Patent ID: 9581386
Date: 2017-02-28
CPC Classifications: F25J

Claim:
1. A process for separating air by cryogenic distillation to produce a gaseous product, the process comprising the steps of: a) sending a cooled, purified, and compressed air into a column system comprising a medium-pressure column and a low-pressure column; b) withdrawing from the low-pressure column, an oxygen-rich stream which has a nominal flow, and withdrawing an oxygen-rich liquid purge stream at the bottom of the low-pressure column, wherein the oxygen-rich liquid purge stream is richer in oxygen and in heavy impurities than the oxygen-rich stream, wherein the oxygen-rich liquid purge stream has a first flow rate that constitutes not more than 2% of the nominal production flow rate of the oxygen-rich stream, wherein the oxygen-rich stream comprises a fluid selected from the group consisting of an oxygen-rich liquid and an oxygen-rich gas, wherein if the fluid is the oxygen-rich gas, the oxygen-rich gas forms an oxygen-rich gaseous product, wherein if the fluid is the oxygen-rich liquid, the step further includes evaporating the oxygen-rich liquid stream in a main evaporator to form the oxygen-rich gaseous product; c) sending the oxygen-rich liquid purge stream into a storage facility at the first flow rate; and d) providing a control system configured to control the level of liquid in the storage facility, wherein if the control system detects that the level of liquid in the storage facility exceeds a threshold corresponding to the maximum capacity of the storage facility, the control system is configured to initiate a withdrawal of a storage liquid stream from the storage facility at a second flow rate this is approximately equal to the first flow rate, and a sending of the storage liquid to a standby evaporator, to make up part of the oxygen-rich gaseous product, wherein if the control system detects that the level of liquid in the storage facility is below the threshold corresponding to the maximum capacity of the storage facility, the control system is configured to initiate continued sending of the oxygen-rich liquid purge stream to the storage facility at the first flow rate, while only sending the storage liquid stream from the storage facility to the standby evaporator in the case of a reduction in production of the oxygen-rich gaseous product by the column system or of an increase in demand by a customer for the oxygen-rich gaseous product.