Effects of the secondary air inlet position and gasifying agents on grape branch gasification in an improved downdraft gasifier

Abstract

Gasification experiments on grape branches were carried out in a self-improved downdraft gasifier at 800 °C, under atmospheric pressure, using air, steam, and air–steam as gasifying agents. The effects of the secondary air inlet position (0–75 cm beneath the reactor's top), ER (0.1–0.3), S/B mass ratio (0.5–2.5 g g⁻¹), and S/B mass ratio (0.3–1.2 g g⁻¹) with ER = 0.1 on the characteristics of biomass gasification were investigated. The results suggested that when the secondary air inlet position is 45 cm beneath the reactor's top, the gas yield, combustible gas content and CGE all reached the maximum value. In this case, a high-temperature zone with the largest volume and uniform temperature formed in the oxidation and reduction zones for better tar cracking and reduction reactions. The highest CGE of 59.14% was achieved when using air as the gasifying agent with the ER at 0.2. Increasing the S/B mass ratio causes an increase in H₂ content, gas yield, CCE, and CGE, but a decrease in CO content and LHV. Due to the low loading rate of the gasifier, the negative effects of steam were not observed in the S/B mass ratio range of 0.5 to 2.5 g g⁻¹. The air addition releases extra heat by boosting oxidation reactions, resulting in a greater gas yield, CCE, CGE, and H₂ yield than pure steam gasification. It is advised that the ER be kept lower or equal to the optimum value and S/B mass ratio slightly higher than the optimum value to maximize H₂ production.