Natural gas pyrolysis in double-walled reactor tubes using thermal plasma or concentrated solar radiation as external heating source

The thermal pyrolysis of natural gas as a clean hydrogen production route is examined. The concept of a double-walled reactor tube is proposed and implemented. Preliminary experiments using an external plasma heating source. are carried out to validate this concept. The results point out the efficient CH(4) dissociation above 1850 K (CH(4) conversion over 90%) and the key influence of the gas residence time. Simulations are performed to predict the conversion rate of CH(4) at the reactor outlet, and are consistent with experimental tendencies. A solar reactor prototype featuring four independent double-walled tubes is then developed. The heat in high temperature process required for the endothermic reaction of natural gas pyrolysis is supplied by concentrated solar energy. The tubes are heated uniformly by radiation using the blackbody effect of a cavity-receiver absorbing the concentrated solar irradiation through a quartz window. The gas composition at the reactor outlet, the chemical conversion of CH(4), and the yield to H(2) are determined with respect to reaction temperature, inlet gas flow-rates, and feed gas composition. The longer the gas residence time, the higher the CH(4) conversion and H(2) yield, whereas the lower the amount of acetylene. A CH(4) conversion of 99% and H(2) yield of about 85% are measured at 1880 K with 30% CH(4) in the feed gas (6 L/min injected and residence time of 18 ms). A temperature increase from 1870 K to 1970 K does not improve the H(2) yield.