A scale inhibitor special for papermaking black liquor and a preparation method thereof

Abstract

This invention provides a scale inhibitor specifically for papermaking black liquor and its preparation method. The scale inhibitor is characterized by being formulated from sodium acrylamide sulfonate and deionized water, with the sodium acrylamide sulfonate comprising 42-47% of the total mass of the scale inhibitor. The scale inhibitor has a pH of 2.5-3.8 at room temperature and a density of 1.09-1.22 g / cm³. This invention effectively ensures the continuous and efficient heat exchange performance of MVR evaporators, stabilizes equipment evaporation capacity, significantly reduces the frequency of downtime for cleaning due to scaling, significantly extends the continuous and stable operation cycle of the alkali recovery MVR system, effectively reduces power consumption, steam consumption, equipment maintenance, and manual descaling costs during production, and significantly improves the operational stability and production economy of the PRC-APMP pulping alkali recovery system, making it suitable for large-scale continuous industrial production applications.

Description

Technical Field

[0001] This invention relates to the field of papermaking black liquor treatment technology, and in particular to a special scale inhibitor for papermaking black liquor and its preparation method. Background Technology

[0002] In the production process of alkaline hydrogen peroxide bleached chemimechanical pulp (PRC-APMP), hydrogen peroxide is the core bleaching agent. In order to ensure the bleaching effect, inhibit the ineffective decomposition of hydrogen peroxide, and stabilize the working conditions of the bleaching system, special bleaching chelating agents and bleaching stabilizers need to be added in conjunction with the process.

[0003] Currently, commonly used chelating agents, stabilizers, and other chemical auxiliaries in the market generally contain phosphorus in their formulations. These phosphorus-containing components remain in the pulping system during the bleaching reaction and eventually flow into the pulping black liquor along with the process wastewater. Simultaneously, the wood chips used in pulping naturally carry calcium salts. Under the alkaline, high-temperature bleaching environment, the calcium components in the raw materials continuously dissolve and leach out, significantly increasing the concentration of free calcium ions in the black liquor system. Furthermore, under the strong oxidative bleaching effect of hydrogen peroxide, the lignin macromolecular structure in the pulp undergoes oxidative breakage and degradation, generating a large number of small-molecule organic acid ions such as oxalate, further enriching the scale-forming ion system in the black liquor.

[0004] In the subsequent mechanical vapor recompression (MVR) evaporation and concentration process, the free calcium ions in the black liquor can rapidly combine with phosphate and oxalate ions in the system to continuously generate insoluble calcium phosphate and calcium oxalate crystals, which adhere and accumulate on the plates of the MVR evaporator and the inner walls of the heat exchange pipes, forming a dense and difficult-to-remove hard scale layer.

[0005] This scaling problem significantly reduces the heat exchange efficiency of the evaporator, hinders the heat transfer of black liquor and the material concentration process, directly causes a decrease in equipment evaporation capacity and an increase in production energy consumption, significantly increases production electricity consumption, steam consumption and equipment operation and maintenance costs, and seriously restricts the stable, efficient and low-consumption operation of the alkali recovery system of the PRC-APMP pulping production line. Summary of the Invention

[0006] In view of the above technical problems, the present invention provides a special scale inhibitor for papermaking black liquor and its preparation method, which inhibits the formation and growth of calcium scale nuclei from the source of materials, effectively slows down the crystallization rate of calcium scale, improves the solubility of scale-forming ions, and avoids the agglomeration and adhesion of microcrystalline particles.

[0007] This invention provides a scale inhibitor for papermaking black liquor and its preparation method, characterized in that it is prepared by mixing sodium acrylamide sulfonate and deionized water, and the mass fraction of sodium acrylamide sulfonate is 42~47% based on the total mass of the scale inhibitor; the scale inhibitor has a pH of 2.5~3.8 at room temperature and a density of 1.09~1.22 g / cm3.

[0008] The sodium acrylamide sulfonate is sodium 2-acrylamido-2-methylpropanesulfonate.

[0009] This scale inhibitor was applied to the cleaning and evaporation of calcium scale in the chemical mechanical pulp black liquor system.

[0010] The specific steps for applying this scale inhibitor to the evaporation and scale inhibition of chemical mechanical pulp black liquor include: Step 1: Filter and pre-evaporate the dilute black liquor from the chemical mechanical pulp to complete the initial purification and concentration; Step 2: Add the scale inhibitor to the pretreated chemical mechanical slurry dilute black liquor, mix evenly, and then preheat to obtain the dilute black liquor to be evaporated; Step 3: The preheated dilute black liquor is concentrated by MVR evaporation to obtain concentrated black liquor.

[0011] The dosage of scale inhibitor in step two is 0.015 kg to 0.03 kg per cubic meter of dilute black liquor. After the dilute black liquor of the chemical mechanical slurry is fully mixed with the scale inhibitor, it is preheated by heat exchange using the waste heat water of the system. The temperature of the heat exchange preheating is controlled at 100℃ to 103℃.

[0012] Step one specifically involves: after the dilute black liquor from the chemical pulp is filtered to remove impurities, it is introduced into the evaporation wastewater tank to complete the initial pre-evaporation, and then transported to the dilute black liquor storage tank for later use.

[0013] The specific operation of step three, which involves MVR evaporation and concentration of the preheated dilute black liquor, is as follows: the preheated dilute black liquor is sent into the MVR evaporator by a transfer pump, and evaporation and concentration are completed by high-temperature steam heat exchange to obtain concentrated black liquor. The temperature of the high-temperature steam is 120℃~125℃, the temperature of the concentrated black liquor is 105℃~109℃, and the mass concentration of the concentrated black liquor is 10%~15%.

[0014] The beneficial effects of this invention are as follows: 1. Compared with traditional conventional additives, this invention has developed a special scale inhibitor specifically adapted to the PRC-APMP chemimechanical pulp black liquor MVR evaporation system. It selects sodium acrylamide sulfonate with high compatibility as the core functional component and strictly controls key parameters such as pH and density of the scale inhibitor to build a stable and efficient scale inhibition system.

[0015] This scale inhibitor molecule is rich in a large number of negatively charged hydrophilic functional groups. After being added to the black liquor system, it can play a dual core scale inhibition role: on the one hand, it can precisely attach to the active growth sites of calcium phosphate and calcium oxalate microcrystal nuclei through electrostatic adsorption, occupy the normal growth channel of crystals, destroy the regular crystal lattice structure of crystals, and cause lattice distortion, so that the originally regular and dense scale crystals cannot continue to grow, stack and aggregate, thus preventing hard scale layers from being deposited and formed on the surface of evaporator plates and heat exchange pipes from the root. On the other hand, this functional component has excellent calcium ion chelation and complexation properties, which can stably bind with free Ca²⁺ in black liquor, effectively reducing the activity of free calcium ions in the system, significantly weakening the effective collision probability of scale-forming ions in black liquor, and making it difficult for the ion products of [Ca²⁺]×[PO₄³⁻] and [Ca²⁺]×[C₂O₄²⁻] in the system to reach the solubility product constant (Ksp) of calcium phosphate and calcium oxalate, effectively delaying and inhibiting the crystallization and precipitation process of scale-forming ions, and significantly reducing the tendency of black liquor to scale. 2. This invention breaks away from the traditional end-of-pipe descaling and passive scale prevention treatment mode. It innovatively selects to add a special scale inhibitor at the inlet of the MVR evaporator, which can achieve full-area and uniform mixing of scale inhibitor components with the dilute black liquor of the chemical mechanical slurry. This allows the scale inhibitor components to act fully on the scale-forming ion system of the black liquor in advance, inhibiting the generation and growth of calcium scale nuclei from the source of materials, effectively slowing down the calcium scale crystallization rate, improving the solubility of scale-forming ions, and avoiding the agglomeration and adhesion of microcrystalline particles.

[0016] This pretreatment process can significantly reduce the scaling and enrichment effect under high-temperature evaporation conditions in MVR systems, suppressing scaling, adhesion, and fouling on evaporator plates throughout the entire process. Based on this, combined with routine online alkaline liquid cleaning and periodic manual descaling, the scaling rate of the MVR evaporator heat exchange plates and pipes can be reduced and slowed down comprehensively and at multiple levels.

[0017] This invention can effectively ensure the continuous and efficient heat exchange performance of MVR evaporators, stabilize the evaporation capacity of the equipment, significantly reduce the frequency of downtime cleaning due to scaling, significantly extend the continuous and stable operation cycle of the alkali recovery MVR system, effectively reduce the power consumption, steam consumption, equipment maintenance, and manual descaling costs in the production process, and greatly improve the operational stability and production economy of the PRC-APMP pulping alkali recovery system, making it suitable for large-scale continuous industrial production applications. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the process for controlling the evaporation and scale inhibition of black liquor in the chemical mechanical pulp of this invention. Detailed Implementation

[0019] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for 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. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0021] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances. Furthermore, the technical features involved in the different embodiments of this invention described below can be combined with each other as long as they do not conflict with each other. Example 1

[0022] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings.

[0023] As shown in the figure, the present invention provides a scale inhibitor for papermaking black liquor, the scale inhibitor comprising sodium acrylamide sulfonate with a mass fraction of 42-47%; the scale inhibitor has a pH of 2.5-3.8 and a density of 1.09-1.22 g / cm3; the sodium acrylamide sulfonate is sodium 2-acrylamido-2-methylpropanesulfonate.

[0024] Specifically, the scale inhibitor is CMP1800 scale inhibitor, preferably an aqueous solution of sodium acrylamide sulfonate (Na-AMPS).

[0025] This scale inhibitor has inhibitory, dispersing, and chelating effects to delay or inhibit crystal precipitation. The specific scale inhibition principle is as follows: (1) Inhibition effect - lattice distortion Adsorption: The copolymer chain in the scale inhibitor has a large number of negatively charged functional groups (-COO⁻ and -SO3⁻). These functional groups will strongly adsorb onto the active growth points of the newly formed calcium phosphate microcrystal nuclei. Since the calcium phosphate crystal nuclei themselves are positively charged, they are combined with the negatively charged functional groups through electrostatic attraction. Blocking growth points: Functional groups on copolymer chains, especially the bulky sulfonic acid groups (-SO3⁻), once adsorbed onto the crystal nucleus, will block the growth points where they combine with other ions (Ca²⁺, PO4³⁻) in the crystal nucleus; Lattice distortion: When a normal, ordered crystal is disturbed during growth, it cannot grow according to a perfect lattice structure and is forced to become distorted, forming an irregular, loose, twisted crystal. Difficult to deposit: These distorted crystals are unstable and difficult to grow into a hard scale layer. Even if a deposit is formed, it is a soft, muddy substance that is easily washed away by water flow and will not adhere firmly to the surface of pipes or equipment.

[0026] (2) Dispersion effect - electrostatic repulsion The sulfonic acid group (-SO3⁻) provided by the scale inhibitor is a strongly ionized group with a strong negative charge. It gives the entire copolymer molecular chain a high negative charge density. These negatively charged copolymer chains not only adsorb onto the crystal nuclei, but also wrap around the already formed tiny scale particles. All the wrapped particles have the same negative charge on their surface. According to the principle of like charges repelling each other, these particles will repel each other and are difficult to aggregate and grow, thus inhibiting the Ostwald curing process. This charge repulsion also makes it difficult for particles to approach and deposit on the surface of metal equipment, which is usually negatively charged.

[0027] (3) Chelation effect – threshold effect The carboxyl groups (-COO⁻) and sulfonic acid groups (-SO3⁻) in the copolymer molecules have a certain chelating ability for calcium ions (Ca²⁺), which can "bind" some free calcium ions. This is equivalent to temporarily reducing the effective concentration of Ca²⁺ in the solution, making it difficult for the ion product of [Ca²⁺] × [PO4³⁻] to reach the solubility product constant (Ksp) of calcium phosphate, thereby delaying or inhibiting the crystallization process. Example 2

[0028] See appendix Figure 1 This invention provides a scale inhibitor specifically for papermaking black liquor. The specific steps for applying this scale inhibitor to the evaporation and scale inhibition of chemical mechanical pulp black liquor include: S1, filter and pre-evaporate the dilute black liquor from the pulp; Specifically, the chemical mechanical pulp dilute black liquor is filtered by a filter and then enters an evaporation wastewater tank for preliminary evaporation before being stored in a dilute black liquor storage tank. The dilute black liquor of the chemimechanical pulp is an alkaline hydrogen peroxide bleached chemimechanical pulp (PRC-APMP) dilute black liquor with a concentration of ≤3%, a fiber content of ≤50ppm, and a temperature of 90~95℃. S2, add the MVR scale inhibitor to the dilute black liquor of the chemical mechanical slurry, and preheat to obtain dilute black liquor; Specifically, before entering the MVR evaporator, the chemical mechanical slurry dilute black liquor and the MVR scale inhibitor are mixed, and the waste heat generated by the MVR evaporator is used to preheat the two by heat exchange, so that the temperature rises from 90~95℃ to 100~103℃, and the dilute black liquor is obtained. The MVR scale inhibitor is added at a rate of 0.015~0.03 kg scale inhibitor / m3 of dilute black liquor, and the MVR scale inhibitor is added at the inlet of the delivery pump of the MVR evaporator. S3, the dilute black liquor is evaporated and concentrated to obtain concentrated black liquor; Specifically, the dilute black liquor is pumped to the MVR evaporator and heated by high-temperature steam at 120-125°C to achieve evaporation and concentration, thereby obtaining the concentrated black liquor. The temperature of the concentrated black liquor is 105-109°C, and the concentration of the concentrated black liquor is increased to 10-15%.

[0029] This invention innovatively adds the MVR scale inhibitor to the inlet of the MVR evaporator, allowing it to mix thoroughly with the dilute black liquor of the chemical mechanical slurry. This slows down and inhibits the crystallization rate of calcium scale, improves solubility, and, in conjunction with alkaline liquid cleaning and manual descaling, effectively reduces and slows down the scaling rate of the evaporation plates in the MVR evaporator. This helps to extend the stable operating cycle of the equipment and reduce the production costs of enterprises. Example 3

[0030] This embodiment discloses the operating status of the MVR evaporator before and after using an MVR scale inhibitor. The MVR scale inhibitor in this embodiment comprises 45% sodium acrylamide sulfonate by mass, and has a pH of 3 and a density of 1.15 g / cm³.

[0031] Before using the MVR scale inhibitor, the operating conditions of the MVR evaporator were as follows: Runtime (h) 14 24 24 24 24 24 24 Volume of dilute black liquor treated (m³) 2981 5011 4596 4586 4576 4647 4672 Wind turbine power consumption (kWh) 25268 45208 43555 44102 45071 45469 43233 Heavy condensate (m³) 231 405 380 386 437 396 361 MVR cleaning condensate (m³) 1988 3436 3129 3080 3074 3047 2854 <![CDATA[MVR evaporation specific energy consumption (kWh / m 3 )]]> 11.39 11.77 12.41 12.72 12.84 13.21 13.45 12.54 Forced low-pressure steam (t) 83 178 198 197 194 202 251 Forced lightly soiled condensate (m³) 365 734 814 816 809 828 1023 Forced evaporation ratio (m³ / t) 4.40 4.13 4.12 4.13 4.18 4.09 4.07 4.16 Before using the MVR scale inhibitor, the operating conditions of the MVR evaporator were as follows: Runtime (h) 24 24 24 15 24 24 24 Volume of dilute black liquor treated (m³) 5076 4904 4741 2971 4895 4490 4488 Wind turbine power consumption (kWh) 44785 44706 44041 27005 44713 41949 42273 Heavy condensate (m³) 417 410 380 238 367 310 369 MVR cleaning condensate (m³) 3396 3267 3276 2027 3378 3073 2972 <![CDATA[MVR evaporation ratio (kWh / m 3 )]]> 11.75 12.16 12.05 11.92 11.94 12.40 12.65 12.12 Forced low-pressure steam (t) 182 191 183 96 193 198 221 Forced lightly soiled condensate (m³) 742 774 748 403 775 800 879 Forced evaporation ratio (m³ / t) 4.07 4.04 4.08 4.20 4.01 4.04 3.98 4.06 Therefore, comparing the operation of the MVR evaporator before and after using the scale inhibitor, it can be seen that the power consumption and steam consumption of the MVR compressor fan are reduced after using the scale inhibitor, which helps to reduce production costs. In addition, from the trend of MVR evaporation ratio, the evaporation efficiency of the MVR evaporator decreases more slowly with the increase of operating time after using the scale inhibitor, indicating that the scale inhibitor can effectively reduce and delay the scaling rate of the evaporation plates and extend the stable operation cycle of the equipment. Example 4

[0032] This embodiment discloses the scale inhibition effect measured by changes in phosphate and calcium ions in black liquor under different MVR scale inhibitor dosages. Specifically, the MVR scale inhibitor in this embodiment comprises 45% sodium acrylamide sulfonate by mass, and the scale inhibitor has a pH of 3 and a density of 1.15 g / cm³. Note: Phosphate scale inhibition rate = concentrated black liquor orthophosphate / [dilute black liquor orthophosphate × (concentrated black liquor solid content / dilute black liquor solid content] × 100%; Total calcium scale inhibition rate = Calcium hardness of concentrated black liquor / [Calcium hardness of dilute black liquor × (Solid content of concentrated black liquor / Solid content of dilute black liquor] × 100%.

[0033] Therefore, as the dosage of the scale inhibitor increases, the scale inhibition rate of phosphoric acid and the scale inhibition rate of total calcium scale also increase. Example 5

[0034] This embodiment discloses the scale inhibition effect measured by the change in MVR fan power consumption under different MVR scale inhibitor dosages. The MVR scale inhibitor in this embodiment comprises 45% sodium acrylamide sulfonate by mass, and the scale inhibitor has a pH of 3 and a density of 1.15 g / cm³.

[0035] (1) The MVR scale inhibitor was not used. (2) The amount of the MVR scale inhibitor added is 0.015 kg scale inhibitor / m3 dilute black liquor. (3) The amount of the MVR scale inhibitor added is 0.02 kg scale inhibitor / m3 dilute black liquor. <![CDATA[Dilute black liquor treated by MVR evaporator (m 3 )]]> 4508 4501 2749 4602 4435 4159 Power consumption of MVR compressor (kWh) 39957 40959 21945 42829 42173 37572 <![CDATA[Amount of light polluted condensate from MVR evaporation (m 3 )]]> 3019 2978 1567 3152 2899 2723 <![CDATA[MVR evaporation of heavily contaminated condensed water (m 3 )]]> 410 408 233 445 395 378 MVR evaporator evaporation ratio (kWh / t water) 11.65 12.10 12.19 11.91 12.80 12.12 (5) The amount of the MVR scale inhibitor added is 0.03 kg scale inhibitor / m3 dilute black liquor. Therefore, as the dosage of the MVR scale inhibitor gradually increases, the power consumption of the fan decreases, the MVR evaporation ratio also decreases, the plate heat exchange effect is good, and the scaling situation is improved. Example 6

[0036] This embodiment discloses a combination of manual high-pressure cleaning and measures the scale inhibition effect on the evaporator by the change in MVR fan power consumption. Specifically, the MVR scale inhibitor in this embodiment comprises 45% sodium acrylamide sulfonate by mass, and the scale inhibitor has a pH of 3 and a density of 1.15 g / cm³.

[0037] No manual high-pressure cleaning was performed. Manual high-pressure cleaning Therefore, with manual cleaning of the heat exchange plates, the fan power consumption is reduced, the MVR evaporation ratio is reduced, the heat exchange effect of the plates is good, and the scale inhibition is improved. Example 7

[0038] This embodiment discloses that the scale inhibition effect on the evaporator is measured by the change in MVR fan power consumption before and after using the aforementioned MVR scale inhibitor. Specifically, the MVR scale inhibitor in this embodiment comprises 45% sodium acrylamide sulfonate by mass, and the scale inhibitor has a pH of 3 and a density of 1.15 g / cm³.

[0039] (1) Statistics on the change in power consumption of MVR fan before using the MVR scale inhibitor 1 4767 41828 3254 374 11.53 2 3044 27436 2078 235 11.86 3 4475 41819 3124 353 12.03 4 4579 43586 3062 373 12.69 5 4547 43527 2948 362 13.15 6 4514 41462 2727 334 13.54 7 4426 41941 2699 348 13.77 8 4494 43288 2661 364 14.31 9 2981 29570 1903 242 13.79 10 4543 44005 2969 336 13.31 11 4369 41967 2748 336 13.61 average value 4249 40039 2743 332 13.05 (2) Statistics on the change in power consumption of MVR fan after using the aforementioned MVR scale inhibitor 1 4822 41716 3439 314 11.12 2 2897 25800 1747 215 13.15 3 4606 39824 3157 382 11.25 4 424 1206 89 7 12.64 5 4569 43068 3467 365 11.24 6 2638 22861 1838 230 11.06 7 4635 43127 3227 444 11.75 8 2790 26302 1984 255 11.74 9 4560 41709 3193 423 11.54 10 2757 26019 1938 257 11.86 11 4473 41447 3167 389 11.66 12 2808 26970 1988 269 11.95 13 4600 42124 3248 421 11.48 14 2926 27292 2057 286 11.65 15 4789 43284 3398 440 11.28 16 3068 28855 2192 312 11.53 17 4649 42744 3323 483 11.23 18 4461 40484 3201 399 11.25 19 2898 26021 1929 287 11.75 20 4812 43179 3385 448 11.27 21 2824 26128 1926 274 11.88 22 4508 41111 3175 411 11.47 23 2807 25615 1941 221 11.85 24 4477 40952 3150 377 11.61 25 2618 23058 1715 202 12.03 26 4275 39266 3020 323 11.75 27 2291 21293 1599 158 12.12 28 4297 40360 3037 368 11.85 29 2511 24662 1809 195 12.31 30 4154 39033 2926 332 11.98 31 2516 22777 1646 194 12.38 32 1927 17343 1287 164 11.96 average value 3543 32363 2475 308 11.74 Therefore, after using MVR scale inhibitor, the scaling rate of MVR plates slows down, the increase in fan power consumption slows down, and the running time of MVR evaporator becomes longer.

[0040] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. The various components mentioned in this invention are common technologies in the existing field. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A scale inhibitor specifically for papermaking black liquor, characterized in that... It is prepared by mixing sodium acrylamide sulfonate and deionized water. The mass fraction of sodium acrylamide sulfonate is 42-47% based on the total mass of the scale inhibitor. The scale inhibitor has a pH of 2.5-3.8 at room temperature and a density of 1.09-1.22 g / cm3.

2. The scale inhibitor for papermaking black liquor according to claim 1, characterized in that... The sodium acrylamide sulfonate is sodium 2-acrylamido-2-methylpropanesulfonate.

3. The scale inhibitor for papermaking black liquor according to claim 2, characterized in that... This scale inhibitor was applied to the cleaning and evaporation of calcium scale in the chemical mechanical pulp black liquor system.

4. The scale inhibitor for papermaking black liquor according to claim 3, characterized in that... The specific steps for applying this scale inhibitor to the evaporation and scale inhibition of chemical mechanical pulp black liquor include: Step 1: Filter and pre-evaporate the dilute black liquor from the chemical mechanical pulp to complete the initial purification and concentration; Step 2: Add the scale inhibitor to the pretreated chemical mechanical slurry dilute black liquor, mix evenly, and then preheat to obtain the dilute black liquor to be evaporated; Step 3: The preheated dilute black liquor is concentrated by MVR evaporation to obtain concentrated black liquor.

5. A scale inhibitor for papermaking black liquor according to claim 4, characterized in that... The dosage of scale inhibitor in step two is 0.015 kg to 0.03 kg per cubic meter of dilute black liquor. After the dilute black liquor of the chemical mechanical slurry is fully mixed with the scale inhibitor, it is preheated by heat exchange using the waste heat water of the system. The temperature of the heat exchange preheating is controlled at 100℃ to 103℃.

6. A scale inhibitor for papermaking black liquor according to claim 4, characterized in that... Step one specifically involves: after the dilute black liquor from the chemical pulp is filtered to remove impurities, it is introduced into the evaporation wastewater tank to complete the initial pre-evaporation, and then transported to the dilute black liquor storage tank for later use.

7. The scale inhibitor for papermaking black liquor according to claim 4, characterized in that... The specific operation of step three, which involves MVR evaporation and concentration of the preheated dilute black liquor, is as follows: the preheated dilute black liquor is sent into the MVR evaporator by a transfer pump, and evaporation and concentration are completed by high-temperature steam heat exchange to obtain concentrated black liquor. The temperature of the high-temperature steam is 120℃~125℃, the temperature of the concentrated black liquor is 105℃~109℃, and the mass concentration of the concentrated black liquor is 10%~15%.

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