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    Guidelines for small scale biochar production system to optimise carbon sequestration outcome : a thesis presented in partial fulfilment of the requirements for the degree of Master of Engineering in Bioprocessing Engineering at Massey University, Palmerston North, New Zealand
    (Massey University, 2019) Cortez Pires de Campos, Arthur
    Biochar is made in a 60 kg batch pyrolysis reactor developed by Massey University in both prior work and during this project. This thesis details the design and control features necessary to produce biochar (charcoal) at temperatures ranging from 400-700°C. It also examines the emissions abatement necessary to achieve the best possible carbon footprint by combusting the gases to avoid release to the atmosphere. The feedstock for this work was Pinus radiata without bark. The biochar reactor is a vertical drum mounted on top of a combustion chamber containing two forced draft LPG burners. The combustion gases pass through an outer annular drum and so heat the biomass through the external wall. Evolving pyrolysis gases then move toward a central perforated core inside the drum, then descend into the combustion chamber where they are partially combusted. The range of highest treatment temperatures (400-700°C) was extended by controlling the partial combustion by varying a secondary air supply into the combustion chamber (previously only 700°C was achievable). Effective emissions abatement requires complete combustion. This work reveals that the flammability of the pyrolysis gases is not high enough to self-combust and so does not remove soot and other products of incomplete combustion, such as CO and CH4. Therefore, supplementary fuel is always needed. Here, this was achieved using modulated LPG burners at the flare. This system has the problem of batch pyrolysis reactors, where the release of volatiles from the reactor is uncontrolled, making the design of a variable rate flare system a non-trivial matter. Modifications made to the reactor design in this project include insulating the flare chimney, extending it to provide sufficient residence time, and installing adjustable vents to ensure sufficient air entrainment for complete combustion. This achieved emissions of CO and CxHy (hydrocarbon, mostly CH4) of 32 and 51 ppm respectively, which were well within the US EPA limits for both suspension and fluidised bed biomass burners(2.400 and 240 ppm respectively). The net environmental impact was determined for char made at 700°C, through carbon footprint analysis. An efficient system is needed to achieve a net sequestration benefit. Here, even with emissions abatement and the above mentioned very low CO and CxHy emissions, no net benefit was achieved. With the flare working, the net fractional sequestration was -0,14 (kg C sequestered)/(kg C in biomass). Then, when the flare is turned OFF, the net fractional sequestration was -1,2401 (kg C sequestered)/(kg C in biomass). Therefore, another frame of reference for well-operated systems is that the permissible emission should be less than 0.001 (kg C emitted as CO)/(kg C biomass), without considering methane or other GHGs.
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    Design and performance assessment for a novel friction smoke generator : a thesis presented in partial fulfilment of the requirements for the degree of Master of Engineering in Chemical and Bioprocessing at Massey University, Palmerston North, New Zealand
    (Massey University, 2018) Seraj, Muhammad Abdulrahman M.
    Friction is one of the methods used to generate smoke for food smoking applications. The method involves pressing a plank of wood against a spinning wheel, roughened to provide frictional heating. The heating raises the interface temperature above 240 °C, where smouldering occurs. The primary objective of this project was to understand the dynamics of a novel friction smoke generator, designed in a prior project, but optimised here. Subobjectives included understanding the frictional system and its thermodynamic behaviour, and preliminary attempts to define the composition of the smoke. The novel aspect of the design is supplementary heating additional to the heat generated by friction. This means the interface temperature is less dependent on frictional heating. A system control strategy was developed to control temperature and force. Twenty seven experiments were carried out. Nine of them investigated the smouldering limits without supplementary heating for various pressing forces and sliding speeds. The other twelve runs were conducted with supplementary heating for 100, 150 and 200 ˚C and various forces at constant sliding speed. The last six experiments were selected runs from the previous experiments where smoke was collected for composition analysis. With no supplementary heating, pyrolysis takes place when the pressing force is ≥49.1 N and the wheel speed is at ≥2500 rpm. These conditions generate interfacial temperatures within the pyrolysis range. When the system was heated, the limit where smouldering starts when 9.81 N and 200 ˚C were applied. Two significant results were obtained. First, the progression of smouldering, resulted in a low and high wear rate of wood. The shift between these is proposed to be an endothermic to exothermic transition. Second, the time to reach this shift is a function of the pressing force and system temperature, becoming instantaneous at 200°C for forces > 29.4 N. These allowed insight to be gained into the dynamics of heat and mass transfer during friction smoking. The smoke composition analysis indicates that controlling the volatiles formation is highly achievable by varying the smoking conditions (i.e. auxiliary heat, pressing force). The current design has some limitations, which include uncertainties in the conversion of electrical to mechanical power, vibration of the wood plank, conduction along the motor shaft and ingress of air. Recommendations are to address these by placing a thermal break on the shaft, preventing ambient air ingress into the chamber and adding a torque transducer. Further study is also recommended on the roughness and design of the friction wheel, and on scale up.
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    Pilot scale pyrolyser : compliance and mechanistic modeling : a thesis presented in partial fulfillment of the requirement for the degree of Master of Engineering in Chemical and Process Engineering at Massey University, Palmerston North, New Zealand
    (Massey University, 2017) Caco, Nadeem Salahaddin Abdul
    "A pyrolysis reactor was built in a previous project by Bridges et al (2013).The reactor is cylindrical in geometry, with a height of 1000 mm and an internal diameter of 750 mm, it stands vertically. There is a 900 mm tall and 100 mm in diameter perforated core in the center of the reactor. At the base, a combustion chamber provides the hot gases required for heating. The hot gases produced travel up and around the reactor through an annulus region of 11 mm. Heat from the gases is transferred to the reactor wall and then to the wood-chips inside. As drying and pyrolysis reactions occur, gases flow in the same direction as the heat towards the perforated core at the center. Hot pyrolysis gases then flow downwards towards the combustion chamber where they are partially combusted before flowing around the reactor and out the flue stack. This project aimed at mathematically modeling this reactor and also improving the way emissions are released so that it complies with EPA air quality standards. A mathematical model of an ‘open source’ pilot-scale pyrolysis reactor was produced to predict the product yield, carbon foot-print, biochar quality and the time taken to achieve complete pyrolysis. A non-equilibrium thermodynamic approach was used which allowed for the use of COMSOL Multi-Physics to solve the model. The Finite Element Method (FEM) was used to solve the system of equations. Pyrolysis kinetics are complex and no single model has yet been widely accepted, therefore simplifications were necessary in this model so that a reasonable solution time could be achieved while producing acceptable results. The model profile of the centre temperature closely followed that of the experimental results and thus the model was considered valid. In addition, modifications were made to the original design of the pyrolyser in order to improve emissions compliance and improve operations of the pyrolysis. It was important to manage fugitive emissions and completely combust any volatile vapours that would be released into the atmosphere while controlling the operating parameters. In order to achieve this, the following were implemented: 1) The combustion chamber was sealed completely so that no fugitive emissions can escape while limiting the ingress of oxygen. 2) A secondary blower was installed in order to better control the oxygen supply to the burners. 3) The original steel lid, which warped during pyrolysis runs resulting in gaseous leaks, was replaced with a more rigid ceramic lid that doesn’t effectively expand when heated. 4) Two 3.4 kW burners were added to the single 3.4 kW burner flare. This gives a total power of 10.2 kW, which is estimated to be enough to completely burn all gaseous products leaving the system"--Preface
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    A study of the importance of secondary reactions in char formation and pyrolysis : a dissertation presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Process Engineering at Massey University, Manawatū, New Zealand
    (Massey University, 2016) Ripberger, Georg Dietrich
    Anthropogenic climate change, caused primarily by excessive emissions of carbon dioxide, has led to a renewed interest in char, the solid product of pyrolysis. When applied to soil as biochar it can both sequester carbon and improve soil function. To make its manufacture environmentally friendly and economically viable it is important to maximise char yield, which can be done by promoting secondary reactions. This research shows that secondary reactions, which are enhanced by prolonged vapour-phase residence time and concentration, not only increase the char yield but are the source of the majority of the char formed. All four biomass constituents (extractives, cellulose, hemicellulose and lignin) undergo secondary reactions concurrent with primary reactions over the entire pyrolysis range ≈ 140 to 500 °C, which makes it practically impossible to separate them. Secondary char formation was confirmed to be exothermic which affects the overall heat of pyrolysis. Impregnating the feedstock with the elements K, Mg and P, which are plant macro-nutrients naturally present in biomass, resulted in the catalysis of secondary char formation. The results reveal that a first order reaction model does not describe pyrolysis accurately when char formation is enhanced by catalysis and secondary reactions. Secondary char can be enhanced by increasing the particle size but there is a limit due to increased cracking and fracturing of the pyrolysing solid. This limitation is overcome by pyrolysis in an enclosed vessel, termed autogenous pressure pyrolysis, which was discovered to cause significant changes in the volatile pyrolysis products; indicating the co-production of a high quality liquid. This process, however, negatively affects the char properties relevant for biochar like the surface area, similar to self-charring and co-carbonisation of condensed volatile pyrolysis products. To increase research capabilities a unique high temperature/ high pressure reactor (600 °C at 20 MPa) was designed to allow the detailed characterisation of all three pyrolysis product classes under extreme pyrolysis conditions. This was demonstrated to be invaluable for understanding the underlying pyrolysis mechanism and physical processes at play.
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    Design and characterisation of an 'open source' pyrolyser for biochar production : a thesis presented in partial fulfilment of the requirements for the degree of Master of Engineering in Chemical and Bioprocess Engineering at Massey University, Palmerston North, New Zealand
    (Massey University, 2013) Bridges, Rhonda
    An 'open source' field-scale batch pyrolyser was designed and constructed to produce biochar, which is the solid residue formed when biomass thermally decomposes in the absence of oxygen. The design approach was focused on simplicity for the intended target user, a hobby farmer. This is achieved in a batch process, where temperature ramp rates, gas flows and the end-point are controlled. Solids handling is only required at either end of the process. LPG is used as the initial heating source and later as the ignition source when pyrolysis gases are recycled. A mathematical model formulation of the process was developed to predict the proportions of products produced as well as the time taken to achieve complete pyrolysis. Reaction kinetics are complex and not fully understood. In this model, simplifications were taken to provide guidelines for the reactor design as well as the effects of moisture on the process efficiencies. The quality performance of the 'open source' pyrolyser was determined by comparing its biochar to that produced in a lab scale gas fired drum pyrolyser. Parameters varied on the lab drum pyrolyser were highest treatment temperature in the range 300 to 700 °C, sample size, moisture content and grain direction for Pinus radiata. The properties that were investigated are elemental composition (C, H, N, S), proximate analysis (moisture, volatile matter and fixed carbon) and char yield (% wt/wt). The ash content was determined by residue on ignition. For the lab scale experiments, it was found with increasing peak temperature that yield, volatile matter and hydrogen to carbon ratio decrease. Yield was unaffected by moisture, size and grain direction. The design of the pilot reactor followed the principle observed with particle size that, in order to get maximum residence time of the vapour and tar in the reactor, the reactor was designed with a perforated core so that the vapours have a tortuous path of travel. This design also meant that heat and mass transfer occurred in the same direction, from the outer wall to the perforated core. In comparison to the lab scale pyrolyser, the same trends were observed in regards to temperature. High yields of 29.7 wt % and 28.8 wt % were obtained from wood with an initial moisture content of 21.9 wt % and 60.4 wt % respectively, confirming yield is unaffected by moisture. Mass and energy balances were conducted on both the lab scale and pilot scale pyrolysers. For every kilogram of carbon in LPG used on the lab scale pyrolyser, an average of 0.25 kilograms of carbon is produced at 700 °C. Based on the optimum run for the pilot scale, for every kilogram of carbon in LPG used, 2.6 kilograms of carbon is produced at 700 °C.