Process employing hydrogen to strip dissolved hydrogen sulfide from the liquid effluent of a petroleum distillate hydrotreater

Abstract

The liquid hydrotreated effluent stream from a hydrotreating unit containing dissolved hydrogen sulfide downstream of a high-pressure separator is cooled and reduced in pressure to within a predetermined range before being stripped with process hydrogen to remove the dissolved hydrogen sulfide and recovering the effluent as the final product, the process being particularly suitable for hydrotreating naphtha, kerosene or diesel products to produce an ultra-low sulfur product without the need for further fractionation.

1 . A process for the treatment of a sulfur-containing liquid hydrocarbon feedstream to reduce its sulfur content, where the feedstream is naphtha, kerosene or diesel, the process comprising:
 a. mixing the sulfur-containing liquid feedstream and a high-pressure hydrogen-rich stream to produce a mixed feed and charging the mixed feed to a hydrotreating zone to produce a hydrotreating zone effluent;   b. introducing the hydrotreating zone effluent into a cooling zone and then into a high-pressure separation zone and recovering a gas phase effluent comprising excess hydrogen and hydrogen sulfide gases and a liquid phase effluent comprising hydrogen sulfide dissolved in the hydrotreated hydrocarbon;   c. passing the gas phase effluent comprising hydrogen sulfide gas from the high-pressure separation zone to a high-pressure amine absorbent zone to remove the hydrogen sulfide gas from the gas phase effluent and recovering a sweetened hydrogen-rich gas stream;   d. mixing the sweetened hydrogen-rich gas stream with a hydrogen-rich stripping unit recycle stream to form a hydrogen-rich mixed recycle stream;   e. compressing the hydrogen-rich mixed recycle stream in a recycle compressor to produce the high-pressure hydrogen-rich stream of step (a);   f. passing the liquid phase effluent containing dissolved hydrogen sulfide from the high-pressure separator through a control valve to reduce the pressure to provide a cooled hydrotreated liquid. effluent stream comprising dissolved hydrogen sulfide that is at a temperature in the range of from 20° C. to 80° C. and at a pressure in the range of from 0 bar to 10 bar;   g. passing the cooled hydrotreated effluent stream containing dissolved hydrogen sulfide and a stripping stream consisting of hydrogen to a stripping zone to strip the dissolved hydrogen sulfide from the cooled hydrotreated effluent stream and recovering a cooled hydrotreated liquid ultra-low sulfur fuel product containing 10 ppmw or less of sulfur that is substantially free of H 2 S and a top stream comprising hydrogen sulfide, hydrogen and light hydrocarbons; and   h. removing the hydrogen sulfide from the top stream in a low-pressure amine absorber to produce the hydrogen-rich stripping unit recycle stream of step (d).   
     
     
         2 . (canceled) 
     
     
         3 . (canceled) 
     
     
         4 . The process of  claim 1 , wherein the temperature of the hydrotreating zone effluent is reduced in the cooling zone of step (b) to a temperature of from 20° C. to 80° C. 
     
     
         5 . The process of  claim 1 , wherein the temperature of the hydrotreating zone effluent is reduced by passing the effluent through one or more heat exchangers. 
     
     
         6 . The process of  claim 1 , wherein the stripping zone comprises a column having a plurality of trays or a packed column containing packing material through which the cooled hydrotreated effluent stream containing dissolved hydrogen sulfide passes in descending counter-current flow with ascending hydrogen stripping gas that displaces the hydrogen sulfide from the effluent stream. 
     
     
         7 . The process of  claim 6 , wherein the operating conditions of temperature and pressure in the stripping zone are predetermined based upon the characteristics of the packing material loaded into the packed column or the configuration and number of trays in the column. 
     
     
         8 . The process of  claim 7 , wherein the operating conditions are predetermined on the basis of theoretical plate calculations. 
     
     
         9 . The process of  claim 8 , wherein the number of theoretical plates is between 4 and 10 to achieve a sulfur content of less than 1 ppmw. 
     
     
         10 . The process of  claim 1 , wherein all or a portion of the hydrogen.-rich stripping unit recycle stream of step (e) is mixed with a fresh hydrogen stream to produce the stream of stripping hydrogen for use in step (g). 
     
     
         11 . A system for the production of ultra-low sulfur hydrocarbon product streams from sulfur-containing liquid hydrocarbon feedstream that comprises:
 a. a hydrotreating zone containing a catalyst adapted for receiving a mixture of the sulfur-containing liquid hydrocarbon feedstream and a high-pressure hydrogen-rich stream and for discharging a hydrotreating zone effluent;   b. a cooling zone in fluid communication with the hydrotreating zone and adopted for receiving and cooling the hydrotreating zone effluent;   c. a high-pressure separation zone in fluid communication with the cooling zone and adapted for receiving the cooled hydrotreating zone effluent and discharging a gas phase effluent comprising excess hydrogen and hydrogen sulfide gases and a separate liquid phase effluent comprising the hydrotreated hydrocarbon stream containing dissolved hydrogen sulfide;   d. pressure reducing means in fluid communication with the high-pressure separation zone and adapted to receive and reduce the pressure of the liquid-phase hydrotreated hydrocarbon stream containing dissolved hydrogen sulfide to a predetermined lower pressure;   e. a stripping zone in fluid communication with the pressure reducing means and adapted to:   i. receive and pass the hydrotreated hydrocarbon stream containing dissolved hydrogen sulfide in counter-current flow with a hydrogen stripping stream;   ii. discharge a stripping zone top stream comprising hydrogen sulfide, hydrogen and light hydrocarbons; and   discharge a stripping zone bottom stream that is a cooled hydrotreated hydrocarbon product that is substantially free of hydrogen sulfide.   
     
     
         12 . The system of  claim 11  which includes a low-pressure amine absorber in fluid communication with the stripping zone top stream and adapted to remove the hydrogen sulfide and discharge a hydrogen-rich amine absorber recycle stream. 
     
     
         13 . The system of  claim 12  which includes a recycle compressor in fluid communication with the low-pressure amine absorber and a high-pressure amine absorption zone, and adapted to receive the hydrogen-rich recycle stream, and to mix and compress it with a sweetened hydrogen stream recovered from the high-pressure amine absorbent zone to form a hydrogen-rich mixed recycle stream. 
     
     
         14 . The system of  claim 11  in which the stripping zone includes a column that operates with the equivalent of at least 4 theoretical plates. 
     
     
         15 . The system of  claim 14  in which the stripping zone includes a column that operates with the equivalent of 6 to 12 theoretical plates.