Top-lit Updraft Gasifier Research Articles

Multi-Criteria Optimization of a Laboratory Top-Lit Updraft Gasifier in Order to Reduce Greenhouse Gases and Particulate Matter Emissions

Air pollution from combustion processes is harming human health and the environment. To mitigate this, one needs to adopt cleaner energy production methods, in particular, to optimize combustion systems in order to minimize pollutants and increase efficiency. Flue gas analysis and particulate matter (PM) monitoring, starting from the prototype phase, is crucial to minimize and regulate pollutant emissions. This article analyses the emissions of pollutants and particulate matter from a combustion test gasifier working on the Top-Lit Updraft (TLUD) principle in order to optimize functionality and reduce exhaust emissions. Three experiments were performed in which the primary (gasification) air flow rate (GA) was kept constant at 25 L/min, and the secondary (combustion) air flow rate (CA) was adjusted to obtain a CA/GA ratio of 2 (50 L/min), 3 (75 L/min), and 4 (100 L/min) respectively. Based on a multi-criterial analysis, the optimal CA/GA ratio for TLUD combustion is 3, offering a well-rounded performance in output temperatures, PM and greenhouse gases (GHG) emissions, and efficiency, while the CA/GA ratio of 4 has good PM and GHG emissions performance but lower efficiency, and the CA/GA ratio of 2 is the least favorable due to its poor performance in output temperatures, PM and GHG emissions.

Emission of volatile organic compounds during open fire cooking with wood biomass: Traditional three-stone open fire vs. gasifier cooking stove in rural Kenya

Cooking with wood biomass fuels releases hazardous air pollutants, including volatile organic compounds (VOCs), that often disproportionally affect women and children. This study, conducted in Kwale and Siaya counties in Kenya, employed thermal desorption gas chromatography – mass spectrometry to analyse VOC emissions from cooking with a wood biomass three-stone open fire vs. top-lit updraft gasifier stove. In kitchens with adequate ventilation, total VOC levels increased from 35–252 μg∙m−3 before cooking to 2235–5371 μg∙m−3 during open fire cooking, whereas use of a gasifier stove resulted in reduced emissions from cooking by 48–77 % (506–2778 μg∙m−3). However, in kitchens with poor ventilation, there was only a moderate difference in total VOC levels between the two methods of cooking (9034–9378 μg∙m−3 vs. 6727–8201 μg∙m−3 for the three-stone open fire vs. gasifier stove, respectively). Using a non-target screening approach revealed significantly increased levels of VOCs, particularly benzenoids, oxygenated and heterocyclic compounds, when cooking with the traditional open fire, especially in closed kitchens, highlighting the effects of poor ventilation. Key hazardous VOCs included benzene, naphthalene, phenols and furans, suggesting potential health risks from cooking. In kitchens with good ventilation, use of the gasifier stove markedly reduced emissions of these priority toxic VOCs compared to cooking with an open fire. Thus, substituting open fires with gasifier stoves could help to improve household air quality and alleviate health risks. The study revealed that VOCs were present prior to cooking, possibly originating from previously cooked food (buildup) or the outside environment. VOC emissions were also exacerbated by reduced air flow in high humidity during rainfall, suggesting an area for further research. The findings underscore the importance of adopting cleaner cooking technologies and enhancing kitchen ventilation to mitigate the impacts of VOCs in developing countries.

Composition and morphology of biomass-based soot from updraft gasifier system

Soot is an aerosol formed by incomplete combustion of carbonaceous materials, and its formation in biomass gasification is inevitable. It is crucial to know the properties of the soot produced in the exhaust of gasification reactors in order to appreciate both its advantages and disadvantages. In this study, a variety of analytical techniques were used to examine the content and morphology of biomass soot produced by a top-lit updraft gasifier. The results of the experiment revealed that carbon and oxygen make up the majority of the soot, with minor amounts of other components. Both aromatic and aliphatic groups with significant oxygen concentrations can be seen in the soot based on the distribution of functional groups. The morphology revealed an uneven, stratified, amorphous sample. Meanwhile, the sample had a surface area of 193.8 m2/g and a pore diameter of 2.68 nm. These porous qualities point to a potential use of the soot sample as an adsorbent in water filtration after activation.

Design and simulation of a novel top-lit downdraft gasifier cookstove and performance comparison with a conventional top-lit updraft cookstove

This study designed and fabricated a novel top-lit downdraft gasifier stove (TLDDGS), which was compared with a traditional top-lit updraft gasifier stove (TLUDGS) in terms of modeling and performance. The experimental and simulation results demonstrated that the novel TLDDGS exhibits a downward-flow configuration. The average fuel consumption measured in the experiments was 4.57 ± 0.933 g/min. The average flame temperature from the experiment was 608 ± 43 °C. The TLDDGS mean flame temperature remained stable throughout the experiment. The O2, H2, CO2, CO, CH4, and N2 in the diluted syngas from the experiment were 16.07, 0.33, 0.66, 2.56, 0.34, and 80.04% by volume, respectively. The total suspended particulates and CO in TLDDGS and TLUDGS were 15 and 28 mg/m3 and 335 and 69 ppm, respectively, which are within the limits specified by the local standard. Thus, the developed TLDDGS is a promising alternative for sophisticated cooking applications because of its superior performance in terms of flame stability.

Co-gasification of biomass and coal in a top-lit updraft fixed bed gasifier: Syngas composition and its interchangeability with natural gas for combustion applications

The co-gasification of biomass and coal is a promising approach for efficiently integrating the unique advantages of different gasification feedstock with syngas production. Additionally, syngas from the co-gasification of locally available biomass and coal could supplement the natural gas used in household and industrial burners. The top-lit updraft gasifier features a moving ignition front that starts at the top and propagates downward through the solids bed, while air enters from the bottom and the gas product flows upwards. This study assesses the co-gasification performance of palm kernel shell and high-volatile bituminous coal in a top-lit updraft fixed bed gasifier using 70, 85, and 100 vol% biomass and equivalence ratios ranging from 0.26 to 0.34. The results indicate that the ignition front propagates faster and is more uniform as the biomass volume increases. Micro GC analysis revealed that the H2/CO ratio remained in the range of 0.57–0.59, 0.49–0.51, and 0.42–0.46 for experiments with 70, 85, and 100 vol% biomass, respectively. A gas interchangeability analysis showed that syngas-natural gas blends with up to 15 vol% of syngas could combust in atmospheric natural gas burners without modifications. Thus, the top-lit updraft gasifier shows excellent potential for the co-gasification of coal and biomass. Further research on this technology should explore steam as a gasification agent to enhance the syngas energy content and continuous solids feeding.

Emission minimization of a top-lit updraft gasifier cookstove based on experiments and detailed CFD analyses

Around 2.7 billion people worldwide have no access to clean cooking equipment, which leads to major health problems due to high emissions of unburned products (VOC, CO and soot). A top-lit updraft gasifier cookstove with forced draft was identified as the technology with the highest potential for reducing harmful emissions from incomplete combustion in simple cookstoves. The basic variant of the stove was equipped with a fan for efficient mixing of product gas with air and fired with pellets to increase the energy density of low-grade residues. The development was conducted based on water boiling test experiments for wood and rice hull pellets and targeted CFD simulations of flow, heat transfer and gas phase combustion with a comprehensive description of the reaction kinetics, which were validated by the experiments. Emphasis was put on the reduction of CO emissions as an indicator for the burnout quality of the flue gas. The optimisation was carried out in several steps, the main improvements being the design of a sufficiently large post-combustion chamber and a supply of an appropriate amount of primary air for a more stable fuel gasification. The experiments showed CO emissions <0.2 g/MJdel for wood and rice hull pellets, which corresponds to a reduction by a factor of about 15 to 20 compared to the basic forced draft stove concept. Furthermore, these values are between 5 and 10 times lower than published water boiling test results of the best available cookstove technologies and are already close to the range of automatic pellet furnaces for domestic heating, which are considered to be the benchmark for the best possible reduction of CO emissions.

Modeling product distribution of top-lit updraft gasification

A kinetic model for predicting biochar, producer gas, and tar formations of top-lit updraft (TLUD) gasification was developed. The three main zones within the TLUD gasifier, the pyrolysis, incomplete combustion, and reduction reaction zones, were incorporated into the model and sequentially solved. Validated with experimental data, the model was found capable of predicting biochar yield on pine woodchips at varying airflow rates, biomass moisture contents, and biomass compactness. However, when the particle size was varied, the model underestimated biochar yield. The model also accurately predicted the higher heating value of the producer gas that varied from 3.45 to 3.98 MJ/m3 compared to 3.61 to 3.67 MJ/m3 for the experimental results. The model qualitatively predicted tar content in the producer gas at varying conditions. However, accurate quantification of tar generation in TLUD gasification was not achieved.

The Effect of Gasification Conditions on the Surface Properties of Biochar Produced in a Top-Lit Updraft Gasifier

The effect of airflow rate, biomass moisture content, particle size, and compactness on the surface properties of biochar produced in a top-lit updraft gasifier was investigated. Pine woodchips were studied as the feedstock. The carbonization airflow rates from 8 to 20 L/min were found to produce basic biochars (pH &gt; 7.0) that contained basic functional groups. No acid functional groups were presented when the airflow increased. The surface charge of biochar at varying airflow rates showed that the cation exchange capacity increased with airflow. The increase in biomass moisture content from 10 to 14% caused decrease in the pH from 12 to 7.43, but the smallest or largest particle sizes resulted in low pH; therefore, the carboxylic functional groups increased. Similarly, the biomass compactness exhibited a negative correlation with the pH that reduced with increasing compactness level. Thus, the carboxylic acid functional groups of biochar increased from 0 to 0.016 mmol g−1, and the basic functional group decreased from 0.115 to 0.073 mmol g−1 when biomass compactness force increased from 0 to 3 kg. BET (Brunauer-Emmett-Teller) surface area of biochar was greater at higher airflow and smaller particle size, lower moisture content, and less compactness of the biomass.

Effect of air flow rate and secondary air jets on the operation of TLUD gasifier cookstove

ABSTRACTThe current article presents experimental results of the operation of top-lit updraft (TLUD) gasifier cookstove. The independent variables for the experiments are secondary airflow rate, the ratio of the secondary to the primary air flow rate, and the secondary air jet velocity. Based on the mass, temperature, and gas measurements the stove performance variables like effectiveness, combustion efficiency, AF, and power are calculated. The results show that varying the secondary airflow rate and jet velocities affect the fuel consumption rate for the flow rates considered. Combustion efficiency is relatively constant around 98%. Increasing the secondary air decreases the CO emission. Effectiveness starts to saturate beyond AF of 10. Useful power is found to be a strong function of secondary air.

Participatory trials of on-farm biochar production and use in Tamale, Ghana

Urban agriculture is characterized by fast rotation of cropping cycles and high inputs and outputs on relatively small areas of land. Depletion of soil organic carbon and low nutrient use efficiency are severe agricultural constraints in the sandy soils of West Africa. We hypothesized that such an intensive system would provide ideal preconditions for the use of biochar, that biochar would enhance yields in urban horticulture, and that farmers would be able to produce biochar for on-farm use in Tamale, Ghana. Therefore, we studied the opportunities and challenges of biochar using a semi-participatory research approach. Working with 12 participant farmers, we defined research questions which were relevant to their livelihoods and collected qualitative and observational data, which determined the selection of variables to measure quantitatively. Different quality parameters such as leaf color and stiffness of lettuce were important to farmers and marketers when assessing the agronomic benefits of biochar. By adding biochar to their normal agricultural practice farmers were able to increase lettuce yields by 93%. This remarkable increase might be partially caused by farmers’ improved management of biochar plots: they concentrated their resources where they expected to yield the largest returns. Using a simple top-lit updraft gasifier, a special chimney for rice husk carbonization, it was relatively simple for farmers to produce biochar in the field, with an efficiency of 15–33%. These stoves’ payback times were between 1 and 2 months. Yet, rather than the efficiency of the carbonization technology, often emphasized in biochar research, the availability of feedstock and labor considerations determine the technology selected by farmers for biochar production. This is a novel approach to considering the economic realities of farmers in a semi-participatory appraisal where farmers both produce and apply biochar. This is crucial in order to understand and identify meaningful and economically viable uses of biochar.

Effects of operational mode on particle size and number emissions from a biomass gasifier cookstove

Interest in the size distribution of particles emitted from biomass cookstoves stems from the hypothesis that exposure to ultrafine particles is more detrimental to human health than exposure to accumulation mode or other size regimes. Previous studies have reported that gasifier cookstoves emit smaller particles than other cookstove designs under steady operating conditions. In the present study, the number size distribution of particles emitted from a forced-air gasifier cookstove was measured at 1 Hz as the stove transitioned between several steady and transient operating modes. During normal operation, when the stove functioned as a top-lit updraft gasifier, the distribution was bimodal, with peaks at 10 nm and 40 nm, when a pot of water was on the stove. The distribution became unimodal with a peak at 10 nm when the pot was removed. Once the fuel bed had completely gasified and the secondary flame extinguished, the concentration of particles increased and the peak in number concentration shifted to a...

Airflow and insulation effects on simultaneous syngas and biochar production in a top-lit updraft biomass gasifier

Abstract The objective of this study was to understand the effect of airflow and insulation on syngas and biochar generations of rice hulls and woodchips in a top-lit updraft gasifier. Biochar yield decreased with increasing airflow. The highest biochar yields of 39% and 27% were achieved at 8 L/min airflow for rice hulls and woodchips, respectively. The mass fraction of syngas in the products increased with increasing airflow, which ranged from 88–89% for rice hulls and 93–94% for woodchips. The H 2 composition in syngas also increased at higher airflow rates; it peaked at 4.2–4.4% for rice hulls and 5.7–6.6% (v/v) for woodchips, which was not affected by insulation. The carbon monoxide content in syngas ranged from approximately 12 to 15% (v/v) and was not affected by airflow or insulation. Average tar content in syngas decreased for both biomasses when airflow increased, but adding insulation resulted in significantly higher tar content in syngas. The biomass type also had significant effects on gasifier performance. Biochar yields from rice hulls were greater than that from woodchips at all airflow rates. The lowest tar contents in syngas were approximately 1.16 and 11.88 g/m 3 for rice hulls and woodchips, respectively.

Phosphorus Sorption Behavior of Torrefied Agricultural Byproducts under Sonicated Versus Non-Sonicated Conditions

The application of agrichar derived from organic feedstocks has the potential to improve soil fertility and crop production by providing major nutrients like phosphorus (P) to the crop, and in some cases also reducing P leaching. The effect of agrichar on the leaching of P in soils is not uniform and can vary depending on the type of agrichar and amount applied. The objective of this study was to (i) evaluate the behavior of four agrichars (rice hulls RH, palm fronds PF, horse bedding HB, and bagasse BG) for their ability to retain/release P and (ii) determine the effect of wet sonication on P sorption behavior. The feedstocks were torrefied at 500 °C using a top-lit updraft gasifier and used in multiple batch incubation experiments to evaluate equilibrium phosphorus concentration, maximum P sorption capacity (Smax), and adsorption/desorption potential. Both, RH (12.6 g kg-1) and HB (11.5 g kg-1) contained 10-15 times higher total P concentration than PF and BG, rendering RH and HB as potentially suitable products to be used as soil amendments. However, this initial P content of the agrichar seemed to have an overriding effect on the P sorption behavior of the agrichar. PF had Smax of 676 (±127) mg kg-1 for the non-sonicated agrichar, and 237 (±91) mg kg-1 following sonication. There was significant increase in CEC for PF and BG agrichar upon sonication. PF agrichar increased from 27 (±3) cmolc kg-1 to 41 (±4) cmolc kg-1 with sonication. Similarly, BG agrichar CEC increased from 21 (±2) cmolc kg-1 to 45 (±5) cmolc kg-1 with sonication. Initial total P and Ca concentration and their ratios was found to play significant roles on P adsorption and desorption. Major cations like Ca, Fe, Al and Mn are found to act as active sorption site for phosphorus controlling its fate and mobility along with compounding effects of other physicochemical parameters.

Characterization of Biochar from Rice Hulls and Wood Chips Produced in a Top-Lit Updraft Biomass Gasifier

<abstract> <b><sc>Abstract.</sc></b> The objective of this study was to characterize biochar produced from rice hulls and wood chips in a top-lit updraft gasifier. Biochar from four airflows (8, 12, 16, or 20 L min^-1) and two insulation conditions (not insulated or insulated with 88.9 mm of fiberglass on the external wall of the gasifier) were evaluated. Measurement of elemental composition, higher heating value (HHV), and BET surface area and proximate analyses of the biochar were carried out. It was found that the airflow rate and reactor insulation significantly influenced the chemical composition of the biochar depending on the biomass type. For instance, the carbon content of biochar from rice hulls decreased from 40.9% to 27.2% and the HHV decreased from 14.8 to 10.2 MJ kg^-1 as the airflow increased from 8 to 20 L min^-1 when the reactor was insulated. In contrast, the carbon content of biochar from wood chips increased from 82% to 86% and the HHV stayed stable at 32.0 to 33.2 MJ kg^-1 at the same conditions. Despite these variations, the BET surface area of biochar from both biomass types increased with increased airflow and additional insulation. For example, rice hull biochar had a maximum BET surface area of 183Â m² g^-1 at 20 L min^-1 airflow with insulation. The BET surface of biochar from wood chips peaked at 405 m² g^-1 at the same conditions.

The Effect of Biomass Physical Properties on Top-Lit Updraft Gasification of Woodchips

The performance of a top-lit updraft gasifier affected by biomass (pine wood) particle size, moisture content and compactness was studied in terms of the biochar yield, biomass burning rate, syngas composition and tar content. The highest biochar yield increase (from 12.2% to 21.8%) was achieved by varying the particle size from 7 to 30 mm, however, larger particles triggered tar generation that reached its maximum of 93.5 g/m3 syngas at 30-mm biomass particles; in contrast, the hydrogen content in syngas was at its minimum of 2.89% at this condition. The increase in moisture content from 10% to 22% reduced biochar yield from 12% to 9.9%. It also reduced the tar content from 12.9 to 6.2 g/m3 which was found to be the lowest range of tar content in this work. Similarly, the carbon monoxide composition in syngas decreased to its minimum of 11.16% at moisture content of 22%. Finally, the biomass compactness increased biochar yield up to 17% when the packing mass was 3 kg. However, the addition of compactness also increased the tar content in syngas, but little effect was noticed in syngas composition.

Improved Gasification of Rice Husks for Optimized Biochar Production in a Top Lit Updraft Gasifier

Biochar is a solid material obtained from the carbonization of biomass. If properly produced, it is useful for soil application to enrich plant values. Rice husk (RH) waste, an abundant agricultural by-product, was gasified in a top-lit updraft Belonio rice husk gasifier with a biochar yield of 29.0% ± 1.9%. The equivalence ratio (ER) for optimum biochar production was identified and its effect on biochar properties such as pH, volatile matter (VM), fixed carbon (FC) and ash content (AC), electricity consumption, biochar yield, specific gasification rate (SGR) as well as reactor temperature investigated and statistically analyzed. As ER increased from 0.292 ± 0.005 to 0.442 ± 0.016, the SGR decreased from 85.4 ± 4.5 kg/(m2hr) to 51.6 ± 2.4 kg/(m2hr) whereas reactor temperature increased linearly with ER. The original VM content of RH was found to be 76.1% ± 1.2% and decreased with increasing ER from 14.1% ± 0.2% to 10.6% ± 0.3%. The original FC and AC of 5.49% ± 0.22% and 9.10% ± 1.23% increased with ER from 50.5% ± 0.7% to 51.3% ± 0.4% and 33.7% ± 0.4% to 36.7% ± 0.1% respectively. The biochar pH at low, medium and high ER was 9.36 ± 0.11, 9.64 ± 0.03 and 9.42 ± 0.01, respectively. Results revealed a significant change in biochar yield and proximate values as ER changes from low to high.

Using Formative Research to Design a Behavior Change Strategy to Increase the Use of Improved Cookstoves in Peri-Urban Kampala, Uganda

Household air pollution from cooking with biomass fuels negatively impacts maternal and child health and the environment, and contributes to the global burden of disease. In Uganda, nearly 20,000 young children die of household air pollution-related pneumonia every year. Qualitative research was used to identify behavioral determinants related to the acquisition and use of improved cookstoves in peri-urban Uganda. Results were used to design a behavior change strategy for the introduction of a locally-fabricated top-lit updraft gasifier (TLUD) stove in Wakiso district. A theoretical framework—opportunity, ability, and motivation—was used to guide the research and behavior change strategy development. Participants consistently cited financial considerations as the most influential factor related to improved cookstove acquisition and use. In contrast, participants did not prioritize the potential health benefits of improved cookstoves. The theoretical framework, research methodology, and behavior change strategy design process can be useful for program planners and researchers interested in identifying behavioral determinants and designing and evaluating improved cookstove interventions.