Process for the removal of selenium from selenium-containing aqueous streams

A process for removing selenium from selenium-containing sour water streams generated in multiple hydroprocessing units which process selenium-containing feedstocks by contacting said feedstocks at hydroprocessing temperatures with hydrogen, which process comprises:

• a. withdrawing from a first hydroprocessing unit a first selenium-containing sour water stream containing ammonia, hydrogen sulfide and selenium;
• b. withdrawing from a second hydroprocessing unit a second selenium-containing sour water stream containing ammonia, hydrogen sulfide and selenium;
• c. combining the first sour water stream and the second sour water stream to form a combined sour water stream;
• d. introducing the combined sour water stream into a sour water stripper unit;
• e. recovering from the sour water stripper unit one or more overhead vapor streams containing either ammonia or hydrogen sulfide or both ammonia and hydrogen sulfide and a selenium-containing stripped sour water stream as a bottoms stream;
• f. recycling a major portion of the selenium-containing stripped sour water to the first and second hydroprocessing units for further use;
• g. directing a minor portion of the selenium-containing stripped sour water to a water storage tank in a delayed coker unit having a coker furnace for heating coke feedstock, a coke drum containing hot solid coke, a storage tank for holding quenching water and cutting water and a receiving device for recovering the resulting solid coke product;
• h. injecting the selenium-containing stripped sour water stream into the coke drum containing hot solid coke thereby quenching the temperature in the coke drum to a temperature range from about 150.degree. F. to about 220.degree. F. and forming a solid selenium-coke product in which the selenium is non-water soluble and a substantially selenium-free overhead gas;
• i. breaking up the solid selenium-coke product in the coke drum by injecting a pressurized cutting water stream maintained at a pH above about 6.5 into the coke drum;
• and
• j. recovering the selenium-coke product from the coke drum in a receiving device.

A process for removing selenium from a selenium-containing sour water stream generated in a one or more hydroprocessing units which process selenium-containing feedstocks, which process comprises:

• a. withdrawing from the one or more hydroprocessing units a selenium-containing sour water steam containing ammonia, hydrogen sulfide and selenium;
• b. introducing the sour water stream into a sour water stripper unit;
• c. recovering from the sour water stripper unit one or more overhead vapor streams containing either ammonia or hydrogen sulfide or ammonia and hydrogen sulfide and a selenium-containing stripped sour water stream as a bottoms stream;
• d. recycling a major portion of the selenium-containing stripped sour water to the hydroprocessing unit for further use;
• e. directing a minor portion of the selenium-containing stripped sour water to a storage tank in a delayed coker unit having a coker furnace for heating coke feedstock, a coke drum containing hot solid coke, a storage tank for holding quenching water and cutting water and a receiving device for recovering the resulting solid coke product;
• f. injecting the selenium-containing stripped sour water stream into the coke drum containing hot solid coke thereby quenching the temperature in the coke drum to a temperature range from about 150.degree. F. to about 200.degree. F. and forming a selenium-coke product in which the selenium is non-water soluble and a substantially selenium-free overhead gas;
• g. injecting a pressurized cutting water stream maintained at a pH above about 6.5 into the coke drum thereby breaking up the solid selenium-coke product;
• and
• h. recovering the selenium-coke product from the coke drum.