Experimental Study of Hydrolysis Lignin Torrefaction

Abstract

The article presents the results of experiments on studying the thermochemical processing (torrefaction) of hydrolysis lignin obtained from long-term waste dumps of the Arkhangelsk hydrolysis plant. These dumps have for a long period of time produced a serious environmental burden on the region in view of their behaving as soil and water contamination sources, and posing potential fire hazards. The main aim of the research was to analyze the lignin pyrolysis in the temperature range of 300–400°C with a view to determine the finished solid product energy potential and select the optimal conditions of its use as power-generating fuel. The experiments were carried out in a laboratory retort-type reactor with vertical loading, designed for replicating the torrefaction and pyrolysis processes of various biomass kinds. During the experiments, the temperatures inside the reactor and pyrolysis gas temperature were recorded, due to which it was possible to compare the process flow features under different heating conditions. The analysis results have shown that the hydrolysis lignin torrefaction features a sequential structure and includes the following stages: moisture removal, initial pyrolysis, and active pyrolysis. The gas medium maximum temperatures equal to 96–97°C were observed in all experiments; however, the pattern in which they are reached depends on the final operating conditions. The most predictable process development pattern and highly stable parameters were recorded at the initial raw material temperature in the reactor equal to 400°C, when the reactor reached the target temperature (401°C) without essential deviations. During the operation at lower temperatures (300–375°C), excessive temperature values were noted in holding as a consequence of the installation’s thermal inertia and exothermal nature of the reactions. This, the operation at 400°C can be regarded as the most controllable process for carrying out hydrolysis lignin torrefaction. Under such operating conditions, stable temperature parameters and a high level of lower heating value per analytic mass are obtained, a circumstance that confirms good prospects of using it for industry-grade processing of accumulated waste and obtaining torrefied fuel with increased added value.