Triple-effect countercurrent falling film evaporation system for increasing caustic soda concentration
By adding an alkaline solution and steam condensate heat recovery unit to the triple-effect countercurrent falling film evaporation system, the waste heat was effectively utilized, solving the problems of waste heat waste and environmental pollution, and reducing production energy consumption.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- HEBEI BAWEI CHEM CO LTD
- Filing Date
- 2025-07-07
- Publication Date
- 2026-05-26
AI Technical Summary
The existing triple-effect countercurrent falling film evaporation system fails to effectively utilize the waste heat generated in each stage of the evaporation chamber, resulting in energy waste and environmental thermal pollution, and increasing production energy consumption costs.
By adding an alkali heat recovery unit and a steam condensate heat recovery unit, heat is exchanged between high-concentration caustic soda and low-concentration caustic soda and steam condensate through dual heat recovery, thereby improving heat utilization efficiency and reducing primary steam consumption.
It improves thermal energy utilization, reduces production energy costs, and reduces waste heat emissions, thus meeting the requirements of green production.
Smart Images
Figure CN224270163U_ABST
Abstract
Description
Technical Field
[0001] This utility model belongs to the field of caustic soda evaporation and concentration technology, specifically relating to a triple-effect countercurrent falling film evaporation system for increasing caustic soda concentration. Background Technology
[0002] In the chemical production field, caustic soda (sodium hydroxide) is an important basic chemical raw material, widely used in many industries such as papermaking, textiles, printing and dyeing, chemical fibers, pharmaceuticals, pesticides, and petrochemicals. During the production of caustic soda, it is often necessary to concentrate low-concentration caustic soda solutions to obtain high-concentration caustic soda that meets different production needs.
[0003] Countercurrent falling film evaporation is currently the most commonly used method in caustic soda concentration. In this system, steam enters the system from the first-effect evaporator and then passes through the first, second, and third-effect evaporators in sequence, forming a co-current flow of steam. Low-concentration caustic soda enters the system from the third-effect evaporator and then passes through the third, second, and first-effect evaporators in sequence, forming a countercurrent flow of alkali solution. This countercurrent operation effectively increases the heat transfer temperature difference, improves heat transfer efficiency, and thus reduces energy consumption in the production process.
[0004] However, existing triple-effect countercurrent falling film evaporation systems do not effectively utilize the waste heat generated in each stage of the evaporation chamber during operation. During evaporation, high-concentration caustic soda carries a significant amount of heat energy when discharged from the evaporation chamber, and the condensation of steam into condensate also releases a large amount of latent heat. However, in current technologies, this waste heat is often not properly recovered and utilized, but is directly released into the environment. This not only wastes energy and increases energy costs in the production process, but may also cause thermal pollution to the environment. Therefore, how to effectively recover and utilize this waste heat and improve energy efficiency has become an urgent technical problem to be solved in this field. Utility Model Content
[0005] To address the problems existing in the prior art, this utility model provides a triple-effect countercurrent falling film evaporation system for increasing caustic soda concentration. By adding an alkali heat recovery unit and a steam condensate heat recovery unit, heat energy is recovered. The high-concentration caustic soda at a higher temperature and the steam condensate are used to exchange heat with the low-concentration caustic soda at a lower temperature. Through dual heat recovery, the heat energy utilization rate is improved, the primary steam consumption is reduced, and thus the production energy consumption cost is reduced.
[0006] The specific technical solution adopted in this utility model is as follows:
[0007] A triple-effect countercurrent falling film evaporation system for increasing caustic soda concentration includes a first-effect evaporation chamber, a second-effect evaporation chamber, and a third-effect evaporation chamber connected in series. The low-concentration caustic soda and primary steam flow in opposite directions within the first-effect, second-effect, and third-effect evaporation chambers. An alkali heat recovery unit and a steam condensate heat recovery unit are added. The low-concentration caustic soda exchanges heat with the high-concentration caustic soda through the alkali heat recovery unit, and the low-concentration caustic soda exchanges heat with the steam condensate of the next-stage evaporation chamber through the steam condensate heat recovery unit.
[0008] Furthermore, the liquid phase input terminal of the triple-effect evaporator is connected to the output terminal of the low-concentration caustic soda, the liquid phase output terminal of the triple-effect evaporator is connected to the liquid phase input terminal of the second-effect evaporator, the liquid phase output terminal of the second-effect evaporator is connected to the liquid phase input terminal of the first-effect evaporator, the gas phase input terminal of the first-effect evaporator is connected to the output terminal of the primary steam, the gas phase output terminal of the first-effect evaporator is connected to the gas phase input terminal of the second-effect evaporator, and the gas phase output terminal of the second-effect evaporator is connected to the gas phase input terminal of the first-effect evaporator.
[0009] Furthermore, the alkali heat recovery unit includes a first-effect alkali heat exchanger, a second-effect alkali heat exchanger, and a third-effect alkali heat exchanger. The shell-side input end of the first-effect alkali heat exchanger is connected to the liquid phase output end of the second-effect evaporation chamber, the shell-side output end of the first-effect alkali heat exchanger is connected to the liquid phase input end of the first-effect evaporation chamber, the tube-side input end of the first-effect alkali heat exchanger is connected to the liquid phase output end of the first-effect evaporation chamber, and the tube-side output end of the first-effect alkali heat exchanger is connected to the tube-side input end of the second-effect alkali heat exchanger. The shell-side input end of the first-effect caustic soda heat exchanger is connected to the liquid phase output end of the third-effect evaporation chamber. The shell-side output end of the second-effect caustic soda heat exchanger is connected to the liquid phase input end of the second-effect evaporation chamber. The tube-side output end of the second-effect caustic soda heat exchanger is connected to the tube-side input end of the third-effect caustic soda heat exchanger. The shell-side input end of the third-effect caustic soda heat exchanger is connected to the output end of the low-concentration caustic soda. The shell-side output end of the third-effect caustic soda heat exchanger is connected to the liquid phase input end of the third-effect evaporation chamber. The tube-side output end of the third-effect caustic soda heat exchanger is connected to the finished product tank area.
[0010] Furthermore, the steam condensate heat recovery unit includes a first-effect condensate heat exchanger, a second-effect condensate heat exchanger, and a third-effect condensate heat exchanger. The shell-side input of the first-effect condensate heat exchanger is connected to the shell-side output of the first-effect alkaline heat exchanger, and the shell-side output of the first-effect condensate heat exchanger is connected to the liquid phase input of the first-effect evaporation chamber. The tube-side input of the first-effect condensate heat exchanger is connected to the condensate output of the first-effect evaporation chamber. The shell-side input of the second-effect condensate heat exchanger is connected to the shell-side output of the second-effect alkaline heat exchanger. The shell-side output end of the heat exchanger is connected to the liquid phase input end of the second-effect evaporation chamber. The tube-side input end of the second-effect condensate heat exchanger is connected to the condensate output end of the second-effect evaporation chamber and the tube-side output end of the first-effect condensate heat exchanger, respectively. The shell-side input end of the third-effect condensate heat exchanger is connected to the shell-side output end of the third-effect alkaline heat exchanger. The shell-side output end of the third-effect condensate heat exchanger is connected to the steam condensate recovery zone. The tube-side input end of the third-effect condensate heat exchanger is connected to the condensate output end of the third-effect evaporation chamber and the tube-side output end of the second-effect condensate heat exchanger, respectively.
[0011] Furthermore, the triple-effect evaporation chamber is connected to a vacuum pump, and the chamber of the triple-effect evaporation chamber is subjected to negative pressure by means of the vacuum pump.
[0012] The beneficial effects of this utility model are:
[0013] 1. This utility model recovers heat energy by adding an alkali heat energy recovery unit and a steam condensate heat energy recovery unit. It uses high-concentration caustic soda at a higher temperature and steam condensate to exchange heat with low-concentration caustic soda at a lower temperature. Through dual heat energy recovery, the heat energy utilization rate is improved, the amount of primary steam used is reduced, thereby reducing production energy consumption costs. It also avoids the direct discharge of waste heat into the environment, reduces thermal pollution, and meets the requirements of green production.
[0014] 2. In this utility model, the condensate heat exchanger and the alkali heat exchanger are connected in series, and the low-concentration alkali solution is subjected to gradient heat exchange from low temperature to high temperature, which can enable the low-concentration alkali solution to absorb more heat energy and improve the heat recovery rate. Attached Figure Description
[0015] Figure 1 This is a schematic diagram of the triple-effect countercurrent falling film evaporation system of this utility model. Detailed Implementation
[0016] The present invention will be further described below with reference to the accompanying drawings and specific embodiments:
[0017] Specific embodiments, such as Figure 1As shown, this utility model provides a triple-effect countercurrent falling film evaporation system for increasing caustic soda concentration, including a first-effect evaporation chamber, a second-effect evaporation chamber, and a third-effect evaporation chamber connected in series. The low-concentration caustic soda and primary steam flow in opposite directions in the first-effect evaporation chamber, the second-effect evaporation chamber, and the third-effect evaporation chamber. An alkali heat recovery unit and a steam condensate heat recovery unit are added. The low-concentration caustic soda exchanges heat with the high-concentration caustic soda through the alkali heat recovery unit, and the low-concentration caustic soda exchanges heat with the steam condensate of the next-stage evaporation chamber through the steam condensate heat recovery unit.
[0018] Existing triple-effect countercurrent falling film evaporation systems do not effectively utilize the waste heat generated in each stage of the evaporation chamber. During evaporation, high-concentration caustic soda carries a significant amount of heat energy when discharged from the evaporation chamber, and the condensation of steam into condensate also releases a large amount of latent heat. However, in current technologies, this waste heat is often not properly recovered and utilized, but is directly released into the environment. This not only wastes energy and increases energy costs in the production process, but may also cause thermal pollution to the environment. Therefore, how to effectively recover and utilize this waste heat and improve energy efficiency has become an urgent technical problem to be solved in this field.
[0019] Therefore, this utility model recovers heat energy by adding an alkali heat recovery unit and a steam condensate heat recovery unit. It uses high-concentration caustic soda at a higher temperature and steam condensate to exchange heat with low-concentration caustic soda at a lower temperature. Through dual heat recovery, the heat energy utilization rate is improved, the amount of primary steam used is reduced, thereby reducing production energy consumption costs. It also avoids the direct discharge of waste heat into the environment, reduces thermal pollution, and meets the requirements of green production.
[0020] The liquid phase input terminal of the triple-effect evaporator is connected to the output terminal of the low-concentration caustic soda. The liquid phase output terminal of the triple-effect evaporator is connected to the liquid phase input terminal of the second-effect evaporator. The liquid phase output terminal of the second-effect evaporator is connected to the liquid phase input terminal of the first-effect evaporator. The gas phase input terminal of the first-effect evaporator is connected to the output terminal of the primary steam. The gas phase output terminal of the first-effect evaporator is connected to the gas phase input terminal of the second-effect evaporator. The gas phase output terminal of the second-effect evaporator is connected to the gas phase input terminal of the first-effect evaporator.
[0021] In this invention, the alkali solution flows in the opposite direction to the steam, forming countercurrent heat exchange, increasing the heat transfer temperature difference, and improving heat transfer efficiency. The residual heat energy in the secondary steam is fully utilized through staged evaporation. First, 32% caustic soda enters the triple-effect evaporator. Utilizing the negative pressure environment in the triple-effect evaporator, secondary steam at approximately 80°C from the second-effect evaporator heats and boils the 32% caustic soda, concentrating it to 38% concentration. Then, the 38% caustic soda enters the second-effect evaporator, where secondary steam at approximately 110°C from the first-effect evaporator heats and boils it, concentrating it to 45% concentration. Finally, the 45% caustic soda enters the first-effect evaporator, where primary steam at approximately 140°C provided by the boiler heats and boils it, concentrating it to 50% concentration. Through the above process, when the steam flows in the forward direction, the secondary steam generated in the previous steam chamber can be used as a heat source for the next steam chamber, and in combination with the countercurrent flow of the alkali solution, the consumption of primary steam is reduced.
[0022] The alkali heat recovery unit includes a first-effect alkali heat exchanger, a second-effect alkali heat exchanger, and a third-effect alkali heat exchanger. The shell-side input of the first-effect alkali heat exchanger is connected to the liquid phase output of the second-effect evaporation chamber, the shell-side output of the first-effect alkali heat exchanger is connected to the liquid phase input of the first-effect evaporation chamber, the tube-side input of the first-effect alkali heat exchanger is connected to the liquid phase output of the first-effect evaporation chamber, and the tube-side output of the first-effect alkali heat exchanger is connected to the tube-side input of the second-effect alkali heat exchanger. The shell-side input end of the liquid heat exchanger is connected to the liquid phase output end of the triple-effect evaporation chamber; the shell-side output end of the double-effect alkali heat exchanger is connected to the liquid phase input end of the double-effect evaporation chamber; the tube-side output end of the double-effect alkali heat exchanger is connected to the tube-side input end of the triple-effect alkali heat exchanger; the shell-side input end of the triple-effect alkali heat exchanger is connected to the output end of low-concentration caustic soda; the shell-side output end of the triple-effect alkali heat exchanger is connected to the liquid phase input end of the triple-effect evaporation chamber; and the tube-side output end of the triple-effect alkali heat exchanger is connected to the finished product tank area.
[0023] This invention achieves the step-by-step recovery of caustic soda heat energy through the series design of first-effect, second-effect, and third-effect caustic soda heat exchangers. Since the 50% caustic soda output from the first-effect evaporation chamber contains a large amount of heat energy, it gradually exchanges heat with the low-concentration caustic soda entering the first-effect, second-effect, and third-effect evaporation chambers, reducing the demand for steam during each effect's evaporation and further reducing energy consumption.
[0024] When the 50% caustic soda solution exchanges heat with the alkali solution output from the second-effect evaporator, the temperature of the first-stage heat-exchanged alkali solution is still relatively high, higher than that of the alkali solution output from the third-effect evaporator. Therefore, the first-stage heat-exchanged alkali solution continues to exchange heat with the alkali solution output from the third-effect evaporator. Similarly, the second-stage heat-exchanged alkali solution continues to exchange heat with the 32% concentration alkali solution. This method allows the heat carried by the 50% caustic soda solution to be recovered step by step, ensuring that the heat absorbed by each stage of low-concentration alkali solution is higher than the required heat, while avoiding the severe thermal expansion and contraction of the equipment due to excessive temperature differences.
[0025] The steam condensate heat recovery unit includes a first-effect condensate heat exchanger, a second-effect condensate heat exchanger, and a third-effect condensate heat exchanger. The shell-side input of the first-effect condensate heat exchanger is connected to the shell-side output of the first-effect alkaline heat exchanger, and the shell-side output of the first-effect condensate heat exchanger is connected to the liquid phase input of the first-effect evaporation chamber. The tube-side input of the first-effect condensate heat exchanger is connected to the condensate output of the first-effect evaporation chamber. The shell-side input of the second-effect condensate heat exchanger is connected to the shell-side output of the second-effect alkaline heat exchanger. The shell-side output end of the triple-effect condensate heat exchanger is connected to the liquid phase input end of the second-effect evaporation chamber. The tube-side input end of the triple-effect condensate heat exchanger is connected to the condensate output end of the second-effect evaporation chamber and the tube-side output end of the first-effect condensate heat exchanger, respectively. The shell-side input end of the triple-effect condensate heat exchanger is connected to the shell-side output end of the triple-effect alkaline heat exchanger. The shell-side output end of the triple-effect condensate heat exchanger is connected to the steam condensate recovery zone. The tube-side input end of the triple-effect condensate heat exchanger is connected to the condensate output end of the triple-effect evaporation chamber and the tube-side output end of the second-effect condensate heat exchanger, respectively.
[0026] First, this invention uses a first-effect, second-effect, and third-effect condensate heat exchanger to transfer the heat energy of the high-temperature steam condensate generated in each effect evaporation chamber to the alkaline solution. At the same time, this invention specifies the order in which the condensate heat exchanger and the alkaline solution heat exchanger are connected.
[0027] In the existing technology, the condensate heat exchanger and the alkali heat exchanger are set in parallel. That is, the low-concentration alkali solution is usually separated into two streams and exchanged heat with the condensate heat exchanger and the alkali heat exchanger respectively. However, this method will result in the low heat absorption efficiency of the low-concentration alkali solution.
[0028] The temperature of the condensate steam discharged from the first-effect evaporator is higher than that of the discharged 50% concentration alkali solution. The condensate temperature is about 140°C, while the temperature of the 50% concentration alkali solution is about 130°C. Assuming that under ideal heat exchange conditions, the low-concentration alkali solution is divided into two equal parts and exchanges heat with the two solutions respectively, the temperatures of the two low-concentration alkali solutions after heat exchange are 140°C and 130°C respectively, and the temperature of the mixed low-concentration alkali solution is 135°C. However, by using the condensate heat exchanger and the alkali heat exchanger connected in series in this invention, under ideal heat exchange conditions, the low-concentration alkali solution first heats up to 130°C and then heats up to 140°C.
[0029] Therefore, by using the series connection of the condensate heat exchanger and the alkali heat exchanger in this invention, gradient heat exchange can be performed on the low-concentration alkali solution from low temperature to high temperature, which can enable the low-concentration alkali solution to absorb more heat energy and improve the heat recovery rate.
[0030] The triple-effect evaporation chamber is connected to a vacuum pump. The chamber of the triple-effect evaporation chamber is created under negative pressure by means of the vacuum pump. Since the secondary steam discharged from the second-effect evaporation chamber is at a low temperature, it is not possible for the 32% concentration caustic soda to boil. Therefore, a vacuum pump is provided to create a negative pressure environment in the triple-effect evaporation chamber, thereby lowering the boiling point of the 2% concentration caustic soda and enabling it to boil at a lower temperature.
Claims
1. A three-effect countercurrent falling-film evaporation system for increasing the concentration of caustic soda, comprising a first-effect evaporation chamber, a second-effect evaporation chamber, and a third-effect evaporation chamber connected in series in that order, the flow direction of low-concentration caustic soda and primary steam being opposite in the first-effect evaporation chamber, the second-effect evaporation chamber, and the third-effect evaporation chamber, characterized in that, An alkaline solution heat recovery unit and a steam condensate heat recovery unit are added. Low-concentration caustic soda exchanges heat with high-concentration caustic soda through the alkaline solution heat recovery unit, and low-concentration caustic soda exchanges heat with the steam condensate in the next stage evaporation chamber through the steam condensate heat recovery unit.
2. The triple-effect countercurrent falling film evaporation system for increasing caustic soda concentration according to claim 1, characterized in that, The liquid phase input terminal of the triple-effect evaporator is connected to the output terminal of the low-concentration caustic soda. The liquid phase output terminal of the triple-effect evaporator is connected to the liquid phase input terminal of the second-effect evaporator. The liquid phase output terminal of the second-effect evaporator is connected to the liquid phase input terminal of the first-effect evaporator. The gas phase input terminal of the first-effect evaporator is connected to the output terminal of the primary steam. The gas phase output terminal of the first-effect evaporator is connected to the gas phase input terminal of the second-effect evaporator. The gas phase output terminal of the second-effect evaporator is connected to the gas phase input terminal of the first-effect evaporator.
3. The triple-effect countercurrent falling film evaporation system for increasing caustic soda concentration according to claim 1, characterized in that, The alkali heat recovery unit includes a first-effect alkali heat exchanger, a second-effect alkali heat exchanger, and a third-effect alkali heat exchanger. The shell-side input of the first-effect alkali heat exchanger is connected to the liquid phase output of the second-effect evaporation chamber, the shell-side output of the first-effect alkali heat exchanger is connected to the liquid phase input of the first-effect evaporation chamber, the tube-side input of the first-effect alkali heat exchanger is connected to the liquid phase output of the first-effect evaporation chamber, and the tube-side output of the first-effect alkali heat exchanger is connected to the tube-side input of the second-effect alkali heat exchanger. The shell-side input end of the liquid heat exchanger is connected to the liquid phase output end of the triple-effect evaporation chamber; the shell-side output end of the double-effect alkali heat exchanger is connected to the liquid phase input end of the double-effect evaporation chamber; the tube-side output end of the double-effect alkali heat exchanger is connected to the tube-side input end of the triple-effect alkali heat exchanger; the shell-side input end of the triple-effect alkali heat exchanger is connected to the output end of low-concentration caustic soda; the shell-side output end of the triple-effect alkali heat exchanger is connected to the liquid phase input end of the triple-effect evaporation chamber; and the tube-side output end of the triple-effect alkali heat exchanger is connected to the finished product tank area.
4. The triple-effect countercurrent falling film evaporation system for increasing caustic soda concentration according to claim 3, characterized in that, The steam condensate heat recovery unit includes a first-effect condensate heat exchanger, a second-effect condensate heat exchanger, and a third-effect condensate heat exchanger. The shell-side input of the first-effect condensate heat exchanger is connected to the shell-side output of the first-effect alkaline heat exchanger, and the shell-side output of the first-effect condensate heat exchanger is connected to the liquid phase input of the first-effect evaporation chamber. The tube-side input of the first-effect condensate heat exchanger is connected to the condensate output of the first-effect evaporation chamber. The shell-side input of the second-effect condensate heat exchanger is connected to the shell-side output of the second-effect alkaline heat exchanger. The shell-side output end of the triple-effect condensate heat exchanger is connected to the liquid phase input end of the second-effect evaporation chamber. The tube-side input end of the triple-effect condensate heat exchanger is connected to the condensate output end of the second-effect evaporation chamber and the tube-side output end of the first-effect condensate heat exchanger, respectively. The shell-side input end of the triple-effect condensate heat exchanger is connected to the shell-side output end of the triple-effect alkaline heat exchanger. The shell-side output end of the triple-effect condensate heat exchanger is connected to the steam condensate recovery zone. The tube-side input end of the triple-effect condensate heat exchanger is connected to the condensate output end of the triple-effect evaporation chamber and the tube-side output end of the second-effect condensate heat exchanger, respectively.
5. A triple-effect countercurrent falling film evaporation system for increasing caustic soda concentration according to claim 1, characterized in that, The triple-effect evaporation chamber is connected to a vacuum pump, and the chamber of the triple-effect evaporation chamber is subjected to negative pressure by means of the vacuum pump.