Exploring new ways for treating and pelletizing cellulosic biomass

从“化石燃料经济”过渡到“生物经济”需要大量的生物质作为一种全球商品进行交易。由于低堆积密度和高水分含量，诸如颗粒化之类的致密化过程被认为是长距离运输生物质以受益于规模经济的必要条件。然而，尽管体积密度增加，但目前的木屑颗粒易受湿度和机械力的影响，因此在运输和处理过程中容易破裂。高湿条件下的低稳定性对加拿大颗粒行业来说尤其具有挑战性，加拿大颗粒行业依赖海运向欧洲出口大部分颗粒。拟议的发现补助金旨在从根本上了解控制生物质颗粒的耐久性和强度的因素。通过这样做，我们希望开发有效的方法来改善颗粒在不同环境条件下的性能，同时使我们能够将它们用作生产所有不同形式的化石燃料等价物的原料。

Transition from a “fossil fuel economy” to a “bioeconomy” requires large volumes of biomass to be traded as a global commodity. Due to low bulk density and high moisture content, densification processes such as pelletisation is recognised to be essential to transport biomass over long distances to benefit the economies of scale. However, despite an increase in the bulk density, current wood pellets are susceptible to humidity and mechanical forces, thus easily falling apart during transport and handling. Low stability at high humid conditions is challenging particularly to the Canadian pellet industry, which depends on ocean transport for exporting most of their pellets to Europe. The proposed discovery grant aims at fundamental understanding of the factors governing the durability and strength of biomass pellets. By doing so, we hope to develop effective methods to improve the pellet properties under varying environmental conditions while enabling us to use them as a feedstock for producing all different forms of fossil fuel equivalents. This Discovery Research program primarily explores the effect of physical and compositional properties of biomass on densification, handling and subsequent processing. This will be done by employing two main approaches. The first approach develops a protective outer layer for the commercial pellets that can preserve the integrity of pellets during storage, transport and handling. The second approach modifies the location and properties of cell wall polymers in biomass by a catalysed steam conditioning step prior to pelletisation with the objective of enhancing the binding characteristics of biomass particles and making pellets moisture proof. The protective coating around the pellet will be developed by using suitable coating solutions compatible with the pellet surface. At first, we propose to design a suitable method of coating with uniform thickness. Subsequently, surface modification by plasma etching will be compared with the efficiency of the protective layer produced by dry as well as wet external coating agents. The coated pellets would be then evaluated for their ability to resist moisture ingress and mechanical stress using “representative methods” which better defines the stability of the pellets at industrially relevant conditions. Our recent work has shown that the use of “SO2 catalysed steam conditioning” prior to pelletisation can substantially enhance the pellet properties while minimising the forces required for densification. In the proposed program, we intend to investigate what modifications in the cell wall polymers make the steam pretreated particles to better bind and get compacted during pelletisation and why the required energy for densification was reduced. We anticipate this fundamental knowledge would help us design and standardise more effective methods to produce durable wood pellets with minimum energy and chemical consumption. In addition to optimising the appropriate conditions of steam pretreatment, we will compare the suitability of SO2 with alkaline catalysts such as Ca(OH)2, NH3, and Na2SO3. The proposed research program is expected to conclude with an assessment of environmental impact and techno-economic analysis of both “pellet encapsulation” and “steam conditioning”. This evaluation would help the industrial community to select an environmentally benign, yet cost effective coating material and/or process configurations for conditioning biomass prior to pelletisation. The project will train one PDF, one PhD, and four undergraduate students.