Downdraft Gasifier Research Articles

Effect of limestone catalyst on co-gasification of coconut fronds and wood chips

Biomass energy via gasification is an attractive substitute of fossil fuels. The distribution of biomass on the earth is scattered, so transportation and collection of biomass complicates the supply of biomass especially when the gasification rely on one type of biomass. Therefore, cogasification of different biomass is proposed as a potential solution for interruption-free gasification. Beside, unwanted by-products such as tar that cause blockage in downstream equipment can be minimized through the use of catalyst in gasification to accelerate tar reforming process. In this study, catalytic co-gasification of blended feedstock of 70% wood chips and 30% coconut fronds was carried out in a downdraft gasifier using limestone as primary catalyst. The effects of catalyst loading (0%, 30%, 50%, and 70% w/w) on syngas composition, gas yield, carbon conversion efficiency and heating value of syngas were investigated. The results showed that at 50% biomass to catalyst ratio, maximum H2 content of 11.39%, CO of 17.88%, carbon conversion efficiency of 69.49%, gas yield of 1.68 Nm3/kg and higher heating value of syngas 5.11 MJ/Nm3 were achieved. Higher catalyst loading (70%) blocked the air passage, which caused poor gasification. No more than 50% catalyst suggested for stable co-gasification operation.

Bio-gasification based Externally Fired Combined Cogeneration Plant: Thermo-economic Performance Analysis

Thermo-economic performance analyses of an externally fired biomass gasification based combined cogeneration plant (EF-BGCCP) is reported in the present paper. The plant is capable of producing 700-800 kW electrical power, the gas turbine (GT) providing a fixed output of 500 kWe and the bottoming steam turbine (ST) providing the rest. Utility heat of 100 kW or more is also available from the plant. Saw dust is considered as fuel feed to the plant which undergoes gasification in a downdraft gasifier. A combustor-heat exchanger (CHX) duplex unit is used in the topping GT cycle to heat up the working fluid. Effects of plant design parameters, such as, topping cycle pressure ratio (rp=4-12), gas turbine inlet temperature (TIT=900-1100 oC), cold end temperature difference (CETD=230-280 oC) of the heat exchanger of CHX unit and outlet temperature of the economizer (EOUT=130-180 oC) on the energetic and techno-economic performance is reported in the study. Energetic performance of the EF-BGCCP reveals that, plant efficiency along with fuel energy savings ratio (FESR) is maximized at a particular value of rp, for a given GT TIT. Higher TIT results in higher efficiency and FESR value. However increased CETD value results in decreased overall area (UAHX) of the exchanger. Also, increased value of EOUT results in decrease in plant efficiency and increase in FESR of the plant. Techno-economic analysis of the plant suggest that levelized unit cost of electricity (LUCE) and levelized unit cost of heat (LUCH) change with changes in operating conditions of the plant. LUCE value is minimized at a particular value of pressure ratio, for a fixed GT TIT. Also, higher TIT results in higher LUCE and LUCH delivered to the consumers. Again, higher CETD value of the heat exchanger results in decreased LUCE value as the size of the heat exchanger decreases with increase in CETD. Delivered LUCH value as well as heat to power ratio of the plant is found to be decreased at higher economizer outlet temperature.

Production of fuel gases from reed by using downdraft gasifier

This study was conducted to investigate the ability of reed as a Production of gases via gasification technique by using special gasifier made for this purpose and to evaluate the produced gases (CO, H2, CO2 and CH4). The results showed that the percentage of production gases was 15.6%, 10.2%, 7.81% and 1.69% for carbon monoxide, carbon dioxide, hydrogen and methane respectively. In addition, it showed that the highest temperature up to the gasifier was 700°C and the time required to complete gasification process was 23 min. The results indicated that 5 kg of reed was capable of producing 10 m3 of gases which produces about 1 HP-hr. that equivalent to 3.75 kWh.

Co-gasification of Corn and Coconut Residues in Downdraft Gasifier

Reliance on a single biomass to generate electrical power can cause disruption due to the inconsistencies in the supply of biomass feedstock. Co-gasification of different biomass can mitigate the problem of inconsistence biomass supply. The aim of this study to investigate thermochemical properties of corn residues (CR) and coconut shells (CS) and syngas performance produced from co-gasification of CR and CS. Biomass materials were characterized in order to understand their physical properties in relation to thermochemical conversion. Co-gasification of CR and CS was carried out in externally heated downdraft gasifier at CR:CS ratio of 50:50, 40:60 and 20: 80. CO composition obtained from blended feedstock is higher as compared to the without blended feedstock. The CO2 and CH4 concentration were increased as CS proportion increased in blend. Biomass with higher moisture content plays important role in the H2 production due to the supercritical water gasification. The blending ratio of CR and CS at 20:80 had a positive synergetic effect as evident by increase in the gas composition for CO, CH4 and H2. It is concluded that co-gasification results of CR and CS is practical and can be considered to complement each other.

Comparison of downdraft and updraft gasification of biomass in a fixed bed reactor

The aim of this study was to compare and analyze the gasification process of beech wood. The experimental investigation was conducted inside a gasifier, which can be operated in downdraft and updraft gasification system. The most important operating parameter studied in this paper was the influence of the amount of supply air on the temperature distribution, biomass consumption and syngas calorific value. The results show that the amount of air significantly influences the temperature in the combustion zone for the downdraft gasification process, where temperature differences reached more than 150 °C. The increased amount of air supplied to the gasifier caused an increase in fuel consumption for both experimental setups. Experimental results regarding equivalence ratio show that for ER below 0.2, the updraft gasification is characterized by a higher calorific value of producer gas, while for ER=0.22 a similar calorific value (6.5 MJ/Nm3) for both gasification configurations was obtained. Above this value, an increase in ER causes a decrease in the calorific value of gas for downdraft and updraft gasifiers.

Effect of Blending Ratio on Quality of Producer Gas From Co-Gasification of Wood and Coconut Residual

Biomass gasification often encounters the shortage of biomass supply for continuous operation. Co-gasification of different biomass materials is a promising solution that can address the shortage of biomass supply for the continuous gasification process. However, the effectiveness of co-gasification is not well understood. Furthermore, there is nearly no reported work of co-gasification of two or more biomass materials. In this study, two Malaysian local biomass materials, wood residual and coconut shells were co-gasified in a 33.6 kW thermal capacity downdraft gasifier to investigate the effect of blending ratio the on quality of the producer gas. The results show that producer gas composition increased as coconut shells proportion increased in blends of up to 60%. A blend of 40:60 W/CS results in a synergetic effect as compared to discrete gasification of both feedstock. The maximum H2 and CO were obtained as; 11.46 vol.% and 23.99 vol.% respectively at 40:60 W/CS blending ratio. The results achieved from 40:60 W/CS blend were 16.70% and 10.96% higher as compared to pure wood gasification for H2 and CO respectively. It is concluded that coconut shells can be utilized a substitute of wood residual in form of blends or as discrete feedstock for the continuous gasification process without the change in gasifier geometry.

The Integration of Gasification Systems with Gas Engine by Developing Wet Tar Scrubbers and Gas Filter to Produce Electrical Energy from Biomass

The need for energy especially biomass-based renewable energy continues to increase in Indonesia. The objective of this research was to design downdraft gasifier machine with high content of combustible gas on gas engine. Downdraft gasifier machine was adjusted with the synthetic gas produced from biomass. Besides that, the net energy ratio, net energy balance, renewable index, economic analysis and impact assessment also been conducted. Gas engine that was designed in this research had been installed with capacity of 25 kW with diameter and height of reactorwere 900 mm and 1 000 mm respectively. The method used here werethe design the Detailed Engineering Design, assembly, and performance test of gas engine. The result showed that gas engine for biomass can be operated for 8 h with performance engine of 84 % and capacity of 25 kW. Net energy balance, net energy ratio, and renewable index was 30 MJ/kW h electric; 0.89; 0.76 respectively. The value of GHG emission of Biomass Power Generation is 0.03 kg-CO2 eq per MJ. Electrical production cost for Biomass Power Generation is about IDR 1 500 per kW h which is cheaper than solar power generation which is about of IDR 3 300 per kW h.

Downdraft Co-gasification of Oil Palm Frond with Other Oil Palm Residues: Effects of Blending Ratio

As the largest amount of biomass residues produced from the palm oil industry, the oil palm frond (OPF) is a promising solid fuel resource for gasification. However, the difficulty in processing OPF into solid fuel may affect the solid fuel production rate and consequently the gasifier operation. To ensure a continuous gasifier operation unaffected by the shortage of OPF fuel, empty fruit bunch (EFB), palm mesocarp fiber (PMF) and palm kernel shell (PKS) were introduced as a pairing fuel with OPF for co-gasification. The potentials of the fuel mixes and the effects of the fuel blending ratio on syngas higher heating value, specific syngas yield, carbon conversion efficiency and cold gas efficiency were studied. The experiments concluded that all fuel mixes of all blending ratios satisfied all the syngas quality indicator requirements and that all the tested fuel mixes can be utilized for downdraft co-gasification to produce results similar to the downdraft gasification of 100% OPF.

Simple pyrolysis experiments for the preliminary assessment of biomass feedstocks and low-cost tar cracking catalysts for downdraft gasification applications

The pyrolysis behaviour of beech wood, two rice husk variants from Brazil (BRH) and Thailand (TRH) and a solid waste water treatment residue from textile manufacture (TIR) were investigated using a lab-scale, 2-stage fixed-bed reactor at 773 K. Char yields increased and volatile yields decreased with increasing ash content. The TRH released 40% less tar than the BRH which was attributed to the substantially higher potassium content of the Thai species. The combustion reactivity of the TRH char in air at 773 K was similar to the BW char and almost double the reactivity of the BRH and TIR chars. The BW and TRH chars had a greater volume of macropores indicating that char combustion occurs predominantly through the growth and extension of the macroporous pore network. A different trend was observed for the char gasification reactivity with CO2 at 1173 K. The Ca and Mg content of the chars were found to have a more important catalytic role in the char gasification reactions with CO2.The effect of exposing volatile products from beech wood pyrolysis to elevated temperatures (973–1173 K) and sand beds containing calcined limestone or dolomite in a simulated downdraft gasification environment was also investigated. Tar yields decreased after exposure to elevated temperature and calcined limestone or dolomite. Tar cracking favoured the production of CO. CO yields were between 22 and 23 wt% at 1173 K. Calcined dolomite was slightly more effective at cracking tar than calcined limestone, eliminating 98 wt% of the tar at 1173 K.

Improving downdraft gasifier stability by robust instrumentation and control systems

In updraft, fluidized bed and downdraft gasifiers, tar concentrations are typically produced around the 10-20%, 1-5%, 0.1% levels respectively. If gasifiers are operated under specific conditions a clean syngas with low tar concentrations will be produced [1]. The principal objective of this research is to develop a set of robust and inexpensive instrumentation systems to measure gasification parameters and inform control systems to improve gasification performance e.g. temperature, liquid flow and biomass weight for real time mass balance calculations. In the present case nine K-type thermocouples were connected to different positions on an in-house downdraft gasifier that allowed temperature and mass balance profiling. The moisture / bio-oil flow was measured by a liquid flow sensor that gave real time flow rates (L/min) and total quantities (mL) [2]. The Arduino platform was used as the core of the instrumentation and control system and integrated with Makerplot software (GUI). These systems offered a high level of control and robustness for low cost with an open source protocol, allowing other developers to benefit and expand the core of this research. The results from preliminary runs are presented which is currently allowing ignition optimization and overall system improvements.

Investigating the thermochemical conversion of biomass in a downdraft gasifier with a volatile break-up approach

An affordable, reliable and clean energy supply is the major challenge facing by the modern world. Biomass energy is playing a promising role to that, but gasification technology able to convert biomass efficiently to valuable gases for power and heat generation is a vital need. The aim of this study is to develop a robust computational fluid dynamics (CFD) model to better understand the gasification thermochemical processes of a selected biomass (rubber wood) in a 20 kW downdraft gasifier, which includes all the four zones, drying, pyrolysis, oxidation and reduction. A step-by-step approach is proposed to evaluate the composition of different species as a result of volatile break-up during gasification. Effect of the equivalence ratio on the synthesis gas composition is studied with results validated against a kinetic model. Further, in this study temperature profile in the gasifier at different equivalence ratio (ER) has been studied.

Biomass gasification coupled to an EFGT-ORC combined system to maximize the electrical energy generation: A case applied to the olive oil industry

This research presents the modelling and simulation of an innovative small-scale power system composed of a downdraft gasifier, an externally fired gas turbine (EFGT) and an Organic Rankine Cycle (ORC) as a bottoming unit for increasing the electrical energy generation. Olive tree pruning (217 kg/h) was the biomass used, producing more than 200 kWe and an electrical efficiency of 20.7%. The producer gas achieved suitable mole composition (H2: 14.8%, CO: 19.5%, CH4: 2.2%, CO2: 9.3%, H2O: 12.0% and N2: 41.5%), lower calorific value (4.53 MJ/kg) and gasification efficiency (89%). The hot producer gas was burnt directly at atmospheric pressure in an EFGT, producing 150 kWe and exhaust gases at 290 °C. Five ORC working fluids were studied to maximize the electricity generation: isopentane, benzene, cyclohexane, R113, R245fa. Isopentane was the most suitable fluid, reaching 57.1 kWe and 20.45% of ORC thermal efficiency. On the other hand, despite R113 gave minor electricity production (49.1 kWe), this allowed to generate thermal power for CHP applications.

High Temperature Steam Gasification of Corn Straw Pellets in Downdraft Gasifier: Preparation of Hydrogen-Rich Gas

The main objective of this study is to investigate the characteristics of corn straw pellets conversion to syngas using a steam gasification process in downdraft gasifier. A lab scale gasifier was built to perform the gasification experiment. The effects of temperature and steam flow on the non-catalytic gasification process were investigated, and the variation rules of gasification indexes such as product component were summarized. Based on the principle of gasification thermodynamics, the reason of the rules is analyzed. The experimental results clearly indicate that hydrogen-rich gas can be prepared by using downdraft gasifier. When the temperature is above 750 °C, volume fraction of H2 in product gas is higher than 50%, little variation with temperature is observed, while it can be increased significantly by increasing steam flow. The maximum H2 content of 56.7% is obtained at steam flow of 1.2 kg/h, and the volume fraction of H2 + CO can reach 94.62%, the range of LHV is 9 ~ 11 MJ/Nm3. At 950 °C, the gas yield and carbon conversion rate reach 2.06 Nm3 and 91.6%, respectively.

Numerical and experimental investigation of hydrogen-rich syngas production via biomass gasification

In this work, the relation between hydrogen-rich syngas production and the gasification parameters such as equivalence ratio (ER), gasification temperature and biomass moisture content were studied. Stoichiometric equilibrium model that developed during this study was used to investigate the optimum hydrogen output generated from woody biomass in a fixed bed downdraft gasifier by considering the thermodynamic equilibrium limit. The mathematical model, based on thermodynamic equilibrium is necessary to understand complicated gasification process that will contribute to obtain maximum attainable hydrogen production. The effects of different oxidizing agents on the hydrogen concentration in the product gas as well as the effect of various air-biomass, oxygen-biomass and steam-biomass ratios were investigated. For validation, the results obtained from the mathematical model were compared with the experimental data obtained from the gasifier that uses air as gasification medium. The validated mathematical model was used to represent the gasifier that uses both oxygen and air-steam mixture as the gasification medium and the theoretical results were obtained for both cases. The theoretical results clearly show that the gasification process specially ones that use the air-steam mixture as the gasification medium can be used for hydrogen production.

Effects of operating parameters on performance of a downdraft gasifier in steady and transient state

A mathematical model of downdraft gasifier has been developed to simulate steady and transient state of gasification process. The model is based on lumped capacitance method and chemical equilibrium in pyrolysis and oxidation zone and one-dimensional reaction kinetics in reduction zone. Effects of the equivalence ratio (0.37–0.45), steam to biomass ratio (0–4) and mass flow rate of biomass (18–25 kg h−1) on the steady and transient characteristics of gasifier have been studied. The model gains good agreement with experimental results for exit gas composition.A steady analysis reveals that higher equivalence ratio (ER), lower steam to biomass ratio (S/B) result in a higher reaction temperature, which promotes the yield of H2 and CO and the char conversion into syngas in this work. For S/B = 0 and mass flow rate of biomass equal to 20.9 kg h−1, char conversion rate increases from 76% to 100% due to increasing of ER from 0.39 to 0.43. For ER = 0.43 and mass flow rate of biomass equal to 20.9 kg h−1, char conversion rate decreases from 84% to 24% due to increasing of S/B from 1 to 4.The molar fraction of gas composition almost remains stable for mass flow rate of biomass in the range of 18–22 kg h−1.The large mass flow rate of biomass is obviously unfavorable for char conversion due to low temperature. For steam flow rate equal to 0.247 mol s−1 and air flow rate equal to 0.5326 mol s−1, the char conversion rate declines from 100% to 71% due to mass flow rate of biomass increasing from 19 to 22 kg h−1.The higher flow rate of H2O relies on less yield of H2 if ER is less or S/B is higher corresponding to more steam inducted into gasifier. Transient analysis shows that flow rate of H2 goes down then up with increasing of ER due to competition between oxidation and reduction reactions. As S/B changing alone, the yield of H2O is absolutely dominated by inlet steam whether flow rate of H2 increases or not.

Modeling of downdraft gasification process: Studies on particle geometries in thermally thick regime

In this study, a downdraft gasifier model is coupled with a single-particle model to analyze the effects of particle geometries such as slab, cylindrical, and spherical on different parameters. Simulations were performed using particles in a thermally thick regime with larger particle sizes of 0.003–0.05 m, which are generally used in commercial gasifiers. This combination of the downdraft gasifier model and single particle model was implemented using Comsol Multiphysics software program. The results obtained are in good agreement with those of obtained in previous studies. The low thermal conductivity of biomass (kB), small particle size (dp), high gas temperature (Tg), higher molar fraction of oxygen in primary air (XO2), and high mass-transfer coefficient (km) favor the formation of carbon monoxide (CO), hydrogen (H2), high tar conversion, and higher lower heating value. To maximize the CO composition and tar conversion, the initial gas temperature (Tg) is more crucial. The least sensitive parameter is the thermal conductivity of biomass (kB) in relation to product composition of CO, carbon dioxide (CO2), H2, and methane (CH4). The sensitivity for all the parameters is found to be the highest for the spherical geometry and is least for the slab geometry.

Scale-up of a downdraft gasifier system for commercial scale mobile power generation

Abstract The overall goal of this study was to scale-up a patented downdraft gasifier system for development of a mobile power plant. A 100 kg/h up-scaled downdraft gasifier system was designed, built and evaluated using switchgrass and eastern redcedar as feedstocks. The effect of equivalence ratio (0.15–0.30) were studied for each of biomass feedstock. Performance parameters, including composition, syngas yield, heating value, tar content, and gasification efficiencies were measured and analyzed. Results showed that biomass type and equivalence ratio have a significant influence on the syngas compositions and calorific value. Maximum gasification efficiencies for switchgrass and redcedar were 64 and 80% at optimal equivalent ratios of 0.22 and 0.24, respectively. Based on syngas quality, the performance of the scaled-up gasifier system was superior to the laboratory-scale reactor.

Gasification of yeast industry treatment plant sludge using downdraft Gasifier.

Sludges produced in biological wastewater treatment plants have rich organic materials in their characteristics. Recent research studies have focused on the energy recovery from sludge due to its high organic content. The gasification process is a thermal conversion technology transforming the chemical energy contained in a solid fuel into thermal energy and electricity. The produced syngas as a mixture of CO, CH4, H2 and other gases can be used to generate electrical energy. The gasification of yeast industry sludge has been experimentally evaluated in a pilot scale downdraft-type gasifier as a route towards the energy recovery. The gasifier has 20 kg biomass/h fuel capacity. During gasification, the temperature achieved was more than 1,000°C in the gasifier, and then the syngas was transferred to the gas engine to yield the electricity. A load was connected to the grid box and approximately 1 kWh electrical power generation for 1 kg dry sludge was determined. The characteristics of residuals - ash, glassy material - were also analyzed. It was found that most of the heavy metals were fixed in the glassy material. Experimental results showed that the yeast industry sludge was an appropriate material for gasification studies and remarkable energy recovery was obtained in terms of power production by using syngas.

Design and experimental study of pilot scale throat-less downdraft gasifier fed by rice husk and wood sawdust

ABSTRACTIn this work, pilot scale throat-less downdraft gasifier is fabricated and tested on rice husk and blend of rice husk-sawdust. The test aims to investigate effect of equivalence ratio on temperature profile, propagation front (flame propagation rate, bed movement rate, and effective propagation rate), and performance of the gasifier (composition of producer gas, heating value of producer gas, and thermal efficiency of the gasifier). Equivalence ratio investigated are 0.15, 0.20, and 0.25, while the blend ratio is 1:1 by mass. The results show that axial temperatures in the reactor surge faster with increasing equivalence ratio during the rice husk gasification and the blend gasification. Typically, flame propagation rate, bed movement rate, and effective propagation rate improve with rising equivalence ratio from 0.15 to 0.25. The best higher heating values and thermal efficiencies are obtained at equivalence ratio of 0.2 and 0.15 for the rice husk gasification and the blend gasification, respectively.

A Study of Throat Size Effect on Downdraft Biomass Gasifier Efficiency

The present research article aims to study the throat size effect on downdraft biomass gasifier efficiency. Two type of biomass; eucalyptus and leucaena were used as fuel for producing producer gas by gasification process. The downdraft gasifier has a 30 cm diameter and 250 cm high. For combustion zone, the throat size was varied to 10, 15, 20 and 25 cm respectively. The consumption of biomass was 10 kg with the size of biomass was 5-10 mm thick and moisture content less than 15%. The air flow rate into the combustion chamber was set at 1 – 5 m3/hr. to determine the gasifier efficiency and composition of producer gas. The experimental results showed that the gasifier efficiency increase with the air flow rate increase. The throat size 20 cm and air flow rate at 5 m3/hr showed the highest efficiency. The gasifier efficiency of the downdraft biomass gasifier was calculated as 35.30 % for leucaena and 43.36 % for eucalyptus. A heating value was calculated as 3.84 MJ/Nm3 and 4.87 MJ/Nm3 for eucalyptus and leucaena respectively.