Top-lit Updraft Research Articles

Design of a Top-Lit Up-Draft Micro-gasifier Biomass Cookstove by Thermodynamic Analysis and Fluent Modeling

In this work the complete thermo-mechanical design of a biomass top-lit up-draft (TLUD) cookstove is presented. A design methodology which is based on mass and energy balances, geometry relations among the main dimensions of the cookstove, and fluent modeling is proposed. Three models were designed, sized, and simulated through computational fluid dynamics (CFD) conducted in ANSYS Fluent 15.0.7. These designs allowed analyzing the effect of cookstove design, primary and secondary air inlets (diameter and air supply setup) required in the gasification and combustion processes, respectively. Simulations indicated that compressed air is not a suitable way to supply the air flow for gasification and combustion stages, due to the poor velocity distribution across the grate and secondary holes. Therefore, the final stove design will operate with axial fans to favor a good mixture between biomass and the air in the gasification stage, and between producer gas and the air in the combustion zone. Operation with axial fans, in the final cookstove design, allowed obtaining a low standard deviation of air velocity through the grate holes and through secondary air ring holes (±0.13 m/s, and ±0.45 m/s, respectively), which entails a better cookstove performance. This air supply system, also presented combustion air velocities through the secondary ring holes according to the ones reported in the literature (3.02 m/s), which is important for the suitable air and producer gas mixing.

Chemical and physical properties of Paulownia elongata biochar modified with oxidants for horticultural applications

Treatment of biochar with oxidants such as acids and hydrogen peroxide has been shown to alter porosity, increase adsorption of chemicals, and introduce functional groups on the biochar surfaces, all of which are desirable for their use in horticultural applications. Biochar was produced from the pyrolysis of wood from seven-year-old Paulownia elongata (PE) trees using a top-lit updraft design stove. PE biochar was subsequently treated with 30% (v/v) sulfuric acid, 30% (w/v) oxalic acid, and 10 and 30% (w/w) H2O2. After thorough rinsing with deionized water to remove residual acids and H2O2, biochars were examined for chemical and physical properties. All of the biochars had high carbon percentages, due to the high temperatures (>1000°C) reached during pyrolysis. Surface areas, micropore surface areas, % micropore surface areas, pH values, cation exchange capacities and electrical conductivities decreased with all oxidant treatments. Analysis of surface functionality by ATR-FTIR showed limited changes resulting from the treatments. TPO/MS analysis showed that all treatments resulted in chars with higher oxidation temperatures suggesting that these are more stable toward oxidation. Unlike reports of biochar derived from different feedstocks and different pyrolysis methods, it appears that treatment of PE biochar with oxidants is unnecessary for its use in horticultural applications.

Energetic performance of a top-lit updraft (TLUD) cookstove

The performance of a top-lit updraft (TLUD) cookstove using three different fuel types – wood chips, coconut shell and rice husk briquettes was investigated. Two standard biomass cookstove testing protocols were used: water boiling test (WBT) which quantified the thermal efficiency, firepower, specific fuel consumption, time to boil, burning rate and turn down ratio of the cookstove, and controlled cooking test (CCT) which measured the specific energy consumption associated with a local cooking task. It was observed that the performance of the cookstove was significantly influenced (p < 0.05) by the type of fuel used. On the basis of the low power phase of the WBT, wood chips generally offered better stove performance followed by rice husk briquette and coconut shell. In the CCT, 1.02 kg of yam was boiled and the lowest specific fuel consumption of 686.26 ± 0.25 g/kg (8.54 ± 0.00 kJ/kg) was recorded for rice husk briquette while the lowest total cooking time of 10 ± 0.5 min was recorded for wood chip. In comparison to an existing cookstove, the TLUD cookstove performed better in all the performance parameters investigated in the low power. The TLUD cookstove was ranked with respect to fuel use and safety based on ISO/IWA biomass cookstove performance ranking tier.

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.

Natural draft and forced primary air combustion properties of a top-lit up-draft research furnace

Worldwide, over four million people die each year due to emissions from cookstoves. To address this problem, advanced cookstoves are being developed, with one system, called a top-lit up-draft (TLUD) gasifier stove, showing particular potential in reducing the production of harmful emissions. A novel research furnace analogy of a TLUD gasifier stove has been designed to study the TLUD combustion process. A commissioning procedure was established under natural draft and forced primary air conditions. A visual assessment was performed and the temperature and emissions profiles were recorded to identify the combustion phases. The efficiency was evaluated through the nominal combustion efficiency (NCE = CO2/(CO2 + CO)), which is very high in the migrating pyrolysis phase, averaging 0.9965 for the natural draft case. Forced primary air flows yield similar efficiencies. In the lighting phase and char gasification phase the NCE falls to 0.8404 and 0.6572 respectively in the natural draft case. When providing forced primary air flows, higher NCE values are achieved with higher air flows in the lighting phase, while with lower air flows in the char gasification phase. In the natural draft case high H2 emissions are also found in the lighting and char gasification phases, the latter indicating incomplete pyrolysis. From the comparison of the natural draft with the forced draft configurations, it is evident that high efficiency and low emissions of incomplete combustion can only be achieved with high controllability of the air flow in the different phases of combustion.

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.

Influence of coal-particle size on emissions using the top-lit updraft ignition method

Despite the Government’s intervention of an intensive electrification program in South Africa, which has resulted in more than 87% of households being connected to the grid, a majority of low-income households still depend on solid fuel (coal and wood) as a primary source of energy, especially on the central Highveld. In informal settlements, combustion of coal is done in inefficient self-fabricated braziers, colloquially known as imbaulas. Emissions from domestic coal combustion result in elevated household and ambient air pollution levels that often exceed national air quality limits. Continued dependence on coal combustion exposes households to copious amounts of health-damaging pollutants. Despite the health significance of coal-burning emissions from informal braziers, there is still a dearth of emissions data from these devices. Consequently, evaluating the emission characteristics of these devices and to determine the resultant emission factors is needed. The effects of ignition methods and ventilation rates on particulate and gaseous emission from coal-burning braziers are reported in literature. However, to date there are no studies carried out to investigate the influence of the size of coal pieces on brazier emission performance. In this paper, we report on controlled combustion experiments carried out to investigate systematically, influences of coal particle size on gaseous and condensed matter (smoke) emissions from informal residential coal combustion braziers. Results presented are averages of three identical burn-cycles of duration three hours or fuel burn-out, whichever was the soonest.

Factors Influencing the Acquisition and Correct and Consistent Use of the Top-Lit Updraft Cookstove in Uganda

This study looked at the effects of select behavior change interventions on the purchase and the correct and consistent use of a locally fabricated top-lit updraft (TLUD) stove in Uganda. Behavior change interventions included training of community sales agents and village health team volunteers on household air pollution and correct use, referral of interested community members to sales agents, community cooking demonstrations, information flyers, and direct sales of TLUDs and processed wood. Qualitative and quantitative research methods shaped interventions and were used to understand attitudes and practices related to TLUD stove acquisition and use. Results showed that TLUDs were appreciated because they use wood efficiently, cook quickly, reduce smoke, and produce charcoal. However, the substantial purchase price barrier, combined with the cost of processed wood, effectively eliminated the cost savings from its significant fuel efficiency. This made it difficult for the TLUD to be a meaningful part of most households’ cooking practices.

Producing biochar using a custom designed Top-lit Updraft (TLUD) gasifier

Biochar can be produced in a wide variety of ways; some are complex, while others are relatively simple. Researchers at the University of Florida Everglades Research and Education Center in Belle Glade, FL, designed and built a top-lit updraft (TLUD) gasifier that can generate biochar from locally acquired feedstock. This 4-page fact sheet describes its design and evaluates the biochar recovery of four locally available feedstocks. Written by Jehangir H. Bhadha, Stephen Jennewein, Julio Sanchez, and Timothy A. Lang, and published by the UF Department of Soil and Water Science, September 2014.&#x0D; SL413/SS626: Producing Biochar Using a Custom Designed Top-Lit Updraft (TLUD) Gasifier (ufl.edu)

Evaluation of biochar-anaerobic potato digestate mixtures as renewable components of horticultural potting media

Various formulations are used in horticultural potting media, with sphagnum peat moss, vermiculite and perlite currently among the most common components. We are examining a dried anaerobic digestate remaining after the fermentation of potato processing wastes to replace organic components such as peat moss, and biochars produced from several feedstocks as replacements for inorganic media components such as vermiculite and perlite. Biochars were prepared using a top-lit updraft pyrolytic stove from wood pellets, pelletized wheat straw and field pennycress presscake. Biochar yields and heats of combustion were highest with the field pennycress presscake and lowest with the wood pellets. Because all three biochars had basic pHs, they were treated with citric acid solutions to lower pH values to 6.0 before being used in plant experiments. All three acidified biochars were combined in 1:1 ratios with the digestate and compared against a 1:1 sphagnum peat moss:vermiculite control substrate containing slow-release chemical fertilizers. All digestate:biochar substrates had higher bulk densities and levels of soluble salts than the control. Greenhouse experiments were conducted using tomato (Solanum lycopersicum L.) and marigold (Tagetes erecta L.) plants grown in 2.5-L pots. Combining potato anaerobic digestate with acidified wood pellet biochar resulted in increased growth of tomato plants as compared to the peat:vermiculite control, while the digestate:acidified wheat straw pellet biochar substrate was equal to the control for marigold growth. Plants of both species grown in the digestate:pennycress presscake biochar substrate had less growth than the control. From these results it appears that both the digestate:acidified wood pellet biochar and the digestate:acidified straw pellet biochar would likely be acceptable alternatives to peat:vermiculite substrates, and would also be an option for certified organic producers.

The effects of fuel type and stove design on emissions and efficiency of natural-draft semi-gasifier biomass cookstoves

To assess the effects of stove design and fuel type on efficiency and emissions, five configurations of natural-draft, top-lit up-draft (TLUD) semi-gasifier cookstoves were tested with two biomass fuels. An energy balance model was developed using measured temperature data to identify the major sources of efficiency loss. Emissions and efficiency varied substantially with stove design and fuel type, and transient increases in CO emission correlated with refueling. The highest measured thermal efficiency was 42%. The lowest CO and PM emissions were 0.6gMJd−1 and 48gMJd−1. These results fall within Tier 3 for high-power efficiency and emissions and suggest that development of a Tier 4 natural-draft semi-gasifier cookstove is possible. The energy balance illustrates that up to 60% of the energy input as fuel can remain as char once the fuel has gasified. This result suggests that both thermal and overall efficiencies should be calculated when evaluating TLUD cookstoves.

Simplifying pyrolysis: Using gasification to produce corn stover and wheat straw biochar for sorptive and horticultural media

Biochar is a renewable, useful material that can be utilized in many different applications. Biochar is commonly produced via pyrolysis methods using a retort-style oven with inert gas. Gasification is another method that can utilize pyrolysis to produce biochar. This method has significant processing advantages; it can be carried out in normal atmospheric conditions, eliminating the use of inert gas, is more amenable to scale up, and provides heat that can be used to generate power and/or help recoup processing costs. In this work, a simple gasification process using a top-lit updraft style cookstove was used to produce biochars from corn stover, wheat straw, and wheat straw treated with glycerin, which were then compared to biochars made using the more conventional retort oven pyrolysis process. The glycerin-treated wheat straw biochar from the gasification process had carbon content>70% and an ash content of 25% which was equal or better than the same biochar produced using the retort oven. This biochar has also shown successful use as a peat moss replacement in horticultural applications. This shows that gasification is a simpler, more cost-effective means to produce biochars and should be considered for horticultural and other similar applications.

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.

A Biochar-producing, Dung-burning Cookstove for Humanitarian Purposes

Over three billion people worldwide cook with traditional stoves, which typically consist of three stones and an open fire. The harmful emissions produced from these types of stoves are known to cause fatal illnesses. Traditional stoves claim the lives of up to 4 million people every year and cause the death of more children under the age of five than any other single cause. In addition, widespread land degradation and deforestation have resulted from inefficient fuel consumption of traditional stoves. In order to address these issues, investigations into the use of dung-burning top-lit up-draft (TLUD) microgasifier cookstoves, that produces biochar as a byproduct, have been conducted at the University of Adelaide. Results indicate that dung from various grazing animals burnt in the TLUD stove have similar heating properties, implying that the stove is applicable to a wide client-base. Additionally, biochar from cow-dung combustion is as good, if not better than some commercially available biochar.

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.

Life Cycle Assessment to Evaluate the Environmental Impact of Biochar Implementation in Conservation Agriculture in Zambia

Biochar amendment to soil is a potential technology for carbon storage and climate change mitigation. It may, in addition, be a valuable soil fertility enhancer for agricultural purposes in sandy and/or weathered soils. A life cycle assessment including ecological, health and resource impacts has been conducted for field sites in Zambia to evaluate the overall impacts of biochar for agricultural use. The life cycle impacts from conservation farming using cultivation growth basins and precision fertilization with and without biochar addition were in the present study compared to conventional agricultural methods. Three different biochar production methods were evaluated: traditional earth-mound kilns, improved retort kilns, and micro top-lit updraft (TLUD) gasifier stoves. The results confirm that the use of biochar in conservation farming is beneficial for climate change mitigation purposes. However, when including health impacts from particle emissions originating from biochar production, conservation farming plus biochar from earth-mound kilns generally results in a larger negative effect over the whole life cycle than conservation farming without biochar addition. The use of cleaner technologies such as retort kilns or TLUDs can overcome this problem, mainly because fewer particles and less volatile organic compounds, methane and carbon monoxide are emitted. These results emphasize the need for a holistic view on biochar use in agricultural systems. Of special importance is the biochar production technique which has to be evaluated from both environmental/climate, health and social perspectives.

An analysis of combustion from a top-lit up-draft (TLUD) cookstove

It is estimated that three billion people worldwide cook with traditional stoves. These stoves generaly consist of three stones and an open fire, and produce harmful emissions that are known to cause fatal illnesses. Traditional stoves claim the lives of 1.6 million people every year and cause the death of more children under the age of five than any other single cause. In addition, widespread land degradation and deforestation have resulted from inefficient fuel consumption of traditional stoves. This paper presents some results from an extensive investigation into design and experimental evalation of top-lit up-draft (TLUD) microgasifier cookstoves aimed at addressing problems associated with traditional cooking approaches. Results indicate that geometric variations of the stove and fuel size influence burn rates and emissions production, and must therefore be considered for any design and implementation.