Proposal and evaluation of a near-zero carbon emissions hydrogen production system coupled with photovoltaic, photothermal and coal gasification

Significant attention has been given to achieving near-zero carbon emissions via the efficient and clean synergistic conversion of solar energy and coal. This study proposes a system for hydrogen production coupled with photovoltaic, photothermal and coal gasification. Its distinctive feature lies in the combustion of residual purge gas, obtained after separating hydrogen from hydrogen-rich synthesis gas, with pure oxygen from electrolyzed water. Combustion with pure oxygen results in carbon dioxide and steam as the only products, enabling carbon dioxide separation and capture through simple condensation, thereby achieving near-zero carbon emissions. The findings indicate that the overall system achieves exergy and energy efficiencies of 38.47 % and 36.66 %, respectively, representing enhancements of 6.64 and 6.33 percentage points over the baseline system. In the near-zero emissions system, hydrogen chemical energy is 997.69 MW, which is an increase of approximately 20.86 % over the 825.46 MW produced by the baseline system. Furthermore, to validate the feasibility of oxygen and hydrogen production through water electrolysis, a 1 kW high-temperature solid oxide electrolysis experimental platform is constructed to carry out the experimental research. The experimental results reveal that within the electrolysis temperature range of 650–800 °C, as the current density increases from 0.03 to 0.56 A/cm2, the electrolysis voltage of a single-cell stack increases from 0.96 V, 0.94 V, 0.93 V, and 0.89 V to 1.96 V, 1.75 V, 1.69 V, and 1.69 V. Additionally, the conversion rate of the water electrolysis reaction also increases. This work provides a clean, efficient, and near-zero carbon solution approach for the thermochemical complementary use of coal with solar energy.