Characteristics of cyclone gasification of rice husk

The gasification characteristics of the rice husk were studied in a cyclone gasifier using air as the gasifying medium to generate the fuel gas with available heating value and less tar content. The influence of equivalence ratio on temperature profiles, composition and low heating value of the produced gas, tar content, carbon conversion and cold gas efficiency was investigated. The equivalence ratios considered in this study were 0.20–0.32. The results show that the optimal equivalence ratio is 0.29 and the maximum temperature of gasification should be lower than 1000 °C. In order to optimize the performance of the cyclone gasifier, the main body of the gasifier was lengthened and air staged gasification was carried out. The low heating value of the produced gas, carbon conversion, cold gas efficiency and tar content are 4.72 MJ/Nm³, 57.5%, 37.3% and 1.85 g/Nm³, respectively.     

Hydrogen-rich syngas production from municipal solid waste gasification through the application of central composite design: An optimization study

This study aims to investigate the influence and interaction of experimental parameters on the production of optimum H₂ and other gases (CO, CO₂, and CH₄) from gasification of municipal solid waste (MSW). Response surface method in assistance with the central composite design was employed to design the fifteen experiments to find the effect of three independent variables (i.e., temperature, equivalence ratio and residence time) on the yields of gases, char and tar. The optimum H₂ production of 41.36 mol % (15.963 mol kg-MSW⁻¹) was achieved at the conditions of 757.65 °C, 0.241, and 22.26 min for temperature, ER, and residence time respectively. In terms of syngas properties, the lower heating value and molar ratio (H₂/CO) ranged between 9.33 and 12.48 MJ/Nm³ and 0.45–0.93. The predicted model of statistical analysis indicated a good fit with experimental data. The gasification of MSW utilizing air as a gasifying agent was found to be an effective approach to recover the qualitative and quantitate products (H₂ and total gas yield) from the MSW.     

Effect of the type of gasifying agent on gas composition in a bubbling fluidized bed reactor

It is commonly accepted that gasification of coal has a high potential for a more sustainable and clean way of coal utilization. In recent years, research and development in coal gasification areas are mainly focused on the synthetic raw gas production, raw gas cleaning and, utilization of synthesis gas for different areas such as electricity, liquid fuels and chemicals productions within the concept of poly-generation applications. The most important parameter in the design phase of the gasification process is the quality of the synthetic raw gas that depends on various parameters such as gasifier reactor itself, type of gasification agent and operational conditions. In this work, coal gasification has been investigated in a laboratory scale atmospheric pressure bubbling fluidized bed reactor, with a focus on the influence of the gasification agents on the gas composition in the synthesis raw gas. Several tests were performed at continuous coal feeding of several kg/h. Gas quality (contents in H₂, CO, CO₂, CH₄, O₂) was analyzed by using online gas analyzer through experiments. Coal was crushed to a size below 1 mm. It was found that the gas produced through experiments had a maximum energy content of 5.28 MJ/Nm³ at a bed temperature of approximately 800 °C, with the equivalence ratio at 0.23 based on air as a gasification agent for the coal feedstock. Furthermore, with the addition of steam, the yield of hydrogen increases in the synthesis gas with respect to the water–gas shift reaction. It was also found that the gas produced through experiments had a maximum energy content of 9.21 MJ/Nm³ at a bed temperature range of approximately 800–950 °C, with the equivalence ratio at 0.21 based on steam and oxygen mixtures as gasification agents for the coal feedstock. The influence of gasification agents, operational conditions of gasifier, etc. on the quality of synthetic raw gas, gas production efficiency of gasifier and coal conversion ratio are discussed in details.     

Gasification and power generation characteristics of woody biomass utilizing a downdraft gasifier

Energy utilization from biomass resources has started to attract public attention as a method to reduce CO₂ emissions. In this study, the characteristics of syngas production from biomass gasification were investigated in a downdraft gasifier that was combined with a small gas engine system for power generation. Syngas temperatures from the gasifier were maintained at a level of 700-1000 °C. When the air ratio for gasification was 0.3-0.35, the low heating value of syngas was 1100-1200 kcal Nm⁻³ and the cold gas efficiency 69-72%. Tar concentration in raw syngas was around 3.9-4.4 g Nm⁻³. Syngas combustion in the gas engine after purification showed that HC concentration was below 200 ppm, and NOx concentration was below 40 ppm in the exhaust gas.     

Hydrogen gas yield and trace pollutant emission evaluation in automotive shredder residue (ASR) gasification using prepared oyster shell catalyst

This work examines the hydrogen gas yield and trace pollutants partitioning in automobile shredder residue (ASR) catalytic gasification by fixed bed and fluidized bed gasifier with controlling at equilibrium ratio (ER) 0.2, temperature 900 °C, and 5%–15% prepared catalyst addition. Oyster shell (OS) is a valuable resource due to its higher calcium content that it could prepare as a catalyst for enhancing the hydrogen production in ASR gasification. In the case of the fixed bed gasifier experiments, the highest lower heating value (LHV) and syngas production were found at 900 °C and 10% OS catalyst addition. The maximum H₂ and CO composition were 6.57% and 5.97%, respectively. The LHV of syngas was approximately 4.43 MJ/Nm³. The fluidized bed gasifier could provide a good ASR decomposition and heat transfer behavior. The syngas yield results indicated the maximum H₂ and CO composition were 12.12% and 10.59%, respectively. It was obviously showed that the syngas production and energy conversion efficiency were enhanced by applying fluidized bed gasifier. The maximum produced gas LHV was 10.77 MJ/Nm³ as well as the cold gas efficiency (CGE) of produced gas was 71.62%. On the other hand, the volatile sulfur and chlorine speciation formed in ASR gasification were mainly partitioned in the solid and/or liquid phase. It implied that tested OS catalysts could inhibit the volatile sulfur and chlorine speciation emission in the produced gas as well as enhance the produced gas quality. In summary, this research could provide basic insight into enhanced syngas production and quality in ASR catalytic gasification using the prepared OS catalyst.     

Biomass-based hydrogen production: A review and analysis

In this study, various processes for conversion of biomass into hydrogen gas are comprehensively reviewed in terms of two main groups, namely (i) thermo-chemical processes (pyrolysis, conventional gasification, supercritical water gasification (SCWG)), and (ii) biological conversions (fermentative hydrogen production, photosynthesis, biological water gas shift reactions (BWGS)). Biomass-based hydrogen production systems are discussed in terms of their energetic and exergetic aspects. Literature studies and potential methods are then summarized for comparison purposes. In addition, a biomass gasification process via oxygen and steam in a downdraft gasifier is exergetically studied for performance assessment as a case study. The operating conditions and strategies are really important for better performance of the system for hydrogen production. A distinct range of temperatures and pressures is used, such as that the temperatures may vary from 480 to 1400 °C, while the pressures are in the range of 0.1–50 MPa in various thermo-chemical processes reviewed. For the operating conditions considered the data for steam biomass ratio (SBR) and equivalence ratio (ER) range from 0.6 to 10 and 0.1 to 0.4, respectively. In the study considered, steam is used as the gasifying agent with a product gas heating value of about 10–15 MJ/Nm³, compared to an air gasification of biomass process with 3–6 MJ/Nm³. The exergy efficiency value for the case study system is calculated to be 56.8%, while irreversibility and improvement potential rates are found to be 670.43 and 288.28 kW, respectively. Also, exergetic fuel and product rates of the downdraft gasifier are calculated as 1572.08 and 901.64 kW, while fuel depletion and productivity lack ratios are 43% and 74.3%, respectively.     

Hydrogen-rich gas production from biomass steam gasification in an updraft fixed-bed gasifier combined with a porous ceramic reformer

This paper investigates the hydrogen-rich gas produced from biomass employing an updraft gasifier with a continuous biomass feeder. A porous ceramic reformer was combined with the gasifier for producer gas reforming. The effects of gasifier temperature, equivalence ratio (ER), steam to biomass ratio (S/B), and porous ceramic reforming on the gas characteristic parameters (composition, density, yield, low heating value, and residence time, etc.) were investigated. The results show that hydrogen-rich syngas with a high calorific value was produced, in the range of 8.10–13.40 MJ/Nm³, and the hydrogen yield was in the range of 45.05–135.40 g H₂/kg biomass. A higher temperature favors the hydrogen production. With the increasing gasifier temperature varying from 800 to 950 °C, the hydrogen yield increased from 74.84 to 135.4 g H₂/kg biomass. The low heating values first increased and then decreased with the increased ER from 0 to 0.3. A steam/biomass ratio of 2.05 was found as the optimum in the all steam gasification runs. The effect of porous ceramic reforming showed the water-soluble tar produced in the porous ceramic reforming, the conversion ratio of total organic carbon (TOC) contents is between 22.61% and 50.23%, and the hydrogen concentration obviously higher than that without porous ceramic reforming.     

Effect of design and operating parameters on the gasification process of biomass in a downdraft fixed bed: An experimental study

The main objective of this paper is to study the effect of design and operating parameters, mainly reactor geometry, equivalence ratio and biomass feeding rate, on the performance of the gasification process of biomass in a three air stage continuous fixed bed downdraft reactor. The gasification of corn straw was carried out in the gasifier under atmospheric pressure, using air as gasifying agent. The results demonstrated that due to the three stage of air supply, a high and uniform temperature was achieved in the oxidation and reduction zones for better tar cracking. The designing of both the air supply system and rotating grate avoided bridging and channeling. The gas composition and tar yield were affected by the parameters including equivalence ratio (ER) and biomass feeding rate. When biomass feeding rate was 7.5 kg/h and ER was 0.25–0.27, the product gas of the gasifier attained a good condition with lower heating value (LHV) about 5400 kJ/m³ and cold gas efficiency about 65%. An increase in equivalence ratio led to higher temperature which in turn resulted in lower tar yield which was only 0.52 g/Nm³ at ER = 0.32. Increasing biomass feeding rate led to higher biomass consumption rate and process temperature. However, excessively high feeding rate was unbeneficial for biomass gasification cracking and reforming reactions, which led to a decrease in H₂ and CO concentrations and an increase in tar yield. When ER was 0.27, with an increase of biomass feeding rate from 5.8 kg/h to 9.3 kg/h, the lower heating value decreased from 5455.5 kJ/Nm³ to 5253.2 kJ/Nm³ and tar yield increased from 0.82 g/Nm³ to 2.78 g/Nm³.     

Comparison of green waste gasification performance in updraft and downdraft fixed bed gasifiers

This study aimed to investigate the gasification potential of municipal green waste in different fixed-bed gasifier configurations as updraft and downdraft. Both reactor systems were constructed from stainless-steel with a cyclone separator to increase synthesis gas yield and reduce tar production. Green waste collected from parks and gardens by Manisa Metropolitan Municipality, Turkey, was used in the experiments. After full-characterization of green waste, gasification experiments were performed above 700 °C to produce syngas with more than 40% (volumetric) H₂ and heating value around 12.54 MJ/Nm³. Dry air (DA) and pure oxygen (PO) were used as gasification agents. DA was applied with the flow-rates ranged between 0.4 and 0.05 L/min while the flow-rate of PO was 0.01 L/min. The maximum H₂ production as 45 vol% was obtained in downdraft reactor while it was about 51 vol% in updraft system. CH₄ production was obtained as higher value (app. 19 vol%) in downdraft reactor than that (13 vol%) in the updraft one. In the experiments with DA above 700 °C, the H₂/CO ratio varied between 1 and 3, and in the experiments with PO, it increased up to a maximum value of 4. The study has found a suitable set of gasification process parameters for two reactor systems. Therefore, the findings have been compared and discussed in detail.     

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.     

Experimental study on biomass gasification in a double air stage downdraft reactor

This work presents an experimental study of the gasification of a wood biomass in a moving bed downdraft reactor with two-air supply stages. This configuration is considered as primary method to improve the quality of the producer gas, regarding its tar reduction. By varying the air flow fed to the gasifier and the distribution of gasification air between stages (AR), being the controllable and measurable variables for this type of gasifiers, measuring the CO, CH₄ and H₂ gas concentrations and through a mass and energy balance, the gas yield and its power, the cold efficiency of the process and the equivalence ratio (ER), as well as other performance variables were calculated. The gasifier produces a combustible gas with a CO, CH₄ and H₂ concentrations of 19.04, 0.89 and 16.78% v respectively, at a total flow of air of 20 Nm³ h⁻¹ and an AR of 80%. For these conditions, the low heating value of the gas was 4539 kJ Nm⁻³. Results from the calculation model show a useful gas power and cold efficiency around 40 kW and 68%, respectively. The resulting ER under the referred operation condition is around 0.40. The results suggested a considerable effect of the secondary stage over the reduction of the CH₄ concentration which is associated with the decreases of the tar content in the produced gas. Under these conditions the biomass devolatilization in the pyrolysis zone gives much lighter compounds which are more easily cracked when the gas stream passes through the combustion zone.     

Downdraft gasifier structure and process improvement for high quality and quantity producer gas production

The current study reveals several efficient amenities that can affect the gasification process to improve syngas quality and yield. A comprehensive study was carried out using a 24 kW downdraft gasifier to evaluate the effect of uniform air distribution in the oxidation zone, additional throat on the reactor temperature distribution and the overall gasification process. The effect of fuel moisture, equivalence ratio, gasifying agent type and pre-treatment of the gasifying agent on producer gas yield and composition were also evaluated. The biomass feeding rate was 30–40 kg/h, and the maximum gas flow rate was 90 m³/h. When corn cobs and waste wood (carpenter waste) with moisture content from 5 to 30% were used as feed stock, with 70 °C air as the gasifying/oxidizing agent, the energy value of the producer/syngas obtained was 6.31 and 6.66 MJ/m³, respectively. The heating value was improved to 6.72 and 8.43 MJ/m³ when using 150 °C air-steam mixture as the gasifying agent, with the optimum equivalence ratio of 0.30. The methane, hydrogen and carbon monoxide concentration (on volume basis) were 6.20, 19.32 and 21.00. The average amount of syngas produced from 1 kg of corn cobs and waste wood were 2.94 and 2.62 m³, while the average amount of tar produced was 2.2 and 1.8 g/Nm³ respectively. The investigation revealed that uniform air distribution in the oxidation zone, fuel moisture content, gasifying agent type and the pre-treatment of gasifying agent played a significant role in enhancing the quantity and quality of the producer gas.     

Assessment of low-rank coal and biomass co-pyrolysis system coupled with gasification

To utilize low-rank coal and biomass in a highly efficient and environmental-friendly manner, a co-pyrolysis system coupled with char gasification is investigated. This system has five main units, namely, the drying and mixing, pyrolysis, cooling and separation, combustion, and gasification units, which are simulated by ASPEN plus based on experimental data. Results show that 37% of the pyrolysis char is burned to supply heat for pyrolysis and drying processes based on cascade utilization of heat energy, whereas the rest is sent to a gasifier. The sensitivity analysis is performed to investigate the impacts of steam and O₂ injection on gas composition, gasification temperature, carbon conversion efficiency, heating value of gas during gasification, and gas production efficiency. The fractions of H₂, CH₄, CO, and CO₂ demonstrate diverse variation tendencies with an increasing equivalence ratio and steam-to-char (S/C) ratio. However, carbon conversion efficiency reaches its peak of 99.91% when the equivalence ratio is approximately 4 regardless of S/C ratio. An equivalence ratio of 4 and S/C ratio of 0.15 are used as decent examples to calculate the mass balance and to simulate the overall system. Results show that 1000 kg/h coal and 500 kg/h biomass can produce 285.83 m³/h pyrolysis gas and 2580.78 m³/h gasification gas with low heating values of 8.20 and 9.746 MJ/m³, respectively.     

Modelling of biomass gasifier and microturbine for the olive oil industry

The olive oil industry generates several solid wastes. Among these residues are olive tree leaves, prunings, and dried olive pomace (orujillo) from the extraction process. These renewable energy sources can be used for heat and power production. The aim of this paper consists of modelling and simulation of a small‐scale combined heat and power (CHP) plant (fuelled with olive industry wastes) incorporating a downdraft gasifier, gas cleaning and cooling subsystem, and a microturbine as the power generation unit. The gasifier was modelled with thermodynamic equilibrium calculations (fixed bed type, stratified and with an open top). This gasifier operates at atmospheric pressure with a reaction temperature about 800°C. Simulation results (biomass consumption, gasification efficiency, rated gas flow, calorific value, gas composition, etc.) are compared with a real gasification technology. The product gas obtained has a low heating value (4.8–5.0 MJ Nm^?3) and the CHP system provides 30 kW_e and 60 kW_th. High system overall CHP efficiencies around 50% are achievable with such a system. The proposed system has been modelled using Cycle‐Tempo software^®. Copyright © 2010 John Wiley & Sons, Ltd.     

Experimental analysis of air-steam gasification of biomass with coal-bottom ash

Biomass gasification is an attractive option for producing high-quality syngas (H₂+CO) due to its environmental advantages and economic benefits. However, due to some technical problems such as tar formation, biomass gasification has not yet been able to achieve its purpose. The purpose of this work was to study the catalytic activity of coal-bottom ash for fuel gas production and tar elimination. Effect of gasification parameters including reaction temperature (700–900 °C), equivalence ratio, EQR (0.15–0.3) and steam-to-biomass ratio, SBR (0.34–1.02) and catalyst loading (5.0–13 wt %) on gas distribution, lower heating value (LHV) of gas steam, tar content, gas yield and H₂/CO ratio was studied. The tar content remarkably decreased from 3.81 g/Nm³ to 0.97 g/Nm³ by increasing char-bottom ash from 5.0 wt% to 13.0 wt%. H₂/CO significantly increased from 1.12 to 1.54 as the char-bottom ash content in the fuel increased from 5.0 wt% to 13.0 wt%.     

Co-gasification between coal/sawdust and coal/wood pellet: A parametric study using response surface methodology

This study had compared raw biomass and pre-treated biomass co-gasified with coal with the aim of investigating the reliability of pre-treated biomass for enhancing gasification performance. Sawdust (SD) and wood pellet (palletisation form of sawdust - WP) and blends of these two feedstocks with sub-bituminous coal (CL), were gasified in an air atmosphere using an external heated fixed-bed downdraft gasifier system. Response surface methodology (RSM) incorporating the central composite design (CCD) was applied to assist the comparison of all operating variables. The three independent variables were investigated within a specific range of coal blending ratios from 25% to 75%, gasification temperature from 650 °C to 850 °C and equivalence ratio from 0.20 to 0.30 against the dependent variables, namely the H₂/CO ratio and higher heating value of the syngas (HHVsyngas). The results revealed the H₂/CO ratio and a higher heating value of the syngas of more than 1.585 and 6.072 MJ/Nm³, respectively. Findings also showed that the H₂/CO ratio in the syngas from CL/WP possessed a higher value than the CL/SD. In contrast, CL/SD possessed a higher heating value for syngas with about 1% difference compared to the CL/WP. Therefore, co-gasified coal with wood pellets could potentially be a substitute for sawdust.     

Hydrogen-rich gas production from biomass air and oxygen/steam gasification in a downdraft gasifier

Biomass gasification is an important method to obtain renewable hydrogen. However, this technology still stagnates in a laboratory scale because of its high-energy consumption. In order to get maximum hydrogen yield and decrease energy consumption, this study applies a self-heated downdraft gasifier as the reactor and uses char as the catalyst to study the characteristics of hydrogen production from biomass gasification. Air and oxygen/steam are utilized as the gasifying agents. The experimental results indicate that compared to biomass air gasification, biomass oxygen/steam gasification improves hydrogen yield depending on the volume of downdraft gasifier, and also nearly doubles the heating value of fuel gas. The maximum lower heating value of fuel gas reaches 11.11 MJ/N m³ for biomass oxygen/steam gasification. Over the ranges of operating conditions examined, the maximum hydrogen yield reaches 45.16 g H₂/kg biomass. For biomass oxygen/steam gasification, the content of H₂ and CO reaches 63.27–72.56%, while the content of H₂ and CO gets to 52.19–63.31% for biomass air gasification. The ratio of H₂/CO for biomass oxygen/steam gasification reaches 0.70–0.90, which is lower than that of biomass air gasification, 1.06–1.27. The experimental and comparison results prove that biomass oxygen/steam gasification in a downdraft gasifier is an effective, relatively low energy consumption technology for hydrogen-rich gas production.     

Co–gasification of coal/biomass blends in 50 kWe circulating fluidized bed gasifier

This paper reports gasification of coal/biomass blends in a pilot scale (50 kWe) air-blown circulating fluidized bed gasifier. Yardsticks for gasification performance are net yield, LHV and composition and tar content of producer gas, cold gas efficiency (CGE) and carbon conversion efficiency (CCE). Net LHV decreased with increasing equivalence ratio (ER) whereas CCE and CGE increased. Max gas yield (1.91 Nm³/kg) and least tar yield (5.61 g/kg of dry fuel) was obtained for coal biomass composition of 60:40 wt% at 800 °C. Catalytic effect of alkali and alkaline earth metals in biomass enhanced char and tar conversion for coal/biomass blend of 60:40 wt% at ER = 0.29, with CGE and CCE of 44% and 84%, respectively. Gasification of 60:40 wt% coal/biomass blend with dolomite (10 wt%, in-bed) gave higher gas yield (2.11 Nm³/kg) and H₂ content (12.63 vol%) of producer gas with reduced tar content (4.3 g/kg dry fuel).     

Gasification of rice straw in an updraft gasifier using water purification sludge containing Fe/Mn as a catalyst

This study investigated the feasibility of gasification of rice straw using an Fe/Mn sludge as a catalyst. The Fe/Mn sludge contained iron and manganese compounds produced from a water purification plant. The gasification temperature and equivalent ratio (ER) was set at 900 °C and 0.30, respectively, with an amended catalyst ratio of 0%–15%. Experimental results indicated that the combustible gas production was increased from 0.61 m³/kg to 0.72 m³/kg with the Fe/Mn sludge addition. The lower heating value (LHV) of combustible gas and energy density (ED) were also increased with an increase in Fe/Mn sludge addition. The LHV and ED increased from 14.76 MJ/Nm³ to 15.82 MJ/Nm³ and from 1.37 MJ/MJ to 1.47 MJ/MJ, respectively. In conclusion, the catalytic gasification of rice straw was more efficient on an energy yield basis with the Fe/Mn sludge addition. The Fe/Mn sludge used in this research has been developed as a potential catalyst for the application of rice straw gasification.     

Integrated catalytic adsorption (ICA) steam gasification system for enhanced hydrogen production using palm kernel shell

This paper investigates the integrated catalytic adsorption (ICA) steam gasification of palm kernel shell for hydrogen rich gas production using pilot scale fluidized bed gasifier under atmospheric condition. The effect of temperature (600–750 °C) and steam to biomass ratio (1.5–2.5 wt/wt) on hydrogen (H₂) yield, product gas composition, gas yield, char yield, gasification and carbon conversion efficiency, and lower heating values are studied. The results show that H₂ hydrogen composition of 82.11 vol% is achieved at temperature of 675 °C, and negligible carbon dioxide (CO₂) composition is observed at 600 °C and 675 °C at a constant steam to biomass ratio of 2.0 wt/wt. In addition, maximum H₂ yield of 150 g/kg biomass is observed at 750 °C and at steam to biomass ratio of 2.0 wt/wt. A good heating value of product gas which is 14.37 MJ/Nm³ is obtained at 600 °C and steam to biomass ratio of 2.0 wt/wt. Temperature and steam to biomass ratio both enhanced H₂ yield but temperature is the most influential factor. Utilization of adsorbent and catalyst produced higher H₂ composition, yield and gas heating values as demonstrated by biomass catalytic steam gasification and steam gasification with in situ CO₂ adsorbent.