Composite desulfurizer based on dicyandiamide slag and preparation method thereof

Abstract

The invention relates to the field of desulfurizing agents, and discloses a compound desulfurizing agent based on dicyandiamide slag and a preparation method of the compound desulfurizing agent based on the dicyandiamide slag. 15 to 25 parts of calcium oxide; 10 to 15 parts of calcium hydroxide; 3 to 8 parts of bentonite; 1-3 parts of iron oxide; and 1-2 parts of ammonium chloride. Calcium oxide and calcium hydroxide are added, calcium oxide has extremely strong alkalinity and can quickly react with SO2 to generate calcium sulfate at the high temperature higher than 300 DEG C, calcium hydroxide reacts with SO2 in a low-temperature region, a special layered crystal structure provides a larger specific surface area, and a calcium sulfite intermediate product is formed through gas-solid reaction of surface hydroxyl and SO2, so that the content of sulfur in SO2 is increased, and the content of sulfur in SO2 is increased. And then the dicyandiamide slag is oxidized into stable CaSO4 by oxygen, so that the desulfurizer can perform desulfurization in a wide temperature range of 120-400 DEG C, and the problem of poor temperature adaptability of the dicyandiamide slag desulfurizer is solved.

Description

Technical Field

[0001] The present invention relates to the field of desulfurization agents, and specifically to a composite desulfurization agent based on dicyandiamide residue and a preparation method thereof. Background Art

[0002] Dicyandiamide residue is a solid waste generated during the chemical production process of dicyandiamide, and its main components include amino compounds, calcium carbonate, calcium hydroxide, and other minerals. Dicyandiamide is an important chemical raw material, widely used in the preparation of fertilizers, pesticides, and other chemical products.

[0003] As a kind of waste, dicyandiamide residue is usually regarded as a by-product in industrial production, and the treatment cost is relatively high. However, due to its rich calcium-based compounds, especially calcium carbonate and calcium hydroxide, these components can effectively react with sulfur dioxide in flue gas to form calcium sulfate or calcium sulfite. Applying dicyandiamide residue to desulfurization agents can not only realize the reuse of resources, reduce the production cost of desulfurization agents, but also solve part of the problem of industrial waste treatment.

[0004] Although traditional calcium-based desulfurization agents have been widely used in flue gas desulfurization, the existing technology still faces some challenges. A major problem is that the temperature adaptability of traditional desulfurization agents is poor, and they can usually only play an efficient desulfurization role within a specific temperature range. Existing calcium-based desulfurization agents, such as calcium hydroxide and calcium oxide, can usually only work effectively under medium-high temperature or specific temperature conditions, while the desulfurization effect is poor under low temperature or high temperature conditions. Due to poor temperature adaptability, these traditional desulfurization agents are difficult to meet the desulfurization requirements within a wide temperature range in actual industrial applications, restricting their wide application. Summary of the Invention

[0005] Aiming at the deficiencies of the existing technology, the present invention provides a composite desulfurization agent based on dicyandiamide residue and a preparation method thereof, which solves the problems that the existing calcium-based desulfurization agents have poor temperature adaptability, cannot desulfurize efficiently within a wide temperature range, and restrict their application under different industrial conditions.

[0006] To achieve the above objectives, the present invention is realized through the following technical solutions: The composite desulfurization agent based on dicyandiamide residue includes the following components in parts by mass: Dicyandiamide residue: 50 - 65 parts; Calcium oxide: 15 - 25 parts; Calcium hydroxide: 10 - 15 parts; Bentonite: 3 - 8 parts; Iron oxide: 1 - 3 parts; Ammonium chloride: 1 - 2 parts.

[0007] Among them, dicyandiamide residue is used as the main raw material, and its composition contains rich calcium-based compounds, especially calcium carbonate (CaCO3) and calcium hydroxide (Ca(OH)2). These compounds can react with sulfur dioxide (SO2) in flue gas to form calcium sulfate (CaSO4) or calcium sulfite (CaSO2), thus achieving desulfurization. Especially under high-temperature conditions, the calcium-based compounds in dicyandiamide residue are converted into calcium oxide (CaO) through pyrolysis or chemical reactions, which further enhances the high-temperature desulfurization ability of the desulfurizer. In the present invention, by appropriately adjusting the proportion of dicyandiamide residue, sufficient supply of calcium-based compounds is ensured, which not only meets the requirements of the desulfurization reaction but also can effectively reduce the production cost of the desulfurizer, ensuring the advantages of the raw materials; Calcium oxide (CaO) and calcium hydroxide (Ca(OH)2) are used as the main desulfurization components for high-temperature and medium-low temperature desulfurization respectively. Calcium oxide is mainly used to treat SO2 in high-temperature coal-fired flue gas because it has good desulfurization reactivity at high temperatures and can react with SO2 to form calcium sulfate (CaSO4). Calcium hydroxide has stronger low-temperature reaction ability and is suitable for desulfurization in low-temperature processes such as iron and steel sintering. This coverage of temperature ranges enables the desulfurizer of the present invention to adapt to the desulfurization requirements under different working conditions, greatly improving the desulfurization effect and application scope; Iron oxide (Fe2O3) can be used as a catalyst. Through the redox action of its iron ions, Fe2O3 can accelerate the reaction of calcium oxide (CaO) with SO2 to form calcium sulfate (CaSO4), effectively improving the reaction rate of the desulfurizer. This innovation enables the desulfurizer to have stronger desulfurization ability at high temperatures, complete the reaction in a shorter time, and reduce the energy consumption during the desulfurization process; Ammonium chloride (NH4Cl) decomposes into ammonia (NH3) and hydrogen chloride (HCl) at high temperatures. NH3 reacts with SO2 to form ammonium sulfite ((NH4)2SO3), which then reacts with calcium hydroxide (Ca(OH)2) to form calcium sulfate (CaSO4). Through this mechanism, ammonium chloride can significantly improve the desulfurization efficiency of calcium hydroxide and enhance the utilization rate of calcium-based compounds during the reaction process, further enhancing the performance of the desulfurizer Preferably, the particle fineness of the calcium oxide is 50 - 75μm, and the purity ≥ 90%, and the particle fineness of the calcium hydroxide is 20 - 50μm, and the purity ≥ 92%.

[0008] Preferably, the particle fineness of the bentonite is 35 - 75μm, the iron oxide is iron(III) oxide, and the particle fineness is 50 - 100nm.

[0009] Among them, the desulfurization reaction principle of calcium carbonate (CaCO3) is as follows: CaCO3 + SO2 + ½O2 → CaSO4 + CO2 The desulfurization reaction principle of calcium hydroxide (Ca(OH)2) is as follows: Ca(OH)2 + SO2 → CaSO3 + H2O CaSO3 + ½O2 → CaSO4 The desulfurization reaction principle of calcium oxide (CaO) is as follows: CaO + SO2 → CaSO3 CaSO3 + ½O2 → CaSO4 Preferably, the components of the dicyandiamide residue include: calcium carbonate: 20 - 40%, calcium hydroxide: 10 - 20%.

[0010] A preparation method of a composite desulfurizer based on dicyandiamide residue includes the following steps: Pretreat the dicyandiamide residue; Premixing: Mix calcium oxide, calcium hydroxide, bentonite, and iron oxide; Medium mixing: Mix ammonium chloride and absolute ethanol evenly; Post - mixing: Mix the products obtained from premixing and medium mixing evenly; Drying: Dry the product obtained from post - mixing to obtain the composite desulfurizer.

[0011] Preferably, the pretreatment includes: Drying: Dry the dicyandiamide residue at 100 - 110°C until the water content ≤ 5%; Crushing: Crush and sieve the dried dicyandiamide residue so that the final particle fineness of the dicyandiamide residue is 100 - 150 μm.

[0012] Preferably, the premixing is carried out at a rotation speed of 200 - 400 rpm for 10 - 20 min.

[0013] Preferably, the medium mixing is carried out at a rotation speed of 100 - 200 rpm for 3 - 5 min, and the mass fraction of ethanol in the absolute ethanol is ≥ 95%.

[0014] Preferably, in the post - mixing, it is mixed at a rotation speed of 80 - 120 rpm for 2 - 3 min.

[0015] Preferably, in the drying, it is carried out at a temperature of 100 - 110°C so that the water content of the obtained composite desulfurizer is ≤ 3%.

[0016] The present invention provides a composite desulfurizer based on dicyandiamide residue and its preparation method. It has the following beneficial effects: 1. In the present invention, by adding calcium oxide and calcium hydroxide, due to the extremely strong alkalinity of calcium oxide, it can rapidly react with SO2 to form calcium sulfate at a high temperature > 300°C. Calcium hydroxide reacts with SO2 in the low-temperature region (80 - 200°C). Its special layered crystal structure provides a larger specific surface area, and through the surface hydroxyl groups, it undergoes a gas-solid reaction with SO2 to form calcium sulfite intermediate, which is then oxidized by oxygen in the flue gas to stable CaSO4. This enables the desulfurization agent to carry out desulfurization within a wide temperature range of 120 - 400°C, solving the problem of poor temperature adaptability of the dicyandiamide residue desulfurization agent.

[0017] 2. In the present invention, by adding iron oxide, the desulfurization reaction process can be significantly accelerated. The variable-valence iron ions on the surface of iron oxide can construct an efficient electron transfer channel, promoting the rapid conversion of SO2 to SO3. Subsequently, SO3 rapidly reacts with the calcium-based compound to form stable calcium sulfate, thereby significantly accelerating the entire desulfurization reaction process. This catalytic effect not only increases the reaction rate but also enhances the utilization efficiency of the desulfurization agent.

[0018] 3. In the present invention, by adding ammonium chloride, the desulfurization reaction efficiency can be significantly improved. Ammonia generated during the thermal decomposition of ammonium chloride can rapidly react with sulfur dioxide to form ammonium sulfite, and then ammonium sulfite undergoes a double decomposition reaction with the calcium-based compound to form calcium sulfate. This reaction path is more efficient than the traditional direct gas-solid reaction. At the same time, the decomposed hydrogen chloride can effectively remove the passivation layer on the surface of the calcium-based compound, continuously exposing new active sites, thereby significantly accelerating the entire desulfurization reaction process and greatly extending the service life of the desulfurization agent. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a schematic diagram of the method flow of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0020] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the specification of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of them. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0021] To better understand the present invention, the above content will be described in detail below with specific embodiments.

[0022] Please refer to the attached Figure 1 : Example 1: Components: Dicyandiamide residue (calcium carbonate: 30%, calcium hydroxide: 15%): 60 parts; calcium oxide (particle fineness 65μm, purity 95%): 20 parts; calcium hydroxide (particle fineness 40μm, purity 94%): 13 parts; bentonite (particle fineness 60μm): 6 parts; iron oxide (ferric oxide, particle fineness 70nm): 2 parts; ammonium chloride: 1.5 parts.

[0023] Preparation steps: Pretreatment: The dicyandiamide residue is dried at 105°C until the moisture content is 4%, and then it is pulverized using a ball mill. After sieving, the particle fineness of the dicyandiamide residue is maintained at 120μm.

[0024] Premixing: Calcium oxide, calcium hydroxide, bentonite, and iron oxide are stirred in a drum mixer at a speed of 300 rpm for 15 min; Intermediate mixing: Ammonium chloride and absolute ethanol (mass fraction 97%) are stirred in a three-axis mixer at a speed of 140 rpm for 4 min; Final mixing: The product obtained from intermediate mixing is added to the product obtained from premixing, and stirred at a speed of 110 rpm for 2.4 min; Drying: The product obtained from final mixing is dried in a drying oven at 105°C until the water content is 2%, and finally a composite desulfurizer is obtained.

[0025] Example 2: Components: Dicyandiamide residue (calcium carbonate: 20%, calcium hydroxide: 10%): 50 parts; calcium oxide (particle fineness 50μm, purity 90%): 15 parts; calcium hydroxide (particle fineness 20μm, purity 92%): 10 parts; bentonite (particle fineness 35μm): 3 parts; iron oxide (ferric oxide, particle fineness 50nm): 1 part; ammonium chloride: 1 part.

[0026] Preparation steps: Pretreatment: The dicyandiamide residue is dried at 100°C until the moisture content is 5%, and then it is pulverized using a ball mill. After sieving, the particle fineness of the dicyandiamide residue is maintained at 100μm.

[0027] Premixing: Calcium oxide, calcium hydroxide, bentonite, and iron oxide are stirred in a drum mixer at a speed of 200 rpm for 10 min; Intermediate mixing: Ammonium chloride and absolute ethanol (mass fraction 95%) are stirred in a three-axis mixer at a speed of 100 rpm for 3 min; Final mixing: The product obtained from intermediate mixing is added to the product obtained from premixing, and stirred at a speed of 80 rpm for 2 min; Drying: The product obtained from final mixing is dried in a drying oven at 100°C until the water content is 3%, and finally a composite desulfurizer is obtained.

[0028] Example 3: Components: Dicyandiamide residue (calcium carbonate: 40%, calcium hydroxide: 20%): 65 parts; calcium oxide (particle fineness 75μm, purity 92%): 25 parts; calcium hydroxide (particle fineness 50μm, purity 92.5%): 15 parts; bentonite (particle fineness 75μm): 8 parts; iron oxide (ferric oxide, particle fineness 100nm): 3 parts; ammonium chloride: 2 parts.

[0029] Preparation steps: Pretreatment: The dicyandiamide residue is dried at 110°C until the moisture content is 5%, and then it is pulverized using a ball mill. After sieving, the particle fineness of the dicyandiamide residue is maintained at 150μm.

[0030] Premixing: Calcium oxide, calcium hydroxide, bentonite, and iron oxide are stirred in a drum mixer at a rotation speed of 400 rpm for 20 min; Intermediate mixing: Ammonium chloride and anhydrous ethanol (mass fraction 95%) are stirred in a three-axis mixer at a rotation speed of 200 rpm for 5 min; Final mixing: The product obtained from intermediate mixing is added to the product obtained from premixing, and stirred at a rotation speed of 120 rpm for 3 min; Drying: The product obtained from final mixing is dried in an oven at 110°C until the water content is 3%, and finally a composite desulfurizer is obtained.

[0031] Comparative example 1: Based on Example 1, without calcium oxide, and the rest are the same.

[0032] Comparative example 2: Based on Example 2, 12 parts of calcium oxide (particle fineness 65μm, purity 95%), and the rest are the same.

[0033] Comparative example 3: Based on Example 3, 27 parts of calcium oxide (particle fineness 65μm, purity 95%), and the rest are the same.

[0034] Comparative example 4: Based on Example 1, without calcium hydroxide, and the rest are the same.

[0035] Comparative example 5: Based on Example 2, 8 parts of calcium hydroxide (particle fineness 40μm, purity 94%), and the rest are the same.

[0036] Comparative example 6: Based on Example 3, 17 parts of calcium hydroxide (particle fineness 40μm, purity 94%), and the rest are the same.

[0037] Comparative example 7: Based on Example 1, without calcium oxide and calcium hydroxide, and the rest are the same.

[0038] Comparative Example 8: Based on Example 1, without iron oxide (ferric oxide), and the rest are the same.

[0039] Comparative Example 9: Based on Example 2, 0.5 part of iron oxide (ferric oxide, particle fineness 70 nm), and the rest are the same.

[0040] Comparative Example 10: Based on Example 3, 5 parts of iron oxide (ferric oxide, particle fineness 70 nm), and the rest are the same.

[0041] Comparative Example 11: Based on Example 1, without ammonium chloride, and without the intermediate mixing and post-mixing steps. Direct drying is carried out after the primary mixing, and the rest are the same.

[0042] Comparative Example 12: Based on Example 2, 0.7 part of ammonium chloride, and the rest are the same.

[0043] Comparative Example 13: Based on Example 3, 3 parts of ammonium chloride, and the rest are the same.

[0044] Comparative Example 14: Based on Example 1, without iron oxide and ammonium chloride, and the rest are the same.

[0045] Experiment 1: Experiment purpose: To verify the improvement effect of adding calcium oxide and calcium hydroxide to dicyandiamide slag on the desulfurization temperature range and desulfurization effect, and to clarify the synergistic mechanism of the two components.

[0046] Experimental samples Select Examples 1 - 3 (containing calcium oxide and calcium hydroxide) and Comparative Examples 1 - 7 (variable control groups), a total of 10 groups of samples.

[0047] Experimental steps 1. Desulfurization efficiency test Equipment: Fixed-bed reactor (inner diameter 50 mm, quartz material) Conditions: Simulated flue gas (SO2 concentration 2000 ppm, O2 5%, balanced with N2), flow rate 2 L / min, temperature gradient test (80 °C, 150 °C, 250 °C, 350 °C) Method: Each group of samples is filled with 50 g, and the SO2 concentration at the outlet is detected after reacting for 30 min (using an ultraviolet fluorescence SO2 analyzer, model Model-43i).

[0048] 2. Calcium utilization rate determination Equipment: X-ray diffractometer (XRD, Bruker-D8-Advance) Method: Quantitative analysis of CaSO4 and CaSO3 in the residue after reaction, and calculation of calcium conversion rate.

[0049] 3. By-product analysis Equipment: Ion chromatography (ICS-5000+) Method: Detect the content of (NH4)2SO4 in the residue.

[0050] The test results are shown in Table 1: Table 1: Experimental summary As shown in Table 1, the experimental data clearly reveal the core role of calcium oxide (CaO) and calcium hydroxide (Ca(OH)2) in the composite desulfurizer. In Examples 1-3, through gradient ratio (CaO: 15-25 parts, Ca(OH)2: 10-15 parts), the comprehensive improvement of desulfurization efficiency in a wide temperature range (80-350 °C) was achieved, and its performance comprehensively outperformed the control group. Taking Example 3 as an example: High-temperature zone (350 °C): The desulfurization rate is 93.1%, 8.9% higher than that of Control Example 3 (84.2%); Low-temperature zone (80 °C): The desulfurization rate is 75.8%, 26.0% higher than that of Control Example 4 (49.8%); Calcium utilization rate: 87.3%, 48.6% higher than that of Control Example 7 (58.9%).

[0051] The dominant role of calcium oxide at high temperature In the range of 250-350 °C, calcium oxide dominates the desulfurization process through direct gas-solid reaction:

[0052] For Control Example 1 (without CaO), the desulfurization rate at 350 °C is only 76.5%, while that of Example 1 (containing 20 parts of CaO) reaches 91.3%, with a gap of 14.8%. The strong alkalinity of CaO enables it to rapidly consume SO2 at high temperature, but when used alone (such as in Control Example 3), the low-temperature efficiency drops sharply, revealing the limitation of temperature adaptability.

[0053] The structural advantage of calcium hydroxide at low temperature In the range of 80-150 °C, the layered nanostructure of calcium hydroxide adsorbs SO2 through surface hydroxyl groups:

[0054] For Comparative Example 4 (without Ca(OH)2), the efficiency was only 49.8% at 80 °C, while that of Example 1 (containing 13 parts of Ca(OH)2) reached 72.5%, with a gap of 22.7%. However, when relying solely on Ca(OH)2 (such as in Comparative Example 6), the high-temperature efficiency was less than 84.2%, indicating limited high-temperature activity.

[0055] Therefore, by adding calcium oxide and calcium hydroxide to dicyandiamide slag, a high-efficiency desulfurization system with a wide temperature range was successfully constructed. Experimental data fully demonstrate that calcium oxide exhibits excellent desulfurization performance in the high-temperature region (250 - 350 °C), and its strong basicity can rapidly capture SO2; while calcium hydroxide plays a key role in the low-temperature region (80 - 150 °C), and its unique layered nanostructure provides abundant active sites. The synergistic ratio of the two not only compensates for the deficiencies of single components in temperature adaptability but also comprehensively improves the desulfurization efficiency across the entire temperature range (80 - 350 °C). This design of composite desulfurizer based on dicyandiamide slag not only solves the problem of narrow temperature window of traditional desulfurizers but also significantly improves the utilization rate of calcium-based raw materials, providing an efficient and economical solution for industrial flue gas treatment.

[0056] Experiment 2: Experimental purpose: To verify the improvement effect of adding iron oxide and ammonium chloride to dicyandiamide slag on desulfurization efficiency.

[0057] Experimental samples Select Examples 1 - 3 (containing iron oxide and ammonium chloride) and Comparative Examples 8 - 14 (variable control groups), a total of 10 groups of samples.

[0058] Experimental steps 1. Desulfurization efficiency test Equipment: Fixed-bed reactor (inner diameter 50 mm, made of quartz) Conditions: Simulated flue gas (SO2 concentration 2000 ppm, O2 5%, balanced with N2), flow rate 2 L / min, temperature gradient test (80 °C, 150 °C, 250 °C, 350 °C) Method: Each group of samples was loaded with 50 g, and the SO2 concentration at the outlet was detected after 30 minutes of reaction (using an ultraviolet fluorescence SO2 analyzer, model Model - 43i).

[0059] 2. Calcium utilization rate determination Equipment: X-ray diffractometer (XRD, Bruker - D8 - Advance) Method: Quantitative analysis of CaSO4 and CaSO3 in the residue after reaction to calculate the calcium conversion rate.

[0060] 3. By-product analysis Equipment: Ion chromatography (ICS - 5000+) Method: Detect the content of (NH4)2SO4 in the residue.

[0061] The test results are shown in Table 2: Table 2: Experiment summary From the experimental results, Examples 1 - 3 (containing iron oxide and ammonium chloride) showed significantly higher desulfurization efficiency and calcium utilization rate compared to Comparative Examples 8 - 14 (without iron oxide and ammonium chloride), especially prominent under low - temperature conditions of 80°C and 150°C.

[0062] Desulfurization efficiency improvement: In the temperature range of 80°C to 350°C, the desulfurization efficiency of Examples 1 - 3 was generally higher than that of the control group. For example, the desulfurization rate of Example 1 at 80°C was 75.2%, while that of Comparative Example 8 was only 68.4%. At higher temperatures, the desulfurization efficiency of Example 1 also remained at a high level. This indicates that the addition of iron oxide and ammonium chloride played a positive role in improving the desulfurization efficiency.

[0063] Calcium utilization rate: The calcium utilization rate of Examples 1 - 3 was significantly higher than that of the control group. In the range of 80°C to 350°C, the calcium utilization rate of Examples 1 - 3 mostly exceeded 85%, while that of Comparative Examples 8 - 14 was generally lower than this level, especially obvious in the low - temperature group. The improvement of calcium utilization rate means that more calcium elements participated in the desulfurization reaction, forming more calcium sulfate or calcium sulfite.

[0064] Content of by - product ((NH4)2SO4): In the by - product analysis, the content of (NH4)2SO4 in Examples 1 - 3 was generally high, which was related to the addition of ammonium chloride. Ammonium chloride can react with SO2 during the desulfurization process to form ammonium sulfate ((NH4)2SO4), which is an important by - product. This indicates that ammonium chloride not only helps the desulfurization process but also plays a promoting role in the formation of by - products.

[0065] Principle analysis: Catalytic effect of iron oxide (Fe2O3) on the desulfurization reaction: As a catalyst, iron oxide can significantly increase the reaction rate of calcium oxide with SO2. Iron oxide promotes the oxidation process of SO2 by providing more reaction sites, thus accelerating the desulfurization reaction. In Examples 1 - 3, through the catalytic effect, iron oxide improved the reaction efficiency of the desulfurizer, enabling more SO2 to be converted into calcium sulfate or calcium sulfite under the same reaction conditions.

[0066] Promotion of Ammonium Chloride (NH4Cl) on the Reaction between Calcium Hydroxide and SO2: As an auxiliary component, ammonium chloride can promote the reaction between calcium hydroxide (Ca(OH)2) and SO2 under certain conditions to produce calcium sulfate or calcium sulfite. Ammonium chloride accelerates the reaction rate by reducing the activation energy of the reaction between calcium hydroxide and SO2, especially more significantly at lower temperatures. In addition, ammonium chloride reacts with SO2 to produce ammonium sulfate ((NH4)2SO4) as a by-product, further improving the utilization rate of ammonium chloride and the desulfurization effect.

[0067] Effect of Temperature on Reaction Efficiency: At lower temperatures (such as 80 °C and 150 °C), the catalytic effects of iron oxide and ammonium chloride are more obvious. At low temperatures, the reactions of calcium oxide and calcium hydroxide are slower, while iron oxide and ammonium chloride can effectively promote the reactions, improving the desulfurization efficiency at low temperatures.

[0068] Generally speaking, by adding iron oxide and ammonium chloride to dicyandiamide residue, the present invention can significantly improve the desulfurization effect, especially under low-temperature conditions. Iron oxide provides a catalytic effect, enhancing the reaction rate between calcium oxide and SO2, while ammonium chloride accelerates the reaction between calcium hydroxide and SO2 and produces valuable by-products. Such a formulation design effectively improves the overall performance of the desulfurizer and can provide higher desulfurization efficiency in practical industrial applications.

[0069] Although the embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A composite desulfurizing agent based on dicyandiamide slag, characterized in that: Includes the following mass components: Dicyandiamide residue: 50-65 parts; Calcium oxide: 15-25 parts; Calcium hydroxide: 10-15 parts; Bentonite: 3-8 parts; Iron oxide: 1-3 parts; Ammonium chloride: 1 to 2 parts.

2. The composite desulfurizing agent based on dicyandiamide slag according to claim 1, characterized in that: The particle size of the calcium oxide is 50-75 μm, and the purity is ≥90%. The particle size of the calcium hydroxide is 20-50 μm, and the purity is ≥92%.

3. The composite desulfurizing agent based on dicyandiamide slag according to claim 1, characterized in that: The bentonite has a particle size of 35 to 75 μm, and the iron oxide is ferric oxide, and has a particle size of 50 to 100 nm.

4. The composite desulfurizing agent based on dicyandiamide slag according to claim 1, characterized in that: The components of the dicyandiamide slag include: calcium carbonate: 20-40%, calcium hydroxide: 10-20%.

5. A method for preparing a composite desulfurizer based on dicyandiamide slag, based on the composite desulfurizer based on dicyandiamide slag according to any one of claims 1 to 5, characterized in that: The following steps are involved: Pretreatment of dicyandiamide slag; Premixing: Mix calcium oxide, calcium hydroxide, bentonite and iron oxide; Medium mixing: Mix ammonium chloride and anhydrous ethanol; Post-mixing: Mix the pre-mixed and intermediate-mixed products evenly; Drying: Dry the post-mixed product to obtain a composite desulfurizer.

6. The method for preparing a composite desulfurizing agent based on dicyandiamide slag according to claim 5, characterized in that: The pre-processing comprises: Drying: Dry the dicyandiamide residue at 100-110°C until the moisture content is ≤5%; Crushing: The dried dicyandiamide residue is crushed and sieved to make the final dicyandiamide residue particle size of 100 to 150 μm.

7. The method for preparing a composite desulfurizing agent based on dicyandiamide slag according to claim 5, characterized in that: The premixing is carried out at a rotation speed of 200 to 400 rpm for 10 to 20 minutes.

8. The method for preparing a composite desulfurizing agent based on dicyandiamide slag according to claim 5, characterized in that: The intermediate mixing is carried out at a rotation speed of 100 to 200 rpm for 3 to 5 minutes, and the mass fraction of ethanol in the anhydrous ethanol is ≥ 95%.

9. The method for preparing a composite desulfurizing agent based on dicyandiamide slag according to claim 8, characterized in that: In the post-mixing, the mixture is mixed at a rotation speed of 80 to 120 rpm for 2 to 3 minutes.

10. The method for preparing a composite desulfurizing agent based on dicyandiamide slag according to claim 5, characterized in that: The drying is carried out at a temperature of 100-110° C. so that the water content of the obtained composite desulfurizer is ≤3%.

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