J. Abeln

Hydrothermal gasification of biomass and organic wastes

Wet biomass and organic wastes can be efficiently gasified under hydrothermal conditions to produce a hydrogen rich fuel gas. New experiments in two tubular flow reactors and in two batch autoclaves with carbohydrates, with aromatic compounds, with glycine as a model compound for proteins and with real biomass are reported for different residence times, temperatures and pressures. It was found that at 600°C and 250 bar all compounds are completely gasified by addition of KOH or K2CO3, forming a H2 rich gas containing CO2 as the main carbon compound. Concentrations of CO, CH4 and C2–C4 hydrocarbons are low in the product gas (<1, ∼3 and <1 vol%, respectively). Carbon balances for the smaller flow reactor are closed to better than 96%. Ranges of product concentrations are given as estimated from experimental reproducibility. Some reflections for the engineering of a pilot plant are presented.

Supercritical Water Oxidation: State of the Art

The oxidation of harmful organic compounds contained in aqueous waste effluents known as supercritical water oxidation, SCWO, has been worked out since the 1980s. This highly efficient end of the pipe process operates at pressures and temperatures above 221 bar and 374°C, the critical point of water. R&D experience and the technological state including economical and regulatory aspects are reviewed and further R&D needs are discussed in this article. Future applications are also seen in coupling supercritical CO 2 extraction with oxidation to treat contaminated materials and in supercritical water gasification, SCWG, to convert biomass and organic wastes to hydrogen.

Supercritical Water Oxidation (SCWO) Using a Transpiring Wall Reactor: CFD Simulations and Experimental Results of Ethanol Oxidation

Supercritical Water Oxidation (SCWO) was studied at the Institute of Technical Chemistry, ITC-CPV. SCWO is a high-pressure-high-temperature process with high space-time yield to destroy organic hazardous compounds present in industrial waste effluents to form water and carbon dioxide. Heteroatoms were mineralized to the corresponding acids or salts; nitrous oxides formation was suppressed due to low oxidation temperatures. Results obtained in a tube reactor system showed destruction efficiency (D.E.) values close to 100% of the organic content, but indicate plugging and corrosion of the tube when treating salt and/or acid containing solutions. Hence, the application of SCWO process is limited. To enlarge the potential of SCWO process for industrial applications, new reactor concepts were developed. Among these, the transpiring wall reactor (TWR) concept is considered to have very good prospects to overcome these limitations. The TWR installed at ITC-CPV is designed for T = 630°C, P = 32 MPa, wastewater fl...

Hazardous Waste Disposal by Supercritical Fluids

In the presence of water or carbon dioxide in the supercritical state, organic materials can be oxidized by oxygen practically completely within seconds. The report contains descriptions of test rigs and experimental findings. Additional R&D work is necessary for technical-scale application in cleaning organically polluted liquid effluents.

Oxidation of organic material in supercritical water and carbon dioxide

Publisher Summary This chapter discusses the oxidation of organic material in supercritical water and carbon dioxide. The industrial application of the supercritical water oxidation (SCWO) process strongly depends on the solution of two major technical problems: the corrosion of the reactor material when halogenated compounds are processed and the precipitation of inorganic product salts plugging the reactor. The methods of supercritical extraction and of supercritical oxidation in carbon dioxide can favorably be integrated in one process if the extracted solute has to be disposed. Salt precipitation and corrosion are the technical key problems of the economical solution that make the SCWO process an important tool for the treatment of hazardous organic wastes. The development of a corrosion resistant material may take a time too long for industrial implementation in a competitive market situation.

Model and simulation of supercritical water oxidation

Publisher Summary This chapter describes a model for tubular flow supercritical water oxidation (SCWO) reactors and demonstrates the use of the model to understand time-dependent temperature instabilities. A simple model of lumped kinetics for SCWO included in the partial differential equations for temperature and organic concentrations allows to qualitatively simulate the dynamic process behavior in a tubular reactor. Process parameters can be estimated from measured operational data. The standard method of least-square fitting the model parameters from experimental data is only applicable if the deviation of estimated parameter-based model results from measured data can be explicitly calculated. To obtain the matrix of model error changes with the individual changes of each parameter for a series of time dependent data points as measured in a dynamic process requires the repeated solution of the model equations for every iterations of the estimation procedure. By using an integrated environment for data acquisition, simulation, and parameter estimation, it seems possible to perform an online update of the process parameters needed for the prediction of process behavior.