Effect of reactor volume on autothermal natural gas conversion and allothermal gasification of organic waste by ultrasuperheated steam

The pulsed detonation gun (PDG) technology was applied for autothermal high-temperature conversion of natural gas and allothermal oxygen-free gasification of liquid/solid organic wastes with ultrasuperheated steam (USS) at atmospheric pressure using two flow reactors of significantly different volumes: 100 and 40 l. The PDG operated at a frequency f of 1 Hz on a mixture of natural gas and oxygen. Waste machine oil and sawdust with a moisture content of 10 to 30 %(wt.) were used as liquid and solid organic wastes. It was expected that a decrease in the volume of the flow reactor from 100 to 40 l, on the one hand, should not affect the natural gas conversion and, on the other hand, could lead to an increase in the gasification temperature in the flow reactor and, accordingly, to an increase in the quality of the product syngas (H₂ + CO). As expected, complete conversion of natural gas to syngas was achieved in the PDG with H₂/CO and CO₂/CO ratios of 1.25 and 0.25 which were independent of the reactor volume. Liquid and solid wastes were converted in the flow reactors into gas containing H₂, CO, CO₂, and CH₄. The steady-state values of the H₂/CO and CO₂/CO ratios in the syngas obtained from waste machine oil were 0.8 and 0.5 in the 100-liter reactor and 0.9 and 0.2 in the 40-liter reactor, respectively, which indicates an expected increase in the syngas quality. At the same time, the maximum mass flow rate of feedstock in the 40-liter reactor increased by a factor of more than 4 compared to the 100-liter reactor. The steady-state values of the H₂/CO and CO₂/CO ratios in the syngas obtained from a batch of sawdust of a fixed mass (2 kg) were 0.5 and 0.8 for both reactors and the gasification time in both reactors was about 5–7 min. It has been shown that the measured volume fractions of H₂, CO, and CO₂ in the syngas produced both by autothermal high-temperature conversion of natural gas and by allothermal oxygen-free gasification of liquid/solid organic wastes in the USS medium at atmospheric pressure and $f=1$ Hz are almost independent of the feedstock and reactor volume which is associated with high values of the local instantaneous gasification temperature.