Catalyst Fouling Rate

The design of a hydrocracker unit is based on a specified conversion rate of the feed and a specified catalyst life, usually 2-3 years between catalyst regeneration. During the course of the run, the activity of the catalyst declines due to coke and metal deposits, and to maintain the design conversion rate, the temperature of the catalyst has to be increased. The catalyst manufacturers specify a maximum temperature, called the end of run temperature, which signifies the EOR condition. When this temperature is reached, the catalyst must be regenerated or discarded.

The rate of increase in average reactor catalyst temperature (to maintain the design conversion rate) with time is called the catalyst fouling rate. It is an important parameter, used to make an estimate of time when the EOR conditions are likely to be reached. The refinery keeps a record of the reactor average temperature with time, starting from the day the feed is introduced into the reactor after the new catalyst has been loaded. A graph is drawn between the time on stream vs. the average reactor temperature (Figure 3-7). The data may show scatter, so a straight line is drawn through the data. From this curve, an estimate of the catalyst fouling rate and remaining life of the catalyst can be estimated.

800 F

2

Tl-151

778

C3LL

5s tr e

cc

TI-152

770

TI-153

781

1-r> o

TI-154

793

AVG. 794

Tl -155

794

Tl -156

795

QUENCH BED 2 = MMSCFD BED 2

2

Tl -157

770

AVG. 774

REACTOR AVG. BED AT

24° F

TI-158

780

Tl -159

771

OUT

TI-160

799

AVG. 798

TI-161

796

Tl -162

799

QUENCH BED 3 = 18.7 MMSCFD BED 3

2

TI-163

770

AVG. 774

REACTOR AVG. BED AT

20°F

Tl -164

776

TI-165

775

ID O

Tl -166

797

AVG. 794

Tl -167

799

TI-168

801

QUENCH BED 4 = 18.7 MMSCFD

2

TI-169

774

CC CM

tr

TI-170

771

Tl -171

779

| UPPER MID

TI-172

795

AVG. 796

TI-173

786

TI-174

s o

TI-175

795

AVG. 795

Tl -176

792

TI-177

798

DESULFURAZATION BED

o

Tl-178

799

AVG. 803

BED AT 20°F

Tl -179

802

Tl -180

805

Figure 3-6. Hydrocracker reactor temperature profile.

TRENDS IN AVG REACTOR

TRENDS IN AVG REACTOR

Temperature Profile Column Distillation

Figure 3-7. Estimating the remaining catalyst life. EXAMPLE 3-1

Figure 3-7. Estimating the remaining catalyst life. EXAMPLE 3-1

The design start of run (SOR) temperature of a hydrocracker reactor is 775°F. After the unit is onstream for 12,000 hours, the CAT (weighted average bed temperature) is 800°F. Estimate the remaining life of the catalyst if the design EOR temperature of the catalyst is 805°F:

5 0.00208

= 2404 hr or 3.33 months

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    How to maintain average reactor catalyst temperature?
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