RL Blogs
By Norm Lieberman
Jul 24, 2017Key process monitoring tip for atmospheric crude distillation. |
One of the most important aspects of crude unit monitoring is to measure the diesel content of the crude tower bottoms. Measure the 650 deg F (minus) (D-86 ASTM), which is basically diesel. Any number above 6% is excessive.
To reduce the diesel content of crude tower bottoms:
Reduce flash zone pressure - A 2 psia reduction will have the same effect as raising flash zone temperature by 5 deg F. Increasing pumparound heat extraction will unload overhead condenser and reduce tower pressure. Next, try to increase tower bottoms stripping steam. A good number is 6 – 8 pounds of steam per barrel of atm resid.
Redesign stripping trays so that each tray develops 2” – 3” of dry tray pressure drop.
Raise flash zone temperature - A good heater outlet is 720 deg F - 735 deg F (max). A very low flash zone temperature is 680 deg F - 690 deg F, which equates to a heater outlet of 700 deg F.
Diesel losses to AGO are smaller than to atmospheric resid. 650 deg F minus (D-86) of 20%, or less, is excellent. 650 deg F minus in AGO of 35% plus is bad. Suggest using 10 – 12 lbs. per barrel of stripping steam. Much higher steam rates will accomplish little.
If LVGO and AGO are used as FCU feed, about 20% of diesel will be degraded to catalytic coke and fuel gas. The remainder will be LCO, with degraded cetane number. |
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