Method for producing calcium-carbon-based biochar ceramsite by sewage sludge and carbide slag in cooperation

Abstract

The application discloses a method for producing calcium-carbon-based biochar ceramsite by sewage sludge and carbide slag, which comprises the following steps: mixing sewage sludge, carbide slag and fly ash by stirring; pressure forming the mixed materials to obtain wet-based columnar particles; sending the wet-based columnar particles to a low-temperature aerobic pyrolysis rotary reactor; preheating the wet-based columnar particles by using tail gas waste heat at the front end to reduce the water content of the particles; forming biochar by aerobic pyrolysis of the biomass contained in the sludge in the low-temperature aerobic pyrolysis zone, and at the same time, the carbide slag reacts with the ambient atmosphere or CO2 generated by pyrolysis to directly provide the mechanical strength of the particles; removing the surface liquid phase product by instantaneous combustion at the end of the reactor; and finally forming calcium-carbon-based biochar ceramsite which is maintenance-free and has high mechanical strength. The application replaces the raw materials such as quicklime and cement in the original biochar ceramsite with carbide slag, greatly reduces the cost, and is maintenance-free, on the basis of retaining the excellent adsorption and phosphorus removal efficiency of the original biochar ceramsite and the performance of adsorbing carbon-containing organic matters of biochar.

Description

Technical Field

[0001] This invention belongs to the field of resource utilization of solid waste in environmental engineering, and particularly relates to a method for co-producing calcium-carbon-based biochar ceramsite from sewage sludge and calcium carbide slag. Background Technology

[0002] Wastewater treatment plant sludge, as a major solid waste from urban wastewater treatment plants, is being produced in increasing quantities year by year. There is still significant room for development in the low-carbon and resource-based treatment and disposal of wastewater sludge. Sludge pyrolysis to prepare biochar is a commonly used method for sludge resource utilization. The prepared biochar has advantages such as a large specific surface area, stable pore structure, and abundant surface functional groups, and has great application potential in removing various specific pollutants from gaseous and aqueous phases.

[0003] Chinese patent CN115477527A discloses a method for producing biochar ceramsite granular packing material. This method involves heating and stirring sewage sludge with industrial waste such as fly ash, quicklime, and phosphogypsum, followed by mechanical dehydration, pressure molding and granulation, granule preheating, aerobic pyrolysis, combustion, and wet curing to produce biochar ceramsite. This method utilizes low-temperature aerobic pyrolysis technology to achieve the low-temperature harmlessness of sewage sludge and form biochar ceramsite with a spatially porous structure, which can be used for the adsorption of pollutants in gas-liquid phase multi-media applications.

[0004] However, the mechanical strength of this biochar ceramsite product comes from the "volcanic ash effect" of fly ash, which requires wet curing to form cementitious substances such as hydrated calcium silicate and hydrated calcium aluminate to achieve the final mechanical strength.

[0005] Actual experiments in the preparation of biochar ceramsite show that, to ensure high mechanical strength of the biochar ceramsite product, the proportion of quicklime (an activator of the "volcanic ash effect") in the raw materials should be greater than 5%, and the curing time should be 7-14 days. This preparation method has a high cost of quicklime raw materials and a long wet curing time. Therefore, the raw material ratio and curing time further limit the reduction of costs and the optimization of the preparation process in the biochar ceramsite preparation process.

[0006] In summary, the key challenge is to optimize the raw material ratio in the preparation process of biochar ceramic particles while preserving their original adsorption properties, thereby reducing raw material costs and achieving biochar ceramic particle products with excellent mechanical strength through shorter wet curing time or even no curing required. Summary of the Invention

[0007] The problems that need to be solved in the existing technology are as follows: (1) A certain proportion of quicklime (>5%) needs to be added to the biochar ceramsite product as an activator of the "volcanic ash effect" of fly ash, and the raw material cost is high; (2) Biochar ceramsite needs to be wet-cured for a long time (7-14d) to form a certain mechanical strength.

[0008] To address the aforementioned problems, this invention provides a method for co-producing calcium-carbon-based biochar ceramsite from sewage sludge and carbide slag. This method involves mixing sewage sludge, carbide slag, and fly ash, and then converting the organic carbon in the sludge into biochar through a low-temperature aerobic pyrolysis reaction under an O2-CO2 atmosphere, thereby achieving the harmless treatment of the sewage sludge. The reaction of the carbide slag with carbon dioxide in the ambient atmosphere and generated during pyrolysis directly provides the mechanical strength of the particles, ultimately forming a maintenance-free calcium-carbon-based biochar ceramsite product with high mechanical strength.

[0009] The technical solution adopted in this invention is as follows:

[0010] A method for co-producing calcium-carbon-based biochar ceramsite from sewage sludge and carbide slag, the method comprising:

[0011] (1) Mix the sewage sludge, carbide slag and fly ash together;

[0012] (2) The above mixture is fed into a twin-screw extruder and pressure-formed into wet-based columnar granules with a moisture content of 40-50%.

[0013] (3) The above-mentioned wet-based columnar particles are sent to a low-temperature aerobic pyrolysis rotary reactor; the wet-based columnar particles are preheated at the front end of the reactor using the waste heat of the tail gas to reduce the moisture content of the particles to 20-30%; in the low-temperature aerobic pyrolysis zone in the middle of the reactor, the biomass contained in the sewage sludge is aerobically pyrolyzed to form biochar, and at the same time, the carbide slag reacts with CO2 in the ambient atmosphere or CO2 generated by pyrolysis to directly provide the mechanical strength of the particles; at the end of the reactor, the surface liquid phase products are removed by instantaneous combustion; finally, the calcium-carbon-based biochar ceramic particles with high mechanical strength and no maintenance are formed.

[0014] Furthermore, in step (1), the mass ratio of sewage sludge: fly ash: carbide slag is (3-4): (1-1.5): (1-2); the stirring time is 2-10 min.

[0015] Furthermore, the sewage sludge is first dewatered, and the moisture content of the sewage sludge after dewatering is <80%.

[0016] Furthermore, the diameter of the wet-based columnar particles is 3-20 mm and the length is 5-20 mm.

[0017] Furthermore, in the low-temperature aerobic pyrolysis zone, the biomass contained in the sewage sludge is converted into biochar through aerobic pyrolysis by means of reaction heating and self-oxidation exothermic reaction. The carbide slag reacts with CO2 in the ambient atmosphere and the CO2 generated by pyrolysis to generate calcium carbonate, thereby providing mechanical strength to the biochar.

[0018] Furthermore, in step (3): the preheating temperature is 150-200℃, the residence time is 5-10min, and capillary water and adhering water in the particles are removed; the low-temperature aerobic pyrolysis temperature is 300-350℃, the residence time is 20-30min; the instantaneous combustion temperature is 800-1000℃, and the reaction time is 10-15s.

[0019] Furthermore, in step (3): the proportion of air and industrial flue gas to be added is determined based on the content of carbide slag and the oxygen demand of low-temperature aerobic pyrolysis.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0021] (1) The present invention uses carbide slag to replace quicklime, cement and other raw materials in the original biochar ceramsite production raw materials. The prepared products do not require wet curing process and can be directly cured without curing. The test cycle is greatly shortened, saving time and effort.

[0022] (2) The present invention uses carbide slag to replace quicklime, cement and other raw materials in the original biochar ceramsite production raw materials, which greatly reduces the raw material cost and reduces cost expenditure, making it suitable for industrial production.

[0023] (3) Based on retaining the excellent phosphorus removal efficiency of the original biochar ceramsite and the adsorption performance of biochar on carbon-containing organic matter, this invention uses carbide slag to replace quicklime, cement and other raw materials in the original biochar ceramsite production raw materials. The calcium carbonate generated by the carbide slag and the atmosphere and the CO2 generated by pyrolysis directly provides the mechanical strength of the particles, forming a calcium-carbon-based biochar ceramsite product with high mechanical strength. The product has high mechanical strength and is not easily damaged when used as a packing material in a biological filter.

[0024] (4) The calcium-carbon-based biochar ceramic particles prepared by the present invention have a large porosity and specific surface area, and achieve spatial communication between internal and external pores, resulting in good environmental decontamination capabilities.

[0025] (5) The present invention produces biochar ceramsite by low-temperature aerobic pyrolysis under an atmosphere of CO2 from industrial flue gas and O2 from air. The production process realizes the harmless co-treatment and resource utilization of solid waste such as sewage sludge and carbide slag. At the same time, the carbide slag is used to fix industrial flue gas and CO2 generated by pyrolysis, reducing carbon emissions in the biochar ceramsite preparation process, and has high economic and environmental benefits.

[0026] (6) This invention utilizes high-moisture biomass waste (such as sewage sludge) and industrial waste (carbide slag and fly ash) to produce novel calcium-carbon-based biochar ceramsite. The raw materials are readily available, the cost is low, the process is simple and practical, and the environmental impact is small, resulting in good economic and environmental benefits. Attached Figure Description

[0027] Figure 1 This is a process flow diagram of the method for co-producing calcium-carbon-based biochar ceramsite from sewage sludge and carbide slag according to the present invention. Detailed Implementation

[0028] To make the technical means, creative features, objectives and effects of this invention easier to understand, the technical solutions in the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings.

[0029] This embodiment provides a method for co-producing calcium-carbon-based biochar ceramsite from sewage sludge and carbide slag, including the following:

[0030] Step 1): Dewatered sewage sludge (moisture content < 80%) is used as the main ingredient in the formula (sludge proportion greater than 50%), and fly ash and carbide slag are used as auxiliary ingredients in the formula. The materials are thoroughly mixed evenly in a drum mixer or other mechanical mixing equipment at a certain mass ratio.

[0031] Preferably, the mass ratio of sludge:fly ash:carbide slag is 3:1:1 or 3:1:2; and the stirring time is 2 to 10 minutes.

[0032] Step 2): The uniformly mixed material is fed into a twin-screw extruder and pressure-formed to obtain wet-based columnar granules with a certain strength.

[0033] Preferably, extrusion molding yields wet-based columnar particles with a diameter of 3-20 mm and a length of 5-20 mm.

[0034] Step 3): The wet-based columnar granules are conveyed to the inlet of the low-temperature aerobic pyrolysis rotary reactor. The reactor front end utilizes the waste heat from the tail gas to preheat the granules, further reducing their moisture content. The granules then enter the low-temperature aerobic pyrolysis section, where they undergo aerobic pyrolysis through system heating and self-oxidation to convert biomass into biochar. The carbide slag reacts with the ambient atmosphere and carbon dioxide generated during pyrolysis to produce calcium carbonate, providing the granules with mechanical strength. They then enter the instantaneous combustion section to remove the liquid products generated during pyrolysis. The final product is a maintenance-free calcium-carbon-based biochar ceramsite product with high mechanical strength.

[0035] Preferably, the low-temperature aerobic pyrolysis rotary reactor is the horizontal rotary aerobic pyrolysis furnace described in Chinese Patent CN 115477527A.

[0036] Preferably, the temperature of the preheating section of the low-temperature aerobic pyrolysis equipment is controlled at 150-200℃, with a residence time of 5-10 minutes, to remove capillary water, adhering water, etc. from the particles; the temperature of the low-temperature aerobic pyrolysis section is controlled at 300-350℃, with a residence time of 20-30 minutes; and the temperature of the instantaneous combustion stage is 800-1000℃, with a residence time of 10-15 seconds.

[0037] Preferably, the proportion of air and industrial flue gas added is determined based on the content of carbide slag and the oxygen demand of low-temperature aerobic pyrolysis.

[0038] Example 1:

[0039] (1) Dewatered sewage sludge (70% moisture content) is used as the main ingredient of the formula (sludge proportion greater than 50%), and fly ash and carbide slag are used as auxiliary ingredients of the formula. The materials are mixed thoroughly and evenly in a drum mixer or other mechanical mixing equipment at a mass ratio of 3:1:1 for 10 minutes.

[0040] (2) Using a shaftless screw, the uniformly mixed material is added to a twin-screw extruder and pressure-formed to obtain wet-based columnar particles with a certain strength, a diameter of 10 mm, and a length of 10 mm.

[0041] (3) Wet-based columnar granules are conveyed to the inlet of a low-temperature aerobic pyrolysis rotary reactor. At the reactor front end, the granules are preheated using waste heat from the tail gas (temperature set at 150℃, residence time 5 min) to remove capillary water and attached water, further reducing the granule moisture content. The granules then enter the low-temperature aerobic pyrolysis section (temperature set at 300℃, residence time 20 min), where the biomass is converted into biochar through aerobic pyrolysis via system heating and self-oxidation. Calcium carbonate is generated from the calcium carbide slag reacting with the ambient atmosphere (inlet air: industrial flue gas = 3:1) and carbon dioxide produced by pyrolysis, providing the granules with mechanical strength. Finally, the granules enter the instantaneous combustion section (temperature set at 900℃, residence time 10 s) to remove liquid products generated during pyrolysis. The final product is a maintenance-free calcium-carbon-based biochar ceramsite with high mechanical strength, compressive strength: 67.2 N; specific surface area: 14.0779 m². 2 / g; Average pore size: 14.0779m 2 / g; Total pore volume: 0.056835cm³ 3 / g.

[0042] Example 2:

[0043] (1) Dewatered sewage sludge (70% moisture content) is used as the main ingredient of the formula (sludge proportion greater than 50%), and fly ash and carbide slag are used as auxiliary ingredients of the formula. The materials are mixed thoroughly and evenly in a drum mixer or other mechanical mixing equipment at a mass ratio of 3:1:1 for 10 minutes.

[0044] (2) Using a shaftless screw, the uniformly mixed material is added to a twin-screw extruder and pressure-formed to obtain wet-based columnar particles with a certain strength, a diameter of 15 mm, and a length of 10 mm.

[0045] (3) Wet-based columnar granules are conveyed to the inlet of a low-temperature aerobic pyrolysis rotary reactor. At the reactor front end, the granules are preheated using waste heat from the tail gas (temperature set at 200℃, residence time 5 min) to remove capillary water and attached water, further reducing the granule moisture content. The granules then enter the low-temperature aerobic pyrolysis section (temperature set at 300℃, residence time 30 min), where the biomass is converted into biochar through aerobic pyrolysis via system heating and self-oxidation. Calcium carbonate is generated from the calcium carbide slag reacting with the ambient atmosphere (inlet air: industrial flue gas = 3:1) and carbon dioxide produced by pyrolysis, providing the granules with mechanical strength. Finally, the granules enter the instantaneous combustion section (temperature set at 900℃, residence time 10 s) to remove liquid products generated during pyrolysis. The final product is a maintenance-free calcium-carbon-based biochar ceramsite with high mechanical strength, compressive strength: 70.4 N; specific surface area: 15.5371 m². 2 / g; Average pore size: 19.0634m 2 / g; Total pore volume: 0.058621cm³ 3 / g.

[0046] Example 3:

[0047] (1) Dewatered sewage sludge (70% moisture content) is used as the main ingredient of the formula (sludge proportion greater than 50%), and fly ash and carbide slag are used as auxiliary ingredients of the formula. The materials are mixed thoroughly and evenly in a drum mixer or other mechanical mixing equipment at a mass ratio of 3:1:2 for 10 minutes.

[0048] (2) Using a shaftless screw, the uniformly mixed material is added to a twin-screw extruder and pressure-formed to obtain wet-based columnar particles with a certain strength, a diameter of 20 mm, and a length of 10 mm.

[0049] (3) Wet-based columnar granules are conveyed to the inlet of a low-temperature aerobic pyrolysis rotary reactor. At the reactor front end, the granules are preheated using waste heat from the tail gas (temperature set at 200℃, residence time 10min) to remove capillary water and attached water, further reducing the granule moisture content. The granules then enter the low-temperature aerobic pyrolysis section (temperature set at 350℃, residence time 30min), where the biomass is converted into biochar through aerobic pyrolysis via system heating and self-oxidation. Calcium carbonate is generated from the calcium carbide slag reacting with the ambient atmosphere (inlet air: industrial flue gas = 4:1) and carbon dioxide produced by pyrolysis, providing the granules with mechanical strength. Finally, the granules enter the instantaneous combustion section (temperature set at 900℃, residence time 15s) to remove liquid products generated during pyrolysis. The final product is a maintenance-free calcium-carbon-based biochar ceramsite with high mechanical strength, compressive strength: 72.1N; specific surface area: 16.2173m². 2 / g; Average pore size: 18.9255m 2 / g; Total pore volume: 0.060407cm³3 / g.

[0050] Comparative Example 1:

[0051] The method described in steps (1)-(5) of Example 2 of Chinese Patent CN 115477527 B is adopted:

[0052] (1) Add a small amount of lime to the dewatered cake of biomass waste with a moisture content of 80% and heat and stir it at 60°C for pretreatment.

[0053] (2) The pretreated material is placed in a plate and frame filter press to further reduce the moisture content of the material to 50% as the main material, accounting for 50%. Fly ash, phosphogypsum and lime are prepared in a mass ratio of about 8:1:1. Waste plastic residue is crushed to less than 2mm. The main and auxiliary materials are added to the intermittently running horizontal mixing tank by screw conveyor according to a mass ratio of 6%.

[0054] (3) The uniformly mixed material is fed into the inlet of the twin-screw extruder. The extruder die head is equipped with a 5mm perforated plate and an automatic scraper. The mixture is processed into wet-based columnar particles with a diameter of 5mm and a length of 5-10mm by pressure molding (moisture content 30-40%).

[0055] (4) The wet-based columnar particles are conveyed to the inlet of the horizontal rotary aerobic pyrolysis furnace via a belt conveyor. The wet-based columnar particles are heated to 150°C and the moisture content is reduced to 25% after passing through the waste heat tail gas preheating and drying section. Then they enter the low-temperature aerobic pyrolysis section, where the temperature is gradually raised to 250°C. The particles are slowly rotated and the residence time is 35 minutes. Finally, the particles enter the instantaneous combustion section. At 250-350°C, natural gas or other combustible gases are used as fuel and the particles are subjected to short-time combustion treatment using annular porous burner technology to burn off the liquid phase products. Finally, the dry-based particle products are discharged from the pyrolysis furnace outlet and are naturally cooled in the air-cooling section before entering the wet curing tank.

[0056] (5) The dry-based particles were humidified with water mist and the temperature was controlled at 50°C by electric heating in a wet curing tank for 5 days to obtain the environmentally friendly biochar ceramic particle product with a compressive strength of 14.63N, a BET specific surface area of ​​10.9021m2 / g, an average pore size of 7.3225nm (mainly mesopores), and a total pore volume of 0.027538cm3 / g.

[0057] The above description is merely a preferred embodiment of the present invention and does not constitute a limitation on the scope of protection of the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for co-producing calcium-carbon-based biochar ceramsite from sewage sludge and carbide slag, characterized in that, The method includes: (1) Mix sewage sludge, carbide slag and fly ash. The mass ratio of sewage sludge: fly ash: carbide slag is (3~4):(1~1.5):(1~2). (2) The above mixture is fed into a twin-screw extruder and pressure-formed into wet-based columnar granules with a moisture content of 40-50%; (3) The above-mentioned wet-based columnar particles are sent to a low-temperature aerobic pyrolysis rotary reactor; the wet-based columnar particles are preheated at the front end of the reactor using the waste heat of the tail gas at a temperature of 150~200℃ and a residence time of 5~10min to remove capillary water and attached water from the particles, thereby reducing the moisture content of the particles to 20~35%; in the low-temperature aerobic pyrolysis zone in the middle of the reactor, the temperature of the low-temperature aerobic pyrolysis is 300~350℃ and the residence time is 20~30min to remove the biological substances contained in the sewage sludge. The calcium carbide slag undergoes aerobic pyrolysis to form biochar. Simultaneously, the calcium carbide slag reacts with CO2 in the ambient atmosphere or CO2 generated during pyrolysis to produce calcium carbonate, which directly provides the mechanical strength of the particles. At the end of the reactor, the instantaneous combustion temperature is 800~1000℃, and the reaction lasts for 10~15s, with instantaneous combustion removing surface liquid phase products. Finally, maintenance-free calcium-carbon-based biochar ceramic particles with high mechanical strength are formed. The proportion of intake air and industrial flue gas added to the ambient atmosphere is determined based on the calcium carbide slag content and the oxygen demand of low-temperature aerobic pyrolysis.

2. The method for co-producing calcium-carbon-based biochar ceramsite from sewage sludge and carbide slag as described in claim 1, characterized in that, Step (1): The stirring time is 2~10 min.

3. The method for co-producing calcium-carbon-based biochar ceramsite from sewage sludge and carbide slag as described in claim 2, characterized in that, The sewage sludge needs to be dewatered first, and the water content of the sewage sludge after dewatering is less than 80%.

4. A method for co-producing calcium-carbon-based biochar ceramsite from sewage sludge and carbide slag as described in any one of claims 1-3, characterized in that, The wet-based columnar particles have a diameter of 3-20 mm and a length of 5-20 mm.

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