Sludge ash-based chlorine fixation agent suitable for cement industry co-processing solid waste pyrolysis and preparation thereof

Abstract

The application discloses sludge ash-based solid chlorine agent suitable for cement industry collaborative solid waste pyrolysis and preparation thereof, relates to the technical field of solid chlorine agent and solid waste treatment, and realizes waste treatment by waste by adopting sludge ash as a preparation raw material of the solid chlorine agent, main components of the sludge ash, i.e., silicon oxide, are used for modifying natural limestone, so that the natural limestone is suitable for high-temperature in-situ solid chlorine in solid waste pyrolysis, and the sintering resistance of the solid chlorine agent is improved; and the natural limestone and kaolin are used as main raw materials, so that the solid chlorine agent after pyrolysis can be added into cement mortar as cement mixing material, harmless recycling is realized, and cost is saved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of chlorine fixation agents and solid waste treatment, in particular to a sludge ash-based chlorine fixation agent suitable for cement industry co-processing of solid waste pyrolysis and a preparation method thereof. BACKGROUND

[0002] Pyrolysis is a thermochemical conversion technology that heats materials in an inert atmosphere to decompose into solid coke, liquid tar and pyrolysis gas. Compared with the current mainstream landfill treatment, which occupies and damages the land, the advantages of pyrolysis technology mainly include: (1) high weight and volume reduction rate of solid waste; (2) less pollution emission; (3) high resource utilization rate of products. The solid, liquid and gas products produced by pyrolysis of solid waste can be used twice, which has high economic value.

[0003] At present, the process route of co-processing organic solid waste using the cement industry facilities supported by the city is gradually attracting people's attention. The cement industry has many advantages such as sufficient waste heat, large treatment scale, no waste residue discharge, etc. The three-state products obtained by pyrolysis of solid waste can be further combined with the cement industry. The solid semi-coke can be directly used as a mixing material for cement clinker to improve the compressive strength and heavy metal solidification capacity of the clinker. The liquid tar and pyrolysis gas can be used as high-calorific-value fuel to enter the cement kiln for combustion.

[0004] However, the municipal solid waste contains various plastics represented by polyvinyl chloride (PVC), which will produce a large amount of HCl and Cl2 upon heating and decomposition, not only affecting the atmospheric environment and human health, but also causing serious corrosion of the kiln wall and pipeline in the cement kiln, and producing skinning and plugging phenomena in the equipment, shortening the service life of the equipment. At the same time, the increase of chlorine content in the kiln requires the addition of dry inhibitors to control acid gases. Once the amount of dry inhibitors such as quicklime exceeds the demand of all acid oxides, it will exist in the form of free calcium oxide, affecting the composition of cement clinker and thus affecting the quality of cement. Therefore, in the process of solid waste pyrolysis, in-situ inhibition of hydrogen chloride emission and solidification of chlorine elements in the pyrolysis semi-coke as much as possible are of great significance to improve the ability of cement kiln to co-process chlorine-containing organic solid waste, ensure the stable operation of cement kiln system and the quality of cement.

[0005] Calcium oxide as a common chlorine fixation agent, there is coking phenomenon at high temperature, its hydrogen chloride trapping capacity will be greatly reduced, which is not conducive to in-situ trapping in high temperature environment, and the cost is high while the chlorine fixation efficiency is low, so it is urgent to dope and modify the existing chlorine fixation agent to improve the chlorine fixation capacity and reduce the production cost. After the complete utilization of organic matter in sludge in pyrolysis, incineration and other steps, the remaining sludge ash contains a large amount of inert materials, which can be used to enhance the anti-sintering performance of the chlorine fixation agent. At the same time, the various metal oxides in the sludge ash can modify the calcium oxide to improve the chlorine fixation performance. After use, the chlorine fixation agent can also be added as a concrete admixture with solid waste residues to realize the green and high-value utilization of the whole process product of cement industry and solid waste pyrolysis. However, due to the different treatment methods of each sewage treatment plant, the composition of sludge ash is also unstable, and different components will lead to uncontrollable transfer path of chlorine element to solid or liquid phase in the pyrolysis process.

[0006] Therefore, in the current solid waste pyrolysis work, it is a task keeping pace with the times to develop a chlorine fixation agent with controllable chlorine migration path, excellent chlorine fixation effect, simple preparation process, low price and environmental friendliness. SUMMARY

[0007] The purpose of the present application is to overcome the shortcomings of the prior art, provide a sludge ash-based chlorine fixation agent suitable for cement industry and solid waste pyrolysis and a preparation method thereof. The chlorine fixation agent can inhibit the emission of hydrogen chloride in solid waste pyrolysis, reduce the proportion of water-soluble chlorine in solid, and increase the compressive strength of cement clinker.

[0008] The technical problems to be solved by the present application are solved by the following technical solutions:

[0009] The first purpose of the present application is to provide a preparation method of a sludge ash-based chlorine fixation agent, comprising the following steps:

[0010] (1) adding an adjusting agent to the sludge ash, stirring, filtering, and drying to obtain adjusted sludge ash;

[0011] (2) wet grinding the natural limestone and then calcining it in a tube furnace to obtain calcined limestone;

[0012] (3) mixing the adjusted sludge ash, calcined limestone and kaolin to obtain a mixture;

[0013] (4) calcining the mixture in a tube furnace to obtain a sludge ash-based chlorine fixation agent.

[0014] The second purpose of the present application is to provide a sludge ash-based chlorine fixation agent obtained by the above preparation method.

[0015] The third purpose of the present application is to provide the application of the above sludge ash-based chlorine fixation agent in cement industry and solid waste pyrolysis.

[0016] A fourth object of the present application is to provide a method for using the aforementioned sludge ash-based chlorine fixation agent in the cement industry for co-processing solid waste pyrolysis, comprising the following steps:

[0017] (1) drying and crushing the solid waste to obtain solid waste crushed material;

[0018] (2) mixing the solid waste crushed material with the chlorine fixation agent to obtain a mixture;

[0019] (3) pyrolyzing the mixture at high temperature to obtain high-value combustible gas with extremely low hydrogen chloride content and pyrolysis coke rich in chlorine.

[0020] The working principle of the present application is as follows:

[0021] The large amount of silicon oxide in sludge ash can enhance the anti-sintering ability of natural limestone as a skeleton, and metal oxides can improve the chlorine fixation effect. However, due to different treatment methods of sewage treatment plants in different regions, the content of sludge components differs greatly. Alumina and calcium oxide can promote the migration of chlorine to the solid phase and form stable normative salt (3CaO-Al2O3-CaCl2-10H2O), while iron oxide promotes the migration of chlorine to the solid phase while some chlorine is dissolved in the liquid phase in the form of iron chloride, and some acidic substances remaining on the surface of sludge ash will also hinder the solidification of hydrogen chloride to some extent. Therefore, the present application adjusts the types of surface metal oxides and pH of different component sludge ash by using a conditioning agent, washes the surface of sludge ash with high alumina and calcium oxide content with oxalic acid to remove iron oxide, adjusts the pH to weak alkaline with sodium bicarbonate, and only uses sludge ash rich in silicon oxide, alumina and calcium oxide to modify natural limestone to improve the anti-sintering performance and chlorine fixation performance of the chlorine fixation agent. For sludge ash with low alumina and calcium oxide content and high iron oxide content, sodium hydroxide solution is used for washing to generate iron hydroxide, which reduces the generation and dissolution of iron chloride while promoting the migration of chlorine to the solid phase.

[0022] The beneficial effects of the present application are as follows:

[0023] 1. The present application uses sludge ash as the raw material for preparing the chlorine fixation agent, realizing waste treatment with waste, which is of great significance to environmental protection.

[0024] 2. The present application modifies natural limestone with silicon oxide in sludge ash, making it suitable for high-temperature in-situ chlorine fixation in solid waste pyrolysis, and improving the anti-sintering performance of the chlorine fixation agent.

[0025] 3. The present application pretreats different component sludge ash with a conditioning agent, improves the proportion of effective chlorine fixation components in sludge ash, reduces the transfer path of chlorine elements to gas and liquid phases, and makes the proportion of gas phase chlorine emission in total chlorine not more than 20%.

[0026] 4. This invention uses natural limestone and kaolin as the main raw materials, which is beneficial for the solidified chlorine agent after pyrolysis to be added to cement mortar as a cement admixture, so as to achieve subsequent harmless reuse and save costs. Detailed implementation method:

[0027] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below with reference to specific embodiments.

[0028] This invention provides a method for preparing a sludge ash-based chlorine-fixing agent, comprising the following steps:

[0029] (1) Add a conditioner to the sludge ash, stir, filter, and dry to obtain the conditioned sludge ash;

[0030] (2) After wet grinding of natural limestone, it is placed in a tube furnace for calcination to obtain calcined limestone;

[0031] (3) Mix the sludge ash, calcined limestone and kaolin to obtain a mixture;

[0032] (4) The mixture is placed in a tubular furnace and calcined to obtain a sludge ash-based chlorine-fixing agent.

[0033] In step (1), the sludge ash is the solid waste remaining after sludge is pyrolyzed and burned.

[0034] In step (1), the regulator is at least one of oxalic acid, sodium bicarbonate, and sodium hydroxide, and water is used as the solvent.

[0035] In step (1), the concentration of the pH adjuster is 0.5-2 mol / L, and 10-20 mL of pH adjuster is added per gram of sludge ash.

[0036] In step (1), the stirring is carried out at room temperature for 20-24 hours.

[0037] In step (1), the drying temperature is 100-105℃ and the time is 20-24h.

[0038] In step (2), the wet milling uses anhydrous ethanol as the milling medium, the diameter of the milling beads is 3.5-10 mm, and the ball-to-material ratio is (5-10):1.

[0039] In step (2), the calcination temperature is 800-900℃, the calcination time is 2-3h, and the carrier gas is N2.

[0040] In step (3), the mass ratio of the adjusted sludge ash, calcined limestone and kaolin is (5-15):(60-80):(10-20).

[0041] In step (4), the calcination temperature is 700-800 DEG C, the calcination time is 2-3 h, and the carrier gas is N2.

[0042] The application further provides a sludge ash-based chlorine-fixing agent obtained by the preparation method.

[0043] The application further provides application of the sludge ash-based chlorine-fixing agent in the cement industry in the synergistic solid waste pyrolysis.

[0044] The application further provides a method for applying the sludge ash-based chlorine-fixing agent in the cement industry in the synergistic solid waste pyrolysis, comprising the following steps:

[0045] (1) drying and crushing the solid waste to obtain a solid waste crushed material;

[0046] (2) mixing the solid waste crushed material with the chlorine-fixing agent to obtain a mixture;

[0047] (3) high-temperature pyrolyzing the mixture to obtain high-value combustible gas with extremely low chlorine content and pyrolysis coke rich in chlorine.

[0048] In step (1), the solid waste includes sludge, garbage screen overs and other solid waste. The sludge is a byproduct after sewage treatment in a sewage treatment plant, and the garbage screen overs are screen residues after treatment by a garbage screen in a garbage plant. The mass ratio of the sludge to the garbage screen overs is (20-40):(60-80).

[0049] In step (1), the drying temperature is 100-105 DEG C, and the drying time is 20-30 h.

[0050] In step (1), the crushing is crushing the dried solid waste in a high-speed crusher for 20-40 min.

[0051] In step (2), the mass percentage of the chlorine-fixing agent in the solid waste crushed material is 30-50 wt%.

[0052] In step (3), the high-temperature pyrolysis is performed in a continuous feeding rotary pyrolysis furnace, the pyrolysis temperature is 500-700 DEG C, the pyrolysis time is 15-45 min, and the carrier gas is N2.

[0053] In step (3), according to the total chlorine percentage, the chlorine content in the high-value combustible gas accounts for no more than 20% of the total chlorine in the solid waste, the chlorine content in the pyrolysis coke accounts for no less than 65% of the total chlorine in the solid waste, and the free chlorine content in the pyrolysis coke accounts for no more than 10% of the total chlorine in the solid waste.

[0054] Example 1

[0055] 1. The embodiment provides a preparation method of a sludge ash-based chlorine-fixing agent, comprising the following steps:

[0056] (1) Add 10 mL of conditioning agent to each gram of sludge ash, stir at room temperature for 24 h and filter, and dry at 105℃ for 24 h to obtain conditioned sludge ash.

[0057] The sludge ash contains 38.6% silicon dioxide, 15.2% aluminum oxide, 11.9% calcium oxide, and 21% iron oxide; the conditioning agents are 1 mol / L oxalic acid solution and 0.5 mol / L sodium bicarbonate solution.

[0058] (2) Using anhydrous ethanol as the ball milling medium, with a ball milling bead diameter of 3.5 mm and a ball-to-material ratio of 5:1, natural limestone was wet-milled in a planetary ball mill at a speed of 500 r / min for 3 h, and then calcined in a tube furnace at 900 °C and N2 environment for 2 h. After calcination, N2 was continuously introduced to cool down to room temperature to obtain calcined limestone.

[0059] (3) The sludge ash, calcined limestone and kaolin are mixed in a ball mill at a mass ratio of 15:70:15 to obtain a mixture.

[0060] (4) The mixture was placed in a tube furnace at 800℃ and N2 environment and heated for 2 hours. After the heating was completed, N2 was continued to be introduced to cool down, and powdered solid chlorine agent was obtained.

[0061] 2. This embodiment provides a method for applying the sludge ash-based chlorine-fixing agent prepared above in the co-processing of solid waste pyrolysis in the cement industry, including the following steps:

[0062] (1) Mix sludge and garbage screen material at a mass ratio of 20:80, dry at 105℃ for 24 hours and crush to obtain solid waste crushed material.

[0063] (2) Mix the pulverized solid waste material with the solid chlorine agent prepared above at a mass ratio of 10:5 until they are evenly mixed to obtain a mixture.

[0064] (3) The mixture is pyrolyzed at 500°C and N2 environment for 30 minutes in a continuously fed rotary pyrolysis furnace to obtain high-value combustible gas and pyrolytic coke.

[0065] Test Analysis:

[0066] The sludge ash washed with the conditioner contained 17.4% aluminum oxide, 13.1% calcium oxide, and 4.4% iron oxide.

[0067] Gaseous chlorine in high-value combustible gases accounts for 16.7% of the total chlorine in solid waste, while chlorine in pyrolytic coke accounts for 74.3%. After high-temperature pyrolysis, a chlorine-fixing agent replaces cement by mass of the effective components to prepare mortar, resulting in a water-soluble free chloride ion content of 0.32%.

[0068] Example 2

[0069] The preparation method and application method of the solid chlorine agent of this example are the same as those of Example 1, except that the mass ratio of the adjusted sludge ash, calcined limestone and kaolin in the preparation step (3) of the solid chlorine agent is adjusted to 10:75:15.

[0070] The gas-phase chlorine in the high-value combustible gas accounts for 17.9% of the total chlorine of the solid waste, and the chlorine in the pyrolysis coke accounts for 70.6% of the total chlorine of the solid waste. The solid chlorine agent is replaced by cement in an equal mass of effective components after high-temperature pyrolysis to prepare a mortar, and the water-soluble free chlorine ion content of the mortar is 0.41%.

[0071] Example 3

[0072] The preparation method and application method of the solid chlorine agent of this example are the same as those of Example 1, except that the mass ratio of the adjusted sludge ash, calcined limestone and kaolin in the preparation step (3) of the solid chlorine agent is adjusted to 5:80:15.

[0073] The gas-phase chlorine in the high-value combustible gas accounts for 19.8% of the total chlorine of the solid waste, and the chlorine in the pyrolysis coke accounts for 68.1% of the total chlorine of the solid waste. The solid chlorine agent is replaced by cement in an equal mass of effective components after high-temperature pyrolysis to prepare a mortar, and the water-soluble free chlorine ion content of the mortar is 0.47%.

[0074] Example 4

[0075] The preparation method and application method of the solid chlorine agent of this example are the same as those of Example 1, except that the sludge ash and the adjusting agent in the preparation step (1) of the solid chlorine agent are replaced by: the content of silicon oxide in the sludge ash is 42.3%, the content of aluminum oxide is 5.2%, the content of calcium oxide is 7.4%, and the content of iron oxide is 27.7%; and the adjusting agent is a sodium hydroxide solution with a concentration of 1 mol / L.

[0076] The gas-phase chlorine in the high-value combustible gas accounts for 18.2% of the total chlorine of the solid waste, and the chlorine in the pyrolysis coke accounts for 67.3% of the total chlorine of the solid waste. The solid chlorine agent is replaced by cement in an equal mass of effective components after high-temperature pyrolysis to prepare a mortar, and the water-soluble free chlorine ion content of the mortar is 1.45%.

[0077] Comparative Example 1

[0078] The preparation method and application method of the solid chlorine agent of this example are the same as those of Example 1, except that the mass ratio of the adjusted sludge ash, calcined limestone and kaolin in the preparation step (3) of the solid chlorine agent is adjusted to 0:70:15.

[0079] The gaseous phase chlorine in the high-value combustible gas accounts for 34.8% of the total chlorine in the solid waste, the chlorine in the pyrolysis coke accounts for 46.2% of the total chlorine in the solid waste, the solid chlorine agent replaces cement to prepare mortar after high-temperature pyrolysis according to the effective components in equal mass, and the water-soluble free chlorine ion content of the mortar is 3.46%.

[0080] Comparative Example 2

[0081] The preparation method and application method of the solid chlorine agent of the present comparative example are the same as those of Example 1, except that no adjusting agent is added in the preparation step (1) of the solid chlorine agent.

[0082] The gaseous phase chlorine in the high-value combustible gas accounts for 17.1% of the total chlorine in the solid waste, the chlorine in the pyrolysis coke accounts for 59.4% of the total chlorine in the solid waste, the solid chlorine agent replaces cement to prepare mortar after high-temperature pyrolysis according to the effective components in equal mass, and the water-soluble free chlorine ion content of the mortar is 6.27%.

[0083] In summary, the effective components in the sludge incineration ash can be reasonably utilized to prepare a solid chlorine agent with high solid chlorine performance, the emission of gaseous phase chlorine is greatly reduced, and the chlorides are fixed in a more stable form in the solid phase, so that the resource utilization of the solid waste pyrolysis products is realized, and the solid chlorine cost is reduced.

[0084] As can be seen from Examples 1 and 2, the more the amount of sludge ash added within a certain range, the better the solid chlorine effect of the solid chlorine agent.

[0085] As can be seen from Examples 1 and 3, the pretreatment of sludge ash with the adjusting agent can effectively control the main solid chlorine components in the sludge ash, and further reduce the migration of chlorine to the gas-liquid two phases.

[0086] As can be seen from Examples 1, Comparative Example 1 and Comparative Example 2, when no sludge incineration ash or no adjusting agent is added, the components in the sludge incineration ash cannot meet the conditions defined in the present application, the solidification effect on chlorine is poor, and a large amount of chlorine migrates in gaseous and liquid forms.

[0087] The above shows and describes the basic principles and main features of the present application and the advantages of the present application. It should be understood by those skilled in the art that the present application is not limited by the above examples, and the above examples and descriptions in the specification are only to illustrate the principles of the present application, and various changes and improvements can be made without departing from the spirit and scope of the present application, and these changes and improvements all fall within the scope of the present application. The scope of protection of the present application is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a sludge ash-based chlorine-fixing agent, characterized in that: Includes the following steps: (1) Add a conditioner to the sludge ash, stir, filter, and dry to obtain conditioned sludge ash; (2) After wet grinding of natural limestone, it is placed in a tube furnace for calcination to obtain calcined limestone; (3) Mix the sludge ash, calcined limestone and kaolin to obtain a mixture; (4) The mixture is placed in a tubular furnace and calcined to obtain a sludge ash-based chlorine-fixing agent; In step (1), the sludge ash is the solid waste remaining after sludge is pyrolyzed and burned; the regulator is at least one of oxalic acid, sodium bicarbonate, and sodium hydroxide; the regulator is used to adjust the type of surface metal oxides and pH of sludge ash with different components.

2. The preparation method according to claim 1, characterized in that: In step (1), the concentration of the pH adjuster is 0.5-2 mol / L, and 10-20 mL of pH adjuster is added per gram of sludge ash.

3. The preparation method according to claim 1, characterized in that: In step (1), the stirring is carried out at room temperature for 20-24 hours.

4. The preparation method according to claim 1, characterized in that: In step (1), the drying temperature is 100-105℃ and the time is 20-24 h.

5. The preparation method according to claim 1, characterized in that: In step (2), the wet milling uses anhydrous ethanol as the milling medium, the diameter of the milling beads is 3.5-10 mm, and the ball-to-material ratio is (5-10):

1.

6. The preparation method according to claim 1, characterized in that: In step (2), the calcination temperature is 800-900℃, the calcination time is 2-3h, and the carrier gas is N2.

7. The preparation method according to claim 1, characterized in that: In step (3), the mass ratio of the adjusted sludge ash, calcined limestone and kaolin is (5-15): (60-80): (10-20); In step (4), the calcination temperature is 700-800℃, the calcination time is 2-3h, and the carrier gas is N2.

8. The sludge ash-based chlorine-fixing agent obtained by the preparation method according to any one of claims 1-7.

9. The application of the sludge ash-based chlorine-fixing agent according to claim 8 in the co-processing of solid waste pyrolysis in the cement industry.

10. The application method of the sludge ash-based chlorine-fixing agent according to claim 8 in the co-processing of solid waste pyrolysis in the cement industry, characterized in that: Includes the following steps: (1) Dry and crush solid waste to obtain solid waste crushed material; (2) Mix the pulverized solid waste with the solid chlorine agent to obtain a mixture; (3) The mixture is subjected to high-temperature pyrolysis to obtain combustible gas and pyrolytic coke.

11. The application method as described in claim 10, characterized in that: In step (1), the solid waste includes sludge and waste screen material.

12. The application method as described in claim 11, characterized in that: The sludge mentioned in step (1) is a byproduct of sewage treatment in a sewage treatment plant, and the waste on the garbage screen is the residue left after the domestic waste screening machine in the garbage plant has processed it.

13. The application method as described in claim 11, characterized in that: In step (1), the mass ratio of sludge to waste screen material is (20-40): (60-80).

14. The application method as described in claim 10, characterized in that: In step (1), the drying temperature is 100-105℃ and the time is 20-30 h.

15. The application method as described in claim 10, characterized in that: In step (1), the crushing is the crushing of dried solid waste in a high-speed crusher for 20-40 min.

16. The application method as described in claim 10, characterized in that: In step (2), the solid chlorine agent accounts for 30-50 wt% of the mass of the solid waste pulverized material.

17. The application method as described in claim 10, characterized in that: In step (3), the high-temperature pyrolysis is carried out in a continuously fed rotary pyrolysis furnace, with a pyrolysis temperature of 500-700℃, a pyrolysis time of 15-45 min, and N2 as the carrier gas. Based on the percentage of total chlorine, the chlorine content of the combustible gas shall not exceed 20% of the total chlorine in the solid waste, the chlorine content of the pyrolysis coke shall not be less than 65% of the total chlorine in the solid waste, and the free chlorine content of the pyrolysis coke shall not exceed 10% of the total chlorine in the solid waste.