多层流化床褐煤热解半焦特性与自燃倾向性抑制

Characterization and suppression of spontaneous combustion propensity of lignite char by multi-stage fluidized bed pyrolysis

为揭示多层流化床热解用于褐煤提质的技术优势,利用多层流化床热解实验装置在不同床层数的操作模式下连续进料制备半焦产品,并评价其特性与自燃倾向性。随着多层流化床床层数由单层增加为3层,半焦的燃点从369.2℃显著增大到459.6℃,自燃倾向性判定指数从880增大到1 953(1 200为转折点),表明褐煤半焦的自燃倾向性显著减低,由"自燃"转化为"不易自燃"。与单层流化床直接部分气化相比,经多层流化床(两层以上)的上部热解和底部部分气化,延长了煤在热解段的停留时间,所制备的褐煤半焦其挥发分含量大幅降低,表面官能团大部分被脱除,使得褐煤半焦的稳定性显著提高。

In order to reveal the technical advantages of the multi-stage fluidized bed pyrolysis for upgrading lignite,the characteristics and spontaneous combustion propensity of char from lignite pyrolysis in a multi-stage fluidized bed were investigated with respect to different numbers of bed stages and operating conditions. With the increase of the bed stage from one to three,the ignition temperature of the produced char increases from 369. 2 ℃ to 459. 6 ℃ and the index of spontaneous combustion propensity correspondingly increases from 880 to 1 953( 1 200 is the inflection point),indicating an obvious decrease in the spontaneous combustion propensity of the lignite char from the so-called 'possible to occur spontaneous combustion'to 'difficult to occur spontaneous combustion'. Comparing with the single-stage fluidized bed partial gasification of the same lignite,the char obtained by combining coal pyrolysis in the upper stage and char partial gasification in the bottom stage in the multi-stage fluidized bed( the stage number > 2),which in fact prolongs the residence time of coal in the pyrolysis section,exhibites obviously higher stability due to the lower volatile content in the produced char and the removal of most functional groups from the char surface.