Production Test of Torrefied Woody Biomass Solid Fuel in an Original Small Scale Plant: (2) Effects of Automatic Temperature Control in Torrefaction and the Use of Additives in Pelletization

Abstract

A small-scale demonstration plant, which consists of a rotary kiln-type oven and a ring die-type pelletizer, was manufactured to produce upgraded wood fuel by torrefaction. In this study, we improved the temperature control and the pelletization methods. The oven and pelletization operations were optimized by implementing automatic temperature control of the torrefaction oven, and the use of additives in pelletization; which resulted in improvements in pellet productivity. A commercial scale image of the torrefaction plant was designed for operation in a local community. Torrefied fuel could be used for both large-scale power generation and small-scale use, such as for cooking and heating (e.g. in restaurants), in the outdoors, and during emergencies.

Water Resistance of Torrefied Wood Pellets Prepared by Different Methods

“…At the same time, domestic pellet production was only~140,000 t from~150 domestic pellet mills [13], indicating that the production of local pellet mills in Japan has been operating on a small scale. Recently, the concept of producing torrefied pellets using small-scale production in rural areas has been proposed [14][15][16], in which case the torrefied fuel would require heat use and stable storage. After their fundamental studies on the effects of torrefaction treatment conditions on mass yields, calorific values, and mechanical durability at a laboratory scale [17][18][19], Yoshida et al [16,20,21] constructed a demonstration plant aiming at small-scale use, using a treatment amount of 20 kg/h to continuously produce torrefaction chips from raw wood chips.…”

“…Recently, the concept of producing torrefied pellets using small-scale production in rural areas has been proposed [14][15][16], in which case the torrefied fuel would require heat use and stable storage. After their fundamental studies on the effects of torrefaction treatment conditions on mass yields, calorific values, and mechanical durability at a laboratory scale [17][18][19], Yoshida et al [16,20,21] constructed a demonstration plant aiming at small-scale use, using a treatment amount of 20 kg/h to continuously produce torrefaction chips from raw wood chips. Burning trials of the torrefied pellets produced in this demonstration plant for a commercial pellet stove revealed that the torrefied pellets exhibited a faster ignition time than normal pellets [20].…”

“…Burning trials of the torrefied pellets produced in this demonstration plant for a commercial pellet stove revealed that the torrefied pellets exhibited a faster ignition time than normal pellets [20]. Then, a commercial-scale plant was designed to produce torrefied wood pellets at a small scale (~3000 t of torrefied fuel annually) using local wood resources [16]. Torrefied pellets also have the advantage of better water resistance than normal pellets [7,8], which is crucial for both storage and use in hygroscopic conditions.…”

Water Resistance of Torrefied Wood Pellets Prepared by Two Methods

“…As a result of burning trials for the torrefied pellets in a commercial pellet stove, we found that the torrefied pellets demonstrated faster ignition time than normal pellets. We thus designed a commercial-scale plant to produce torrefied wood pellets at a small scale (3,000 t of torrefied fuel per year) using local wood resources [9]. However, as pointed out in the report, these pellets should have a higher cost than normal wood pellets in production [2,4,9].…”

“…We thus designed a commercial-scale plant to produce torrefied wood pellets at a small scale (3,000 t of torrefied fuel per year) using local wood resources [9]. However, as pointed out in the report, these pellets should have a higher cost than normal wood pellets in production [2,4,9]. Production at a large scale, such as for coal co-firing power, achieves cost-effectiveness by including transportation to a power station and subsequent preparation prior to combustion.…”