System modeling of supercritical water gasification processes: Thermo-fluid one-dimensional modeling in Modelica language

System modeling of supercritical water gasification processes: Thermo-fluid one-dimensional modeling in Modelica language

Schönlein, C.M.

De Jong, W. (mentor)
Yakaboylu, O. (mentor)
Harinck, J. (mentor)

Mechanical, Maritime and Materials Engineering

Process and Energy

Sustainable Process and Energy Technology

2016-05-03

Supercritical water gasi?cation (SCWG) is a conversion process for wet biomass feedstock into synthetic natural gas at conditions above the critical point of water (220.9 bar and 374.15 °C). A high energy and conversion ef?ciency of the process is achieved by using supercritical water as a reaction medium which avoids the necessity of an energy-intensive drying process. Moreover, heat recovery is applied in order to minimize the system energy input while sustaining conversion-supporting process conditions such as heating rates and residence times. A literature study was done to review the theory of convective heat transfer of water at supercritical pressure, free convective heat transfer of cylindrical geometries surrounded by air, friction pressure losses of internal channel ?uid ?ows and ?uidization behavior of ?uidized bed at supercritical condition. In order to support design efforts to increase the performance of a SCWG process setup, a model library for a steady-state one-dimensional thermo-?uid system model assuming non-reacting pure water as ?uid medium for the relevant process components (heat exchanger, ?uidized bed reactor and heater) was developed in Dymola modeling environment using Modelica language. The models include different heat transfer and hydrodynamics phenomena while they also account for the in?uence of biomass conversion on the thermal behavior of the system using enthalpy corrections provided by a kinetic AspenPlus® model. The range of investigated process operating conditions includes temperature levels of 20-600 °C, pressure levels of 220-300 bar and mass ?ow rates of 35-1000 kg/h. To validate the model, experiments have been performed with a research dedicated setup (SCWG-100) developed by Gensos B.V.. The acquired data allowed for a qualitative and quantitative validation of the preheater section, heat exchanger operating at supercritical pressure and trans-critical temperature conditions. Moreover, one data-set of the novel scaled-up gasi?cation unit (SCWG-500) with patented ?uidized bed reactor and advanced heat recovery was used for further model validation. The main focus for the validation was on the various preselected heat transfer correlations for supercritical water of which the correlation of Yamagata et al. caused the best alignment with the measured data predicting the inlet-outlet temperatures with a mean error of 1.9 K. The validation of the enthalpy correction approach showed good agreements with the measurement data. It was concluded that 1D modeling is found to well-predict the thermal heat transfer behavior at given conditions on system level. Subsequently, an extensive heat exchanger sensitivity analysis was performed with respect to the resulting heat exchanger effectiveness. A similarly comprehensive study on the heat exchanger behavior at supercritical pressure and trans-critical temperature levels is not available in literature. Furthermore, simulations of the SCWG-100 and SCWG-500 setups were performed in system con?guration at multiple relevant operating conditions. The expected effect of heat transfer enhancement in the reactor due to the presence of bed particles was successfully investigated by introducing a heat transfer coef?cient enhancement factor. The results provide essential information on potential design changes to further optimize the thermal behavior with respect to conversion condition criteria. The heating rates of both setups showed good results compared to other studies concluding heating rates constraints in order to avoid tar/char formation and therefore increase the carbon gasi?cation ef?ciency. The residence times predicted by the models indicate potential for further optimization which has to be experimentally con?rmed for the variety of different biomass feedstock and concentration.

supercritical water gasi?cation
supercritical heat transfer
Modelica
heat recovery
supercritical ?uidized bed
biomass

http://resolver.tudelft.nl/uuid:6013de71-1dda-4425-bc25-de7f9bfccb99

Student theses

master thesis

(c) 2016 Schönlein, C.M.