Fly ash water washing and incineration flue gas carbonization treatment method

Abstract

The invention relates to the technical field of environmental protection, and particularly discloses a fly ash water washing and incineration flue gas carbonization treatment method, which adopts three-stage countercurrent water washing consisting of first-stage water washing, second-stage water washing and third-stage water washing to wash fly ash, under the condition of mechanical stirring, introducing incineration flue gas into the fly ash slurry for aeration, adding ammonia water, carbonizing the fly ash slurry to form a washing carbonized solution, performing solid-liquid separation treatment on the washing carbonized solution to generate a fly ash mud cake and filtrate, and performing post-treatment on the filtrate. According to the method, in the first-stage washing process, by means of the mode of combining mechanical stirring and aeration stirring, the fly ash washing effect is enhanced, meanwhile, calcium and magnesium ions and heavy metal are removed in the carbonization process, and the removal efficiency is improved; carbon dioxide in incineration flue gas is absorbed in the carbonization process, and negative carbon emission is achieved.

Description

Technical Field

[0001] The present invention relates to the field of environmental protection technology, and in particular to a method for carbonizing fly ash water-washing co-incineration flue gas. Background Art

[0002] Fly ash from the incineration of municipal solid waste has hazardous properties such as high chlorine content, heavy metal content, and dioxin content. Before promoting the resource utilization of fly ash, these three hazardous properties must be effectively removed. Among the many treatment methods, fly ash washing is one of the most commonly used fly ash resource utilization methods. During the fly ash washing treatment, the soluble chlorine in the fly ash will be washed out, and at the same time, calcium, magnesium ions and soluble heavy metals will also enter the washing liquid. After the washing liquid is subsequently filtered, the resulting fly ash washing water needs to be specifically treated to remove calcium, magnesium and heavy metals. Only when the washing water treatment meets the relevant standards can the salt extraction process be further carried out, ultimately achieving resource recovery and reuse.

[0003] Under current technologies and equipment, fly ash wash water treatment is costly and cumbersome. For example, the industry generally uses sodium carbonate to remove calcium and magnesium ions. Sodium carbonate ionizes in water to produce carbonate ions, which combine with calcium and magnesium ions in the wash water to form calcium carbonate and magnesium carbonate precipitates, achieving initial removal of the ions. However, the relatively high market price of sodium carbonate significantly increases treatment costs. Furthermore, the precipitated calcium and magnesium carbonates, while valuable as building materials, require further precipitation and collection, returning to the fly ash wash process and ultimately being incorporated into the washed fly ash. In the subsequent heavy metal removal stage, sodium sulfide is commonly used. The sulfur ions in sodium sulfide react chemically with heavy metal ions to form metal sulfide precipitates, thereby removing the heavy metals. However, due to the difficulty in precisely controlling reaction conditions in practice, sodium sulfide is often added in excess, resulting in a large amount of excess sulfur remaining in the wash water. To eliminate this residual sulfur, ferrous chloride must be added for subsequent desulfurization. Ferrous ions in ferrous chloride react with sulfur ions to form ferrous sulfide precipitate. Actual cost accounting shows that water treatment chemicals account for over 40% of the total cost of fly ash washing, which undoubtedly restricts the large-scale promotion and efficient application of fly ash washing technology. Summary of the Invention

[0004] The purpose of the present invention is to provide a fly ash water washing and coordinated incineration flue gas carbonization treatment method. In the first-level water washing process, mechanical stirring and aeration stirring are combined to enhance the fly ash water washing effect, and the carbonization process is carried out at the same time to achieve the removal of calcium, magnesium ions and heavy metals and increase their removal efficiency; the carbonization process is used to absorb carbon dioxide in the incineration flue gas to achieve negative carbon emissions.

[0005] To achieve this object, the present invention adopts the following technical solutions:

[0006] A fly ash water washing and co-incineration flue gas carbonization treatment method is provided, which uses a three-stage countercurrent water washing consisting of a primary water washing, a secondary water washing and a tertiary water washing to wash the fly ash:

[0007] In the primary water washing process, fly ash is mixed with an aqueous solution to form a water-ash slurry. Under mechanical stirring conditions, combustion flue gas is introduced into the fly ash slurry for aeration and ammonia is added to carbonize the fly ash slurry to form a water-washed carbonized liquid.

[0008] The washed carbonized liquid is subjected to solid-liquid separation treatment to produce fly ash cake and filtrate, the fly ash cake is sequentially subjected to secondary water washing and tertiary water washing, and the filtrate produced after the primary water washing is post-treated.

[0009] In the present invention, the fly ash slurry in the primary water washing process is mechanically stirred to make the fly ash fully contact with the aqueous solution for preliminary washing; at the same time, the incineration flue gas is introduced to aerate the fly ash slurry; at the same time, ammonia water is added to promote the CO2 in the incineration flue gas to react with the fly ash slurry to generate carbonate ions, calcium and magnesium ions combine with the carbonate ions to form compounds with low solubility (such as CaCO3, MgCO3), and heavy metals form carbonate precipitates, thereby forming a water-washed carbonized liquid containing calcium and magnesium ions and part of the heavy metal precipitates; the water-washed carbonized liquid is subjected to solid-liquid separation to form a fly ash mud cake and a filtrate, thereby completing the separation of fly ash and water-washed wastewater.

[0010] In the prior art, the three-stage countercurrent water washing process is a conventional technology for fly ash washing. The present invention improves the existing three-stage countercurrent water washing process, and uses a combination of mechanical stirring and aeration stirring to enhance the fly ash washing effect, while improving the removal rate of calcium, magnesium ions and heavy metals during the carbonization process. In the fly ash slurry during the first-stage water washing process, incineration flue gas is introduced for aeration, and the carbonization process is used to absorb carbon dioxide in the incineration flue gas to achieve negative carbon emissions. The present invention can be combined to replace multiple conventional water treatment process flows, making the entire treatment process more efficient, significantly reducing the cost of water treatment agents for washing water, and at the same time reducing water treatment investment costs.

[0011] In the present invention, the aqueous solution used in the primary water washing comes from the wastewater generated by the secondary water washing, i.e., the secondary water washing water; the secondary water washing refers to the water washing of the fly ash mud cake after the primary water washing, and the aqueous solution used comes from the wastewater generated by the tertiary water washing, i.e., the tertiary water washing water; the tertiary water washing refers to the water washing of the fly ash mud cake after the secondary water washing, and the aqueous solution used is MVR condensed water and / or fresh water, wherein the post-treatment of the filtrate generated by the primary water washing refers to the sequential wastewater treatment, reagent recovery, and MVR salt separation treatment of the filtrate generated by the primary water washing, and the MVR condensed water generated during the MVR salt separation treatment can be reused for the tertiary water washing, and fresh water can be supplemented when the MVR condensed water is insufficient; the specific water washing process will not be described in detail.

[0012] Among them, the fly ash slurry after the first-stage water washing, the second-stage water washing and the third-stage water washing is subjected to solid-liquid separation using a conventional plate and frame filter press.

[0013] As a further embodiment of the fly ash water-washing and incineration flue gas carbonization treatment method, the volume ratio of the aqueous solution to the incineration flue gas flow rate is 1:2-6, expressed in L:L / min. By controlling the volume ratio of the aqueous solution to the incineration flue gas flow rate, the carbonate ions formed from the carbon dioxide in the incineration flue gas can fully react with the calcium, magnesium ions, and heavy metals in the fly ash slurry.

[0014] As a further solution of the fly ash water washing and co-incineration flue gas carbonization treatment method, the ratio of the volume of the aqueous solution to the flow rate of the incineration flue gas is 1:4, with the unit being L:L / min.

[0015] As a further solution of the fly ash water washing and co-incineration flue gas carbonization treatment method, in the first-stage water washing process, the mass ratio of fly ash to aqueous solution is 2-4 to improve the fly ash water washing effect.

[0016] As a further solution of the fly ash water washing and co-incineration flue gas carbonization treatment method, in the first-stage water washing process, the mass ratio of fly ash to aqueous solution is 2.2-3.

[0017] As a further solution of the fly ash water washing and coordinated incineration flue gas carbonization treatment method, in the first-level water washing process, the incineration flue gas is formed by mixing fresh incineration flue gas and water-washed waste gas after participating in the carbonization reaction.

[0018] Specifically, during the first-level water washing process, the waste gas generated after the aeration of the incineration flue gas is combined with the original fresh incineration flue gas and introduced into the fly ash slurry, so that the carbon dioxide in the incineration flue gas can fully participate in the carbonization reaction; the aeration time is about 15min-30min, and the waste gas after the reaction of carbon reduction is incorporated into the incineration main line flue gas treatment system.

[0019] As a further solution to the fly ash water washing and co-incineration flue gas carbonization treatment method, in the primary water washing process, post-treatment of the filtrate refers to recovering ammonia water after wastewater treatment of the filtrate, and the recovered ammonia water is added to the fly ash slurry again.

[0020] As a further solution of the fly ash water washing and co-incineration flue gas carbonization treatment method, the molar ratio of ammonium ions in the ammonia water added to the fly ash slurry to calcium ions in the fly ash slurry is 1.5-3.5.

[0021] As a further solution of the fly ash water washing and co-incineration flue gas carbonization treatment method, the molar ratio of ammonium ions in the ammonia water added to the fly ash slurry to calcium ions in the fly ash slurry is 2-2.5.

[0022] Beneficial effects of the present invention:

[0023] Innovative agent substitution reduces costs: This invention innovatively utilizes low-concentration carbon dioxide in incineration flue gas to replace traditional sodium carbonate for precipitation and removal of calcium, magnesium ions and soluble heavy metals in wash water, thereby achieving efficient utilization of resources and significant cost reduction.

[0024] Improve treatment efficiency: The present invention can combine and replace multiple water treatment process flows, making the entire treatment process more efficient and reducing water treatment investment costs.

[0025] Double gains in treatment effect: The fly ash washing process in the present invention is carried out simultaneously with the carbonization process. By combining mechanical stirring with aeration stirring, the fly ash washing effect is enhanced, while the removal rate of calcium, magnesium ions and heavy metals in the carbonization process is improved. At the same time, the steps of the water washing water treatment process are reduced, thereby improving the overall treatment efficiency.

[0026] Achieve carbon reduction and environmental protection: The present invention absorbs carbon dioxide in the flue gas through the carbonization process, solving the problem of fly ash washing while achieving the carbon reduction goal and contributing to environmental protection. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 Schematic diagram of the fly ash water washing carbonization kettle according to an embodiment of the present invention.

[0028] Figure 2 This is a process flow chart of the fly ash water washing and coordinated incineration flue gas carbonization treatment method described in an embodiment of the present invention. DETAILED DESCRIPTION

[0029] The technical solution of the present invention is further illustrated below through specific implementation methods.

[0030] Unless otherwise specified, the various raw materials of the present invention can be purchased commercially or prepared according to conventional methods in the art.

[0031] Example 1

[0032] In this embodiment, the fly ash water washing carbonization kettle is used for the primary water washing of fly ash. Figure 1 As shown, it includes an exhaust gas circulation pipe 3, an exhaust gas discharge pipe 4, a dosing pipe 5, a kettle body 6, an agitator 7 and an aeration pipe 8. The blades of the agitator 7 are located in the kettle body 6. One end of the aeration pipe 8 is connected to the incineration flue gas inlet pipe 1, and the other end extends into the kettle body 6 and extends to the bottom of the kettle body 6. The dosing pipe 5 is connected to the kettle body 6. One end of the exhaust gas discharge pipe 4 is connected to the top of the kettle body 6, and the other end is connected to the aeration pipe 8. A valve 2 is provided on the aeration pipe 8, and a fly ash slurry inlet 9 is provided on the top of the kettle body 6; the exhaust gas discharge pipe 4 is connected to the exhaust gas circulation pipe 3, and the flow direction of the exhaust gas is adjusted by the corresponding valve provided on the pipe.

[0033] The fly ash water washing and carbonization kettle of this embodiment plays the dual role of fly ash water washing and stirring and flue gas carbonization. Through reasonable stirring and aeration design, the comprehensive treatment of fly ash water washing, calcium and magnesium ion removal and heavy metal precipitation is achieved in the same kettle.

[0034] Preferably, a plurality of aeration pipes 8 are evenly distributed at the bottom of the kettle body 6 to ensure that the flue gas (containing CO2) is fully in contact with the aqueous solution.

[0035] In a specific example, the effective volume of the fly ash water washing carbonization kettle is 500L.

[0036] In a specific embodiment, fly ash is mixed with an aqueous solution (wastewater from secondary water washing, i.e., secondary water washing water) to form a water washing slurry, which is then delivered to the kettle 6 through the fly ash slurry inlet 9. A dosing line 5 is used to add reagents such as aqueous ammonia. An aeration line 8 is used to add incineration flue gas to the kettle 6. A stirrer 7 includes a motor, a stirring shaft, and blades connected to the motor via a stirring shaft. The structure of stirrer 7 is conventional, and stirrer 7 stirs the fly ash slurry in the kettle.

[0037] The process flow of the fly ash water washing and co-incineration flue gas carbonization treatment method of this embodiment is as follows: Figure 2 As shown, the three-stage countercurrent process includes a primary water wash, a secondary water wash, and a tertiary water wash. The specific steps are as follows:

[0038] First-stage water washing: Add reagent (ammonia water), incineration flue gas and fly ash slurry into the fly ash water washing carbonization kettle respectively. The fly ash slurry is washed with water under the action of agitator 7. The generated waste gas is returned to the kettle body 1 after merging with the waste gas circulation pipe 3 and the aeration pipe 8. The volume of the fly ash slurry is 431L, which is made of 0.1t fly ash (density 0.8g / cm 3 , volume approximately 125 L) and 306 L of secondary wash water (i.e., wastewater from the secondary wash) were mixed in a ratio of 1:3.06 (mass ratio). The calcium ion concentration in the fly ash slurry was approximately 22,000 mg / L. The flow rate of the incineration flue gas in aeration pipe 8 was 1224 L / min (ratio of aqueous solution (L) (excluding ammonia) to incineration flue gas flow (L / min) = 1:4), and the aeration time was 20-40 minutes. The amount of ammonia water used was 25 L (25% concentration), and the molar ratio of ammonium ions in the solution to calcium ions in the fly ash slurry was 2. Agitator 7 stirred the fly ash slurry with ammonia water. After 60 minutes of water washing, the water washing was completed, forming a water-washed carbonized liquid. The generated waste gas was discharged through waste gas discharge pipe 4 for waste gas treatment. The washed carbonized liquid is subjected to filter pressing to form fly ash cake and filtrate, the filtrate is subjected to conventional wastewater treatment, and then the reagent (ammonia water) is recovered and the recovered ammonia water is added back into the kettle 6 to replace most of the ammonia water raw materials.

[0039] Secondary washing: The fly ash cake produced by the primary washing process is washed in the No. 1 washing tank. The aqueous solution used is derived from the wastewater produced by the tertiary washing process, i.e., the tertiary washing water. The mass ratio of the tertiary washing water to the dry fly ash (the mass of the dry fly ash can be calculated by measuring the moisture content of the fly ash cake after the primary washing process) is 1:4.45. After the washing process is completed, a filter press treatment is performed to produce the fly ash cake and wastewater (secondary washing water). The wastewater is then reused for the primary washing process.

[0040] Tertiary water washing: Add MVR condensate and fresh water to the No. 2 water washing tank to wash the fly ash cake produced by the secondary water washing. The mass ratio of water to dry fly ash (the mass of dry fly ash can be calculated by testing the moisture content of the fly ash cake after the secondary water washing) is 1:4.67. After the water washing is completed, filter press treatment is carried out to produce fly ash cake and wastewater (tertiary water washing water). The wastewater is reused for the secondary water washing.

[0041] Example 2

[0042] This embodiment is basically the same as the above-mentioned embodiment 1, and the volume of the fly ash slurry is also the same as that of the above-mentioned embodiment 1. The difference is that the ratio of the volume of the aqueous solution (L) (excluding ammonia water) in the first-level water washing to the incineration flue gas flow rate (L / min) is 1:2.

[0043] Example 3

[0044] This embodiment is basically the same as the above-mentioned embodiment 1, and the volume of the fly ash slurry is also the same as that of the above-mentioned embodiment 1. The difference is that the ratio of the volume of the aqueous solution slurry (L) (excluding ammonia water and fly ash) in the first-level water washing to the incineration flue gas flow rate (L / min) is 1:1.

[0045] According to GB8978-1996, the concentrations of calcium, magnesium and heavy metals in the fly ash slurry (excluding ammonia water and fly ash) during the primary water washing process in Examples 1-3 were tested every 5 or 10 minutes. The test results are shown in Tables 1-3.

[0046] Table 1. Detection results of calcium and magnesium ions and heavy metal concentrations in fly ash slurry of Example 1

[0047] Reaction time Zn (mg / L) Pb (mg / L) Cd (mg / L) Ni (mg / L) Cr (mg / L) Cu (mg / L) Ca (mg / L) 0min 2.37 67.42 0.005 0.07 0 1.15 11898 10min 2.325 0.015 0.005 0.07 0.005 1.04 7288 20min 2.395 0.005 0.005 0.075 0.005 1.07 4346 30min 2.185 0.04 0.005 0.08 0.005 1.06 126 35min 1.305 0.085 0.005 0.08 0.005 1.03 20 40min 1.335 0.105 0.005 0.08 0.005 1.01 15 45min 0.115 0.35 0.005 0.08 0.005 0.93 13 50min 0.105 0.36 0.005 0.075 0.005 0.845 13 55min 0.07 0.365 0 0.075 0 0.725 15 60min 0.075 0.375 0 0.065 0.005 0.68 20

[0048] Table 2. Detection results of calcium and magnesium ions and heavy metal concentrations in the fly ash slurry of Example 2

[0049] Reaction time Zn (mg / L) Pb (mg / L) Cd (mg / L) Ni (mg / L) Cr (mg / L) Cu (mg / L) Ca (mg / L) 0min 2.37 67.42 0.005 0.07 0 1.15 11898 10min 1.975 0.005 0.005 0.075 0.005 0.96 7578 20min 1.985 0.01 0.005 0.075 0.005 0.98 5439 30min 2.19 0.015 0.005 0.08 0.005 0.995 2877 40min 1.83 0.125 0.005 0.085 0.005 1.1 359 50min 0.38 0.135 0.005 0.085 0.005 1.05 74 55min 0.075 0.12 0.005 0.08 0.005 0.94 54 60min 0.105 0.085 0.005 0.055 0.005 0.495 42

[0050] Table 3. Detection results of calcium and magnesium ions and heavy metal concentrations in fly ash slurry of Example 3

[0051] Reaction time Zn (mg / L) Pb (mg / L) Cd (mg / L) Ni (mg / L) Cr (mg / L) Cu (mg / L) Ca (mg / L) 0min 2.37 67.42 0.005 0.07 0 1.15 11898 10min 2.26 1.125 0.005 0.07 ND 1.095 9332 20min 2.34 0.035 0.005 0.075 ND 1.12 8522 30min 2.27 0 0.005 0.07 0 1.08 7464 40min 2.34 ND 0.005 0.075 ND 1.11 6084 50min 2.31 ND 0.005 0.075 0 1.135 4539 60min 2.34 0 0.005 0.075 0 1.14 2793 70 minutes 2.31 0.005 0.005 0.08 0 1.115 335 80 minutes 2.10 0.07 0.005 0.08 0 1.09 16 90 minutes 1.50 0.06 0.005 0.08 0 1.07 11 100min 0.39 0.08 0.005 0.075 0 0.99 11 110 minutes 0.04 0.1 0 0.065 0 0.895 10 120 minutes 0.02 0.12 0 0.06 0 0.775 13

[0052] As shown in Tables 1-3, the process of this embodiment successfully eliminates the calcium and magnesium removal steps in the water treatment process, and is expected to also eliminate the heavy metal removal step. This reduces treatment time by an estimated 30%-50%, significantly improving treatment efficiency and reducing equipment investment and operating costs. The calcium and magnesium ion removal rates exceed 98%, the Zn and Pb heavy metal removal rates exceed 90%, and the Cu heavy metal removal rate exceeds 50%. This meets the requirements for MVR crystallization and salt separation.

[0053] The present invention can significantly reduce the cost of fly ash washing water treatment chemicals, and is expected to reduce the chemical cost by more than 50%.

[0054] The soluble chlorine content in the original fly ash, single-wash carbonized fly ash, double-washed fly ash, and triple-washed fly ash was tested according to HJ1134 standard. The test results are shown in Table 4.

[0055] Table 4. Soluble chlorine content test results

[0056]

[0057] As can be seen from Table 4, the synergistic effect of mechanical stirring and aeration stirring can improve the removal rate of chlorine in fly ash and enhance the fly ash washing effect by about 20%.

[0058] The above embodiment has significant carbon reduction benefits. For every ton of fly ash processed, about 50 kilograms of carbon dioxide can be absorbed, which has significant environmental benefits.

[0059] The above examples are intended only to illustrate the detailed methods of the present invention. The present invention is not limited to the above detailed methods, nor does it mean that the present invention must rely on the above detailed methods to be implemented. Those skilled in the art will understand that any improvements to the present invention, equivalent replacements of raw materials for the products of the present invention, addition of auxiliary ingredients, and selection of specific methods, etc., all fall within the scope of protection and disclosure of the present invention.

Claims

1. A method for treating fly ash water washing and co-incineration flue gas carbonization, characterized in that: The fly ash is washed using a three-stage countercurrent water washing system consisting of a primary water washing system, a secondary water washing system, and a tertiary water washing system. Among them, in the primary water washing process, fly ash is mixed with an aqueous solution to form a water-ash slurry, and incineration flue gas is introduced into the fly ash slurry under mechanical stirring conditions for aeration and ammonia water is added. The fly ash slurry is carbonized to form a water-washed carbonized liquid, and the water-washed carbonized liquid is subjected to solid-liquid separation to produce fly ash mud cake and filtrate, which is then post-treated.

2. The fly ash water washing and coordinated incineration flue gas carbonization treatment method according to claim 1 is characterized in that: The volume ratio of the aqueous solution to the flow rate of the incineration flue gas is 1:2-6, with the unit being L:L / min.

3. The fly ash water washing and coordinated incineration flue gas carbonization treatment method according to claim 1 is characterized in that: The volume ratio of the aqueous solution to the flow rate of the incineration flue gas is 1:4, with the unit being L:L / min.

4. The fly ash water washing and coordinated incineration flue gas carbonization treatment method according to claim 1 is characterized in that: During the primary water washing process, the mass ratio of fly ash to aqueous solution is 2-4.

5. The fly ash water washing and coordinated incineration flue gas carbonization treatment method according to claim 1 is characterized in that: During the primary water washing process, the mass ratio of fly ash to aqueous solution is 2.2-3.

6. The fly ash water washing and co-incineration flue gas carbonization treatment method according to claim 1 is characterized in that: During the primary water washing process, the incineration flue gas is formed by mixing fresh incineration flue gas and water-washed waste gas after participating in the carbonization reaction.

7. The fly ash water washing and coordinated incineration flue gas carbonization treatment method according to claim 1 is characterized in that: In the primary water washing process, post-treatment of the filtrate refers to recovering the ammonia water after the filtrate is treated as wastewater, and the recovered ammonia water is added to the fly ash slurry again.

8. The fly ash water washing and co-incineration flue gas carbonization treatment method according to any one of claims 1 to 7, characterized in that: The molar ratio of ammonium ions in the ammonia water added to the fly ash slurry to calcium ions in the fly ash slurry is 1.5-3.

5.

9. The fly ash water washing and co-incineration flue gas carbonization treatment method according to claim 8, characterized in that: The molar ratio of ammonium ions in the ammonia water added to the fly ash slurry to calcium ions in the fly ash slurry is 2-2.5.

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