Low-temperature flue gas desulfurization and denitrification treatment process

Abstract

The invention discloses a low-temperature flue gas desulfurization and denitrification treatment process, and relates to the technical field of flue gas desulfurization and denitrification. According to the characteristics of oxidation denitration composite desulfurization of low-temperature flue gas with the emission temperature lower than 150 DEG C, sulfur dioxide and nitric oxide in the flue gas are oxidized by using an oxidizing agent compounded by hydrogen peroxide and an oxidation enhancer, then absorption is performed by using an alkaline absorption liquid, and calcium sulfate and calcium nitrate are byproducts; in the slurry absorbing sulfur dioxide and nitrogen oxide, the solubility difference between calcium sulfate and calcium nitrate is large, so that calcium sulfate can be directly produced through a filtering device; and for unsaturated water flue gas and calcium nitrate slurry, impurity removal and thickening can be carried out by utilizing initial flue gas, and then high-purity calcium nitrate crystals are produced through cooling crystallization, so that the low-temperature flue gas desulfurization and denitrification cost is remarkably reduced.

Description

Technical Field

[0001] The invention relates to the technical field of flue gas desulfurization and denitrification, and in particular to a low-temperature flue gas desulfurization and denitrification treatment process. Background Art

[0002] Industrial furnaces are usually made of coal, which will produce a large amount of sulfide and nitrogen oxides during combustion. The sulfide is sulfur dioxide, about 90% of nitrogen oxides are NO, and the remaining 10% is mainly NO2. If the above sulfide and nitrogen oxides are directly discharged into the atmosphere without treatment, they will produce photochemical smog, acid rain, haze, and damage the ozone layer. Therefore, the desulfurization and denitrification of flue gas is a key research issue.

[0003] The main methods for controlling nitrogen oxides (NOx) are SCR (selective chemical reduction) and SNCR (selective non-chemical reduction), activated coke adsorption, oxidation absorption, complex absorption electrochemical reduction, etc. Among them, SCR denitrification is also called selective catalytic reduction denitrification. The reducing agent is NH3 or urea, which can selectively chemically reduce NOx in the flue gas to eventually generate nitrogen and water. The SCR reaction requires the flue gas to reach a high temperature of at least 180°C, while industrial furnaces are basically designed for energy saving, and the flue gas temperature is usually below 150°C. Therefore, the use of SCR denitrification requires secondary heating of the flue gas. SNCR denitrification selects a temperature range of 850°C to 1100°C, sprays atomized urea solution or ammonia water, treats NOx, and generates nitrogen and water. The problem is that the efficiency is low (less than 50%), and the ammonia escape exceeds the standard. The activated coke denitrification method is used in the treatment of sintering machine flue gas in steel enterprises. It mainly uses the chemical properties of activated coke to reduce NO to N2 under the action of reducing agent NH3. The system process is complicated, and the regeneration of activated coke requires a high temperature of 500℃, the regeneration efficiency is not high, and new activated coke materials need to be added regularly. The investment and operating costs are high. The electrochemical denitrification method mainly uses a complex absorption liquid to convert NO in the flue gas into N2. X It is absorbed from the flue gas into the liquid phase, and then quickly reacts with reducing agents such as urea under the action of electric field force. There is almost no requirement for the temperature of the flue gas, and low temperature is conducive to the absorption of NO. However, it is currently only in the laboratory and small-scale test stage. In industrial production, the timeliness and absorption efficiency of the denitrification agent are greatly reduced after several hours of operation. The absorption efficiency ultimately does not exceed 20%, making it difficult to ensure that the flue gas meets emission standards.

[0004] For low-temperature flue gas below 150°C, oxidation is the most suitable and economical method. XThe chemical agents currently used for oxidation absorption into the liquid phase are mainly strong oxidants such as ozone, hydrogen peroxide, sodium hypochlorite and composite oxidants, which have significant disadvantages of large reagent consumption and difficult treatment of denitrification absorption waste liquid. Therefore, it is particularly necessary to optimize the oxidation absorption process to achieve efficient desulfurization and denitrification of low-temperature flue gas at a low cost. Summary of the invention

[0005] The purpose of the present invention is to provide a low-temperature flue gas desulfurization and denitrification treatment process to solve the problems existing in the above-mentioned prior art.

[0006] To achieve the above object, the present invention provides the following solutions:

[0007] The present invention provides a low-temperature unsaturated water flue gas desulfurization and denitrification treatment process, wherein the temperature of the low-temperature unsaturated water flue gas is ≤150°C, and the desulfurization and denitrification process comprises the following steps:

[0008] The sulfur dioxide and nitrogen oxides in the low-temperature unsaturated water flue gas are oxidized by an oxidant, and then the flue gas subjected to the oxidation treatment is passed into an alkaline absorption liquid, and after absorption treatment by the alkaline absorption liquid, a desulfurized and denitrified flue gas is obtained;

[0009] The slurry obtained after the alkaline absorption liquid absorption treatment is filtered to obtain calcium sulfate solid, and the filtrate is concentrated by the low-temperature unsaturated water smoke, and then crystallized to obtain calcium nitrate crystals.

[0010] Furthermore, in the low-temperature unsaturated water smoke, 2000 mg / Nm 3 ≥NO X Content ≥50mg / Nm 3 , 2000mg / Nm 3 ≥Sulfur dioxide content ≥20mg / m 3 , dust content: ≤10mg / Nm 3 .

[0011] Furthermore, the oxidant is a mixture of hydrogen peroxide and an oxidation enhancer; the alkaline absorption liquid is a slurry of calcium oxide, calcium hydroxide or calcium carbonate. More preferably, the mass concentration of the alkaline absorption liquid is ≥4%.

[0012] Furthermore, the oxidation enhancer is one or more of weakly reducing organic amines, quinones or ferrous salts.

[0013] Furthermore, organic amines include but are not limited to: melamine, propylenediamine, butylenediamine, acrylamide, etc.; ferrous salts include but are not limited to: ferrous sulfate, ferrous chloride, ferrous nitrate and organic ferrous EDTA2-Fe salt.

[0014] Furthermore, the molar ratio of the hydrogen peroxide to the oxidation enhancer is 1:1.

[0015] The present invention also provides a low-temperature saturated water flue gas desulfurization and denitrification treatment process, wherein the temperature of the low-temperature saturated water flue gas is ≤150°C, and the desulfurization and denitrification process comprises the following steps:

[0016] The sulfur dioxide and nitrogen oxides in the low-temperature unsaturated water flue gas are oxidized by an oxidant, and then the flue gas subjected to the oxidation treatment is passed into an alkaline absorption liquid, and after absorption treatment by the alkaline absorption liquid, a desulfurized and denitrified flue gas is obtained;

[0017] The slurry obtained after the alkaline absorption liquid absorption treatment is filtered to obtain calcium sulfate solid, and the filtrate is crystallized to obtain calcium nitrate crystals.

[0018] Furthermore, in the low-temperature saturated water smoke, 2000 mg / Nm 3 ≥NO X Content ≥50mg / Nm 3 , 2000mg / Nm 3 ≥Sulfur dioxide content ≥20mg / m 3 , dust content: ≤10mg / Nm 3 .

[0019] Furthermore, the oxidant is a mixture of hydrogen peroxide and an oxidation enhancer.

[0020] Furthermore, the oxidation enhancer is an organic amine, a quinone or a ferrous salt.

[0021] Furthermore, organic amines include but are not limited to: melamine, propylenediamine, butylenediamine, acrylamide, etc.; ferrous salts include but are not limited to: ferrous sulfate, ferrous chloride, ferrous nitrate and organic ferrous EDTA2-Fe salt.

[0022] Furthermore, the molar ratio of the hydrogen peroxide to the oxidation enhancer is 1:1.

[0023] The present invention enhances the oxidizability of hydrogen peroxide so that it can ensure the oxidation capacity of NO and sulfur dioxide between 20-150°C, and optimizes the post-treatment process of the acid gas absorbent to obtain by-product calcium sulfate and calcium nitrate. The by-product calcium sulfate does not need to be oxidized by air; the purity of the by-product calcium nitrate can reach more than 99%, which can be used as agricultural fertilizer or other industrial purposes, significantly reducing the cost of low-temperature flue gas desulfurization and denitrification, making the theoretical value of the removal cost per kg of NO less than 2 yuan.

[0024] The present invention discloses the following technical effects:

[0025] According to the characteristics of low-temperature flue gas oxidation denitration and composite desulfurization with an emission temperature below 150°C, the present invention utilizes an oxidant compounded with hydrogen peroxide and an oxidation enhancer to oxidize sulfur dioxide and nitrogen oxides in the flue gas, and then utilizes an alkaline absorption liquid for absorption. The process of the present invention can simultaneously remove nitrogen oxides and sulfur dioxide from the flue gas, and produce calcium sulfate and calcium nitrate as by-products; the slurry after absorbing sulfur dioxide and nitrogen oxides can be directly produced through a filtering device because the solubility difference between calcium sulfate and calcium nitrate is very large, and both the liquid and solid calcium nitrates can meet the demand for agricultural nitrogen fertilizers, and the calcium nitrate can be further purified as an industrial raw material; for unsaturated water flue gas, the calcium nitrate slurry can also utilize the initial flue gas for impurity removal and concentration, and then through crystallization, high-purity calcium nitrate crystals are produced, thereby significantly reducing the cost of low-temperature flue gas desulfurization and denitrification. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0027] Figure 1 It is a process flow chart of low-temperature unsaturated water flue gas desulfurization and denitrification treatment of the present invention; wherein, 01-flue gas fan, 02-salt concentration tower, 03-sewage pump, 04-salt liquid circulation tank, 05-concentrated brine circulation pump, 06-crystallization tank, 07-centrifuge, 08-oxidizing agent tank, 09-oxidizing agent pump, 10-oxidizing absorption tower, 11-oxidizing agent circulation pump, 12-absorption liquid tank, 13-absorption liquid circulation pump, 14-alkali liquid pump, 15-powder bin, 16-conveyor, 17-alkali liquid preparation tank, 18-filter press.

[0028] Figure 2 This is a process flow chart of low-temperature saturated water flue gas desulfurization and denitrification treatment of the present invention. Among them, 01- flue gas fan, 02- oxidizing agent tank, 03- oxidizing absorption tower, 04- oxidizing agent pump, 05- oxidizing agent circulation pump, 06- absorption liquid tank, 07- absorption liquid circulation pump, 08- powder silo, 09- conveyor, 10- alkali solution preparation tank, 11- filter press, 12- salt concentration device, 13- alkali solution pump. DETAILED DESCRIPTION

[0029] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0030] It should be understood that the terms described in the present invention are only for describing a particular embodiment and are not intended to limit the present invention. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper and lower limits of the scope is also specifically disclosed. The intermediate value in any stated value or stated range, and each smaller range between any other stated value or intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0031] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0032] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention description without departing from the scope or spirit of the present invention. Other embodiments derived from the present invention description will be apparent to those skilled in the art. The present invention description and examples are exemplary only.

[0033] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0034] Example 1

[0035] The process flow chart of desulfurization and denitrification of low-temperature unsaturated water flue gas is shown in Figure 1 The processing flow is as follows:

[0036] The flue gas volume treated is 100000Nm 3 / h of unsaturated water flue gas from furnace enterprises, the nitrogen oxide content in the initial flue gas is: 320mg / Nm 3 , sulfur dioxide content: 56mg / Nm 3 , dust content: 10mg / Nm 3 , moisture: 8%, temperature: 120℃.

[0037] 1. Flue gas process: The above-mentioned unsaturated water flue gas from the furnace enterprise enters the salt concentration tower 02 after passing through the flue gas fan 01, and is fully mixed with the salt solution sprayed from the atomization device on the top of the tower. During the mixing process, the water in the salt solution enters the flue gas, making the flue gas rich in water, and the water content in the salt solution is reduced to achieve concentration, while controlling the temperature of the water-rich flue gas to ≤80°C. The flue gas is then discharged from the top of the salt concentration tower 02 into the oxidation absorption tower 10, fully contacting with the oxidant circulating in the tower, and NO and SO2 in the flue gas are oxidized to high-valent NO X and SO3. High-priced NO X The SO3 fully reacts with the alkali solution sprayed in the oxidation absorption tower 10, and enters the absorption liquid tank 12 after being absorbed by the alkali solution, completing the removal of nitrogen oxides and sulfur dioxide in the flue gas. The treated flue gas is discharged into the exhaust pipe through the top of the oxidation absorption tower 10 and enters the atmosphere.

[0038] 2. Liquid phase process:

[0039] Two circulation sections are arranged in the oxidation absorption tower 10, namely, an oxidant circulation section and an alkali solution circulation section.

[0040] (1) Oxidant preparation: hydrogen peroxide is added into the oxidant tank 08, and a metering device is provided in the oxidant tank 08, and an oxidation enhancer (melamine) is added at a molar ratio of 1:1 to obtain an oxidant. In this state, hydrogen peroxide will form a peroxidation or free radical oxygen state, which fully activates the oxidizing property of hydrogen peroxide and reduces the reaction temperature.

[0041] (2) The oxidant in the oxidant tank 08 is pumped into the atomization device of the oxidation absorption tower 10 through the oxidant pump 09, and fully reacts with NO and SO2 in the flue gas from the salt concentration tower 02 to oxidize them into high-valent NO X and SO3, the unreacted oxidant is circulated in the oxidation absorption tower 10 through the oxidant circulation pump 11. At the same time, part of the circulating liquid after the oxidant circulation pump 11 is collected and enters the alkali solution preparation tank 17 to participate in the alkali solution preparation.

[0042] (3) The calcium hydroxide in the powder bin 15 is transported to the alkali solution preparation tank 17 via the conveyor 16 and is prepared into a 4% calcium hydroxide turbid solution. The alkali solution is then pumped into the absorption liquid tank 12 via the alkali solution pump 14. The alkali solution in the absorption tank 12 is pumped into the oxidation absorption tower 10 via the absorption liquid circulation pump 13 to fully mix with the flue gas to react and remove the high-valent NO contained in the flue gas. X It is absorbed into the liquid phase with SO3 to react and generate a mixed turbid liquid of calcium sulfate and calcium nitrate. The mixed turbid liquid is returned to the absorption liquid tank 12 for recycling, ensuring that the pH of the circulating liquid is ≥ 6.5.

[0043] (4) Collect part of the circulating liquid after the absorption liquid circulation pump 13 and filter it through the filter press 18 to remove calcium sulfate. The obtained filtrate enters the salt solution circulation tank 04. The collection of circulating liquid process and the process of replenishing alkali solution are linked and controlled to control the pH value of the circulating alkali solution to be ≥6.5. The filter cake of the filter press 18, namely calcium sulfate, is loaded on a truck for delivery or take-away.

[0044] (5) The salt solution from the filter press 18 of the oxidation absorption section enters the salt solution circulation tank 04 of the salt concentration section, and is partially pumped into the salt concentration tower 02 through the concentrated salt water circulation pump 05 to be fully mixed with the unsaturated water flue gas entering from the bottom of the salt concentration tower 02. During the mixing process, heat and mass transfer occurs, the flue gas becomes water-rich flue gas, the water in the salt solution enters the flue gas, and the salt solution becomes concentrated. The Baume degree is controlled between 55-60Be and the pH value is between 5.5-6.5 by the number of cycles.

[0045] (6) After collecting part of the concentrated brine, the brine enters the crystallization tank 06 and is cooled to 50° C., where it is crystallized to obtain calcium nitrate tetrahydrate. After the crystallization liquid passes through the centrifuge 07, calcium nitrate crystals (purity 99.8%) are separated, and the mother liquor returns to the brine circulation tank 04 for continued circulation and concentration.

[0046] (7) Impurities at the bottom of the salt concentration tower 02 are sent to the oxidation stage filter press 18 via the sewage pump 03 to remove calcium sulfate produced in the salt concentration stage.

[0047] Nitrogen oxide content in the treated flue gas: 25mg / Nm 3 , sulfur dioxide content: 2.1mg / Nm 3 , dust content: 3mg / Nm 3 , moisture: 8%, temperature: 50℃. Exhaust gas flow rate 100000Nm 3 / h.

[0048] Comparative Example 1

[0049] The flue gas working condition is the same as that of Example 1. The only difference is that only hydrogen peroxide is added to the oxidizing agent tank 08, and no oxidizing enhancer is added.

[0050] The results of comparative example 1 show that the nitrogen oxide content is 50 mg / Nm 3 , sulfur dioxide content: 5mg / Nm 3 , dust content: 5mg / Nm 3 , moisture: 9%, temperature: 50℃. Exhaust gas flow rate 100000Nm 3 / h.

[0051] The hydrogen peroxide consumption of Example 1 is only 17 kg / h, and the hydrogen peroxide consumption of Comparative Example 1 is 48 kg / h. The addition of the oxidation enhancer can greatly reduce the hydrogen peroxide consumption.

[0052] Example 2

[0053] The process flow chart of desulfurization and denitrification of low-temperature saturated water flue gas is shown in Figure 2 , the processing flow is as follows:

[0054] The flue gas treated comes from a high-purity and high-white calcium carbonate production enterprise with a production capacity of 300t / d and a flue gas volume of 45000Nm 3 / h, initial flue gas nitrogen oxide content: 250mg / Nm 3 , sulfur dioxide content: 35mg / Nm 3 , dust content: 18mg / Nm 3 , moisture: 17%, temperature: 60℃.

[0055] 1. Flue gas process: The saturated water flue gas is passed through the flue gas fan 01 into the oxidation absorption tower 03. The flue gas is fully contacted with the oxidant circulating in the tower 03, and the NO and SO2 in the flue gas are oxidized to high-valent NO X and SO3. High-priced NO X SO3 fully reacts with the alkali solution sprayed in the oxidation absorption tower 03, is absorbed by the alkali solution and enters the absorption liquid tank 06, and the flue gas completes the removal of nitrogen oxides and sulfur dioxide. The flue gas is then discharged into the exhaust pipe through the top of the oxidation absorption tower 03 and enters the atmosphere.

[0056] 2. Liquid phase process:

[0057] Two circulation sections are arranged in the oxidation absorption tower 03, namely, an oxidant circulation section and an alkali solution circulation section.

[0058] (1) Oxidant preparation: Add hydrogen peroxide into the oxidant tank 02, which is equipped with a metering device, and add the oxidation enhancer (melamine) at a molar ratio of 1:1. In this state, hydrogen peroxide will form a peroxidation or free radical oxygen state, which fully activates the oxidizing property of hydrogen peroxide and reduces the reaction temperature.

[0059] (2) The prepared oxidant is pumped into the oxidation absorption tower 03 by the oxidant pump 04, where it fully reacts with NO and SO2 in the flue gas from the kiln, oxidizing them into high-valent NO X The unreacted oxidant is recycled in the oxidation absorption tower through the oxidant circulation pump 5. At the same time, part of the circulating liquid after the oxidant circulation pump 5 is collected and enters the alkali solution preparation tank 10 to participate in the alkali solution preparation.

[0060] (3) The calcium hydroxide in the powder bin 08 is transported by the conveyor 09 to the alkali solution preparation tank 10 to be prepared into a 4% calcium hydroxide turbid solution, and then sent to the absorption liquid tank 06 by the alkali solution pump 13. After that, the alkali solution is pumped into the oxidation absorption tower 03 by the absorption liquid circulation pump 07 to fully mix with the flue gas to react and remove the high-priced NO contained in the flue gas. XIt is absorbed by SO3 and enters the liquid phase to react to form a mixed turbid liquid of calcium sulfate and calcium nitrate. The mixed turbid liquid is returned to the absorption liquid tank 06 for recycling, ensuring that the circulating liquid PH ≥ 6.5.

[0061] (4) Collect part of the circulating liquid after the absorption liquid circulation pump 07, and then remove calcium sulfate through the filter press 11 to enter the salt concentration device 12. The collection of circulating liquid process and the process of replenishing alkali solution are linked to control the pH value of the circulating alkali solution ≥ 5.5. The filter cake removed by the plate and frame is the calcium sulfate filtrate, which is the salt solution. The filter cake is loaded and delivered or taken away. The filtrate enters the salt concentration device 12. The salt concentration device 12 selects single-effect, multi-effect or MVR according to the process to evaporate and crystallize the salt solution to produce anhydrous calcium nitrate or evaporate and cool and crystallize tetrahydrate calcium nitrate with a purity of more than 99.5%.

[0062] The nitrogen oxide content in the treated flue gas is 32mg / Nm 3 , sulfur dioxide content: ≤3.2mg / Nm 3 , dust content: 3mg / Nm 3 , moisture, 17%, temperature: 45℃. Exhaust gas flow rate: 45000Nm 3 / h.

[0063] Comparative Example 2

[0064] The flue gas working condition is the same as that of Example 2, except that only hydrogen peroxide is added to the oxidizing agent tank 02, without adding an oxidizing enhancer.

[0065] The results showed that less than 10% of NO and SO2 in the oxidation absorption tower 02 were oxidized to high-valent NO X and SO3.

[0066] Nitrogen oxide content in the treated flue gas: 200mg / Nm 3 , sulfur dioxide content: ≤33mg / Nm 3 , dust content: 3mg / Nm 3 , moisture content is 17%, temperature: 45℃.

[0067] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A low-temperature unsaturated water flue gas desulfurization and denitrification treatment process, characterized in that: The temperature of the low-temperature unsaturated water flue gas is ≤150°C, and the desulfurization and denitrification process comprises the following steps: The sulfur dioxide and nitrogen oxides in the low-temperature unsaturated water flue gas are oxidized by an oxidant, and then the flue gas subjected to the oxidation treatment is passed into an alkaline absorption liquid, and after absorption treatment by the alkaline absorption liquid, a desulfurized and denitrified flue gas is obtained; The slurry obtained after the alkaline absorption liquid absorption treatment is filtered to obtain calcium sulfate solid, and the filtrate is concentrated by using the low-temperature unsaturated water smoke, and then crystallized to obtain calcium nitrate crystals.

2. The low-temperature unsaturated water flue gas desulfurization and denitrification treatment process according to claim 1, characterized in that: In the low-temperature unsaturated water smoke, 2000mg / Nm 3 ≥NO X Content ≥50mg / Nm 3 , 2000mg / Nm 3 ≥Sulfur dioxide content ≥20mg / m 3 , dust content: ≤10mg / Nm 3 .

3. The low-temperature unsaturated water flue gas desulfurization and denitrification treatment process according to claim 1, characterized in that: The oxidant is a mixture of hydrogen peroxide and an oxidation enhancer.

4. The low-temperature unsaturated water flue gas desulfurization and denitrification treatment process according to claim 3 is characterized in that: The oxidation enhancer is one or more of organic amines, quinones or ferrous salts.

5. The low-temperature unsaturated water flue gas desulfurization and denitrification treatment process according to claim 4 is characterized in that: The molar ratio of the hydrogen peroxide to the oxidation enhancer is 1:

1.

6. A low-temperature saturated water flue gas desulfurization and denitrification treatment process, characterized in that: The temperature of the low-temperature saturated water flue gas is ≤150°C, and the desulfurization and denitrification process comprises the following steps: The sulfur dioxide and nitrogen oxides in the low-temperature unsaturated water flue gas are oxidized by an oxidant, and then the flue gas subjected to the oxidation treatment is passed into an alkaline absorption liquid, and after absorption treatment by the alkaline absorption liquid, a desulfurized and denitrified flue gas is obtained; The slurry obtained after the alkaline absorption liquid absorption treatment is filtered to obtain calcium sulfate solid, and the filtrate is crystallized to obtain calcium nitrate crystals.

7. The low-temperature saturated water flue gas desulfurization and denitrification treatment process according to claim 6, characterized in that: In the low-temperature saturated water smoke, 2000mg / Nm 3 ≥NO X Content ≥50mg / Nm 3 , 2000mg / Nm 3 ≥Sulfur dioxide content ≥20mg / m 3 , dust content: ≤10mg / Nm 3 .

8. The low-temperature saturated water flue gas desulfurization and denitrification treatment process according to claim 6, characterized in that: The oxidant is a mixture of hydrogen peroxide and an oxidation enhancer.

9. The low-temperature unsaturated water flue gas desulfurization and denitrification treatment process according to claim 8, characterized in that: The oxidation enhancer is one or more of organic amines, quinones or ferrous salts.

10. The low-temperature unsaturated water flue gas desulfurization and denitrification treatment process according to claim 9, characterized in that: The molar ratio of the hydrogen peroxide to the oxidation enhancer is 1:1.

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