WO2023075629A1

WO2023075629A1 - Device for producing nitric oxide

Info

Publication number: WO2023075629A1
Application number: PCT/RU2021/000465
Authority: WO
Inventors: Сергей Николаевич БУРАНОВ; Владимир Иванович КАРЕЛИН; Виктор Дмитриевич СЕЛЕМИР; Александр Сергеевич ШИРШИН
Priority date: 2021-10-27
Filing date: 2021-10-27
Publication date: 2023-05-04

Abstract

The invention relates to the production of nitric oxide from air using electrical discharge and can be used in medicine, biology and scientific research. For this purpose, high-voltage pulses are fed to electrodes, of which a first electrode (3) is configured in the form of a disc with an inlet channel (4). In addition, a second electrode (5) is configured in the form of a sector of a disc having a sharp, angled edge and an outlet channel (6), and the device is equipped with a source of ultraviolet light (11) for illuminating the sharp edge of the second electrode, wherein the spectral range of the ultraviolet light is selected in order that a photoelectric emission of λ ≤ 1240/А is produced, where A is the work function of the material of the electrodes (eV) and λ is the wavelength of the ultraviolet light (nm), and the size of the angle is selected in order that the first electrode is illuminated with UV light reflected from the angled edge of the second electrode, wherein the outlet of a gas filter (7) is connected to the inlet channel, and the outlet channel is connected to the inlet of a pump (8), the outlet of which is connected to the inlet of a purification unit (9). The technical result is an increase in the reliability of the device.

Description

DEVICE FOR OBTAINING NITRIC OXIDE

The field of technology to which the invention belongs

The invention relates to plasma chemistry, in particular to the production of nitric oxide (NO) from atmospheric air using an electric discharge and can be used in medicine (inhalation NO - therapy, cardiac surgery, as well as therapy for wound, inflammatory, vascular and other pathologies), in scientific research (experimental modeling of physical processes in the upper layers of the Earth's atmosphere), biology (the impact of NO on biological objects).

Prior Art

The process of nitrogen oxidation in electric discharge plasma, in particular arc and spark discharge, is widely used in science and medicine [Plasma Chem Process (2016) 36:737-766, IEEE Transactions of Plasma Science, Vol.28, No. l, February 2000] and industry. The advantages of electric discharge installations in comparison with others (for example, chemical, photolytic) are readily available reserves of raw materials (atmospheric nitrogen and oxygen), equipment reliability and the possibility of placing an electric discharge installation in close proximity to the place of application of NO - containing mixture.

An important feature of installations based on a pulsed discharge is the possibility of wide-range precise control of the content of nitric oxide in the output stream, which is a particularly necessary factor in medical applications requiring the possibility of implementing strictly dose-dependent individual therapy [Nitric Oxide, 60 (2016) 16-23 and Nitric Oxide, 75 (2018) 70-76].

A device for the formation of NO-containing gas flow of the authors A.V. Peksheva, A. B. Vagapova, S.V. Grachev and others according to the description of the invention to the Russian patent [RU 2183474, A 61 M l 1/00, publ. 06/20/2002]

The known device includes a discharge chamber, two high-voltage electrodes electrically isolated from each other, placed inside the discharge chamber in such a way that there is an interelectrode space between said electrodes, inlet and outlet channels, and an air pump.

In a known device, atmospheric air through the inlet channel is pumped into the discharge chamber. Simultaneously with the supply of air, a constant voltage of about 400 V is applied to the mentioned electrodes and a stationary arc discharge is formed with the help of an initiator, ensuring stable generation in the interelectrode space of an air plasma with a temperature of about 3700°C, which is optimal for the synthesis of nitric oxide in it in accordance with the plasma-chemical reaction N ₂ +O2*- ^> 2NO.

From the interelectrode space, an NO-containing air-plasma flow with a temperature of about 3200°C enters the outlet channel, which includes a hardening chamber, intermediate and final cooling paths. In the quenching chamber, there is a rapid cooling (10 ⁷ -10 ⁸ deg/sec) of the gas to a temperature of about 1000°C, which ensures the fixation (quenching) of nitrogen oxide. Then, from the hardening chamber, the gas flow passes through the intermediate and final cooling paths, in which the temperature drops to 150°C and 30°C, respectively. From the outlet of the exhaust channel, the cooled NO-containing gas is supplied to the consumer. A disadvantage of the known device is the high operating temperature of the gas. This is due to the fact that under conditions of an arc discharge, the parameters of the air plasma are very close to equilibrium (T _el /T _gas ~1), where T _el is the average electron temperature, T _gas is the average gas temperature. To suppress other products of electrosynthesis (nitrous oxide, nitrogen dioxide, ozone) and ensure efficient production of NO, the bulk of the energy should be spent on heating the plasma as a whole to a temperature of 3400–3700°C. In this case, high thermal loads on the design elements of the discharge chamber and the outlet channel reduce the reliability of the device.

In addition, heat removal from said electrodes and outlet channel elements is carried out by means of a combined cooling system, which includes a plurality of built-in channels with high-temperature seals, which also reduces reliability.

Known "Device for plasma-chemical production of nitric oxide" authors R. Castor, T. Hammer according to the description of the US patent [US 6955790 B2, 01 J 19/08, publ. 18.10.2005] In a known device, the synthesis of nitric oxide is carried out in the plasma barrier discharge (BD).

The known device includes a discharge chamber, two coaxial high-voltage electrodes electrically isolated from each other, placed inside the discharge chamber in such a way that there is an interelectrode space between said electrodes, an inlet channel and at least one outlet channel, a gas filter, an air pump, a purification unit.

In the known device, the source gas, purified from mechanical impurities in the gas filter, is fed by means of a pump through a heat exchanger, a thermostatically controlled heater and an inlet channel into the interelectrode space of the discharge chamber. At the same time, on said electrodes supply a high-voltage alternating or pulsed alternating voltage with a frequency above 1 kHz and an amplitude sufficient for electrical breakdown of the gas interelectrode space. The presence of a dielectric layer (barrier) on the outer electrode from the side of the interelectrode space provides a breakdown of the mentioned space in the form of a sequence of groups of short-lived (no more than 100 nanoseconds) microdischarges, called a barrier discharge [see Fig. Samoilovich V.G., Gibalov V.I., Kozlov K.V. Physical chemistry of barrier discharge. M.: Publishing House of Moscow State University. 1989. 176 p.]. In a BR, the average electron energy is about 3.5 eV (T _el /T _gas > 1), there is an effective formation of O-atoms as a result of the dissociation of O ₂ by electron impact. The gas itself remains relatively cold (about 100°C) and the main product of electrosynthesis is ozone (Oz). To suppress the formation of Oz and shift the balance of reactions towards active production of NO, the gas supplied to the discharge chamber is preheated to 800°C. From the interelectrode space, an NO-containing gas flow with a significant amount of NO ₂ (nitrogen dioxide) impurity enters through the outlet channels into the purification unit. Further, the gas stream purified from NO ₂ passes through a heat exchanger and a cooler for intermediate and final cooling. The NO-containing gas mixture cooled to room temperature enters the gas analyzer and is sent to the consumer.

The disadvantage of the known device is that one of the high-voltage electrodes is made with a dielectric coating. The breakdown of the gas gap in the presence of a dielectric barrier occurs in the form of a set of microdischarges with a characteristic diameter of ~0.3 mm and a current density in the channel of ~100 A/cm ² . In this case, along the surface of the dielectric, a sharply inhomogeneous distribution of currents. This inhomogeneity causes local overheating, a strong temperature gradient and mechanical stress, which leads to a decrease in the strength of the dielectric barrier and, as a result, reduces reliability.

Another drawback of the known device is related to the fact that at low temperatures the oxidation reaction NO + O ₃ —>NO ₂ +O ₂ plays an important role, as a result of which, due to a significant amount of ozone, the concentration of NO in the BR cannot reach a noticeable value. And only at a gas temperature of about 800 ° C, the concentration of O ₃ drops so much that favorable conditions are created for the reaction N + O ₂ - > N0 + 0, which provides the required concentration of NO. As a result, the known device additionally contains an initial mixture heater, a heat exchanger and a refrigerator, which reduces the temperature of the NO-containing gas to room temperature, which is a disadvantage, since they complicate the design and reduce the reliability of the device.

From a technological point of view, spark discharges at a gas pressure of the order of atmospheric are attractive for obtaining nitric oxide. Compared to BR in spark discharges, due to the lower average electron energy (1-2 eV), the mechanism of NO synthesis through the vibrationally excited states of nitrogen molecules N ₂ *, which occurs at low temperatures of the source gas (100-200 ° WITH). In particular, in a discharge excited by high-voltage pulses with a duration of T _imp = 1–10 μs, it is possible to achieve that the average electron energy is at the maximum of the vibrational excitation cross section of nitrogen molecules N ₂ , and the specific energy input exceeds the threshold value W = 1 W/cm ³ . Under these conditions, elementary reactions with the participation of oxygen atoms and vibrationally excited nitrogen molecules prevail. since the main energy of rapidly populated N ₂ vibrational levels is directed to the nitric oxide synthesis reaction, and not to heating the gas. As a result, the maximum achievable NO concentration increases [cf. ed. Smirnova B.M. Plasma Chemistry: Sat. articles. Issue. 5. M.: Atomizdat. 1978. S. 328].

Known generator of nitric oxide from the air by the author W.M. Zapol according to the description of the US patent [US 5396882, A 61 M 11/00, publ. March 14, 1995]. The known device contains a discharge chamber, including two high-voltage rod electrodes placed oppositely to form an interelectrode space, an inlet and outlet channel, a gas filter, an air pump, a cleaning unit, wherein the inlet of said pump is connected to the gas filter, the outlet of said pump is connected to the inlet channel of the discharge chamber, and the input of the said cleaning unit is connected to the discharge channel of the discharge chamber.

In the known device, the source gas (air) purified in the filter is pumped through the inlet channel into the discharge chamber, which includes the interelectrode space. Under the action of an alternating voltage of industrial frequency (50-60 Hz), a spark discharge is formed between high-voltage electrodes, in the plasma of which nitric oxide and a certain amount of other gases (ozone, nitrogen dioxide, etc.) are synthesized. To remove unwanted impurities, the gas mixture is discharged through the outlet channel to the purification unit. The purified NO-containing gas mixture is supplied to the consumer.

In a known device, the discharge occurs periodically (twice during the period of industrial frequency), and its appearance is associated with the achievement of a breakdown voltage on the mentioned electrodes interelectrode space, and extinction corresponds to the moment when the voltage becomes less than the discharge burning voltage.

Due to the low frequency (50-60 Hz) of the power supply network, the threshold specific energy input (W/v>l J/cm ³ , where W is the energy input in the pulse, v is the gas flow volumetric velocity) in a known device can be provided if each a single train has a large amount of energy. This is disadvantageous because it leads to excessive heat generation near the electrode surface and severe erosion, which reduces reliability.

Another disadvantage that reduces reliability is the execution of the electrode system in the form of an axisymmetric rod structure with transverse blowing, since in this case there is a binding of spark channels to the sharp edges of the electrodes, local overheating and erosion.

The next disadvantage of the known device is the high instability of the discharge supply. This is due to the fact that a slowly increasing voltage is applied to the interelectrode space, and the moment of electrical breakdown has a large time spread. So, the magnitude of the breakdown voltage of the interelectrode space, which varies significantly from pulse to pulse, entails fluctuations in the electrical parameters of the train (average current, energy, etc.). In particular, at too low values of the breakdown voltage, the value of the specific energy content can be below the threshold value of 1 J/cm ³ , which briefly disrupts the above mechanism of nitric oxide synthesis. In this case, unspent oxygen atoms participate mainly in the competing reaction of ozone synthesis. The destruction of this unwanted gas requires additional equipment, which reduces reliability. Known generator of nitric oxide from the air of the author Shu Xiao according to the description of the Chinese patent [CN 201010523 (Y), C 01 21/24, publ. 01/23/2008] The known device contains a discharge chamber, including at least two high-voltage electrodes placed oppositely to form an interelectrode space, an inlet and outlet channel, a gas filter, an air pump and an additional voltage pulse generator connected to the high-voltage electrodes.

In the known device, the air purified in the filter is pumped through the inlet channel into the discharge chamber, which includes the interelectrode space. Under the action of a high-frequency alternating voltage of a resonant-type generator, a continuous electric discharge is formed between the high-voltage electrodes, in the plasma of which nitric oxide is synthesized. The NO-containing gas mixture leaving the outlet channel is fed into a medical, technological or biological system.

In the known device, the problem of erosion of high-voltage electrodes was tried to be solved by the possibility of controlling the frequency and magnitude of the alternating current flowing through the discharge, providing, on the one hand, the required number of nitric oxide molecules and, on the other hand, an acceptable level of erosion.

The disadvantage of this approach is that there is a narrow range of the above parameters that allow you to form a discharge with the required energy input and continuously maintain it. Moreover, in the case of low gas flow rates, low concentrations of NO in the known device were obtained by removing most of the produced nitrogen oxide from the gas path using an additional device associated with the safe removal of the NO-containing stream and its utilization, which reduces reliability. Known generator of nitric oxide from the air author FJ Montgomery and others according to the description of the US patent [US 9573110 B2, C 01 21/24, publ. 02/21/2017] The known device contains a discharge chamber, including at least two high-voltage rod electrodes placed oppositely to form an interelectrode space, an inlet and outlet channel, a gas filter, an air pump and a voltage pulse generator connected to the high-voltage electrodes.

In the known device, the voltage pulse generator operates in pulse-width mode (PWM) with a short-term increase in voltage at high-voltage electrodes at the beginning of each pulse. The peak values of voltage and current are sufficient for electrical breakdown of the air interelectrode space and excitation of a spark discharge, in the plasma of which the physicochemical reactions of nitric oxide formation start. The required amount of nitric oxide is set due to the possibility of regulating the pulse duration at relatively low voltage and current values, which reduces the wear of high-voltage electrodes. To provide the specified algorithm for obtaining nitric oxide, the known device uses two power circuits, connected in series by electronic keys. At the same time, due to transient processes in the high-voltage summation circuit, the switches are subject to the destructive effects of short-term overvoltages. This factor is a disadvantage that reduces reliability.

In a known device, depending on the required value of the concentration of nitric oxide, the duration of the electric discharge is varied over a wide range of 0.1 - 10 ms. However, under conditions of a long discharge duration, even at low discharge currents (less than 0.1 A), the gas temperature in the contact area rises significantly. plasma from the surface of the electrodes, which reduces the reliability due to their thermal erosion.

The closest technical solution to the claimed invention is a device for obtaining nitric oxide from the air of the authors S.N. Buranov, V.I. Karelin, V.D. Selemir, A. S. Shirshin according to the description of the Russian patent [RU 2553290 Cl, C 01 B 21/24, C 01 B 21/32 publ. 06/10/2015], which discloses an alternative approach to preventing wear of high-voltage electrodes due to high-energy arc (spark) discharges.

A known device for producing nitric oxide, includes a cylindrical discharge chamber, a gas filter, a pump, a cleaning unit, a high-voltage voltage pulse generator with an adjustable pulse repetition rate, the chamber contains two electrically isolated high-voltage electrodes with an interelectrode space between them, an inlet and an outlet channel , the first high-voltage electrode is made in the form of a disk with a central hole for the inlet channel, is installed transversely to the axis of the discharge chamber, the second high-voltage electrode is installed along the axis of the discharge chamber, and the high-voltage pulse generator is connected to the high-voltage electrodes.

For the electrosynthesis of nitric oxide, the authors used periodic microsecond pulses with an adjustable repetition rate f, which excited a spark discharge in the air flow between the disk electrode and the semicircular wire electrode, while air was introduced into the discharge chamber along its central axis through a hole in the disk electrode.

The reason for this choice was that under the above conditions, stable combinations of the parameters of the pulsed periodic discharge (voltage, current, discharge channel diameter) and gas flow velocity through the central hole in the electrode, providing the condition W/v>l J/cm ³ in a wide range of f, which determines the effective formation of NO in the reaction O+N ₂ *— NO +N with the participation of vibrationally excited nitrogen molecules N ₂ *. At the same time, the rate of the ozone synthesis reaction competing with it was much lower, so that the presence of Oz in the output stream was not actually observed, which increased reliability (ozone as a strong oxidizing agent in many applications is an undesirable impurity). In addition, on the one hand, it was possible to prevent compression (contraction) of the discharge channel and, on the other hand, ensured the active movement of its brightly luminous part over the surface of the electrodes, which reduced thermal erosion of the latter and increased reliability.

In the known device, due to the short duration of the power pulses, it was very important to ensure a stable breakdown delay time t _d within the rise time of the voltage pulse on the electrodes (~3 μs). In turn, t _d consists of the sum of the statistical time t _c required for the formation of at least one initial (starting) electron in the proper region of the gap and the time tf during which this electron is able to break down. Since at atmospheric pressure (p ~ 760 Torr) and the interelectrode gap (d ~ 0.3 cm) the first term is significantly greater than the second, the main attention was paid to reducing the time t _c . This problem was solved by using a gap with a sharply inhomogeneous electric field geometry near the wire electrode with a small radius of curvature (~0.25 mm). Here, due to the high field strength, ionization processes proceed in an advanced manner, increasing the initial emission current of electrons emerging from dielectric films, which initially are present on the surface of the wire, which reduced the statistical delay time t _c to an acceptable value.

However, under the action of the discharge plasma, some of the films can evaporate, which entails an increase in the time interval t _d . If the latter exceeds the duration of the power pulses, a failure will inevitably occur in the formation of the planned discharge and, accordingly, the process of electrosynthesis of nitric oxide. This circumstance is a disadvantage that reduces the reliability of the device.

The disadvantage is also the design of one of the electrodes, made of stainless wire with a diameter of 0.5 mm. This electrode cannot be effectively cooled by heat transfer in the attachment area due to its small cross section. Therefore, with an increase in the discharge power, overheating of its central region occurs, which reduces reliability.

The next drawback is a consequence of the installation of an air pump in front of the discharge chamber inlet. Accidental squeezing (reducing the cross section) of the gas path causes an increase in pressure in the discharge chamber, the transition of the discharge combustion to the compressed (contracted) channel mode at a practically unchanged current value, which increases the thermal erosion of the electrodes and reduces reliability.

Disclosure of invention

When creating the claimed invention, the problem of creating a device for obtaining, under the influence of a repetitively pulsed discharge in a gas stream, a controlled exact amount of nitric oxide (NO concentration) was solved.

The technical result in solving this problem was to increase the reliability of the device. This technical result is achieved by the fact that, in comparison with the known device for producing nitric oxide, including a cylindrical discharge chamber, a gas filter, a pump, a cleaning unit, a high-voltage voltage pulse generator with an adjustable pulse repetition rate, the chamber contains two high-voltage electrodes electrically isolated from each other with an interelectrode space between them, inlet and outlet channels, the first high-voltage electrode is made in the form of a disk with a central hole for the inlet channel, is installed transversely to the axis of the discharge chamber, the second high-voltage electrode is installed along the axis of the discharge chamber, and the high-voltage pulse generator is connected to high-voltage electrodes, new is that the second high-voltage electrode is made in the form of a disc sector with a sharp edge beveled at an angle and with a side hole for the outlet channel, the device is equipped with a source of ultraviolet radiation to illuminate the sharp edge of the second electrode, while the spectral range of ultraviolet radiation is selected from the condition for obtaining photoelectronic emission < 1240/A, where A is the work function of the electrode material, eV, is the wavelength of ultraviolet radiation, nm, and the angle a is selected from the condition of illuminating the first electrode with UV radiation reflected from the beveled edge of the second electrode, and the output of the gas filter connected to the inlet channel, the outlet channel is connected to the inlet of the pump, the outlet of which is connected to the inlet of the cleaning unit.

Also, the source of ultraviolet radiation is made on the basis of an ultraviolet LED.

Also, the source of ultraviolet radiation is made on the basis of a gas-discharge quartz lamp. Also, the source of ultraviolet radiation makes it possible to form a collimated beam.

Also, the source of ultraviolet radiation makes it possible to form a converging beam, the focus of which is at the intersection of the axis of the discharge chamber with the edge of a sharp edge.

The claimed device uses a source of ultraviolet radiation for direct illumination of the second electrode and illumination of the first electrode by light reflected from the surface of the second electrode beveled at an appropriate angle. In this case, photons have an energy higher than the work function (A) from the electrode material (condition X < 1240/A), which causes a single-photon photoelectric effect. Compared to the emission mechanism of supplying electrons from films to near-electrode regions, the photoelectric effect produces electrons more stably and in larger quantities. Photoelectrons are accumulated near the electrodes in advance with a short time t _c , even at the beginning of the high-voltage pulse front. Here, by the time of the maximum voltage rise rate, a significant photoelectron current, amplified by electron avalanches, forms a high-conductivity plasma channel that bridges the gap. The formation time of a highly conductive channel (breakdown) tf at atmospheric pressure is no more than 0.1 μs [Mesyats G.A., Uspekhi fizicheskikh nauk, October 2006, Volume 176, No. 10, pp. 1069 - 1091]. Therefore, the breakdown delay time t _d does not exceed the rise time in any of the high-voltage pulses in the series, starting from the first, which entails the stabilization of the average current, the energy (P) invested during the pulse, and the specific energy input W/v=P*f/ v. As a result, under the action of a series of voltage pulses in a wide range of f, the condition W/v>l J/cm ³ is ensured, which determines the effective formation of NO in the reaction O + N ₂ * - »NO + N with the participation of vibrationally excited nitrogen molecules N ₂ *, which increases reliability.

In microsecond discharges of atmospheric pressure (р~760 Torr) at short intervals (d~0.3 cm), the well-known Townsend mechanism of formation of a sufficiently wide plasma channel with moderate energy release in the region of its adjunction to the electrode surface is realized. The air pump is installed after the outlet of the discharge chamber, as a result of which it ensures the passage of the gas mixture through the interelectrode gap at a pressure not higher than atmospheric, and in a wide range of changes in the resistance of the gas path at the outlet of the device. At the specified pressure, instabilities do not have time to develop in a repetitively pulsed discharge of microsecond duration, leading to a significant narrowing (contraction) of the plasma channel, an increase in the specific energy release and thermal erosion of the electrodes, which increases reliability.

The design of the second electrode, made in the form of a disk sector with a built-in outlet channel, allows it to be intensively cooled by heat transfer in the attachment area due to its larger cross section and the gas flow passed through the outlet channel. Therefore, with an increase in the discharge power, efficient heat removal from its central region takes place, which increases reliability.

UV radiation is introduced from the side wall of the discharge chamber and ensures that the light source is located at a sufficiently large distance from high-voltage electrodes, which protects the source from electrical breakdown and increases reliability.

In addition, the source of ultraviolet radiation can be made on the basis of a pulsed discharge lamp, giving bursts of radiation of very high brightness at millisecond durations. This increases the magnitude of the emission current of photoelectrons in the region near the electrodes and provides a breakdown of the interelectrode gap at the front of microsecond voltage pulses, which increases reliability.

In addition, the UV source can be made on the basis of an UV LED, which has a low supply voltage (< 8 V), a long service life (~ 20 thousand hours), and almost instant readiness for operation, which increases reliability.

In addition, the source of ultraviolet radiation can be made with the formation of a collimated beam, the diameter of which is matched to the size of the interelectrode gap. Now the gap length is not a critical parameter that determines the breakdown efficiency, which increases reliability.

In addition, the source of ultraviolet radiation can be made with beam focusing in the area of intersection of the axis of the discharge chamber with the edge of the sharp edge of the second electrode. An increase in the electric charge of photoelectrons in the region with the maximum electric field strength reduces the time spread of the breakdown time delay, which improves reliability.

Brief description of the drawings

Figure 1 shows a block diagram of the proposed device for producing nitric oxide, where:

1 - discharge chamber, 2 - interelectrode space, 3 - first high-voltage electrode, 4 - inlet channel, 5 - second high-voltage electrode, 6 - outlet channel, 7 - gas filter, 8 - air pump, 9 - purification unit, 10 - high-voltage generator voltage pulses, I - source of ultraviolet (UV) radiation, 12 - beam.

Figure 2 shows a block diagram of the proposed device for producing nitric oxide in the example of the best implementation, where:

1 - discharge chamber, 2 - interelectrode space, 3 - first high-voltage electrode, 4 - inlet channel, 5 - second high-voltage electrode, 6 - outlet channel, 7 - gas filter, 8 - pump, 9 - purification unit, 10 - high-voltage generator voltage pulses, 11 - ultraviolet (UV) radiation source (ultraviolet diode), 12 - beam, 13 - respiratory (therapeutic) circuit, 14 - NO and NO ₂ monitoring unit, 15 - neutralizer.

The claimed device comprises a gas filter 7 connected in series, a discharge chamber 1, a pump 8, a cleaning unit 9, a high-voltage generator 10 of voltage pulses with an adjustable repetition rate f. In this case, the discharge chamber 1 contains two high-voltage electrodes 3, 5 electrically isolated from each other with an interelectrode space 2 between them, inlet 4 and outlet 6 channels, the first high-voltage electrode 3 is made in the form of a disk with a central hole for the inlet channel 4, installed perpendicular to the axis discharge chamber, the second high-voltage electrode 5 is installed along the axis of the discharge chamber, and the high-voltage pulse generator 10 is connected to the high-voltage electrodes 3.5.

In addition, in the claimed device, the second high-voltage electrode 5 is made in the form of a disk sector 3-5 mm thick with a side hole for the outlet channel 6 and with a sharp edge beveled at an angle a ~ 45 ° ± 5 °, in the direction of which the beam 12 of ultraviolet radiation is directed source 11 installed transversely axis of the discharge chamber. Moreover, the spectral range of ultraviolet radiation is selected from the condition for obtaining photoelectron emission X < 1240/A, where A is the work function of the electrode material, eV, X is the wavelength of ultraviolet radiation, nm. The value of the angle a is chosen from the condition of illumination of the first electrode by UV radiation reflected from the beveled edge of the second electrode. In this case, the outlet of the gas filter 7 is connected to the inlet channel 4, the outlet channel 6 is connected to the inlet of the pump 8, the outlet of which is connected to the inlet of the purification unit 9.

Additionally, in the claimed device, the source of ultraviolet radiation 11 can be made on the basis of an ultraviolet LED or a gas-discharge quartz lamp. Moreover, the source of ultraviolet radiation 11 can form a collimated (parallel) beam or a converging beam, the focus of which is at the intersection of the axis of the discharge chamber with the edge of a sharp edge.

The discharge chamber 1, made of polyamide with an inner diameter of 18 mm, includes two high-voltage electrodes 3, 5, electrically isolated from each other, made of stainless steel 12X18H10T. The first of the mentioned electrodes 3 is made in the form of a disk. The second of the mentioned electrodes 5 is made in the form of a sector cut out of a disk 3 mm thick (the angle at the top is 30°).

In the center of the disk electrode 3 there is a hole with a diameter of 1.5 mm for the inlet channel 4. Closer to the base of the sector electrode 5 there is a side hole with a diameter of 1.5 mm for the outlet channel 6. The length of the interelectrode space 2 between electrodes 3 and 5 is 3 mm. The edge of the sector electrode 5 is beveled at an angle a = 45° and is sharp with a radius of not more than 0.1 mm. Opposite the beveled edge in the body of the discharge chamber 1 a hole is made for the input of the beam 12 of ultraviolet radiation of the source I. The input angle between the optical axis of the beam 12 and the axis of symmetry of the discharge chamber is 90°. The radiation wavelength of the source satisfies the condition of direct (single-photon) photoelectron emission from stainless steel < 288 nm (A = 4.31 eV, see Fomenko V. S. Emission properties of materials: Handbook. Edition 3. Kiev.: Naukova Dumka. 1970. S. 20). The discharge chamber is intended for the electrosynthesis of nitric oxide in the flow of air passing through the space 2 under the action of high-voltage pulses applied to the said electrodes 3 and 5 with spark control by ultraviolet radiation.

Gas filter 7 is a main filter or a microfilter. It can also be made in the form of their sequential modular assembly. The main filter is designed to remove solid particles larger than 5 microns from the air, as well as water and oil condensate. Water separation efficiency 99%. The principle of operation is based on the effect of merging small drops into larger ones in the filter element. The formed large drops flow down to the bottom of the tank with a built-in automatic condensate drain. The microfilter removes solid particles larger than 0.3 microns. The oil content at its outlet is not more than 1 mg/m ³ .

As an air pump 8, a compressor is used, in the process of operation, including continuous, which does not introduce oil pollution into the pneumatic line. Compressor capacity up to 1 l/min with free gas flow. Compressor parts in contact with the pumped medium are made of corrosion-resistant materials: stainless steel, duralumin, PTFE compound. The compressor is designed for pumping neutral and low-aggressive gases in medical, laboratory and analytical equipment.

Soda lime was used as purification unit 9, including 96% calcium hydroxide and 4% sodium hydroxide (in terms of dry matter). The purification unit 9 is designed to purify the NO-containing stream leaving the discharge chamber 3 from nitrogen dioxide.

The purpose of the high-voltage pulse generator 10 is to generate power pulses for the discharge chamber 1 with a given repetition rate f. The mentioned high-voltage generator 10 generates pulses of alternating polarity with an amplitude of up to 12 kV and a duration of up to 4 μs (at half-height of the pulse) using a resonant current inverter made according to a well-known bridge circuit on IGBT transistors IRG4IBC20UD with built-in reverse diodes (see Romash E.M. ., Drabovich Yu.I., Yurchenko N.N., Shevchenko N.N. High-frequency transistor converters. - M: Radio and communication. - 1988. - P. 228.).

The claimed device works as follows.

The gas pump 8 is turned on. In the gas filter 7, air pollution is removed. Filtration fineness, oil and water separation efficiency correspond to the required class, depending on the purpose of the installation. An oil-free pump 8 pumps air through the discharge chamber 1, including the interelectrode space 2. At the same time, due to the negative pressure drop between the outlet 6 and the inlet 4 channel, the gas pressure in the discharge chamber 1 is slightly lower than atmospheric. Almost simultaneously, a high-voltage voltage pulse generator 10 and a UV source 1 1 with a wavelength < 288 nm are activated (actually, the UV source is a little earlier), irradiating the second electrode with a direct beam and reflected beam - the first electrode. The duration interval of UV radiation is such that several (3 - 5) voltage pulses fall into it without fail, following even with the lowest possible frequency from the specified regulation range f. In fact, the radiation power with a photon energy of more than 4.31 eV is sufficient to create the required number of initial (starting) photoelectrons in the region of electrodes 3, 5 already during the front of the first of the series of pulses, causing a breakdown of the interelectrode space 2. The deliberate choice of an overestimated duration radiation prevents the possibility of disruption of electrosynthesis in the supplied series of voltage pulses, if, nevertheless, the breakdown does not occur in the first pulse, which further increases reliability.

The generator of high-voltage pulses 10 in the process of formation of spark discharges carries out resonant energy transfer. Upon reaching the breakdown voltage on the electrodes 3, 5 and ignition of the spark discharge, the high-voltage generator invests energy in the discharge plasma. In the initial stage of the breakdown, due to the high electric field strength, oxygen dissociation occurs and nitrogen molecules are transferred to an excited state, giving rise to nitric oxide synthesis reactions. However, the discharge of atmospheric pressure, which is formed and proceeds at high field strengths, is unstable - it tends to pass into other types of discharge. In the claimed device, to prevent the transition of spark discharges into a low-efficiency NO synthesis, but actively evaporating electrodes arc combustion mode, microsecond pulses are applied to the electrodes. And - alternating polarity, in order to avoid excessive accumulation of charges of the same sign at each of the electrodes, to achieve a more uniform heat release along the length of the spark discharge and reduce the thermal load on the electrodes, which further improves reliability. After the voltage drops below the burning threshold, the unused part of the energy in the pulse returns to the high-voltage generator and is used in the next cycle.

The repetition frequency f of the pulses determines the concentration of NO in the gas stream. The upper limit of the f _MaKC range is approximately 10 kHz and is determined by the characteristic reaction time T= ^10'4 sec of the formation of NO molecules due to the accumulated vibrationally excited nitrogen molecules: f _MaKC <l/T. When f _MaKC is exceeded, frequency control becomes ineffective due to strong non-linearity. The lower limit of the f _MHH range is determined by the parameter of the specific energy input W/ _v =P _MaKC *f _MHH /v>l J/ ^cm excited nitrogen molecules N ₂ *. The rate of this reaction is higher than the rate of the ozone synthesis reaction competing with it O ₂ + O + M ^ O ₃ + M, where M is any molecule or atom. The main part of the energy invested in the discharge is spent on the synthesis of NO. Therefore, maintaining the specific energy input above the above-mentioned limit ensures the virtual absence of ozone at the outlet of the discharge chamber, which additionally increases the reliability.

Thus, under the action of a pulsed voltage in the interelectrode space 2 formed by disk electrode 3 and sector electrode 5, spark discharges are formed, in the plasma of which nitric oxide and a certain amount of other nitrogen oxides (for example, nitrogen dioxide) are synthesized. The source gas enters the discharge chamber 3 through the inlet channel 4 in the center of the disk electrode 3. The NO-containing mixture through the outlet channel 6 in the sector electrode 5 is removed by the pump 8 to the purification unit 9. Next purified from unnecessary nitrogen dioxide (NO2) NO - containing gas stream is sent to the outlet.

Best Implementation

Currently, abroad and in Russia, nitric oxide for inhalation is obtained by chemical synthesis at stationary stations. The short shelf life of NO, complex logistics, and high cost limit the availability of NO therapy. The claimed device can make a significant contribution to solving clinical and technical problems of improving the effectiveness of treatment and ensuring the reliability of NO-producing equipment. This will be clear from the following description and the drawing attached thereto (FIG. 2).

In the proposed embodiment, the output of the cleaning unit 9 is connected to one of the inputs of the respiratory (therapeutic) circuit 13, to the other input of which the output of the ventilator (or any other source of the main respiratory mixture) is connected, one of the outputs of the respiratory circuit 13 is connected to the patient, the other the outlet of the respiratory circuit 13 is connected to the input of the NO and NO2 monitoring unit 14, the output of which is connected to the input of the neutralizer 15, while the source of ultraviolet radiation is made on the basis of an ultraviolet diode 11 with a radiation wavelength equal to X = 280 nm and a collimated radiation beam 12 with a diameter of about 8 mm, capturing the entire length of gap 2 and the width of the beveled edge of the second electrode.

The respiratory circuit 13 is used to receive and transfer the flow of therapeutic NO-mixture, satisfying the minute volume of the patient's breathing. Connections to the cleaning unit 9 and the monitoring unit 14 are made using detachable connections of the Luer-Lock type.

The monitoring unit 14 is designed to measure the mass concentrations of nitrogen oxide, nitrogen dioxide, gas flow rate and signals the appearance of dioxide and nitrogen oxide with a concentration above the permissible value. Calibration of measuring sensors - automatic. The measurement results are displayed on an alphanumeric display. On the front panel of the unit there is a keyboard for managing monitoring, obtaining additional information and setting alarm thresholds.

The neutralizer 15 is designed to clean the gas sample from NO and NO ₂ after monitoring. The neutralizer is a two-component adsorption-catalytic destructor. For NO ₂ adsorption, a purification unit based on calcium hydroxide is used. To neutralize NO, a catalytic decomposition method is used. The concentration of NO and NO ₂ in the gas mixture at the outlet of the converter does not exceed the MPC according to GOST 12.1.005. MPC NO ₂ \u003d 2 mg / m ³ (1.05 ppm). MPC N0=5 mg/m ³ (4.01 ppm).

According to the scheme shown in figure 2, the work is carried out as follows. The monitoring unit 14 and the ventilator are turned on, which, when inhaled, creates the main flow through the respiratory circuit 13. The main flow rate is set depending on the minute volume of breathing. Next, NO-containing air is fed into the breathing circuit. In the circuit, nitric oxide is mixed with the main respiratory stream, which is supplied from the ventilator. In front of the patient (patient mask), a sample is taken from the breathing circuit for analysis, which is carried out by electrochemical NO and NO ₂ sensors in monitoring unit 14. The effect of the supply of NO-containing air on the initial flow of the respiratory mixture is minimized by matching the volumetric flow rate supplied to breathing circuit, and the flow taken for analysis. After monitoring, the gas mixture is cleaned from nitrous gases in the neutralizer 15. It should be noted that during therapy, NO and NO ₂ concentrations in the respiratory circuit are monitored continuously. To prevent the risk of cross-contamination, virus-bacterial hydrophobic filters (not shown in figure 2) are installed on the NO supply line and the NO and NO ₂ monitoring line.

In the embodiment shown in FIG. 2, the following main technical characteristics were obtained.

The concentration of nitric oxide in the respiratory circuit was regulated from 1 to 100 ppm by changing the pulse repetition rate of the high-voltage pulse generator from 50 to 5000 Hz and the rate of the main respiratory flow from 1.5 to 20 l/min. At the same time, the volumetric flow rate of NO-containing air supplied to the breathing circuit was about 0.5 l/min. The step in the entire range of regulation of the NO concentration was 1 pp. There was no ozone in the respiratory tract outlet (with an accuracy of 0.01 ppm). When testing the proposed device in the maximum performance mode for 900 hours (including 10 days of continuous operation), the values of the above parameters of the NO concentration did not go beyond ± 20%, the depth of plasma erosion of the disk electrode did not exceed 0.05 mm, and the sector electrode did not exceed 0 .15 mm, which made it possible to reliably deliver the NO-containing mixture to the patient, even with prolonged therapy.

Practical (industrial) application

The medical device with the claimed device for obtaining nitric oxide has passed technical tests and clinical trials in 55 adult patients.

The results demonstrated the clinical efficacy of therapy and the high reliability of the device used, generating nitric oxide from the ambient air, including in comparison with traditional therapy using equipment with the supply of NO-containing gas from a 150-atmospheric cylinder.

Claims

27 Claims

1. A device for producing nitric oxide, including a cylindrical discharge chamber, a gas filter, a pump, a purification unit, a high-voltage generator with an adjustable pulse repetition rate, the chamber contains two high-voltage electrodes electrically isolated from each other with an interelectrode space between them, inlet and outlet channels, the first high-voltage electrode is made in the form of a disk with a central hole for the inlet channel, it is installed transversely to the axis of the discharge chamber, the second high-voltage electrode is installed along the axis of the discharge chamber, and the high-voltage generator is connected to the high-voltage electrodes, characterized in that the second high-voltage electrode is made in the form of a disk sector with sharp edge beveled at an angle a and with a side hole for the outlet channel, the device is equipped with a source of ultraviolet radiation to illuminate the sharp edge of the second electrode, while the spectral range of ultraviolet radiation is selected from the condition for obtaining photoelectron emission A, < 1240/A, where A is the work function from the electrode material, eV, L is the wavelength of ultraviolet radiation, nm, and the angle a is selected from the condition of illumination of the first electrode by UV radiation reflected from the beveled edge of the second electrode, moreover, the gas filter outlet is connected to the inlet channel, the outlet channel is connected to the inlet pump, the output of which is connected to the input of the cleaning unit.

2. The device according to claim 1, characterized in that the source of ultraviolet radiation is made on the basis of an ultraviolet LED.

3. The device according to claim 1, characterized in that the source of ultraviolet radiation is made on the basis of a gas-discharge quartz lamp.

4. The device according to claim 1, characterized in that the source of ultraviolet radiation allows you to form a collimated beam.

5. The device according to claim 1, characterized in that the source of ultraviolet radiation allows you to form a converging beam, the focus of which is at the intersection of the axis of the discharge chamber with the edge of a sharp edge.