Patent ID: 9097459
Filing Date: 2015-08-04
Classification: F25J

Abstract:
1. An air separation process for producing elevated pressure nitrogen using an air separation unit having a low pressure (LP) column, a medium pressure (MP) column, a first vaporizer, a main heat exchanger, a second vaporizer, a condenser and a first turbine, the process comprising the steps of: introducing a cooled air stream to the MP column and conditions effective to separate the cooled air stream into a nitrogen enriched stream and an oxygen enriched stream; withdrawing the nitrogen enriched stream from a top portion of the MP column; withdrawing the oxygen enriched stream from a bottom portion of the MP column; introducing the oxygen enriched stream to the first vaporizer for separation therein; condensing the nitrogen enriched stream in the first vaporizer and then using the nitrogen enriched stream as reflux for the top of the MP column; withdrawing a bottoms liquid stream from the first vaporizer and introducing said bottoms liquid stream into the LP column for separation therein; withdrawing a boil-off gas from the top of the first vaporizer; warming a first portion of the boil-off gas in the main heat exchanger to an intermediate temperature to produce an intermediate stream; expanding the intermediate stream in the first turbine to produce a quantity of work and a low pressure intermediate stream, wherein the low pressure intermediate stream is at a temperature lower than the intermediate stream; introducing the low pressure intermediate stream to the LP column for separation therein; condensing a second portion of the boil-off gas within the second vaporizer, wherein the second vaporizer provides reboil duty for the LP column; withdrawing a low pressure nitrogen stream from a top portion of the LP column; condensing the low pressure nitrogen stream in the condenser to produce a cooled nitrogen stream; pressurizing a first portion of the cooled nitrogen stream to produce a liquid nitrogen stream; and exporting a first portion of the liquid nitrogen stream as product.