Caprolactam rectification heat energy coupling utilization system

Abstract

The utility model provides a caprolactam rectification heat energy coupling utilization system, which comprises a cyclohexane refining tower, a cyclohexene separation tower and a debenzolization tower which are communicated in sequence, in the system, high-temperature gas-phase materials generated by the cyclohexane refining tower and the cyclohexene separation tower and kettle bottom liquid in the next tower are subjected to heat exchange treatment through a falling film evaporator, and the cyclohexene separation tower and the kettle bottom liquid in the next tower are separated; the feeding temperature of the next tower is increased, so that the heat utilization of high-temperature steam is improved, the use of steam is reduced, and the production cost is reduced; meanwhile, the use of fire coal is reduced, the emission of waste gas is reduced, and the environment is protected.

Description

Technical Field

[0001] The utility model belongs to the technical field of caprolactam production, and relates to a caprolactam rectification heat energy coupling utilization system. Background Art

[0002] Caprolactam is a white crystalline powder and an important chemical intermediate for synthesizing polyamide fibers, engineering plastics, etc., and is widely used in industries such as textiles and plastics.

[0003] In the production process of caprolactam, rectification is a key separation and purification step. In the traditional rectification process, each rectification tower is independent of each other. Each rectification tower requires a large amount of heat energy to achieve separation, and this heat energy is often not effectively utilized and recovered, lacking effective heat integration and coupling, resulting in a low overall thermodynamic efficiency of the system. This not only causes waste of energy, but also increases production costs and environmental burdens. Summary of the Utility Model

[0004] The purpose of the utility model is to provide a caprolactam rectification heat energy coupling utilization system to solve the problem of excessive energy consumption in the existing caprolactam production process.

[0005] To achieve the above purpose, the utility model adopts the following technical solutions:

[0006] The utility model provides a caprolactam rectification heat energy coupling utilization system, including a cyclohexane refining tower, a cyclohexene separation tower, and a debenzolization tower that are connected in sequence; wherein,

[0007] The top of the cyclohexane refining tower is connected in sequence to a first compressor, a first falling film evaporator, and a cyclohexane flash tank. The cyclohexane flash tank is connected to the first compressor, and the first falling film evaporator is connected to the bottom of the cyclohexene separation tower through a first falling film circulation pump;

[0008] The top of the cyclohexene separation tower is connected in sequence to a second compressor, a second falling film evaporator, and a cyclohexene flash tank. The cyclohexene flash tank is connected to the second compressor, and the second falling film evaporator is connected to the bottom of the debenzolization tower through a second falling film circulation pump;

[0009] The top of the debenzolization tower is also connected to the middle part of the cyclohexene separation tower.

[0010] Preferably, the cyclohexane flash tank is also connected in sequence to a first cooler, a first reflux tank, a first reflux pump, and the top of the cyclohexane refining tower.

[0011] Preferably, the cyclohexene flash tank is also connected in sequence to a second cooler, a second reflux tank, a second reflux pump, and the top of the cyclohexene separation tower.

[0012] Preferably, the top of the benzene stripper is sequentially connected to a condenser, a third reflux drum, and a third reflux pump, and the third reflux pump is connected to the top of the benzene stripper.

[0013] Preferably, a cyclohexene separation column is also connected between the third reflux pump and the benzene stripper.

[0014] Preferably, the top of the benzene stripper is connected to the middle of the cyclohexene separation column through a benzene stripper compressor.

[0015] The utility model has the following beneficial effects:

[0016] The utility model provides a caprolactam rectification thermal energy coupling utilization system. In this system, the high-temperature gas-phase materials generated by the cyclohexane refining column and the cyclohexene separation column are heat-exchanged with the bottom liquid in the next column through a falling-film evaporator, which improves the feed temperature of the next column, thereby improving the thermal utilization of high-temperature steam, reducing steam usage, and lowering production costs. At the same time, it also reduces the use of coal for burning, reduces waste gas emissions, and protects the environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic structural diagram of the caprolactam rectification thermal energy coupling utilization system provided by the embodiment of the present application. DETAILED DESCRIPTION

[0018] Next, the technical solutions in the embodiments of the present utility model will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present utility model. Obviously, the described embodiments are only a part of the embodiments of the present utility model, rather than all the embodiments. Based on the embodiments of the present utility model, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present utility model.

[0019] The embodiment of the present application provides a caprolactam rectification thermal energy coupling utilization system, which includes a cyclohexane refining column, a cyclohexene separation column, and a benzene stripper that are sequentially connected, as shown in the attached Figure 1 figure.

[0020] Specifically, the top of the cyclohexane refining column is sequentially connected to a first compressor, a first falling-film evaporator, and a cyclohexane flash drum, and the cyclohexane flash drum is connected to the first compressor. The first falling-film evaporator is connected to the bottom of the cyclohexene separation column through a first falling-film circulation pump.

[0021] In the cyclohexane refining tower, the cyclohexane produced by the cyclohexane reactor is subjected to distillation treatment. Vapor-phase cyclohexane with a higher temperature is obtained at the top of the tower; refined cyclohexane is obtained at the bottom of the tower. The vapor-phase cyclohexane is compressed by a first compressor to increase the pressure and temperature of the vapor-phase cyclohexane to 5.7 bar and 149 °C. The heated vapor-phase cyclohexane is transported to a first falling-film evaporator for heat exchange treatment.

[0022] The top of the cyclohexene separation tower is successively connected to a second compressor, a second falling-film evaporator, and a cyclohexene flash tank. The cyclohexene flash tank is connected to the second compressor. The second falling-film evaporator is connected to the bottom of the debenzene tower through a second falling-film circulation pump.

[0023] In the cyclohexene separation tower, the mixture of cyclohexane and cyclohexene produced by the debenzene tower is subjected to distillation treatment. Vapor-phase cyclohexane with a higher temperature is obtained at the top of the tower, and refined cyclohexene is obtained at the bottom of the tower. The vapor-phase cyclohexane is compressed by a second compressor to increase the pressure and temperature of the vapor-phase cyclohexane to 4.9 bar and 145 °C. The heated vapor-phase cyclohexane is transported to the second falling-film evaporator. After controlling the pressure of the refined cyclohexene obtained at the bottom of the tower to 0.8 bar, it is transported to the first falling-film evaporator through a first falling-film circulation pump.

[0024] The vapor-phase cyclohexane and the refined cyclohexene exchange heat in the first falling-film evaporator. After heat exchange, the refined cyclohexene enters the bottom of the cyclohexene separation tower for distillation treatment. To make full use of the latent heat of the vapor phase, the vapor-phase cyclohexane after heat exchange enters the cyclohexane flash tank for flash evaporation treatment to obtain flash gas and flash liquid. The flash gas re-enters the first compressor so that after compression and heating, it exchanges heat with the refined cyclohexene produced by the cyclohexene separation tower in the first falling-film evaporator to realize the reuse of the latent heat of the vapor phase.

[0025] The flash liquid is cooled by a first cooler and then enters the first reflux tank for temporary storage, and then re-enters the top of the cyclohexane refining tower through a first reflux pump. To avoid cavitation of the first reflux pump, the flash liquid is cooled to the saturated vapor pressure by the first cooler and then enters the top of the cyclohexane refining tower.

[0026] In the embodiment of the present application, the cyclohexane refining tower is an extractive distillation tower, and the extractant DMAC enters from the middle and upper part of the cyclohexane refining tower. The concentration of the extractant DMAC in the liquid phase in the cyclohexane refining tower has an important influence on the relative volatility between the original components. To keep the concentration of the extractant DMAC high enough and evenly distributed in the cyclohexane refining tower, in addition to adding the extractant, the cyclohexane refining tower is fed with saturated steam to make the liquid-phase flow rates in the rectifying section and the stripping section of the cyclohexane refining tower substantially the same, so that the concentrations of the extractant DMAC in the liquid phases of the two sections are basically the same.

[0027] The top of the benzene stripper is also connected to the middle of the cyclohexene separation column. Specifically, in the benzene stripper, the DMAC transported by the benzene recovery column reacts with the mixture of benzene, cyclohexene and cyclohexane transported by the dehydration column to carry out the benzene stripping reaction. A mixture of cyclohexane and cyclohexene is obtained at the top of the column, and a mixture of benzene and DMAC is obtained at the bottom of the column. In the mixture of cyclohexane and cyclohexene obtained at the top of the column, 35% by volume of the mixture of cyclohexane and cyclohexene is pressurized to 2.0 bar by the benzene stripper compressor and then enters the middle of the cyclohexene separation column; another part of the mixture of cyclohexane and cyclohexene enters the third reflux drum for temporary storage after being condensed by the condenser, and then re-enters the benzene stripper through the third reflux pump. The bottom pressure of the benzene stripper is controlled at 80 kPa and the temperature is controlled at 125 °C. The mixture of benzene and DMAC enters the second falling film evaporator through the second falling film circulation pump.

[0028] The gaseous cyclohexane and the mixture of benzene and DMAC are heat-exchanged in the second falling film evaporator. After heat exchange, the mixture of benzene and DMAC enters the bottom of the benzene stripper to carry out the benzene stripping reaction. To make full use of the latent heat of the gas phase, the gaseous cyclohexane after heat exchange enters the cyclohexene flash tank for flash evaporation treatment to obtain flash gas and flash liquid. The flash gas re-enters the second compressor so that after being compressed and heated, it can be heat-exchanged with the mixture of benzene and DMAC generated by the benzene stripper in the second falling film evaporator to realize the reuse of the latent heat of the gas phase.

[0029] The flash liquid is cooled by the second cooler and then enters the second reflux drum for temporary storage, and then re-enters the top of the cyclohexene separation column through the second reflux pump. To avoid cavitation of the second reflux pump, the flash liquid is cooled to the saturated vapor pressure by the second cooler and then enters the top of the cyclohexene separation column.

[0030] Furthermore, to prevent the entrainment of impurities in the material from affecting the operation of the first compressor and the second compressor, filters are also added to the material transportation pipeline. The filters are preferably arranged between the cyclohexane refining column and the first compressor, and between the cyclohexene separation column and the second compressor. Of course, filters can also be added to other transportation pipelines.

[0031] Since the compression conditions of the first compressor and the second compressor operate at the critical temperature and critical pressure, liquid is inevitably generated. To avoid affecting the later heat transfer, in the embodiments of the present application, vapor-liquid buffer tanks are added at the discharge ports of the first compressor and the second compressor to slow down the influence of the generated liquid on the later heat transfer. The vapor-liquid buffer tanks in the embodiments of the present application are vertical storage tanks.

[0032] In addition, reboilers are respectively provided at the bottoms of the cyclohexane refining tower, the cyclohexene separation tower, and the benzene removal tower. When the system is started up in the early stage, the reboiler at the bottom of the cyclohexane refining tower is first used to heat the materials in the tower to evaporate the materials in the tower, and a gas phase is generated at the top of the tower; then the latent heat generated by the gas phase is used as the heat source for the cyclohexene separation tower.

[0033] The usage process of the caprolactam rectification heat energy coupling utilization system provided by the embodiment of the present application is as follows:

[0034] S01: The cyclohexane generated by the cyclohexane reactor enters the cyclohexane refining tower for rectification treatment. Among them, the pressure in the cyclohexane refining tower is 20 - 60 kPa, and the temperature is 120 - 160 °C. High-temperature gaseous cyclohexane is obtained at the top of the cyclohexane refining tower, and refined cyclohexane is obtained at the bottom. To recover the latent heat of the gas phase generated at the top, the gaseous cyclohexane is compressed by a first compressor to increase the pressure and temperature of the gaseous cyclohexane to 5.7 bar and 149 °C. The heated gaseous cyclohexane is transported to a first falling film evaporator for heat exchange treatment.

[0035] S02: The mixture of cyclohexane and cyclohexene generated by the benzene removal tower enters the cyclohexene separation tower for rectification treatment. Among them, the pressure in the cyclohexene separation tower is 80 kPa, and the temperature is 144 °C. High-temperature gaseous cyclohexane is obtained at the top of the cyclohexene separation tower, and refined cyclohexene is obtained at the bottom. To recover the latent heat of the gas phase generated at the top, the gaseous cyclohexane is compressed by a second compressor to increase the pressure and temperature of the gaseous cyclohexane to 4.9 bar and 145 °C. The heated gaseous cyclohexane is transported to the second falling film evaporator. After controlling the pressure of the refined cyclohexene obtained at the bottom to 0.8 bar, it is transported to the first falling film evaporator through a first falling film circulation pump.

[0036] S03: The gaseous cyclohexane and the refined cyclohexene exchange heat in the first falling film evaporator; among them, when exchanging heat, the feed mass ratio of the gaseous cyclohexane to the refined cyclohexene is 0.2.

[0037] S04: After heat exchange, the temperature of the gaseous cyclohexane is 118 °C, and the temperature of the refined cyclohexene is 120 °C. The refined cyclohexene enters the bottom of the cyclohexene separation tower for rectification treatment. To make full use of the latent heat of the gas phase, the gaseous cyclohexane after heat exchange enters a cyclohexane flash tank for flash evaporation treatment to obtain flash gas and flash liquid. The flash gas re-enters the first compressor so that after being compressed and heated, it exchanges heat with the refined cyclohexene generated by the cyclohexene separation tower in the first falling film evaporator to realize the reuse of the latent heat of the gas phase.

[0038] The flash liquid is cooled by the first cooler and then enters the first reflux drum for temporary storage, and then re-enters the top of the cyclohexane refining column through the first reflux pump. To avoid cavitation of the first reflux pump, the flash liquid is cooled to the saturated vapor pressure by the first cooler and then enters the top of the cyclohexane refining column.

[0039] S05: The DMAC (N,N-Dimethylacetamide) transported by the benzene recovery column is mixed with the mixed liquid of benzene, cyclohexene and cyclohexane transported by the dehydration column in the benzene removal column. Due to the addition of DMAC, the relative volatility between benzene, cyclohexene and cyclohexane changes, and then a separation reaction occurs in the benzene removal column. A mixture of cyclohexane and cyclohexene is obtained at the top of the column, and a mixture of benzene and DMAC is obtained at the bottom of the column. In the mixture of cyclohexane and cyclohexene obtained at the top of the column, the mixture of cyclohexane and cyclohexene with a volume content of 35% is pressurized to 2.0 bar by the benzene removal column compressor and then enters the middle of the cyclohexene separation column; another part of the mixture of cyclohexane and cyclohexene enters the third reflux drum for temporary storage after being condensed by the condenser, and then re-enters the benzene removal column through the third reflux pump. The bottom pressure of the benzene removal column is controlled at 80 kPa and the temperature is controlled at 125 °C. The mixture of benzene and DMAC enters the second falling film evaporator through the second falling film circulation pump.

[0040] S06: The gaseous cyclohexane is heat-exchanged with the mixture of benzene and DMAC generated at the bottom of the benzene removal column in the second falling film evaporator.

[0041] S07: After heat exchange, the mixture of benzene and DMAC enters the bottom of the benzene removal column for benzene removal reaction. To make full use of the latent heat of the gas phase, the gaseous cyclohexane after heat exchange enters the cyclohexene flash drum for flash treatment to obtain flash gas and flash liquid. The flash gas re-enters the second compressor so that after compression and temperature increase, it can be heat-exchanged with the mixture of benzene and DMAC generated by the benzene removal column in the second falling film evaporator to realize the reuse of the latent heat of the gas phase.

[0042] The flash liquid is cooled by the second cooler and then enters the second reflux drum for temporary storage, and then re-enters the top of the cyclohexene separation column through the second reflux pump. To avoid cavitation of the second reflux pump, the flash liquid is cooled to the saturated vapor pressure by the second cooler and then enters the top of the cyclohexene separation column.

[0043] The above are only the preferred embodiments of the present application and are not used to limit the present application. For those skilled in the art, the present application can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A caprolactam rectification thermal energy coupling utilization system, characterized in that, It includes a cyclohexane refining tower, a cyclohexene separation tower, and a debenzolization tower that are connected in sequence; among them, the top of the cyclohexane refining tower is connected in sequence to a first compressor, a first falling film evaporator, and a cyclohexane flash tank. The cyclohexane flash tank is connected to the first compressor, and the first falling film evaporator is connected to the bottom of the cyclohexene separation tower through a first falling film circulation pump; the top of the cyclohexene separation tower is connected in sequence to a second compressor, a second falling film evaporator, and a cyclohexene flash tank. The cyclohexene flash tank is connected to the second compressor, and the second falling film evaporator is connected to the bottom of the debenzolization tower through a second falling film circulation pump; the top of the debenzolization tower is also connected to the middle part of the cyclohexene separation tower.

2. The caprolactam rectification thermal energy coupling utilization system according to claim 1, characterized in that The cyclohexane flash tank is also connected in sequence to a first cooler, a first reflux tank, a first reflux pump, and the top of the cyclohexane refining tower.

3. The caprolactam rectification thermal energy coupling utilization system according to claim 1, characterized in that The cyclohexene flash tank is also connected in sequence to a second cooler, a second reflux tank, a second reflux pump, and the top of the cyclohexene separation tower.

4. The caprolactam rectification thermal energy coupling utilization system according to claim 1, characterized in that, The top of the debenzolization tower is also connected in sequence to a condenser, a third reflux tank, and a third reflux pump. The third reflux pump is connected to the top of the debenzolization tower.

5. The caprolactam rectification thermal energy coupling utilization system according to claim 4, characterized in that A cyclohexene separation tower is also connected between the third reflux pump and the debenzolization tower.

6. The caprolactam rectification thermal energy coupling utilization system according to claim 1, characterized in that, The top of the debenzolization tower is connected to the middle part of the cyclohexene separation tower through a debenzolization tower compressor.

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