Continuous solid-liquid separation and recovery method and system for sodium hypophosphite

Abstract

The invention discloses a continuous solid-liquid separation and recovery method and system for sodium hypophosphite. The method comprises the following steps: conveying sodium hypophosphite mixed slurry into a hydrocyclone group for pre-concentration; wherein concentrated slurry with high solid content is discharged from an underflow port of the first-stage cyclone, overflow liquid of the concentrated slurry enters the second-stage cyclone for secondary separation, slurry with low solid content is discharged from an underflow port of the second-stage cyclone, and clear liquid is discharged from an overflow port of the second-stage cyclone to serve as finished product mother liquor; respectively, simultaneously and continuously conveying the underflow concentrated slurry and the underflow slurry to different feeding points in a horizontal spiral discharge sedimentation centrifuge; in a centrifugal machine, one or more strands of washing liquid are adopted to carry out continuous countercurrent washing on a solid-phase filter cake which is being conveyed, so that a diluted sodium hypophosphite solution generated by washing and separated mother liquid are converged in a rotary drum in a partitioned manner. The full-closed and continuous technological process is adopted, and the defects that traditional intermittent operation is low in efficiency, high in labor intensity and prone to product loss are effectively overcome.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of chemical industry, in particular to a continuous solid-liquid separation and recovery method and system for sodium hypophosphite. BACKGROUND

[0002] In the field of chemical production, sodium hypophosphite, as an important reducing agent and chemical raw material, has a growing market demand. The traditional production process usually involves chemical reaction to generate mixed slurry, and then efficient solid-liquid separation is needed to obtain pure sodium hypophosphite solution for subsequent crystallization. The efficiency and yield of the separation process directly determine the purity, cost of the final product, and the economy and environmental protection of the production process.

[0003] Currently, the industry generally uses batch or semi-continuous operation mode for solid-liquid separation of mixed slurry after sodium hypophosphite reaction. The typical approach is to first introduce the slurry into an intermediate storage tank for buffering and homogenization, and then use a plate and frame filter press or a batch centrifuge for batch processing. After separation, in order to recover the effective components entrained in the filter cake, manual operation is often required for filter cake unloading, scattering and re-slurry washing. This process is tedious and difficult to achieve continuous operation.

[0004] The above existing technical approach has obvious limitations. First, batch operation results in low production efficiency, frequent start and stop of equipment, and cannot meet the needs of large-scale continuous production, and manual operation is intensive. Second, the simple separation process cannot effectively handle slurry with complex composition and wide particle size distribution, which can lead to incomplete separation, serious loss of fine particles, or high moisture content in the solid phase, resulting in product loss. SUMMARY

[0005] In view of the deficiencies of the prior art, the purpose of the present application is to provide a continuous solid-liquid separation and recovery method and system for sodium hypophosphite, which aims to solve the above problems described in the prior art.

[0006] The first aspect of the present application provides a continuous solid-liquid separation and recovery method for sodium hypophosphite, which comprises: delivering the sodium hypophosphite mixed slurry to a hydrocyclone group for pre-concentration; wherein the underflow port of the first-stage cyclone discharges concentrated slurry with high solid content, and the overflow liquid enters the second-stage cyclone for secondary separation, and the underflow port of the second-stage cyclone discharges slurry with low solid content, and the overflow port discharges clear liquid as the mother liquor of the finished product; delivering the underflow concentrated slurry of the first-stage cyclone and the underflow slurry of the second-stage cyclone to different feeding points in the horizontal screw unloading sedimentation centrifuge respectively, simultaneously and continuously; In the horizontal screw discharge sedimentation centrifuge, one or more washing liquids are used to continuously wash the solid-phase filter cake being conveyed in a countercurrent manner, so that the dilute sodium hypophosphite solution generated by the washing is collected in the drum in a partitioned manner together with the separated mother liquor.

[0007] According to an aspect of the above technical solution, the underflow concentrated slurry of the first-stage hydrocyclone is delivered to a main feed inlet in the middle of the drum of the horizontal screw discharge sedimentation centrifuge, and the underflow slurry of the second-stage hydrocyclone is delivered to a secondary feed inlet between the main feed inlet and the solid-phase outlet of the horizontal screw discharge sedimentation centrifuge.

[0008] According to an aspect of the above technical solution, the dilute sodium hypophosphite solution generated by the washing and the clear liquid discharged from the overflow outlet of the second-stage hydrocyclone are collected separately.

[0009] According to an aspect of the above technical solution, the dilute sodium hypophosphite solution generated by the washing is returned to the previous reaction process or used to prepare the washing liquid after being collected.

[0010] According to an aspect of the above technical solution, the washing liquid is any one of hot water, dilute sodium hypophosphite solution or steam condensate.

[0011] According to an aspect of the above technical solution, the feed pressure of the hydrocyclone group is controlled at 0.2-0.8 MPa.

[0012] According to an aspect of the above technical solution, the valve opening degree of the underflow outlet of the first-stage hydrocyclone in the hydrocyclone group is adjusted to control the weight percentage of the solid matter in the underflow concentrated slurry to be 40%-60%.

[0013] According to an aspect of the above technical solution, the rotational speed difference between the drum and the screw pusher in the horizontal screw discharge sedimentation centrifuge is 2-15 rpm.

[0014] The second aspect of the present application provides a sodium hypophosphite continuous solid-liquid separation and recovery system, which is applied to the method in the above technical solution, and the system comprises: a hydrocyclone group comprising a first-stage hydrocyclone and a second-stage hydrocyclone; a horizontal screw discharge sedimentation centrifuge, the underflow outlet of the first-stage hydrocyclone and the underflow outlet of the second-stage hydrocyclone being respectively connected to different feed points in the horizontal screw discharge sedimentation centrifuge.

[0015] According to an aspect of the above technical solution, the overflow outlet of the first-stage hydrocyclone is connected to the material inlet of the second-stage hydrocyclone. The underflow of the first stage hydrocyclone is connected to a main feed inlet in the middle of the bowl of the horizontal screw discharge decanter centrifuge, and the underflow of the second stage hydrocyclone is connected to a secondary feed inlet between the main feed inlet and a solid phase outlet of the horizontal screw discharge decanter centrifuge.

[0016] Compared with the prior art, the sodium hypophosphite continuous solid-liquid separation and recovery method and system has the beneficial effects that: The two-stage series hydrocyclone group shown in the present application performs efficient classification and pre-concentration on the mixed slurry, not only greatly reduces the processing load of the main centrifuge, but also recovers most of the clear liquid as the product mother liquor in the pretreatment stage, thereby improving the overall efficiency. Moreover, the slurry with different concentrations is accurately sent to the optimal position of the horizontal screw centrifuge, effectively avoiding the mutual interference of the materials, creating the best sedimentation conditions for coarse and fine particles, thereby ensuring a very high solid recovery rate while obtaining a drier solid phase and a clearer liquid phase. The continuous countercurrent washing process integrated in the centrifuge maximizes the recovery of high-value products entrained in the solid phase, and combined with the mother liquid partitioning and collecting technology, the material grading optimization of direct recovery of thick mother liquor and recycling of dilute washing liquid is realized, which significantly improves the product yield of sodium hypophosphite, reduces fresh water consumption and wastewater treatment cost. The fully closed and continuous process effectively overcomes the disadvantages of low efficiency, high labor intensity and product loss of traditional batch operation. BRIEF DESCRIPTION OF DRAWINGS

[0017] The above and / or additional aspects and advantages of the present application will become apparent and more readily appreciated from the following description, taken in conjunction with the following drawings, in which: Figure 1 A flowchart of a sodium hypophosphite continuous solid-liquid separation and recovery method according to an embodiment of the present application is shown in the figure. Figure 2 A block diagram of a sodium hypophosphite continuous solid-liquid separation and recovery system according to an embodiment of the present application is shown in the figure. DETAILED DESCRIPTION

[0018] In order to make the objectives, features and advantages of the present application more apparent and easy to understand, the specific embodiments of the present application will be described in detail below with reference to the accompanying drawings. However, the present application can be realized in many different forms, and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present application more thorough and comprehensive.

[0019] It should be understood that when an element is referred to as being "on" another element, it can be directly on the other element or intervening elements can also be present. In addition, it should be understood that when an element is referred to as being "connected, coupled or linked to" another element, it can be directly connected, coupled or linked to the other element or intervening elements can also be present. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0020] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the description of the application herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0021] Embodiment one Referring to Figure 1 The first embodiment of the present application provides a continuous solid-liquid separation and recovery method of sodium hypophosphite, which comprises steps S10-S30: Step S10, the sodium hypophosphite mixed slurry is transported to the hydrocyclone group for pre-concentration.

[0022] Among them, the underflow port of the first-stage cyclone discharges high-solid-concentration concentrated slurry, and the overflow liquid enters the second-stage cyclone for secondary separation. The underflow port of the second-stage cyclone discharges low-solid-concentration slurry, and the overflow port discharges clear liquid as a finished product mother liquor. Moreover, the feed pressure of the hydrocyclone group is controlled at 0.2-0.8 MPa.

[0023] Specifically, the present embodiment realizes the preliminary classification and upgrading of the mixed slurry through multi-stage centrifugal pre-concentration, creating optimal feed conditions for the subsequent precision separation unit. The sodium hypophosphite mixed slurry from the previous reaction process has complex components, usually including target product sodium hypophosphite solution, fine particles of incomplete reaction, heavy metal particles used as catalysts, and salt crystals generated by side reactions, etc. The particle size distribution of these solid particles is extensive, and the density difference is large. If they are directly fed into the main separation equipment, it is easy to cause excessive equipment load, poor separation effect, and even blockage.

[0024] As shown above, the hydrocyclone group adopts a two-stage series configuration, and its working principle is to make the slurry produce strong rotational motion by using a specific tangential feed structure, and to produce different centrifugal sedimentation speeds in the high-speed rotational flow field based on the density difference between solid particles and liquid. Among them, the solid particles with large density are thrown to the inner wall of the cyclone under the action of centrifugal force and spiral downward, and finally discharged in the form of concentrated slurry from the underflow port, while the liquid containing fine particles forms an inner vortex and is discharged from the overflow port at the top.

[0025] More specifically, the first stage hydrocyclone mainly performs coarse concentration, separating most of the coarse and heavy particles quickly to form a concentrated slurry with high solid content (e.g. 40%-60%, w / w), which is mainly achieved by adjusting the opening degree of the underflow valve of the first stage hydrocyclone in the hydrocyclone group, which not only significantly reduces the solid load of the subsequent treatment, but also realizes the preliminary enrichment of the valuable catalyst.

[0026] In addition, the overflow of the first stage hydrocyclone still contains a large amount of fine particles that are difficult to settle, which also needs to be introduced into the second stage hydrocyclone for fine separation in this embodiment. Among them, the second stage hydrocyclone usually adopts a smaller diameter and different structural parameters to produce a stronger centrifugal force field, and the low solid content slurry discharged from the underflow port is mainly composed of fine particle components, while the overflow port discharges clear liquid that has reached the process requirements, which can be directly sent to the subsequent evaporation crystallization section as high-quality product mother liquor.

[0027] Step S20, the underflow concentrated slurry of the first stage hydrocyclone and the underflow slurry of the second stage hydrocyclone are respectively, simultaneously and continuously transported to different feeding points in the horizontal screw unloading sedimentation centrifuge.

[0028] Among them, the underflow concentrated slurry of the first stage hydrocyclone is transported to the main feeding port in the middle of the drum of the horizontal screw unloading sedimentation centrifuge, and the underflow slurry of the second stage hydrocyclone is transported to the auxiliary feeding port between the main feeding port and the solid phase outlet of the horizontal screw unloading sedimentation centrifuge.

[0029] Specifically, since the underflow concentrated slurry from the first stage hydrocyclone has high solid concentration, relatively large particle size and fast settling speed, it is fed from the main feeding port in the middle of the drum, so that it enters the largest settling area of the centrifuge. In this area, the slurry has the longest axial travel and sufficient residence time, and under the action of strong centrifugal force, the solid particles can be fully settled and deposited on the inner wall of the drum. Subsequently, during the pushing process by the screw pusher, the high-concentration solid phase layer experiences a long dehydration zone, and the mother liquor is squeezed out to the maximum extent, so as to obtain a higher solid content before discharge.

[0030] And the underflow slurry from the second stage hydrocyclone has low solid concentration and is mainly composed of fine and slow-settling particles. If it is mixed with high-concentration slurry and fed from the main feeding port, not only will it dilute the high-concentration slurry and reduce the processing efficiency of the centrifuge, but the fine particles may also interfere with the settling process of the coarse particles. Therefore, in this embodiment, it is directly fed through the auxiliary feeding port to an area closer to the end of the settling area, which makes the fine particles bypass the main settling area that may cause interference and directly enter a strong centrifugal force field, so that they can be quickly and efficiently settled, effectively preventing the problem of loss with the clear liquid due to too long settling path.

[0031] By intelligently distributing the total load to different sections of the equipment according to particle characteristics, the above not only avoids mutual interference caused by mixing of different slurries, but also balances the solid distribution inside the equipment, making the centrifuge run more smoothly.

[0032] Step S30, in the horizontal screw discharge sedimentation centrifuge, one or more washing liquids are used to continuously countercurrently wash the solid phase filter cake being transported, so that the dilute sodium hypophosphite solution generated by washing and the separated mother liquor are collected in different zones in the bowl.

[0033] Among them, the difference in rotational speed between the bowl and the screw pusher in the horizontal screw discharge sedimentation centrifuge is 2-15 rpm.

[0034] Specifically, inside the centrifuge, the solid phase deposited on the inner wall of the bowl after centrifugal separation is pushed by the screw pusher to move towards the solid phase outlet. On this transportation path, one or more washing liquids, such as hot water, dilute sodium hypophosphite solution or steam condensate, are precisely injected from a position closer to the solid phase outlet, and their flow direction is generally opposite to the solid phase transportation direction, constituting countercurrent washing. When the washing liquid penetrates the solid phase layer, it effectively displaces and washes out the concentrated mother liquor remaining on the surface and in the gaps of the solid particles by utilizing the concentration difference.

[0035] Among them, countercurrent washing is more efficient than parallel flow washing because the cleanest washing liquid always meets the solid phase with the lowest liquid content but the highest liquid concentration, thereby achieving the highest washing concentration difference driving force and the best washing effect with the least amount of washing liquid. The dilute sodium hypophosphite solution produced after washing is naturally collected in different zones in the bowl under the action of centrifugal force due to the different entry positions and concentrations of the concentrated mother liquor separated from the main sedimentation zone, and is discharged through independent overflow weirs respectively.

[0036] In addition, the high-concentration product mother liquor separated can be directly sent to the subsequent refining section, and the dilute solution produced by washing can be recycled, for example, returned to the previous reaction process or directly used to prepare washing liquid.

[0037] Compared with the prior art, the sodium hypophosphite continuous solid-liquid separation and recovery method shown in the embodiment has the beneficial effects that: The two-stage series hydrocyclone group shown in the embodiment can efficiently grade and pre-concentrate the mixed slurry, not only greatly reducing the processing load of the main centrifuge, but also recycling most of the clear liquid as the finished product mother liquor in the pretreatment stage, thereby improving the overall efficiency. Moreover, the slurry with different concentrations is accurately sent to the optimal position of the horizontal screw centrifuge, effectively avoiding the mutual interference of materials, creating the best sedimentation conditions for coarse and fine particles, thereby ensuring a very high solid recovery rate while obtaining a drier solid phase and a clearer liquid phase. The integrated continuous countercurrent washing process in the centrifuge maximizes the recovery of high-value products entrained in the solid phase, and combined with the mother liquor partitioning technology, the material grading optimization of direct recovery of thick mother liquor and recycling of dilute washing liquid is realized, significantly improving the product yield of sodium hypophosphite, reducing fresh water consumption and wastewater treatment cost. The fully closed and continuous process effectively overcomes the disadvantages of low efficiency, high labor intensity and product loss of traditional batch operation.

[0038] Embodiment three For reference Figure 2 The third embodiment of the present application provides a continuous solid-liquid separation and recovery system for sodium hypophosphite, which is applied to the method described in the above embodiments, and the system comprises: A hydrocyclone group comprising a first-stage cyclone 11 and a second-stage cyclone 12. A horizontal screw discharge sedimentation centrifuge, the underflow outlet of the first-stage cyclone 11 and the underflow outlet of the second-stage cyclone 12 are respectively connected to different feeding points in the horizontal screw discharge sedimentation centrifuge 20.

[0039] The overflow outlet of the first-stage cyclone 11 is connected to the material inlet of the second-stage cyclone 12. The underflow outlet of the first-stage cyclone 11 is connected to the main feeding port in the middle of the drum of the horizontal screw discharge sedimentation centrifuge 20, and the underflow outlet of the second-stage cyclone 12 is connected to the auxiliary feeding port between the main feeding port and the solid phase outlet of the horizontal screw discharge sedimentation centrifuge 20.

[0040] Compared with the prior art, the sodium hypophosphite continuous solid-liquid separation and recovery system shown in the embodiment has the following beneficial effects: The two-stage series connection hydrocyclone group shown in the embodiment can efficiently grade and pre-concentrate the mixed slurry, not only greatly reducing the processing load of the main centrifugal machine, but also making most of the clear liquid be recovered as the finished product mother liquor in the pretreatment stage, thereby improving the overall efficiency. Moreover, the slurry with different concentrations is accurately sent to the optimal position of the horizontal screw centrifugal machine, effectively avoiding the mutual interference of the materials, and creating the best sedimentation conditions for coarse and fine particles, so that a drier solid phase and a clearer liquid phase are obtained while ensuring a very high solid recovery rate. The continuous countercurrent washing process integrated in the centrifugal machine maximizes the recovery of high-value products entrained in the solid phase, and in combination with the mother liquid partitioning and collecting technology, realizes the material grading optimization of thick mother liquid direct recovery and dilute washing liquid recycling, significantly improves the product yield of sodium hypophosphite, and reduces the fresh water consumption and wastewater treatment cost. The fully closed and continuous process effectively overcomes the disadvantages of low efficiency, high labor intensity and product loss of the traditional batch operation.

[0041] In the description of the present specification, the description referring to the terms "one embodiment", "some embodiments", "an example", "a specific example", or "some examples" and the like means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present specification, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0042] The above-described embodiments only express several implementation manners of the present application, and the description is relatively specific and detailed, but it should not be understood as a limitation on the patent scope of the present application. It should be noted that, for those skilled in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which are all within the protection scope of the present application. Therefore, the protection scope of the patent of the present application should be subject to the appended claims.

Claims

1. A continuous solid-liquid separation and recovery method for sodium hypophosphite, characterized in that, The method includes: Sodium hypophosphite mixed slurry is transported to a hydrocyclone group for pre-concentration; the high solids content concentrated slurry is discharged from the underflow port of the first-stage hydrocyclone, and its overflow enters the second-stage hydrocyclone for secondary separation; the low solids content slurry is discharged from the underflow port of the second-stage hydrocyclone, and its overflow port discharges clear liquid as the finished product mother liquor. The underflow concentrated slurry from the first-stage hydrocyclone and the underflow slurry from the second-stage hydrocyclone are simultaneously and continuously fed to different feed points in the horizontal screw discharge sedimentation centrifuge. Inside the horizontal screw discharge sedimentation centrifuge, one or more streams of washing liquid are used to continuously countercurrently wash the solid filter cake being conveyed, so that the dilute sodium hypophosphite solution generated during washing and the separated mother liquor are collected in separate sections within the drum.

2. The continuous solid-liquid separation and recovery method for sodium hypophosphite according to claim 1, characterized in that, The underflow concentrated slurry from the first-stage hydrocyclone is conveyed to the main feed inlet in the middle of the drum of the horizontal screw discharge sedimentation centrifuge, and the underflow slurry from the second-stage hydrocyclone is conveyed to the auxiliary feed inlet between the main feed inlet and the solid phase outlet of the horizontal screw discharge sedimentation centrifuge.

3. The continuous solid-liquid separation and recovery method for sodium hypophosphite according to claim 1, characterized in that, The dilute sodium hypophosphite solution produced after washing and the clear liquid discharged from the overflow port of the second-stage hydrocyclone are collected separately.

4. The continuous solid-liquid separation and recovery method for sodium hypophosphite according to claim 3, characterized in that, The dilute sodium hypophosphite solution generated after washing is collected and refluxed to the upstream reaction process or used to prepare the washing solution.

5. The continuous solid-liquid separation and recovery method for sodium hypophosphite according to claim 4, characterized in that, The washing liquid is any one of hot water, dilute sodium hypophosphite solution, or steam condensate.

6. The continuous solid-liquid separation and recovery method for sodium hypophosphite according to any one of claims 1-5, characterized in that, The feed pressure of the hydrocyclone assembly is controlled between 0.2 MPa and 0.8 MPa.

7. The continuous solid-liquid separation and recovery method for sodium hypophosphite according to claim 6, characterized in that, By adjusting the opening of the underflow valve of the first-stage hydrocyclone in the hydrocyclone assembly, the weight of solid matter in the underflow concentrated slurry is controlled to account for 40%-60% of the total weight.

8. The continuous solid-liquid separation and recovery method for sodium hypophosphite according to claim 6, characterized in that, The speed difference between the drum and the screw feeder in the horizontal screw discharge sedimentation centrifuge is 2 rpm to 15 rpm.

9. A continuous solid-liquid separation and recovery system for sodium hypophosphite, characterized in that, The system, applicable to the method of any one of claims 1-8, comprises: Hydrocyclone assembly, including a first-stage hydrocyclone and a second-stage hydrocyclone; A horizontal screw discharge sedimentation centrifuge, wherein the underflow port of the first-stage hydrocyclone and the underflow port of the second-stage hydrocyclone are respectively connected to different feed points in the horizontal screw discharge sedimentation centrifuge.

10. The continuous solid-liquid separation and recovery system for sodium hypophosphite according to claim 9, characterized in that, The overflow port of the first-stage hydrocyclone is connected to the material inlet of the second-stage hydrocyclone; The underflow port of the first-stage hydrocyclone is connected to the main feed port in the middle of the drum of the horizontal screw discharge sedimentation centrifuge, and the underflow port of the second-stage hydrocyclone is connected to the auxiliary feed port between the main feed port and the solid phase outlet of the horizontal screw discharge sedimentation centrifuge.

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