Evan Almberg

Environmental Considerations of Torrefaction

When considering any new technology, one must be cognizant of the environmental implications of the technology once it is implemented. This is especially important when pursuing technologies that can cause a paradigm shift in producing energy and other products. If we explore the history of game-changing technologies that have impacted the manner in which societies live, work, and transport themselves, they all have had positive and negative consequences. Examples of technologies that caused significant paradigm shifts include motorized transportation, globalized manufacturing, resource mining and harvesting, computing and communication, among others.

Torrefaction Bioenergy Generation

Torrefaction is well-suited to providing a wide array of bioenergy generation options. However, using torrefaction as the core of a system for producing renewable bioenergy and value-added products requires understanding of several fundamental parameters such as the desired type and profile of generated energy, the desired end products and byproducts (if any), feedstock characteristics, and conversion characteristics.

Fundamental Theories of Torrefaction by Thermochemical Conversion

Torrefaction is a thermochemical conversion process used to transform biomass into a more energy dense and hydrophobic product with a number of additional desirable characteristics. Since torrefaction is relatively new in energy engineering, references contain varying baseline values for reaction time and temperature.

Introduction to Thermochemical Conversion Processes

This book advocates a different pathway for producing value-added products and fuels—torrefaction. Torrefaction, also known as mild pyrolysis, is a thermochemical conversion process that introduces a solid feedstock within an elevated temperature oxygen-limited environment and upgrades it to a more energy dense, storable product. Torrefaction is achieved at a temperature of 200–300°C (392–572°F), in which the feedstock is slowly heated, causing the feedstock to release moisture and volatile gases. The end products include (1) a solid biochar material, similar to charcoal and (2) combustible off gases, commonly referred to as torr-gas, both of which may be burned for thermal energy at a later time. A third product of torrefaction, waste heat, may be utilized for a colocated process. As an added benefit, all the end products of torrefaction are biobased and renewable.

Torrefaction Bioenergy Applications

The world currently relies on nonrenewable fuels to provide a majority of the energy we consume. Oil, coal, natural gas, and nuclear are nonrenewable energy sources in that they are finite resources and will eventually become depleted. In addition, fossil fuel consumption emit billions of tons of carbon into the atmosphere, while spent nuclear fuels have their own disposal concerns. Staying reliant on nonrenewable fuels has the inherent danger of attempting to survive by modern standards when these fuel sources are depleted, or highlights a limiting factor for growth and development in regions where these nonrenewable energy resources are currently in limited supply. This chapter identifies how torrefied biomass can be used for supplemental renewable energy, Zero Energy Buildings (ZEB), and off-grid applications.

Introduction to Feedstocks

Biomass is considered a suitable source for renewable energy and biobased products due to its organic nature, carbon stability, and abundant supply. The classification and availability of biomass feedstock for these products are key factors in determining the most effective application for biomass. The classification of the feedstock provides relative insight on the composition and preferred conversion process, while the availability of the feedstock is important when considering the availability of the biomass source. Having a thorough understanding of the feedstock enables one to make a complete assessment of biomass energy production processes in terms of supply chain economics and optimum reactor designs. There are three key factors when considering biomass for bioenergy production: • Assessing the availability of biomass feedstocks,

Design Practices for Torrefaction Systems

Biomass feedstock comes in a variety of shapes, sizes, and energy contents. Fossil fuels have a relatively higher energy density and mass density when compared to biomass, making them more efficient to transport and process in many situations. Grinding raw biomass feedstock is essential to make biomass more easily converted into value added products or fuels. Grinding reduces the particle size of the biomass and increases the total amount of surface area of the feedstock. The decreased particle size combined with the increased surface area is better suited for thermochemical processing to efficiently transport, heat, and compress the material.

Techno-Economic Considerations of Torrefaction

The conversion of biomass feedstocks into value-added products are growing in interest and application as the global desire to become more sustainable becomes more prevalent. This intensifying global desire results in the need to meet stricter governmental environmental mandates, increase renewable product options, and farm using more sustainable agricultural practices. Biomass such as corn stover can be harvested or grazed for livestock feeding, refined in processes to create solid and liquid biofuels, as well as be converted into value added bioproducts. Although biomass is widely available there are currently few applications for it apart from agricultural use. Some progress has been made to use corn stover as feedstock for cellulosic ethanol, but many challenges have risen with this process, and consequently, the market for cellulosic corn stover ethanol is yet to expand. Other uses of biomass have been developed, such as for building materials and fuel pellets, but as with other applications the use is yet to become widespread.