A method and system for in-situ co-processing of sludge and steel slag

Abstract

The application discloses a method for in-situ collaborative processing of sludge and steel slag, which comprises the following steps: mixing the steel slag and the sludge according to a certain proportion, then performing hot-press dewatering on the mixed materials, and recycling the separated water to a sewage treatment plant; transporting the dry materials after the hot-press dewatering to a steel plant for high-temperature pyrolysis, obtaining pyrolysis volatile matter and pyrolysis residue; cooling, screening and magnetic separation are performed on the pyrolysis residue, obtaining carbon-containing powder, steel slag tailings and iron-containing magnetic substances, which are recycled respectively, the pyrolysis volatile matter is directly incinerated to obtain high-temperature flue gas, the high-temperature flue gas is introduced into a pyrolyzer to provide a heat source for the material pyrolysis, the heat-exchanged flue gas is introduced into a secondary heat exchanger to release heat and generate steam, the steam is introduced into a steam pipe network of the steel plant, and the heat energy is utilized step by step. Through the collaborative processing of the sludge and the steel slag, the sludge disposal and utilization can be realized with low energy consumption, the iron element in the steel slag can be recycled by using the sludge, the harmless disposal and high-value utilization of the sludge and the steel slag can be realized, and the industrial application is easy.

Description

Technical Field

[0001] This invention belongs to the field of sludge and steel slag co-processing technology, specifically relating to a method and system for in-situ co-processing of sludge and steel slag. Background Technology

[0002] Sludge, a byproduct of wastewater treatment, presents a significant challenge due to its high water content, complex composition, and strong odor. Sludge dewatering is a prerequisite for its disposal and utilization. The water in sludge can be divided into four parts: interstitial water, capillary water, adsorbed water, and bound water. Mechanical dewatering and gravity thickening can only remove interstitial water and a small portion of capillary water; the majority of the remaining water is strongly bound to the sludge surface and is difficult to remove using a single mechanical method. Currently, methods for the harmless and resource-based disposal of sludge mainly include landfill, incineration, anaerobic digestion, and pyrolysis. Among these, pyrolysis, with its advantages of high efficiency, resource recovery, and low pollution, has become the technological development direction for the efficient resource utilization of sludge.

[0003] Steel slag, a solid waste generated during the iron and steel smelting process, accounts for 10%-15% of total steel production. Currently, the main use of steel slag in my country is in the production of 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, building materials made from it are prone to cracking. Steel slag contains large amounts of elements such as Fe, Mn, and Si. Among these, Fe mainly exists in the form of FeO and Fe2O3, accounting for approximately 20%-40%. It can be reduced to metallic iron at high temperatures, giving it certain economic value.

[0004] Chinese patent CN102557387A discloses a composite sludge flocculation and dewatering conditioner prepared from steel slag. This conditioner uses steel slag as the main raw material and fly ash as an auxiliary raw material, and is prepared by reacting the filtrate after hydrochloric acid treatment with the solution obtained after treating the filter residue with an alkaline solution. This composite sludge flocculation and dewatering conditioner can significantly reduce the specific resistance of sludge, making it easier to dewater. Chinese patent CN112159063A discloses a safe resource utilization process for sludge pyrolysis, which couples and integrates processes such as low-conductivity green conditioning of sludge, deep dewatering, low-temperature drying, sludge pyrolysis, energy utilization of pyrolysis gas, and utilization of sludge-based biochar, realizing the energy and material utilization of sludge. While the above methods can improve sludge dewatering and realize sludge resource utilization, the processes are complex and time-consuming, failing to meet actual industrial needs. Summary of the Invention

[0005] The purpose of this invention is to provide a method and system for in-situ co-processing of sludge and steel slag, which can deeply dewater the sludge and recover materials such as magnetite and metallic iron from the steel slag, thereby achieving high-value utilization of sludge and steel slag resources.

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

[0007] S1 Material Preparation: Mix sludge and steel slag to obtain a mixture;

[0008] S2 Input: Quantitatively input the mixture into the mold;

[0009] S3 Hot Press Dehydration: The mold containing the mixture is placed into the hot press, and the mixture is hot pressed to dehydrate it, resulting in dry material and dehydrated water;

[0010] S4 Demolding: Open the mold and remove the dry material from the mold;

[0011] S5 Dry Material Pyrolysis: Dry material is quantitatively fed into the pyrolyzer to obtain pyrolysis residue and pyrolysis volatiles;

[0012] S6 pyrolysis residue processing and utilization: The pyrolysis residue obtained from S5 is cooled, screened, and processed by iron selection to obtain carbon-containing powder, steel slag tailings and iron-containing magnetic materials.

[0013] S7 Pyrolysis Volatiles Processing and Utilization: The pyrolysis volatiles obtained from S5 are sent to a burner for combustion to generate high-temperature flue gas. The high-temperature flue gas is introduced into a pyrolyzer for heat exchange, providing energy for the pyrolysis of materials in the pyrolyzer. The flue gas after heat exchange is supplied to a secondary heat exchanger, which introduces water to generate steam, and the steam is then incorporated into the steam network of the steel plant.

[0014] S8 exhaust gas purification: The exhaust gas after secondary heat exchange in S7 is blown into the exhaust gas purifier, and steel slag powder is used as the exhaust gas purification agent to remove harmful components in the flue gas.

[0015] S9 Waste Heat Recovery: High-temperature pyrolysis residue is fed into a residue cooler for heat exchange to generate steam, which is then incorporated into the steam network of the steel plant.

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

[0017] As a further aspect of the present invention, the weight ratio of sludge to steel slag is: sludge: steel slag = 9:1 to 5:5.

[0018] As a further aspect of the present invention: the hot-press dehydration temperature is 90℃-130℃, the pressure is 1MPa-9MPa, and the dehydration time is 10min-60min.

[0019] As a further aspect of the present invention: the pyrolysis temperature of the dry material is 500℃-900℃, the pyrolysis time is 10min-60min, and the pyrolysis pressure is atmospheric pressure.

[0020] A system for in-situ co-processing of sludge and steel slag, capable of realizing the above-mentioned method for in-situ co-processing of sludge and steel slag, includes a mixer, a hot press, a dry material conveyor, a dry material buffer silo, a dry material top beam feeder, and a pyrolyzer connected in sequence. The mixer is connected to a sludge quantitative feeder and a steel slag quantitative feeder at its front end. The pyrolyzer is divided into three paths: one path is connected to a burner, the second path is connected in sequence to a residue cooler, a residue conveyor, and a screening machine, and the third path is connected in sequence to a secondary heat exchanger, a tail gas purifier, and an induced draft fan.

[0021] The steam generated by the secondary heat exchanger and the steam produced by the residue cooler are both connected to the steam 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 dewatering of sludge can not only effectively reduce the energy consumption of sludge drying, but also provide a reducing agent for the high-temperature reduction and recovery of metallic iron resources by steel slag, thus achieving low-energy disposal and efficient utilization of both.

[0024] 2) The sludge dewatering speed is fast, the energy consumption is low, the cost is low, the equipment system occupies a small area, and the investment is small;

[0025] 3) While improving the quality of sludge pyrolysis oil, this invention achieves the harmless and resource-based utilization of two types of solid waste, thus achieving the goals of environmental protection, waste resource utilization, and sustainable development. Therefore, this invention has obvious comprehensive advantages and is easy to industrially transform and apply. Attached Figure Description

[0026] Figure 1 This is a process flow diagram of the present invention;

[0027] Figure 2 The diagram shows the moisture content of the sludge under different steel slag additions in the examples.

[0028] Figure 3 The diagram shows the moisture content of the sludge under different pressures in the examples.

[0029] Figure 4 The diagram shows the moisture content of the sludge under different hot-pressing times in the examples.

[0030] Figure 5 The graph shows the moisture content of the sludge at different temperatures in the examples.

[0031] Figure 6 The diagram shows the moisture content of the sludge under different material quantities in the examples.

[0032] Figure 7 The XRD diffraction patterns of the pyrolysis residues at 500℃ corresponding to different steel slag dosages in the examples are shown.

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

[0034] The present invention will be further illustrated by the following examples.

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

[0036] S1 Material Preparation: Mix sludge and steel slag to obtain a mixture;

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

[0038] S2 Input: Quantitatively input the mixture into the mold;

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

[0040] S3 Hot Press Dehydration: The mold containing the mixture is placed into the hot press, and the mixture is hot pressed to dehydrate it, resulting in dry material and dehydrated water;

[0041] Specifically, the hot press using electric heating has a hot pressing dehydration temperature of 90℃-130℃, a pressure of 1MPa-9MPa, and a dehydration time of 10min-60min.

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

[0043] S5 Dry Material Pyrolysis: Dry material is quantitatively fed into the pyrolyzer to obtain pyrolysis residue and pyrolysis volatiles;

[0044] Specifically, the pyrolyzer using hot flue gas heating, under air-isolated conditions, has a pyrolysis temperature of 500℃-900℃ for dry materials, a pyrolysis time of 10min-60min, and a pyrolysis pressure of atmospheric pressure.

[0045] S6 pyrolysis residue processing and utilization: The pyrolysis residue obtained from S5 is cooled, screened, and processed by iron selection to obtain carbon-containing powder, steel slag tailings, and iron-containing magnetic materials; these are then sent to the corresponding finished product warehouses via corresponding product conveyors and iron selectors.

[0046] Carbon-containing powder can be used as a sintering raw material in steel production; iron-containing magnetic materials can be used to recover iron from steel slag in ironmaking and steelmaking; and steel slag tailings can be used as building materials.

[0047] S7 Pyrolysis Volatiles Processing and Utilization: The pyrolysis volatiles obtained from S5 are sent to a burner for combustion to generate high-temperature flue gas. The high-temperature flue gas is introduced into a pyrolyzer for heat exchange, providing energy for the pyrolysis of materials in the pyrolyzer. The flue gas after heat exchange is supplied to a secondary heat exchanger, which introduces water to generate steam. This steam is then incorporated into the steam network of the steel plant to achieve waste heat recovery and utilization.

[0048] S8 exhaust gas purification: The exhaust gas after secondary heat exchange in S7 is blown into the exhaust gas purifier, and steel slag powder is used as the exhaust gas purification agent to remove harmful components in the flue gas.

[0049] S9 Waste Heat Recovery: High-temperature pyrolysis residue is fed into a residue cooler for heat exchange to generate steam, which is then incorporated into the steel plant's steam network to achieve waste heat recovery and utilization.

[0050] A system for in-situ co-processing of sludge and steel slag, capable of realizing the above-mentioned method for in-situ co-processing of sludge and steel slag, includes a mixer, a hot press, a dry material conveyor, a dry material buffer silo, a dry material top beam feeder, and a pyrolyzer connected in sequence. The mixer is connected to a sludge quantitative feeder and a steel slag quantitative feeder at its front end. The pyrolyzer is divided into three paths: one path is connected to a burner, the second path is connected in sequence to a residue cooler, a residue conveyor, and a screening machine, and the third path is connected in sequence to a secondary heat exchanger, a tail gas purifier, and an induced draft fan.

[0051] The steam generated by the secondary heat exchanger and the steam produced by the residue cooler are both connected to the steam network of the steel plant.

[0052] The principle of this invention: Steel slag has good water absorption properties. 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, the mixture can easily squeeze out the water in the steel slag under pressure. Steel slag contains a large amount of free calcium oxide (f-CaO), 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 sludge and accelerate the release of bound water inside the sludge. Under the action of pressure and heat, the mixture can promote the reaction, thereby accelerating the sludge dewatering speed. Under the triple action of pressure, heat, and steel slag, deep dewatering of sludge is completed. Meanwhile, sludge contains abundant carbon and hydrogen elements, which can be used as a high-temperature reducing agent for iron oxide in steel slag. Under high-temperature pyrolysis conditions, magnetite and metallic iron in steel slag can be recovered. The main oxygen-containing functional groups in sludge pyrolysis oil are carboxyl, ketone and hydroxyl groups. 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 implementation method is as follows:

[0054] The original sludge came from a wastewater treatment plant in Jiangsu Province, with a moisture content of 80.61%. The steel slag came from a steel plant in Jiangsu Province, and the dried sludge was dewatered. In this invention, the steel slag content in the original sludge was 0%, 10%, 20%, 30%, 40%, and 50%; the hot-pressing temperature was set to 90℃-130℃, specifically 90℃, 100℃, 110℃, 120℃, and 130℃; the pressure was set to 1MPa-9MPa, specifically 1MPa, 3MPa, 5MPa, 7MPa, and 9MPa; the hot-pressed sludge mass was set to 400g-1200g, specifically 400g, 600g, 800g, 1000g, and 1200g; and the hot-pressing time was set to 10min-60min, specifically 10min, 20min, 30min, 40min, 50min, and 60min. In this invention, the steel slag content in the dry sludge is 0%-100%, specifically set to 0%, 10%, 30%, 50%, 70%, 90%, and 100%. The pyrolysis reactor used in this invention is a Φ80×1200mm corundum temperature-controlled reactor. The pyrolysis temperature is set to 500℃-900℃, specifically set to 500℃, 600℃, 700℃, 800℃, and 900℃; the pyrolysis time is set to 10min-60min, specifically set to 10min, 20min, 30min, 40min, and 60min; and the heating rate is 10℃ / min.

[0055] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments thereof.

[0056] Examples 1-23

[0057] Preheat the hot press to the set temperature and pre-set the required pressure. Mix a certain amount of sludge and steel slag according to a certain ratio, and stir with a disperser for 5 minutes. Place the mixed sludge and steel slag mixture in a mold and measure its material layer thickness. Then place the mold into the hot press and perform hot pressing dewatering for a certain time under a certain temperature and pressure. After the hot pressing dewatering is completed, remove the material from the mold and measure the thickness and moisture content of the filtered material. The specific conditions are listed in the table.

[0058] The water content of the sludge after hot pressing in Examples 1-23 was tested according to the industry standard "GJ / T 221-2005 Method for Testing Sludge from Urban Wastewater Treatment Plants", and the moisture content was calculated according to Equation ①. The results are shown in the figure. Figures 2 to 6 See Table 1.

[0059]

[0060] Examples 24-38

[0061] Dry sludge and steel slag were mixed in a certain proportion. 10g of the mixture was spread evenly in a quartz boat and placed in a pyrolysis vessel with a diameter of 80×1200mm. The nitrogen flow rate was set to 100mL / min. Nitrogen was purged for 30min before the experiment. Following the pyrolysis program, the temperature was increased from 50℃ to the set temperature at a rate of 10℃ / min and held at this temperature for a certain period. After the reaction, the condensable gas produced was cooled, dehydrated, and impurity-removed, and its composition was analyzed using gas chromatography-mass spectrometry. After the tubular furnace cooled, the gas flow was stopped. The pyrolysis residue was weighed and its mineral composition was analyzed using X-ray diffraction (XRD). Specific experimental conditions are listed in Table 2. The pyrolysis residues of Examples 24-34 were analyzed, and the results are shown in Table 2. Figures 7 to 8 And Table 3.

[0062] Table 1. Parameters and dewatering data of sludge and steel slag co-co-heat pressing in Examples 1-23

[0063]

[0064]

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

[0066] Table 2 Parameters for co-pyrolysis of sludge and steel slag in Examples 24-38

[0067]

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

[0069]

[0070]

[0071] Under the conditions of a dry sludge to steel slag mass ratio of 1:1, a heating rate of 10℃ / min, a pyrolysis temperature of 500℃, and a pyrolysis time of 60min, obvious magnetite was generated in the pyrolysis residue; under the condition that other conditions remained unchanged, at a pyrolysis temperature of 800℃, obvious metallic iron was generated in the pyrolysis residue, and the metallic iron content increased significantly as the pyrolysis temperature reached 900℃.

[0072] Under the conditions of a heating rate of 10℃ / min, a pyrolysis temperature of 500℃, and a pyrolysis time of 60min, 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%, thus improving the quality of the sludge pyrolysis oil.

[0073] The synergistic hot-pressing dewatering method for sludge and steel slag provided by this invention has better dewatering effect and shorter dewatering time than hot-pressing dewatering of sludge alone. The co-pyrolysis of dewatered sludge and steel slag results in higher added value and greater economic benefits than pyrolysis of sludge alone.

Claims

1. A method for in-situ co-processing of sludge and steel slag, characterized in that, Includes the following steps: S1 Material Preparation: Mix sludge and steel slag to obtain a mixture; S2 Input: Quantitatively input the mixture into the mold; S3 Hot Press Dehydration: The mold containing the mixture is placed into the hot press, and the mixture is hot pressed to dehydrate it, resulting in dry material and dehydrated water; S4 Demolding: Open the mold and remove the dry material from the mold; S5 Dry Material Pyrolysis: Dry material is quantitatively fed into the pyrolyzer to obtain pyrolysis residue and pyrolysis volatiles; S6 pyrolysis residue processing and utilization: The pyrolysis residue obtained from S5 is cooled, screened, and processed by iron selection to obtain carbon-containing powder, steel slag tailings and iron-containing magnetic materials. S7 Pyrolysis Volatiles Processing and Utilization: The pyrolysis volatiles obtained from S5 are sent to a burner for combustion to generate high-temperature flue gas. The high-temperature flue gas is introduced into a pyrolyzer for heat exchange, providing energy for the pyrolysis of materials in the pyrolyzer. The flue gas after heat exchange is supplied to a secondary heat exchanger, which introduces water to generate steam, and the steam is then incorporated into the steam network of the steel plant. S8 exhaust gas purification: The exhaust gas after secondary heat exchange in S7 is blown into the exhaust gas purifier, and steel slag powder is used as the exhaust gas purification agent to remove harmful components in the flue gas. S9 Waste Heat Recovery: High-temperature pyrolysis residue is fed into a residue cooler for heat exchange to generate steam, which is then incorporated into the steam network of the steel plant.

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

0.

3. A method for in-situ co-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 to 5 :

5.

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

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

6. A system for in-situ co-processing of sludge and steel slag, characterized in that, The method for in-situ co-processing of sludge and steel slag as described in any one of claims 1 to 5 includes a mixer, a hot press, a dry material conveyor, a dry material buffer silo, 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 is divided into three paths: one path is connected to a burner, the second path is connected in sequence to a residue cooler, a residue conveyor, and a screening machine, and the third path is connected in sequence to a secondary heat exchanger, a tail gas purifier, and an induced draft fan. The steam generated by the secondary heat exchanger and the steam produced by the residue cooler are both connected to the steam network of the steel plant.

Images