Cryogenic distillation method and apparatus for producing pressurized air by means of expander booster in linkage with nitrogen expander for braking

Abstract

Provided are a method and apparatus for producing nitrogen and oxygen by means of cryogenic distillation of air. Nitrogen products are extracted only from the top of a tower. If a customer needs nitrogen with lower pressure, part of pure nitrogen that is partially located at a first nitrogen product pressure is reheated in a main heat exchanger, then decompressed to a second nitrogen product pressure by means of a nitrogen expander, further reheated by means of the main heat exchanger, and output as a low-pressure nitrogen product. The nitrogen expander can be braked by an expander booster for compressing air. By means of the method, nitrogen with different pressures can be suitably produced, and the energy consumption for producing the pressurized air can be reduced by utilizing the expansion work of nitrogen.

1 - 17 . (canceled) 
     
     
         18 . A method for producing nitrogen and oxygen by means of the cryogenic distillation of air, comprising:
 (a) providing a first tower working at a higher pressure and a second tower working at a lower pressure, wherein the first tower and the second tower are brought into communication by means of heat exchange via a main condensing evaporator;   (b) providing at least one air pre-cooling system, one air purification system, one main air compressor, at least one air booster, at least one main heat exchanger, and one supercooler;   (c) further pre-cooling and purifying an air feed gas, which has been pressurized to a first pressure range by means of the main air compressor, then sending part of the air feed gas to the main heat exchanger for heat exchange with gas products produced by means of rectification and then to the first tower, subjecting the other part of the air feed gas to pressurization by means of the air booster and several stages of expander boosters, to heat exchange in the main heat exchanger with gas and liquid products produced by means of rectification and then to expansion or throttling for decompression to the first pressure range, and then sending this other part to the first tower, or supercooling a part by means of the supercooler, followed by throttling and sending to the second tower;   (d) rectifying the air feed gas in the first tower, extracting oxygen-enriched liquid air at the bottom of the first tower, pure liquid nitrogen at the top, and optionally impure liquid nitrogen in the middle part, and sending same to the supercooler for supercooling and then to the second tower as reflux liquids;   (e) extracting pure liquid oxygen in the main condensing evaporator, and sending the pure liquid oxygen to a liquid oxygen pump for pressurization and then to the main heat exchanger for heat exchange with the air feed gas pressurized by means of the air booster and the several stages of expander boosters, followed by evaporation and vaporization for output as a product;   (f) extracting impure nitrogen from the second tower, and sending the impure nitrogen to the supercooler for warming and then to the main heat exchanger for further reheating; and   (g) extracting pure nitrogen at a first nitrogen product pressure from the top of the first tower and sending the pure nitrogen to the main heat exchanger for reheating,   wherein a part of pure nitrogen at the first nitrogen product pressure is partially reheated in the main heat exchanger, decompressed to a second nitrogen product pressure by means of a nitrogen expander, then further reheated by means of the main heat exchanger, and output as a product; and the nitrogen expander is braked by means of a first expander booster, the first expander booster further pressurizes the part of air feed gas that has been pressurized by means of the air booster and reaches a second pressure range to a third pressure range, and the air feed gas within the third pressure range enters, directly or optionally after undergoing further pressurization, the main heat exchanger for heat exchange with the gas and liquid products produced by means of rectification, and is then decompressed to the first pressure range by means of a liquid expander and then sent to the first tower, or a part of decompressed liquid is supercooled by means of the supercooler, then throttled and sent to the second tower.   
     
     
         19 . The method of  claim 18 , wherein the main heat exchangers include a high pressure plate heat exchanger and a low pressure plate heat exchanger, or an integral combined heat exchanger. 
     
     
         20 . The method of  claim 19 , wherein the part of air feed gas that has been pressurized by means of the air booster and reaches the second pressure range is partially cooled in the main heat exchanger, then decompressed to the first pressure range by means of an air expander, and then sent to the first tower. 
     
     
         21 . The method of  claim 20 , wherein the nitrogen expander is braked by means of a second expander booster, the second expander booster further pressurizes the air feed gas that has been pressurized by means of the air booster and reaches the second pressure range to the third pressure range, and the air feed gas within the third pressure range enters the main heat exchanger for heat exchange with the gas and liquid products produced by means of rectification, and is then decompressed to the first pressure range by means of the liquid expander and then sent to the first tower. 
     
     
         22 . The method of  claim 21 , wherein the air feed gas that has been pressurized by means of the air booster and reaches the second pressure range is divided into three parts, wherein a first part is pressurized to the third pressure range by means of the first expander booster; a second part is partially cooled in the main heat exchanger, then decompressed to the first pressure range by means of the air expander, and then sent to the first tower; and a third part is pressurized to the third pressure range by means of the second expander booster, the pressurized first part and third part of air feed gas are combined, then sent to the main heat exchanger for heat exchange with the gas and liquid products produced by means of rectification, then decompressed to the first pressure range by means of the liquid expander and then sent to the first tower. 
     
     
         23 . The method of  claim 20 , wherein the nitrogen expander is braked by means of a second expander booster, the second expander booster further pressurizes the air feed gas that has been pressurized by means of the first expander booster, the air feed gas is sent to the main heat exchanger for heat exchange with the gas and liquid products produced by means of rectification, then decompressed to the first pressure range by means of the liquid expander and then sent to the first tower. 
     
     
         24 . The method of  claim 23 , wherein the air feed gas that has been pressurized by means of the first expander booster is all sent to the second expander booster for further pressurization. 
     
     
         25 . The method of  claim 21 , wherein the liquid expander is braked by means of an electric generator. 
     
     
         26 . The method of  claim 18 , wherein a part of the liquid air feed gas within the first pressure range cooled by means of the main heat exchanger is supercooled by means of the supercooler, then throttled and sent to the second tower as a reflux liquid. 
     
     
         27 . The method of  claim 18 , wherein the pure liquid oxygen extracted in the main condensing evaporator is partially supercooled by means of the supercooler and then sent to a liquid oxygen storage tank. 
     
     
         28 . The method of  claim 18 , wherein the pure liquid oxygen extracted in the main condensing evaporator is pressurized by means of the liquid oxygen pump, and a part is expanded or throttled for decompression, and then sent to the main heat exchanger for heat exchange with the air feed gas, followed by evaporation and vaporization for output as a product. 
     
     
         29 . The method of  claim 18 , wherein after the part of pure nitrogen at the first nitrogen product pressure is completely reheated in the main heat exchanger, part of this part of pure nitrogen is output as a first nitrogen product, and the other part is pressurized to a third nitrogen product pressure by means of the nitrogen booster and output as a third nitrogen product. 
     
     
         30 . An apparatus for producing nitrogen and oxygen by means of the cryogenic distillation of air, comprising:
 (a) a first tower working at a higher pressure and a second tower working at a lower pressure, wherein the first tower and the second tower are brought into communication by means of heat exchange via a main condensing evaporator;   (b) at least one main air compressor, one air pre-cooling system, one air purification system, one air booster, a first expander booster, at least one main heat exchanger, one nitrogen expander, at least one liquid expander, one liquid oxygen pump and one supercooler;   (c) a pipeline for sending an air feed gas to the first tower via the main air compressor, the air pre-cooling system, the air purification system and the main heat exchanger;   (d) a pipeline for sending oxygen-enriched liquid air at the bottom of the first tower to the supercooler for supercooling and to the second tower;   (e) a pipeline for sending pure liquid nitrogen at the top of the first tower to the supercooler for supercooling and to the upper part of the second tower;   optionally, a pipeline for sending impure liquid nitrogen in the middle part of the first tower to the supercooler for supercooling and to the second tower;   (g) a pipeline for extracting impure nitrogen from the second tower and sending the impure nitrogen to the supercooler for warming and to the main heat exchanger for reheating;   (h) a pipeline for extracting pure liquid oxygen from the main condensing evaporator and sending the pure liquid oxygen to the liquid oxygen pump for pressurization and then through the main heat exchanger; and   (i) a pipeline for extracting pure nitrogen from the top of the first tower and sending the pure nitrogen to the main heat exchanger; and   (j) a pipeline for sending a part of pure nitrogen, which has been reheated, from the main heat exchanger to the nitrogen expander, and returning the expanded pure nitrogen to the main heat exchanger for reheating, wherein the nitrogen expander is braked by means of the first expander booster, and the main air compressor, the air booster and the first expander booster are sequentially connected in series, and are connected to the main heat exchanger, the liquid expander and then the first tower via a pipeline.   
     
     
         31 . The apparatus of  claim 30 , further comprising a pipeline for bringing the air booster into communication with the main heat exchanger, and a pipeline that penetrates out from the middle part of the main heat exchanger and connects the air expander and the first tower in sequence. 
     
     
         32 . The apparatus of  claim 31 , wherein the nitrogen expander is braked by means of a second expander booster, and the apparatus further comprises a pipeline for bringing the air booster into communication with the second expander booster, and then sequentially connecting the main heat exchanger, the liquid expander and the first tower. 
     
     
         33 . The apparatus of  claim 32 , wherein the air booster is directly connected to the second expander booster, or the air booster is connected to the second expander booster via the first expander booster. 
     
     
         34 . The apparatus of  claim 30 , wherein the main heat exchangers include a high pressure plate heat exchanger and a low pressure plate heat exchanger, or an integral combined heat exchanger.