Method and apparatus for improving efficiency of a front-end purification unit of an air separation plant

A method for reducing heat bumps following regeneration of adsorbers in an air separation unit, wherein the air separation unit comprises a front-end purification unit, a main air compressor, a higher-pressure heat exchanger, a lower-pressure heat exchanger, a distillation column system, a regeneration gas heater, and a chiller water tower, wherein the front-end purification unit comprises two adsorbers, the method comprising the steps of:

• providing a wet main air stream that was previously compressed in a main air compressor and then chilled in a direct-contact water tower;
• purifying the wet main air stream in the front-end purification unit to remove water and carbon dioxide to form a dry main air stream;
• further boosting a first portion of the dry main air stream in a booster air compressor to form a boosted air stream;
• cooling a second portion of the dry main air stream in the lower-pressure heat exchanger by indirect heat exchange to form a cooled air stream;
• cooling the boosted air stream in the higher-pressure heat exchanger by indirect heat exchange to form a cooled boosted air stream;
• introducing the cooled air stream and the cooled boosted air stream to the distillation column system under conditions effective for rectification of air into nitrogen and oxygen;
• withdrawing a first waste nitrogen gas and a second waste nitrogen gas from the distillation column system and warming said first waste nitrogen gas in higher-pressure heat exchanger and warming said second waste nitrogen gas in the lower-pressure heat exchanger;
• wherein each of the adsorbers of the front-end purification unit undergoes a processing cycle comprising a regeneration cycle and an adsorption cycle, wherein the regeneration cycle comprises a warming period and a cooling period,
• wherein during the warming period, the first waste nitrogen gas from the higher-pressure heat exchanger is further warmed in a regeneration heater prior to being introduced to the adsorber that is undergoing regeneration,
• wherein during the cooling period, flow of the first waste nitrogen gas to the adsorber undergoing regeneration is stopped and the second waste nitrogen gas from the lower-pressure heat exchanger is introduced to the adsorber that is undergoing regeneration until the adsorber undergoing regeneration reaches a targeted temperature, wherein the targeted temperature is at or above a temperature of the wet main air stream and below a temperature of the regeneration gas exiting a warm end of the higher-pressure heat exchanger.

An apparatus for reducing heat bumps following regeneration of adsorbers in an air separation unit, wherein the apparatus comprises:

• a main air compressor configured to compress an air stream to form a compressed main air stream;
• a front-end purification unit configured to purify the compressed main air stream of water and carbon dioxide to form a dry main air stream, wherein the front-end purification unit comprises two adsorbers, wherein each adsorber is configured to operate with an adsorption cycle and a regeneration cycle, wherein the regeneration cycle comprises a warming period and a cooling period;
• a lower-pressure main heat exchanger configured to cool a lower pressure dry main air stream to a cryogenic temperature suitable for rectification of air;
• a higher-pressure heat exchanger configured to cool a higher pressure dry main air stream to a cryogenic temperature suitable for rectification of air;
• a distillation column system configured to receive the lower pressure and the higher pressure dry main air streams from low-pressure and high-pressure main heat exchangers after cooling, wherein the distillation column system is configured to separate the lower pressure and the higher pressure dry main air streams into nitrogen and oxygen;
• a regeneration gas heater in fluid communication with a warm end of the higher-pressure heat exchanger and the front-end purification unit, wherein the regeneration gas heat is configured to heat a first waste nitrogen stream sourced from the distillation column system during the warming period of the regeneration cycle;
• and
• wherein a warm end of the lower-pressure heat exchanger is in fluid communication with the front-end purification unit, such that a second waste nitrogen stream is used during the cooling period of the regeneration cycle.