Anthony K Lau

Crop residues (straw) as the alternative feedstocks for the pellet industry could reduce the dependence on woody biomass, the price of which is increasing. Yet, the lack of natural binders (such as lignin) and high ash content are impediments to produce durable pellets from herbaceous biomass feedstocks. This research aimed at improving the durability of agri-pellets using mild hydrothermal treatment of biomass prior to pelletization. Different ways of steam generation were explored at a mild-to-high temperature range (80-220 °C) to determine the effects on pellet quality improvement. The relationships between treatment severity factor and the main properties of the pellets were then developed. Results indicated that the pellet durability first increased but subsequently decreased as the severity factor increased. Energy consumption showed positive correlation while equilibrium moisture content showed negative correlation with the severity factor. The optimal treatment temperature was found to be 140 ℃ for biomass with 50% moisture content (wb), and 180 ℃ was able to produce high quality pellets with lower ash content. Pellet durability, energy consumption during pelletization, and water sorption were all affected by an increase in lignin content due to the decomposition of hemicellulose together with the change of particle size distribution. Overall, this study has explored a relatively wide range of hydrothermal treatment conditions, which includes low to high biomass moisture content, treatment temperature, and treatment time. It not only considers the potential for commercial-scale agri-pellet production, but also detects the potential of lower treatment severity for the biomass, utilizing less water and energy for pelletization. Moreover, from the biomass quality perspective, this study also detects the best conditions for producing the pellets with greater durability, higher calorific value, and lower ash content.

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Biomass as a renewable energy source can be burnt with coal in a coal-fired plant to reduce the impact of fossil fuel on the environment. The aim of this research is to investigate methods that can improve the co-firing of biomass with coal. Initially, a CFD model was validated by comparison with experimental data reported in the literature. Three mesh sizes were tested to prove that simulation results are mesh independent. The model was then applied to simulate the co-firing process with a 3:2 biomass-to-coal mixing ratio. Unsophisticated modifications of the furnace geometry near the inlet and the swirl angle were introduced to study their effect on co-firing. CFD simulations were extended to study the influence of particle shrinkage on co-firing due to biomass pelletization. Furthermore, fine coal tailings generated from coal processing (CT), raw biomass (RB), and torrefied biomass (TB) were characterized for subsequent CFD investigation on mono-firing and co-firing of the different fuels. Simulation results show that the modified furnace geometry with gradual expansion and a larger swirl angle leads to uniform temperature distribution (1650-1720 K) in the furnace vs. a more variant temperature profile (950-1500 K) for the original furnace geometry. Besides, an increase in the tangential component of gas velocity near the center from 1 m/s to 3 m/s with the modified furnace geometry results in a longer residence time of the particles and further reduction of unburnt fixed carbon by 55% from coal at the exit. With biomass pelletization, simulation outputs show that the compressed particles with particle density 1000 kg/m³ have slower volatilization rate and surface reaction, as well as a shorter residence time. This in turns causes a higher percentage of unburnt fixed carbon at the exit though NO emission is slightly lower. As for the co-firing of biomass with fine coal tailings, results indicate that CT alone, CT+TB, and CT+RB blended fuel are associated with 13%, 10% and 28% unburnt carbon, respectively. It may be concluded that co-firing coal tailings with torrefied biomass is better for co-firing since CT+TB also has the lowest NO emission among the different fuels.

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Wood pellets may unintentionally be exposed to liquid water (rain) and water vapor (humid air) during their storage, handling, and transportation to markets. This dissertation aims to analyze the impact of incidental rain on the reduction of durability and the potential for self-heating of wood pellets. Initially, wood pellets spread in a pan were exposed to sprayed water to simulate rainfall. The durability values for wetted pellets were assessed using the standard tumbler test. The constant durability 96.5% as a dependent value vs. varying rain intensity (mm/h) and rain duration (h) were graphically presented on a two-dimensional (x-y) coordinate. Subsequent tests were conducted to compare the durability of pellets exposed to liquid water and to water vapor. For liquid water, the dried pellets at 0% m.c. were immersed in water at 30 °C. For water vapor, the dried pellets were placed in a humidity chamber at 90% RH and temperature of 30 °C. When exposed to liquid water, the durability of wood pellets decreased from over 99% to below 80% when their moisture content increased to 20% (wb) within six minutes. When exposed to water vapor, the durability of wood pellets first decreased from over 99% to 95% when their moisture content increased from zero to 10.7% (wb) within four hours. The temperature rise due to self heating of wood pellets was measured using a thermocouple placed in 200 ml liquid water and 100 g pellets. The temperature rise in humid air was measured by inserting a thermocouple inside a pellet placed in the humidity chamber at 95% RH and 33 °C. The maximum heat of wetting of wood pellets immersed in water was determined to be 66 kJ/kg dry mass. An average differential heat of water vapor adsorption of 403 kJ/kg water was calculated as a derivative of the heat of wetting data. By including the equation for heat of wetting and differential heat of adsorption, the mathematical heat and moisture transfer model quantified the contribution of moisture adsorption to the self-heating phenomenon in wood pellets.

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In the published literature, there is a lack of detailed data relevant to full-scale gasification plants that operate on variable quality of biomass feedstock, especially those originating from urban sources. The objectives of this study are to characterize the spatial and temporal variations in the physical properties of waste wood supplied to the UBC industrial gasification system; and to conduct an analysis of variations in fuel properties vs. gasifier performance in terms of system reliability, steam production, syngas quality, tar formation, and gasification efficiencfy. The measured values of fuel properties were in compliance with the fuel specifications. Large variation in steam production during the earlier years of operation was attributed partly to the variations in feedstock moisture content and particle size. Subsequent data collection and analysis revealed that fuel moisture content affects the production of steam the most. Fuel moisture content (mc), gasifier bed temperature, and fuel feeding rate were identified to be the key factors that affect syngas quality, tar formation, and gasifier efficiency. Multi-variable regression models were developed to quantify these relationships. Despite a wide variation of the data collected from the industrial gasifier, our results are in line with the trends reported in the literature based on lab-scale and pilot-scale studies. Research findings indicated that even for a commercial updraft gasifier, syngas quality and steam production would be enhanced if the fuel moisture content could be maintained around 20% (wb). With air as the gasifying agent, when fuel moisture content decreased to 20%, the carbon monoxide (CO) concentration (~30%) and calorific value (>4 MJ/m³) would be higher, whereas tar concentration (
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The overall objective of this dissertation was to evaluate the economic performance of a commercial-scale biorefinery given the volatility in the market price of the final product and the variability in the biomass delivered cost. To this end, a risk analysis methodology comprised of five steps was developed: 1) construct the supply area geographical data base, 2) perform Monte Carlo simulation via the Integrated Biomass Supply Analysis and Logistics Multi-Crop model (IBSAL-MC) to produce the biomass delivered cost distribution, 3) conduct economic analysis by combining the biomass delivered cost distribution with the product market price to generate a ROI (return on investment) heat map, 4) repeat Steps 1 to 3 for an alternative scenario and 5) compare heat maps from different scenarios to quantify the effectiveness and incentive available for achieving an alternative scenario.The proposed methodology was applied to a cellulosic sugar plant under construction in Southwestern Ontario, Canada. Three biorefinery scenarios were considered including small-scale (175 dry tonnes (dt)/day), medium-scale (520 dt/day) and large-scale (860 dt/day). Results showed that the magnitude of the required logistical resources and their associated upfront and administrative costs hindered the biorefinery’s economic performance as its scale increased. The risk analysis approach was then applied to the small-scale scenario. Potential economic incentives for participating biomass producers were quantified as the participation rate increased from 20% to 30%, 40% and 50. While increasing farm participation rate was economically beneficial to the biorefinery, there were more economic benefits if the sugar market price was in a favourable range. When a farmers’ co-operative was introduced to the supply system, if the biorefinery could secure a long-term consumer of the produced sugar in the price range of $425-575/tonne, the farmers’ co-operative and other investors of the biomass project were both more likely to achieve an acceptable annual ROI that exceeds 10%.

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The goal of the present study is to characterize the ground chip and ground pellet particles with respect to their size, shape, density, flow properties, drying and pyrolysis mass loss. Commercial wood pellets and pulp-quality wood chips are used in this study. These commercial samples are ground in the laboratory using a range of grinder screen sizes. The grinder power input is measured. The ground particles are examined for their size and shape. The ground particles are thermally treated in a micro TGA equipment and in a lab-scale thin-layer drying/pyrolysis equipment. The grinding results show that grinding a whole pellet to the desirable particle sizes for pyrolysis (~1 mm) takes around 1/7 of energy required to grind a whole wood chip to the same mean particle size. Pellet particles are denser, more spherical and shorter than the needle-shape chip particles. The spheroid shape of ground pellet particles lowers the compressibility of bulk, lowers the cohesion among the particles and facilitates their flowability. Higher density and random fiber orientation of the pellet particles prolong the duration of their drying significantly compared to the drying time of thin and long wood chip particles. Further moisture diffusion modeling shows that the moisture diffusion rate inside the pellet particles is half of those inside the chip particles. Although chip and pellet particles show the same level of shrinkage in size of a single particle due to drying, ground pellet particles exhibit a larger reduction in their bed porosity than the bed porosity measured for ground chip particles. Both chip and pellet particles reach their fiber saturation point at a moisture content of around 0.50 (dry basis). The pyrolysis kinetic parameters are determined experimentally and a two-zone kinetic mechanism is modeled and validated using the experimental thin-layer pyrolysis data.

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Biological hydrogen production via anaerobic fermentation of organic waste can be potentially a greener and sustainable technology. Thus far, most research has been conducted using continuous stirred tank reactors (CSTR). Anaerobic sequencing batch reactors (ASBR) have advantages over CSTR, but there are disadvantages in terms of their operation. The overall goal of the thesis research is to enhance hydrogen production by optimizing the operational conditions in an ASBR using agri-food wastewater as substrate. An ASBR with 6-L working volume was inoculated with sewage sludge from the anaerobic zone of a sewage treatment facility and was not pretreated to select the hydrogen-producing bacteria. Hydrogen productivity was estimated by hydrogen content (%), hydrogen production rate (HPR) and hydrogen yield as the performance indicators in response to changes in pH, hydraulic retention time (HRT), organic loading rate (OLR), and cyclic duration (CD) as the key operational parameters. Using dairy wastewater as substrate, the suppression of methanogenesis was feasible without pretreatment of inoculum under the conditions of higher OLR and shorter HRT, which favoured hydrogen production. With carbohydrate-rich synthetic wastewater as substrate, the combination of relatively low pH 4.5 and HRT 30 hr was found to be the optimal condition for hydrogen production. For higher hydrogen production, ethanol-to-acetic acid ratio of 1.25 and food-to-microorganism ratio of 0.84 were revealed as threshold values. Higher hydrogen productivity at longer CD was not necessarily accompanied with higher microbial growth that occurred at shorter CD. Subsequently, real sugar refinery wastewater was used in the tests for biohydrogen production. Based on statistical analysis and curve fitting by the modified Gompertz model of the data as well as microbial identification, the operational setting of (pH 5.5, HRT 10 hr, OLR 15 kg/m³.d) was concluded to be optimal with the performance indicators of (71.8±10.5% H₂, HPR 2.11±0.31 L H₂/L reactor.d and yield 0.95±0.13 mol H₂/mol sucrose). Taxonomic analysis confirmed the presence of dominant hydrogen-producing bacteria among the diverse microbial genera, and in particular, the Clostridia spp. without the pretreatment of inocula. Further studies with the optimization of operational conditions would contribute towards making the best possible decision for ASBR.

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Moisture sorption and gas emissions are major processes associated with biomass storage. Depending on the storage conditions, these processes alter the structure and composition of biomass. The objectives of this research are (1) to develop moisture relations for woody biomass exposed to drying and wetting environments; (2) to quantify gas emissions from biomass stored under aerobic and anaerobic conditions; and (3) to develop dry matter loss equations for the stored biomass. Moisture adsorption and desorption (drying) experiments were carried out on Aspen branches in a controlled temperature and humidity chamber. Frequent wetting-drying cycles were simulated by spraying water on the biomass. A lump model for simulating moisture adsorption-desorption was developed and calibrated with experimental results. The model was applied to the Aspen bales stored for one year in the field under natural conditions. The predicted moisture contents using the lump moisture transfer model were found to be in reasonably good agreement with the moisture contents measured in the stored bales. In another set of experiments, gas emissions from stored Western Red Cedar (WRC) and Douglas fir (DF) were analyzed. The emissions of CO₂, CO, H₂ and CH₄, and the depletion of O₂ were measured. The highest total CO₂ emissions from WRC stored in the non-aerobic and aerobic reactors were 2.8 g/kg DM and 6.6 g/kg DM, respectively. Higher gas emissions were measured from stored DF materials than from WRC. Common volatile organic compounds (VOCs) measured using GC-MS were methanol, aldehydes, terpene, acid, acetone, hexane, ketone, benzene, ethers and esters from WRC and DF. The total VOC concentrations were found to have a positive correlation with temperature. The results of microbial analysis were compatible with gas emission results. Positive correlations between percent dry matter losses and gas emissions were found for both aerobic and non-aerobic storage conditions. The summation of gas emissions from aerobic reactors is greater than accumulated gas emissions from non-aerobic reactors over the same storage period. It was found that DF is more readily degradable than WRC. Greens (leaves and twigs) degrade faster than wood chips.

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Traditional measures used in the composting industry for ammonia and odor emissions control are those involving collection and treatment such as thermal oxidation, adsorption, wet scrubbing and biofiltration. However, these methods do not address the source of the odor generation problem. The primary objective of this thesis research was to develop preventive means to minimize ammonia and odor emissions, and maximize nitrogen conservation to increase the agronomic value of compost. Laboratory-scale experiments were performed to examine the effectiveness of various technologies to minimize these emissions during the active phase of composting. These techniques included precipitating ammonium into struvite in composting matrix before it release to outside environment; the use of chemical and biological additives in the form of yeast, zeolite and alum; and the manipulation of key operational parameters during the composting process. The fact that struvite crystals were formed in manure composting media, as verified by both XRD and SEM-EDS analyses, represents novel findings from this study. This technique was able to reduce ammonia emission by 40-84%, while nitrogen content in the finished compost was increased by 37-105%. The application of yeast and zeolite with dosages of 5-10% enhanced the thermal performance of composting and the degree of degradation, and ammonia emission was reduced by up to 50%. Alum was found to be the most effective additive for both ammonia and odor emission control; ammonia emission decreased by 45-90% depending on the dosage, and odor emission assessed via an dynamic dilution olfactometer was reduced by 44% with dosages above 2.5%. This study reaffirmed that aeration is the most influential factor to odor emission. An optimal airflow rate for odor control would be 0.6 L/min.kg dry matter with an intermittent aeration system. Quantitative relationships between odor emission and key operational parameters were determined, which would enable “best management practices” to be devised and implemented for composting.An empirical odor predictive model was developed to provide a simple and direct means for simulation of composting odor emissions. The effects of operating conditions were incorporated into the model with multiplicative algorithm and linearization approximation approach. The model was validated with experimental observations.

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