A denitration agent for flue gas after oxidation and a denitration process thereof

Abstract

The present application relates to a kind of for flue gas after oxidation denitration agent and its denitration process.Flue gas is oxidized after oxidizing agent, part NO is converted into NO2;In lime silo or the bottom of circulating fluidized bed semi-dry method reactor, the denitration agent is added, the denitration agent includes Ca base denitration agent and modified Ca base denitration agent, wherein, Ca base denitration agent includes four kinds of core components, such as calcium sulfite, calcium hydroxide, calcium carbonate and calcium sulfate;Modified Ca base denitration agent is added with a small amount of modifier, such as sulfur base denitration enhancer, free radical trapping agent, phase transfer agent, on the basis of four kinds of core components.Ca base denitration agent four kinds of core components realize NO2 and NO removal, compared with the traditional lime simultaneous desulfurization and denitrification technology, the present application can significantly improve NO2 removal effect and remove part NO, reduce O3 usage and escape, improve desulfurization and denitrification slag quality.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of flue gas pollution control, and relates to a powder-like Ca-based denitration agent for flue gas after oxidation and a denitration process thereof. BACKGROUND

[0002] Nitrogen oxides (NOx, including nitrogen dioxide (NO2) and nitric oxide (NO)) emitted by the combustion of fossil energy are the cause of photochemical smog, acid rain, and ozone layer depletion, and a series of other problems, causing great damage to the environment. The state has increasingly strict requirements for the emission of nitrogen oxides, and has proposed a nitrogen oxide ultra-low emission policy (NOx≤50mg / Nm 3 ) in the exported flue gas. The ammonia selective catalytic reduction technology (NH3-SCR) is used in flue gas of large coal-fired power plants to achieve ultra-low emission. However, this technology is only suitable for flue gas with a temperature of 300-400℃. Nowadays, the flue gas temperature of sintering machines, industrial boilers, and glass kilns is below 180℃, and is not suitable for direct use of the NH3-SCR technology. In addition, in view of the problem of wet flue gas desulfurization, the share of circulating fluidized bed (CFB) semi-dry desulfurization technology is gradually increasing. For flue gas below 180℃, the flue gas oxidation + CFB semi-dry desulfurization and denitration technology has appeared in current engineering applications, i.e., O3, ClO2, or plasma is used to oxidize the difficult-to-absorb NO in the flue gas to convert as much as possible into NO2, and then NO2 and SO2 are removed by CFB semi-dry desulfurization. This technology has achieved certain scale of industrial application, and has good development prospects due to low investment, no waste liquid, and no wet flue gas.

[0003] However, in the flue gas oxidation + CFB semi-dry desulfurization and denitration technology, SO2 is well absorbed, but NO2 is still difficult to absorb, and unoxidized NO is even more difficult to absorb. Most projects are difficult to achieve ultra-low emission of nitrogen oxides, and are accompanied by yellow smoke or even red smoke emission (NO2 coloration); some projects also achieve ultra-low emission of nitrogen oxides, but the concentration of NO2 in the exhaust gas is >20mg / Nm 3 , and yellow smoke is emitted; some projects also use a large excess of ozone to oxidize NO to N2O5, and then absorb N2O5 to achieve denitration, but the O3 is excessively high, the operation cost is too high, and there is serious O3 escape. Therefore, how to significantly reduce NO2 and a part of NO at a relatively low O3 concentration to ensure ultra-low emission and no yellow smoke is a problem to be solved by the present application. SUMMARY

[0004] The application aims to provide a Ca-based denitration agent for flue gas after oxidation and a denitration process thereof.

[0005] A Ca-based denitration agent for flue gas after oxidation, which is in powder form and comprises, in mass percentage:

[0006]

[0007] Preferably, the particle size of the Ca-based denitration agent satisfies 200 mesh≤particle size≤300 mesh.

[0008] A modified Ca-based denitration agent for flue gas after oxidation, which is in powder form and comprises a Ca-based denitration agent and a modifier, wherein the mass of the modifier satisfies modifier / (Ca-based denitration agent+modifier)=5-20%, and the modifier comprises one or more of a sulfur-based denitration enhancer, a free radical capturing agent and a phase transfer agent.

[0009] Preferably, the denitration enhancer is one or more of calcium sulfide, sulfur and calcium thiosulfate.

[0010] Preferably, the free radical capturing agent is triethanolamine.

[0011] Preferably, the phase transfer agent is one or both of polyethylene glycol and quaternary ammonium salt.

[0012] The preparation method of the Ca-based denitration agent comprises the following steps:

[0013] Step (1), mixing: in a closed container, calcium sulfite, calcium sulfate, calcium carbonate and calcium hydroxide are sequentially added, and compressed air with a pressure of 0.2-0.4 MPa is introduced to mix the four substances in step (1), which ensures that the stabilizers calcium carbonate and calcium sulfate have ideal dispersibility;

[0014] Step (2), particle size: the sample obtained in step (1) is ground to satisfy 200 mesh≤particle size≤300 mesh, which ensures the fluidization performance of the three components.

[0015] For the case that the nitrogen oxides in the flue gas to be treated (imported flue gas) are >200 mg / Nm 3 or SO2<600 mg / Nm 3 NO2 is difficult to remove, a modified Ca-based denitration agent needs to be used for denitration, and the preparation method of the modified Ca-based denitration agent comprises the following steps: using the same process as the Ca-based denitration agent to prepare the modifier, and uniformly mixing the modifier with the Ca-based denitration agent.

[0016] The denitration process based on the Ca-based denitration agent or the modified Ca-based denitration agent comprises the following steps: S1, the injection amount of the denitration agent is: the total denitration agent mass of the day / the total slaked lime mass of the day=0.3-0.8, according to the slaked lime (calcium hydroxide) production capacity of the digester, the injection inlet of the denitration agent injected into the CFB semi-dry reactor is selected: when the slaked lime production rate / denitration agent injection rate>=1 / 6, the denitration agent is injected from the first injection inlet at the top of the slaked lime bin; when the slaked lime production rate / denitration agent injection rate<1 / 6, the denitration agent is injected from the second injection inlet at the bottom end of the CFB semi-dry reactor located on the flue;

[0017] S2, the to-be-treated flue gas (imported flue gas) is reacted with the oxidant (such as O3, ClO2 or plasma) generated by the oxidant generating device to convert part of NO in the flue gas into NO2, and the general NO oxidation rate is >80%, the oxidized flue gas enters the CFB semi-dry reactor, the pressure of the CFB semi-dry reactor is adjusted to be-0.8--1.3kPa, the water in the water tank is sprayed into the CFB semi-dry reactor through the pump via the spray gun, the oxidized flue gas is reacted with the denitration agent, the treated flue gas is discharged from the top of the CFB semi-dry reactor and enters the dust collecting device, the dust is recovered through the dust collecting device, the purified flue gas (exported flue gas) is discharged into the atmosphere through the chimney, the NO and NO2 contents in the treated flue gas are adjusted by controlling the oxidant amount, and the NO and NO2 contents are respectively ensured to be 0-40mg / Nm 3 and 0-30mg / Nm 3 ; meanwhile, the treated flue gas temperature is adjusted by controlling the water spraying amount, and the flue gas temperature is ensured to be 53-90℃;

[0018] S3, part of the dust recovered through the dust collecting device is returned to the CFB semi-dry reactor through the return feeder, the return feeder opening degree (valve opening degree) is 40%-65%, and the other part enters the slag bin through the slag discharger, and the slag discharger opening frequency is 0-12 times / h.

[0019] Compared with the prior art, the application has the following advantages and beneficial effects:

[0020] 1, due to the synergistic effect of the key components of the Ca-based denitration agent and the synergistic effect of the modified Ca-based denitration agent components based thereon, the denitration agent has better removal effect on NO2 and NO, and has higher denitration rate.

[0021] 2. Taking the use of O3 as an oxidant as an example, since the denitrification agent described in this invention removes NO2 and NO, it avoids the problem of using a large amount of O3 to oxidize NO into N2O5 and thus absorb nitrogen oxides when no denitrification agent is used. Therefore, by using this denitrification agent, the amount of O3 used is small, the operating cost is low, and O3 escape is suppressed to achieve the same denitrification effect. Similarly, when using ClO2 or plasma as an oxidant to oxidize nitrogen oxides, the amount of the corresponding oxidant can also be reduced, thereby reducing operating costs.

[0022] 3. After using the denitrification agent described in this invention, the reaction between low-valence sulfur species and NO2 and NO is enhanced, resulting in an increase in the generation of high-valence hexavalent sulfur and nitrite. Due to the increased content of these two reaction products, it is beneficial for the waste residue produced after the overall reaction to be used in the construction industry. Therefore, the quality of the desulfurization and denitrification product waste residue can be improved.

[0023] 4. Due to the efficient removal of nitrogen oxides, the amount of slaked lime used is reduced, avoiding the problems of excessive dosage and poor denitrification effect caused by using slaked lime alone as a denitrification agent when the denitrification agent described in this invention is not used. This saves operating costs and improves the denitrification effect.

[0024] 5. Since the structure of the CFB semi-dry reactor and its auxiliary equipment is not changed and no new equipment is added, the use of this invention requires almost no equipment modification or additional investment costs. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the CFB semi-dry process system described in this invention.

[0026] Figure 2 This is a schematic diagram of the structure of the fixed-bed tubular reactor denitrification system described in this invention.

[0027] Figure 1 In the diagram, 1 is the ozone generator, 2 is the CFB semi-dry reactor, 3 is the digester, 4 is the first injection port, 5 is the solid weighing scale, 6 is the slaked lime silo, 7 is the water tank, 8 is the pump, 9 is the induced draft fan, 10 is the dust collection device, 11 is the return feeder, 12 is the slag silo, 13 is the second injection port, 14 is the slag discharger, 15 is the circulating flue gas control valve, and 16 is the chimney. Detailed Implementation

[0028] In order to better understand the present application, the following examples further illustrate the content of the present application, but the content of the present application is not limited to the following examples, i.e. the following examples further illustrate the content of the present application, and should not be understood as a limitation of the present application. Modifications and replacements of the method, steps or conditions of the present application, without departing from the spirit and essence of the present application, all belong to the scope of the present application. If not specifically pointed out, the technical means used in the examples is the conventional means known to those skilled in the art.

[0029] The technical principle of the present application mainly lies in:

[0030] The four core substances of the denitration agent include calcium sulfite, calcium hydroxide, calcium carbonate and calcium sulfate. The four substances have a synergistic effect on the removal of NO2 and NO within the content range described in the present application: calcium sulfite can undergo an oxidation-reduction reaction with NO2, and the intermediate free radicals generated in the reaction can oxidize NO to NO2 - ; calcium hydroxide promotes the dissolution of NO2 and participates in the denitration reaction, while providing an alkaline environment to inhibit the decomposition of the denitration product NO2 - , and enables calcium sulfite to maintain denitration activity and storage stability; calcium carbonate in the system does not react with NO2 and NO as well as SO2, and its role is as follows: (1) dispersing calcium sulfite to inhibit the consumption caused by the self-oxidation of the free radical chain reaction generated in the reaction; (2) it has a heat insulation effect to inhibit the decomposition of the denitration product NO2 - ; (3) hydrophilicity ensures uniform and stable liquid film, and promotes gas-solid reaction. The calcium sulfate in the denitration agent does not react with NO2 and NO as well as SO2 in the system, and its role is to inhibit the conversion of sulfite to sulfate in the primary denitration reaction (the denitration agent first contacts with the flue gas), thereby stabilizing calcium sulfite.

[0031] For imported flue gas with high concentration of nitrogen oxides (>200mg / Nm 3 ) or flue gas with SO2 <600mg / Nm 3 , it is necessary to modify the Ca-based denitration agent. The modifier includes one or more of sulfur-based denitration enhancer, free radical capturing agent and phase transfer agent. Among them, the sulfur-based denitration enhancer includes one or more of calcium sulfide, sulfur and calcium sulfite; the free radical capturing agent includes triethanolamine; and the phase transfer agent includes one or both of polyethylene glycol and quaternary ammonium salt. In the denitration process, the contents of calcium sulfite, calcium hydroxide, calcium carbonate and calcium sulfate in the Ca-based denitration agent are dominant.

[0032] The denitration agent described in the present application includes the above-mentioned Ca-based denitration agent or modified Ca-based denitration agent, and the selection of the two is that, for imported flue gas with low concentration of nitrogen oxides (imported NOx≤200mg / Nm 3or high SO2 concentration (imported SO2 ≥ 600 mg / Nm³) 3 Under certain conditions, or when nitrogen oxide emission reduction requirements are not high, Ca-based denitrification agents can be used to achieve ultra-low nitrogen oxide emissions and NO2 emissions ≤20mg / Nm³. 3 In response to the high concentration of nitrogen oxides in imported flue gas (imported NOx > 200 mg / Nm³), 3 Or the SO2 concentration in the flue gas is low (inlet SO2 < 600 mg / Nm³). 3 When NO2 is difficult to remove, or when there are high requirements for nitrogen oxide emission reduction, it is necessary to select a modified Ca-based denitrification agent.

[0033] Based on this, strict process control is required to maintain the denitrification effect of the above components, thereby achieving efficient absorption of nitrogen oxides. The denitrification process based on the above-mentioned Ca-based or modified Ca-based denitrification agent (hereinafter referred to as denitrification agent in process steps S1-S5) is described in the process flow diagram below. Figure 1 The entire CFB semi-dry process system includes an oxidation unit, a CFB semi-dry reactor, a digestion unit, a recovery unit, and a water spraying unit. The oxidation unit described in this invention uses an ozone generator. The digestion unit produces quicklime (which removes SO2 from the flue gas; its dosage is based on a Ca / S molar ratio of 1.2–2.5). The recovery unit recovers dust from the outlet flue gas. The water spraying unit sprays water into the CFB semi-dry reactor to control the temperature of the treated flue gas. Specifically, the process includes the following steps:

[0034] S1, the injection rate of the denitrifying agent is: total daily denitrifying agent mass / total daily slaked lime mass = 0.3~0.8, preferably 0.5. Based on the slaked lime (calcium hydroxide) production capacity of the digester 3 in the digestion unit, the injection port of the denitrifying agent into the CFB semi-dry reactor 2 is selected: when the slaked lime production rate / denitrifying agent injection rate ≥ 1 / 6, the amount of slaked lime used is sufficient to meet desulfurization requirements, and this amount can ensure an alkaline environment for the denitrifying agent, promoting the reaction. In this case, the denitrifying agent is injected from the first injection port 4 at the top of the slaked lime silo 6 in the digestion unit; when the slaked lime production rate / denitrifying agent injection rate < 1 / 6, the slaked lime silo needs to be fully fed with slaked lime to ensure the desulfurization effect. In this case, the denitrifying agent is injected from the second injection port 13 located at the bottom of the CFB semi-dry reactor 2 tower on the flue. The slaked lime produced by the digester 3 is weighed by the solid weighing scale 5 and then enters the slaked lime silo 6.

[0035] S2, the flue gas is oxidized by O3 generated by the ozone generator, part of the NO in the flue gas is oxidized to NO2 by O3; the oxidation rate of NO is generally > 80%, the oxidized flue gas enters the CFB semi-dry reactor 2, the power of the induced draft fan 9 is adjusted, and the circulating flue gas control valve 15 is finely adjusted to adjust the pressure of the CFB semi-dry reactor 2 to -0.8~ -1.3kPa, and the pressure is preferably -1.1kPa, which improves the fluidization effect and flow rate of the denitration agent; the water in the water tank 7 is sprayed into the CFB semi-dry reactor 2 by the pump 8 through the lance, the oxidized flue gas reacts with the denitration agent, and the treated flue gas is discharged from the top of the CFB semi-dry reactor 2 into the dust collection device 10 of the recovery device, and the dust (containing unreacted denitration agent and reaction products) is recovered by the dust collection device 10, and the purified flue gas is discharged into the atmosphere through the chimney 16; by controlling the amount of oxidant, the content of NO and NO2 in the outlet flue gas is adjusted to ensure that the content of NO and NO2 is 0~40mg / Nm 3 and 0~30mg / Nm 3 When the denitration agent exists in the system, the outlet flue gas contains NO, the denitration agent has low consumption, the amount of O3 used is not large, the utilization rate is high, the escape of O3 is inhibited, and O3 is preferably used as the oxidant, and the content of NO is controlled to be <15mg / Nm 3 , the content of NO2 is <15mg / Nm 3 ; at the same time, the water injection amount of the pump 8 is controlled to adjust the temperature of the treated flue gas, and the temperature of the flue gas is ensured to be 53~90℃, and the temperature of the flue gas is preferably controlled to be 80.5℃, which has two effects: reducing the temperature can enhance the solubility of NO2 and NO in the liquid film of the denitration agent; water is a substance participating in the denitration reaction of the denitration agent, and at the same time, a liquid film is formed on the denitration agent to improve the reaction rate, and the final product of the reaction is calcium nitrite and calcium nitrate;

[0036] S3, the unreacted denitration agent and the desulfurization and denitration products are discharged from the top of the CFB semi-dry reactor 2 into the dust collection device 10 and are captured, and are settled at the bottom of the dust collection device 10;

[0037] S4, part of the captured material in step S3 enters the return feeder 11, the opening degree of the return feeder 11 and the opening degree of the discharger 14 are controlled to control the size of the return amount, change the material level height in the CFB semi-dry reactor 2 and the flow rate of the return material, and inhibit the reverse generation of a large amount of nitrite generated by the denitration agent to generate NO, the opening degree of the return feeder 11 is 40%~65%, and the opening degree of the return feeder is preferably 55%;

[0038] S5, the partially captured material in step S3 enters the slag bin 12 through the slag extractor 14. The opening degree of the slag extractor 14 is controlled to control the amount of the discharged material, and the pressure difference of the dust collection device 10 is adjusted to prevent the excessive pressure difference from causing the reverse generation of NO from a large amount of nitrite generated by the denitration agent. The opening frequency of the slag extractor 14 is 0-12 times / h, and preferably, the opening degree of the slag extractor 14 is 8 times / h. In the following examples 1-17, the raw materials are industrial grade and contain impurities that do not react with NO2, NO and SO2.

[0039] Example 1

[0040] Into a closed container, calcium sulfite, calcium sulfate, calcium carbonate and calcium hydroxide are sequentially added, and the mass content of the pure substances is 55%, 7%, 30% and 5% respectively, and the remaining components are impurities in the raw materials. Into the closed container, compressed air with a pressure of 0.20 Mpa is introduced to mix the calcium sulfite, calcium hydroxide and calcium carbonate, and the mixing time is 30 min. The mixture is ground to 200 mesh.

[0041] Example 2

[0042] Into a closed container, calcium sulfite, calcium sulfate, calcium carbonate and calcium hydroxide are sequentially added, and the mass content of the pure substances is 60%, 3%, 30% and 5% respectively, and the remaining components are impurities in the raw materials. Into the closed container, compressed air with a pressure of 0.20 Mpa is introduced to mix the calcium sulfite, calcium hydroxide and calcium carbonate, and the mixing time is 30 min. The mixture is ground to 200 mesh.

[0043] Example 3

[0044] Into a closed container, calcium sulfite, calcium sulfate, calcium carbonate and calcium hydroxide are sequentially added, and the mass content of the pure substances is 42%, 5%, 40% and 12% respectively, and the remaining components are impurities in the raw materials. Into the closed container, compressed air with a pressure of 0.3 Mpa is introduced to mix the calcium sulfite, calcium hydroxide and calcium carbonate, and the mixing time is 30 min. The mixture is ground to 200 mesh.

[0045] Example 4

[0046] Into a closed container, calcium sulfite, calcium sulfate, calcium carbonate and calcium hydroxide are sequentially added, and the mass content of the pure substances is 25%, 5%, 55% and 12% respectively, and the remaining components are impurities in the raw materials. Into the closed container, compressed air with a pressure of 0.3 Mpa is introduced to mix the calcium sulfite, calcium hydroxide and calcium carbonate, and the mixing time is 30 min. The mixture is ground to 200 mesh.

[0047] Example 5

[0048] Add calcium sulfite, calcium sulfate, calcium carbonate, and calcium hydroxide to a sealed container. The mass contents of the pure substances are 42%, 5%, 43%, and 7%, respectively. The remaining components are impurities in the raw materials. Introduce compressed air at a pressure of 0.3 MPa into the sealed container to mix the calcium sulfite, calcium hydroxide, and calcium carbonate for 30 minutes. Grind the mixture to 200 mesh.

[0049] Example 6

[0050] Add calcium sulfite, calcium sulfate, calcium carbonate, and calcium hydroxide to a sealed container. The mass contents of the pure substances are 30%, 5%, 35%, and 25%, respectively. The remaining components are impurities in the raw materials. Introduce compressed air at a pressure of 0.3 MPa into the sealed container to mix the calcium sulfite, calcium hydroxide, and calcium carbonate for 30 minutes. Grind the mixture to 200 mesh.

[0051] The proportions of each raw material in the Ca-based denitrification agents prepared in Examples 1-6 are shown in Table 1.

[0052] For example, a certain sintering plant Figure 1 Taking the CFB semi-dry process system as an example, the oxidant is O3, the inlet flue gas conditions are listed in Table 2, the lime production rate / denitrile injection rate is ≥1 / 6, the Ca-based denitrile agent prepared in Examples 1-6 is selected for injection at the first injection port, the operating conditions for using the Ca-based denitrile agent are listed in Table 3, and the denitrification effect is shown in Table 4.

[0053] For example, a certain sintering plant Figure 1 Taking the CFB semi-dry system as an example, the oxidant is O3, the inlet flue gas conditions are listed in Table 5, the lime production rate / denitrile injection rate is <1 / 6, the Ca-based denitrile agent prepared in Examples 1-6 is injected through the second injection port, the operating conditions for using the Ca-based denitrile agent are listed in Table 6, and the denitrification effect is shown in Table 7.

[0054] Table 1. Content of each substance in Examples 1-6

[0055]

[0056] Table 2 Inlet flue gas conditions when using the first injection port

[0057] Exhaust gas type Flue gas volume (Nm 3 / h) SO2(mg / Nm 3 )]]> NOx(mg / Nm 3 )]]> Flue gas temperature (°C) Sintering flue gas 1000000～1100000 About 1200 About 195 132～143

[0058] Note: Operating time is calculated based on 24 hours / day; the volume content of imported NOx is more than 95% NO, and the remainder is NO2.

[0059] Table 3 Operating conditions when using the first injection port

[0060] Denitration agent injection port Injection amount (tons / day) Reactor top temperature (°C) Pressure (kPa) Reverberatory opening (%) First injection port 30～60 81 -1.1 55

[0061] Note: O3 usage is adjusted to the power of the ozone generator to adjust the outlet flue gas to NO+NO2 < 50 mg / Nm 3 , and NO < 30 mg / Nm 3 , NO2 < 20 mg / Nm 3 . Some of the denitrification agents exceed the above-mentioned targets, which is related to the denitrification limit of the denitrification agent.

[0062] Table 4 Denitrification effect when using the first injection port

[0063]

[0064]

[0065] Note: NOx includes NO and NO2. Denitrification rate: (Inlet NOx - (Outlet NO2 + Outlet NO x 46 / 30)) ÷ Inlet NOx.

[0066] Table 5 Inlet flue gas conditions when using the second injection port

[0067] Exhaust gas type Flue gas volume (Nm 3 / h) SO2(mg / Nm 3 )]]> NOx(mg / Nm 3 )]]> Flue gas temperature (°C) Sintering flue gas 550000～650000 About 1200 About 105 135～146

[0068] Note: The operating time is calculated as 24 hours / day; the volume content of more than 95% in the inlet NOx is NO, and the rest is NO2.

[0069] Table 6 Operating conditions when using the second injection port

[0070] Denitration agent injection port Injection amount (tons / day) Reactor top temperature (°C) Pressure (kPa) Reverberatory opening (%) Second injection port 25～34 82 -1.2 56

[0071] Note: O3 usage is adjusted to the power of the ozone generator to adjust the outlet flue gas to NO+NO2 < 50 mg / Nm 3 , and NO < 30 mg / Nm 3 , NO2 < 20 mg / Nm 3 . Some of the denitrification agents exceed the above-mentioned targets, which is related to the denitrification limit of the denitrification agent.

[0072] Table 7 Denitrification effect when using the second injection port

[0073]

[0074] Note: NOx includes NO and NO2. Denitrification rate: (Inlet NOx - (Outlet NO2 + Outlet NO x 46 / 30)) ÷ Inlet NOx.

[0075] As can be seen from Table 4 and Table 7, when the content of calcium sulfite is 25% (which is the lowest content of calcium sulfite in each example), the Ca-based denitration agent has the worst removal effect on NO2 and NO under the same conditions, thus calcium sulfite plays a role in removing NO2 and NO. This can be attributed to the fact that calcium sulfite reacts with NO2 to generate calcium sulfate and calcium nitrite, and in this process, the sulfite radical is an intermediate, which has oxidizing property and oxidizes NO to NO2 - . As can be seen from the comparison of the denitration effects of Example 1 and Example 2, the more calcium sulfite is not necessarily better, and when there is sulfate in the system, NO2 decreases significantly (NO2 can cause yellow smoke, which is the nitrogen oxide to be controlled first). This phenomenon can be attributed to the fact that the sulfate in the Ca-based denitration agent inhibits the reaction of sulfite with itself to form sulfate, and even if the reaction equilibrium moves in the reverse direction, the sulfite is preserved and promotes its reaction with NO2, thereby improving the denitration effect. As can be seen from the comparison of Example 1 and Example 3, when the content of calcium sulfite in the Ca-based denitration agent decreases and the contents of calcium carbonate and calcium hydroxide increase, the Ca-based denitration agent has a significant removal effect on NO2 and a slight rebound on NO, and the overall denitration rate increases. This phenomenon shows that calcium carbonate promotes the absorption of NO2, and from the chemical reaction, calcium carbonate does not have ideal redox properties and will not undergo redox reaction with NO2, thus it is not that calcium carbonate reacts with NO2, but that calcium carbonate acts as a stabilizer to effectively disperse calcium sulfite, inhibit the free radical chain reaction of self-oxidized sulfite, and at the same time, it has a heat insulation effect to inhibit the decomposition of the denitration product NO2 - (the content of the reaction product NO2 - increases); at the same time, its hydrophilicity ensures uniform and stable liquid film, and promotes gas-solid reaction. In addition, the increase in the content of calcium hydroxide also contributes to denitration, and this phenomenon can be attributed to the fact that calcium hydroxide promotes the dissolution of NO2 and participates in the denitration reaction, at the same time, provides an alkaline environment to inhibit the decomposition of the denitration product NO2 - , and makes calcium sulfite maintain denitration activity. It is found that when calcium hydroxide is contained in the components during the storage of the Ca-based denitration agent, the storage time of the denitration agent can be extended through the alkaline environment, thus calcium hydroxide can maintain the stability of the Ca-based denitration agent. As can be seen from the comparison of Example 3 and Example 5, reducing calcium hydroxide and increasing calcium carbonate can further improve the removal of NO2, which also shows the stability of calcium carbonate, and calcium hydroxide is not necessarily the more the better, and it can be reduced from 12% to 7%. As can be seen from the comparison of Example 5 and Example 6, when the content of calcium sulfite decreases, the content of calcium hydroxide further increases, and the content of calcium carbonate decreases, the denitration and the removal of NO2 and NO all decrease. This phenomenon shows that the sulfite plays a role in removing NO2, and the intermediate oxidizes NO, and reducing the content of calcium carbonate reduces the dispersibility of calcium sulfite, which inhibits the denitration reaction.

[0076] Comparative Example 1

[0077] Ca-based denitration agent comparative example, according to the formula in Table 8, calcium sulfite, calcium sulfate, calcium carbonate, calcium hydroxide were put into the laboratory small fixed bed tube reactor in turn to evaluate the denitration effect, the mass content was 0%, 0%, 100%, 0% in turn, and the denitration effect was shown in Table 9.

[0078] Comparative Example 2

[0079] Ca-based denitration agent comparative example, according to the formula in Table 8, calcium sulfite, calcium sulfate, calcium carbonate, calcium hydroxide were put into the laboratory small fixed bed tube reactor in turn to evaluate the denitration effect, the mass content was 100%, 0%, 0%, 0% in turn, and the denitration effect was shown in Table 9.

[0080] Comparative Example 3

[0081] Ca-based denitration agent comparative example, according to the formula in Table 8, calcium sulfite, calcium sulfate, calcium carbonate, calcium hydroxide were put into the laboratory small fixed bed tube reactor in turn to evaluate the denitration effect, the mass content was 0%, 0%, 0%, 100% in turn, and the denitration effect was shown in Table 9.

[0082] Comparative Example 4

[0083] Ca-based denitration agent comparative example, according to the formula in Table 8, calcium sulfite, calcium sulfate, calcium carbonate, calcium hydroxide were put into the laboratory small fixed bed tube reactor in turn to evaluate the denitration effect, the mass content was 0%, 100%, 0%, 0% in turn, and the denitration effect was shown in Table 9.

[0084] Comparative Example 5

[0085] Ca-based denitration agent comparative example, according to the formula in Table 8, calcium sulfite, calcium sulfate, calcium carbonate, calcium hydroxide were put into the laboratory small fixed bed tube reactor in turn to evaluate the denitration effect, the mass content was 50%, 0%, 50%, 0% in turn, and the denitration effect was shown in Table 9.

[0086] Comparative Example 6

[0087] Ca-based denitration agent comparative example, according to the formula in Table 8, calcium sulfite, calcium sulfate, calcium carbonate, calcium hydroxide were put into the laboratory small fixed bed tube reactor in turn to evaluate the denitration effect, the mass content was 0%, 0%, 50%, 50% in turn, and the denitration effect was shown in Table 9.

[0088] Comparative Example 7

[0089] Ca-based denitration agent comparative example, according to the formula in Table 8, calcium sulfite, calcium sulfate, calcium carbonate, calcium hydroxide were put into a laboratory small fixed bed tube reactor in turn to evaluate the denitration effect, the mass content was 0%, 50%, 50%, 0% in turn, and the denitration effect was shown in Table 9.

[0090] Comparative Example 8

[0091] Ca-based denitration agent comparative example, according to the formula in Table 8, calcium sulfite, calcium sulfate, calcium carbonate, calcium hydroxide were put into a laboratory small fixed bed tube reactor in turn to evaluate the denitration effect, the mass content was 0%, 50%, 50%, 0% in turn, and the denitration effect was shown in Table 9.

[0092] Comparative Example 9

[0093] Ca-based denitration agent comparative example, according to the formula in Table 8, calcium sulfite, calcium sulfate, calcium carbonate, calcium hydroxide were put into a laboratory small fixed bed tube reactor in turn to evaluate the denitration effect, the mass content was 0%, 50%, 50%, 0% in turn, and the denitration effect was shown in Table 9.

[0094] Comparative Example 10

[0095] Ca-based denitration agent comparative example, according to the formula in Table 8, calcium sulfite, calcium sulfate, calcium carbonate, calcium hydroxide were put into a laboratory small fixed bed tube reactor in turn to evaluate the denitration effect, the mass content was 0%, 50%, 50%, 0% in turn, and the denitration effect was shown in Table 9.

[0096] Comparative Example 11

[0097] Ca-based denitration agent comparative example, according to the formula in Table 8, calcium sulfite, calcium sulfate, calcium carbonate, calcium hydroxide were put into a laboratory small fixed bed tube reactor in turn to evaluate the denitration effect, the mass content was 0%, 50%, 50%, 0% in turn, and the denitration effect was shown in Table 9.

[0098] Comparative Example 12

[0099] Ca-based denitration agent comparative example, according to the formula in Table 8, calcium sulfite, calcium sulfate, calcium carbonate, calcium hydroxide were put into a laboratory small fixed bed tube reactor in turn to evaluate the denitration effect, the mass content was 0%, 50%, 50%, 0% in turn, and the denitration effect was shown in Table 9.

[0100] Comparative Example 13

[0101] Ca-based denitration agent comparative example, according to the formula in Table 8, calcium sulfite, calcium sulfate, calcium carbonate, calcium hydroxide were put into a laboratory small fixed bed tube reactor in turn to evaluate the denitration effect, the mass content was 0%, 50%, 50%, 0% in turn, and the denitration effect was shown in Table 9.

[0102] Comparative Example 14

[0103] According to the formulation in Table 8, calcium sulfite, calcium sulfate, calcium carbonate, and calcium hydroxide were sequentially added to a small-scale fixed-bed tubular reactor in the laboratory to evaluate the denitrification effect. The mass contents were 50%, 35%, 15%, and 5%, respectively. The denitrification effect is shown in Table 9.

[0104] Comparative Example 15

[0105] According to the formulation in Table 8, calcium sulfite, calcium sulfate, calcium carbonate, and calcium hydroxide were sequentially added to a small-scale fixed-bed tubular reactor in the laboratory to evaluate the denitrification effect. The mass contents were 50%, 10%, 35%, and 5%, respectively. The denitrification effect is shown in Table 9.

[0106] The proportions of each raw material in the denitrification agents prepared in Comparative Examples 1 to 15 are shown in Table 8.

[0107] The Ca-based denitrifying agent obtained in Example 5 was compared and verified with the denitrifying agents obtained in Comparative Examples 1 to 15.

[0108] by Figure 2 The laboratory-scale fixed-bed tubular reactor shown is a device for evaluating denitrification performance. The oxidant is O3, the flue gas flow rate is 3 L / min, the flue gas composition is NO, and the content is 300 mg / Nm³. 3 The O3 / NO molar ratio is approximately 1.3. After oxidation by O3, the flue gas contains 20 mg / Nm³ of NO and 20 mg / Nm³ of NO. 3 and 280mg / Nm 3 about.

[0109] The denitrification effects of Example 5 and Comparative Examples 1-15 are listed in Table 9.

[0110] Table 8 shows the content of each substance in Comparative Examples 1–15.

[0111]

[0112] Table 9 shows the denitrification test results of Comparative Examples 1-15 and Example 5.

[0113]

[0114]

[0115] Note: Denitrification rate: (Imported NO2 + Imported NO - Exported NO2 - Exported NO) ÷ (Imported NO2 + Imported NO).

[0116] From the denitration effect of Comparative Examples 1, 2, 3, 4 in Table 9, it can be seen that the denitration effect is not ideal when calcium sulfite, calcium sulfate, calcium carbonate, and calcium hydroxide are used alone, among which the denitration effect of calcium sulfite and calcium hydroxide is relatively better. It can be seen from Comparative Examples 6, 7, 10 which do not contain calcium sulfite that the corresponding NO2 absorption effect is not ideal, and therefore, calcium sulfite is the main substance that reacts with nitrogen oxides in the synergistic effect of the four substances.

[0117] It can be seen from the effect of Comparative Example 8 in Table 9 that when calcium sulfite and calcium hydroxide are contained in the system, the denitration effect is ideal after 10 minutes of reaction, indicating that calcium sulfite can further strengthen the denitration effect under the action of calcium hydroxide. The poor denitration effect of Comparative Example 5 and Comparative Example 9 which contain calcium sulfite but do not contain calcium hydroxide, and the poor denitration effect of Comparative Example 6 and Comparative Example 10 which contain calcium hydroxide but do not contain calcium sulfite, also indicate that calcium sulfite can further strengthen the denitration effect under the action of calcium hydroxide. This phenomenon can be attributed to the fact that calcium hydroxide promotes the dissolution of NO2 and participates in the denitration reaction, at the same time, provides an alkaline environment to inhibit the decomposition of denitration product NO2 - (detection of product shows that the content of NO2 - increases when calcium hydroxide is present), and enables calcium sulfite to maintain denitration activity. The denitration effect of Comparative Example 13 which does not contain calcium hydroxide is obviously lower than that of Comparative Example 8, and therefore, it is also indicated that calcium hydroxide plays a role in denitration. However, after 30 minutes, the content of NO2 in Comparative Example 8 rises to 32 mg / Nm 3 , while Example 4 still maintains a good denitration effect. It is indicated that the stabilizers calcium carbonate and calcium sulfate further play a role in denitration effect. Comparative Examples 11 and 12 include calcium sulfite and calcium hydroxide, and the denitration activity is ideal, indicating the role of calcium sulfite and calcium hydroxide. In addition, Comparative Example 11 includes calcium carbonate, and Comparative Example 12 includes calcium sulfate, and the denitration activity of Comparative Examples 11 and 12 is improved compared with that of Comparative Example 8, and at the same time, the denitration activity of Comparative Examples 11 and 12 is further improved compared with that of Comparative Example 8 after 30 minutes of testing, and therefore, calcium carbonate and calcium sulfate play a role in the stability of denitration effect.

[0118] It can be seen from the comparison of the denitration effect of Comparative Examples 14 and 15 that when the content of calcium carbonate decreases to 10% and the content of calcium sulfate increases to 35%, the denitration activity of Comparative Example 14 decreases. This phenomenon indicates that the relatively high content of calcium carbonate plays a role in the stability of the denitration agent compared with the content of calcium sulfate. This phenomenon can be attributed to the fact that a high content of calcium carbonate can play the following roles: as a stabilizer, it can effectively disperse calcium sulfite and inhibit the self-oxidation of free radicals generated in the reaction; at the same time, it has a heat insulation effect and inhibits the decomposition of denitration product NO2 - (detection of product shows that the content of NO2 -The content of calcium sulfate is controlled to be less than 10%, which can inhibit the conversion of sulfite to sulfate (control the reaction equilibrium) and ensure the uniformity and stability of the liquid film, promote the gas-solid reaction, and improve the denitration performance.

[0119] As shown by the comparison of the denitration effects of Comparative Examples 1-15 and Example 5, when the mass contents of the pure calcium sulfite, calcium sulfate, calcium carbonate and calcium hydroxide are 42%, 5%, 43% and 7% respectively, the 5 min denitration performance and 10 min denitration performance are ideal, and the four core substances play a synergistic role to improve the denitration performance.

[0120] Table 10: Ozone usage and ozone escape test results of Example 5 and Comparative Example 3

[0121]

[0122] Note: The concentrations of NO2 and NO in the flue gas after oxidation are 280 mg / Nm 3 and 20 mg / Nm 3 respectively.

[0123] As shown by the test results in Table 10, compared with the traditional lime as an absorbent to remove NO2 and NO, the Ca-based denitration agent has a small O3 escape under the condition that the molar ratio of O3 / NO is 1.3. In addition, under the condition that the removal of NO2 and NO is basically the same, the Ca-based denitration agent uses a smaller amount of O3 (Comparative Example 3 uses O3 / NO molar ratio of 3.0 to reduce NO2 to 4 mg / Nm 3 and NO to 5 mg / Nm 3 . The traditional lime denitration method uses a large amount of O3 to convert NO to N2O5, and then realizes denitration. Therefore, compared with the traditional lime denitration, the Ca-based denitration agent can reduce the amount of O3 used in the denitration process and effectively reduce the escape of O3.

[0124] Table 11: Denitration effect after increasing the amount of calcium hydroxide

[0125]

[0126] Note: The concentrations of NO2 and NO in the flue gas after oxidation are 280 mg / Nm 3 and 20 mg / Nm 3 respectively.

[0127] As shown by the test results in Table 11, when the amount of calcium hydroxide is increased, i.e. the amount of calcium hydroxide is tripled, the outlet NO2 and outlet NO are both significantly decreased, but there are still 75 mg / Nm 3 and 11 mg / Nm 3Therefore, increasing the amount of calcium hydroxide will improve the denitration effect, but the denitration effect is still not ideal. In actual engineering, some projects also use a large amount of lime to strive for denitration, but the denitration effect is not ideal, and the lime is wasted seriously. Therefore, since the Ca-based denitration agent can efficiently remove nitrogen oxides, the amount of lime can be reduced, avoiding the problem of using too much lime as a denitration agent when not using the Ca-based denitration agent, and the problem of poor denitration effect when using lime alone as a denitration agent. The operation cost can be saved, and the denitration effect can be improved. In addition, since the Ca-based denitration agent is used, the reaction product is high-valence sulfur and nitrite, both of which have high content and are needed in the construction industry; using lime alone for denitration will increase the proportion of lime in the desulfurization and denitration product slag due to the large amount of lime used; therefore, using the Ca-based denitration agent will be beneficial to the use of the waste slag produced after the total reaction in the construction industry.

[0128] Example 7

[0129] A closed container was added with 93 parts by weight of the Ca-based denitration agent of Example 5, and 7 parts by weight of calcium sulfide as a modifier, the particle size of the calcium sulfide was 200 mesh, and compressed air with a pressure of 0.25 MPa was introduced into the above-mentioned material mixture, the mixing time was 15 min. A modified Ca-based denitration agent was obtained.

[0130] Example 8

[0131] A closed container was added with 91 parts by weight of the Ca-based denitration agent of Example 5, and 9 parts by weight of sulfur as a modifier, the particle size of the sulfur was 200 mesh, and compressed air with a pressure of 0.20 MPa was introduced into the above-mentioned material mixture, the mixing time was 15 min. A modified Ca-based denitration agent was obtained.

[0132] Example 9

[0133] A closed container was added with 93 parts by weight of the Ca-based denitration agent of Example 5, and 7 parts by weight of calcium sulfide (dry basis) as a modifier, and compressed air with a pressure of 0.40 MPa was introduced into the above-mentioned material mixture, the mixing time was 15 min. A modified Ca-based denitration agent was obtained.

[0134] Example 10

[0135] A closed container was added with 85 parts by weight of the Ca-based denitration agent of Example 5, and 5 parts by weight of calcium sulfide, 5 parts by weight of sulfur, and 5 parts by weight of calcium sulfide (dry basis), the particle size of the calcium sulfide and sulfur was 200 mesh, and compressed air with a pressure of 0.40 MPa was introduced into the above-mentioned material mixture, the mixing time was 15 min. A modified Ca-based denitration agent was obtained.

[0136] Example 11

[0137] Into a closed container, 94 parts by weight of the Ca-based denitration agent of Example 5 was added, and 6 parts by weight of triethanolamine was added. The above materials were mixed by introducing compressed air with a pressure of 0.35 MPa for 15 min. A modified Ca-based denitration agent was obtained.

[0138] Example 12

[0139] Into a closed container, 94 parts by weight of the Ca-based denitration agent of Example 5 was added, and 6 parts by weight of polyethylene glycol was added. The above materials were mixed by introducing compressed air with a pressure of 0.35 MPa for 15 min. A modified Ca-based denitration agent was obtained.

[0140] Example 13

[0141] Into a closed container, 92 parts by weight of the Ca-based denitration agent of Example 5 was added, and 8 parts by weight of a quaternary ammonium salt was added. The above materials were mixed by introducing compressed air with a pressure of 0.35 MPa for 15 min. A modified Ca-based denitration agent was obtained.

[0142] Example 14

[0143] Into a closed container, 87 parts by weight of the Ca-based denitration agent of Example 5 was added, and 7 parts by weight of calcium sulfide, 6 parts by weight of triethanolamine was added, wherein the particle size of the calcium sulfide was 200 mesh. The above materials were mixed by introducing compressed air with a pressure of 0.35 MPa for 15 min. A modified Ca-based denitration agent was obtained.

[0144] Example 15

[0145] Into a closed container, 87 parts by weight of the Ca-based denitration agent of Example 5 was added, and 7 parts by weight of calcium sulfide, 6 parts by weight of polyethylene glycol was added, wherein the particle size of the calcium sulfide was 200 mesh. The above materials were mixed by introducing compressed air with a pressure of 0.35 MPa for 15 min. A modified Ca-based denitration agent was obtained.

[0146] Example 16

[0147] Into a closed container, 88 parts by weight of the Ca-based denitration agent of Example 5 was added, and 6 parts by weight of triethanolamine, 6 parts by weight of polyethylene glycol was added. The above materials were mixed by introducing compressed air with a pressure of 0.35 MPa for 15 min. A modified Ca-based denitration agent was obtained.

[0148] Example 17

[0149] Add 81 parts by weight of the Ca-based denitrification agent from Example 5 to a sealed container, then add 7 parts by weight of calcium sulfide, 6 parts by weight of triethanolamine, and 6 parts by weight of polyethylene glycol, wherein the calcium sulfide has a particle size of 200 mesh. Mix the above materials with compressed air at a pressure of 0.40 MPa for 15 minutes. The modified Ca-based denitrification agent is obtained.

[0150] The proportions of each modifier raw material in the Ca-based denitrification agents prepared in Examples 7-17 are shown in Table 12.

[0151] For example, a certain sintering plant Figure 1 Taking the CFB semi-dry process system as an example, the oxidant is O3, the inlet flue gas conditions are listed in Table 13, the slaked lime production rate / denitrifier injection rate is ≥1 / 6, the modified Ca-based denitrifier prepared in Examples 7 to 17 and the Ca-based denitrifier prepared in Example 5 are selected for injection at the first injection port, the operating conditions for using the denitrifier are listed in Table 14, and the denitrification effect of the denitrifier in each example is shown in Table 15.

[0152] For example, a certain sintering plant Figure 1 Taking the CFB semi-dry process system as an example, its oxidant is O3, the inlet flue gas conditions are listed in Table 16, the slaked lime production rate / denitrification agent injection rate is <1 / 6, the modified Ca-based denitrification agent prepared in Examples 7 to 17 and the Ca-based denitrification agent prepared in Example 5 are selected for injection through the second injection port, the operating conditions for using the denitrification agent are listed in Table 17, and the denitrification effect of the denitrification agent in each example is shown in Table 18.

[0153] Table 12 Content of each modifier in Examples 7-17

[0154]

[0155] Table 13 Inlet flue gas conditions when using the first injection port

[0156] Exhaust gas type Flue gas volume (Nm 3 / h) SO2(mg / Nm 3 )]]> NO x (mg / Nm 3 )]]> Flue gas temperature (°C) Sintering flue gas 1000000～1100000 About 800 About 300 137～143

[0157] Note: Operating time is calculated based on 24 hours / day.

[0158] Table 14 Operating conditions when injecting through the first injection port

[0159]

[0160] Note: O3 usage refers to the conditional ozone generator power, adjusted until the outlet flue gas NO+NO2 < 50 mg / Nm³. 3 And NO < 30 mg / Nm 3 NO2 < 20 mg / Nm 3 The fact that some denitrification agents exceed the above-mentioned performance indicators is related to the limited denitrification limit of these agents.

[0161] Table 15 Denitrification effect when using the first injection port

[0162]

[0163] Note: NOx includes NO and NO2. Denitrification rate: (Inlet NOx- (Outlet NO2+ Outlet NO x 46 / 30)) ÷ Inlet NOx.

[0164] Table 16 Inlet flue gas conditions when using the second injection port

[0165] Exhaust gas type Flue gas volume (Nm 3 / h) SO2(mg / Nm 3 )]]> NO x (mg / Nm 3 )]]> Flue gas temperature (°C) Sintering flue gas 480000～570000 About 450 About 150 135～141

[0166] Note: Running time is calculated as 24 hours / day.

[0167] Table 17 Operating conditions when using the second injection port

[0168]

[0169]

[0170] Note: O3 usage is the condition ozone generator power, adjusted to outlet flue gas NO+NO2 < 50 mg / Nm 3 , and NO < 30 mg / Nm 3 , NO2 < 20 mg / Nm 3 . Partial denitrification agent effect exceeds the above index, which is related to the denitrification limit of the denitrification agent.

[0171] Table 18 Denitrification effect when using the second injection port

[0172]

[0173] Note: NOx includes NO and NO2. Denitrification rate: (Inlet NOx- (Outlet NO2+ Outlet NO x 46 / 30)) ÷ Inlet NOx.

[0174] When the NO content in the target flue gas is high or the SO2 concentration in the flue gas is low or the nitrogen oxide emission reduction requirement is high, a modified Ca-based denitrification agent needs to be selected. The reasons are as follows: (1) When the NO content in the flue gas is high, more O3 is used, and more NO2 is generated. The use amount of the unmodified Ca-based denitrification agent is large, but the volume of the CFB reactor is limited, which reduces the use amount of the desulfurization agent, and further affects the desulfurization effect. Meanwhile, in the limited volume of the CFB reactor, there is an upper limit to the denitrification capacity. At the same time, too much NO2 will accelerate the oxidation of calcium sulfite and inhibit the reaction. Therefore, a modified Ca-based denitrification agent is needed to strengthen the denitrification effect. (2) The SO2 concentration in the appropriate range is beneficial to denitrification. It is found that when using an unmodified Ca-based denitrification agent, the SO2 concentration needs to be in the range of 800-1700 mg / Nm 3The lower SO2 concentration has no significant effect on the denitration, and thus the Ca-based denitration agent needs to be modified to enhance the denitration effect.

[0175] As can be seen from Table 15 and Table 18, under the same conditions, when the inlet nitrogen oxide concentration is high or the SO2 concentration is low, the flue gas condition is harsh, and the denitration result is not ideal when the unmodified Ca-based denitration agent such as the Ca-based denitration agent prepared in Example 5 is used, and the ultra-low emission requirement cannot be met. However, the Ca-based denitration agent still has a denitration rate of more than 70%, and thus the four core components still have significant denitration capacity.

[0176] When the denitration enhancer calcium sulfide, sulfur, calcium thiosulfate or the mixture of the three is added to the Ca-based denitration agent, the denitration effect of Examples 7, 8, 9 and 10 is significant, which shows that the sulfide with reducing property can enhance the denitration performance, which is consistent with the denitration mechanism of calcium sulfite, but has stronger reducing property and better denitration property. In the denitration process, the synergistic effect of calcium sulfate, calcium carbonate and calcium hydroxide still exists, and thus the denitration enhancer with reducing property is suitable.

[0177] When the radical capturing agent triethanolamine is added to the Ca-based denitration agent, the denitration effect of Example 11 is significant. This phenomenon can be attributed to the fact that the speed of the free radicals generated by calcium sulfite in the denitration process to oxidize NO is slower than the speed of the oxidized sulfite to generate sulfate, and thus the triethanolamine captures the free radicals, retains the content of the main denitration agent, promotes the removal of NO2, and at the same time, calcium carbonate and calcium sulfate still play a role, thereby improving the denitration effect.

[0178] When the phase transfer agent is added to the Ca-based denitration agent, the denitration effect of Examples 12 and 13 is significant. This phenomenon can be attributed to the fact that on the basis of the hydrophilicity of calcium carbonate to ensure the uniformity and stability of the liquid film, the phase transfer agent further enhances the mass transfer of nitrogen oxide in the liquid film and improves the denitration effect.

[0179] As can be seen from Examples 14, 15 and 16, the denitration effect of Examples 14 and 15 containing denitration enhancers is significantly better than that of Example 16, which shows that the reduced sulfur species of the denitration enhancer plays a role in improving the denitration effect, and the radical capturing agent and the phase transfer agent play an auxiliary role.

[0180] After adding the denitration enhancer, the free radical capturing agent and the phase transfer agent into the Ca-based denitration agent, the denitration effect of the denitration agent of Example 17 is the most remarkable, which indicates that the denitration effect is improved under the joint action of the denitration enhancer, the free radical capturing agent and the phase transfer agent. In addition, compared with the denitration effect of the Ca-based denitration agent prepared in Example 5 (Tables 15 and 18), which still has a denitration rate of more than 70%, it can be known that the main contribution to the denitration is still the synergistic effect of calcium sulfite, calcium sulfate, calcium carbonate and calcium hydroxide, and the modifier plays a synergistic role.

Claims

1. A Ca-based denitration agent for flue gas after oxidation, characterized by, The Ca-based denitration agent is in powder form and comprises, by mass percentage: calcium sulfite 42% calcium hydroxide 7% calcium carbonate 43% calcium sulfate 5%; The Ca-based denitration agent has a particle size of 200 mesh; The Ca-based denitration agent is used in the case where nitrogen oxides NOx≤ 200 mg / Nm 3 or SO2≥ 600 mg / Nm 3 of flue gas to be treated.

2. A modified Ca-based denitration agent for flue gas after oxidation, characterized by, The modified Ca-based denitration agent is in powder form and comprises 19 parts by weight of a modifier and 81 parts by weight of the Ca-based denitration agent as claimed in claim 1, wherein the modifier is 7 parts by weight of a sulfur-based denitration enhancer calcium sulfide, 6 parts by weight of a free radical capturing agent triethanolamine, and 6 parts by weight of a phase transfer agent polyethylene glycol; The modified Ca-based denitration agent is used in the case where nitrogen oxides NOx> 200 mg / Nm 3 or SO2< 600 mg / Nm 3 of the flue gas to be treated.

3. A process for the removal of NOx using a CFB semi-dry system, characterized in that, The method comprises the following steps: S1. The injection amount of the denitration agent as claimed in claim 1 or 2 is: total denitration agent mass of the day / total slaked lime mass of the day = 0.3-0.8, and according to the capacity of the slaker for producing slaked lime, the injection inlet for injecting the denitration agent into the CFB semi-dry reactor is selected: when the slaked lime production rate / denitration agent injection rate ≥ 1 / 6, the denitration agent is injected from the first injection inlet at the top of the slaked lime bin; when the slaked lime production rate / denitration agent injection rate < 1 / 6, the denitration agent is injected from the second injection inlet at the bottom end of the CFB semi-dry reactor located on the flue; S2, the flue gas to be treated is reacted with the oxidant generated by the oxidant generating device to convert part of the NO in the flue gas into NO2, and the oxidized flue gas enters the CFB semi-dry reactor, the pressure of the CFB semi-dry reactor is adjusted to -0.8~-1.3kPa, water is sprayed into the CFB semi-dry reactor by a spray gun, the oxidized flue gas is reacted with the denitration agent, the treated flue gas is discharged from the top of the CFB semi-dry reactor and enters the dust collecting device, dust is recovered by the dust collecting device, and the purified flue gas is discharged to the atmosphere, the content of NO and NO2 in the treated flue gas is adjusted by controlling the amount of oxidant, so that the content of NO and NO2 is 0~40mg / Nm 3 and 0~30mg / Nm 3 ; at the same time, the temperature of the treated flue gas is adjusted by controlling the amount of water sprayed, so that the temperature of the flue gas is 53~90℃; S3. Part of the dust recovered by the dust collecting device is returned to the CFB semi-dry reactor through a return feeder, and the opening degree of the return feeder is 40%-65%; the other part of the dust is discharged into a slag bin through a slag discharger, and the opening frequency of the slag discharger is 0-12 times / h.

Images