A novel system for high-purity hydrogen production based on solar thermal cracking of methane and liquid-metal technology: Thermodynamic analysis

A novel zero-carbon-emission system for producing high-purity hydrogen and carbon nanoparticles was proposed in this paper. Concentrated solar energy as the only energy source was utilized in a cascaded way. That is to say, concentrated solar energy was first used to provide heat with high temperature for the thermal cracking of methane, and then used to drive the heat-to-power cycle for the output of mechanical work or electricity. The produced mechanical work or electricity was used for separating hydrogen from the unreacted methane based on the membrane technology. The performances of the whole system and its major facilities were studied through the first law thermodynamics. The results showed that, receiver loses about 35% of the input energy due to the high operating temperature, and about 59% of the input energy is used for the purification of hydrogen. The system performance is mainly affected by four key parameters including the heat loss of receiver, the conversion rate of methane in the reactor, the operating pressure of the membrane separator, and the heat-to-power rate of the power generation cycle. Decreasing the operating pressure of the membrane separator is one of the most efficient ways to improve the system efficiency. With the partial pressure of hydrogen in the retentive-side of separator decreasing from 791 to 200 kPa, the ideal system efficiency increases from 0.4 to 0.8.