Sylvia H. Larsson

High quality biofuel pellet production from pre-compacted low density raw materials

In this study, pre-compaction was evaluated as a method to enhance stable reed canary grass pellet production. An experimental design of the factors raw material moisture content, steam addition, raw material bulk density, and die temperature was used to find production conditions for high quality pellets by multiple linear regression modelling of responses. Response variables being modelled were variability of pelletizer current (as a measurement of uneven production), pellet bulk density, and pellet durability. By pre-compacting the raw material from a bulk density of 150 kg/m3 to 270kg/m3, continuous production could be obtained at minimum raw material moisture content of 13.8%. Bulk density and durability were both highly correlated to raw material moisture content, but showed different optima. Multiple response optimization was used to target process settings for production of high quality reed canary grass pellets with bulk density >650kg/m3 and durability >97.5%.

Drying characteristics and equilibrium moisture content of steam-treated Douglas fir (Pseudotsuga menziesii L.)

Douglas fir (Pseudotsuga menziesii L.) particles were exposed to high pressure saturated steam (200 and 220 °C for 5 and 10 min) to improve the durability and hydrophobicity of pellets produced from them. Depending on treatment severity, the moisture content of the particles increased from 10% to 36% (wet basis). Douglas fir particles steam-treated at 220 °C for 10 min had the fastest drying rate of 0.014 min(-1). The equilibrium moisture content (EMC) of steam-treated samples decreased with increasing steam temperature and treatment time. The Giggnheim-Anderson-deBoer (GAB) equilibrium model gave a good fit with the equilibrium data with R(2) = 0.99. The adsorption rate of untreated pellets exposed to humid air (30 °C, 90% RH) for 72 h was 0.0152 min(-1) while that of steam-treated pellets ranged from 0.0125 to 0.0135 min(-1) without a clear trend with steam treatment severity. These findings are critical to develop durable and less hygroscopic pellets.

Near infrared image analysis for online identification and separation of wood chips with elevated levels of extractives.

Forest-based biorefinery feedstocks are usually broken up into wood chips prior to any form of processing. These wood chips have a complex and highly variable composition, although they may look identical to an inexperienced observer. Some chips have high contents of valuable extractives. Therefore, it would be desirable to separate such chips that are rich in extractives. Various fractions of pine and spruce wood were used to acquire near infrared (1000–2498 nm) hyperspectral images in order to explore the usefulness of multivariate image analysis for detection and separation purposes. Multivariate modelling by image principal component analysis detected large variations in extractive content among wood chips of different biomass types, for example, sapwood, heartwood and knotwood. The extractive parts could be classified in the images and their content could be reasonably well predicted. Partial least squares (PLS) regression models could be made between collected spectra and measured extractive contents. These worked better for milled and homogenised bulk samples than for average image spectra. Regression coefficients showed that the C–H bonds in the spectra were responsible for the validity of the models. The average image PLS models could be used to make prediction images showing the location of the regions with high extractive content in knotwood. The results indicate that extremely rapid spectral-based fractionation could be used to separate tailored biomass streams of wood chips.

Effect of Temperature, Time, Particle size and Moisture content on Physical and Chemical Properties of Steam Exploded Woody Biomass

The effects of steam explosion processing conditions and feedstock parameters on physical and chemical properties of woody biomass were studied. The moisture contents of treated samples ranged between 14.5% and 32.2% and were higher than the initial moisture content of the untreated samples at 10% and 15%. The solid yield of treated samples varied between 46% and 86%. The mean value for solid yield was significantly (a=0.05) lower for samples treated at 220oC, compared to samples treated at 200oC. The pressure of steam before releasing the samples from high pressure cooking chamber to ambient (i.e. explosion pressure) ranged between 1169.83 – 1316.90 kPa for samples at 200oC and between 1732.86 – 1935.15 kPa for samples treated at 220oC, respectively. The steam pressure at pressure release point were modeled with multilinear regression with time and temperature with R2=0.85. Size reduction effect of steam explosion leading to particle fragmentation was observed. The relative geometric mean diameter of samples ground with 3.175 mm screen size were modeled with R2= 0.87 from the factors temperature, time, and moisture content. Relative bulk densities of steam treated samples ranged from 1.25 to 2.51, and relative tapped bulk densities from 1.12 to 2.23. A multilinear regression model for relative tapped bulk density with R2=0.91 was created from the factors temperature (T), time (t), particle size (p), moisture content (m), and the interaction terms T×p, T×m, and t×p. The lignin content and extractives increased with temperature and time. The lignin content and extractives of samples treated at 220oC were significantly higher than that of samples treated at 200oC. The equilibrium moisture content of treated samples decreased with increasing temperature from moisture sorption test.

Process water properties from hydrothermal carbonization of chemical sludge from a pulp and board mill

Hydrothermal carbonization (HTC) can be used to break down sludge structure and generate carbonaceous hydrochar suitable for solid fuel or value-added material applications. The separation of char and the reaction medium however generates a filtrate, which needs to treated before potential discharge. Thus, this work determined filtrate properties based on HTC temperature and sludge moisture content and estimated the discharge emissions and the potential increase in analyte loads to an industrial wastewater treatment plant based on derived regression models. Direct discharge of HTC filtrate would significantly increase effluent emissions at the mill, indicating the filtrate treatment is crucial for the future implementation of HTC at pulp and paper mills. Recycling the HTC filtrate to the wastewater plant would lead to only a nominal increase in effluent flow, but would increase the suspended solids, BOD, COD and total nitrogen loads by 0.1-0.8%, 3.8-5.3%, 2.7-3.1% and 42-67%, respectively, depending on HTC temperature.