Downdraft Gasifier Research Articles

Development of stability criteria for biomass open-top downdraft gasifiers

In the past, few researchers have presented objective criteria that can be applied for the stability assessment of a gasification process for woody biomass. When exploring new operating points, however, an objective rating of the operation must be performed. Therefore, in this paper, a useful stability criterion by comparing different statistical parameters (i.e., standard deviation, relative standard deviation, interquartile range and stability index) for several gasifier variables (i.e., temperatures, pressure loss, air flow, permanent gases, total hydrocarbon content THC and flame front position) is described. Therefore, 124 operating points from different evaluations in a commercial open-top gasifier operated with wood chips were used. These data points include fuel water contents from 2 m% to 21 m%, exhaust gas recirculation, loads within the range of ±20% of the nominal load, water injection and air preheating. By taking this novel approach, three main findings were revealed: (1) The summarized standard deviation of the gasifier temperatures is suitable to rate the process stability; however, the temperature fluctuations showed no influence on the permanent gases. (2) A correlation was found between the standard deviation of the air flow and the absolute value of the THC; this enables an estimation of the gas quality with a cheap air flow sensor. (3) A novel method was developed to identify stable operating timespans during post-processing based on the moving standard deviation. This procedure enables researchers to objectively rate operating points in future gasification development.

Investigating the Effect of Producer Gas in Pipelines of Downdraft Gasifier

With energy demand and for promoting the energy supply to remote areas the fuel from biomass initiative is carried. Gasification technology is an efficient conversion technique for biomass resources to energy. The production of producer gas by gasification are used for various applications including electricity generation. Utilization of the Producer gas for applications involves the flow of gas through pipes from reactor to applications. During the flow, the producer gas is subjected to wet scrubbers and passes through various filters for gas clean-up. The pipelines suffer corrosion due to moisture deposits and chemical components in the Producer gas. In this paper, the influence of producer gas to the inner surface of pipelines in downdraft gasifiers is investigated. The inlet pipe exhibits reduction ranging 68 to 72 HRB in the hardness comparing to the outlet pipe ranging 77 to 78 HRB from the coarse filters.

Study on Predicting the Gasification Process of Acacia Wood on a Downdraft Gasifier: Using the Non-stoichiometric Equilibrium Model

This study presents a prediction of acacia wood of Vietnam gasification in a downdraft gasifier based on the thermodynamic equilibrium model. Analytical solution for the mathematical model obtained by using an EES (Engineering Equation Solver) program. In the survey, moisture content per mole of biomass MC= 10 ¸ 30%, The ratio of the actual amount of oxygen used for gasification with the amount of oxygen for complete combustion of the biomass ER= 0.21 ¸ 0.4. Results indicated that the lower heating value of syngas decreases with increasing MC or ER. Thermal efficiency tends to increase with rising ER from 0.21 to 0.374, and it will decrease if ER continues to increase. The lower heating value of dry products from 4.51 to 6.51 MJ/nm3, the heat efficiency from 49.62 to 75.53%. The carbon conversion factor tends to increase with an increase as MC or ER. The influence of MC on the carbon conversion factor is insignificant. The content of CO2 and CH4 increased, the content of CO decreased with increased MC or ER. The composition of H2 increases as MC increases while the H2 component increases slightly and then decreases with increasing ER.

Tar cracking enhancement by air sparger installation in the combustion zone of the downdraft gasifier

In the present article, experimental studies are performed on Imbert downdraft gasifier using two different air distribution systems (two-nozzle and air-sparger) for the combustion zone. A novel air distribution system (air-sparger) is designed to supply uniform air across the combustion zone for achieving uniform temperature and enhancing the tar cracking. The effect of operating parameters (Equivalence ratio, temperature, air flow rate, and biomass consumption) on the tar cracking and producer gas compositions are investigated. Tar is measured in the producer gas before and after the gas cleaning units using a stack monitoring system. The experiments are performed by varying the airflow rate between 3 and 7 Nm3 h−1, and the equivalence ratio varies from 0.24 to 0.38. The operating parameters and air-sparger have significantly influenced the zone's temperature, producer gas composition, and the tar content in the producer gas. The maximum temperature of the combustion zone and reduction zone increases from 764 to 975 °C and 467 to 760 °C respectively with the air-sparger compared to the two-nozzle conventional air distribution system at the airflow rate of 7 Nm3 h−1. The lower heating value of the producer gas and the cold gas efficiency of the gasifier increased from 4.28 to 4.37 MJ Nm−3 and 48.55–55.05%, respectively, with the air-sparger. The incorporation of air-sparger reduces tar in producer gas from 23.95 to 0.97 g Nm−3 before gas cleaning unit at the airflow rate of 7 Nm3 h−1. Air-sparger has shown the adequate potential to enhance tar cracking and improve the overall gasifier performance.

Gasification and Co-gasification of paper-rich, high-ash refuse-derived fuel in downdraft gasifier

Among the various waste-to-energy conversion methods, gasification is a technically feasible option for municipal solid waste valorization, meeting current emission limits and reducing landfill disposal burden. This work investigates the potential of paper rich (⁓ 76 % wt.) commercial refuse-derived fuel (RDF) having high ash content (⁓ 17 % wt.) for gasification and co-gasification in downdraft gasifier. The ash formed from RDF, with higher proportion of alkaline earth metals (Ca and Mg) and lower proportion of alkali metals (Na and K), can effectively avoid agglomeration and clinker formation during gasification. The producer gas obtained from RDF gasification reports a maximum lower heating value of 4.34 MJ/Nm3at an equivalence ratio of 0.34 with corresponding cold gas efficiency of 59.24%.Co-gasification of RDF with biomass was examined as a strategy to reduce overall ash content of the mixture, using sawdust. Co-gasification has exhibited a synergy between RDF and sawdust when the RDF fraction in feedstock is at the higher side. A maximum lower heating value of 4.65 MJ/Nm3 was obtained during the co-gasification and the tar yield reduced from 13.6 g/Nm3to 8.8 g/Nm3 when RDF in the feed increased from 25% to 75% (w/w).

Preliminary evaluation of surface dielectric barrier discharge non-thermal plasma for reforming syngas derived from a downdraft gasifier

Measurement by NASA has indicated an increase in carbon dioxide levels in the air from 381 to 417 ppm from 2006 to 2022. Gasification is a proven technology that can reduce carbon accumulations in the air as it can convert renewable organic materials into syngas, including hydrogen as future clean energy fuel, and sequester carbon in the form of biochar. However, tar in syngas still remains a challenge, requiring complex gas cleaning system. This study presents a critical evaluation of reforming syngas directly from a gasifier for increased hydrogen (H2) production while reducing syngas tar using dielectric barrier discharge (DBD) plasma. Results showed an increase in H2 (from 4.8 to 9.5 vol%) with a slight increase in CO (from 31.9 to 34.7 % vol.%) and a decrease in heavier hydrocarbons, such as C2H6 (from 8.5 to 4.6 vol%). Syngas tar decreased by 88 %, from 25 to 3 g/Nm3. At steady-state operation, the power consumption for operating the plasma system was 160 W, resulting in energy density of 0.19 kWh/m3. The outcome of this study is critical for further development of existing gasification systems capable of treating diverse organic feed streams, including biomass, coal, municipal solid waste (MSW), and plastic.

Application of parametric trend life cycle assessment for investigating the carbon footprint of ammonia as marine fuel

PurposeThis study aimed to determine whether ammonia can genuinely help to reduce the carbon footprint of maritime activities. Given this, it was decided to investigate the life cycle of ammonia and its impact on the environment regarding the global warming potential.MethodsTo achieve this goal, the parametric trend life cycle assessment was applied to yield a general and reliable observation. The research was combined with a comprehensive dataset of over 2061 bulk carriers and eight different ammonia production methods: steam methane reforming, photovoltaics, electrolysis via wind, biomass downdraft gasifier, biomass circulating fluidized bed gasifier (CFBG) system, underground coal gasification (UCG) with carbon capture and storage (CCS), UCG without CCS, and 3-step Cu-Cl cycle. In addition, an existing ME-LGI (ME-liquid gas injection) engine was selected as the propulsion system.ResultsThe results from PT-LCA revealed that for estimating the carbon impact of ammonia as marine fuel from a well-to-wake (WTW) perspective, it is mandatory to focus on the well-to-tank (WTT) phase. The lowest carbon production pathway for the global warming potential (GWP) is the 3-step Cu-Cl cycle and eventually is the most potential route for using ammonia as fuel in the maritime industry. Finally, this study concludes with some formulas, based on regression analysis, which serves as rapid indications for comparing the overall carbon impact of thousands of bulk carriers equipped with the ME-LGI engine, carrying ammonia as fuel from different production methods.ConclusionsGiven these fuel production routes, the research has also demonstrated that ME-LGI engines can be a groundbreaking way to reduce the carbon footprint of ships. Additionally, the research findings showed that the environmental indicators proposed in this article have the potential to make a significant contribution to the industry. They are anticipated to assist stakeholders in overcoming the discrepancy problem generated by past studies that were so dissimilar from case to case that the scope, boundary of analysis, data, and assumptions they employed were far from current standards and rules. In addition, the GWP according to the ship power was compared and reviewed in terms of the well-to-wake (WTW). Thus, the proposed methodology for developing ammonia ship environmental indicators is to provide valuable insight into environmental policy and decision-making processes.

Clean cooking with downdraft biomass gasifier cookstove: Effect of gasifier performance

Two downdraft gasifier cookstoves, one of 4 kWth and another of 2.5 kWth input power ratings have been developed by the authors for domestic cookstove application. The downdraft gasifier cookstove has a gasifier unit followed by a partially aerated burner. Thus, the efficiency of the gasifier cookstove is the product of the gasification efficiency of the gasifier unit and the burner efficiency. The present work reports the effects of the output parameters of the gasifier, viz. gas flow rate, gas composition as reflected by the lower calorific value (LCV) of producer gas, and the gas temperature, on thermal performance and emissions of the cookstoves. Laboratory-based water boiling tests were conducted on both the cookstoves to study the effect of these parameters on cookstove efficiency, burner efficiency and emission factors of CO and PM2.5. The turn down ratios of 4 kWth and 2.5 kWth gasifier cookstoves were 2.2 and 2.8 respectively. The maximum efficiency for 4 kWth cookstove (44.6%) occurred at input power of 4.4 kW whereas that for 2.5 kWth cookstove (45.1%) occurred at 3.2 kW. Average CO emission factor for 4 kWth and 2.5 kWth cookstoves was 4.2 g/MJd and 2.84 g/MJd respectively.

Effect of Air Velocity, Type and Size of Biomass on Performance of Downdraft Gasifier

Investigation on thermal gasification of different biomass materials viz., Pigeon pea stalk (Cajanus cajan),Cotton stalk (Gossypium hirsutum) and Vilaytee babool (Prosopis juliflora) in a downdraft gasifier (1 Kw capacity) was conducted to study the effect of air velocity, type and particle size of biomass. The influenceof three different particle sizes viz. 25-50, 50-75, 75-100 mm, at three different air velocities viz., 2.4, 7.4 and12.4 m s-1 on biomass consumption rate, gas flow rate and gasification yield was investigated. With theincrease in particle size, the reduction in biomass consumption rate was observed, whereas the increase inair velocity increased the biomass consumption rate. Similar trend was observed in gas flow rate andgasification yield respectively. Under the experiment conditions, the biomass consumption rate, gas flowrate and gasification yield of selected biomass material varied in the range of 3.80 to 7.76 kg h-1, 6.13 to 14.40Nm3 h-1 and 1.40 to 2.30 Nm3 kg-1, respectively. The experimental results showed that the gasificationperformance was better for Vilaytee babool (Prosopis juliflora) biomass with 25-50 mm size at 7.4 m s-1 airvelocity.

Enhanced tar removal in syngas cleaning through integrated steam catalytic tar reforming and adsorption using biochar

Steam catalytic tar reforming (SCTR) using biochar is a popular technique for tar removal in syngas cleaning. However, its efficacy drops while treating syngas at low temperatures (<750 °C) typically encountered in fluidized or downdraft gasifiers. This work proposes integrating an adsorption section post reforming, that operates at a relatively lower temperature (220 °C) to additionally remove the light tar components using biochar. The integrated approach was assessed for the removal of mallee-wood generated tar using mallee-wood biochar as catalyst and adsorbent. Tar yield estimates revealed overall removal by ∼80 %, with reforming contributing ∼40 % and adsorption ∼60 % of the residual tar. Elaborate tar analysis based on UV-spectroscopy proved substantial removal of light tar compounds in the two-step process. Biochar structural analysis based on Raman spectroscopy revealed a growing predominance of higher aromatics in adsorbent during biochar-volatile interactions, due to adsorption of both heavy and light tar compounds. The evolution trends were validated by correlating the specific reactivity of utilized biochar samples based on thermogravimetric analysis. Biochar morphological analysis through BET analysis showed a steep drop in surface area from 101.40 to 0.043 m2/g, implying pore surface coverage by tar compounds which were also evident from FESEM images.

Low‐tar, highly burnable gas production from the gasification of pelletized palm empty fruit bunch

AbstractGasification is an attractive method to convert lignocellulosic biomass into a combustible gas mixture for electricity and power generation. To control the tar concentration in the produced gas to be within the allowable limit of downstream applications, it is important for a gasification system to be integrated with a tar removal process. In this study, an integrated gasification system consisting of a downdraft gasifier and a secondary catalytic tar‐cracking reactor was designed and tested for the gasification of pelletized oil palm empty fruit bunch. To further purify the producer gas, the system was also integrated with a cyclone, a water scrubber, and a carbon‐bed filter. Biomass was fed at a rate of 5 kg/h, while the air equivalence ratio (ER) and the gasification temperature were set at 0.1 and 800°C, respectively. In total, 5 kg of the specially developed low‐cost Fe/activated carbons (AC) catalyst was used in the hot gas catalytic tar‐cracking reactor. Results indicate that our integrated gasification system was able to produce a clean burnable gas with a lower heating value (LHV) of 9.05 MJ/Nm3, carbon conversion efficiency (CCE) of 79.4%, cold gas efficiency (CGE) of 89.9%, and H2 and CH4 concentrations of 29.5% and 10.3%, respectively. The final outlet gas was found to only contain 32.5 mg/Nm3 of tar, thus making it suitable for internal combustion engine (ICE) application.

Air-CO2 and oxygen-enriched air-CO2 biomass gasification in an autothermal downdraft gasifier: Experimental studies

The mounting CO2 emission and rapid depletion of fossil fuels are two significant challenges for sustaining growing energy requirements and keeping the environment clean. Biomass gasification using CO2 as a gasifying agent may be one of the alternative techniques to tackle such emerging problems. CO2 behaves as an inert gas at low temperatures and can be converted to CO at high temperatures. In the present study, air-CO2 and oxygen-enriched air-CO2 biomass gasification are successfully conducted in the autothermal reactor. The impacts of varying concentrations of CO2 and oxygen in the gasifying agent on the performance of the gasifier are analyzed. The CO2 content in the gasifying agent is varied from 0 to 45 vol% at two different oxygen concentrations (21 and 35 vol%). The reactor used is an Imbert-type downdraft gasifier with a thermal capacity of approximately 10 kW. The results reveal that the yield of CO in the producer gas increases compared to air gasification resulting in a higher heating value of the producer gas. However, the average temperature in the gasifier reduces with increasing CO2 percentage in the gasifying agent. Upon increasing the O2 fraction from 21 to 35 vol%, while keeping 30 vol% CO2 content constant, CO content is found to upsurge from 23.96 to 31.37 vol%. The inclusion of CO2 inside the gasifier promotes the endothermic Boudouard reaction that causes the conversion of CO2 into CO.

Stratified downdraft gasification of wood chips with a significant bark content

The strict fuel quality limitations are amongst the main barriers preventing the success of small-scale downdraft gasification. In a first step towards alternative fuels, the application of wood chips with bark content must be investigated. Therefore, this paper presents the results of thermogravimetric analyses (TGA) and the gasification of wood chips with a significant larch bark content (up to 50%) in a stratified downdraft gasifier. The TGA revealed, that bark generated twice as much char as wood during pyrolysis. The gasification zones in the downdraft reactor did not shift when the fuel was switched, which allows its utilization in the same setup as pure wood chips. The concentrations of CO, H2 and CO2 were also almost unaffected at approximately 21.5 vol%, 14.6 vol% and 9.1 vol%, respectively. The highest gasification efficiency was achieved with 20% fuel bark content. The most significant effect was the reduction of the non-methane hydrocarbon content by up to 80% when bark was in the fuel, due to reduced tar generation and enhanced cracking. Therefore, the addition of bark up to a certain level even improved the gas quality and performance. These novel results predict a bright future for forestry residues in downdraft gasification.

The continuous carbonisation of rice husk on the gasifier for high yield charcoal production

The aim of this research was to new design and develop a metal kiln for a continuous carbonisation of rice husk on the downdraft gasifier, utilising flue gas, to produce high yield rice husk charcoal. The cylindrical metal kiln was constructed of a steel pipe, 114 mm in diameter and 510 mm in length. The screw conveyor, which rotates at 3 rpm inside a cylindrical metal kiln, is powered by a 24 V DC motor. The rice husk pyrolysis is caused by direct heating from the flue gas. The flue gas was obtained from the burning of some parts of the rice husk in combination with the pyrolysis gas in the reactor beneath. The results showed that the pyrolysis temperature ranged from 460 to 475 °C. The capacity operation of the reactor was 11.237 kg (rice husk)/h and the rice husk charcoal could produce 3.565 kg (charcoal)/h. The yield of rice husk charcoal was 36.97% (by weight). The proximate analysis properties of rice husk charcoal have a volatile matter of 12.75% (by weight), a fixed carbon value of 48.89% (by weight), and a high ash content of 36.13% (by weight). The higher heating value of the rice husk charcoal is 19,859 kJ/kg. The energy conversion efficiency from biomass to charcoal and the high reactor's thermal efficiency were 48.57% and 41.46%, respectively. The rice husk charcoal obtained from this research is suitable for use as a material in the production of charcoal briquettes, and it can be mixed with other organic materials to make organic fertilizers that can be used instead of chemical fertilizers. This cuts costs for farmers.

Performance Evaluation of a Continuous Downdraft Gasification Reactor Driven by Electric Motors with Manual Mode of Operation

Gasification is considered a promising option for harnessing energy potential from agricultural waste, such as rice husks. This paper presents a 10-kW rice husk fixed bed gasifier system. This system is an improved version of a prototype previously developed by our research group. Some of the optimized features added to the gasifier include the use of a circular air intake, an improved gas cleaning system, and electric motors that are regulated by a programmable logic controller. Keeping the gasifier system’s operation stable is critical for producing high-quality synthetic gas (syngas). Therefore, performance evaluation of the presented gasifier system was conducted, and the resulting syngas outputs were analyzed. The evaluation also included an investigation into the performance of the motors, particularly those used for feeding and char removal, which are critical components of the system. The results showed that the improved gasifier system was stable with a proper feedstock. A discussion of the parameters affecting the composition of the synthetic gas is also presented.

Gasification of Biowaste Based on Validated Computational Simulations: A Circular Economy Model to Handle Poultry Litter Waste

Converting waste biomass resources through downdraft gasification can generate a producer gas for a combined heat and power unit. The study includes feedstock analysis, process modelling using ECLIPSE simulation software, and experimental analysis of materials in a pilot-scale fixed-bed downdraft gasifier. Anaerobic digestate and miscanthus were investigated for comparing the gasification potential of poultry litter as an energy source. Models validated through experimental analysis were applied to a case study based on a typical poultry farm in Northern Ireland.; Results found producer gas with a lower heating value up to 4.15 MJ/Nm3 can be generated. Sufficient poultry waste is generated on-site to produce the required heat and electricity for each shed, allowing the farm to switch from fossil fuels to a local renewable resource and addressing the waste disposal issue.; Downdraft gasification coupled with cogeneration could have a payback period of 4–5 years given the correct conditions. The net present value is positive for all technologies considered (i.e. internal combustion engine and the Organic Rankine cycle combined heat and power unit) under different subsidies, showing the economic viability of the solution. The break-even selling price could be lower than the current grid electricity selling price (£120/MWh) when incentives such as: (i) avoiding disposal cost of £30/tonne, (ii) selling the biochar by-product at £200/tonne and (iii) fuel displacement costs of 1.5p/kWh are considered.Graphical abstract

Assessing the power generation potential and quality of producer gas from blended of the cotton stalk and pistachio shell in an open core downdraft gasifier

: - The increasing energy demands require a sustainable eco-friendly renewable source of energy. Biomass as a sustainable and pollution-free source of energy is the most promising alternative. In the present study, a mix of the cotton stalk and pistachio shells as a feedstock in a weight ratio of 3:1 are gasified. The air is used as a gasifying agent in a downdraft gasifier. In the experimental work, the equivalence ratio (ø) is varied from 0.186 to 0.267. As a result, the maximum power is calculated as 62.795 kW with a feed rate of 39 kg/hr at an equivalence ratio of 0.267. The experimental analysis shows the maximum cold gas efficiency and calorific value of PG as 87.5% and 6.6332 MJ/m3, respectively at an equivalence ratio of 0.241. The maximum values of CH4 and H2 of PG are measured as 3.94% and 16.78 at an equivalence ratio of 0.227 and 0.247, respectively.

INVESTIGATION OF MICROALGAE GASIFICATION UNDER STEAM ATMOSPHERE IN DOWNDRAFT GASIFIER BY USING ASPEN PLUS®

Energy production is facing the environmental and economic issues due to growing population and uncertainties about the fossil fuels. These concerns prompt the researchers to find widely available and renewable alternative such as biomass instead of the fossil fuels. Microalgae is one of the promising biofuels owing to its rapid growth speed and higher calorific value. Steam gasification is an alternative way converting biomass to syngas with higher H2 and lower CO2 content compared with the other thermochemical conversion processes. In the present work, the downdraft gasifier model was developed by using Aspen Plus® program that has the capability to investigate the performance of microalgae gasification. Before the performance evaluation of the gasification, validation of the model successfully completed and exit gas compositions of H2, CO2, CO and CH4 were found very close for experimental study and the developed model. Effects of the main parameters of the process such as steam/biomass ratio and gasification temperature were assessed on the syngas composition and higher heating value (HHV) of syngas. The obtained results were stated that the increment in the temperature showed great effect on the H2 and CO compositions of syngas, they increased from 50.72% to 56.47% and 28.11% to 28.84% respectively. The simulation results also illustrated that the rising of the S/B ratio was favored the steam related reactions and increased the H2 content in syngas. However decreasing trend of the CH4 caused reducing of the HHV of syngas as a function of temperature and steam as well.

Effect of Air Fuel Ratio to Quality of Municipal Solid Waste Using Downdraft Gasification

Gasifikasi menggunakan limbah padat kota (MSW) berdampak pada peningkatan kualitas lingkungan dan peningkatan pasokan listrik untuk daerah-daerah yang sulit dijangkau, khususnya di Indonesia. Namun proses gasifikasi membutuhkan proses pengujian kualitas terlebih dahulu agar dapat menghasilkan produk syngas dan kelistrikan yang maksimal. Maka dalam penelitian ini dilakukan proses pengujian pengaruh variasi Air Fuel Ratio (AFR) terhadap kualitas proses gasifikasi (Cold Gas Efficiency (CGE), Carbon Conversion Efficiency (CCE), dan specific fuel consumption (sfc) atau konversi konsumsi spesifik). Penelitian dilakukan dengan melakukan proses gasifikasi dengan tipe downdraft pada nilai AFR 0,5; 0,51; 0,53; 0,54; 0,55. Hasil penelitian ini menunjukkan adanya peningkatan nilai syngas seiring dengan peningkatan nilai AFR. Sedangkan nilai CGE meningkat seiring dengan meningkatnya AFR proses gasifikasi MSW. Peningkatan terjadi dari 9 menjadi 13%, meskipun hasil ini masih sangat rendah. Di sisi lain, CCE juga mengalami peningkatan dengan meningkatnya AFR gasifikasi MSW. Peningkatan nilai terlihat dari 33-43%. Hasil ini juga masih tergolong kecil, artinya efisiensi konversi karbon pada proses ini sangat rendah. Pada akhirnya, dapat dilihat bahwa nilai scf menurun dengan meningkatnya AFR. Penurunan yang didapat adalah dari 5,3 menjadi 2.

An Aspen Plus Kinetic Model for the Gasification of Biomass in a Downdraft Gasifier

An Aspen Plus Kinetic Model for the Gasification of Biomass in a Downdraft Gasifier