Le Dinh , C., Ngo Xuan , A. and Ngo Thanh , H. 2017. Movement of hot zone and an explanation of processes occurring inside a downdraft gasifier. Petrovietnam Journal. 6, (Jun. 2017), 45 - 52. DOI:https://doi.org/10.25073/petrovietnam journal.v6i0.226.