Reactor Temp Mgmt

Chapter from the Hydroprocessing Operations Guide.

REACTOR TEMPERATURE MANAGEMENT

WABT Concepts

WABT (Weighted Average Bed Temperature) is the primary performance tracking variable for fixed-bed catalytic reactors.

WABT = Σ(T_avg_zone × V_zone) / Σ(V_zone)
Where T_avg_zone = (T_inlet + T_outlet)/2 for each zone, V_zone = catalyst volume in zone

For a single bed: WABT = (T_inlet + 2 × T_outlet) / 3 (common approximation)
This weighting accounts for more reaction occurring near the outlet (higher temperature).

Why WABT Matters:
• Normalizes reactor performance to a single number
• Allows comparison across different operating periods
• Catalyst deactivation tracked as WABT increase over time at constant product quality
• WABT limit defines end-of-run (EOR): typically 750-790°F depending on metallurgy

Normalized WABT: adjusted for changes in feed quality, throughput, and product spec
• Required to separate true deactivation from operating condition changes
• Normalization factors: LHSV correction, H2PP correction, feed nitrogen correction

Quench System Design & Operation

Interbed quench injects cold hydrogen between catalyst beds to:
1. Control peak temperature (prevent exceeding metallurgical or catalyst limits)
2. Manage ΔT per bed (redistribute heat if one bed is running hot)
3. Redistribute hydrogen (replenish H2 consumed in upstream beds)

Quench Design:
• Source: recycle gas (cold H2-rich gas from HP separator)
• Mixing device: quench deck / distributor tray between beds
• Control: individual quench valve per interbed space
• Typical quench ΔT: 30-100°F temperature drop per quench

Operational Guidelines:
• Total quench should not exceed 20-25% of total recycle gas (recycle gas balance)
• Quench to each bed adjusted to maintain balanced WABTs
• If one bed is deactivating faster: increase its inlet T via reduced quench
• Monitor radial ΔT after quench — poor mixing shows as imbalanced temperatures
• Quench too cold (e.g., from cold separator): can cause thermal shock on internals

Catalyst Deactivation Monitoring

Deactivation Type	Mechanism	Rate	Reversible?	Indicators	Mitigation
Fouling (coke)	Carbon deposition on active sites	Gradual (months)	Partially (regeneration)	Increasing WABT, ΔP increase	Adequate H2PP, avoid temperature excursions
Sintering	Thermal agglomeration of active metals	Gradual (years)	No	Activity loss at constant WABT	Avoid temperature excursions above design
Poisoning (metals)	Ni/V/Fe deposition on catalyst	Progressive	No	Guard bed ΔP, metals in deposits	Guard beds, feed metals control
Poisoning (nitrogen)	Temporary activity suppression	Immediate	Yes (wash out)	Activity drop when N increases	Stable feed quality, blending
Maldistribution	Flow bypassing, channeling	Appears as fast deactivation	N/A (not true deactivation)	Radial ΔT, poor conversion	Proper loading, distributor maintenance

Source: Hydroprocessing_Ops_Guide_v1.xlsx · sheet “Reactor Temp Mgmt”

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