Downdraft Fixed-bed Gasifier Research Articles

Recycling municipal solid waste utilizing gasification technology: a case study

Reliable, affordable, and clean energy supply is of considerable importance for the society, economy, and the environment. Renewable energy sources can provide several times the world’s energy demand. Biomass energy is considered a promising clean energy option for the reduction in greenhouse gas emissions and energy dependency. Among feasible technologies, biomass gasification has been considered as an enabling technology for municipal solid waste (MSW) conversion systems. The synthesis gas produced in waste-to-energy gasification of MSW can lead to their increased role in electricity generation in the future and reduces waste disposal costs. In this study, a thermodynamic equilibrium model was developed based on the downdraft fixed-bed gasifier to evaluate the effect of waste moisture content on synthesis gas composition. Besides, the equilibrium temperature of the gasifier and heating value of synthesized gas from the downdraft fixed-bed gasifier have been analyzed. Municipal solid waste of Tehran is considered as the main feed of the proposed system. The modeling results showed reasonable agreement with the experiment. The effect of operating condition on fuel moisture content and gasifier temperature was investigated. The effect of fuel moisture content on syngas compositions was also studied. The hydrogen content in the synthesis gas composition increases slightly initially to 17.9% (in moisture content 18%) but then starts reducing again. Besides, the effect of reactor temperature on synthesis gas composition was investigated.

Application of Recycle System on a Cocoa Pod Husks Gasification in a Fixed-Bed Downdraft Gasifier to Produce Low Tar Fuel Gas

Biomass gasification is potentially generating not only producer gas but also tarry components. Practically, the gas may substitute traditional fuel in an internal combustion engine after reducing the tar. This research examined a producer gas recycle system to reduce tar component of producer gas generated with cocoa pod husks gasification using air as gasifying agent in a fixed-bed downdraft gasifier. Cocoa pod husks feed sizes were +1” sieve, -1”+ 0.5” sieve, and -0.5” sieve. The gasification process was operated at the temperature range of 491 – 940oC and at various gasifying agent volumetric rates of 62.84; 125,68; and 188.53 NL/min or at equivalent ratio range of 0.014 – 0.042. A recycle system of outlet producer gas to gasifier was set at volumetric rates of 0.139; 0.196; and 0.240 L/min. The performance of the system was evaluated with analyzing the tar component using gravimetric method of ASTM D5068-13, and the gas component of CO, H2, CO2 and CH4 compositions in producer gas were analyzed using Gas Chromatography GC-2014 Shimadzu sensor TCD-14. This recycle system succeeded in reducing tar content as much as 97.19% at 0.139 L/min of recycle volumetric rate and at biomass feed size of -1”+0.5” sieve. The producer gas contained CO, H2, CO2 and CH4 of 23.29%, 2.66%, 13.30%, and 14.18% respectively. The recycle system cold gas efficiency was observed 65.24% at gasifying agent volumetric rate of 188.53 L/min and at biomass feed size of +1” sieve.

Predictive modeling of biomass gasification with machine learning-based regression methods

Biomass gasification is a promising power generation process due to its ability to utilize waste materials and similar renewable energy sources. Predicting the outcomes of this process is a critical step to efficiently obtain the optimal amount of products. For this purpose, various kinetic and equilibrium models are proposed, but the assumptions made in these models significantly reduced their practical usability and consistency. More recently, machine learning methods have started been employed, but the limited selection of methods and lack of implementation of cross-validation techniques caused insufficiency to obtain unbiased performance evaluations. In this study, we employed four regression techniques, i.e., polynomial regression, support vector regression, decision tree regression and multilayer perceptron to predict CO, CO2, CH4, H2 and HHV outputs of the biomass gasification process. The data set is experimentally collected via downdraft fixed-bed gasifier. PCA technique is applied to the extracted features to prevent multicollinearity and to increase computational efficiency. Performances of the proposed regression methods are evaluated with k-fold cross validation. Multilayer perceptron and decision tree regression performed the best among other methods by achieving R2> 0.9 for the majority of outputs and were able to outperform other modeling approaches.

Performance analysis of a commercial fixed bed downdraft gasifier using palm kernel shells

This work analyzes the use of palm kernel shells (PKS) produced by the Colombian palm oil mill industry, for purposes of fueling a commercial downdraft fixed bed gasifier (Ankur Scientific WGB- 20) designed to operate with wood chips. Operational parameters such as hopper shaking time, ash removal time, and airflow were varied in order to get the highest gasifier performance, computed as the ratio between producer gas chemical energy over biomass feeding energy. Experiments were carried out following a half fraction experimental design 24-1. Since these parameters affect the equivalence ratio (ER), behavior indicators were analyzed as a function of ER. It was found that the shaking time and airflow had a significant effect on higher-heating-value (HHV) and process efficiency, while the removal time is not significant. The highest performance for palm shell was reached at ER=0.35, where the resulting gas HHV and process efficiencies were 5.04 MJ/Nm3 and 58%, respectively.

Experimental study on the performance of gasification of corncobs in a downdraft fixed bed gasifier at various conditions

An experimental investigation on the gasification of corncobs was conducted in an 18 kW pilot-scale fixed bed system for power generation. The main objective was to determine the effect of gasifying corncob mixtures with fines content (particle size below 10 mm) on the performance of the system. To achieve the objective, a 2× 3 factorial arrangement was developed. The analysis considered three resistive loads connected to the generator (4, 8, and 12 kW) and two different size ranges of biomass (one with 100% of chips within the actual recommended size (10–40 mm)) and the other with a content of 15% of fine particles (particle size below 10 mm).An increase of 15% in fine material content in the feedstock and a stable electricity demand close to the rated capacity, significantly increased the temperature of the process and decreased the mean specific fuel consumption – SFC (2.06 kg/kWh at 67% of rated capacity). H2 and CO production increased by increasing reactor temperature, reaching concentrations of 16.7% and 17% respectively at the higher resistive load (12 kW). Cold gas efficiency varied in the range of 33.7%–37.0%, increasing slightly with the blend of fines content and higher applied load.

Analysis of pollutants in the product gas of a pilot scale downdraft gasifier fed with wood, or mixtures of wood and waste materials

Small scale gasification of Solid Recovered Fuels (SRF) in downdraft reactors could be an alternative to large scale waste-to-energy schemes. In this perspective, the assessment of the pollutant emissions at pilot scale is necessary. This work compares pollutant emissions from wood and SRF air gasification in a downdraft fixed bed gasifier. Five fuels have been studied: Poplar wood, SRF wood, and three different mixtures containing mass fractions of 80% SRF wood with 20% of either tire, plastic waste or sewage sludge. Air gasification was performed in a pilot scale reactor in fed-batch mode using a fuel mass ranging from 5 to 8 kg and an air inlet flow of 170–180 L min−1 (at 0 °C and 101 325 Pa). Depending on the fuel, Equivalence Ratios (ER) ranged from 0.22 to 0.29 and gasification temperatures from 690 to 850 °C. Emissions analyses were performed on product gas, condensable species and remaining chars, with a particular focus on sulfur, nitrogen and heavy metals. Regarding sulfur, wood and SRF wood led to low H2S contents (6–8 μmol mol−1), when SRF mixes led to higher concentrations (44–96 μmol mol−1) in addition to of up to 11 heavier sulfur compounds. Regarding nitrogen, SRF produced higher ammonia concentrations (2.1–7.6 mmol mol−1) than Wood (619 μmol mol−1), as a result of initial nitrogen mass fractions17 to 27 times higher in the SRF mixes. Heavy metals analyzed in remaining solids after gasification showed low recovery rates (<0.4%), and tend to accumulate in fine particles, as a result of their volatility.

Comparison of the gasification performance in the downdraft fixed-bed gasifier fed by different feedstocks: Rice husk, sawdust, and their mixture

In order to figure out the compatibility of downdraft gasifiers on different feedstocks, performance of a fixed-bed downdraft gasifier fed by rice husk, sawdust, and their mixture (1:1 by mass) are compared in the present work. Gasification is performed with varying equivalence ratio, i.e. 0.15, 0.20, and 0.25. Gasification air is injected into the reactor via three tuyers located at 330 mm above the grate. Gasification characteristics (temperature profile of the reactor, fuel consumption rate, volume fraction of CO, H2, and CH4 in the producer gas) and performance of the gasifier (lower heating value of the producer gas and cold gas efficiency of the gasifier) are observed and analyzed. The results indicate that the gasifier is compatible for rice husk, sawdust, or their mixture. Optimum equivalence ratio for gasification of the rice husk, sawdust, and the mixture are 0.20, 0.20, and 0.15, respectively. At the optimum equivalence ratios, lower heating values of the producer gas are 3.13, 2.69, and 0.35 MJ/Nm3 for rice husk, sawdust, and the mixture. Meanwhile, cold gas efficiencies are 72.73%, 69.27%, and 82.08%, correspondingly.

Experimental study on hydrogen-rich syngas production via gasification of pine cone particles and wood pellets in a fixed bed downdraft gasifier

The main objective of this research is to investigate gasification of pine cones particles and wood pellets in a pilot scale 10 kWth downdraft fixed bed gasifier using air as an oxidizing agent. In this work, it was found that syngas produced by gasification of pinecones particles is rich in environmentally friendly hydrogen and that would be a clean alternative energy carrier for the production of clean energy. In addition, the effect of gasification temperature and equivalence ratio on the composition of syngas and gasification performance for pine cones and wood pellet were analysed comparatively. During the experimental works gasification took place with air, in a temperature range of 701–1046 °C, for various air equivalence ratios (0.14–0.37) and under atmospheric pressure. It is found that H2 and CO production increased by increasing reactor temperature. Another finding is that the mean cold gas efficiency was 65% for pinecone particles and 80% for wood pellet gasification.

Investigation of municipal sludge gasification potential: Gasification characteristics of dried sludge in a pilot-scale downdraft fixed bed gasifier

This study presents the research results acquired from conducting municipal sludge gasification in a downdraft type gasifier at pilot scale. The assessment of the results was not only focused on syngas characteristics, but also on the gasification residues: char ash and glassy material. The gasification temperature was varied from 1000 to 1150 °C during the gasification trials. The produced high quality syngas was transferred to the engine to generate the electricity. About 1 kWh electrical power was achieved for approximately 1.2 kg municipal sludge gasified. Most of the heavy metals available in the sludge was found as fixed form in the glassy material. The gasification residues evaluated as valuable materials regarding their characteristics have reuse potential for different beneficial usage alternatives. Based on the costs for the investment and operation and incomes, the return on the investment for this pilot scale system was roughly found as 3.3 years. This study showed that the municipal sludge had an important fuel merit and the energy recovery from the sludge was possible via the gasification application. In this paper, the research results were discussed in detail to make better insight to full-scale applications as a promising alternative for sludge disposal.

Biomass gasification in a fixed bed downdraft reactor with oxygen enriched air: a modified equilibrium modeling study

Biomass conversion by gasification process is increasingly becoming attractive, especially for ceramic making industry, to transform biomass materials into combustible fuel gas called producer gas. This producer gas can then be used to fully or partially substitute liquefied petroleum gas in ceramic firing process. However, air gasification is known to generate low calorific value of gaseous fuel (3-6 MJ/Nm3) which may not be able to generate sufficiently high temperature (> 1200 oC) flame required by ceramic firing process. Use of oxygen enriched air is therefore of great interest if medium to high calorific value producer gas is required. In this work, a modified equilibrium model of global gasification reactions is developed to predict the resultant distribution of combustible gas species in the producer gas and to study the effect of operating parameters (oxygen content in air, and equivalence ratio) in a gasification process of agro-residues in a fixed bed downdraft gasifier at a fixed temperature. The modified equilibrium model of global gasification reactions developed in this work is based on thermodynamically stoichiometric approach due to its simplicity and reduced computational time. Model predictions of reaction kinetic constants for gasification reactions and gas concentration are validated by comparing with available experimental data. Simulation of influence of oxygen content in air (21-50%) and equivalence ratio (0.15-0.35) on composition of combustible gas and its heating value is carried out. The preliminary model simulation is found to give good qualitative prediction of experimental results. For maximum calorific value of producer gas generated, oxygen content in air should be 50%, and the equivalence ratio should be 0.15, respectively. For better accuracy of this modified equilibrium model, unconverted char and tar should be further considered.

A hot syngas purification system integrated with downdraft gasification of municipal solid waste

Gasification of municipal solid waste (MSW) with subsequent utilization of syngas in gas engines/turbines and solid oxide fuel cells can substantially increase the power generation of waste-to-energy facilities and optimize the utilization of wastes as a sustainable energy resources. However, purification of syngas to remove multiple impurities such as particulates, tar, HCl, alkali chlorides and sulfur species is required. This study investigates the feasibility of high temperature purification of syngas from MSW gasification with the focus on catalytic tar reforming and desulfurization. Syngas produced from a downdraft fixed-bed gasifier is purified by a multi-stage system. The system comprises of a fluidized-bed catalytic tar reformer, a filter for particulates and a fixed-bed reactor for dechlorination and then desulfurization with overall downward cascading of the operating temperatures throughout the system. Novel nano-structured nickel catalyst supported on alumina and regenerable Ni-Zn desulfurization sorbent loaded on honeycomb are synthesized. Complementary sampling and analysis methods are applied to quantify the impurities and determine their distribution at different stages. Experimental and thermodynamic modeling results are compared to determine the kinetic constraints in the integrated system. The hot purification system demonstrates up to 90% of tar and sulfur removal efficiency, increased total syngas yield (14%) and improved cold gas efficiency (12%). The treated syngas is potentially applicable in gas engines/turbines and solid oxide fuel cells based on the dew points and concentration limits of the remaining tar compounds. Reforming of raw syngas by nickel catalyst for over 20 h on stream shows strong resistance to deactivation. Desulfurization of syngas from MSW gasification containing significantly higher proportion of carbonyl sulfide than hydrogen sulfide, traces of tar and hydrogen chloride demonstrates high performance of Ni-Zn sorbents.

A novel real-time monitoring and control system for waste-to-energy gasification process employing differential temperature profiling of a downdraft gasifier

A novel, cost-effective and real-time process monitoring and control system was developed to maintain stable operation of waste-to-energy gasification process. It comprised a feedback loop control that utilized the differential temperatures of the oxidation and reduction zones in the gasifier to determine the regional heat-flow (endothermic or exothermic), to assess the availability of oxidizing agent (for instance, air or O2) at the char bed and to calculate the fuel feeding rate. Based on the correlations developed, the air-to-fuel ratio or the equivalence air ratio (ER) for air gasification could be instantaneously adjusted to maintain stable operation of the gasifier. This study demonstrated a simplification of complex reaction dynamics in the gasification process to differential temperature profiling of the gasifier. The monitoring and control system was tested for more than 70 h of continuous operation in a downdraft fixed-bed gasifier with refuse-derived fuel (RDF) prepared from municipal solid wastes (MSW). With the system, fuel feeding rate could be adjusted accurately to stabilize the operating temperature and ER in the gasifier and generate syngas with consistent properties. Significant reductions in the fluctuations of temperature profiles at oxidation and reduction zones (from higher than 100 °C to lower than 50 °C), differential temperatures (from ±200 to ±50 °C) in gasifier and the flow rate (from 16 ± 6.5 to 12 ± 1.8 L/min), composition of main gas components, LHV (from 6.2 ± 3.1 to 5.7 ± 1.6 MJ/Nm3) and tar content (from 8.0 ± 9.7 to 7.5 ± 4.2 g/Nm3) of syngas were demonstrated. The developed gasifier monitoring and control system is adaptable to various types (updraft, downdraft, and fluidized-bed) and scales (lab, pilot, large scale) of gasifiers with different types of fuel.

Comparative analysis of wood and solid recovered fuels gasification in a downdraft fixed bed reactor

This study aims to qualify air gasification performances of Solid Recovered Fuels (SRF) in a downdraft fixed bed gasifier. Five fuels have been studied: Wood, SRF wood, and three different mixtures of SRF wood and 20 %w of either SRF tire (mix A), SRF plastics (mix B) or SRF sewage sludge (mix C). The tests were carried out in a pilot scale reactor in a batch-fed mode using a fuel mass ranging from 5 to 8 kg, and an air inlet flow of 170–180 L/min, which led to an Equivalence Ratio (ER) ranging between 0.20 and 0.29. Considering Poplar wood as a reference, we observed a similar syngas quality for SRF wood, but SRF mixes led to a slight decrease of H2 and CO contents along with an increase of CO2, CH4, C2H4 and C2H6 contents. However syngas Low Heating Value (LHV) remained close and ranged between 4.9 and 5.4 MJ/m3 which led to a Cold Gas Efficiency (CGE) ranging from 38 to 52%. Wood and SRF wood had a similar condensate content (159–202 g/m3), but adding 20 %w of non-woody fuel led to an increased condensate content up to 369 g/m3 for mix A and 411 g/m3 for mix C. Tar analyses confirmed the similarity of Wood, SRF wood and mix C in air gasification, but highlighted large increases in aromatics and Polycyclic Aromatic Hydrocarbon (PAH) contents when adding 20 %w of tire. This study confirms the ability of downdraft gasifier to handle non-woody fuels, with an upper limit of 20%w share in a wood-based fuel.

Developing a novel downdraft fixed bed gasifier for hydrogen production from sawdust to improve an SI engine exhaust emissions

The presence of vast forests is the largest source of abundant biomass in Iran. Wood waste can be used as the primary source of energy generation. In the present research, sawdust was employed to produce the syngas. For this purpose, a downdraft gasifier was designed and the produced syngas was evaluated in a spark ignition (SI) engine. Based on results, the production yield of biohydrogen and its heating value at 960 ℃ were about 786 mL/g biomass and 3.75 MJ/m3, respectively. The synthesized syngas compositions were Hydrogen (13.82%), CH4 (1.52%), CO2 (2.75%), CO (13.6%), N2 (65.31%) and water vapor (3%). Increasing the temperature of the combustion zone inside the gasification reactor from 650 to 960 ℃, increased the H2, CH4, and CO contents of syngas. Moreover, the results indicated that, using syngas in engine reduces CO2 and UHC emissions about 58.6% and 16.6%, respectively compared to those for gasoline fuel.

Evaluation of potential of energetic development in isolated zones with wide biodiversity: NIZ Chocó-Colombia case study

The implementation of a hybrid biomass gasification-photovoltaic system for electricity generation in isolated regions was evaluated. Experiments were carried out to test the gasification of agricultural residual biomass in a downdraft fixed-bed gasifier coupled to an internal combustion engine and a photovoltaic system with this set-up, electricity was successfully generated by means of rice husk (RH) gasification, which produced a synthesis gas with a calorific value below 3–5 MJ/N m3. The gas was purified sufficiently to make it profitable in an engine through a simple cleaning system. The main contribution is given by the proposal of a hybrid system adapted to climatic conditions and renewable resources settled in the region; In order to have a portable and autonomous system. Where it can be concluded that a hybrid solar-biomass system is a versatile alternative to contribute to the generation and efficient use of electrical energy. The hybrid system provided a stable electricity supply of 24–27 kWh. Along with the analysis of residual biomass availability in the Chocó region, this indicates that the implementation of technological alternatives such as the ones tested in this research are able to sustainably fulfill the energy needs of isolated communities by making use of the resources coming from their own agricultural activities. Also, the conclusions show that the best hybrid system, from the technician-economic point of view for the energy.

Kinetic Reaction Modeling of the Reduction Zone of Bamboo Gasification in a Fixed Bed Downdraft Gasifier

Kinetic Reaction Modeling of the Reduction Zone of Bamboo Gasification in a Fixed Bed Downdraft Gasifier

Modeling and Simulation of Corn Stover Gasifier and Micro-turbine for Power Generation

This paper focuses on modeling the performance of a small-scale combined heat and power (CHP) plant fueled with corn stover pieces (CSP) as very potential biomass resource in Egypt. The developed power plant can be used to satisfy the heat and electricity needs. The proposed power plant performance is simulated using the professional Cycle-Tempo® software. The power plant is divided into three stages; the gasification unit (downdraft fixed bed gasifier and air supply system), gas cleaning and cooling units and the micro-turbine (MT) as an electrical generation unit. In the first stage, the CSP feedstock is converted to producer gas at atmospheric pressure with a reaction temperature about 1028.6 °C, using air as a gasifying agent. The efficiency of gasification process at a regulated air–biomass ratio of 1.5 kg/kg is 77.92% with calorific value (LHV) of 3.87 MJ/kg. Cleaning and cooling stage used to dispose the undesirable gas constitutes such as; tar, flying ash, and etc. The clean gas is passing through the MT as power generator for CHP applications with turbine inlet temperature of 850 °C. Ultimately, the simulation revealed that the CHP overall efficiency of this developed plant is 63.21% providing an electrical power of 94.81 kWel and thermal power of 187.55 kWth.

Producer gas production of Indonesian biomass in fixed-bed downdraft gasifier as an alternative fuels for internal combustion engines

downdraft biomass gasification reactors, coupled with reciprocating internal combustion engines (ICE) are a viable technology for small scale heat and power generation. The direct use of producer gas as fuel subtitution in an ICE could be of great interest since Indonesia has significant land area in different forest types that could be used to produce bioenergy and convert forest materials to bioenergy for use in energy production and the versatility of this engine. This paper will look into the aspect of biomass energie as a contributor to energy mix in Indonesia. This work also contains information gathered from numerous previews study on the downdraft gasifier based on experimental or simulation study on the ability of producer gas as fuels for internal combustion engines aplication. All data will be used to complement the preliminary work on biomass gasification using downdraft to produce producer gas and its application to engines.

Investigation of Co-gasification Characteristics of Wood-coconut Fibers Pellet and Rice Husk Mixtures in a Downdraft Fixed Bed Gasifier

Investigation of Co-gasification Characteristics of Wood-coconut Fibers Pellet and Rice Husk Mixtures in a Downdraft Fixed Bed Gasifier

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.