Energetic improvement of supercritical water hydrolysis process of biomass

In this research, the heat and pressure integration possibilities of the supercritical water hydrolysis process are analyzed. The main objective is to improve the global energetic efficiency and therefore reduce the consumption of utilities.

Fig 1. Supercritical Water Hydrolysis: Process simulation.

The research is focused on the substitution of the expansion valve which is able to stop the reaction in milliseconds avoiding the loss of selectivity. This device is not energetic efficient as pressure is dissipated and the enthalpy of the stream which is expanded is not used in the generation of work as in the case of a turbine. The starting point for the analysis is the combination of the hydrolysis process with a gas turbine whose flue gases provides the required thermal energy to heat up the stream of pressurized water which becomes then supercritical and is used in the hydrolysis reactor. The objective is the substitution of the gas turbine by a more environmental friendly device which would achieve a greater degree of independency of fossil fuels in the process. Moreover, if the valve is substituted, heat of a higher quality is also available. This extra energy, would allow heating up the pressurized feed stream ina simple heat exchanger reducing the consumption of fuel in the boiler.

In the supercritical hydrolysis process of biomass, reaction conditions are really extreme (T=400ºC, P = 250 bara). In order to achieve a high selectivity in the products (around 99%), the residence time in the reactor varies in the order of milliseconds. For this reason and in order to perform accurate predictions of the variations of the physical properties in this range of time, CFD (Computational Fluids Dynamics) simulations are carried out. CFD is a powerful tool which simulates fluid flow with a high degree of accuracy. With this tool it is possible to analyze new configurations of mixers and splitters which will redesign the reactor improving the global efficiency of the process.

Fig 2. Heat and Pressure integration analysis: CFD modeling.

Luis Vaquerizo

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