Pilot-scale Fluidized Bed Gasifier Research Articles

Catalytic steam gasification of soy hull pellets in a fluidized bed gasifier

The catalytic effects of inherent alkali-based metal catalysts present in biomass residues on biomass pellets were explored in this work. Gasification experiments were carried out in a pilot scale fluidized bed gasifier in the presence of alkali metal catalysts. By using a response surface methodology experimental design technique, soy hull biomass pellets were subjected to steam gasification within a temperature range of 750–950 °C. Additionally, the effects of steam-to-biomass (S/B) ratio and the catalyst loading on the gas and tar yields, and gaseous compositions were investigated. It was found that lower temperature resulted in the formation of more tar residue since the temperature was insufficient to crack the tar formed. Lower S/B ratio led to increased tar yield. Addition of catalyst significantly reduced the tar residue produced during the gasification experiments. An increase in the catalyst loading led to a steady decrease in the tar yield with up to 52% reduction at 950 °C. Further increasing catalyst loading beyond 5% had no significant effect on tar reduction. Gas yield increased slightly with catalytic gasification of the biomass pellets compared to the non-catalyzed reactions earlier studied. The reaction mechanism of the catalyzed reactions and effect on tar decomposition were discussed. Catalytic effects on tar composition were also investigated. The results from these experiments provide further insight into considering co-pelletization of catalysts during production of pellets for better gasification performance in terms of increased yields of the major gaseous components.

Sewage sludge and digestate gasification in an atmospheric fluidized bed gasifier

AbstractThe gasification of sewage sludge (SS) and digestate was investigated in a pilot-scale fluidized bed gasifier with an output of 100 kWt. The treatment of these by-products is an ongoing challenge for sustainable development. SS and digestate are most commonly used as fertilizers. However, regulations restrict their use, mainly because of the content of heavy metals, pathogens and bacteria. Gasification of these by-products instead of application to agricultural land seems to be more efficient, as the syngas can subsequently be used for combined heat and power (CHP) generation. A series of measurements were carried out to get a better understanding of the gasification process of these fuels and to study the effects of gasifying agent on the syngas composition, particulate matter (PM) and tar. The produced syngas and tar were analyzed using a gas chromatograph with mass spectrometry (GC–MS). The results showed that no ash slagging was observed and therefore it is feasible to operate digestate and SS gasification at 750°C. The lower heating value (LHV) of the syngas from digestate and SS with air as the gasifying agent is comparable, 4.06 MJ·Nm−3 for digestate and 4.11 MJ·Nm−3 for SS. The addition of steam had a positive effect on the amount of tar and the tar dew point, which was below 150°C. Tar reduction in digestate was 5037.3 mg·Nm−3 to 3566.3 mg·Nm−3 and in SS 7447.7 mg·Nm−3 to 3390.3 mg·Nm−3. Furthermore, the concentrations of the individual tar compounds were determined and subsequently divided into tar classes.

Parametric and hydrodynamics studies on gasification performance of biomass pellets in a pilot-scale fluidized bed gasifier

Parametric and hydrodynamics studies on gasification performance of biomass pellets in a pilot-scale fluidized bed gasifier

Steam - oxygen gasification of refuse derived fuel in fluidized beds: Modelling and pilot plant testing

A one-dimensional kinetic model for steam‑oxygen gasification of refuse derived fuel in a bubbling fluidized bed reactor has been developed. The model incorporates the reaction network of steam‑oxygen gasification within the fluid dynamics of a fluidized bed to predict waste and tars conversion, gas composition and overall gasification performance. The model was validated by comparing outlet products composition and temperature profile with experimental data from a pilot-scale fluidized bed gasifier, operated at different conditions. The model showed accurate predictive capability and ease of computation. The effects of the operating conditions on gas yield and process efficiency were evaluated and the most appropriate fuel feeding height, equivalent ratio and the relative amount of steam to inject were identified.

Enhanced hydrogen production in co-gasification of sewage sludge and industrial wastewater sludge by a pilot-scale fluidized bed gasifier

This research provides a perspective on sludge-to-energy using sewage sludge (SS) and industrial wastewater sludge (IS) co-gasification in a pilot-scale fluidized bed gasifier with temperature controlled at (600–800 °C) using IS addition ratio (0%–60%), and steam-to-biomass ratio (S/B) (0–1.0). The experimental results show that the increase in thermal reaction activity occurred in concordance with the increase in the IS addition. The explanation for such phenomena is that relatively high catalytic Fe/Mn content in industrial wastewater sludge could lower the activation energy. Hydrogen production was increased from 9.1% to 11.94% with an increase in industrial wastewater sludge ratios from 0% to 60%. The produced gas heating value ranged from 4.84 MJ/Nm3 to 5.11 MJ/Nm3, which was coupled with the cold gas efficiency (CGE) ranging from 33.91% to 36.15%. Enhanced hydrogen production in sewage sludge and industrial wastewater sludge co-gasification is investigated in this study.

Experimental Bench-Scale Study of Residual Biomass Syngas Desulfurization Using ZnO-Based Adsorbents.

Dry-bed adsorptive desulfurization of biomass-based syngas with a low- to medium sulfur content using ZnO was studied as an alternative to conventional wet-scrubbing processes for a small- to medium-scale biomass-to-liquid process concept. Following laboratory-scale long-term H2S breakthrough experiments in a previous study, desulfurization tests were scaled-up to bench-scale with actual bio-syngas to verify the lab-scale results under more realistic process conditions. A desulfurization unit was constructed and connected to a steam-blown atmospheric pilot-scale fluidized bed gasifier. Two successful 70+ h test campaigns were conducted with H2S removal below the breakthrough limit using full-sized ZnO adsorbent particles. Scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy elemental analysis, and Brunauer–Emmett–Teller (BET) surface area characterization of the fresh and spent adsorbent pellets were performed. SEM micrographs displayed the outward enlarging particle size in the sulfided layer. Characterization showed significant core–shell sulfidation behavior with a few hundred micron-thick sulfided layer leaving the majority of ZnO unutilized. Adsorbents lost most of their porosity in use, which was evident from BET surface area results. Simultaneous COS removal was found possible by the hydrolysis reaction to H2S. Furthermore, evidence of minor chlorine adsorption was found, thus highlighting the need for a dedicated HCl removal step upstream of desulfurization.

Co-gasification of high ash Indian coal-biomass blends in a pilot-scale fluidized bed gasifier

Conventional coal-based technologies are experiencing several disadvantages due to its high ash content as well as a significant amount of greenhouse gas emission. Focus is shifting towards the utilization of renewable resources like biomass. The efficient use of coal and biomass in a clean manner has been the driving force in developing gasification technologies. In the present investigation, an effort has been made to study the gasification performance of selected coal with two types of biomass, namely rice husk and sawdust in different proportions in a pilot-scale bubbling fluidized bed gasifier. Gasification was conducted with a mixture of air and steam at a temperature between 900–950 °C and atmospheric pressure. Mainly, three blends were prepared by adding 10, 20, and 40% of biomass with the selected coal. It was found that up to 40% of biomass loading, gasifier is operated in a trouble-free manner without the formation of tar or any agglomerate by maintaining proper fluidization with smooth and controlled variation in the process parameters like temperature, airflow, and steam flow rate. Due to the synergistic influence between coal and biomass, overall carbon conversion, gas yield, and gas heat value were found to increase with increasing biomass loading.

Study on the gasification of pine sawdust with dolomite catalyst in a pilot-scale fluidized bed gasifier

ABSTRACTAn experimental study on air-blown gasification of pine sawdust was conducted in a pilot-scale bubbling fluidized bed gasifier. Pine sawdust was fed into lower-center of the gasifier continuously with 60 kg/h and air as the gasifying agent was introduced from the bottom into a distributor. A mixture of inert silica sand and calcined dolomite with different ratios was used as the bed material in order to maintain stable fluidization and to realize the catalytic cracking of in-situ tar. The whole test run was performed as a continuous operation without any interruptions or operational problems.

Energy recovery from plastic and biomass waste by means of fluidized bed gasification: A life cycle inventory model

The study provides for the first time a life cycle inventory model for the fluidized bed gasification of wastes, based on a large amount of high-quality data. All of them have been obtained from a pilot scale fluidized bed gasifier, fed with ten types of waste and biomass, under a wide range of operating conditions. The model refers to commercial scale gasifiers having a “thermal configuration”, where the generated syngas is immediately burned downstream of the reactor. Key relationships between process- and waste-specific parameters have been defined. The model quantifies the main inputs and outputs of the gasification process (emissions, energy recovery, ash disposal, resource consumptions), providing high-quality data that could contribute to improve life cycle assessment modelling of waste gasification. Finally, some case studies have been implemented in the EASETECH software to illustrate the model applicability, evaluate the role of main parameters, and compare the environmental performances of gasification power units with that of the European electricity mix. The performances appear highly affected by metal contents in the waste-derived fuels, while the model results to a limited extent are sensitive to the equivalence ratio and the net electrical efficiency of the energy conversion.

Improving the properties of producer gas using high temperature gasification of rice husk in a pilot scale fluidized bed gasifier (FBG)

Abstract Biomass gasification is a well-studied thermo-chemical conversion route for the generating producer gas, a renewable energy carrier, for thermal and power applications as well as for bio-fuel production. High energy efficiency and clean gaseous fuel with low tar and suspended particulate matters (SPM) contents are some of the major challenges with biomass gasification. Herein, we report non-catalytic high temperature (720–855 °C) gasification of rice husk using fluidized bed gasifier (FBG). Producer gas mainly comprising of CO and H2 exhibited good higher heating value (HHV) and lower heating value (LHV) of 3.6 and 3.2 MJ/Nm3 respectively. Our experimental observations revealed that 790 °C is the optimum temperature for rice husk gasification with high carbon conversion efficiency (91.6%), thermal efficiency (75%) and high gas yield 2.7 m3/kg. High temperature gasification also resulted into reduced tar + SPM content (0.33 g/Nm3). Rice husk derived producer gas with good heating value and low tar + SPM content can be used as replacement of conventional fossil fuels for thermal applications in many processing industries.

Fluid dynamics model on fluidized bed gasifier using agro-industrial biomass as fuel

The present study shows the experimental and numerical results of thermal gasification of biomass, on the energy potential of agro-industrial waste from the Portalegre region. Gasification tests were performed in a pilot-scale fluidized bed gasifier, in order to study the behavior of peach stones and miscanthus to investigate the effect of gasification temperatures at 750°C, 800°C and 850°C at a constant biomass flow rate of 45kg/h. In order to optimize the operating conditions of the biomass gasification process, a numerical model is developed namely COMMENT code. This model is a computer model of two dimensions describing the biomass gasification processes in a fluidized bed gasifier using peach stone and miscanthus as fuel. Both phases, solid and gaseous, were described using an Eulerian-Eulerian approach exchanging mass, energy, and momentum. The numerical model results are then compared with experimental results. The produced results show the impact of the increased temperature in the calorific value of the syngas. The tests carried out at 750°C shown an increase in CO2 and N2 and a decrease of CO in the range of 5% comparing to the tests carried out at 850°C. In addition, increased temperature favors a decrease in tar production in thermal gasification process. Numerical results shows to be in good agreement with the experimental data.

Multi-stage optimization in a pilot scale gasification plant

A 2-D multiphase CFD model was coupled with advanced statistical methods to find the best operating conditions to maximize a set of selected responses that characterize the normal operation of a pilot scale fluidized bed gasifier running Municipal Solid Waste. After using CFD simulations to compute 7 responses at 27 different operating conditions, a single response optimization based on the response surface method was carried out to identify the best operating conditions. Then, the desirability concept was advantageously used to proceed with a multiple optimization where all the responses were targeted under normal industrial conditions. The operating conditions that set the optimized responses not always coincide with the most stable process. To target both optimized and robust conditions a multiple optimization combining the response surface and the propagation of error methods were employed. Finally, the tolerance intervals were reduced to increase the process Cpk and six sigma standards about 20%. New measures to further increase the process performance were identified and the transmitted variation to the response from input factors was computed.

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.

Enriched-air fluidized bed gasification using bench and pilot scale reactors of dairy manure with sand bedding based on response surface methods

Enriched-air gasification was performed in fluidized bed reactors using the processed dairy manure which was mixed with sand bedding. The effects of temperature, modified equivalence ratio (ERm), and oxygen concentration on the gas products were investigated based on the statistical models using a bench-scale reactor in order to obtain empirical correlations. Then, the empirical equations were applied to compare the produced gases from a pilot-scale fluidized bed gasifier. The empirical and actual H2 and CH4 compositions were within a 10% error, while the sum of produced CO and CO2 gases showed similar composition within 3% error. The most influential factors for the syngas heating value were temperature followed by the oxygen concentration and ER (equivalence ratio). The composition of H2 (2.1–11.5%) and CO (5.9–20.3%) rose with an increase in temperature and oxygen concentration. The variation of CO2 (16.8–31.6%) was mainly affected by the degree of oxygen concentration in the gasifying agent. The ranges of the LHV (lower heating value), carbon conversion efficiency and cold gas efficiency were discussed. An economic review showed favorable indications for on-site dairy manure gasification process for electric power based on the depreciable payback period and the power production costs.

Agglomeration behaviour of high ash Indian coals in fluidized bed gasification pilot plant

Although gasification of high ash Indian coals is gaining importance, the resultant uncertainties associated with agglomerate formation are still unresolved. To address this, a suitable pilot scale Fluidized Bed Gasifier was utilized in this study. Stabilized operating conditions in terms of coal feed rate, air feed rate, bed temperature, etc., already identified for maximum possible carbon conversion, were maintained in all experiments and the steam flow rate was only varied. Though the ash fusion temperature of the coals were above 1200 °C, agglomerate was formed during gasification at 950 °C with ‘steam to coal ratio’ less than 0.15 (kg/kg). On increasing this ratio above 0.2 local heat-concentration and agglomeration could be avoided with certainty. Chemical composition alone was not sufficient to explain the relative strength of ash-agglomerates. Compositional variation and state of iron within the matrix were assessed through SEM-EDX and electron paramagnetic resonance (EPR) study, respectively. The probing also required the ash-loading and iron-loading factors to be freshly defined in the context of gasification. Localized heat, large compositional variation, presence of iron in Fe2+ state, ash-loading/iron-loading factors influenced intensity of agglomerate formation. Finally, low temperature agglomerate formation was explained by SiO2–Al2O3–FeO phase diagram.

Analysis of trace contaminants in hot gas streams using time-weighted average solid-phase microextraction: Pilot-scale validation

A new method was developed for collecting, identifying and quantifying contaminants in hot process gas streams using time-weighted average (TWA) passive sampling with retracted solid-phase microextraction (SPME) and gas chromatography. The previous lab scale proof-of-concept with benzene was expanded to include the remaining major tar compounds of interest in syngas: toluene, styrene, indene, and naphthalene. The new method was tested on high T (⩾100°C) process gas from a pilot-scale fluidized bed gasifier feeding switchgrass and compared side-by-side with conventional impingers-based method. Fourteen additional compounds were identified, representing 40–60% improvement over the conventional method’s detection capacity. Differences between the two methods were 1–20% and as much as 40–100% depending on the sampling location. Compared to the inconsistent conventional method, the SPME-TWA offered a simplified, solvent-free approach capable of drastically reducing sampling and sample preparation time and improving analytical reliability. The improved sensitivity of the new method enabled identification and quantification of VOCs beyond the capability of the conventional approaches, reaching concentrations in the ppb range (low mg/m3). RSDs associated with the TWA-SPME were <10%, with most lab-based trials yielding <2%. Calibrations were performed down to the lowest expected values of tar concentrations in ppb ranges (low mg/Nm3, with successful measurement of tar concentrations at times >4000ppm (up to 10g/Nm3). The new method can be a valid alternative to the conventional method for light tar quantification under certain conditions. The opportunity also exists to exploit TWA-SPME for process gas streams analysis e.g., pyrolysis vapors and combustion exhaust.

Co-gasification of petroleum coke with lignite coal using fluidized bed gasifier

Co-gasification of waste material with coal is a potentially effective method to utilize industrial wastes for power/heat and/or syngas generation and to solve their disposal problems. Canada with its large-scale oil sand industry is a major producer of unconventional oil. Petroleum coke is one of the main waste streams from oil sand refining processes. This study is an investigation of the effects of feed ratio, equivalence ratio and average particle size on the syngas production by means of co-gasification of petroleum coke with lignite coal in a stainless steel pilot scale fluidized bed gasifier with an inside diameter of 7cm at 800°C. Central composite design methodology was used for designing the experiments. Runs for 20wt.% of petroleum coke in the feed at different equivalence ratios and particle sizes showed positive synergetic effects for syngas yield (up to 61.0mol/kg of feed), H2+CO yield (up to 33.2mol/kg of feed), carbon efficiency (up to 70.2%), and lower heating value (up to 9020kJ/m3). Increasing the equivalence ratio improved gasification performance, but gas heating value and H2/CO decreased. The effect of particle size (70–500μm) was insignificant. The use of petroleum coke (20wt.% in the feed) has resulted in an improvement in the lignite coal gasification performance and can be considered as an effective utilization method for petroleum coke.

Analysis of Syngas Quality from Portuguese Biomasses: An Experimental and Numerical Study

A comprehensive two-dimensional multiphase model was developed to describe the gasification of three large available Portuguese biomasses in a pilot scale fluidized bed gasifier within the computational fluid dynamics Fluent framework. An Eulerian–Eulerian approach was implemented to handle both the gas and the dispersed phases. The kinetic theory of granular flows was used to evaluate the constitutive properties of the dispersed phase, and the gas-phase behavior was simulated employing the k–ε turbulent model. Devolatilization phenomenon was also modeled. Results from the numerical model were later compared with experimental data also gathered for the three Portuguese biomasses. The simulated syngas compositions are in good agreement with the experimental results with maximum deviations of 20% (considering all simulations and biomasses). The effect of the gasification temperature and steam-to-biomass ratio on the syngas composition was evaluated as well as the cold gas efficiency, H2/CO ratio, CH4/H2 ratio, and carbon conversion. From this analysis, it was possible to define which biomass has the greater potential to be used concerning the selected application. Among the three biomasses, it was concluded that coffee husks and vine-pruning residues show better H2/CO ratios, while the higher CH4/H2 ratios are obtained by using the forest residues. The highest cold gas efficiencies were obtained by using the vine-pruning residues. These data are crucial to describe scenarios concerning the potential use of biomass as a source of energy in Portugal.

Gasification of Canola Meal and Factors Affecting Gasification Process

Non-catalytic gasification of canola meal for the production of syngas was studied in lab-scale fixed bed gasifier and pilot-scale fluidized bed gasifier. Various experiments were undertaken in order to study the effects of different gasification parameters on gas composition, H2/CO ratio, gas yield, syngas yield, lower heating value (LHV), and carbon efficiency (CE). Fixed-bed experiments were performed to study the effects of operating temperature in the range of 650–850 °C and equivalence ratio in the range of 0.2–0.4. Steam, carbon dioxide (CO2), and oxygen (O2) were used as gasifying agents. The experimental results show that steam gasification delivers a gaseous product with a high H2/CO ratio (2.7) and LHV (193.0 MJ/m3). Oxygen gasification attributed to maximum CE (65.5 %). CO2 gasification contributes to high gas yield (82.8 mol/kg biomass). During fluidized bed gasification study, it was found that using steam as gasifying agent leads to more H2 production as compared to that for O2 and CO2 gasifying agents. Thus, it leads to high H2/CO ratio, syngas yield, and LHV of product gas. Regarding CE for O2 gasification and gas yield for CO2, observations were similar to those for fixed bed system.

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.