Method of purification of carbon dioxide from low-boiling impurities

 

(57) Abstract:

The method includes compressing the mixture in the compressor, serial cooling water refrigerator and heat exchanger-liquefier, drying in the adsorption unit, condensation and subsequent treatment in a distillation column. Part of the initial mixture after drying is sent to the coil of the distillation column, and after the cooling coil condensate together with the rest of the original mixture and before applying the treatment in a distillation column is sent to the subcooler for subcooling the main part of the liquid flow use a portion of the condensed initial mixture, dresselian to a pressure of 0.7-0.8 MPa. The use of this invention eliminates the use of external heat to the heater, and the flow of CO2applied to the top of the column consists of only one liquid phase. 2 C.p. f-crystals, 2 Il.

The invention relates to techniques for the production of pure carbon dioxide and can be used in the food industry, in mechanical engineering and other industries.

A method of obtaining CO2from natural gas rich in CO2[1], which includes chilled pasie components, getting into Cuba columns of the target product in the form of liquid CO2.

However, the concentration of the produced liquid CO2when implementing this method does not exceed 98.5% of CO2(volume). In addition, the coil of the distillation column is fed all the partial flow of the mixture, resulting in the need to increase the heat transfer surface of the coil and, as a consequence, the overall dimensions of the distillation column.

These drawbacks are largely deprived of the method of extraction of CO2proposed in [2]. According to this method, the initial mixture, containing, along with CO2impurities of N2or CH4, compremises, cooled, condensed and separated in the evaporator pairs mixture, after heating in the heater, proceed to the Stripping column where they are separated low-boiling impurities and the result is a target product in the form of liquid CO2.

However, the disadvantage of this method is that the heating steam flow separation in the Stripping column is produced by an external source of heat and the flow of liquid CO2applied to the irrigation of the column enters the liquid pump in a state of saturated liquid, the mod of the liquid due to external heat gain and heat of friction. Eventually this leads to the reduction of the flow of the fluid supplied to the top of the column and, consequently, deterioration of the process of rectification in the column. In addition, this method does not solve the problem of drying a mixture containing CO2and fed to the separation in a distillation column.

The problem to which the invention is directed to develop a way of purification of CO2from low-boiling impurities, in which, in comparison with the prototype, to preheat the gaseous CO2do not use external heat to the heater, and the flow of CO2supplied to the top of the column consists of only one liquid phase.

The technical result that can be obtained by using the proposed method, is to supply the parts cleaned CO2in the coil of the distillation column after the adsorption drying, applied for subcooling liquid initial mixture in the subcooler part of the initial mixture, dresselian to a pressure of 0.7-0.8 MPa, and after its re-evaporation dresselian to a pressure close to atmospheric; in the heated portions of the original mixture by cooling part of the purified CO2taken after compression in the compressor.

To achieve this technical result leaving the subcooler dresselian thread again drossellied, served on the cooling part of the stream compressed in the compressor of the original mixture, and then sent to the suction of the compressor.

The achievement of the technical result is driven by the fact that the coil of the distillation column direct part of the flow of the original mixture, which after drying is additionally heated in the heat exchanger-heater, the cooling portion of the compressed stream in compressores after block adsorption drying at positive temperature, eliminates the need to install additional external heater to heat the mixture before it is supplied to the coil. When installing additional heat exchanger-heater on the flow of the mixture supplied to the coil of the column, where it is additionally heated by cooling the part compressed in the compressor flow mixture, the decreasing flow directed into the coil, and, consequently, reducing the size of the coil and columns in General. The use of a minor part of the liquid of the original mixture, dresselian to a pressure of 0.7-0.8 MPa, which excludes the possibility of obtaining a solid phase CO2after throttling, with the aim of hypothermia is the main part of the liquid stream before it enters the pump helps to ensure reliable operation of the liquid pump and eliminates partial vaporization in the liquid stream fed to the top of the distillation column. The presence in this thread only the liquid phase improves the process of rectification in the column.

In Fig. 1 shows a schematic diagram of an installation for implementing this method. Installation of purification of carbon dioxide from low-boiling impurities contains the compressor 1, the terminal hole is 7, distillation column 8 with the coil 9, the liquid pump 10, the subcooler 11, the intermediate tank liquid CO212, the capacity of production of high-purity CO213, the throttle valves 14 and 15, the valves 16-21, 23-25 and end cooler 22.

The method is as follows. The initial mixture containing up to 98% CO2(volume), impurity H2N2CH4, CO, Ar and a pair of H2O, is compressed in the compressor 1 to P=1.5 and 1.7 MPa, and after the compressor is directed to the cooling apparatus 2 and 22. In the end the refrigerator for 2 main thread of the original mixture is cooled by water, and in the end the cooler 22 and the remaining portion of the original mixture of gaseous CO2passing through it under pressure slightly above atmospheric.

After cooling to limit the refrigerator for 2 main flow of the mixture enters the separator 3, where it is separated condensed moisture. Subsequent cooling of this stream is carried out in a heat exchanger-the liquefier 4, in which when lowering the temperature of the initial mixture to 276-K condensed portion of the vapor. Until the same temperature is cooled and a portion of the original mixture in the limit cooler 22. Then both threads original mixed the ne mixture is carried out in the adsorption unit 6. Each of the adsorbers unit 6 has a dual charge adsorbents, with which dehydration of the mixture and its purification from high-boiling impurities. Next, the flow of the mixture supplied to the capacitor 7, which is due to the boiling of the cooling agent is a condensation of the original mixture at a temperature 242-244 K. Nscontainerframe gases collecting in the upper part of the condenser periodically blown off by opening the valve 25.

Part of the flow of the original mixture is taken out of the adsorption unit 6 is supplied to the coil 9, located in the bottom part of the distillation column 8. Upon cooling of this stream in the coil 9 is diverted from him, the heat supplied to the bottom of the liquid columns in the cube, and the resulting vapor rises up the column, ensuring the process of rectification. The output from the coil 9 of this thread as the main thread of the original mixture, is fed to the condenser 7.

From the condenser 7 of the liquid source mixture enters the subcooler 11. Part of the flow of the original mixture is withdrawn before the subcooler 11 and enters the orifice 14, after which the liquid-vapor mixture at P=0,7-0,8 MPa is used for cooling the main part is the W part of the flow of the mixture to overcooling of the primary fluid flow, supplied with pump 10 in column 8, ensures stable operation of the pump and eliminates the formation of the vapor phase in this thread.

The original liquid mixture supplied to the top of the column 8, flowing down the column, in the process of rectification with rising on steam it is freed from low-boiling impurities, which are in pairs and must be removed from the top of the column through the valve 25 or received in the condenser 7 through the valve 24.

In Cuba, the column 8 is going pure liquid CO2that through the valve 18 is given in the intermediate tank 12, where is then drained through the valve 20 in capacity net production of carbon dioxide 13. Through valves 19 and 21 of the tanks 12 and 13 are disposed a pair of CO2going to the condenser 7.

Part of the flow of the mixture after passing through the throttle 15 is fed into the tail cooler 22, which is heated to a temperature close to ambient temperature, and then is fed to the suction of the compressor 1.

In Fig. 2 is a schematic diagram of the setup that implements this method, in which, in contrast to the schematic setup is shown in Fig. 1, includes an additional heat exchanger-heater 26.

In Dan the aqueous stream initial mixture and before entering the coil 9 is additionally heated in the heat exchanger, the heater 26, taking away heat from a portion of the flow of the mixture entering the heat exchanger after compression in the compressor. Increasing the temperature of the stream fed to the evaporator 9, allows to reduce its size and to reduce the dimensions of the evaporator. In the rest of the directions of flow for the circuit, as shown in Fig. 2, coincide with the direction of their movement on the setup diagram shown in Fig. 1.

Sources of information

1. The application of Germany N 3639779, MKI C 01 B 51/20, published 01.06.88.

2. U.S. patent N 4762545, MKI F 25 J 5/02, published 09.08.88.

1. Method of purification of carbon dioxide from low-boiling impurities, including compression of the mixture in the compressor, serial cooling water refrigerator and heat exchanger-liquefier, drying, condensation and subsequent treatment in a distillation column, characterized in that the portion of the initial mixture after drying in the adsorption unit is sent to the coil of the distillation column, and after the cooling coil condensate together with the rest of the original mixture and before applying the treatment in a distillation column is sent to the subcooler for subcooling the main part of the liquid flow use part of the MSE of the tives such as those that leaving the subcooler dresselian thread again drossellied, served on the cooling part of the stream compressed in the compressor of the original mixture, and then sent to the suction of the compressor.

3. The method according to p. 1, characterized in that the coil of the distillation column direct part of the flow of the original mixture, which after drying is additionally heated in the heat exchanger-heater, the cooling portion of the compressed stream in the compressor of the original mixture.

 

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