Downdraft Wood Research Articles

Improvement of syngas quality from two-stage downdraft wood gasification through steam and oxygen injection

The transition from fossil fuels to clean energy sources requires the supply of gaseous fuels from renewable origin for a number of applications. Such applications include in particular high-temperature heat for industries, and Combined Heat and Power (CHP) for flexible, decentralized power production. Gasification of lignocellulosic biomass is a good candidate to this end, converting solid biomass such as wood residues into a more versatile and CO2-neutral gaseous fuel. Today, the use of syngas remains limited due to its relatively low energy density and challenges related to its residual tar content.To improve the quality of syngas on these two aspects, we have studied the injection of steam and oxygen in a pilot two-stage downdraft gasifier. Replacing secondary air by oxygen enhances the Lower Heating Value (LHV) by 65%, while steam injection boosts the H2/CO ratio and damps the temperature rise due to oxygen. The gasification efficiency is enhanced by both oxygen and steam. As a drawback, oxy-steam conditions yield more Class III and IV tars in the syngas. The combined use of oxygen and steam can enhance the volumetric power of syngas-based CHP engines, and provide a sustainable fuel for high-temperature industrial applications.In future research, longer runs should be done to confirm the effects of steam and oxygen on conversion efficiency. The injection of steam and oxygen at the primary stage should also be studied. The presented results will help choosing whether to use oxygen and steam in downdraft gasification applications, and support the validation of numerical models.

ผลของการเผาซ้ำต่อสมบัติเชิงกลและลักษณะทางกายภาพของอิฐดินดิบทนไฟที่ใช้ก่อเตาเผาเซรามิกชนิดใช้ฟืนทางเดินลมร้อนลง

ผลของการเผาซ้ำต่อสมบัติเชิงกลและลักษณะทางกายภาพของอิฐดินดิบทนไฟที่ใช้ก่อเตาเผาเซรามิกชนิดใช้ฟืนทางเดินลมร้อนลง

Studies for removal of tar from producer gas in small scale biomass gasifiers using biodiesel

Biomass gasification based electricity generation systems are emerging as an important component of the decentralised energy supply systems in rural India. Each type of gasifier has different reaction conditions, temperature, residence time, pressure, feedstock, reactor design, and therefore the tar and particulate matter (PM) compositions and concentrations are found to vary. A field study was conducted on a 35 kWe downdraft gasifier to measure and characterize the tar in producer gas using GC-MS, for rice husk and pine needles as the two biomass feeds. Use of water-based scrubbers for removal of tar and PM is prevalent, however it is often the case that such clean-up is not adequate for meeting the engine manufacturers’ requirements for the quality of intake gas. Limited attempts have been reported for the use of organic solvent based gas cleaning in small scale downdraft gasifiers in the range 15–50 kWe. In the present work, toluene, naphthalene and phenol were selected as representative compounds of tar, and methyl oleate was selected to represent biodiesel as an organic solvent. A bench scale packed bed scrubber was designed for 95% removal of toluene. An 86–97% removal of toluene from the gas stream was achieved, and similar results were obtained for phenol and naphthalene. Further experiments were carried out with actual producer gas from a 1 kWe downdraft wood gasifier. Pongamia pinnata based biodiesel was used as the solvent, and 88–92% of the tar removal from the producer gas stream was achievable.

An Experimental Investigation on Gasification Characteristic of Pongamia Residue (Shell and De-Oiled Cake) as a Source of Energy for Rural Areas

This paper has been aimed for thermochemical gasification of Pongamia residue (mixture of shells and de-oiled cake) generated from the oil expellers and biodiesel production plants. Pongamia mixture pellets (with 11.5 mm diameter and average length in the range of 10–62 mm) were prepared and gasify in an open top downdraft wood gasifier. The temperature in various zones of the gasifier was measured by using S-type thermocouples. The calorific value of producer gas generated from pellets was in the range of 4.56–5.39 MJ/Nm3. The gasifier conversion efficiency was 94 % for pellets which is higher to that of wood gasification (74 %). Producer gas generated with these pellets was used in the spark ignition engine. The performance and emission characteristics of the engine were evaluated by varying load and spark timings. The engine brake thermal efficiency was 26 % at spark ignition timing 30° before top dead centre (bTDC) at full load condition. However, the de-rating of 4.5 % was observed when working with 100 % producer gas at compression ratio of 10. Emission parameters were on lower side at spark timing 30obTDC. The producer gas generated from the Pongamia mixture pellets could be used for heat and or power generation for rural areas.

Experimental investigation on gasification characteristic of high lignin biomass (Pongamia shells)

Pongamia residue (shells) is the byproduct from the biodiesel processing industry, which is a lignocellulosic biomass material. It is not suitable as feedstock in downdraft wood gasifier due to low bulk density (146 kg/m3) of shells as compared to wood (more than 350 kg/m3). Pelletization and gasification of pelletized shells was carried out in the present work. The heat transfer analysis in pellets of 17 mm and 11.5 mm was also carried out to evaluate thermal properties of this biomass. Shell pellets of 17 mm and 11.5 mm diameter and length in the range of 10–60 mm were gasified in a 20 kWe downdraft wood gasifier. The complete gasification of pellets with 17 mm diameter could not be achieved because of less porosity and presence of larger thermal gradient within the pellets. The gasification efficiency was 73% for 17 mm diameter pellets which is lower than that of 11.5 mm diameter pellets which was 95%. The calorific value of producer gas generated from smaller diameter pellets was higher (4.66 MJ/N m3) as compared to larger diameter pellets (3.98 MJ/N m3). Tar formation during gasification of smaller diameter pellets was low as compared to larger diameter pellets.

Thermal degradation and gasification characteristics of Tung Shells as an open top downdraft wood gasifier feedstock

Tung (Aleurites Fordii) is cultivated in China, Argentina, Paraguay, Africa, India, and United States. Tung oil has various applications like as a drying agent for paints and varnishes, termite control as well as cleaning and polishing compounds. The Tung shell and de-oiled cake are residues after decortications of the Tung seeds. This paper has been aimed for thermal degradation and gasification of Tung shells. Thermal degradation of the Tung shell was carried out at heating rates of 10, 15, and 20 °C/min from room temperature to 750 °C under non-isothermal conditions, and N2 was used as a carrier gas. Based on the thermogravimetric analysis and differential thermogravimetric analysis results, it was found that Tung shells have low thermal stability. These shells were gasified in the downdraft wood gasifier. The calorific value of producer gas was calculated to be 4.75 MJ/Nm3. The conversion efficiency of the gasifier for Tung shells was higher (93 %) as compared to the wood (84 %). The producer gas generated from shells could be used for heat and or power generation for rural areas. Also a solution to reduce the disposal problem of toxic Tung shells generated from oil expellers.

Experimental Study on Gasification of Jatropha Shells in a Downdraft Open Top Gasifier

Thermochemical gasification characteristics of Jatropha shells were investigated in this study. Jatropha shells were gasified in a downdraft wood gasifier for two air nozzles opened and top opened condition. The temperature variation in the various zones of the gasifier was measured during gasification process. Operating parameters were calculated for the gasifier. Producer gas generated from gasification of Jatropha shells has low calorific value (2.55 MJ/Nm3) as compared to the wood (4.48 MJ/Nm3). The gasification efficiency or coefficient of thermal conversion was 64 % for shells which is lower than that of wood gasification which was 84 %. The complete gasification of shells could not be achieved because of low bulk density and irregular shape. Jatropha shells are not suitable for gasification in downdraft open top gasifier.

Emission Abatement at Small-Scale Biomass Combustion Unit with High-Temperature Catalysts

A newly designed downdraft wood stove achieved low-emission heating by integrating an alumina-supported mixed metal oxide catalyst in the combustion chamber operated under high temperature conditions. In the first step, a catalyst screening has been carried out with a lab-scale plug flow reactor in order to identify the potentially active mixed metal oxide catalysts. Mixed metal oxide catalysts have been the center of attention because of their expected high temperature stability and activity. The catalyst has been synthesized through two novel routes, and it has been integrated into a downdraft wood stove. The alumina-supported mixed metal oxide catalyst reduced the volatile hydrocarbons, carbon monoxide and carbonaceous aerosols by more than 60%.

Pyrolysis and gasification characteristics of Pongamia residue (de-oiled cake) using thermogravimetry and downdraft gasifier

General research in the area of gasification of biomass includes either study of kinetics of pyrolysis or gasification of selected bios mass. A combined kinetic investigation of the pyrolysis of the de-oiled cake at various heating rates along with gasification of pelletized biomass was carried out in the present work. It is found that the thermal decomposition of de-oiled cake occurs in three stages. Most of the material decomposed (∼60%) in stage-II between 166 °C and 480 °C. Kinetic parameters were obtained by differential and FWO methods. The activation energies are obtained in the range of 68.8–177.9 kJ/mol and 41.3–161.8 kJ/mol by differential method and FWO methods respectively. These results were consistent with those obtained in the literature. The TGA results show that a minimum heating rate (10 °C/min) and minimum activation energy (162 kJ/mol) is required for pyrolysis and gasification of de-oiled cake. The results of TGA were used to select the suitable size of pellets. De-oiled cake pellets of 17 mm and 11.5 mm diameter and length in the range of 10–68 mm were prepared and gasified in a 20 kWe downdraft wood gasifier. The complete gasification of pellets could not be achieved because of less porosity and more elasticity and presence of larger thermal gradient within the pellets. Pongamia de-oiled cake pellets of 17 mm and 11.5 mm diameters are not suitable for gasification.

Modeling a stratified downdraft wood gasifier with primary and secondary air entry

A detailed mathematical model, comprehensive of the main chemical and physical processes, is proposed for the open-core downdraft gasification of wood pellets, which permits a dual air entry: from the top section (primary air) and at a certain height of the packed bed (secondary air). A transition is simulated from a single, top-stabilized front (zero percentage of secondary air), to a double front stabilization (percentages of secondary air up to 60–70%) and finally to a single, forced center-stabilized front at the position of secondary air injection. For sufficiently high percentages of secondary air, following the complete or partial separation between the zone of primary wood degradation and a high-temperature, oxygen-rich zone and higher temperatures along the char bed, tar and char conversion is highly enhanced. Good agreement is obtained between model predictions and measurements for a pilot-scale plant.

Experimental studies on molar distribution of CO/CO2 and CO/H2 along the length of downdraft wood gasifier

Abstract Experimental studies on molar distribution of CO/CO2 and CO/H2 along the length of downdraft wood gasifier are reported in this paper. Sixteen numbers of special probes have been prepared and installed in various zones of the laboratory scale downdraft wood gasifier for generating data through exhaustive measurements of simultaneous concentration and temperature profiles along the length of gasifier using four different woody biomass materials in different shapes and sizes as a feedstock. Eight molar distribution for CO/CO2 and seven for CO/H2 have been derived using these data of concentration and temperature profiles along the length of gasifier, while best molar distribution for both was decided based on comparison of their average absolute and bias errors and validated with present and published experimental data points of other biomass also. Both CO/CO2 and CO/H2 distribution proposed in present work are found very close to measured values and thereby establish its acceptability.

04/01069 Computer simulation of a downdraft wood gasifier for tea drying: Jayah, T. H. et al. Biomass and Bioenergy, 2003, 25, (4), 459–469

04/01069 Computer simulation of a downdraft wood gasifier for tea drying: Jayah, T. H. et al. Biomass and Bioenergy, 2003, 25, (4), 459–469

Computer simulation of a downdraft wood gasifier for tea drying

A gasifier has been fabricated in Sri Lanka for the tea industry, but there is a lack of knowledge of the effect of certain key operating parameters and design features on its performance. Experimental testing of the design under various conditions has produced data that has then been used to calibrate a computer program, developed to investigate the impact of those parameters and features on conversion efficiency. The program consists of two sub-models of the pyrolysis and gasification zones, respectively. The pyrolysis sub-model has been used to determine the maximum temperature and the composition of the gas entering the gasification zone. The gasification zone sub-model has been calibrated using data gathered from the experiments. It was found that a wood chip size of 3– 5 cm with a moisture content below 15% (d.b.) should be used in this gasifier. Feed material with a fixed carbon content of higher than 30% and heat losses of more than 15% should be avoided. For the above parameters, the gasification zone should be 33 cm long to achieve an acceptable conversion efficiency.

Economic potential of producer gas fueled irrigation

For commercialization of producer gas fueled irrigation to occur there must be an economic potential. To encourage further technical development, the economic potential of fueling a 56 ha center pivot irrigation system with producer gas is evaluated for market conditions in the Southeastern United States. Simulation modeling is used to explore the conditions under which using a downdraft wood gasifier to replace diesel fuel for a 56 kW engine is economically reasonable. Investing in the gasifier is reasonable under most market conditions, even when diesel fuel is decreased from $0·29 to $0·25 litre −1 during the 10-year life.