Preparation method and application of modified calcium hydroxide

Abstract

The invention relates to the field of industrial dechlorination, and particularly discloses a preparation method and application of modified calcium hydroxide. According to the preparation method, mixed water, ethyl alcohol and triethanolamine are used as a digestion solution, the digestion solution is mixed with calcium oxide particles for a digestion reaction, modified calcium hydroxide is obtained, the added ethyl alcohol and triethanolamine can effectively improve the dispersion degree of the calcium oxide particles, the severe degree of the digestion reaction is relieved, and the calcium oxide particles can be effectively dispersed. The specific surface area of the obtained calcium hydroxide is increased; the surface property is improved. The modified calcium hydroxide prepared by the method has a relatively high specific surface area and a rich pore structure, is beneficial to contact with hydrogen chloride in flue gas, and improves the dechlorination performance. When the modified calcium hydroxide is used for treating flue gas, most hydrogen chloride can be removed within a short contact time, good dechlorination efficiency is shown, and actual use is facilitated.

Description

Technical Field

[0001] The invention relates to the field of industrial dechlorination, and in particular to a preparation method and application of modified calcium hydroxide. Background Art

[0002] Chlorine is one of the main elements that cause pollution after the combustion of coal or biomass. After combustion, chlorine mainly exists in the form of chloride in flue gas and fly ash. Chlorine in flue gas accounts for more than 80% of the total chlorine content, mainly hydrogen chloride (HCl). Its harm is mainly manifested in the corrosion and contamination and blockage of boiler equipment, auxiliary equipment and pipelines during and after the combustion process. At present, the wet desulfurization system used in thermal power plants can achieve the simultaneous removal of chlorine in flue gas, but the removed chlorine is mainly transferred to the desulfurization slurry and desulfurization gypsum and enriched in the desulfurization system. Excessive chloride ion concentration is easy to cause equipment corrosion and desulfurizer poisoning problems, and it is often necessary to continuously discharge high-concentration chlorine-containing wastewater, which requires thermal power plants to add wastewater treatment equipment, increasing production costs and treatment difficulties.

[0003] According to the chlorine balance calculation of the desulfurization system of a thermal power plant using coal or biomass as fuel, the chloride ions in the wastewater mainly come from the chlorine in the combustion flue gas. Therefore, removing the chlorine in the flue gas is the most effective way to reduce the chloride ion content in the wastewater of a thermal power plant. At present, the direct removal of hydrogen chloride in the flue gas mainly relies on the direct contact of the dechlorinating agent with the flue gas, reacting with the hydrogen chloride in the flue gas to generate harmless products, and realizing flue gas dechlorination. However, the existing dechlorinating agent mainly uses hydroxides or carbonates of alkali metals or alkaline earth metals as the main components. The performance of a single-component dechlorinating agent is poor, and multiple components need to cooperate with each other, and it often needs to be used in an integral or molded form. The flue gas passes through a long time, which affects the dechlorination efficiency. Summary of the invention

[0004] The purpose of the present invention is to overcome the problems of poor flue gas dechlorination performance and complex process in the prior art, and to provide a preparation method and application of modified calcium hydroxide. The method uses an improved digestion solution, ethanol and triethanolamine as additives to the digestion solution, and digests calcium oxide to obtain modified calcium hydroxide, which overcomes the defects of large and uneven calcium hydroxide particles and small specific surface area obtained when pure water is used as the digestion solution, and the reaction process is more uniform and stable. The modified calcium hydroxide prepared by the method has a large specific surface area and rich pore structure, which is conducive to rapid contact with hydrogen chloride in the flue gas and improves the dechlorination performance. The modified calcium hydroxide is directly contacted with the flue gas, which can achieve a good dechlorination effect in a very short contact time and show a high dechlorination efficiency.

[0005] In order to achieve the above object, the present invention provides a method for preparing modified calcium hydroxide, comprising the following steps:

[0006] (1) providing calcium oxide particles with a particle size of 200-300 mesh and a purity of 80-95wt%;

[0007] (2) mixing water, ethanol and triethanolamine to obtain a digestion solution;

[0008] (3) Mixing the calcium oxide particles and the digestion solution to react.

[0009] Preferably, in step (2), in the digestion solution, the volume ratio of the ethanol to the water is 0.2-0.5:1.

[0010] Preferably, in step (2), in the digestion solution, the mass fraction of triethanolamine is 0.1-1.5 wt %.

[0011] Preferably, in step (3), the molar ratio of the calcium oxide particles in terms of calcium to the digestion solution in terms of water is 1:1-1.25.

[0012] Preferably, in step (3), the reaction conditions include: time of 4-11 min, and termination temperature of 190-220°C.

[0013] The second aspect of the present invention provides a modified calcium hydroxide prepared by the above method.

[0014] The third aspect of the present invention provides a use of the aforementioned modified calcium hydroxide as a dechlorinating agent.

[0015] A fourth aspect of the present invention provides a flue gas treatment method, the method comprising: contacting the flue gas with the aforementioned modified calcium hydroxide.

[0016] Preferably, the contact conditions include: temperature of 100-350°C, flue gas flow rate of 2800-4000Nm 3 / h, time is 2-10s.

[0017] Preferably, the molar ratio of the modified calcium hydroxide to the hydrogen chloride in the flue gas is 3-7:1, calculated as calcium.

[0018] Preferably, the concentration of hydrogen chloride in the flue gas is 40-80 mg / m 3 .

[0019] According to the preparation method of modified calcium hydroxide described in the present invention, water with added ethanol and triethanolamine is used as the digestion solution, so that modified calcium hydroxide with small and uniform particle size, large specific surface area and rich pore structure can be obtained, which is conducive to obtaining better flue gas dechlorination performance and making the reaction process more uniform and stable.

[0020] The modified calcium hydroxide prepared by the preparation method of the present invention uses an improved digestion solution, ethanol and triethanolamine as additives of the digestion solution, and calcium oxide is digested to obtain the modified calcium hydroxide, thereby overcoming the defects of large and uneven calcium hydroxide particles and small specific surface area obtained when pure water is used as the digestion solution.

[0021] According to the flue gas treatment method of the present invention, the modified calcium hydroxide is directly contacted with the flue gas, which can achieve a better dechlorination effect in a very short contact time, show a higher dechlorination efficiency, and is conducive to industrial application. DETAILED DESCRIPTION

[0022] The specific embodiments of the present invention are described in detail below. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0023] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0024] The present invention provides a method for preparing modified calcium hydroxide, comprising the following steps:

[0025] (1) providing calcium oxide particles with a particle size of 200-300 mesh and a purity of 80-95wt%;

[0026] (2) mixing water, ethanol and triethanolamine to obtain a digestion solution;

[0027] (3) Mixing the calcium oxide particles and the digestion solution to react.

[0028] In the preparation method of the present invention, preferably, in step (2), in the digestion solution, the volume ratio of the ethanol to the water is 0.2-0.5:1, more preferably 0.25-0.45:1, and most preferably 0.3-0.4:1. In the present invention, the above-mentioned amount of ethanol added can reduce the overall surface tension of the digestion solution, increase the affinity and permeability of water molecules to calcium oxide, slow down the rate of the digestion reaction, avoid agglomeration of modified calcium hydroxide, generate more uniform and smaller particles, which is conducive to obtaining modified calcium hydroxide with a high specific surface area and improving its dechlorination performance.

[0029] In the preparation method of the present invention, preferably, in step (2), in the digestion solution, the mass fraction of triethanolamine is 0.1-1.5wt%, more preferably 0.5-1.3wt%, and most preferably 0.8-1.2wt%. In the present invention, the above-mentioned amount of triethanolamine added can effectively disperse the calcium oxide particles, so that the calcium oxide is fully in contact with water molecules, which is more conducive to obtaining modified calcium hydroxide with small particles and large specific surface area.

[0030] In the preparation method of the present invention, preferably, in step (3), the molar ratio of the calcium oxide particles in terms of calcium to the digestion solution in terms of water is 1:1-1.25, more preferably 1:1-1.20, and most preferably 1:1-1.10. In the present invention, by adopting the above molar ratio, a slightly excessive amount of water can avoid the loss caused by evaporation due to the exothermic reaction, and the calcium oxide can be fully digested into modified calcium hydroxide.

[0031] In the preparation method of the present invention, preferably, in step (3), the reaction conditions include: time of 4-11 minutes, and end temperature of 190-220°C. More preferably, the reaction conditions include: time of 5-9 minutes, and end temperature of 200-220°C. Most preferably, the reaction conditions include: time of 5-7 minutes, and end temperature of 205-215°C. In the present invention, the end temperature is the temperature at the center of the digestion reaction material; the above reaction conditions enable the calcium oxide particles to fully contact with the digestion solution and react to generate modified calcium hydroxide.

[0032] The preparation method of the modified calcium hydroxide disclosed by the present invention uses water added with ethanol and triethanolamine as a digestion solution. The ethanol is decomposed during the digestion process, which is beneficial to the formation of certain hydroxyl functional groups on the surface of slaked lime, promotes the chemical reaction of chlorine, slows down the rate of the digestion reaction, and avoids the agglomeration of the modified calcium hydroxide. The added triethanolamine can effectively disperse the calcium oxide particles, so that the calcium oxide is fully in contact with water molecules, and the modified calcium hydroxide with a small and uniform particle size, a large specific surface area and a rich pore structure can be obtained, which is beneficial to obtaining better flue gas dechlorination performance.

[0033] The present invention also provides a modified calcium hydroxide prepared by the above method, wherein the modified calcium hydroxide is obtained by digesting calcium oxide using an improved digestion solution and using ethanol and triethanolamine as additives of the digestion solution, thereby overcoming the defects of large and uneven calcium hydroxide particles and small specific surface area obtained when pure water is used as the digestion solution; the modified calcium hydroxide has a higher specific surface area and better dechlorination performance, and the specific surface area can reach 43.04 m 2 / g, when it is used as a dechlorination agent to remove hydrogen chloride in flue gas, the dechlorination efficiency can reach 81.7% in a shorter contact time.

[0034] The present invention also provides a flue gas treatment method, which comprises: bringing the flue gas into contact with the modified calcium hydroxide.

[0035] In the treatment method of the present invention, preferably, the contact conditions include: temperature of 100-350°C, flue gas flow rate of 2800-4000Nm 3 / h, time is 2-10s. More preferably, the contact conditions include: temperature of 105-330°C, flue gas flow rate of 2800-4000Nm 3 / h, time is 3-9s. Most preferably, the contact conditions include: temperature is 110-320°C, flue gas flow rate is 2800-4000Nm 3 / h, the time is 4-7s. In the present invention, the above contact conditions are adopted to fully remove high concentration of hydrogen chloride in a short time and minimize the interference of other components in the flue gas.

[0036] In the treatment method of the present invention, preferably, the molar ratio of the modified calcium hydroxide to the hydrogen chloride in the flue gas is 3-7:1, more preferably 4-7:1, and most preferably 4-6:1. In the present invention, the above molar ratio can effectively ensure the adsorption efficiency of the modified calcium hydroxide on hydrogen chloride and minimize the concentration of hydrogen chloride in the flue gas after treatment.

[0037] In the treatment method of the present invention, preferably, the concentration of hydrogen chloride in the flue gas is 40-80 mg / m 3 , more preferably 45-75 mg / m 3 , most preferably 50-70 mg / m 3 .

[0038] In a specific embodiment of the present invention, the flue gas treatment method comprises the following steps:

[0039] (1) pre-treating the calcium oxide raw material (such as screening, cyclone separation, etc.) to obtain calcium oxide particles with a particle size of 200-300 mesh and a purity of 80-95wt%;

[0040] (2) mixing water, ethanol and triethanolamine to obtain a digestion solution, wherein the volume ratio of the ethanol to the water is 0.2-0.5:1, and the mass fraction of the triethanolamine is 0.1-1.5wt%;

[0041] (3) mixing the calcium oxide particles with the digestion solution for reaction, and then naturally cooling the obtained product to obtain modified calcium hydroxide, wherein the molar ratio of the calcium oxide particles in terms of calcium to the digestion solution in terms of water is 1:1-1.25, and the reaction conditions include: a reaction time of 4-11 minutes and a termination temperature of 190-220° C.;

[0042] (4) Spraying the modified calcium hydroxide containing 40-80 mg / m 3 Hydrogen chloride, temperature 100-350℃ flue gas, contact 2-10s, where the flue gas flow rate is 2800-4000Nm 3 / h.

[0043] The flue gas treatment method of the present invention directly contacts the modified calcium hydroxide with the flue gas, which can achieve a good dechlorination effect within a very short contact time, exhibits a high dechlorination efficiency, and is conducive to industrial application.

[0044] In the present invention, the flue gas is the flue gas discharged from the boiler used in the coal-fired thermal power plant or the biomass-fired thermal power plant, which mainly contains carbon dioxide, carbon monoxide, nitrogen oxides, water vapor, oxygen, hydrogen chloride, sulfur dioxide, fly ash, etc.

[0045] In the present invention, the dechlorination efficiency is calculated as the percentage of the difference in concentration of hydrogen chloride in the flue gas before and after treatment to the initial concentration of hydrogen chloride under standard conditions.

[0046] The following examples are used to further illustrate the preparation method and application of modified calcium hydroxide of the present invention. The examples are implemented on the premise of the technical solution of the present invention, and detailed implementation methods and specific operation processes are given, but the protection scope of the present invention is not limited to the following examples.

[0047] The experimental methods in the following examples, unless otherwise specified, are all conventional methods in the art. The experimental materials used in the following examples, unless otherwise specified, are all commercially available.

[0048] Example 1

[0049] (1) sieving the calcium oxide raw material to obtain calcium oxide particles with a particle size of 300 mesh and a purity of 90 wt%;

[0050] (2) 630 mL of deionized water, 252 mL of ethanol, and 8.40 g of triethanolamine were mixed to obtain a digestion solution;

[0051] (3) Weighing 2000 g of the calcium oxide particles and 840 g of the digestion solution, mixing and reacting, the reaction time is 5 min 14 s, and the reaction termination temperature is measured to be 211° C., and then the obtained product is naturally cooled to obtain modified calcium hydroxide Ca-1;

[0052] (4) The modified calcium hydroxide Ca-1 was sprayed into a 60 mg / m 3 Hydrogen chloride, flow rate 3800Nm 3 / h, the temperature is 110℃ flue gas, and the contact time is 4s.

[0053] Example 2

[0054] (1) sieving the calcium oxide raw material to obtain calcium oxide particles with a particle size of 300 mesh and a purity of 90 wt%;

[0055] (2) 660 mL of deionized water, 198 mL of ethanol, and 8.27 g of triethanolamine were mixed to obtain a digestion solution;

[0056] (3) Weighing 2000 g of the calcium oxide particles and 827 g of the digestion solution, mixing and reacting, the reaction time is 5 min 43 s, and the reaction termination temperature is measured to be 213° C., and then the obtained product is naturally cooled to obtain modified calcium hydroxide Ca-2;

[0057] (4) The modified calcium hydroxide Ca-2 was sprayed into a 60 mg / m 3 Hydrogen chloride, flow rate 3800Nm 3 / h, the temperature is 110℃ flue gas, and the contact time is 4s.

[0058] Example 3

[0059] (1) sieving the calcium oxide raw material to obtain calcium oxide particles with a particle size of 200 mesh and a purity of 85 wt%;

[0060] (2) 623 mL of deionized water, 249.2 mL of ethanol, and 8.31 g of triethanolamine were mixed to obtain a digestion solution;

[0061] (3) Weighing 2000 g of the calcium oxide particles and 831 g of the digestion solution, mixing them for a reaction time of 5 min 58 s, and measuring the reaction termination temperature to be 209° C., and then naturally cooling the obtained product to obtain modified calcium hydroxide Ca-3;

[0062] (4) The modified calcium hydroxide Ca-3 was sprayed into a 60 mg / m 3 Hydrogen chloride, flow rate is 3590Nm 3 / h, the temperature is 110℃ flue gas, and the contact time is 4s.

[0063] Example 4

[0064] The method according to Example 1 is different in that step (4) is replaced by the following steps:

[0065] (4) The modified calcium hydroxide Ca-1 was sprayed into a 60 mg / m 3 Hydrogen chloride, flow rate 3900Nm 3 / h, the temperature is 250℃ flue gas, and the contact time is 6s.

[0066] Example 5

[0067] The method according to Example 1 is different in that step (4) is replaced by the following steps:

[0068] (4) The modified calcium hydroxide Ca-1 was sprayed into a 60 mg / m 3 Hydrogen chloride, flow rate 3800Nm 3 / h, the temperature is 320℃ flue gas, and the contact time is 4s.

[0069] Example 6

[0070] The method according to Example 2 is different in that step (4) is replaced by the following steps:

[0071] (4) The modified calcium hydroxide Ca-2 was sprayed into a 60 mg / m 3 Hydrogen chloride, flow rate 3000Nm 3 / h, the temperature is 320℃ flue gas, and the contact time is 4s.

[0072] Example 7

[0073] The method according to Example 3 is different in that step (4) is replaced by the following steps:

[0074] (4) The modified calcium hydroxide Ca-3 was sprayed into a 60 mg / m 3 Hydrogen chloride, flow rate 3000Nm 3 / h, the temperature is 320℃ flue gas, and the contact time is 3s.

[0075] Comparative Example 1

[0076] The method described in Example 1 is followed, except that deionized water is used to replace the digestion solution, and the resulting calcium hydroxide is recorded as D1.

[0077] Comparative Example 2

[0078] The method described in Example 1 is different in that triethanolamine is not added to the digestion solution, and the obtained modified calcium hydroxide is recorded as D2.

[0079] Comparative Example 3

[0080] The method described in Example 1 is different in that the calcium oxide particles obtained in step (1) are directly used to replace the modified calcium hydroxide in step (4) without going through steps (2) and (3).

[0081] Test Example 1

[0082] The specific surface area, average pore size and total pore volume of samples Ca-1 to Ca-3 obtained in Examples 1 to 3 and samples D1 and D2 obtained in Comparative Examples 1 to 3 and undigested calcium oxide particles (300 mesh, 90 wt% purity) were tested using a fully automatic specific surface area and pore size analyzer F-Sorb 3400, as shown in Table 1:

[0083] Table 1

[0084] sample <![CDATA[Specific surface area m 2 / g]]> Average pore size nm <![CDATA[Total pore volume cm 3 / g]]> Ca-1 43.04 10.65 0.165 Ca-2 38.41 12.33 0.147 Ca-3 35.76 14.56 0.135 D1 17.21 22.88 0.076 D2 31.85 20.04 0.100 Calcium oxide particles 4.92 34.91 0.042

[0085] As can be seen from Table 1, the modified calcium hydroxide prepared by the method of the present invention generally has a larger specific surface area and total pore volume, and has a larger specific surface area and a richer pore structure than the calcium hydroxide obtained by directly using water as the digestion solution, the modified calcium hydroxide obtained by not adding triethanolamine to the digestion solution, or the undigested calcium oxide particles, indicating that the addition of ethanol and triethanolamine is beneficial to improving the dispersion degree of the modified calcium hydroxide, adjusting the surface properties, helping to obtain a large specific surface area and a rich pore structure, which is beneficial to the contact reaction with hydrogen chloride in the flue gas and improving the dechlorination efficiency.

[0086] Test Example 2

[0087] The laser gas analyzer uLAS-200 of Shengnuo Company was used to test the initial concentration of hydrogen chloride in the flue gas of step (4) of Examples 1-6 and Comparative Examples 1-3, as well as the concentration of hydrogen chloride in the flue gas after treatment in step (4). The dechlorination efficiency of Examples 1-6 and Comparative Examples 1-3 was calculated based on the difference between the two and the percentage ratio of the initial hydrogen chloride concentration, as shown in Table 2:

[0088] Table 2

[0089]

[0090]

[0091] As can be seen from Table 2, the modified calcium hydroxide prepared by the method of the present invention shows better dechlorination efficiency than the calcium hydroxide obtained by directly using water as the digestion solution, the modified calcium hydroxide obtained by not adding triethanolamine to the digestion solution, or the undigested calcium oxide particles; the modified calcium hydroxide can remove most of the hydrogen chloride in the flue gas within a very short contact time (4s) with the flue gas, and shows good dechlorination performance at a lower (110°C in Examples 1-3) or higher (250°C in Example 4 or 320°C in Examples 5-7) temperature, and has a wider range of application; the obtained powder is directly sprayed into the flue gas and collected together with the solid particles such as fly ash in the flue gas, the process is simple and controllable, and the overall efficiency of flue gas treatment is effectively improved.

[0092] Test Example 3

[0093] In order to verify the positive effect of adding triethanolamine in the digestion solution, the present invention also carried out a fixed bed adsorption experiment of the dechlorinating agent. Calcium oxide particles with a purity of 90wt% and a purity of 300 mesh were used. The volume ratio of ethanol to deionized water in the digestion solution used was 0.4:1. Four modified calcium hydroxide samples 1-4 were prepared according to the mass fraction of triethanolamine used in Table 3 (the digestion reaction starting temperature was 25°C, the end temperature was 210°C, and the reaction time was 5min30s). Under the experimental conditions of 320°C simulating flue gas in the laboratory, the adsorption was continued for 1000s. The laser gas analyzer uLAS-200 of Shengnuo Company was used to test the concentration of hydrogen chloride gas in the flue gas before and after dechlorination treatment, and the amount of adsorbed hydrogen chloride and the removal efficiency were calculated. The results are shown in Table 3:

[0094] Table 3

[0095] serial number Triethanolamine dosage wt% Adsorption of HCl mg / g HCl removal efficiency % 1 0 24.37 61 2 0.3 29.11 71 3 0.5 31.57 77 4 1 36.08 90

[0096] It can be seen from Table 3 that with the increase of the amount of triethanolamine in the digestion solution, the amount of HCl adsorbed and the HCl removal efficiency of the modified calcium hydroxide obtained also increase accordingly. The results obtained in the above experiments and the examples confirm each other, further proving that the addition of triethanolamine is beneficial to improving the dechlorination performance of the modified calcium hydroxide.

[0097] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for preparing modified calcium hydroxide, characterized in that, The method comprises the following steps: (1) providing calcium oxide particles with a particle size of 200-300 mesh and a purity of 80-95wt%; (2) mixing water, ethanol and triethanolamine to obtain a digestion solution; (3) Mixing the calcium oxide particles and the digestion solution to react.

2. The method according to claim 1, characterized in that In step (2), in the digestion solution, the volume ratio of the ethanol to the water is 0.2-0.5:

1.

3. The method according to claim 1 or 2, characterized in that In step (2), in the digestion solution, the mass fraction of triethanolamine is 0.1-1.5wt%.

4. The method according to claim 1, characterized in that: In step (3), the molar ratio of the calcium oxide particles in terms of calcium to the digestion solution in terms of water is 1:1-1.

25.

5. The method according to claim 1 or 4, characterized in that: In step (3), the reaction conditions include: time of 4-11 min, and termination temperature of 190-220°C.

6. The modified calcium hydroxide prepared by any one of the methods described in claims 1-5.

7. Use of the modified calcium hydroxide according to claim 6 as a dechlorinating agent.

8. A flue gas treatment method, characterized in that: The method comprises: contacting flue gas with the modified calcium hydroxide described in claim 6.

9. The method according to claim 8, characterized in that The contact conditions include: temperature of 100-350°C, flue gas flow rate of 2800-4000Nm 3 / h, time is 2-10s; Preferably, the molar ratio of the modified calcium hydroxide to the hydrogen chloride in the flue gas is 3-7:1, calculated as calcium.

10. The method according to claim 8, characterized in that The concentration of hydrogen chloride in the flue gas is 40-80 mg / m 3 .

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