Sylvain Rodat

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

Abstract 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 CH4 dissociation above 1850 K (CH4 conversion over 90%) and the key influence of the gas residence time. Simulations are performed to predict the conversion rate of CH4 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 CH4, and the yield to H2 are determined with respect to reaction temperature, inlet gas flow-rates, and feed gas composition. The longer the gas residence time, the higher the CH4 conversion and H2 yield, whereas the lower the amount of acetylene. A CH4 conversion of 99% and H2 yield of about 85% are measured at 1880 K with 30% CH4 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 H2 yield.

Experimental Evaluation of Indirect Heating Tubular Reactors for Solar Methane Pyrolysis

Solar thermal pyrolysis of natural gas is studied for the co-production of hydrogen, a promising energy carrier, and Carbon Black, a high-value nano-material, with the bonus of zero CO2 emissions. A 10 kW multi-tubular solar reactor (SR10) based on the indirect heating concept was designed, constructed and tested. It is composed of an insulated cubic cavity receiver (20 cm side) that absorbs concentrated solar irradiation through a quartz window by a 9 cm-diameter aperture. The solar concentrating system is the 1 MW solar furnace of CNRS-PROMES laboratory. An argon-methane mixture flows inside four graphite tubular reaction zones each composed of two concentric tubes that are settled vertically inside the cavity. Experimental runs mainly showed the key influence of the residence time and temperature on the reaction extent. Since SR10 design presented a weak recovery of carbon black in the filter, a single tube configuration was tested with an external plasma heating source. Complete methane conversion and hydrogen yield beyond 80% were achieved at 2073K. Hydrogen and carbon mass balances showed that C2H2 intermediates affect drastically the carbon black production yield: about half of the initial carbon content in the CH4 was found as C2H2 in the outlet gas. Nevertheless, the carbon black recovery in the filtering device was improved with this new configuration. Data are extrapolated to predict the possible hydrogen and carbon production for a future 50 kW solar reactor. The expected production was estimated to be about 2.47 Nm3/h H2 and 386 g/h carbon black for 1.47 Nm3/h of CH4 injected.

A high temperature drop-tube and packed-bed solar reactor for continuous biomass gasification

Biomass gasification is an attractive process to produce high-value syngas. Utilization of concentrated solar energy as the heat source for driving reactions increases the energy conversion efficiency, saves biomass resource, and eliminates the needs for gas cleaning and separation. A high-temperature tubular solar reactor combining drop tube and packed bed concepts was used for continuous solar-driven gasification of biomass. This 1 kW reactor was experimentally tested with biomass feeding under real solar irradiation conditions at the focus of a 2 m-diameter parabolic solar concentrator. Experiments were conducted at temperatures ranging from 1000°C to 1400°C using wood composed of a mix of pine and spruce (bark included) as biomass feedstock. The aim of this study was to demonstrate the feasibility of syngas production in this reactor concept and to prove the reliability of continuous biomass gasification processing using solar energy. The study first consisted of a parametric study of the gasification conditions to obtain an optimal gas yield. The influence of temperature and oxidizing agent (H2O or CO2) on the product gas composition was investigated. The study then focused on solar gasification during continuous biomass particle injection for demonstrating the feasibility of a continuous process. Regarding the energy conversion efficiency of the lab scale reactor, energy upgrade factor of 1.21 and solar-to-fuel thermochemical efficiency up to 28% were achieved using wood heated up to 1400°C.Biomass gasification is an attractive process to produce high-value syngas. Utilization of concentrated solar energy as the heat source for driving reactions increases the energy conversion efficiency, saves biomass resource, and eliminates the needs for gas cleaning and separation. A high-temperature tubular solar reactor combining drop tube and packed bed concepts was used for continuous solar-driven gasification of biomass. This 1 kW reactor was experimentally tested with biomass feeding under real solar irradiation conditions at the focus of a 2 m-diameter parabolic solar concentrator. Experiments were conducted at temperatures ranging from 1000°C to 1400°C using wood composed of a mix of pine and spruce (bark included) as biomass feedstock. The aim of this study was to demonstrate the feasibility of syngas production in this reactor concept and to prove the reliability of continuous biomass gasification processing using solar energy. The study first consisted of a parametric study of the gasification...