Method for synergistically treating various pollutants in flue gas through ultraviolet radiation

Abstract

The invention belongs to the field of flue gas purification in the field of environmental protection, and particularly relates to a method for synergistically treating various pollutants in flue gas through ultraviolet radiation. Industrial flue gas contains various pollutants such as SO2, NOx, CO, VOCs, NH3, H2S and the like, and the current processes (such as desulfurization, denitrification and the like) mostly treat a certain pollutant independently. The invention provides an ultraviolet radiation treatment method (GFSD process), which adopts ultraviolet rays with specific frequency and is combined with a light source arrangement method, so that various pollutants in flue gas can be removed at the same time. Besides, after the flue gas containing SO2 is treated by the GFSD process and then is subjected to wet desulfurization, dry desulfurization or semi-dry desulfurization, desulfurization products containing sulfate, such as calcium sulfate and magnesium sulfate, can be generated, so that the generation of sulfite (mainly calcium sulfite) after the flue gas is directly subjected to desulfurization treatment by the dry method or the semi-dry method and the like is avoided.

Description

Technical Field

[0001] The present invention belongs to the field of flue gas purification in the field of environmental protection, and in particular relates to a method for synergistically treating multiple pollutants in flue gas by ultraviolet radiation. Background Art

[0002] Usually the flue gas produced by combustion contains a variety of pollutants, such as SO2, NO x , CO, VOCs, H2S, etc., the current common practice is to treat them separately, but the problems are large equipment investment, high energy consumption, and contradictions between processes. For example, in the sintering flue gas treatment in the steel industry, due to the high concentration of ultrafine dust after electrostatic precipitator, denitrification is often performed after desulfurization. Since desulfurization reduces the flue gas temperature, and flue gas denitrification requires a high temperature of 300℃-400℃, the flue gas must be heated, which consumes a lot of fuel. Large sintering machines consume more than 10,000 cubic meters of blast furnace gas per hour, and at the same time, pollutant emissions will increase. In order to reduce fuel consumption and recover waste heat, GGH heat exchangers must be added, which increases investment and equipment operation and maintenance costs, and also brings a lot of trouble to production operations.

[0003] At present, the ammonia reduction method is usually used for flue gas denitrification. The ammonia production process itself is energy-intensive and highly polluting. Using ammonia for denitrification not only increases energy consumption, but also increases pollutant emissions. At the same time, ammonia denitrification inevitably produces ammonia escape. After ammonia enters the atmosphere, 100% of it will generate aerosols, which is the cause of PM2.5. 2.5 The increased pollutants are also the main causes of ozone pollution.

[0004] At present, many regions have begun to reduce CO emissions due to long-term high CO in the atmosphere. A certain amount of CO exists in many combustion flue gases, especially in the sintering process and hot blast furnace flue gases in the steel industry. The CO concentration in the flue gas is usually 4000-7000 mg / Nm 3 At present, catalytic oxidation is used for treatment. The catalyst usually uses precious metal platinum, and the cost of catalytic materials is high. The flue gas temperature is low and needs to be heated, which consumes a lot of energy. The removal efficiency is low, usually 50%-60%. The catalyst is easily poisoned and the maintenance cost is high. In general, the current CO removal process is not mature, the removal efficiency is low, the process cost is high, and the enterprise burden is heavy.

[0005] Many industrial flue gases contain SO2, NO x In addition to CO, it also contains a large amount of VOCs, including highly toxic organic gases such as dioxins or benzopyrene. For example, the sintering flue gas in the steel industry has a high VOCs content, especially when anthracite is used as sintering fuel. Each ton of anthracite emits more than 100 kilograms of VOCs, which is the largest VOCs emission among all industrial flue gases. If all are treated separately, the equipment investment will be huge and the operating cost will also be high.

[0006] At present, flue gas desulfurization mainly removes SO2 from flue gas. Due to the low solubility of SO2 in water, a large amount of water is often required for spraying, and in order to fix sulfur, the desulfurizer needs to be sprayed together with water, which can easily cause the spray head to be blocked; the desulfurization liquid produced by spraying contains a large amount of desulfurizer and desulfurization products. A part of the desulfurization liquid will enter the subsequent process with the flue gas, causing the flue gas dust to exceed the standard, and will also introduce new impurities, affecting the subsequent process effect; SO2 in the desulfurization liquid reacts with water to generate sulfurous acid, which reacts slowly with the desulfurizer, has poor ability, and has high requirements for the desulfurizer. Dry and semi-dry desulfurization generates calcium sulfite, which is difficult to utilize as a resource and has high treatment costs. It is currently basically a solid waste. Summary of the invention

[0007] In order to solve the above problems, the present invention provides a method for synergistically treating multiple pollutants in flue gas by ultraviolet radiation (GFSD process), that is, using ultraviolet radiation of a specific frequency to make certain substances in the flue gas enter an excited state or an ionized state, so that they react with each other, and at the same time eliminate SO2, NO x , CO, VOCs (including dioxins, benzopyrene), NH3, H2S and other pollutants; the substances in the flue gas must contain both oxidizing substances and reducing substances; the oxidizing substances include NO x , O2, etc., the reducing substances include one or more of CO, SO2, VOCs, NH3, H2S, etc.; the frequency of the ultraviolet rays is ≥1.18×10 15 Hz; the flue gas temperature is 25°C-350°C.

[0008] If the flue gas does not have a denitrification task (removal of nitrogen oxides NO x ), but when removing reducing substances, the ultraviolet frequency is selected according to the bond energy of O2 molecules, and the ultraviolet frequency is ≥1.18×10 15 Hz; preferably ultraviolet frequency ≥ 1.25×10 15 Hz.

[0009] If flue gas needs to be denitrated, the UV frequency should be selected according to the bond energy of NO, and the UV frequency should be selected ≥1.52×10 15 Hz; the preferred frequency is ≥1.62×10 15 Hz; There must be enough reducing substances in the flue gas to solidify NO x The atomic O2 dissociated by light radiation prevents N2 and O2 from recombining, thus improving the denitrification efficiency. The molar concentration of the reducing substance must be greater than that of NO x Molar concentration, preferably (molar concentration of reducing substances / NO x Molar concentration) ≥5.

[0010] The photolysis process for removing reductive pollutants is as follows:

[0011]

[0012] The photolysis process of denitrification reaction is as follows:

[0013] 2NO+2hv→N2+2O (6)

[0014] 2NO2+2hv→N2+4O (7)

[0015] In the GFSD process, tubular light sources are preferred, and are arranged horizontally parallel to the horizontal direction or vertically perpendicular to the horizontal direction. The center line of the light source in the length direction is perpendicular to the flue gas flow direction, and adjacent rows of light sources are evenly arranged crosswise, so that the flue gas forms turbulence during the radiation process to avoid the formation of biased flow. The advantage of horizontal arrangement is that it is easy to maintain, but the dust on the top of the light source needs to be cleaned regularly; the advantage of vertical arrangement is that the light source has no dust accumulation surface and is not easy to accumulate dust, but it is difficult to install and maintain.

[0016] When arranging light sources, the distance between lamps is preferably 150-500mm, and the distance between adjacent rows is preferably equal to the distance between adjacent lamps in the same row, so that the flue gas can form turbulence and receive more uniform radiation. The spacing between light sources is determined according to the power of the light source, the density of the effective photons emitted, and the concentration of the treated pollutants. The larger the power of the light source, the larger the distance between the light sources, and the smaller the power of the light source, the smaller the distance between the light sources; the density of light source arrangement cannot be too large, otherwise the flow resistance of the flue gas will be very large.

[0017] The light source power selection range is 10-320 watts. If the GFSD process is required to treat the flue gas, and the dust concentration in the flue gas is greater than 20mg / Nm 3 When the light source is used, it is preferred to arrange it vertically, use a low-power light source (such as 10-100 watts), and increase the density of the light source arrangement to reduce the radiation transmission path and reduce the attenuation of dust on the utilization rate of light radiation.

[0018] Generally, the flue gas should be retained in the radiation chamber for 0.1-2 seconds. The excitation or dissociation reaction of ultraviolet rays is completed instantly, but the reaction between the excitation product or dissociation product and the reducing substance requires diffusion and mass transfer time. The time required for mass transfer varies with the degree of flue gas turbulence. The residence time depends on the flue gas diffusion conditions and ultraviolet density. The greater the radiation intensity, the shorter the radiation time required, and the greater the concentration of flue gas pollutants, the longer the radiation time required. It can be selected according to the flue gas flow state, or it can be determined through experiments. Based on the determined radiation residence time, the length of the radiation reaction chamber is designed according to the flue gas flow rate. When a certain removal efficiency cannot meet the demand, an excessive design can be adopted to extend the length of the radiation chamber, divide the light source into several groups, and independently control the start / shutdown status of each group of light sources to achieve multi-stage graded control.

[0019] After the flue gas is treated with ultraviolet radiation, if the pollutant concentration is lower than the emission limit by 30%-50% or O3 is detected, gradually turn off some ultraviolet light sources until the pollutant concentration is lower than the emission limit by 10%-20% and there is no O3, then stop turning off the light source; if the treated pollutant emission reaches the design limit, increase the working light source, extend the treatment time and space, increase the amount of radiation photons, and stop increasing the working light source when the pollutant concentration is lower than the emission limit by 10%-20%.

[0020] When the flue gas temperature is lower than the dew point or acid dew point, in order to avoid the adhesion of droplets, wet dust, organic droplets, etc. on the surface of the light source and cause ultraviolet attenuation, dehumidification or removal of the above substances with adsorption materials, so that the acid dew point and dew point are lower than the flue gas temperature, and then ultraviolet radiation treatment is carried out; the acid dew point at this time is the acid dew point corresponding to the original sulfur trioxide in the flue gas and the sulfur dioxide in the flue gas converted into sulfur trioxide. The acid dew point is related to humidity, and lowering the humidity can reduce the acid dew point. Especially when treating high-sulfur flue gas, if the flue gas temperature is lower than the acid dew point, acid dew is easy to adhere to the wall of the light source tube. Lime powder can be sprayed into the flue gas before the dust collector to absorb moisture and reduce the humidity of the flue gas, increase the acid dew point of the flue gas, and enter the GFSD process after dust removal. The lime powder collected in the dust collector can be used for desulfurization or sintering raw material recycling. Before ultraviolet radiation treatment, start the ultraviolet light source for 20-60 minutes to preheat the system to avoid low-temperature condensation of the system and acid dew corrosion. When treating sulfur-containing flue gas, acid corrosion-resistant materials should be selected for the radiation treatment chamber.

[0021] If the flue gas needs to remove SO2, after the flue gas is treated by the GFSD process, the SO2 in the flue gas is basically oxidized to SO3, and the flue gas containing SO3 is then subjected to wet desulfurization, dry desulfurization or semi-dry desulfurization using calcium or magnesium, to generate desulfurization products containing sulfates such as calcium sulfate and magnesium sulfate, that is, the flue gas is desulfurized after being treated by the GFSD process to avoid the generation of sulfites (mainly calcium sulfite) after the flue gas is directly treated by dry or semi-dry desulfurization. The wet desulfurization in the present invention refers to the use of waste slag water to absorb SO3 in the flue gas to form a desulfurization liquid, and then the desulfurization liquid is mixed with alkaline substances such as calcium carbonate, magnesium carbonate, and steel slag to react and neutralize excess sulfuric acid, and at the same time generate desulfurization products such as calcium sulfate and magnesium sulfate, which can be used as raw materials for building materials. The waste slag water includes alkaline water or neutral water such as blast furnace slag water, steel slag slag water, and coal-fired boiler ash slag soaking water. The flue gas is treated by the GFSD process before desulfurization, which avoids the reaction of SO2 with desulfurizers such as calcium and magnesium to produce solid wastes such as calcium sulfite and magnesium sulfite in the traditional desulfurization method. It can also avoid problems such as clogging of the spray head caused by spraying the desulfurizer powder and water at the same time.

[0022] The beneficial effects of the present invention are as follows:

[0023] 1. NO can be achieved x, CO, VOCs, H2S, NH3 and other pollutants; it can oxidize SO2 into SO3, making the subsequent desulfurization easier, which not only reduces the cost of wet desulfurization, but also solves the problem of resource utilization of dry and semi-dry desulfurization products.

[0024] 2. When the flue gas has a denitrification task, the use of non-ammonia denitrification can avoid secondary pollution caused by ammonia escape from ammonia denitrification.

[0025] 3. Compared with catalytic CO removal, it has high removal efficiency, no temperature requirements, and can remove multiple pollutants at the same time.

[0026] 4. Ultraviolet radiation equipment requires little investment, is easy to maintain, and has low operating and maintenance costs. It only consumes electricity during operation, is low-cost and energy-saving, and will not produce secondary pollution. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a schematic diagram of the lateral arrangement of the tubular light source of the GFSD process of the present invention, wherein (a) is the main view, (b) is the left view, and (c) is the top view.

[0028] Figure 2 Schematic diagram of the vertical arrangement of tubular light sources in the GFSD process of the present invention, wherein (a) is the main view, (b) is the left view, and (c) is the top view.

[0029] Figure 3 This is a schematic diagram of the process of introducing the GFSD process to treat flue gas in Scheme 1 of Example 1.

[0030] Figure 4 This is a schematic diagram of the process of treating flue gas by introducing the GFSD process in Scheme 2 of Example 1.

[0031] Figure 5 This is a schematic diagram of the process of introducing the GFSD process to treat flue gas in Example 2.

[0032] Figure 6 This is a schematic diagram of the process of introducing the GFSD process to treat flue gas in Example 3. DETAILED DESCRIPTION

[0033] In each embodiment, a tubular light source is used, and the light source is arranged horizontally as follows: Figure 1 As shown, the vertical arrangement is as follows Figure 2 As shown, the arrows in the top view indicate the direction of flue gas flow; the flue gas is irradiated with ultraviolet light for 0.3-2 seconds; before ultraviolet radiation treatment, the ultraviolet light source is started for 20-60 minutes to preheat the system to prevent the system from being corroded by acid dew. The test conditions of pollutant concentration in each embodiment are standard state, dry basis, and 16% reference oxygen.

[0034] When the dust content in the flue gas is large, the frequency of cleaning the dust of the light source can be increased to reduce the light attenuation caused by dust accumulation of the light source, and the adjustment can be made appropriately according to different flue gas treatment conditions. The present invention has conducted preliminary experiments and determined the flue gas treatment conditions in the embodiment according to the preliminary experimental data. The inner wall of the radiation chamber is a reflective material. The control working mode in the embodiment is based on the data of the equipment terminal detection instrument. After the parameters are designed, the big data modeling automatically directs the equipment operation.

[0035] In actual production, the efficiency of pollutant treatment is related to the amount of radiation received by the flue gas. If the designed flue gas flow rate is fast, the length of the radiation chamber should be relatively long; if the light source power is large, the radiation chamber should be relatively short. When treating a large amount of flue gas, choosing a light source with a higher power can make the equipment smaller. After the total radiation per unit time is determined, the smaller the light source power and the more light sources, the larger the equipment size will be, the larger the equipment resistance will be, and the installation and maintenance will be large. However, the radiation intensity will be more uniform and the treatment effect will be better. On the contrary, the greater the light source power and the fewer light sources, the smaller the equipment size and the smaller the equipment resistance will be, and the installation and maintenance will be small, but the treatment effect will not be as good as the former. At present, the treatment projects are basically the transformation of the original equipment space, and the choice should be made according to the existing project space and treatment tasks.

[0036] Since the reaction equilibrium will lag behind, the flue gas will continue to react for a period of time after leaving the radiation reaction chamber. Therefore, the flue gas composition detection instrument is best delayed for a certain distance. The specific distance should be determined according to the on-site space. In theory, the farther the distance, the more balanced the reaction.

[0037] Example 1

[0038] A steel company has two sintering machines, each with a flue gas volume of 800,000 Nm 3 / h standard condition, the original flue gas treatment process is: flue gas → electrostatic precipitator → limestone gypsum desulfurization → GGH heating → SCR ammonia denitrification → GGH cooling → chimney. After desulfurization, GGH is added to heat the flue gas to 300℃-370℃, SCR ammonia denitrification is set at the rear, and then it is discharged after GGH cooling.

[0039] After the original process was treated with electrostatic precipitator, the flue gas temperature was 160℃ and the dust content was 40-60mg / Nm 3 The pollutant content in the flue gas is as follows: SO2 is 2000-3000mg / Nm 3 , NO x 250-350mg / Nm 3 , CO is 4000-8000mg / Nm 3 , H2S is 25-30mg / Nm 3 , VOCs is 5200-5600mg / Nm 3 .

[0040] After the original process treatment, when the flue gas is discharged through the chimney, the concentration of each substance in the flue gas is as follows: SO2 is ≤30mg / Nm 3 , NO x ≤45mg / Nm 3 , dust ≤10mg / Nm 3 , CO, H2S and VOCs have not changed.

[0041] The current problem is that the SCR catalyst is often poisoned by potassium and sodium dust, which leads to unstable nitrogen oxide indicators. It is necessary to frequently clean the poisoned catalyst and spray ammonia to reduce NO x Emissions meet standards, but ammonia escape often exceeds standards.

[0042] In order to solve the problems of SCR catalyst poisoning, excessive ammonia escape, and CO and other pollutants, the steel plant decided to introduce the GFSD process of the present invention to treat flue gas. Two sets of sintering machines were transformed using Scheme 1 and Scheme 2 respectively, and the two schemes were compared. The specific schemes are as follows:

[0043] Option 1: One of the sintering machines is equipped with a GFSD process after the original dust removal process, and the selected frequency is 1.62×10 15 Hz ultraviolet light source. The GFSD process is followed by a desulfurization process. The flue gas after desulfurization is discharged from the chimney. The combustion chamber, GGH and SCR denitrification devices are removed. Figure 3 shown.

[0044] This scheme requires less transformation work and investment, and has a high flue gas temperature. The flue gas volume of this scheme is larger than that of scheme 2. Since the dust concentration after electrostatic precipitator is as high as 40-60mg / Nm 3 There is no space for dust removal modification. The design intentionally uses a 40W / piece low-power light source, the length of the light source is 900mm, the total radiation power is 104kW, the spacing between adjacent rows of light sources and the distance between adjacent light sources in the same row are 160mm, which is a dense arrangement, which can shorten the distance between light sources and reduce the attenuation of light transmission caused by high dust concentration. At the same time, the light sources are arranged vertically and evenly vertically to the ground to avoid dust accumulation on the upper part of the light source when arranged horizontally with the ground. The light source is divided into 10 groups for control design. According to the terminal detection index after the flue gas leaves the GFSD process, the number of working light sources is adjusted to ensure that the treated pollutants meet the standards and avoid excessive radiation to produce O3. When the pollutants treated by the GFSD process are all lower than the target value by 30%, it is set to automatically gradually shut down some radiation light sources, so that all pollutants are lower than the target value by 20%, and the operation of shutting down the light source can be stopped. If any pollutant index reaches the emission limit, it is set to gradually start the radiation light source that is not working until all pollutant indexes are lower than the target value by 20%, and the operation of starting the light source can be stopped. Due to the low power of a single light source and the large number of light sources, the manufacturing and maintenance costs of the light radiation equipment are slightly higher than those of Scheme 2.

[0045] The project has been running for 5 months and all indicators have been stable. Of the 10 groups of light sources designed, 8 are often started and 9 are occasionally started.

[0046] After the flue gas after electrostatic precipitator is treated by GFSD process, the contents of various substances in the flue gas are as follows: NO x Reduced to ≤20mg / Nm 3 , CO dropped to ≤900mg / Nm 3 , H2S drops to 0mg / Nm 3 , SO2 reduced to ≤30mg / Nm 3 , almost all SO2 is oxidized into SO3, and VOCs are reduced to ≤300mg / Nm 3 .

[0047] After the flue gas is treated by the GFSD process, it continues to undergo subsequent desulfurization treatment. Since SO2 in the flue gas is almost completely oxidized to SO3, which is an anhydride and can easily dissolve in water and become sulfuric acid, sulfuric acid can easily react with alkaline substances, the subsequent desulfurization efficiency is significantly improved, and the desulfurization agent consumption is significantly reduced. When oxygen exposure is stopped, calcium sulfite is almost invisible in the desulfurization product.

[0048] In order to further reduce the consumption of desulfurizers, the desulfurization with desulfurizers in the original process was changed to desulfurization by spraying with blast furnace slag water. The pH value of the desulfurization liquid formed by spraying is 4-6. Stop adding limestone powder to the desulfurization liquid and send the desulfurization liquid back to the blast furnace slag. The alkaline substances in the blast furnace slag can easily react with the sulfuric acid in the desulfurization liquid, which can quickly neutralize and solidify the sulfur in the desulfurization liquid. The desulfurization liquid forms slag water after slag flushing. The pH value of the slag water is greater than 7 and can be recycled for spray desulfurization. The pipeline for sending the desulfurization liquid to the slag flushing area has been treated with acid corrosion protection. Since no desulfurizer is added, only the alkaline water after the blast furnace slag flushing reacts with the flue gas, so the particulate matter in the desulfurization liquid is reduced, and the dust concentration of the flue gas after desulfurization is significantly reduced. The dust concentration of the flue gas at the end after desulfurization is reduced to ≤8mg / Nm 3 , SO2 reduced to ≤10mg / Nm 3 . The energy consumption of the circulation system is significantly reduced.

[0049] After 4 months of operation, the desulfurization, denitrification and carbon monoxide removal have reached the standard stably, and the removal effects of H2S and VOCs are also very significant. The total designed operating power of the equipment is 104kW, and the actual average operating power is about 90kW.

[0050] Option 2: Another sintering machine adds a flue gas demisting device after the original limestone gypsum desulfurization process, and adds a GFSD process after the flue gas demisting device. After the GFSD process, the flue gas is discharged from the chimney. The selected frequency is 1.62×10 15 Hz ultraviolet light source. The process flow is as follows Figure 4 shown.

[0051] The temperature of flue gas after desulfurization is about 50℃; the sulfur content in flue gas after desulfurization is already very low, and the acid dew point does not need to be considered; but the humidity is relatively high, and it is wet flue gas containing droplets. In order to prevent droplets from scaling on the wall of the light source tube and causing increased light attenuation, a demisting device is added before the GFSD process to remove droplets in the flue gas. The equipment investment is slightly higher than that of Plan 1. Since the amount of dust in the flue gas is significantly reduced after desulfurization, the dust concentration is ≤10mg / Nm 3 The power of the light source used is 200W / piece, the length of the light source is 1500mm, and the total radiation power is 80kW. It is an over-design. The light source is controlled in 8 groups, and the light source is arranged evenly horizontally with the ground. According to the online detection indicators after the flue gas leaves the GFSD process, the number of light sources put into operation is increased or decreased. The specific method is similar to that of Scheme 1. The distance between adjacent rows of light sources and the distance between adjacent light sources in the same line are both 200mm. At this time, compared with the flue gas after electrostatic precipitator in Scheme 1, the flue gas to be treated has a lower temperature, a reduced operating flue gas volume, a low dust concentration, a reduced light decay, a slightly reduced light radiation equipment, and less equipment maintenance. After the transformation, the original SCR ammonia denitrification device and the GGH heating device were dismantled.

[0052] After GFSD process treatment, the contents of various substances in the flue gas are as follows: NO x Reduced to ≤15mg / Nm 3 , CO dropped to ≤1300mg / Nm 3 , SO2 is ≤30mg / Nm after desulfurization 3 Reduced to 0mg / Nm 3 , H2S drops to 0mg / Nm 3 , dust concentration is reduced to ≤5mg / Nm 3 .

[0053] The desulfurization process has almost no effect on VOCs. VOCs are 5200-5600mg / Nm 3 , after radiation treatment, it is reduced to ≤450mg / Nm 3 The removal effect of CO and VOCs is slightly inferior to that of Scheme 1, which may be due to the decrease in flue gas temperature during GFSD process treatment.

[0054] The project has been running for 5 months and all indicators have been stable. Of the 8 groups of light sources designed, 6 are often started, the 7th is started occasionally, and the 8th is started rarely. The average operating power is about 64kW.

[0055] By comparing Scheme 1 with Scheme 2, it can be seen that the GFSD process of the present invention, combined with the light source frequency and the light source arrangement method, can simultaneously and efficiently degrade various pollutants in complex flue gas. When the dust content in the flue gas is low, the average operating power is lower and the energy-saving effect is better.

[0056] Example 2

[0057] A steel company has a 360㎡ sintering machine. The flue gas adopts CFB semi-dry desulfurization + SCR denitrification device. The inlet flue gas volume of the sintering machine desulfurization and denitrification system is 1.34 million Nm 3 / h standard condition, the inlet flue gas temperature is 120~150℃. The initial pollutant content in the flue gas is: SO2 concentration is 1100-1500mg / Nm 3 , NO x Concentration is 280-350mg / Nm 3 , CO concentration is 6500-7000mg / Nm 3 , dust concentration ≤10mg / Nm 3 .

[0058] The original process first uses CFB semi-dry desulfurization and dust removal, and then uses SCR denitrification process to purify the flue gas. The SO2 concentration in the flue gas is ≤35mg / Nm 3 , NO x Concentration ≤50mg / Nm 3 , the dust concentration is still ≤10mg / Nm 3 , CO concentration has not changed. Due to the low temperature of flue gas after desulfurization, GGH is needed to heat the flue gas to above 300℃ before denitrification treatment. The natural gas consumption exceeds 300,000m3 3 The process has high energy consumption and cannot meet the energy-saving requirements or the requirements for removing CO. If catalytic oxidation is used to remove CO, the temperature must be further raised to 350°C-400°C, which will also generate a lot of energy consumption.

[0059] Therefore, the GFSD process is introduced to treat flue gas. The specific plan is as follows:

[0060] After desulfurization and dust removal, the GFSD process is added. The flue gas after the GFSD process is discharged from the chimney, and the original SCR denitrification device and GGH heating and heat exchange device are removed. Figure 5 After semi-dry desulfurization, the flue gas temperature is higher than 120℃ and the SO2 concentration is ≤35mg / Nm 3 , NO x The concentration of CO and dust is basically unchanged, and the concentration of dust is ≤10mg / Nm 3 The humidity is far from saturation, which fully meets the GFSD process requirements. The light source frequency is selected as 1.62×10 15Hz ultraviolet light source, the light source power is selected as 150W / piece, the length is 1520mm, the total power is set to 135kW, the radiation light source is controlled in 9 groups, each group has 100 pieces, and they are evenly arranged horizontally. The spacing between adjacent rows of light sources and adjacent lamp tubes is 180mm. According to the online detection indicators after the flue gas leaves the GFSD process, the control software controls that when the reductive pollutants reach the emission limit, the control system gradually starts some non-working light sources, so that the concentration of all pollutants is lower than the target value by 20%, and the operation of starting the light source can be stopped; when all reductive pollutants are lower than the target value by 30%, the control system gradually shuts down some working light sources, so that all reductive pollutants are lower than the emission target value by 20%, and the operation of shutting down the light source can be stopped. At this time, there will be no O3 emissions, that is, no excessive radiation will be generated.

[0061] 9 groups of light sources are designed, 8 groups are in regular operation, and the 9th group is started occasionally, with an average operating power of about 125kW. After GFSD process treatment, the contents of various substances in the flue gas are as follows: NO x ≤10mg / Nm 3 , SO2 concentration is ≤5mg / Nm 3 , CO concentration ≤ 1000mg / Nm 3 .

[0062] The equipment has been running for 3 months and its indicators have been very stable.

[0063] Example 3

[0064] A steel company, blast furnace with hot blast stove, flue gas volume 170,000 Nm 3 / h standard condition, flue gas temperature 250℃-350℃, the concentration of each substance in the flue gas is as follows: O2 content is about 13%, SO2 concentration is 280-350mg / Nm 3 , CO concentration is 4000-4500mg / Nm 3 , dust concentration ≤10mg / Nm 3 The flue gas from the hot blast furnace is discharged after CFB semi-dry desulfurization and bag dust removal. The SO2 concentration in the flue gas is ≤35mg / Nm 3 , dust concentration ≤10mg / Nm 3 , CO concentration 4000-4500mg / Nm 3 , the flue gas temperature drops to 220℃-320℃. Since there is no denitration requirement for hot blast furnaces at present, the method of the present invention is used to remove CO from hot blast furnaces, requiring CO to be removed to 2000mg / Nm 3 More than 60% of the original desulfurization product is calcium sulfite, which is solid waste.

[0065] The GFSD process is introduced to treat flue gas. The specific plan is as follows:

[0066] The fuel of the hot blast furnace is blast furnace gas, and the dust concentration is less than 10mg / Nm 3 GFSD process is added before desulfurization. The flue gas treated by GFSD process is discharged from the chimney after CFB semi-dry desulfurization and dust removal. Figure 6 As shown in the figure, there is no denitration requirement, the flue gas temperature is relatively high, and the O2 dissociation energy is reduced, so the selected frequency is 1.18×10 15 Hz, the photon energy level at this frequency is already greater than the O2 dissociation energy at this temperature. Due to the small amount of flue gas, the light source is selected to be 30W / piece, the light source length is 900mm, and the total radiation power is set to 18kW. For excessive design, the light source control is divided into 6 groups, each with 100 pieces, and is arranged evenly horizontally. The row spacing and tube spacing are both 150mm. According to the detection data of the CO and O3 online detectors after the flue gas leaves the GFSD process, the control system automatically adjusts the number of light sources put into operation. The specific method is similar to Example 2, so that the CO emitted from the flue gas meets the emission standards, and at the same time, it will not produce excessive radiation to produce O3. Five groups are usually in operation, and occasionally six groups are in operation at the same time, with an average operating power of about 16kW.

[0067] After GFSD process treatment, the SO2 concentration in the flue gas is ≤5mg / Nm 3 , CO concentration has been controlled at 1000-1500mg / Nm 3 , no O3 is produced.

[0068] After desulfurization through GFSD process, desulfurizer consumption is reduced by 25%, more than 90% of the desulfurization products are calcium sulfate, and calcium sulfite is less than 3%, which are sold to cement production plants as raw materials without generating solid waste.

[0069] The indicators have been stable for 4 months.

Claims

1. A method for synergistically treating multiple pollutants in flue gas by ultraviolet radiation, characterized in that: Using ultraviolet radiation of a specific frequency to make the substances in the flue gas enter an excited or ionized state and react, while eliminating a variety of pollutants in the flue gas; The substances in the flue gas include both oxidizing substances and reducing substances; The reducing substances include one or more of CO, SO2, VOCs, NH3, H2S, and the oxidizing substances include NO x , O2 or more; The pollutants include SO2, NO x , CO, VOCs, NH3, H2S; The frequency of the ultraviolet rays is ≥1.18×10 15 Hz.

2. The method for synergistically treating multiple pollutants in flue gas by ultraviolet radiation according to claim 1, characterized in that: The flue gas temperature is 25°C-350°C; If the flue gas needs to remove reducing substances and does not need denitrification, the ultraviolet frequency should be selected according to the bond energy of O2 molecules. The ultraviolet frequency should be ≥1.18×10 15 Hz; If the flue gas needs to be denitrated, the UV frequency should be selected according to the key energy of NO, and the UV frequency should be ≥1.52×10 15 Hz.

3. The method for synergistically treating multiple pollutants in flue gas by ultraviolet radiation according to claim 2, characterized in that: If the flue gas needs to remove reducing substances but does not need denitrification, the ultraviolet frequency should be ≥1.25×10 15 Hz; If flue gas needs to be denitrated, the ultraviolet frequency should be ≥1.62×10 15 Hz; the molar concentration of the reducing substance is greater than NO x Molar concentration.

4. The method for synergistically treating multiple pollutants in flue gas by ultraviolet radiation according to claim 3, characterized in that: The molar concentration of reducing substances / NO x Molar concentration ≥5.

5. The method for synergistically treating multiple pollutants in flue gas by ultraviolet radiation according to claim 1, characterized in that: The ultraviolet light source is a tubular light source, which is arranged horizontally parallel to the horizontal direction or vertically perpendicular to the horizontal direction. The center line of the light source in the length direction is perpendicular to the flue gas flow direction, and adjacent rows of light sources are evenly arranged in a cross manner.

6. The method for synergistically treating multiple pollutants in flue gas by ultraviolet radiation according to claim 5, characterized in that: The distance between the light sources is 150-500mm, the distance between adjacent rows is equal to the distance between adjacent lamp tubes in the same row; the power of the light source is 10-320W.

7. The method for synergistically treating multiple pollutants in flue gas by ultraviolet radiation according to claim 6, characterized in that: When the dust concentration in the flue gas is greater than 20 mg / Nm 3 When using low-power light sources of 10-100W, the light sources are arranged vertically to increase the density of light source arrangement.

8. The method for synergistically treating multiple pollutants in flue gas by ultraviolet radiation according to claim 1, characterized in that: The time for the flue gas to be treated by ultraviolet radiation is 0.1-2S; The total power of the light source is designed to be excessive, and the light sources are divided into several groups, and the start / stop status of each group of light sources is independently controlled; After the flue gas is treated with ultraviolet radiation, if the pollutant concentration is 30%-50% lower than the emission limit or O3 is detected, some ultraviolet light sources are gradually turned off. When the pollutant concentration is 10%-20% lower than the emission limit and there is no O3, the operation of shutting down the light source is stopped; if the pollutant emission reaches the design limit, the non-working light source is started. When the pollutant concentration is 10%-20% lower than the emission limit, the operation of starting the non-working light source is stopped; multi-stage hierarchical control of the light source is realized.

9. The method for synergistic treatment of multiple pollutants in flue gas by ultraviolet radiation according to claim 1, characterized in that: Before UV radiation treatment, start the light source for 20-60 minutes to preheat the system; When treating sulfur-containing flue gas, when the flue gas temperature is lower than the dew point or acid dew point, first dehumidify to make the acid dew point and dew point lower than the flue gas temperature, and then carry out ultraviolet radiation treatment; the acid dew point at this time is the acid dew point corresponding to the original sulfur trioxide in the flue gas and the sulfur dioxide in the flue gas converted into sulfur trioxide; acid corrosion-resistant materials are selected for the radiation treatment room.

10. The method for synergistic treatment of multiple pollutants in flue gas by ultraviolet radiation according to any of the above claims, characterized in that: If SO2 needs to be removed from flue gas, after the flue gas is treated with ultraviolet radiation, SO2 in the flue gas is oxidized into SO3, and then after wet desulfurization, dry desulfurization or semi-dry desulfurization, a desulfurization product containing sulfate is generated, thus avoiding the generation of sulfite after direct desulfurization of the flue gas; The wet desulfurization process includes using waste slag water to absorb SO3 in flue gas to form a desulfurization liquid, and then mixing the desulfurization liquid with an alkaline substance to neutralize sulfuric acid in the desulfurization liquid and generate a desulfurization product at the same time; The dry desulfurization or semi-dry desulfurization both include methods of using calcium agent desulfurization and magnesium agent desulfurization; The waste slag water includes blast furnace slag flushing water, steel slag slag water, and coal-fired boiler ash slag soaking water; The alkaline substance includes one or more of calcium carbonate, magnesium carbonate and steel slag; The sulfate-containing desulfurization product includes one or both of calcium sulfate and magnesium sulfate; The sulfite includes one or both of calcium sulfite and magnesium sulfite.

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