Resourceful treatment method for desulfurization and denitrification waste liquid

Abstract

The invention belongs to the technical field of chemical environmental protection, and particularly relates to a resourceful treatment method for desulfurization and denitrification waste liquid. Comprising the following steps: mixing the desulfurization and denitrification waste liquid with an oxidizing agent, and adjusting the pH value to 5-6, so that part of organic matters in the desulfurization and denitrification waste liquid are oxidized, and part of metal ions form metal sulfate precipitates, thereby obtaining primary treatment waste liquid; mixing the primary treatment waste liquid with a polymer, and adjusting the pH value to 8-12, so that residual metal ions in the primary treatment waste liquid form hydroxide precipitates; meanwhile, the polymer adsorbs suspended solids in the primary treatment waste liquid and gathers into large-particle flocs, and secondary treatment waste liquid is obtained; and carrying out solid-liquid separation on the secondary treatment waste liquid to obtain solid-liquid and liquid as raw materials for subsequent resource utilization. Through cooperative treatment, high salt, high suspended solids and high COD in the desulfurization and denitrification waste liquid are efficiently removed, so that the effluent meets the reuse water inlet requirement, and the method is an environment-friendly treatment technology.

Description

Technical Field

[0001] The present invention belongs to the technical field of chemical environmental protection, and in particular relates to a method for resource recovery treatment of desulfurization and denitrification waste liquid. Background Art

[0002] With the continuous escalation of air pollution control requirements, desulfurization and denitrification technologies for regeneration flue gas from catalytic cracking units in the oil refining industry have achieved comprehensive purification, significantly reducing emissions of nitrogen oxides and sulfur oxides. However, the desulfurization and denitrification wastewater produced by this process, due to its complex pollutant composition, has become a new challenge hindering environmental governance and resource utilization.

[0003] During operation, catalyst loss in this catalytic cracking unit results in high concentrations of particulate matter in the desulfurization and denitrification wastewater, ranging from 1,500 mg / L to 5,000 mg / L. Furthermore, the alkaline solution readily absorbs sulfur dioxide, generating large amounts of sulfate and sodium sulfite in the wastewater, reaching concentrations of 7,000 mg / L to 70,000 mg / L. This results in chemical oxygen demand (COD) levels as high as 1,000 mg / L to 4,000 mg / L. The high salinity, turbidity, and COD characteristics of this desulfurization and denitrification wastewater make it impractical for direct discharge or resource recovery. Treatment is required to ensure compliance with discharge standards or for resource recovery.

[0004] At present, the mainstream treatment process for this type of desulfurization and denitrification wastewater usually adopts a three-stage treatment process of "sedimentation-filtration-oxidation". This treatment process includes physical separation and chemical oxidation to remove suspended matter and COD in the wastewater. However, the removal of suspended matter by physical separation enhances the colloid stability in a high-salt environment, resulting in a decrease in the efficiency of solid-liquid separation and significant fluctuations in the effluent turbidity; chemical oxidation utilizes Fenton oxidation or ozone oxidation to degrade COD, but high concentrations of sulfate and sulfite consume a large amount of oxidant, significantly increasing the cost of reagents, and oxidation by-products are prone to secondary pollution; moreover, muddy wet solids still remain in the treated wastewater, resulting in high treatment costs and limited resource utilization. Summary of the Invention

[0005] In order to solve the technical problems that the above-mentioned desulfurization and denitrification waste liquid has strong colloid stability in a high-salt environment, resulting in reduced physical separation efficiency and the need to consume a large amount of oxidant and residual muddy wet solids, the present invention provides a resource recovery method for desulfurization and denitrification waste liquid with high stability, strong adaptability and resource utilization.

[0006] The present invention regulates the pH of the desulfurization and denitrification wastewater in stages, utilizing acidic and alkaline environments to disrupt the stability of colloids in the wastewater in high-salinity environments. This allows the metal ions in the wastewater to be gradually precipitated and removed. Simultaneously, an oxidant is used to degrade the difficult-to-oxidize organic matter in the wastewater. The increased oxidation potential of the oxidant in an alkaline environment further degrades the difficult-to-oxidize organic matter in the wastewater, significantly reducing COD. This reduces oxidant consumption and reagent costs in traditional chemical oxidation treatments. The flocculation effect of a polymer is then used to aggregate the colloidal particles and fine suspended matter into large flocs. Solid-liquid separation is then performed using an inorganic membrane. The separated low-salinity liquid can be directly used in the desulfurization system or as circulating cooling water, serving as a raw material for subsequent resource utilization. This addresses the existing technical issues of desulfurization and denitrification wastewater, which suffer from strong colloid stability in high-salinity environments, resulting in reduced physical separation efficiency, high sulfate concentrations in the wastewater requiring large amounts of oxidant, significantly increasing reagent costs, and residual muddy wet solids in the treated wastewater.

[0007] The present invention first adjusts the desulfurization and denitrification waste liquid to be weakly acidic or neutral. Under weakly acidic or neutral conditions, easily precipitated metal ions preferentially react to form metal sulfate precipitates. Under the action of an oxidant, some reducing substances are oxidized, thereby reducing the COD in the desulfurization and denitrification waste liquid. The desulfurization and denitrification waste liquid is then adjusted to be alkaline. Under alkaline conditions, the remaining metal ions in the desulfurization and denitrification waste liquid are prompted to form hydroxide precipitates, thereby strengthening the precipitation of insoluble salts. At the same time, the oxidation potential of the oxidant in an alkaline environment is increased, which can further degrade the difficult-to-oxidize organic matter in the desulfurization and denitrification waste liquid and significantly reduce the COD. On this basis, polymers are used to aggregate colloidal particles and tiny suspended solids into large particle flocs. Solid-liquid separation is then performed using an inorganic membrane. The separated low-salt liquid can be directly used in the desulfurization system or circulating cooling water as a raw material for subsequent resource utilization.

[0008] The purpose of the present invention is to provide a method for resource recovery of desulfurization and denitrification waste liquid, comprising the following steps: The desulfurization and denitrification wastewater is mixed with an oxidant and the pH is adjusted to 4-6 to oxidize some of the organic matter in the wastewater. Simultaneously, some of the metal ions in the wastewater form metal sulfate precipitates, resulting in the primary treated wastewater. The primary treated wastewater is then mixed with a polymer and the pH is adjusted to 8-12 to precipitate the remaining metal ions in the wastewater as hydroxides. Simultaneously, the polymer absorbs suspended matter in the primary treated wastewater, aggregating it into large flocs, resulting in the secondary treated wastewater. The secondary treated wastewater is then subjected to solid-liquid separation, yielding solids and liquids, which serve as raw materials for subsequent resource utilization.

[0009] It should be noted that desulfurization and denitrification wastewater contains inorganic particles and metal salts. The metal salts include, but are not limited to, metal sulfates, metal sulfites, and metal nitrates. The metal ions in the metal salts are at least one of calcium and magnesium ions. The mass percentage of inorganic particles in the desulfurization and denitrification wastewater is 0-10%, and the mass percentage of metal salts in the desulfurization and denitrification wastewater is 0.5-10%.

[0010] The present invention adds an oxidant to the desulfurization and denitrification wastewater and adjusts the wastewater to a weakly acidic state. The oxidant selectively oxidizes some organic matter, including reducing substances such as sulfites and thiosulfates, destroying macromolecular structures and reducing the COD in the desulfurization and denitrification wastewater. Simultaneously, under acidic conditions, some metal ions in the desulfurization and denitrification wastewater react primarily with sulfate ions in the desulfurization and denitrification wastewater to form metal sulfate precipitates, thereby removing some of the metal ions and sulfate ions in the desulfurization and denitrification wastewater. By controlling the reaction time and stirring intensity, partial precipitation of calcium sulfate and magnesium sulfate is achieved, resulting in a primary treated wastewater.

[0011] On this basis, the present invention adds a polymer to the primary treatment waste liquid and adjusts the pH of the primary treatment waste liquid to alkaline; under alkaline conditions, the remaining metal ions in the primary treatment waste liquid react with hydroxide ions to promote the formation of more hydroxide precipitates. Specific hydroxide precipitates include: calcium hydroxide and magnesium hydroxide precipitates. This is because calcium hydroxide and magnesium hydroxide are both insoluble or slightly soluble compounds, and calcium-magnesium precipitates are generated in an alkaline environment. Moreover, under strong alkaline conditions, the oxidation potential of the oxidant is increased, which can further degrade difficult-to-oxidize organic matter and significantly reduce COD. The added polymer can enhance flocculation, and through charge neutralization and adsorption bridging, tiny suspended matter and precipitates are aggregated into large-particle flocs, thereby improving the efficiency of solid-liquid separation.

[0012] Since the dosage of the reagent directly affects the formation efficiency and treatment effect of precipitates or suspended matter in the desulfurization and denitrification waste liquid, the present invention determines the dosage of the reagent based on the initial concentration of metal ions and sulfate ions in the desulfurization and denitrification waste liquid, the pH value of the desulfurization and denitrification waste liquid, and the target treatment effect. The present invention is optimized through experiments. Preferably, the mass ratio of the desulfurization and denitrification waste liquid to the oxidant is 100:0.01~1, and more preferably, the mass ratio of the desulfurization and denitrification waste liquid to the oxidant is 100:0.1~1. Within this dosage range, the metal ions and sulfate ions in the desulfurization and denitrification waste liquid can fully react with the reagent to form sufficient precipitates, while avoiding secondary pollution or increased treatment costs caused by excessive reagents.

[0013] Preferably, the mass ratio of the primary treatment waste liquid to the polymer is 100:0.1-0.8.

[0014] Preferably, the conditions for mixing the desulfurization and denitrification waste liquid and the oxidant are the same as those for mixing the primary treatment waste liquid and the polymer, namely: the mixing time is 5 min to 30 min, and the mixing temperature is 50° C. to 65° C.

[0015] The present invention utilizes an inorganic membrane for solid-liquid separation. The membrane pore size can effectively intercept suspended matter and unprecipitated colloidal particles while allowing the permeation of soluble low-molecular salts, thereby achieving selective salt separation. Preferably, the pore size of the inorganic membrane is 0.1 μm.

[0016] Preferably, the inorganic membrane is made of ceramic, titanium, or carbon. Leveraging the inorganic membrane's resistance to high salt and high temperatures, it avoids fouling of the organic membrane caused by salt crystallization or organic adsorption. Furthermore, the separated low-salt liquid can be directly used in the desulfurization system or in circulating cooling water, serving as a raw material for subsequent resource utilization.

[0017] Preferably, the inorganic membrane is flat or tubular.

[0018] Preferably, the oxidant is hydrogen peroxide.

[0019] The polymer is polymerized iron or polymerized aluminum.

[0020] Compared with the prior art, the present invention has the following technical effects: 1. The present invention regulates the pH of the desulfurization and denitrification waste liquid in stages, and utilizes acidic and alkaline environments to break the stability of the colloids in the desulfurization and denitrification waste liquid in a high-salt environment, so that the metal ions in the desulfurization and denitrification waste liquid are gradually precipitated and removed. At the same time, by adding an oxidant, the difficult-to-oxidize organic matter in the desulfurization and denitrification waste liquid is degraded, and the COD of the desulfurization and denitrification waste liquid is reduced; and the oxidation potential of the oxidant in an alkaline environment is increased, which can further degrade the difficult-to-oxidize organic matter in the desulfurization and denitrification waste liquid and significantly reduce the COD; thereby reducing the consumption of oxidants in traditional chemical oxidation treatment and reducing the cost of reagents. Then, by utilizing the flocculation effect of the polymer, the colloidal particles and tiny suspended matter are aggregated into large-particle flocs for removal, and through solid-liquid separation, the separated low-salt liquid can be directly used in the desulfurization system or circulating cooling water as a raw material for subsequent resource utilization. The present invention solves the technical problems in the prior art that the colloid stability of the desulfurization and denitrification waste liquid is strong in a high-salt environment, resulting in reduced physical separation efficiency, the high concentration of sulfate in the desulfurization and denitrification waste liquid requiring a large amount of oxidant, which greatly increases the cost of the reagents, and muddy wet solids still remain in the treated waste liquid.

[0021] 2. This invention uses synergistic treatment to efficiently remove high salt, suspended solids, and COD content from desulfurization and denitrification wastewater, ensuring that the effluent meets the requirements for reuse. This is an environmentally friendly treatment technology. The treated liquid can be used as raw material for subsequent resource utilization, and the solids can be processed through a dehydration device for resource utilization.

[0022] 3. The method of the present invention can be quickly applied to desulfurization and denitrification process equipment, is adaptable to different water quality conditions, and has broad industrial application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is the technical flow chart for desulfurization and denitrification waste liquid.

[0024] Reference numerals: D101-first reaction unit; D102-second reaction unit; D103-concentration tank; D104-inorganic membrane; D105-water production tank; D106-sludge tank. DETAILED DESCRIPTION

[0025] In order to enable those skilled in the art to better understand and implement the technical solutions of the present invention, the present invention will be further described below with reference to specific embodiments and accompanying drawings. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative work are within the scope of protection of the present invention.

[0026] It should be noted that TDS stands for Total Dissolved Solids, which represents the total amount of dissolved solids in water.

[0027] Example 1 A method for recycling desulfurization and denitrification waste liquid comprises the following steps: In this embodiment, the COD of the desulfurization and denitrification wastewater is 3000 mg / L, the turbidity is 1200 NTU, the TDS is 25000 mg / L, the concentration of sulfate ions is 15000 mg / L, and the concentration of metal ions is 6000 mg / L, wherein the metal ions include Ca 2+ and Mg 2 + .

[0028] Step 1: Introduce the desulfurization and denitrification waste liquid into the first reaction device D101, add 5 kg / t of hydrogen peroxide into the first reaction device D101 filled with the desulfurization and denitrification waste liquid, stir and react for 15 minutes, adjust the pH value of the desulfurization and denitrification waste liquid in the first reaction device to 5.6, and obtain primary treated waste liquid.

[0029] Step 2: Introduce the primary treated waste liquid into the second reaction device D102, add 2kg / t of soda ash and 3kg / t of polymeric iron into the second reaction device D102 containing the primary treated waste liquid, stir and react for 10 minutes, so that the pH value of the primary treated waste liquid in the second reaction device is 9.4, and obtain secondary treated waste liquid.

[0030] Step 3: The secondary treated wastewater is introduced into the concentration tank D103 and then pumped to the ceramic membrane inorganic membrane for solid-liquid separation. The separated liquid enters the water production tank D105 for recycling, and the separated sludge enters the sludge tank for dehydration treatment.

[0031] Example 2 A method for recycling desulfurization and denitrification waste liquid comprises the following steps: In this embodiment, the COD of the desulfurization and denitrification wastewater is 3000 mg / L, the turbidity is 1200 NTU, the TDS is 25000 mg / L, the concentration of sulfate ions is 15000 mg / L, and the concentration of metal ions is 6000 mg / L, wherein the metal ions include Ca 2+ and Mg 2 + .

[0032] Step 1: Introduce the desulfurization and denitrification waste liquid into the first reaction device D101, add 10 kg / t of hydrogen peroxide into the first reaction device D101 filled with the desulfurization and denitrification waste liquid, stir and react for 15 minutes, adjust the pH value of the desulfurization and denitrification waste liquid in the first reaction device to 4, and obtain primary treated waste liquid.

[0033] Step 2: Introduce the primary treated waste liquid into the second reaction device D102, add 2kg / t of soda ash and 8kg / t of polymeric iron into the second reaction device D102 containing the primary treated waste liquid, stir and react for 10 minutes, so that the pH value of the primary treated waste liquid in the second reaction device is 10, and obtain secondary treated waste liquid.

[0034] Step 3: The secondary treated wastewater is introduced into the concentration tank D103 and then pumped to the ceramic membrane inorganic membrane for solid-liquid separation. The separated liquid enters the water production tank D105 for recycling, and the separated sludge enters the sludge tank for dehydration treatment.

[0035] like Figure 1 As shown, the present invention introduces the desulfurization and denitrification waste liquid into the first reaction device D101, adds reagents, and uses a stirring rod to carry out a stirring contact reaction. After the reaction is completed; the primary treatment waste liquid in the first reaction device D101 is introduced into the second reaction device D102, adds reagents, and uses a stirring rod to carry out a stirring contact reaction. After the reaction is completed; the secondary treatment waste liquid in the second reaction device D102 is introduced into the concentration tank D103, and then pumped to the ceramic membrane D104 for solid-liquid separation. The separated liquid enters the water production tank D105 for recycling, and the separated sludge enters the sludge tank D106 for dehydration treatment.

[0036] Table 1 Properties of the waste liquid after treatment in Example 1 Note: “ / ” means not tested.

[0037] As shown in Table 1, after only step 1 treatment, the COD in the primary treated wastewater dropped to 1500 mg / L compared with the initial desulfurization and denitrification wastewater due to the oxidation or precipitation of some organic matter; some suspended matter precipitated, causing the turbidity to drop to 600 NTU; at the same time, under acidic conditions, some sulfate ions in the desulfurization and denitrification wastewater reacted with some metal ions to form metal sulfate precipitates, causing the TDS to drop to 1500 mg / L; the concentration of sulfate ions dropped to 800 mg / L, and the concentration of metal ions dropped to 700 mg / L, which was mainly due to the reaction of some sulfate ions with calcium ions to form calcium sulfate precipitates. After step 2, due to the acidic conditions, some sulfate precipitation has already occurred; at the same time, some reducing substances have also been oxidized. Under alkaline conditions, the oxidation potential of the oxidant increases, further degrading difficult-to-oxidize organic matter and significantly reducing COD to 300 mg / L. The remaining metal ions react with hydroxide ions to form hydroxide precipitates, mainly calcium hydroxide and magnesium hydroxide, reducing the metal ion concentration to 200 mg / L, the sulfate ion concentration to 800 mg / L, and the TDS to 1000 mg / L. In addition, under the flocculation effect of the polymer, the adsorbed micro-suspended matter and the precipitate aggregate into large flocs, reducing the turbidity to 100 NTU. In the embodiments of the present invention, the pH is adjusted and different treatments are performed to remove easily precipitated metal salts and insoluble metal salts in the desulfurization and denitrification waste liquid in steps. At the same time, the reducing substances in the desulfurization and denitrification waste liquid are oxidized through oxidation treatment under acidic conditions and deep oxidation treatment under alkaline conditions to reduce COD. The solid-liquid separation of the ceramic membrane removes most of the suspended matter and sediment in the secondary treatment waste liquid, so that the COD of the separated liquid is ≤50 mg / L and the turbidity is ≤5 NTU.

[0038] Table 2 Properties of the waste liquid after treatment in Example 2 Note: “ / ” means not tested.

[0039] As shown in Table 2, after only step 1 treatment, due to the oxidation or precipitation of some organic matter, the COD in the primary treated wastewater was reduced to 6000 mg / L compared to the initial desulfurization and denitrification wastewater; some suspended matter precipitated, causing the turbidity to drop to 600 NTU; at the same time, some sulfate ions in the desulfurization and denitrification wastewater reacted with some metal ions to form metal sulfate precipitates, causing the TDS to drop to 1500 mg / L; the concentration of sulfate ions dropped to 1000 mg / L, and the concentration of metal ions dropped to 800 mg / L, mainly due to the reaction of some sulfate ions with calcium ions to form calcium sulfate precipitates. After step 2 treatment, under alkaline conditions, the oxidation potential of the oxidant increased, which could further degrade the difficult-to-oxidize organic matter and significantly reduce the COD to 300 mg / L; the remaining metal ions reacted with hydroxide ions to form hydroxide precipitates, mainly calcium hydroxide and magnesium hydroxide, which reduced the concentration of metal ions to 300 mg / L, the concentration of sulfate ions to 800 mg / L, and the TDS to 2000 mg / L. Furthermore, the polymer's flocculation action absorbs tiny suspended solids and sediments, aggregating them into large flocs and reducing turbidity to 100 NTU. The ceramic membrane's solid-liquid separation removes most suspended solids and sediments from the secondary wastewater, resulting in a COD of ≤50 mg / L and a turbidity of ≤5 NTU after separation.

[0040] Obviously, those skilled in the art may make various modifications and variations to the present invention without departing from the spirit and scope of the present invention. Thus, if such modifications and variations fall within the scope of the claims and their equivalents, the present invention is intended to encompass such modifications and variations. The above-described embodiments are merely preferred embodiments for the purpose of fully illustrating the present invention and are not intended to limit the scope of protection.

Claims

1. A method for recycling desulfurization and denitrification waste liquid, characterized in that: The following steps are included: The desulfurization and denitrification waste liquid is mixed with an oxidant and the pH value is adjusted to 4-6, so that part of the organic matter in the desulfurization and denitrification waste liquid is oxidized. At the same time, part of the metal ions in the desulfurization and denitrification waste liquid forms metal sulfate precipitation to obtain a primary treated waste liquid; The primary treatment wastewater is mixed with the polymer and the pH value is adjusted to 8-12 so that the remaining metal ions in the primary treatment wastewater form hydroxide precipitation; at the same time, the polymer absorbs the suspended matter in the primary treatment wastewater and aggregates it into large particle flocs to obtain the secondary treatment wastewater; The secondary treatment waste liquid is subjected to solid-liquid separation to obtain solid and liquid as raw materials for subsequent resource utilization.

2. The resource recovery treatment method for desulfurization and denitrification waste liquid according to claim 1, characterized in that: The mass ratio of the desulfurization and denitrification waste liquid to the oxidant is 100:0.01~1.

3. The resource recovery treatment method for desulfurization and denitrification waste liquid according to claim 1, characterized in that: The mass ratio of the desulfurization and denitrification waste liquid to the oxidant is 100:0.1~1.

4. The resource recovery treatment method for desulfurization and denitrification waste liquid according to claim 1, characterized in that: The oxidant is hydrogen peroxide.

5. The resource recovery treatment method for desulfurization and denitrification waste liquid according to claim 1, characterized in that: The mass ratio of the primary treatment waste liquid to the polymer is 100:0.1-0.

8.

6. The resource treatment method for desulfurization and denitrification waste liquid according to claim 1, characterized in that: The polymer is polymerized iron or polymerized aluminum, the degree of polymerization of the polymerized iron is 10-100, and the degree of polymerization of the polymerized aluminum is 10-100.

7. The resource recovery treatment method for desulfurization and denitrification waste liquid according to claim 1, characterized in that: The conditions for mixing the desulfurization and denitrification waste liquid with the oxidant are the same as those for mixing the primary treatment waste liquid with the polymer, namely: The mixing time is 5 min to 30 min, and the mixing temperature is 50°C to 65°C.

8. The resource recovery treatment method for desulfurization and denitrification waste liquid according to claim 1, characterized in that: The desulfurization and denitrification waste liquid contains inorganic particles and metal salts.

9. The resource recovery treatment method for desulfurization and denitrification waste liquid according to claim 7, characterized in that: The mass percentage of inorganic particles contained in the desulfurization and denitrification waste liquid is 0-10%, and the mass percentage of metal salts contained in the desulfurization and denitrification waste liquid is 0.5%-10%.

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