Supercritical Water Oxidation of Solid Particulates

Abstract

In the application of supercritical water oxidation (SCWO) to the treatment of aqueous solid wastes, particle size will be an important processing parameter. The particle size will impact feed preparation requirements such as slurry concentration, pumping requirements, and, in terms of the destruction of the solid particles, rate of reaction and reactor size. To address these issues, an experimental research program was undertaken to evaluate the effect of particle size on the reaction kinetics in SCWO of solid particulates (wheat straw and cellulose particles in this case). The experiments also included evaluation of the effects of temperature, pressure, and agitation rate. A two-step reaction mechanism was revealed, with a very rapid initial dissolution period followed by a longer particle reaction period. Empirically based mathematical relationships were developed that can be used for SCWO system design.

Hydrothermal ethanol flames in Co-flow jets

“…The primary products of this oxidation mechanism are carbon dioxide and water, with the inorganic material precipitated out of solution as salt or converted into acids which can be neutralized in the effluent stream. SCWO is a promising technology [5] for processing solid entrained liquid waste streams since (i) pre-drying of waste is not required, (ii) product streams are benign, microbially inert, and easily reclaimed, (iii) organic waste conversion is complete and relatively fast, and (iv) with proper design and operation, reactions can be self-sustaining. In addition, because of the absence of inter-phase reactant transport due to the single phase nature of SCWO reactions, reaction timescales are greatly reduced and many of the complications associated with two-phase transport and processing in reduced gravity environments are eliminated which is an advantage for space missions.…”

Effluent recirculation enables near-complete oxidation of organics during supercritical water oxidation at mild conditions: A proof of principle

“…80% for SCWO operated at a residence time of ca. 20 s, 382 C and an OER as high as 10.0 (Pisharody et al, 1996).…”

“…The formation of solids could inhibit organics from subsequent oxidation (Zhang et al, 2018). At OERs between 1.5 and 10.0, efficiencies close to 100% can be reached depending on other parameters, like the residence time (Pisharody et al, 1996;Zhang et al, 2013;Gong et al, 2016). The synergy of elevated operating temperatures and OERs enhances the oxidation of the recalcitrant intermediates, like acetic acid, formed during the SCWO of organic carbon (Meyer et al, 1995;Jin et al, 2001;Portela et al, 2001).…”

“…The hypothesis was investigated for cellulose and lignin being the two most abundant molecules in nature (Pisharody et al, 1996;Drews et al, 2000;Fedyaeva et al, 2019), and for acetic acid being a model compound for soluble recalcitrant intermediates (Mizuno et al, 2000;Cabeza et al, 2011). As a proof-of-principle, the hypothesis has been tested in this work in a semi-continuous manner, as to simulate the recirculation of effluent, and for the convenience in sample analysis.…”

A techno-economic assessment of the potential for combining supercritical water oxidation with ‘in-situ’ hydrothermal synthesis of nanocatalysts using a counter current mixing reactor

“…destruction of the contaminants whilst simultaneously producing nanomaterials that can act as catalysts to increase the oxidation kinetics. Certainly catalysts could be added to the contaminant flow prior to the rapid heating and oxidation phase, but this would mean pumping particulate slurries into the system which potentially create new issues with settling [34], poor dispersion [35] and pump head wear [36].…”