CN112642265A

CN112642265A - Exhaust gas purification system and purification method

Info

Publication number: CN112642265A
Application number: CN202010022101.4A
Authority: CN
Inventors: 高境; 赵传峰; 李艳萍; 杨宝勇; 段承希; 赵雯; 高迪
Original assignee: Individual
Current assignee: Individual
Priority date: 2020-01-09
Filing date: 2020-01-09
Publication date: 2021-04-13
Also published as: WO2021139815A1

Abstract

The invention provides a method and a system for removing gaseous pollutants in exhaust gas, wherein the method comprises the following steps of enabling the exhaust gas to pass through a channel between sheet-shaped members by using a gaseous pollutant removing device comprising the sheet-shaped members which are parallel to each other, enabling the temperature of the outer surface of each sheet-shaped member to be lower than the dew point temperature of at least part of vapor in the exhaust gas, condensing the vapor in the exhaust gas to form liquid drops by cooling the exhaust gas, adsorbing gaseous substances by using the liquid drops through the high specific surface area of the liquid drops, and then wetting and settling the liquid drops on the outer surface of each sheet-shaped member to realize the removal of; the liquid drops are collected to a certain amount and then drop, and the gaseous pollutants can be recycled. The method and the system can effectively remove gaseous pollutants in the waste gas, particularly vapor pollutants and insoluble gas pollutants in high-humidity waste gas, and reduce the concentration of the gaseous pollutants.

Description

Exhaust gas purification system and purification method

Technical Field

The invention relates to the field of industrial waste gas and air purification, in particular to a method and a system for removing gaseous pollutants in waste gas, especially gaseous pollutants in moisture-containing waste gas.

Background

Gaseous contaminants are contaminants that exist in a molecular state at normal, atmospheric pressure. The gaseous contaminants include gaseous contaminants and vapor contaminants. The gas is a substance existing in a gaseous form at normal temperature and pressure. Common gaseous contaminants are: CO, SO₂、NO₂、NH₃、H₂S, low boiling point organic substances (such as propane, butane and the like) and the like. A vapor is a gas that is vaporized from a substance that is liquid or solid at room temperature, such as a gaseous substance formed by sublimation of a solid or volatilization of a liquid. The steam can be obtained only through high-temperature conversion and is unstable at normal temperature. It can be seen that the range of steam and gas varies with operating temperature. For example, butane has a boiling point of 0.50 ℃ and is a gas at 20 ℃ but is a liquid at-20 ℃ and is a vapor in air. Common vapor contaminants are: volatile Organic Compounds (VOCs), volatile heavy metals (such as mercury, arsenic and selenium vapor), and SO₃Steam, and the like. The vapor can still gradually recover to the original solid or liquid state when cooled.

Gaseous pollutants can be further divided into primary pollutants and secondary pollutants. Primary pollutants refer to the original pollutants that are discharged directly into the atmosphere from a pollution source; the secondary pollutant is a new pollutant with different properties from the primary pollutant, which is generated by a series of chemical or photochemical reactions between the primary pollutant and components existing in the atmosphere or among several primary pollutants. Primary pollutants generally regarded as important in air pollution control include sulfur oxides, nitrogen oxides, carbon oxides, organic compounds, and the like; the secondary pollutants include sulfuric acid fumes and photochemical fumes.

Usually for gaseous contaminants that are readily soluble in water, such as SO₂、NH₃Etc. which can be absorbed into the body of water by water sprays to effect removal from the exhaust gases; but for gases that are poorly soluble in waterWhen the pollutants, such as butane, are sprayed with conventional water, the pollutants are difficult to remove due to the fact that the pollutants are difficult to dissolve in water, poor in absorption effect and difficult to remove, and the pollutants need to be removed through combustion decomposition or activated carbon adsorption, but when the humidity in waste gas is high, the combustion is difficult to continue, and the activated carbon is difficult to adsorb butane due to preferential adsorption of water vapor, so that good removal effect is difficult to achieve.

And vapor contaminants, such as SO₃Steam can absorb moisture and convert into aerosol particles when being sprayed by water, has small particle size (about 50 nanometers), is difficult to be collided and captured by sprayed water drops, and has low removal efficiency.

The removal of gaseous pollutants in waste gas is the key point of the current atmospheric environment treatment, and many gaseous pollutants have recovery value, wherein the removal and recovery of gaseous pollutants and vapor pollutants in high-humidity waste gas are more technical difficulties of the current atmospheric environment treatment.

Disclosure of Invention

The invention aims to provide a purification system and a purification method which can effectively remove and/or recover gaseous pollutants in exhaust gas, and the method is particularly suitable for the purification system and the purification method which can remove and/or recover insoluble gaseous pollutants and/or vapor pollutants in high-humidity exhaust gas.

In one aspect, the present invention provides a method for removing gaseous pollutants from an exhaust gas, comprising: passing the exhaust gas through a gaseous pollutant removing device comprising a gas flow channel and a cooling device arranged in the gas flow channel, the cooling device comprising at least two sheet-like members, the sheet-like members being substantially parallel to each other and substantially parallel to the flow direction of the exhaust gas, the exhaust gas passing between adjacent sheet-like members, the exhaust gas flow rate being not higher than 10 m/s; the temperature of the outer surface of the sheet-like member is lower than the dew point temperature of at least part of the vapour component in the exhaust gas, and at least part of the vapour in the exhaust gas is condensed into liquid drops by cooling the exhaust gas, and the gaseous pollutants in the exhaust gas are adsorbed on the liquid drops and are deposited on the outer surface of the sheet-like member along with the liquid drops in a wet mode.

In some embodiments, the method further comprises: recovering the droplets wet-settled to the outer surface of the sheet member.

In some embodiments, the flow velocity of the exhaust gas is not higher than 9m/s, or not higher than 8m/s, or not higher than 7m/s, or not higher than 6m/s, or not higher than 5m/s, or not higher than 4m/s, or not higher than 3m/s, or not higher than 2m/s, or not higher than 1 m/s.

In some embodiments, the ratio of the spacing between adjacent sheet members to the length of the sheet members in the direction of airflow flow is less than 0.5, less than 0.2, less than 0.1, or less than 0.05.

In some embodiments, the relative humidity of the exhaust gas is greater than or equal to 60%, greater than or equal to 80%, or greater than or equal to 90%.

In some embodiments, the cooling device is a plate heat exchanger.

In some embodiments, the cooling device is a finned tube heat exchanger, the fins on the heat exchanger comprising the fin members.

In some embodiments, the finned tube heat exchanger is a finned heat pipe heat exchanger.

In some embodiments, the cooling device is made of a metallic material.

In some embodiments, the metal components made of steel, copper or aluminum in the cooling device are sprayed or passivated by an anticorrosive material.

In some embodiments, the sheet member is a semiconductor thermoelectric sheet, the cooling device includes two semiconductor thermoelectric sheets having cold ends opposite to each other, and the exhaust gas passes between the cold ends of the two semiconductor thermoelectric sheets.

In some embodiments, the exhaust gas is pre-treated prior to passing the exhaust gas through the cooling device, the pre-treatment comprising any one or more of increasing the vapor content of the exhaust gas, adding an acidic substance to the exhaust gas, subjecting the exhaust gas to an oxidation treatment, adding a basic substance to the exhaust gas, and pressurizing the exhaust gas.

In some embodiments, increasing the vapor content of the off-gas comprises injecting into the off-gas a substance that forms a vapor in the off-gas. In a preferred embodiment, these substances preferably drop in temperature below their dew point temperature during the desuperheating cooling of the exhaust gas, so that droplets can form. In some embodiments, these materials are water, ethanol, ethylene glycol, other materials that may be present in the exhaust gas in the vapor state (e.g., organics), or solutions containing any of these, or vapors of these materials.

In some embodiments, the acidic species is an acidic species that can combine with water vapor in the exhaust gas to form an acid mist having a high dew point temperature, such as SO₃HCl and/or acetic acid.

In some embodiments, the basic species is a species that can react with a portion of the gaseous contaminants to produce a species with a higher boiling point and/or that is more water soluble, such as ammonia NH₃Sodium carbonate, quicklime CaO, or sodium hydroxide solution.

In some embodiments, the oxidation treatment comprises adding an oxidizing substance to the exhaust gas and/or passing the exhaust gas through a photocatalytic oxidation device.

In some embodiments, the oxidizing species is one or more of a species that can oxidize a portion of the gaseous contaminants to higher boiling and/or more droplet soluble species, such as ozone, sodium chlorite.

In some embodiments, the method further comprises spraying a mixture of any one or more of water, an aqueous solution, and an organic solvent onto the outer surface of the sheet-like member.

In some embodiments, the gaseous pollutant removing means comprises a set of cooling means arranged side by side in a cross-section in the flow direction of the exhaust gas.

In some embodiments, the gaseous pollutant removing device comprises a plurality of sets of cooling devices arranged in the flow direction of the exhaust gas, each set of cooling devices being arranged side by side on one cross section of the flow direction of the exhaust gas.

In some embodiments, two adjacent sets of cooling devices are arranged in staggered or in-line.

In some embodiments, after the exhaust gas passes through the cooling device, the large particle size droplet particulates are further removed with other particulate capture devices.

In some embodiments, the other particulate trapping device is a mist eliminator or dust remover.

In some embodiments, the method further comprises allowing droplets of the wet settled to the outer surface of the sheet member to drip or run off. In some embodiments, the dropped or run-off droplets are recovered.

In some embodiments, the flowing away of the liquid droplets wet-settled on the outer surface of the sheet member is performed by flushing the liquid droplets wet-settled on the outer surface of the sheet member off the outer surface of the sheet member by spraying and then flowing away through the drainage channel.

Another aspect of the present invention provides a system for removing gaseous pollutants from exhaust gas, comprising: a gaseous pollutant removal device for passing and treating exhaust gases, said gaseous pollutant removal device comprising a gas flow channel and a cooling device arranged in the gas flow channel, said cooling device comprising at least two sheet-like members, said sheet-like members running substantially parallel to each other and substantially parallel to the gas flow.

In some embodiments, the ratio of the spacing between adjacent sheet members to the length of the sheet members in the direction of airflow flow is less than 0.5, less than 0.2, less than 0.1, or less than 0.05. .

In some embodiments, the cooling device is a plate heat exchanger.

In some embodiments, the cooling device is made of a metallic material.

In some embodiments, the sheet member is a semiconductor thermoelectric sheet and the cooling device includes two semiconductor thermoelectric sheets with cold ends opposite.

In some embodiments, an injection device is disposed on the upstream side of the cooling device, and is used for injecting any one or more of a substance capable of forming steam in the exhaust gas, an oxidizing substance, an acidic substance and a basic substance into the exhaust gas.

In some embodiments, an oxidation device is provided on an upstream side of the cooling device for subjecting the exhaust gas to oxidation treatment.

In some embodiments, the oxidation device is a photocatalytic oxidation device.

In some embodiments, a pressurizing device is provided on the upstream side of the cooling device for pressurizing the exhaust gas.

In some embodiments, a spraying device is disposed on one side or both sides of the gaseous pollutant removing device for spraying one or a mixture of several of water, aqueous solution, and organic solvent onto the outer surface of the sheet member.

In some embodiments, the gaseous contaminant removal device comprises a set of cooling devices arranged side-by-side across the cross-section of the gas flow channel.

In some embodiments, the gaseous contaminant removal device includes a plurality of sets of cooling devices arranged in a row along the gas flow channel, each set of cooling devices being arranged in parallel on one cross-section of the gas flow channel.

In some embodiments, the cooling device is followed by another particulate trap device.

In some embodiments, the system further comprises a drainage channel for the exit and/or recovery of droplets through the drainage channel.

The device for removing the gaseous pollutants is used for treating the waste gas, the structure of the device is favorable for condensing steam to form liquid drops, and the gaseous pollutants are efficiently adsorbed by means of the high specific surface area of the liquid drops; further adopting a metal sheet member which has strong heat-conducting property, when the metal sheet member is used as a cooler, a larger temperature gradient can be formed between the surface of the sheet member and waste gas, and the thermophoretic force is utilized to push liquid drops adsorbed with gaseous pollutants to move towards the surface of the sheet member; the liquid drops wet and settle on the outer surface of the sheet-shaped component, and then drop after gathering to a certain amount, so that the gaseous pollutants are removed in the waste gas.

Specifically, the present invention relates to the following scheme:

scheme 1. a method of removing gaseous pollutants from an exhaust gas comprising: passing the exhaust gas through a gaseous pollutant removing device comprising a gas flow channel and a cooling device arranged in the gas flow channel, the cooling device comprising at least two sheet-like members, the sheet-like members being substantially parallel to each other and substantially parallel to the flow direction of the exhaust gas, the exhaust gas passing between adjacent sheet-like members, the exhaust gas flow rate being not higher than 10 m/s; the temperature of the outer surface of the sheet-like member is lower than the dew point temperature of at least part of the vapour component in the exhaust gas, and at least part of the vapour in the exhaust gas is condensed into liquid drops by cooling the exhaust gas, and the gaseous pollutants in the exhaust gas are adsorbed on the liquid drops and are deposited on the outer surface of the sheet-like member along with the liquid drops in a wet mode.

The method of claim 1, further comprising: recovering the droplets wet-settled to the outer surface of the sheet member.

The method according to

claim

1 or 2, wherein the flow velocity of the exhaust gas is not higher than 5 m/s.

A method according to any of claims 1 to 3, wherein the ratio of the spacing between adjacent sheet-like members to the length of the sheet-like members in the direction of flow of the gas stream is less than 0.5.

The method according to any one of claims 1-4, wherein the relative humidity of the exhaust gas is greater than or equal to 60%.

The process according to any of claims 1-5, wherein the cooling device is a plate heat exchanger.

A process according to any one of claims 1 to 5, wherein the cooling apparatus is a finned tube heat exchanger, the fins on the heat exchanger constituting the fin-like member.

The process according to claim 7, wherein the finned tube heat exchanger is a finned heat pipe heat exchanger.

The method according to any one of claims 6 to 8, wherein the cooling device is made of a metallic material.

The method of claim 9, wherein the metal member of steel, copper or aluminum in the cooling device is sprayed or passivated with an anticorrosive material.

The method according to any of claims 1-5, wherein the sheet member is a semiconductor thermoelectric sheet, the cooling device comprises two semiconductor thermoelectric sheets having opposite cold ends, and the exhaust gas passes between the cold ends of the two semiconductor thermoelectric sheets.

The method according to any one of claims 1 to 11, wherein the exhaust gas is subjected to a pretreatment comprising any one or more of increasing the vapor content of the exhaust gas, adding an acidic substance to the exhaust gas, subjecting the exhaust gas to an oxidation treatment, adding a basic substance to the exhaust gas, and pressurizing the exhaust gas before passing the exhaust gas through the cooling device.

The method of claim 12, wherein increasing the vapor content of the exhaust gas comprises injecting into the exhaust gas a substance that forms vapor in the exhaust gas.

The method of claim 13, wherein the oxidative treatment comprises adding an oxidizing substance to the exhaust gas and/or passing the exhaust gas through a photocatalytic oxidation device.

The method according to any one of claims 1 to 14, further comprising spraying a mixture of any one or more of water, an aqueous solution, and an organic solvent onto the outer surface of the sheet-like member.

The method according to any one of claims 1 to 15, wherein the gaseous pollutant removing means comprises a set of cooling means arranged side by side in a cross section in the flow direction of the exhaust gas.

The method according to any one of claims 1 to 16, wherein the gaseous pollutant removing means comprises a plurality of sets of cooling means arranged in the flow direction of the exhaust gas, each set of cooling means being arranged in parallel on one cross section in the flow direction of the exhaust gas.

The method of claim 17, wherein adjacent cooling units are arranged in staggered or sequential rows.

A method according to any one of claims 1 to 18, wherein after said exhaust gas has passed through said cooling means, further large particle size droplet particles are removed using further particle capture means.

The method of claim 19, wherein said other particulate capture device is a mist eliminator or dust remover.

The method of claims 1-19, further comprising allowing droplets of the wet settled onto the outer surface of the sheet member to drip or run off.

The method of claim 21, wherein the step of draining away the droplets of the liquid that have settled wet to the outer surface of the sheet member comprises spraying the droplets of the liquid that have settled wet to the outer surface of the sheet member away from the outer surface of the sheet member and draining the droplets of the liquid through the drainage channels.

Scheme 23. a system for removing gaseous pollutants from an exhaust gas, comprising: a gaseous pollutant removal device for passing and treating exhaust gases, said gaseous pollutant removal device comprising a gas flow channel and a cooling device arranged in the gas flow channel, said cooling device comprising at least two sheet-like members, said sheet-like members running substantially parallel to each other and substantially parallel to the gas flow.

The system of claim 23, wherein the ratio of the spacing between adjacent sheet members to the length of the sheet members in the direction of flow of the gas stream is less than 0.5.

The system according to claim 23 or 24, wherein the cooling device is a plate heat exchanger.

A system according to claim 23 or 24, wherein the cooling means is a finned tube heat exchanger, the fins on the heat exchanger constituting the fin-like member.

The system according to claim 26 wherein the finned tube heat exchanger is a finned heat pipe heat exchanger.

The system according to any one of claims 23-27, wherein said cooling means is made of a metallic material.

The system of claim 28, wherein the metal components of steel, copper or aluminum in the cooling device are sprayed or passivated with an anti-corrosive material.

The system of claim 23, wherein said sheet member is a semiconductor thermoelectric chip and said cooling means comprises two semiconductor thermoelectric chips having opposite cold sides.

The system according to any one of claims 23 to 30, wherein an injection means for injecting any one or more of a substance that can form a vapor in the exhaust gas, an oxidizing substance, an acidic substance, and a basic substance into the exhaust gas is provided on an upstream side of the cooling means.

The system according to any one of claims 23 to 31, wherein an oxidizing device is provided on an upstream side of the cooling device for subjecting the exhaust gas to an oxidizing treatment.

The system of claim 32, wherein the oxidation device is a photocatalytic oxidation device.

The system according to any one of claims 23 to 33, wherein a pressurizing means is provided on the upstream side of the cooling means for pressurizing the exhaust gas.

A system according to any of claims 23-34, wherein spraying means are provided on one or both sides of said gaseous contaminant removal means for spraying one or a mixture of several of water, aqueous solution, organic solvent onto the outer surface of said sheet like member.

The system according to any of claims 23-35, wherein said gaseous contaminant removal means comprises a bank of cooling means arranged side-by-side in the cross-section of the gas flow channel.

The system according to any one of claims 23-35, wherein said gaseous contaminant removal means comprises a plurality of sets of cooling means arranged in a row along the gas flow path, each set of cooling means being arranged in parallel on one cross-section of the gas flow path.

The system of claim 37, wherein adjacent cooling devices are arranged in staggered or in-line rows.

The system of any of claims 23-38, wherein the cooling device is followed by another particulate trap device.

The system of claim 39, wherein said other particulate capture device is a mist eliminator or dust remover.

A system according to any of claims 23 to 40, further comprising a drainage channel for the exit and/or recovery of droplets through said drainage channel.

Drawings

Fig. 1 is a schematic view of a gaseous pollutant removing device.

Fig. 2 is a schematic structural view of an embodiment of the gaseous pollutant removing device.

Fig. 3 is a schematic diagram of an arrangement of a set of cooling devices.

FIG. 4 is a schematic diagram of an arrangement of multiple cooling devices.

FIG. 5 is a schematic view of the construction of the finned tube heat exchanger.

FIG. 6 is a schematic view of another embodiment of a gaseous contaminant removal device.

FIG. 7 is a schematic view of another embodiment of a gaseous contaminant removal device.

FIG. 8 is a schematic view of another embodiment of a gaseous contaminant removal device.

FIG. 9 is a schematic view of another embodiment of a gaseous contaminant removal device.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in further detail with reference to the accompanying drawings in conjunction with the following detailed description. It should be understood that the description is intended to be exemplary only, and is not intended to limit the scope of the present invention. Moreover, in the following description, descriptions of partially known structures and techniques are omitted so as to not unnecessarily obscure the concepts of the present invention.

Unless otherwise defined, all terms used herein should be interpreted in the manner commonly understood in the art. The description of the theoretical and specific embodiments of the present invention is for better understanding of the present invention and should not be taken as limiting the scope of the present invention.

The present inventors have found that removal of gaseous pollutants from exhaust gases can be achieved by adsorption and/or absorption of the gaseous pollutants by small particle size droplets.

In the present invention, the gaseous pollutant means a pollutant existing in the form of molecules in the exhaust gas. The gaseous contaminants include gaseous contaminants and/or vapor contaminants.

The gaseous pollutants described herein are pollutants that are present in gaseous form in the exhaust gas. The gaseous pollutants have a boiling point lower than the temperature of the exhaust gas and are thus present in gaseous form. Gaseous pollutants include, but are not limited to, CO, SO₂、NO、NH₃、H₂S and low-boiling point organic matters (such as low-boiling point alkane, such as propane, butane, isobutane, neopentane and the like). Part of the volatile organic compounds (VOCs for short) may also be present in the exhaust gas in gaseous form, constituting gaseous pollutants. It is known to those skilled in the art that whether a certain gas component in the exhaust gas belongs to a gas pollutant can be determined based on common knowledge, and the determination can be easily made based on the kind, boiling point, temperature of the exhaust gas, and the like of the gas component.

The vapor contaminants referred to herein refer to contaminants present in the exhaust gas as vapors. The vapor contaminants have a boiling point higher than the exhaust gas temperature but a dew point lower than the exhaust gas temperature and thus exist in the exhaust gas as vapor. Vapor contaminants include, but are not limited to, a portion of volatile organics (e.g., isopentane, benzene, acetic acid, furfural, etc.), volatile heavy metals (e.g., mercury, arsenic, selenium vapor), SO₃Steam (may also be referred to as sulfuric acid vapor), and the like. One skilled in the art can easily determine whether a component in the exhaust gas belongs to the vapor contaminant based on the common sense, and can easily determine the type, boiling point, temperature of the exhaust gas, and the like of the component.

When gas molecules (adsorbates) move to the surface of a liquid droplet (adsorbent), the gas molecules stay on the surface of the liquid droplet due to the interaction between the gas molecules and the molecules on the surface of the liquid droplet, a phenomenon called adsorption of the gas molecules on the surface of the liquid droplet. For example, gas molecules (adsorbates) enter the interior of the droplet further to form a solution, a process called absorption. Generally, the adsorption capacity of a droplet (adsorbent) is mainly directly correlated to its surface free energy and specific surface area. The surface free energy of water in common liquids is the largest; the specific surface area of a droplet is generally inversely proportional to its size, and the smaller the droplet size, the larger the specific surface area of the droplet, and thus nano-micron sized droplets (e.g., mist droplets, which typically have a particle size on the order of microns) are a good adsorbent. In the scientific research of atmospheric environment, the fog has good adsorption effect on gaseous pollutants, even hydrophobic (insoluble in water) gaseous pollutants, and the content of hydrophobic organic compounds in fog drops is ten to thousands times higher than that of rain drops (the grain diameter is usually in millimeter magnitude).

Inspired by the phenomenon, the inventor finds that a large amount of small-particle-size liquid drops can be obtained by cooling the waste gas, the small-particle-size liquid drops can further adsorb and/or absorb other gaseous pollutants in the waste gas, the liquid drops realize wet sedimentation through thermophoretic force and the like, are aggregated to form larger liquid beads or liquid films and are removed, and the gaseous pollutants in the waste gas can be effectively removed.

The liquid beads or films containing the gaseous contaminants can be collected and recycled for reuse of the gaseous contaminant components. For example, the main components of oil and gas pollutants, tar pollutants and the like are organic mixtures, and the organic mixtures can be added into gasoline or other oils again after being recovered to realize reutilization.

The exhaust gas containing vapor can form liquid drops when the temperature of the exhaust gas is reduced and cooled, and the temperature of the exhaust gas is reduced to the dew point or below of the contained vapor, and the vapor is subjected to phase change at the dew point temperature to form liquid drops. Under the condition that the vapor has high supersaturation degree, small-particle-size liquid drops can be formed, the particle size of the small-particle-size liquid drops can be in the nanometer micron order, and the formed small-particle-size liquid drops in the nanometer micron order can also be called fog drops in the invention.

The inventive concept will be better understood by the following non-limiting description. In order to remove the gaseous pollutants in the exhaust gas by the adsorption and/or absorption of the gaseous pollutants by the small-particle-size droplets, a substance a and a substance B should be present in the exhaust gas, the substance a refers to one or more substances existing in a vapor state in the exhaust gas, and the temperature of the substance a is reduced to the dew point or below the dew point during the temperature reduction and cooling process of the exhaust gas, so that a large number of droplets are formed. These droplets formed from species a further adsorb and/or absorb species B, further aggregate into larger droplets or liquid films after wet settling, and are subsequently removed. Substance a may comprise a portion of the vapor pollutants, water vapor, and/or any other substance that may be present in the exhaust gas in a vapor state (e.g., alcohol), and substance B refers to the vapor pollutants in addition to other vapor pollutants and/or gaseous pollutants present as substance a. And judging which substances in the waste gas belong to the substance A and which substances belong to the substance B, wherein the judgment needs to be determined according to the boiling point temperature, the dew point temperature, the target temperature reduction temperature and the like of each substance. In some embodiments, a portion of the gaseous pollutants in the exhaust gas are contained in species a and a portion are contained in species B. In some embodiments, substance a comprises water vapor and a portion of vapor contaminants, substance B comprises gas contaminants and a portion of vapor contaminants, and during the desuperheating cooling of the exhaust gas, substance a condenses into liquid droplets, absorbs and/or adsorbs substance B and wets and settles to the external surface of the cooling device, and eventually substance a and substance B are effectively removed.

To enhance the removal effect, the exhaust gas can be pretreated by the following two ways: increasing the amount of a species, for example, adding steam or other species that may be present in the exhaust in a vapor state (e.g., alcohol) to the exhaust to increase the vapor content of the exhaust, or adding acidic species to the exhaust to introduce acid mist, or pressurizing the exhaust to increase the partial pressure (relative humidity) of the a species; and secondly, modifying the substance B to enable the substance B to be absorbed and/or adsorbed by the liquid drops formed by the substance A more easily, for example, oxidizing the waste gas and/or adding alkaline substances into the waste gas, and the like, wherein the modification can convert at least part of the substance B into substances with higher boiling points and/or substances with higher solubility in the liquid drops through chemical reaction.

Dew point temperature refers to the temperature at which a gas (vapor) is cooled to saturation without changing either the gas content or the gas pressure. The dew point temperature can be determined from a map of the saturated vapor partial pressure at different temperatures of the gas. Taking water as an example, the dew point temperature of water is a saturation temperature corresponding to the partial pressure of water vapor, and the dew point temperature of water vapor contained in air is a temperature at which it becomes dew. The dew point temperature of the water vapor may be referred to as the water dew point temperature, and the dew point temperature at which the acid gas combines with the water vapor in the exhaust gas to form an acid mist may be referred to as the acid dew point temperature. In the present invention, the dew point temperature may refer to the dew point temperature of any vapor present in the exhaust gas, and may refer to either water dew point temperature or vapor dew point temperature, or acid dew point temperature.

The vapor may also be referred to as a vapor species, and in the present invention, it refers to a species having a boiling point higher than the temperature of the exhaust gas but a dew point lower than the temperature of the exhaust gas, and existing in the exhaust gas in a vapor state. The exhaust gas may contain one or more vapors, which may be water vapor, any vapor contaminants, and/or any other substance that may be present in the exhaust gas in a vapor state (e.g., ethanol, SO)₃Hg, etc.) the exhaust gas may thus contain water vapor, one or more vapor contaminants, and/or any other substance that may be present in the exhaust gas in a vapor state (e.g., ethanol vapor, SO)₃Steam, Hg vapor, etc.), or mixtures thereof.

The liquid droplets are formed by the temperature reduction and cooling of the steam in the exhaust gas. The dew point temperatures of different types of vapor contained in the exhaust gas are different, and the vapor with higher dew point forms liquid drops firstly in the process of cooling the exhaust gas. In the present invention, it is not essential to reduce all the vapor in the exhaust gas to the dew point or below, and at least a part of the vapor in the exhaust gas may be reduced to the dew point or below to form droplets.

The vapor used to form the droplets may be water vapor contained in the exhaust gas, any vapor contaminants, and/or any other substance that may be present in the exhaust gas in a vapor state (e.g., ethanol), without limitation to water vapor. It should be understood that the exhaust gas does not necessarily contain water vapor, but rather contains steam (any vapor species).

The content of the vapor in the exhaust gas is not particularly limited as long as small-particle-size droplets are formed when the exhaust gas is cooled. It will be appreciated that the more vapour contained in the exhaust gas, the more droplets are formed during the desuperheating cooling and the more other gaseous pollutants are adsorbed and/or absorbed, the better the removal. In some embodiments, high humidity exhaust gases are preferred, such as exhaust gases having a relative humidity of 60% or greater, a humidity of 80% or greater, or a humidity of 90% or greater. In some embodiments, the exhaust gas may be pretreated to increase the vapour content of the exhaust gas, for example by adding to the exhaust gas substances which form vapours in the exhaust gas, preferably at a temperature below its dew point during desuperheating of the exhaust gas, so as to enable droplet formation. These substances may be, for example, water, ethanol, ethylene glycol, other substances that may be present in the exhaust gas in the vapor state (e.g., organic substances), or solutions containing any of these substances, or vapors of these substances. In some embodiments, these species may be injected into the exhaust gas, for example, to increase the vapor content of the exhaust gas. In some embodiments, the relative humidity of the exhaust gas may be brought to greater than or equal to 60%, greater than or equal to 80%, or greater than or equal to 90%. The formed liquid drop composition is different according to the types of vapor in the waste gas, the dew point temperature of the vapor, the temperature of the waste gas and the temperature reduction temperature, and can comprise one or more of water drops, liquid drops formed after the temperature reduction of vapor pollutants, liquid drops of aqueous solutions of the vapor pollutants and liquid drops of ethanol solutions of the vapor pollutants.

In some embodiments, the pretreatment may further comprise pressurizing the off-gas to increase the partial pressure of the vapor contained therein. Partial pressure of each component in the pressurized waste gas is improved in equal proportion, and the original unsaturated steam component partial pressure is increased, and then the partial pressure of the original unsaturated steam component can reach supersaturation, so that the unsaturated steam component is condensed into liquid drops, and even if other steam components do not reach supersaturation, the partial pressure of the unsaturated steam component is higher and is easier to be condensed into liquid drops through small-amplitude temperature reduction. For example, the exhaust gas may be pressurized by a pressurization device and then passed through a gaseous pollutant removal device. The pressurizing means may be, for example, an air compressor, and isothermally pressurize the off-gas, and the pressure of the off-gas may be increased from, for example, a normal 1 atmosphere to 2 atmospheres or higher, 3 atmospheres or higher, 4 atmospheres or higher, or 5 atmospheres or higher.

When the waste gas contains acidic gas (such as SO)₃HCl, acetic acid, etc.) to combine with water vapor in the exhaust gas, the resulting material is called acid mist, and the condensation temperature of the acid mist is called acid dew point, which is much higher than the water dew point. With SO₃For example, the higher the concentration content, the higher the acid dew point, and the acid dew point in the exhaust gas can reach 140-160 ℃ or even higher. SO (SO)₃The acid dew point can be calculated as follows:

tp＝20LgVso₃+α

wherein tp is the acid dew point temperature

Vso₃SO in flue gas₃The volume fraction%

Alpha-the water constant of the water content,

when the water content is 5 percent, alpha is 184

When the water content is 10%, alpha is 194

When the water content is 15%, alpha is 201

Therefore, if the acid gas in the exhaust gas is comparatively high, the small-particle-size droplets can be formed more quickly, and the gaseous pollutant removal efficiency will be higher as more small-particle-size droplets are formed.

In some embodiments, the pretreatment of the exhaust gas may further include adding an acidic substance to the exhaust gas containing water vapor (e.g., high humidity exhaust gas) that may combine with the water vapor in the exhaust gas to form an acid mist with a high dew point temperature, thereby forming smaller size droplets faster and forming more smaller size droplets, increasing gaseous pollutant removal efficiency. . Those skilled in the art can know, based on conventional physicochemical knowledge, which acidic substances can combine with water vapor in the exhaust gas to form an acid mist having a high dew point temperature, examples of which includeIncluding SO₃HCl and/or acetic acid, and the like. In some embodiments, steam and the above-described acidic species may also be added to the off-gas simultaneously. In some embodiments, the acidic species described above may be injected into an exhaust gas containing water vapor.

The droplets formed by the temperature reduction of the vapors in the exhaust gas further adsorb other gaseous pollutants. If the gas adsorbed on the surface of the adsorbent is only one molecule thick, it is referred to as monolayer adsorption; if the thickness of the adsorption layer exceeds one molecule, it is called multi-molecular layer adsorption. When the temperature of the adsorbate is below its normal boiling point, adsorption of the polymolecular layer tends to occur, so the higher the boiling point of the gaseous pollutant, the more easily it is adsorbed.

The droplets can further absorb the adsorbed gaseous pollutants, and the absorption degree is related to the diffusion rate of the molecules of the gaseous pollutants, the solubility of the gaseous pollutants in the droplets (such as water droplets), and the reactivity of the gaseous pollutants in the droplets (such as aqueous solution).

The adsorbed gaseous pollutants may be those gaseous pollutants that have not reached their dew point temperature during the desuperheating cooling of the exhaust gas, and may include vapor pollutants and/or gaseous pollutants that have not reached their dew point temperature. .

In order to make the remaining gaseous pollutants in the exhaust gas more readily adsorbed and/or absorbed, the pretreatment of the exhaust gas may also comprise converting the gaseous pollutants contained in the exhaust gas into gaseous substances having a higher boiling point (the gaseous substances having a higher boiling point are more readily adsorbed onto the liquid droplets), or converting the gaseous pollutants contained in the exhaust gas into gaseous pollutants that are more soluble in the liquid droplets (e.g. more water-soluble when the liquid droplets consist of water or an aqueous solution), i.e. more highly soluble in the liquid droplets, which conversions may be achieved, for example, by chemical reactions. For example, oxidizing and/or basic substances can be added (e.g., injected) to the exhaust gas. The oxidizing substance may oxidize a portion of the gaseous contaminants to a higher boiling and/or more droplet soluble materialThe choice of oxidizing substance depends on the gaseous pollutant content of the exhaust gas, e.g. by adding ozone O₃Sodium chlorite NaClO₂Can oxidize NO into NO₂The person skilled in the art can determine the oxidizing substance used on the basis of the composition of the gaseous pollutants and general physicochemical knowledge. Non-limiting examples of the oxidizing substance include one or more of ozone, sodium chlorite. As a non-limiting example, oxidizing substances, such as ozone and sodium chlorite, may be injected into the flue gas to oxidize NO in the flue gas to higher boiling NO, which is also more water soluble₂、N₂O₅For better absorption and/or adsorption by the droplets. As another non-limiting example, for example, ozone may be injected into the exhaust gas to oxidize the 167 degree furfural to 232 degree furfural acid, which forms more droplets that can be captured by wet settling. The basic species may react with a portion of the gaseous contaminants (e.g., be adsorbed by the droplets and further react with the gaseous contaminants) to produce a species with a higher boiling point and/or that is more water soluble. For example, a basic substance may be added to the exhaust gas to cause it to absorb a portion of the acidic gaseous pollutants. The person skilled in the art can determine the alkaline substance used on the basis of the composition of the gaseous pollutants and general physicochemical knowledge. Examples of the alkaline substance include ammonia NH₃Sodium carbonate, quicklime CaO, or sodium hydroxide solution. By way of non-limiting example, ammonia gas may be injected into the exhaust gas, adsorbed by the droplets and in the droplets with NO₂、N₂O₅Etc. to cause the droplets to adsorb and/or absorb NO₂、N₂O₅More. It is also possible to subject the exhaust gas to an oxidative treatment by other means, for example by passing the exhaust gas through a photocatalytic oxidation device or the like, to effect oxidation of part of the gaseous pollutants to substances with higher boiling points and/or more soluble in liquid droplets.

The cooling of the exhaust gas can be achieved by using a cooling device (e.g. a heat exchanger) which can bring the temperature (in the present invention) of the outer surface of the cooling device (i.e. the surface of the cooling device which is in contact with the exhaust gas)Also referred to herein as a target pull-down temperature) is below the dew point temperature of at least a portion of the vapors in the exhaust gas (which portion of the vapors may also be referred to as species a) such that the at least a portion of the vapors form droplets during the cooling process. Means for maintaining the temperature of the outer surface of the cooling device are well known to the person skilled in the art and may for example be provided by means of a cooling fluid or cooling gas or any other suitable cooling source. The temperature of the outer surface of the cooling device may be determined according to the type, content, dew point temperature, etc. of the vapor contained in the exhaust gas, and may be lower than the dew point temperature of at least one, at least two, at least three, or more vapors contained in the exhaust gas, which should be at least lower than the highest dew point temperature of the exhaust gas, which is the temperature at which condensation droplets start to appear during cooling of the exhaust gas under otherwise constant conditions, and may also be understood as the dew point temperature of the component having the highest dew point temperature among the different components contained in the exhaust gas, which are the components having the dew point temperature, such as acid mist, water vapor, or other vapor components, etc. For example, for vapors containing acid mist, the temperature of the exterior surfaces of the cooling device can be made lower than the acid dew point temperature of the exhaust gas, i.e., the dew point temperature of the acid mist contained in the exhaust gas, and if there are multiple acid mist in the exhaust gas, there are correspondingly multiple acid dew point temperatures, at which point the temperature of the exterior surfaces of the cooling device can be made lower than any one of more acid dew point temperatures, e.g., lower than the highest acid dew point temperature. For example, for an exhaust gas, the moisture content is 10%, and the SO content is₃Has a volume concentration of 10PPm and further has a concentration of 5PPm of a sparingly soluble organic vapor, whose SO is calculated according to the above formula for calculating the dew point temperature of acid₃The acid dew point temperature is 94 ℃, the water dew point temperature is 47 ℃, the waste gas can pass through the plate heat exchanger, the circulating water with the temperature of 20 ℃ flows on the other side of the plate heat exchanger, the temperature of the gas side wall surface of the plate heat exchanger is 25 ℃, the waste gas passes through the cold wall surface, a certain amount of sulfuric acid fog drops and a larger amount of water fog drops are formed, and the organic steam can be efficiently adsorbed.

The size of the droplets formed during the cooling of the exhaust gas is related to the degree of supersaturation of the vapour in which the droplets are formed after cooling. Taking water vapor as an example, the phase change process from water vapor to liquid water is called nucleation process. At a particular degree of supersaturation, a plurality of water vapor molecules may form a molecular mass (or germ). The formation of embryo can be regarded as that the embryo is formed by the random condensation of water vapor molecules, and whether the embryo can stably continue to exist or not is mainly considered according to the particle size of embryo drops and the water vapor supersaturation degree in waste gas. Research shows that the higher the supersaturation degree is, the smaller the particle size of the embryo drops which can exist stably is, the larger the specific surface area of the formed water mist is, and the stronger the adsorption capacity is (the theory can be seen in atmospheric environmental chemistry, second edition, advanced education press, 2006, 5 months, chapter five, third section). As the exhaust gas passes through the cooling device, supersaturated vapour is only stabilised in the boundary layer, and the closer to the outer surface of the cooling device, the higher its degree of supersaturation, due to the temperature and vapour pressure gradients at the surface of the cooling device only in the boundary layer. Therefore, in order to make the particle diameter of the formed droplets as small as possible and to exert the adsorption capability of the droplets, it is necessary to have a large boundary layer space on the outer surface of the cooling device.

The boundary layer is a thin flow layer formed on the solid wall surface when the fluid flows through the solid wall surface, and is also called as a flow boundary layer and a boundary layer. It is generally considered that the temperature gradient and the flow velocity gradient are mainly present in the boundary layer, and the fluid flow above the boundary layer can be regarded as the same temperature and flow velocity. The formula for the boundary layer thickness is:

where θ is the boundary layer thickness, L is the characteristic length, and Re is the Reynolds number. The smaller the reynolds number, the larger the boundary layer thickness.

Calculation of the characteristic length and reynolds number is within the skill of one skilled in the art. The reynolds number is a dimensionless ratio of the inertial force to the viscous force of a fluid under flow conditions. The reynolds number may characterize fluid flow characteristics (i.e., laminar or turbulent flow).

The Reynolds number Re is calculated by the formula:

in the formula: ρ is the fluid density, v is the fluid flow rate, μ is the fluid viscosity, and L is the characteristic length.

The term "characteristic length" is well known to those skilled in the art. For example, when gas flows through a circular pipe, the term "characteristic length" is the equivalent diameter of the pipe. The term "characteristic length" is the distance traveled back from the end of a plate as fluid flows across the plate.

In the process of the present invention, it is preferred that the exhaust gas flow rate is 10m/s or less, more preferably 9m/s or less, still more preferably 8m/s or less, still more preferably 7m/s or less, still more preferably 6m/s or less, still more preferably 5m/s or less, still more preferably 4m/s or less, still more preferably 3m/s or less, still more preferably 2m/s or less, still more preferably 1m/s or less.

The cooling device of the present invention employs a sheet-like member. In some embodiments, the cooling device comprises at least two parallel sheet members, the sheet members being substantially parallel to each other and to the flow direction of the exhaust gas, channels being formed between adjacent sheet members such that the exhaust gas passes between the channels. The temperature of the outer surface of the sheet member is below the dew point temperature of at least a portion of the vapors in the exhaust gas. The sheet-like member may provide a larger contact area with the exhaust gas and thus a larger boundary layer area. It is preferred that the length of the channels formed by adjacent sheet members in the direction of flow of the gas stream is relatively long, for example at least 30mm, preferably at least 45mm, more preferably at least 60mm, more preferably at least 90mm, so that the residence time of the gas stream through the sheet members is sufficiently long. Preferably, the spacing between the sheet-like members is small, for example 45mm or less, more preferably 30mm or less, more preferably 15mm or less, more preferably 10mm or less, more preferably 5mm or less, so that the boundary layer occupies a large space in the cooling device. Further preferably, a ratio of a spacing between adjacent sheet members to a length of the sheet members in the airflow flow direction is less than 0.5, less than 0.2, less than 0.1, or less than 0.05. The pitch between adjacent sheet members may be a pitch between center lines of the adjacent sheet members; the distance between the adjacent outer surfaces of the adjacent sheet-like members may be, for example, the distance between the lower surface of the upper sheet-like member and the upper surface of the lower sheet-like member (when the sheet-like members are placed vertically adjacent to each other), or the distance between the inner surface of the outer sheet-like member and the outer surface of the inner sheet-like member (when the sheet-like members are placed inside and outside adjacent to each other, the side closer to the observer is referred to as "outer" and the side farther from the observer is referred to as "inner").

When a cooling device in the form of a sheet-like member is used, when the surface temperature of the sheet-like member is lower than the dew point temperature of at least a part of the vapor component, a part of the vapor component condenses on the wall surface of the cooling device, and another part condenses in the boundary layer to form droplets, and since a high degree of supersaturation (up to 200% or more) of the vapor component can be formed in the boundary layer, the vapor component can be formed by homogeneous nucleation, and the droplets formed have a particle size of less than 1 micron, even only about 10 nm, and a number concentration of up to 10⁵-10⁷Per cm³The specific surface area is so high that it adsorbs and/or absorbs other gaseous pollutants that have not yet reached their dew point temperature. Even if other gaseous contaminants are difficult to be absorbed by the droplets of the vapor component, a high adsorptive trapping effect can be obtained. The adsorbed droplets are less than 10 microns in size and are difficult to settle by gravity, but can be wet-settled by thermophoretic and vapor pressure gradient forces within the boundary layer at a suitable wind speed (e.g., 10m/s, preferably less than 5 m/s) and onto the walls of the cooling device, and can be subsequently removed.

Wet and dry settling generally refer to two major self-cleaning mechanisms for particulate matter in the atmosphere. Dry sedimentation, also called gravity sedimentation, refers to the process in which particles are captured by gravity sedimentation, which is generally referred to as dry sedimentation, where gravity sedimentation is only effective for particles having a diameter greater than 10 microns. The wet sedimentation is a process of removing pollutants in the gas after the pollutants are condensed and nucleated in the gas and is divided into two stages of in-cloud removal and under-cloud removal. The cloud elimination refers to that the liquid drops capture particles in the gas through an inertia collision process and a Brownian diffusion effect in a falling process, so that the particles are eliminated from the gas and are mainly effective on larger particles. The in-cloud removal refers to that fine particles serve as condensation nuclei, condensation grows, and a large amount of fine particles are removed in gas through Brownian motion, migration (including thermophoresis, pushing of vapor pressure gradient force and the like) or inertial collision process, and the in-cloud removal is mainly effective on the fine particles below 1 micron. The term "wet settling" as used in the present invention refers to a process in which gaseous pollutants in the exhaust gas are removed by inertial coalescence, brownian motion and/or migration after condensation nucleation.

The term "thermophoretic force" as used herein refers to a force that pushes fine particles (e.g., liquid droplets) toward the cold wall due to a temperature gradient between the outer surface of the cooling device and the air flow (caused by a temperature difference between the outer surface of the cooling device and the air flow), the greater the temperature difference, the greater the temperature gradient, and the greater the thermophoretic force.

When the particles move in the fluid with the temperature gradient, because the momentum transferred when the molecules of the cold and hot areas collide with the particles is different, the particles are subjected to a force opposite to the direction of the temperature gradient (namely thermophoretic force), so that the particles generate a movement speed opposite to the temperature gradient and are deposited on the low-temperature surface, and the thermophoretic effect is called. Since the temperature gradient exists within the boundary layer of the cold wall, the thermophoresis effect is a short-range effect, occurring only in the wall boundary layer.

The formula for calculating thermophoretic force (see aerosol mechanics, scientific press, 1960) is:

where F is the thermophoretic force, Xa is the gas thermal conductivity, Xi is the particle thermal conductivity, η is the gas viscosity, R is the particle radius, Γ a is the temperature gradient, ρ is the gas density, and T is the gas temperature. Since a temperature gradient exists within the boundary layer, the greater the temperature difference, the greater the temperature gradient, for the same boundary layer thickness.

According to the theory of hydrodynamics, viscous drag is the force in a gas flow that is created on the particles (e.g., droplets) that are in contact, and the magnitude of the viscous drag is proportional to the square of the flow velocity and proportional to the square of the particle diameter. The viscous drag force is calculated by the formula:

in the formula: f is the viscous drag, xi is the drag coefficient, π R²-projected area of particles, ρ -gas density, U-gas flow velocity.

The calculation formula of the thermophoretic force and the viscous drag force shows that the thermophoretic force is in direct proportion to the temperature gradient and the first power of the diameter of the liquid drop, and the viscous drag force is in direct proportion to the square of the diameter of the liquid drop, so that under the same condition, the smaller the diameter of the liquid drop is, the larger the ratio of the thermophoretic force to the viscous drag force is, and the more obvious the effect of realizing sedimentation by utilizing the thermophoretic force is. The lower the airflow velocity, the smaller the viscous drag force, and the more obvious the effect of realizing sedimentation by utilizing thermophoretic force.

For vapor with dew point temperature higher than the temperature of the outer surface of the cooling device, one part of the vapor condenses on the wall surface, the vapor pressure at the wall surface is reduced, the other part of the vapor is cooled in the boundary layer to form supersaturated vapor, a vapor pressure gradient difference is generated between the supersaturated vapor and the outer surface of the cooling device, and at the moment, the liquid drops are subjected to vapor pressure gradient force directed to the outer surface of the cooling device, and the force can push the liquid drops to be settled on the outer surface of the cooling device.

The principle of the vapor pressure gradient force is that when the supersaturated vapor is condensed, vapor pressure gradient between the gas flow and the condensation wall surface is caused, and gas molecular flow towards the condensation wall surface is formed, so that molecular collision of the gas on opposite surfaces of particles in the gas flow is different, the particles are caused to migrate, and the movement direction of the particles is directed to the condensation surface. Like thermophoretic forces, vapor pressure gradient forces are also microscopic forces, and vapor pressure gradients mainly exist in the boundary layer of the cold wall surface. The calculation of the vapor pressure gradient force is complex and can be regarded as a numerical value between two calculated numerical values, namely the pressure gradient force generated when the partial pressure of other gas components is not considered and only the vapor pressure gradient exists and the driving force of Stefin flow generated when the total gas pressure is assumed to be unchanged and the partial pressure of vapor is changed. Simply stated, the magnitude of the vapor pressure gradient is proportional to the vapor pressure gradient. The higher the vapor content of the condensable droplets in the off-gas, the smaller the boundary layer thickness and the larger the vapor pressure gradient.

The vapor pressure gradient force can be superposed with thermophoretic force to jointly push liquid drops to be wet and settled on the outer surface of the cooling device.

The liquid drops deposited on the outer surface of the cooling device can be gathered into larger liquid drops, and the larger liquid drops can be naturally dropped or flowed away, so that the liquid drops are removed, and the gaseous pollutants are removed. In some aspects, the droplets may be flushed away by spraying away from the outer surface of the sheet member. In some embodiments, the droplets may be caused to flow away through a drainage channel. In some embodiments, the dripping or run-off droplets may be collected for recycling, for reuse. In some embodiments, the dripping or run-off droplets may be collected in a container. In other embodiments, the drained liquid drops can be collected by draining through the drainage channel.

As shown in fig. 1, the apparatus 1 for removing gaseous pollutants of the present invention has a gas flow path for the passage of the exhaust gas, in which gas flow path a cooling device 2 is arranged, which cooling device comprises at least two sheet-like members, which sheet-like members run substantially parallel to each other and substantially parallel to the gas flow.

For removing the gaseous pollutants in the exhaust gas, the exhaust gas can be made to pass through the gaseous pollutant removing device and pass between the adjacent sheet-shaped members, and the flow speed of the exhaust gas is controlled to be not higher than 10 m/s; and controlling the temperature of the outer surface of the sheet-like member to be lower than the dew point temperature of at least part of the vapour component of the exhaust gas by a temperature difference sufficient to cause at least part of the vapour in the exhaust gas to condense into liquid droplets, at least part of the vapour in the exhaust gas condensing into liquid droplets by cooling the exhaust gas, the gaseous pollutants in the exhaust gas adsorbing on the liquid droplets and settling on the outer surface of the sheet-like member with the liquid droplets.

The gaseous pollutants can be removed by removing the liquid drops deposited on the outer surface of the sheet-shaped member. For example, droplets of liquid that have settled on the outer surface of the sheet-like member can be caused to drip or run off, and these droplets can be further caused to run off through the drainage channel. In some embodiments, these droplets may be recovered to facilitate reuse of certain gaseous contaminant components. The droplets may be collected, for example, by a drainage channel, or may be further collected in a container, for example, by draining the droplets into the container.

In use, the gaseous pollutant removing device of the present invention may be placed in the flow path of exhaust gas so that the exhaust gas flows through the gaseous pollutant removing device. For example, if the exhaust gas passes through a closed gas flow passage (e.g., a flue), the gaseous pollutant removing device may be interposed in the middle of the gas flow passage, for example, a part of the gas flow passage may be replaced with the gaseous pollutant removing device, or the gas flow passage may be cut off from the middle and connected to a gas flow inlet and a gas flow outlet of the gaseous pollutant removing device, respectively. It should be understood that the gaseous contaminant removal device of the present invention may also be applied to a non-enclosed exhaust stream, as long as the exhaust gas is caused to flow through the gaseous contaminant removal device.

The number of sheet-like members in the cooling device is at least 2, i.e. may be 2 or more, such as 3, 4, 5 or more.

The "sheet member" of the present invention means a substantially sheet-like member, and the outer surface of the member may have a certain curvature or angle, and may be formed into a corrugated shape by, for example, pressing, as long as it is substantially sheet-like as a whole. When using the device of the invention for removing gaseous pollutants from exhaust gases, the device should be placed in such a position that the parallel members run substantially parallel to the gas flow.

The term "substantially parallel" as used herein does not exclude arcs or angles of parallel lines and/or planes, but merely requires substantially the same distance between them, and in general, includes a completely parallel state and a non-completely parallel but substantially parallel state in which the desired effect is substantially achieved. Specifically, the term "substantially parallel" includes the state where lines and planes or planes and planes are completely parallel, and the case where they are relatively shifted from the completely parallel state by 0 ° to about 10 ° -20 °.

The sheet members may be connected to each other in any manner that can fix them in a substantially parallel state, for example, at the edges of the sheet members by connecting members, or at any position on the plate surface of the sheet members by connecting members, which may be in the form of plates, bars, tubes, columns, or any shape suitable for connecting the sheet members. The connector should not block the direction of the airflow flow, but the connector should allow for disturbance of the airflow flow.

The sheet member outer surface may be maintained at a desired temperature by any suitable means known in the art, such as by contact of a cooling gas, liquid or source with the sheet member or semiconductor refrigeration principles such that the sheet member outer surface temperature is below the dew point temperature of at least a portion of the vapor component. For example, exhaust gas may be caused to flow through one side of the sheet member while cooling gas or liquid is passed through the other side of the sheet member. For example, the sheet-like member may be sealed around to form a circumferentially closed channel, with exhaust gas passing through the interior of the channel and a cooling source or cooling fluid outside the channel. Or, for example, a hollow tube or a heat-conducting solid tube may be disposed in the sheet member, the hollow tube may flow a cooling liquid, and the solid tube may be externally connected to a cooling source. The cooling liquid is well known in the art, and may be any one or a mixture of more of water, freon, methanol, ethanol, acetone, ammonia water, and the like. The cooling gas may be, for example, one or a mixture of more of air, flue gas, or any other gas.

Since the heat conductivity of the metal material is higher than that of the non-metal material, in order to ensure a larger temperature difference and facilitate the realization of the thermophoresis effect, the sheet-shaped member of the cooling device is preferably made of a metal material, such as one or more of aluminum, copper and steel. In order to further prolong the service life of the metal member, special anti-corrosion treatment can be carried out on the metal member. Such as spraying or passivating the metal components made of steel, copper, aluminum and the like with anticorrosive materials.

In some embodiments, the sheet member is a semiconductor thermoelectric sheet and the cooling device includes two semiconductor thermoelectric sheets with cold ends opposite. As shown in fig. 2, in the gaseous pollutant removing device 1, the cooling device includes an upper semiconductor thermoelectric chip 7 and a lower semiconductor thermoelectric chip 10, an upper hot terminal 9 and an upper cold terminal 8 are formed after a dc power is turned on in the upper semiconductor thermoelectric chip 7 by an upper power supply 6, a lower hot terminal 12 and a lower cold terminal 11 are formed after a dc power is turned on in the lower semiconductor thermoelectric chip 10 by a lower power supply 13, and exhaust gas passes between the upper cold terminal 8 and the lower cold terminal 11.

The term "semiconductor thermoelectric chip" is also called semiconductor cooling chip. It is a refrigeration technique based on the peltier effect. Its simple theory of operation is: when an N-type semiconductor material and a P-type semiconductor material are connected into a galvanic couple pair, energy transfer can be generated after direct current is switched on in the circuit, and the current flows to the joint of the P-type element from the N-type element to absorb heat to form a cold end; the junction from the P-type element to the N-type element releases heat to become the hot end. The temperature difference of the cold and hot ends of the semiconductor refrigerating sheet can reach 40-65 ℃, and if the temperature of the hot end is reduced in an active heat dissipation mode, the temperature of the cold end can be correspondingly reduced, so that the lower temperature is reached. When the semiconductor thermoelectric pieces with the two opposite cold ends are in a working state, waste gas flows through a channel between the cold ends of the two semiconductor thermoelectric pieces, and the waste gas is contacted with the cold ends and forms a temperature difference with the cold ends.

In other embodiments, the cooling device is a plate heat exchanger or a finned tube heat exchanger,

the plate heat exchanger is made up by using thin metal plate to press heat-exchanging plate sheets with a certain corrugated form, then stacking them, and fastening them by using clamping plate and bolt. Thin rectangular channels are formed between the plates, and heat exchange is carried out through the plates. The working fluid flows through the narrow and tortuous passage formed between the two plates. The circulating cooling water and the waste gas respectively pass through two adjacent channels, an interlayer plate is arranged in the middle to separate the two channels, and heat exchange is carried out through the plate. The plate heat exchanger has small space and long stroke, and is beneficial to forming boundary layer space with higher proportion. When a plate heat exchanger is used, the heat exchanger plates constitute said plate-like member.

As shown in fig. 5. When the finned tube heat exchanger is used, the fins constitute the above-mentioned fin members, and the outer diameter D of the fins corresponds to the length of the fin members. For ease of measurement and calculation, when using a finned tube heat exchanger, the spacing between the outer surfaces of the fin members may be represented by the fin pitch. The fin pitch t is preferably less than 15mm, more preferably less than 10mm, more preferably less than 9mm, more preferably less than 8mm, more preferably less than 5 mm. The fin height h is preferably greater than 10mm, more preferably greater than 15mm, more preferably greater than 18 mm.

"finned tube heat exchangers" are well known to those skilled in the art. The finned tube is also called as a finned tube or a ribbed tube and is generally formed by combining a base tube and fins additionally arranged on the surface of the base tube, so that the surface of the base tube is expanded, fluid inside and outside the tube exchanges heat through the tube wall and the fins, and the fins enlarge the heat transfer area, so that the heat exchange efficiency is improved. The base pipe is usually a round pipe, but can also be a flat pipe or an oval pipe. The fins may be of any suitable shape and may be provided on the inside of the tube and/or on the outside of the tube, depending on the application of the heat exchanger and the particular type of fluid inside and outside the base tube of the heat exchanger. The base tube of the finned tube heat exchanger can be filled with cooling liquid, waste gas flows between fins outside the tube, and the heat of the waste gas is transferred to the cooling liquid inside the tube through the fins and the tube wall, so that the heat exchange inside and outside the finned tube is realized.

More preferably, in the present invention, the finned tube heat exchanger employed is a finned heat tube heat exchanger. Heat pipes are also known as "closed two-phase heat transfer systems", i.e. devices that transfer heat by virtue of a change in the phase of a fluid (liquid to vapor and vapor to liquid) in a closed system. The heat pipe has excellent heat transfer characteristic because of the phase change heat transfer of the working medium. The heat pipe has a thermal conductivity higher than that of Cu or Al by tens or hundreds times, so it is called a super heat conductor. Compared with the common finned tube heat exchanger with the same overall dimension, the heat tube has good axial isothermality when transmitting the same power, and can form larger heat transfer temperature difference. The typical heat pipe heat exchanger consists of a pipe shell, a wick and an end cover, wherein the pipe is pumped to a certain negative pressure and then filled with a proper amount of working liquid, so that the wick capillary porous material tightly attached to the inner wall of the pipe is filled with liquid and then sealed. One end of the tube is an evaporation section (heating section), the other end is a condensation section (cooling section), and a heat insulation section can be arranged between the two sections according to application requirements. When one end of the heat pipe is heated, the liquid in the capillary wick is evaporated and vaporized, the vapor flows to the other end under a small pressure difference to release heat and condense into liquid, and the liquid flows back to the evaporation section along the porous material under the action of capillary force. The circulation is not completed, and the heat is transferred from one end of the heat pipe to the other end. In the present invention, a split heat pipe heat exchanger is preferably used.

Other methods of creating a temperature differential between the outer surface of the cooling device (which may also be referred to herein as the outer surface of the sheet member) and the exhaust gas are known to those skilled in the art.

When the amount of the off-gas is large, two or more (e.g., three, four, five or more) cooling devices (also referred to as a group of cooling devices, in which a plurality of cooling devices are spaced from each other by an appropriate distance) may be arranged in parallel on a cross-section in the flow direction of the off-gas, as shown in fig. 3. Considering that one group of cooling devices has limited effect, two or more groups (e.g., three, four, five or more groups) of cooling devices may be arranged along the flow direction of the exhaust gas, each group of cooling devices is located on one cross section of the flow direction of the exhaust gas, and two adjacent groups of cooling devices may be arranged in parallel or in staggered arrangement, as shown in fig. 4.

When a plurality of cooling devices are used, the reynolds number, the boundary layer thickness, the thermophoretic force, the viscous drag force, and the like are calculated individually for each cooling device.

In some embodiments, as shown in fig. 6, a spraying device 3 may be disposed on one side of the cooling device 2, and the spraying device 3 is used for spraying any suitable liquid, including any one or a mixture of water, aqueous solution and organic solvent, onto the outer surface of the sheet member to clean the outer surface of the sheet member and prevent the fouling of the wall surface, and also to remove the liquid drops deposited on the wall surface. In some embodiments, spray means for spraying the outer surface of the sheet member may be provided on both sides of the cooling means. The spraying device may be disposed inside the gaseous pollutant removing device, or may be disposed outside the gaseous pollutant removing device, for example, may be disposed in the gas flow channel upstream of the gaseous pollutant removing device. Preferably the spray means is close to the sheet member for better rinsing effect.

In some embodiments, a device for pretreating the exhaust gas may be provided, for example, an injection device for the exhaust gas may be further provided upstream of the cooling device, for injecting a substance capable of forming vapor in the exhaust gas into the exhaust gas to increase the vapor content of the exhaust gas, and the injection device may be further used for injecting an acidic substance into the exhaust gas to generate an acid mist with a high dew point temperature; the injection device may also be used to inject oxidizing and/or basic substances into the exhaust gas to modify certain gaseous components of the exhaust gas. The description of the substance capable of forming vapor in the exhaust gas, the acidic substance, the oxidizing substance, and the basic substance is as described above. The injection device for the exhaust gas may be one or more injection devices, or may be an injection device with two or more nozzles, and different nozzles may inject different substances. The injection device may be used to inject any one, any two, or any more of a substance that can form a vapor in the exhaust gas, an acidic substance, an oxidizing substance, and a basic substance. For example, any one, any two, or any more of the substance that forms a vapor in the exhaust gas, the acidic substance, the oxidizing substance, and the basic substance may be injected separately by a plurality of injection devices, different substances may be injected separately by different nozzles by an injection device having two or more nozzles, or a mixture of different substances may be injected by the same nozzle of the same injection device, provided that the different substances in the mixture do not chemically react (it is understood that, for example, the acidic substance and the basic substance cannot be injected together by mixing together through one nozzle). Any of the substances which form a vapour in the exhaust gas, the acidic substance, the oxidizing substance, the basic substance, may optionally be sprayed in pure form or in solution, may optionally also be sprayed in liquid form or in gaseous form (for example in gas or vapour form), for example in the case of water, atomized water droplets may be sprayed, and water vapour may also be sprayed. Upstream of the cooling device, a device for oxidation treatment of the exhaust gas, such as a photocatalytic oxidation device, may also be provided. Means for pressurising the exhaust gas (e.g. an air compressor) may also be provided upstream of the cooling means. The various injection devices, oxidation treatment devices, and pressurizing devices may be optionally provided as needed, and for example, may be provided in combination, or may be provided in only one kind, two kinds, or more kinds. These pre-treatment means may be provided either internally or externally of the gaseous pollutant removal means, for example in the gas flow path upstream of the gaseous pollutant removal means. The positions of these pretreatment devices with respect to each other are not particularly limited and may be set as desired, and in a non-limiting example, the pressurizing device may be disposed after the injection device and/or the oxidation treatment device. It will be appreciated that to enhance the pre-treatment effect, these pre-treatment means are preferably located remotely from the cooling means so that the exhaust gases are passed through the cooling means after being sufficiently pre-treated. When the pretreatment devices coexist with a spray device for spraying the outer surface of the sheet member, it is preferable that the distance between the pretreatment devices and the sheet member is larger than the distance between the spray device and the sheet member.

After the exhaust gas passes through the cooling device, the escaped liquid drops can be taken as condensation nuclei to absorb moisture and grow up, so that in some embodiments, other particulate matter trapping devices 4, such as a demister, a dust remover and the like, can be arranged after the cooling device to trap the grown liquid drops again, as shown in fig. 7. The precipitator may be, for example, a wet electro precipitator or a venturi precipitator. The particulate matter trapping device may be provided inside the gaseous pollutant removing device or outside thereof, for example, may be provided in the gas flow passage downstream of the gaseous pollutant removing device.

In some embodiments, a spray device 3 may be provided on one or both sides of the cooling device, while another particulate trap device 4 is provided after the cooling device, as shown in fig. 8.

In some embodiments, as shown in fig. 9, a flow guide channel 5 may be provided at a lower portion of the gaseous contaminant removal device so as to allow the liquid droplets to flow away, or the liquid droplets may be introduced into the container through the flow guide channel 5 to be recovered. It should be understood that the flow guiding channel may be provided in any one of the gaseous pollutant removing devices according to the present invention, and is not limited to the specific structure shown in fig. 9.

The waste gas in the invention can be any waste gas containing gaseous pollutants, for example, oil gas containing low-boiling point organic matters discharged from gas stations, high-humidity clean flue gas containing organic matters after dust removal and desulfurization of coal-fired boilers, high-humidity flue gas containing nitrogen oxides and organic components after combustion of natural gas, high-humidity waste gas containing acetic acid and furfural components discharged from furfural production workshops, high-humidity waste gas discharged from wood treatment workshops, air containing volatile organic matters and acidic gases, and the like. The exhaust gas of the present invention includes, but is not limited to, high humidity exhaust gas, particularly high humidity exhaust gas after water spray treatment. The exhaust gas preferably comprises mainly gaseous pollutants, wherein "mainly comprises" means that the content of gaseous pollutants in the exhaust gas is higher than the content of any other type of pollutants (e.g. particulate pollutants, i.e. pollutants present in particulate form in the exhaust gas), or that the content of gaseous pollutants is higher than the sum of the contents of all other types of pollutants.

If the relative concentration of the vapor contained in the exhaust gas is not high enough to rapidly form droplets in the cooling device, the vapor content may be increased by pretreatment, such as increasing the water vapor content (i.e., moisture content, such as by adding steam, pre-cooling, spraying water, etc.) or spraying alcohol vapor, and then passed through a gaseous pollutant removal device. For example, a nozzle or a spraying device can be additionally arranged in front of the gaseous pollutant removing device to spray one or more mixtures of water or ethanol or other organic matters, so that the steam content in the waste gas is increased; a pre-heat exchanger can be additionally arranged in front of the gaseous pollutant removing device to pre-cool the waste gas and improve the steam content of the waste gas (including improving the relative humidity of the waste gas or improving the relative content of other steam in the waste gas). The pre-heat exchanger may take the form of any heat exchanger, such as a plain tube heat exchanger.

The difference between the invention and the conventional condensation method and the conventional atomization spraying method is as follows:

the conventional condensation method mainly utilizes a light pipe heat exchanger, waste gas firstly contacts the windward surface of the light pipe heat exchanger, the stroke length is short, the boundary layer is thin, and then the waste gas contacts the back dust surface of the light pipe heat exchanger, turbulence is easily formed on the back dust surface of the light pipe heat exchanger due to the vortex street effect, and the formation of the boundary layer of the back dust surface is damaged, so that the average thickness of the boundary layer on the outer surface of the light pipe heat exchanger is thin, vapor substances are mainly condensed on the wall surface of the heat exchanger after being condensed to a dew point to form bead-shaped or film-shaped condensation, an effective atomization area is difficult to form outside the heat exchanger, and the condensation process can only capture the vapor substances reaching the dew point temperature and cannot capture other gaseous pollutants. Even if a plate type heat exchanger is used for heat exchange in a certain project, the design of the heat exchanger is based on the heat exchange efficiency, the air flow speed is higher and is generally more than 10m/s (the higher the air speed is, the thinner the boundary layer is, the higher the heat exchange coefficient of the heat exchanger, and the higher the heat exchange efficiency of the heat exchanger is), the number of formed nano-micron droplets is small, the thermophoretic force and the steam pressure gradient force are difficult to effectively play a role in trapping the droplets at a high flow speed, and no obvious trapping effect is generated on the nano-micron droplets and other gaseous pollutants adsorbed on the nano-micron.

The conventional atomization spraying method is to spray liquid substances into gas to be purified through various atomization methods, and is limited by atomization capacity and trapping capacity, the particle size of sprayed liquid drops is more than 20-100 micrometers (which is convenient to trap in a demister behind), the specific surface area of the liquid drops is small, gaseous pollutants can be further adsorbed if being absorbed by the vapor substances after being adsorbed on the mist drops, and if not being absorbed by the vapor substances, the gaseous pollutants can not be trapped after surface adsorption is finished. Typically, after the gaseous contaminants are captured, they are collected by the mist eliminator as the sprayed droplets settle by gravity, or other inertial force methods, without wet settling, particularly in-cloud removal processes.

Example 1

The oil gas is the volatile matter of gasoline, and the gas vent of gasoline storage tank usually has a large amount of oil gas volatilization, needs to carry out condensation recovery, finally controls its emission concentration.

The gasoline component is C4-C12, wherein the proportion of C4-C6 is 35%, and the proportion of C7-C12 is 65%. In oil gas, C4 and C5 are main components, wherein the boiling point of pentane is 36 ℃, the boiling point of isopentane is 28 ℃, the boiling point of pentane is steam at normal temperature, the boiling point of neopentane is 10 ℃, the boiling point of butane is 0.50 ℃, the boiling point of isobutane is-11.73 ℃, the pentane is gas at normal temperature, and the neopentane and the isobutane are gaseous pollutants.

The prior recovery scheme is that a tubular heat exchanger is used for cooling to-15 ℃ and recovering condensate, but the gaseous pollutants form fine particles after condensation, so that the tubular heat exchanger has weak interception capability on the fine particles, the removal efficiency is below 20 percent, and if higher removal efficiency is required, the temperature needs to be reduced to lower temperature or oil gas needs to be pressurized to promote condensation.

The scheme is changed as follows: the device for removing the gaseous pollutants by introducing the oil gas discharged by the gasoline storage tank is characterized in that: in the multi-row finned tube heat exchanger, oil gas passes through the outside of the finned tubes at the airflow velocity of 7m/s, the working medium in the finned tubes is Freon 134A, the working medium temperature is-15 ℃, the fin pitch is 5mm, the fin height is 15mm, the outer diameter of the finned tubes is 55mm, and the temperature of the outer surfaces of the fins is lower than-10 ℃. And a spraying device is arranged before the heat exchange of the fins and is used for spraying ethanol solution.

The heat exchanger exchanges partial heat in the oil gas, temperature reduction of the oil gas is achieved, pollutants such as pentane, isopentane and neopentane in the oil gas are partially condensed into fog drops, the fog drops absorb other gaseous pollutants such as butane and isobutane in the waste gas while being formed, and then wet and subside to the outer surface of the fin through thermophoresis effect among fin tubes, and the fog drops drop after accumulating to a certain amount and are recovered through a liquid outlet.

The lower ethanol solution of freezing point forms the atomizing through spraying, can wash the fin surface, strengthens the recovery to the oil gas liquid drop that catches.

The removal/recovery efficiency of the whole oil gas pollutants reaches over 90 percent, and the recovered oil gas pollutants can be further dissolved into the gasoline for reutilization.

Example 2

3 ten thousand Nm of process waste gas of a furfural production plant with a slag bin³H is saturated moisture, and the temperature is about 80 ℃, wherein the content of acetic acid is 70mg/Nm³Furfural 70mg/Nm³5mg/Nm of Formaldehyde³，SO₃ 12mg/Nm³And a small amount of dust, and has a significant sour odor.

The airflow channel connected with the exhaust port of the slag bin firstly passes through the photocatalytic oxidation system to oxidize part of gaseous organic matters, and part of gaseous organic matters are completely oxidized and decomposed into CO₂And water, and most of the rest gaseous organic matters are oxidized into organic matters with higher boiling points so as to be conveniently adsorbed by the fog drops.

Be equipped with multiunit gaseous pollutant remove device behind the photocatalytic oxidation system, the form is: the finned tube heat exchanger is characterized in that a finned tube is subjected to metal composite rolling, the fin pitch is 6mm, the fin height is 16mm, the outer diameter of the finned tube is 64mm, circulating water with the temperature of 20 ℃ flows in a base tube, the temperature of the outer surface of the fin is about 30 ℃, the temperature is greatly lower than the acid dew point and the water dew point of waste gas, air flow passes through a gaseous pollutant removing device, and the air flow velocity is 4 m/s.

Spraying devices are arranged on two sides of the condensing section (in the clean flue) to spray aqueous solution.

The finned tube heat exchanger exchanges partial heat in the wet flue gas to realize the cooling of the waste gas, wherein SO₃Acetic acid and water vapor are condensed into liquid drops, other gaseous organic pollutants in the waste gas are adsorbed by the liquid drops, the liquid drops are wet-settled on the outer surface of the finned tube and are dripped after a certain amount of liquid drops are accumulated, and the removal efficiency of the organic pollutants is over 80 percent.

Example 3

The flue gas generated by a 300MW coal-fired boiler is subjected to wet desulphurization to become nearly saturated wet flue gas (the relative humidity is more than 95%), and the flue gas amount is 120 ten thousand meters³The smoke temperature is about 50 ℃, and the content of particles is 2mg/Nm³Sulfuric acid SO₃Vapor 10mg/Nm³Volatile organic 13mg/Nm³The volatile organic compounds are mainly aliphatic hydrocarbon, halogenated hydrocarbon, aromatic hydrocarbon, oxygen-containing organic compounds and the like, and the types of gaseous pollutants reach more than 100And (4) seed preparation.

Be equipped with multiunit gaseous pollutant remove device in the clean flue that links to each other with the desulfurizing tower, this gaseous pollutant remove device form is: in the metal finned tube heat exchanger, the cooling liquid is circulating water at 20 ℃, the finned tubes are made of metal, the temperature of the outer surfaces of the fins is about 30 ℃ and is greatly lower than the acid dew point and the water dew point of flue gas, air flow passes through a gaseous pollutant removing device, and the flow velocity of the air flow is 4 m/s.

Spraying devices are arranged on two sides of the gaseous pollutant removing device and used for spraying aqueous solution.

The finned tube heat exchanger exchanges partial heat of wet flue gas, realizes cooling and condensation of the wet flue gas, forms a large amount of liquid drops including sulfuric acid fog drops and water drops, volatile organic compounds are adsorbed to the surface of the liquid drops, the liquid drops are wet-settled on the outer surface of the finned tube under the pushing of thermophoretic force and vapor pressure gradient force, and the liquid drops drop after accumulating to a certain amount, so that the sulfuric acid vapor and the volatile organic compounds in the waste gas are removed, and the removal efficiency is respectively more than 70% and more than 80%.

Example 4

The gas boiler discharges nearly saturated wet flue gas (relative humidity is more than 90%), the flue gas temperature is about 80 ℃, and the flue gas contains NO100mg/Nm³。

An ultraviolet light catalytic oxidation device is arranged in the flue to realize the conversion of NO to NO₂And N₂O₅Conversion for removal of gaseous contaminants (higher boiling point) followed by a gaseous contaminant removal device in the form of: the common fin tube type heat exchanger has the fin pitch of 5mm, the fin height of 16mm, the outer diameter of the fin tube of 64mm, the temperature difference between the fin and the flue gas of more than 10 ℃ and the flue gas flow velocity of 5 m/s.

The heat exchanger exchanges partial heat in the wet flue gas to realize the cooling of the wet flue gas, the water vapor is condensed into liquid drops, and the liquid drops adsorb/absorb NO₂、N₂O₅And then the waste water is settled on the outer surface of the finned tube, and is dripped after a certain amount of waste water is accumulated, and the NOx removal efficiency is over 40 percent.

Spraying water devices are arranged on two sides of the gaseous pollutant removing device, the spraying water is common process water, and a proper amount of Na is added₂CO₃Or NaOH for washing the finsTube and can increase the alkalinity of condensed water to facilitate NO_xAbsorption of (2).

The demister is arranged behind the gaseous pollutant removing device, and the washing water drops and escaping liquid drops are further removed by the demister.

It is to be understood that the above-described embodiments of the present invention are merely illustrative of or explaining the principles of the invention and are not to be construed as limiting the invention. Therefore, any modification, equivalent replacement, improvement and the like made without departing from the spirit and scope of the present invention should be included in the protection scope of the present invention. Further, it is intended that the appended claims cover all such variations and modifications as fall within the scope and boundaries of the appended claims or the equivalents of such scope and boundaries.

Claims

1. A method of removing gaseous pollutants from an exhaust gas comprising: passing the exhaust gas through a gaseous pollutant removing device comprising a gas flow channel and a cooling device arranged in the gas flow channel, the cooling device comprising at least two sheet-like members, the sheet-like members being substantially parallel to each other and substantially parallel to the flow direction of the exhaust gas, the exhaust gas passing between adjacent sheet-like members, the exhaust gas flow rate being not higher than 10 m/s; the temperature of the outer surface of the sheet-like member is lower than the dew point temperature of at least part of the vapour component in the exhaust gas, and at least part of the vapour in the exhaust gas is condensed into liquid drops by cooling the exhaust gas, and the gaseous pollutants in the exhaust gas are adsorbed on the liquid drops and are deposited on the outer surface of the sheet-like member along with the liquid drops in a wet mode.

2. The method of claim 1, further comprising: recovering the droplets wet-settled to the outer surface of the sheet member.

3. A process according to claim 1 or 2 wherein the cooling apparatus is a finned tube heat exchanger, the fins on the heat exchanger constituting the laminar member; or the sheet-shaped component is a semiconductor thermoelectric sheet, the cooling device comprises two semiconductor thermoelectric sheets with opposite cold ends, and the waste gas passes between the cold ends of the two semiconductor thermoelectric sheets.

4. A method according to any one of claims 1 to 3, wherein the exhaust gas is subjected to a pre-treatment prior to passing the exhaust gas through the cooling means, the pre-treatment comprising any one or more of increasing the vapour content of the exhaust gas, adding an acidic substance to the exhaust gas, subjecting the exhaust gas to an oxidation treatment, adding a basic substance to the exhaust gas, and pressurising the exhaust gas.

5. A system for removing gaseous pollutants from an exhaust gas, comprising: a gaseous pollutant removal device for passing and treating exhaust gases, said gaseous pollutant removal device comprising a gas flow channel and a cooling device arranged in the gas flow channel, said cooling device comprising at least two sheet-like members, said sheet-like members running substantially parallel to each other and substantially parallel to the gas flow.

6. The system of claim 5 wherein the cooling device is a finned tube heat exchanger, fins on the heat exchanger comprising the sheet member; or the sheet member is a semiconductor thermoelectric sheet, and the cooling device includes two semiconductor thermoelectric sheets having cold ends opposite to each other.

7. A system according to claim 5 or 6, wherein an injection means for injecting any one or more of a substance which can form a vapor in the exhaust gas, an oxidizing substance, an acidic substance, and a basic substance into the exhaust gas is provided on an upstream side of said cooling means.

8. A system according to any one of claims 5 to 7, wherein an oxidizing device is provided on an upstream side of the cooling device for subjecting the exhaust gas to an oxidizing treatment.

9. A system according to any one of claims 5 to 8, wherein a pressurizing device is provided on the upstream side of the cooling device for pressurizing the exhaust gas.

10. A system according to any of claims 5-9, further comprising a drainage channel for leading out and/or recovering droplets through the drainage channel.