PTQ Q4 2026 Issue

Bed 2 and 3 quench rates

400

12.0 10.0 16.0 14.0 18.0 20.0

Bed 2 quench Bed 3 quench

380

360

340

0.0 2.0 4.0 6.0 8.0

320

300

+1 +2 +3 +4 +5 +6 +7

Constant outlet temperature

Reduced H quench

Month

over time until EOR. This was the preferred operating strategy because it avoided implementing a large process change at once. Rather than a large and immediate reduc - tion in hydrogen quench rate, it was reduced incrementally as the catalyst aged. By maintaining higher H₂ partial pressure across the catalyst versus an immediate reduction of H₂ quench to its minimum, the catalyst deactivation rate was slightly reduced, which provided additional run length. The same base case was used, with catalyst deactivation evaluated on a monthly basis, as in the previous hydrogen quench reduction scenario. The resulting EOR WABT was lower than the immedi - ate reduction of hydrogen quench to minimum (396.0°C versus 398.1°C). As in the previous scenario, the furnace duty reached approximately the base value at the end of the eight-month extension period. Figure 3 depicts the decrease in hydrogen quench rate over time. Figure 4 shows reactor bed outlet temperatures through EOR. There was an increasing temperature spread as hydrogen quench progressively decreased. At the end of the eight-month outlook period, Bed 1 outlet temperature increased by only 2°C, whereas the Bed 3 outlet temper - ature gained 8°C. The next question was whether reduc - ing hydrogen treat gas could relieve the furnace constraint without causing an unacceptable adverse impact to cata - lyst life. Evaluating an alternative strategy When reducing treat gas, maintaining a minimum hydro- gen availability is important to prevent accelerated catalyst coking and maintain an acceptable deactivation rate. The minimum acceptable value varies by unit and depends on feed composition, operating severity, and quantity of treat gas in the base case. For the unit under consideration, a 10% reduction in treat gas maintained the unit operation within acceptable guidelines (as discussed in the following dialogue). The treat gas was reduced in the model by 10% from the base case, resulting in an initial WABT increase of 0.4°C, a reduction in furnace duty of 0.5 Gcal/hour (2.2%), and a marginal increase in catalyst deactivation rate. The Figure 3 Hydrogen quench reduction at constant furnace duty

Figure 2 Reactor bed temperature profiles

For the base case, the hydrogen quench flows were set to maintain equivalent outlet temperatures from each reactor bed. To evaluate the primary strategy, the hydro- gen quench was reduced in the model to a minimum while holding the furnace outlet temperature constant, resulting in an increasing temperature profile across the reactors. The net impact of reduced hydrogen partial pressure and an increase in WABT was a lower sulphur level in the die - sel product. The furnace outlet temperature (Bed 1 inlet) was then adjusted until the sulphur matched the base case value of 8 ppm. Figure 2 illustrates reactor temperature profiles for the base and step-out cases. After reducing H₂ quench, the furnace outlet temperature decreased by 2.0°C while Bed 3 outlet temperature increased by 6.9°C. WABT increased by 3.1°C relative to the base case. The furnace inlet tempera - ture simultaneously increased by 1.7°C due to the increase in heat transferred through the feed/effluent exchangers. The reduced furnace temperature rise of 3.7°C resulted in a decreased furnace duty (for each train) of 1.3 Gcal/hour (6.2%). To determine the remaining run length, simulations were completed for each successive month over the remainder of the cycle. The model predicted catalyst deactivation rates of 0.7 to 0.8°C WABT/month, which were used to estimate a WABT of 398.1°C at the end of the targeted eight-month extension, remaining below the EOR limit of 400°C. The furnace duty requirement had returned to approximately the base level, indicating that the target was marginally achievable with the hydrogen quench reduction strategy. The analysis demonstrated that the refinery could safely trade a modest increase in catalyst deactivation for a mean- ingful reduction in furnace duty, extending unit operation by several months without reducing throughput. The net effect of the proposed change was to keep both the WABT and furnace duty at or below their respective constraints and effectively utilising the available catalyst activity. Optimising the initial results The primary strategy was adjusted to maintain constant furnace duty by gradually reducing hydrogen quench flow

PTQ Q4 2026