Abstract
A 100 kWth dual fluidized bed steam gasification pilot plant has been developed at TU Wien to convert different types of biogenic fuels into a valuable product gas. In this paper, the conversion of different biogenic fuels in combination with the utilization of CO2 as alternative gasification agent was investigated in the mentioned pilot plant. For this purpose, five experimental campaigns were carried out aiming at the investigation of softwood as reference fuel, and rapeseed cake, bark and lignin as alternative fuels. Pure olivine as well as a mixture (90/10 wt%) of olivine and limestone were used as bed materials. The product gas compositions of the different biogenic fuels changed depending on the elemental composition of the biogenic fuels. Thus, a high amount of carbon in the fuel enhanced CO formation, whereas an increased content of oxygen led to higher CO2 contents. Additionally, the presence of alkali metals in the biomass ash favoured the production of CO. The addition of limestone enhanced the H2 and CO contents via the water gas shift reaction as well as steam and dry reforming reactions, but had no significant effect on tar contents. Overall, this paper presents the feasibility of the dual-fluidized bed gasification process of different biogenic fuels with CO2 as gasification agent.
Highlights
In November 2016, the European Union published a recast of the Renewable Energy Directive–Recast to 2030 (RED II) to strengthen the awareness of the countries regarding the mitigation of the effects of the climate change
Through the gasification of biomass and the recycling of produced CO2 within the process, a high-valuable product gas can be generated, which could be further upgraded to synthetic fuels
This work focuses on the dual fluidized bed (DFB) CO2/steam biomass gasification, which has a great potential in this field and is a main research topic at TU Wien since many years
Summary
In November 2016, the European Union published a recast of the Renewable Energy Directive–Recast to 2030 (RED II) to strengthen the awareness of the countries regarding the mitigation of the effects of the climate change. Due to the fact that CO2 emissions account for about 80% of the overall greenhouse gas emissions [3], negative values of CO2 emissions are required to mitigate the climate change effects This was reported by IPCC in 2014 [4]. The development of efficient technologies with the aim of recycling CO2 within the processes is necessary In this way, it is possible to influence the closing of the overall carbon cycle in a positive way and reduce CO2 emissions at the same time. The use of CO2 instead of steam presents a novel possibility of reducing CO2 emissions within the DFB process and producing a CO-rich product gas. The following points make the use of CO2 as gasification agent in the DFB biomass gasification process attractive: a) The recycling and reuse of CO2 within the process. b) The decrease of CO2 emissions at the same time. c) The positive influence on the overall carbon cycle. d) No heat and water requirement, which would be needed for the generation of steam [6, 7]
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