Conversion of tar in supercritical water/oxygen fluid with soot suppression

Abstract

An autothermal mode of tar conversion was implemented in a vertical tubular reactor. The pressure was 30 MPa; the tar and water flows were 4.9 and 6.9 g/min, respectively; the oxygen flow varied: 0, 2.9, 4.5 and 5.8 g/min. The tar was supplied from above, at the first stage into a counter-flow of supercritical water (SCW) and at the subsequent ones into a flow of SCW/O₂ fluid. The high-molecular sedimentary layer (HSL) that formed at the first stage was replenished continuously at the subsequent stages, consisted of tar components depositing on the bottom of the reactor and was suppressing formation of soot. The autothermal mode of the process was achieved due to heat release in the combustion of the lower part of the HSL in the SCW/O₂ fluid. With increased O₂ flow, the power of ohmic heaters was reduced to zero and the reactor wall temperature increased from the initial 723 K to 818 K. Elemental and mass spectrometric analyses of the liquid and volatile conversion products collected at the outlet of the reactor, as well as of the solid conversion residue taken from the reactor, enabled determination of their amount and composition. This in turn allowed us to write down the gross reaction of tar conversion in the SCW/O₂ fluid and determine the characteristics of the equivalent fuel and the thermal effects of its oxidation