Alkali recovery system for chemi-mechanical pulp production waste liquid

Abstract

According to the alkali recovery system for the chemical-mechanical pulp production waste liquid, the chemical-mechanical pulp waste liquid is primarily concentrated through the multiple-effect evaporation tank group, and then the forced circulation tank group is used for intensively concentrating, so that the low-concentration waste liquid is processed into the high-concentration waste liquid required by the alkali recovery furnace. A medicine source filled with a scale inhibitor is arranged on the side edge of the multi-effect evaporation tank group, and the scale inhibitor is conveyed into each evaporation tank through a dosing pump and a dosing pipeline to flow along with the chemical-mechanical pulp waste liquid. According to the utility model, the waste liquid is treated by adopting an evaporation process, the scale inhibitor can effectively inhibit scaling in the evaporation tank in the flowing process, and the formed scale is loose, so that the inside of the evaporation tank can be conveniently cleaned manually or mechanically, and the effective working time of the evaporation tank is prolonged.

Description

Technical Field

[0001] This utility model relates to a waste liquid recovery system, and more particularly to an alkali recovery system for waste liquid from chemical pulp production. Background Technology

[0002] Evaporation concentration is a common processing method in the recovery of wastewater from chemical pulping. Its basic principle is to concentrate the wastewater generated in the papermaking pulping process through evaporation in an evaporator until it reaches the specific concentration required by the alkali recovery boiler. Black liquor is produced during pulping, and its main components include fibers, impurities, and silt. These components deposit on the walls of the heat exchange tubes during the operation of the evaporation system, gradually accumulating over time to form scale. This reduces the heat exchange capacity of the evaporator and lowers its wastewater treatment capacity. Scale accumulation necessitates system shutdown for maintenance, significantly reducing the continuous operating time of the evaporation system and impacting the efficiency of the recovery process. Utility Model Content

[0003] To solve the above-mentioned technical problems, this utility model provides an alkali recovery system for chemical pulp production waste liquid, including a low-concentration waste liquid tank, a multi-effect evaporator group, a forced circulation tank group, a high-concentration waste liquid tank, and an alkali recovery furnace connected in sequence along the waste liquid flow direction. The multi-effect evaporator group is composed of multiple evaporators connected in series. A chemical source is also provided on the side of the multi-effect evaporator group. The chemical source is filled with scale inhibitor and is connected to the multi-effect evaporator group through a dosing pump and a dosing pipeline.

[0004] Furthermore, the multi-effect evaporator group has four to eight effects, and the steam outlet of the preceding effect is connected to the steam inlet of the following effect.

[0005] Furthermore, the forced circulation tank group is a set of forced circulation tanks or a combination of multiple forced circulation tanks connected in parallel.

[0006] Furthermore, the dosing pipeline is equipped with a dosing valve to regulate the dosing amount.

[0007] Furthermore, the scale inhibitor is an alkaline scale inhibitor with a pH of 10.5-11.4.

[0008] Furthermore, the dosing pipeline is connected to at least the last evaporator of the multi-effect evaporator group.

[0009] Furthermore, flash tanks are installed between the forced circulation tank group, the multi-effect evaporator group, and the high-concentration waste liquid tank.

[0010] Furthermore, the steam inlet of the first-effect evaporator of the multi-effect evaporator group is connected to a fresh steam source.

[0011] This invention provides an alkali recovery system for chemimechanical slurry production wastewater. The system uses a multi-effect evaporator group to initially concentrate the chemimechanical slurry wastewater, followed by enhanced concentration using a forced circulation tank group, to process the low-concentration wastewater into the high-concentration wastewater required for the alkali recovery furnace. A scale inhibitor source is installed on the side of the multi-effect evaporator group. The scale inhibitor is delivered to each evaporator via a dosing pump and pipeline, flowing with the chemimechanical slurry wastewater. This invention uses an evaporation process to treat the wastewater. The scale inhibitor effectively inhibits scale formation inside the evaporator during its flow, resulting in loose scale that is easy to clean manually or mechanically, thus increasing the effective working time of the evaporator. Attached Figure Description

[0012] Figure 1 This is a schematic diagram of the planar structure of an alkali recovery system for chemical pulp production waste liquid according to this utility model. Detailed Implementation

[0013] like Figure 1 The system described herein is an alkali recovery system for chemimechanical pulp production waste liquid, used to concentrate the waste liquid generated during the pulping process into a specific high-concentration concentrated waste liquid. The recovery system includes a low-concentration waste liquid tank, a multi-effect evaporator group, a forced circulation tank group, a high-concentration waste liquid tank, and an alkali recovery furnace, connected sequentially along the waste liquid flow direction. The chemimechanical pulp production waste liquid is collected in the low-concentration waste liquid tank and transferred to the multi-effect evaporator group, where some of the liquid is evaporated, thus achieving initial concentration of the waste liquid. The forced circulation tank group then enhances the evaporation and circulation of the waste liquid, resulting in concentrated waste liquid in the high-concentration waste liquid tank. Finally, the concentrated waste liquid is sent to the alkali recovery furnace for combustion and recovery treatment.

[0014] The multi-effect evaporator group consists of evaporators from the first to the eighth effect connected in series. The steam outlet at the front is connected to the steam inlet at the rear. Fresh steam is supplied by three parallel first-effect evaporators, where the pressure is highest. The secondary steam generated by the preceding evaporators provides heat for evaporation in the subsequent evaporators, gradually increasing the vacuum level. The waste liquid flows in the opposite direction to the steam, entering from the eighth-effect evaporator at the end, where the concentration is lowest. The concentration gradually increases during the flow, while the concentration in each effect evaporator remains relatively stable. Specifically, a top condenser is connected between the fourth and fifth effect evaporators within the multi-effect evaporator group, providing the refrigeration cycle for the entire group.

[0015] The black liquor from pulping contains impurities such as fibers, slag, and silt. These materials adhere to the walls of the heat exchange tubes in the evaporator during evaporation, accumulating over time and forming scale on the tubes, thus reducing heat exchange efficiency. Therefore, this embodiment includes a chemical source on the side of the multi-effect evaporator group to remove scale buildup within the evaporators. The chemical source, filled with a scale inhibitor, is connected to the multi-effect evaporator group via a dosing pump and pipeline. The agent flows with the waste liquor into the evaporators, reducing scale formation in each tank. A dosing valve is installed on the dosing pipeline to precisely control the amount of scale inhibitor added to the evaporators.

[0016] In the treatment of wastewater from chemical pulp production, the main components of scaling materials are calcium oxalate and calcium carbonate. To prevent corrosion of the evaporator walls, an alkaline agent with a pH between 10.5 and 11.4 is selected as the scale inhibitor. The scale inhibitor can be added through dosing ports on the walls of each evaporator, allowing for individual dosing. In this embodiment, due to the long flow path of the black liquor, the scale inhibitor is distributed across the third, fifth, and eighth effects. The eighth effect evaporator is the initial inflow point for the wastewater, and the dosage there is set to the maximum, allowing the scale inhibitor to flow with the wastewater throughout the multi-effect evaporator group. The third and fifth effects are used to replenish the scale inhibitor content in the wastewater, ensuring sufficient scale inhibition in each evaporator. Specifically, the total scale inhibitor dosage is 40 ppm (approximately 200 kg) of the total wastewater volume, with 50% added in the eighth effect and 25% each in the third and fifth effects. After using scale inhibitors, the scale deposits formed inside the evaporator become significantly looser, greatly reducing the difficulty of manual and mechanical cleaning.

[0017] After the waste liquid is concentrated by the multi-effect evaporator array, its concentration will increase accordingly. A forced circulation tank array is installed downstream of the multi-effect evaporator array. This forced circulation tank array consists of one or more sets of tanks connected in parallel. Fresh steam is introduced into the forced circulation tanks to create a higher pressure. Compared to ordinary evaporators, the forced circulation tanks can fully circulate and heat the waste liquid, enhancing the concentration effect and ultimately obtaining the desired high-concentration waste liquid.

[0018] Furthermore, a flash tank (No. 1) and a flash tank (No. 2) are installed between the forced circulation tank group, the multi-effect evaporator group, and the high-concentration waste liquid tank, respectively, to accelerate the flash evaporation process of the waste liquid. The waste liquid is processed sequentially through the multi-effect evaporator group, the flash tank (No. 1), the forced circulation tank group, and the flash tank (No. 2) before flowing to the high-concentration waste liquid tank for collection.

[0019] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A system for recovering alkali from waste liquid in chemical pulp production, characterized in that: It includes a low-concentration waste liquid tank, a multi-effect evaporator group, a forced circulation tank group, a high-concentration waste liquid tank, and an alkali recovery furnace, which are connected in sequence along the waste liquid flow direction. The multi-effect evaporator group is composed of multiple evaporators connected in series. A chemical source is also provided on the side of the multi-effect evaporator group. The chemical source is filled with scale inhibitor and is connected to the multi-effect evaporator group through a dosing pump and a dosing pipeline.

2. The alkali recovery system for chemical mechanical pulp production waste liquid as described in claim 1, characterized in that: The multi-effect evaporator group has four to eight effects, and the steam outlet of the previous effect is connected to the steam inlet of the subsequent effect.

3. The alkali recovery system for chemical mechanical pulp production waste liquid as described in claim 1, characterized in that: The forced circulation tank group is a set of forced circulation tanks or a combination of multiple forced circulation tanks connected in parallel.

4. The alkali recovery system for chemical pulp production waste liquid as described in claim 1, characterized in that: The dosing pipeline is equipped with a dosing valve to regulate the dosing amount.

5. The alkali recovery system for chemical mechanical pulp production waste liquid as described in claim 1, characterized in that: The scale inhibitor is an alkaline scale inhibitor with a pH of 10.5-11.

4.

6. The alkali recovery system for chemical mechanical pulp production waste liquid as described in claim 1, characterized in that: The dosing pipeline is connected to at least the last evaporator of the multi-effect evaporator group.

7. The alkali recovery system for chemical mechanical pulp production waste liquid as described in claim 1, characterized in that: Flash tanks are installed between the forced circulation tank group, the multi-effect evaporator group, and the high-concentration waste liquid tank.

8. The alkali recovery system for chemical mechanical pulp production waste liquid as described in claim 1, characterized in that: The steam inlet of the first-effect evaporator in the multi-effect evaporator group is connected to a fresh steam source.

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