## 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
 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

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