Experimental heat transfer in supercritical water flowing inside channels (survey)

Biofuels are liquid or gaseous fuels that are predominantly produced from biomass for transport sector applications. As biofuels are renewable, sustainable, carbon neutral and environmentally benign, they have been proposed as promising alternative fuels for gasoline and diesel engines. This paper reviews state-of-the-art application of the supercritical fluid (SCF) technique in biofuels production that includes biodiesel from vegetable oils via the transesterification process, bio-hydrogen from the gasification and bio-oil from the liquefaction of biomass, with biodiesel production as the main focus. The global biofuel situation and biofuel economics are also reviewed. The SCF has been shown to be a promising technique for future large-scale biofuel production, especially for biodiesel production from waster oil and fat. Compared with conventional biofuel production methods, the SCF technology possesses a number of advantages that includes fast kinetics, high fuel production rate, ease of continuous operation and elimination of the necessity of catalysts. The harsh operation environment, i.e. the high temperature and high pressure, and its request on the materials and associated cost are the main concerns for its wide application.

Supercritical fluids technology for clean biofuel production

Dimensionless parameters in stability analysis of heated channels with fluids at supercritical pressures

Corrosion behavior of Hastelloy C-276 in supercritical water

The corrosion behavior of a ferritic/martensitic steel P92 exposed to supercritical water (SCW) at 500–600 °C and 25 MPa was investigated by means of gravimetry, scanning electron microscope/energy dispersive X-ray spectroscopy and X-ray diffraction. A dual-layered oxide scale, which was mainly composed of an outer magnetite layer and an inner magnetite/spinel-mixed layer, formed on P92. The initial oxide scale was rather porous, while the porosity decreased with an increase of exposure time. Oxidation rates at three different temperatures followed the parabolic law. The oxidation at 600 °C was so severe that cracks occurred along grain boundaries in the oxide scale. A probable corrosion mechanism for P92 exposed in SCW was proposed based on the above observations, focusing on oxide formation by oxygen absorption without any metallic dissolution.

R. Kyrki-Rajamäki

Papers

High performance light water reactor