Highly effective technology has been developed providing preparation of various especially pure cryogenic products, production schemes are provided for automated rectification modules, and a procedure has been developed for the design.Currently, the main cryoproducts (oxygen, nitrogen, and argon), prepared with air separation, are used extensively in various branches of science and technology. In a number of production processes, particularly high specifications are laid down for purity of these products, in accordance with which the content of individual impurities should be several orders of magnitude lower than those that are permitted in relation to these products in existing GOST and TU.These high specifications are made for purity of a number of gases, for example hydrogen, helium, neon, and carbon dioxide. The limiting overall content of microimpurities for individual components in a number of cases should not exceed 10 -5 -10 -7 % (vol.).In low-temperature technology in order to prepare particularly pure gases methods of low-temperature rectification and adsorption are used. Depending on the composition of the mixture being separated, its parameters and volume in a NTU, designated for preparing especially pure gas, it is possible to use one of these methods or two successively.In order to prepare technically pure air separation products (such nitrogen, oxygen and argon), cryogenic air separation units (ASU) are used, in whose separation assembly a method of low-temperature rectification is used. However, in those cases when it would be necessary to separate one of the components in especially pure form, use of standard ASU appears to be undesirable. This is explained by the fact that in a production scheme the device is quite complicated and its operation presents particular difficulties.In these cases, the most rational solution of this problem may be achieved as a result of preparing particularly pure cryoproducts from those of technical purity in special automated cryogenic modules. This makes it possible to organize production of especially pure cryoproducts not only for those products where technically pure products of air separation are obtained, but also directly for the user of particularly pure cryoproducts.In the Cryogenic Technology Department of the St. Petersburg State University of Low Temperatures and Food Technology highly efficient technology has been developed making it possible to provide preparation of various especially pure cryoproducts. As a result of this scientific research with the aim of cryoproduct preparation in liquid and gaseous states with the minimum amount of impurities production schemes have been proposed for automatic rectification modules and a procedure for designing them has been developed.During analysis of various design solutions, the main energy properties of the purification process have been determined making it possible to evaluate the efficiency of the design solutions adopted.
Lentekhgas Corporation is the primary specialized plant supplying the products of fractionation of air to plants and organizations of the northwestern region of Russia. In types KzhAr-l.6 and KzhAr-2 air fractionation units, gaseous argon is produced in addition to liquid and gaseous oxygen and nitrogen. Damp argon obtained in the basic rectification unit of an air fractionation unit is cleansed of oxygen by the catalytic hydration method and of nitrogen in a type BRA-2 low-temperature rectification unit. As a result, high-purity commercial-grade (more than 99.99 vol. % Ar) is obtained.Until recently, argon was supplied to users only in gaseous form in tanks under a pressure of 15-16.5 MPa. However, in connection with the increase in transportation costs as the results of supplying users with gaseous argon in tanks and a decrease in delivery of it on days off and those before, the necessity has arisen of supplying a number of users with liquid argon with subsequent gasification of it at the point of use.In connection with this, the Department of Cryogenic Technology of Saint Petersburg State Academy for Low Temperature and Food Technologies has developed a unit for liquefaction of argon, which at present has been placed in service in Lentekhgas Corporation. A significant portion of industrial oxygen is supplied to users in gaseous form in tanks. For this purpose a small quantity of gaseous oxygen which runs off from air fractionation units operating under liquid conditions, and also the vapors of liquid oxygen from its storage tanks is used. In a number of cases these volumes of gaseous oxygen are insufficient and it is necessary to gasify a portion of the liquid oxygen. The cold obtained in gasification of liquid oxygen may be used for cooling and condensation of argon.The basic plan of the unit for cooling of argon is shown in Fig. 1. Compressed argon received from BRA-2 and containers enters the countercurrent heat exchanger 1, where it is cooled and then throttled, passing through the throttle 2, to a pressure of p = 0.3 MPa and fed to the tube space of condenser-evaporator 3, from which the liquid argon flows to the TRZhK-3 vessel 5. Condensation and cooling of the argon occurs as the result of liquid oxygen supplied from the TRZhK-7M vessel 4 to the intertube space of the condenser-evaporator 3, where it boils at p = 0.11 MPa. The oxygen vapors formed enter the heat exchanger 1, where the compressed argon is cooled. From the heat exchanger 1 the gaseous oxygen, heated to a temperature close to the temperature of the compressed argon entering the heat exchanger, is delivered to the gas holder. In condensation of argon in the tube space of the condenser-evaporator it is possible to reduce somewhat the quantity of residual microimpurities of hydrogen and nitrogen by exhausting an insignificant quantity of uncondensed gas from the upper portion of the tube space of the condenser-evaporator.In making the thermal calculation of the unit the basic parameters of flow of argon and oxygen were determined. Taking into...
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