PTQ Q4 2026 Issue

Evaluation of hydrogen reduction strategies

Engineering question

Why it mattered

Evaluation

Outcome

Can furnace duty be reduced while maintaining throughput?

Furnace duty had become the controlling operating constraint.

Hydrogen quench reduction

Significant reduction in

furnace duty while maintaining acceptable catalyst performance.

Can the operating strategy

Immediate reductions could create

Progressive hydrogen quench Preferred strategy because

be improved?

unnecessary operating risk.

reduction

it involved gradual shifts rather than a large step change in operation. Beneficial, but insufficient to

Could treat gas reduction achieve the same objective?

Lower hydrogen circulation also

Treat gas sensitivity analysis

reduces furnace load.

achieve the desired run length extension.

Can hydrogen supply to the reactors be reduced safely?

Catalyst protection remained essential despite the changed

Hydrogen availability

Confirmed that the

assessment

recommended operating strategy maintained acceptable operating margins.

operating stategy.

Table 1

driving refinery profitability. Earlier work had successfully increased unit throughput mid-run, while feed control and operational stability were improved to protect catalyst life. While this initiative achieved its objective, the higher unit charge rate increased the load on the feed furnaces as the unit approached EOR. Analysis showed that the furnaces would limit the unit operation before reaching the target EOR WABT of 400°C. Without adjusting the operating strategy, a unit rate reduction or early catalyst changeout would be required. The natural response to this situation is to continue operating with the primary objective of preserving catalyst activity. Particularly from the perspective of a catalyst ven- dor, the main consideration is to ensure that their product achieves its expected performance. From a refinery-wide profitability perspective, however, the question was no longer how to preserve catalyst life. It was how to extract the greatest value from the catalyst life that remained. Mitigation steps were investigated to overcome the fur- nace constraint with the goal of extending the unit run length by eight months without reducing charge rate. Conventional approaches were first considered, including furnace debottlenecking and various means to increase furnace inlet temperature. However, the available mitiga- tion options were insufficient to achieve the desired run length extension. As the furnaces emerged as the primary operating constraint, the operating strategy had to change. The refiner needed a creative solution to avoid charge rate reduction or an early shutdown. Updating the operating strategy New strategies were developed that could mitigate the increase in furnace load as the unit approached EOR condi- tions. Rather than focusing solely on catalyst life, the objec- tive shifted towards maximising refinery throughput while maintaining acceptable catalyst performance. If WABT was not the first operating variable to limit the unit, what variable would be optimised instead? The identi- fied solution was strategically controlling hydrogen circula- tion to effectively use the remaining catalyst activity for the operating cycle.

Reducing hydrogen circulation is a counterintuitive approach since it results in reduced hydrogen partial pres- sure, directionally accelerating catalyst deactivation and potentially shortening run length. Why reduce hydrogen when the traditional objective is to protect catalyst life? Because the furnace, rather than the catalyst, had become the governing constraint. The engineering objective had fundamentally changed. Two new strategies were evalu- ated to reduce hydrogen circulation: • Primary strategy: Reducing hydrogen quench allows the temperature to rise on the second and third reactor beds. The higher-temperature reactor outlet stream exchanges heat with the feed, thus increasing the furnace inlet tem- perature. At the same time, a lower reactor inlet (furnace outlet) temperature is required due to the increased WABT. The net result is a lower temperature rise with a corre- sponding reduced duty requirement for the furnace. • Alternative strategy: Reducing treat gas to the reactor inlet directly reduces furnace load by removing the addi- tional mass of hydrogen to be heated. The key question was whether the increase in catalyst deactivation due to the lower hydrogen partial pressure remained acceptable once furnace duty had become the controlling operating constraint. • Unit modelling: A DHTR-SIM model was developed and calibrated to represent the DHT unit operation. The model quantified the impact of the proposed strategies on the reactor temperature profile and catalyst deactivation rate, taking into account kinetic effects of increased WABT and reduced hydrogen partial pressure. Updated reactor pro- files were generated for each successive month until reach- ing the EOR WABT or unit run length target. A summary of the hydrogen reduction strategies and outcomes is pre- sented in Table 1 . Testing the H₂ quench reduction strategy The first step towards reducing hydrogen quench was to determine the minimum flow to keep the quench system active and maintain stable flow control. In this case, it was found that a 70% reduction was appropriate to use for the minimum H₂ quench flow analysis.

PTQ Q4 2026