FR2598790A1 - LOW TEMPERATURE RECTIFICATION AIR CLEANING PROCESS AND DEVICE. - Google Patents

Abstract

THE PROCESS ACCORDING TO WHICH THE AIR IS CONDENSED TO A MAXIMUM PRESSURE OF 0.7 MPA AND AT LEAST ONE LIQUEFIED VAPORIZED COMPONENT TO OBTAIN A PREPURIFIED AND REMARKABLE GAS IN THAT ISOBARIZED VAPORIZATION OF THE LIQUEFIED OXYGEN TO COOL AIR CONDENSES TO BE BROKEN DOWN INTO THAT IT IS SUBJECT TO ADSORPTION AT CHANGE IN PRESSURE AND POSSIBLY TO CONDENSATION IN THE GASEOUS FORM OF AT LEAST A PARTIAL QUANTITY OF THE OXYGEN THAT IS PRODUCED.

Description

i 2597 U0O The subject of the invention is a method and a device

  air purification by rectification at low temperature, where the air is condensed to a maximum pressure of 7 bars (0.7 MPa) and in which at least one liquefied component is vaporized to

get a pre-purified gas.

  To obtain argon, it is known to combine a rectification followed by an adsorption. German Democratic Republic patent 126,953 describes a process for obtaining very pure argon in which pure argon is obtained by adsorption and / or distillation, after a first decomposition of the air and a double rectification. Japanese Patent 84,030,646 illustrates and describes a process by which very pure argon is obtained after a

  two-step rectification in a two-stage adsorption process. Japanese Patent 54,061,091 also discloses a combination of a multistage rectification and at least one adsorption stage to obtain argon.

  For a large number of technical installations, the preparation of a large quantity of oxygen is an essential prerequisite. Particularly in steelworks, oxygen is required on the one hand to obtain high combustion temperatures and

  on the other hand to refine the steel, and this, in most cases with different degrees of purity depending on the uses. In particular, for refining, very pure oxygen is required, while for combustion, lower purity is sufficient.

  For oxygen production on an industrial scale, cryogenic plants and in particular low temperature rectification processes are most often the most suitable solution.

  economic. However, the capacity of installations of this type is hardly adjustable and they must be operated as soon as they are put into service with the rated load. When, for example, converters must receive a new lining, the sampling of very pure oxygen must be interrupted, and this for periods of 48 hours, generally necessary for the installation of the new coating of the converters; it is not profitable to shut down the oxygen production plant, given the long start-up times and energy considerations.

  Low temperature rectification plants are above all a particularly profitable operation when they can be operated under a relatively low pressure by renouncing a high degree of purity for oxygen. For example, a pure gas containing up to 95% oxygen can be obtained under operating pressures of a maximum of 7 bar (0.7 MPa), in particular 5 bar (0.5 MPa). Further purification of oxygen, up to 99% for example, requires considerably higher pressures and much more complex technical installations. For most users, oxygen of lower purity is sufficient and if the known installations are not profitable, it is also, among other things, because they produce very pure oxygen, with the additional costs that this

  implies for uses where lower purity oxygen would suffice.

  The object of the invention is therefore to develop an economical process making it possible to continuously obtain oxygen of sufficient purity, with reduced energy consumption, and allowing, if necessary,

2598 90

  produce very pure oxygen. To solve this problem, the process according to the invention starts from a rectification & low temperature process recalled by adopting a pressure of 7 bars (0.7 MPa) at most. The invention essentially resides in that liquefied oxygen is isobarically vaporized to cool the condensed air to be decomposed and in that at least a partial quantity of the pressurized oxygen thus produced is subjected to a process. pressure change adsorption and if necessary condensed in gaseous form. Since the low temperature rectification process can be followed by a pressure change adsorption process, the degree of oxygen purity obtained by use can be further increased to a very great extent. a little pressure. The switching on and off of a suitable device, considerably smaller, for carrying out the pressure change adsorption process, also gives facilities for setting up the installation in which very oxygen pure is only produced as needed or, for example, when the main quantity of oxygen of lesser purity is not used. The combination of the pressure change adsorption process and a low temperature rectification process used under a relatively small pressure, allows on the one hand, an adjustment of the process in order to adapt it to the needs and, allows on the other hand, an implementation of the process under clearly more economical conditions and at lower cost. This control of the process has the advantage of making it possible to take oxygen directly from the pressure of the grinding at low temperature, and to make it possible to dispense with costly devices requiring 1O

20 25

35

  great maintenance to condense oxygen, at least for the main quantity of oxygen produced.

  In the context of the process according to the invention, the pressure change adsorption can be carried out directly with the oxygen at the pressure at which it is withdrawn from the low temperature rectification installation, and subsequently cyclically, so that the pressure change adsorbers containing the molecular filtering material are washed before a new loading, by using a pure condensed inlet gas, in particular oxygen, and so that the washing is sent to the pre-purified gas evacuation pipe after it has left the pressure change adsorber. The oxygen condenser necessary for this process can have significantly smaller dimensions since it only has to condense the partial quantity of gas which will then be purified further and since the mounting of an oxygen condenser after pressure change adsorber provides not only the desired operating pressure for pure oxygen, but also gives the possibility of using this high purity oxygen under pressure to purify or wash the molecular filtering material.

  The device according to the invention in particular for the implementation of this process comprises an air condenser and a low temperature rectification installation in which liquid oxygen is vaporized isobarically, and is essentially characterized by that a branch leading to pressure loading is connected to the gas line for pressurized gaseous oxygen. The configuration is advantageously designed in such a way that an oxygen condenser is mounted in the pure gas evacuation pipe, connected to the pressure change adsorbers, and that a washing gas recycling pipe is connected. to the pressure change adsorber, after the condenser, which makes it possible, on the one hand, to have very pure oxygen at the desired pressure and, on the other hand, washing gas at a pressure markedly higher than the pressure of operation of the 10 pressure change adsorbers. The recycling of very pure oxygen under pressure intended for washing pressure-change adsorbers makes it possible to adjust a pressure difference between the operating pressure and the washing pressure, which means that it is no longer necessary to vacuum as is the case with many adsorbers

  pressure change when you want to clean them.

  To further reduce the oxygen losses in the installation according to the invention, provision can advantageously be made for mounting an adjustable throttling or pressure reduction member in the product line between the pre-purified gas and the pressure change adsorber, in particular for recycling the washing gas. The gas of lower purity which is collected after cleaning of the pressure change adsorber and in particular the oxygen obtained which again contains large quantities of nitrogen, is thus recycled in the product gas line, which contains oxygen of lower purity, and this oxygen can be used for example without further treatment for combustion. Other features of the invention

  emerge from the detailed description which follows. 35

15

25 30 35

  An installation according to the invention is illustrated schematically on the principle plan of the pipes.

  In the figure, the reference 1 designates an air condenser which can be followed by a first molecular filter 2 which is used to pre-purify the gas to be separated. In the low-temperature rectification installation 3, oxygen is liquefied and vaporized isobarically, so that at the outlet, oxygen can be taken under pressure via a line 4 and nitrogen not compressed by a line 5. By applying an operating pressure of approximately 7 bars (0.7 MPa), it is possible to obtain by the line 4 95% oxygen. In the nitrogen line, a nitrogen condenser 6 can be mounted to also produce nitrogen under a pressure comparable to that of the oxygen line.

  A bypass 7 connected to the product gas line 4, leads to pressure change adsorbers 8. The adsorbers 8 are lined with molecular filter material; controllable or adjustable valves 9 are mounted in the inlet and outlet pipes of these adsorbers 8. When pre-purified oxygen is sent to the adsorbers 8 by the bypass 7, it is possible to take from the discharge pipe 10, very pure oxygen which is sent to an oxygen condenser 11 to then be conveyed to the user, under the desired operating pressure, for example 40 bars (4 MPa), via a pipe 12.

  From this line 12, a recycling line 13 for the washing gas leads to corresponding connections 14 of the adsorbers 8, valves 15 being again mounted in this recycling line 13 for the washing gas. The washing gas can be recycled again in the product gas line 4, by adjustable throttling members 16, after cleaning of the molecular filter material and reducing the pressure to that prevailing in this line.

Claims (5)

  1. Method of air purification by rectification & low temperature, according to which the air is condensed to a maximum pressure of 7 bars (0.7 MPa) and according to which at least one liquefied component is vaporized to obtain a prepurified gas , characterized in that liquefied oxygen is isobarically vaporized to cool the condensed air to be decomposed and in that at least a partial amount of the pressurized oxygen thus produced is subjected to a loading adsorption of pressure and if necessary condensed in gaseous form.   2. Method according to claim 1, characterized in that the pressure change adsorbers (8)   containing molecular filtering material are washed before re-loading, using pure gas, in particular oxygen, condensed with respect to the inlet pressure, and in that the washing gas is sent into the discharge line (10) of the pre-purified gas, after it has left the adsorber (8).   3. Device for implementing in particular the method according to claim 1 or 2, comprising an air condenser (1) and a low temperature rectification installation (3), in which liquid oxygen is vaporized from isobaric, characterized in that a bypass (7) leading to the adsorbers (8) is connected to the gas line   (4) gaseous oxygen under pressure.   4. Device according to claim 3,   characterized in that an oxygen condenser (11) is mounted in the evacuation pipe (10) for the purified gas, connected to the adsorbers (8) and in that downstream of the condenser (11), a supply pipe recycling 35 (13) of the washing gas is connected to the adsorbers (8). 9 2598790   5. Device according to claim 3 or 4, characterized in that an adjustable throttling or pressure reduction member (16) is mounted in the product line (4) between the gas of pre-purified product and the adsorbers (8), in particular   for recycling the washing gas (13).