Multistage solvent extraction process and apparatus

Abstract

Process and apparatus for two-stage solvent extraction of hydrocarbon products is disclosed. The process comprises passing a heavy hydrocarbon feed stream and a first fresh solvent to a first extraction column to generate a first overhead stream and a first bottom stream. The first overhead stream is passed to a first stripping column to generate a first product stream and a first stripped solvent stream. The first bottom stream is passed to a second extraction column to generate a second overhead stream and a second bottom stream. A second fresh solvent stream is passed to a second extraction column. The second overhead stream is passed to a second stripping column to generate a second product stream and a second stripped solvent stream. Passing the first stripped solvent stream and the second stripped solvent stream to a solvent recovery column and passing the second bottom stream to a pitch stripper.

1 . A multi-stage solvent extraction process comprising:
 passing a heavy hydrocarbon feed stream and a first fresh solvent to a first extraction column to generate a first overhead stream and a first bottom stream;   passing the first overhead stream to a first stripping column to generate a first product stream and a first stripped solvent stream;   passing the first bottom stream from the first extraction column and a second fresh solvent to a second extraction column to generate a second overhead stream and a second bottom stream;   passing the second overhead stream to a second stripping column to generate a second product stream and a second stripped solvent stream.   
     
     
         2 . The process of  claim 1  further comprising:
 passing the first stripped solvent stream from the first stripping column to a solvent recovery column to generate a first recovered solvent stream; and 
 passing the second stripped solvent stream from the second stripping column to the solvent recovery column to generate a second recovered solvent stream. 
 
     
     
         3 . The process of  claim 2  further comprising:
 recycling at least a portion of the first recovered solvent stream to the first extraction column; and 
 recycling at least a portion of the second recovered solvent stream to the second extraction column. 
 
     
     
         4 . The process of  claim 1  further comprising passing the second bottom stream from the second extraction column to a pitch stripper to generate a pitch stream from a bottom of the pitch stripper and a heavy stripped solvent stream from an overhead of the pitch stripper. 
     
     
         5 . The process of  claim 4  further comprising passing the heavy stripped solvent stream from the pitch stripper to the solvent recovery column to generate a heavy recovered solvent stream. 
     
     
         6 . The process of  claim 1  further comprising:
 passing the first overhead stream from the first extraction column to a first separation vessel prior to passing the first overhead stream to the first stripping column to generate a first recycle solvent stream from an overhead of the first separation vessel and a first separator bottoms stream from a bottom of the first separation vessel; and 
 passing the first separator bottoms stream to the first stripping column to generate the first product stream from a bottom of the first stripping column and the first stripped solvent stream from an overhead of the first stripping column. 
 
     
     
         7 . The process of  claim 6  further comprising passing the first recycle solvent stream from the overhead of the first separation vessel to the first extraction column. 
     
     
         8 . The process of  claim 1  further comprising:
 passing the second overhead stream from the second extraction column to a second separation vessel prior to passing the second overhead stream to the second stripping column to generate a second recycle solvent stream from an overhead of the second separation vessel and a second effluent stream from a bottom of the second separation vessel; and 
 passing the second effluent stream to the second stripping column to generate the second product stream from a bottom of the second stripping column and the second stripped solvent stream from an overhead of the second stripping column. 
 
     
     
         9 . The process of  claim 8  further comprising passing the second recycle solvent stream from the overhead of the second separation vessel to the second extraction column. 
     
     
         10 . The process of  claim 1  further comprising:
 passing the second bottom stream and a third fresh solvent to a third extraction column to generate a third overhead stream and a third bottom stream; 
 passing the third overhead stream from the third extraction column to a third separation vessel to generate a third recycle solvent stream from an overhead of the third separation vessel and a third effluent stream from a bottom of the third separation vessel; and 
 passing the third effluent stream from the bottom of the third separation vessel to a third stripping column to generate a third product stream from a bottom of the third stripping column and a third stripped solvent stream from an overhead of the third stripping column. 
 
     
     
         11 . The process of  claim 10  further comprising passing the third recycle solvent stream from the overhead of the third separation vessel to the third extraction column. 
     
     
         12 . The process of  claim 10  further comprising:
 passing the third stripped solvent stream from the third stripping column to the solvent recovery column to generate a third recovered solvent stream; and 
 recycling at least a portion of the third recovered solvent stream from the solvent recovery column to the third extraction column. 
 
     
     
         13 . A multi-stage solvent extraction process comprising:
 passing a heavy hydrocarbon feed stream and a first fresh solvent to a first extraction column to generate a first overhead stream and a first bottom stream;   passing the first overhead stream to a first stripping column to generate a first product stream and a first stripped solvent stream;   passing the first bottom stream from the first extraction column and a second fresh solvent to a second extraction column to generate a second overhead stream and a second bottom stream;   passing the second overhead stream to a second stripping column to generate a second product stream and a second stripped solvent stream;   passing the second bottom stream from the second extraction column and a third fresh solvent to a third extraction column to generate a third overhead stream and a third bottom stream; and   passing the third bottom stream to a pitch stripping column to generate a pitch stream from a bottom of the pitch stripper and a heavy stripped solvent stream from an overhead of the pitch stripper.   
     
     
         14 . The process of  claim 13  further comprising:
 passing the first stripped solvent stream, the second stripped solvent stream, and the heavy stripped solvent stream to a solvent recovery column; and 
 recovering from the solvent recovery column at least a portion of the first recovered solvent stream, at least a portion of the second recovered solvent stream, and at least a portion of the heavy recovered solvent stream. 
 
     
     
         15 . The process of  claim 13  further comprising:
 recycling at least a portion of the first recovered solvent stream to the first extraction column; 
 recycling at least a portion of the second recovered solvent stream to the second extraction column; and 
 recycling at least a portion of the heavy recovered solvent stream to the third extraction column. 
 
     
     
         16 . The process of  claim 13  further comprising:
 passing the third overhead stream to a third separation vessel to generate a third recycle solvent stream from an overhead of the third separation vessel and a third effluent stream from a bottom of the third separation vessel; and 
 passing the third effluent stream from the bottom of the third separation vessel to a third stripping column to generate a third product stream from a bottom of the third stripping column and a third stripped solvent stream from an overhead of the third stripping column. 
 
     
     
         17 . The process of  claim 16  further comprising passing at least a portion of the third recycle solvent stream to the third extraction column. 
     
     
         18 . The process of  claim 16  further comprising passing the third stripped solvent stream from the third stripping column to the solvent recovery column;
 recovering from the solvent recovery column at least a portion of the third recovered solvent stream; and 
 recycling at least a portion of the third recovered solvent stream to the third extraction column. 
 
     
     
         19 . An apparatus for multi-stage solvent extraction comprising:
 a first extraction column to produce a first overhead stream and a first bottom stream;   a first stripping column in downstream communication with an overhead line of the first extraction column to produce a first product stream and a first stripped solvent stream from the first overhead stream;   a second extraction column in downstream communication with a bottoms line of the first extraction column to produce a second overhead stream and a second bottom stream from the first bottom stream; and   a second stripping column in downstream communication with an overhead line of the second extraction column to produce a second product stream and a second stripped solvent stream from the second overhead stream.   
     
     
         20 . An apparatus of  claim 19  further comprising a solvent recovery column in downstream communication with an overhead line of the first stripping column, an overhead line of the second stripping column and an overhead line of the pitch stripper.