Effect of temperature and hydrogen on product distribution and evolution of char structure during pyrolysis of bituminous coal in a drop tube furnace

Abstract

This paper aims to investigate the hydropyrolysis behavior of pulverized bituminous coal in a drop-tube furnace (DTF) with a temperature of 800–1000 °C. The effects of temperature and hydrogen on the compositions (gases and tar) and the structure of products (char) were investigated. Hydropyrolysis between 800 and 1000 °C resulted in a high yield of methane, and tar production decreased with increasing temperature. Besides, the light components of tar, especially the naphthalene, were significantly increased with hydrogen. The methane yield firstly increased to a peak value of 72.83 ml/g(air-dried coal) at 900 °C and then decreased with increasing temperature during hydropyrolysis. Hydrogen significant improved the yield of gaseous hydrocarbon (C2H2, C2H4, and C2H6) when the temperature below 900 °C, while rarely change that at a higher temperature. At the temperature above 900 °C, the content of graphite in the hydropyrolysis char was lower than that of pyrolysis char in nitrogen. The graphite contents in the char decreased to a minimum at 950 °C and then gradually increased with increasing temperature. The char from hydropyrolysis has a higher condensation degree structure and higher saturation. The small aromatic molecules transformed into large aromatic molecules with increasing temperature under both pyrolysis and hydropyrolysis.