Downdraft Gasifier Research Articles

Effect of Air Supply Location and Equivalence Ratio on Thermal Performance of Downdraft Gasifier Fed by Wood Sawdust

Effect of Air Supply Location and Equivalence Ratio on Thermal Performance of Downdraft Gasifier Fed by Wood Sawdust

Theoretical study of a downdraft gasifier, microturbine, and organic Rankine cycle fuelled by date molasses waste for distributed generation applications in Iraq

AbstractThe main objective of this work is the modeling of a combined heat and power (CHP) system that transforms waste from manufacturing date molasses in the Babylon province in central Iraq into electrical and thermal energy. A compact CHP facility that uses date waste (pomace and pits) as a feedstock is the subject of theoretical modeling and simulation research. The planned power plant consists of a downdraft gasifier, a microturbine (MT), and an organic Rankine cycle engine (ORC) as a bottom unit to maximize electric generation by recovering the MT exhaust gas heat and achieving a maximum electric output. The net electric production is 361.68 kW (280 kW from the MT unit and 81.68 kW from the ORC unit). To determine the best‐working fluid for the ORC system as a whole, three working fluids, including isopentane, benzene, and R113, were investigated. The temperature difference between the heat source and the fluid's boiling point is a key factor in choosing a more appropriate ORC working fluid. Isopentane is the most suitable working fluid for CHP applications, according to the findings of the simulation. The electric efficiency achieved is 30%, and the overall efficiency of the CHP plant was 56.87% from the gasification of date pits. The simulation results showed a satisfactory producer gas lower calorific value of 3.92 MJ k‐g‐1 for date pomace and 4.65 MJ k‐g‐1 for date pits, and cold gasification efficiencies of 73% and 76% for pomace and pits, respectively. © 2023 Society of Industrial Chemistry and John Wiley & Sons Ltd.

Energy and Exergy Analysis of Palm Tree Pruning Residues Gasification

Gasification is the process of obtaining syngas containing combustible gases such as H2, CO and small amounts of CH4 from biomass by performing partial combustion with a limited oxygen supply or with the help of suitable oxidants such as CO2 and water vapor. The efficiency of the gasification process is the most important parameter that determines the success of the system. In this study, the performance of the system in the gasification of palm pruning residues was evaluated by energy and exergy analysis methods. The gasification process was carried out at 7.6 Nm3/h and 10.2 Nm3/h air flow rates in the laboratory type fixed bed downdraft gasification unit manufactured in the Biosystems Engineering Department. The lower heating value of the syngas obtained as a result of gasification was found to be 4.09 MJ/Nm3 at 7.6 Nm3/h air flow rate and 3.76 MJ/Nm3 at 10.2 Nm3/h air flow rate. It has been observed that the lower heating value of the syngas is lower at high air flow rate. Energy efficiencies of the gasification system at 7.6 and 10.2 Nm3/h air flow rate were calculated as 47.6% and 52.8%, and exergy efficiencies were calculated as 43.7% and 48.1%, respectively. Exergy efficiencies were found to be lower than energy efficiencies in both air flow rates. However, as the air flow rate increased, the energy and exergy efficiencies also increased. The results obtained are similar to the results of previous studies on gasification of biomass.

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

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

Syngas production from municipal sewage sludge by gasification Process: Effects of fixed bed reactor types and gasification agents on syngas quality

In this experimental study, the results obtained from sewage sludge gasification carried out in two different fixed bed gasifiers, up draft and down draft, are presented. In addition, the effects of using three different heating temperatures (700, 800, 900 °C), two different gasification agents (dry air and pure oxygen), and their different flow rates (0.05, 0.1, 0.2, 0.4 L/min for dry air, 0.01 L/min for pure oxygen) on gasification efficiency are investigated. 75 g of sludge sample was used in each experimental study. The syngas composition produced from sludge gasification studies was measured by using online syngas analyzers. The maximum H2 content in syngas from updraft and downdraft gasifiers was achieved as 42 vol% and 46 vol% by using dry air as gasifying agent. H2 content for updraft and downdraft gasifiers was also obtained as 40 vol% and 45 vol%, respectively in the case of pure oxygen used as a gasifying agent. This paper presents a critical discussion identifying key points and contributing to a deeper understanding of its remarkable potential for sludge gasification by using different fixed bed gasifier configurations.

Olive mill solid waste gasification in a pilot-scale downdraft gasifier with three-stage air supply: performance, mass-energy balance and fate of inorganic elements

Olive mill solid waste (OMSW), also called olive pomace, is a biomass waste available in many Mediterranean countries, including developing countries. In this study, OMSW has been tested as a fuel in an original pilot-scale downdraft gasifier with three-stage air supply, and extensive metrology was implemented. After pelletizing and characterization of the biomass waste, gasification was investigated by operating a 2-day campaign using air as a gasifying agent. The evolution over time of operating parameters such as flowrates, temperatures and pressure drop were recorded. The syngas (including tars) and solid residues were analyzed. The fate of inorganic elements was investigated. Mass and energy balances were performed and the performance of the gasifier was evaluated. The syngas contained 14 % v/v H2 and 17 % v/v CO (dry and tar-free basis) and its lower heating value was 4.7 MJ/Nm3 (wet basis). The solid residues were rich in potassium and phosphorus and could be considered as an organic amendment. Cold gas efficiency was 68 % and carbon conversion efficiency was 89 %. The points of caution concerned the low melting point of the ash, the relatively high tar content in the syngas and the high NOx content of the flue gases after syngas combustion in a boiler. The energy potential of OMSW is substantial and could help reduce the pressure on fossil fuels.

The Experimental Study of the Efficiency of the Gasification Process of the Fast-Growing Willow Biomass in a Downdraft Gasifier

In this work, a study was performed on the influence of the ratio of height to the diameter of the reduction zone of a small-size downdraft gasifier as well as of the fuel fraction sizes on the gas quality (the quality was evaluated for CO content). The ratio of a full side area to the volume of a fuel fraction (SVR) was used as a fuel parameter. The maximum CO concentration was observed when using a small fuel fraction with SVR—0.7–0.72 mm−1 and when adhering to the ratio of height to the diameter of the reduction zone H/D—0.5–0.6. The maximum electric power for gasoline generators (nominal power equaled 4 kW) when using the gas received from the fast-growing hybrid willow biomass equaled 2.4 kW. This power is 37.5% lower than when using gasoline and 7.0% lower than when using the gas received from the hardwood biomass. The emissions of harmful gases into the atmosphere by the gasoline generator engine equaled 0.12–0.14% CO and 24–27 mln−1 CxHy. The emissions were 64.8 times less for CO and 8.5 times less for CxHy when compared with using gasoline.

A novel two-zone sequential optimization model for pyro-oxidation and reduction reactions in a downdraft gasifier.

A robust mathematical model is developed for prediction and optimization of syngas in a downdraft gasifier. The gasifier is modelled for two distinct zones i.e. pyro-oxidation zone (zone I) and reduction zone (zone II). A thermodynamic equilibrium model is implemented for the prediction of syngas composition in zone I, while zone II is modelled by implementing a finite kinetic approach. For each zone five control parameters are identified for sequential maximization of carbon conversion efficiency (CCE). Maximization of H2 and CO yield in syngas and minimization of char contaminants is the main objective in the present analysis. The Taguchi method is implemented for process optimization while ANOVA is used to determine the most influential parameter. The optimized model gives 17.79% improvement in calorific value of syngas, while the final CCE obtained was 96.04%. For zone I the equivalence ratio was found to be the most influential parameter with 97% contribution, while for zone II the reduction zone temperature was the most influential parameter with 88% contribution.

Effects of throat sizing and gasification agents in a biomass downdraft gasifier: towards CO2-free syngas production.

The gasification process in a downdraft biomass gasifier is investigated using Computational Fluid Dynamics (CFD). The aim is to develop a novel approach to reduce CO2 emissions from producer syngas while increasing the higher heating value (HHV). To this end, the effects of varying the throat diameter of the gasifier and gasifying media (air and oxygen) on the performance of gasification are investigated. The results reveal that as the throat ratio decreases for oxy-gasification, more CO, H2, and CH4 are produced, thus resulting in a HHV of 12.1 MJ Nm-3. For the same working conditions (ER, MC, and feedstock), the suggested design/optimum throat ratio of 0.14 is found to reduce CO2 by ∼55% compared to any other higher throat ratios, while simultaneously increasing HHV by ∼20% for both air and oxy-gasification cases. Additionally, the suggested throat ratio increases the gasification efficiency, carbon conversion and producer gas yield by 19%, 33%, and 22% respectively. Therefore, it shows a significant potential for CO2-free syngas production in the gasification process, demonstrating a promising technique that does not require any solvents, catalysts, absorbers, or additional CO2 removal. Lower throat ratios further favour the higher yield of syngas, HHV, gasification and conversion efficiencies, with better gasifier performance.

Experimental and CFD analysis of wire coil turbulators in biomass boilers

To achieve as complete fuel burnout with as little excess air as possible, small wood log boilers (< 50 kW) use stage combustion. The first stage is often a process similar to downdraft gasification that consequently produces a flue gas laden with particulates. To prevent the build-up of solids and promote heat transfer in pipes of the convective part of these boilers, wire coils are used. The paper presents their in-situ examination together with CFD analysis. The analysis is carried out in a 460 mm long pipe, with a diameter of 82.5 mm, equipped with different wire coils for flue gas temperatures in the range between 300?C and 150?C. The analyzed coils are with and without a conical spring at their free end. The addition of this conical top is economical and should influence the rotation of the core flow. Proper pipe surface cleaning limited the analyzed wire coil designs to the dimensionless pitch, p/d, in the range between 0.36-0.61, dimensionless wire diameter e/d = 0.04-0.1, and pitch to wire diameter ratios p/e = 3.75-14.3, and three different angles (60?, 90?, and 120?) of the conical top. The goals are to find the optimal flue gas velocity for the given operating conditions, pipe, and wire coil dimensions, and to investigate the addition of the conical top on heat transfer enhancement. Several evaluation criteria are used to achieve the goals.

First and second law thermodynamic analysis of a single and dual-stage ignition biomass downdraft gasifier

The dual-stage ignition biomass downdraft gasifier is an enormous tar reduction technology as against a single-stage ignition biomass gasification. Exergetic analysis of the system guides toward a possible performance enhancement. In dual-stage gasification, around 67.76% of input exergy is destructed in the several components, while 9.16% is obtained as a useful exergy output and 24.34% is found to be as a useful energy output there. The entire unit was assessed with a progressively rising electric load from 15.24 kW to 38.86 kW. The enhanced producer gas quality comes from 57% combustible gas with a higher heating value of 6.524 MJ/Nm3 and tar content of 7 mg/Nm3 after the paper filter, whereas the biomass consumption rate is 58 kg/h at the greatest load with the grate temperature of 1310–1370 °C. The samples of exhaust gas emissions are obtained environmentally favorable. The results even described that the dual-stage ignition biomass downdraft gasifier has significantly greater energetic and exergetic efficiency as compared to the single-stage gasifier.

Experiment and Simulation of Rice husk Gasification Process with a Downdraft Gasifier

Experiment and Simulation of Rice husk Gasification Process with a Downdraft Gasifier

Biomass oxy-CO2 gasification process for bio-methane production: an experimental and numerical activity

Biomass gasification is a thermochemical process in which the biomass is converted into a mixture of gases, called syngas, commonly utilised in thermal machines to produce electricity and heat. In the present research activity, the conventional air-gasification in downdraft gasifier is replaced by oxy-CO2 gasification technology. This strategy allows to obtain a nitrogen-free syngas, mainly composed by CO, H2, CO2 and CH4, which can be used into the synthesis of various bio-fuels like methanol or synthetic natural gas (SNG). Carbon dioxide is utilized as gasifying agent together with oxygen to mitigate the reactivity of the latter, which can lead to excessive reaction temperatures. In particular, the present work shows the preliminary results of an experimental campaign carried on utilizing a small scale downdraft gasifier (max thermal power of roughly 100 kW) fed with wood pellet and using a mixture of oxygen and CO2 as gasification agent. The experimental results have been utilized to calibrate a pseudo-kinetic model of the oxy-CO2 gasification process, implemented in Aspen Plus environment. To analyse the possibility to transform the produced syngas into methane, an additional numerical model of a methanation plant was then utilised. As a whole, the numerical analysis confirms its usefulness in predicting the performance of the gasifier, which can reach a cold gas efficiency of around 70%, while the methanation plant can achieve a production of roughly 20 kg of methane per 100 kg of gasified wood.

Simulation of Air Gasification Process of Sunflower Husk Pellets to Produce Purified Syngas

The results of numerical studies of the utilization of sunflower husk pellets obtained by simulating the air gasification process in downdraft gasifier and subsequent purification of the produced syngas from CO2 are presented. Numerical studies were conducted with varying the air-fuel ratio from 0.25 to 0.5 to define the optimum value of this coefficient to obtain gas of a given quality. It was determined that with increasing oxidizer consumption the calorific value of syngas decreases from 3179 to 1971 kJ/m3, due to the increasing concentration of nitrogen and carbon dioxide, and the gasification efficiency increases from 38 to 59 %. The optimal value of the oxidizer excess coefficient for the air gasification of sunflower husk pellets is 0.35.

Experimental assessment of producer gas generation using agricultural and forestry residues in a fixed bed downdraft gasifier

The gasification of biomass waste integrated with thermal usage and power generation is a sustainable approach to generate energy. Present work focuses on operational assessment of an open-top downdraft gasifier at different flow rates of 10.5 and 12.5 g/s using corn cob and eucalyptus wood waste as feedstocks. Gasification characteristics (performance and syngas parameters), morphological characteristics (X-ray Diffraction, Fourier Transform Infrared Spectroscopy, Scanning Electron Microscopy), and thermogravimetric analysis are performed and analysed. The results indicate that values of the lowest hydrogen and carbon monoxide mole fractions, for corncob are 10.81 and 10.11 at the equivalence ratio (ER) of 0.278 and moisture content of 10%. Whereas the highest mole fraction of hydrogen and carbon monoxide for eucalyptus in the producer gas are 14.1 and 12.58 at ER of 0.125 and moisture of 15%. The syngas obtained from eucalyptus wood waste was better in terms of hydrogen content as compared to that from corn cob feedstock as the future vies greater role for hydrogen based fuels.

CFD modelling of spatiotemporal evolution of detailed tar species in a downdraft gasifier

The rising demand for renewable energy around the world has sparked interest in biomass gasification. However, the technology greatly suffers because of tar species produced during the gasification process, which limits direct use of the produced gas. To address this issue, the paper presents a novel piece of work that focuses on the formation and evolution of tar species consisting of benzene, naphthalene, toluene, and phenol. A two-dimensional numerical model for a downdraft biomass gasifier is developed with a total of 20 thermochemical kinetic reactions to investigate the formation of tar species in the gasifier with the effect of residence time. The model's predictions are validated with the experimental and kinetic data and found to be in good agreement. Besides, the model's ability to simulate the producer gas production from a downdraft gasifier is examined. Reaction rates for volatiles decomposition, combustion, and gasification reactions under different working conditions are investigated. Overall, benzene has the highest concentration of the selected tar species, followed by naphthalene, and with relatively modest amounts of phenol and toluene.

Experimental investigation of Segregated Dry Municipal Solid Waste (SDMSW) and biomass blends in the gasification process

Abstract Producing sustainable energy to meet the world’s current demands is a major concern. Municipal Solid Waste (MSW) is a good source for producing sustainable energy and currently gets abundantly generated in India. Usually MSW is screened to prepare Segregated Dry Municipal Solid Waste (SDMSW) pellets before subjecting it to gasification to produce producer gas. But, generation of hazardous byproducts is a key issue in the conversion of SDMSW to producer gas. In the present work a multi-purpose downdraft gasifier has been designed and developed that can process biomass and SDMSW pellets blend while reducing undesirable byproducts such as tar and ash. The calorific value, chemical composition and byproduct content of the SDMSW pallets blended with biomass are determined prior to gasification. The feedstock is characterised using ultimate and proximate analysis, and the calorific value is determined using a bomb calorimeter. Gas chromatography is used to assess the quality of the producer gas. The results indicate that adding 50% SDMSW to Biomass results in good efficiency.

Energy and Economic Assessment of a System Integrated by a Biomass Downdraft Gasifier and a Gas Microturbine

This work focuses on the energy and economic evaluation of a power generation system composed of a downdraft gasifier and gas microturbine. The gasification process was studied using wood pellets as fuel, while the influence of two gasification agents (air and oxygen-enriched air) on parameters, such as low heating value (LHV), composition, and yield of syngas, were analyzed. The syngas produced from oxygen-enriched air gasification in a downdraft gasifier had an LHV higher than 8 MJ/Nm3, being suitable to be supplied in the gas microturbine. Subsequently, syngas use in the gas microturbine was evaluated, and the results demonstrated that microturbine efficiency dropped from 33.00% to 21.35%, while its power decreased from 200 kW to 81.35 kW. The power generation system was modeled using Aspen Plus® v 11.0 software and validated using results obtained from published experimental studies. Accordingly, the integrated generation system presented an overall efficiency of 11.82% for oxygen-enriched air gasification cases. On the other hand, an economic assessment through risk analysis using Monte Carlo simulations was performed using Crystal Ball® v11.1.2.4.850 software. The economic results indicated that the implementation of a generation system was economically unfeasible, however, if the electricity rate price was increased by 63%, the proposed configuration could be feasible.

CFD analysis of the downdraft gasifier using species-transport and discrete phase model

In the present study, a 2-D axisymmetric steady-state computational fluid dynamics (CFD) model has been developed for biomass gasification in a fixed bed Imbert downdraft gasifier. A discrete phase model (DPM) based on the Euler-Lagrangian approach with species transport is applied to the gasifier having the capacity of ≈ 5 kW. The use of DPM for the particle-continuous phase interaction leads to capture more realistic gasification phenomena. The proposed model is an effort to carry forward the CFD technique by implementing an alternative chemical kinetic scheme to study the various gasification parameters. The model is validated at different values of equivalence ratios (0.19–0.33) for producer gas composition and found to be in better agreement with the experimental values reported in the literature. The standard estimated error for the present model is 6.64, 7.55, 2.92, and 5.28 % for carbon monoxide, hydrogen, methane, and carbon dioxide, respectively. Moreover, the calculated standard deviation is 0.44 only. The biomass feed and airflow rates vary from 3.43 to 5.82 kg/h and 2.41–8.02 Nm3/h, respectively. It has been found that an equivalence ratio in the range of 0.25 to 0.30 is the most appropriate condition in the present operating range of the gasifier. The proposed scheme allows accurate prediction under various operating conditions, which may enable the designer to optimise the operating conditions. The model predictions would help to design the process integration of gasification with any existing commercial energy-producing unit based on conventional fuels. Hence, it deliberates significant contribution and value addition in the current literature for the CFD modelling of biomass gasification. The present study not only helps to improve the overall performance of the gasifier but also provides the profiles of essential design variables across the length of the gasifier.

Gasification of Solid Recovered Fuels with Variable Fractions of Polymeric Materials

Gasification is a promising thermochemical technology used to convert waste materials into energy with the introduction of low amounts of an oxidant agent, therefore producing an environmental impact that is lower when compared to incineration and landfilling. Moreover, gasification allows a sustainable management of wastes and reduces the use of fossil fuels responsible for the increment of greenhouse gases. This work aimed to perform gasification tests with solid recovered fuels (SRF) containing organic fractions mainly retrieved from construction and demolition wastes to assess the potential for energy conversion. Tests were conducted in a pilot-scale downdraft gasifier (maximum feedstock input of 22 kg/h) at c.a. 800 °C, using SRF samples containing different proportions of polymeric wastes ranging between 0 and 20 wt %. Gas and chars obtained as by-products were analysed to evaluate their properties and to establish valid pathways for their valorisation. The addition of polymeric wastes reduced char production but rose both tar and HCl concentrations in the gas. The SRF with 10 wt % of polymeric wastes generated the best results, producing the highest calorific value for the gas (3.5 MJ/Nm3) and the highest cold-gas efficiency (45%). Possible char applications include their use as catalysts for tar decomposition, or as an additive in construction materials. Gasification can therefore be considered a valid solution for the energetic valorisation of these SRFs.