure (Pa) as a function of the distance in the same set-up as shown in Fig. 16.

[0069]

[0055] Fig. 19 is the result of a simulation, showing flow patterns in an expansion chamber where a flow of quenching medium is introduced, resulting in efficient mixing. The hot gas enters from the left, passes through a converging portion and is then released into the expansion chamber. Here, a flow of quenching medium is introduced vertically, from the top, and it can be seen how at least a part of the quenching medium flows counter current. Turbulence is also detected below the main flow.

[0070] Detailed description

[0071]

[0056] Before the present invention is described, it is to be understood that the terminology employed herein is used for the purpose of describing particular embodiments only and is not intended to be limiting, since the scope of the present invention will be limited only by the appended claims and equivalents thereof.

[0072] 240060PC_251217_FINAL

[0057] It must be noted that, as used in this specification and the appended claims, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise.

[0073]

[0058] In the present specification and the appended claims, the term "about" is used to indicate a range of ±10% of the specified value, unless otherwise indicated in the context of the specific disclosure.

[0074]

[0059] A thermal reactor arrangement, and in particular a thermal reactor arrangement for the synthesis of nitrogen oxides (NOx), can be designed in different ways. One key aspect is the rapid quenching of the product gases through expansion, to achieve a lower temperature and preventing reverse reactions, followed by the addition of quenching / cooling medium to maintain the temperature.

[0075]

[0060] Since a substantial portion of the reactants remains unreacted in the plasma reactor, recycling this gas offers considerable benefits. Although a small fraction of the gases reacts in subsequent oxidation steps, the majority remains as unreacted feed gas. This results in a high cycle count, necessitating careful cleaning of the recycled gas mixture to remove undesired species, preventing corrosion, and ensuring the longevity of the plant. Recycling also allows the use of gas that already has a high oxygen content and pressure, which results in significant energy savings compared to an open system without recirculation. With recirculation, only the fresh feed gas requires the steps of separation, concentration and pressurization.

[0076]

[0061] It can be noted that in a thermal reactor arrangement according to the present invention, the reactor operates at a pressure above atmospheric pressure. Accordingly, the feed gas is compressed to an absolute pressure of at least 1.1 bar, such as at least 1.2 bar, such as at least 1.3 bar, such as at least 1.5 bar, such as at least 5 bar, such as at least 10 bar, such as a pressure in the range of about 1.2 to about 100 bar, such as about 5 to about 100 bar, such as about 10 to about 100 bar using one or more compressors. In the case of a pressurized reactor, a skilled person understands that the pressure and feed of the recycled gas need to be adapted to the pressure inside the reactor.

[0077] 240060PC_251217_FINAL

[0062] Two fundamental process alternatives, each with several subvariants, were developed and designated as the single-pressure and dual-pressure processes. The single-pressure process encompasses all process variants that do not involve an expansion turbine or pressure change with energy recovery. The pressure drop in these processes results solely from pressure losses through process components and reactions. In contrast, process cycles that integrate one or more expansion turbines are classified as dual-pressure processes. In these, pressure is deliberately reduced by converting the potential energy of the gas into mechanical or electrical energy. Since all variants involve recirculating processes with high flow rates, it is crucial that this pressure reduction is efficiently utilized to offset the subsequent pressure buildup to the process pressure, ensuring a net energy savings.

[0078]

[0063] In a single-pressure process as shown in Fig. 1 and 2, it is possible to essentially maintain a high pressure through the downstream treatment step (7) for example comprising an absorption column (70). This makes the set-up more compact, facilitates the second expansion to NO2, and facilitates the absorption and formation of HNO3. Further, less energy is required for the compressor that will compensate for the pressure drop through the downstream parts of the reactor. The rapid expansion results in an initial drop in pressure which effectively stops unwanted chemical reactions, such as the Zeldovich reaction, causing loss of NO back to N2 and O2. Further, the subsequent introduction of quenching medium can be adapted to give the gas flow the desired temperature optimized for the downstream processing. The choice of quenching medium and its volume can be more freely chosen, as the initial pressure drop, and the initial cooling has already been achieved by the expansion.

[0079]

[0064] The fast reduction of temperature entails further advantages with regard to controlling the chemical reactions. At the high temperatures involved, the chemical reactions proceed very fast, but at the lower temperatures reached after expansion cooling, the reactions are slower, and accordingly potential backward reactions proceed significantly more slowly.

[0080] 240060PC_251217_FINAL

[0065] Specifically in a single-pressure process as shown in Fig. 2, where the gas is recirculated via a heat exchanger (2) in order to recover process heat while preheating the gas feed before the reactor (3), the inventive expansion and subsequent quenching makes it possible to control the composition, pressure and temperature of the recirculated gas so that efficient contact and heat transfer takes place in the heat exchanger (2).

[0081]

[0066] The dual-pressure process variants closely resemble the single-pressure process but introduce expansion turbines (5) at different positions downstream of the plasma reactor (3) and the expansion chamber (4) to improve energy recovery. The process is called a dual-pressure process as it features two primary pressure levels: a high-pressure level at the reactor inlet and a lower pressure upstream of the separation unit, for example an absorption column. The turbines, placed directly in the gas flow, expand the high-temperature, high-pressure fluid, converting excess thermal energy into mechanical power. This results in a net energy gain, despite the increased work required for recompression, as the mechanical energy is recovered as electricity generated by the turbine or turbines. Injecting water as a quenching media in (4) upstream of the turbine not only increases the quenching speed and reduction of temperature, but also increases the specific heat capacity, density and volume of the gas mixture, enhancing the turbine's power output.

[0082]

[0067] The turbine must however be designed to withstand the harsh conditions, including high inlet temperatures, oxygen partial pressures, and water vapor content. This dual-pressure approach, with its turbine integration, offers significant energy recovery potential, especially if pressure can be recovered after the expansion cooling, as the velocity of the gas is being reduced. This approach however requires careful management of fluctuating operating conditions, corrosive environment, and thermal material limitations.

[0083]

[0068] In a dual-pressure high temperature process as shown in Fig. 3, the turbine can be regarded as a second quenching mechanism, and the inventive expansion and subsequent addition of quenching medium makes it possible to optimize the

[0084] 240060PC_251217_FINAL operating conditions of the turbine, and in particular regulating the temperature of the gases reaching the turbine.

[0085]

[0069] In the dual-pressure low-temperature process, as shown in Figure 4, the turbine operates under milder conditions. In this configuration, the turbine (5) is positioned downstream of a heat exchanger (2) and upstream of a downstream treatment / separation stage (7), for example comprising an absorption column (70) where the turbine expands the still relatively hot process gases. After reaching a defined end temperature of approximately 1300 to 1600 K through the sequential expansion and quenching in (4), these gases transfer part of their thermal energy to the reactor inlet gas in the heat exchanger (2), thus preheating the inlet gas before it flows into the plasma reactor (3). This configuration enables maximum heat exchanger inlet temperatures and therefore optimizes preheating efficiency, as the temperature is not constrained by the turbine's inlet temperature limit. This also means that the turbine cannot be used as an additional quenching mechanism, so the required temperature is instead adjusted by the expansion and quenching taking place in (4). The combination of expansion and quenching adds flexibility to this adjustment.

[0086]

[0070] Operating a thermal reactor at elevated pressures enhances nitrogen fixation efficiency, but the down-stream pressure and high temperatures require specialized materials and safety precautions. The inventive expansion and quenching make it possible to rapidly reduce the temperatures, and the introduction of quenching media can serve several purposes in addition to further reducing temperature: adding fresh gases to the reaction influencing reaction kinetics, adding medium to neutralize corrosive conditions, adding water to increase the heat transfer capacity in downstream heat recovery, etc.

[0087]

[0071] If water is used as a quenching media, it is an advantage that the water can now be added to an expanded gas that has already reached a lower temperature. By comparison, performing the quenching by adding water to the plasma chamber may lead to the undesired formation of reactive hydrogen radicals.

[0088] 240060PC_251217_FINAL

[0072] A further advantage is that the plasma in the plasma chamber is not disturbed, as the quenching is performed in a separate expansion chamber, not in the plasma reactor itself. This is the case in particular when a supersonic gas flow is achieved through the transition from plasma chamber to expansion chamber, as this leads to a choked flow where no information such as vibrations etc can go backwards.

[0089]

[0073] The inventors surprisingly found that, in a plasma process as disclosed herein, the high pressure and high temperature conditions cause the expansion to exhibit an isenthropic cooling behaviour. While isenthalpic cooling is typically irreversible, it results in a temperature drop as pressure is reduced. In practice, the gas cools initially as the pressure drops and the velocity increases. However, as the flow decelerates further in the expansion chamber, temperature may rise again due to recompression effects or viscous dissipation. The addition of a quenching medium compensates for - and even prevents - this temperature increase, thereby ensuring rapid and irreversible quenching.

[0090]

[0074] Further, the addition of quenching medium can be performed in a way as to create favourable flow patterns in the expansion chamber, centering and stabilizing the jet of hot gases, but also ensuring efficient mixing and rapid cooling, as desired. Examples of this are illustrated in the figures, starting with Fig. 7, which schematically shows how the Venturi effect acts on quenching medium, creating turbulence and efficient mixing. The addition of a quenching medium thus enhances and increases the cooling achieved by the expansion.

[0091]

[0075] Figs. 5 through 12 illustrate different positions for introducing quenching medium. In Fig. 8, the inlets (301, 302, 303) are arranged in the plasma chamber (3), for example in the downstream portion thereof, before the converging transition (37) or opening (36) leading to the expansion chamber (4). In such configurations, the quenching medium is introduced before the expansion takes place and thus exerts an effect already in an early stage of expansion. The inlets (301. 302, 303) are preferably configured to create a desired flow pattern, for example a swirl or a vortex surrounding the plasma jet, stabilizing the same, and

[0092] 240060PC_251217_FINAL helping to protect the walls of the plasma chamber (3) and the walls of the outlet (36, 37, 38) from the high temperatures of the plasma.

[0093]

[0076] Fig. 9 shows an embodiment where inlets (411) are arranged outside but adjacent to the opening (38) though which the hot gas mixture enters the expansion chamber. The inlets are preferably symmetrically arranged around said outlet, for example as illustrated in Fig. 12B 1, where three outlets are shown. The inlets are preferably evenly spaced, for example two inlets, which are pair-wise opposed, 180 degrees apart; shifted 120 degrees apart in the case of three inlets, or shifted 90 degrees apart in the case of four inlets and so on. These inlets (411) are preferably configured to create a desired flow pattern, for example a swirl or a vortex surrounding the flow of expanded gas, stabilizing the same, and helping to protect the walls of the expansion chamber (4) from high temperatures.

[0094]

[0077] In Fig. 10, inlets (412) are shown as arranged in the side walls of the expansion chamber (4). In one embodiment, these inlets are evenly positioned, for example as shown in Fig. 12B 2, exhibiting rotational symmetry, for example shifted 120 degrees apart in the case of three inlets, or shifted 90 degrees in relation each other in the case of four inlets. In one embodiment said inlets are configured to create a tangential flow of quenching medium at least initially following the walls of the expansion chamber (4) and preferably creating a swirl or a vortex which follows the flow of the expanded gas mixture downstream in the expansion chamber. The inlets (412) may also be arranged to create turbulence and maximize the mixing and thus increase the cooling rate and ensure rapid and irreversible cooling.

[0095]

[0078] Fig. 11 shows an embodiment where multiple inlets (413, 414) are arranged, configured to introduce quenching medium in different locations of the expansion chamber, here shown as in the outlet (38) and the side walls of the expansion chamber (4) and preferably introducing the quenching medium in directions which differ from the main direction of the flow of expanded gas. It is also contemplated that quenching media of different composition is introduced in different locations of the expansion chamber. The provision of several sets of inlets adds flexibility to the

[0096] 240060PC_251217_FINAL process, allowing precision control of the conditions in the quenching chamber with regard to temperature, mixing, flow dynamics, chemical reactions and reaction kinetics, and so on.

[0097]

[0079] The introduction of quenching media into the expanded gas offers a possibility cool the gases much faster, which helps to minimize the loss of NO due to backwards reactions, and to stabilize, balance and center the jet of hot gas entering the expansion chamber, or, if desired, to create turbulence, a vortex, or even counter-current flow patterns to further increase the rate of cooling, and to protect the walls of the expansion chamber from extreme temperatures.

[0098]

[0080] Fig. 12 shows two main embodiments illustrating how quenching media is introduced into the expansion chamber. In Fig. 12A 1, inlets (301, 302, 303) are shown as openings in the end portion of the plasma chamber (3) surrounding the inlet (31) In Fig. 12A 2, inlets are show arranged in the side wall of the plasma chamber (3). In Fig. 12B 1, inlets (411) are symmetrically arranged around the downstream opening (38) of the outlet (32) through which hot gas enters the expansion chamber from the plasma chamber. A symmetrical arrangement of the inlets will create a flow of quenching media surrounding the hot gas entering the expansion chamber. Fig. 12B 2 shows an alternative arrangement, freely combinable with the previous, where inlets (412, 413) are arranged to tangentially introduce quenching media into the expansion chamber. This arrangement creates a swirl or vortex of quenching medium following the side walls of the expansion chamber, and then moving downstream, towards the outlet of the expansion chamber.

[0099] Examples

[0100]

[0081] Simulations of the fluid dynamics have shown that the temperature drop is very fast, and that the temperature of the gas mixture is practically halved within the first centimetres of the expansion chamber. When quenching medium is added after expansion, the temperature drop is even more accentuated. Figs. 13, 14, and 15 show how the temperature, velocity and pressure drop when the gas enters an expansion chamber. There is however a temperature spike and subsequent

[0101] 240060PC_251217_FINAL temperature oscillation seen in Fig. 13, as well as shock waves clearly visible as velocity and pressure oscillations in Figs. 14 and 15.

[0102]

[0082] Conversely, the introduction of quenching medium into the expanded gas, as illustrated in Fig. 16 results in a significantly more effective reduction of temperature. Additionally, Fig. 17 illustrates how, after an initial spike and supersonic velocities when passing the throat of the transition, the velocity oscillations are significantly reduced. Finally, Fig. 18 shows how the pressure is rapidly reduced from above 1.200 kPa to a stable level of about 500 kPa.

[0103]

[0083] Simulations also indicate that the instant pressure drop creates a turbulence which brings cooler gas to the inner surface of the expansion chamber, protecting the walls of the expansion chamber from extreme temperatures. An example of the flow pattern is shown in Fig. 19, showing the result of simulations of a set-up where a flow of quenching medium is introduced into the jet of expanded gas.

[0104]

[0084] Additionally, the introduction of quenching media has been shown to interact in a favourable way with the expanding reaction gas, stabilizing the flow and keeping it in the center of the expansion chamber, ensuring good mixing and efficient cooling, and creating a swirl which protects the walls of the chamber, and in some configurations, also creating - at least in parts of the expansion chamber - a turbulent flow and locally even a counter-current flow of gas due to the Venturi effect. Directing a flow of cooler gas to the walls of the expansion chamber allows the use of materials and material dimensions that reduce the cost of the equipment.

[0105]

[0085] The introduction of quenching medium into the expanded gas also gives the possibility to counteract shock waves and reduce the sound as well as the mechanical strain on the components. Experience gathered when operating experimental reactors indicates that the introduction of quenching media can reduce the noise generated in the plasma reactor (3) and expansion chamber (4).

[0106]

[0086] Preliminary results obtained by the present inventors indicate that the rapid pressure drop in the initial expansion effectively reduces the temperature, and that the subsequent quenching by introducing quenching medium further stabilizes the

[0107] 240060PC_251217_FINAL flow of gas, counteracts the formation of shock waves, achieves efficient mixing and protects the walls of the expansion chamber. Importantly, creating a choked flow, being the result of reaching supersonic velocity through the outlet from the plasma reactor, makes it possible to perform the expansion and quenching without disturbing the plasma, and without interfering with the formation of NOx.

[0108]

[0087] In fact, the inventive expansion and quenching will prevent or at least minimizes the occurrence of backward reactions. The inventors have shown that an efficient and very rapid cooling is achieved in a very short distance. Additionally, the volume of quenching medium is minimized, which minimizes the dilution of the gas.

[0109]

[0088] To summarize, the claimed reactor arrangement and method offer several key technical and operational advantages, which can be grouped into efficiency, selectivity, and process control. These advantages support both industrial feasibility and patentability.

[0110]

[0089] The use of plasma heating enables very high temperatures (>2300 K), promoting fast and complete reactions, while the combination of a plasma generation zone and a reaction zone allow precise control over the temperature and pressure conditions under which reactive species (e.g. nitrogen and oxygen) dissociate and form desired products like NOx.

[0111]

[0090] Further, the introduction of a tangential quenching flow creates a vortex that protects the walls of the reactor chambers, and in particular the walls of the passage from the plasma chamber to the expansion chamber, reduces residence time of reactive intermediates, and, in the expansion chamber, helps to rapidly quench the hot gas stream, thereby preventing unwanted side reactions or decomposition of target products. In total, this improves selectivity towards the desired reaction products, here exemplified as NOx, and reduces formation of undesired by-products.

[0112]

[0091] The inclusion of a separate expansion chamber, with a carefully designed pressure drop (e.g. to 30-70% of initial pressure), allows very energy-efficient expansion and cooling. There are also indications that also a smaller pressure drop, such as lowering the pressure to 95 - 97 % of the initial pressure, can achieve

[0113] 240060PC_251217_FINAL significant quenching. Further, the use of the pressure differential promotes flow and mixing without mechanical moving parts. Additionally, the claimed design allows operation at elevated pressures (up to 100 bar), which is favourable for reaction kinetics and industrial scalability.

[0114]

[0092] The creation of a swirling flow in the plasma chamber, and in particular maintaining this swirling flow in the gas when it passes from the plasma chamber into the expansion chamber, has several advantages, one being that it helps to protect the walls of the passage from the high temperatures.

[0115]

[0093] Additional advantages include enhanced flow dynamics, as the inlets can be used to promote uniform temperature distribution, prevent backflow or stagnant zones, and facilitate rapid heat dissipation and stabilization of reactive species. The system also allows multiple quenching strategies and provides flexibility to adapt the reactor arrangement for different chemical reactions or process conditions.

[0116]

[0094] These advantages demonstrate that the claimed invention provides a technical solution to the problem of efficiently carrying out high-temperature gasphase reactions with high control, improved product quality, and scalable operation.

[0117]

[0095] Without further elaboration, it is believed that a person skilled in the art can, using the present description, including the examples, utilize the present invention to its fullest extent. Also, although the invention has been described herein with regard to its preferred embodiments, which constitute the best mode presently known to the inventors, it should be understood that various changes and modifications as would be obvious to one having the ordinary skill in this art may be made without departing from the scope of the invention which is set forth in the claims appended hereto.

[0118]

[0096] Thus, while various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims.

[0119] 240060PC_251217_FINAL

Claims

Claims1. A thermal reactor arrangement comprising a plasma chamber (3) having a gas inlet (31) configured to introduce a gas mixture, a heater (33) configured to heat said gas mixture to generate a plasma in a plasma-generation zone (32), a reaction zone (34) downstream of said plasma-generation zone (32), and a gas outlet (36) configured to release gas from said reaction zone (34); wherein a separate expansion chamber (4) is arranged in fluid connection with said gas outlet (36), and wherein at least one inlet (301, 302, 303) is arranged in said plasma chamber (3), configured to introduce a quenching medium, said at least one inlet configured to introduce the quenching medium tangentially, parallel to the inner surface of the plasma chamber (3), creating a vortex in the plasma chamber (3) that travels downstream, toward the gas outlet (36), wherein said expansion chamber (4) further comprises an outlet (42) configured to release expanded and quenched gas.

2. The thermal reactor arrangement according to claim 1, wherein said at least one inlet (301, 302, 303) is configured to create a vortex which passes through the gas outlet (36) and preferably to maintain a swirling flow in the expansion chamber (4).

3. The thermal reactor arrangement according to claim 1 or 2, wherein at least one inlet (411, 412, 413) is arranged in the expansion chamber (4) and configured to cause at least a portion of the quenching medium to flow tangentially along the inner surface of said expansion chamber (4) in a direction towards the outlet (42) of the expansion chamber.

4. The thermal reactor arrangement according to claim 1 or 2, wherein at least one inlet (411, 412, 413) is arranged in the expansion chamber (4) and configured to cause at least a portion of the quenching medium to initially flow in a direction substantially opposite to the gas entering the expansion chamber (4) creating turbulence.240060PC_251217_FINAL5. The thermal reactor arrangement according to claim 1, wherein at least one dimension of said expansion chamber (4), such as diameter or length, is selected in relation to the corresponding dimension of the plasma chamber (3) to create a pressure drop to a pressure in the expansion chamber (4) which is about 30 to 70 % of the pressure in the plasma chamber (3), preferably about 30 to 60 %, more preferably about 50 %, and most preferably about 40 % or less of the pressure in the plasma chamber (3).

6. The thermal reactor arrangement according to claim 1, wherein the pressure in the expansion chamber (4) is at least 1 bar (100 kPa) absolute pressure.

7. The thermal reactor arrangement according to claim 1, wherein a diameter (D) of the expansion chamber (4) is greater than a diameter (d) of the plasma chamber (3), preferably at least two times, more preferably 3 times the diameter (d) of the plasma chamber (3).

8. The thermal reactor arrangement according to claim 7, wherein said reaction zone (34) and said expansion chamber (4) both are rotationally symmetric about their longitudinal axis, and wherein the diameter (D) of said expansion chamber (4) is at least two times, preferably at least three times the diameter (d) of said reaction zone (34).

9. The thermal reactor arrangement according to claim 1, wherein the quenching medium is selected from nitrogen, oxygen, air, and water, or mixture thereof, wherein the quenching medium is introduced as a liquid, gas, or mixture thereof.

10. The thermal reactor arrangement according to claim 1, wherein said heater (33) is chosen from a microwave generator, a radio wave generator, a laser generator, an inductively coupled plasma (ICP), a transformer coupled plasma (TCP), or an electric discharge generator.

11. The thermal reactor arrangement according to any one of claims 1 - 10, wherein said thermal reactor arrangement is configured for the synthesis of240060PC_251217_FINALnitrogen oxides (NOx) wherein the plasma (P) is held in the reaction zone (34) at a temperature and pressure sufficient to dissociate nitrogen and oxygen molecules.

12. A method for operating a thermal reactor for performing a desired chemical reaction, comprising the following steps: providing a gas mixture; and heating said gas mixture in a plasma chamber to form a plasma at a temperature and pressure at which the desired chemical reaction takes place, forming a mix of reaction products and unreacted gas, wherein the resulting mixture of reaction products and unreacted gas is transferred to an expansion chamber and expanded to form an expanded gas mixture of a pressure which is about 70 % of the pressure at which nitrogen and oxygen molecules dissociate, preferably about 60 %, more preferably about 50 %, and most preferably about 40 % or less of the pressure at which nitrogen and oxygen molecules dissociate, and wherein a quenching medium is introduced tangentially, parallel to the inner surface of the plasma chamber creating a vortex which travels downstream, toward an outlet leading into said expansion chamber.

13. The method according to claim 12, wherein said tangential vortex flow is maintained through the outlet of said plasma chamber into said expansion chamber.

14. The method according to claim 12, wherein quenching medium is introduced in said expansion chamber to further reduce the temperature of the expanded gas mixture.

15. The method according to claim 12, wherein quenching medium is introduced in said expansion chamber causing at least a portion of the quenching medium to initially flow in a direction substantially opposite to the gas entering the expansion chamber (4) creating turbulence.240060PC_251217_FINAL2716. The method according to claim 12, wherein said quenching medium is chosen from nitrogen, oxygen, air, and water, or mixture thereof, and wherein said quenching medium is introduced in the form of a liquid, a gas, or a mixture thereof.

17. The method according to claim 12, wherein said thermal reactor is operated to form nitrogen oxides (NOx), and wherein said gas mixture comprises oxygen and nitrogen, and a plasma (P) is generated and held in said reaction zone at a temperature and a pressure at which nitrogen and oxygen molecules dissociate.

18. The method according to claim 17, wherein a gas mixture comprising oxygen and nitrogen is heated to a temperature of at least 2300 K and held at a pressure of 2 - 100 bar, such as 5 - 100 bar, or a pressure of 10-100 bar, forming a gas mixture comprising NOx.

19. The method according to claim 17, wherein said gas mixture is expanded to form a gas mixture at a pressure of at least about 1 bar (100 kPa), preferably a pressure of 1 - 50 bar (100 - 5000 kPa), such as 1 - 30 bar (100 - 1000 kPa), such as 1 - 10 bar (100 - 1000 kPa).240060PC_251217_FINAL

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