Method and device for separating air by cryogenic distillation

Abstract

A method for separating air by cryogenic distillation, wherein air is compressed in a first compressor, cooled in a heat exchanger and then separated in a system of columns, liquid oxygen is vaporized in the heat exchanger countercurrent to a flow of pressurized gas which pseudo-condenses, a flow of gas which is air or a gas delivered from the system of columns is expanded in a cryogenic expansion turbine having a single wheel, the turbine having an inlet temperature lower than −100° C., a gas which is air or a gas delivered from the system of columns is compressed in a first booster compressor having a single wheel, with an inlet temperature higher than −50° C., a gas which is air or a gas delivered from the system of columns.

1 .- 15 . (canceled) 
     
     
         16 . A method for separating air by cryogenic distillation, wherein air is compressed in a first compressor, cooled in a heat exchanger and then separated in a system of columns, liquid oxygen is vaporized in the heat exchanger countercurrent to a flow of pressurized gas which pseudo-condenses, a flow of gas which is air or a gas delivered from the system of columns is expanded in a cryogenic expansion turbine having a single wheel, the turbine having an inlet temperature lower than −100° C., a gas which is air or a gas delivered from the system of columns is compressed in a first booster compressor having a single wheel, with an inlet temperature higher than −50° C., a gas which is air or a gas delivered from the system of columns, this gas having already been compressed in the first booster compressor, is compressed in a second booster compressor having a single wheel with an inlet temperature lower than −100° C., the gas compressed in at least the first booster compressor cools in the heat exchanger, contributes to the vaporization of liquid oxygen by exchange of heat in the exchanger, and is pseudo-liquefied on leaving the cold end of the heat exchanger, wherein:
 a) the work generated by the expansion turbine is used for the compression step in the first booster compressor and for the compression step in the second booster compressor, 
 b) the operating conditions for the wheel of the expansion turbine, the wheel of the first booster compressor and the wheel of the second booster compressor are defined such that these three wheels have the same rotational speed, 
 c) i) the wheel of the first booster compressor, the wheel of the second booster compressor and the wheel of the turbine are mounted on the same rotation shaft, or
 ii) the first and the second booster compressor are connected to the wheel of the expansion turbine, each by a rotation shaft, these shafts rotating at the same rotational speed, or 
 iii) the first booster compressor and the wheel of the expansion turbine are connected to the second booster compressor, each by a rotation shaft, these shafts rotating at the same rotational speed, and 
 
 d) the first compression step allows work to be generated outside the cold box, and this generates cooling power for the air separation method. 
 
     
     
         17 . The method as claimed in  claim 16 , comprising a second expansion turbine, wherein the first expansion turbine and the second expansion turbine operate in parallel and the flow of gas which is air or a gas delivered from the system of columns is divided into two fractions, each being expanded in one of the two turbines. 
     
     
         18 . The method as claimed in  claim 17 , wherein, of the expansion wheel, the wheel of the second expansion turbine, the wheel of the first booster compressor and the wheel of the second booster compressor, at least one has an efficiency lower than that which it would have, under the same operating conditions, at another rotational speed. 
     
     
         19 . The method as claimed in  claim 16 , wherein the gas compressed in the first and the second booster compressor is air used for distillation. 
     
     
         20 . The method as claimed in  claim 16 , wherein at least some of the air, or even all of the air or at least some of the gas, or even all of the gas, compressed in the first booster compressor is then compressed in the second booster compressor. 
     
     
         21 . The method as claimed in  claim 16 , wherein the work produced by the turbine is not transferred to a generator, to an oil brake or to a compressor other than the first and second booster compressors. 
     
     
         22 . The method as claimed in  claim 16 , wherein the inlet temperature of the turbine is lower than the inlet temperature of the second booster compressor and/or the inlet temperature of the first booster compressor. 
     
     
         23 . The method as claimed in  claim 16 , wherein the air is compressed first in the first booster compressor and then in the second booster compressor. 
     
     
         24 . The method as claimed in  claim 23 , wherein all the air compressed in the first booster compressor is then compressed in the second booster compressor. 
     
     
         25 . The method as claimed in  claim 16 , wherein the air expanded in the turbine has been compressed in the first booster compressor. 
     
     
         26 . The method as claimed in  claim 25 , wherein the air expanded in the turbine has already been compressed in the first booster. 
     
     
         27 . The method as claimed in  claim 16 , wherein the air expanded in the turbine has not been compressed in the first or the second booster compressor. 
     
     
         28 . A apparatus for separating air by cryogenic distillation, comprising a heat exchanger, a pipe for sending air compressed in a first compressor to be cooled in the heat exchanger, a system of columns, a pipe for sending the air cooled in the heat exchanger to be separated in the system of columns, a pipe for sending liquid oxygen from the system to be vaporized in the heat exchanger, a pipe for sending a flow of pressurized gas into the heat exchanger, a cryogenic expansion turbine having a single wheel, a pipe connected to an intermediate point of the heat exchanger for sending a flow of gas which is air or a gas delivered from the system of columns from the heat exchanger to be expanded in the cryogenic expansion turbine, the turbine having an inlet temperature lower than −100° C., a first single-stage booster compressor with an inlet temperature higher than −50° C., a pipe for sending a gas which is air or a gas delivered from the system of columns, to be compressed in the first booster compressor, a second single-stage booster compressor with an inlet temperature lower than −100° C., a pipe connected to an intermediate point of the heat exchanger for sending a gas which is air or a gas delivered from the system of columns to be compressed in the second booster compressor, a means for sending at least some of the gas, or even all of the gas, compressed in the first booster compressor to be compressed in the second booster compressor), a pipe for sending the gas compressed in at least the first booster compressor to be cooled in the heat exchanger and thus contribute to the vaporization of liquid oxygen by exchange of heat in the exchanger, wherein:
 a) the wheel of the expansion turbine, possibly the wheel of the second turbine, the wheel of the first booster compressor and the wheel of the second compressor are connected to one another in such a way that each wheel can have the same rotational speed, and 
 b) i) the wheel of the first booster compressor, the wheel of the second booster compressor and the wheel of the turbine is mounted on the same rotation shaft, or
 ii) the first and the second booster compressor are connected to the wheel of the expansion turbine, and possibly to the wheel of the second turbine, each by a rotation shaft, these shafts being capable of rotating at the same rotational speed, or 
 iii) the first booster compressor and the wheel of the expansion turbine are connected to the second booster compressor, each by a rotation shaft, these shafts being capable of rotating at the same rotational speed. 
 
 
     
     
         29 . The apparatus as claimed in  claim 28 , wherein the gas compressed in the first and the second booster compressor is air intended for distillation. 
     
     
         30 . The apparatus as claimed in  claim 28 , comprising a means for sending at least some of the air, or even all of the air, compressed in the first booster compressor to be compressed in the second booster compressor.