Method and system for in-situ synergistic processing of sludge and steel slag

Abstract

The invention discloses a sludge and steel slag in-situ synergistic processing method which comprises the following steps: mixing steel slag and sludge according to a certain proportion, then carrying out hot-pressing dehydration on the mixed material, and recycling dehydrated water to a sewage treatment plant; conveying the hot-pressed and dehydrated dry material to an iron and steel plant for high-temperature pyrolysis to obtain pyrolysis volatile components and pyrolysis residues; cooling, screening and magnetically separating pyrolysis residues to obtain carbon-containing powder, steel slag tailings and iron-containing magnetic substances, respectively recycling the carbon-containing powder, the steel slag tailings and the iron-containing magnetic substances, directly incinerating pyrolysis volatile components to obtain high-temperature flue gas, introducing the high-temperature flue gas into a pyrolyzer to provide a heat source for material pyrolysis, introducing the flue gas subjected to heat exchange into a secondary heat exchanger to release heat to generate steam, and recycling the steam; and the steam enters a steam pipe network of a steel plant to realize step-by-step utilization of heat energy. Through synergistic processing of the sludge and the steel slag, sludge treatment and utilization can be achieved with low energy consumption, iron elements in the steel slag can be recycled through the sludge, harmless treatment and high-value utilization of the sludge and the steel slag are achieved at the same time, and industrial application is easy.

Description

Technical Field

[0001] The present invention belongs to the technical field of sludge and steel slag co - treatment, and particularly relates to a method and system for in - situ co - processing of sludge and steel slag. Background Art

[0002] As a by - product of sewage treatment, sludge has become a difficult problem in the sludge treatment process due to its high water content, complex composition, and strong odor. Sludge dehydration is a prerequisite for sludge disposal and utilization. The water in sludge can be divided into four parts: interstitial water, capillary water, adsorbed water, and bound water. Generally, mechanical dehydration and gravity thickening dehydration can only remove interstitial water and a small part of capillary water in sludge, while most of the remaining water has a very strong binding force with the sludge surface and is difficult to remove by a single mechanical method. At present, the methods for harmless and resource - based disposal of sludge mainly include landfill, incineration, anaerobic digestion, and pyrolysis. Among them, due to the advantages of high efficiency, resource recovery, and low pollution of pyrolysis, it has become the technical development direction for the efficient resource utilization of sludge.

[0003] As a solid waste discharged during the iron and steel smelting process, steel slag accounts for 10% - 15% of the total steel output. At present, the main utilization way of steel slag in China is to produce building materials such as cement and concrete. However, due to the presence of unstable components such as free calcium oxide (f - CaO) in steel slag, the building materials made of steel slag will crack. Steel slag contains a large amount of elements such as Fe, Mn, and Si. Among them, the Fe element mainly exists in the forms of FeO and Fe2O3, accounting for about 20% - 40%. It can be reduced to metallic iron at high temperature and has certain economic value.

[0004] Chinese Patent CN102557387A discloses a composite sludge flocculation dehydration conditioner prepared from steel slag. The conditioner uses steel slag as the main raw material and fly ash as the auxiliary raw material, and is prepared by reacting the filtrate after hydrochloric acid treatment and the solution obtained by treating the filter residue with an alkaline solution. This composite sludge flocculation dehydration conditioner can significantly reduce the specific resistance of sludge and make the sludge easy to dehydrate; Chinese Patent CN112159063A discloses a process for the safe resource utilization of sludge pyrolysis, which couples and integrates processes such as low - conductivity green conditioning of sludge, deep dehydration, low - temperature drying, sludge pyrolysis, energy utilization of pyrolysis gas, and utilization of sludge - based biochar, realizing the energy utilization and material utilization of sludge. Although the above - mentioned methods can improve sludge dehydration and realize the resource utilization of sludge, they have complex processes and long cycles and cannot meet the actual industrial requirements. Summary of the Invention

[0005] The purpose of the present invention is to provide a method and system for in - situ co - processing of sludge and steel slag, which can deeply dehydrate sludge and at the same time recover materials such as magnetite and metallic iron in steel slag, and can realize the high - value utilization of sludge and steel slag resources.

[0006] To achieve the above object, the present invention provides a method for in-situ collaborative processing of sludge and steel slag, comprising the following steps:

[0007] S1 Preparation of materials: Mix sludge and steel slag to obtain a mixed material;

[0008] S2 Feeding into the mold: Quantitatively input the mixed material into the mold;

[0009] S3 Hot pressing and dehydration: Place the mold filled with the mixed material into a hot press to dehydrate the mixed material by hot pressing, obtaining dry material and dehydrated water;

[0010] S4 Demolding: Open the mold to remove the dry material in the mold;

[0011] S5 Pyrolysis of dry material: Quantitatively feed the dry material into a pyrolyzer to obtain pyrolysis residue and pyrolysis volatiles;

[0012] S6 Processing and utilization of pyrolysis residue: Cool, screen, and iron-select the pyrolysis residue obtained in S5 to obtain carbon-containing powder, steel slag tailings, and iron-containing magnetic substances;

[0013] S7 Processing and utilization of pyrolysis volatiles: Feed the pyrolysis volatiles obtained in S5 into a burner for incineration to generate high-temperature flue gas. The high-temperature flue gas is introduced into the pyrolyzer for heat exchange to provide energy for the pyrolysis of the material in the pyrolyzer. The flue gas after heat exchange is supplied to a secondary heat exchanger. The secondary heat exchanger introduces water to generate steam, and the steam is incorporated into the steam network of the steel plant;

[0014] S8 Tail gas purification: Blow the tail gas after secondary heat exchange in S7 into a tail gas purifier, and use steel slag powder as a tail gas purification agent to remove harmful components in the flue gas;

[0015] S9 Waste heat recovery: Input the high-temperature pyrolysis residue into a residue cooler for heat exchange to generate steam, and the steam is incorporated into the steam network of the steel plant.

[0016] As a further scheme of the present invention: The sludge is the primary dewatered sludge from a sewage treatment plant, with a moisture content of 60 - 85%, and the steel slag is the calcium-containing steel slag produced in steelmaking, with a particle size larger than 200 mesh and an alkalinity greater than 2.0.

[0017] As a further scheme of the present invention: The weight ratio of sludge to steel slag is: sludge∶steel slag = 9∶1 - 5∶5.

[0018] As a further scheme of the present invention: The temperature for hot pressing and dehydration is: 90°C - 130°C, the pressure is 1 MPa - 9 MPa, and the dehydration time is 10 min - 60 min.

[0019] As a further scheme of the present invention: The pyrolysis temperature of the dry material is 500°C - 900°C, the pyrolysis time is 10 min - 60 min, and the pyrolysis pressure is normal pressure.

[0020] A system for in-situ collaborative processing of sludge and steel slag, which can realize the above-mentioned method for in-situ collaborative processing of sludge and steel slag, includes a mixer, a hot press, a dry material conveyor, a dry material buffer bin, a dry material top beam feeder, and a pyrolyzer connected in sequence. The front end of the mixer is connected to a sludge metering feeder and a steel slag metering feeder. The pyrolyzer has three branches. One branch is connected to a burner, the second branch is connected to a residue cooler, a residue conveyor, and a screening machine in sequence, and the third branch is connected to a secondary heat exchanger, a tail gas purifier, and a draft fan in sequence;

[0021] The steam generated by the secondary heat exchanger and the steam produced by the residue cooler are both incorporated into the steam pipe network of the steel plant.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] 1) Using steel slag for deep hot pressing and dehydration of sludge can not only effectively reduce the energy consumption of sludge drying, but also the sludge can provide a reducing agent for the high-temperature reduction and recovery of metal iron resources from steel slag, realizing the low-energy disposal and efficient utilization of both;

[0024] 2) The sludge has a fast dehydration speed, low energy consumption, low cost, a small footprint of the equipment system, and low investment;

[0025] 3) While improving the quality of sludge pyrolysis oil, the harmless and resourceful utilization of two solid wastes is realized, achieving the purposes of environmental protection, waste resource utilization, and sustainable development. Therefore, the present invention has obvious comprehensive advantages and is easy to be industrially transformed and applied. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 is the process flow chart of the present invention;

[0027] Figure 2 is the moisture content diagram of sludge under different steel slag dosages in the embodiment;

[0028] Figure 3 is the moisture content diagram of sludge under different pressures in the embodiment;

[0029] Figure 4 is the moisture content diagram of sludge under different hot pressing times in the embodiment;

[0030] Figure 5 is the moisture content diagram of sludge under different temperatures in the embodiment;

[0031] Figure 6 is the moisture content diagram of sludge under different material amounts in the embodiment;

[0032] Figure 7 is the XRD diffraction pattern of the 500 °C pyrolysis residue corresponding to different steel slag dosages in the embodiment;

[0033] Figure 8 The XRD diffraction patterns of the pyrolysis residues with a steel slag content of 50% at different pyrolysis temperatures in the embodiment are shown. DETAILED DESCRIPTION

[0034] The present invention will be further described below by way of examples.

[0035] like Figure 1 As shown, a method for in-situ collaborative processing of sludge and steel slag comprises the following steps:

[0036] S1 material preparation: mixing sludge and steel slag to obtain a mixed material;

[0037] Specifically, the sludge is primary dewatered sludge from a sewage treatment plant, having a moisture content of 60-85%, and the steel slag is calcium-containing steel slag produced by steelmaking, having a particle size greater than 200 meshes and an alkalinity greater than 2.0;

[0038] S2: feeding the mixed material into the mold in a quantitative manner;

[0039] Specifically, the weight ratio of sludge to steel slag is: sludge: steel slag = 9:1 to 5:5;

[0040] S3 hot pressing and dehydration: placing the mold containing the mixed material into a hot press to perform hot pressing and dehydration on the mixed material to obtain dry material and remove water;

[0041] Specifically, a hot press machine with electric heating is used, the hot pressing dehydration temperature is: 90℃-130℃, the pressure is 1MPa-9MPa, and the dehydration time is 10min-60min;

[0042] S4 demoulding: open the mold and remove the dry material from the mold; S2-S4 cycle to produce dry material;

[0043] S5 dry material pyrolysis: the dry material is quantitatively fed into the pyrolyzer to obtain pyrolysis residue and pyrolysis volatile matter;

[0044] Specifically, the pyrolysis temperature of the dry material is 500-900°C, the pyrolysis time is 10-60 minutes, and the pyrolysis pressure is normal pressure under air-isolation conditions.

[0045] S6 pyrolysis residue processing and utilization: The pyrolysis residue obtained in S5 is cooled, screened, and iron-selected to obtain carbon-containing powder, steel slag tailings, and iron-containing magnetic materials; these are respectively delivered to the corresponding finished product bin via corresponding product conveyors and iron selectors;

[0046] Carbon powder can be used as sintering raw material for steel production, ferromagnetic materials can be used in iron and steel making to recover iron from slag, and slag tailings can be used as building materials;

[0047] Utilization of pyrolysis volatiles from S7: Feed the pyrolysis volatiles obtained from S5 into a burner for incineration to generate high-temperature flue gas. Introduce the high-temperature flue gas into the pyrolyzer for heat exchange to provide energy for the pyrolysis of materials in the pyrolyzer. The flue gas after heat exchange is supplied to a secondary heat exchanger. The secondary heat exchanger introduces water to generate steam, and this steam is incorporated into the steam pipe network of the steel plant to achieve waste heat recovery and utilization.

[0048] Tail gas purification in S8: Feed the tail gas after secondary heat exchange in S7 into a tail gas purifier, and use steel slag powder as a tail gas purification agent to remove harmful components in the flue gas.

[0049] Waste heat recovery in S9: Input the high-temperature pyrolysis residue into a residue cooler for heat exchange to generate steam, and this steam is incorporated into the steam pipe network of the steel plant to achieve waste heat recovery and utilization.

[0050] A system for in-situ collaborative processing of sludge and steel slag, which can implement the above method for in-situ collaborative processing of sludge and steel slag, includes a mixer, a hot press, a dry material conveyor, a dry material buffer bin, a dry material top beam feeder, and a pyrolyzer connected in sequence. The front end of the mixer is connected to a sludge metering feeder and a steel slag metering feeder. The pyrolyzer has three branches. One branch is connected to a burner, the second branch is connected to a residue cooler, a residue conveyor, and a screening machine in sequence, and the third branch is connected to a secondary heat exchanger, a tail gas purifier, and a draft fan in sequence.

[0051] The steam generated by the secondary heat exchanger accessing water and the steam produced by the residue cooler are both incorporated into the steam pipe network of the steel plant.

[0052] Principle of the present invention: Steel slag has good water absorption performance. During the mixing process of sludge and steel slag, the interstitial water, adsorbed water, and capillary water in the sludge can be absorbed into the steel slag. Due to the high permeability coefficient of steel slag, after the mixed material is subjected to pressure, it is easy to squeeze out the water in the steel slag. A large amount of free calcium oxide (f-CaO) is contained in the steel slag, which can react with the water in the sludge to form Ca(OH)2. At the same time, alkaline substances such as CaO and Ca(OH)2 have a significant cell wall breaking effect, which can destroy the structure of the sludge and accelerate the release of bound water inside the sludge. Under the action of pressure, heat, and steel slag, the reaction can be promoted, thereby accelerating the sludge dehydration speed. Under the triple action of pressure, heat, and steel slag, deep dehydration of the sludge is completed. At the same time, the sludge contains rich carbon and hydrogen elements, which can be used as high-temperature reducing agents for iron oxide in the steel slag. Under high-temperature pyrolysis conditions, magnetite and metallic iron in the steel slag can be recovered. The main oxygen-containing functional groups in the sludge pyrolysis oil are carboxyl, ketone, and hydroxyl groups, and the addition of steel slag promotes the decomposition of -COOH, -C=O, and -OH, thereby reducing the oxygen content. The decomposition of oxygen-containing compounds can be attributed to the adsorption of H2 by the active sites of steel slag and the activation of oxygen-containing functional groups.

[0053] The specific embodiments are as follows:

[0054] The source of the raw sludge is a sewage treatment plant in Jiangsu, with a sludge moisture content of 80.61%. The steel slag comes from a steel plant in Jiangsu, and the dry sludge is the dehydrated sludge. In the present invention, the dosage of steel slag in the raw sludge is 0%, 10%, 20%, 30%, 40%, 50%; the hot pressing temperature is set at 90°C - 130°C, specifically 90°C, 100°C, 110°C, 120°C, 130°C; the pressure is set at 1MPa - 9MPa, specifically 1MPa, 3MPa, 5MPa, 7MPa, 9Mpa; the mass of the hot-pressed sludge is set at 400g - 1200g, specifically 400g, 600g, 800g, 1000g, 1200g; the hot pressing time is set at 10min - 60min, specifically 10min, 20min, 30min, 40min, 50min, 60min. In the present invention, the dosage of steel slag in the dry sludge is 0% - 100%, specifically 0%, 10%, 30%, 50%, 70%, 90%, 100%. In the present invention, the pyrolyzer used is a corundum temperature-controlled reactor with a size of Φ80×1200mm, the pyrolysis temperature is set at 500°C - 900°C, specifically 500°C, 600°C, 700°C, 800°C, 900°C; the pyrolysis time is set at 10min - 60min, specifically 10min, 20min, 30min, 40min, 60min; the heating rate is 10°C / min.

[0055] Next, the technical solutions in the present invention will be clearly and completely described in conjunction with the embodiments in the present invention.

[0056] Examples 1 - 23

[0057] Preheat the hot press to the set temperature in advance and set the required pressure in advance. Mix a certain amount of sludge and steel slag according to a certain ratio, stir with a disperser for 5 minutes, place the mixed sludge-steel slag mixture in a mold, and measure its layer thickness; then place the mold in the hot press and perform hot pressing dehydration for a certain time at a certain temperature and pressure. After the hot pressing dehydration is completed, take out the material in the mold and measure the thickness and moisture content of the filtered material. The specific conditions are listed in the table.

[0058] Detect the water content of the sludge after hot pressing in Examples 1 - 23 according to the industry standard "GJ / T 221-2005 Test Methods for Sludge in Urban Sewage Treatment Plants", and calculate the moisture content according to Equation ①. The results are shown in Figures 2 to 6 and Table 1.

[0059]

[0060] Examples 24 - 38

[0061] Mix dry sludge and steel slag in a certain proportion. Weigh 10 g of the mixed material and spread it evenly in a quartz boat. Place it in a pyrolyzer with a size of Φ80×1200 mm. Set the nitrogen flow rate to 100 mL / min. Before the experiment, pass nitrogen for 30 min in advance. According to the pyrolysis program, heat from 50 °C to the set temperature at a heating rate of 10 °C / min and keep it constant at this temperature for a certain time. After the reaction, the condensable gas generated is cooled, dehydrated, and purified, and then analyzed for its composition using a gas chromatography-mass spectrometry instrument. Stop passing gas after the tubular furnace cools down. Weigh the pyrolysis residue and analyze its mineral composition using an X-ray diffractometer (XRD). The specific experimental conditions are listed in Table 2. Analyze the pyrolysis residues of Examples 24 - 34, and the results are shown in Figures 7 to 8 and Table 3.

[0062] Table 1 Co - hot pressing parameters and dehydration data of sludge and steel slag in Examples 1 - 23

[0063]

[0064]

[0065] Under the conditions of a steel slag content of 30%, a sludge mass of 800 g, a pressure of 9 MPa, a hot pressing time of 60 min, and a temperature of 130 °C, the moisture content of the sludge can be reduced to less than 9%.

[0066] Table 2 Co - pyrolysis parameters of sludge and steel slag in Examples 24 - 38

[0067]

[0068] Table 3 Mineral composition and semi - quantitative analysis of pyrolysis residues in Examples 24 - 34

[0069]

[0070]

[0071] Under the conditions of a mass ratio of dry sludge to steel slag of 1:1, a heating rate of 10 °C / min, a pyrolysis temperature of 500 °C, and a pyrolysis time of 60 min, obvious magnetite is generated in the pyrolysis residue; under the condition that the rest remains unchanged and the pyrolysis temperature is 800 °C, obvious metallic iron is produced in the pyrolysis residue, and as the pyrolysis temperature reaches 900 °C, the content of metallic iron increases significantly.

[0072] Under the conditions of a heating rate of 10 °C / min, a pyrolysis temperature of 500 °C, and a pyrolysis time of 60 min, as the mass ratio of dry sludge to steel slag increased from 1:0 to 1:1, the alkane content in the pyrolysis oil increased from 4.13% to 24.63%, the olefin content increased from 5.16% to 21.64%, and the oxygenated compound content decreased from 30.29% to 12.69%, improving the quality of the sludge pyrolysis oil.

[0073] Using the sludge and steel slag co-thermal pressing dehydration method provided by the present invention has better dehydration effect and less dehydration time than the sludge single thermal pressing dehydration. Using the dehydrated sludge and steel slag for co-pyrolysis has higher added value and better economic benefits than the sludge single pyrolysis product.

Claims

1. A method for in-situ collaborative processing of sludge and steel slag, characterized in that, It includes the following steps: S1 Stock preparation: Mix sludge and steel slag to obtain a mixed material; S2 Molding: Quantitatively input the mixed material into a mold; S3 Hot press dehydration: Place the mold filled with the mixed material into a hot press to dehydrate the mixed material by hot pressing, obtaining dry material and dehydrated water; S4 Demolding: Open the mold and remove the dry material from the mold; S5 Pyrolysis of dry material: Quantitatively feed the dry material into a pyrolyzer to obtain pyrolysis residue and pyrolysis volatiles; S6 Processing and utilization of pyrolysis residue: Cool, screen, and iron-select the pyrolysis residue obtained in S5 to obtain carbon-containing powder, steel slag tailings, and iron-containing magnetic substances; S7 Processing and utilization of pyrolysis volatiles: Send the pyrolysis volatiles obtained in S5 into a burner for incineration to generate high-temperature flue gas. The high-temperature flue gas is introduced into the pyrolyzer for heat exchange to provide energy for the pyrolysis of the material in the pyrolyzer. The flue gas after heat exchange is supplied to a secondary heat exchanger. The secondary heat exchanger introduces water to generate steam, and this steam is incorporated into the steam network of the steel plant; S8 Tail gas purification: Blow the tail gas after secondary heat exchange in S7 into a tail gas purifier, and use steel slag powder as a tail gas purification agent to remove harmful components from the flue gas; S9 Waste heat recovery: Input the high-temperature pyrolysis residue into a residue cooler for heat exchange to generate steam, and this steam is incorporated into the steam network of the steel plant.

2. The method for in-situ collaborative processing of sludge and steel slag according to claim 1, characterized in that The sludge is the primary dewatered sludge from a sewage treatment plant, with a moisture content of 60%-85%. The steel slag is calcium-containing steel slag produced in steelmaking, with a particle size larger than 200 mesh and an alkalinity greater than 2.

0.

3. A method for in-situ collaborative processing of sludge and steel slag according to claim 1 or 2, characterized in that, The weight ratio of sludge to steel slag is: sludge∶steel slag = 9∶1 - 5∶5.

4. A method for in-situ collaborative processing of sludge and steel slag according to claim 3, characterized in that The hot press dehydration temperature is: 90°C - 130°C, the pressure is 1 MPa - 9 MPa, and the dehydration time is 10 min - 60 min.

5. A method for in-situ collaborative processing of sludge and steel slag according to claim 3, characterized in that, The pyrolysis temperature of the dry material is 500°C - 900°C, the pyrolysis time is 10 min - 60 min, and the pyrolysis pressure is normal pressure.

6. A system for in-situ collaborative processing of sludge and steel slag, characterized in that, A method capable of realizing the in-situ collaborative processing of sludge and steel slag as described in any one of claims 1 to 5, including a mixer, a hot press, a dry material conveyor, a dry material buffer bin, a dry material top beam feeder, and a pyrolyzer connected in sequence. The front end of the mixer is connected to a sludge quantitative feeder and a steel slag quantitative feeder. The pyrolyzer has three branches. One branch is connected to a burner, the second branch is connected to a residue cooler, a residue conveyor, and a screening machine in sequence, and the third branch is connected to a secondary heat exchanger, a tail gas purifier, and an induced draft fan in sequence; The steam generated by the secondary heat exchanger accessing water and the steam produced by the residue cooler are both incorporated into the steam network of the steel plant.

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