Anthony K Lau

Associate Professor

Relevant Thesis-Based Degree Programs


Graduate Student Supervision

Doctoral Student Supervision

Dissertations completed in 2010 or later are listed below. Please note that there is a 6-12 month delay to add the latest dissertations.

Hydrothermal pretreatments to make durable pellets from herbaceous biomass (2022)

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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Investigating methods to improve the co-firing of biomass with coal using CFD simulations (2021)

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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Moisture-related physical properties and self-heating of wood pellets (2021)

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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Logistics of wood chips supply and performance analysis of an industrial updraft gasifier (2020)

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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Development of a quantitative risk analysis approach to evaluate the economic performance of an industrial-scale biorefinery (2018)

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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Physical and thermal characterization of ground wood chip and ground wood pellet particles (2017)

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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Anaerobic fermentation for biological hydrogen production in a sequencing batch reactor (2013)

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 during the storage of high moisture woody biomass (2013)

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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Preventive control of ammonia and odor emissions during the active phase of poultry manure composting (2009)

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/ 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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Master's Student Supervision

Theses completed in 2010 or later are listed below. Please note that there is a 6-12 month delay to add the latest theses.

Physical properties of leached and pelletized agricultural and woody biomass residues (2023)

In Canada, the agricultural sector produces 50 million dry tonnes of residues every year. These residues have a large potential for bioenergy application to replace fossil fuels. However, the disadvantages of using agricultural residues are its high ash content and low bulk density. Pelletization increases the bulk density of agricultural biomass and allows the agri pellets to be transported economically. Two types of methods were used for the preprocess of the feedstock, which were water leaching and pressing. Washing was applied with a water-to-biomass weight ratio of 25:1. The pressing process was done using 2 MPa pressure and 30 s residence time. The results show that washing and pressing (W&P) process led to a decrease in the angle of repose. After washing and pressing, the wt% of finer fraction of the particles (
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Improving the quality of crop residues by the reduction of ash content and inorganic constituents (2019)

Fuel pellet producers in Canada have started to consider alternative feedstocks that include agricultural crop residues. Yet, the higher ash content and inorganic constituents of crop residues can impose problems on the equipment, the quality of products, and the environment due to air emission. In this study, mechanical size fractionation in combination with leaching was conducted to improve the quality of crop residues by reducing the ash content to target value of 6% db following the applicable standard. Experimental results of mechanical size fractionation suggest that the finest fraction of ground crop residues had much higher ash contents than the coarser fractions. Results also indicate that size fractionation can reduce the need for leaching as ash removal technique, and it is most effective for corn stover when compared to canola straw and wheat straw. For the leaching tests, the leaching performance is affected by the leaching conditions whereas particle size can have some impact. Under the same leaching conditions, non-fractionated ground crop residues with larger average particle size had higher ash removal efficiency than the finest fraction of crop residues. Among the three species of crop residues, canola straw was found to have the best leaching performance, regardless of whether mechanical size fractionation was used prior to leaching. Canola straw had the highest ash removal efficiencies, K₂O removal efficiency (greater than 90%) and SiO₂ removal efficiency (more than 50%). The results also demonstrate that the effect of leaching temperature on K₂O removal efficiency is negligible while SiO₂ removal efficiency increases significantly as water temperature increases from 25 to 45 °C upon leaching for 12 h. A preliminary cost analysis was performed to estimate the total production cost (TPC) of agro-pellets based on different process designs with respect to the ash removal techniques. TPC for the base case of pellet production without ash removal pretreatment was estimated to be US$102/dry tonne (dt) pellets, and it would increase by 30% to US$133/dt for Option 1 (pretreatment by mechanical size fraction plus water leaching) and increase by 66% to US$169/dt for Option 2 (pretreatment by water leaching only).

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Calorific Value of Wood Pellets (2015)

The export of wood pellets from Canada to Europe has been increasing steadily in recent years (roughly 1.8 million ton in 2013). Due to distances involved, wood pellets remain in transit and storage for months before their final consumption. The net calorific value determines the price of wood pellets purchased in Europe. There have been concerns about the changes of net calorific values over time. In this study, the effects of storage time, storage configuration, storage temperature, and wood pellet quality on the net calorific value of wood pellets for a period of 6 months were investigated. Storage configurations were “open” or “closed” and storage temperatures were 25°C, 35°C and 45°C. Two types of wood pellets used: white (10% bark) and mixed (40% bark). The results in the “closed” storage scenario indicated that storage time had a positive effect on the net calorific value, where the net calorific value increased by 1 to 2% over the storage period. In the open storage scenario, the moisture content had the most significant impact on the net calorific value. A multivariable linear regression and analysis of variance performed verified the graphical results. It was postulated that the higher energy potential compounds – low molecular weight aldehyde and ketone or off-gasses such as carbon monoxide, methane and hydrogen – produced during pellet storage, caused the increase in net calorific values.

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Logistics Modeling of Biomass Supply Chain in Ontario (2015)

The overall goal of this research is to investigate the logistics of agricultural biomass in Ontario, Canada using the Integrated Biomass Supply Analysis and Logistics Model (IBSAL). The applicability of IBSAL is demonstrated through simulating three case studies. Case A is for the supply of corn stover to Ontario Power Generation (OPG) in Lambton. Case B concerns the supply of baled switchgrass from three farms to a greenhouse operation. Case C is for the supply of straw or switchgrass bales from 5 growing regions to Mushroom Producers Coop Inc. (MPCI).For Case A, five scenarios of delivering corn stover to the OPG power plant in Lambton Ontario are investigated: (1) base scenario, (2) central storage scenario, (3) direct scenario, (4) barge scenario, (5) railroad scenario. The net amount of annual biomass demand at the power plant is estimated to be 124,264 dry metric ton (Mg). For scenarios 1 to 5 the amount of biomass required to be harvested is respectively 160123, 155730, 151141,172480, and 170686 Mg per year. Also the total cost estimated to be respectively $37/Mg, $49/Mg, $33/Mg, $94/Mg, and $81/Mg.For Case B, the annual heating demand of a greenhouse located on southwestern Ontario near Lake Huron is calculated as 20,730 GJ/year. Roughly 2,200 Mg of switchgrass is required. Cost, energy consumption and carbon emission associated with the supply chain are $66/Mg, 151.3 MJ/Mg and 10.4 kg CO₂/Mg, respectively. The dry matter loss is calculated to be 805 Mg.For Case C, the following scenarios are modeled: (1) Base case scenario, (2) Straw location scenario, (3) Straw field to MPCI, (4) Switchgrass location scenario. Delivery costs of the first scenario vary in the range of $50-69/Mg. In the second scenario, the total average costs were $74/Mg, $68/Mg, and $70/Mg for the storage on gravel, storage on gravel with pad and protected under shed. Scenario 3 showed how sorted and unsorted bales affect the cost. The forth scenario the average total costs were reported to be $106.7/Mg, $91.4/Mg, and $90.8/Mg respectively for storage on the gravel pad on the gravel pad and protected under shed.

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Durability of Wood Pellets (2011)

Durability is used for quantifying the quality of pellets by measuring the percentage of broken pellets. This work conducted durability measurement using different approaches, including Dural, Tumbler and drop test, and established relationship between them. In particular, 1) we developed a robust method that measures durability based on Dural. A series of experiments were conducted using eight different machine settings and four types of pellets. It was found that both pellet types and machine settings are statistically significant. The setting represented by 200 g sample, testing duration 15 s and rotational speed 1516 rpm was found to be the most appropriate for Dural. 2) We also conducted drop test for unveiling the effect of different factors on breakage of pellets, such as height, sample size, number of repeated drops, type of bedding and type of pellet. The relation between breakage and height was found to be linear. Harder surface had more impact on pellets. The percentage of dust increased significantly after each drop as the pellets tended to break more readily and the accumulation of fines was approximately 10% after five drops. An asymptote was observed for sample size greater than 1000 g. 3) Finally, we investigated correlations of durability measurement among Tumbler, Dural and drop test. When wood pellets were used, a strong correlation (R² = 0.76) was observed between the Tumbler-measured durability and the Dural-measured durability with a logarithmic curve. The correlation between the durability derived from the drop test versus the Dural tester was significantly stronger (R² = 0.81) than when it was compared to the Tumbler tester (R² = 0.63).

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