Studies of low-temperature pyrolysis characteristics of the binder cold-briquetted lignite-II: Three-phase pyrolytic products

Briquetting and pyrolysis technology is of crucial importance in the development and efficient multi-level use of low-rank pulverized lignite. The main aim is to study the influence of pyrolysis and entering temperature (350 °C-800 °C), heating rate (5 °C min−1 ∼ 30 °C min−1), residence time (0-140 min), and particle size (0.45 mm-30 mm) on the characteristics of pyrolytic products of binder cold-briquetted lignite (BCBL). Characterization of gas pyrolyzates, semi-char, and tar are characterized by Gas chromatography (GC), FTIR spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, and gas chromatography-mass spectroscopy (GC-MS). The results indicate that the residence time and pyrolysis temperature have little effect on the pyrolysis products, whereas, heating rate, the fast heating from high entering temperature and particle size show a crucial effect relatively. With increasing pyrolysis temperature, the effects on carbon, oxygen, hydrogen, nitrogen, and sulfur contents are studied. H2 and CH4 start evolving at 375-400 °C and their rates increase gradually. Various functional groups are partially removed during pyrolysis and the crystallinity of semi-char increases. As the pryolysis temperature increasing, the concentrations of CC/CH increase, whereas, that of CO, COO- and CO decrease, which was consistent with the results of FTIR spectra. The results reported in this work provide a theoretical and technical basis on comprehensive utilization of the low-rank pulverized coal.