Supercritical Water Oxidation Reactor

Reactor Conditions

Temperature 450 °C

Pressure 25.0 MPa

Residence time τ 20 s

Excess O₂ ratio 1.5×

Live Reactor State

Water density

Rate constant k

Destruction eff.

Inorganic salt (e.g. Na₂SO₄)

How it works

Above water's critical point (T_c = 374 °C, P_c = 22.1 MPa) there is no liquid/vapor distinction — a single supercritical phase forms in which nonpolar organics and O₂ become fully miscible with water (unlike normal liquid water, which barely dissolves either). That miscibility is what makes SCWO work: organics, oxidant and water react homogeneously in one phase instead of across a gas-liquid interface.

Plug-flow destruction:  DE = 1 - e^(-k·τ)
Arrhenius rate:         k = A·e^(-Ea / R·T)
  Ea ≈ 125 kJ/mol, A ≈ 1.0×10^10 s⁻¹ (typical organics)
  τ = reactor residence time (s), T in kelvin

The reactor below is a plug-flow tube: each particle entering the inlet has a per-instant probability of oxidizing that compounds over its transit, so the measured conversion at the outlet converges on the DE formula above for the chosen τ. Full O₂ stoichiometry is needed to reach it — with excess O₂ < 1× the achievable conversion is capped proportionally.

Water's density collapses from ~1000 kg/m³ (liquid) toward ~100 kg/m³ (gas-like) across the critical region — the density model here is a simplified engineering correlation anchored to the true (T_c, P_c) point, with the transition midpoint shifting to higher T as pressure rises above P_c (the real "pseudocritical" line). Dissolved inorganic salts, ionic in a polar liquid, become essentially insoluble once density drops below roughly 0.3 g/cm³ and precipitate out — a genuine SCWO engineering problem, since accumulated salt can foul heat exchangers and plug the reactor.

Temperature / Pressure — set the operating point; together they fix water density and oxidation rate k.
Residence time τ — how long waste stays in the reactor; longer τ raises destruction efficiency for a given k.
Excess O₂ ratio — oxidant supplied relative to the stoichiometric demand; sub-stoichiometric O₂ caps achievable destruction regardless of τ.

Organic waste O₂ CO₂ + H₂O (oxidized) Dissolved salt Precipitated salt

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