Nitrogen generating device and nitrogen generating method

Abstract

A nitrogen generating method for producing product nitrogen using a nitrogen generating device comprising a main heat exchanger for cooling feed air, a nitrogen rectification column into which the feed air cooled in the main heat exchanger is introduced, and a nitrogen condenser which condenses a vapour stream fed from the nitrogen rectification column and circulates the same to the nitrogen rectification column, the method including a control step for discharging liquid nitrogen condensed by the nitrogen condenser and stored in a liquid nitrogen buffer, which is provided in an upper gas phase portion of the nitrogen rectification column or separately from the nitrogen rectification column, to a rectification portion of the nitrogen rectification column in response to an increase in an amount of product nitrogen or an increase in a flow rate of the feed air.

What is claimed is: 
     
         1 . A nitrogen generating device comprising:
 a main heat exchanger configured to cool feed air;   at least one nitrogen rectification column in fluid communication with the main heat exchanger, such that the at least one nitrogen rectification column is configured to receive the feed air cooled in the main heat exchanger;   at least one nitrogen condenser configured to condense and circulate a vapour stream fed from the at least one nitrogen rectification column;   a liquid nitrogen buffer which is provided in the nitrogen rectification column or separately from the nitrogen rectification column, wherein the liquid nitrogen buffer is configured to store liquid nitrogen condensed by the at least one nitrogen condenser;   a liquid nitrogen discharge means for discharging the stored liquid nitrogen from the liquid nitrogen buffer; and   a control unit for controlling the liquid nitrogen discharge means to discharge the liquid nitrogen from the liquid nitrogen buffer to the at least one nitrogen rectification column in response to an increase in an amount of product nitrogen.   
     
     
         2 . The nitrogen generating device according to  claim 1 , further comprising a feed air flowmeter configured to measure a flow rate of the feed air, wherein the control unit controls the liquid nitrogen discharge means to discharge the liquid nitrogen from the liquid nitrogen buffer to a rectification portion in response to an increase in the flow rate of the feed air, as per a measured value from the feed air flowmeter. 
     
     
         3 . The nitrogen generating device according to  claim 1 , wherein the control unit determines the amount of liquid nitrogen to be discharged from the liquid nitrogen buffer by calculating a required amount of reflux liquid using the amount of feed air as a variable, such that a reflux liquid to vapour stream ratio (L/V) does not drop below a predetermined control value when the amount of product nitrogen is increased. 
     
     
         4 . The nitrogen generating device according to  claim 1 , further comprising a differential pressure gauge for measuring a pressure difference between an upper gas phase portion of the nitrogen rectification column and a bottom portion of the liquid nitrogen buffer. 
     
     
         5 . The nitrogen generating device according to  claim 1 , further comprising a distributor which is provided above the rectification portion to distribute the reflux liquid or the liquid nitrogen evenly to the rectification portion. 
     
     
         6 . The nitrogen generating device according to  claim 1 , further comprising: a distributor which is provided above the rectification portion to distribute the reflux liquid or the liquid nitrogen evenly over a planar region of the rectification portion; and a distributor differential pressure gauge for measuring a pressure difference between an upper portion and a bottom portion of the distributor. 
     
     
         7 . The nitrogen generating device according to  claim 1 , further comprising a rectification portion differential pressure gauge for measuring a pressure difference between an upper portion and a lower portion of the rectification portion. 
     
     
         8 . The nitrogen generating device according to  claim 1 , further comprising:
 an expansion turbine for expanding gas that has been discharged from above the nitrogen condenser and that has been subjected to heat exchange by being passed through the main heat exchanger;   a waste gas pipeline for causing the gas discharged from above the nitrogen condenser to pass through the main heat exchanger and the expansion turbine, and then pass again through the main heat exchanger and be extracted as waste gas;   a branch pipeline that branches off from the waste gas pipeline upstream of the expansion turbine between the main heat exchanger and the expansion turbine, and merges with the waste gas pipeline downstream of the expansion turbine between the expansion turbine and the main heat exchanger;   a flow rate regulating valve provided in the branch pipeline to regulate a flow rate of gas diverted from the waste gas pipeline to the branch pipeline;   an upper gas phase portion pressure gauge for measuring the pressure in the upper gas phase portion of the nitrogen rectification column; a waste gas pressure gauge which is provided in the waste gas pipeline upstream of the expansion turbine between the main heat exchanger and the expansion turbine or in the waste gas pipeline upstream of the branch pipeline, to measure the gas pressure; and   a waste gas supply pressure control unit for opening and closing the flow rate regulating valve or for performing flow rate control thereof, on the basis of measurement results from the upper gas phase portion pressure gauge and the waste gas pressure gauge, so as to reduce the pressure of a waste gas stream on an inlet side of the expansion turbine or to reduce the pressure on a low-temperature side of the nitrogen condenser.   
     
     
         9 . The nitrogen generating device according to  claim 1 , further comprising: a rectification portion provided above the nitrogen condenser; a recycle pipeline which allows gas discharged from an upper part of the rectification portion to pass through the main heat exchanger and merge with the feed air pipeline upstream of the main heat exchanger; and a recycle compressor provided in the recycle pipeline to compress the gas that has been discharged from the upper part of the rectification portion and that has been subjected to heat exchange by means of the main heat exchanger. 
     
     
         10 . The nitrogen generating device according to  claim 1 , further comprising a circulating liquid branch pipe that branches off from the circulating liquid pipe leading out from the nitrogen condenser to feed the liquid nitrogen to the liquid nitrogen buffer provided separately from the nitrogen rectification column, and a differential pressure gauge for measuring a pressure difference between a bottom portion and an upper portion of the liquid nitrogen buffer in order to measure the amount of liquid nitrogen stored in the liquid nitrogen buffer, wherein the liquid nitrogen discharge means is provided with: a third discharge pipe leading out from a bottom portion of the liquid nitrogen buffer; a liquid feed pump provided in the circulating liquid branch pipe or the third discharge pipe; and a third regulating valve provided in the third discharge pipe. 
     
     
         11 . A nitrogen generating device comprising:
 a main heat exchanger configured to cool feed air;   a first nitrogen rectification column fluid communication with the main heat exchanger, such that the first nitrogen rectification column is configured to receive the feed air cooled in the main heat exchanger, wherein the first nitrogen rectification column comprises a gas phase portion of a rectification portion or a bottom portion into which the feed air cooled in the main heat exchanger is introduced;   a first nitrogen condenser configured to condense a vapour stream fed from an upper gas phase portion of the first nitrogen rectification column and circulate the same to the upper gas phase portion;   a second nitrogen rectification column including a rectification portion that is in fluid communication with the bottom portion of the first nitrogen rectification column, such that the second nitrogen rectification column is configured to receive oxygen-enriched liquid from the bottom portion of the first nitrogen rectification column;   a second nitrogen condenser configured to condense a vapour stream fed from an upper gas phase portion of the second nitrogen rectification column and circulate the same to the upper gas phase portion;   a liquid nitrogen buffer configured to store condensate returning to the upper gas phase portion of the second nitrogen rectification column;   a liquid nitrogen discharge means configured to discharge the stored liquid nitrogen from the liquid nitrogen buffer; and   a control unit configured to control the liquid nitrogen discharge means to discharge the liquid nitrogen from the liquid nitrogen buffer to the upper gas phase portion of the first nitrogen rectification column or the rectification portion in response to an increase in an amount of product nitrogen or an increase in a flow rate of the feed air.   
     
     
         12 . A nitrogen generating method for producing product nitrogen using the nitrogen generating device according to  claim 1 , the method comprising the steps of:
 feeding the feed air to the main heat exchanger;   withdrawing the feed air from the main heat exchanger and introducing the feed air to the at least one nitrogen rectification column for separation therein;   withdrawing liquid nitrogen using the liquid nitrogen discharge means; and   controlling the liquid nitrogen discharge means to discharge the liquid nitrogen from the liquid nitrogen buffer to the at least one nitrogen rectification column in response to an increase in an amount of product nitrogen.   
     
     
         13 . The nitrogen generating method according to  claim 12 , wherein the control step involves controlling the amount of liquid nitrogen to be discharged from the liquid nitrogen buffer by calculating a required amount of reflux liquid using an amount of feed air (flow rate measured value, calculated value) as a variable, so as to maintain the purity of the product nitrogen when the amount of product nitrogen is increased. 
     
     
         14 . The nitrogen generating method according to  claim 12 , wherein the control step involves monitoring the discharge amount of the liquid nitrogen stored in the liquid nitrogen buffer on the basis of a pressure difference between the upper gas phase portion and a bottom portion of the liquid nitrogen buffer, and controlling the amount being discharged. 
     
     
         15 . The nitrogen generating method according to  claim 12 , wherein the control step involves controlling the discharge amount of the liquid nitrogen stored in the liquid nitrogen buffer on the basis of a pressure difference between an upper portion and a bottom portion of a distributor for distributing a reflux liquid or a pressure difference between an upper part and a lower part of the rectification portion.