CN114210187A

CN114210187A - Method for removing nitrogen oxides from exhaust gases and injection device

Info

Publication number: CN114210187A
Application number: CN202111538771.2A
Authority: CN
Inventors: 方诗清; 彼得·万凯姆潘; 刘奔; 李金龙
Original assignee: LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
Current assignee: LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
Priority date: 2021-12-15
Filing date: 2021-12-15
Publication date: 2022-03-22

Abstract

The invention discloses a method for removing nitrogen oxides from exhaust gas and an injection device, wherein the injection device comprises an air guide pipe and an injection end, the air guide pipe is used for conveying ozone, the injection end is at least provided with an injection port and a flow guide part, the flow guide part comprises a spacing piece and a top cover, and a flow guide groove is formed between every two adjacent spacing pieces. Ozone is radially injected into the reactor device via at least one injection device, the ozone being mixed with the exhaust gas to oxidize nitrogen oxides in the exhaust gas. The method of the invention can treat various types of waste gas containing nitrogen oxides in a limited space at a lower temperature so as to meet stricter and stricter emission regulations, reduce the investment cost and have high treatment efficiency.

Description

Method for removing nitrogen oxides from exhaust gases and injection device

Technical Field

The invention relates to the field of industrial waste gas removal, in particular to an improved method for removing nitrogen oxides from waste gas and an injection device.

Background

The exhaust gases from various industrial processes often contain nitrogen oxides NO_x(x is the atomic ratio of O to N in the nitrogen oxide), sulfur oxide SO_y(y is the atomic ratio of O to S in the sulfur oxide), particulates, heavy metals, or other acid gases. Taking an industrial combustion process as an example, pollutants in the flue gas stream produced by it need to be removed before being discharged to the atmosphere. The nitrogen oxides in the flue gas stream are mainly composed of insoluble and non-reactive Nitric Oxide (NO). It is known to remove nitrogen oxides from flue gas streams by dry or wet methods and to remove sulfur oxides by dry or wet scrubbing. In wet scrubbing, NO can be removed by water scrubbing negligible, since NO is a poorly water soluble gas.

SNCR (Selective Non-Catalytic Reduction ) and SCR (Selective Catalytic Reduction, Selective Catalytic Reduction denitration) have certain effects on solving the emission of nitrogen oxides, but have limitations. SNCR requires the use of an amino-containing reducing agent, such as ammonia (NH)₃) Or urea water solution, and spraying a reducing agent in a temperature range suitable for denitration reaction, such as 760 ℃ to 1090 ℃, so as to reduce nitrogen oxides in the flue gas into harmless nitrogen and water, wherein the denitration rate of the SNCR is generally between 20% and 50%. SCR is a well-established flue gas denitration technology after the furnace, and most of the SCR is used for TiO₂The catalyst is a carrier catalyst, the reaction temperature range is 315-400 ℃, the denitration efficiency is high, but the catalyst is not suitable for an exhaust gas treatment process with low temperature, and the investment and maintenance cost of the device are extremely high.

Low temperature oxidation processes for ozone have also been developed in the prior art, based on the chemical action of nitrogen oxides reacting with ozone to form higher oxides of nitrogen. Due to Nitrogen Oxides (NO)_x) The solubility of (b) increases significantly with higher valency, so the reaction is run forward to form specific NO₂Oxides with higher valences can more easily be removed completely in the form of higher nitrogen oxides by wet scrubbing. If all NO is present_xAll in the form of Nitric Oxide (NO), converting NO to N₂O₅Desired odorThe oxygen stoichiometry is such that 1.5 moles of ozone are required per mole of NO. If NO is present_xAre both NO₂In the form of (1), 0.5 mol of ozone is required. Such as N₂O₅Are not only very soluble, but also highly reactive, and are easily removed in dry, semi-dry or wet scrubbing equipment.

Ozone is an unstable gas that is typically produced on-site on demand using gaseous oxygen. Most commercially available starting materials are pure oxygen (oxygen purity)>90%) of the ozone generator provides 8 to 12% by weight of the conversion of oxygen to ozone. FIG. 1 shows a graph based on a study of the thermal decomposition of ozone at different temperatures over time, [ O ]₃]/[O₃]₀Representing the ratio of the measured concentration of ozone to the initial concentration, it can be seen that the higher the temperature, the faster the decomposition rate of ozone. Under the condition of 150 ℃, the decomposition rate of ozone is not high. Thus, at typical flue gas exhaust and heat-exchanged temperatures, the self-decomposition of ozone to O₃With NO_xThe reaction between them has little influence. At 150 ℃ of O₃With NO_xThe reaction time between the two steps is only about 0.01 second.

In the prior art, Chinese patent publication No. CN104941410B discloses an integrated method and a device for removing flue gas by low-temperature two-step oxidation and denitration by active molecular ozone, wherein the flue gas after dust removal sequentially enters a flue reactor and a wet washing tower. As shown in fig. 2, in the figure, 1 is a flue, 2 is an active molecule generating device, 3 is a flue reactor, 4 is a wet scrubbing tower, 5 is an induced draft fan, 6 is a chimney, 7 is a gypsum dewatering device, 8 is a nitrogen and sulfur element recovery device, 9 is a flue grid, 10 is a demister, 11 is a dilution fan, and 12 is a waste heat recovery device. Wherein the active molecule ozone participates in the reaction in two stages: a part of the gas is sprayed from the front end of the flue reactor 3 to oxidize NO in the flue gas into NO₂(ii) a The rest is sprayed into the tail end of the flue reactor 3 or the middle section of the wet scrubbing tower 4 to continuously inject NO in the flue gas₂By oxidation to NO₃Or N₂O₅. Sulfur oxides and NO in flue gas₃Or N₂O₅Together with the slurry of the wet scrubbing towerAnd (4) absorbing the liquid to realize the integrated removal of the sulfur and nitrate pollutants. The two-step removal requires the arrangement of a flue grid inside the flue reactor for strengthening the flue gas and the active molecule O₃The mixing effect of (1). However, the complicated flue reactor structure not only increases the processing and manufacturing difficulty, but also reduces the complete reaction amount of ozone and nitrogen oxides only by injecting partial ozone at the front end, which is not beneficial to the oxidation of the nitrogen oxides by the ozone.

In view of the above, it is an objective of the present invention to provide an improved method and injection device for removing nitrogen oxides from exhaust gas, so as to overcome the above-mentioned drawbacks and deficiencies of the prior art.

Disclosure of Invention

The object of the invention is to provide an improved method and injection device for removing nitrogen oxides from exhaust gases. These include exhaust gases from any complete or partial combustion source or thermal process, as well as process exhaust gases from petroleum refining, petrochemical, organic, inorganic and fine chemical production processes.

In the method provided by the application, ozone is introduced into the waste gas containing nitrogen oxides, the ozone is injected into the waste gas radially by the injection device which is arranged at an angle with the flow direction of the waste gas, and a vortex is formed on the radial section of the injection device to promote high mixing of the ozone and the waste gas.

In a first aspect of the invention, a method for removing nitrogen oxides from exhaust gas is disclosed, comprising the steps of:

(1) feeding the waste gas at a temperature below 180 ℃ to a reactor device which is provided with an inner wall surrounding in radial direction,

(2) injecting ozone radially into the reactor device via at least one injection device, the ozone mixing with the exhaust gas to oxidize nitrogen oxides in the exhaust gas;

wherein the radial wall-hitting time of the ozone is less than 0.05 seconds, preferably less than 0.02 seconds.

Further, the reactor device comprises a reaction zone, and the ratio X/D of the length X of the reaction zone in the axial direction of the reactor device to the longest axis D of the reaction zone is between 2 and 5.

Further, the temperature inside the reactor device is below 180 ℃, preferably below 160 ℃, more preferably below 150 ℃.

Further, in the reactor device, the injection means is arranged at an angle, preferably 90 °, to the flow direction of the exhaust gases.

Further, the method comprises the steps of: the waste gas treated by the reactor device is supplied to a washing tower for washing.

Further, the molar ratio of ozone to nitric oxide to be removed in the exhaust gas is 1.0:1 to 1.5: 1.

further, the ozone is injected at the upstream end of the reaction zone means.

Further, the ozone injection position is located at the center of the radial cross section of the reactor device.

Further, the step (2) further comprises: oxygen of purity greater than 90% is provided to an ozone generator to produce ozone.

Further, the volume fraction of NO in the nitrogen oxides in the total nitrogen oxides is greater than or equal to 30%.

In a second aspect, the present invention provides a spraying device applied to the method of the first aspect of the present invention, the spraying device comprises an air duct and a spraying end, the air duct is used for delivering ozone, the spraying end is provided with at least one spraying opening and a flow guiding member, wherein the flow guiding member comprises a spacing member and a top cover, and a flow guiding groove is formed between every two adjacent spacing members.

Further, each channel extends in a radial direction from the center of the top cover and has a curvature between the center of the top cover and the edge of the baffle. This may cause the ozone to swirl at the edge of the baffle.

Further, the spacers are equally spaced from each other by 360 °/n, where n is equal to the number of spacers.

Further, the number of the spacers is 6-8.

Further, a flow dividing structure is disposed at the center of the top cover on the side facing the air guide pipe, and the flow dividing structure disperses ozone in the radial direction.

Further, the flow dividing structure is a cone-shaped or multi-edge-shaped protrusion.

Further, the injection port of the injection end is located at the center of the injection end.

Compared with the prior art, the technical scheme provided by the invention has the following advantages:

1. the removal rate of NOx in the exhaust gas containing nitrogen oxides by adopting the injection device and the method provided by the invention can reach more than 95%, and the device and the method are independent of the process of exhaust gas generation.

2. Compared with the traditional SCR or SNCR denitration method, the method can treat various types of waste gas, especially low-temperature industrial waste gas, at lower temperature (generally lower than 200 ℃) and in limited space so as to meet stricter emission regulations, reduce investment cost and have high efficiency.

3. In particular, the injection device selected according to the invention allows excellent mixing of ozone with the exhaust gases within a very short distance, so that nitrogen oxides are oxidized from the lower valence state to the higher valence state within a very short time.

Drawings

The advantages and spirit of the present invention can be further understood by the following detailed description of the invention and the accompanying drawings.

FIG. 1 shows the thermal decomposition of ozone over time at different temperatures;

FIG. 2 is a schematic view of the apparatus disclosed in the Chinese patent publication No. CN 104941410B;

FIGS. 3a to 3d are schematic views showing the structure of the spraying device of the present invention;

FIG. 4 is a schematic diagram of a process for removing nitrogen oxides from a flue gas stream according to an embodiment of the present invention;

FIG. 5 shows a schematic flow chart of the process for removing nitrogen oxides in the tail gas of the nitration plant in the second embodiment of the present invention.

Detailed Description

Specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. However, the present invention should be understood not to be limited to such an embodiment described below, and the technical idea of the present invention may be implemented in combination with other known techniques or other techniques having the same functions as those of the known techniques.

In the following description of the embodiments, for purposes of clearly illustrating the structure and operation of the present invention, directional terms are used, but the terms "front", "rear", "left", "right", "outer", "inner", "outward", "inward", "axial", "radial", and the like are to be construed as words of convenience and are not to be construed as limiting terms.

In the following description of the specific embodiments, it is to be understood that the terms "length," "width," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," and the like are used in an orientation or positional relationship indicated in the drawings for convenience in describing the invention and to simplify the description, but are not intended to indicate or imply that the referenced device or element must have a particular orientation, be constructed and operated in a particular orientation, and are not to be construed as limiting the invention.

Furthermore, the terms "first" and "second" are used for descriptive purposes only and are not intended to limit the temporal order, quantity, or importance, but are not intended to indicate or imply relative importance or implicitly indicate the number of technical features indicated, but merely to distinguish one technical feature from another technical feature in the present disclosure. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of the present invention, "a plurality" means two or more unless specifically stated otherwise. Similarly, the appearances of the phrases "a" or "an" in various places herein are not necessarily all referring to the same quantity, but rather to the same quantity, and are intended to cover all technical features not previously described. Similarly, unless a specific number of a claim recitation is intended to cover both the singular and the plural, and embodiments may include a single feature or a plurality of features. Similarly, modifiers similar to "about", "approximately" or "approximately" that occur before a numerical term herein typically include the same number, and their specific meaning should be read in conjunction with the context.

It should be understood that in the present application, "at least one" means one or more, "a plurality" means two or more. "and/or" is used to describe the association relationship of the associated objects, meaning that there may be three relationships, for example, "a and/or B" may mean: only A, only B and both A and B are present, wherein A and B may be singular or plural. The character "/" generally indicates that the former and latter associated objects are in an "or" relationship. "at least one of the following" or similar expressions refer to any combination of these items, including any combination of single item(s) or plural items. For example, at least one (one) of a, b, or c, may represent: a, b, c, "a and b", "a and c", "b and c", or "a and b and c", wherein a, b and c may be single or plural.

The terms "unit", "piece", "object", and "module" described in the present specification denote units for processing at least one of functions and operations, and may be implemented by hardware components or software components, and a combination thereof.

In the present invention, the terms "mounted," "connected," "secured," and the like are to be construed broadly unless otherwise specifically indicated and limited. For example, the connection can be fixed, detachable or integrated; can be mechanically or electrically connected; either directly or indirectly through intervening media, either internally or in any other suitable relationship. The specific meanings of the above terms in the present invention can be understood by those skilled in the art according to specific situations. "fixedly connected" or "non-movably connected" is understood to mean that the connection between two or more structural members is not configured to provide relative movement. An example of a fixed connection is a welded joint or a bolted joint, and in some cases a welded joint and a bolted joint. "movably connected" or "movable" or "movably connected" is understood to mean a connection between two or more structural members that allows for horizontal and/or vertical relative movement between the members under extreme dynamic loads. Such connections are generally not permitted to move under static or generally dynamic loads (e.g., as imposed by wind forces from mild/moderate).

The term "sealing connection" or "sealable connection" means the following features: the two component containers are connected or connectable by a welded connection, an adhesive connection, a screw thread or other means, so that no contents can leak out of the multi-chamber mixing container through the sealed connection when pressure is built up in order to empty the multi-chamber mixing container.

The terms "upstream" and "downstream" as used herein are defined with respect to the intended flow of fluid (e.g., exhaust gas), with the upstream end corresponding to the end closest to the inlet at which the fluid is introduced into the device and the downstream end corresponding to the outlet end at which the fluid exits the device.

Unless clearly indicated to the contrary, each aspect or embodiment defined herein may be combined with any other aspect or embodiments. In particular, any feature indicated as being preferred or advantageous may be combined with any other feature indicated as being preferred or advantageous.

As used herein, "central axis" and "axis" have the same meaning herein and refer to the axis of rotation, axis of symmetry, or centerline of the reactor apparatus. The direction of extension of the "central axis" herein may be parallel to the flow direction of the exhaust gas. As used herein, the term "axial" may refer to a direction extending relative to the central axis, and the terms "radial", "radial direction" may refer to a direction or relationship of a line extending perpendicularly outward relative to the central axis.

As used herein, "reaction zone" refers to a region within the reactor apparatus where ozone and nitrogen oxides come into contact due to diffusion of gases and oxidation reactions occur. The reaction zone has a cross-section in the radial direction of the reactor apparatus and has a length X in the axial direction of the reactor apparatus.

As used herein, "the longest axis D of the reaction zone" refers to the longest line segment available in each radial cross-section of the reaction zone, connecting any two points. For example, for a substantially circular radial cross-section, the longest axis is the diameter of the circle. As another example, for a substantially elliptical radial interface, the longest axis is the major axis of the ellipse. As another example, for a substantially rectangular radial cross-section, the longest axis is the diagonal of the rectangle.

As used herein, "radial injection" refers to injecting ozone into the exhaust gas fluid at an angle substantially perpendicular to the direction of exhaust gas flow for thorough mixing.

As used herein, "radial wall-strike time" refers to the time required for ozone to be radially sprayed from the center of the spraying device to the inner wall of the reactor device.

As used herein, the exhaust gas may be from any complete or partial combustion source and thermal process, as well as process gas streams of an inorganic or organic chemical plant. For example, if the exhaust gas is a flue gas stream generated by combustion, the volume flow rate can reach 5000m³/h～200000m³/h。

Ozone is generated in an ozone generator, and commercial ozone generators using pure oxygen as a gas source generally generate about 10% of the mass of ozone. The rapid and uniform distribution of ozone in the exhaust gas is important to ensure complete mixing. Because if the ozone distribution is not proper, the decomposition rate of ozone will be increased with time, resulting in NO_xThe removal rate of (a) is lowered and consequently a number of problems arise in the washing process which lead to non-compliance with the object of the invention. Most of the nitrogen oxides in the flue gas stream from the combustion process are in the insoluble and non-reactive NO form and cannot be removed by conventional sorbents or scrubbers. The volume fraction of NO in this portion of the flue gas to total nitrogen oxides is typically above 30%.

In the reaction zone, NOx is oxidized in the presence of ozone, the main reactions being as follows:

NO+O₃→NO₂+O₂ (1)

NO₂+O₃→N₂O₃+O₂ (2)

2N₂O₃+2NO₂→3N₂O₅ (3)

2NO₂→N₂O₄ (4)

among the above reactions, the reaction (1) is faster than the reactions (2) and (3), and the reactions (1), (2) and (3) are continuous reactions. Ozone oxidation of NO_xThe main reaction of (2) is the oxidation of NO to NO as described in equation (1)₂And NO described in the reaction formula (2)₂Further oxidized to N₂O₃Reaction of (3) N₂O₅The synthesis of (2) also requires a sufficient amount of N₂O₃. In the case of treating nitrogen oxide exhaust gas with ozone, the nitrogen oxide concentration is generally in the ppm range, and the pressure is low, so that the reaction (4) is less likely to occur.

The ozone of the present invention is injected further upstream or forward of the scrubber. Radially injecting ozone (O) at a temperature of less than 200 ℃ in the reactor unit, preferably at a temperature of less than 160 ℃₃). After mixing with the waste gas and ensuring proper reaction time, the ozone can oxidize NO in the waste gas into high-valence nitrogen oxide NO which is easily dissolved in water and alkaline detergent₂、N₂O₃And N₂O₅. The subsequent off-gas is passed through one or a series of scrubbers to remove nitrogen oxides. The nitric oxide removal efficiency of the invention can reach 95 percent, and is independent of the process of waste gas generation.

Ozone is injected into the exhaust gas radially by the injection device, a vortex is formed uniformly over the entire radial cross section, and the ozone can reach the inner wall of the reactor device extremely quickly, within 0.05 second, even within 0.02 second, so that the ozone is distributed quickly and uniformly over the entire radial cross section of the exhaust gas flow and is mixed with the exhaust gas sufficiently and quickly.

The injection means is located at the upstream end of the reaction zone and is arranged substantially perpendicular to the flow direction of the exhaust gases.

Fig. 3a to 3d show a schematic structural view of the flow guide. As shown in fig. 3b, the spraying device includes a gas-guiding tube 303 and a spraying end 304, the gas-guiding tube 303 is used for delivering ozone, and the spraying end 304 is configured with at least a spraying port (not shown) and a guiding member. As shown in fig. 3c, the flow guide comprises spacers 302 and caps 305, with flow channels 301 formed between each adjacent spacer 302. Ozone enters the injection end 304 from the gas guide pipe 303 through the injection port and is guided to be radially injected into the reactor device through the guide groove 301. Each channel 301 extends in a radial direction from the center of the top cover 305 and has a curvature between the center of the top cover and the edge of the spray device. The spacers are equally spaced from each other by 360/n, where n is equal to the number of said spacers. For example, the number of spacers may be 6 or 8, and the angle between the channels may be 60 ° or 45 °. Illustratively, the distance from the center of the top cover to the edge of the diversion trench is 2-3 cm. The speed that the ozone that spouts like this reachs the guiding gutter edge can make ozone disperse in whole reactor device effectively, can form the vortex at the guiding gutter edge even, makes the abundant flash mixed of ozone of waste gas and radial injection like this, has also led into this kind of strong oxidizer of ozone in the waste gas that contains nitrogen oxide.

As shown in fig. 3d, on the side of the top cover 305 facing the gas duct 303, the center of the top cover is provided with a flow dividing structure 306 for dispersing ozone in a radial direction. The shape of the flow dividing structure can be a cone-shaped or multi-edge-shaped bulge.

The reactor device is provided with an inner wall in the radial direction. The reactor device of the present invention may be, for example, a cylindrical shape having a circular radial cross section, and the reactor device inlet, the reaction zone and the reactor device outlet are provided in this order along the flow direction of the exhaust gas. The ozone uniformly forms a vortex flow over the entire radial cross section of the reactor device, improving the injection efficiency.

The arrangement of the injection device is required to achieve the object of allowing the oxidation reaction to proceed rapidly and sufficiently. I.e. within a short time, e.g. within 0.05 seconds, more preferably within 0.02 seconds, the ozone sprayed from the spraying means can diffuse throughout the radial cross section of the reactor device, when the radial cross section of the reaction zone is equal to the radial cross section of the reactor device. The above object can be achieved by various means.

For example, in the first case, the shape, size, number of channels, thickness, etc. of the injection device are selected according to the shape, size, ozone flow rate, and pressure difference between the inlet end of the injection device and the ambient pressure in the reactor device, and the pressure of the ozone injection is generally 0.49-1.47 bar (preferably 0.78-0.98 bar) higher than the ambient pressure. The parameters of the injection device can be calculated by a person skilled in the art on the basis of the above-mentioned known operating conditions, and the invention is not intended to be limited to the way of calculation.

For example, in the second case, as an embodiment, two or more injection devices may be provided in the reactor device, and the arrangement of each injection device is determined according to the ozone flow rate at the inlet end of each injection device, the pressure difference between the inlet end of each injection device and the ambient pressure in the reactor device, the reaction time, the radial wall-hitting time, and the effective cross-sectional area that the ozone can cover in the radial direction.

As an embodiment, the injection position of ozone may be on any plane perpendicular to the flow direction of the exhaust gas and be injected in the radial direction. The radial cross-section of the reaction zone generally coincides with the radial cross-section of the reactor apparatus and may be circular, oval, square or rectangular. To ensure complete reaction, the reactor apparatus should extend in the axial direction beyond the length X of the reaction zone after ozone injection. Preferably, X is greater than 2 times the corresponding circular diameter, major axis of the ellipse or diagonal D of the square/rectangle, preferably, X/D is between 2 and 5.

In one embodiment, the ozone injection location is after the dust separator and before the first stage scrubber.

As an embodiment, the molar mass ratio of the injected ozone to the nitrogen monoxide to be removed in the exhaust gas is 1.0:1 to 1.5: 1.

as an embodiment, the washing liquid in the washing column may be water or an alkaline washing liquid, preferably a sodium hydroxide solution, a potassium hydroxide solution, a calcium hydroxide solution, a magnesium hydroxide solution or an ammonium hydroxide solution. A wet scrubber is a widely used industrial plant for separating material or removing contaminants from a gaseous stream. Enhanced NO removal from flue gas streams by nitrate formation in wet scrubber towers and reduced need for disposal of other contaminants such as sulfur scrubbing_xThe efficiency is improved, and the cost is reduced. The treated off-gas leaving the reaction zone is introduced into a scrubber, which may be single or multistage, for contacting with a liquid stream of the liquid phase. The scrubber tower may be a packed tower, a spray tower or a tray tower. To enhance the contact of the off-gas with the scrubbing liquid, the scrubbing tower can be made cross-current, counter-current or co-current. NO_xAnd SO and highly oxidized forms of_yAnd other readily soluble gases are contacted with the liquid phase in the scrubber and scrubbed.

Raw materials and apparatus

An ozone generator: after oxygen gas with the purity of more than 90% passes through the ozone generator, ozone with the mass concentration range of 6-12% or higher is formed according to the power of current discharge. The ozone-containing gas stream is mixed with the exhaust gas in the reaction zone, where the distribution of ozone is important to ensure complete mixing to increase NO_xThe removal rate of (3).

Specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

Example 1

The embodiment is illustrated by a schematic diagram of removing nitrogen oxides from a flue gas stream.

As shown in FIG. 4, fuel and oxygen-enriched air are fed to combustor C via lines 7 and 8, respectively. In some processes, oxygen gas 9 may be enriched with oxygen from oxygen source A via line 3 and fed to the burner to achieve improved combustion. The NO formed by this combustion process constitutes the majority of the nitrogen oxides in the flue gas stream. One oxygen branch of oxygen source a is diverted to ozone generator B via line 2.

Containing flue gases discharged from the burners CThe gas stream is treated (not shown) to a suitable temperature (about 200 c or less) and enters the reaction zone of the reactor apparatus via line 10. In this example, the reaction zone is located upstream of the scrub column F. The nitrogen oxides in the reaction zone are oxidized to higher nitrogen oxides, especially N in pentavalent form, in combination with ozone and maintained for a suitable period of time₂O₅. Generally, the molar ratio of the ozone to the nitric oxide to be removed is maintained at 1.0: 1-1.5: 1 to ensure a sufficient supply of ozone.

The waste gas after the reaction is fed into a washing tower F through a pipeline 12, wherein the washing liquid is an alkaline sodium hydroxide solution. And (4) absorbing the oxidized high-valence nitrogen oxides by the washing liquid, and then discharging the high-valence nitrogen oxides into the atmosphere. The nitrate solution discharged from the scrubbing tower can be used as a raw material for other production units.

Specifically, after pre-tail gas treatment and heat exchange, the flue gas flow rate is 45000Nm3/h, the initial NO in the flue gas_xThe concentration is about 300mg/Nm³(the reduced oxygen basis for flue gas pollutant emission concentration is 11% O₂) With the aim of converting NO_xTo a concentration of 50mg/Nm³The following (reduced oxygen basis for flue gas pollutant emission concentration is 11% O₂)。

By adopting the device and the method, the temperature of the ozone injection position is about 110 ℃, and the running capacity of the configured ozone generator is 18 kg/h. The ozone spraying device is made of SS316L material and has a diameter of 50 mm.

After entering a cylindrical reactor device (material is SS316L) with the diameter of 1.4 m and the length of 7 m, the waste gas of the nitrogen oxides is uniformly and quickly mixed with ozone from an ozone generator at the front end of the reactor device, and the ozone is sprayed along the vertical direction of flue gas. It was detected that at 2.8 meters downstream of the ozone injection device, ozone had been thoroughly mixed with the flue gas to complete the reaction.

The flue gas enters an alkaline washing tower for washing after being oxidized and denitrated by ozone, the nitrogen oxides are removed, and NO in the discharged tail gas_xIs stabilized at 50mg/Nm³The following (reduced oxygen basis for flue gas pollutant emission concentration is 11% O₂)。

Example 2

In this embodiment, the removal of nitrogen oxides from the exhaust gas after the treatment of the tail gas from the nitration plant of a certain chemical plant is taken as an example.

As shown in FIG. 5, NO in the nitration plant off-gas after passing through multiple stages of water wash and caustic wash towers in the preceding off-gas treatment line_xHas been reduced to about 1000mg/Nm³. In this case, the volume ratio of NO is usually more than 70% of the total nitrogen oxide volume.

After the waste gas flow containing nitrogen oxide is fed into a cylindrical reactor device with the diameter of 1 m, the waste gas flow is uniformly and quickly mixed with ozone from an ozone generator at the front end of the reactor device, and the ozone is sprayed along the radial direction. And after the reaction is finished, the waste gas enters an alkaline washing tower, the alkaline washing liquid is NaOH solution, and after the oxidized high-valence nitrogen oxides are removed, the waste gas is discharged into the atmosphere. At this time NO_xThe concentration is lower than 200mg/Nm³. The nitrate solution discharged by the alkaline washing tower is mixed with the nitrate solution discharged by the alkaline washing tower of the upstream tail gas treatment unit and then is used as a raw material of other production units of a factory.

In the embodiment, the operating capacity of the configured ozone generator is 40kg/h, and the molar ratio of the operating capacity to the nitrogen monoxide to be reacted in the waste gas is 1.0: 1-1.5: 1. after detection, the concentration of ozone and various nitrogen oxides at the position 3 meters downstream of the ozone injection device is kept unchanged, which indicates that the reaction is finished.

For most factory exhaust gas, after the exhaust gas passes through the preposed multistage water washing and alkaline washing towers, the content of nitrogen oxides can not be obviously reduced any more, and the method and the equipment provided by the invention can continuously treat the exhaust gas in a limited space so as to meet the stricter and stricter emission regulations.

The embodiments described in the specification are only preferred embodiments of the present invention, and the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit the present invention. Those skilled in the art can obtain technical solutions through logical analysis, reasoning or limited experiments according to the concepts of the present invention, and all such technical solutions are within the scope of the present invention.

Claims

1. A method of removing nitrogen oxides from exhaust gases, comprising the steps of:

2. The process of claim 1, wherein the reactor apparatus comprises a reaction zone therein, and the ratio X/D of the length X of the reaction zone in the axial direction of the reactor apparatus to the longest axis D of the reaction zone is between 2 and 5.

3. A method according to claim 1, characterized in that in the reactor device the injection means are arranged at an angle, preferably 90 °, to the flow direction of the exhaust gases.

4. The method according to claim 1, characterized in that the method further comprises the step of: the waste gas treated by the reactor device is supplied to a washing tower for washing.

5. The method of claim 1, wherein the nitrogen oxides comprise NO, and the molar ratio of ozone to NO to be removed in the exhaust gas is 1.0:1 to 1.5: 1.

6. the method of claim 1, wherein the volume fraction of NO in the nitrogen oxides based on the total nitrogen oxides is greater than or equal to 30%.

7. An injector device for use in the method of claim 1, wherein the injector device comprises an air duct for delivering ozone and an injector tip, the injector tip being provided with at least one injector orifice and a flow guide, wherein the flow guide comprises spacers and a cap, and wherein flow guide channels are formed between adjacent spacers.

8. The spray device of claim 7 wherein each channel extends in a radial direction from the center of the cap and has a curvature between the center of the cap and the edge of the baffle.

9. The spraying device of claim 7, wherein the spacers are equally spaced from each other by 360 °/n, where n is equal to the number of spacers.

10. The spraying device of claim 7, wherein a flow dividing structure is disposed at the center of the top cover on a side facing the air guide pipe, the flow dividing structure dispersing ozone in a radial direction.