Biomass properties can be improved for heat and power applications through combined torrefaction and pelleting. Good pellet quality in terms of durability, density, moisture absorption, fines production and heating value paired with a low power consumption in the pellet mill render the densification process of torrefied materials challenging. The aim of this study is to identify the lignin components/intermediates and the corresponding mechanisms during torrefaction of wood that play a role in pelleting behaviour and pellet quality. The importance of lignin lies in its ability to act as a natural binder during densification.

Structural differences caused by torrefaction of spruce and poplar (270 °C, 32–45 min) were studied by using NMR and TD-GC/MS as well as by pressing single pellets. Spruce chips were torrefied (280 °C, 35–45 min) and conditioned in steam in a pilot plant. The products were ground on a 4-mm sieve and densified in a single-pellet press, where differences in the measured responses were explained on basis of their lignin properties. The lignin was isolated from the spruce samples by organosolv fractionation and characterised in terms of amount, molecular weight distribution (SEC) and glass-transition temperature (DSC).

The results of the tests and analyses indicate that torrefied softwood should be densified immediately after production. Furthermore, pellet quality of the torrefied material was found to depend on the binding ability of its lignin in the presence of moisture during densification. Additionally, storage of torrefied spruce prior to densification causes reduced binding ability of its lignin leading to pellets of lower quality.

通过联合焙烧和制粒，可以改善热能和生物能的生物质能。在耐用性，密度，吸湿性，细粉产量和发热量方面，良好的颗粒质量以及制粒机中的低功耗使其对烘焙材料的致密化过程提出了挑战。这项研究的目的是确定木质素组分/中间体以及木材在焙干过程中的相应机制，这些机制对制粒行为和颗粒质量起着重要作用。木质素的重要性在于其在致密化过程中充当天然粘合剂的能力。

通过使用NMR和TD-GC / MS以及压制单个小球，研究了由云杉和杨树的烘烤引起的结构差异（270°C，32–45分钟）。将云杉片切碎（280°C，35-45分钟），并在中试工厂的蒸汽中进行调理。将产物在4-mm筛上研磨并在单丸压机中压实，其中根据木素的性质解释了所测得响应的差异。通过有机溶剂分馏从云杉样品中分离出木质素，并对其数量，分子量分布（SEC）和玻璃化转变温度（DSC）进行了表征。

测试和分析的结果表明，生产后应立即对经过焙烧的软木进行致密化处理。此外，发现在致密化过程中，在湿气存在下，烘焙过的材料的丸粒质量取决于其木质素的结合能力。另外，在致密化之前储存焙烤的云杉会降低其木质素的结合能力，从而导致较低质量的颗粒。