Supercritical water oxidation for energy production by hydrothermal flame as internal heat source. Experimental results and energetic study

Abstract

This work presents experimental and model results from a new configuration of a cooled wall reactor working with two outlets: an upper outlet through which a salt-free hot effluent (500 -600 • C) is obtained and a lower outlet through which an effluent at subcritical temperature dissolving the precipitated salts is obtained. Different flow distributions were tested in order to find the best elimination conditions. Total organic carbon removal over 99.99% was obtained at injection temperatures as low as room temperature, when the fraction of products leaving the reactor in the upper effluent is lower than 70% of the feed flow. The performance of the reactor was tested with the oxidation of a recalcitrant compound such as ammonia, using isopropyl alcohol as co-fuel.Removals higher than 99% of N-NH + 4 were achieved in both effluents, working with temperatures near 700 • C. Slightly better eliminations were obtained in the bottom effluent because its residence time in the reactor is longer. The behavior of the reactor working with feeds with a high concentration of salts was also tested. Feeds containing up to 2.5% wt Na 2 SO 4 could be injected * Corresponding author. Phone: +34 983423166Email addresses: palabreras@gmail.com (Pablo Cabeza), joao.deq@gmail.com (Joao Paulo Silva Queiroz), mcriado_sastre@hotmail.com (Manuel Criado), crisbaterna@gmail.com (Cristina Jimenez), mdbermejo@iq.uva.es (Maria Dolores Bermejo), fidel@iq.uva.es (Fidel Mato), mjcocero@iq.uva.es (Maria Jose Cocero) 1 Present address: Dept. of Chemical Engineering -Universidade Federal de PernambucoProf. Artur de Sá, s/n, -Cidade Universitária -50740-521, Recife, PE -Brazil Preprint submitted to Energy March 2, 2015 in the reactor without plugging problems and a total organic carbon removal of 99.7% was achieved in these conditions. Upper effluent always presented a concentration of salt lower than 30 ppm. Finally, a theoretical analysis of the energy recovery of the reactor working with two outlets was made.

Supercritical water processes: Future prospects

“…Additionally, oxygen is the most commonly used oxidant in order to reduce the air compressor energy consumption. The implementation of hydrothermal flames as the internal heat source in the supercritical water oxidation processes opens up the opportunity for the SCWO to achieve an energetically selfsufficient process, and to produce energy [51]. • The reduced residence times (in the order of milliseconds) encourage the construction of smaller reactors (micro-combustors).…”

“…As the reactor size decreases significantly, the operation with air as the oxidant could be a more economical alternative. On an industrial scale, it could also be possible to implement oxidation with air, as opposed to the conventional SCW facilities that operate with cryogenic oxygen [51].…”

“…We have calculated that it is possible to operate with air as the oxidant, or to use enriched air through the direct expansion of the effluent in a turbine, and thus produce net energy [51][52][53]. Even when the option of direct expansion of the effluent is, by far, the most energetically efficient, it will be not applicable in the short term.…”

“…Thus, technical issues concerning the expansion of two-phase streams prevent the effective implementation of direct expansion in the short term. Furthermore, the detailed design of a dedicated, effective turbine would be costly and would take some time to implement [51][52][53][54].…”

Review on an Advanced Combustion Technology: Supercritical Hydrothermal Combustion

“…For example, to explore the hydrothermal spallation drilling of methanol [24,25] and ethanol [26], the ETH water-cooled hydrothermal burner (WCHB) has been upgraded to the fourth generation [23,27], and equipped with advanced measuring [22] and ignition devices [23]. Taking methanol [28,29] and isopropanol [17,[30][31][32][33][34][35][36][37] as the auxiliary fuels, the University of Valladolid has optimized their TWRs [33,37] to study the characteristics and effects of hydrothermal flame enhanced SCWO treatment for recalcitrant pollutants. Xi'an Jiaotong University has been gradually expanding its research from coal [20] to high-concentration textile wastewater [38] to methanol [39,40], sludge [38] and quinoline [41] and a series of other fuels in its self-designed reactor [42].…”