Chemical-electrochemical coupled water pretreatment process for waste heat recovery of blast furnace slag flushing water

Abstract

The invention relates to the technical field of industrial water treatment, and discloses a chemical-electrochemical coupled water pretreatment process for waste heat recovery of blast furnace slag flushing water. The method comprises three steps of chemical treatment, electric flocculation and electrochemical water softening. The method comprises the following steps: firstly, adding an agent into the slag washing water for chemical water softening, and enabling the softened slag washing water to enter an inclined plate precipitation tank for solid-liquid separation; the supernate is introduced into an electric flocculation water softening unit, scale forming components are removed under the action of an aluminum anode and a stainless steel cathode, and softened slag flushing water is obtained; and finally, the softened slag flushing water is introduced into an electrochemical water softening unit, and the water quality finally reaches a stable index under the action of a DSA anode and a stainless steel cathode. Different from an existing technical route of adding the medicament or optimizing the heat exchanger, the method has the advantages that the treatment effect and the medicament input cost can be considered at the same time, the problems of scaling and blockage of the heat exchanger are effectively solved, long-period stable operation of the conventional heat exchanger is realized, and the method has important practical application value.

Description

Technical Field

[0001] This invention relates to the field of water treatment technology, specifically to a water pretreatment process for waste heat recovery from blast furnace slag flushing water. Background Technology

[0002] The temperature of blast furnace slag flushing water is typically 70-85℃, making it a low-temperature industrial waste heat source with potential for waste heat recovery. However, its high hardness and suspended solids content make it highly susceptible to scaling and clogging on heat exchanger surfaces during waste heat recovery. A certain thickness of scale can form quickly during slag flushing water heat exchange. When the scale thickness on the tube wall reaches approximately 0.5 mm, the heat transfer coefficient decreases by about 30%, making it difficult to achieve long-term stable operation of the heat exchange system.

[0003] To address the scaling and clogging issues that easily occur in heat exchangers during slag flushing waste heat recovery, current methods primarily involve adding chemicals to the flushing water to regulate water quality. One approach is to add chemical agents to induce precipitation reactions and reduce the concentration of scale-forming ions, including methods such as chemical coagulation and the lime-soda ash process. Another approach is to add scale inhibitors, such as the high-temperature resistant scale inhibitor specifically developed for blast furnace slag flushing water systems using patent CN103359839A. While these technical approaches alleviate the scaling problem in heat exchangers to some extent, they generally suffer from high chemical consumption, high input costs, and high suspended solids content. In addition, relevant technical personnel have also considered the issue from the perspective of heat exchanger materials and equipment. One approach is to reduce the deposition rate of scale on the tube wall surface by changing the heat exchanger material. For example, CN105779674B uses a 316 stainless steel heat exchanger tube bundle with a corrugated structure, which delays the scaling induction period of the heat exchanger while also having a certain self-cleaning function. Another method is to improve the anti-clogging capability of the heat exchanger by optimizing its structure. For example, CN103090708A proposes a welded plate structure for a slag flushing water heat exchanger. Although this type of technical approach can improve the heat exchanger's adaptability to slag flushing water to a certain extent, its effect is difficult to maintain in the long term. Under continuous operation conditions, the heat exchanger still faces scaling and clogging problems.

[0004] Therefore, developing a water treatment process suitable for flushing water with high hardness and high suspended solids to solve the problem of scale formation in heat exchangers during waste heat recovery, thereby ensuring the long-term stable operation of the heat exchange system, has significant engineering application value. Summary of the Invention

[0005] This invention aims to provide a water pretreatment process for blast furnace slag flushing water waste heat recovery, particularly suitable for treating slag flushing water with high hardness, low alkalinity, and high suspended particulate matter. This process couples chemical-electrocoagulation-electrochemical water softening technologies. First, some of the calcium in the water is removed chemically. 2+The addition of alkalinity creates favorable conditions for subsequent electrochemical reactions, removing both colloids and suspended solids. Furthermore, the aluminum ions released during the electrocoagulation process through the dissolution of the aluminum anode form flocs that remove colloids, suspended solids, and silicon, while the localized high pH environment near the cathode further removes some calcium. 2+ and Mg 2+ Finally, the water quality is stabilized through an electrochemical water softening unit, and residual Al is removed. 3+ The specific steps are as follows: S1. Chemical water softening: A certain amount of chemical agent that can reduce water hardness is added to the blast furnace slag flushing water. The reaction time is 10-30 min. The softened water is introduced into the inclined plate sedimentation tank, and solid-liquid separation is carried out by gravity sedimentation. S2 Electrocoagulation water softening: The supernatant obtained in step S1 is introduced into the electrocoagulation reaction unit, and water softening is carried out by adjusting the current density and reaction time. S3. Electrochemical water softening: The flushing water after step S2 is introduced into the electrochemical reaction unit, and water softening is carried out by adjusting the current density and reaction time.

[0006] Furthermore, the chemical agent in step S1 is one of sodium carbonate, sodium bicarbonate, or a mixture of sodium carbonate and sodium bicarbonate.

[0007] Furthermore, the certain amount of medicine in step S1 is based on... Figure 1 The relationship between hardness change and dosage of the agent is determined.

[0008] Furthermore, in step S2, the anode of the electrocoagulation water softening equipment is an aluminum electrode, and the cathode is a stainless steel electrode. The electrode shapes include plate-shaped and mesh-shaped patterns.

[0009] Furthermore, in step S2, the current density of the electrocoagulation water softening unit is 24-72 A / m. 2 The reaction time is 10-30 min.

[0010] Furthermore, in step S3, the anode of the electrochemical water softening device is a DSA electrode with a titanium surface coated with metal oxide, and the cathode is a stainless steel electrode. The electrode shape includes plate-shaped and mesh-shaped patterns.

[0011] Furthermore, in step S3, the current density of the electrochemical water softening unit is 12-60 A / m. 2 The reaction time is 5-30 min.

[0012] Furthermore, the water softening process system includes a chemical water softening unit, an electrocoagulation water softening unit, and an electrochemical water softening unit connected in sequence, along with their supporting online water quality monitoring devices and control units; the chemical water softening unit is equipped with a reagent addition device; the electrocoagulation water softening unit and the electrochemical water softening unit are respectively connected to a DC power supply.

[0013] Furthermore, the online water quality monitoring device is installed at the outlets of the chemical water softening unit, the electrocoagulation water softening unit, and the electrochemical water softening unit. The detection device includes sensors for key indicators such as hardness, alkalinity, pH, conductivity, turbidity, silicate, and sulfate. The reagent addition device includes a reagent storage tank, a metering pump, and a dosing pipeline. The control unit adjusts the reagent dosage and the operating parameters of the electrochemical treatment unit based on the monitoring results of the online water quality monitoring device.

[0014] Compared with the prior art, the present invention has the following advantages and beneficial effects: This invention introduces electrocoagulation-electrochemical water softening technology into the field of blast furnace slag flushing water treatment, targeting the specific characteristics of the slag flushing water, and constructs a chemical-electrochemical coupled water treatment process. This process effectively reduces the concentration of various scaling components in the slag flushing water through the synergistic effect of chemical water softening, electrocoagulation water softening, and electrochemical water softening. While achieving good treatment results, it also helps control overall operating costs, and is particularly suitable for treating slag flushing water with high hardness, low alkalinity, and high suspended particulate matter. Slag flushing water treated by this process can solve the scaling and clogging problems of heat exchangers, enabling long-term stable operation of conventional heat exchangers, thus demonstrating good energy-saving and consumption-reducing effects and practical application value. Attached Figure Description

[0015] Figure 1 To investigate the relationship between the hardness of blast furnace slag flushing water in the chemical water softening unit and the amount of reagent used, the reduction in hardness of the blast furnace slag flushing water was calculated by changing the amount of reagent added.

[0016] Figure 2 The RSI index of blast furnace slag flushing water after treatment in Examples 1-3 and Comparative Examples 1-4 is measured at 80°C, 50°C, and 30°C.

[0017] Figure 3 The removal rates of calcium hardness, magnesium hardness, and silicate in the blast furnace slag flushing water after treatment in Examples 1-3 and Comparative Examples 1-4 are given.

[0018] Figure 4 The condition of the heat exchanger wall after 120 hours of operation of the untreated blast furnace slag flushing water and the blast furnace slag flushing water treated in Example 3. Detailed Implementation

[0019] The following examples illustrate specific implementations of the present invention. These examples are carried out based on the solution described in the present invention, and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following examples.

[0020] Example 1: This implementation case focuses on the daily hardness increment (150 mg CaCO3 / L) of blast furnace slag flushing water (initial hardness: calcium hardness 2514.92 mg CaCO3 / L, magnesium hardness 177.8 mg CaCO3 / L), based on " Figure 1 (The relationship between the hardness of blast furnace slag flushing water in the chemical water softening unit and the dosage of reagents) determines the dosage of reagents while controlling the water hardness to be maintained within the range of 500-700 mgCaCO3 / L. S1. Chemical water softening: Add 1912.46 mg / L of sodium bicarbonate to the blast furnace slag flushing water, and react for 30 min. The softened water is then introduced into an inclined plate sedimentation tank, where solid-liquid separation is achieved through gravity settling. S2. Electrocoagulation water softening: The supernatant obtained in step S1 is introduced into the electrocoagulation water softening unit. The anode is an aluminum plate electrode, and the cathode is a stainless steel mesh electrode. The current density is 48 A / m. 2 Water softening treatment was carried out under the condition of a reaction time of 20 min; S3 Electrochemical Water Softening: The flushing water from step S2 is introduced into the electrochemical water softening unit. The anode is a DSA mesh electrode, and the cathode is a stainless steel mesh electrode. The current density is 36 A / m. 2 Water softening treatment was carried out under the condition of a reaction time of 20 min.

[0021] The water softening process system includes a chemical water softening unit, an electrocoagulation water softening unit, and an electrochemical water softening unit connected in sequence, along with their supporting online water quality monitoring devices and control units. The chemical water softening unit is equipped with a reagent addition device. The electrocoagulation water softening unit and the electrochemical water softening unit are respectively connected to a DC power supply. The online water quality monitoring device is located at the outlets of the chemical water softening unit, the electrocoagulation water softening unit, and the electrochemical water softening unit. The monitoring device includes sensors for key indicators such as hardness, alkalinity, pH, conductivity, turbidity, and silicate. The reagent addition device includes a reagent storage tank, a metering pump, and a dosing pipeline. The control unit adjusts the reagent dosage and the operating parameters of the electrochemical treatment unit based on the monitoring results from the online water quality monitoring device.

[0022] Example 2: The difference from Example 1 is that: in the chemical water softening unit, the reagent is a mixture of sodium bicarbonate and sodium carbonate, and the dosage is 1965.14 mg / L; in the electrocoagulation water softening unit, the current density is 36 A / m 2 The reaction time was 30 min; in the electrochemical water softening unit, the current density was 24 A / m. 2 The reaction time was 30 min. Other conditions were the same as in Example 1.

[0023] Example 3: The difference from Example 1 is that in the chemical water softening unit, the reagent is sodium carbonate, the dosage is 2017.83 mg / L, and the reaction time is 10 min; in the electrocoagulation water softening unit, the current density is 60 A / m. 2 The reaction time was 10 min; in the electrochemical water softening unit, the current density was 48 A / m. 2 The reaction time was 10 min. Other conditions were the same as in Example 1.

[0024] Comparative Example 1: Comparative Example 1 uses traditional chemical water softening technology to treat blast furnace slag flushing water. The specific steps are as follows: Add 3180.08 mg / L of sodium carbonate to the slag flushing water and react for 30 min to obtain chemically softened slag flushing water. The softened water is then introduced into an inclined plate sedimentation tank for solid-liquid separation by gravity settling. Comparative Example 2: Comparative Example 2 uses electrochemical water treatment technology to soften the blast furnace slag flushing water. The specific steps are as follows: S1. Electrocoagulation water softening: Slag flushing water is introduced into the electrocoagulation reaction unit. The anode is an aluminum plate electrode, and the cathode is a stainless steel mesh electrode. The current density is 48 A / m³. 2 Water softening treatment was carried out under the condition of a reaction time of 30 min; S2. Electrochemical Water Softening: The flushing water treated in step S1 is introduced into the electrochemical reaction unit. The anode is a DSA mesh electrode, and the cathode is a stainless steel mesh electrode. The current density is 36 A / m. 2 Water softening treatment was carried out under the condition of a reaction time of 30 min.

[0025] Comparative Example 3 Comparative Example 3 involves sequentially using chemical water softening and electrochemical water softening technologies to soften the blast furnace slag flushing water. The specific steps are as follows: S1. Chemical water softening: Add 3180.08 mg / L of sodium carbonate to the slag flushing water, react for 20 min, and introduce the softened water into the inclined plate sedimentation tank for solid-liquid separation by gravity settling. S2. Electrochemical water softening: The supernatant obtained in step S1 is introduced into the electrochemical water softening unit. The anode is a DSA mesh electrode, and the cathode is a stainless steel mesh electrode. The current density is 48 A / m. 2 Water softening treatment was carried out under the condition of a reaction time of 50 min.

[0026] Comparative Example 4 Comparative Example 4 involves sequentially using chemical water softening and electrochemical water softening technologies to soften the blast furnace slag flushing water. The specific steps are as follows: S1. Chemical water softening: Add a mixture of 2650.07 mg / L sodium carbonate and 20 mg / L PAC to the slag flushing water. The reaction time is 20 min. The softened water is introduced into an inclined plate sedimentation tank, where solid-liquid separation is achieved through gravity settling. S2. Electrochemical water softening: The supernatant obtained in step S1 is introduced into the electrochemical water softening unit. The anode is a DSA mesh electrode, and the cathode is a stainless steel mesh electrode. The current density is 60 A / m. 2 Water softening treatment was carried out under the condition of a reaction time of 30 min.

[0027] The water softened in Examples 1-3 and Comparative Examples 1-4 of this application was analyzed, and the experimental data shown in Table 1 were obtained and compared with the initial water quality.

[0028] Table 1 Water quality test data

[0029] Based on the data in Table 1, the calcium hardness of the slag flushing water treated by the process in Comparative Example 1 decreased to 198.78 mg CaCO3 / L. However, its effect on removing magnesium hardness and silicate ions was limited, and the pH of the effluent increased to 9.06, with a turbidity of 43.4 NTU. The RSI index indicates that scaling problems still exist in the slag flushing water during heat exchange even after chemical water softening treatment. After treatment by the process in Comparative Example 2, the pH of the blast furnace slag flushing water could be controlled at 7.05, and the silicate ion concentration decreased to 21.88 mg / L. However, the simple electrochemical treatment technology was not effective in removing hardness ions, and the treated slag flushing water showed a significant tendency to corrosion during heat exchange. Comparative Examples 3 and 4 employ a combined approach of chemical and electrochemical water softening. While this approach can reduce magnesium hardness, alkalinity, and silicate concentration in the flushing water to some extent and improve turbidity, it still relies on high reagent dosages, failing to effectively reduce reagent costs. Furthermore, due to the lack of a synergistic control process, the formed calcium carbonate particles will redissolve during subsequent treatment, leading to a renewed increase in water calcium hardness. This hinders the deep softening effect of the electrochemical unit, and the treated flushing water still exhibits a tendency to scale, making it difficult to meet the requirements for long-term stable operation of the heat exchanger. The results of Examples 1-3 show that the flushing water treated by this process has a stable pH of around 7, effectively reducing the risk of calcium carbonate scaling during subsequent heat exchange. Simultaneously, by precisely controlling reagent dosage through hardness regulation, reagent input costs are reduced. Figure 2 , Figure 3 It is known that this process can achieve the synergistic removal of magnesium ions and silicates, which helps to reduce the possibility of magnesium hydroxide and silicate deposition in the flushing water during the heat exchange process, thereby improving the operational compatibility of the flushing water with the heat exchange system.

[0030] During the cyclic operation of this process, based on an increase in water calcium hardness of approximately 150 mg CaCO3 / L, a sodium carbonate price of 1250 yuan / t, and an industrial electricity cost of 0.35 yuan / kWh, the reagent consumption cost is estimated to be approximately 2.52 yuan / m³. 3 The power consumption per unit volume of the electrocoagulation process is 1.28 kWh / m³. 3 The electrochemical water softening unit volume power consumption is 1.224 kWh / m³. 3 The total cost is approximately 3.40 yuan / m². 3 In contrast, industrial applications using conventional chemical water softening technology, considering a 10% excess reagent factor, have a treatment cost of 3.76 yuan / m³. 3 Around [amount], which is higher than the operating cost of this process. Figure 4As shown, under the same conditions, untreated blast furnace flushing water formed a significant scale layer on the heat exchanger surface after 120 hours of continuous operation in the heat exchange system. However, after 120 hours of continuous operation, the heat exchanger wall remained smooth with no obvious scaling, further demonstrating that this process can effectively reduce the scaling rate of flushing water on the heat exchanger wall and is beneficial for ensuring the continuous and stable operation of the waste heat recovery system. If this process is adopted and operated continuously for one heating season (180 days), it can effectively avoid the decrease in heat exchange efficiency caused by severe scaling on the heat exchanger surface, thereby reducing heat loss by approximately 203,400 GJ, equivalent to approximately 6,942 tce of standard coal.

[0031] Therefore, this process can not only effectively inhibit heat exchanger scaling and reduce the risk of heat exchange efficiency degradation, but also has significant energy-saving and consumption-reducing effects and engineering application value.

[0032] The above description is merely a preferred embodiment of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the spirit and scope of the present invention, and all such modifications and improvements should fall within the protection scope of the present invention.

Claims

1. A chemical-electrochemical coupled water pretreatment process for waste heat recovery from blast furnace slag flushing water, characterized in that... The blast furnace slag flushing water pretreatment process involves chemical, electrocoagulation, and electrochemical water softening steps. The specific process steps are as follows: S1. Chemical water softening: A certain amount of chemical agent that can reduce water hardness is added to the blast furnace slag flushing water. The reaction time is 10-30 min. The softened water is introduced into the inclined plate sedimentation tank, and solid-liquid separation is carried out by gravity sedimentation. S2 Electrocoagulation water softening: The supernatant obtained in step S1 is introduced into the electrocoagulation reaction unit, and water softening is carried out by adjusting the current density and reaction time. S3. Electrochemical water softening: The flushing water after step S2 is introduced into the electrochemical reaction unit, and water softening is carried out by adjusting the current density and reaction time.

2. The chemical-electrochemical coupled water pretreatment process for waste heat recovery of blast furnace slag flushing water according to claim 1, characterized in that: The chemical agent in step S1 is one of sodium carbonate, sodium bicarbonate, or a mixture of sodium carbonate and sodium bicarbonate.

3. The chemical-electrochemical coupled water pretreatment process for waste heat recovery from blast furnace slag flushing water according to claim 1, characterized in that: The amount of agent in step S1 is determined based on the relationship between hardness change and agent dosage in Figure 1.

4. The chemical-electrochemical coupled water pretreatment process for waste heat recovery of blast furnace slag flushing water according to claim 1, characterized in that: In step S2, the anode of the electrocoagulation water softening equipment is an aluminum electrode, and the cathode is a stainless steel electrode. The electrode shapes include plate-shaped and mesh-shaped.

5. A chemical-electrochemical coupled water pretreatment process for blast furnace slag flushing water waste heat recovery according to claim 1, characterized in that: In step S2, the current density of the electrocoagulation water softening unit is 24-72 A / m. 2 The reaction time is 10-30 min.

6. The chemical-electrochemical coupled water pretreatment process for waste heat recovery of blast furnace slag flushing water according to claim 1, characterized in that: In step S3, the anode of the electrochemical water softening device is a DSA electrode with a titanium surface coated with metal oxide, and the cathode is a stainless steel electrode. The electrode shape includes plate-shaped and mesh-shaped patterns.

7. A chemical-electrochemical coupled water pretreatment process for blast furnace slag flushing water waste heat recovery according to claim 1, characterized in that: In step S3, the current density of the electrochemical water softening unit is 12-60 A / m. 2 The reaction time is 5-30 min.

8. The chemical-electrochemical coupled water pretreatment process for waste heat recovery of blast furnace slag flushing water according to claim 1, characterized in that: The water softening process system includes a chemical water softening unit, an electrocoagulation water softening unit, and an electrochemical water softening unit connected in sequence, along with their supporting online water quality monitoring devices and control units; the chemical water softening unit is equipped with a reagent addition device; the electrocoagulation water softening unit and the electrochemical water softening unit are respectively connected to a DC power supply.

9. A chemical-electrochemical coupled water pretreatment process for waste heat recovery of blast furnace slag flushing water according to claim 8, characterized in that: In the chemical water softening unit, the online water quality monitoring device is installed at the outlets of the chemical water softening unit, the electrocoagulation water softening unit, and the electrochemical water softening unit. The detection device includes sensors for key indicators such as hardness, alkalinity, pH, conductivity, turbidity, silicate, and sulfate. The reagent addition device includes a reagent storage tank, a metering pump, and a dosing pipeline. The control unit adjusts the reagent dosage and the operating parameters of the electrochemical treatment unit based on the monitoring results of the online water quality monitoring device.

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