Comparative life cycle energy, water consumption and carbon emissions analysis of deep in-situ gasification based coal-to-hydrogen with carbon capture and alternative routes

In order to clarify the competitiveness of deep in-situ gasification based coal-to-hydrogen (deep IGCtH) in the context of carbon-constrained development, based on simulation results, the energy, water consumption and carbon emissions were quantitatively assessed and compared with large-scale fossil energy based routes, using life cycle assessment model from feedstock to hydrogen that covers process energy production and utilization. The results indicate when producing 1 kg of hydrogen, deep IGCtH requires 349.55 MJ of external primary fossil energy input and generates 30.47 kg CO2-eq of emissions, which are 24.88% and 16.32% lower than 465.34 MJ and 36.41 kg CO2-eq of Lurgi surface gasification based coal-to-hydrogen (Lurgi SGCtH), and also 7.38% lower than 377.39 MJ of coke-oven gas-to-hydrogen (COGtH). Furthermore, deep IGCtH can not only reduce coal consumption by 19.7% compared with Lurgi SGCtH, but also reduce oil consumption required to obtain process energy by 81.84%, which also reaches 80.09% compared with COGtH. Due to the high methane content, the exhaust gas and flue gas of deep IGCtH contributes 9.78 kg and 8.84 kg of CO2 emissions, and under the CO2 capture rate of 80%, the carbon emissions adopting exhaust gas and flue gas simultaneous capture reach 25.88 kg CO2-eq, higher than the 23.1 kg CO2-eq adopting exhaust gas single capture, of which waste gas only contributes 3.87 kg of emissions, but electricity consumption causes 15.11 kg CO2-eq of emissions, indicating the key to adopting such scheme to achieve further emissions reduction lies in reducing emissions caused by electricity consumption.