Production and characterization of biochar from biomasses

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Reducing Emissions from Current Clean-Burn Wood Stove Technology by Automating the Combustion Air Supply and Improving the End-User Interaction – Two Important Primary Measures

The current work concerns two of the most important primary measures to reduce emissions from small scale appliances for space heating; improvement and optimization of current technology and user behavior, where the latter is related to the effects of the ignition procedure, fuel quality and type, and amount of wood when loading and re-loading. Air-control both concerns user behavior and technology improvement. A recently developed in-house automatic air-control system was compared to manual operation. The ignition procedure is important and affects the quality of the combustion, not only for the ignition period itself but also for the subsequent burning periods. Two self-defined categories of primary measures were studied, primary measure A and B, as PMA (automated air flow) and PMB (manual operation varying the ignition procedure, wood specie, amount of fuel, log size and moisture content), respectively

Gasification of Wood Powder in a Small-scale Entrained Flow Gasifier

Gasification of wood powder milled from commercially available wood pellets have been performed in a small-scale entrained flow gasifier. The main aim of this study is to investigate operational and feedstock requirements (mainly particle size distribution, (PSD)) for this small-sized gasifier to perform with good carbon conversion ratio. The effects of several parameters were investigated, resulting in variable performance. The investigated parameters were equivalence ratio (lambda, ?), oxidant type (air or oxygen), thermal load, pressure, burner head configuration and PSD. The syngas quality, defined as cold gas efficiency (CGE) and/or carbon conversion efficiency (CC) was reported as function of the above parameters. The gasifier ?achieved a satisfactory conversion when using oxygen as oxidant and at elevated pressure (8.2 bar(a))

Thermal Decomposition Kinetics of Woods with an Emphasis on Torrefaction

The pyrolysis kinetics of Norwegian spruce and birch wood was studied to obtain information on the kinetics of torrefaction. Thermogravimetry (TGA) was employed with nine different heating programs, including linear, stepwise, modulated and constant reaction rate (CRR) experiments. The 18 experiments on the 2 feedstocks were evaluated simultaneously via the method of least-squares. Part of the kinetic parameters could be assumed common for both woods without a considerable worsening of the fit quality. This process results in better defined parameters and emphasizes the similarities between the woods. Three pseudo-components were assumed. Two of them were described by distributed activation energy models (DAEMs), while the decomposition of the cellulose pseudo-component was described by a self-accelerating kinetics. In another approach, the three pseudo-components were described by n-order reactions. Both approaches resulted in nearly the same fit quality, but the physical meaning of the model, based on three n-order reactions, was found to be problematic. The reliability of the models was tested by checking how well the experiments with higher heating rates can be described by the kinetic parameters obtained from the evaluation of a narrower subset of 10 experiments with slower heating. A table of data was calculated that may provide guidance about the extent of devolatilization at various temperature residence time values during wood torrefaction

Kinetic Behavior of Torrefied Biomass in an Oxidative Environment

The combustion of four torrefied wood samples and their feedstocks (birch and spruce) was studied at slow heating programs, under well-defined conditions by thermogravimetry (TGA). Particularly low sample masses were employed to avoid the self-heating of the samples due to the huge reaction heat of the combustion. Linear, modulated and constant-reaction rate (CRR) temperature programs were employed in the TGA experiments in gas flows of 5 and 20% O2. In this way the kinetics was based on a wide range of experimental conditions. The ratio of the highest and lowest peak maxima was around 50 in the experiments used for the kinetic evaluation. A recent kinetic model of Várhegyi et al. [Energy & Fuels 2012, 26, 1323-1335] was employed with modifications. This model consists of two devolatilization reactions and a successive char burn-off reaction. The cellulose decomposition in the presence of oxygen has a self-accelerating (autocatalytic) kinetics. The decomposition of the non-cellulosic parts of the biomass was described by a distributed activation model. The char burn-off was approximated by power-law (n-order) kinetics. Each of these reactions has its own dependence on the oxygen concentration that was expressed by power-law kinetics, too. The complexity of the applied model reflects the complexity of the studied materials. The model contained 15 unknown parameters for a given biomass. Part of these parameters could be assumed common for the six samples without a substantial worsening of the fit quality. This approach increased the average experimental information for an unknown parameter by a factor of 2 and revealed the similarities in the behavior of the different samples

The effect of kaolin on the combustion of demolition wood under well-controlled conditions

In an attempt to look at means for reduction of corrosion in boilers, combustion experiments are performed on demolition wood with kaolin as additive. The experiments were performed in a multi-fuel reactor with continuous feed of pellets and by applying staged air combustion. A total characterization of the elemental composition of the fuel, the bottom ash and some particle size stages of fly ash was performed. This was done in order to follow the fate of some of the problematic compounds in demolition wood as a function of kaolin addition and other combustion-related parameters. In particular chlorine and potassium distribution between the gas phase, the bottom ash and the fly ash is reported as a function of increased kaolin addition, reactor temperature and air staging. Kaolin addition of 5 and 10% were found to give the least aerosol load in the fly ash. In addition, the chlorine concentration in aerosol particles was at its lowest levels for the same addition of kaolin, although the difference between 5 and 10% addition was minimal. The reactor temperature was found to have a minimal effect on both the fly ash and bottom ash properties

The effect of peat ash addition to demolition wood on the formation of alkali, lead and zinc compounds at staged combustion conditions

Combustion experiments were performed in a multi-fuel reactor with continuous feed of pellets by applying staged air combustion. Total characterization of the elemental composition of the fuel, the bottom ash and some particle size stages of fly ash was performed. This was done in order to follow the fate of some of the problematic compounds in demolition wood as a function of peat-ash addition and other combustion related parameters. A method was developed to estimate the composition and speciation of the salt part of aerosols based on SEM/EDX analysis. The results show that the concentrations of zinc and lead account for 40-50% of the salts produced for the small particles (0.093 mu m) and up to 90% for the larger particles (1.59 mu m). A considerable part of these metals are chemically bound to chlorides and sulfates together with potassium and sodium indicating extensive volatilization of zinc and lead. The experiments show that the reactions of potassium, zinc and lead are the most affected. This gives rise to higher concentrations of zinc and lead in the aerosols. The chloride content in the aerosols decreases with increased peat ash addition. This will have an inhibiting effect on corrosion, but the higher Zn and especially Pb concentrations will lead to a lower first melting point of the aerosol particles. This may promote deposition and cause corrosion