A low ozone-plasma air disinfection device

Abstract

The application provides a low-ozone-plasma air disinfection device, an oxygen removal catalyst containing manganese series metal is arranged at an air inlet, an ozone decomposition catalyst containing titanium dioxide is arranged at an air outlet 2, a high-voltage electrode of a plasma generator is connected with a high-voltage end of a high-frequency microsecond pulse power supply, a ground electrode is connected with a low-voltage end of the high-frequency microsecond pulse power supply, the high-voltage electrode is a metal plate with a plurality of needle tubes for guiding air flow, the ground electrode is a metal plate with through holes, an insulating green oil medium is attached to the surface of the metal plate, and the specification of the metal plate of the ground electrode corresponds to the specification of the metal plate of the high-voltage electrode. The application solves the problem of ozone and other by-products from three aspects of power supply pulse driving mode, electrode structure optimization and catalyst decomposition technology, guarantees that the ozone concentration at the air outlet is lower than 0.01ppm, and has good engineering application value.

Description

A low-ozone-plasma air sterilization device Technical Field

[0001] This invention belongs to the field of air disinfection and relates to a low ozone-plasma air disinfection device. Background Technology

[0002] Traditional air disinfection technologies primarily employ ultraviolet (UV) disinfection, ozone disinfection, and chemical disinfection. UV disinfection is highly susceptible to environmental factors: dust or glass can act as a barrier, and indoor humidity, disinfection distance, and disinfection time all affect its effectiveness. Furthermore, UV disinfection requires prolonged exposure in an unoccupied environment to meet disinfection requirements. Ozone disinfection, due to the harmful effects of ozone on humans, must be performed in an unoccupied environment, and at least a half-hour interval must be observed after disinfection before anyone can enter the disinfected space to ensure safety; the entire disinfection cycle is very long. Chemical disinfection primarily involves spraying chemical reagents, which can easily leave chemical residues, polluting the environment and posing safety hazards to human health.

[0003] Plasma is the fourth state of matter after solid, liquid, and gas. It is rich in high-energy electrons, ions, excited-state atoms, free radicals, and other active components, making it a novel method of molecular activation. Atmospheric pressure cryogenic plasma is a non-equilibrium plasma generated under open atmospheric pressure using gas discharge. Because the electron temperature in this system is much higher than the heavy particle temperature, it can maintain a near-room temperature while achieving high chemical activity, thus being widely used in disinfection, sterilization, and waste gas purification.

[0004] To address the need for air disinfection, researchers have developed various air disinfection devices. Existing devices primarily utilize dielectric barrier discharge and corona discharge to ionize and generate plasma. They mainly utilize the reactive oxygen and nitrogen substances produced during ionization to disrupt the biological structure of microorganisms, thereby achieving air disinfection.

[0005] However, it has the following drawbacks: ① Existing plasma sterilization devices inevitably produce a certain amount of ozone during the plasma generation process, which is harmful to human health and limits the application of plasma air sterilization devices. ② Existing technologies use adsorbents such as activated carbon or catalysts such as metal oxides to absorb and decompose the generated ozone, but they do not solve the problem of ozone generation at its source, namely the design of the electrode structure and the mode of the driving power supply. Summary of the Invention

[0006] 1. The technical problem to be solved:

[0007] Existing plasma disinfection devices generate ozone, which is harmful to human health and limits the application of plasma air disinfection devices.

[0008] 2. Technical Solution:

[0009] To address the above problems, this invention provides a low-ozone plasma air disinfection device, comprising a housing, with a plasma generator located within the housing. The housing has an air inlet and an air outlet. An oxygen-degrading catalyst containing manganese-based metals is disposed at the air inlet, and an ozone-decomposing catalyst containing titanium dioxide is disposed at the air outlet. The plasma generator includes a high-voltage electrode and a ground electrode. The high-voltage electrode is connected to the high-voltage end of a high-frequency microsecond pulse power supply, and the ground electrode is connected to the low-voltage end of the high-frequency microsecond pulse power supply. The high-voltage electrode is a metal plate with multiple needles for conducting airflow, and the ground electrode is a metal plate with through holes drilled in it. The specifications of the ground electrode correspond to those of the high-voltage electrode.

[0010] The through hole on the ground electrode metal plate is located directly below the tip of the high-voltage electrode tube.

[0011] The plasma discharge region is mainly generated by the potential difference between the tube tip and the through hole on the ground electrode. The tube tip is the plasma generation region. The plasma develops from the tube tip to the through hole, forming a cone-shaped plasma region with the tube tip as the apex and the circular cross-section of the through hole as the base.

[0012] The air inlet and air outlet have the same structure, both being plate-shaped with ventilation holes.

[0013] The diameter of the vent hole is larger than the diameter of the needle tube.

[0014] The high-frequency microsecond pulse power supply adopts the Burst pulse power drive method. The Burst pulse power drive method is a method that uses DSP digital signal processing technology in conjunction with a corresponding processor module to generate a specific PWM signal through program control and editing, thereby controlling the on and off states of the switching devices in the microsecond power supply module, and thus controlling the output voltage waveform of the power supply module to present a pulse train state.

[0015] The surface of the ground electrode metal plate is coated with a layer of insulating green oil in the non-through-hole area.

[0016] The needle tube is 30-40mm long, with an outer diameter of 0.8-1.2mm and an inner diameter of 0.6-0.8mm. The metal plate is a cube with a side length of 220-235mm and a thickness of 1.2-181.8mm. The center-to-center distance between adjacent needle tubes is 5-8mm. The diameter of the through hole 204 is 2.5-3.5mm, and the center-to-center distance between every two through holes is 5-8mm.

[0017] The high-frequency microsecond pulse power supply is connected to the mains power.

[0018] A fan is installed at the air inlet.

[0019] 3. Beneficial effects:

[0020] This invention provides a solution to the problem of ozone and other byproducts by combining three aspects: power pulse modulation driving method, optimized electrode structure, ozone concentration at the air outlet below 0.01ppm, and catalyst decomposition technology. This invention has great engineering application value.

[0021] The airflow structure of this invention, with air entering through plate holes and exiting through pipe holes, ensures that the air for target disinfection remains in the plasma space region for a sufficiently long time, thereby ensuring a highly efficient air disinfection effect.

[0022] Based on the electric field simulation method, the optimal hollow needle tube-plate DBD electrode structure in this invention ensures that a uniform "conical" plasma space discharge area is formed between the tube tip and the corresponding plate hole, so that the target disinfection air can fully contact the discharge plasma during the air intake stage of the plate hole, forming a highly efficient primary disinfection.

[0023] This invention optimizes the design of a Burst pulse power driving method, which uses intermittent high-frequency microsecond unipolar pulses to drive the hollow needle tube-plate DBD to perform short-term transient strong discharge. Under the condition that the air is mainly composed of N2 and O2 as the working gas for discharge, it can more easily excite more nitrogen-active substances RNS, which interact with airborne viruses and other microorganisms to achieve the purpose of disinfection. From the perspective of plasma discharge and disinfection mechanism, it suppresses the generation of O3 without losing the disinfection function.

[0024] Meanwhile, in terms of overall design, the air inlet of this invention is designed with a deoxygenation adsorption unit to reduce the O2 content entering the plasma discharge area, while the air outlet is designed with an O3 decomposition catalyst and adsorption unit to further reduce O3 emissions. This ensures that even if the whole machine operates in a closed space for a long time, the O3 content in the air in the entire closed space is extremely low, thus protecting human health and safety. Attached Figure Description

[0025] Figure 1 is an overall schematic diagram of the present invention.

[0026] Figure 2 is an overall side sectional view of the present invention.

[0027] Figure 3 is a schematic diagram of the plasma generator.

[0028] Figure 4 is a schematic diagram of the plasma generator.

[0029] Figure 5 is a schematic diagram of the air inlet and air outlet of the present invention.

[0030] Figure 6 is an overall framework diagram of the present invention.

[0031] Figure 7 is a schematic diagram of the discharge region.

[0032] Figure 8 shows the electric field distribution.

[0033] Figure 9 shows the discharge image.

[0034] Figure 10 is a schematic diagram of the airflow handling channel.

[0035] Figure 11 is a schematic diagram of the airflow in the discharge region unit.

[0036] Figure 12 is a schematic diagram of the PWM signal and corresponding output voltage waveform controlled and edited by DSP technology.

[0037] Figure 13 is a light-emitting image of the present invention under normal operating conditions.

[0038] Figure 14 shows the voltage circuit waveform under normal operating conditions.

[0039] Figure 15 shows actual images of different fungi treated at different times.

[0040] Figure 16 is a line graph showing the number of different types of bacteria sterilized at different times.

[0041] Explanation of reference numerals in the attached diagram: 1. Air inlet; 2. Plasma generator 2; 3. Air outlet; 4. High-frequency microsecond pulse power supply; 5. Fan; 201. High-voltage electrode; 202. Ground electrode; 203. Tube tip; 204. Through hole; 205. Discharge area surface; 206. Insulating green oil. Detailed Implementation

[0042] The present invention will now be described in detail with reference to the accompanying drawings.

[0043] As shown in Figures 1, 2, and 5, the low-ozone plasma air disinfection device includes an air inlet 1, a plasma generator 2, an air outlet 3, and a high-frequency microsecond pulse power supply 4. The air inlet 1 contains a deoxygenation catalyst primarily composed of manganese-based metals, whose main function is to remove a portion of the oxygen from the air, reducing the ozone content generated in the plasma generator. The air outlet 3 contains an ozone decomposition catalyst primarily composed of titanium dioxide, which mainly catalyzes the decomposition of a small amount of ozone generated by the plasma reactor. Neither of these catalysts requires energy, produces no toxic or harmful substances, has a long service life, and can be recycled after certain treatments. This energy-saving and environmentally friendly approach ensures the biosafety of the invention.

[0044] As shown in Figures 3 and 4, the plasma generator 2 includes a high-voltage electrode 201 and a ground electrode 202. The high-voltage electrode 201 is connected to the high-voltage end of the high-frequency microsecond pulse power supply 4, and the ground electrode 202 is connected to the low-voltage end of the high-frequency microsecond pulse power supply. The high-voltage electrode 201 is a metal plate with multiple needle tubes for conducting gas flow. The ground electrode 202 is a metal plate with through holes 204 drilled in it. The surface of the metal plate is covered with a layer of insulating green oil 206 in the non-through hole areas, which serves as the medium in the dielectric barrier discharge. The specifications of the ground metal plate correspond to those of the high-voltage electrode metal plate. The through holes 204 on the ground electrode 202 metal plate are the channels through which the gas flows, and their positions are directly below the tip 203 of the high-voltage electrode tube.

[0045] As shown in Figure 7, the plasma discharge region 205 is mainly generated by the potential difference between the tube tip 203 and the through-hole 204 on the ground electrode 202. The tube tip 203 is the main plasma generation area. The plasma develops from the tube tip 203 towards the through-hole 204, forming a cone-shaped plasma region 205 with the tube tip 203 as the apex and the circular cross-section of the through-hole 204 as the base. The electric field of the electrode structure was analyzed and observed using the simulation software COMSOL. The results are shown in Figure 8. The electric field strength of the high-voltage electrode 201 is the strongest, while the electric field strength of the ground electrode 202 decreases from the edge of the through-hole 204 outwards, and the decreasing trend is basically uniform, ensuring that a uniform "cone" plasma space discharge region 205 is formed between the tube tip and the corresponding plate hole. Under the excitation of the high-frequency microsecond pulse power supply 4, its discharge image is shown in Figure 9. After the untreated air containing bacteria enters through the through-hole 204, it comes into full contact with the cone-shaped plasma region 205, thereby achieving a good disinfection effect.

[0046] As shown in Figure 6, the air disinfection device is powered by mains electricity. A high-frequency microsecond pulse power supply 4 boosts the voltage to meet the requirements for driving the electrodes of the air disinfection device. The entire process is as follows: Untreated air containing bacteria enters through the inlet unit 1 containing a deoxygenation catalyst under the action of the fan 5. It then enters the plasma discharge region through the through-hole 204 on the metal plate of the ground electrode 202. After sufficient contact with the plasma, the disinfected air flows out through the hollow metal needle tube on the high-voltage electrode 201 and flows back into the outside air through the outlet unit 2 containing an ozone catalyst.

[0047] As shown in Figure 10, the normal operating process involves untreated air entering through inlet 1 under the action of fan 5, where a portion of the oxygen is removed by the manganese-based metal catalyst. At this point, the gas flowing to plasma generator 2 mainly consists of nitrogen molecules and a small amount of incompletely removed oxygen molecules. The partially deoxygenated gas enters the plasma reaction zone through through-hole 204 on the grounded metal plate 202. Plasma generator 2 is powered by a high-frequency microsecond pulse power supply 4. Under pulse modulation, the high-frequency microsecond pulse power supply 4 generates a pulse voltage with high amplitude, narrow pulse width, high burst repetition frequency, and long pulse delay time, enabling plasma reactor 2 to operate in Burst mode. This ionizes the untreated air, minimizing ozone production and better breaking down nitrogen molecules, creating a plasma enrichment region primarily composed of RNS (reactive nitrogen substances). Bacteria and other microbial pathogens in the untreated gas are located in this RNS-enriched region; under the action of the plasma, their genetic material is destroyed, thus achieving sterilization and disinfection. Under the continuous action of the blower 5, the unsterilized gas comes into full contact with the plasma between the high-voltage electrode 201 and the ground electrode 202. After complete sterilization, the gas flows out from the hollow metal needle tube of the high-voltage electrode 201 and into the outside air through the outlet 3. At the same time, the ozone catalyst and titanium dioxide catalyst in the outlet 3 further decompose a small amount of toxic and harmful substances such as ozone generated during the plasma reaction. After the treatment is completed, the high-frequency microsecond pulse power supply 4 and the blower 5 are turned off, and the entire process ends.

[0048] In one embodiment, for the plasma discharge area unit to achieve long-term airflow residence and disinfection, the diameter of the air inlet orifice is larger than the diameter of the air outlet needle orifice, and the needle length is appropriately increased, so that the target disinfected air resides and circulates in the plasma discharge area, prolonging the contact time, making full use of the plasma active material, and improving the disinfection effect, as shown in Figure 11.

[0049] By utilizing pulse modulation technology, a pulse voltage with high amplitude, narrow pulse width, high burst repetition frequency, and long pulse delay time is generated. Under air conditions, primarily composed of N2 and O2 as the working gas for discharge, this more readily excites nitrogen-reactive substances (RNS), suppressing O3 production without sacrificing the disinfection function. Therefore, this patent optimizes the design of a Burst pulse power driving method, using pulse modulation technology to generate intermittent high-frequency microsecond unipolar pulses, enabling the needle-plate DBD electrode to operate in a short-duration transient strong discharge state.

[0050] In one embodiment, the "Burst pulse power drive method" of this invention is a pulse modulation technique that utilizes DSP digital signal processing technology in conjunction with a corresponding processor module to generate specific PWM signals through program control. These signals control the on / off states of the switching devices (silicon carbide MOSFETs) in the microsecond power module, thereby controlling the output voltage waveform of the power module to present a "pulse train" state. The "pulse train" state of the output voltage waveform involves first discharging at a higher frequency of 10kHz within the pulse train, during which the switching transistors undergo corresponding frequency state transitions. Then, it enters a period outside the pulse train frequency, during which the switching transistors remain inactive. Considering the time of discharge at the 10kHz high-frequency discharge within the pulse train and the time during which the switching transistors are inactive as one cycle, the overall power discharge frequency is a lower frequency of 1kHz. The PWM signal controlled and edited by DSP technology and the corresponding output voltage waveform are shown in Figure 12.

[0051] For power supplies, the Burst pulse power drive method not only reduces losses caused by transistor switching in microsecond power supplies and improves energy utilization efficiency, but also provides sufficient heat dissipation time for transistors in microsecond power supplies, reducing the probability of transistor damage and improving the stability of the power supply and the entire device.

[0052] For plasma-generated active material disinfection using electrode discharge: high voltage, narrow pulse width, and instantaneous high frequency output voltage can generate a large number of active particles in a short time. Since the existence time of active particles is limited, active particles still exist even when not discharging in the Burst pulse power drive mode. They can fully exert their effect in the target disinfection air, and no further power input is required at this time. Therefore, the energy input is reduced without weakening the disinfection effect. In addition, the electrodes in the Burst pulse power drive mode are more likely to excite nitrogen-active substances (RNS) in the air, inhibiting the generation of O3. While ensuring the disinfection effect, ozone generation is reduced, which is more conducive to achieving low-ozone disinfection.

[0053] The device proposed in this invention can discharge normally under the Burst pulse power drive mode. To verify the discharge uniformity of the tube-plate DBD electrode in the device, its operating state was observed at a microsecond power supply output voltage of 9kV. The emission image under its operating state is shown in Figure 13, and the voltage and current waveforms are shown in Figure 14. It can be seen that the device can work normally under the Burst pulse power drive mode, and the tube-plate electrode discharge is relatively uniform, with all needles producing a "fan-shaped" plasma discharge region.

[0054] To verify the ozone emission level under normal operating conditions, the tube-plate electrode and ozone detector, as described in section 2.4.1, were simultaneously placed in a transparent, sealed box measuring 50cm x 50cm x 60cm. The device was operated continuously for 5 minutes, and the ozone detector reading was observed. It was observed that the ozone detector did not detect ozone during the 5 minutes of continuous operation.

[0055] Therefore, the ozone content generated by the low ozone-ion plasma air disinfection device based on the Burst pulse power drive mode designed in this invention meets the requirements of the "General Hygiene Requirements for Air Disinfection Machines" WS / T 648—2019 issued by the National Health Commission of the People's Republic of China.

[0056] To verify the sterilization performance of the device, three common bacteria—Pseudomonas aeruginosa, Escherichia coli, and Staphylococcus aureus—were targeted for sterilization. In the sterilization experiment, three groups of bacterial suspension samples (A: P. aeruginosa, B: E. coli, C: S. aureus) were prepared and used, 3 mL for each group. The bacterial suspensions were then centrifuged and the culture medium was poured off. 3 mL of physiological saline was added and the mixture was shaken well before the device was treated with bacteria. The device was then exposed to the discharge plasma region of the designed hollow needle-plate DBD electrode at different time intervals. Subsequently, serial dilutions were performed, and the samples were coated and incubated in an incubator. The number of surviving cells was counted using colony-forming units (CFU). The results are shown in Figure 15, where the initial concentration of all three bacteria was 10⁷ CFU / mL, and the control group consisted of untreated original colonies.

[0057] The efficiency of air-based multi-needle tube-plate discharge sterilization can be investigated by calculating the sterilization rates of the three types of bacterial colonies:

[0058]

[0059] in This is the number of viable bacteria in the control group. It is the number of viable bacteria in the hollow needle-tube sheet DBD plasma electrode reactor treatment group.

[0060] Figure 16 shows the sterilization effects of the designed hollow needle-tube-plate DBD plasma electrode reactor at various time points. At 1 minute of treatment, the sterilization rates of *E. coli* reached 94.22%, *S. aureus* 96.18%, and *P. aeruginosa* 98.87%. At 3 minutes of treatment, a clear inflection point appeared on the curves for the sterilization effects of the three colonies; after 3 minutes, the sterilization effect gradually slowed down and approached saturation. Overall, *P. aeruginosa* and *E. coli* were more effective than *S. aureus* under plasma treatment, but after 5 minutes, the sterilization effect of all three colonies reached 99.99%. The curves clearly show the acceleration and deceleration of bacterial numbers over time. This verifies the feasibility of the designed hollow needle-tube-plate DBD plasma electrode reactor for sterilizing airborne bacteria, viruses, and other microorganisms.

Claims

1. A low-ozone-plasma air disinfection device, comprising a housing, a plasma generator (2) located within the housing, the housing being provided with an air inlet (1) and an air outlet (3), characterized in that: The air inlet (1) is provided with a deoxygenation catalyst containing manganese metals, and the air outlet (3) is provided with an ozone decomposition catalyst containing titanium dioxide. The plasma generator (2) includes a high-voltage electrode (201) and a ground electrode (202). The high-voltage electrode (201) is connected to the high-voltage end of the high-frequency microsecond pulse power supply (4), and the ground electrode (202) is connected to the low-voltage end of the high-frequency microsecond pulse power supply. The high-voltage electrode (201) is a metal plate with multiple needle tubes for conducting airflow. The ground electrode (202) is a metal plate with through holes (204) drilled in it. The specifications of the metal plate of the ground electrode (202) correspond to the specifications of the metal plate of the high-voltage electrode (201). The through holes (204) on the metal plate of the ground electrode (202) are located directly below the tip (203) of the high-voltage electrode tube. The plasma discharge region (205) is mainly generated by the potential difference between the tube tip (203) and the through hole (204) on the ground electrode (202). The tube tip (203) is the plasma generation region. The plasma develops from the tube tip (203) to the through hole (204), forming a conical plasma region (205) with the tube tip (203) as the apex and the circular cross-section of the through hole (204) as the base. The high-frequency microsecond pulse power supply (4) adopts the Burst pulse power drive mode. The Burst pulse power drive mode is a method that uses digital signal processing technology in conjunction with a corresponding processor module to generate a specific PWM signal through program control editing, which controls the on and off states of the switching transistor devices in the microsecond power supply module, thereby controlling the output voltage waveform of the power supply module to present a pulse train state.

2. The low-ozone-plasma air sterilization device as described in claim 1, characterized in that: The air inlet (1) and air outlet (3) have the same structure, both being plate-shaped with ventilation holes.

3. The low-ozone-plasma air sterilization device as described in claim 2, characterized in that: The diameter of the vent hole is larger than the diameter of the needle tube.

4. The low-ozone-plasma air sterilization device according to any one of claims 1-3, characterized in that: The surface of the metal plate of the ground electrode is coated with a layer of insulating green oil (206) in the non-through-hole area.

5. The low-ozone-plasma air sterilization device according to any one of claims 1-3, characterized in that: The needle tube is 30-40mm long, with an outer diameter of 0.8-1.2mm and an inner diameter of 0.6-0.8mm. The metal plate is a cube with a side length of 220-235mm. The center-to-center distance between adjacent needle tubes is 5-8mm. The diameter of the through hole (204) is 2.5-3.5mm, and the center-to-center distance between every two through holes (204) is 5-8mm.

6. The low-ozone-plasma air sterilization device according to any one of claims 1-3, characterized in that: The high-frequency microsecond pulse power supply (4) is connected to the mains power.

7. The low-ozone-plasma air sterilization device according to any one of claims 1-3, characterized in that: A fan (5) is installed at the air inlet (1).

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