Bed Biomass Steam Gasification Research Articles

Experimental investigation on the methanation of hydrogen-rich syngas in a bubbling fluidized bed reactor utilizing an optimized catalyst

Catalytic methanation processes allow the production of natural gas substitutes on a sustainable and renewable basis. This study investigates the catalytic methanation of syngas from dual fluidized bed steam gasification of biomass in an innovative bubbling fluidized bed methanation reactor with an optimized catalyst. Syngas from conventional gasification and a novel combination with syngas from sorption enhanced reforming were investigated. The applied fluidized bed reactor allowed an almost isothermal operation with optimal reaction temperatures between 320 °C–360 °C. Simultaneously, no chemical deactivation or mechanical attrition during 200 h of operation indicates a high long-term stability of the catalyst. The methane concentration downstream the methanation reactor increased from 43 to 74 vol.-%db through the methanation of a hydrogen-rich syngas produced via sorption enhanced reforming. Simultaneously, the methane yield is doubled to 95% and the hydrogen, carbon monoxide and carbon dioxide conversions are improved. Furthermore, it could be shown that a CO2 content below 1 vol.-%db is feasible in the (raw) synthetic natural gas, allowing grid injection without CO2 separation. The results indicate that sorption enhanced reforming in combination with an optimized fluidized bed methanation can lead to technical and economic improvements in sustainable synthetic natural gas production.

Apparent kinetics of the catalyzed water–gas shift reaction in synthetic wood gas

The catalysis of the water–gas shift reaction employing two commercially available catalysts was investigated. The applied feed was a synthetic gas mixture simulating the wood gas derived from the dual fluidized bed steam gasification of biomass. A Co/Mo- and an Fe/Cr-based catalyst were compared in a differentially operated plug flow reactor. The influence of the partial pressures of all reaction partners as well as the effect of temperature were studied, allowing the formation of two power law rate models.(1)r(Co/Mo)=0.044exp-66RTpCO1.28pH2O0.03pCO2-0.11pH2-0.351-1KpCO2pH2pCOpH2O(2)r(Fe/Cr)=300exp-102RTpCO1.37pH2O0.23pCO2-0.16pH2-0.111-1KpCO2pH2pCOpH2OThe CO conversion rates over both catalysts were strongly dependent on the sulfur load in the feed. The presented models were established at a constant H2S concentration of 100vol.ppmdb. At this sulfur load the Fe/Cr-based catalyst should be preferred to the Co/Mo-based catalyst. The partial pressure of H2S could not be included in the power law models because of its influence on the other coefficients of the model.

Reforming of tar contained in a raw fuel gas from biomass gasification using nickel-mayenite catalyst

Catalytic steam reforming of tar is a very efficient process to clean the gas produced by biomass gasification. Ni catalysts remain an affordable solution for this problem, even if this catalytic material suffers degradation due to carbon deposition and sulphur poisoning. In this study, the properties of a new catalyst Ni/Mayenite (Mayenite as binder), prepared by impregnation method and tested with a real gas obtained from a bench scale fluidized bed steam gasification of biomass, were investigated. Experiments were carried out in a microreactor fed by a slipstream coming from the bench scale gasifier to evaluate gas cleaning and upgrading options. Preliminary tests were carried out at three different temperatures, 700, 750 and 800 °C. In all the tests, the catalysts showed high activities reaching to a conversion rate of 90% in the case at highest temperature (800 °C). The conversion efficiency remained stable around this value during a 3 h test. A decrease in the performance was observed at 700 and 750 °C, even if the conversion remained stable around a lower value. An increase of H2 (>50%) and a decrease of CH4 were observed at all the temperatures, due to the occurrence of steam reforming reaction. A long duration test (12 h) was carried out at 800 °C and demonstrated that, at this temperature, the conversion was stable for a longer period.

Sorption-enhanced reforming with limestone from iron production

In this work, the experimental performance of sorption-enhanced reforming using limestone as bed material, which is used in raw iron production, is presented. Steam gasification of solid biomass by sorption-enhanced reforming process (SER) leads to product gas with high hydrogen content and low tar content. The product gas can be used for a wide range of applications. This includes heat and electricity production, synthetic fuels, and other downstream processes. On the basis of dual fluidized bed steam gasification of biomass (dual fluid gasification), a reactive bed material is used to enhance the formation of hydrogen. Blast furnaces in iron production operate on the principle of chemical reduction, whereby carbon monoxide and hydrogen reduce the iron to its elemental form. The present paper summarizes the results of an experimental investigation into SER with limestone usually used as a part of iron production. The illustrated results reflect the operation of sorption-enhanced reforming within an experimental facility at the Vienna University of Technology.

Corrosion behaviour of ceramic filter candle materials for hot gas filtration under biomass gasification conditions at 850°C

A compact version of a gasifier realised by integrating the fluidised bed steam gasification of biomass and the hot gas cleaning and conditioning system into one reactor vessel was the aim of the ‘UNIQUE’ project. Hot gas filtration systems are designed to protect the gas turbine or fuel cell from erosion and particle contamination, clean the process gases for production of synthetic fuels and indirectly improve efficiency and decrease maintenance. Knowledge of critical points of the porous ceramic filter elements is essential for the successful operation of the hot gas filtration. The corrosion behaviour of ceramic filter materials in contact with different biomass ashes under simulated gasification conditions was investigated for aluminium oxide, based SiC with mullite filter layer and mullite based filter candles. Analyses by energy dispersive X-ray spectroscopy show the influence of potassium on filter candle materials.

Laboratory investigations on chemical hot gas cleaning of inorganic trace elements for the “UNIQUE” process

The UNIQUE project aims at integrating the fluidized bed steam gasification of biomass and the hot gas cleaning and conditioning system into one reactor vessel. This paper outlines thermodynamic calculations and lab-scale experimental investigations on alkali removal and sour gas control. The results show that the alkali concentration in gasifier derived gases can be limited to values below 100ppbv using aluminosilicates. The H2S concentration can be limited to values above 100ppmv using conventional Ca or Cu based sorbents and to values below 1ppmv by a new Ba containing sorbent developed by Forschungszentrum Jülich. In addition, the Ba containing sorbent can also limit the HCl concentration to values below 1ppmv.

Performance of fluidized bed steam gasification of biomass – Modeling and experiment

This paper presents the investigation of the performance from different biomasses in a fluidized bed gasifier where steam has been used as gasifying as well as fluidizing agent. An experimental setup is fabricated to study the gasification performance of rice husk, which is of special relevance to rice-producing countries like China and India. An equilibrium modeling approach is deployed to predict the gas composition which has been compared with the experimental results. Calibration of the model with appropriate modeling coefficients was necessary to achieve close resemblance with the experimental values. Further, the model is used to predict the gas compositions from other biomass and benchmarked with the performance of coal. In this study, the gasification temperature is varied from 650 °C to 800 °C, whereas the steam-to-biomass ratio ( S/ B) is varied from 0.75 to 2.00. As the gasification temperature increases, the production of H 2 and CO increases but the generation of CH 4 and CO 2 reduces. The steam-to-biomass ratio was again found to influence the production rates. With increasing steam input, H 2, CO 2 and CH 4 were found to increase while CO reduces.

Comparison of dual fluidized bed steam gasification of biomass with and without selective transport of CO2

Abstract A comparison of dual fluidized bed gasification of biomass with and without selective transport of CO 2 from the gasification to the combustion reactor is presented. The dual fluidized bed technology provides the necessary heat for steam gasification by circulating hot bed material that is heated in a separate fluidized bed reactor by combustion of residual biomass char. The hydrogen content in producer gas of gasifiers based on this concept is about 40 vol% (dry basis). Addition of carbonates to the bed material and adequate adjustment of operation temperatures in the reactors allow selective transport of CO 2 (absorption enhanced reforming—AER concept). Thus, hydrogen contents of up to 75 vol% (dry basis) can be achieved. Experimental data from a 120 kW Fuel input pilot plant as well as thermodynamic data are used to determine the mass- and energy-balances. Carbon, hydrogen, oxygen, and energy balances for both concepts are presented and discussed.

Steam reforming of tar from a biomass gasification process over Ni/olivine catalyst using toluene as a model compound

A Ni/olivine catalyst, previously developed for biomass gasification and tar removal during fluidized bed steam gasification of biomass, was tested in a fixed bed reactor in toluene steam reforming as a tar destruction model reaction. The influence of the catalyst preparation parameters (nickel precursor, calcination temperature and nickel content) and operating parameters (reaction temperature, steam to carbon S/C ratio and space-time) on activity and selectivity was examined showing a high toluene conversion and a low carbon formation compared to olivine alone. The steam reforming of toluene was found to be of zero order for water and first order for toluene. Activation energy required for Ni/olivine was determined to be about 196kJmol−1 in accordance with literature. Catalyst activity and stability and its resistance against carbon formation were discussed on the basis of X-ray diffraction (XRD), transmission electron microscopy (TEM) and temperature programmed oxidation (TPO) results. Characterization before test (XRD, temperature programmed reduction (TPR), Mössbauer spectroscopy) have shown the presence of NiO–MgO solid solution, formed on the surface of olivine support, which explains the efficiency of the catalyst calcined at 1100°C. After test, Ni–Fe alloys were observed (TEM, Mössbauer spectroscopy). It was suggested that magnesium oxide enhanced steam adsorption, facilitating the gasification of surface carbon and that Ni–Fe alloys prevented carbon deposition by dilution effect.

Characterization of Ni−Fe/MgO/Olivine Catalyst for Fluidized Bed Steam Gasification of Biomass

Tar removal catalyst development is the main hurdle to improving the process of steam biomass gasification in a fluidized bed. A Ni/olivine catalyst has been previously developed to enhance the catalytic properties of calcined natural olivine and showed excellent performance and stability during biomass steam gasification in the fast internally circulating fluidized bed (FICFB) gasifier. However, the origin of its active phase was not well-understood. The present work explains the mechanism of formation and the nature of the active phase of the Ni/olivine catalyst, characterized before testing, after calcination, and after reduction by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), temperature-programmed reduction (TPR), and 57Fe Mossbauer spectroscopy. Two phenomena contribute to the formation of this active system: the formation of a NiO−MgO solid solution on the olivine surface during calcination and Ni−Fe alloys during the reduction, both of which are known to have beneficial e...