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 H-2, 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.