White water treatment method based on paper machine white water recovery treatment system

Abstract

The invention relates to a white water treatment method based on a paper machine white water recovery treatment system. The recovery treatment system comprises a white water tank, a water feeding pump, a dissolved air tank and a shallow air flotation device which are connected in sequence; a clarified liquid outlet of the shallow air floatation device is connected with a filter, and a clarified liquid outlet of the filter is connected with a clarified white water tank; a wet strength agent feeding point is arranged between an outlet of the white water tank and an inlet of the water feeding pump; the white water treatment method comprises the following steps: adding a wet strength agent at a wet strength agent feeding point, enabling white water to be treated to flow into a dissolved air tank together with the wet strength agent from a white water tank through a water feeding pump, and introducing compressed air into the dissolved air tank to treat a mixture; the treated white water is input into a shallow-layer air flotation device for separation, and the separated clear liquid is input into a clear white water tank after passing through a filter. Compared with the prior art, the air floatation treatment effect and the overall operation efficiency of the paper machine white water recovery treatment system are remarkably improved.

Description

Technical Field

[0001] The invention belongs to the technical field of papermaking, and in particular relates to a white water treatment method based on a paper machine white water recovery and treatment system. Background Art

[0002] Shallow flotation technology is an advanced white water recovery technology used in the papermaking field, mostly used for white water recovery of paper machines. After the white water from the paper machine is collected, part of the white water is separated from the pulp and water through shallow flotation, and the recovered pulp is reused in the pulp system. The separated clarified white water can be used for flushing and partial spraying.

[0003] In the shallow flotation process, it is often necessary to add flocculants to the sewage to promote the formation of easily separable flocs from suspended solids and colloids in the wastewater, thereby achieving solid-liquid separation. In the shallow flotation tank, flocculants are often added when the sewage enters the pipe. However, due to many instabilities and hidden dangers in the use of flocculants, it is easy to cause abnormal production of paper machines. Traditional flocculants are high molecular polymers, and although they have improved the flotation treatment effect to a certain extent, excessive flocculation will make it difficult to disperse the flocs. The reuse of this part of the recycled pulp in the system will lead to unstable production, the formation of paper diseases, and even the risk of being unable to continue production.

[0004] If flocculants are not added, the separation effect of pulp and water in the flotation process will be poor, and the suspended solids content in the effluent water will be high, which will clog the subsequent filter equipment. The filter blockage will further lead to insufficient clarified water, and additional clean water will be required. At the same time, clarified white water with high suspended solids content will cause the wet end guide roller to entangle with the pulp and throw it, which will reduce the operating efficiency of the paper machine.

[0005] Therefore, the problems of low separation efficiency and decreased paper machine operating efficiency in existing white water recovery treatment need to be solved urgently. Summary of the invention

[0006] The purpose of the present invention is to provide a white water treatment method based on a paper machine white water recovery and treatment system in order to overcome the defects of the prior art that the steam flotation separation efficiency is low and easily leads to a decrease in the operating efficiency of the paper machine.

[0007] The purpose of the present invention can be achieved by the following technical solutions:

[0008] A white water treatment method based on a paper machine white water recovery and treatment system, the recovery and treatment system comprises a white water tank, a water supply pump, an air dissolving tank and a shallow flotation device connected in sequence; the clarified liquid outlet of the shallow flotation device is connected to a filter, and the clarified liquid outlet of the filter is connected to a clarified white water tank;

[0009] A wet strength agent feeding point is provided between the outlet of the white water tank and the inlet of the water supply pump;

[0010] The white water treatment method comprises the following steps: adding a wet strength agent at a wet strength agent feeding point, the white water to be treated flows from the white water tank into an air dissolving tank together with the wet strength agent through a water supply pump, and is mixed with compressed air in the air dissolving tank; the treated white water is input into a shallow flotation device for separation, and the clarified liquid after separation is input into a clarified white water tank after passing through a filter.

[0011] Furthermore, the fiber outlet of the shallow flotation device is connected to a recovery pulp tank.

[0012] Furthermore, the slurry outlet of the filter is connected to a slurry recovery tank.

[0013] Furthermore, the filter is a rotary gravity filter.

[0014] Furthermore, the water supply capacity of the water supply pump is 150-200m 3 / h.

[0015] Furthermore, the gas flow rate of the compressed air is 7.5-10m 3 / h.

[0016] Furthermore, the addition amount of the wet strength agent is 0.8-1.8 kg / ton of paper.

[0017] Furthermore, the solid content of the wet strength agent is 10-15%, preferably 12.5%.

[0018] Furthermore, the wet strength agent is a cationic polyamide epichlorohydrin resin.

[0019] Furthermore, the turbidity of the flotation water from the shallow flotation device is ≤60NTU.

[0020] Furthermore, the flotation efficiency of the shallow flotation device is >80%.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] (1) The present invention adds a wet strength agent at the feeding point between the white water tank and the upper water pump, which can not only significantly improve the flotation treatment effect of the shallow flotation device, but also reduce the subsequent filter blockage and the defects of the recovered pulp being unusable due to low concentration, thereby improving the overall operating efficiency of the paper machine white water recovery and treatment system.

[0023] (2) The present invention significantly improves the effluent quality, significantly alleviates the clogging of the gravity filter, and significantly improves the wet part environment by adding the wet strength agent. The wet strength agent is added from the original position close to the shallow flotation to before and after the pump. Due to more complete mixing, the fine fibers and the wet strength agent colloid are more fully combined, and micro-flocculation is more easily formed, thereby improving the flotation efficiency and achieving a better flotation treatment effect.

[0024] (3) The present invention confirms the reasonable range of the amount of wet strength agent added by comprehensively considering the flotation treatment efficiency and the addition cost, and the flotation efficiency is greater than 85%, which is conducive to the actual papermaking production. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a structural schematic diagram of the paper machine white water recovery and treatment system of the present invention.

[0026] Description of the markings in the figure:

[0027] 1-white water tank, 2-water supply pump, 3-dissolved air tank, 4-shallow flotation device, 5-filter, 6-clarified white water tank, 7-wet strength agent feeding point, 8-recovery slurry tank. DETAILED DESCRIPTION

[0028] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0029] In the present invention, it should be noted that the orientation or positional relationship indicated by the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, which is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention; the terms "first", "second", and "third" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance; in addition, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be an indirect connection through an intermediate medium, or it can be the internal communication of two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to the specific circumstances. It should be noted that similar numbers and letters represent similar items in the following drawings, so once an item is defined in one drawing, it does not need to be further defined and explained in the subsequent drawings.

[0030] Unless otherwise specified, the reagents, methods, instruments and equipment used in the present invention are conventional reagents, methods, instruments and equipment in the art. Unless otherwise specified, the reagents and materials used in the following examples are commercially available. Among them, the wet strength agent is polyamide epichlorohydrin with a solid content of 12.5%, a cationic amber liquid, model HK-2, purchased from Suzhou Hengkang.

[0031] The paper machine white water recovery and treatment system in the following embodiments and comparative examples all include a white water tank 1, a water supply pump 2, an air dissolving tank 3 and a shallow flotation device 4 connected in sequence. The clarified liquid outlet of the shallow flotation device 4 is connected to a filter 5, and the clarified liquid outlet of the filter 5 is connected to a clarified white water tank 6, and the filter 5 is a rotary gravity filter. The fiber outlet of the shallow flotation device 4 is connected to a recovery slurry tank 8, and the slurry outlet of the filter 5 is connected to the recovery slurry tank 8. A wet strength agent feeding point 7 is provided between the outlet of the white water tank 1 and the inlet of the water supply pump 2.

[0032] Embodiment 1:

[0033] The white water treatment method of this embodiment is as follows: wet strength agent is added at wet strength agent feeding point 7, and the white water to be treated flows from white water tank 1 through water supply pump 2 and wet strength agent into air dissolving tank 3, and is mixed with compressed air in air dissolving tank 3. The treated white water is input into shallow flotation device 4 for separation, and the clarified liquid after separation is input into clarified white water tank 6 after passing through filter 5.

[0034] The water supply capacity of the water supply pump 2 in this embodiment is 180m 3 / h, the gas flow rate of compressed air is 9m 3 / h, the amount of wet strength agent added is 0.8kg / ton of paper.

[0035] Embodiment 2:

[0036] The white water treatment method of this embodiment is as follows: wet strength agent is added at wet strength agent feeding point 7, white water to be treated flows from white water tank 1 through water supply pump 2 together with wet strength agent into air dissolving tank 3, and compressed air is introduced into air dissolving tank 3 to treat the mixture. The treated white water is input into shallow flotation device 4 for separation, and the separated clarified liquid is input into clarified white water tank 6 after passing through filter 5.

[0037] The water supply capacity of the water supply pump 2 in this embodiment is 180m 3 / h, the gas flow rate of compressed air is 9m 3 / h, the amount of wet strength agent added is 1.2kg / ton of paper.

[0038] Embodiment 3:

[0039] The white water treatment method of this embodiment is as follows: wet strength agent is added at wet strength agent feeding point 7, white water to be treated flows from white water tank 1 through water supply pump 2 together with wet strength agent into air dissolving tank 3, and compressed air is introduced into air dissolving tank 3 to treat the mixture. The treated white water is input into shallow flotation device 4 for separation, and the separated clarified liquid is input into clarified white water tank 6 after passing through filter 5.

[0040] The water supply capacity of the water supply pump 2 in this embodiment is 180m 3 / h, the gas flow rate of compressed air is 9m 3 / h, the amount of wet strength agent added is 1.8kg / ton of paper.

[0041] Comparative Example 1:

[0042] This comparative example provides a white water treatment method, which is different from Example 1 in that no wet strength agent is added in this comparative example.

[0043] Comparative Example 2:

[0044] This comparative example provides a white water treatment method, which is different from Example 1 in that a wet strength agent is added at the inlet of the shallow flotation device 4 in this comparative example.

[0045] Comparative Example 3:

[0046] This comparative example provides a white water treatment method, which is different from Example 1 in that the amount of wet strength agent added in this comparative example is 0.3 kg / ton of paper.

[0047] Comparative Example 4:

[0048] This comparative example provides a white water treatment method, which is different from Example 1 in that the amount of wet strength agent added in this comparative example is 2.5 kg / ton of paper.

[0049] The present invention tests the flotation efficiency of the white water treatment methods of the above embodiment and comparative example, and the specific operation is: using a turbidity meter to measure the turbidity (unit NTU) of the flotation inlet and outlet water, and then calculating the flotation efficiency. The test results of the flotation efficiency of the above embodiment and comparative example are shown in Table 1.

[0050] Table 1 Test results of flotation efficiency of various embodiments and comparative examples

[0051]

[0052] As can be seen from the table above, in the white water treatment methods of Examples 1-3, by adding the wet strength agent, the turbidity of the flotation effluent water is significantly reduced, the effluent water quality is significantly improved, and the flotation efficiency is >85%. The clogging phenomenon of the gravity filter is significantly alleviated, the wet end environment is significantly improved, and the operating efficiency of the entire paper machine white water recovery and treatment system is also greatly improved.

[0053] Wet strength agents are mainly used to combine with fibers to increase the wet strength of paper during the papermaking process. Considering that wet strength agents are needed for household paper, and their positive charge characteristics can combine with fine fibers (fine fibers carry negative charges), the fine fibers after combination have a larger specific surface area, which makes it easier to float during the flotation process, thereby improving the flotation efficiency and making it easier to separate the pulp and water. Through the effective combination of the fiber and air flocs in the air dissolving tank and the dispersion of the water pump, the flocculated fiber clusters can float faster when the white water reaches the shallow flotation device to achieve the separation effect. Traditional flocculants are high molecular polymers, and although they have a certain improvement in the flotation treatment effect, excessive flocculation will make it difficult to disperse the flocs. The reuse of this part of the recycled pulp in the system will lead to unstable production, the formation of paper diseases, and even the risk of being unable to continue production.

[0054] In contrast, the white water of Comparative Example 1 without the addition of a wet strength agent will bring in more fibers during the shallow flotation treatment process, and will easily clog the screen when the gravity filter is used later, causing a large amount of effluent to enter the recovered pulp, resulting in a reduction in the amount of filtered water, and then insufficient water when using this part of the recycled water, thereby increasing the amount of clean water used. The entry of a large amount of white water into the recovered pulp will also cause the recovered pulp concentration to be too low, and when mixed into the pulp, it will lower the pulp concentration, causing the concentration to be unstable and unable to be used, and can only be discharged, resulting in a waste of pulp. It can be seen from this that the treatment method of adding a wet strength agent to the inlet of the water pump of the present invention not only improves the efficiency of the flotation treatment, but also further reduces the subsequent clogging of the rotary gravity filter and the introduction of a large amount of white water into the recovered pulp.

[0055] Comparing Example 1 with Comparative Example 2, the addition position of the wet strength agent is changed from the original position close to the shallow flotation position to before the water supply pump. Due to more complete mixing, the fine fibers and the wet strength agent colloid are more fully combined and it is easier to form microflocculation, thereby improving the flotation efficiency and achieving a better flotation treatment effect.

[0056] In the actual production process, it is also necessary to comprehensively consider the actual factors of the additive cost, so that the addition of the wet strength agent can not only improve the flotation efficiency, but also achieve good economic benefits. From the data of Examples 1-3 and Comparative Examples 1, 3, and 4, as the content of the wet strength agent continues to increase, the flotation efficiency also continues to increase, and the flotation efficiency can gradually reach a relatively ideal removal efficiency value. When the amount of wet strength agent added increases from 1.8 to 2.5 kg / ton of paper, the flotation efficiency only increases from 88.28% to 88.58%. Increasing the amount of wet strength agent used does not bring about a further improvement in the effluent water quality as the amount increases, and it also consumes more drug costs.

[0057] The above description of the embodiments is to facilitate the understanding and use of the invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the scope of protection of the present invention.

Claims

1. A white water treatment method based on a paper machine white water recovery and treatment system, characterized in that: The recycling and treatment system comprises a white water tank (1), a water supply pump (2), an air dissolving tank (3) and a shallow flotation device (4) which are connected in sequence; the clarified liquid outlet of the shallow flotation device (4) is connected to a filter (5), and the clarified liquid outlet of the filter (5) is connected to a clarified white water tank (6); A wet strength agent feeding point (7) is provided between the outlet of the white water tank (1) and the inlet of the water supply pump (2); The white water treatment method comprises the following steps: a wet strength agent is added at a wet strength agent feeding point (7); the white water to be treated flows from a white water tank (1) through a water supply pump (2) and the wet strength agent into an air dissolving tank (3) and is mixed with compressed air in the air dissolving tank (3); the treated white water is input into a shallow flotation device (4) for separation; and the clarified liquid after separation passes through a filter (5) and is input into a clarified white water tank (6).

2. The white water treatment method based on the paper machine white water recovery and treatment system according to claim 1 is characterized in that: The fiber outlet of the shallow flotation device (4) is connected to the recovery pulp tank (8).

3. The white water treatment method based on the paper machine white water recovery and treatment system according to claim 2 is characterized in that: The slurry outlet of the filter (5) is connected to the slurry recovery tank (8).

4. The white water treatment method based on the paper machine white water recovery and treatment system according to claim 1 is characterized in that: The filter (5) is a rotary gravity filter.

5. The white water treatment method based on the paper machine white water recovery and treatment system according to claim 1 is characterized in that: The water supply capacity of the water supply pump (2) is 150-200m 3 / h.

6. The white water treatment method based on the paper machine white water recovery and treatment system according to claim 1 is characterized in that: The gas flow rate of the compressed air is 7.5-10m 3 / h.

7. The white water treatment method based on the paper machine white water recovery and treatment system according to claim 1 is characterized in that: The addition amount of the wet strength agent is 0.8-1.8 kg / ton of paper.

8. The method for treating white water based on a paper machine white water recovery and treatment system according to claim 1, characterized in that: The wet strength agent is a cationic polyamide epichlorohydrin resin.

9. The white water treatment method based on the paper machine white water recovery and treatment system according to claim 1, characterized in that: The turbidity of the flotation water from the shallow flotation device (4) is ≤60NTU.

10. The white water treatment method based on the paper machine white water recovery and treatment system according to claim 1, characterized in that: The flotation efficiency of the shallow flotation device (4) is >80%.

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