Fluidized Bed Biomass Gasifier Research Articles

The effect of biomass feeding location on rice husk gasification for hydrogen production

The objective of this study is to investigate the impact of biomass feeding location on rice husk gasification for hydrogen production. By comparing the results between top-feed and bottom-feed of the feedstock of the fluidized bed biomass gasification at the reaction temperature between 600∼1000 °C and ER = 0.2, 0.27, and 0.33 without steam, the optimum low heating value was increase by 2.35 kJ/g-rice husk by the top-feed to gasifier. Although the yield of hydrogen was decreased by 42% for the rice husk gasification by the top-feed operation, the yield of CO, CO2, and CH4 were highly increased, which enhancing the heating value of the effluent gas. The study results suggested the potential route of the biomass gasification at the different feeding location.

Three-dimensional modelling and optimization of an industrial dual fluidized bed biomass gasification decoupling combustion reactor

Dual fluidized bed biomass gasification decoupling combustion technology, as a promising technology to realizing the highly efficient and stable combustion for high-water-containing biomass fuel and lower NOx emission, has drawn worldwide attention from researchers in recent years. In this work, a three-dimensional industrial dual fluidized bed biomass gasification decoupling combustion reactor was modelled using the reactive multiphase particle-in-cell approach, and the secondary air operating parameters concerning total secondary air ratio, upper secondary air ratio, upper secondary air height, and upper secondary air injection models of the biomass gasification combustion reactor were optimized to enhance its performance further. Results show that the biomass gasification combustion model, established and comprehensively verified by comparing the simulated values with measured data in this work, shows a good prediction accuracy of gas–solid flow, heat transfer, and biomass combustion processes. With the total secondary air ratio, the upper secondary air ratio and the upper secondary air height increase, the gas-phase entrainment effects on the axial particle concentration distribution below the upper secondary air feed port in the dense zone weakens, and the overall biomass combustion efficiency decreases. Compared with the single injection model for the upper secondary air injection, the gas-phase entrainment effects on the axial particle concentration distribution were enhanced, and the overall biomass combustion efficiency was improved when adopting the opposite injection or circular injection model. Finally, the optimal secondary air operating parameters for the biomass gasification combustion reactor were obtained from the combustion and gasification views, providing an essential theoretical reference for industrial-scale dual fluidized bed biomass gasification decoupling combustion reactor optimization, biomass gasification decoupling combustion process enhancement, and efficient biomass energy utilization.

Evaluating the impacts of temperature on a bubbling fluidized bed biomass gasification using CPFD simulation model

Biomass gasification and subsequently fuel and chemicals synthesis allow for a seamless transition from fossil raw materials to a renewable economy. A computational particle fluid dynamics (CPFD) simulation model is developed for biomass gasification in a bubbling fluidized bed reactor with steam as the fluidizing gas. CPFD methodology incorporates the multiphase particle-in-cell (MP-PIC) method and the particle parceling algorithm to solve the gas phase as a continuous fluid in a Eulerian grid of cells where particles are modeled as discrete Lagrangian points. The model has been validated by experimental results and shows good agreement. Reactor temperature effects as a key process operating parameters have been investigated and the results of the product gas composition on the temperature of 950, 1000, 1050, 1100, 1150, and 1200 K are shown. The results illustrate that at a higher temperature, the product of CO and H2 is promoted whereas the generation of CO2 and CH4 is diminished.

Multi-Scale Modelling of Fluidized Bed Biomass Gasification Using a 1d Particle Model Coupled to Cfd

Multi-Scale Modelling of Fluidized Bed Biomass Gasification Using a 1d Particle Model Coupled to Cfd

Correlations between tar content and permanent gases as well as reactor temperature in a lab-scale fluidized bed biomass gasifier applying different feedstock and operating conditions

The major problem of fluidized bed biomass gasification is the high tar contamination of the producer gas which is associated with the complex and time-consuming sampling and analysis of these tars. Therefore, correlations to predict the tar content are a helpful tool for the development and operation of biomass gasifiers. Correlations between tars and gas composition as well as reactor temperature derived for a steam-blown lab-scale bubbling fluidized bed gasifier are investigated in this study to assess their applicability. A comprehensive data set containing over 80 experimental points was obtained for various operation conditions, including variations in temperature from 700 to 800 °C, feedstock, amount of steam for fluidization, as well as the addition of oxygen. Linear correlations between tar and permanent gases show good accuracy for H2 and CH4 when using pure steam. However, experiments conducted with steam-oxygen mixtures show high deviations for the CH4-based correlation and smaller but still significant deviations for the H2-based correlation. No relation between tar and CO or CO2 was found. The correlation between tar and temperature shows highest accuracy, including good agreement with the steam-oxygen experiments. All tar correlations showed useful results over a broad operating range. However, significant deviations can be obtained when considering just one gas compound. Therefore, a combination of different correlations considering gas components and temperature seems to be the best method of tar prediction. This leads to a powerful tool for fast online tar monitoring for a broad range of operating conditions, once a calibration measurement was conducted.

Dynamic Modeling for Temperature Prediction in a Fluidized Bed Biomass Gasification Process

A long short-term memory (LSTM) based artificial neural network (ANN) model is developed to predict the temperatures of the fluidized bed and freeboard as well as of the outlet gas temperature during the fluidized bed biomass gasification process. The various available equilibrium models and the kinetic models to simulate this process are often found impractical at a large scale due to the assumptions on which these models are framed. Instead of solving complex kinetic and equilibrium models, this study explores the potential of utilizing an LSTM model for the dynamic modeling of a fluidized bed biomass gasifier. The influence of various hyperparameters on LSTM model performance are also studied. Among many tested activation functions, tanh has the lowest mean squared error overall. Adagrad and SGD are identified as the most suitable optimizers for our LSTM model. Single and two layered LSTM models are compared. The LSTM model is validated with the spatio-temporally resolved experimental data of the pilot plant fluidized bed gasifier. The LSTM model is further examined for temperature predictions at three future points (1 min, 3 min, and 5 min ahead). Overall, the LSTM model offers a sufficiently accurate alternative for temperature prediction in fluidized bed biomass gasifier.

Solubility of Tar Model Compounds in Various Solvents for Tar Removal in a Dual Fluidized Bed Biomass Gasification Process

Production of high quality product gas via biomass steam gasification is a promising technology. However, impurities in the product gas, namely tars, cause problems in the downstream gas processing operations and thus they need to be removed efficiently. Oil scrubbing is an effective solution for tar removal due to its non-polar characteristic which is similar to tar nature. In this research, solubility values of five simulated tar compounds were experimentally investigated for selecting the new scrubbing solvent. The simulated tar compounds investigated represent those found in the dual fluidized bed steam gasification of wood biomass, which are: naphthalene, biphenyl, anthracene, fluoranthene, and pyrene. The scrubbing solvents tested in this research are classified into biodiesels, vegetable oils, and diesel. Biodiesel used are rapeseed methyl ester (RME) and 2 different palm methyl esters (denoted as PME1 and PME2). Vegetable oils are sunflower oil, refined palm oil, Thai rice bran oil, and crude palm oil. All of the solubility tests were performed in the laboratory-scale test-rig at 30, 50, 70, and 80°C. Biodiesels are found to be the effective solvent in dissolving the tar compounds. PME1 shows the similar tar removal performance to RME but is more readily available; therefore, PME1 is chosen to be used as a scrubbing solvent at the Thailand 1 MWel prototype DFB gasifier at Nong Bua district in Nakhon Sawan province, Thailand.

How to Avoid Bed Agglomeration in the Bubbling Fluidized Bed Biomass Gasification: Two-Stage Gasification at 600 °C

How to Avoid Bed Agglomeration in the Bubbling Fluidized Bed Biomass Gasification: Two-Stage Gasification at 600 °C

Analysis of fluidized bed gasification of biomass assisted by solar-heated particles

Although biomass gasification using concentrated solar energy is an attractive technology for the production of storable renewable energy and CO2 reduction, several challenges have stalled its deployment over the last decades: high temperature and/or large reactor volume required for complete fuel (char) conversion, the achievement of a steady syngas generation independent of solar radiation variation, and accomplishing effective heat supply at high temperature in large-scale reactors. An alternative approach overcoming these technical challenges is analyzed in this paper. It is based on conducting the gasification of biomass with steam in a fluidized bed using solid particles that are separately heated in a solid particle receiver using concentrating solar energy. The present study includes the thermodynamic and kinetic analysis of solar steam gasification in a completely allothermal single fluidized bed gasifier as well as in a partially allothermal dual fluidized bed gasification system. A theoretical analysis of the reactor performance and its integration with the solar receiver is examined and the state of the art of the most important aspects for developing the proposed technology is reviewed.

Air-steam gasification of biomass based on a multi-composition multi-step kinetic model: A clean strategy for hydrogen-enriched syngas production

Biomass, as a renewable energy source, has high potential for supplying the energy needs of modern societies. Gasification is a thermochemical route for converting biomass into combustible gas at high temperatures. The main purpose of the present study was to develop an Aspen Plus model of air-steam gasification of biomass (sawdust) to predict the gasification characteristics and performances. The prediction capability of the model was evaluated by comparison with experimental data obtained in a fluidized bed biomass gasifier. First, the influence of gasification temperature on gas composition, product yields and gasifier performances was investigated. The biomass feeding rate and air flow rate were set at~0.445 kg/h and 0.5 Nm3/h, respectively, while the gasifier temperature was varied between 700 °C to 800 °C. With the increase of temperature, the gas yield (DGY) increased steadily from 1.72 to 2.0 Nm3/kg, while the HHV of the produced syngas (HHVgas) increased initially from 5.38 to 5.73 MJ/Nm3 and then decreased to 5.69 MJ/Nm3. After determining optimal temperature (800 °C), the influence of equivalence ratio (ER) and steam/biomass ratio (S/B) on gasification characteristics, dry gas yield (DGY) and tar yield (TRY) was studied. As ER increased from 0.19 to 0.23, TRY decreased from 9.13 g/Nm3 to 8.45 g/Nm3. In contrast, DGY initially increased from 2.02 Nm3/kg to 2.43 Nm3/kg as ER increased from 0.19 to 0.21 and then dropped to 2.24 Nm3/kg at ER of 0.23. An increase in S/B from 0.61 to 2.7 also resulted in a slight increase in HHVgas; however, TRY showed a decreasing trend (from 9.65 g/Nm3 to 8.95 g/Nm3). The results showed that the model developed in this paper is a promising tool for simulating the biomass gasification at various operating conditions.

Conversion of CO2 during the DFB biomass gasification process

In many industrial processes, the climate-damaging gas CO2 is produced as undesired by-product. The dual fluidized bed biomass gasification technology offers the opportunity to tackle this problem by using the produced CO2 within the process as gasification agent. Therefore, a 100 kWth pilot plant at TU Wien was used to investigate the use of CO2 as gasification agent by converting softwood as fuel and olivine as bed material into high-valuable product gas. A parameter variation was conducted, where the typically used gasification agent steam was substituted stepwise by CO2. Thereby, the amount of CO and CO2 increased and the content of H2 decreased in the product gas. These trends resulted in a declining H2/CO ratio and a decreasing lower heating value when CO2 was increased as gasification agent. In contrast to these declining trends, the carbon utilization efficiency showed an increasing course. As second part of this work, a temperature variation from 740 to 840 °C was conducted to investigate the change of the main product gas components. With increasing temperature, CO and H2 increased and CO2 decreased. To determine the degree of conversion of CO2 in the DFB reactor system, two approaches were selected: (1) a carbon balance and (2) a hydrogen balance. This way, it was found out that a certain amount of CO2 was indeed converted at the investigated process conditions. Furthermore, under certain assumptions, the reverse water-gas shift reaction was identified to be the predominant reaction during CO2 gasification.

Kinetic modeling of biomass gasification and tar formation in a fluidized bed gasifier using equivalent reactor network (ERN)

A chemical kinetic based simulation model of a bubbling fluidized bed biomass gasifier has been developed using an Equivalent Reactor Network (ERN). The pyrolysis zone is modeled using a thermodynamic equilibrium model and a kinetic-controlled perfectly stirred reactor (PSR) placed in succession. The gasification zone and the freeboard are simulated as perfectly stirred reactor (PSR) and plug flow reactor (PFR), respectively. A detailed chemical reaction mechanism is used to describe the chemistry of reaction during devolatilization and gasification stages. The formation and evolution of gaseous and tar species in different zones of the gasifier are estimated and the major reaction paths have been identified. The influence of equivalence ratio (ER) on the gasifier performance and tar species formation has been studied. Out of the three ERs considered (0.27, 0.24 and 0.19), the best performance of the gasifier is exhibited at ER = 0.24 in terms of cold gas efficiency.

Surface characterization of ash-layered olivine from fluidized bed biomass gasification

The present study aims to present a comprehensive characterization of the surface of ash-layered olivine bed particles from dual fluidized bed gasification. It is well known from operation experience at industrial gasification plants that the bed material is activated during operation concerning its positive influence on gasification reactions. This is due to the built up of ash layers on the bed material particles; however, the chemical mechanisms are not well understood yet. Olivine samples from long-term operation in an industrial-scale gasification plant were investigated in comparison to fresh unused olivine. Changes of the surface morphology due to Ca-enrichment showed a significant increase of their surface area. Furthermore, the Ca-enrichment on the ash layer surface was distinctively associated to CaO being present. The presence of CaO on the surface was proven by adsorption tests of carbon monoxide as model compound. The detailed characterization contributes to a deeper understanding of the surface properties of ash layers and forms the basis for further investigations into their influence on gasification reactions.

Numerical Investigations of a Fluidized Bed Biomass Gasifier Coupling Detailed Tar Generation and Conversion Kinetics with Particle-Scale Hydrodynamics

Biomass tar as a byproduct during gasification process can lead to many problems, such as condensation and subsequent plugging of downstream. However, the knowledge of the correlations between the ...

Comparison of Ash Layer Formation Mechanisms on Si-Containing Bed Material during Dual Fluidized Bed Gasification of Woody Biomass

Quartz, feldspar, and olivine are minerals commonly used as bed materials for dual fluidized bed gasification of biomass. During their interaction with biomass ash, the materials develop surface layers rich in ash-derived elements. These layers decrease the concentration of tar which is an unwanted side product of gasification. The interactions of quartz, feldspar, and olivine with woody biomass ash leading to the formation of active layers were studied with X-ray diffraction, scanning electron microscopy–energy dispersive X-ray spectroscopy, and iime-of-flight secondary ion mass spectrometry, and the results were compared to calculations done with FactSage. It was found that the interaction causes the formation of three-layered structures for all materials: a Mg-rich surface layer, a Ca-rich intermediate layer, and an inner layer which varies among the three materials. For quartz and feldspar, the integration of Ca and Mg into the structure causes a transition by depolymerizing the tectosilicate structure via an inosilicate intermediate to finally a nesosilicate. As the olivine structure is a nesosilicate from the beginning, no further depolymerization of the silicate structure can occur and a substitution of Mg by Ca occurs, leading to an accumulation of expelled MgO on the surface. The interaction of the materials with K was found to differ, causing melt formation for quartz, a substitution of Na-rich feldspar by K-rich feldspar, and the formation of feldspathoids for alkali feldspar, or retention as a separate phase for olivine.

Three-dimensional simulation of biomass gasification in a full-loop pilot-scale dual fluidized bed with complex geometric structure

Based on the Eulerian-Lagrangian framework, a reactive multi-phase particle-in-cell (MP-PIC) method is used to simulate biomass gasification in a three-dimensional pilot-scale dual fluidized bed (DFB) with complex geometric structure. After model validation, the optimal parameters for the simulation are derived via the independence tests. Thermochemical behaviors of bed materials and biomass particles are explored and the effects of temperature, steam-to-biomass ratio, and equivalence ratio on gasification performance are unveiled. The results show that the tendency of gas and solid temperature is opposite in the gasifier and combustor. The DFB can effectively control temperature, showing an excellent circulating and heat transfer feature. The pressure gradient distribution is highly related to the solid holdup distribution. Higher temperature and steam-to-biomass ratio increase lower heating value (LHV) and combustible gas concentration, resulting in the enhancement of gasification performance. Higher equivalence ratio decreases the LHV and combustible gas concentration, giving rise to a negative influence on the gasification performance.

Modeling the transient response of a fluidized-bed biomass gasifier

The dynamic response of a bubbling fluidized-bed biomass gasifier (FBG) is examined. A transient model is developed by extending a previous steady-state model to account for key processes occurring during the ramp-up and/or changes in loading of fuel and gasification agent. The model is validated against measurements from transient tests in a laboratory-scale FBG. The model results are also compared with steady-state measurements and previous FBG models from the literature. A sensitivity analysis is performed to identify the most influencing parameters. The model is then used to study the transient response of industrial FBG under different operating conditions. It is shown that for given operational conditions (biomass flowrate, equivalence ratio, initial temperature, and initial char inventory in the bed), there is always an optimal start-up procedure (rate of change in feeding the gasifying agent and/or the fuel) leading to the shortest start-up time and lowest peak temperature. The transient period can be reduced by up to 75% compared to the reference value, in which the transient response can extend for more than an hour, due to the slow change in the inventory of char in the reactor. The model can be used to optimize the operation of hybridized power plants with biomass gasification and thermal energy storage.

Single-Bubble Dynamics in a Dense Phase Fluidized Sand Bed Biomass Gasification Environment

Biomass gasification in fluidized beds is a process of important commercial value. The simulation of these fluidized bed units strongly depends on establishing bubble dynamics in dense phase sand f...

Distribution and particle-scale thermochemical property of biomass in the gasifier of a dual fluidized bed

Steam-gasification of biomass feedstock via dual fluidized bed has been proven to be an efficient and promising approach for the thermochemical conversion of biogenic fuels into the high-quality nitrogen-free syngas. However, very little is known about the actual behavior of the biomass fuels in the bed. In this work, the reactive gas-solid flow in a full-loop pilot-scale (1MWth) dual fluidized bed biomass gasifier is numerically simulated with the multiphase particle-in-cell approach. The aim of this study is to explore the species segregation and particle-scale thermochemical property of biomass material. The results show that the species segregation induced by the size and density differences gives rise to a preferential distribution of biomass material close to the bed surface. The undesired segregation phenomenon inhibits the sufficient mixing of biomass and heat carrier, and results in the particular distribution of thermochemical property of biomass material, which therefore requires further optimization of geometrical design. Lagrangian tracking of solid phase provides insight in the particle-scale thermochemical properties (i.e., temperature, heat transfer coefficient, carbon content) of biomass material. The observation of lognormal distribution and large value in the splash zone of biomass heat transfer coefficient enhances the understanding of the heat transfer behavior of biomass material. Biomass locating near the bed surface has the largest temperature. The promoting effect of wider size distribution of heat carrier on biomass dispersion provides a guidance for the process operation. The results of this study provide a fundamental understanding of the high-fidelity microscopic biomass property in the gasifier of dual fluidized bed, which will be beneficial for the optimization of the process designs.

Experimental and computational studies on biomass gasification in fluidized beds

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