A green desuperheater for an energetic efficient alternative to the decompression valve in biomass supercritical water ultrafast hydrolysis process

Abstract

The supercritical water hydrolysis (SCWH) of biomass (P=250bara & T=400ºC) allows directly obtaining sugars, which are high value products in the chemical industry, in reaction times lower than 0.2s. The process is characterized by the high selectivity values which can be obtained controlling the reaction time. Reaction kinetics show that glucose degradation is only retarded at temperatures below 250ºC. Therefore, in the traditional SCWH process, degradation control is achieved expanding the hydrolysis stream in a valve which instantaneously cools down the products. Although the selectivity values obtained are greater than 96%, the pressure is wasted on the valve expansion decreasing the global energetic efficiency of the process. In this paper a CFD simulation of a desuperheater which mixes the hydrolysis product with pressurized cooling water is presented. The temperature of the hydrolysis stream decreases below 250ºC in cooling times lower than 20ms maintaining the selectivity value over 93%. Furthermore, the pressure remains at 250bara increasing the global energetic efficiency of the process.Keywords: Biomass, Hydrothermal Medium, CFD Model, Water Turbine. Highlights:-The hydrolysis product is cooled down in less than 20ms.-The reduced cooling times allows obtaining a selectivity value of 93%.-The hydrolysis pressure, 250bara, is maintained after controlling the reaction.-Energetic efficiency increased due to heat and pressure integration possibilities.

Tailoring the Structure and Morphology of Low-Molecular-Weight Cellulose Produced during Supercritical Water Hydrolysis

“…The first solution is to further concentrate the product using a flash separator . The second solution is to use a so-called desuperheater instead of a needle valve to stop the reaction, which can in theory lower the temperature while keeping the pressure high, thus limiting the energy loss during depressurization …”

Production of saccharides from sugar beet pulp by ultrafast hydrolysis in supercritical water

“…In a 301 previous study, both processes were compared for sugar cane bagasse hydrolysis and it was 302 concluded that SCW technology allowed reducing the total investment of the biorefinery 303 and the water intake (Albarelli et al, 2017). Moreover, several alternatives were proposed 304 to improve the energetic efficiency of the FASTSUGARS process, from the coupling of the 305 ultrafast reactors to commercial combined heat and power (CHP) systems (Cantero et al,306 2015c) to the use of a green desuperheater as an alternative to decompression valve 307 (Vaquerizo & Cocero, 2018). So that, the improved yields obtained in the case of SBP and 308 the lower cost associated to SCW technology, proved that FASTSUGARS process is a 309 promising and versatile technology to convert biomass into sugars in a sustainable way.…”

Supercritical water processes: Future prospects

“…It is possible to reduce the operation cost by improving the energy and work recovery, for example, by recovering the work associated with the depressurization, and implementing energy integration [39].…”