Abstract
A continuous supercritical water oxidation reactor was designed and constructed to investigate the conversion of a feces simulant without the use of a co-fuel. The maximum reactor temperature and waste conversion was determined as a function of stoichiometric excess of oxygen in order to determine factor levels for subsequent investigation. 48% oxygen excess showed the highest temperature with full conversion. Factorial analysis was then used to determine the effects of feed concentration, oxygen excess, inlet temperature, and operating pressure on the increase in the temperature of the reacting fluid as well as a newly defined non-dimensional number, NJa representing heat transfer efficiency. Operating pressure and stoichiometric excess oxygen were found to have the most significant impacts on NJa. Feed concentration had a significant impact on fluid temperature increase showing an average difference of 46.4°C between the factorial levels.
Highlights
(Kruse, 2008; Marrone, 2013; Vadillo et al, 2013)
Recent studies into the behavior of hydrothermal flames in supercritical water oxidation (SCWO) have demonstrated the capacity to operate at near complete conversion with very short residence times (Bermejo and Cocero, 2006)
Cabeza et al (2011) extended this work to study the destruction of recalcitrant compounds, acetic acid and ammonia, under hydrothermal flame conditions using isopropyl alcohol as a co-fuel demonstrating that a minimum of a 2% IPA solution must be added to achieve ignition
Summary
The use of supercritical water for processing of these carbon residues has shown promising developments in recent years prompting an increased focus on supercritical water oxidation as a potential wastewater, sludge, or sewage treatment method Demonstrating this focus is the number of companies who have, or are currently attempting to operate this process at a commercial scale including the Aquacritox process, General Atomics, Hanwha, and SRI International (Marrone, 2013). The work presented in the current study expands on the knowledge developed by the University of Valladolid by potentially operating under the hydrothermal flame regime without the need of an alcohol co-fuel which is a significant limitation of their work In current practice, both commercially and at the bench top scale, a variety of both organics and some inorganics are being processed using SCWO. These experiments served to define the optimal operating conditions for process variables that will later be used to design and operate a SCWO unit that has a capacity on the order of 100 kg/day of dry solids
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