Hydrogen production from oilfield wastewater by gasification in supercritical water with a continuous system

[Display omitted] •Quantitative results of coke supported the total gasification of oilfield wastewater.•Continuous H2 production was achieved at a wide concentration range of 20–40 wt%.•Optimal operating parameters for the continuous system were obtained.•The CE of 96% and the H2 yield of 51.03 mol/kg were obtained. Multi-component supercritical thermal fluid (MCSCTF) generated based on supercritical water gasification (SCWG) technology can significantly enhance heavy oil recovery. In this paper, the performance of oilfield wastewater SCWG was systematically investigated with a continuous system. Thermodynamic analysis showed that total gasification of oilfield wastewater in supercritical water (SCW) was feasible due to the inhibition of coke generation. The addition of Na2CO3 or K2CO3 can facilitate steam reforming and water–gas shift reactions to achieve high H2 yields and carbon gasification efficiency (CE). The generation of the abundant gas was attributed to the rapid decomposition of the liquid products by free radical reactions at high temperatures. As the feedstock concentration increased, the oil–water emulsion structure may favor the intense pyrolysis reaction over the steam reforming reaction resulting in lower CE. The suitable ratio of emulsion to preheat water flow (1:5) can increase the heating rate of the feedstock and ensure the decomposition time of the intermediate products to obtain high CE (96%). The trends in the change of gas products at different operating parameters were supported by thermodynamic calculations. This work can provide the basis for the subsequent coupled hydrogen oxidation technology to generate MCSCTF.