Gasification of pure and mixed feedstock components: Effect on syngas composition and gasification efficiency

The aim of this work was to investigate whether the use of individual tree components (i.e., stem wood, bark, branches, and needles of spruces) as feedstocks during oxygen blow gasification is more efficient than using mixtures of these components. Experiments were performed at three oxygen levels in an 18-kW oxygen blown fixed bed gasifier with both single and mixed component feedstocks. The composition of the resulting syngas and the cold gas efficiency based on CO and H-2 (CGE(fuel)) were used as response variables to evaluate the influence of different feedstocks on gasification performance. Based on the experimental results and data on the composition of similar to 26000 trees drawn from a national Swedish spruce database, multivariate models were developed to simulate gasifier performance under different operating conditions and with different feedstock compositions. The experimental results revealed that the optimal CGE(fuel) with respect to the oxygen supply differed markedly between the different spruce tree components. Additionally, the models showed that co-gasification of mixed components yielded a lower CGE(fuel )than separate gasification of pure components. Optimizing the oxygen supply for the average tree composition reduced the CGE(fuel) by 1.3-6.2% when compared to optimal gasification of single component feedstocks. Therefore, if single-component feedstocks are available, it may be preferable to gasify them separately because doing so provides a higher gasification efficiency than co-gasification of mixed components

Hierarchical porous carbon foam electrodes fabricated from waste polyurethane elastomer template for electric double-layer capacitors

Plastic waste has become a major global environmental concern. The utilization of solid waste-derived porous carbon for energy storage has received widespread attention in recent times. Herein, we report the comparison of electrochemical performance of porous carbon foams (CFs) produced from waste polyurethane (PU) elastomer templates via two different activation pathways. Electric double-layer capacitors (EDLCs) fabricated from the carbon foam exhibited a gravimetric capacitance of 74.4 F/g at 0.1 A/g. High packing density due to the presence of carbon spheres in the hierarchical structure offered excellent volumetric capacitance of 134.7 F/cm3 at 0.1 A/g. Besides, the CF-based EDLCs exhibited Coulombic efficiency close to 100% and showed stable cyclic performance for 5000 charge–discharge cycles with good capacitance retention of 97.7% at 3 A/g. Low equivalent series resistance (1.05 Ω) and charge transfer resistance (0.23 Ω) due to the extensive presence of hydroxyl functional groups contributed to attaining high power (48.89 kW/kg). Based on the preferred properties such as high specific surface area, hierarchical pore structure, surface functionalities, low metallic impurities, high conductivity and desirable capacitive behaviour, the CF prepared from waste PU elastomers have shown potential to be adopted as electrodes in EDLCs

High temperature aerosol formation and emission minimisation during combustion of wood pellets

Combustion of solid biomass under fixed bed conditions is a common technique to generate heat and power in both small and large scale grate furnaces (domestic boilers, stoves, district heating plants). From both an environmental and economical perspective, one of the most interesting alternatives to replace oil and electricity for heating of family houses and apartments in Sweden is wood pellets made of stem wood sawdust from pine and spruce. Unfortunately, combustion of biomass (also wood pellets) will produce particle emissions that may have a negative implication on the human health. The smallest ( 10 microns) are produced from residual fly ash particles (refractory metals) that have left the fuel bed and been carried by the gas upwards. The finest particles ( 10 microns). The mass concentration of the middle mode (~1 microns) are significantly lower then both the fine and the coarse mode. The particle concentration in the flue gas channel is affected by both operating and fuel parameters. The results showed that both the temperature and the flow pattern in the combustion zone affect the particle emissions. Increasing combustion temperature yields decreasing emissions of coarse fly ash (> 10 microns) and soot particles, however, the emissions of submicron fly ash particles increases simultaneously. Increased mixing rate in the combustion chamber will also decrease the emissions of soot particles. In addition to the operating conditions, significant differences in particle emissions were found between different biomass fuels. For the particles that were dominated by ash elements the particle emissions were correlated to the ash concentration in the unburned fuel. However, if the combustion condition allowed for organic particles, the sooting tendency of each fuel becomes important. Furthermore, the results showed that in general the fuel type affects the particle emissions stronger than the influence from different operating and construction parameters.Godkänd; 2005; 20061003 (ysko

Detailed experimental investigation of the formation of submicron aerosols in wood pellets flames

Godkänd; 2004; 20070914 (ysko

The effect of grate and combustor aerodynamics on particle emissions in a commercial wood pellets stove

Upprättat; 2006; 20080203 (ohmmar

State-of-the-art of small-scale biomass combustion with respect to fine particle emissions : country report from Sweden

Godkänd; 2008; 20100308 (esbpet

Real-time, in situ, atomic scale observation of soot oxidation

The oxidation of soot is a complex process due to the heterogeneous structure of the material. Several mechanisms have been hypothesized based on ex situ studies, but need confirmation from in situ observation; furthermore, deeper insight is needed to develop and validate structure-dependent reaction mechanisms. In this work, soot oxidation was for the first time observed at atomic scale in situ, in real-time, using a spherical aberration-corrected Environmental Transmission Electron Microscope. The transformation of individual soot particles was followed through from initiation to complete conversion. Observations clearly showed the existence of different burning modes and particle fragmentation previously hypothesized in the literature. Furthermore, transitioning between the modes—affected by temperature and O2 pressure—was unambiguously observed, explaining previous observations regarding structure-dependent and time-varying oxidation rates. A new mode of burning in which oxidation happens rapidly in the bulk phase with the disruption of long-range lamellar order was observed and is suspected to be dominant at practically relevant conditions. The ability to unambiguously relate different burning modes in terms of nanostructure will be of importance for optimizing both soot emission abatement and properties of nanoparticulate carbon products

Laser-Based, Optical, and Traditional Diagnostics of NO and Temperature in 400 kW Pilot-Scale Furnace

A fast sensor for simultaneous high temperature (above 800 K) diagnostics of nitrogen oxide (NO) concentration and gas temperature (T) based on the spectral fitting of low-resolution NO UV absorption near 226 nm was applied in pilot-scale LKAB’s Experimental Combustion Furnace (ECF). The experiments were performed in plasma and/or fuel preheated air at temperatures up to 1550 K, which is about 200 K higher than the maximal temperature used for the validation of the developed UV NO sensor previously. The UV absorption NO and T measurements are compared with NO probe and temperature measurements via suction pyrometry and tuneable diode laser absorption (TDL) using H2O transitions at 1398 nm, respectively. The agreement between the NO UV and NO probe measurements was better than 15%. There is also a good agreement between the temperatures obtained using laser-based, optical, and suction pyrometer measurements. Comparison of the TDL H2O measurements with the calculated H2O concentrations demonstrated an excellent agreement and confirms the accuracy of TDL H2O measurements (better than 10%). The ability of the optical and laser techniques to resolve various variations in the process parameters is demonstrated