Desulfurization and denitrification method using chlorine dioxide

Abstract

A desulfurization and denitration method using chlorine dioxide, comprising: (1) a step of adding an aqueous chlorate solution, a peroxide solution, and an aqueous sulfuric acid solution to a chlorine dioxide generator and reacting them to obtain chlorine dioxide gas, and mixing the chlorine dioxide gas with air to obtain a mixed gas, wherein the chlorine dioxide gas accounts for 4 to 10 vol% of the mixed gas; (2) a step of contacting the mixed gas with flue gas in a flue gas pipe before introduction into a desulfurization and denitration tower to obtain an oxidized flue gas, wherein the molar ratio of chlorine dioxide in the mixed gas introduced into the flue gas pipe per unit time to nitric oxide contained in the flue gas is 1 to 1.8; and (3) a step of introducing the oxidized flue gas into a desulfurization and denitration tower, mixing it with a sprayed dry powder alkaline absorbent, and spraying water into the desulfurization and denitration tower to obtain a desulfurized and denitrated flue gas.

Description

[Technical field]

[0001] The present invention relates to a desulfurization and denitrification method using chlorine dioxide. [Background technology]

[0002] Coal-fired flue gas contains large amounts of harmful gases such as sulfur dioxide and nitrogen oxides, which cause indelible damage to the atmospheric environment, such as acid rain and photochemical smog. Effective removal of sulfur dioxide and nitrogen oxides from flue gas has always been a hot topic for researchers, and the removal of NO is particularly difficult.

[0003] When denitrifying flue gas, the NO in the flue gas must first be oxidized to higher valence nitrogen oxides, and the oxidation process requires the involvement of an oxidizing agent. As a gas-phase oxidizing agent, chlorine dioxide has attracted much attention due to its strong oxidizing properties and has been widely used in denitrification projects in recent years. Chlorine dioxide gas is unstable and prone to explosion, and is difficult to store and transport. CN106621712A discloses a flue gas desulfurization and denitrification method, which uses an ozone generator to prepare ozone, adds a strong oxidizing system to oxidize NO in flue gas to generate high valent nitrogen oxides, and then uses an absorbing solution to remove sulfur dioxide and high valent nitrogen oxides together to achieve the purpose of flue gas purification. The oxidation of NO by ozone is highly efficient and has a clear removal effect, but there are problems such as the ozone generator being expensive, requiring a large area, and the initial cost being relatively high.

[0004] CN104028103A discloses a method for catalytically oxidizing flue gas while desulfurizing and denitrifying it using liquid-phase chlorine dioxide. The chlorine dioxide aqueous solution is generated by a chlorine dioxide preparation device and has a concentration of 0.0015-0.015 mol / L. It is sprayed into an absorption tower to oxidize NO in the flue gas. However, the chlorine dioxide has a low concentration and a large amount to be sprayed, which increases the volume of the absorption tower and the initial equipment investment, making it difficult to implement the process.

[0005] CN106975337A discloses an integrated process for gas-phase oxidation of chlorine dioxide, and desulfurization and denitrification. In the absorption tower, both the oxidation process of chlorine dioxide and the desulfurization and denitrification processes are carried out. After spraying the desulfurization agent into the flue gas, NO is oxidized to high-valent nitrogen oxides by chlorine dioxide sprayed from the gasification spray pipe, and removed by the action of the denitrification agent sprayed from the upper layer of the separator. Chlorine dioxide reacts with the desulfurization absorbent, which not only causes waste of chlorine dioxide and desulfurization absorbent, but also affects the desulfurization efficiency.

[0006] Therefore, the development of a low-energy-consumption and highly efficient desulfurization and denitrification process using chlorine dioxide is highly necessary. Summary of the Invention

[0007] In view of this, one object of the present invention is to provide a method for desulfurization and denitrification using chlorine dioxide synthesized in situ, which has the characteristics of high desulfurization and denitrification efficiency, simple process, and low cost.

[0008] In order to achieve the above-mentioned object, the present invention employs the following configuration. The present invention is a method for desulfurization and denitrification using chlorine dioxide, A step (1) of adding a chlorate solution, a peroxide solution and an aqueous sulfuric acid solution to a chlorine dioxide generator, reacting them to obtain chlorine dioxide gas, and mixing the chlorine dioxide gas with air to obtain a mixed gas, the chlorine dioxide gas accounting for 4 to 10 vol% of the mixed gas; A step (2) of contacting the mixed gas with a flue gas in a flue gas pipe before being introduced into a desulfurization and denitrification tower to obtain an oxidized flue gas, in which the molar ratio of chlorine dioxide in the mixed gas introduced into the flue gas pipe per unit time to nitric oxide contained in the flue gas is 1 to 1.8; (3) introducing the oxidized flue gas into a desulfurization and denitrification tower, mixing it with the sprayed dry powder of alkaline absorbent, and spraying water into the desulfurization and denitrification tower to obtain a desulfurized and denitrified flue gas; The present invention provides a method for desulfurization and denitrification comprising the steps of:

[0009] According to the method of the present invention, preferably, in step (1), the chlorate is sodium chlorate, the concentration of the aqueous sodium chloride solution is 15 to 40 wt %, and the concentration of the aqueous sulfuric acid solution is 30 to 60 wt %.

[0010] According to the method of the present invention, preferably in step (1), the peroxide solution is 25-28 wt % hydrogen peroxide or 34-38 wt % hydrogen peroxide.

[0011] According to the method of the present invention, preferably, in step (1), the molar ratio of chlorate, hydrogen peroxide, and sulfuric acid added to the chlorine dioxide generator is 1:0.55 to 1:0.5 to 1, and the reaction temperature of the chlorine dioxide generator is 40 to 90°C.

[0012] According to the method of the present invention, preferably, in step (2), the flue gas introduced into the flue gas pipe has a sulfur content of 600 to 4000 mg / Nm 3 and the nitrogen content is 200-600mg / Nm 3 The oxygen content is 5 to 23 wt% and the moisture content is 5 to 12 wt%.

[0013] According to the method of the present invention, preferably, in step (2), the flow velocity of the flue gas in the flue gas pipe is 6 to 15 m / s, and the time for which the mixed gas is contacted with the flue gas in the flue gas pipe before being introduced into the desulfurization / denitrification tower is 1 to 3 s.

[0014] According to the method of the present invention, preferably, in step (3), the dry powder of the alkaline absorbent is calcium oxide and / or calcium hydroxide, and the particle size of the dry powder of the alkaline absorbent is 150 to 350 mesh.

[0015] According to the method of the present invention, preferably, in step (3), the flow velocity of the oxidized flue gas in the desulfurization / denitrification tower is 1 to 7 m / s, and the contact time of the oxidized flue gas with the dry powder of the alkaline absorbent in the desulfurization / denitrification tower is 2 to 15 s.

[0016] According to the method of the present invention, in the step (3), the molar ratio Ca / S of the calcium element contained in the dry powder of the alkaline absorbent introduced per unit time to the sulfur element in the flue gas introduced per unit time is preferably 1.1 to 1.5.

[0017] According to the method of the present invention, in the step (3), the molar ratio Ca / N of the calcium element contained in the dry powder of the alkaline absorbent introduced per unit time to the nitrogen element in the flue gas introduced per unit time is preferably 0.5 to 1.5.

[0018] The desulfurization and denitrification method of the present invention uses in-situ synthesized chlorine dioxide gas as an oxidizing agent to perform desulfurization and denitrification, and can achieve a desulfurization efficiency of 99% or more and a denitrification efficiency of 91% or more. Furthermore, by using chlorine dioxide in gas form and through a specific process method, it is possible to reduce the consumption of chlorine dioxide and cut costs. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] The present invention will be further described below with reference to specific examples, but the technical scope of the present invention is not limited to these. This invention provides an integrated process for flue gas desulfurization and denitrification by CFB method, which prepares chlorine dioxide as oxidant from sodium chlorate, and then combines with calcium-based absorbent. The reaction principle is as follows: (1) Preparation of chlorine dioxide gas 2NaClO3+H2O2+H2SO4→2ClO2+Na2SO4+H2O+O2(main reaction) (2) Oxidation of nitric oxide 2ClO2+5NO+H2O→2HCl+5NO2(main reaction) 2ClO2+4NO→Cl2+4NO2(side reaction) 2NO2+H2O→HNO2+HNO3(side reaction) 5HNO2+2ClO2+H2O→5HNO3+2HCl (side reaction) (3) Denitrification of flue gas NO+NO2+Ca(OH)2→Ca(NO2)2+H2O (main reaction) Ca(NO2)2+O2→Ca(NO3)2(main reaction) HNO2+HNO3+1 / 2O2+Ca(OH)2→Ca(NO3)2+2H2O(side reaction) 4ClO2+2Ca(OH)2→Ca(ClO2)2+Ca(ClO3)2+2H2O(side reaction) 2Cl2+2Ca(OH)2→CaCl2+Ca(ClO)2+2H2O(side reaction) (4) Flue gas desulfurization SO2+H2O→H2SO3 (main reaction) 3H2SO3+2Ca(OH)2→Ca(HSO3)2+CaSO3+4H2O(main reaction) Ca(HSO3)2+2CaSO3+2O2+Ca(OH)2→4CaSO4+2H2O (main reaction)

[0020] The flue gas desulfurization and denitrification method according to the present invention includes a chlorine dioxide gas preparation step (1), a flue gas oxidation step (2), and a desulfurization and denitrification step (3). A detailed description is given below.

[0021] <Chlorine dioxide gas preparation process> A chlorine dioxide generating device reacts an aqueous solution of a chlorate salt, a peroxide solution, and an aqueous solution of sulfuric acid to obtain chlorine dioxide gas. Chlorine dioxide gas and air are mixed to obtain a mixed gas. In the present invention, the percentage of chlorine dioxide gas in the mixed gas may be 4 to 10 vol%, preferably 5 to 8 vol%, and more preferably 7 to 8 vol%. By mixing chlorine dioxide gas and air in the above ratio, it is possible to produce chlorine dioxide safely and improve the conversion rate of nitric oxide.

[0022] The peroxide solution can be selected from an aqueous hydrogen peroxide solution and the like. According to one embodiment of the present invention, the concentration of hydrogen peroxide in the aqueous hydrogen peroxide solution may be 25-28 wt%, preferably 26-28 wt%, and more preferably 27-28 wt%. According to another embodiment of the present invention, the concentration of hydrogen peroxide in the aqueous hydrogen peroxide solution may be 34-38 wt%, preferably 34.5-37 wt%, and more preferably 35-36 wt%. By using a peroxide in the above-mentioned concentration range, the reaction rate can be controlled and the safety of the production of chlorine dioxide gas can be improved.

[0023] The chlorate is one selected from sodium chlorate, potassium chlorate and magnesium chlorate, preferably the chlorate is one selected from sodium chlorate or potassium chlorate, more preferably the chlorate is sodium chloride. The molar ratio of sodium chloride in the chlorate aqueous solution, hydrogen peroxide in the hydrogen peroxide aqueous solution and sulfuric acid in the sulfuric acid aqueous solution added to the chlorine dioxide generator is 1:0.55-1:0.5-1, preferably 1:0.6-1:0.6-1, more preferably 1:0.7-1:0.7-1. The reaction temperature of the chlorine dioxide generator is 50-90°C, preferably 60-80°C, more preferably 70-80°C. By adopting the above-mentioned molar ratio and reaction temperature range, the generation rate of chlorine dioxide can be controlled, the safety of production can be improved, and the purity of the generated chlorine dioxide gas can be improved.

[0024] The chlorine dioxide gas generated in the chlorine dioxide generator is mixed with air added into the chlorine dioxide generator to form a mixed gas, which is then output from the induced draft fan.

[0025] <Flue gas oxidation process> The mixed gas is brought into contact with the flue gas in the flue gas pipe before being introduced into the desulfurization and denitrification tower to obtain an oxidized flue gas. In the present invention, the molar ratio of chlorine dioxide in the mixed gas introduced into the flue gas pipe per unit time to nitric oxide contained in the flue gas may be 1 to 1.8, preferably 1.1 to 1.6, and more preferably 1.2 to 1.5. By using the above-mentioned molar ratio, it is possible to save the amount of chlorine dioxide used and to improve the oxidation rate of nitric oxide.

[0026] According to one embodiment of the present invention, the chlorine dioxide gas generated in the chlorine dioxide generator is mixed with the added air in the chlorine dioxide generator to form a mixed gas, which is output by an induced draft fan and introduced into a flue gas pipe and contacted with the flue gas introduced into the flue gas pipe. The molar ratio of the chlorine dioxide in the mixed gas introduced into the flue gas pipe per unit time to the nitric oxide contained in the flue gas is 1.2 to 1.5.

[0027] The sulfur content of the flue gas introduced into the flue gas pipe (sulfur content means sulfur dioxide content) is 600-4000mg / Nm 3 and preferably 1000 to 3000 mg / Nm 3 More preferably, it is 1500 to 2500 mg / Nm 3 The nitrogen content of the flue gas introduced into the flue gas pipe (nitrogen content means nitric oxide content) is 200-600mg / Nm 3 and preferably 200 to 400 mg / Nm 3 and more preferably 220 to 250 mg / Nm 3 The oxygen content of the flue gas introduced into the flue gas pipe may be 5 to 23 wt%, preferably 10 to 20 wt%, and more preferably 15 to 20 wt%. The moisture content of the flue gas introduced into the flue gas pipe may be 5 to 12 wt%, preferably 8 to 12 wt%, and more preferably 10 to 12 wt%. The adoption of the sulfur content, nitrogen content, oxygen content, and moisture content of the flue gas described above is helpful in improving the desulfurization and denitrification effect of the flue gas.

[0028] The flue gas has a flow velocity in the flue gas pipe of 6 to 15 m / s, preferably 8 to 15 m / s, and more preferably 10 to 12 m / s. The mixed gas has a contact time of 1 to 3 s with the flue gas in the flue gas pipe before being introduced into the desulfurization / denitrification tower. By controlling the flow velocity of the flue gas within the above-mentioned range, not only can the oxidation rate of nitric oxide in the flue gas be secured, but also the treatment rate can be secured.

[0029] Dust content of flue gas is 80-200mg / Nm 3 Preferably, the concentration is 100 to 150 mg / Nm 3 More preferably, it is 120 to 150 mg / Nm 3 According to one embodiment of the present invention, the flue gas is subjected to a dust pre-removal treatment before being introduced into the flue gas pipe to obtain a dust pre-removed flue gas, which is then introduced into the flue gas pipe. In the present invention, the dust pre-removal treatment is performed on the flue gas using an electrostatic precipitator.

[0030] <Desulfurization / Denitration process> In the desulfurization and denitrification process, the oxidized flue gas is introduced into the desulfurization and denitrification tower, where it is mixed with the sprayed dry powder of alkaline absorbent, and water is sprayed into the desulfurization and denitrification tower to obtain the desulfurized and denitrified flue gas.

[0031] In the present invention, the dry powder of the alkaline absorbent may be calcium oxide and / or calcium hydroxide, preferably, the dry powder of the alkaline absorbent is calcium oxide and / or calcium hydroxide, more preferably, the dry powder of the alkaline absorbent is calcium hydroxide. In the present invention, the purity of calcium oxide may be 80-99 wt%, preferably 80-95 wt%, more preferably 80-90 wt%. The purity of calcium hydroxide may be 80-99 wt%, preferably 80-95 wt%, more preferably 80-90 wt%. In the present invention, the particle size of the dry powder of the alkaline absorbent may be 150-350 mesh, preferably 200-350 mesh, more preferably 200-300 mesh. When dry absorption is performed using an alkaline absorbent in the above-mentioned particle size range, the desulfurization and denitrification effect can be improved.

[0032] The flow velocity of the oxidized flue gas in the desulfurization / denitrification tower may be 1 to 7 m / s, preferably 2 to 5 m / s, and more preferably 3 to 4 m / s. The contact time of the oxidized flue gas with the dry powder of the alkaline absorbent in the desulfurization / denitrification tower may be 2 to 15 s, preferably 3 to 12 s, and more preferably 5 to 10 s.

[0033] The molar ratio Ca / S of calcium element contained in the alkaline absorbent dry powder introduced per unit time to sulfur element contained in the flue gas introduced per unit time may be 1.1 to 1.5, preferably 1.2 to 1.5, and more preferably 1.2 to 1.3. By adopting the above-mentioned Ca / S molar ratio, it is possible to reduce costs and improve desulfurization efficiency.

[0034] The molar ratio Ca / N of the calcium element contained in the alkaline absorbent dry powder introduced per unit time to the nitrogen element contained in the flue gas introduced per unit time may be 0.5 to 1.5, preferably 0.5 to 1.0, and more preferably 0.6 to 0.8. By adopting the above-mentioned Ca / N molar ratio, it is possible to reduce costs and improve the denitrification efficiency.

[0035] The temperature of the oxidized flue gas at the inlet of the desulfurization / denitrification tower may be 110 to 200°C, preferably 110 to 180°C, and more preferably 120 to 150°C.

[0036] According to one embodiment of the present invention, the desulfurized and denitrified flue gas is passed through a bag filter at the top of the desulfurization and denitrification tower to remove dust, and the purified flue gas is discharged from the chimney. The resulting solid ash is either transported to an ash storage tank or sprayed into the desulfurization and denitrification tower to be reused as a dry alkaline absorbent powder.

[0037] Example 1 The sodium hydrochloride aqueous solution, the hydrogen peroxide aqueous solution and the sulfuric acid aqueous solution were transported to the chlorine dioxide generator by a metering pump, where they were reacted to obtain chlorine dioxide gas. The gas mixture was mixed with the air introduced into the chlorine dioxide generator to obtain a mixed gas, which was then supplied to the flue gas pipe by an induced draft fan.

[0038] The flue gas was subjected to dust removal treatment using an electrostatic precipitator and then introduced into a flue gas pipe, where it was brought into contact with a mixed gas outputted by an induced draft fan, and nitric oxide in the flue gas was oxidized to nitrogen oxides to obtain an oxidized flue gas.

[0039] The oxidized flue gas was introduced into a desulfurization and denitrification tower, where it was mixed with dry calcium hydroxide powder sprayed inside the tower, and water was then sprayed into the tower to remove nitrogen oxides and sulfur dioxide from the oxidized flue gas, thereby obtaining a desulfurized and denitrified flue gas.

[0040] The above method was applied to 90m 2 This was applied to a desulfurization and denitrification project using a sintering machine, and the operating parameters are shown in Table 1. The parameters of the purified flue gas, which was subjected to dust removal using a bag filter at the top of the desulfurization and denitrification tower, are shown in Table 2.

[0041] [Table 1]

[0042] [Table 2]

[0043] Comparative Example 1 In this comparative example, except for the operating parameters listed in Table 3, all other operating parameters were the same as in Example 1. The parameters of the purified flue gas obtained in this comparative example are shown in Table 4 below.

[0044] [Table 3]

[0045] [Table 4]

[0046] Comparative Example 2 In this comparative example, except for the operating parameters listed in Table 5, all other operating parameters were the same as in Example 1. The parameters of the purified flue gas obtained in this comparative example are shown in Table 6 below.

[0047] [Table 5]

[0048] [Table 6] The present invention is not limited to the above-mentioned embodiments. Any modifications, improvements, and substitutions that can be thought of by those skilled in the art without departing from the gist of the present invention are included within the scope of the present invention.

Claims

1. A step (1) of adding an aqueous chlorate solution, a peroxide solution and an aqueous sulfuric acid solution to a chlorine dioxide generator and reacting them to obtain chlorine dioxide gas, and mixing the chlorine dioxide gas with air to obtain a mixed gas, wherein the chlorine dioxide gas is 4 to 10 vol% of the mixed gas; A step (2) of contacting the mixed gas with a flue gas in a flue gas pipe before being introduced into a desulfurization and denitrification tower to obtain an oxidized flue gas, in which the molar ratio of chlorine dioxide in the mixed gas introduced into the flue gas pipe per unit time to nitric oxide contained in the flue gas is 1 to 1.8; (3) introducing the oxidized flue gas into a desulfurization and denitrification tower, mixing it with the sprayed dry powder of the alkaline absorbent, and spraying water into the desulfurization and denitrification tower to obtain a desulfurized and denitrified flue gas; In step (1), the chlorate is sodium chlorate, the concentration of the sodium chlorate aqueous solution is 15-40 wt %, the concentration of the sulfuric acid aqueous solution is 30-60 wt %, and the peroxide solution is a 25-28 wt % hydrogen peroxide aqueous solution or a 34-38 wt % hydrogen peroxide aqueous solution; In step (1), the molar ratio of sodium chlorate in the chlorate aqueous solution, hydrogen peroxide in the hydrogen peroxide aqueous solution, and sulfuric acid in the sulfuric acid aqueous solution added to the chlorine dioxide generator is 1:0.55-1:0.5-1, and the reaction temperature of the chlorine dioxide generator is 40-90°C; A desulfurization and denitrification method that uses chlorine dioxide.

2. In step (2), the flue gas introduced into the flue gas pipe has a sulfur content of 600-4000 mg / Nm 3 and the nitrogen content is 200-600mg / Nm 3 2. The method according to claim 1, characterized in that the oxygen content is 5-23 wt.% and the moisture content is 5-12 wt.%.

3. The method according to claim 1, characterized in that in step (2), the flow velocity of the flue gas in the flue gas pipe is 6 to 15 m / s, and the time for which the mixed gas is contacted with the flue gas in the flue gas pipe before being introduced into the desulfurization and denitrification tower is 1 to 3 s.

4. The method according to claim 1, characterized in that in step (3), the alkaline absorbent dry powder is calcium oxide and / or calcium hydroxide, and the particle size of the alkaline absorbent dry powder is 150-350 mesh.

5. The method according to claim 1, characterized in that in step (3), the flow velocity of the oxidized flue gas in the desulfurization and denitrification tower is 1 to 7 m / s, and the time for which the oxidized flue gas is contacted with the alkaline absorbent dry powder in the desulfurization and denitrification tower is 2 to 15 s.

6. The method according to claim 4, characterized in that in step (3), the molar ratio Ca / S of elemental calcium contained in the dry powder of alkaline absorbent introduced per unit time to elemental sulfur contained in the flue gas introduced per unit time is 1.1 to 1.

5.

7. 7. The method according to claim 6, wherein in step (3), a molar ratio Ca / N of calcium element contained in the alkaline absorbent dry powder introduced per unit time to nitrogen element contained in the flue gas introduced per unit time is 0.5-1.5.

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