Barrel and feed unit

Chain-type elevators, such as arm and tray units, are commonly used for drums and barrels. Shght gravity runs at feed and discharge allow these units to roll on and off the conveyor easily and without special equipment. 

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. 

The environmental impact of SOj emissions has gained much attention over the past ten years. The United States Environmental Protection Agency (EPA) New Source Performance Standards (NSPS) went into effect in 1989. The ruling covers new, modified, and reconstructed FCC units since January 1994. It should be noted that the Southern California Air Quality Management District (SCAQMD) board has established a limit of 60 kilograms of SO per 1,000 barrels of feed for the existing FCC units. 

Fig. 7 Extruder and extrusion. 1 Drive unit, 2 barrel inlet, 3 temperature control, 4 feed hopper and dosing unit, 5 vacuum vent, 6 barrel, 7 screw. (Reproduced with permission from Reifenhauser)...

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.

Flue gas leaving the cyclones contains a small r esidual concentration of catalyst and is passed through a Cottrell electrostatic precipitator recovered catalyst is returned to the regenerated-catalyst hopper. Catalyst losses for this type of unit have been reported to be within the range of 0.12 to 0.4 lb. per barrel of feed (232,233). The losses are compensated for by the intermittent addition of fresh catalyst. 

Catalyst recovery. Catalyst losses in downflow units are typically in the range of 0.2 to 0.4 Ib./barrel of feed (100,234). Cyclones recover most of the catalyst from vapors leaving the reaction vessels. Catalyst that escapes from the reactor cyclones is recovered in the bottoms from the fractionating tower. The upflow units and the early downflow units were equipped with Cottrell electrostatic precipitators to recover en-i rained catalyst from the flue gas leaving the regenerator cyclones. It... 

These developments have led to dramatic reductions in the size (elevation, volume, catalyst inventory) and, hence, costs of an FCC unit per barrel of feed charged and converted. 

A typical arrangement for a direct screw-transfer injection-molding machine for thermosets is shown in Figure 2.16. The machine has two sections mounted on a common base. One section constitutes the plasticizing and injection unit, which includes the feed hopper, the heated barrel that en closes the screw, the hydraulic cylinder which pushes the screw forward to inject the plasticized material into the mold, and a motor to rotate the screw. The other section clamps and holds the mold halves together under pressure during the injection of the hot plastic melt into the mold. 

In a 60,000 barrels-per-day unit processing a typical mixture of vacuum gas oils, the total catalyst in the unit (the inventory ) is 400 to 500 tons. To maintain activity, about 0.5 to 1 wt% of the inventory is replaced each day. If the feed to the unit contains significant amounts of residue, the replacement rate is higher. The discharged catalyst is cooled and shipped either to a land fill for disposal or to another refiner, which may have a particular use for conditioned FCC catalyst. 

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