Bubbling Fluidized Bed Gasifier Research Articles

Influence of distributor plate design on mixing characteristics of rice husk biomass in a bubbling fluidized bed gasifier: An experimental and CFD study

This study investigates the mixing characteristics of rice husk biomass in a bubbling fluidized bed gasifier (BFBG) using different distributor plates: perforated, 45° slotted, and hybrid plates. The study explores the fluidization characteristics of a biomass/sand mixture using three distributor plates, observing the maximum difference in initial minimum fluidization velocity (Umf,i) and final minimum fluidization velocity (Umf,f) for perforated plate, indicating axial mixing and segregation, while the 45° slotted plate represents uniform bed expansion and fluidization, and the hybrid plate exhibits an intermediate behavior. Axial and lateral biomass distribution is also studied, and it is found that with the 45° slotted plate the highest axial distribution of rice husk is observed at the lower portion due to lateral and swirling flow whereas perforated plate causes the highest deviation at the lower portion but approaches ideal mixing at the mid and upper sections due to axial dominant flow. The hybrid plate exhibits a blend of axial and lateral flows, resulting in intermediate axial distribution at lower and upper section of gasifier. Radially, the perforated plate has the highest concentration of biomass at maximum height whereas the 45° slotted plate has concentration near the walls, and the hybrid plate has optimal mixing throughout. The hybrid plate also achieves the highest mixing index at all air velocities. Overall, the study provides insights into biomass mixing in BFBGs and highlights the superior performance of the hybrid distributor plate.The CFD study also carried out to complement the experimental results in terms of pressure drop and mixing behavior by employing different distributor plats. Multiphase two fluid model (TFM) with kinetic theory of granular flow has been employed for CFD simulations with the engagement of k-epsilon turbulence model. The simulation results are in good agreement with experimental results in terms of bed pressure drop quantitatively and mixing characteristics of rice husk biomass qualitatively.

Synergistic effect of coal and biomass gasification and organo-inorganic elemental impact on gasification performance and product gas

The current study demonstrates the synergistic effect of co-gasification of high-ash Indian coal and biomass (press mud and sawdust) blends in varying proportions in a pilot-scale bubbling fluidized bed gasifier (BFBG) with a capacity of 20 kg/h. The effect of blending on product gas yield, composition and heating value, carbon conversion, and cold gas efficiency was critically analyzed. Mineralogical transformations and catalytic effects were investigated during co-gasification, wherein minerals in ash residue, such as hematite, sylvite, chlorite, K-feldspar, CaO, and MgO, showed a catalytic role in co-gasification, increasing the product gas compositions, and reverse the trend for kaolinite and phosphate minerals. Blending coal with biomass enhances the porosity and reactivity of blends, surface morphology, gasification performance, and product gas yield. So, high ash coal and biomass are suitable for gasification. The high ash coal gasification comprises the volumetric product gas composition (%) of CO (9.79), CO2 (8.75), H2(13.6), and CH4(1.12) with the maximum blends (40%) of biomass, the volumetric composition (%) is enhanced comprising CO (17.71), CO2 (14.8), H2(19.9) and CH4(2.05) for press mud blend, and CO(15.84), CO2(14.2), H2(18.3) and CH4(2.29) for sawdust blend, respectively, and HHV increases from 3.42 (MJ/Nm3) to 5.59(MJ/Nm3).

Performance evaluation of an innovative 100 kWth dual bubbling fluidized bed gasifier through two years of experimental tests: Results of the BLAZE project

In this work, the results of two years of experimental tests on an innovative dual bubbling fluidized bed gasifier are reported. These are related to the activities of the BLAZE project (Horizon 2020) for the integration of steam biomass gasification and solid oxide fuel cell. Several tests were carried out on the pilot-scale reactor at various operating conditions, and in this work the results are reported in terms of dry gas composition and yield, organic and inorganic contaminants (tar, particulate matter, H2S). The compact design of the gasifier (a single reactor with two concentric chambers and in-situ hot gas cleaning and conditioning) reduces the heat losses and produces close to nitrogen-free syngas. Preliminary tests using a filter candle filled with conventional catalyst, installed in the freeboard of the gasifier, show that the tar content dropped to about 2 g/Nm3, and the H2 concentration increased up to 41%vol,dry.

Experimental evaluation of wood and grass pellets in a bubbling fluidized bed gasifier

Biomass gasification is an attractive technology capable of producing a versatile product gas that can be used for heat and power production as well as used as a feedstock for biofuels and higher-value chemicals synthesis. A fluidized bed gasifier is one of the better choices for an industrial scale operation. However, the specification and performance of different feedstocks must be characterized to use in a specific application with acceptable efficiency. In this article, the authors took two different feedstocks (i.e., wood and grass pellets) for the experimental characterization in a 20-kW pilot-scale bubbling fluidized bed gasifier. Equivalence ratio was varied between 0.1 to 0.2 for the grass pellets and 0.214 to 0.371 for the wood pellets. Frequent agglomerations were observed during the experiment with the grass pellets at a temperature of 800 °C and above. The carbon conversion for the gasification of grass pellets was observed to be lower compared to the gasification of wood pellets. Gasification of wood pellets gave a carbon conversion of around 60% at a temperature of around 850 °C.

Exergy Analysis of Self-Bed Feedstock in Rice Husk Bubbling Fluidized Bed Gasifier

This study will use the result simulation of bubbling fluidized bed gasifier (BFBG) in CFD to know the value of producer gas (CO2, CO, H2, CH4, O2, and N2). Commonly in BFBG silica sand is used as bed material in the gasification process but in this study silica sand or bed material is absented in the gasification process. The energy and exergy analysis will be evaluated in this study to indicate the performance of BFBG without bed material. In this study rice husk is used as a feedstock with feed rate 0.2 kg/s, and air is used as medium gasification in the range of ER (equivalence ratio) between 0.24 to 0.45. Variation of ER affect the value of energy and exergy, where the higher ER applied the higher exergy destruction that occur and decrease the efficiency of exergy. It was calculated that the best efficiency was obtained when the value of ER is 0.24, with the total value of energy and exergy are 2544 and 2335 kJ per kg biomass, sequentially.

Ilmenite as low-cost catalyst for producer gas quality improvement from a biomass pilot-scale gasifier

In this work, in-situ application of natural occurring ilmenite (FeTiO3) for upgrading the producer gas from a pilot-scale bubbling fluidized bed gasifier was performed and its influence on the gas characteristics and gasifier performance was analyzed.Without using ilmenite, the producer gas average composition (volumetric basis, dry gas) was 15.2% CO, 7.6% H2, 3.8% CH4 and 15.6% CO2, with 0.50 H2:CO molar ratio and 5.0 MJ/Nm3 lower heating value. For this condition, 1.6 Nm3 gas/kg biomass (dry basis) specific dry gas production, 44.5% cold gas efficiency and 68.4% carbon conversion efficiency were attained.Using ilmenite as catalyst, the producer gas average composition (volumetric basis, dry gas) was 13.9% CO, 11.7% H2, 4.0% CH4 and 17.9% CO2, with 0.84 H2:CO molar ratio and 5.1 MJ/Nm3 lower heating value. For this condition, 1.7 Nm3 gas/kg biomass (dry basis) specific dry gas production, 49.8% cold gas efficiency and 75.5% carbon conversion efficiency were attained. Thus, in-situ application of ilmenite generally improved the gasifier performance and induced an increase of H2 concentration and H2:CO molar ratio in the producer gas of 35.1% and 40.7%, respectively, improving its suitability for advanced gas applications that require high H2:CO ratios, such as liquid fuels and chemicals synthesis.

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.

Experimental Evaluation of Biomass Medium-Temperature Gasification with Rice Straw as the Fuel in a Bubbling Fluidized Bed Gasifier

Abstract Our previous pilot-scale studies (Bioresource Technology 2018, 267: 102–109) preliminarily demonstrated the feasibility of performing air gasification with a novel two-stage system, including a medium-temperature bubbling fluidized bed (BFB) reactor and a high-temperature swirl-flow furnace reactor, using rice husk as the fuel. As an extension of that work, this study aims to further investigate the reaction mechanism and application prospect of this technology in the use of a more representative biomass fuel, i. e. rice straw. The operation stability, flow behaviors and reaction characteristics in the first-stage medium-temperature gasification reactor are studied in a lab-scale BFB gasifier. The effects of important operating conditions on the syngas quality, tar yield, compositions of carbon residue, and risk of agglomeration are elucidated in depth. The results have shown that an increase in the gasification temperature can promote syngas quality, gasification efficiency, and carbon conversion, but also increases the risk of agglomeration. An increase in the gasification equivalent ratio leads to positive effects on the syngas yield, carbon conversion, and tar concentration, but also has negative effects on the syngas heating value, tar yield, and especially the restrain of agglomeration. An increase in the raw material moisture content has negative influence on the gasification performance of rice straw, in terms of the gasification efficiency, carbon conversion, tar yield, and so on. However, the increase of moisture content can reduce the cost of raw material drying, and avoid the fluctuation of bed temperature, and therefore, a practical gasification system is recommended to be designed and operated under a certain conditions with moderate moisture contents.

Assessment of biomass energy potential for SRC willow woodchips in a pilot scale bubbling fluidized bed gasifier

The current study investigates the short rotation coppice (SRC) gasification in a bubbling fluidized bed gasifier (BFBG) with air as gasifying medium. The thermochemical processes during combustion were studied to get better control over the air gasification and to improve its effectiveness. The combustion process of SRC was studied by different thermo-analytical techniques. The thermogravimetric analysis (TGA), derivative thermogravimetry (DTG), and differential scanning calorimetry (DSC) were performed to examine the thermal degradation and heat flow rates. The product gas composition (CO, CO2, CH4 and H2) produced during gasification was analyzed systematically by using an online gas analyzer and an offline GC analyzer. The influence of different equivalence ratios on product gas composition and temperature profile was investigated during SRC gasification. TG/DTG results showed degradation occur in four stages; drying, devolatilization, char combustion and ash formation. Maximum mass loss ~70% was observed in devolatilization stage and two sharp peaks at 315–500 °C in TG/DSC curves indicate the exothermic reactions. The temperature of gasifier was increased in the range of 650–850 °C along with the height of the reactor with increasing equivalent ratio (ER) from 0.25 to 0.32. The experimental results showed that with an increment in ER from 0.25 to 0.32, the average gas composition of H2, CO, CH4 decreased in the range of 9–6%, 16–12%, 4–3% and CO2 concentration increased from 17 to 19% respectively. The gasifier performance parameters showed a maximum high heating value (HHV) of 4.70 MJ/m3, Low heating value (LHV) of 4.37 MJ/m3 and cold gas efficiency (CGE) of 49.63% at 0.25 ER. The ER displayed direct effect on carbon conversion efficiency (CCE) of 95.76% at 0.32 ER and tar yield reduced from 16.78 to 7.24 g/m3 with increasing ER from 0.25 to 0.32. All parametric results confirmed the reliability of the gasification process and showed a positive impact of ER on CCE and tar yield.

Simulation of biomass gasification in a BFBG using chemical equilibrium model and restricted chemical equilibrium method

Biomass gasification in fluidized beds is a promising thermo-chemical conversion technology. Bubbling fluidized bed gasifier (BFBG) is considered in the present study, to specify an appropriate model for almond shell gasification. Therefore, the chemical equilibrium model (CEM) and restricted chemical equilibrium method (RCEM) are developed using Aspen Plus. Then, the accuracy of the results obtained from these two modelling approaches is evaluated by comparing with the experimental data. More consistent results are obtained by using RCEM. A sensitivity analysis study is also performed with the specified modelling approach (RCEM) to investigate the effect of operating parameters on the gasification performance. For this purpose, the range of the gasification temperature and steam to biomass ratio are extended and a new parameter (biomass moisture content) is incorporated into the parametric study. Increasing temperature is shown to have a positive effect on cold gas efficiency (CGE) while it has a negative effect on lower heating value (LHV). There is no considerable change in gas heating value and CGE above 850 °C. Both steam to biomass (S/B) ratio and biomass moisture content have a favorable effect on H2 production. However, these parameters have adverse effect on gas heating value and CGE. LHV and CGE reach maximum values for S/B ratio of 0.5 and moisture content of 0.

Experimental Evaluation of Napier Grass Gasification in an Autothermal Bubbling Fluidized Bed Reactor

Air gasification of Napier grass (NG) was studied with the target of producing combustible synthesis gas to be used in direct combustion for power generation. A small-scale autothermal bubbling fluidized bed gasifier was used to investigate the effect of reactor temperature, equivalence ratio (ER), and static bed height (SBH) on gasification performance and combustibility of the producer gas. The main generated species in syngas were identified through gas chromatography (GC) analysis. Minimum fluidization conditions were determined at different levels of SBH. Experiments carried out with two intentions of first, to achieve the highest composition of combustible species to ensure the maximum Lower Heating Value (LHV) of syngas and second, to obtain a high performance process with maximum yield of syngas and minimum residues. The results showed that the temperature and ER have significant effects on syngas yield and composition. SBH was found have a substantial effect on the production of H2 and CO. The results from this study was compared to other gasification studies from literature which have evaluated biomass gasification in bubbling fluidized bed reactors with different scales but almost similar method of experimentation. The purpose of verification was to demonstrate the effect of different reactor scales and heating characteristics on the results.

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.

Process analysis of hydrogen production from biomass gasification in fluidized bed reactor with different separation systems

Gasification is one of the most effective and studied methods for producing energy and fuels from biomass as different biomass feedstock can be handled, with the generation of syngas consisting of H2, CO, and CH4, which can be used for several applications. In this study, the gasification of hazelnut shells (biomass) within a circulating bubbling fluidized bed gasifier was analyzed for the first time through a quasi-equilibrium approach developed in the Aspen Plus environment and used to validate and improve an existing bubbling fluidized bed gasifier model. The gasification unit was integrated with a water-gas shift (WGS) reactor to increase the hydrogen content in the outlet stream and with a pressure swing adsorption (PSA) unit for hydrogen separation. The amount of dry H2 obtained out of the gasifier was 31.3 mol%, and this value increased to 47.5 mol% after the WGS reaction. The simulation results were compared and validated against experimental data reported in the literature. The process model was then modified by replacing the PSA unit with a palladium membrane separation module. The final results of the present work allowed comparison of the effects of the two conditioning systems, PSA and palladium membrane, indicating a comparative increase in the hydrogen recovery ratio of 28.9% with the palladium membrane relative to the PSA configuration.

Cold model testing of an innovative dual bubbling fluidized bed steam gasifier

Biomass gasification by a dual fluidized bed reactor is a very promising process to produce a hydrogen rich syngas from biomass wastes. In this process, the bed material circulation must be enough to transport heat from the combustor to the steam gasifier, and at the same time siphons/loop-seals must be properly designed to avoid gas leakage between the two reactor chambers (such as N2 from the combustor to the gasifier). A cold model of an innovative pilot scale dual bubbling fluidized bed gasifier (100 kWth as biomass input) has been realized. The Hybrid Lagrangian Particle Tracking (HLPT) technique and tracer gas analysis, both applied to the cold model, have been used to evaluate the flow rate of bed material circulation and the gas leakage between the steam gasification and the combustion chambers. The results have shown that the bed material circulation is 2–3 times the minimum required to assure allothermal gasification, while gas leakage is negligible for every operating condition evaluated experimentally.

Ash Deposition in Air-Blown Gasification of Peat and Woody Biomass in a Fluidized-Bed Gasifier

The ash deposition behaviors in air-blown gasification of a woody biomass and a Canadian peat were studied using a pilot-scale bubbling fluidized bed gasifier operating at an equivalence ratio (ER) of 0.2 to 0.35. An air-cooled probe was installed in the furnace of the gasifier to collect ash deposits on its surface. Four different bed materials including olivine, dolomite, limestone, and iron ore were used in this study to compare their effects on ash deposition rate during the gasification. The experimental results demonstrated that among the four bed materials, the use of olivine resulted in the lowest ash deposition rate <1.0 g–2 h–1, compared with ∼16 g–2 h–1 for limestone in the gasification of pine sawdust at an ER of 0.35. The superb performance of olivine in retarding ash deposition could be accounted for by its outstanding thermal stability and mechanical strength. The other three bed materials, in particular, limestone, were fragile during the fluidized bed gasification, and the fractured fines...

The effect of different operational parameters on hydrogen rich syngas production from biomass gasification in a dual fluidized bed gasifier

Biomass energy will be a crucial constitution of renewable energy in the future and hydrogen production from biomass on a large scale may contribute to a renewable development of energy. However, due to high-energy consumption in all technologies of hydrogen production from biomass, progress is impeded and this technology remaining restricted to a laboratory scale. In this research, Hydrogen production via biomass gasification in a dual bubbling fluidized bed gasifier is investigated. In order to model the gasification process inside the reactor, a one dimensional model is generated. The generated model consists of a highly nonlinear set of eleven differential equations in which the effect of various parameters such as flow hydrodynamics, diffusion, convection and chemical reactions are considered on interaction and transfer of different species in the reactor and final produced syngas composition. The obtained results are validated by use of existed experimental data in the literature which show an acceptable compatibility. Finally, the reactor operation is investigated in various working conditions and the effect of parameters such as temperature, gasification agent inlet flow rate, humidity, particle size and reactor size on Hydrogen production is studied in order to clarify the optimum operating condition of reactor with regards to Hydrogen production.

Kinetic Model of Steam Gasification of Biomass in a Bubbling Fluidized Bed Reactor

A simple kinetic model is developed for biomass gasification in a bubbling fluidized bed (BFB) with steam as the fluidizing gas. The biomass pyrolysis is described by a two-step kinetic model in which the primary pyrolysis is modeled by three parallel first-order reactions producing noncondensable gas, tar (bio-oil), and char, and the secondary pyrolysis is modeled by a first-order reaction representing homogeneous thermal cracking of tar. In addition to the yields of pyrolysis products that are often modeled as lumped species, the proportions of major compounds in the pyrolysis gas are predicted based on CHO elemental balances. By incorporating homogeneous and heterogeneous biomass gasification reactions, a seamless kinetic model of a BFB gasifier is developed. An ideal reactor model is used for the BFB gasifier assuming perfectly mixed solids and plug flow of the gas phase. This predictive model is a useful tool to relate biomass gasification product yields and composition to key process operating param...

Tars from Fluidized Bed Gasification of Raw and Torrefied Miscanthus x giganteus

The current study investigates the effect of temperature, equivalence ratio, and biomass composition on tar yields and composition. Torrefied and raw Miscanthus x giganteus (M×G) were used as biomass feedstocks in an atmospheric bubbling fluidized bed gasifier for experiments undertaken between 660 and 850 °C and equivalence ratios from 0.18 to 0.32. Tar was sampled according to the solid phase adsorption method and analyzed by gas chromatography. There is an indication that torrefied M×G produces higher amounts of total GC-detectable tar as well as higher yields of 20 individually quantified tar compounds compared with those of raw M×G. Under similar gasification conditions (800 °C and an equivalence ratio of 0.21), the total GC-detectable tar for torrefied M×G is approximately 42% higher than that for raw M×G. Higher tar yields are observed to be related to higher lignin and lower moisture content of torrefied M×G. The effect of temperature on tar yields is in good agreement with the literature. The hig...

Biomass Gasification Using Carbon Dioxide: Effect of Temperature, CO2/C Ratio, and the Study of Reactions Influencing the Process

Gasification of southern pine using carbon dioxide as an oxidizing medium was carried out in a bench-scale atmospheric bubbling fluidized bed gasifier, and the results were compared with an oxygen gasification study from literature. Evolution of gases (CO, CO2, H2, and CH4) was quantified as a function of temperature in the range 700 °C to 935 °C and CO2/C ratios in the range of 0.5–1.5 (wt/wt). The main aim of this study was to determine the effect of temperature and CO2/C ratios on the output syngas and to understand which reactions were influential within the operational limits of the experimental parameters. Additionally, results from CO2 gasification and oxygen gasification were thoroughly compared. Statistical analyses were performed to determine the significance of changes in operating parameters on the process. Variation in temperature seemed to have a significant effect on the output, whereas the effects of CO2/C ratios were not that profound. The analyses of the gas evolution trends suggested th...

Equilibrium potassium coverage and its effect on a Ni tar reforming catalyst in alkali- and sulfur-laden biomass gasification gases

Biomass conversion to syngas via gasification produces certain levels of gaseous by-products, such as tar and inorganic impurities (sulfur, potassium, phosphorus etc.). Nickel, a commonly used catalyst for hydrocarbon steam reforming, suffers reduced reforming activity by small amounts of sulfur (S) or potassium (K), while resistance against deleterious carbon whisker formation increases. Nevertheless, the combined effect of biomass derived gas phase alkali at varying concentrations together with sulfur on tar reforming catalyst performance under realistic steady-state conditions is largely unknown. Prior to this study, a methodology to monitor these effects by precise K dosing as well as K co-dosing with S was successfully developed. A setup consisting of a 5kW biomass fed atmospheric bubbling fluidized bed gasifier, a high temperature hot gas ceramic filter, and a catalytic reactor operating at 800°C were used in the experiments. Within the current study, two test periods were conducted, including 30h with 1ppmv potassium chloride (KCl) dosing followed by 6h without KCl dosing. Besides an essentially carbon-free operation, it can be concluded that although K, above a certain threshold surface concentration, is known to block active Ni sites and decrease activity in traditional steam reforming, it appears to lower the surface S coverage (θs) at active Ni sites. This reduction in θs increases the conversion of methane and aromatics in tar reforming application, which is most likely related to K-induced softening of the SNi bond. The K-modified support surface may also contribute to the significant increase in reactivity towards tar molecules. In addition, previously unknown relevant concentrations of K during realistic operating conditions on typical Ni-based reforming catalysts are extrapolated to lie below 100μgK/m2, a conclusion based on the 10–40μgK/m2 equilibrium coverages observed for the Ni/MgAl2O4 catalyst in the present study.