Downflow knockback condenser

Abstract

An apparatus and method useful for partially condensing vapor in the upper section of a fractionation tower to separate and remove a lighter gaseous fraction from a condensed liquid component, such as nitrogen from natural gas. A downflow, knockback condenser is disclosed that utilizes a vapor riser to introduce a flow of vapor into a headspace above a vertical tubular heat exchanger, thereby establishing a downflow of condensed liquid and a lighter gaseous fraction through the heat exchange tubes.

1 . A condenser apparatus useful for removing gaseous nitrogen from nitrogen-containing natural gas, the apparatus comprising: 
 a substantially cylindrical shell;    a plurality of substantially vertical heat exchange tubes disposed inside the shell;    a riser introducing vapor comprising natural gas and nitrogen into a headspace above the tubes;    a refrigerant flowing upwardly through the shell around the tubes and sufficiently cooling the tubes to condense natural gas passing downwardly through the tubes, thereby liquefying the natural gas and separating it from the gaseous nitrogen;    an outlet disposed below the tubes for receiving gaseous nitrogen exiting the tubes; and    a receptacle disposed below the outlet for receiving liquefied natural gas exiting the tubes.    
   
   
       2 . The apparatus of  claim 1  disposed in the top of a fractionation tower.  
   
   
       3 . The apparatus of  claim 1 , further comprising upper and lower tube sheets disposed transversely across the shell, the tube sheets supporting the plurality of heat exchange tubes and providing fluid communication through the tubes between the headspace and a zone below the lower tube sheet.  
   
   
       4 . The apparatus of  claim 3 , further comprising a refrigerant inlet port through the shell, the port being disposed slightly above the lower tube sheet.  
   
   
       5 . The apparatus of  claim 4 , further comprising a refrigerant outlet port through the shell, the port being disposed slightly below the upper tube sheet.  
   
   
       6 . The apparatus of  claim 5 , the tube sheets cooperating with the shell to define a refrigerant flow path around the tubes between the refrigerant inlet port and the refrigerant outlet port.  
   
   
       7 . The apparatus of  claim 1  wherein the receptacle is defined by the shell and by a liquid trap plate disposed below the outlet.  
   
   
       8 . The apparatus of  claim 7  wherein the liquid trap plate provides liquid communication with a downwardly extending reflux liquid return seal leg.  
   
   
       9 . The apparatus of  claim 8  wherein the reflux liquid return seal leg provides fluid communication with a reflux seal pan disposed below the liquid trap plate.  
   
   
       10 . The apparatus of  claim 9 , further comprising a liquid distributor disposed below the reflux seal pan.  
   
   
       11 . The apparatus of  claim 7  wherein the riser comprises an inlet end disposed below the liquid trap plate.  
   
   
       12 . The apparatus of  claim 1  wherein the riser is substantially cylindrical and comprises an inlet end having an oblique opening.  
   
   
       13 . The apparatus of  claim 3  wherein the riser traverses the upper and lower tube sheets and liquid trap plate.  
   
   
       14 . Apparatus useful for partially condensing vapor in the upper section of a fractionation tower to separate a lighter gaseous fraction from a condensed liquid component, the apparatus comprising: 
 a substantially cylindrical shell;    a condenser section having upper and lower tube sheets attached transversely to the inside of the shell, the tube sheets supporting a plurality of spaced-apart, vertically oriented, heat exchange tubes extending between the upper and lower tube sheets, and providing fluid communication through the tubes;    refrigerant inlet and outlet ports disposed so as to establish a generally upward flow of refrigerant around the heat exchange tubes between the lower and upper tube sheets;    a vapor riser providing fluid communication between a space in the fractionation tower disposed below the lower tube sheet and a headspace disposed above the upper tube sheet, thereby establishing an upward flow of vapor through the riser and a downward flow of vapor, condensed liquid and lighter gaseous fraction through the heat exchange tubes;    a vapor outlet port disposed below the lower tube sheet to receive the lighter gaseous fraction and any remaining vapor exiting the lower tube sheet; and    condensed liquid recovery apparatus disposed below the lower tube sheet and below the vapor outlet port to receive liquid condensed from the vapor.    
   
   
       15 . The apparatus of  claim 14  wherein the vapor comprises natural gas and nitrogen.  
   
   
       16 . The apparatus of  claim 15  wherein the lighter gaseous fraction is nitrogen.  
   
   
       17 . The apparatus of  claim 14  wherein the refrigerant inlet port is disposed slightly above the lower tube sheet.  
   
   
       18 . The apparatus of  claim 14  wherein the refrigerant outlet port is disposed slightly below the upper tube sheet.  
   
   
       19 . The apparatus of  claim 14  wherein the condensed liquid recovery apparatus further comprises a liquid trap plate disposed below the vapor outlet port.  
   
   
       20 . The apparatus of  claim 19  wherein the liquid trap plate provides liquid communication with a downwardly extending reflux liquid return seal leg.  
   
   
       21 . The apparatus of  claim 20  wherein the reflux liquid return seal leg provides fluid communication with a reflux seal pan disposed below the liquid trap plate.  
   
   
       22 . The apparatus of  claim 21 , further comprising a liquid distributor disposed below the reflux seal pan.  
   
   
       23 . The apparatus of  claim 19  wherein the riser comprises an inlet end disposed below the liquid trap plate.  
   
   
       24 . The apparatus of  claim 14  wherein the riser is substantially cylindrical and comprises an inlet end having an oblique opening.  
   
   
       25 . The apparatus of  claim 14  wherein the riser traverses the upper tube sheet and the lower tube sheet.  
   
   
       26 . A method for partially condensing a vapor to separate a lighter gaseous fraction from a condensed liquid fraction, the method comprising the steps of: 
 providing a condenser having a substantially cylindrical, vertically oriented shell, upper and lower tube sheets attached transversely to the inside of the shell, the tube sheets supporting a plurality of spaced-apart, vertically oriented, heat exchange tubes extending between the upper and lower tube sheets, and providing fluid communication through the tubes;    providing refrigerant inlet and outlet ports disposed in the shell so as to establish a generally upward flow of refrigerant around the heat exchange tubes between the lower and upper tube sheets; providing a vapor riser providing fluid communication between a space in the shell disposed below the lower tube sheet and a headspace disposed above the upper tube sheet;    establishing an upward flow of vapor through the riser and a downward flow comprising vapor, condensed liquid and lighter gaseous fraction through the heat exchange tubes, the refrigerant having sufficient cooling capacity to condense a desired liquid fraction from the vapor while passing through the heat exchange tubes; and    separately recovering the lighter gaseous fraction and condensed liquid below the heat exchange tubes.    
   
   
       27 . The method of  claim 26 , including recovering the lighter gaseous component through a gaseous vapor outlet port in the shell, said gaseous outlet vapor port being disposed below the lower tube sheet.  
   
   
       28 . The method of  claim 27 , including recovering the condensed liquid in apparatus disposed below the lower tube sheet and below the gaseous vapor outlet port.  
   
   
       29 . The method of  claim 26  wherein the vapor comprises natural gas and nitrogen.  
   
   
       30 . The method of  claim 29  wherein the lighter gaseous fraction is nitrogen.  
   
   
       31 . The method of  claim 29  wherein the condensed liquid is natural gas.