Liquefied gas supply system and air separation unit comprising same

Abstract

An air separation unit comprises a first rectification column, having a top condenser and a second rectification column placed side by side, a heat exchanger, a first pump and a second pump connected in parallel, the first pump being capable of producing liquid at a first liquid pressure and the second pump being capable of producing liquid at a second liquid pressure, higher than the first pressure, each pump having an inlet connected to the second column, a first outlet of the first pump being connected to a first outlet conduit, a second outlet of the second pump being connected to a second outlet conduit, the first and second outlet conduits being connected to the condenser section

What is claimed is: 
     
         1 . An air separation unit comprising:
 a first rectification column having an operating pressure, which is a first pressure;   a second rectification column having an operating pressure, which is a second pressure, less than the first pressure, wherein the first rectification column comprises a top condenser enclosed within a condenser section having an operating pressure which is the second pressure;   a supply source, which is a lower region of the second rectification column, wherein the first rectification column and the second rectification column are disposed side by side;   a heat exchanger;   means for sending feed air to the heat exchanger to be cooled and from the heat exchanger to the first rectification column;   means for sending a gas from the condenser section to the bottom of the second rectification columns;   a conduit configured to send the gas removed from the top of the second rectification column to the heat exchanger to be warmed;   a first pump and a second pump connected in parallel, the first pump being configured to produce liquid at a first liquid pressure and the second pump being configured to produce liquid at a second liquid pressure, higher than the first pressure, each pump having an inlet connected to the supply source;   a first outlet of the first pump being connected to a first outlet conduit; and   a second outlet of the second pump being connected to a second outlet conduit, the first outlet conduit being connected at a first removal point via a first valve to the condenser section and the second outlet conduit being connected at a second removal point via a second valve to the condenser section.   
     
     
         2 . The air separation unit according to  claim 1 , further comprising means for mixing liquid removed via the first valve with liquid removed via the second valve and sending the mixed liquid in a common conduit to the condenser. 
     
     
         3 . The air separation unit according to  claim 1 , wherein the first valve and the second valve are connected to the condenser section via separate conduit means. 
     
     
         4 . The air separation unit according to  claim 1 , wherein the first removal point is upstream of the third removal point and/or the second removal point is upstream of the fourth removal point. 
     
     
         5 . An air separation process comprising the steps of:
 providing a first rectification column operating at a first pressure, a second rectification column operating at a second pressure, less than the first pressure, the first rectification column having a top condenser enclosed within a condenser section operating at the second pressure, wherein the second rectification comprises a supply source that is disposed in a lower region of the second rectification column, the first rectification column and the second rectification column being placed side by side;   sending feed air to a heat exchanger to be cooled and then from the heat exchanger to the first rectification column;   sending a gas from the condenser section to a bottom section of the second rectification column;   removing a top gas is removed from a top section of the second rectification column, and then sending the top gas from the top section to the heat exchanger to be warmed,   wherein in normal operation, the process further comprises the steps of:   using a first pump and a second pump that are connected in parallel to pressurise liquid from the bottom of the second rectification column, the first pump producing liquid at a first liquid pressure and the second pump producing liquid at a second liquid pressure, higher than the first liquid pressure, and   using the first pump to send liquid at the first liquid pressure to the condenser section and   using the second pump to send liquid at the second liquid pressure to the heat exchanger, wherein liquid at the second liquid pressure is at least sometimes sent from the second pump to the condenser section.   
     
     
         6 . The process according to  claim 5 , wherein no liquid is sent in normal operation from the first pump to the heat exchanger. 
     
     
         7 . The process according to  claim 5 , wherein the liquid at the second liquid pressure sent from the second pump to the condenser section has a flowrate corresponding to between 3 and 100%, or to between 3 and 50% or even between 3 and 15%, preferably between 5 and 10% of the flowrate of the liquid at the first liquid pressure sent from the first pump to the condenser section in normal operation. 
     
     
         8 . The process according to  claim 5 , wherein the liquid at the second pressure is not expanded between the second removal point and the condenser section. 
     
     
         9 . The process according to  claim 5 , wherein the liquid at the first liquid pressure and the liquid at the second liquid pressure are mixed upstream of the condenser section. 
     
     
         10 . The process according to  claim 5 , wherein the first and second liquid pressures differ by no more than 10 bars, preferably by no more than 7 bars. 
     
     
         11 . The process according to  claim 5 , wherein part of the refrigeration for the process is provided by liquid nitrogen from an external source. 
     
     
         12 . The process according to  claim 5 , wherein liquid at the second liquid pressure is sent from the second pump to the condenser section if the first pump is not operating. 
     
     
         13 . The process according to  claim 12 , wherein during normal operation liquid at the second liquid pressure is not sent from the second pump to the condenser section. 
     
     
         14 . The process according to  claim 5 , wherein liquid at the second liquid pressure is sent from the second pump to the condenser section if the first pump is operating at a reduced rate as compared to the rate during normal operation. 
     
     
         15 . The process according to  claim 14 , wherein the liquid at the second liquid pressure is reduced in pressure upstream of the condenser section. 
     
     
         16 . The process according to  claim 5 , wherein the first outlet conduit is connected at a third removal point via a third valve to the heat exchanger and the second outlet conduit is connected at a fourth removal point via a fourth valve to the heat exchanger. 
     
     
         17 . An air separation unit comprising a liquefied gas supply system, the liquefied gas supply system comprising:
 a first liquid feed pump which is used to feed a first liquefied gas from a supply source to a low-pressure supply destination for low-pressure purposes;   a second liquid feed pump which is used to feed a second liquefied gas from the supply source to a high-pressure supply destination for high-pressure purposes; and   a control unit for controlling the first liquid feed pump and the second liquid feed pump, wherein   the control unit:   implements first circulation liquid in-feed processing for feeding in the first liquefied gas from the supply source to the low-pressure supply destination by means of the first liquid feed pump which is in a low-pressure operating mode; and first product liquid in-feed processing for feeding in the second liquefied gas from the supply source to the high-pressure supply destination by means of the second liquid feed pump which is in a high-pressure operating mode; and/or   implements second circulation liquid in-feed processing for feeding in the first liquefied gas from the supply source to the low-pressure supply destination by means of the first liquid feed pump which is in the low-pressure operating mode, and also for feeding in a portion of the second liquefied gas from the supply source to the low-pressure supply destination by means of the second liquid feed pump which is in the high-pressure operating mode; and second product liquid in-feed processing for feeding in the remainder of the second liquefied gas from the supply source to the high-pressure supply destination by means of the second liquid feed pump which is in the high-pressure operating mode.   
     
     
         18 . The air separation unit according to  claim 17 , wherein the control unit is configured to:
 control an amount of the first liquefied gas fed from the supply source to the low-pressure supply destination by means of the first liquid feed pump, and controls an amount of the second liquefied gas fed from the supply source to the high-pressure supply destination by means of the second liquid feed pump, correspondingly with liquid amount data from a liquid amount measurement unit for measuring an amount of liquid at the supply source; and/or   control an amount of the first liquefied gas fed from the supply source to the low-pressure supply destination by means of the first liquid feed pump, and controls an amount of the second liquefied gas fed from the supply source to the high-pressure supply destination by means of the second liquid feed pump, correspondingly with liquid amount data from a flow rate measurement unit for measuring an amount of liquid fed to the low-pressure supply destination.   
     
     
         19 . The air separation unit according to  claim 17 , wherein the control unit is configured to:
 when the first liquid feed pump is in a stopped state, implements first liquid feed pump stoppage processing for feeding in a portion of the second liquefied gas from the supply source to the high-pressure supply destination and for feeding in the remainder of the second liquefied gas to the low-pressure supply destination by means of the second liquid feed pump; and   when the second liquid feed pump is in a stopped state, implements second liquid feed pump stoppage processing for feeding in a portion of the first liquefied gas from the supply source to the low-pressure supply destination and for feeding in the remainder of the first liquefied gas to the high-pressure supply destination by means of the first liquid feed pump.   
     
     
         20 . The air separation unit according to  claim 17 , further comprising:
 a pipe configuration in which a first low-pressure liquid feed line running from the first liquid feed pump to the low-pressure supply destination, and a second low-pressure liquid feed line running from the second liquid feed pump to the low-pressure supply destination do not merge, or merge; and   a pipe configuration in which a first high-pressure liquid feed line running from the first liquid feed pump to the high-pressure supply destination, and a second high-pressure liquid feed line running from the second liquid feed pump to the high-pressure supply destination do not merge, or merge.