Process for pyrolyzing coal using a recycled hydrogen donor

Abstract

A process for pyrolyzing coal using a recycled hydrogen donor includes introducing a coal feed to a pyrolysis zone and heating the coal feed to a temperature of about 300° C. in the absence of hydrogen. A hydrogen donor solvent is introduced to the pyrolysis zone after the coal feed is heated to about 300° C., and the temperature of the coal feed and the hydrogen donor solvent is increased to about 475° C., while increasing a pressure in the pyrolysis zone to at or above a vapor pressure of the hydrogen donor solvent. At least an aromatic hydrocarbon rich fraction is separated from the coal tar stream and hydrogenated. The hydrogenated aromatic hydrocarbon rich fraction is recycled to the pyrolysis zone as the hydrogen donor solvent.

What is claimed is: 
     
         1 . A process for pyrolyzing coal using a recycled hydrogen donor, comprising:
 introducing a coal feed to a pyrolysis zone;   heating the coal feed to a temperature of about 300° C. in the absence of hydrogen;   introducing a hydrogen donor solvent to the pyrolysis zone after the coal feed is heated to the temperature of about 300° C.;   increasing the temperature of the coal feed and the hydrogen donor solvent, while increasing a pressure in the pyrolysis zone to at or above a vapor pressure of the hydrogen donor solvent to evolve coal tar from the pyrolysis zone;   increasing the temperature of the coal feed and the hydrogen donor solvent while maintaining the pressure in the pyrolysis zone at or above the vapor pressure of the hydrogen donor solvent to produce a coke stream and a coal tar stream until no further coal tar is evolved from the pyrolysis zone;   reducing the pressure in the pyrolysis zone to approximately atmospheric pressure while increasing the temperature of the coal feed and the hydrogen donor solvent to about 1,000° C. to about 2,000° C.;   separating at least an aromatic hydrocarbon rich fraction from the coal tar stream;   hydrogenating the aromatic hydrocarbon rich fraction; and,   recycling the hydrogenated aromatic hydrocarbon rich fraction to the pyrolysis zone as the hydrogen donor solvent.   
     
     
         2 . The process of  claim 1 , wherein the hydrogenated aromatic hydrocarbon fraction comprises one or more hydrogenated polycyclic aromatic compounds. 
     
     
         3 . The process of  claim 2 , wherein the hydrogenated aromatic hydrocarbon fraction comprises one or more of tetralin and decalin. 
     
     
         4 . The process of  claim 1 , wherein said separating comprises distillation. 
     
     
         5 . The process of  claim 1 , wherein said separating comprises aromatic extraction. 
     
     
         6 . The process of  claim 1 , wherein an output volume of the coke stream is controlled based on an amount of the hydrogen donor solvent introduced into the pyrolysis zone relative to an amount of coal feed introduced to the pyrolysis zone. 
     
     
         7 . The process of  claim 6 , wherein a ratio of the hydrogen donor solvent to the coal feed is set so as to raise a molar ratio of hydrogen to carbon present in the pyrolysis zone into the range of 0.5 to 0.7. 
     
     
         8 . The process of  claim 1 , wherein reducing the pressure in the pyrolysis zone to approximately atmospheric pressure while increasing the temperature of the coal feed and the hydrogen donor solvent comprises reducing the pressure in the pyrolysis zone to approximately atmospheric pressure while increasing the temperature of the coal feed and the hydrogen donor solvent to about 1,100° C. 
     
     
         9 . The process of  claim 1  wherein the aromatic hydrocarbon rich fraction comprises hydrocarbons having an initial boiling point in a range of about 180° C. to about 270° C. 
     
     
         10 . A process for controlling a volume of a coke output during coal pyrolysis, comprising:
 introducing coal to a pyrolysis zone;   heating the coal to a temperature of about 300° C. in the absence of hydrogen;   introducing a hydrogen donor solvent to the pyrolysis zone;   increasing the temperature of the coal and the hydrogen donor solvent to a temperature of about 475° C., while increasing a pressure in the pyrolysis zone to at or above a vapor pressure of the hydrogen donor solvent;   increasing the temperature of the coal and the hydrogen donor solvent to about 600° C. while maintaining the pressure in the pyrolysis zone to produce a coke stream and a coal tar stream; and,   reducing the pressure in the pyrolysis zone to approximately atmospheric pressure while increasing the temperature of the coal feed and the hydrogen donor solvent to about 1,000° C. to about 2,000° C.,   wherein an amount of the hydrogen donor solvent introduced into the pyrolysis zone relative to an amount of coal introduced to the pyrolysis zone is varied to control an amount of coke produced in the coke stream.   
     
     
         11 . The process of  claim 10 , wherein a ratio of the hydrogen donor solvent to the coal is set so as to raise the molar ratio of hydrogen to carbon present in the pyrolysis zone into the range of 0.5 to 0.7. 
     
     
         12 . The process of  claim 10 , wherein the hydrogen donor solvent comprises one or more hydrogenated polycyclic aromatic compounds. 
     
     
         13 . The process of  claim 12 , wherein the hydrogen donor solvent comprises one or more of tetralin and decalin. 
     
     
         14 . The process of  claim 10 , further comprising:
 separating at least an aromatic hydrocarbon rich fraction from the coal tar stream; and,   hydrogenating the aromatic hydrocarbon rich fraction.   
     
     
         15 . The process of  claim 14  further comprising recycling the hydrogenated aromatic hydrocarbon rich fraction to the pyrolysis zone as the hydrogen donor solvent. 
     
     
         16 . The process of  claim 14 , wherein said separating comprises distillation. 
     
     
         17 . The process of  claim 14 , wherein said separating comprises aromatic extraction. 
     
     
         18 . The process of  claim 10 , wherein reducing the pressure in the pyrolysis zone to approximately atmospheric pressure while increasing the temperature of the coal feed and the hydrogen donor solvent comprises reducing the pressure in the pyrolysis zone to approximately atmospheric pressure while increasing the temperature of the coal feed and the hydrogen donor solvent to about 1100° C. 
     
     
         19 . The process of  claim 14  wherein the aromatic hydrocarbon rich fraction comprises hydrocarbons having an initial boiling point in a range of about 180° C. to about 270° C. 
     
     
         20 . The process of  claim 15  wherein the aromatic hydrocarbon rich fraction comprises hydrocarbons having an initial boiling point in a range of about 180° C. to about 270° C.