Improved syngas quality with biochar at mild conditions in a two-stage gasifier

Demand for syngas produced by gasifiers is increasing but its required quality varies depending on its use. Several technologies and operating conditions are therefore employed. For this reason, a two-stage gasifier was employed in this study to understand the influence of biochar at mild operating conditions for improving the syngas quality. This is of high relevance in several gasification and combustion applications, where the syngas goes through an increasing hot char bed and where reactions occur even in mild conditions. Wood pellets were gasified in a primary reactor at 725 °C with a steam to fuel ratio of 1.11. Wood, shrubland and rice husk chars were introduced in a secondary reactor as catalytic beds for syngas enhancement, with temperatures equal or lower than 800 °C and gas residence times in the secondary char bed of 0.27–0.54 s. Wood char produced the most H 2 , reduced tar content and CO concentration by improved water–gas shift, tar reforming and char gasification reactions. Rice husk reduced tar but barely affected the non-condensable gas composition and underwent almost no char gasification. Shrubland produced H 2 and reduced CO concentration as wood, but the tar reduction was lower. Increasing temperature and bed height improved water–gas shift, tar reforming and char gasification. The trifecta wood char, high temperature and bed height resulted in the best conditions for improving gas quality, obtaining up to a 35 % increase in H 2 /CO and 69 % tar reduction compared to the no catalytic bed reference case, which is especially relevant for specific applications and indicates positive catalytic biochar performance even at these mild conditions.