Dual Fluidized Bed Gasifier Research Articles

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.

AkzoNobel and Gasunie study a large hydrogen plant in the Netherlands

The performance of the dual fluidized bed gasification plant Oberwart was evaluated by means of an extensive measurement campaign and calculation of mass and energy balances using IPSEpro. Process simulation was also applied to identify future optimization potentials. Different aspects are discussed such as the reduction of gasification temperature and the reduction of steam for gasification and air for combustion. Gasification pilot plant experience is integrated in the simulation models to increase significance of the simulation results. The mass and energy balances confirm that the performance of the CHP plant Oberwart is highly satisfactory and currently achieves an electrical efficiency of 29%. The variations of plant parameters provide deeper insight in the process itself and show interdependencies of different process units. With lower gasification temperatures and reduction in combustion air, the electrical efficiency can be increased to 31%.

Characterization of a dual fluidized bed gasifier with blended biomass/coal as feedstock

A one-dimensional model is built based on the commercial Aspen Plus software to kinetically simulate the biomass/coal co-gasification process in a dual fluidized bed gasifier. The synergistic effect on the co-gasification kinetics is allowed for, and is coupled with the gas–solid flow hydrodynamics. With the developed model, the effects of different key operating parameters including the biomass blending ratio (Rb), the initial bed temperature (Tg), the feedstock mass flow rate (Ffs), the bed material flux (Fbm) and the steam to carbon ratio (Rsc) on the resultant syngas composition and the supplemental fuel mass flow rate (Fsf) are investigated, and the operation parameters are optimized. It is found that increasing Rb and Tg can enhance the gasification, while increasing Ffs and Rsc restricts the gasification. Increasing Fbm has slight effect on the gasification results but can reduce Fsf. The cold gas efficiency is up to 78.9% under the proposed optimum condition.

Application and Discussion of Dual Fluidized Bed Reactor in Biomass Energy Utilization

As an important clean and renewable energy, biomass has a broad market prospect. The dual fluidized bed is widely used in biomass gasification technology, and has become an important way of biomass high-value utilization. This paper describes the basic principle of dual fluidized bed gasification, from the gas composition, tar content and thermal efficiency of the system point of view, analyzes and summarizes several typical dual fluidized bed biomass gasification technologies, points out the existence of gas mixing, the external heat source, catalyst development problems on gas. Finally, it is clear that the gasification of biomass in dual fluidized bed is of great industrial application and development prospect.

Online Measurements of Alkali Metals during Start-up and Operation of an Industrial-Scale Biomass Gasification Plant

Alkali metal compounds may have positive influences on biomass gasification by affecting char reactivity and tar reforming, but may also disturb the process by formation of deposits and agglomerates. We herein present results from online measurements of alkali compounds and particle concentrations in a dual fluidized bed gasifier with an input of 32 MWth. A surface ionization detector was used to measure alkali concentrations in the product gas, and aerosol particle measurement techniques were employed to study concentrations and properties of condensable components in the gas. Measurements were performed during start-up and steady-state operation of the gasifier. The alkali concentration increased to approximately 200 mg m-3 when fuel was fed to the gasifier and continued to rise during activation of the olivine bed by addition of potassium carbonate, while the alkali concentration was in the range from 20 to 60 mg m-3 during steady-state operation. Addition of fresh bed material and recirculated ash had...

Experimental development of sorption enhanced reforming by the use of an advanced gasification test plant

Dual fluidized bed steam gasification of solid fuels enables the production of a nitrogen-free medium calorific product gas. Several commercial industrial sized plants are already operating the dual fluidized bed gasification process. The present work illustrates an improvement of the gasification process itself by the use of wood as fuel and calcite as bed material to produce a hydrogen-rich gas. Hereby, in the combustion reactor calcite (CaCO3) is calcined to calcium oxide (CaO) by the release of carbon dioxide (CO2) at high temperatures (∼850 °C). In the gasification reactor, CaO acts as a sorbent for CO2 from the produced calorific gas stream at lower temperatures (∼650 °C). Experimental results from two different test plants are compared by the use of a process simulation software. The results illustrate the observed improvements with respect to process performance by the application of an advanced reactor design operating this so called sorption enhanced reforming process. It is shown that the water conversion rate in the gasification reactor is raised up to 36% and the overall cold gas efficiency was improved from 58 to 71% with the advanced reactor design. Since the sorption enhanced reforming process is highly dependent on temperature, the influence of gasification temperature and further, bed material circulation rate are discussed as well. It is demonstrated, that a hydrogen (H2) to carbon monoxide (CO) ratio between 9 and 2 can be set by operating the gasification reactor with a certain temperature. Further, it is shown that a low bed material circulation rate is favorable to obtain high hydrogen (H2) contents in the product gas.

Influence of controlled handling of solid inorganic materials and design changes on the product gas quality in dual fluid bed gasification of woody biomass

Utilizing biomass feedstock in thermal conversion technologies to reduce greenhouse gas emissions is a promising way to substitute for fossil fuels. Gasification of biomass allows for the production of electricity, district heat, high-grade fuels for transportation and synthetic chemicals. Investigations at the HGA Senden industrial-scale dual fluidized bed gasification power plant have shown the potential for improving gas quality by the controlled handling of solid inorganic materials in the reactor. Two measures for optimization were implemented and investigated on-site. First, improving the bed material and ash loops in the system led to significant reduction of undesirable tars in the product gas. This was based on reutilizing used, layered, olivine particles with higher catalytic activity compared to that of fresh olivine. Second, improving the mixing of feedstock or char particles with catalytically active bed material in the gasification reactor, and also ensuring steam, as reaction medium, was available local to the area of the fuel input, led to further decrease of tars in the product gas. This was achieved by incorporating additional fluidization nozzles in the gasification reactor.In summary, the optimization measures for controlled handling of inorganic materials had a major influence on the product gas quality in the dual fluidized bed gasification of biomass. As a consequence, long-term operation at significantly higher capacity than before could be achieved at the HGA Senden industrial-scale power plant.

Economic evaluation of synthetic ethanol production by using domestic biowastes and coal mixture

Biowastes, such as cow manure, waste paper, and wood waste, are recognized as an essential source of renewable energy, and their importance increased significantly over time. However, the insufficient supply of biowastes for commercial thermochemical conversion processes is a major problem that needs to be addressed. Therefore, the co-utilization of biowastes and coal has been developed globally. In this study, we investigated the feasibility of biowaste and coal mixtures in an ethanol conversion process. A commercial-scale thermochemical process consisting of a dual fluidized bed gasifier, compressor, tar reformer, catalytic reactor, and auxiliary facilities was used and analyzed. In particular, the effects of material costs including both transportation and collection costs of biowastes and mix percentages on the economic value of synthetic ethanol were analyzed. In addition to the limitations of biowaste collection, the scale of co-utilization processes could be a critical factor for the commercialization of converting biowaste and coal mixtures to ethanol.

Kinetic Model of Steam Gasification of Biomass in a Dual Fluidized Bed Reactor: Comparison with Pilot-Plant Experimental Results

By incorporating reaction kinetics and reactor hydrodynamics, a steady-state two-phase one-dimensional reactor model for biomass steam gasification in the bubbling fluidized bed gasifier of a dual fluidized bed reactor is developed. The generic two-step kinetic model adopted for biomass pyrolysis allows for prediction of tar generation and cracking, as well as predicting pyrolysis product yield and composition based on CHO elemental balances. This model is capable of predicting species concentrations, solids holdup, temperature, pressure, and superficial gas velocity profiles along the gasifier. By performing mass and energy balances over the two interconnected fluidized beds, key operating parameters such as solids circulation rate and additional fuel required for stable operation of the process are approximated. This predictive reactor model, which will provide a useful tool for designing, evaluating, and improving a dual fluidized bed gasifier, is compared with experimental data from the pilot dual flu...

Impact of retrofitting existing combined heat and power plant with polygeneration of biomethane: A comparative techno-economic analysis of integrating different gasifiers

It is vital to identify and evaluate the optimal gasifier configuration that could be integrated with existing or new combined heat and power (CHP) plants to maximize the utilization of boiler operating capacity during off-peak hours with minimal effect on the boiler performance. This study aims to identify technically and economically most suitable gasification configuration and the reasonable operational limits of a CHP plant when integrated with different types of gasifiers. The selected gasifiers for the study are, (i) indirectly heated dual fluidized bed gasifier (DFBG), (ii) directly heated circulating fluidized bed gasifier (CFBG), and (iii) entrained flow gasifier (EFG). The gasifiers are selected on their ability to produce high-quality syngas from waste refused derived fuel (RDF). The syngas from the gasifiers is utilized to produce biomethane, whereas the heat and power from the CHP plant are consumed to run the gasification process. A detailed techno-economic analysis is performed using both flexible capacity and fixed capacity gasifiers and integrated with the CHP plant at full load. The results reveal that the integration leads to increase in operating time of the boiler for all gasifier configurations. The indirectly heated DFBG shows the largest biomethane production with less impact on the district heat and power production. Extra heat is available for biomethane production when the district heat and biomethane are prioritized, and the electric power is considered asa secondary product. Furthermore, the economic indicators reflect considerable dependency of integrated gasification performance on variable prices of waste biomass and biomethane.

Online Measurements of Alkali and Heavy Tar Components in Biomass Gasification

Tar and alkali metal compounds are released during biomass gasification and have a major impact on the operation and performance of gasification processes. Herein we describe a novel method for characterization of alkali and heavy tar compounds in the hot product gas formed during gasification. Gas is continuously extracted, cooled and diluted, which results in condensation of tar and alkali into aerosol particles. The thermal stability of these particles is subsequently evaluated using a volatility tandem differential mobility analyzer (VTDMA) method. The technique is adopted from aerosol science where it is frequently used to characterize the thermal properties of aerosol particles. Laboratory studies show that pure and mixed alkali salts and organic compounds evaporate in well-defined temperature ranges, which can be used to determine the chemical composition of particles. The performance of the VTDMA is demonstrated at a 4 MWth dual fluidized bed gasifier using two different types of online sampling s...

Study on the Cold Experiment of a Multi-Combined Circulating Fluidized Bed Gasification

The dual fluidized bed biomass gasification technology is an important technology to convert low-quality biomass into high-grade hydrogen. In order to further reduce the tar content in gas, we proposed a new multi-combined circulating fluidized bed gasification basing on the existing researches of the dual fluidized bed gasification. Moreover, we designed and built a cold state test system, focusing on the influence of bed material, low speed area fluidization velocity, the fluidization velocity ratio of high and low speed area to the gasification chamber pressure distribution and the solid circulation of output loop. They will be the foundation for construction and commissioning of multi-combined circulating fluidized bed gasification thermal test system.

Study on the Cold Experiment of a Multi-Combined Circulating Fluidized Bed Gasification

The dual fluidized bed biomass gasification technology is an important technology to convert low-quality biomass into high-grade hydrogen. In order to further reduce the tar content in gas, we proposed a new multi-combined circulating fluidized bed gasification basing on the existing researches of the dual fluidized bed gasification. Moreover, we designed and built a cold state test system, focusing on the influence of bed material, low speed area fluidization velocity, the fluidization velocity ratio of high and low speed area to the gasification chamber pressure distribution and the solid circulation of output loop. They will be the foundation for construction and commissioning of multi-combined circulating fluidized bed gasification thermal test system.

Measurement of solids circulation rate in a high-temperature dual fluidized bed pilot plant

A number of fluidized bed reactor processes operating at high temperature require that solid particles be circulated back and forth between two reactor vessels. Since the circulation rate strongly affects mass and energy balances, and therefore greatly influences hydrodynamics and performance of the system, a reliable technique for its accurate measurement would be helpful in monitoring and modeling the process. However, there are no reported techniques suitable for measuring solid circulation rates at elevated temperatures typical of gasification systems.A novel thermal-tracing technique was developed for measuring the solids circulation rate between two reactors. Particles at room temperatures (cold particles) are injected into a downward-moving packed bed of solids at elevated temperature (hot particles), creating reduced-temperature zones inside the moving bed. The transit time of the cold-particle-clusters between pairs of thermocouples is determined by cross correlation allowing the flux to be estimated. The technique was shown to provide sensitive and reproducible data for a cold model unit with injection of dry ice. The technique was then applied to determine the solids circulation rate between the bubbling bed gasifier and the riser combustor of a pilot scale dual fluidized bed gasification system. A number of conditions are imposed on the data to eliminate unsatisfactory data at high temperatures. Data which satisfy the discrimination criteria are shown to lead to measured solids circulation fluxes up to 133kg/m2-s at temperatures up to 856°C in the gasifier test section. The technique provides high-temperature solids circulation rate information beyond the capability of other techniques.

System Optimization for Fischer–Tropsch Liquid Fuels Production via Solar Hybridized Dual Fluidized Bed Gasification of Solid Fuels

A new configuration of solar hybridized dual fluidized bed (DFB) gasification process is proposed with char separation for the production of Fischer–Tropsch (FT) liquid fuels from solid fuels of biomass and/or coal. The addition of carbon capture with sequestration and FT reactor tail-gas recycle configurations is also assessed. The studied FT liquid fuels production systems are simulated by using a pseudodynamic model incorporating a year long, hourly averaged solar insolation time-series. For the case with a solar multiple (i.e., the heliostat field area relative to that required to meet the demand of the DFB gasifier at the point of peak solar thermal output) of 2.64 and bed material storage capacity of 16 h, the calculated annual solar share of the solar hybridized coal-to-liquids system can be increased from 12.2 to 20.3% by the addition of the char separation for a char gasification conversion of 80%. To achieve the well-to-wheel greenhouse gas emissions for FT liquid fuels parity with diesel derive...

A Study on the Optimal Operating Condition of a Dual Fluidized-Bed (DFB) with Biomass and SRF

This study has a focus on deriving the optimal operating conditions of biomass and waste plastic film SRF under dual fluidized bed gasification and on its domestic commercialization. From the analysis results, it was proven that the carbon conversion of biomass was optimized as 81% at 826℃ with 1,334 g/hr steam stream and 5.56 L/min air stream. On the other hand, that of waste plastic film SRF was 71% at 750℃ with 754 g/hr steam stream and 18.8 L/min air stream. In case of operation on waste plastic film SRF, temperature should be under 750℃ to prevent from agglomeration of bed materials.

목재 바이오매스를 활용한 이중유동층 가스화기의 SNG 생산

목재 바이오매스를 활용한 이중유동층 가스화기의 SNG 생산

Operating parameter effects on the solids circulation rate in the CFD simulation of a dual fluidized-bed gasification system

The solids circulation is crucial for sustaining biomass gasification within dual fluidized-bed gasification systems, because the heat utilization between the gasifier and combustor is mainly implemented through the circulation of bed material. In this work, a three-dimensional model was established to simulate the hydrodynamics of a dual fluidized-bed gasification system. The purpose of this work was to find effective ways to improve the solids circulation. In this CFD (computational fluid dynamics) model, the MP-PIC (multiphase particle-in-cell) method was applied to simulate the gas-solid flows in the dual fluidized-bed system. This model simulated the hydrodynamics of the bubbling fluidized-bed gasifier, chute, pneumatic-riser combustor, cyclone separator, and loop-seal in the dual fluidized-bed system. Studies of grid resolution and numerical parcel were conducted to examine the model accuracy. A series of case studies were implemented to investigate the impact of operating parameters on the solids circulation rate, such as particle diameter, solid inventory, steam supply to gasifier, and air supplies to combustor.

Compartment model for a dual fluidized bed biomass gasifier

A variety of novel processes are being proposed in order to face global challenges such as degradation of the environment and the efficient utilization of energy. Modeling and simulation tools play a crucial role in the understanding and enhancing of the execution, design and construction of these processes. Although different computational tools are available to quantify the process at different levels, they are normally utilized independently and on a stand-alone basis. This decoupled approach may undermine the true potential of these tools. The present study highlights the advantages of interlinked process modeling at different levels. This study focuses on a promising gasification technology, namely the dual fluidized bed gasifier. A computational fluid dynamics (CFD) model was used to understand the flow patterns inside a fluidized bed. This elevated the understanding of the hydrodynamics of the gasifier freeboard, which is neglected by the conventional two-phase methodology. The CFD simulation was utilized to perform a residence time distribution (RTD) analysis of the reactor. Four tracer approaches namely the frozen velocity approach, the snapshot approach, the data sampling approach and the transient approach, were compared. The RTD analysis formed the basis of a steady-state compartment model that was developed in ASPEN Plus simulation software. The ASPEN Plus gasifier model decoupled the pyrolysis, gasification, and combustion sections of the gasifier to affect a better comprehension of the process and results. The model predicated satisfactory results upon validation. Additionally, the model could also be used to predict the output for different biomass feedstocks.

Experimental investigation of biomass devolatilization in steam gasification in a dual fluidised bed gasifier

In this study, biomass devolatilization, which is the initial stage of steam gasification, was experimentally investigated in a 100kW dual fluidised bed gasifier. In the experiments, pellets of radiata pine sawdust were used as the feedstock, and silica sand was used as the bed material. The operating temperature in the gasifier was varied from 700 to 800°C and N2 was used as the fluidisation agent. Once the devolitilization test was completed, corresponding gasification experiment was conducted at the same operation condition but N2 was switched to steam as gasification and fluidisation agent.From the experimental results, it is found that, in the devolatilization stage, gas yield was increased, and tar yield and concentration were decreased with increase in operation temperature. In this study, significant correlation was observed for gas yield and gas composition between the devolatilization stage and the gasification stage. Correlations on tar concentrations and yield were also clear for gases produced from the devolatilization and gases from the subsequent gasification. This study provides fundamental information for understanding and optimization of the biomass steam gasification.