• Energy Research

AbstractIn many industrial processes, the climate-damaging gas CO2is produced as undesired by-product. The dual fluidized bed biomass gasification technology offers the opportunity to tackle this problem by using the produced CO2within the process as gasification agent. Therefore, a 100 kWthpilot plant at TU Wien was used to investigate the use of CO2as 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 CO2increased and the content of H2decreased in the product gas. These trends resulted in a declining H2/CO ratio and a decreasing lower heating value when CO2was 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 H2increased and CO2decreased. To determine the degree of conversion of CO2in 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 CO2was 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 CO2gasification.

Abstract The use of CO2 as gasification agent in the 100 kWth dual fluidized bed gasification pilot plant was investigated at TU Wien. For this purpose, steam was replaced stepwise by CO2 as gasification agent. Softwood was used as fuel and olivine as bed material. Starting from 100 vol.-% steam as gasification agent, substituting it by 32, 45 and finally 68 vol.-% CO2. All loop seals were fluidized further with steam, which resulted in these volume percentages. Additionally, a CO2 gasification test campaign converting softwood with a mixture (90/10 wt.-%) of olivine and limestone was investigated. For this case, the gasification agent was composed of 65 vol.-% CO2 and 35 vol.-% steam. The use of CO2 as gasification agent led to changes of the product gas. Instead of a H2-enriched product gas, which was produced during steam gasification, CO and CO2 occupied the major share of the product gas. Consequently, the H2/CO ratios as well as the lower heating values decreased when substituting steam by CO2. Tar contents were lower for CO2/steam gasification compared to pure steam gasification.

Understanding layer formation on bed materials used in fluidized beds is a key step for advances in the application of alternative fuels. Layers can be responsible for agglomeration-caused shut-dow ...

AbstractIn many processes proposed for biorefineries, recycling procedures, and industrial or agricultural production processes, residue is generated which could be further transformed by thermochemical conversion via gasification. The technology of dual fluidized bed steam gasification is capable of producing a valuable product gas out of such residue. The generated nitrogen-free product gas can be used for heat and power production and is suitable for separating gases (e.g. hydrogen). However, if the product gas is cleaned, its use as syngas is more beneficial for manufacturing renewable chemical substances, like synthetic natural gas, methanol, Fischer–Tropsch liquids, or mixed alcohols. This paper presents the results of experimental research from gasification test runs of different biogenic fuels, carried out with an advanced 100 kW pilot plant over the last 5 years at TU Wien. The focus is to provide an overview of measured results validated by mass and energy balances and to present key calculated performance indicating key figures of the test runs. In this way, the influence of various operational parameters and the composition of the product gas are evaluated. The presented results form the basis for the proper design of suitable gas-cleaning equipment. Subsequently, the clean syngas is available for several synthesis applications in future biorefineries.

Abstract Within this paper, investigations to convert softwood with four different types of bed materials in the 100 kWth dual fluidized bed steam gasification pilot plant at TU Wien are presented and discussed. The results of ten different experiments were compared. Quartz, olivine and feldspar were mixed with limestone in mass ratios of 100/0, 90/10, 50/50 and 0/100. Limestone was used due to its catalytic activity at high temperatures as CaO and thus enhanced tar, char and water conversion of quartz, olivine and feldspar. The admixture of limestone to quartz, olivine and feldspar shifted the product gas compositions towards higher hydrogen and carbon dioxide and lower carbon monoxide contents. By using 100 wt.-% limestone as bed material a hydrogen content of 47.4 vol.-% could be generated. Additionally, the tar concentrations as well as the tar dew points decreased and especially the heavy tar compounds could be reduced. Already small amounts of limestone (

Abstract The impact of the counter-current column of the gasification reactor of a 100 kWth dual fluidized bed steam gasification pilot plant on the product gas quality was investigated. Through the advanced design of the gasification reactor by operating the lower part as bubbling bed and the upper part as counter-current column, the gas-solid interactions between downward flowing hot bed material particles with upwards flowing product gas could be enhanced. This was realized by equipping the counter-current column with constrictions, which increase the residence time and the bed material hold-up. Thus, the conversion efficiency of the fuel including the tar was improved. For the investigations three different experimental campaigns converting softwood pellets using a mixture of olivine and limestone (50/50 wt.-%), a mixture of feldspar and limestone (50/50 wt.-%), and 100 wt.-% quartz as bed materials were conducted. Higher H2 contents and lower contents of higher hydrocarbons could be detected along the height of the counter-current column. Especially heavy tar compounds could be reduced significantly. These two effects are explained by enhanced water gas shift and steam reforming reactions. In case of catalytically inactive quartz, only thermal effects are available and therefore lower effects on tar reduction could be obtained.

Liquid phase pyrolysis oil was hydrodeoxygenated continuously with biogenous syngas by in situ water gas shift reaction.

AbstractEspecially carbon-intensive industries are interested in a decarbonization of their processes. A technology, which can contribute to a significant reduction of the carbon footprint, is the so-called sorption enhanced reforming process. The sorption enhanced reforming process uses a dual fluidized bed reactor system with limestone as a bed material for the thermochemical conversion of biomass into a valuable nitrogen-free product gas. This product gas can be used for further synthesis processes like methanation. The dependency of the product gas composition on the gasification temperature is already a well-known fact. Nevertheless, detailed investigations and models of the effect on elemental balances (especially carbon) of the process are missing in the literature and are presented in this work. Therefore, previously published data from different pilot plants is summarized and is discussed on a mass balance. Based on this information, investigations on the product gas equilibrium composition are presented and conclusions are drawn: it can be shown that the sorption enhanced reforming process can be divided into two sub-processes, namely “carbonation dominated sorption enhanced reforming” and “water-gas shift dominated sorption enhanced reforming.” The sub-process carbonation dominated SER is characterized by a high deviation from the water-gas shift equilibrium and a nearly constant CO content in the product gas over gasification temperature (< 700 °C). The sub-process water-gas shift dominated SER can be identified by a steep increase of the CO content in the product gas over temperature and nearly equilibrium state of the water-gas shift reaction (700–760 °C).