Method for starting up a cryogenic air separation unit and associated air separation unit

Patent metadata

Field	Value
Publication number	US-12061045-B2
Application number	US-201817415688-A
Country	US
Kind code	B2
Filing date	Dec 19, 2018
Priority date	Dec 19, 2018
Publication date	Aug 13, 2024
Grant date	Aug 13, 2024

Abstract

In a process for starting up an air separation unit, which is at a temperature of above 0° C., the air separation unit comprising a main air compressor for compressing the feed air, a booster driven by a turbine and a venting conduit connected downstream of the booster and upstream of the main heat exchanger wherein in order to start up the air separation unit, once the turbine is operating at said given speed, the venting conduit is opened to send at least part of the air compressed in the booster from the booster outlet to the atmosphere.

First claim

The invention claimed is:

1. A process for starting up an air separation unit which is at a temperature of above 0° C., the air separation unit comprising:
a main air compressor for compressing a feed air,
a main heat exchanger,
a conduit for sending compressed air from the main air compressor to the main heat exchanger to be cooled,
a booster,
a conduit for sending at least part of the compressed air cooled in the main heat exchanger to the booster,
means for sending air to the main heat exchanger from the booster, there being no means for cooling the air downstream of the booster and upstream of the main heat exchanger,
a column system,
at least one turbine connected to receive compressed air from the main air compressor, the at least one turbine being connected to the column system to provide air to be distilled in the column system,
a conduit for removing an oxygen enriched product from the column system and sending the oxygen enriched product to be warmed in the main heat exchanger,
a conduit for removing a nitrogen enriched product from the column system and sending the nitrogen enriched product to be warmed in the main heat exchanger;
wherein, during normal operation, the air separation unit is configured such that air is sent from the main air compressor to the main heat exchanger, cooled in the main heat exchanger, compressed in the booster, cooled in the main heat exchanger and separated in the column system, air is sent from the main heat exchanger, expanded in the turbine and separated in the column system, and the nitrogen enriched product and the oxygen enriched product are warmed in the main heat exchanger;
wherein the air separation unit comprises a venting conduit connected downstream of the booster and upstream of the main heat exchanger, inlet;
wherein, during start-up of the air separation unit, the method comprises the steps of:
i) compressing air in the main air compressor and then sending said air to a booster inlet;
ii) sending air to a turbine inlet; and
iii) biasing the venting conduit to a closed position before the turbine is operating at a given fraction of its critical speed, and once the turbine is operating at said given fraction or above, opening the venting conduit to send at least part of the air compressed in the booster from a booster outlet to an atmosphere.

2. The process according to claim 1 , wherein in normal operation, a first air stream is sent from the booster to a second booster and a second air stream is sent from the main heat exchanger to the turbine and during start up, air is sent to the booster and is sent to the turbine via a by-pass conduit.

3. The process according to claim 2 , wherein during at least part of the start-up, no air is sent to the second booster.

4. The process according to claim 1 , wherein during start up, whilst air is compressed in the main air compressor and then sent to the booster inlet, air is sent to the turbine and the venting conduit is open whilst the turbine is operating at at least said given fraction of its critical speed, the main heat exchanger cools down and if a temperature within the main heat exchanger is detected to be below a given threshold, the venting conduit is closed progressively.

5. The process according to claim 1 , wherein a booster outlet temperature downstream the booster and upstream of the main heat exchanger is detected and whilst air is compressed in the main air compressor and then sent to the booster inlet, air is sent to the turbine and the venting conduit is at least partially open if the booster outlet temperature is above a given temperature and the venting conduit is closed completely if the booster outlet temperature is below the given temperature.

6. The process according to claim 1 , wherein the air separation unit comprises a bypass conduit for sending air directly from the booster to an airstream compressed in the main air compressor without passing via the main heat exchanger and in step i) air is compressed in the main air compressor and mixed with air from the booster outlet via the bypass conduit.

7. The process according to claim 6 , wherein during start up, a booster outlet temperature downstream the booster and upstream of the main heat exchanger is detected, air is compressed in the main air compressor, sent to the booster inlet, air is sent to the turbine and
i) the bypass conduit to send air from the booster to be mixed with air from the main air compressor without passing through the main heat exchanger is at least partially open if the booster outlet temperature is above a given temperature and
ii) the bypass conduit is closed completely and air is sent from the booster to the main heat exchanger without being mixed with another air stream, if the booster outlet temperature is below the given temperature.

8. The process according to claim 1 , wherein in normal operation, liquefied air is sent to the column system and a liquid product from the column system is vaporized in the main heat exchanger.

9. The process according to claim 1 , wherein during the start-up process,
i) initially no liquid product from the column system is vaporized in the main heat exchanger and no liquefied air is sent to the column system, and
ii) subsequently, a liquid product is withdrawn from the column system and vaporized in the main heat exchanger and liquefied air is sent to the column system.

Assignees

• Air Liquide
• Day Eric
• Gao Fei
• Xie Huali
• Air Liquide

Inventors

• Day Eric
• Gao Fei
• Xie Huali

Classifications

• F25J2245/40

  the recycled stream being air · CPC title

• F25J2240/10

  the fluid being air · CPC title

• F25J2240/04

  Multiple expansion turbines in parallel · CPC title

• F25J2230/40

  the fluid being air · CPC title

• F25J2230/08

  Cold compressor, i.e. suction of the gas at cryogenic temperature and generally without afterstage-cooler · CPC title