Bench-scale Fluidized Bed Gasifier Research Articles

Quantitative analysis of mass and energy flow in rice straw gasification based on mass and carbon balance

There have been some pilot-scale trials of the fluidized bed and its derivatives for rice and wheat straw gasification in China. Before the industrial promotion, the quantitative data is imperative in preliminary engineering and optimization. A series of experiments were performed on a bench-scale fluidized bed gasifier to obtain data in process in different heat exchange situations. The uncertainty was evaluated and the balance of carbon and mass was performed to verify the quantitative data. Based on the experimental results, the mass and energy flows were established and illustrated in Sankey diagrams. The results show that, as temperature improves from 650 °C to 800 °C, the energy proportion of gas climbs from 27.2 to 64%. When the equivalence ratio decreases, although the calorific value of gas increases from 2.7 to 4.2 MJ/Nm3, the energy proportion of gas does not change much because the gas yield decreases. Finally, the heat exchange, temperature and ER were coupled by interpolation and illustrated in a contour map.

Steam gasification of lignite and solid recovered fuel (SRF) in a bench scale fluidized bed gasifier

The reduction of CO2 emissions and solid waste disposal are critical issues with high importance for the environmental protection. Gasification is a promising process for sustainable energy production, because it can produce a versatile gaseous fuel starting from a wide range of organic feedstocks, and with reduced greenhouse gas emissions compared to combustion. Lignite is an abundant carbonaceous resource in Europe and in this work, gasification tests were carried out with lignite and a lignite and Solid Recovered Fuel (SRF) mixture, to evaluate the quality of gas produced from co-gasification of waste materials, in view of the final uses of the gas. Experimental gasification tests were carried out in a bench scale fluidized bed gasifier at different operating temperatures; the results were evaluated in terms of gas composition, tar content and conversion rates. In addition, characterization analyses were carried out on materials before and after the tests, and pressure fluctuation signals were analysed in order to evaluate the fluidization quality of the bed inventory.

Steam Gasification of Lignite in a Bench-Scale Fluidized-Bed Gasifier Using Olivine as Bed Material

The gasification of lignite could be a promising sustainable alternative to combustion, because it causes reduced emissions and allows the production of syngas, which is a versatile gaseous fuel that can be used for cogeneration, Fischer-Tropsch synthesis, or the synthesis of other bio-fuels, such as methanol. For the safe and smooth exploitation of syngas, it is fundamental to have a high quality gas, with a high content of H2 and CO and minimum content of pollutants, such as particulate and tars. In this work, experimental tests on lignite gasification are carried out in a bench-scale fluidized-bed reactor with olivine as bed material, chosen for its catalytic properties that can enhance tar reduction. Some operating parameters were changed throughout the tests, in order to study their influence on the quality of the syngas produced, and pressure fluctuation signals were acquired to evaluate the fluidization quality and diagnose correlated sintering or the agglomeration of bed particles. The effect of temperature and small air injections in the freeboard were investigated and evaluated in terms of the conversion efficiencies, gas composition, and tar produced.

Syngas conditioning by ceramic filter candles filled with catalyst pellets and placed inside the freeboard of a fluidized bed steam gasifier

Gasification is a very advantageous conversion process to obtain a fuel gas from organic wastes, however it also generates by-products, such as particulate and tar. These should be removed from the syngas for its smooth utilization in power generation devices and/or biofuels production. In this work, biomass gasification tests were carried out in a bench-scale fluidized bed gasifier with a ceramic filter candle filled with commercial Ni-catalyst pellets integrated in its freeboard, for the abatement of particulate and tar. The activity of catalyst was studied at different operating conditions (temperature and catalyst bed layout) and the results were analysed in terms of residual tar content and composition of the product gas. The catalyst resulted very effective, particularly in tests at higher temperature and with the partially filled candle configuration. Tars were reduced to 250 mg/Nm3 in the best case. The Ni-catalyst did not show deactivation during tests lasting 4 h.

Poplar from phytoremediation as a renewable energy source: gasification properties and pollution analysis

Biomass gasification is a very efficient process to produce clean energy in the form of a fuel gas (syngas). Hazelnut shells and poplar have good energy production potential and they are abundant in nature. Hazelnut shells have the characteristics of a very good fuel and poplar is among the fastest growing trees; furthermore, poplar demonstrated the capability to absorb organic contaminants (i.e. heavy metals) from the soil in which they are cultivated. However, poplar is not usually used for biomass gasification and its potential is not fully assessed. Here, 3 types of biomass, hazelnut shells (HS), simple poplar (P) and poplar coming from a phytoremediation procedure (PHYP), were chosen as representative samples to be characterized and tested in a steam gasification process carried out on a bench scale fluidized bed gasifier. A comparison is reported on gasification results, such as gas composition, tar production and gas yield for the biomass feedstocks mentioned above. It was concluded that hazelnut shells and poplar (P and PHYP) could be easily gasified in a fluidized bed gasifier, thus producing a good quality gas with low polluting by-products. The PHYP sample showed lower tar content and higher gas yield. It is guessed that Ca and Mg, found in higher quantities in the PHYP sample, could have had a catalytic effect in tar reforming thus producing lower quantity of heavy hydrocarbons.

Gasification of potato shoots: An experimental and theoretical investigation

A thermodynamic equilibrium model was developed to predict the gasification process in a bench-scale fluidized bed gasifier. Potato shoot (leaves and stems) was used as the feedstock of the gasifier. The experiments were done in five different gasification zone temperatures (650, 700, 750, 800 and 850°C), with a feeding rate of 0.166 kg/hour, and two equivalence ratios (ER: 0.2 and 0.25). The produced gas was analyzed and the portion of each component was calculated from a thermodynamic equilibrium model. The data from the experiments were compared with those of the modeling in order to validate the model. For 650°C, the closest results of the model to experiment data were observed for CO2 at ER = 0.2, followed by CO at ER = 0.25 with errors of 7% and 21%, respectively. The least difference between the model data and the experimental data at 700°C was observed for N2 with the error of 26% and 22% for ER= 0.2 and 0.25, respectively. At 750°C, the predicted values conformed reasonably well to the experimental data for CO with error less than 7%. Regarding the least error, the most admissible results were seen at 800°C for N2 with ER= 0.25 with an error of 7%. In this case, the most acceptable results of the model were obtained for 850°C, in which the error in predicting the amount of CH4 at ER= 0.25 was 0. Owing to the applicability of potato shoot in the gasification process, it can play a great role in energy production.

Physicochemical properties and gasification reactivity of the ultrafine semi-char derived from a bench-scale fluidized bed gasifier

Zhundong coalfield is the largest intact coalfield worldwide and fluidized bed gasification has been considered as a promising way to achieve its clean and efficient utilization. The purpose of this study is to investigate the physicochemical properties and gasification reactivity of the ultrafine semi-char, derived from a bench-scale fluidized bed gasifier, using Zhundong coal as fuel. The results obtained are as follows. In comparison to the raw coal, the carbon and ash content of the semi-char increase after partial gasification, but the ash fusion temperatures of them show no significant difference. Particularly, 76.53% of the sodium in the feed coal has released to the gas phase after fluidized bed gasification. The chemical compositions of the semi-char are closely related to its particle size, attributable to the distinctly different natures of diverse elements. The semi-char exhibits a higher graphitization degree, higher BET surface area, and richer meso- and macropores, which results in superior gasification reactivity than the coal char. The chemical reactivity of the semi-char is significantly improved by an increased gasification temperature, which suggests the necessity of regasification of the semi-char at a higher temperature. Consequently, it will be considered feasible that these carbons in the semi-char from fluidized bed gasifiers are reclaimed and reused for the gasification process.

Quantifying uncertainty of a reacting multiphase flow in a bench-scale fluidized bed gasifier: A Bayesian approach

Adequate assessment of the uncertainties is becoming an integral part of the engineering design. This study is based on several efforts that are underway to investigate the uncertainty quantification (UQ) methods that are applicable to multiphase flows. Although particular emphasis has been given on identifying, characterizing and managing uncertainties in computational fluid dynamics (CFD) simulations, experimental data used in the validation of the CFD model is as critical. Hence, the goal of this paper is to demonstrate application of non-intrusive Bayesian uncertainty quantification methodology in multiphase (gas-solid) flows with experimental data as part of our research efforts to determine the most suited approach for UQ. For this purpose, a bench scale fluidized bed gasifier experiment from a prior study is used to demonstrate the applicability of Bayesian techniques on sparse data. Global sensitivity analysis performed as part of the UQ study shows that among the three operating factors, steam to oxygen ratio has the most influence on syngas composition in the gasifier. An analysis for forward propagation of uncertainties shows that an increase in steam to oxygen ratio leads to an increase in H2 mole fraction and a decrease in CO mole fraction. These findings are in agreement with the reference experimental study. Another contribution in addition to the UQ analysis is the optimization-based approach employed to identify next best set of additional experimental samples. Hence, the surrogate models constructed as part of the UQ analysis is employed to improve the information gain and make incremental recommendation, should the possibility to add more experiments arise. The insight gained from this study has been extensively used in the follow-up UQ study with the CFD modeling of the same gasifier configuration.

Nonintrusive Uncertainty Quantification of Computational Fluid Dynamics Simulations of a Bench-Scale Fluidized-Bed Gasifier

Uncertainty quantification (UQ) analysis is increasingly becoming one of the major requirements of simulation-based engineering to assess the confidence in the results and make better-informed decisions based on the insight derived from the simulations. In an earlier study, Bayesian UQ analysis was applied to existing bench-scale fluidized-bed gasifier experiment results. In the current study, a series of simulations were carried over with the open-source computational fluid dynamics software MFiX to reproduce the experimental conditions, where three operating factors, i.e., coal flow rate, coal particle diameter, and steam-to-oxygen ratio, were systematically varied to understand their effect on the syngas composition. Bayesian UQ analysis was this time performed on the numerical results for comparison purposes. This is part of ongoing research efforts to explore the applicability of advanced UQ methods and processes such as Bayesian methods for large-scale complex multiphase flow simulations. As part of Bayesian UQ analysis, a global sensitivity analysis was performed based on the simulation results, which shows that the predicted syngas composition is strongly affected not only by the steam-to-oxygen ratio (which was observed in experiments as well) but also by variation in the coal flow rate and particle diameter (which was not observed in experiments). The carbon monoxide mole fraction is underpredicted at lower steam-to-oxygen ratios and overpredicted at higher steam-to-oxygen ratios. The opposite trend is observed for the carbon dioxide mole fraction. These discrepancies are attributed to either excessive segregation of the phases that leads to the fuel-rich or -lean regions or alternatively the selection of reaction models, where different reaction models and kinetics can lead to different syngas compositions throughout the gasifier.

Development of a modified equilibrium model for biomass pilot-scale fluidized bed gasifier performance predictions

The objective of this work is to develop a thermodynamic model considering non-stoichiometric restrictions. The model validation was done from experimental works using a bench-scale fluidized bed gasifier with wood chips, dairy manure, and sorghum. The model was used for a further parametric study to predict the performance of a pilot-scale fluidized biomass gasifier. The Gibbs free energy minimization was applied to the modified equilibrium model considering a heat loss to the surroundings, carbon efficiency, and two non-equilibrium factors based on empirical correlations of ER and gasification temperature. The model was in a good agreement with RMS <4 for the produced gas. The parametric study ranges were 0.01 < ER < 0.99 and 500 °C < T < 900 °C to predict syngas concentrations and its LHV (lower heating value) for the optimization. Higher aromatics in tar were contained in WC gasification compared to manure gasification. A wood gasification tar simulation was produced to predict the amount of tars at specific conditions. The operating conditions for the highest quality syngas were reconciled experimentally with three biomass wastes using a fluidized bed gasifier. The thermodynamic model was used to predict the gasification performance at conditions beyond the actual operation.

Air gasification of rice husk in bubbling fluidized bed reactor with bed heating by conventional charcoal

An experimental study of air gasification of rice husk was conducted in a bench-scale fluidized bed gasifier (FBG) having 210mm diameter and 1600mm height. Heating of sand bed material was performed using conventional charcoal fuel. Different operating conditions like bed temperature, feeding rate and equivalence ratio (ER) varied in the range of 750–850°C, 25–31.3kg/h, and 0.3–0.38, respectively. Flow rate of air was kept constant (37m3/h) during FBG experiments. The carbon conversion efficiencies (CCE), cold gas efficiency, and thermal efficiency were evaluated, where maximum CCE was found as 91%. By increasing ER, the carbon conversion efficiency was decreased. Drastic reduction in electric consumption for initial heating of gasifier bed with charcoal compared to ceramic heater was ∼45%. Hence rice husk is found as a potential candidate to use directly (without any processing) in FBG as an alternative renewable energy source from agricultural field.

Effects of Temperature and Equivalence Ratio on Pine Syngas Primary Gases and Contaminants in a Bench-Scale Fluidized Bed Gasifier

Effects of equivalence ratio (ER = 0.15, 0.25, and 0.35 at 934 °C) and temperature (790, 934, and 1078 °C at 0.25 ER) were investigated in air gasification of pine for primary gases and contaminants. CO and H2 increased while CO2 and CH4 decreased from 790 to 1078 °C. Opposite trends were observed for ER. Based on overall contaminant weight, tar was highest at all temperatures (7.81, 8.24, and 8.93 g/kg dry biomass) and ERs (13.08, 8.24, and 2.51 g/kg dry biomass). NH3 varied from 1.63 to 1.00 g/kg dry biomass between 790 and 1078 °C and from 1.76 to 1.47 g/kg dry biomass between 0.15 and 0.35 ER. H2S ranged between 0.13 and 0.17 g/kg dry biomass from 790 to 1078 °C and between 0.154 and 0.18 g/kg dry biomass from 0.15 to 0.35 ER. Finally, HCl yields ranged from 13.63 to 0 mg/kg dry biomass and from 11.51 to 0.28 mg/kg dry biomass over the range of temperature and ER, respectively.

Hydrogen-Rich Gas Production from Palm Kernel Shell by Applying Air Gasification in Fluidized Bed Reactor

An experimental study of gasification of palm kernel shell residues from the palm oil industry, as a potential hydrogen feedstock, is investigated. The gasification is conducted in a bench-scale fluidized bed gasifier with 55 mm diameter and 850 mm height. The operating conditions were studied in the following ranges: reaction temperature in gasification zone (750–1100 °C), feeding rate (0.20–1.21 kg/h), feedstock particle size (0.1–5 mm), and equivalence ratio (ER) (0.23–0.27). The increasing temperature and equivalence ratio was found to significantly influence the gas yield (up to 90 wt % conversion on the raw biomass) at 1000 °C and hence hydrogen composition (40 vol %). The feedstock particle size and feeding rate only showed minor influence. In conclusion, palm kernel shell is a potential candidate for hydrogen production.

Study on the fate of metal elements from biomass in a bench-scale fluidized bed gasifier

Two types of biomass fuel were gasified in a steam atmosphere using a bench-scale fluidized bed reactor. Filter char, bed material and the product gas stream were sampled and analyzed for a total of 21 elements including Al, Ca, Fe, K, Mg, Na and Si defined as major elements (ME), and Ba, Cd, Co, Cr, Cu, Mn, Mo, Ni, P, Sr, Pb, Ti, V, and Zn defined as trace elements (TE). The effects of the sampling system and gasification system on the measurement were determined. Mass balances for ME and TE are reported for individual elements and overall. It was found that most ash particles or metal elements can be captured by a silicon carbide candle filter that removes small particles from the gas phase, but some of volatile elements pass through the filter and are present in the gas stream.

Air Gasification of Agricultural Waste in a Fluidized Bed Gasifier: Hydrogen Production Performance

Recently, hydrogen production from biomass has become an attractive technology for power generation. The main objective pursued in this work is to investigate the hydrogen production potential from agricultural wastes (coconut coir and palm kernel shell) by applying the air gasification technique. An experimental study was conducted using a bench-scale fluidized bed gasifier with 60 mm diameter and 425 mm height. During the experiments, the fuel properties and the effects of operating parameters such as gasification temperatures (700 to 900°C), fluidization ratio (2 to 3.33 m/s), static bed height (10 to 30 mm) and equivalence ratio (0.16 to 0.46) were studied. It was concluded that substantial amounts of hydrogen gas (up to 67 mol%) could be produced utilizing agricultural residues such as coconut and palm kernel shell by applying this fluidization technique. For both samples, the rise of temperature till 900°C favored further hydrocarbon reactions and allowed an increase of almost 67 mol% in the release of hydrogen. However, other parameters such as fluidizing velocity and feed load showed only minor effects on hydrogen yield. In conclusion, agricultural waste can be assumed as an alternative renewable energy source to the fossil fuels, and the environmental pollution originating from the disposal of agricultural residues can be partially reduced.

Experimental Study Examining the Evolution of Nitrogen Compounds during the Gasification of Dried Sewage Sludge

Gasification of dried sewage sludge, which contains a high percentage of nitrogen, was experimentally studied to determine the effects of some operational parameters, such as freeboard temperature and equivalence ratio, on the partitioning of the fuel nitrogen among nitrogenous species. Experiments were performed using a bench-scale fluidized-bed gasifier and according to a well-specified procedure implemented to recover and quantify the nitrogen compounds. A mixture of argon and oxygen in similar proportions to air was used as a gasification agent in order to correctly quantify the N2 produced in the gasification process in an experimental way. Important findings of this research include the following: applying the analytical procedure developed in this work, a reasonably good inventory of nitrogen in the gasification products was obtained (mass balance closures near to 100%); most of the nitrogen goes to form gaseous products, N2 being the main gaseous nitrogen-containing product obtained; concentrations of N2, NH3, and N-tar in the producer gas strongly depend on the freeboard temperature, an increase of which causes an important decrease of both NH3 and N-tar contents and a substantial increase of the N2 amount.

Steam–air fluidized bed gasification of distillers grains: Effects of steam to biomass ratio, equivalence ratio and gasification temperature

In this study, thermochemical biomass gasification was performed on a bench-scale fluidized-bed gasifier with steam and air as fluidizing and oxidizing agents. Distillers grains, a non-fermentable byproduct of ethanol production, were used as the biomass feedstock for the gasification. The goal was to investigate the effects of furnace temperature, steam to biomass ratio and equivalence ratio on gas composition, carbon conversion efficiency and energy conversion efficiency of the product gas. The experiments were conducted using a 3 × 3 × 3 full factorial design with temperatures of 650, 750 and 850 °C, steam to biomass ratios of 0, 7.30 and 14.29 and equivalence ratios of 0.07, 0.15 and 0.29. Gasification temperature was found to be the most influential factor. Increasing the temperature resulted in increases in hydrogen and methane contents, carbon conversion and energy efficiencies. Increasing equivalence ratio decreased the hydrogen content but increased carbon conversion and energy efficiencies. The steam to biomass ratio was optimal in the intermediate levels for maximal carbon conversion and energy efficiencies.

An experimental investigation of hydrogen production from biomass gasification

An experimental study of hydrogen production from biomass was conducted using a benchscale fluidized bed gasifier. Parametric experiments were performed to determine the effects of reactor temperature, equivalence ratio, and steam to biomass ratio. Experimental measurements of gas composition and yield were used to calculate the hydrogen yield potential, the capacity of the gas stream for hydrogen production by shifting carbon monoxide and steam reforming higher hydrocarbons. Over the ranges of experimental conditions examined, hydrogen yield potential proved to be most sensitive to equivalence ratio, varying from 62 g H 2 kg −1 of dry, ash-free biomass at an equivalence ratio of 0.37, to 128 g H 2 kg −1 of dry, ash-free biomass at an equivalence ratio of 0.0. Of the conditions tested, the highest hydrogen yield potential, 128 g H 2 kg −1 of dry, ash-free biomass, was achieved at a reactor temperature of 850 °C, equivalence ratio of 0.0, and a steam to biomass ratio of 1.7. This is 78% of the theoretical maximum yield of 165 g H 2 kg −1 of dry, ash-free biomass for this feedstock.

Fluidized-bed steam gasification of rice hull

Steam gasification of grain by-products can be a significant biomass conversion technology because of the need to utilize agricultural waste for non-food applications including energy resources. The most obvious beneficiary will be the developing countries whose economies are often tied to agricultural produce and are lacking in conventional fuels. One agricultural by-product that shows promise is the rice hull; it is found in abundance in the rice mills of producer countries and is considered as a waste material. Although gasification of rice hull has been proposed as a potential waste disposal and energy recovery method, little has been done to fully realize this proposition. In the present work, data were obtained for steam gasification of rice hull in a bench-scale fluidized-bed gasifier, a technology which has proven to be feasible for other grain by-products. The produced gas, which is rich in hydrogen, has been found to have a heating value ranging between 12.1 and 11.1 MJ m −3 at the respective reactor temperatures of 700 and 800°C; energy recovery varies between 35 and 59%.