PTQ Q4 2026 Issue

Hydrogen availability

Bed outlet temperature prole @ constant furnace duty

Basis

Inlet to Bed 1

Total H₂ inc. quench

398.0

Bed 3 Bed 1 Bed 2

Guidelines

396.0

Industry typical Recommended

2 - 5 3 - 4

394.0

Minimum

4 Base and step-out case operation

392.0

390.0

DHT base

2.3 2.3

4.4 3.0 4.2

DHT – 70% quench reduction

388.0

DHT – 10% treat gas reduction 2.1

0 +1 +2+3+4 +5+6+7

Month

Table 2

reduced treat gas rate was maintained throughout the study period. New monthly reactor profiles were gener - ated to account for the projected catalyst deactivation rate. After eight months, the WABT was lower than the hydro- gen quench reduction cases, reaching a value of 394.1°C. This indicates a lower rate of catalyst deactivation, which can be expected since higher hydrogen partial pressure was maintained under this scenario. Although there was less catalyst deactivation, this approach was insufficient to achieve the desired eight-month run length extension. The furnace duty exceeded its base value by month four and required an increase of 0.5 Gcal/hour by month eight. This was not achievable since the furnaces were already at their operating limit in the base case. Selecting the best approach The scenarios under consideration are unit-dependent. H 2 quench reduction generally results in a larger benefit since it truncates the furnace delta T (ΔT) by simultaneously increasing the furnace inlet temperature while decreasing the outlet temperature. However, the impact of hydrogen quench and/or treat gas reduction will vary on a case-by- case basis. In certain situations, a hybrid approach may be the preferred solution. The optimum can be identified for any scenario through rigorous unit modelling, considering the changes to temperature profiles and kinetic effects that impact the catalyst deactivation rate. Defining safe operating limits Minimum acceptable hydrogen availability should be con- sidered when reducing hydrogen to the reactors. Insufficient hydrogen can lead to an excessive rate of coke formation on the catalyst and a possible earlier-than-expected EOR. Hydrogen availability is defined as the ratio of hydrogen entering the reactors versus the chemical hydrogen con- sumption, as per the following formula. Chemical hydrogen consumption is derived from kinetic reactor modelling, such as the DHTR-SIM model: Figure 4 Reactor outlet temperatures at constant furnace duty

Determining the minimum acceptable excess hydrogen above that required for reaction for any operating scenario requires engineering judgement. A larger hydrogen reduc- tion will yield more benefit in terms of reduced furnace duty but carries a higher risk of elevated catalyst deactivation or impact on product quality. A minimum hydrogen availability should be chosen to avoid a large step change in catalyst deactivation rate that may exceed kinetic predictions. There may be flexibility, however, near EOR to take advantage of remaining catalyst activity without strict conformance to guidelines designed to protect the catalyst over the full cycle length. Close unit monitoring after adjusting hydrogen flow is essential to verify catalyst deactivation rate and ensure there are no product quality issues that can arise at elevated operating temperatures. Hydrogen availability guidelines are based on either the quantity of hydrogen entering the first reactor bed or the total hydrogen in the reactor system, including quench flows. Industry guidelines and results for both approaches are summarised in Table 2 . Catalyst vendors often calculate hydrogen availability including hydrogen quench flow. The Bed 1 inlet approach, however, was more important for this analysis as it ensures that adequate hydrogen exists at the inlet to the first reactor, regardless of quench flow, and that sufficient excess hydrogen is also present at the final reac - tor outlet. The purpose of hydrogen quench is to improve catalyst utilisation by equilibrating the reactor outlet temperatures. Without quench, the temperature would rise to the limiting value on the last reactor bed while usable catalyst remains in the first beds. An early unit shutdown for catalyst replace - ment would be required to avoid undesirable side reactions, colour constraints, or mechanical limits. DHT units, therefore, are designed with sufficient hydro - gen quench for operational control. In other words, the first approach ensures catalyst integrity, whereas the second primarily applies to unit optimisation and design. In the previous quench reduction cases, there was no impact on hydrogen availability at the inlet to Bed 1 because the treat gas rate was kept constant. From a total hydrogen quench perspective, the result dropped below the recommended minimum listed in Table 2. This was considered acceptable, however, since it is more of an

H₂ availability =

H₂:oil ratio, Nm³/m3 Chemical H 2 consumption, Nm3/m3

PTQ Q4 2026