Pretreatment method for step-by-step impurity removal of high-calcium-magnesium wastewater

Abstract

The invention discloses a pretreatment method for step-by-step impurity removal of high-calcium-magnesium wastewater. The pretreatment method comprises the following steps: carrying out impurity filtration on the high-calcium-magnesium wastewater by utilizing a grating assembly to obtain filtered slurry; the filtered slurry is introduced into the pre-sedimentation part and stays for at least 3 h, and supernate is obtained; introducing the supernate into a regulating tank, staying for 6-12 hours to balance the water quality and water quantity, and adding a pH regulator to stabilize the pH of the supernate to 6-8 to obtain a pretreatment solution. According to the application, particle impurities and suspended solids are sequentially removed from the high-calcium-magnesium wastewater through impurity filtration, pre-precipitation, water quality homogenization and pH adjustment; by balancing water quality and water quantity, reducing hardness fluctuation impact and finally adjusting the pH value, the pH value of the high-calcium-magnesium wastewater is stabilized to 6-8, and conditions are created for selective precipitation and calcium removal of the high-calcium-magnesium wastewater and crystallization and recovery of magnesium ions.

Description

Technical Field

[0001] This application relates to the field of power plant circulating water treatment technology, specifically to a pretreatment method for stepwise impurity removal of high-calcium and magnesium wastewater. Background Technology

[0002] With the deepening of industrial water conservation and emission reduction goals, industrial circulating cooling water systems, as major water consumers in power plants, are increasingly attracting attention for their water-saving, energy-saving, and resource recovery potential. After long-term circulation and concentration, the circulating water in power plants has extremely high concentrations of calcium and magnesium ions, and is also accompanied by impurities such as suspended solids (silt, corrosion products), carbonates, sulfates, and silicides. The harmful mechanisms and removal conditions of different impurities vary.

[0003] One of the key research areas in this field is how to recover magnesium from power plant circulating water in the form of high-purity, easily filterable magnesium hydroxide, magnesium carbonate, or magnesium oxide to achieve the construction of a green and low-carbon system. However, suspended solids in power plant circulating water can encapsulate calcium and magnesium ions, hindering the reaction between subsequent chemical agents and calcium and magnesium. Simultaneously, suspended solids can clog the pores of pipes, filter membranes, or ion exchange resins, causing equipment blockage and reduced treatment efficiency. Therefore, how to perform step-by-step impurity removal in high-calcium and magnesium wastewater to achieve pretreatment before calcium and magnesium ion recovery—by removing suspended solids—and clearing obstacles for subsequent softening treatment, is a technical problem that those skilled in the art need to solve first. Summary of the Invention

[0004] This application aims to at least partially address one of the technical problems in the related art.

[0005] Therefore, embodiments of this application propose a stepwise pretreatment method for removing impurities from high-calcium and magnesium wastewater. This application achieves the sequential removal of particulate impurities and suspended solids from high-calcium and magnesium wastewater through impurity filtration, pre-precipitation, water homogenization, and pH adjustment; and reduces the impact of hardness fluctuations by balancing water quality and quantity, and finally adjusts the pH value to stabilize the pH of high-calcium and magnesium wastewater at 6-8, creating conditions for selective precipitation of calcium and magnesium ion crystallization in high-calcium and magnesium wastewater.

[0006] An embodiment of this application provides a pretreatment method for stepwise impurity removal from high-calcium and magnesium wastewater, comprising the following steps: High-calcium and magnesium wastewater is filtered for impurities using a bar screen assembly to obtain a filtered slurry. The filtered slurry is passed into the pre-sediment and left to stand for at least 3 hours to obtain the supernatant. The supernatant is passed into an equalization tank and left to stand for 6-12 hours to balance the water quality and quantity. Then, a pH adjuster is added to stabilize the pH of the supernatant to 6-8 to obtain a pretreated solution.

[0007] In some embodiments, the grid assembly includes a first grid, a second grid, and a multi-media filter layer arranged sequentially upstream and downstream; wherein the spacing between the first grid, the second grid, and the multi-media filter layer decreases sequentially.

[0008] In some embodiments, the spacing of the first grid is 5-20 mm and the spacing of the second grid is 1-10 mm.

[0009] In some embodiments, the multi-media filter layer includes sand particles with a particle size of 0.5-1.2 mm, coal slag with a particle size of 2.0-5.0 mm, and stones with a particle size of 1-2 mm, wherein the high-calcium magnesium wastewater passes sequentially through the coal slag, the sand particles, and the stones.

[0010] In some embodiments, the thickness ratio of the slag layer, the stone layer and the sand layer composed of the slag, the stone and the sand is (10-20):(5-10):(15-20).

[0011] In some embodiments, the density of the coal slag is less than that of the sand particles; the density of the sand particles is less than that of the stones.

[0012] In some embodiments, the density of the coal slag is 0.6-1.0 g / cm³; the density of the sand is 2.0-2.5 g / cm³; and the density of the stone is not less than 2.65 g / cm³.

[0013] In some embodiments, the pre-sinking member is a circular lower cone structure with an internal stirring device.

[0014] In some embodiments, the equalization tank is provided with an aeration device to perform aeration homogenization when the supernatant is introduced.

[0015] In some embodiments, the pH adjuster includes an alkaline adjuster and an acidic adjuster; the alkaline adjuster includes lime milk or NaOH; the acidic adjuster includes sulfuric acid with a concentration of 5-20 wt%.

[0016] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0017] Figure 1 This is a flowchart of the pretreatment method for stepwise impurity removal of high-calcium and magnesium wastewater proposed in the embodiments of this application. Detailed Implementation

[0018] The embodiments of this application are described in detail below, with examples of these embodiments illustrated in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this application, and should not be construed as limiting this application.

[0019] The embodiments of this application provide a pretreatment method for stepwise impurity removal from high-calcium and magnesium wastewater, such as... Figure 1 As shown, it includes the following steps: S1: High-calcium and magnesium wastewater is filtered for impurities using a bar screen assembly to obtain a filtered slurry; S2: Pass the filtered slurry into the pre-sedimentation chamber and let it remain for at least 3 hours to obtain the supernatant; S3: After passing the supernatant into the equalization tank and letting it stand for 6-12 hours to equalize the water quality and quantity, add a pH adjuster to stabilize the pH of the supernatant to 6-8 to obtain the pretreated solution.

[0020] In step S1, the high-calcium-magnesium wastewater is filtered for impurities using a grid assembly. The initial high-calcium-magnesium wastewater contains large particulate impurities such as hair and silt, large particulate suspended solids, as well as suspended solids such as grease, scum, and some colloids. Before selectively treating the calcium and magnesium ions in the high-calcium-magnesium wastewater, the initial high-calcium-magnesium wastewater needs to be pretreated to remove macroscopic impurities, creating optimal conditions for the subsequent efficient, economical, and stable ion recovery unit.

[0021] If the initial high-calcium and magnesium wastewater is not effectively pretreated, direct selective precipitation and recovery of calcium and magnesium ions will lead to clogging and damage of related equipment, waste of large amounts of energy and reagents to treat useless impurities, and the resulting precipitates and crystals will be of extremely low purity and worthless. Therefore, pretreatment is an essential step in wastewater resource recovery and is crucial to ensuring the successful operation of the entire resource recovery project.

[0022] In this embodiment, the bar grid assembly includes a first grid, a second grid, and a multi-media filter layer arranged sequentially upstream and downstream; wherein the spacing between the first grid, the second grid, and the multi-media filter layer decreases sequentially. In other words, the bar grid assembly of this application includes a first grid, a second grid, and a multi-media filter layer, and the spacing of the first grid is greater than that of the second grid, and the spacing of the second grid is greater than that of the multi-media filter layer. According to the flow direction of the high-calcium magnesium wastewater, it passes through the first grid, the second grid, and the multi-media filter layer sequentially. As can be seen from the above, the high-calcium magnesium wastewater first passes through the first grid with a larger spacing to intercept large particulate impurities such as hair and silt; after being filtered by the first grid, the high-calcium magnesium wastewater then passes through the second grid, which further filters and retains particulate impurities, suspended particulate matter, scum, and some colloids. After being filtered by the second grid, the high-calcium magnesium wastewater then passes through the multi-media filter layer with the smallest spacing, which further removes the smallest particulate impurities, thereby achieving distributed and phased impurity removal of the high-calcium magnesium wastewater.

[0023] For example, the spacing of the first grid is 5-20 mm and the spacing of the second grid is 1-10 mm. In some embodiments, the multi-media filter layer includes sand particles with a particle size of 0.5-1.2 mm, coal slag with a particle size of 2.0-5.0 mm and stones with a particle size of 1-2 mm, wherein the high-calcium and magnesium wastewater passes through the coal slag, sand particles and stones in sequence.

[0024] For example, the spacing of the first grid may be 5mm, 8mm, 10mm, 13mm, 15mm, 17mm, or 20mm. If the spacing of the first grid is too large, larger debris (such as fabrics, plastic sheets, and sawdust) will entangle or clog the second grid, affecting the pretreatment efficiency and process of the high-calcium-magnesium wastewater. If the spacing of the first grid is too small, the filtered screenings will accumulate too high and eventually overflow the first grid into subsequent processes. Similarly, the spacing of the second grid may be 1mm, 3mm, 5mm, 7mm, or 10mm. If the spacing of the second grid is too large, larger debris (such as fabrics, plastic sheets, and sawdust) will entangle or clog the downstream multi-media filter layer, affecting the pretreatment efficiency and process of the high-calcium-magnesium wastewater. If the spacing of the second grid is too small, the filtered screenings will accumulate too high and eventually overflow the second grid into subsequent processes. Therefore, a reasonable spacing design for the first and second grids is a crucial step in protecting subsequent processes and effectively removing fibers, hair, and small debris. The first and second grids can be rotary grids, stepped grids, internal flow fine grids, etc.

[0025] In particular, the multi-media filter layer of this application is composed of cinders, stones, and sand, wherein the cinders, stones, and sand are arranged sequentially as a cinder layer, a stone layer, and a sand layer. The particle size of the cinders is 2.0-5.0 mm, the particle size of the stones is 1-2 mm, and the particle size of the sand is 0.5-1.2 mm. The density of the cinders is less than that of the sand, and the density of the sand is less than that of the stones. For example, the density of the cinders is 0.6-1.0 g / cm³, the density of the sand is 2.0-2.5 g / cm³, and the density of the stones is not less than 2.65 g / cm³. According to the flow direction of the high-calcium-magnesium wastewater, the wastewater passes through the cinder layer, the sand layer, and the stone layer sequentially.

[0026] The cinder layer has the coarsest particles and lowest density, serving as the first line of defense for high-calcium-magnesium wastewater as it flows through the multi-media filtration layer. It effectively traps most of the larger suspended solids in the wastewater. Because of its coarse particles and large pores, the cinder allows contaminants in the wastewater to penetrate deeper, resulting in high dirt-holding capacity and preventing rapid surface clogging. The sand layer, located downstream of the cinder layer, traps medium-sized suspended solids. Since the cinder layer has removed large particles, the flow velocity of the high-calcium-magnesium wastewater is more stable when it reaches this layer, and the smaller pores provided by the sand layer allow for further fine filtration. The stone layer, as the final barrier, maintains its high density and remains stable at the bottom after backwashing.

[0027] The thickness ratio of the cinder, stone, and sand layers in the example is (10-20):(5-10):(15-20), for example, (10, 12, 13, 15, 16, 18, 20):(5, 6, 8, 9 or 10):(15, 16, 18, 19, 20). When high-calcium-magnesium wastewater passes sequentially through the cinder and sand layers, the pore size of the filter media decreases as the wastewater flows from top to bottom. This allows suspended solids to be trapped layer by layer throughout the multi-media filter layer according to their size, rather than simply accumulating on the surface. This significantly improves the dirt-holding capacity of the entire multi-media filter layer and extends the filtration cycle.

[0028] Secondly, due to the significant density differences among the three materials—coal slag, sand, and stone—the filter media is completely flushed up and fluidized during backwashing (water or combined air-water washing). After backwashing, the densest stones settle the fastest and fall to the bottom layer; the medium-density sand falls to the middle layer; and the lightest coal slag falls to the top layer last. This layered structure makes it easier to remove and clean the contaminants from the surface of the filter media (especially the coal slag), resulting in a better backwashing effect.

[0029] In some embodiments, the pre-settling element is a circular lower cone structure with an internal stirring device. The pre-settling element has an inner circular structure, with water flow distributed radially, eliminating dead zones and avoiding the short-flow and vortex zones common in rectangular tanks, resulting in a more uniform distribution of water and sludge. Furthermore, its lower cone structure causes the cross-sectional area of ​​the pre-settling element to gradually decrease from top to bottom, forming a stable, upward-flowing zone. The narrowing space at the bottom of the cone facilitates the formation of a stable sludge suspension layer or achieves efficient thickening. Although the pre-settling element has a three-dimensional structure, its separation principle is based on inclined tube / plate sedimentation or sludge suspension layer filtration technology, offering advantages such as a large effective separation area and short settling distance. Therefore, its settling efficiency is far higher than that of traditional horizontal flow sedimentation tanks.

[0030] For example, the cone-shaped bottom structure naturally forms a sludge compression zone. The settled sludge is continuously compressed and concentrated at the bottom of the cone, resulting in a high solids content, which facilitates subsequent sludge dewatering and reduces sludge volume. The resulting sludge suspension layer itself acts as a dynamic filter, capturing finer particles and providing a buffer against fluctuations in influent water quality and volume. The integrated stirring device promotes full contact between the sludge and wastewater, ensuring effective sedimentation. This pre-sedimentation unit achieves advantages such as small footprint, high treatment efficiency, stable effluent quality, and high sludge concentration.

[0031] In some embodiments, an aeration device is provided in the equalization tank to aerate and homogenize the supernatant when it is introduced. The aeration device allows the supernatant entering the equalization tank at different times to remain for 6-12 hours to balance the water quality and quantity and reduce the impact of hardness fluctuations; thus achieving true water quality homogenization and stabilizing the effluent concentration.

[0032] In some embodiments, the pH adjuster includes an alkaline adjuster and an acidic adjuster; the alkaline adjuster includes lime milk or NaOH; the acidic adjuster includes sulfuric acid with a concentration of 5-20 wt%. This application initially stabilizes the pH of the supernatant at 6-8 through pH adjustment, creating favorable conditions for subsequent selective calcium removal. This application achieves the sequential removal of particulate impurities and suspended solids from high-calcium and magnesium wastewater through impurity filtration, pre-precipitation, water homogenization, and pH adjustment; and by balancing water quality and quantity, reducing the impact of hardness fluctuations, and finally adjusting the pH value, the pH of the high-calcium and magnesium wastewater is stabilized at 6-8, creating favorable conditions for the selective precipitation separation and crystallization recovery of calcium and magnesium ions in the high-calcium and magnesium wastewater.

[0033] In the description of this application, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc., indicating the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application.

[0034] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0035] In this application, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0036] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. A pretreatment method for step-by-step impurity removal of high calcium and magnesium wastewater, characterized in that, The method comprises the following steps: Filtering the high calcium magnesium wastewater by using a grid assembly to obtain a filtered slurry; Passing the filtered slurry into the pre-sedimenting device to stay for at least 3 hours to obtain supernatant; After the supernatant is passed into the adjusting tank to stay for 6-12 hours to balance the water quality and quantity, a pH adjusting agent is added to stabilize the pH of the supernatant to 6-8 to obtain a pretreated liquid.

2. The method of claim 1, wherein, The grid assembly comprises a first grid, a second grid and a multi-medium filter layer arranged in sequence from upstream to downstream; the intervals in the first grid, the second grid and the multi-medium filter layer are sequentially reduced.

3. The method of claim 2, wherein, The interval of the first grid is 5-20 mm and the interval of the second grid is 1-10 mm.

4. The method according to claim 2 or 3, characterized in that, The multi-medium filter layer comprises sand particles with a particle size of 0.5-1.2 mm, coal cinders with a particle size of 2.0-5.0 mm and stone blocks with a particle size of 1-2 mm; the high calcium magnesium wastewater passes through the coal cinders, the sand particles and the stone blocks in sequence.

5. The method of claim 4, wherein, The thickness ratio of the coal cinder layer, the stone block layer and the sand particle layer composed of the coal cinders, the stone blocks and the sand particles is (10-20):(5-10):(15-20).

6. The method of claim 4, wherein, The density of the coal cinders is less than that of the sand particles; the density of the sand particles is less than that of the stone blocks.

7. The method of claim 6, wherein, The density of the coal cinders is 0.6-1.0 g / cm3; the density of the sand particles is 2.0-2.5 g / cm3; the density of the stone blocks is not less than 2.65 g / cm3.

8. The method according to any one of claims 1 to 7, characterized in that, The pre-sedimenting device is a circular lower cone structure with an internal stirring device.

9. The method of claim 8, wherein, An aeration device is arranged in the adjusting tank to aerate and homogenize when the supernatant is passed in.

10. The method of claim 8, wherein, The pH adjusting agent comprises an alkaline adjusting agent and an acidic adjusting agent; the alkaline adjusting agent comprises lime milk or NaOH; the acidic adjusting agent comprises sulfuric acid with a concentration of 5-20 wt%.

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