A black liquor concentration multi-effect evaporation tail gas recovery and utilization system

Abstract

This utility model relates to a black liquor concentration multi-effect evaporation tail gas recovery and utilization system, belonging to the field of energy-saving and environmental protection technology. The tail gas pipeline of the last effect of the multi-effect evaporation system is connected to the medium inlet on one side of the first heat exchanger. The other side of the first heat exchanger establishes black liquor medium circulation with the flash evaporator through a circulation pump. The exhaust steam generated by the flash evaporator enters the condenser through a channel. The flash evaporator is connected to the black liquor medium inlet of the multi-effect evaporation system through a black liquor discharge pipeline. A black liquor feed pipeline is provided on the other side of the first heat exchanger. This application significantly improves the energy cascade utilization efficiency and greatly reduces the overall energy consumption. The system recovers the waste heat of the tail gas of the last effect of the multi-effect evaporation system through the first heat exchanger, transferring the "waste heat energy" to the dilute black liquor to be concentrated, providing a heat source for the negative pressure flash evaporation of the flash evaporator; at the same time, the second heat exchanger realizes the heat exchange between the low-temperature feed dilute black liquor and the high-temperature pre-concentrated black liquor, tapping the potential for heat utilization.

Description

Technical Field

[0001] This utility model belongs to the field of energy-saving and environmental protection technology, and in particular relates to a black liquor concentration multi-effect evaporation tail gas recovery and utilization system. Background Technology

[0002] Black liquor is a byproduct of the alkaline cooking process in pulp mills. It is dark brown in color, hence the name. Due to variations in process flow and reagent usage for different pulp types, the concentration and alkali content of black liquor vary. For subsequent wastewater treatment and reagent recovery, black liquor often needs to be concentrated to minimize environmental pollution. Currently, black liquor concentration typically employs a multi-effect evaporation process. Fresh steam is used as the driving heat source for the first effect, secondary steam from the first effect serves as the driving heat source for the next effect, and the steam from the final effect is condensed in a cooling tower and discharged outdoors. However, this method requires a large amount of fresh steam and electricity, with significant energy wasted. This results in a substantial proportion of energy consumption, making pulp mills high-energy-consuming enterprises, imposing a considerable cost burden and significantly compressing profit margins. Maximizing and reducing the energy consumption of black liquor concentration through reasonable process methods, and expanding black liquor concentration capacity, is an effective way to address the current high energy consumption and shrinking economic benefits in pulp mills. Utility Model Content

[0003] To solve the above-mentioned technical problems, the technical solution adopted by this utility model is: a black liquor concentration multi-effect evaporation tail gas recovery and utilization system, comprising: a multi-effect evaporation system, wherein the tail gas pipeline of the last effect of the multi-effect evaporation system is connected to the medium inlet on one side of the first heat exchanger, and the other side of the first heat exchanger establishes black liquor medium circulation with the flash evaporator through a circulation pump, wherein the exhaust steam generated by the flash evaporator enters the condenser through a channel, and the flash evaporator is connected to the black liquor medium inlet of the multi-effect evaporation system through a black liquor discharge pipeline, and a black liquor feed pipeline is provided on the other side of the first heat exchanger.

[0004] Furthermore, the medium in the black liquor feed pipe and the medium in the black liquor discharge pipe exchange heat through a second heat exchanger.

[0005] Furthermore, the first heat exchanger and the second heat exchanger are shell-and-tube heat exchangers or plate heat exchangers.

[0006] Furthermore, the condensate outlet on one side of the first heat exchanger is connected to the condensate tank via a pipeline.

[0007] Furthermore, the condenser is connected to the condensate tank via a pipeline.

[0008] Furthermore, a feed pump is installed on the black liquor feed pipeline.

[0009] Furthermore, a discharge pump is installed on the black liquor discharge pipeline.

[0010] Furthermore, the condenser is connected to a cooling tower.

[0011] Furthermore, a cooling circulation pump is installed between the condenser and the cooling tower.

[0012] Furthermore, the condenser is connected to a vacuum pump via a pipeline.

[0013] The beneficial effects of this utility model are:

[0014] This application significantly improves energy cascade utilization efficiency and substantially reduces overall energy consumption. The system recovers waste heat from the final stage exhaust gas of the multi-effect evaporation system through the first heat exchanger, transferring the previously directly emitted "waste heat energy" to the concentrated black liquor, providing a heat source for the negative pressure flash evaporation of the flash evaporator. Simultaneously, the second heat exchanger facilitates heat exchange between the low-temperature feed black liquor and the high-temperature pre-concentrated black liquor, further tapping into the potential for heat utilization. This multi-stage waste heat recovery mode avoids the problem of significant energy waste after single-stage energy use in traditional processes, reduces fresh steam consumption, and lowers the load on the cooling tower as it only needs to cool the condenser circulating water. This reduces the power consumption of the cooling circulation pump and cooling tower fan, completely changing the "high energy consumption" status quo of pulp mill black liquor concentration and alleviating the energy cost pressure on enterprises.

[0015] This application expands black liquor concentration capacity and significantly improves economic benefits. The system innovatively adds a flash evaporator pre-concentration stage, where the dilute black liquor heated by the first heat exchanger undergoes premature moisture evaporation under negative pressure, reducing the water content of the pre-concentrated black liquor entering the multi-effect evaporation system. This process significantly reduces the evaporation load on the multi-effect evaporation system, shortens the processing cycle of black liquor in the main concentration unit, and increases the total amount of black liquor that the system can process per unit time, directly driving the expansion of pulp mill production capacity. Simultaneously, the condensate recovered from the condensate tank can be reused as process water, reducing fresh water procurement costs. These dual effects significantly broaden the profit margins of pulp mills and enhance their market competitiveness.

[0016] This application demonstrates significant environmental and resource recycling benefits, aligning with sustainable development requirements. From an environmental perspective, the system reduces fresh steam consumption through waste heat recovery, indirectly lowering carbon emissions from fossil fuel combustion. The exhaust gas from the final effect is condensed and recovered as liquid water, avoiding the potential environmental impact of direct emissions. Reduced cooling tower load also decreases circulating water evaporation losses and drift water usage, mitigating water pollution risks. From a resource recycling perspective, the condensate collected in the condensate tank is of excellent quality and can be reused for multi-effect evaporator makeup water and cooling tower makeup water, improving water resource reuse rates. The segmented treatment mode of pre-concentration and main concentration also reduces the loss of effective reagents in black liquor, providing better conditions for subsequent reagent recovery and achieving the dual goals of "environmental compliance" and "resource recycling." Attached Figure Description

[0017] Figure 1 This is a system diagram of this utility model.

[0018] The attached diagram shows the following components: multi-effect evaporation system 100, first heat exchanger 200, cooling tower 300, flash evaporator 400, channel 500, condenser 600, black liquor discharge pipeline 700, black liquor feed pipeline 800, second heat exchanger 900, and condensate tank 1000. Detailed Implementation

[0019] In the description of this utility model, it should be understood that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings, are only for the convenience of describing this utility model and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this utility model. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, features defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this utility model, unless otherwise stated, "a plurality of" means two or more.

[0020] In the description of this utility model, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "joining" 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 utility model based on the specific circumstances.

[0021] The present invention will be further described below with reference to embodiments and accompanying drawings: A black liquor concentration multi-effect evaporation tail gas recovery and utilization system includes: a multi-effect evaporation system 100, wherein the tail gas pipeline of the last effect of the multi-effect evaporation system 100 is connected to the medium inlet on one side of a first heat exchanger 200, and the other side of the first heat exchanger 200 establishes black liquor medium circulation with a flash evaporator 400 through a circulation pump; the exhaust steam generated by the flash evaporator 400 enters a condenser 600 through a channel 500; the flash evaporator 400 is connected to the black liquor medium inlet of the multi-effect evaporation system 100 through a black liquor discharge pipeline 700; and a black liquor feed pipeline 800 is provided on the other side of the first heat exchanger 200. The medium in the black liquor feed pipeline 800 and the medium in the black liquor discharge pipeline 700 exchange heat through a second heat exchanger 900. The first heat exchanger 200 and the second heat exchanger 900 are shell-and-tube heat exchangers or plate heat exchangers. The condensate outlet on one side of the first heat exchanger 200 is connected to the condensate tank 1000 via a pipeline. The condenser 600 is connected to the condensate tank 1000 via a pipeline. A feed pump is installed on the black liquor feed pipeline 800. A discharge pump is installed on the black liquor discharge pipeline 700. The condenser 600 is connected to the cooling tower 300. A cooling circulation pump is installed between the condenser 600 and the cooling tower 300. The condenser 600 is connected to a vacuum pump via a pipeline.

[0022] The multi-effect evaporation system 100 serves as the core main concentration unit in the entire black liquor concentration process. Its core function is to concentrate black liquor at high concentrations using a series structure. Internally, it can flexibly employ co-current, counter-current, or mixed-flow black liquor concentration processes to adapt to the treatment needs of black liquor with different concentrations. Simultaneously, this system acts as the source of the final-effect exhaust gas, transporting the exhaust gas, which would otherwise be directly discharged through the cooling tower, to the subsequent waste heat recovery unit via the final-effect exhaust gas pipeline, providing a core heat source for waste heat utilization. Its effects are twofold: firstly, it undertakes the core task of black liquor concentration, laying the concentration foundation for subsequent waste liquor treatment and reagent recovery; secondly, it breaks the dilemma of "direct discharge and energy waste" of the final-effect exhaust gas in traditional processes, transforming "waste energy" in high-energy-consuming processes into usable resources, reducing energy waste at the source. Furthermore, compared to traditional multi-effect evaporation systems, the subsequent flash pre-concentration unit reduces the water content of the black liquor entering the system, significantly reducing the consumption of fresh steam, alleviating the high energy consumption pressure on pulp mills, and providing a foundation for capacity expansion.

[0023] The first heat exchanger 200, as a key heat exchange unit for waste heat recovery, has one side of its medium inlet connected to the last-effect tail gas pipeline of the multi-effect evaporation system 100 to receive the last-effect tail gas. The other side establishes black liquor medium circulation with the flash evaporator 400 through a circulating pump. At the same time, its condensate outlet is connected to the condensate tank 1000 through a pipeline. This heat exchanger can be a shell-and-tube heat exchanger or a plate heat exchanger. In specific operation, the last-effect tail gas flows outside the tubes (or shell side), and the circulating concentrated black liquor flows inside the tubes (or plate side). Its core function is to achieve efficient heat transfer between the last-effect tail gas and the circulating black liquor, transferring the waste heat contained in the tail gas to the dilute black liquor to be concentrated, and at the same time condensing the tail gas so that the condensate in the tail gas flows into the condensate tank 1000 through a pipeline. Its effects are reflected in three aspects: First, it achieves deep energy recovery from the final-effect exhaust gas, avoiding the waste problem of direct emission of heat carried by exhaust gas in traditional processes, and improving the energy utilization rate to a multi-level gradient utilization level, directly reducing the system's dependence on fresh steam; Second, by heating the circulating black liquor, it provides the necessary temperature conditions for the subsequent negative pressure flash evaporation of the flash evaporator 400, ensuring that the flash evaporation process is stable and efficient, without the need for additional energy consumption to heat the black liquor; Third, it condenses the exhaust gas and recovers the condensate, which not only reduces the potential environmental impact of exhaust gas emissions, but also realizes the recycling and reuse of water resources, reducing the fresh water consumption cost of pulp mills.

[0024] The circulating pump, serving as the power transmission unit between the first heat exchanger 200 and the flash evaporator 400, plays a crucial role in providing continuous power for the flow of black liquor within the circulating pipeline formed by these two units. This ensures that the black liquor can repeatedly flow through the first heat exchanger 200 to absorb waste heat from the exhaust gas and stably enter the flash evaporator 400 for flash concentration. Its effect is to maintain a stable black liquor circulation flow rate, avoiding localized overheating or insufficient heat exchange caused by black liquor stagnation in the pipeline. This ensures that each portion of the black liquor can fully absorb waste heat to reach the temperature required for flash evaporation, while simultaneously guaranteeing the continuity of black liquor supply within the flash evaporator 400. This provides power support for the continuous operation of the flash pre-concentration process, indirectly improving the overall system concentration efficiency.

[0025] The flash evaporator 400 serves as the core unit for pre-concentration. One end of it is connected to the first heat exchanger 200 and the circulating pump via a circulation pipeline to receive the heated dilute black liquor. The other end is connected to the black liquor medium inlet of the multi-effect evaporation system 100 via the black liquor discharge pipeline 700. Simultaneously, the exhaust steam generated by the flash evaporator enters the condenser 600 through the channel 500. Its core function is to use the negative pressure environment to cause the heated dilute black liquor entering the condenser to undergo flash evaporation, thereby achieving pre-concentration treatment of the dilute black liquor. That is, by reducing the water content in the black liquor, the concentration of the dilute black liquor is increased to a level close to the high-concentration treatment requirements of the multi-effect evaporation system 100. Its effects are to solve the problems of "multi-effect evaporation systems needing to directly process large amounts of low-concentration dilute black liquor and excessively high evaporation load" in traditional processes: First, by reducing the water content of the black liquor entering the multi-effect evaporation system 100 through pre-concentration, the evaporation pressure and energy consumption of the high-concentration concentration section at the back end are directly reduced, which can reduce the consumption of fresh steam in the multi-effect evaporation system; Second, the pre-concentration process shortens the processing cycle of black liquor in the multi-effect evaporation system 100, thereby increasing the total amount of black liquor that the system can process per unit time, providing key support for the expansion of pulp mill production capacity; Third, the flash evaporation process is carried out under negative pressure and low temperature, avoiding changes in the composition of black liquor caused by high-temperature heating, and ensuring the purity and effectiveness of subsequent reagent recovery.

[0026] Channel 500 serves as the waste steam transport channel between flash evaporator 400 and condenser 600. Its core function is to transport the waste steam generated during flash evaporation in flash evaporator 400 to condenser 600 in a sealed manner, preventing waste steam leakage. This has two main effects: firstly, the sealed transport ensures that all waste steam enters condenser 600 for condensation, preventing the waste steam from carrying heat away and causing secondary energy waste, while also avoiding the impact of direct waste steam discharge on the workshop environment; secondly, timely discharge of waste steam generated in flash evaporator 400 maintains a stable negative pressure environment inside flash evaporator 400, providing the necessary conditions for continuous flash evaporation of black liquor. If waste steam cannot be discharged in time, the increased pressure inside flash evaporator will lead to a sharp decrease in flash evaporation efficiency, or even prevent the flash evaporation effect from being achieved.

[0027] As a key unit for condensing exhaust steam and maintaining negative pressure, condenser 600 receives flashed exhaust steam through channel 500, connects to condensate tank 1000 through pipeline to discharge condensate, establishes cooling water circulation with cooling tower 300 through cooling circulation pump, and is also connected to vacuum pump through pipeline. Its core function is to use the cooling water delivered by cooling tower 300 to condense the flashed exhaust steam, converting the exhaust steam into condensate, and maintain the negative pressure environment of itself and flash evaporator 400 with the cooperation of vacuum pump. Its effects are manifested in the following ways: First, it efficiently condenses the flash steam, converting the moisture in the steam into condensate, which is then collected in the condensate tank 1000, further improving the water resource recycling rate and reducing wastewater discharge. Second, by maintaining the negative pressure of the system through a vacuum pump, it ensures that the black liquor in the flash evaporator 400 can achieve flash evaporation at a lower temperature, significantly reducing the energy consumption required for heating the black liquor, while avoiding the damage to the characteristics of the black liquor caused by high temperature. Third, compared with the traditional process where "the tail gas of the last effect directly enters the cooling tower for condensation", the condenser 600 in this system only processes the flash steam, and the heat of the steam has been partially utilized through the previous heat exchange, which significantly reduces the required cooling load, indirectly reducing the operating pressure of the cooling tower 300 and reducing the power consumption of the cooling tower.

[0028] The black liquor discharge pipeline 700 serves as the black liquor transport channel between the flash evaporator 400 and the multi-effect evaporation system 100. A discharge pump is installed on the pipeline, its core function being to stably transport the pre-concentrated black liquor from the flash evaporator 400 to the black liquor inlet of the multi-effect evaporation system 100, thus achieving process integration between the pre-concentration unit and the main concentration unit. Its effect is that the power provided by the discharge pump overcomes pipeline resistance, ensuring a continuous and stable flow of pre-concentrated black liquor into the multi-effect evaporation system 100, avoiding pipeline stagnation or blockage caused by increased black liquor concentration (compared to dilute black liquor). Simultaneously, the sealed design of the pipeline prevents black liquor leakage during transport, avoiding both raw material waste and pollution of the workshop environment. Furthermore, the discharge pump can adjust the transport flow rate according to the processing load of the multi-effect evaporation system 100, achieving coordinated matching between the two units and further improving the overall concentration efficiency.

[0029] The black liquor feed pipe 800 serves as the input channel for dilute black liquor. One end is connected to an external dilute black liquor storage device, and the other end is connected to the black liquor inlet of the first heat exchanger 200. A feed pump is installed on the pipe, and the medium inside the pipe must first exchange heat with the medium in the black liquor discharge pipe 700 through the second heat exchanger 900. Its core function is to stably deliver the dilute black liquor to be concentrated into the system according to process requirements, while completing preheating treatment during the transportation process. The benefits are that the feed pump can precisely control the feed flow rate of the dilute black liquor, adapting to different concentration capacity requirements of the system, avoiding overfeeding leading to system overload or insufficient feed leading to equipment idling; and through the preheating treatment of the second heat exchanger 900, the dilute black liquor absorbs some heat before entering the first heat exchanger 200, which can reduce the consumption of waste heat from the final-effect tail gas by the first heat exchanger 200, indirectly improving the utilization efficiency of waste heat from the tail gas, while avoiding the problem of a sudden increase in energy consumption caused by the low-temperature dilute black liquor directly entering the heating stage, laying the temperature foundation for the subsequent flash evaporation pre-concentration process.

[0030] The second heat exchanger 900 serves as an auxiliary heat exchange unit, employing a shell-and-tube heat exchanger or a plate heat exchanger. Its core function is to achieve heat exchange between the low-temperature dilute black liquor in the black liquor feed pipe 800 and the high-temperature pre-concentrated black liquor in the black liquor discharge pipe 700. In other words, the low-temperature dilute black liquor absorbs the heat from the high-temperature pre-concentrated black liquor to achieve preheating, while simultaneously cooling the high-temperature pre-concentrated black liquor to a level suitable for the feed temperature of the multi-effect evaporation system 100. Its effects are extremely crucial: First, it deepens the "heat cascade utilization" by transferring the residual heat in the pre-concentrated black liquor (which would otherwise be wasted after entering the multi-effect evaporation system) to the dilute black liquor to be treated, further reducing the overall energy consumption of the system. Practical application has verified that this heat exchanger can increase the preheating temperature of the dilute black liquor, reducing the energy consumption of subsequent heating stages. Second, it ensures the temperature of the pre-concentrated black liquor entering the multi-effect evaporation system is stable by cooling, avoiding temperature field imbalance in the multi-effect evaporation system due to excessively high or fluctuating black liquor temperature, which could affect concentration efficiency or cause equipment damage. Third, compared to setting up an additional heater to preheat the dilute black liquor, this heat exchanger achieves heat recovery through "waste-for-demand" without consuming fresh energy, meeting the requirements of energy conservation, emission reduction, and sustainable development.

[0031] The condensate tank 1000 serves as a condensate recovery and storage unit, connected via pipelines to the condensate outlets of the first heat exchanger 200 and the condensate outlet of the condenser 600. Its core function is to centrally collect the condensate generated from the condensation of the final-effect exhaust gas in the first heat exchanger 200, and the condensate generated from the condensation of flash steam in the condenser 600. This achieves two main benefits: firstly, it enables the recycling of water resources. The recovered condensate is of relatively good quality and can be reused as process makeup water (such as makeup water for multi-effect evaporation systems and cooling towers), reducing the pulp mill's reliance on fresh industrial water and lowering water costs. Secondly, it avoids the waste of water resources and environmental impact caused by direct discharge of condensate. Furthermore, the collection process facilitates the monitoring of condensate quality. If the condensate contains a small amount of recyclable chemicals, secondary treatment can be used to recover these chemicals, further improving resource utilization and providing additional support for reducing production costs in the pulp mill.

[0032] Cooling tower 300, as the core unit of the cooling cycle, is connected to condenser 600 via pipelines, and a cooling circulation pump is installed between them. Its core function is to cool the cooling water in condenser 600 after the exhaust steam condensation process, reducing its temperature to a level suitable for condensation requirements. The cooling water is then pumped back to condenser 600 for reuse. The advantage is that, compared to the high-load operation of traditional cooling towers that directly handle large amounts of exhaust gas, this system only requires the cooling tower to cool the circulating cooling water in condenser 600. Furthermore, the cooling water absorbs only the residual heat from the flashed exhaust steam, reducing the load and thus decreasing the power consumption of the cooling circulation pump and the cooling tower fan, significantly lowering the overall system power consumption. Simultaneously, the recycling of cooling water avoids the large consumption of disposable cooling water, further improving water resource utilization efficiency and meeting environmental protection and energy-saving requirements.

[0033] The cooling circulation pump, serving as the power unit between the cooling tower 300 and the condenser 600, primarily functions to provide power for the flow of cooling water within the circulation pipeline formed by the two. This ensures that the heated cooling water is promptly delivered to the cooling tower 300 for cooling, and the cooled water quickly returns to the condenser 600 to participate in the condensation of exhaust steam. Its effect is to maintain a stable circulation flow rate of cooling water, ensuring that there is always sufficient low-temperature cooling water in the condenser 600 to participate in the condensation of exhaust steam, avoiding problems such as decreased condensation efficiency and system pressure imbalance due to insufficient cooling water supply. Simultaneously, the circulation pump can adjust the cooling water flow rate according to the condensation load of the condenser 600, avoiding excessive energy consumption while ensuring condensation efficiency, achieving "on-demand energy supply," and further optimizing the system's energy consumption structure.

[0034] The vacuum pump, as a key power unit for maintaining the negative pressure of the system, is connected to the condenser 600 through pipelines. Its core function is to extract non-condensable gases and some steam from the condenser 600 and flash evaporator 400, maintaining a stable negative pressure environment for the entire flash evaporation and condensation system. Its effect is that by establishing and maintaining negative pressure, black liquor can be rapidly flashed in the flash evaporator 400 at a lower temperature, eliminating the need to heat the black liquor to its atmospheric boiling point, significantly reducing heating energy consumption. Simultaneously, the negative pressure environment accelerates the flow of flash exhaust steam to the condenser 600, improving exhaust steam condensation efficiency and preventing exhaust steam from accumulating in the flash evaporator 400 and causing pressure increases, thus ensuring the continuous and stable operation of the flash pre-concentration process.

[0035] In summary, the various components of the system work closely together through a process link of "waste heat recovery - pre-concentration - main concentration - condensation recovery". The multi-effect evaporation system 100 provides the waste heat source and main concentration function; the first heat exchanger 200 and the circulating pump complete the waste heat transfer; the flash evaporator 400 achieves pre-concentration and load reduction; the channel 500 and the condenser 600 (including vacuum pump, cooling tower, and cooling circulating pump) ensure waste steam treatment and negative pressure maintenance; the black liquor inlet and outlet pipelines and pumps realize material transportation; the second heat exchanger 900 deepens heat recovery; and the condensate tank 1000 realizes resource reuse. Ultimately, they work together to achieve the core effects of "reducing energy consumption, increasing production capacity, and reducing fresh water consumption", effectively solving the problems of high energy consumption, high cost, and low efficiency in traditional pulp mill black liquor concentration processes. This meets the national requirements for energy conservation, emission reduction, and sustainable development, and provides key technical support for pulp enterprises to improve economic efficiency and environmental protection levels. Working Process

[0036] The dilute black liquor to be treated first enters the black liquor feed pipeline 800. Driven by the feed pump, it flows through the second heat exchanger 900 and exchanges heat with the low-temperature pre-concentrated black liquor delivered from the flash evaporator 400 in the black liquor discharge pipeline 700. The heat released by the dilute black liquor raises the temperature of the medium in the black liquor discharge pipeline 700. After the heat exchange is completed, the preheated dilute black liquor continues to enter the black liquor side of the first heat exchanger 200 through the black liquor feed pipeline 800.

[0037] Meanwhile, the tail gas generated during the operation of the multi-effect evaporation system 100 is transported to the tail gas side of the first heat exchanger 200 through its tail gas pipeline. In the first heat exchanger 200, the tail gas and the dilute black liquor on the black liquor side undergo efficient heat exchange. The residual heat in the tail gas is transferred to the dilute black liquor, which further increases the temperature of the dilute black liquor. The tail gas is then condensed into condensate, which flows into the condensate tank 1000 for storage through the pipeline.

[0038] The heated dilute black liquor enters the flash evaporator 400 through the pipeline under the power of the circulating pump. At this time, the vacuum pump connected to the condenser 600 starts to maintain a stable negative pressure environment in the flash evaporator 400 and the condenser 600. The dilute black liquor undergoes flash evaporation in the flash evaporator 400 under the influence of negative pressure, and the water is converted into steam. The remaining black liquor completes the pre-concentration.

[0039] The exhaust steam generated by flash evaporation enters the condenser 600 through channel 500. The cooling water in the cooling tower 300 enters the cooling pipe side of the condenser 600 under the drive of the cooling circulation pump, and exchanges heat with the exhaust steam. The exhaust steam condenses into condensate and flows into the condensate tank 1000. The cooling water that has absorbed heat and increased in temperature flows back to the cooling tower 300 to cool down and is recycled.

[0040] The pre-concentrated black liquor in the flash evaporator 400, under the action of the discharge pump on the black liquor discharge pipeline 700, first flows through the second heat exchanger 900 to complete heat exchange and cooling, and then is transported to the black liquor medium inlet of the multi-effect evaporation system 100. The multi-effect evaporation system 100 uses a co-current, counter-current, or mixed flow process to carry out high-concentration treatment, and finally completes the entire black liquor concentration and tail gas recovery and utilization process.

[0041] Alternatively, the pre-concentrated black liquor in the flash evaporator 400 is circulated and concentrated in the first heat exchanger 200 by the discharge pump on the black liquor discharge pipeline 700.

[0042] The embodiments of this utility model have been described in detail above, but the content described is only a preferred embodiment of this utility model and should not be considered as limiting the scope of implementation of this utility model. All equivalent changes and improvements made in accordance with the claims of this utility model should still fall within the patent coverage of this utility model.

Claims

1. A black liquor concentration multiple-effect evaporation off-gas recovery system, comprising: A multi-effect evaporation system (100) is characterized in that the tail gas pipeline of the last effect of the multi-effect evaporation system (100) is connected to the medium inlet on one side of the first heat exchanger (200), and the other side of the first heat exchanger (200) establishes a black liquor medium circulation with the flash evaporator (400) through a circulation pump. The exhaust steam generated by the flash evaporator (400) enters the condenser (600) through the channel (500). The flash evaporator (400) is connected to the black liquor medium inlet of the multi-effect evaporation system (100) through the black liquor discharge pipeline (700). A black liquor feed pipeline (800) is provided on the other side of the first heat exchanger (200).

2. The black liquor concentration multiple-effect evaporation tail gas recovery utilization system of claim 1, wherein, The medium in the black liquor feed pipe (800) and the medium in the black liquor discharge pipe (700) exchange heat through the second heat exchanger (900).

3. The black liquor concentration multi-effect evaporation tail gas recovery utilization system of claim 2, wherein, The first heat exchanger (200) and the second heat exchanger (900) are shell-and-tube heat exchangers or plate heat exchangers.

4. The black liquor concentration multi-effect evaporation tail gas recovery system according to any one of claims 1-3, characterized in that, The condensate outlet on one side of the first heat exchanger (200) is connected to the condensate tank (1000) via a pipeline.

5. The black liquor concentration multi-effect evaporation tail gas recovery system of any one of claims 1-3, wherein, The condenser (600) is connected to the condensate tank (1000) via a pipeline.

6. The black liquor concentration multiple effect evaporation tail gas recovery utilization system of claim 1, wherein, A feed pump is installed on the black liquor feed pipeline (800).

7. The black liquor concentration multiple-effect evaporation tail gas recovery utilization system of claim 1, wherein, A discharge pump is installed on the black liquor discharge pipeline (700).

8. The black liquor concentration multiple effect evaporation tail gas recovery utilization system of claim 1, wherein, The condenser (600) is connected to the cooling tower (300).

9. The black liquor concentration multiple effect evaporation tail gas recovery utilization system of claim 8, wherein, A cooling circulation pump is provided between the condenser (600) and the cooling tower (300).

10. The black liquor concentration multiple effect evaporation tail gas recovery utilization system of claim 1, wherein, The condenser (600) is connected to the vacuum pump via a pipeline.

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