WO2012129815A1

WO2012129815A1 - Method and equipment for denitrifing waste gas produced by combustion system

Info

Publication number: WO2012129815A1
Application number: PCT/CN2011/072393
Authority: WO
Inventors: 熊靓
Original assignee: 深圳市泓耀环境科技发展股份有限公司
Priority date: 2011-04-01
Filing date: 2011-04-01
Publication date: 2012-10-04

Abstract

A method and equipment for denitrifing waste gas produced by combustion system are provided. Said method is : bringing the reductant into the electrode region of the plasma reaction vessel or the reacting region behind the electrode region, where the reductant collides and exchanges energy with plasma and is partially or completely transformed into plasma or activated molecules; transmitting the mixed gas into waste gas channel comprising NO_x and then into the reducing reaction chamber together with the waste gas; reducing the waste gas comprising NO_x to N₂, CO₂, water and other harmless gases under the effect of catalyst or high temperature; and discharging the treated gases from the following discharging equipment. Said method greatly saves the dosage of solid reductant and reduces the risk of reductant component leakage, shortens the reaction time and improves the reaction efficiency of the reaction equipment.

Description

[Inventive name established by ISA according to Rule 37.2] Denitration method and device for exhaust gas generated by combustion system

Technical field

The present application relates to a process for purifying NO _x -containing gas, can be used for pollution control of the exhaust NO _x -containing flue gas plants, and other industrial engine exhaust gas produced by the process.

Background technique

Is well known, the combustion process generates large amounts of NO _x -containing gas, the concentration of NO _x can reach hundreds or even thousands ppmg. NO _x is the generic term for all the nitrogen oxides, of which about 90% to NO. NO _x is released into the atmosphere leads to the formation of acid rain, polluted air, such as NO will result into the stratosphere ozone layer. Flue gas / primary NO _x in the exhaust gas from the oxidation of nitrogen compounds in the fuel, but also a portion from the oxidation of molecular nitrogen in air. Except that the concentration of nitrogen compounds in the fuel, the boiler load, the combustion temperature, the amount of surplus combustion air, and the residence time and other factors are also important factors in _the NO _x concentration in the flue gas determined. As in the actual plant, only changes in boiler load can cause fluctuation of NO _x emissions up to about 4 times. The main countries in the world have implemented the flue gas emissions of NO _x limit its strict emission standards gradual trend, which raised higher and higher requirements for NO _x in the flue gas will be processed.

The prior art flue gas including NO _x -removal been commercialized selective catalytic reduction (SCR) and selective non-catalytic reduction (SNCR). The selective catalytic reduction method injects a compound mainly composed of ammonia (NH ₃ ) and ammonia water into the flue gas, and the ammonia reduces the NO by the action of the catalyst and generates harmless nitrogen and water. Ammonia also contributes to the collection of fly ash in subsequent electrostatic precipitators to increase the operational efficiency of the device. This reaction must be carried out at a temperature of about 300-450 ° C. If the temperature is too low, the reaction efficiency is greatly lowered, and too high, the catalyst is ineffective. In order to utilize the waste heat in the flue gas, in a power plant, the SCR reaction unit is usually placed before the secondary air preheater after the boiler outlet. The SNCR method adopts a similar reduction reaction with SCR. The reducing agent is generally urea. Instead of catalyst catalysis, it is selected to carry out the reaction under high temperature conditions such as 1000-1200 °C. Therefore, when the SNCR method is used, the reducing agent is generally added to the boiler near the outlet. Within the section with the required high temperature.

Since ammonia is an unstable dangerous gas with a pungent odor, there is a safety hazard in the preparation, transportation and storage of ammonia. The ammonia must usually be stored in the form of liquid ammonia or ammonia. In order to ensure a high NO _x removal, in the dosage of ammonia plants generally appropriate excess, this will result in the risk of ammonia leakage. In addition to irritating odor, ammonia is also toxic to animals and the environment. In order to avoid a series of problems caused by the use of ammonia, the researchers proposed a number of alternative SCR or SNCR methods. The most important workaround is to use alternatives to ammonia. The most common alternative to ammonia is urea. Urea is solid at room temperature and is very stable, which is convenient for transportation and storage. However, since it is a solid, the metering and dosing of urea is difficult. In order to uniformly add and form small particles, urea is first dissolved in water to form a 20% solution, and then the solution is sprayed into the flue gas. . Since water needs to absorb heat when it is volatilized into a gas at a temperature of more than 1000 degrees Celsius, the method of adding urea to a solution for doping causes a large amount of energy waste.

US Patent (US 7,008,603 B2) discloses a method and apparatus for hydrolyzing urea into ammonia and then adding it The reaction equation is as follows:

NH ₂ CONH _{2 -} NH ₄ OCN

NHOCN - NH ₃ + HNCO

HNCO + H ₂ O + heat - NH ₃ + CO ₂

The total reaction formula is: NH ₂ CONH ₂ + H ₂ O + heat - 2NH ₃ + CO ₂

The reaction must It can be carried out at high temperature (more than 145 ° C, optimum temperature of 171 ° C) and a certain pressure (such as hundreds of psig). Under certain acids and strong alkalis, the reaction rate will be greatly accelerated, and high-order like phosphoric acid. The mineral acid is a good catalyst for this reaction. Under the action of phosphoric acid The catalytic reaction equation is:

NH ₂ CONH ₂ + 2H ₃ PO ₄ + heat - 2NH ₄ H ₂ PO ₄ + CO ₂

2NH ₄ H ₂ PO ₄ ——-2NH ₃ + 2H ₃ PO ₄

NH ₂ CONH ₂ + H ₂ O + 2NH ₄ H ₂ PO ₄ —— 2(NH ₄ ) ₂ HPO ₄ + CO ₂

2(NH ₄ ) ₂ HPO ₄ + heat - 2NH ₃ + 2NH ₄ H ₂ PO ₄

According to the method, the urea must first be dissolved in water, and then added to the urea hydrolysis reactor to prepare ammonia gas, and the ammonia gas is immediately added to the NO reduction unit after being produced, and the rate of preparing the ammonia gas can be determined according to the actual ammonia gas demand. The rate of ammonia production is adjusted by adjusting the amount of urea and water added to the hydrolysis unit.

US Pat No 2010/0050597 A1 Tell us that when urea is applied to the denitration of automobile exhaust, it is first dissolved in water and then sprayed into the air passage of the internal combustion engine to be utilized in conjunction with the SCR method. After the water evaporates, the urea becomes a solid of very small particles at a temperature greater than 180. At °C, urea is more thoroughly decomposed into ammonia and cyanic acid, while cyanic acid is hydrolyzed into ammonia and carbon dioxide. However, when walking in the city, the temperature of the automobile exhaust is often less than 180 ° C. At this time, the pyrolysis of the urea particles occurs more slowly than the partial polymerization of urea (that is, the polymerization of urea into biuret), so that part of the urea will be It becomes a biuret, and the biuret is rapidly sublimed and decomposed over a large temperature range (greater or less than 180 ° C) on the surface of the acid sites of any catalyst. Biuret decomposition can be expressed by the following equation:

H ₂ NCONHCONH ₂ (solid) + 2H ₂ O (gas) - 3NH ₃ (gas) + 2CO ₂ (gas).

However, at lower temperatures, the decomposition of the biuret is not complete, at which point a high concentration of urea begins to undergo complete polymerization to form a white solid polycyanate ((CNCO)x). This reaction usually only occurs when a high concentration of urea accumulates on the surface of the catalyst and the rate of thermal decomposition or catalytic decomposition is slow. The decomposition of biuret is affected by temperature and increases with increasing temperature. The complete polymerization of urea is affected by the concentration of local urea and the concentration of biuret. The higher the concentration, the faster the polymerization. Therefore, when urea is used in the SCR method, when the temperature is low, the solid polymer covers the surface of the catalyst to cause the catalyst to fail. The decomposition of the cyanic acid polymer requires a higher temperature (usually greater than 450 ° C), and such high temperatures can damage the active site of the catalyst. When the temperature is low (below 180 °C), in order to avoid the urea polymerization reaction, the method of appropriately reducing the amount of urea is adopted. At this time, the amount of urea added must be changed with the change of temperature, and the addition of urea must also be based on the intake air. The NOx concentration and the residual NH3 in the gas are adjusted in time to avoid incomplete or harmful irritating ammonia leakage.

In addition to the above-mentioned urea and ammonia, as a reductant of NO _x also cyanate (isocyanic acid and cyanic acid, HOCN) and cyanuric acid (cyanuric acid). Cyanic acid is also a very active, unstable, and irritating gas (usually used as a tearing agent) at normal temperature and pressure, and it can form polymers relatively easily, so storage and transportation are difficult. The cyanic acid can be stabilized by being attached to the organic group or the surface of the molecule at normal temperature to form an organic cyanate or polymerized to cyanuric acid. U.S. Patent No. 5,342,599 teaches the adsorption of cyanic acid to the surface of adsorbent materials such as molecular sieves or zeolites, activated carbon, metal hydrides, ion exchange resins, etc. to stabilize cyanic acid, and then to analyze the adsorbed cyanide by heating. Acid; reducing pressure or using air and other carrier gases to carry cyanic acid can reduce the polymerization of cyanic acid. The use of adsorption-stabilized cyanic acid avoids the use of cyanuric acid as the original reducing agent, since cyanuric acid is solid at room temperature, requiring higher energy for gasification and decomposition. Cyanic acid can be directly prepared in advance with urea, and the cost is lower than that of cyanuric acid. This method can better adjust the amount of reducing agent, thereby avoiding excessive or insufficient addition.

U.S. Patent No. 4,861,567 teaches that a decomposition chamber (zone) can be set up to decompose cyanuric acid in the absence of oxygen and in the presence of fuel or CO and water to produce cyanic acid at a decomposition temperature of 700-1000 °C. The residence time in the decomposition chamber is between 0.03 and 2 seconds. The product cyanide enters the reaction chamber and reacts with NO under aerobic conditions to form N ₂ , CO ₂ and water. The reaction equation is as follows:

2HNCO + 2NO - O ₂ + 2N ₂ + 2CO ₂ + H ₂ O

This reaction also needs to be carried out at a higher temperature (1000-1500 ° C).

U.S. Patent No. 4,886,650 teaches the use of sublimed cyanuric acid or cyanuramide (ammelide and ammeline) to prepare a denitration reducing agent cyanide. The sublimation temperature is required to be above 300 ° C and at 350-800 ° C. best, transition metal elements consisting of the main catalyst will speed up the reduction of NO isocyanate reaction, a reduction reaction can be carried out at 400-800 ° C, catalyst to promote mainly related free radicals generated, so that the NO _x The reduction reaction becomes easy. Detailed cyanate of NO _x reduction reaction is as follows:

HNCO - H production

H + HNCO - NH ₂ + CO

_{_{NH 2 + NO --N 2 H +}} OH-- N 2 + H + OH - N 2 + H 2 O

N ₂ H - N ₂ + H

OH + CO - CO ₂ + H

It can be seen that the free radicals H and OH participate in the reaction. This method indicates that the addition of CO or its analogs, such as olefins and alkenes (olefins and alkenes), can lower the temperature of the reduction reaction, and their addition promotes the formation of free radicals H, thereby promoting the progress of the NO reduction reaction.

In the treatment of automobile exhaust, the above method cannot be used because the temperature is not high. U.S. Patent No 5,693,300 proposes a cyanate, NH _3, hydrazine (hydrazine, H _₂ NNH _2), or a mixture thereof and the catalyst bed and the contact portion generates active radicals _{NCO, NH 2, NH, H} , OH, NC or mixtures reduction NO _x, so that the reaction temperature can be greatly reduced. The catalyst used is generally a metal oxide. Since the catalyst is not in contact with the exhaust or flue gas, the service life of the catalyst can be extended. The dosage may be adjusted according to the added concentration of NO _x reducing agent is added to prevent excessive. Cyanic acid and ammonia can be prepared from urea, cyanuric acid, isocyanuric acid, ammelide, ammeline, guanidine, and the like. NO _x reduction temperature range from room temperature to approximately 1000 ° C, depending on the specific types of reactants may be.

U.S. Pat Pat No 5,120,516 proposes the reduction to the amine with an alkyl (alkyl amine) as the reducing agent to NO to N _2, which having both functions of the oxidizing agent can oxidize NO to NO _2, NO generated ₂ Remove by washing with water. This reduction reaction can be carried out at 350 to 400 ° C even without the action of a catalyst, which is much lower than the temperature required for reducing NO by a reducing agent such as urea and cyanuric acid under normal conditions.

In summary, there are many options for the preparation and addition techniques of the reducing agents required for existing SCR or SNCR, but all of them have such problems. Ammonia and low molecular weight isocyanate, which is directly used for the reduction reaction of NO _x, but their transportation and storage is difficult, and there is a large security risk, because of their irritating, direct harm to the environment, the use of If the leak occurs, it will have a greater impact on the residents living in the surrounding area. Solid reducing agents such as urea and cyanuric acid are stable at normal temperature and pressure. After heating, they can decompose to form reducing agents (such as ammonia and cyanic acid) required for NO reduction, but because they are solid, they are uniformly added. There are difficulties in metering and adjustment. Since in most gas phase reactions, the smaller the particles of the reactants, the easier the reaction is, and it is difficult to minimize the particles by directly adding solids. Another option is to dissolve the solids in a liquid to form a dilute solution and then spray it into the reaction so that the liquid volatilizes to form small solid particles. However, the liquid volatilization will inevitably take away a part of the heat, resulting in a large waste of energy. When using the SNCR method of urea in coal-fired power plants, the energy carried away by evaporation of water may be as high as 1% of the amount of electricity generated.

A further option is to decompose urea and cyanuric acid into ammonia or cyanic acid in the field and then put it into the reduction reaction. Due to the complete decomposition of urea and cyanuric acid, about 180 °C and 450 °C are needed. Above the high temperature, therefore, the reaction requires higher energy; in order to prevent the polymerization of cyanic acid, the reaction must be carried out under a lower pressure or a larger amount of carrier gas (to reduce the partial pressure), which is bound to cause no operation small trouble, particularly when used in automobile exhaust emission control NO _x, since the low exhaust gas temperatures, often requires strict control of the addition of urea.

A further development is the use of a metal catalyst to cause all or part of ammonia and cyanic acid to become free radically active particles and NO as proposed by US Pat. No. 5,693,300 and US Pat No. 4,886,650. _x carries out the reaction, so that the required reduction reaction temperature can be greatly reduced. However, this method requires the use of a precious metal catalyst, and the use cost is high, and the reaction conditions of the solid catalyst bed are difficult to adjust, and the reaction quality is difficult to carry out. control.

technical problem

The application of the present invention is to provide a denitration method for flue gas and exhaust gas which is more safe and reliable in operation and low in operating cost, especially in the present in the above-mentioned deficiencies in the treatment of exhaust gas such as flue gas exhaust gas. A method of preparing and adding a reducing agent used in the SCR method and the SNCR method and an apparatus therefor.

Technical solution

The object of the present invention is to provide a novel denitration reducing agent preparation and addition method and a denitration process, the core of which is to utilize a non-equilibrium plasma (non-equilibrium) Plasma) or non-thermal plasma The plasma generation and reaction apparatus prepares an active material which can be used for reducing NO from a nitrogen-containing solid material such as urea or cyanuric acid to promote the occurrence and occurrence efficiency of the reaction.

Non-thermal plasma is also called non-completed plasma (non-completed plasma) Plasma) or atmospheric non-thermal plasma Plasma), the electrons contained in this plasma usually have an electron temperature of about 1 ev, but the apparent temperature of the plasma is only a few hundred degrees Celsius or even room temperature. Under this condition, various particles in the plasma did not collide sufficiently, and the temperatures of the various particles were not equal, and the heat balance was not reached. Through this plasma reactor, the solid reducing agent (to distinguish the more direct gas reducing agents such as ammonia and cyanic acid, which we call them as reducing agent precursors) can be quickly gasified and made into all or part of Decomposition, ionization, activation and activation are more effectively used for the reduction reaction of NO. With the present invention, it is possible to flexibly prepare a highly reactive reducing gas for exhaust gas denitration without using an expensive catalyst.

The present application provides a method of denitration of exhaust gases produced by the combustion system, the method is prepared by using a plasma reaction apparatus capable of reducing free radical activity of NO _x and other activation molecules intensified, then prepared and the activity of free radicals other activating molecule into the intensification of NO _x containing exhaust gas passage, in the presence of a catalyst or a temperature of the NO _x is reduced to N ₂ and CO ₂ gas and water harmless.

Specifically, the denitration method is to bring a reducing agent into a reaction zone after an electrode region or an electrode region in a plasma reaction vessel, in which a reducing agent and a plasma collide and exchange energy, thereby being gasified. , and wholly or partially converted to an active radical or intensify activated molecules, this mixed gas (referred to as reductive plasma) is introduced into the NO _x containing exhaust gas passage, and together with the exhaust gas enters the reduction reaction chamber, the catalyst (SCR method), or under the action of high temperature (SNCR process) reducing the NO _x to N ₂ and CO ₂ gas and water harmless, the treated gas is discharged by the apparatus subsequent emissions.

Although the invention is mainly directed to the use of a solid reducing agent or a reducing agent precursor, it can also be used for the treatment of a reducing agent such as ammonia, cyanic acid, isocyanic acid or an alkylamine gas reducing agent which is a gas at normal temperature. these gaseous reducing agent through a plasma of the present invention will become more lively post-treatment of the reaction apparatus so that they react with the NO _x more easily.

The solid reducing agent includes urea, biuret, cyanuric acid, ammelide, ammeline, melamine, hydrazine. Solid compounds containing amino or cyanate which, upon heating, produce ammonia and/or cyanide.

The reaction time for the plasma reduction of the solid reducing agent is 0.01 to 5 seconds.

The temperature required for the plasmaization of the solid or gaseous reducing agent is from room temperature to 1200 °C.

The types of active radicals include NCO, NC, NH ₂ , NH, N, OH, H, and mixtures thereof; the activated activation molecules involved include NH ₃ , HNCO, CO, H ₂ O, H ₂ and their mixture.

Said The plasma reaction device is composed of a reaction vessel, a carrier gas inlet system, positive and negative electrodes, a power source and a solid feeding system. The power source supplies power to the reaction device, and the positive and negative electrodes are disposed in the reaction vessel, and the solid feeding system and the carrier gas enter The gas system is connected, and the body carrier gas inlet system is in communication with the reaction vessel, wherein

1. The reaction vessel is a place for energy exchange and reaction between electrons, plasma and a solid reducing agent to be gasified;

2, The carrier gas inlet system includes a plasma carrier gas system for providing a plasma gas source for the reaction vessel and an auxiliary carrier gas system for providing a carrier for carrying the solid reducing agent into the reaction vessel, and the plasma carrier gas system can also serve as an auxiliary carrier gas system. At this time, the plasma carrier gas system and the auxiliary carrier gas system are combined into one;

3, The positive and negative electrodes provide an electric field for the plasma reactor, and generate a high-voltage discharge in the electric field. The positive and negative electrodes are placed above or below the reactor or at any position in the middle. The electrodes should be placed to ensure that all or most of the plasma carrier gas passes. The space between the electrodes forms a plasma in the electrode region and after passing through the electrode region.

Said The reaction vessel is generally machined from glass, ceramic, engineering plastics, stainless steel or other materials and may take any shape, but preferably cylindrical or cuboid.

Said The inlet of the plasma carrier gas system is generally disposed on the side wall or the upper and lower bottom of the reaction vessel, or is introduced into any position inside the reaction vessel by a conduit, and the inlet port may be single or multiple, and the auxiliary carrier gas system is usually advanced. The components of the material system are used in conjunction with the solids feed system.

The positive and negative electrodes may be a single pair of electrodes or an electrode module composed of a plurality of pairs of electrodes, and the positive and negative electrodes are respectively connected to the two poles of the high voltage power source, and a voltage of 3 kV to 120 kV is generated between the electrodes; The power supply provides high-voltage direct current, high-voltage pulsed direct current, or alternating current to the plasma reaction device. It generally uses a conventional alternating current power supply (90-240 volts) to convert the conventional power supply into a required power supply through a variable voltage frequency modulation circuit; the solid feeding device provides The metering and delivery of the solid feed, typically at the top or side of the reactor, allows the solids to be uniformly added to the reactor and exchange energy with the electrons or high energy plasma generated between the electrodes to be decomposed.

Regardless of the electrode and discharge pattern, the energy (electron temperature) of the free electrons formed in the electrode region is in the range of 0.9-10 eV, and the electron density is between 10 ^{6 and} 10 ¹⁸ /cm ³ . The plasma carrier gas partially becomes a plasma under the action of such electrons, and when the solid combustion additive is added to the electrode region or the electrode region in the reaction device, the plasma reaction region collides with the plasma generated by the plasma carrier gas and exchanges energy. , causing them to vaporize, decompose, become or partially become charged ions or inactivated activated molecules, and the gasification/ionization/intensification activated reducing agent component (this mixed gas in the present invention is called a reducing plasma) is It is introduced into the reduction reaction chamber (zone) to reduction reaction with NO _x.

The plasma carrier gas may be air, or nitrogen, or water vapor, or hydrogen, or argon, or helium, or flue gas exhaust, any gas that facilitates the formation of a reducing plasma. The type of gas that can be used as an auxiliary carrier gas is the same as the plasma carrier gas.

The form of high voltage discharge between electrodes may be a sliding arc discharge (gliding arc) Discharge), corona discharge, or dielectric barrier discharge Discharge and other forms of discharge.

The arrangement of the electrodes and the gas flow of the plasma carrier gas can be designed as a plasma torch (plasma) Torch), plasma shower, plasma nozzle, tubular or plate plasma generator.

The reaction time of the solid reducing agent plasmaization varies with the type of the solid reducing agent, the moisture content of the reducing agent, etc., generally between 0.01 and 5 seconds. If the reaction time is too long, energy is wasted and the generated plasma may be caused. The body is quenched and loses its activity. Of course, if the time is too short, the energy absorption is insufficient, which may result in insufficient plasmaization. The optimum plasma reaction time should be determined by on-site testing.

The temperature required for the plasma reduction of the solid reducing agent is also determined by the type of the solid reducing agent. The desired reaction temperature can be obtained by controlling the power of the plasma generating device and the flow rate of the carrier gas. The apparent temperature of the general plasma needs to be 100. Above °C, there is no special limit to the upper limit of temperature. Only when air or flue gas containing oxygen is used as the carrier gas, the temperature must be controlled below the ignition point of the reducing agent to avoid burning when using air or containing oxygen. when the flue gas as the carrier gas temperature can not exceed 1200 ° C in order to avoid additional oxidation of the nitrogen gas generated NO _x.

The choice of the high-pressure discharge mode of the plasma reactor is not decisive for the preparation of the reducing plasma. The reaction efficiency of the different discharge modes will be slightly different. The key is the regulation of the current and voltage, its frequency and power, and the carrier gas. determining selection of the type and flow control parameters shall be subject to a plasma and to maintain high reducing ability of NO _x in the reaction product. The reductant treatment capacity of the plasmalization reactor is fundamentally dependent on the balance between the energy required to plasma the reductant and the energy that the electrode can provide. The optimum values for the selected reducing agent and its selected plasma discharge mode, the voltage frequency and its power required for operation, and the type and flow rate of the carrier gas must be determined by field testing.

The plasma reactor is also designed as an open system without a reaction vessel. In the open plasma reaction system, the reducing agent precursor and the plasma derived from the plasma carrier gas are in the open space behind the electrode region and the electrode. the reaction occurs, reducing the plasma gas generated by the reaction is mixed with the rapidly approaching NO _x in the molecule and react. Thus, open plasma reaction apparatus suitable for the case of fast reaction before reducing plasma body, and often the reaction unit is provided in the passage of exhaust gas containing NO or the NO _x reduction reaction.

Beneficial effect

The denitration method for the exhaust gas generated by the combustion system described in the application of the present invention has the following advantages:

1, Compared with the conventional flue gas tail gas reduction denitration technology, the fundamental difference is that high pressure discharge is used to promote the generation of reducing plasma, and the plasma can be generated by the solid reducing agent and the carrier gas. The flow rate and current power are adjusted flexibly, so that the dosing of the reducing agent can be changed correspondingly as the flow rate of the gas to be treated and the NOx concentration change. This can avoid excessive addition of reducing agent, thereby greatly reducing the amount of solid reducing agent and reducing the risk of leakage of reducing agent components;

2, Since the reducing plasma retains the reducing characteristics of the basic gas reducing agent and is in an ionized or other excited activation state, it is more likely to react with the NOx of the gas, thereby lowering the temperature required for the reduction reaction and shortening the reaction. time. This allows the reduction process to be carried out over a wider temperature range. The reaction efficiency of the reaction device can be increased, the residence time can be lowered, or the treatment effect can be improved;

3, Since the plasma reaction device can directly treat the solid reducing agent and the produced product is a plasma gas, it is possible to avoid using a large amount of water to dissolve the solid reducing agent, thereby saving the energy consumption caused thereby;

4, By using the reducing agent plasma reaction device of the present invention, it is not necessary to use a catalyst, so that the cost caused by the use of the catalyst can be reduced on the one hand, and the single disadvantage of the catalytic reaction of the catalyst can be eliminated, so that the reducing agent can be selected more flexibly.

DRAWINGS

1 is a block diagram showing the process flow of an embodiment of the present application;

Figure 2 is a block diagram showing the process flow of another embodiment of the present application;

Figure 3 is a block diagram showing the process flow of still another embodiment of the present application.

Embodiments of the invention

The method and apparatus for denitration of exhaust gas generated by a combustion system described in the application of the present invention will be described below with reference to the accompanying drawings, in order to better understand the technical content of the present application, and not to the technical content. Limitations, in fact, improvements to the methods and apparatus within the spirit of the innovation of the present application, including the same or similar structures and processes, conditions, are generally available to those of ordinary skill in the art without the Therefore, they are all within the technical solution claimed in the application of the present invention.

Example 1

As shown in Figure 1, a solids feed system is used to add a solid reducing agent to the auxiliary carrier gas system, and the carrier gas system is used to bring the solid reducing agent into the electrode zone or the reaction zone behind the electrode zone in the plasma reaction vessel. The region, the solid reducing agent and the plasma from the plasma carrier gas system collide and exchange energy, thereby being vaporized and converted into plasma or excited activated molecules in whole or in part, and the reducing plasma is introduced into the The exhaust passage of NOx enters the reduction reaction chamber together with the exhaust gas, and reduces NOx to a harmless gas such as N2 and CO2 and water under the action of a catalyst (SCR method) or a certain temperature (SNCR method), the treated gas Discharged through subsequent discharge devices.

Example 2

As shown in Figure 2, a solids reductant is added directly to the plasma carrier gas system using a solids feed system that carries the solid reductant into the electrode zone within the plasma reaction vessel or the reaction zone behind the electrode. The subsequent steps are the same as in the first embodiment.

Example 3

As shown in Fig. 3, an open plasma reactor is used, and the plasma reaction device is placed in the exhaust gas passage, and the generated reducing plasma is rapidly contacted with the exhaust gas. Such a process arrangement is particularly suitable for a plasma nozzle, a plasma shower. The application of plasma devices such as plasma torches. In such an arrangement, once the plasma is generated, it can quickly enter the reduction reaction, avoiding the quenching of the plasma and quenching. The subsequent steps are the same as in the first embodiment.

Example 4

Solid urea is used as the reducing agent precursor; the plasma reaction device uses the plasma torch; air is used as the carrier carrier gas and the auxiliary carrier gas, the flow rate of the plasma carrier gas is 60 liters/min, and the flow rate of the auxiliary carrier gas is 10 liters/ The power supply adopts a DC variable frequency power supply with a voltage of 10,000 volts and a frequency of 120 Hz, and the rated power is 600 watts. The plasma carrier gas passes through the electrode region between the positive and negative electrodes, and is plasmad under the action of an electric field. The solid urea particles are transported to the outlet of the positive and negative electrode regions through a special intake passage under the aid of the carrier gas. Where it is mixed with the plasma carrier gas passing through the electrode region, and energy exchange occurs; under the action of electrons and plasma, the solid urea is vaporized and completely or partially ionized, and the mixed plasma is formed from The outlet is ejected and a plasma flame is formed; in the plasma flame, the urea gas and other plasma gases continue to react to form a reducing plasma gas; the gas is introduced into the flue to a temperature of 600 - Reduction reaction with NO at 1100 °C. The plasma reaction device processes more than 1 kg of solid urea per hour, and the generated plasma gas can treat the flue gas 3000. In cubic meters, the concentration of NOx is reduced from 700 ppmv to 300 ppmv.

Example 5

The plasma reaction device adopts a sliding arc discharge design, and the power supply adopts a voltage of 100,000 volts and a frequency of 120. Hertz, a pulsed DC power supply with a power of 20 kW. Both the plasma carrier gas and the auxiliary carrier gas are air, the flow rates of the carrier gas and the auxiliary carrier gas are 120 and 20 cubic meters per hour, the reaction stop time is 4 seconds, and the urea gas is processed 40 kg per hour. The anterior section of the SCR treatment unit that is introduced into the flue is mixed with NOx in the flue gas, and is reduced in reaction with NOx by the reduction catalyst in the SCR treatment unit. The system can process 120,000 cubic meters of coal-fired flue gas per hour, which is equivalent to the amount of flue gas generated by a 30 MW coal-fired generating unit. The concentration of NOx after treatment can reach below 100 ppmv.

Claims

A method for denitration of exhaust gas generated by a combustion system, characterized in that: the method comprises: preparing a reactive radical and other activated intensifying molecules capable of reducing NOx by using a plasma reaction device, and then preparing the active radicals and other The activated excited molecules are introduced into the NOx-containing exhaust gas passage, and the NOx is reduced to a harmless gas such as N2 and CO2 and water under the action of a catalyst or a high temperature.
The denitration method according to claim 1, wherein the method comprises introducing a reducing agent into an electrode region in the plasma reaction device or a reaction region behind the electrode region, wherein the reducing agent collides with the plasma in the region. Exchange with energy to be vaporized and converted, in whole or in part, into active radicals or inactivated activated molecules. This mixed gas is introduced into the NOx-containing exhaust gas passage and enters the reduction reaction chamber together with the exhaust gas. The NOx is reduced to a harmless gas such as N2 and CO2 and water under high temperature, and the treated gas is discharged through a subsequent discharge device.
The denitration method according to claim 2, wherein the reducing agent comprises a solid reducing agent at normal temperature or a gas reducing agent which is a gas at normal temperature.
The denitration method according to claim 3, characterized in that the reaction time for the plasma reduction of the solid reducing agent is 0.01 to 5 seconds.
The denitration method according to claim 3, characterized in that the temperature required for the plasmaization of the solid or gaseous reducing agent is from room temperature to 1200 °C.
The denitration method according to claim 3, wherein the solid reducing agent comprises urea, biuret, cyanuric acid, cyanuric acid monoamide, cyanuric acid diamide, melamine or hydrazine. A solid compound containing an amino group or a cyanate group.
The denitration method according to claim 3, wherein the gas reducing agent comprises ammonia gas, cyanic acid, isocyanic acid or an alkylamine gas reducing agent.
The denitration method according to claim 2, wherein the living radicals comprise NCO, NC, NH2, NH, N, OH, H, and mixtures thereof.
The denitration method according to claim 2, wherein said activation-exciting molecules comprise NH3, HNCO, CO, H2O, H2, and mixtures thereof.
A plasma reaction apparatus for denitration of an exhaust gas generated by a combustion system according to claim 1, wherein the reaction apparatus comprises a reaction vessel, a carrier gas intake system, a positive and negative electrode, a power source, and a solid feeding system. The power supply is powered by the reaction device, the positive and negative electrodes are disposed in the reaction vessel, the solid feed system is in communication with the carrier gas intake system, and the carrier gas intake system is in communication with the reaction vessel, wherein

1) where the reaction vessel is an energy exchange and reaction between the electron, the plasma and the solid reducing agent to be gasified;

2) The carrier gas inlet system includes a plasma carrier gas system for providing a plasma gas source for the reaction vessel and an auxiliary carrier gas system for providing a carrier for carrying the solid reducing agent into the reaction vessel, and the plasma carrier gas system can also serve as an auxiliary carrier gas system. At this time, the plasma carrier gas system and the auxiliary carrier gas system are combined into one;

3) The positive and negative electrodes provide an electric field for the plasma reaction device, and generate a high-voltage discharge in the electric field. The positive and negative electrodes are disposed above or below or in the middle of the reactor, and the placement of the electrodes ensures that all or most of the plasma carrier gas passes through the electrodes. A space is formed between the electrode region and the electrode region to form a plasma.
The plasma reactor according to claim 10, wherein the inlet of the plasma carrier gas system is disposed at a side wall or a bottom and bottom of the reaction vessel, or is introduced into the reaction vessel at any position inside the reaction vessel.
The plasma reaction apparatus according to claim 10, wherein the positive and negative electrodes are electrode modules composed of a single pair of electrodes or a plurality of pairs of electrodes, and the positive and negative electrodes are respectively connected to the two poles of the high voltage power source, and the electrodes are A voltage of 3 kV to 120 kV is generated.
The plasma reactor according to claim 10, wherein the plasma carrier gas in the carrier gas intake system and the gas supporting the carrier gas include air, nitrogen, water vapor, hydrogen, argon, helium. Gas, power plant flue gas or car exhaust.
A plasma reactor according to claim 10, wherein said form of high voltage discharge between positive and negative electrodes comprises a sliding arc discharge, a corona discharge or a dielectric barrier discharge.
A plasma reactor according to claim 10, wherein said arrangement of positive and negative electrodes and arrangement of gas flow of plasma carrier gas comprises plasma torch, plasma spray, plasma nozzle or tubular or plate Plasma generator.
The plasma reactor according to claim 10, wherein the material of the reaction vessel comprises glass, ceramic, engineering plastic or stainless steel.
A plasma reactor according to claim 10, wherein said reaction vessel has a shape including a cylinder or a rectangular parallelepiped.