Investigation on a Supercritical Water Gasification System with CO₂ as Transporting Medium

As a benign energy vector, hydrogen has been discussed for a long time. Supercritical water gasification was one of good ways to produce hydrogen. However, supercritical water gasification system with H₂O transporting was energy consuming in the process of heating due to the high specific heat of H₂O. A new supercritical water gasification system was established in this paper with supercritical CO₂ as medium instead. Phenolic plastics were used as the sample transported by CO₂. Production yields, energy flow and exergy flow of the system were collected and the influence of temperature, pressure, gasification concentration and transporting concentration was investigated. Mass flow of H₂O input into the reactor was 1000 kg/h. The typical condition was as follow: temperature 923.15 K, pressure 23 MPa, and the mass ratio of water, sample and transporting medium was 100:9:9. Yield of H₂, CH₄, CO and CO₂ at this condition was 8.1 kg/h, 39.6 kg/h, 6.6 kg/h and 137.5 kg/h, respectively. Similar system with H₂O transporting was used to compare with the supercritical CO₂ transporting system and proved that system with CO₂ transporting could reduce the loss of both energy and exergy while the reduce of each gas production yield was less than 0.1 mol/mol.