Dual Fluidized Bed Biomass Steam Research Articles

Techno-economic assessment of hydrogen production based on dual fluidized bed biomass steam gasification, biogas steam reforming, and alkaline water electrolysis processes

In this paper, three CO2-neutral H2 production processes were investigated. The three employed technologies were dual fluidized bed (DFB) biomass steam gasification, biogas steam reforming (BSR), and alkaline electrolysis (AEL) powered by renewable electricity with their necessary downstream separation and purification process steps. Aspen Plus process simulations were carried out in order to calculate the mass and energy balances of the three processes. In addition, a techno-economic assessment was carried out for a fictitious business producing H2 at a rate of 90kgh−1 in Austria in 2016. This assumption was used so that the economic feasibility of these investigated processes could be directly compared.The simulation results show that the DFB biomass steam gasification process has a higher H2 conversion rate (51.4%) but a lower fuel based H2 production efficiency (38.9%) than the BSR process (27.2% and 47.0%, respectively). Moreover, the alkaline electrolysis process shows the highest energy based H2 conversion efficiency at about 66%.The results of the economic assessment show that the DFB biomass steam gasification process has investment costs of 12.1 MEUR followed by the biogas steam reforming process with investment costs of 9.9 MEUR. The alkaline electrolysis process has investment costs of 4.4 MEUR. However, the after tax H2 break-even price of the DFB process is the lowest with 0.148EURkWh−1. The BSR process has an after tax H2 break-even price of 0.152EURkWh−1 and the AEL process has an after tax H2 break-even price of 0.191EURkWh−1. The net present value (NPV) calculations reveal that the BSR process has the highest NPV, followed by the AEL process and the DFB biomass steam gasification process. However, the NPV of all three processes are very similar. In general, all three H2 production processes perform at the same level based on the results of the process simulation and the chosen economic assumptions.

An experimental approach aiming the production of a gas mixture composed of hydrogen and methane from biomass as natural gas substitute in industrial applications

This work presents an experimental approach aiming the production of a gas mixture composed of H2 and CH4, which should serve as natural gas substitute in industrial applications. Therefore, a lab-scale process chain employing a water gas shift unit, scrubbing units, and a pressure swing adsorption unit was operated with tar-rich product gas extracted from a commercial dual fluidized bed biomass steam gasification plant. A gas mixture with a volumetric fraction of about 80% H2 and 19% CH4 and with minor fractions of CO and CO2 was produced by employing carbon molecular sieve as adsorbent. Moreover, the produced gas mixture had a lower heating value of about 15.5MJ·m−3 and a lower Wobbe index of about 43.4MJ·m−3, which is similar to the typical Wobbe index of natural gas.

Hydrogen production within a polygeneration concept based on dual fluidized bed biomass steam gasification

Dual fluidized bed biomass steam gasification generates a high calorific, practically nitrogen-free product gas with a volumetric H2 content of about 40%. Therefore, this could be a promising route for a polygeneration concept aiming at the production of valuable gases (for example H2), electricity, and heat. In this paper, a lab-scale process chain, based on state of the art unit operations, which processed a tar-rich product gas from a commercial dual fluidized bed biomass steam gasification plant, is investigated regarding H2 production within a polygeneration concept. The lab-scale process chain employed a water gas shift step, two gas scrubbing steps, and a pressure swing adsorption step. During the investigations, a volumetric H2 concentration of 99.9% with a specific H2 production of 30 g kg−1 biomass was reached. In addition, a valuable off-gas stream with a lower heating value of 7.9 MJ m−3 was produced. Moreover, a techno-economic assessment shows the economic feasibility of such a polygeneration concept, if certain feed in tariffs for renewable electricity and H2 exist. Consequently, these results show, that the dual fluidized bed biomass steam gasification technology is a promising route for a polygeneration concept, which aims at the production of H2, electricity, and district heat.

Development and experimental validation of a water gas shift kinetic model for Fe-/Cr-based catalysts processing product gas from biomass steam gasification

This paper introduces an improved kinetic model for the water gas shift reaction catalyzed by an Fe-/Cr-based catalyst. The improved model is based on a former model which was developed previously in order to consider the composition and the catalyst poisons (H2S) of product gas derived from dual fluidized bed biomass steam gasification.rφiT=117.8molgPa1.71s⋅exp−126.6kJmolR⋅T⋅pCO1.77⋅pH2O0.23⋅pCO2−0.17⋅pH2−0.121−KMALKg.\\documentclass[12pt]{minimal}\t\t\t\t\\usepackage{amsmath}\t\t\t\t\\usepackage{wasysym}\t\t\t\t\\usepackage{amsfonts}\t\t\t\t\\usepackage{amssymb}\t\t\t\t\\usepackage{amsbsy}\t\t\t\t\\usepackage{mathrsfs}\t\t\t\t\\usepackage{upgreek}\t\t\t\t\\setlength{\\oddsidemargin}{-69pt}\t\t\t\t\\begin{document}$$ \\begin{array}{c}r\\left({\\varphi}_i,T\\right)=117.8\\ \\frac{\\mathrm{mol}}{g\\ {Pa}^{1.71}\\ s}\\cdot \\mathit{\\exp}\\left(\\frac{-126.6\\ \\frac{\\mathrm{kJ}}{\\mathrm{mol}}}{R\\cdot T}\\right)\\cdot {p}_{CO}^{1.77}\\cdot {p}_{\\mathrm{H}2\\mathrm{O}}^{0.23}\\cdot {p}_{CO2}^{-0.17}\\cdot {p}_{\\mathrm{H}2}^{-0.12}\\\\ {}\\left(1-\\frac{K_{MAL}}{K_g}\\right)\\end{array}. $$\\end{document}Furthermore, this improved model has been validated with experimental data. The data was generated by a WGS reactor which employed a commercial Fe-/Cr-based catalyst and which processed real product gas from the dual fluidized bed biomass steam gasification plant in Oberwart, Austria. Basically, the validation showed good agreement of the measured and the calculated values for the gas composition (absolute errors of the volumetric fractions of up to 1.5 %) and the temperature profile (absolute errors of up to 21 °C) of the WGS reactor. Of all considered gas components, the CO concentration showed the highest error.The results qualify the improved kinetic model for basic design and engineering of a WGS reactor employing a commercial Fe-/Cr-based catalyst which processes product gas from an industrial scale biomass steam gasification plant.

Behavior of GCMS tar components in a water gas shift unit operated with tar-rich product gas from an industrial scale dual fluidized bed biomass steam gasification plant

In this paper, the behavior of gas chromatography mass spectroscopy (GCMS) tar components in a three-stage water gas shift (WGS) unit is discussed. The GCMS tar measurements were carried out during the long-term operation (2250 h) of a WGS unit with tar-rich product gas from the commercial biomass steam gasification plant in Oberwart, Austria. In order to investigate the behavior of the GCMS tar components, four tar measurements were performed during the long-term operation of the WGS unit which employed a commercial Fe/Cr-based catalyst. The tar-rich product gas was extracted before reaching the scrubbing unit of the biomass steam gasification plant, therefore, the extracted gas contained a high amount of tar. In order to investigate the behavior of the GCMS tar in the WGS unit, the GCMS tar concentrations were determined at the inlet and the outlet of the WGS unit. The samples were taken during full load operation and during partial load operation of the WGS unit, respectively, the biomass steam gasification plant. In addition to the increase of the volumetric hydrogen content from about 40 % (d.b.) to 50 % (d.b.), the amount of GCMS tar was reduced (up to 38 %) as the gas passed through the WGS unit. No catalyst deactivation was observed. Furthermore, the efficiency of the hydrogen increase or the GCMS tar reduction did not depend on whether the operation of the WGS unit, respectively, the gasification plant was at partial load or full load.

2250-h long term operation of a water gas shift pilot plant processing tar-rich product gas from an industrial scale dual fluidized bed biomass steam gasification plant

In this paper, the performance of a water gas shift (WGS) pilot plant which processed tar-rich product gas for about 2250 h is investigated. The WGS pilot plant employed a commercial Fe/Cr based catalyst (ShiftMax® 120). The product gas was generated by the industrial scale and commercial dual fluidized bed (DFB) biomass steam gasification plant in Oberwart, Austria. A partial flow of tar-rich product gas was extracted for the WGS pilot plant before the tar scrubber of the gasification plant. The extracted product gas had a temperature of about 150 °C and a GCMS tar content between 2.7 and 8.2 g m−3 (d.b.). In order to investigate the stability of the catalyst and to observe the performance of the WGS pilot plant, extensive chemical analyses were carried out: CO, CO2, CH4, N2, O2, C2H6, C2H4, C2H2, H2S, COS, and C4H4S were measured. In addition, GCMS tar and NH3 analyses were performed. Furthermore, the catalyst's activity was observed by measuring the temperature profiles along the reactors of the three stage WGS pilot plant. During the about 2250 h of operation, no significant catalyst deactivation could be observed. A CO conversion of up to 92% as well as a GCMS tar reduction along the WGS pilot plant was obtained. The results showed that the application of a commercial Fe/Cr based catalyst in a WGS unit seems to be a suitable way for increasing the hydrogen content in a product gas generated by dual fluidized bed biomass steam gasification. Furthermore, with such a technique, it is possible to optimally adjust the required CO/H2 ratio for several synthesis reactions, for example, methanation and Fischer-Tropsch synthesis.

The mechanism of bed material coating in dual fluidized bed biomass steam gasification plants and its impact on plant optimization

The bed material and especially its catalytic activity plays an important role in biomass steam gasification in dual fluidized bed gasifiers. The bed material is modified by interaction with biomass ash during operation of the gasification plant forming layers at the particles which are induced by the biomass ash. Optimization of dual fluidized biomass steam gasification will have significant influence on the process variables such as temperatures, inorganic composition and product gas composition. The influence of these changes on layer formation is still unknown. This paper summarizes results of investigations about bed material characteristics taken from the industrial-scale biomass steam gasification plant in Güssing where woody biomass is used as fuel. Analyses of the surface and the crystal structures of the bed material particles treated in gasification and combustion atmospheres were carried out. The thermal behavior of used olivine and fresh olivine in different atmospheres was analyzed. A suggestion for the mechanism of formation of the layers is presented and the influence of possible optimization measures is discussed. A change in the elemental composition of the surface was not detectable but a slight change in the crystal structure. Thermal investigations show a weak endothermic weight loss with used olivine in a CO2-rich atmosphere which could not be determined with fresh olivine. The formation of layers at the olivine particles is considered to be caused by the intensive contact with burning char particles in the combustion reactor.

Fluid-Dynamic Investigations in a Scaled Cold Model for a Dual Fluidized Bed Biomass Steam Gasification Process: Solid Flux Measurements and Optimization of the Cyclone

Gasification of biomass is an attractive technology for combined heat and power (CHP) production. A dual fluidized bed steam gasifier is in commercial operation at the biomass CHP plant in Guessing/Austria since 2002. For circulating fluidized bed applications the bed material consumption is economically crucial. Thus, cyclones for circulating fluidized beds need to be designed properly. Some erosion and caking in the cyclone of the gasifier could be observed with increasing hours of operation. The influences of these effects as well as the influence of the solid circulation rate between the two units on the separation efficiency were investigated by fluid-dynamic investigations using a scaled cold model. The results show that due to erosion and caking elutriation rates are increased, especially for smaller particles. However, the cyclone achieves fractional separation efficiencies of more than 99.9%.

Model development and validation: Co-combustion of residual char, gases and volatile fuels in the fast fluidized combustion chamber of a dual fluidized bed biomass gasifier

A one-dimensional steady state model has been developed for the combustion reactor of a dual fluidized bed biomass steam gasification system. The combustion reactor is operated as fast fluidized bed (riser) with staged air introduction (bottom, primary and secondary air). The main fuel i.e., residual biomass char (from the gasifier), is introduced together with the circulating bed material at the bottom of the riser. The riser is divided into two zones: bottom zone (modelled according to modified two phase theory) and upper zone (modelled with core-annulus approach). The model consists of sub-model for bed hydrodynamic, conversion and conservation. Biomass char is assumed to be a homogeneous matrix of C, H and O and is modelled as partially volatile fuel. The exit gas composition and the temperature profile predicted by the model are in good agreement with the measured value.

Development of catalytic tar decomposition downstream from a dual fluidized bed biomass steam gasifier

Gasification of biomass is an attractive technology for combined heat and power production. Although a lot of research and development work has been carried out during the past decade the commercial breakthrough for this technology is still to come. One problem that has not been completely solved so far is the tar content in the product gas, which can cause plugging in the colder parts of the plant. Among the possible gas cleaning methods, catalytic hot gas cleaning is rather promising because of the complete destruction of the tars instead of creating a waste stream which is difficult to dispose. Different catalysts were measured in laboratory scale reactors fed by synthetic gas mixtures and tar model compounds. Commercial steam-reforming catalysts for heavy hydrocarbons (particularly naphthas) proved best as tar decomposing catalysts. Based on these results 3 nickel-based monolith type of catalyst were produced and afterwards tested in a laboratory scale reactor fed by slip streams taken from the 8 MW dual fluidized bed steam gasifier plant in Güssing, Austria. Almost complete tar and considerable ammonia decomposition could be achieved over this catalyst at temperatures above 850 °C and space velocities of about 1100 h − 1 .

Modelling and simulation of the biomass fired dual fluidized bed gasifier at Guessing/Austria

l steady state model of the gasification reactor of a dual fluidized bed biomass steam gasification system has been developed. The gasification reactor is operated in bubbling regime. The model distinguishes two zones: dense zone and freeboard zone. The dense zone is the bubbling bed and is modelled with modified two phase theory while freeboard is modelled as a plug flow reactor. The main fuel is biomass (wood) and is introduced into the dense zone. Biomass is modelled as a homogeneous matrix of C, H, and O. The solids within the dense zone are considered to be well mixed while the gases are in plug flow regime. Energy balance is solved globally in each zone. Results show that the wood is only partly converted in the gasifier. The gas composition profile and temperature profile predicted by the model is in good agreement with the values measured at 8 MW (fuel power) plant in Guessing/Austria.

In-Bed Catalytic Tar Reduction in a Dual Fluidized Bed Biomass Steam Gasifier

A nickel-enriched catalytic bed material was tested for tar reduction in a 100 kWth dual fluidized bed biomass steam gasifier. Gas composition and tar content were measured after the reactor and compared with data from gasification tests without a catalytic bed material. H2, CO, CO2, and CH4 contents in the product gas, as well as tar conversion rates, are reported for different amounts of catalytic active bed material and different operating conditions. Water conversions, gas yields, and lower heating values were calculated. The catalyst showed no noticeable deactivation in two tests of 30 and 45 h. These results obtained at the pilot scale represent an important intermediate step in preparing the technical breakthrough of dual fluidized bed biomass steam gasification.