A comprehensive dual-scale wood torrefaction model : application to the analysis of thermal run-away in industrial heat treatment processes

A dual-scale model of the torrefaction of wood was developed and used to study industrial configurations. At the local scale, the computational code solves the coupled heat and mass transfer and the thermal degradation mechanisms of the wood components. At the global scale, the two-way coupling between the boards and the stack channels is treated as an integral component of the process. This model is used to investigate the effect of the stack configuration on the heat treatment of the boards. The simulations highlight that the exothermic reactions occurring in each single board can be accumulated along the stack. This phenomenon may result in a dramatic eterogeneity of the process and poses a serious risk of thermal runaway, which is often observed in industrial plants. The model is used to explain how thermal runaway can be lowered by increasing the airflow velocity, the sticker thickness or by gas flow reversal.

Structural and chemical modifications of typical South African biomasses during torrefaction

Torrefaction experiments were carried out for three typical South African biomass samples (softwood chips, hardwood chips and sweet sorghum bagasse) to a weight loss of 30wt.%. During torrefaction, moisture, non-structural carbohydrates and hemicelluloses were reduced, resulting in a structurally modified torrefaction product. There was a reduction in the average crystalline diameter (La) (XRD), an increase in the aromatic fraction and a reduction in aliphatics (substituted and unsubstituted) (CPMAS 13C NMR). The decrease in the aliphatic components of the lignocellulosic material under the torrefaction conditions also resulted in a slight ordering of the carbon lattice. The degradation of hemicelluloses and non-structural carbohydrates increased the inclusive surface area of sweet sorghum bagasse, while it did not change significantly for the woody biomasses.

PRODUCTION OF BIOFUEL INTERMEDIATES FROM WOODY FEEDSTOCKS VIA FAST PYROLYSIS AND TORREFACTION

The main objective of this research was to investigate pyrolysis and torrefaction of forest biomass species using a micropyrolysis instrument. It was found that 30-45% of the original sample mass remained as bio-char in the pyrolysis temperature range of 500 - 700˚C for aspen, balsam, and switchgrass. The non-char mass was converted to gaseous and vapor products, of which 10-55% was water and syngas, 2-12% to acetic acid, 2-12% to hydroxypropanone, 1-3% to furaldehyde, and 5-15% to various phenolic compounds. In addition, several general trends in the evolution of gaseous species were indentified when woody feedstocks were pyrolyzed. With increasing temperature it was observed that: (1) the volume of gas produced increased, (2) the volume of CO2 decreased and the volumes of CO and CH4 increased, and (3) the rates of gas evolution increased. In the range of torrefaction temperature (200 - 300˚C), two mechanistic models were developed to predict the rates of CO2 and acetic acid product formation. The models fit the general trend of the experimental data well, but suggestions for future improvement were also noted. Finally, it was observed that using torrefaction as a pre-curser to pyrolysis improves the quality of bio-oil over traditional pyrolysis by reducing the acidity through removal of acetic acid, reducing the O/C ratio by removal of some oxygenated species, and removing a portion of the water.

Process simulation of co-firing torrefied biomass in a 220 MWe coal-fired power plant

Torrefaction based co-firing in a pulverized coal boiler has been proposed for large percentage of biomass co-firing. A 220 MWe pulverized coal-power plant is simulated using Aspen Plus for full understanding the impacts of an additional torrefaction unit on the efficiency of the whole power plant, the studied process includes biomass drying, biomass torrefaction, mill systems, biomass/coal devolatilization and combustion, heat exchanges and power generation. Palm kernel shells (PKS) were torrefied at same residence time but 4 different temperatures, to prepare 4 torrefied biomasses with different degrees of torrefaction. During biomass torrefaction processes, the mass loss properties and released gaseous components have been studied. In addition, process simulations at varying torrefaction degrees and biomass co-firing ratios have been carried out to understand the properties of CO₂ emission and electricity efficiency in the studied torrefaction based co-firing power plant. According to the experimental results, the mole fractions of CO ₂ and CO account for 69-91% and 4-27% in torrefied gases. The predicted results also showed that the electrical efficiency reduced when increasing either torrefaction temperature or substitution ratio of biomass. A deep torrefaction may not be recommended, because the power saved from biomass grinding is less than the heat consumed by the extra torrefaction process, depending on the heat sources. 

Analise técnica, econômica e ecológica da incorporação de sistemas de gaseificação de bagaço de cana-de-açúcar no setor sucroalcooleiro: uso de ciclos combinados para o aumento da oferta de eletricidade

Pós-graduação em Engenharia Mecânica - FEG

Development of an optimization model for biofuel facility size and location and a simulation model for design of a biofuel supply chain

To mitigate greenhouse gas (GHG) emissions and reduce U.S. dependence on imported oil, the United States (U.S.) is pursuing several options to create biofuels from renewable woody biomass (hereafter referred to as “biomass”). Because of the distributed nature of biomass feedstock, the cost and complexity of biomass recovery operations has significant challenges that hinder increased biomass utilization for energy production. To facilitate the exploration of a wide variety of conditions that promise profitable biomass utilization and tapping unused forest residues, it is proposed to develop biofuel supply chain models based on optimization and simulation approaches. The biofuel supply chain is structured around four components: biofuel facility locations and sizes, biomass harvesting/forwarding, transportation, and storage. A Geographic Information System (GIS) based approach is proposed as a first step for selecting potential facility locations for biofuel production from forest biomass based on a set of evaluation criteria, such as accessibility to biomass, railway/road transportation network, water body and workforce. The development of optimization and simulation models is also proposed. The results of the models will be used to determine (1) the number, location, and size of the biofuel facilities, and (2) the amounts of biomass to be transported between the harvesting areas and the biofuel facilities over a 20-year timeframe. The multi-criteria objective is to minimize the weighted sum of the delivered feedstock cost, energy consumption, and GHG emissions simultaneously. Finally, a series of sensitivity analyses will be conducted to identify the sensitivity of the decisions, such as the optimal site selected for the biofuel facility, to changes in influential parameters, such as biomass availability and transportation fuel price. Intellectual Merit The proposed research will facilitate the exploration of a wide variety of conditions that promise profitable biomass utilization in the renewable biofuel industry. The GIS-based facility location analysis considers a series of factors which have not been considered simultaneously in previous research. Location analysis is critical to the financial success of producing biofuel. The modeling of woody biomass supply chains using both optimization and simulation, combing with the GIS-based approach as a precursor, have not been done to date. The optimization and simulation models can help to ensure the economic and environmental viability and sustainability of the entire biofuel supply chain at both the strategic design level and the operational planning level. Broader Impacts The proposed models for biorefineries can be applied to other types of manufacturing or processing operations using biomass. This is because the biomass feedstock supply chain is similar, if not the same, for biorefineries, biomass fired or co-fired power plants, or torrefaction/pelletization operations. Additionally, the research results of this research will continue to be disseminated internationally through publications in journals, such as Biomass and Bioenergy, and Renewable Energy, and presentations at conferences, such as the 2011 Industrial Engineering Research Conference. For example, part of the research work related to biofuel facility identification has been published: Zhang, Johnson and Sutherland [2011] (see Appendix A). There will also be opportunities for the Michigan Tech campus community to learn about the research through the Sustainable Future Institute.

Development of a Mechanism and Process to Continuously Produce Spherical, Torrefied Biomass

Thesis (Master, Mechanical and Materials Engineering) -- Queen's University, 2016-06-17 02:15:25.215

Comparison of the effect of pre-treatment and catalysts on liquid quality from fast pyrolysis of biomass

The overall objective of this work was to compare the effect of pre-treatment and catalysts on the quality of liquid products from fast pyrolysis of biomass. This study investigated the upgrading of bio-oil in terms of its quality as a bio-fuel and/or source of chemicals. Bio-oil used directly as a biofuel for heat or power needs to be improved particularly in terms of temperature sensitivity, oxygen content, chemical instability, solid content, and heating values. Chemicals produced from bio-oil need to be able to meet product specifications for market acceptability. There were two main objectives in this research. The first was to examine the influence of pre-treatment of biomass on the fast pyrolysis process and liquid quality. The relationship between the method of pre-treatment of biomass feedstock to fast pyrolysis oil quality was studied. The thermal decomposition behaviour of untreated and pretreated feedstocks was studied by using a TGA (thermogravimetric analysis) and a Py-GC/MS (pyroprobe-gas chromatography/mass spectrometry). Laboratory scale reactors (100g/h, 300g/h, 1kg/h) were used to process untreated and pretreated feedstocks by fast pyrolysis. The second objective was to study the influence of numerous catalysts on fast pyrolysis liquids from wheat straw. The first step applied analytical pyrolysis (Py-GC/MS) to determine which catalysts had an effect on fast pyrolysis liquid, in order to select catalysts for further laboratory fast pyrolysis. The effect of activation, temperature, and biomass pre-treatment on catalysts were also investigated. Laboratory experiments were also conducted using the existing 300g/h fluidised bed reactor system with a secondary catalytic fixed bed reactor. The screening of catalysts showed that CoMo was a highly active catalyst, which particularly reduced the higher molecular weight products of fast pyrolysis. From these screening tests, CoMo catalyst was selected for larger scale laboratory experiments. With reference to the effect of pre-treatment work on fast pyrolysis process, a significant effect occurred on the thermal decomposition of biomass, as well as the pyrolysis products composition, and the proportion of key components in bio-oil. Torrefaction proved to have a mild influence on pyrolysis products, when compared to aquathermolysis and steam pre-treatment.

DEVELOPMENT OF A MECHANISM AND PROCESS TO CONTINUOUSLY PRODUCE SPHERICAL, TORREFIED BIOMASS PELLETS

A recently developed novel biomass fuel pellet, the Q’ Pellet, offers significant improvements over conventional white pellets, with characteristics comparable to those of coal. The Q’ Pellet was initially created at bench scale using a proprietary die and punch design, in which the biomass was torrefied in-situ¬ and then compressed. To bring the benefits of the Q’ Pellet to a commercial level, it must be capable of being produced in a continuous process at a competitive cost. A prototype machine was previously constructed in a first effort to assess continuous processing of the Q’ Pellet. The prototype torrefied biomass in a separate, ex-situ reactor and transported it into a rotary compression stage. Upon evaluation, parts of the prototype were found to be unsuccessful and required a redesign of the material transport method as well as the compression mechanism. A process was developed in which material was torrefied ex-situ and extruded in a pre-compression stage. The extruded biomass overcame multiple handling issues that had been experienced with un-densified biomass, facilitating efficient material transport. Biomass was extruded directly into a novel re-designed pelletizing die, which incorporated a removable cap, ejection pin and a die spring to accommodate a repeatable continuous process. Although after several uses the die required manual intervention due to minor design and manufacturing quality limitations, the system clearly demonstrated the capability of producing the Q’ Pellet in a continuous process. Q’ Pellets produced by the pre-compression method and pelletized in the re-designed die had an average dry basis gross calorific value of 22.04 MJ/kg, pellet durability index of 99.86% and dried to 6.2% of its initial mass following 24 hours submerged in water. This compares well with literature results of 21.29 MJ/kg, 100% pellet durability index and <5% mass increase in a water submersion test. These results indicate that the methods developed herein are capable of producing Q’ Pellets in a continuous process with fuel properties competitive with coal.