Design of a Small-Scale Supercritical Water Oxidation Reactor. Part II: Numerical Modeling

A small-scale supercritical water oxidation reactor is designed and fabricated to study the destruction of hazardous wastes. The downward bulk flow is heated with the introduction of pilot fuel (ethanol/water mixture), and oxidant (H2O2/water mixture). Both streams are introduced coaxially. The fuel dilution is varied from 2 to 7 mol% ethanol/water, and the oxidant-to-fuel stoichiometric equivalence ratio (ΦAF), is varied from 1.1 to 1.5. Higher ethanol concentrations in the pilot fuel stream and operation near-stoichiometric results in a more stratified temperature profile, i.e., highest local fluid temperatures near the top and the lowest temperatures at the bottom of the reactor. Steady operation at 603.5 °C is achieved with a nominal residence time of 25.3 s at 7 mol% fuel dilution and ΦAF of 1.1. At the lowest pilot fuel dilution (2 mol%), the temperature profile is nearly uniform, approaching a distributed reaction regime.

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Design of a Small-Scale Supercritical Water Oxidation Reactor. Part II: Numerical Modeling and Validation

10.26434/chemrxiv.13173278 ◽

2020 ◽

Author(s):

Anmol L. Purohit ◽

John Misquith ◽

Stuart Moore ◽

Brian Pinkard ◽

John Kramlich ◽

...

Keyword(s):

Supercritical Water ◽

Water Oxidation ◽

Oxidation Mechanism ◽

Combustion Stability ◽

Small Scale ◽

Supercritical Water Oxidation ◽

Fluid Temperature ◽

Ethanol Decomposition ◽

Reactor Operating ◽

Oxidation Reactor

The experimental data from the laboratory-scale supercritical water oxidation reactor was leveraged to validate the CFD approach allowing for efficient and accurate modeling of the process. The reactor operating on ethanol as a pilot fuel was modeled using CFD with global oxidation mechanism. Fluid properties were determined using polynomial fit approximations, which yielded excellent agreement with NIST data over a range of temperatures at an isobaric pressure of 25 MPa. The model predicts the fluid temperature within 30°C of measured values for different inlet fuel concentrations. The ethanol decomposition of ~99% occurs within 20% of the reactor length at T~600 °C. The analysis of Damkohler (Da) and Reynolds (Re) numbers shows that the reactor operates in a distributed reaction region, owing to the excellent combustion stability of the inverted gravity reactor configuration. The modeling approach can aid the design of future more complex SCWO reactors and process optimization.

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Design of a Small-Scale Supercritical Water Oxidation Reactor. Part I: Experimental Performance and Characterization

10.26434/chemrxiv.13173257.v1 ◽

2020 ◽

Author(s):

Stuart Moore ◽

Brian Pinkard ◽

Anmol L. Purohit ◽

John Misquith ◽

John Kramlich ◽

...

Keyword(s):

Temperature Profile ◽

Supercritical Water ◽

Water Oxidation ◽

Small Scale ◽

Supercritical Water Oxidation ◽

Water Mixture ◽

Pilot Fuel ◽

Reaction Regime ◽

Fuel Dilution ◽

Oxidation Reactor

A small-scale supercritical water oxidation reactor is designed and fabricated to study the destruction of hazardous wastes. The downward bulk flow is heated with the introduction of pilot fuel (ethanol/water mixture), and oxidant (H2O2/water mixture). Both streams are introduced coaxially. The fuel dilution is varied from 2 to 7 mol% ethanol/water, and the oxidant-to-fuel stoichiometric equivalence ratio (ΦAF), is varied from 1.1 to 1.5. Higher ethanol concentrations in the pilot fuel stream and operation near-stoichiometric results in a more stratified temperature profile, i.e., highest local fluid temperatures near the top and the lowest temperatures at the bottom of the reactor. Steady operation at 603.5 °C is achieved with a nominal residence time of 25.3 s at 7 mol% fuel dilution and ΦAF of 1.1. At the lowest pilot fuel dilution (2 mol%), the temperature profile is nearly uniform, approaching a distributed reaction regime.

Download Full-text