A flue gas desulfurization and denitrification system and method

Abstract

The present invention provides a flue gas desulfurization and denitrification system and method, the flue gas desulfurization and denitrification system includes a desulfurization unit, a denitrification unit and an ozone generating unit; the present invention divides the denitrification unit into two denitrification towers, and allows the side line of the first denitrification tower to enter the second denitrification tower, thereby reducing the amount of ozone, improving the denitrification temperature and denitrification efficiency. The flue gas desulfurization and denitrification method is simple to operate, and by reasonably allocating the ratio of ozone to nitrogen oxides, the liquid-gas ratio and selecting a suitable spray liquid composition, the desulfurization and denitrification effect is improved under simple operating conditions, so that the gas after desulfurization and denitrification can meet the emission standards after post-treatment.

Description

Technical Field

[0001] The present invention belongs to the technical field of waste gas treatment, and relates to a flue gas treatment system and method, and in particular to a flue gas desulfurization and denitrification system and method. Background Art

[0002] Large amounts of SO2 and NO are emitted from industrial production X It is one of the main sources of air pollution in my country. The current technologies for desulfurization and denitrification include wet desulfurization process and selective catalytic reduction process. However, the selective catalytic reduction process is not suitable for flue gas and furnace flue gas. The basic method for treating flue gas and furnace flue gas with large temperature fluctuations and easy to cause catalyst poisoning is wet desulfurization.

[0003] NO in flue gas, especially in steel plant flue gas X It mainly comes from the combustion of fuel during the sintering process. The nitrogen oxides produced during the combustion process are mainly NO and NO2, of which the content of NO is above 95%. NO is difficult to dissolve in water, while high-valent NO2 and N2O5 can dissolve in water to form HNO2 and HNO3. Oxidizing NO into NO2 or N2O5 can increase the NO content in flue gas. X water solubility.

[0004] Ozone is a strong oxidant. Ozone denitrification technology utilizes the advanced oxidation of active groups to easily oxidize NO into high-valent compounds such as NO2, N2O3, N2O5, which are easily absorbed and then absorbed by the absorbent in the desulfurization tower.

[0005] CN 103920392 A discloses a process for flue gas denitrification using a lean and rich oxygen alternating reaction, wherein boiler flue gas with a high oxygen content flows through a HC-SCR catalyst layer of a fluidized bed to oxidize and adsorb nitrogen oxides; oxygen after adsorbing nitrogen oxides is collected; a reducing agent gas with a low oxygen content flows through the HC-SCR catalyst layer after adsorbing nitrogen oxides, and steps (1) and (2) are repeated to allow boiler flue gas and reducing agent gas to alternately flow through the HC-SCR catalyst layer. Although this method can realize the adsorption and reduction process by using lean and rich oxygen alternation, the processing capacity during adsorption treatment is limited and the processing efficiency is low.

[0006] CN 107890759 A discloses a circulating fluidized bed boiler flue gas CO2, SO2 and NO xThe synergistic removal system and method are as follows: the pyrolysis gas generated in the pyrolysis furnace is introduced into the boiler and the dilute phase zone, the nitrogen oxides in the flue gas in the boiler are reduced to nitrogen, and most of the nitrogen oxides in the flue gas are removed; the calcium oxide generated in the calcining furnace is transported to the boiler to absorb most of the sulfur dioxide in the flue gas; the oxygen in the boiler that has undergone preliminary desulfurization and denitrification is discharged to the desulfurization and denitrification reactor, the calcium oxide in the desulfurization and denitrification reactor absorbs the remaining sulfur dioxide, and the remaining nitrogen oxides in the flue gas are reduced to nitrogen under the catalysis of the calcium oxide and the reduction of the coke, thereby realizing deep desulfurization and denitrification of the flue gas. However, this method consumes a large amount of calcium oxide and cannot effectively treat NO.

[0007] CN 108339385 A discloses a method for flue gas desulfurization and denitrification by organically combining double-tower ammonia desulfurization and oxidation catalytic denitrification, the method comprising: step A: adding a liquid organic catalyst to the spray liquid; step B: injecting ozone through a pipeline into the reaction zone of the inlet flue of the desulfurization system, and NO in the flue gas is removed. X Ozone is contacted and oxidized to form flue gas after ozone oxidation, and NO is oxidized to NO2; Step C: the flue gas after dust removal and ozone oxidation is introduced into the wet desulfurization tower through the inlet flue; Step D: the flue gas after ozone oxidation enters the ammonia desulfurization system containing organic catalyst. The desulfurization tower used in this method consists of a desulfurization auxiliary tower and a desulfurization main tower, and requires additional catalyst addition, which is costly and cannot flexibly adjust the absorption temperature and absorption flow.

[0008] In this regard, an energy-saving and efficient flue gas desulfurization and denitrification system and method are provided, which has important industrial application value for reducing the cost of flue gas desulfurization and denitrification and improving the efficiency of flue gas desulfurization and denitrification. Summary of the invention

[0009] The object of the present invention is to provide a flue gas desulfurization and denitrification system and method, wherein the flue gas desulfurization and denitrification system can improve the efficiency of desulfurization and denitrification while reducing ozone consumption, thereby reducing the cost of desulfurization and denitrification; the flue gas desulfurization and denitrification method is simple to operate, and by reasonably allocating the ratio of ozone to nitrogen oxides, the liquid-to-gas ratio and selecting a suitable spray liquid composition, the effect of desulfurization and denitrification is improved under simple operating conditions, so that the gas after desulfurization and denitrification can meet the emission standards after post-treatment.

[0010] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0011] In a first aspect, the present invention provides a flue gas desulfurization and denitrification system, which includes a desulfurization unit, a denitrification unit and an ozone generating unit.

[0012] The desulfurization unit comprises a first mixing device and a desulfurization tower which are connected in sequence, and the flue gas flows through the first mixing device and then flows into the desulfurization tower.

[0013] The denitrification unit includes a second mixing device, a first denitrification tower, a third mixing device and a second denitrification tower. The gas outlet of the desulfurization tower is connected to the second mixing device and the first denitrification tower in sequence; the side line outlet of the first denitrification tower is connected to the third mixing device and the second denitrification tower in sequence.

[0014] The ozone generating unit comprises an ozone generating device and a heat exchange device. The ozone generating device is independently connected to the first mixing device, the second mixing device and the third mixing device respectively. The heat exchange device is arranged on the connecting pipes between the ozone generating device and the second mixing device and the third mixing device.

[0015] The heat exchange device of the present invention includes a shell and tube heat exchanger and / or a plate heat exchanger.

[0016] The flue gas is mixed with room temperature ozone in the first mixing device and then passed into the desulfurization tower. Desulfurization is carried out under the action of the alkaline spray liquid in the desulfurization tower, which greatly reduces the concentration of sulfur oxides in the flue gas and preliminarily reduces the nitrogen oxides in the flue gas.

[0017] The flue gas after denitrification is mixed with the heated ozone in the second mixing device and then flows into the first denitrification tower, where it interacts with the denitrification liquid, thereby achieving the purpose of denitrification; the second denitrification tower is discharged from the side line of the packing section, and the gas extracted from the side line is mixed with ozone in the third mixing device and then flows into the second denitrification tower, where it interacts with the denitrification liquid, thereby improving the problem of insufficient driving force for denitrification in the upper part of the packing section.

[0018] Preferably, the first mixing device, the second mixing device and the third mixing device are respectively and independently static mixers. The static mixer described in the present invention is a static mixer commonly used in the art, and those skilled in the art can select a suitable model according to process requirements.

[0019] Preferably, the side line discharge of the first denitration tower is a side line discharge from 1 / 3-1 / 2 of the height of the packing layer based on the bottom of the packing layer.

[0020] Preferably, the heat source of the heat exchange device is flue gas. Flue gas has a relatively high temperature, and the desulfurization and denitrification of the present invention can be carried out at a temperature below 100°C. Therefore, using flue gas to exchange heat with ozone can improve the utilization rate of flue gas heat and improve the desulfurization and denitrification efficiency by improving the problem. When the heat exchange efficiency of flue gas is insufficient, the temperature of ozone can be made to meet the process requirements by supplementing an external heat source or increasing the flue gas flux, and the excess flue gas is circulated to the flue gas inlet for standby use.

[0021] In a second aspect, the present invention provides a method for performing flue gas desulfurization and denitrification using the flue gas desulfurization and denitrification system as described in the first aspect, the method comprising the following steps:

[0022] (1) Flue gas is mixed with ozone, and the resulting mixed gas is countercurrently contacted with an alkaline spray liquid to obtain desulfurized gas;

[0023] (2) After the first heating, ozone is mixed with the desulfurized gas, and the obtained desulfurized mixed gas is in countercurrent contact with the denitrification liquid in the first denitrification tower; after the desulfurized mixed gas extracted from the side line is mixed with the ozone after the second heating, the obtained side line extracted gas is in countercurrent contact with the denitrification liquid in the second desulfurization tower; desulfurized and denitrified gas is obtained from the top of the first denitrification tower and the second denitrification tower.

[0024] Preferably, the concentration of NO in the flue gas is 200-320 mg / Nm 3 , for example, it can be 200mg / Nm 3 、220mg / Nm 3 、240mg / Nm 3 、250mg / Nm 3 、260mg / Nm 3 、270mg / Nm 3 、280mg / Nm 3 、290mg / Nm 3 、300mg / Nm 3 、310mg / Nm 3 or 320mg / Nm 3 , but not limited to the values ​​listed, other values ​​not listed in the numerical range are also applicable; SO2 concentration is 500-2000mg / Nm 3 , for example, it can be 500mg / Nm 3 、600mg / Nm 3 、700mg / Nm 3 、800mg / Nm 3 、900mg / Nm 3 、1000mg / Nm 3 、1100mg / Nm 3 、1200mg / Nm 3 、1300mg / Nm 3 、1400mg / Nm 3 、1500mg / Nm 3 、1600mg / Nm 3 、1700mg / Nm 3 、1800mg / Nm 3 、1900mg / Nm 3 or 2000mg / Nm 3 , but not limited to the listed values, other unlisted values ​​within the numerical range are also applicable.

[0025] Preferably, the flow rate of the flue gas in step (1) is 10000-30000 Nm 3 / h, for example, it can be 10000Nm 3 / h、12000Nm 3 / h、15000Nm 3 / h、18000Nm 3 / h、20000Nm 3 / h、22000Nm 3 / h、25000Nm 3 / h、27000Nm 3 / h or 30000Nm 3 / h, but not limited to the listed values, other values ​​not listed in the numerical range are also applicable, preferably 15000-25000Nm 3 / h.

[0026] Preferably, the temperature of the flue gas in step (1) is 150-350°C, for example, it can be 150°C, 180°C, 200°C, 240°C, 250°C, 270°C, 280°C, 300°C, 320°C or 350°C, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable, preferably 180-300°C.

[0027] Preferably, the molar ratio of ozone to NO in flue gas in step (1) is (1-1.5):1, for example, 1:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1 or 1.5:1, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0028] Preferably, the liquid-to-gas ratio of the alkaline spray liquid to the mixed gas in step (1) is (2-4):1, for example, 2:1, 2.5:1, 3:1, 3.5:1 or 4:1, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0029] Preferably, the alkaline spray liquid in step (1) is KOH solution and / or NaOH solution.

[0030] Preferably, the pH value of the alkaline spray liquid in step (1) is 9-13, for example, 9, 10, 11, 12 or 13, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0031] Preferably, the temperature of the alkaline spray liquid in step (1) is 20-50°C, for example, 20°C, 25°C, 30°C, 35°C, 40°C, 45°C or 50°C, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable, preferably 25-45°C.

[0032] Preferably, in step (2), the temperature of the ozone after the first heating is 40-80°C, for example, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C or 80°C, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable, preferably 60-70°C.

[0033] Preferably, the concentration of NO in the desulfurized gas in step (2) is 100-180 mg / Nm 3 , for example, it can be 100 mg / Nm 3 、110mg / Nm 3 、120mg / Nm 3 、130mg / Nm 3 、140mg / Nm 3 、150mg / Nm 3 、160mg / Nm 3 、170mg / Nm 3 or 180mg / Nm 3 , but not limited to the listed values, other values ​​not listed in the numerical range are also applicable; SO2 concentration ≤ 35mg / Nm 3 .

[0034] Preferably, in step (2), the molar ratio of ozone to NO in the desulfurized gas after the first heating is (0.8-1.2):1, for example, it can be 0.8:1, 0.9:1, 1:1, 1.1:1 or 1.2:1, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0035] Preferably, the liquid-to-gas ratio of the denitrification liquid to the desulfurized mixed gas in step (2) is (2-5):1, for example, it can be 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1 or 5:1, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0036] Preferably, the flow ratio of the desulfurized mixed gas after the side line extraction in step (2) to the desulfurized mixed gas is (0.1-0.3):1, for example, it can be 0.1:1, 0.15:1, 0.2:1, 0.25:1 or 0.3:1, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0037] Preferably, in step (2), the flow ratio of the second heated ozone to the first heated ozone is (0.1-0.3):1, for example, it can be 0.1:1, 0.15:1, 0.2:1, 0.25:1 or 0.3:1, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0038] Preferably, in step (2), the temperature of the ozone after the second heating is 40-80°C, for example, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C or 80°C, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable, preferably 60-70°C.

[0039] Preferably, the liquid-to-gas ratio of the denitrification liquid to the side-line extracted gas in step (2) is (2-5):1, for example, it can be 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1 or 5:1, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0040] Preferably, the solute in the denitrification liquid in step (2) includes any one of urea, sulfite or thiosulfate, or a combination of at least two of them. Typical but non-limiting combinations include a combination of urea and sulfite, a combination of urea and thiosulfate, or a combination of urea, sulfite and thiosulfate, preferably a combination of urea, sulfite and thiosulfate.

[0041] Preferably, the mass concentration of the denitrification liquid is 1-10wt%, for example, it can be 1wt%, 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt% or 10wt%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0042] Preferably, the mass ratio of urea, sulfite and thiosulfate is (1-3):(1-3):(1-3), for example, it can be 1:1:1, 1:2:1, 1:2:3, 2:1:1, 2:1:2, 2:1:3, 3:2:1, 3:1:2 or 3:1:1.

[0043] Preferably, the sulfite comprises any one of sodium sulfite, potassium sulfite or calcium sulfite or a combination of at least two thereof, and typical but non-limiting combinations include a combination of sodium sulfite and potassium sulfite, a combination of potassium sulfite and calcium sulfite, a combination of sodium sulfite and calcium sulfite or a combination of sodium sulfite, potassium sulfite and calcium sulfite.

[0044] Preferably, the thiosulfate comprises any one of sodium thiosulfate, potassium thiosulfate or calcium thiosulfate, or a combination of at least two thereof. Typical but non-limiting combinations include a combination of sodium thiosulfate and potassium thiosulfate, a combination of potassium thiosulfate and calcium thiosulfate, a combination of sodium thiosulfate and calcium thiosulfate, or a combination of sodium thiosulfate, potassium thiosulfate and calcium thiosulfate.

[0045] As a preferred technical solution of the method described in the second aspect of the present invention, the method comprises the following steps:

[0046] (1) Flue gas at 150-350°C is mixed with ozone, and the resulting mixed gas is countercurrently contacted with an alkaline spray liquid at a temperature of 20-50°C and a pH value of 9-13 to obtain desulfurized gas, wherein the molar ratio of ozone to NO in the flue gas is (1-1.5):1, and the liquid-gas ratio of the alkaline spray liquid to the mixed gas is (2-4):1;

[0047] (2) The first heated ozone at 40-80°C is mixed with the desulfurized gas, and the obtained desulfurized mixed gas is countercurrently contacted with the denitrification liquid in the first denitrification tower, and the molar ratio of the first heated ozone to NO in the desulfurized gas is (1-1.5):1, and the liquid-gas ratio of the denitrification liquid to the desulfurized mixed gas is (2-5):1; the desulfurized mixed gas after the side line is mixed with the second heated ozone at a temperature of 40-80°C, and the obtained side line extracted gas is countercurrently contacted with the denitrification liquid in the second desulfurization tower, and the liquid-gas ratio of the denitrification liquid to the side line extracted gas is (2-5):1; the flow ratio of the desulfurized mixed gas after the side line is (0.1-0.3):1 to the desulfurized mixed gas, and the flow ratio of the second heated ozone to the first heated ozone is (0.1-0.3):1; desulfurized and denitrified gas is obtained from the top of the first denitrification tower and the second denitrification tower.

[0048] Compared with the prior art, the present invention has the following beneficial effects:

[0049] (1) The present invention divides the denitration unit into two denitration towers, and allows the side line of the first denitration tower to enter the second denitration tower, thereby reducing the amount of ozone used, improving the denitration temperature and denitration efficiency, and the SO2 removal rate is as high as 99.19%, and the NO removal rate is as high as 94.1%;

[0050] (2) The method for flue gas desulfurization and denitrification provided by the present invention is simple. By reasonably allocating the ratio of ozone to nitrogen oxides, the liquid-to-gas ratio and selecting a suitable spray liquid composition, the desulfurization and denitrification effects are improved under simple operating conditions, so that the gas after desulfurization and denitrification can meet the emission standards after post-treatment. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 A schematic diagram of the structure of the flue gas desulfurization and denitrification system provided in Example 1;

[0052] Figure 2 A schematic diagram of the structure of the flue gas desulfurization and denitrification system provided in Example 2;

[0053] Figure 3 This is a schematic structural diagram of the flue gas desulfurization and denitrification system provided for Comparative Example 1.

[0054] Among them: 1, ozone generator; 2-1, first mixing device; 2-2, second mixing device; 2-3, third mixing device; 3, desulfurization tower; 4, first denitrification tower; 5, second denitrification tower; 6, heat exchanger. DETAILED DESCRIPTION

[0055] The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0056] Example 1

[0057] This embodiment provides a flue gas desulfurization and denitrification system. The structural schematic diagram of the flue gas desulfurization and denitrification system is as follows: Figure 1 As shown, it includes a desulfurization unit, a denitrification unit and an ozone generation unit.

[0058] The desulfurization unit comprises a first mixing device 2-1 and a desulfurization tower 3 which are connected in sequence. The flue gas flows through the first mixing device 2-1 and then flows into the desulfurization tower.

[0059] The denitration unit comprises a second mixing device 2-2, a first denitration tower 4, a third mixing device 2-3 and a second denitration tower 5. The gas outlet of the desulfurization tower 3 is sequentially connected to the second mixing device 2-2 and the first denitration tower 4; the side line discharge port of the first denitration tower 4 is sequentially connected to the third mixing device 2-3 and the second denitration tower 5. The side line discharge of the first denitration tower 4 is measured from the bottom of the packing layer, and the side line discharge is from 1 / 3 of the height of the packing layer.

[0060] The ozone generating unit comprises an ozone generator 1 and a heat exchange device, wherein the ozone generator 1 is independently connected to a first mixing device 2-1, a second mixing device 2-2 and a third mixing device 2-3 respectively; a heat exchange device is arranged on the connecting pipes between the ozone generator 1 and the second mixing device 2-2 and the third mixing device 2-3, wherein the heat exchange device is a shell and tube heat exchanger 6, which utilizes an external heat source to heat ozone.

[0061] The first mixing device 2-1, the second mixing device 2-2 and the third mixing device 2-3 are respectively and independently static mixers.

[0062] The flue gas is mixed with room temperature ozone in the first mixing device 2-1 and then passed into the desulfurization tower 3, where it is desulfurized under the action of the alkaline spray liquid in the desulfurization tower 3, thereby significantly reducing the concentration of sulfur oxides in the flue gas and preliminarily reducing nitrogen oxides in the flue gas.

[0063] The flue gas after denitrification is mixed with the heated ozone in the second mixing device 2-2, and then flows into the first denitrification tower 4, interacting with the denitrification liquid in the first denitrification tower 4, thereby achieving the purpose of denitrification; the second denitrification tower 5 is discharged from the side line of the filling section, and the gas extracted from the side line is mixed with ozone in the third mixing device 2-3 and then flows into the second denitrification tower 5, interacting with the denitrification liquid in the second denitrification tower 5, so that the desulfurized and denitrified gases discharged from the top of the first denitrification tower 4 and the second denitrification tower 5 meet the emission standards.

[0064] Example 2

[0065] This embodiment provides a flue gas desulfurization and denitrification system. The structural schematic diagram of the flue gas desulfurization and denitrification system is as follows: Figure 2 As shown, it includes a desulfurization unit, a denitrification unit and an ozone generation unit.

[0066] The desulfurization unit comprises a first mixing device 2-1 and a desulfurization tower 3 which are connected in sequence. The flue gas flows through the first mixing device 2-1 and then flows into the desulfurization tower.

[0067] The denitration unit comprises a second mixing device 2-2, a first denitration tower 4, a third mixing device 2-3 and a second denitration tower 5. The gas outlet of the desulfurization tower 3 is sequentially connected to the second mixing device 2-2 and the first denitration tower 4; the side line discharge port of the first denitration tower 4 is sequentially connected to the third mixing device 2-3 and the second denitration tower 5. The side line discharge of the first denitration tower 4 is measured from the bottom of the packing layer, and the side line discharge is from 1 / 2 of the height of the packing layer.

[0068] The ozone generating unit comprises an ozone generator 1 and a heat exchange device, wherein the ozone generator 1 is independently connected to a first mixing device 2-1, a second mixing device 2-2 and a third mixing device 2-3 respectively; a heat exchange device is arranged on the connecting pipes between the ozone generator 1 and the second mixing device 2-2 and the third mixing device 2-3, wherein the heat exchange device is a shell and tube heat exchanger 6, which utilizes the heat of flue gas to heat ozone.

[0069] The first mixing device 2-1, the second mixing device 2-2 and the third mixing device 2-3 are respectively and independently static mixers.

[0070] The flue gas is mixed with room temperature ozone in the first mixing device 2-1 and then passed into the desulfurization tower 3, where it is desulfurized under the action of the alkaline spray liquid in the desulfurization tower 3, thereby significantly reducing the concentration of sulfur oxides in the flue gas and preliminarily reducing nitrogen oxides in the flue gas.

[0071] The flue gas after denitrification is mixed with the heated ozone in the second mixing device 2-2, and then flows into the first denitrification tower 4, interacting with the denitrification liquid in the first denitrification tower 4, thereby achieving the purpose of denitrification; the second denitrification tower 5 is discharged from the side line of the filling section, and the gas extracted from the side line is mixed with ozone in the third mixing device 2-3 and then flows into the second denitrification tower 5, interacting with the denitrification liquid in the second denitrification tower 5, so that the desulfurized and denitrified gases discharged from the top of the first denitrification tower 4 and the second denitrification tower 5 meet the emission standards.

[0072] Example 3

[0073] This embodiment provides a flue gas desulfurization and denitrification system, which is the same as that of Embodiment 1 except that the side line discharge is located at the bottom of the packing layer.

[0074] Example 4

[0075] This embodiment provides a flue gas desulfurization and denitrification system, which is the same as that of Embodiment 1 except that the position of the side line discharge is 2 / 3 of the height of the packing layer.

[0076] Comparative Example 1

[0077] This comparative example provides a flue gas desulfurization and denitrification system, the structural schematic diagram of the flue gas desulfurization and denitrification system is as follows Figure 3 As shown, it includes a desulfurization unit, a denitrification unit and an ozone generation unit.

[0078] Except that the denitration unit does not include the third mixing device 2-3 and the second denitration tower 5, that is, the first denitration tower 4 is not provided with a side line discharge, the rest is the same as Example 1.

[0079] Application Example 1

[0080] This application example provides a method for desulfurization and denitrification using the flue gas desulfurization and denitrification system provided in Example 1, comprising the following steps:

[0081] (1) Flue gas at 250°C is mixed with ozone, and the resulting mixed gas is countercurrently contacted with a sodium hydroxide solution at a temperature of 32°C and a pH value of 11 to obtain desulfurized gas. The molar ratio of ozone to NO in the flue gas is 1.3:1, and the liquid-gas ratio of the sodium hydroxide solution to the mixed gas is 3:1. The flow rate of the flue gas is 20,000 Nm 3 / h, the NO concentration in the flue gas is 270mg / Nm 3 , the concentration of SO2 is 1500mg / Nm 3 ;

[0082] (2) The first heated ozone at 65°C is mixed with the desulfurized gas, and the obtained desulfurized mixed gas is countercurrently contacted with the denitrification liquid in the first denitrification tower 4, the molar ratio of the first heated ozone to NO in the desulfurized gas is 1:1, and the liquid-to-gas ratio of the denitrification liquid to the desulfurized mixed gas is 3.5:1; the desulfurized mixed gas after the side line is mixed with the second heated ozone at a temperature of 65°C, and the obtained side line extracted gas is countercurrently contacted with the denitrification liquid in the second desulfurization tower 3, and the liquid-to-gas ratio of the denitrification liquid to the side line extracted gas is 3.5:1; the flow ratio of the desulfurized mixed gas after the side line is 0.2:1 to the desulfurized mixed gas, and the flow ratio of the second heated ozone to the first heated ozone is 0.2:1; desulfurized and denitrified gas is obtained from the top of the first denitrification tower 4 and the second denitrification tower 5.

[0083] The mass concentration of the denitrification liquid in step (2) is 5wt%, which is a mixed solution of urea, sodium sulfite and sodium thiosulfate, wherein the mass ratio of urea, sodium sulfite and sodium thiosulfate is 1:1:1.

[0084] Application Example 2

[0085] This application example provides a method for desulfurization and denitrification using the flue gas desulfurization and denitrification system provided in Example 1, comprising the following steps:

[0086] (1) Flue gas at 180°C is mixed with ozone, and the resulting mixed gas is countercurrently contacted with a potassium hydroxide solution at a temperature of 45°C and a pH value of 10 to obtain desulfurized gas. The molar ratio of ozone to NO in the flue gas is 1.4:1, and the liquid-gas ratio of the potassium hydroxide solution to the mixed gas is 3.5:1. The flow rate of the flue gas is 15000Nm 3 / h, the NO concentration in the flue gas is 240mg / Nm 3 , the concentration of SO2 is 1000mg / Nm 3 ;

[0087] (2) The first heated ozone at 70°C is mixed with the desulfurized gas, and the obtained desulfurized mixed gas is countercurrently contacted with the denitrification liquid in the first denitrification tower 4, the molar ratio of the first heated ozone to NO in the desulfurized gas is 1.1:1, and the liquid-to-gas ratio of the denitrification liquid to the desulfurized mixed gas is 4:1; the desulfurized mixed gas after the side line is mixed with the second heated ozone at a temperature of 70°C, and the obtained side line extracted gas is countercurrently contacted with the denitrification liquid in the second desulfurization tower 3, and the liquid-to-gas ratio of the denitrification liquid to the side line extracted gas is 4:1; the flow ratio of the desulfurized mixed gas after the side line is 0.25:1 to the desulfurized mixed gas, and the flow ratio of the second heated ozone to the first heated ozone is 0.25:1; desulfurized and denitrified gas is obtained from the top of the first denitrification tower 4 and the second denitrification tower 5.

[0088] The mass concentration of the denitrification liquid in step (2) is 7wt%, which is a mixed solution of urea, potassium sulfite and potassium sulfate, wherein the mass ratio of urea, sodium sulfite and sodium thiosulfate is 2:1:1.

[0089] Application Example 3

[0090] This application example provides a method for desulfurization and denitrification using the flue gas desulfurization and denitrification system provided in Example 1, comprising the following steps:

[0091] (1) Flue gas at 300°C is mixed with ozone, and the resulting mixed gas is countercurrently contacted with a sodium hydroxide solution at a temperature of 25°C and a pH value of 12 to obtain desulfurized gas. The molar ratio of ozone to NO in the flue gas is 1.2:1, and the liquid-gas ratio of the sodium hydroxide solution to the mixed gas is 2.5:1; the flow rate of the flue gas is 25000Nm 3 / h, the NO concentration in the flue gas is 300mg / Nm 3 , the concentration of SO2 is 1800mg / Nm 3 ;

[0092] (2) The first heated ozone at 60°C is mixed with the desulfurized gas, and the obtained desulfurized mixed gas is countercurrently contacted with the denitrification liquid in the first denitrification tower 4, the molar ratio of the first heated ozone to NO in the desulfurized gas is 0.9:1, and the liquid-to-gas ratio of the denitrification liquid to the desulfurized mixed gas is 3:1; the desulfurized mixed gas after the side line is mixed with the second heated ozone at a temperature of 60°C, and the obtained side line extracted gas is countercurrently contacted with the denitrification liquid in the second desulfurization tower 3, and the liquid-to-gas ratio of the denitrification liquid to the side line extracted gas is 3:1; the flow ratio of the desulfurized mixed gas after the side line is 0.15:1 to the desulfurized mixed gas, and the flow ratio of the second heated ozone to the first heated ozone is 0.15:1; desulfurized and denitrified gas is obtained from the top of the first denitrification tower 4 and the second denitrification tower 5.

[0093] The mass concentration of the denitrification liquid in step (2) is 3wt%, which is a mixed solution of urea, potassium sulfite and potassium sulfate, wherein the mass ratio of urea, sodium sulfite and sodium thiosulfate is 3:2:1.

[0094] Application Example 4

[0095] This application example provides a method for desulfurization and denitrification using the flue gas desulfurization and denitrification system provided in Example 1, comprising the following steps:

[0096] (1) Flue gas at 350°C is mixed with ozone, and the resulting mixed gas is countercurrently contacted with a sodium hydroxide solution at a temperature of 20°C and a pH value of 9 to obtain desulfurized gas. The molar ratio of ozone to NO in the flue gas is 1:1, and the liquid-gas ratio of the sodium hydroxide solution to the mixed gas is 2:1. The flow rate of the flue gas is 10,000 Nm 3 / h, the NO concentration in the flue gas is 320mg / Nm3 , the concentration of SO2 is 2000mg / Nm 3 ;

[0097] (2) After the first heating of 40°C, the ozone is mixed with the desulfurized gas, and the obtained desulfurized mixed gas is countercurrently contacted with the denitrification liquid in the first denitrification tower 4, and the molar ratio of the first heating ozone to NO in the desulfurized gas is 0.8:1, and the liquid-to-gas ratio of the denitrification liquid to the desulfurized mixed gas is 2:1; after the desulfurized mixed gas extracted from the side line is mixed with the second heating ozone at a temperature of 40°C, the obtained side-extracted gas is countercurrently contacted with the denitrification liquid in the second desulfurization tower 3, and the liquid-to-gas ratio of the denitrification liquid to the side-extracted gas is 2:1; the flow ratio of the desulfurized mixed gas after the side line extraction to the desulfurized mixed gas is 0.1:1, and the flow ratio of the second heating ozone to the first heating ozone is 0.1:1; desulfurized and denitrified gas is obtained from the top of the first denitrification tower 4 and the second denitrification tower 5.

[0098] The mass concentration of the denitrification liquid in step (2) is 10wt%, which is a mixed solution of urea, potassium sulfite and sodium sulfate, wherein the mass ratio of urea, sodium sulfite and sodium thiosulfate is 1:2:3.

[0099] Application Example 5

[0100] This application example provides a method for desulfurization and denitrification using the flue gas desulfurization and denitrification system provided in Example 1, comprising the following steps:

[0101] (1) Flue gas at 150°C is mixed with ozone, and the resulting mixed gas is countercurrently contacted with a sodium hydroxide solution at a temperature of 50°C and a pH value of 13 to obtain desulfurized gas. The molar ratio of ozone to NO in the flue gas is 1.5:1, and the liquid-gas ratio of the sodium hydroxide solution to the mixed gas is 4:1; the flow rate of the flue gas is 30,000 Nm 3 / h, the NO concentration in the flue gas is 220mg / Nm 3 , the concentration of SO2 is 500mg / Nm 3 ;

[0102] (2) After the first heating of 80°C, the ozone is mixed with the desulfurized gas, and the obtained desulfurized mixed gas is countercurrently contacted with the denitrification liquid in the first denitrification tower 4, the molar ratio of the first heating ozone to NO in the desulfurized gas is 1.2:1, and the liquid-to-gas ratio of the denitrification liquid to the desulfurized mixed gas is 5:1; after the desulfurized mixed gas extracted from the side line is mixed with the second heating ozone at a temperature of 80°C, the obtained side-extracted gas is countercurrently contacted with the denitrification liquid in the second desulfurization tower 3, and the liquid-to-gas ratio of the denitrification liquid to the side-extracted gas is 5:1; the flow ratio of the desulfurized mixed gas extracted from the side line to the desulfurized mixed gas is 0.3:1, and the flow ratio of the second heating ozone to the first heating ozone is 0.3:1; desulfurized and denitrified gas is obtained from the top of the first denitrification tower 4 and the second denitrification tower 5.

[0103] The mass concentration of the denitrification liquid in step (2) is 1wt%, which is a mixed solution of urea, sodium sulfite and potassium sulfate, wherein the mass ratio of urea, sodium sulfite and sodium thiosulfate is 1:1:3.

[0104] Application Example 6

[0105] This application example provides a method for desulfurization and denitrification using the flue gas desulfurization and denitrification system provided in Example 2, comprising the following steps:

[0106] (1) Flue gas at 250°C is mixed with ozone, and the resulting mixed gas is countercurrently contacted with a sodium hydroxide solution at a temperature of 32°C and a pH value of 11 to obtain desulfurized gas. The molar ratio of ozone to NO in the flue gas is 1.3:1, and the liquid-gas ratio of the sodium hydroxide solution to the mixed gas is 3:1. The flow rate of the flue gas is 20,000 Nm 3 / h, the NO concentration in the flue gas is 270mg / Nm 3 , the concentration of SO2 is 1500mg / Nm 3 ;

[0107] (2) The first heated ozone at 65°C is mixed with the desulfurized gas, and the obtained desulfurized mixed gas is countercurrently contacted with the denitrification liquid in the first denitrification tower 4, the molar ratio of the first heated ozone to NO in the desulfurized gas is 1:1, and the liquid-to-gas ratio of the denitrification liquid to the desulfurized mixed gas is 3.5:1; the desulfurized mixed gas after the side line is mixed with the second heated ozone at a temperature of 65°C, and the obtained side line extracted gas is countercurrently contacted with the denitrification liquid in the second desulfurization tower 3, and the liquid-to-gas ratio of the denitrification liquid to the side line extracted gas is 3.5:1; the flow ratio of the desulfurized mixed gas after the side line is 0.2:1 to the desulfurized mixed gas, and the flow ratio of the second heated ozone to the first heated ozone is 0.2:1; desulfurized and denitrified gas is obtained from the top of the first denitrification tower 4 and the second denitrification tower 5.

[0108] The mass concentration of the denitrification liquid in step (2) is 5wt%, which is a mixed solution of urea, sodium sulfite and sodium thiosulfate, wherein the mass ratio of urea, sodium sulfite and sodium thiosulfate is 1:1:1.

[0109] Application Example 7

[0110] This application example provides a method for desulfurization and denitrification using the flue gas desulfurization and denitrification system provided in Example 1. Except that the temperatures of the ozone after the first heating and the ozone after the second heating are independently 30°C, the rest are the same as in Application Example 1.

[0111] Application Example 8

[0112] This application example provides a method for desulfurization and denitrification using the flue gas desulfurization and denitrification system provided in Example 1. Except that the temperatures of the ozone after the first heating and the ozone after the second heating are independently 90°C, the rest are the same as in Application Example 1.

[0113] Application Example 9

[0114] This application example provides a method for flue gas desulfurization and denitrification. Except that the applied system is the flue gas desulfurization and denitrification system provided in Example 3, the rest is the same as that of Application Example 1.

[0115] Application Example 10

[0116] This application example provides a method for flue gas desulfurization and denitrification. Except that the applied system is the flue gas desulfurization and denitrification system provided in Example 4, the rest is the same as that of Application Example 1.

[0117] Comparative application example 1

[0118] This comparative application example provides a method for desulfurization and denitrification using the flue gas desulfurization and denitrification system provided in Comparative Example 1, comprising the following steps:

[0119] (1) Flue gas at 250°C is mixed with ozone, and the resulting mixed gas is countercurrently contacted with a sodium hydroxide solution at a temperature of 32°C and a pH value of 11 to obtain desulfurized gas. The molar ratio of ozone to NO in the flue gas is 1.3:1, and the liquid-gas ratio of the sodium hydroxide solution to the mixed gas is 3:1. The flow rate of the flue gas is 20,000 Nm 3 / h, the NO concentration in the flue gas is 270mg / Nm 3 , the concentration of SO2 is 1500mg / Nm 3 ;

[0120] (2) After the first heating to 65°C, ozone is mixed with the desulfurized gas, and the obtained desulfurized mixed gas is countercurrently contacted with the denitrification liquid in the first denitrification tower 4. After the first heating, the molar ratio of ozone to NO in the desulfurized gas is 1:1, and the liquid-to-gas ratio of the denitrification liquid to the desulfurized mixed gas is 3.5:1. Desulfurized and denitrified gas is obtained from the top of the first denitrification tower 4.

[0121] The mass concentration of the denitrification liquid in step (2) is 5wt%, which is a mixed solution of urea, sodium sulfite and sodium thiosulfate, wherein the mass ratio of urea, sodium sulfite and sodium thiosulfate is 1:1:1.

[0122] Use the testo350 flue gas analyzer to correspond to the SO2 concentration and NO in the desulfurized gas and desulfurized and denitrified gas in Example 1-10 and Comparative Application Example 1 X The concentration was measured. The measurement results are shown in Table 1.

[0123] Table 1

[0124]

[0125] It can be seen from Table 1 that when the flue gas desulfurization and denitrification system provided by the present invention is used for desulfurization and denitrification, the removal rate of SO2 is as high as 99.19%, and the removal rate of NO is as high as 94.1%.

[0126] In Application Example 7, the temperature of ozone after the first heating and the second heating is relatively low, at 30°C. The desulfurization efficiency and denitrification efficiency in the second denitrification tower 5 are reduced, the SO2 removal rate is reduced from 99.19% to 98.57%, and the NO removal rate is reduced from 94.1% to 92.8%.

[0127] In Application Example 8, the temperature of ozone after the first heating and the second heating is relatively high, which is 80°C. The desulfurization efficiency and denitrification efficiency in the second denitrification tower 5 have not increased, the SO2 removal rate is still 99.19%, and the NO removal rate is still 94.1%, but the energy consumption increases, which is not conducive to energy saving.

[0128] Application Example 9 applies the flue gas desulfurization and denitrification system provided in Example 3 to carry out desulfurization and denitrification. The side line discharge is located at the bottom of the packed tower, which increases the ozone content in the second denitrification tower 5 and fails to achieve the purpose of improving the desulfurization and denitrification effects. The SO2 removal rate is reduced from 99.19% to 98.49%, and the NO removal rate is reduced from 94.1% to 89.3%.

[0129] Application Example 10 applies the flue gas desulfurization and denitrification system provided in Example 4 to carry out desulfurization and denitrification, and the side line discharge position is 2 / 3 of the height of the packing layer. Since the side line discharge position is too high, the desulfurization and denitrification efficiency in the first denitrification tower 4 is reduced, and the SO2 removal rate is reduced from 99.19% to 98.89%, and the NO removal rate is reduced from 94.1% to 93.4%.

[0130] In comparative application example 1, the desulfurization and denitrification system provided in comparative example 1 was used for desulfurization and denitrification. Since no side line extraction method was used in the denitrification process, the SO2 removal rate was reduced from 99.19% to 98.39%, and the NO removal rate was reduced from 94.1% to 84.3%.

[0131] In summary, the present invention divides the denitrification unit into two denitrification towers, and allows the side line discharge of the first denitrification tower 4 to enter the second denitrification tower 5, thereby achieving the effect of reducing ozone dosage, improving denitrification temperature and denitrification efficiency, and the SO2 removal rate is as high as 99.19%, and the NO removal rate is as high as 94.1%; the flue gas desulfurization and denitrification method provided by the present invention is simple, and through the reasonable allocation of the ratio of ozone to nitrogen oxides, the liquid-to-gas ratio and the selection of a suitable spray liquid composition, the desulfurization and denitrification effect is improved under simple operating conditions, so that the gas after desulfurization and denitrification can meet the emission standards after post-treatment.

[0132] The applicant declares that the above is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention shall fall within the protection scope and disclosure scope of the present invention.

Claims

1. A flue gas desulfurization and denitrification system, characterized in that: The flue gas desulfurization and denitrification system comprises a desulfurization unit, a denitrification unit and an ozone generation unit; The desulfurization unit comprises a first mixing device and a desulfurization tower connected in sequence, and the flue gas flows into the desulfurization tower after passing through the first mixing device; The denitration unit comprises a second mixing device, a first denitration tower, a third mixing device and a second denitration tower, the gas outlet of the desulfurization tower is connected to the second mixing device and the first denitration tower in sequence; the side line outlet of the first denitration tower is connected to the third mixing device and the second denitration tower in sequence; The side discharge of the first denitration tower is measured from the bottom of the packing layer, and the side discharge is from 1 / 3-1 / 2 of the height of the packing layer; The ozone generating unit comprises an ozone generating device and a heat exchange device, wherein the ozone generating device is independently connected to the first mixing device, the second mixing device and the third mixing device respectively; the heat exchange device is arranged on the connecting pipes between the ozone generating device and the second mixing device and the third mixing device; The first mixing device, the second mixing device and the third mixing device are each independently a static mixer.

2. The flue gas desulfurization and denitrification system according to claim 1, characterized in that: The heat source of the heat exchange device is flue gas.

3. A method for flue gas desulfurization and denitrification using the flue gas desulfurization and denitrification system according to claim 1 or 2, characterized in that: The method comprises the following steps: (1) Flue gas is mixed with ozone, and the resulting mixed gas is countercurrently contacted with alkaline spray liquid to obtain desulfurized gas; (2) After the first heating, ozone is mixed with the desulfurized gas, and the obtained desulfurized mixed gas is countercurrently contacted with the denitrification liquid in the first denitrification tower; After the desulfurized mixed gas extracted from the side line is mixed with the second heated ozone, the obtained side line extracted gas is countercurrently contacted with the denitrification liquid in the second desulfurization tower; and the desulfurized and denitrified gas is obtained from the top of the first denitrification tower and the second denitrification tower.

4. The method according to claim 3, characterized in that The concentration of NO in the flue gas is 200-320 mg / Nm 3 , the concentration of SO2 is 500-2000mg / Nm 3 .

5. The method according to claim 3, characterized in that: The flow rate of the flue gas in step (1) is 10000-30000Nm 3 / h.

6. The method according to claim 5, characterized in that The flow rate of the flue gas in step (1) is 15000-25000Nm 3 / h.

7. The method according to claim 3, characterized in that The temperature of the flue gas in step (1) is 150-350°C.

8. The method according to claim 7, characterized in that The temperature of the flue gas in step (1) is 180-300°C.

9. The method according to claim 3, characterized in that: The molar ratio of ozone to NO in flue gas in step (1) is (1-1.5):

1.

10. The method according to claim 3, characterized in that: The liquid-to-gas ratio of the alkaline spray liquid to the mixed gas in step (1) is (2-4):

1.

11. The method according to claim 3, characterized in that The alkaline spray liquid in step (1) is KOH solution and / or NaOH solution.

12. The method according to claim 3, characterized in that The pH value of the alkaline spray liquid in step (1) is 9-13.

13. The method according to claim 3, characterized in that The temperature of the alkaline spray liquid in step (1) is 20-50°C.

14. The method according to claim 13, characterized in that The temperature of the alkaline spray liquid in step (1) is 25-45°C.

15. The method according to claim 3, characterized in that In step (2), the temperature of the ozone after the first heating is 40-80°C.

16. The method according to claim 15, characterized in that In step (2), the temperature of the ozone after the first heating is 60-70°C.

17. The method according to claim 3, characterized in that The concentration of NO in the desulfurized gas in step (2) is 100-180 mg / Nm 3 , SO2 concentration ≤35mg / Nm 3 .

18. The method according to claim 3, characterized in that In step (2), the molar ratio of ozone to NO in the desulfurized gas after the first heating is (0.8-1.2):

1.

19. The method according to claim 3, characterized in that The liquid-to-gas ratio of the denitrification liquid to the desulfurized mixed gas in step (2) is (2-5):

1.

20. The method according to claim 3, characterized in that The flow ratio of the desulfurized mixed gas after the side line extraction in step (2) to the desulfurized mixed gas is (0.1-0.3):

1.

21. The method according to claim 3, characterized in that In step (2), the flow ratio of the second heated ozone to the first heated ozone is (0.1-0.3):

1.

22. The method according to claim 3, characterized in that Step (2) The temperature of the ozone after the second heating is 40-80°C.

23. The method according to claim 22, characterized in that Step (2) The temperature of the ozone after the second heating is 60-70°C.

24. The method according to claim 3, characterized in that The liquid-to-gas ratio of the denitrification liquid to the side-line extracted gas in step (2) is (2-5):

1.

25. The method according to claim 3, characterized in that The solute in the denitrification liquid in step (2) includes any one of urea, sulfite or thiosulfate, or a combination of at least two of them.

26. The method according to claim 25, characterized in that The solute in the denitrification liquid in step (2) is a combination of urea, sulfite and thiosulfate.

27. The method according to claim 3, characterized in that The mass concentration of the denitration liquid is 1-10wt%.

28. The method according to claim 26, characterized in that The mass ratio of urea, sulfite and thiosulfate is (1-3):(1-3):(1-3).

29. The method according to claim 25, characterized in that The sulfite includes any one of sodium sulfite, potassium sulfite or calcium sulfite, or a combination of at least two of them.

30. The method according to claim 25, characterized in that The thiosulfate includes any one of sodium thiosulfate, potassium thiosulfate or calcium thiosulfate, or a combination of at least two of them.

31. The method according to claim 3, characterized in that The method comprises the following steps: (1) Flue gas at 150-350°C is mixed with ozone, and the resulting mixed gas is countercurrently contacted with an alkaline spray liquid at a temperature of 20-50°C and a pH value of 9-13 to obtain desulfurized gas. The molar ratio of ozone to NO in the flue gas is (1-1.5):1, and the liquid-gas ratio of the alkaline spray liquid to the mixed gas is (2-4):1; (2) After the first heating of ozone at a temperature of 40-80°C, the obtained desulfurized mixed gas is countercurrently contacted with the denitrification liquid in the first denitrification tower. The molar ratio of the first heating of ozone to NO in the desulfurized gas is (1-1.5):1, and the liquid-gas ratio of the denitrification liquid to the desulfurized mixed gas is (2-5):1; after the desulfurized mixed gas extracted from the side line is mixed with the second heating of ozone at a temperature of 40-80°C, the obtained side-extracted gas is countercurrently contacted with the denitrification liquid in the second desulfurization tower. The liquid-gas ratio of the denitrification liquid to the side-extracted gas is (2-5):1; the flow ratio of the desulfurized mixed gas extracted from the side line to the desulfurized mixed gas is (0.1-0.3):1, and the flow ratio of the second heating of ozone to the first heating of ozone is (0.1-0.3):1; desulfurized and denitrified gas is obtained from the top of the first denitrification tower and the second denitrification tower.

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