Barrel and feed-unit operation

Cures, the equipment is made of vei y expensive high-alloy steels. Energy and hydrogen costs result in high operating costs, much higher per barrel of feed than the FCC unit. 

A small amount of nickel in the FCC feed has a significant influence on the unit operation. In a clean gas oil operation, the hydrogen yield is about 40 standard cubic feet (scf) per barrel of feed (0.07 wi /r ). This is a manageable rate that most units can handle. If the nickel level increases to 1.5 ppm, the hydrogen yield increases up to 100 scf per barrel (0.17 wt%). Note that in a 50,000 barrel/day unit, this corresponds to a mere 16 pounds per day of nickel. Unless the catalyst addition rate is increased or the nickel in the feed is passivated (see Chapter 3), the feed rate or conversion may need to be reduced. The wet gas will become lean and may limit the pumping capacity of the wet gas compressor. 

Table II, the second example, shows the benefits of metals passivation at a FCCU in a refinery operating to maximize throughput. The FCC catalyst contained 490 ppm nickel and 1200 ppm vanadium, and the unit was operating against both its air blower and gas compressor limits. Hydrogen production was 92 SCF per barrel of FCCU feed with this amount of hydrogen in the gas to the compressor, it was difficult to maintain the compressor governor on control. The high concentration of hydrogen in the fuel gas also affected the steady state operation of the heat control of other processing units.

Economic analysis performed for refineries in certain markets have calculated that the benefit of being able to increase kerosene and jet fuel production yield was an improvement of 3-6 cents per barrel over previous operational conditions. On an 180000 barrel per day crude unit this equates to a benefit of 2000000-4000000 per year. Several other refiners are utilizing NMR analyzers on the feed and products of crude units for control and optimization, AGIP has an NMR analyzer for monitoring the feed. 

Results of operation on the 50-barrel pilot unit are presented in Table I. Figures from the Kellogg report are shown for reference purposes, although strictly these cannot be compared with the 50-barrel-per-day results because of considerable difference in feed stock type, and because the molybdenum catalysts used were not identical. 

Startup of this new unit began on April 22, 1942. Successful operation was achieved on May 25, 1942. By June 3, 1942, the fresh feed rate had been increased to 16,600 barrels per day (128% of design), limited by availability of reduced crude and Cottrell precipitator gas velocities. 

Rigorous models for stand-alone units also can provide significant benefits. Previously, we reported benefits of US 3,000 per day (US 0.15 per barrel) for the initial optimizer on the hydrocracking complex these benefits were in addition to those provided by model-predictive DMC control. For RWO, a revised model based on Aspen Hydrocracker (AHYC) was developed. It includes a catalyst deactivation block, which enhances maintenance turnaround planning by predicting future catalyst activity, product yields and product properties for a variety of assumed feeds and specified operating conditions. This information also is used to impose constraints on present-day operation. 

---