Cryogenic rectification process-based method for producing air product, and air separation system

Abstract

The present invention discloses a cryogenic rectification process-based method for producing an air product, and an air separation system. By adding an air product outlet line and a liquid air booster pump to an existing cryogenic rectification process apparatus, the existing rectification apparatus is used to prepare oxygen-enriched liquid air by pressurizing, cooling and liquefying feed air; and moreover, a high-pressure or ultra-high-pressure air product can be prepared according to customer requirements by adjusting the ratio of the feed air to the oxygen-enriched liquid air, and pressurizing the mixture to a target pressure by the liquid air booster pump before being vaporized via heat exchange with a gas or liquid product produced by rectification through a heat exchange apparatus. According to the present invention, when gas or liquid products of oxygen and nitrogen are produced by means of rectification, a high-pressure or ultra-high-pressure air product can be provided according to customer requirements, and there is no need to provide an additional air compressor or passively increase the discharge pressure of the air booster, so that the production costs are greatly reduced and the energy efficiency level is improved. The method of the present invention can also improve the stability of devices, especially when a small amount of high-pressure/ultra-high-pressure air product needs to be produced.

1 - 26 . (canceled) 
     
     
         27 . A cryogenic rectification process-based method for producing an air product, comprising:
 a. providing an air separation system for preparing a nitrogen product and/or an oxygen product, which comprises: a rectification column, at least one air boost system, at least one air pre-cooling apparatus, at least one air purification apparatus and at least one heat exchange apparatus, wherein the rectification column comprises a first column with a first pressure, a second column with a second pressure and a main condensation and evaporation apparatus arranged at the bottom of the second column; and the air boost system comprises a main air compressor and at least one air booster;   b. after passing feed air sequentially through the main air compressor for pressurization to a first pressure range, the air pre-cooling apparatus for pre-cooling and the air purification apparatus for purification, splitting off one portion thereof as a first air stream for heat exchange through the heat exchange apparatus with a gas or liquid product produced by rectification, and then introducing the first air stream after cooling down into the first column for rectification; and the other portion passing through the air booster for pressurization to a third pressure range before being split into a second air stream and a third air stream, the second air stream passing through the heat exchange apparatus for heat exchange with the gas or liquid product produced by rectification and being discharged from a middle part of the heat exchange apparatus into an air expander for depressurization to the first pressure range before being introduced into the first column for rectification; and the third air stream passing through the heat exchange apparatus for heat exchange with the gas or liquid product produced by rectification, and after cooling down, being depressurized to the first pressure range for introduction into the first column or depressurized to a second pressure range for introduction into the second column;   c. providing a liquid nitrogen line and an oxygen-enriched liquid air line which introduce liquid nitrogen at the top of the first column and oxygen-enriched liquid air at the bottom of the first column, respectively, into the second column as reflux for rectification; and   d. providing an air product outlet line in which at least one liquid air booster pump is arranged, and discharging the oxygen-enriched liquid air or at least partially liquefied feed air of the third air stream from the bottom of the first column through the air product outlet line, into the liquid air booster pump for pressurization to a target pressure, and then into the heat exchange apparatus for vaporization via heat exchange so as to obtain the required air product.   
     
     
         28 . The cryogenic rectification process-based method for producing an air product as claimed in  claim 27 , wherein the air expander uses an expander booster for braking, the third air stream is first pressurized to a fourth pressure range by the expander booster, then enters the heat exchange apparatus for heat exchange with the gas or liquid product produced by rectification, and after cooling down, is depressurized to a first pressure range by a pressure reducing apparatus and then introduced into the first column. 
     
     
         29 . The cryogenic rectification process-based method for producing an air product as claimed in  claim 27 , wherein the pressure reducing apparatus is a throttle valve or a liquid expander. 
     
     
         30 . The cryogenic rectification process-based method for producing an air product as claimed in  claim 29 , wherein the liquid expander is braked by a generator. 
     
     
         31 . The cryogenic rectification process-based method for producing an air product as claimed in  claim 28 , wherein a fourth air stream is further split off from the third air stream that has been depressurized to the first pressure range, and the fourth air stream is introduced into the second column after being throttled and depressurized to the second pressure range by a throttle valve. 
     
     
         32 . The cryogenic rectification process-based method for producing an air product as claimed in  claim 31 , wherein a fifth air stream is further split off from the fourth air stream, the fifth air stream is connected to the air product outlet line, and the flow rate and flow velocity of the fifth air stream are controlled via a first regulating valve. 
     
     
         33 . The cryogenic rectification process-based method for producing an air product as claimed in  claim 27 , wherein the air product outlet line is further provided with a second regulating valve for controlling the flow rate and flow velocity of the oxygen-enriched liquid air. 
     
     
         34 . The cryogenic rectification process-based method for producing an air product as claimed in  claim 27 , wherein the heat exchange apparatus comprises a low-pressure plate heat exchanger and a high-pressure plate heat exchanger, or an integral combined heat exchanger. 
     
     
         35 . The cryogenic rectification process-based method for producing an air product as claimed in  claim 34 , wherein the heat exchange apparatus further comprises a subcooler through which the reflux entering the second column exchanges heat with the gas or liquid product rectified by the second column. 
     
     
         36 . The cryogenic rectification process-based method for producing an air product as claimed in  claim 27 , further comprising: drawing a liquid nitrogen fraction from the first column into the second column as reflux. 
     
     
         37 . The cryogenic rectification process-based method for producing an air product as claimed in  claim 27 , further comprising: drawing liquid oxygen from the main condensation and evaporation apparatus through a liquid oxygen booster pump for pressurization to a required pressure and then into the heat exchange apparatus for vaporization via heat exchange for preparation of the oxygen product. 
     
     
         38 . The cryogenic rectification process-based method for producing an air product as claimed in  claim 27 , further comprising: drawing the liquid nitrogen from the top of the first column directly into the heat exchange apparatus for vaporization via heat exchange for preparation of a first nitrogen product; or, drawing the liquid nitrogen from the top of the first column through a liquid nitrogen booster pump first for pressurization to a required pressure and then into the heat exchange apparatus for vaporization via heat exchange for preparation of a second nitrogen product. 
     
     
         39 . The cryogenic rectification process-based method for producing an air product as claimed in  claim 27 , further comprising: drawing ultra-low-pressure nitrogen from the top of the second column into the heat exchange apparatus for reheating to prepare a third nitrogen product. 
     
     
         40 . The cryogenic rectification process-based method for producing an air product as claimed in  claim 27 , further comprising: drawing waste nitrogen from an upper part of the second column into the heat exchange apparatus for reheating to obtain a waste nitrogen product. 
     
     
         41 . An air separation system for producing an air product based on a cryogenic rectification process, the air separation system comprising:
 a. a rectification column, which comprises: a first column with a first pressure, a second column with a second pressure and a main condensation and evaporation apparatus arranged at the bottom of the second column; and a liquid nitrogen line for guiding liquid nitrogen from the top of the first column through a throttle valve into the second column and an oxygen-enriched liquid air line for guiding oxygen-enriched liquid air from the bottom of the first column through the throttle valve into the second column arranged between the first column and the second column;   b. at least one air boost system, at least one air pre-cooling apparatus, at least one air purification apparatus, at least one heat exchange apparatus, at least one air expander, at least one liquid oxygen booster pump, at least one liquid air booster pump and a plurality of pressure reducing apparatuses, the air boost system comprising a main air compressor and at least one air booster;   c. a first air inlet line for guiding feed air through the main air compressor, the air pre-cooling apparatus, the air purification apparatus and the heat exchange apparatus into the first column; a second air inlet line for guiding feed air through the main air compressor, the air pre-cooling apparatus and the air purification apparatus, out of the heat exchange apparatus and then through the air expander into the first column; and a third air inlet line further branching off from the second air inlet line before the second air inlet line enters the heat exchange apparatus, the third air inlet line passing through the heat exchange apparatus directly and being connected to the first column or the second column via the pressure reducing apparatus;   d. a liquid oxygen product outlet line for discharging liquid oxygen from the main condensation and evaporation apparatus through the at least one liquid oxygen booster pump and then through the heat exchange apparatus; and   e. an air product outlet line connected to the bottom of the first column or the third air inlet line, the air product outlet line being provided with the at least one liquid air booster pump to pressurize at least partially liquefied feed air from the third air inlet line or the oxygen-enriched liquid air discharged from the bottom of the first column to a target pressure for vaporization via heat exchange through the heat exchange apparatus so as to output the required air product.   
     
     
         42 . The air separation system for producing an air product based on a cryogenic rectification process as claimed in  claim 41 , wherein the air expander is braked by an expander booster provided, and the third air inlet line is connected via the expander booster and subsequently the heat exchange apparatus and the pressure reducing apparatus to the first column. 
     
     
         43 . The air separation system for producing an air product based on a cryogenic rectification process as claimed in  claim 42 , further comprising a fourth air inlet line, which branches off from the third air inlet line connecting the pressure reducing apparatus to the first column and is connected to the second column via the throttle valve. 
     
     
         44 . The air separation system for producing an air product based on a cryogenic rectification process as claimed in  claim 43 , wherein a throttle valve or a liquid expander is selected as the pressure reducing apparatus. 
     
     
         45 . The air separation system for producing an air product based on a cryogenic rectification process as claimed in  claim 43 , wherein a fifth air inlet line further branches off from the fourth air inlet line, the fifth air inlet line being connected to the air product outlet line for outputting the required air product discharged through the liquid air booster pump and the heat exchange apparatus. 
     
     
         46 . The air separation system for producing an air product based on a cryogenic rectification process as claimed in  claim 45 , wherein the fifth air inlet line is further provided with a first regulating valve for controlling the flow rate and flow velocity of an air stream. 
     
     
         47 . The air separation system for producing an air product based on a cryogenic rectification process as claimed in  claim 41 , wherein the air product outlet line is further provided with a second regulating valve for controlling the flow rate and flow velocity of the oxygen-enriched liquid air. 
     
     
         48 . The air separation system for producing an air product based on a cryogenic rectification process as claimed in  claim 41 , further comprising: a first nitrogen product outlet line for vaporizing the liquid nitrogen from the top of the first column via heat exchange through the heat exchange apparatus for preparation of a first nitrogen product; or, at least one liquid nitrogen booster pump, and a second nitrogen product outlet line passing the liquid nitrogen drawn from the top of the first column through the at least one liquid nitrogen booster pump first for pressurization to a required pressure and then into the heat exchange apparatus for vaporization via heat exchange for preparation of a second nitrogen product; or, a third nitrogen product outlet line discharging nitrogen from the top of the second column through the heat exchange apparatus. 
     
     
         49 . The air separation system for producing an air product based on a cryogenic rectification process as claimed in  claim 41 , wherein a liquid nitrogen fraction line for guiding a liquid nitrogen fraction from the first column through the throttle valve into the second column is further arranged between the first column and the second column. 
     
     
         50 . The air separation system for producing an air product based on a cryogenic rectification process as claimed in  claim 49 , further comprising a waste nitrogen line for discharging waste nitrogen from the second column through the heat exchange apparatus. 
     
     
         51 . The air separation system for producing an air product based on a cryogenic rectification process as claimed in  claim 41 , wherein the heat exchange apparatus comprises a high-pressure plate heat exchanger and a low-pressure plate heat exchanger, or an integral combined heat exchanger. 
     
     
         52 . The air separation system for producing an air product based on a cryogenic rectification process as claimed in  claim 51 , wherein the heat exchange apparatus further comprises a subcooler for the reflux entering the second column to exchange heat with the gas or liquid product rectified by the second column.