Oxygen backup method and system

A backup system for backing up the supply of oxygen within an air separation plant, said supply system comprising:

• a surge tank and a reserve storage tank adapted to receive streams of an oxygen-rich liquid resulting from indirect heat exchange between downcoming liquid of a lower pressure column and nitrogen-rich vapor column overhead of a higher pressure column of the air separation plant;
• the reserve storage tank of larger volume than the surge tank and situated more remotely from the lower pressure column than the surge tank;
• an auxiliary vaporizer;
• a flow network having a main flow path, an auxiliary flow path and a backup flow path;
• the main flow path connected to a heat exchanger used in cooling at least a portion of the air to a temperature suitable for the cryogenic rectification thereof and containing a main pump for pumping a liquid oxygen stream composed of the oxygen-rich liquid to produce a pumped liquid oxygen stream and to introduce the pumped liquid oxygen stream into the heat exchanger for heating the pumped liquid oxygen stream;
• the auxiliary flow path extending between the main flow path, between the heat exchanger and the main pump and the auxiliary vaporizer for alternately heating the pumped liquid stream and thereby supplying the oxygen;
• the backup flow path extending between the surge tank and reserve storage tank and containing a transfer pump to pump a backup stream of the oxygen-rich liquid to the surge tank and thereby replenish the surge tank with the oxygen-rich liquid;
• and
• a system of control valves within the flow network able to be selectively activated so that:
• during normal operation of the air separation plant, the streams of the oxygen-rich liquid at least on an intermittent basis are fed to the surge tank and the reserve storage tank so that the oxygen rich liquid is accumulated in the surge tank and the oxygen-rich liquid is stored within the reserve storage tank as a backup supply and the pumped liquid oxygen stream is produced in the main flow path and is heated in the heat exchanger to supply the oxygen;
• and
• during a transient operation of the air separation plant where the air separation plant has ceased operation, the surge tank is isolated so that the surge tank does not receive the oxygen-rich liquid, the auxiliary flow path is connected to the main flow path so that the liquid oxygen stream is pumped from the surge tank by the main pump to the auxiliary vaporizer and the pumped liquid oxygen stream vaporizes in the auxiliary vaporizer to supply the oxygen and the surge tank is replenished with the backup stream through the backup flow path with the use of the transfer pump.