Microwave treatment and utilization method for cold-rolled acid regeneration and impurity removal sludge

Abstract

This invention discloses a microwave-based method for the treatment and utilization of cold-rolled acid regeneration sludge. The sludge is crushed and then roasted in a microwave kiln. The roasted iron-containing material is further sintered for utilization. The corrosive chlorine-containing gas generated during roasting is transported to an acid regeneration chlorine-containing gas treatment and utilization system to obtain hydrochloric acid. The exhaust gas generated by the acid regeneration chlorine-containing gas treatment and utilization system meets emission standards. This invention uses green electricity for microwave roasting of cold-rolled acid regeneration sludge, eliminating the need for water washing, reducing waste disposal volume, eliminating the use of fuel gas, and preventing additional waste during the treatment process, thus reducing pollutant emissions. The green electricity-driven equipment does not occupy carbon emission limits. Microwave heating is uniform, resulting in better dechlorination under the same roasting temperature conditions. Under the same dechlorination effect conditions, the roasting temperature is lower, reducing energy consumption and carbon emissions. The amount of flue gas generated during heating is small, the proportion of chlorine-containing gas is high, and the concentration of hydrochloric acid obtained in one step is high, reducing energy consumption in the acid production process.

Description

Technical Field

[0001] This invention belongs to the field of waste utilization technology, specifically relating to a microwave method for the treatment and utilization of cold-rolled acid regeneration and impurity removal sludge. Background Technology

[0002] The wastewater generated from the pickling of steel strips in the cold rolling mill of steel enterprises has a pH <3. Its main component is FeCl2, with small amounts of FeCl3, HCl, and trace amounts of SiO2. Recycling this wastewater using a spray roasting process requires impurity removal. This removal involves forming Fe(OH)3 in the wastewater to adsorb impurities, followed by solid-liquid separation via pressure filtration. The purified liquid produced during separation is roasted to obtain high-purity Fe2O3, which is sold at a high price. The chlorine-containing gas generated during roasting is treated by pre-concentration towers, absorption towers, and washing towers to become HCl concentrate, which is then returned to the steel strip for pickling and reuse. The exhaust gas meets emission standards. The sludge produced during separation has high water and chlorine content and is highly corrosive, requiring special treatment. Currently, the main disposal method is landfill. The sludge's main components are Fe(OH)3, FeO(OH), and small amounts of FeCl3 and trace amounts of FeCl2 and SiO2. Landfill disposal not only wastes the iron resources, the main component of the sludge, but also occupies limited land resources.

[0003] Most raw materials used in ironmaking in steel enterprises contain chlorine. The sintering process in smelting reaches a maximum temperature of around 1350℃, providing excellent dechlorination capabilities and removing approximately 90% of the chlorine from the raw materials. Therefore, some enterprises utilize the high-temperature dechlorination effect of sintering and their comprehensive environmental protection facilities to directly recycle acid-regenerated sludge back to sintering for disposal. However, acid-regenerated sludge is highly corrosive, and direct recycling to sintering causes severe corrosion to equipment entering the sintering process. Furthermore, acid-regenerated sludge cannot be dried at a low temperature of ≤315℃ like ordinary sludge because it contains highly hygroscopic FeCl3. After drying, it easily absorbs moisture and deliquesces upon exposure to air, clogging equipment and affecting its application in sintering.

[0004] Application No. 200810024330.9 describes a device and method for treating desilication filter cake from pickled iron oxide. The invention involves feeding filter cake into a burner on a roasting tower via a feeder. The filter cake falls from the top of the tower and is roasted, heated, dried, and decomposed using fuel gas to generate iron oxide powder. The gas is then absorbed by pure water spray and returned to the pickling process for reuse. However, this invention only describes the functions of each component in the device and method for treating desilication filter cake from pickled iron oxide, lacking specific operational parameters for achieving these functions, and therefore cannot guarantee the effectiveness of the harmless treatment.

[0005] Application No. 202010568356.0 describes a method for treating desilication sludge from cold-rolled acid regeneration. The method involves washing the desilication sludge with water at a water-to-solid ratio of 5–12:1 for 30–60 minutes using agitation, followed by high-pressure dehydration, and then dechlorination by gas-fired roasting at 300–450°C for 30–60 minutes. The roasted residue is used in metallurgical processes, and the flue gas is cooled, deacidified, and purified before being discharged. The resulting dilute acid solution is reused. However, this method has several drawbacks. First, the amount of filtrate after washing increases by approximately 5–12 times. This acidic filtrate is classified as hazardous waste, significantly increasing the amount of hazardous waste generated. Second, to ensure dechlorination effectiveness, this method relies on prolonged high-temperature roasting with gas, which consumes energy and increases pollutant emissions.

[0006] Acid regeneration sludge has high viscosity and becomes dense after filtration. Roasting heating relies on heat conduction from the sludge surface to the interior, easily leading to a "cold core" phenomenon where the outside of the sludge reaches the heating temperature while the inside does not. Current research on roasting dechlorination technology for removing corrosive substances involves gas-fired roasting or electric heating. Due to decreasing heat conduction, the temperature and reaction rate gradually decrease as the sludge penetrates the interior, resulting in uneven heating and affecting the effectiveness. To improve efficiency, gas-fired or electric heating inevitably requires increasing the temperature or extending the roasting time, increasing energy consumption and pollutant emissions. Furthermore, gas-fired roasting generates a large amount of CO2-containing flue gas, which consumes limited corporate carbon emission allowances, restricting the application of gas-fired roasting dechlorination technology in the treatment and utilization of acid regeneration sludge. Summary of the Invention

[0007] The purpose of this invention is to solve the above-mentioned technical problems and provide a microwave method for the treatment and utilization of cold-rolled acid regeneration sludge that can reduce pollution and carbon emissions. This method solves the technical defects of traditional heating methods that rely on increasing temperature or extending roasting time to remove the corrosiveness of sludge, which increases energy consumption and pollutant emissions.

[0008] To achieve the above objectives, this invention provides a microwave-based method for the treatment and utilization of cold-rolled acid regeneration sludge. The cold-rolled acid regeneration sludge is crushed and then roasted in a microwave kiln. The roasted iron-containing material is further sintered for utilization. The corrosive chlorine-containing gas generated during roasting is transported to an acid regeneration chlorine-containing gas treatment and utilization system to obtain hydrochloric acid. The tail gas generated by the acid regeneration chlorine-containing gas treatment and utilization system meets emission standards. The acid regeneration chlorine-containing gas treatment and utilization system is an existing process at the source of acid regeneration sludge production. The main equipment includes a pre-concentration tower, an absorption tower, and a scrubbing tower. Its main purpose is to absorb chlorine-containing gas from the gas through a liquid and concentrate the liquid to increase the HCl content, enabling the liquid to be directly used for acid washing while ensuring that the tail gas meets emission standards.

[0009] The main reaction principle of the roasting process:

[0010] 2Fe(OH)3 (s)=Fe2O3 (s)+3H2O (g)

[0011] 2FeOOH(s)=Fe2O3(s)+H2O(g)

[0012] FeCl3·6H2O(s)=FeCl3(s)+6H2O(g)

[0013] 2FeCl3(s)+3H2O(g)=Fe2O3(s)+6HCl(g)

[0014] Furthermore, the hydrochloric acid obtained from the acid regeneration chlorine-containing gas treatment and utilization system is transported to the pickling process of steel; the waste liquid obtained from the pickling process is crushed after the cold rolling acid regeneration impurity removal sludge produced by the impurity removal and separation process is fed into a microwave kiln; the pure liquid produced by the impurity removal and separation process is roasted in a roasting furnace to obtain high-purity Fe2O3; the chlorine-containing gas produced after roasting is transported to the acid regeneration chlorine-containing gas treatment and utilization system.

[0015] Furthermore, the cold-rolled acid regeneration sludge has a moisture content of 40-60%, and the dry sludge has an iron content of 42-50% and a chlorine content of 7-31%.

[0016] Furthermore, the particle size of the cold-rolled acid regeneration sludge after crushing is less than 25 mm.

[0017] Furthermore, the width of the microwave kiln tube is 50–100 cm.

[0018] Furthermore, the microwave heating temperature of the microwave kiln is 315–400℃, and the heating time is 6–10 minutes. Since the decomposition temperature of FeCl3 is 315℃, drying at temperatures below 315℃ will cause it to absorb moisture and deliquesce upon exposure to air due to its highly hygroscopic FeCl3 content, clogging the equipment and affecting its application in sintering. Therefore, the microwave heating temperature cannot be lower than 315℃.

[0019] Furthermore, the microwave heating system of the microwave kiln is distributed perpendicularly to the kiln tube, and the microwaves generated by heating pass perpendicularly through the kiln tube.

[0020] Furthermore, the microwave kiln body is made of 316L stainless steel, with the inner wall coated with polytetrafluoroethylene; the microwave kiln tube is made of microwave-specific silicon carbide ceramic material, and the insulation system is made of ceramic fiber material; the main shaft and blades of the transmission system are made of stainless steel with a glazed surface.

[0021] Furthermore, the cold-rolled acid regeneration sludge is fed into the crushing conveyor via a hopper, and the steel surface of the hopper in contact with the cold-rolled acid regeneration sludge is covered with a fiberglass layer; the crushing conveyor is a double-screw conveyor made of 316L grade or higher corrosion-resistant stainless steel, and polytetrafluoroethylene is sprayed onto the surface of the material in contact with the cold-rolled acid regeneration sludge.

[0022] Furthermore, the iron-containing material is cooled to ≤30°C and then transported to the raw material plant, where it is mixed with other raw materials and sintered in a blast furnace for ironmaking. The calcined iron-containing material contains ≥55% TFe.

[0023] Compared with existing technologies, the beneficial effects of this invention are as follows: This invention uses green electric microwave roasting of cold-rolled acid regeneration sludge to remove impurities, without water washing, thus not increasing the amount of waste to be disposed of, without using gas, and without generating additional waste during the disposal process, reducing pollutant emissions. The green electric driven equipment does not occupy carbon emission quotas. Microwave heating is uniform, and under the same roasting temperature conditions, the dechlorination effect is better. Under the same dechlorination effect conditions, the roasting temperature is lower, reducing energy consumption and carbon emissions. The amount of flue gas generated by heating is small, the proportion of chlorine gas is high, and the concentration of hydrochloric acid obtained in one go is high, reducing the energy consumption of the acid production process. The iron-containing material generated by roasting is sintered and utilized, reducing the amount of sintered iron ore used, and the utilization process does not cause corrosion to the equipment. It solves the technical defects of traditional heating methods that rely on increasing the temperature or extending the roasting time to remove the corrosiveness of sludge, which increases energy consumption and pollutant emissions. Attached Figure Description

[0024] Figure 1 This is a flowchart of the microwave method for treating and utilizing cold-rolled acid regeneration and impurity removal sludge according to the present invention. Detailed Implementation

[0025] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0026] Example 1

[0027] Start the microwave kiln, hopper, and crushing conveyor. Set the microwave kiln temperature to 330℃ and the holding time to 10 minutes. The dry basis sludge from the cold-rolled acid regeneration sludge contains 42.3% iron and 23.8% chloride. The sludge is fed through the hopper into the operating crushing conveyor and crushed to a particle size of less than 25mm before being conveyed into the microwave kiln. The distributor inside the microwave kiln evenly distributes the sludge to a layer thickness of 40cm. Heating generates 98 Nm³ of flue gas. 3 The gas is discharged at a rate of / h to the acid regeneration chlorine-containing gas treatment and utilization system for treatment and utilization. Heating automatically stops after reaching the set conditions, and the discharge system starts. The resulting material has an iron content of 56.6% and a Cl content of 0.8%. After cooling to 28°C, the iron-containing material is transported to the raw material plant and uniformly mixed with other sintering raw materials for sintering utilization.

[0028] The hydrochloric acid obtained from the acid regeneration chlorine-containing gas treatment and utilization system is transported to the steel pickling process; the waste liquid obtained from the pickling process is crushed after the cold rolling acid regeneration impurity removal sludge produced by the impurity removal and separation process is fed into a microwave kiln; the pure liquid produced by the impurity removal and separation process is roasted in a roasting furnace to obtain high-purity Fe2O3; the chlorine-containing gas produced after roasting is transported to the acid regeneration chlorine-containing gas treatment and utilization system.

[0029] In this embodiment, the width of the microwave kiln tube is 50-100cm, and the microwave heating system of the microwave kiln is vertically distributed with the kiln tube; the kiln body is made of 316L stainless steel, and the inner wall is coated with polytetrafluoroethylene; the kiln tube is made of microwave-specific silicon carbide ceramic material, and the insulation system is made of ceramic fiber material; the main shaft and blades of the transmission system are made of stainless steel with a glazed surface. The steel surface of the hopper in contact with the cold-rolled acid regeneration sludge is covered with a fiberglass layer; the crushing conveyor is a double-screw conveyor made of 316L grade or higher corrosion-resistant stainless steel, and the surface of the material in contact with the cold-rolled acid regeneration sludge is coated with polytetrafluoroethylene.

[0030] Example 2

[0031] The difference between Example 2 and Example 1 is that:

[0032] Start the microwave kiln, hopper, and crushing conveyor. Set the microwave kiln temperature to 360℃ and the holding time to 8 minutes. The dry basis sludge from the cold-rolled acid regeneration sludge contains 43.5% iron and 22.6% chloride. The sludge is fed through the hopper into the operating crushing conveyor and crushed to a particle size of less than 25mm before being conveyed into the microwave kiln. The distributor inside the microwave kiln evenly distributes the sludge to a layer thickness of 60cm. Heating generates 99 Nm of flue gas. 3 The gas is discharged at a rate of / h to the acid regeneration chlorine-containing gas treatment and utilization system for treatment and utilization. Heating automatically stops after reaching the set conditions, and the discharge system starts. The resulting material has an iron content of 59.4% and a Cl content of 0.4%. After cooling to 28°C, the iron-containing material is transported to the raw material plant and uniformly mixed with other sintering raw materials for sintering utilization.

[0033] Example 3

[0034] The difference between Example 3 and Example 1 is that:

[0035] Start the microwave kiln, hopper, and crushing conveyor. Set the microwave kiln temperature to 400℃ and the holding time to 8 minutes. The dry basis sludge from the cold-rolled acid regeneration sludge contains 46.3% iron and 26.5% chloride. The sludge is fed through the hopper into the operating crushing conveyor and crushed to a particle size of less than 25mm before being conveyed into the microwave kiln. The distributor inside the microwave kiln evenly distributes the sludge to a layer thickness of 40cm. Heating generates 100Nm of flue gas. 3 The gas is discharged at a rate of / h to the acid regeneration chlorine-containing gas treatment and utilization system for treatment and utilization. Heating automatically stops after reaching the set conditions, and the discharge system is started. The resulting material has an iron content of 63.2% and a Cl content of 0.1%. After cooling to 30°C, the iron-containing material is transported to the raw material plant and uniformly mixed with other sintering raw materials for sintering utilization.

[0036] Comparative Example 1

[0037] 1) Start the gas-fired roasting furnace, feeding system, crushing system and supporting equipment, set the temperature to 330℃ and the holding time to 20min;

[0038] 2) The acid regeneration and impurity removal sludge contains 42.3% TFe and 23.8% Cl. Place the hopper containing the acid regeneration and impurity removal sludge into the turner, start the turner, and the sludge will be turned and fed into the running double screw conveyor and transported into the calcination furnace.

[0039] 3) Evenly distribute the material in the roasting furnace until the material layer thickness is 40cm;

[0040] 4) Start the heating and exhaust systems of the roasting furnace. Heating produces 1426 Nm³ of flue gas. 3 / h, discharged to the acid regeneration chlorine-containing gas treatment and utilization system for treatment and utilization;

[0041] 5) Heating will automatically stop after the set conditions are reached, and the material will be discharged. The resulting material has an iron content of 52.8% TFe and a Cl content of 6.1%. After cooling to 28°C, the material will be discharged to a transport vehicle.

[0042] 6) Transport to the raw material plant and mix evenly with other sintering raw materials for sintering utilization.

[0043] Comparative Example 2

[0044] 1) Start the electric heating roasting furnace, feeding system, crushing system and supporting equipment, set the temperature to 330℃ and the holding time to 30min;

[0045] 2) The acid regeneration and impurity removal sludge contains 42.3% TFe and 23.8% Cl. Place the hopper containing the acid regeneration and impurity removal sludge into the turning machine, start the turning machine, and turn the sludge into the running double screw conveyor, which will then transport it into the electric heating calcining furnace.

[0046] 3) Evenly distribute the material in the electric heating roasting furnace until the material layer thickness is 40cm;

[0047] 4) Start the heating system and exhaust system of the electric heating roasting furnace. Heating produces 216 Nm³ of flue gas. 3 / h, discharged to the acid regeneration chlorine-containing gas treatment and utilization system for treatment and utilization;

[0048] 5) Heating will automatically stop after the set conditions are reached, and the material will be discharged. The resulting material has an iron content of 52.2% TFe and a Cl content of 6.8%. After cooling to 28°C, the material will be discharged to the transport vehicle.

[0049] 6) Transport to the raw material plant and mix evenly with other sintering raw materials for sintering utilization.

[0050] Partial experimental data of pickling filter cake

[0051]

Claims

1. A microwave method for treating and utilizing cold-rolled acid regeneration sludge, characterized in that: After being crushed, the cold-rolled acid regeneration sludge is roasted in a microwave kiln. The iron-containing material after roasting is further sintered and utilized. The corrosive chlorine-containing gas generated during roasting is transported to the acid regeneration chlorine-containing gas treatment and utilization system to obtain hydrochloric acid. The exhaust gas generated by the acid regeneration chlorine-containing gas treatment and utilization system meets emission standards. The cold-rolled acid regeneration sludge is not washed with water and has a water content of 40-60%. The dry sludge has an iron content of 42-50% and a chlorine content of 7-31%. The particle size of the cold-rolled acid regeneration sludge after crushing is less than 25mm. The microwave heating system of the microwave kiln is vertically distributed with the kiln tube, and the microwave heating temperature of the microwave kiln is 315~400℃ and the heating time is 6~10min.

2. The microwave method for treating and utilizing cold-rolled acid regeneration sludge according to claim 1, characterized in that: The hydrochloric acid obtained by the acid regeneration chlorine-containing gas treatment and utilization system is transported to the steel pickling process; the waste liquid obtained from the pickling process is crushed after the cold rolling acid regeneration impurity removal sludge produced by the impurity removal and separation is put into a microwave kiln; the pure liquid produced by the impurity removal and separation of the waste liquid is roasted in a roasting furnace to obtain high-purity Fe2O3; the chlorine-containing gas produced after roasting is transported to the acid regeneration chlorine-containing gas treatment and utilization system.

3. The microwave method for treating and utilizing cold-rolled acid regeneration sludge according to claim 1, characterized in that: The width of the microwave kiln tube is 50~100cm.

4. The microwave method for treating and utilizing cold-rolled acid regeneration sludge according to claim 1, characterized in that: The microwave kiln body is made of 316L stainless steel with polytetrafluoroethylene coating on the inner wall; the microwave kiln tube is made of microwave-specific silicon carbide ceramic material, and the insulation system is made of ceramic fiber material; the main shaft and blades of the transmission system are made of stainless steel with glaze coating.

5. The microwave method for treating and utilizing cold-rolled acid regeneration sludge according to claim 1, characterized in that: The cold-rolled acid regeneration sludge is fed into the crushing conveyor via a hopper. The steel surface of the hopper in contact with the cold-rolled acid regeneration sludge is covered with a fiberglass layer. The crushing conveyor is a double-screw conveyor made of 316L grade or higher corrosion-resistant stainless steel, and polytetrafluoroethylene is sprayed onto the surface of the material in contact with the cold-rolled acid regeneration sludge.

6. The microwave method for treating and utilizing cold-rolled acid regeneration sludge according to claim 1, characterized in that: After the iron-containing material is cooled to ≤30℃, it is transported to the raw material plant, mixed with other raw materials, and then sintered in the blast furnace for ironmaking. The iron-containing material after roasting has a TFe ≥55%.

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