Torrefaction of Healthy and Beetle Kill Pine and Co-Combustion With Sub-Bituminous Coal

Abstract

Combustion of biomass and co-combustion with fossil fuels are viable means of reducing emissions in electricity generation, and local biomass resources are appealing to minimize life cycle emissions. In the Rocky Mountain Region of the U.S., a bark beetle epidemic is causing widespread forest death and associated safety hazards. This biomass has potential to be a feedstock resource, thereby achieving dual goals of improving forest health while supplying biomass for uses such as co-firing with coal in power plants. In this study, combustion and co-combustion of healthy pine (HP) and beetle kill pine (BK) with coal were conducted to assess the interchangeability of these feedstocks in raw and torrefied forms. HP and BK pine were torrefied at 200, 250, and 300 C to increase energy density and improve grindability, both of which aid in seamless integration into power plants. Grindability was assessed for both feedstocks at each torrefaction condition. The raw feedstocks were pyrolyzed to assess their relative compositions. Raw and torrefied feedstocks were then combusted alone and co-combusted with sub-bituminous Powder River Basin coal using thermogravimetric analysis (TGA). Modulated TGA was used to derive kinetic parameters of coal, raw and torrefied biomass, and coal-biomass blends. Results show increased grindability and pyrolysis mass loss of BK as compared to HP, which are attributed to the degraded state of the wood. Combustion and cocombustion show favorable interchangeability of the HP and BK, and additive behavior when co-combusted with coal.

What Happens to Wood after a Tree Is Attacked by a Bark Beetle?

“…For their study, Howell et al [27] disintegrated wood from beetle-attacked pine and noninfested pine into very fine particles measuring 75-150 µm. Scanning electron microscope images showed that the particles from the noninfested trees showed more uniform fibre orientation than the particles from beetle-attacked trees, which were characterized by a variable fibre orientation resembling disintegrated, degraded wood.…”

“…Scanning electron microscope images showed that the particles from the noninfested trees showed more uniform fibre orientation than the particles from beetle-attacked trees, which were characterized by a variable fibre orientation resembling disintegrated, degraded wood. It is clear that the ongoing degradation of the wood mass was caused by wood-decay fungi that colonized the wood after the tree was attacked by the bark beetle [27]. Of the main biomacromolecular substances of which the wood mass is composed (cellulose, hemicelluloses, and lignin), no difference was observed between the wood of the bark beetle-infested and the noninfested tree.…”

“…It is obvious that in the region where certain tree species are most affected by bark beetles, the properties of the wood of these tree species are investigated, and in other regions where bark beetles attack other tree species, the properties of those other tree species are investigated. For these reasons, research in Central and Eastern Europe deals mainly with spruce (Picea abies, Picea obovata Ledeb) [21][22][23] and in North America mainly pine (Pinus ponderosa Douglas ex C.Lawson, Pinus taeda L.) [24][25][26][27].…”

Synergetic Co-Production of Beer Colouring Agent and Solid Fuel from Brewers’ Spent Grain in the Circular Economy Perspective

“…Torrefaction is sometimes called slow pyrolysis, and it typically takes place at temperatures between 250 • C and 300 • C [44][45][46][47], with residence times ranging between 10 and 60 min [48][49][50][51]. Torrefied biomass can be an attractive fuel for the power industry for combustion and co-firing [52][53][54][55], mainly due to increased grindability [56,57], which extends the time between renovations of the mill [58], and energy density [59][60][61][62]. In addition, reduction of moisture content could be beneficial in many energy conversion processes [45,63,64].…”

Torrefaction of Agricultural Residues: Effect of Temperature and Residence Time on the Process Products Properties

“…Torrefied biomass is often referred to as "biocoal" because its grindable and combustible characteristics are close to those of coal, and it is expected to replace coal in existing heat and power generation plants [7]. Given the above, biochar combustion or co-combustion has been the main subject of studies carried out to date [8][9][10]. Following the idea of the circular economy, however, the remaining process products have recently attracted attention as well.…”