Water-Gas Shift (WGS) Reactor Sizing & Equilibrium Calculator
Thermodynamic equilibrium modeling, catalyst volume sizing, and adiabatic temperature rise for HTS and LTS converters.
1. Reactor Stage & Feed Syngas
2. Gas Composition (Dry Mol %)
3. Thermal & Catalyst Parameters
Simulation & Reactor Sizing Output
Syngas Mass & Equilibrium Telemetry
Thermodynamic Equilibrium Curve & Bed Axial Temperature Profile
Plotting equilibrium conversion limit versus reactor operating line across catalyst depth.
5 Fatal Traps & Industrial Engineering Pitfalls
1. Magnetite Over-Reduction & Fischer-Tropsch Runaway
In High-Temperature Shift reactors, the active catalytic component is magnetite (Fe3O4). If the steam-to-dry-gas ratio drops below approximately 0.30 due to a boiler feed trip or upstream steam valve fluctuation, the reducing potential of CO and H2 drives the reduction of Fe3O4 to metallic alpha-iron (Fe). Metallic iron functions as an active Fischer-Tropsch catalyst, initiating runaway methanation and hydrocarbon synthesis. This side reaction is violently exothermic, triggering uncontrollable thermal spikes exceeding 600 deg C that melt catalyst retainers and rupture reactor shells.
2. Condensation Wetting & Catalyst Pellet Shattering
During startup or plant turndown, if syngas enters the shift converter below the gas dew point (typically 160 to 180 deg C depending on steam partial pressure and operating pressure), liquid water condenses directly into the porous catalyst structure. Both Fe-Cr and Cu-Zn-Al tablets possess zero hydrothermal mechanical strength when exposed to liquid water; capillary pressure destroys the binder, causing pellets to dissolve into soft mud. Upon re-evaporation, the bed collapses into an impermeable plug, causing thousands of kPa of pressure drop and forcing immediate shutdown.
3. Copper Thermal Sintering Above 260 deg C in LTS Beds
Low-Temperature Shift catalysts rely on ultra-fine, nano-dispersed copper crystallites supported on ZnO and alumina. If inlet temperature regulation fails or upstream HTS CO slip surges beyond design (e.g. rising from 3% to 6% CO), the excessive exothermic heat release raises the LTS bed exit temperature above 260 deg C. At this temperature, Tammann mobility initiates irreversible copper sintering; crystallites agglomerate into massive, inactive grains. The catalyst activity drops by 80% within 48 hours and can never be regenerated.
4. Sub-PPM Chlorine & Sulfur Poisoning of LTS Catalysts
While HTS iron-chromium catalysts tolerate up to 50 ppm H2S, copper LTS catalysts are permanently and stoichiometrically poisoned by sulfur and chlorine compounds. Chlorine forms cuprous chloride (CuCl), a volatile compound that mobilizes copper and accelerates sintering at as low as 0.001 ppm (1 ppb). Plant designs must strictly incorporate a sacrificial guard bed or activated alumina chlorine guard upstream of the LTS vessel to guarantee catalyst longevity of 3 to 5 years.
5. Wall Channeling & Thermowell Misalignment
Due to large reactor diameters (often 2.5 to 4.5 meters), improper dense-phase catalyst loading causes severe packing density gradients. Gas bypasses through lower-density zones near the vessel walls. If multipoint thermocouples are only positioned along the centerline, operators receive false indications of normal adiabatic temperature rise while peripheral zones suffer severe CO breakthrough. A multi-radial thermowell array and laser-leveled catalyst surface during loading are mandatory to avoid catastrophic unshifted CO slip to methanation or PSA units.
Chemical Thermodynamic Derivations & Rate Equations
The Water-Gas Shift equilibrium constant $K_{eq}$ as a function of absolute temperature $T$ (in Kelvin) is accurately predicted by the Twigg & Moe thermodynamic relation:
The reaction quotient $Q_p$ and equilibrium composition are related by:
Where $Delta n_{CO}$ is the extent of reaction (moles of CO converted). Because the stoichiometric sum $sum u_i = 0$, operating pressure has zero effect on ideal gas equilibrium conversion, though elevated pressure substantially accelerates intrinsic reaction rates.
The adiabatic temperature rise $Delta T_{ad}$ is computed by integrating the mixture heat capacity:
Where $ar{C}_p approx 30.5 ext{ J/(mol}cdot ext{K)}$ for typical moist syngas mixtures. Catalyst volume $V_{cat}$ is determined by the gas hourly space velocity (GHSV) referenced to dry standard conditions ($0^circ ext{C}, 1 ext{ atm}$):