Device for improving evaporation efficiency of caprolactam MVR (mechanical vapor recompression) system

Abstract

The utility model relates to the technical field of polyamide polymerization extraction water concentration, in particular to a device for improving the evaporation efficiency of a caprolactam MVR (mechanical vapor recompression) system. Caprolactam aqueous solution with a certain concentration is regularly added into the first-effect evaporator, the second-effect evaporator, the third-effect evaporator and the fourth-effect evaporator under the condition of no shutdown according to production requirements, organic impurities such as oligomers attached to the evaporators are dissolved by utilizing the principle of similar intermiscibility, and then scales automatically fall off; the purpose of online cleaning of the evaporator is achieved, manpower and material resources are saved, and use of pure water and generation of waste water are reduced; the evaporation efficiency of the MVR system is improved through regular online cleaning of the evaporator, and steam consumption is reduced; and the continuous and efficient operation time of the MVR system is prolonged, the shutdown cleaning time can be prolonged to 18 months from the original 3-4 months, and the yield loss of a production enterprise is avoided.

Description

Technical Field

[0001] The utility model relates to the technical field of polyamide polymerization extraction water concentration, in particular to a device for improving the evaporation efficiency of a caprolactam MVR system. Background Art

[0002] The conversion rate of domestic caprolactam polymerization to produce polyamide chips can only reach about 90%. The remaining 10% that has not been completely converted is mainly composed of caprolactam monomer, cyclic oligomers and linear oligomers. Untreated chips cannot be directly supplied to downstream spinning. The commonly used method in the industry is to use high-temperature hot water to extract the incompletely converted caprolactam monomer and oligomers in the chips. The extracted chips are then dried and supplied to downstream customers. The mixture of extracted caprolactam monomer, oligomer and hot water (hereinafter referred to as extraction water) has a concentration of about 10%. After being concentrated to 85% by the MVR system and then purified by distillation, the distilled caprolactam is returned to the polymerization production process again to reduce production unit consumption. The commonly used MVR system includes one, two, three and four-effect evaporators, and the four groups of evaporators are arranged in series. The concentration of the extraction water at the bottom of the one, two, three and four-effect evaporators is about 15%, 30%, 70% and 85%. The extraction water contains not only caprolactam monomers and oligomers, but also trace amounts of calcium, magnesium, sodium and other ions. The melting point of the cyclic dimer in the oligomer is as high as 320°C, which is not easy to dissolve at high temperatures and has the characteristics of wrapping and adsorption. With the continuous production, the heat exchange tubes of each effect evaporator gradually form scale. The generation of scale affects the heat transfer efficiency and then affects the evaporation effect of the MVR system, resulting in a decrease in production efficiency and an increase in steam consumption. In order to ensure the normal operation of production, the commonly used cleaning method in the industry is to shut down for more than 3 days every 3-4 months to clean the four groups of evaporators one by one. Each shutdown for cleaning will not only cause a loss of production, but also take a long time to clean, consume a lot of manpower and material resources, use a lot of pure water and produce a lot of wastewater, which increases the production cost of the company's operation, and it is impossible to reduce staff and increase efficiency, reduce costs and increase efficiency. Utility Model Content

[0003] The utility model aims to provide a device for improving the evaporation efficiency of a caprolactam MVR system.

[0004] The utility model provides the following technical solutions:

[0005] The utility model proposes a device for improving the evaporation efficiency of a caprolactam MVR system, comprising a first-effect evaporator, a second-effect evaporator, a third-effect evaporator, a fourth-effect evaporator and a feeding device for adding a caprolactam aqueous solution, wherein the inlet of the first-effect evaporator is connected to a first inlet pipeline; the outlet of the first-effect evaporator is connected to the inlet of the first-effect evaporator and is connected to the inlet of the second-effect evaporator through a second inlet pipeline; the outlet of the second-effect evaporator is connected to the inlet of the second-effect evaporator and is connected to the inlet of the third-effect evaporator through a third inlet pipeline; the outlet of the third-effect evaporator is connected to the inlet of the third-effect evaporator and is connected to the inlet of the fourth-effect evaporator through a fourth inlet pipeline; the outlet of the fourth-effect evaporator is connected to the inlet of the fourth-effect evaporator and a concentrated liquid outlet pipeline, so as to realize MVR multi-effect evaporation and realize efficient evaporation and concentration of large quantities of extracted water.

[0006] The outlet of the replenishing device is connected to the first inlet pipe, the second inlet pipe, the third inlet pipe and the fourth inlet pipe. The caprolactam aqueous solution in the replenishing device enters the evaporator, and the organic impurities such as oligomers on the evaporator are dissolved and the scale falls off automatically, thereby achieving the purpose of online cleaning of the evaporator.

[0007] Furthermore, the replenishing device includes a caprolactam aqueous solution storage tank, the outlet of the caprolactam aqueous solution storage tank is connected to the inlet of a mass flowmeter, the outlet of the mass flowmeter is connected to the first inlet pipe, the second inlet pipe, the third inlet pipe and the fourth inlet pipe; a control valve is arranged between the caprolactam aqueous solution storage tank and the mass flowmeter.

[0008] Furthermore, the bottom outlet of the caprolactam aqueous solution storage tank is higher than the top inlet of any one of the first-effect evaporator, the second-effect evaporator, the third-effect evaporator and the fourth-effect evaporator.

[0009] Furthermore, the top of the caprolactam aqueous solution storage tank is connected to a pure water supply pipe and a caprolactam pipe, a nitrogen pipe is provided between the pure water supply pipe and the caprolactam pipe, and the nitrogen pipe is connected to the bottom of the caprolactam aqueous solution storage tank.

[0010] Furthermore, the height h between the bottom of the nitrogen pipe and the inner bottom of the caprolactam aqueous solution storage tank is 10<h<300mm.

[0011] Compared with the prior art, the utility model has the following beneficial effects: by adding a caprolactam aqueous solution supplementing device, a certain concentration of caprolactam aqueous solution is regularly supplemented into the first-effect evaporator, the second-effect evaporator, the third-effect evaporator and the fourth-effect evaporator without stopping the machine according to production needs, and by utilizing the principle of like dissolves like, organic impurities such as oligomers attached to the evaporator are dissolved and the scale falls off automatically, thereby achieving the purpose of online cleaning of the evaporator, saving manpower and material resources, saving the use of pure water and the generation of wastewater; by regularly cleaning the evaporator online, the evaporation efficiency of the MVR system is improved and the steam consumption is reduced; the time for continuous and efficient operation of the MVR system is extended, and the shutdown time for cleaning can be extended from the original 3-4 months to 18 months, thereby avoiding production losses of production enterprises. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 It is a schematic diagram of the connection relationship of the utility model.

[0013] (The arrows in the figure indicate the direction of material flow in the tube)

[0014] In the figure, 1-single-effect evaporator; 2-second-effect evaporator; 3-triple-effect evaporator; 4-fourth-effect evaporator; 5-first inlet pipe; 6-second inlet pipe; 7-third inlet pipe; 8-fourth inlet pipe; 9-concentrate outlet pipe; 10-feeding device; 101-caprolactam aqueous solution storage tank; 102-mass flowmeter; 103-control valve; 1011-pure water feeding pipe; 1012-caprolactam pipe; 1013-nitrogen pipe; 11-delivery pump. DETAILED DESCRIPTION

[0015] The utility model is further described below in conjunction with the accompanying drawings.

[0016] In one embodiment of the utility model, a device for improving the evaporation efficiency of a caprolactam MVR system comprises a first-effect evaporator 1, a second-effect evaporator 2, a third-effect evaporator 3, a fourth-effect evaporator 4 and a supplementing device 10 for adding a caprolactam aqueous solution, wherein the inlet of the first-effect evaporator 1 is connected to a first inlet pipe 5; the outlet of the first-effect evaporator 1 is connected to the inlet of the first-effect evaporator 1 and to the inlet of the second-effect evaporator 2 through a second inlet pipe 6; the outlet of the second-effect evaporator 2 is connected to the inlet of the second-effect evaporator 2 and to the inlet of the third-effect evaporator 3 through a third inlet pipe 7; the outlet of the third-effect evaporator 3 is connected to the inlet of the third-effect evaporator and to the inlet of the fourth-effect evaporator 4 through a fourth inlet pipe 8; the outlet of the fourth-effect evaporator 4 is connected to the inlet of the fourth-effect evaporator 4 and a concentrated liquid outlet pipe 9;

[0017] The outlet of the replenishing device 10 is connected to the first inlet pipe 5 , the second inlet pipe 6 , the third inlet pipe 7 and the fourth inlet pipe 8 .

[0018] The replenishing device 10 is used to replenish the caprolactam aqueous solution into the first-effect evaporator 1, the second-effect evaporator 2, the third-effect evaporator 3 and the fourth-effect evaporator 4, so as to achieve the purpose of online cleaning of the evaporators.

[0019] In one embodiment of the utility model, the replenishing device 10 includes a caprolactam aqueous solution storage tank 101, the outlet of the caprolactam aqueous solution storage tank 101 is connected to the inlet of a mass flowmeter 102, the outlet of the mass flowmeter 102 is connected to the first inlet pipe 5, the second inlet pipe 6, the third inlet pipe 7 and the fourth inlet pipe 8; a control valve 103 is arranged between the caprolactam aqueous solution storage tank 101 and the mass flowmeter 102; the addition of the caprolactam aqueous solution from the caprolactam aqueous solution storage tank 101 to the evaporator is achieved by controlling the control valve; and the replenishment amount is controlled by the mass flowmeter.

[0020] In the above embodiment, the bottom outlet of the caprolactam aqueous solution storage tank 101 is higher than the top inlet of any one of the first-effect evaporator 1, the second-effect evaporator 2, the third-effect evaporator 3 and the fourth-effect evaporator 4; so that the caprolactam aqueous solution in the caprolactam aqueous solution storage tank 101 can flow into the evaporator.

[0021] In one embodiment of the utility model, the top of the caprolactam aqueous solution storage tank 101 is connected to the pure water supply pipe 1011 and the caprolactam pipe 1012, and a nitrogen pipe 1013 is arranged between the pure water supply pipe 1011 and the caprolactam pipe 1012, and the nitrogen pipe 1013 is connected to the bottom of the caprolactam aqueous solution storage tank 101; nitrogen is introduced to achieve uniform mixing of water and caprolactam solution.

[0022] In the above embodiment, the height h between the bottom of the nitrogen pipe 1013 and the inner bottom of the caprolactam aqueous solution storage tank 1012 is 10<h<300 mm, ensuring that the nitrogen is completely mixed with the introduced caprolactam solution and water.

[0023] In one embodiment of the utility model, a delivery pump 11 is provided between the outlet of the first-effect evaporator 1 and the inlet of the second-effect evaporator 2, between the outlet of the second-effect evaporator 2 and the inlet of the third-effect evaporator 3, between the outlet of the third-effect evaporator 3 and the inlet of the fourth-effect evaporator 4, and between the outlet of the fourth-effect evaporator 4 and the inlet of the fourth-effect evaporator 4; the delivery pump 11 more effectively realizes the circulation of the solution in the pipeline.

[0024] Pure water is added into the caprolactam aqueous solution storage tank 1012 through the pure water adding pipe 1011, caprolactam solution is added into the caprolactam aqueous solution storage tank 1012 through the caprolactam pipe 1012, nitrogen is introduced into the caprolactam aqueous solution storage tank 1012 by means of the nitrogen pipe 1013, so as to achieve mixing of the solutions in the caprolactam aqueous solution storage tank 1012, and the caprolactam aqueous solution in the caprolactam aqueous solution storage tank 1012 is added into the evaporator, so that organic impurities such as oligomers on the evaporator are dissolved and the scale falls off automatically, so as to achieve the purpose of online cleaning of the evaporator.

[0025] The implementation modes of the present invention are provided for the purpose of illustration and description. Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be understood as limitations of the present invention. Ordinary technicians in this field can change, modify, replace and modify the above embodiments within the scope of the present invention.

Claims

1. A device for improving the evaporation efficiency of a caprolactam MVR system, characterized by: It comprises a first-effect evaporator, a second-effect evaporator, a third-effect evaporator, a fourth-effect evaporator and a feeding device for adding a caprolactam aqueous solution, wherein the inlet of the first-effect evaporator is connected to a first inlet pipeline; the outlet of the first-effect evaporator is connected to the inlet of the first-effect evaporator and to the inlet of the second-effect evaporator through a second inlet pipeline; the outlet of the second-effect evaporator is connected to the inlet of the second-effect evaporator and to the inlet of the third-effect evaporator through a third inlet pipeline; the outlet of the third-effect evaporator is connected to the inlet of the third-effect evaporator and to the inlet of the fourth-effect evaporator through a fourth inlet pipeline; the outlet of the fourth-effect evaporator is connected to the inlet of the fourth-effect evaporator and to a concentrated liquid outlet pipeline; The outlet of the replenishing device is connected to the first inlet pipe, the second inlet pipe, the third inlet pipe and the fourth inlet pipe.

2. A device for improving the evaporation efficiency of a caprolactam MVR system according to claim 1, characterized in that: The replenishing device includes a caprolactam aqueous solution storage tank, the outlet of the caprolactam aqueous solution storage tank is connected to the inlet of a mass flowmeter, the outlet of the mass flowmeter is connected to the first inlet pipe, the second inlet pipe, the third inlet pipe and the fourth inlet pipe; a control valve is arranged between the caprolactam aqueous solution storage tank and the mass flowmeter.

3. A device for improving the evaporation efficiency of a caprolactam MVR system according to claim 2, characterized in that: The bottom outlet of the caprolactam aqueous solution storage tank is higher than the top inlet of any one of the first-effect evaporator, the second-effect evaporator, the third-effect evaporator and the fourth-effect evaporator.

4. A device for improving the evaporation efficiency of a caprolactam MVR system according to claim 2, characterized in that: The top of the caprolactam aqueous solution storage tank is connected to a pure water supply pipe and a caprolactam pipe, a nitrogen pipe is arranged between the pure water supply pipe and the caprolactam pipe, and the nitrogen pipe is connected to the bottom of the caprolactam aqueous solution storage tank.

5. A device for improving the evaporation efficiency of a caprolactam MVR system according to claim 4, characterized in that: The height h between the bottom of the nitrogen pipe and the inner bottom of the caprolactam aqueous solution storage tank is 10<h<300mm.

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