Abstract
Based on experiments of biomass gasification in supercritical water, this paper presents the first power cycle using wet biomass as a fuel. In this process biomass (22 wt% in water) is pumped up to 25 MPa in an extruder-feeder and heated up to 600°C in the gasifier. There it is almost completely gasified into a medium heating value gas (15 MJ/kg) after about 30s residence time. The applied catalyst can be different types of charcoal or activated carbon. The output composition is assumed to be the one from the experiments of M.J. Antal et al. from the Hawaii Natural Energy Institute. The syngas is cleaned off ash and tar in a wet scrubber, before it is expanded, and used in a gas turbine for power production. A bottoming cycle converts the remaining heat in the exhaust gases into power.
The process is simulated with ASPEN Plus. The efficiency of this biomass integrated-supercritical gasifier / combined cycle (BISG/CC) is calculated to be 42%. Compared to the efficiency of conventional BIG/CC processes at lower pressures it is competitive. The fact that this process is the first of its kind and that it requires advanced technology, makes it unfeasible right now. Nevertheless the idea of biomass gasification in supercritical water is very promising and should be further studied.
Bachelor Thesis; Dartmouth College (1997)