Product Fractionation

The fractionator bottom product is pumped by P-16 to a vacuum feed surge drum, then the charge is heated to a temperature of about 780°F before it enters the vacuum tower (see Figure 3-14). The flash zone is at 700°F and 26 inch vacuum maintained by steam ejectors.

The feed is fractionated into heavy diesel, heavy vacuum gas oil, and vacuum bottoms.

The heavy diesel is withdrawn as side cut, cooled in air cooler E-52, and sent to storage. The heavy vacuum gas oil (HVGO) side cut is cooled by raising 150psig steam then in air cooler E-54. A part of HVGO is used as diluent in the resid hydrocracker feed, and the rest is used in fuel oil blending.

The vacuum bottoms from the unit are pumped by P-53 to off-site storage tanks and used in fuel oil blending.

The typical operating conditions of resid hydrocracker units are shown in Table 3-9, and yields and product qualities are shown in Tables 3-10 to 3-12.

The liquid hourly space velocity is calculated based on the flow volume of the liquid feed at the reactor operating conditions divided by the volume of the catalyst up to the fluidized bed height. Only the fresh feed flow is considered, since the net recycle flow is zero. Also, the volume of the makeup and recycled hydrogen is neglected.

STRIPPER BOTTOMS

EJECTORS EJ-01.02

VACUUM TOWER V-5Í

STEAM

DRUM V-52

Hydrocracking

—700 F n PRESSURE kse INCH Hg

QUENCHING

P-53

6FW CIRCULATION

M BOILER FEED WATER

HEAVY DIESEL

VACUUM RESID

Figure 3-14. Residuum hydrocracking (distillation section). BFW = boiler feedwater.

Table 3-9

Resid Hydrocracker Operating Conditions

Table 3-9

Resid Hydrocracker Operating Conditions

OPERATING VARIABLE

UNIT

REACTOR AVERAGE TEMP

op

827

REACTOR SYSTEM PRESSURE

psig

2400

HYDROGEN PARTIAL PRESSURE

psig

1895

MAKEUP HYDROGEN

scf/bbl

1400

RECYCLING GAS FLOW

scf/bbl

4300

BLEED GAS FLOW

scf/bbl

700

HYDROGEN CONSUMPTION

scf/bbl

660

LIQUID HOURLY SPACE VELOCITY

(hr"1)

0.906

HP FLASH GAS PRESSURE

psig

500

LP FLASH GAS PRESSURE

psig

43

FEED/H2 MIX TEMPERATURE

°p

748

PLENUM CHAMBER TEMPERATURE

op

811

CATALYST ADDITION RATE

lb/bbl

0.106

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