Method and system for regulating and removing form of nitric oxide in combustion flue gas

Abstract

The invention belongs to the field of pollutant removal, and particularly discloses a method and system for regulating and removing the form of nitric oxide in combustion flue gas, and the method comprises the following steps: the combustion flue gas is sequentially introduced into a dust remover, a cascade cooling tower and a low-temperature adsorption tower; part of flue gas is extracted from an outlet of a dust remover, is cooled by a gas-gas heat exchanger, is mixed with main flue gas at an outlet of a cascade cooling tower, and enters a low-temperature adsorption tower together with the main flue gas; nO2 and N2O are converted into NO in the low-temperature adsorption tower, and then the NO is subjected to low-temperature oxidation, adsorption and removal; and finally, the purified flue gas is heated through a gas-gas heat exchanger and then is emptied. The method can avoid consumption of a catalyst and noble metal elements, realizes form regulation and removal of nitrogen oxides in combustion flue gas, and has the advantages of low cost, high removal rate, wide application range, no environmental safety risk and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of pollutant removal, and relates to a method and system for regulating the morphology and removing nitrogen oxides in combustion flue gas. Background Art

[0002] Nitrogen oxides (NO x , mainly including NO, NO2, and N2O) are a type of gaseous pollutant that causes great harm to the environment and can lead to serious consequences such as photochemical smog, acid rain, and the greenhouse effect. Controlling nitrogen oxide emissions is crucial for protecting the environment and human health.

[0003] Combustion is one of the main sources of nitrogen oxides in the environment and is involved in various large-scale power, thermal, and chemical combustion production equipment. The formation of nitrogen oxides mainly stems from three mechanisms: thermal, fuel, and prompt. The control methods can be mainly divided into in-furnace control and tail-end treatment. In a high-temperature furnace, by optimizing the thermal conversion conditions, such as adjusting the excess air coefficient, thermal conversion temperature, staged thermal conversion, and optimizing the burner design, etc., the generation of NO x can be reduced to a certain extent, but the control effect is limited. Tail-end treatment refers to removing the NO x that has already been generated in the flue gas, and using means such as adsorption, absorption, and reduction to reduce the NO x concentration in the flue gas. Currently, the mainstream technology for combustion flue gas is selective catalytic reduction (SCR), that is, under the action of a catalyst, using a reducing agent (such as ammonia) to reduce NO and NO2 to harmless nitrogen and water, with good removal effect, but it is necessary to control the ammonia slip problem, and the catalyst cost is high. Since the temperature of combustion equipment is usually above 1000°C, the nitrogen oxides generated are mainly NO and NO2, and the control problem of N2O is often overlooked. With the application of multiple fuels (such as biomass, sludge, etc.) and the development of new furnace types (grate furnaces, fluidized beds, etc.), the generation amount of N2O increases greatly in some low-temperature combustion scenarios, and the control problem of N2O also needs to be concerned.

[0004] In the existing technologies for controlling nitrogen oxide emissions in combustion flue gas, they mainly include: (1) CN114832807A discloses an SCR denitration catalyst and its preparation method. Using TiO2 powder as the carrier and vanadium as the catalytically active substance, it solves the problem of vanadium waste in the middle part of the existing SCR denitration catalyst carrier and improves the NO removal efficiency. However, in this method, the catalyst is prone to poisoning and deactivation in complex flue gas, has a short service life, and vanadium is a highly toxic element, and the deactivated catalyst is hazardous waste, causing secondary environmental pollution; (2) CN119368159A discloses an anti-alkali metal, water, and sulfur composite poisoning denitration catalyst and its preparation method and application. Using cerium oxide, manganese oxide, and tungsten oxide as the active components, a cerium-manganese-tungsten composite oxide active component with a porous structure and strong acidity is prepared, which has a high NO removal rate and excellent anti-composite poisoning stability. However, this method requires the consumption of precious metal elements such as cerium, manganese, and tungsten, has a high cost, and requires additional spraying of ammonia as a reducing agent, with additional risks such as ammonia slip; (3) CN116493018A discloses a composite oxide catalyst for catalytic decomposition of high-concentration N2O and its preparation method. By dissolving, mixing, aging, precipitating, drying, and calcining Ni, Nb, Co, alkali metal / alkaline earth metal-based salts, a composite catalyst is obtained. However, this method requires a large amount of consumption of precious metal elements such as Nb, Co, and Ni, has a complex process flow, and is costly.

[0005] Through research, it is found that the existing technologies for controlling nitrogen oxide emissions in combustion flue gas mainly have the following problems: (1) The catalyst is prone to poisoning and deactivation during long-term operation and has a short service life; (2) A large amount of precious metal elements are required for modification, resulting in a high cost; (3) There are secondary environmental problems such as ammonia slip and difficult treatment of highly toxic catalysts. Summary of the Invention

[0006] Aiming at the problems existing in the prior art, the purpose of the present invention is to provide a method and system for regulating the morphology and removing nitrogen oxides in combustion flue gas, aiming to solve the problems such as the need to consume a large amount of catalysts and precious metal elements in the existing nitrogen oxide control, high cost, and secondary environmental risks.

[0007] The present invention is realized through the following technical solutions: A method for regulating the morphology and removing nitrogen oxides in combustion flue gas, comprising the following steps: S1, passing the original combustion flue gas into a dust collector, and after dust removal, dividing it into Route A flue gas and Route B flue gas; S2, passing Route A flue gas into a cascade cooling tower to cool Route A flue gas to the target temperature and simultaneously achieve the absorption and removal of NO2 in Route A flue gas; S3, passing Route B flue gas into the tube side of a gas-gas heat exchanger to cool Route B flue gas; S4. Mix the flue gas of path A that has reached the target temperature with the cooled flue gas of path B and then introduce it into the low-temperature adsorption tower, so that N2O in the flue gas of path A is oxidized by NO2 in the flue gas of path B to form NO, and together with the original NO in the flue gas, it is oxidized and adsorbed by the adsorbent in the low-temperature adsorption tower, realizing the efficient removal of N2O, NO and NO2 in the flue gas; S5. Pass the flue gas purified by the low-temperature adsorption tower in S4 through the shell side of the gas-gas heat exchanger to heat up the flue gas and then discharge it.

[0008] Preferably, in S1, an induced draft fan and a flow control valve are arranged on the flue of the flue gas of path B to control the volume flow ratio of the flue gas of path A to the flue gas of path B to be 4:1 - 49:1.

[0009] Preferably, in S3, a high-voltage ionization device is arranged at the tube side outlet of the gas-gas heat exchanger for ionizing NO2 to form strongly oxidizing O radicals. When the concentration ratio of NO2 to N2O in the original combustion flue gas < 5, the high-voltage ionization device is turned on, and the concentration of the generated O radicals is preferably 5 - 100 mg / m 3 .

[0010] Preferably, a first on-line flue gas component detection device is installed at the outlet of the dust collector to obtain the concentration of nitrogen oxides in the original flue gas and transmit it to the centralized control unit. The centralized control unit calculates the optimal distribution ratio of the flue gas of paths A / B and adjusts the induced draft fan, flow control valve and high-voltage ionization device of path B in real time; A second on-line flue gas component detection device is arranged at the shell side outlet of the gas-gas heat exchanger to monitor the concentration of nitrogen oxides in the purified flue gas and transmit it to the centralized control unit.

[0011] Preferably, in S2, the cascade cooling tower adopts 1 - 3 stages of direct spray cooling, and the coolant in the cascade cooling tower is one or several of water, inorganic salt solution and organic solution.

[0012] Preferably, the target temperature in S2 is -40~10°C, preferably -20~0°C.

[0013] Preferably, in S3, a condensate water collection bypass is arranged on the inner side of the tube of the gas-gas heat exchanger, and the collected condensate water is drained into the cascade cooling tower.

[0014] Preferably, in S3, a corrosion-resistant protective layer is arranged on the inner side of the tube of the gas-gas heat exchanger, and the material is one of fiberglass, glass flake and vinyl resin.

[0015] Preferably, in S4, 3 - 5 layers of adsorbents are filled in the low-temperature adsorption tower; the types of the adsorbents are one or several of coal-based activated carbon, fruit shell activated carbon, wood activated carbon and coconut shell activated carbon, and the specific surface area of the adsorbent is 500 - 2000m2 / g, and the average particle size of the adsorbent is 1 - 30 mm.

[0016] A system for regulating the form and removing nitrogen oxides in combustion flue gas, comprising a dust collector, a cascade cooling tower, a low-temperature adsorption tower, and a gas-gas heat exchanger; The inlet of the dust collector into which the raw flue gas is introduced. The outlet of the dust collector is divided into a flue A and a flue B. Among them, flue A is successively connected to the inlet of the shell side of the cascade cooling tower, the low-temperature adsorption tower, and the gas-gas heat exchanger. Flue B is connected to the inlet of the tube side of the gas-gas heat exchanger. The outlet of the shell side of the gas-gas heat exchanger is connected to the chimney.

[0017] Compared with the prior art, the present invention has the following beneficial technical effects: The present invention proposes a method for regulating the form and removing nitrogen oxides (NO / NO2 / N2O) in combustion flue gas. By setting steps such as flue gas diversion, flue gas temperature regulation, low-temperature oxidation, and enhanced adsorption, N2O is converted into NO by the oxidizing property of NO2 and then efficiently removed in the low-temperature adsorption tower without consuming conventional denitration catalysts, precious metal adsorbents and other materials, realizing the integrated removal of various nitrogen oxides. By setting the flue gas diversion step in the present invention, part of the flue gas is cooled by an indirect heat exchange method, and the oxidizing substance NO2 in the flue gas is retained, realizing the oxidation and further adsorption and removal of N2O without additional input of oxidants, reducing the overall cost of the system.

[0018] Furthermore, the present invention generates the oxidizing substance active O free radicals by setting a high-voltage ionization device, which can cope with the situation of relatively insufficient NO2 content in the combustion flue gas and broaden the applicable conditions of the method. Furthermore, the present invention sets up a nitrogen oxide concentration feedback regulation mechanism. According to the types and concentrations of nitrogen oxides in the raw flue gas, the operation states of the flue gas diversion and the high-voltage ionization device are optimized in real time to achieve the best ratio of NO2 / O oxidant to N2O, ensure the efficient removal of N2O, and reduce the operation cost of the system. Furthermore, by cooling the flue gas to -40 - 10 °C in the present invention, the water vapor in the flue gas can be condensed, separated and recovered, and at the same time, the moisture content of the flue gas in the low-temperature adsorption tower is reduced, avoiding the competitive interference of water vapor on the nitrogen oxide adsorption process and further improving the removal efficiency of pollutants in the low-temperature adsorption tower. Description of the Drawings

[0019] Figure 1It is a schematic diagram provided by a preferred embodiment of the present invention. Among them, 1-5 are flue gas purification devices: 1-dust collector, 2-step cooling tower, 3-low-temperature adsorption tower, 4-gas-gas heat exchanger, 5-chimney; 6 is a high-voltage ionization device, 7 is a first on-line flue gas component detection device, 8 is a second on-line flue gas component detection device, and 9 is a centralized control unit. Detailed implementation manners

[0020] The following further elaborates on the present invention in detail with specific embodiments, which is an explanation rather than a limitation of the present invention.

[0021] In order to enable those skilled in the art to better understand the solution of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0022] The embodiment of the present invention provides a method for regulating and removing the form of nitrogen oxides in combustion flue gas, and the method includes the following steps: S1. Introduce the original combustion flue gas into the dust collector. After dust removal, it is divided into flue gas A and flue gas B. S2. Introduce flue gas A into the step cooling tower to cool flue gas A to the target temperature, and at the same time realize the absorption and removal of NO2 in flue gas A. S3. Introduce flue gas B into the tube side of the gas-gas heat exchanger to cool flue gas B. S4. Mix the flue gas A that has reached the target temperature with the cooled flue gas B and then introduce it into the low-temperature adsorption tower, so that N2O in flue gas A is oxidized by NO2 in flue gas B to form NO, and together with the original NO in the flue gas, it is oxidized and adsorbed by the adsorbent in the low-temperature adsorption tower, realizing the efficient removal of N2O, NO, and NO2 in the flue gas. S5. Pass the flue gas purified by the low-temperature adsorption tower in S4 through the shell side of the gas-gas heat exchanger to heat up the flue gas and then discharge it.

[0023] Specifically, in step S1, first remove the dust pollutants in the original combustion flue gas through the dust collector to prevent dust from entering the subsequent step cooling tower and low-temperature adsorption tower. If dust enters the step cooling tower, it will be trapped by the sprayed coolant, affecting the purity of the coolant and subsequent recycling. If dust enters the low-temperature adsorption tower, it will block the pore structure of the adsorbent, increase the wear and tear of the adsorbent, resulting in a decrease in the purification efficiency of the low-temperature adsorption tower and an increase in the operating cost. By removing the dust in the original combustion flue gas through the dust collector, the adverse effects of dust on the removal of nitrogen oxides are avoided.

[0024] A flue gas diversion is set in the flue after the dust collector to divide the flue gas into Route A and Route B. Among them, the flue gas in Route A is the main flue gas, which successively enters the cascade cooling tower and the low-temperature adsorption tower. A multi-stage spray layer is set in the cooling tower, and the flue gas in Route A is cooled by the direct contact heat exchange between the liquid droplets and the flue gas. At the same time, NO2 in the flue gas in Route A is soluble in water and is absorbed and removed by the spray droplets. The main reaction formula is as follows: NO2 + H2O → HNO3 (1) The flue gas in Route A after cooling and removing NO2 is introduced into the inlet of the low-temperature adsorption tower.

[0025] On the other hand, the flue gas in Route B is the bypass flue gas. After being extracted from the outlet flue of the dust collector, it directly enters the tube side of the gas-gas heat exchanger and is cooled by the indirect heat exchange method. Then it is introduced into the inlet of the low-temperature adsorption tower. A high-voltage ionization device is arranged on the flue between the outlet of the tube side of the gas-gas heat exchanger and the inlet of the low-temperature adsorption tower.

[0026] The flue gas in Route A and the flue gas in Route B converge at the inlet of the low-temperature adsorption tower to form a mixed flue gas, which enters the low-temperature adsorption tower together. Since the solubility of NO and N2O is low and they cannot be removed in the cascade cooling tower, the nitrogen oxides in the flue gas in Route A at the inlet of the low-temperature adsorption tower are mainly NO and N2O. The flue gas in Route B does not pass through the cascade cooling tower. In addition to NO and N2O, the nitrogen oxides it contains also include oxidizing NO2. In the low-temperature adsorption tower, N2O in the mixed flue gas and NO2 carried by the flue gas in Route B undergo an oxidation-reduction reaction under the catalysis of the adsorbent and are converted into NO. The reaction formula is as follows: N2O + NO2 3NO (2) Subsequently, NO is converted into nitrate through an oxidation-adsorption reaction on the surface of the adsorbent. The reaction formulas involved are as follows: 2NO + O2 2NO2 (3) 2NO2 + adsorbent + O2 → 2NO3 - (adsorbed state) (4) Among them, since reaction formula 3 is an exothermic reaction, the rate of reaction 3 is greatly increased under low-temperature conditions, so that NO is completely oxidized to form NO2 in the low-temperature adsorption tower, and then NO2 is adsorbed and removed by the adsorbent through reaction formula 4.

[0027] The outlet flue of the low-temperature adsorption tower is connected to the inlet flue of the shell side of the gas-gas heat exchanger. The purified flue gas (temperature about -20~0°C) after passing through the low-temperature adsorption tower enters the shell side of the gas-gas heat exchanger and exchanges heat indirectly with the high-temperature flue gas in Route B (temperature about 100~200°C), so that the temperature of the flue gas in Route B is reduced and the temperature of the purified flue gas is increased, realizing the recovery and utilization of the cold energy in the purified flue gas. After the flue gas in Route B is cooled, it enters the low-temperature adsorption tower to be mixed with the flue gas in Route A, which can avoid the problems of the increase in the temperature of the mixed flue gas and the deterioration of the removal efficiency caused by the high flue gas temperature.

[0028] Furthermore, in order to achieve the diversion of flue gas in Route A and Route B and accurately control the flow rate ratio of the flue gas in Route A and Route B, a induced draft fan and a flow control valve are arranged on the flue duct of Route B. By the combined use of the induced draft fan and the flow control valve, part of the flue gas is extracted from the flue duct behind the dust collector to form the flue gas in Route B, and the remaining flue gas in the flue duct is the flue gas in Route A. Usually, the concentration of NO2 in the combustion flue gas is higher than that of N2O. To ensure that the concentration ratio of NO2 to N2O in the low-temperature adsorption tower is within the optimal stoichiometric ratio range, that is, the amount of NO2 is slightly higher than that of N2O, so that N2O is completely reduced to NO and there is no large amount of NO2 remaining, it is necessary to reasonably allocate the volume ratio of the flue gas in Route A and Route B according to the concentrations of NO2 and N2O in the flue gas at the outlet of the dust collector. According to the applicant's experimental data and theoretical calculations, the volume flow ratio of the flue gas in Route A and Route B is selected to be 4:1 to 49:1. If the volume flow ratio is lower than this range, the proportion of the volume of the flue gas in Route B is too large, which will lead to an excessive amount of NO2 in the mixed flue gas. A large amount of NO2 is removed by the adsorbent, resulting in waste of the adsorbent. In addition, the excessive flue gas in Route B cannot be effectively cooled by the gas-gas heat exchanger, affecting the low-temperature working environment in the adsorption tower and causing a decrease in the NO x removal efficiency in the low-temperature adsorption tower. If the volume flow ratio is higher than this range, it will lead to insufficient NO2 in the mixed flue gas to completely oxidize N2O to form NO, resulting in a decrease in the N2O removal efficiency.

[0029] Furthermore, a high-voltage ionization device is arranged on the flue duct between the outlet of the tube side of the gas-gas heat exchanger and the inlet of the low-temperature adsorption tower. Under certain conditions, the concentration of N2O in the combustion flue gas is close to that of NO2, or even the concentration of N2O is higher than that of NO2. Only by setting the diversion of the flue gas in Route A / Route B cannot achieve the complete oxidation and efficient removal of N2O. For this condition, the high-voltage ionization device can be turned on to establish a local high-voltage electric field in the flue duct, and stimulate the self-ionization of NO2 and O2 in the flue gas in Route B to generate O free radicals with high oxidation activity. The O free radicals are mixed with the flue gas in Route A at the inlet of the low-temperature adsorption tower along with the flue gas in Route B, and then oxidize N2O in the mixed flue gas to form NO and remove it. According to the applicant's experimental data and theoretical calculations, when the concentration ratio of NO2 to N2O in the original combustion flue gas < 5, turning on the high-voltage ionization device can achieve the efficient oxidation and removal of N2O under a relatively high volume flow ratio of Route A / Route B. The chemical reaction equations involved in the above process are as follows: NO2 NO + O (5) O2 2O (6) N2O + O → 2NO (7) Furthermore, during the combustion process, fluctuations may occur in fuel components, combustion conditions, temperature, etc., resulting in changes in the types and contents of nitrogen oxides in the combustion flue gas. To ensure the stable and efficient removal of nitrogen oxides in the combustion flue gas, online flue gas composition detection devices are installed respectively in the flue after the dust collector and the outlet flue on the shell side of the gas-gas heat exchanger to obtain the concentrations of nitrogen oxides in the raw flue gas and the clean flue gas and transmit them to the centralized control unit. After calculation based on parameters such as the N2O concentration, NO2 concentration, NO concentration, O2 concentration, and temperature in the raw flue gas and the clean flue gas, the centralized control unit obtains the optimal distribution ratio of the two-way flue gas A / B, generates a feedback control signal to adjust the B-side induced draft fan, flow control valve, and high-voltage ionization device in real time, and then changes the ratio of N2O, NO2, and O free radicals in the low-temperature adsorption tower, realizing the dynamic and efficient removal of N2O and NO2 in the low-temperature adsorption tower.

[0030] Furthermore, in step S2, direct spraying and gas-liquid contact heat exchange methods are used in the cascade cooling tower to cool the A-side flue gas. Limited by the heat exchange rate, to reduce the A-side flue gas to the target temperature, according to the temperature, flow rate, and target temperature of the A-side flue gas, 1 to 3 spraying layers are arranged in the cooling tower to cool the A-side flue gas in stages. After being cooled by the cascade cooling tower, the A-side flue gas merges with the B-side flue gas and then enters the low-temperature adsorption tower. To achieve the efficient oxidation adsorption and removal effect of NO x in the low-temperature adsorption tower, the target temperature of the cascade cooling tower is -40 to 10°C. Considering the cooling energy consumption of the cascade cooling tower, the cost of the refrigeration medium, etc., the target temperature is preferably -20 to 0°C. According to the temperature reduction range of each stage of the cascade cooling tower, the coolant is one or several of water, inorganic salt solution, and organic solution. Among them, in the temperature reduction range of 200 to 5°C, water is preferably used as the coolant; in the temperature reduction range of 5 to -20°C, an inorganic salt solution is preferably used as the coolant; in the temperature reduction range of -20 to -40°C, an organic solution is preferably used as the coolant.

[0031] Furthermore, in step S4, an adsorption bed is arranged in the low-temperature adsorption tower. When the mixed flue gas flows through the adsorption bed layer, it contacts the adsorbent, and the above reaction formulas (2)-(4) occur on the surface of the adsorbent, realizing the oxidation of N2O to NO, the oxidation adsorption of NO, and the adsorption and removal of excess NO2. To ensure the full conversion and removal of nitrogen oxides in the low-temperature adsorption tower, multiple adsorption layers need to be arranged in the low-temperature adsorption tower. Considering the removal effect and operating cost comprehensively, the number of adsorbent layers is preferably 3 to 5 layers. The step of oxidizing N2O to NO can be accelerated by the catalytic action of elements such as alkali metals. The step of oxidizing and adsorbing NO can participate in the reaction with the surface active functional groups of the adsorbent to increase the NO oxidation rate. The adsorption step of NO2 is mainly controlled by the physical pore structure of the adsorbent. Considering the above factors comprehensively, the preferred adsorbent types are one or several of coal-based activated carbon, fruit shell activated carbon, wood activated carbon, and coconut shell activated carbon, and the specific surface area of the adsorbent is 500 to 2000m 2 / g, where coconut shell activated carbon has a well-developed physical pore structure, fruit shell activated carbon and wood activated carbon are rich in surface active groups, and coal-based activated carbon is rich in catalytic metal elements. Select a suitable activated carbon and activated carbon combination according to the pollutant components in the flue gas. In addition, the average particle size of the adsorbent is its macroscopic physical size, which determines the packing state of the adsorption bed in the adsorption tower and the gas-solid flow contact. If the average particle size is too large, the contact area between the flue gas and the adsorbent is limited, and a large amount of pollutants escape without reaching the adsorption reaction interface, resulting in a decrease in the efficiency of the adsorption tower; if the average particle size is too small, the packing density of the adsorption bed is high, the flow resistance of the flue gas increases, the energy consumption of the system operation increases, and the too small average particle size will cause secondary emissions of adsorbent dust with the air flow. In summary, the average particle size of the adsorbent is preferably 1-30 mm.

[0032] Further, in step S3, the flue gas in path B is cooled in the gas-gas heat exchanger, and the water vapor in the flue gas condenses and precipitates due to the decrease in saturation, forming liquid water. By setting a condensate collection bypass on the inner side of the gas-gas heat exchanger tube, the condensate is discharged in time to avoid blockage caused by the accumulation of condensate in the tube, and at the same time avoid the risk of insufficient NO2 oxidant in the low-temperature adsorption tower due to the contact and dissolution of NO2 in path B flue gas with the condensate. Further preferably, the collected condensate flows into the cascade cooling tower and is purified and impurity-removed to achieve water resource recycling.

[0033] Further, in step S3, since the flue gas in path B has not been purified by the cascade cooling tower, the acidic gases (such as SO2, HCl, etc.) contained in it will condense or absorb synchronously with the water vapor, resulting in acidic condensate. Long-term operation will cause corrosion and damage of the heat exchange tubes. Therefore, a corrosion-resistant protective layer is provided on the inner side of the gas-gas heat exchanger tube to prevent the acidic condensate from directly contacting and corroding the heat exchange tubes (usually made of metal). Considering the corrosion resistance, thermal conductivity and cost of the material comprehensively, the material of the corrosion-resistant protective layer is preferably one of fiberglass, glass flake, and vinyl resin.

[0034] Such as Figure 1As shown in the figure, the method for regulating the form and removing nitrogen oxides in flue gas provided by the present invention is applied to a certain flue gas purification process. The specific process is as follows: The flue gas generated by the upstream combustion equipment first passes through 1 - dust collector, 2 - cascade cooling tower, 3 - low-temperature adsorption tower, 4 - gas-gas heat exchanger (cold end), and then is discharged from 5 - chimney. Among them, a bypass flue is provided between 1 - dust collector and 2 - cascade cooling tower. Part of the flue gas is extracted and sent to 4 - gas-gas heat exchanger (hot end) and 3 - low-temperature adsorption tower in sequence, and then is discharged from 5 - chimney. A 6 - high-voltage ionization device is arranged in the flue between 4 - gas-gas heat exchanger (hot end) and 3 - low-temperature adsorption tower. The nitrogen oxides in the combustion flue gas include NO2, NO, and N2O. Among them, NO is mainly removed in the 3 - low-temperature adsorption tower. Part of NO2 is removed in the 2 - cascade cooling tower, and the other part reacts with N2O in the 3 - low-temperature adsorption tower to form NO and then is removed. When the NO2 in the 3 - low-temperature adsorption tower is insufficient, additional O radicals are generated through the 6 - high-voltage ionization device to oxidize N2O to NO and then remove it. Through the above steps, the regulation and removal of the form of nitrogen oxides in the combustion flue gas are realized.

[0035] The technical solution provided by the present invention will be further described below according to specific embodiments.

[0036] Example 1 Application object: The content of NO in a certain combustion flue gas is 126 mg / m 3 , the content of NO2 is 95 mg / m 3 , the content of N2O is 15 mg / m 3 , the content of SO2 is 1523 mg / m 3 , the content of HCl is 35 mg / m 3 , and the flue gas temperature at the dust collector outlet is 58 °C.

[0037] Operation process: At the dust collector outlet, the original flue gas is divided into two paths, A and B, and the volume ratio of the flow rates of A and B is 4:1. The flue gas in path A enters the cascade cooling tower (level 1) and is cooled to 10 °C. The coolant is water. The cooled flue gas in path A enters the low-temperature adsorption tower. The flue gas in path B first enters the hot end of the gas-gas heat exchanger. After calculation, the concentration ratio of NO2 / N2O in the original flue gas is 6.3, and the high-voltage ionization device is not turned on. Subsequently, the flue gas in path B enters the low-temperature adsorption tower and is mixed with the flue gas in path A. There are 4 adsorption beds arranged in the low-temperature adsorption tower, and the adsorbent is coconut shell activated carbon with a specific surface area of 1350 m 2 / g and an average particle size of 17 mm. Glass flakes are used as the corrosion-resistant protective layer inside the tubes of the gas-gas heat exchanger.

[0038] After regulating and removing the form of nitrogen oxides in the flue gas through this example, the NO concentration at the chimney outlet is 1.2 mg / m 3 , the removal rate is 99.05%, and the NO2 concentration is 2.2 mg / m 3, the removal rate is 97.68%, and the N2O concentration is 0.2 mg / m 3 , the removal rate is 98.67%.

[0039] Example 2 Application object: In a certain combustion flue gas, the NO content is 290 mg / m 3 , the NO2 content is 220 mg / m 3 , the N2O content is 32 mg / m 3 , the SO2 content is 575 mg / m 3 , the HCl content is 274 mg / m 3 , and the flue gas temperature at the outlet of the dust collector is 138 °C.

[0040] Operation process: At the outlet of the dust collector, the original flue gas is divided into two paths, A and B, and the volume ratio of the flow rates of A / B is 4.6:1. The flue gas in path A enters the cascade cooling tower (3 stages) and is cooled to -20 °C. The coolant is an inorganic salt solution. The cooled flue gas in path A enters the low-temperature adsorption tower. The flue gas in path B first enters the hot end of the gas-gas heat exchanger. After calculation, the NO2 / N2O concentration ratio in the original flue gas is 6.9, and the high-voltage ionization device is not turned on. Subsequently, the flue gas in path B enters the low-temperature adsorption tower and is mixed with the flue gas in path A. There are 5 stages of adsorption beds arranged in the low-temperature adsorption tower, and the adsorbent is shell activated carbon with a specific surface area of 654 m 2 / g and an average particle size of 5 mm. Vinyl resin is used as the corrosion-resistant protective layer inside the tubes of the gas-gas heat exchanger.

[0041] After the nitrogen oxides in the flue gas are regulated and removed in this example, the NO concentration at the chimney outlet is 3.1 mg / m 3 , the removal rate is 98.93%, the NO2 concentration is 2.8 mg / m 3 , the removal rate is 98.73%, the N2O concentration is 0.8 mg / m 3 , and the removal rate is 97.50%.

[0042] Example 3 Application object: In a certain combustion flue gas, the NO content is 285 mg / m 3 , the NO2 content is 35 mg / m 3 , the N2O content is 14 mg / m 3 , the SO2 content is 3580 mg / m 3 , the HCl content is 43 mg / m 3 , and the flue gas temperature at the outlet of the dust collector is 117 °C.

[0043] Operation process: At the outlet of the dust collector, the raw flue gas is divided into two paths, A and B, and the volume ratio of the flow rates of A / B is 4:1. The flue gas in path A enters the cascade cooling tower (3 stages) and is cooled to -20 °C. The coolant is an inorganic salt solution. The cooled flue gas in path A enters the low-temperature adsorption tower. The flue gas in path B first enters the hot end of the gas-gas heat exchanger. After calculation, the concentration ratio of NO2 / N2O in the raw flue gas is 2.5, and the high-voltage ionization device is turned on to generate O free radicals of 5 mg / m 3 Subsequently, the flue gas in path B enters the low-temperature adsorption tower and is mixed with the flue gas in path A. There are 5 stages of adsorption beds arranged in the low-temperature adsorption tower. The adsorbent is fruit shell activated carbon, with a specific surface area of 785 m 2 / g and an average particle size of 8 mm. Vinyl resin is used as the corrosion-resistant protective layer inside the tubes of the gas-gas heat exchanger.

[0044] After the nitrogen oxides in the flue gas are regulated and removed in this embodiment, the NO concentration at the chimney outlet is 2.9 mg / m 3 , the removal rate is 98.98%, the NO2 concentration is 1.4 mg / m 3 , the removal rate is 96.00%, and the N2O concentration is 0.3 mg / m 3 , and the removal rate is 97.86%.

[0045] Example 4 Application object: In a certain combustion flue gas, the NO content is 153 mg / m 3 , the NO2 content is 273 mg / m 3 , the N2O content is 5 mg / m 3 , the SO2 content is 2484 mg / m 3 , the HCl content is 12 mg / m 3 , and the flue gas temperature at the outlet of the dust collector is 123 °C.

[0046] Operation process: At the outlet of the dust collector, the raw flue gas is divided into two paths, A and B, and the volume ratio of the flow rates of A / B is 49:1. The flue gas in path A enters the cascade cooling tower (3 stages) and is cooled to -40 °C. The coolant is an organic solution. The cooled flue gas in path A enters the low-temperature adsorption tower. The flue gas in path B first enters the hot end of the gas-gas heat exchanger. After calculation, the concentration ratio of NO2 / N2O in the raw flue gas is 54.6, and the high-voltage ionization device is not turned on. Subsequently, the flue gas in path B enters the low-temperature adsorption tower and is mixed with the flue gas in path A. There are 5 stages of adsorption beds arranged in the low-temperature adsorption tower. The adsorbent is coconut shell activated carbon, with a specific surface area of 1512 m 2 / g and an average particle size of 18 mm. Fiberglass is used as the corrosion-resistant protective layer inside the tubes of the gas-gas heat exchanger.

[0047] After the nitrogen oxides in the flue gas are regulated and removed in this embodiment, the NO concentration at the chimney outlet is 1.8 mg / m 3, the removal rate is 98.82%, and the NO2 concentration is 4.8 mg / m 3 , the removal rate is 98.24%, and the N2O concentration is 0.1 mg / m 3 , the removal rate is 98.00%.

[0048] Example 5 Application object: In a certain combustion flue gas, the NO content is 78 mg / m 3 , the NO2 content is 27 mg / m 3 , the N2O content is 45 mg / m 3 , the SO2 content is 354 mg / m 3 , the HCl content is 13 mg / m 3 , and the flue gas temperature at the outlet of the dust collector is 121 °C.

[0049] Operation process: At the outlet of the dust collector, the original flue gas is divided into two paths, A and B, and the volume ratio of the flow rates of A / B is 9:1. The flue gas in path A enters a cascade cooling tower (3 stages) and is cooled to -20 °C. The coolant is an inorganic salt solution. The cooled flue gas in path A enters a low-temperature adsorption tower. The flue gas in path B first enters the hot end of the gas-gas heat exchanger. After calculation, the NO2 / N2O concentration ratio in the original flue gas is 0.6, and the high-voltage ionization device is turned on to generate 25 mg / m 3 of O free radicals. Subsequently, the flue gas in path B enters the low-temperature adsorption tower and is mixed with the flue gas in path A. There are 3 stages of adsorption beds arranged in the low-temperature adsorption tower, and the adsorbent is coal-based activated carbon with a specific surface area of 527 m 2 / g and an average particle size of 2 mm. The inside of the tubes of the gas-gas heat exchanger uses glass flakes as a corrosion-resistant protective layer.

[0050] After the nitrogen oxides in the flue gas are regulated and removed in this example, the NO concentration at the chimney outlet is 0.7 mg / m 3 , the removal rate is 99.10%, the NO2 concentration is 0.2 mg / m 3 , the removal rate is 99.26%, and the N2O concentration is 0.9 mg / m 3 , the removal rate is 98.00%.

[0051] Example 6 Application object: In a certain combustion flue gas, the NO content is 125 mg / m 3 , the NO2 content is 80 mg / m 3 , the N2O content is 24 mg / m 3 , the SO2 content is 1780 mg / m 3 , the HCl content is 67 mg / m 3 , and the flue gas temperature at the outlet of the dust collector is 111 °C.

[0052] Operation process: At the outlet of the dust collector, the raw flue gas is divided into two paths, A and B, and the volume ratio of the flow rates of A / B is 19:1. The flue gas in path A enters the cascade cooling tower (2-stage) and is cooled to 0 °C. The coolant is an inorganic salt solution. The cooled flue gas in path A enters the low-temperature adsorption tower. The flue gas in path B first enters the hot end of the gas-gas heat exchanger. After calculation, the concentration ratio of NO2 / N2O in the raw flue gas is 3.3, and the high-voltage ionization device is turned on to generate O free radicals of 10 mg / m 3 Subsequently, the flue gas in path B enters the low-temperature adsorption tower and is mixed with the flue gas in path A. There are 4 stages of adsorption beds arranged in the low-temperature adsorption tower. The adsorbent is coconut shell activated carbon, with a specific surface area of 1923 m 2 / g and an average particle size of 32 mm. The inside of the gas-gas heat exchanger tube uses glass flakes as a corrosion-resistant protective layer.

[0053] After the nitrogen oxides in the flue gas are regulated and removed in this embodiment, the NO concentration at the chimney outlet is 1.5 mg / m 3 , the removal rate is 98.80%, the NO2 concentration is 1.2 mg / m 3 , the removal rate is 98.50%, and the N2O concentration is 0.5 mg / m 3 , the removal rate is 97.92%.

[0054] Example 7 Application object: In a certain combustion flue gas, the NO content is 386 mg / m 3 , the NO2 content is 258 mg / m 3 , the N2O content is 7 mg / m 3 , the SO2 content is 1674 mg / m 3 , the HCl content is 38 mg / m 3 , and the flue gas temperature at the dust collector outlet is 136 °C.

[0055] Operation process: At the outlet of the dust collector, the raw flue gas is divided into two paths, A and B, and the volume ratio of the flow rates of A / B is 32.3:1. The flue gas in path A enters the cascade cooling tower (3-stage) and is cooled to -20 °C. The coolant is an inorganic salt solution. The cooled flue gas in path A enters the low-temperature adsorption tower. The flue gas in path B first enters the hot end of the gas-gas heat exchanger. After calculation, the concentration ratio of NO2 / N2O in the raw flue gas is 36.9, and the high-voltage ionization device is not turned on. Subsequently, the flue gas in path B enters the low-temperature adsorption tower and is mixed with the flue gas in path A. There are 5 stages of adsorption beds arranged in the low-temperature adsorption tower. The adsorbent is wood-based activated carbon, with a specific surface area of 754 m 2 / g and an average particle size of 28 mm. The inside of the gas-gas heat exchanger tube uses glass flakes as a corrosion-resistant protective layer.

[0056] After the nitrogen oxides in the flue gas are regulated and removed in this embodiment, the NO concentration at the chimney outlet is 4.5 mg / m 3, the removal rate is 98.83%, and the NO2 concentration is 3.1 mg / m 3 , the removal rate is 98.80%, and the N2O concentration is 0.3 mg / m 3 , the removal rate is 95.71%.

[0057] Example 8 Application object: In a certain combustion flue gas, the NO content is 45 mg / m 3 , the NO2 content is 20 mg / m 3 , the N2O content is 198 mg / m 3 , the SO2 content is 2410 mg / m 3 , the HCl content is 24 mg / m 3 , and the flue gas temperature at the outlet of the dust collector is 178 °C.

[0058] Operation process: At the outlet of the dust collector, the original flue gas is divided into two paths, A and B, and the volume ratio of the flow rates of paths A and B is 4:1. The flue gas in path A enters a cascade cooling tower (3 stages) and is cooled to -10 °C. The coolant is an inorganic salt solution, and the cooled flue gas in path A enters a low-temperature adsorption tower. The flue gas in path B first enters the hot end of the gas-gas heat exchanger. After calculation, the NO2 / N2O concentration ratio in the original flue gas is 0.1, and the high-voltage ionization device is turned on to generate 98 mg / m 3 of O free radicals. Subsequently, the flue gas in path B enters the low-temperature adsorption tower and is mixed with the flue gas in path A. There are 4 stages of adsorption beds arranged in the low-temperature adsorption tower, and the adsorbent is coal-based activated carbon with a specific surface area of 637 m 2 / g and an average particle size of 12 mm. The inside of the tubes of the gas-gas heat exchanger uses fiberglass as a corrosion-resistant protective layer.

[0059] After the forms of nitrogen oxides in the flue gas are regulated and removed in this example, the NO concentration at the chimney outlet is 0.2 mg / m 3 , the removal rate is 99.56%, the NO2 concentration is 0.3 mg / m 3 , the removal rate is 98.50%, the N2O concentration is 5.7 mg / m 3 , the removal rate is 97.12%.

[0060] In this way, through the method for regulating and removing the forms of nitrogen oxides in combustion flue gas of the present invention, it is possible to avoid consuming expensive denitration catalysts, noble metal adsorbents and other materials, realize the form adjustment and deep removal of N2O, NO and NO2 in the flue gas, effectively reduce the emission of nitrogen oxides in the flue gas, and has the advantages of simple process, low cost, high removal rate, wide application range, etc.

[0061] It should be noted that in the description of the present invention, the terms "first", "second", etc. in the specification, claims and the above-mentioned drawings are used to distinguish similar objects, and do not necessarily describe a specific order or sequence. It should be understood that the data used in this way can be interchanged under appropriate circumstances, so that the embodiments of the present invention described here can be implemented in an order other than those illustrated or described here. In addition, the terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device that includes a series of steps or units does not necessarily limit to those clearly listed steps or units, but may include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0062] In the present invention, unless otherwise clearly defined and limited, the terms "install", "connect", "couple", "fix", etc. should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or integrated; it can be a mechanical connection, an electrical connection, or a communication connection; it can be directly connected, or indirectly connected through an intermediate medium, and can be the internal connection of two components or the interaction relationship between two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances. When a component is referred to as "fixed to" another component, it can be directly on the other component or there may be an intermediate component. When a component is considered to be "connected" to another component, it can be directly connected to the other component or there may be an intermediate component at the same time. When a component is considered to be "disposed on" another component, it can be directly disposed on the other component or there may be an intermediate component at the same time.

[0063] It should be understood that when used in this specification and the appended claims, the terms "include" and "comprise" indicate the presence of the described features, wholes, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, wholes, steps, operations, elements, components and / or their combinations.

[0064] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which this invention belongs. The terms used in the description of the present invention herein are only for the purpose of describing specific embodiments, and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0065] The above are only the preferred embodiments of the present invention, and do not impose any form of limitation on the present invention. Any ordinary technician in the industry can smoothly implement the present invention according to the illustrations in the specification and the above description. However, any equivalent changes made by those skilled in the art in the scope of the technical solution of the present invention, such as slight modifications, improvements, and evolutions using the technical content disclosed above, are all equivalent embodiments of the present invention. At the same time, any equivalent changes, modifications, and evolutions made to the above embodiments based on the substantial technology of the present invention still fall within the protection scope of the technical solution of the present invention.

Claims

1. A method for regulating the form and removing nitrogen oxides in combustion flue gas, characterized in that, It includes the following steps: S1. Feed the raw combustion flue gas into a dust collector. After dust removal, it is divided into Flue Gas A and Flue Gas B; S2. Feed Flue Gas A into a cascade cooling tower to cool Flue Gas A to the target temperature, and at the same time achieve the absorption and removal of NO2 in Flue Gas A; S3. Feed Flue Gas B into the tube side of a gas-gas heat exchanger to cool down Flue Gas B; S4. Mix Flue Gas A that has reached the target temperature with the cooled-down Flue Gas B and then feed them into a low-temperature adsorption tower, so that N2O in Flue Gas A is oxidized by NO2 in Flue Gas B to form NO, and together with the original NO in the flue gas, they are oxidized and adsorbed by the adsorbent in the low-temperature adsorption tower, achieving the efficient removal of N2O, NO, and NO2 in the flue gas; S5. Pass the flue gas purified by the low-temperature adsorption tower in S4 through the shell side of the gas-gas heat exchanger to heat up the flue gas and then discharge it into the air.

2. The method for regulating the form and removing nitrogen oxides in combustion flue gas according to claim 1, characterized in that, In S1, an induced draft fan and a flow control valve are arranged on the flue of Flue Gas B to control the volume flow ratio of Flue Gas A to Flue Gas B to be 4:1 to 49:

1.

3. A method for regulating the form and removing nitrogen oxides in combustion flue gas according to claim 2, characterized in that, In S3, a high-voltage ionization device is provided at the tube side outlet of the gas-gas heat exchanger to ionize NO2 to form strongly oxidizing O free radicals. When the concentration ratio of NO2 to N2O in the raw combustion flue gas is < 5, the high-voltage ionization device is turned on, and the concentration of the generated O free radicals is 5 - 100 mg / m 3 .

4. A method for regulating the form and removing nitrogen oxides in combustion flue gas according to claim 3, characterized in that, A first on-line flue gas component detection device is installed at the outlet of the dust collector to obtain the concentration of nitrogen oxides in the raw flue gas and transmit it to the centralized control unit. After calculation, the centralized control unit obtains the optimal distribution ratio of Flue Gas A / Flue Gas B and adjusts the induced draft fan, flow control valve, and high-voltage ionization device of Flue Gas B in real time; A second on-line flue gas component detection device is arranged at the outlet of the shell side of the gas-gas heat exchanger to monitor the concentration of nitrogen oxides in the purified flue gas and transmit it to the centralized control unit.

5. A method for regulating the form and removing nitrogen oxides in combustion flue gas according to claim 1, characterized in that, In S2, the cascade cooling tower adopts 1 to 3 stages of direct spray cooling, and the coolant in the cascade cooling tower is one or several of water, inorganic salt solution, and organic solution.

6. A method for regulating the form and removing nitrogen oxides in combustion flue gas according to claim 1, characterized in that, The target temperature in S2 is -40 to 10 °C.

7. A method for regulating the form and removing nitrogen oxides in combustion flue gas according to claim 1, characterized in that, In S3, a condensate water collection bypass is arranged on the inner side of the tube of the gas-gas heat exchanger, and the collected condensate water is fed into the cascade cooling tower.

8. A method for regulating the form and removing nitrogen oxides in combustion flue gas according to claim 1, characterized in that, In S3, a corrosion-resistant protective layer is arranged on the inner side of the tube of the gas-gas heat exchanger, and the material is one of fiberglass, glass flake, and vinyl resin.

9. A method for regulating the form and removing nitrogen oxides in combustion flue gas according to claim 1, characterized in that In S4, 3 to 5 layers of adsorbents are filled in the low-temperature adsorption tower; the types of the adsorbents are one or more of coal-based activated carbon, fruit shell activated carbon, wood activated carbon and coconut shell activated carbon, the specific surface area of the adsorbent is 500 to 2000 m 2 / g, and the average particle size of the adsorbent is 1 to 30 mm.

10. A system for regulating the form and removing nitrogen oxides in flue gas from combustion, based on the method for regulating the form and removing nitrogen oxides in flue gas from combustion according to any one of claims 1-9, characterized in that, It includes a dust collector, a cascade cooling tower, a low-temperature adsorption tower, and a gas-gas heat exchanger; the inlet of the dust collector into which the raw flue gas is fed, and the outlet of the dust collector is divided into Flue Gas A flue and Flue Gas B flue; Among them, the Flue Gas A flue is sequentially connected to the inlet of the cascade cooling tower, the low-temperature adsorption tower, and the shell side inlet of the gas-gas heat exchanger, the Flue Gas B flue is connected to the tube side inlet of the gas-gas heat exchanger, and the shell side outlet of the gas-gas heat exchanger is connected to the chimney.

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