Chemical Looping Gasification for Sustainable Production of Biofuels – The CLARA Project

Within the scope of the Horizon 2020 project CLARA, a novel biomassto-biofuel process chain is being developed. The fuel production plant consists of a chemical looping gasifier for the production of a raw syngas, a gas treatment train to provide the required syngas composition for the subsequent synthesis, and a FischerTropsch (FT) reactor to covert the syngas into liquid FT-crude. This crude can then be purified and upgraded to ready-to-use second generation drop-in biofuels in existing state-of-the-art refineries. So far, various oxygen carrier materials were evaluated through lab-scale test regarding their suitability for chemical looping gasification. Ilmenite proved to be the most promising candidate and was therefore selected for further investigations. Successful test campaigns in a small CLG pilot unit supported the findings made in lab-scale units. A novel pre-treatment concept of wheat straw based on pelleting and additivation was developed, which allows for an economic decentralized production and avoids bed agglomeration in a chemical looping gasifier. Furthermore, a novel sour gas separation concept, allowing for an efficient removal of H2S from sour gases, was successfully tested at lab-scale. Based on the underlying technologies, the project partners derived an optimized process layout of the entire biomass-to-liquid chain, achieving competitive figures for the most important key performance indicators, such as attaining negative CO2 emissions and achieving an energetic fuel efficiency of 55 % for the entire process chain. The full process chain has been demonstrated within four weeks of pilot testing at the Technical University of Darmstadt. Currently, the full-chain BtL concept is being assessed by means of risk studies as well as techno-economic and environmental considerations

Effect of pre-treatment of herbaceous feedstocks on behavior of inorganic constituents under chemical looping gasification (CLG) conditions

Biomass chemical looping gasification (BCLG) is a promising key technology for producing carbon neutral liquid biofuels. However, various ash-related issues, such as bed agglomeration, fouling and slagging, or high-temperature corrosion may cause significant economic and ecologic challenges for reliable implementation of BCLG. Biomass pre-treatment methods, such as torrefaction, (water-)leaching and combination of both approaches may significantly improve ash-related characteristics and therefore provide a promising approach for enabling the use of herbaceous residues. This study deals with essential lab-scale investigations under well-defined, gasification-like conditions at 950 °C, joint with thermodynamic equilibrium calculations. Fundamental knowledge on the influence of pre-treatment methods on the release and fate of volatile inorganics as well as on the ash melting behavior of the residual ashes was gained. Molecular Beam Mass Spectrometry (MBMS) was applied for in situ online hot gas analysis of (non-)condensable gas species during gasification of pre-treated feedstocks. Both ash composition and behavior were characterized particularly by X-ray powder diffraction method and hot stage microscopy (HSM). The results obtained by chemical characterization were taken into account for thermodynamic modelling. Based on the results, conclusions were drawn on how different pre-treatment technologies can help to improve and solve ash-related issues during thermochemical conversions. It has been demonstrated that (combined) pre-treatment methods can counteract the above-mentioned problems and have a noticeable effect on the principal inorganic constituents (e.g. K, Ca, Si) originating from the ash by shifting their proportions

Investigations on the Effect of Pre-Treatment of Wheat Straw on Ash-Related Issues in Chemical Looping Gasification (CLG) in Comparison with Woody Biomass

Biomass chemical looping gasification (BCLG) is a promising autothermic route for producing sustainable, N2-free, and carbon neutral syngas for producing liquid biofuels or high value hydrocarbons. However, different ash-related issues, such as high-temperature corrosion, fouling and slagging, bed agglomeration, or poisoning of the oxygen carrier might cause significant ecologic and economic challenges for reliable implementation of BCLG. In this work, lab-scale investigations under gasification-like conditions at 950 °C and thermodynamic modelling were combined for assessing the influence of composition, pre-treatment methods, such as torrefaction and water-leaching, and Ca-based additives on the release and fate of volatile inorganics, as well as on ash melting behavior. A deep characterization of both (non-)condensable gas species and ash composition behavior, joint with thermodynamic modelling has shown that different pre-treatment methods and/or Ca-additives can significantly counteract the above-mentioned problems. It can be concluded that torrefaction alone is not suitable to obtain the desired effects in terms of ash melting behavior or release of problematic volatile species. However, very promising results were achieved when torrefied or water-leached wheat straw was blended with 2 wt% CaCO3, since ash melting behavior was improved up to a similar level than woody biomass. Generally, both torrefaction and water-leaching reduced the amount of chlorine significantl

Combustion properties and quality of the perennial wild plants common tansy (Tanacetum vulgare L.), common knapweed (Centaurea nigra L.) and mugwort (Artemisia vulgaris L.)

Perennial wild plants (PWPs) common tansy, common knapweed and mugwort not only provide biomass for biogas production, but also food supply for pollinators and versatile habitats for open land animals. These ecosystem services could be improved shifting the harvest date from late summer to late winter and using the PWPs for thermochemical conversion instead of anaerobic digestion

Improving the calorific value and overall combustion characteristics of Miscanthus by adding biomass of certain perennial herbaceous wild plant species

Aim and approach used: Miscanthus (ANDERSSON) is a promising perennial industrial crop whose biomass can be used for both bioenergy and biobased products. In view of increasing land use conflicts between food crop cultivation, nature conservation and urbanization, it is a positive aspect that the cultivation of Miscanthus can be carried out on so-called marginal agricultural areas. However, Miscanthus inflorescences do not provide nectar or pollen, so diversification measures are required to increase the biodiversity supporting ecosystem services of Miscanthus-dominated regions. The co-cultivation of perennial flower-rich wild plant species (WPS) could function as biodiversity hotspots in these regions. Furthermore, Miscanthus and the WPS biomass have already showed high suitability for combustion. However, it is still unknown how a substrate mix of Miscanthus and WPS performs qualitatively. This study assesses the effects of mixing the biomass from WPS and Miscanthus on the calorific value and the overall combustion characteristics. Plant material from a long-term field trial in Southwest Germany was used for analyzing both higher heating value, ash melting behavior, lignocellulosic composition and relevant macro and trace elements. The biomass yield was not considered in this study.Scientific innovation and relevance: The innovation of this study lies within the concept of improving the overall ecosystem service performance of Miscanthus cultivation at farm scale, especially with regard to biodiversity friendliness, through agricultural diversification. The results are relevant because they show the possibility to improve both ecosystem services and biomass quality by combining different types of plant biomasses. This will demonstrate the potential synergies between ecosystem services and economic feasibility in biomass production. Results and conclusions: As expected, the addition of WPS biomass did not affect the calorific value of Miscanthus biomass, but it improved the overall combustion characteristics of Miscanthus biomass. The latter was indicated by both an improved ash melting behavior and an increase of the calculated critical temperature (when 100% of ash is molten). For example, the addition of 30% common tansy (Tanacetum vulgare L.) dry matter biomass to Miscanthus dry matter biomass resulted in an increase of the critical temperature from 1000 °C to 1200 °C. These results indicate that the addition of biomass from WPS like common tansy could reduce maintenance costs of incineration plants and thus compensate for lower biomass yield levels compared with Miscanthus. Consequently, this study provides an example for how to improve overall ecosystem services of biomass production at farm scale without impeding economic feasibility, and thereby contributing to the development of a sustainable bioeconomy

Improving the calorific value and overall combustion characteristics of Miscanthus by adding biomass of certain perennial herbaceous wild plant species

Aim and approach used: Miscanthus (ANDERSSON) is a promising perennial industrial crop whose biomass can be used for both bioenergy and biobased products. In view of increasing land use conflicts between food crop cultivation, nature conservation and urbanization, it is a positive aspect that the cultivation of Miscanthus can be carried out on so-called marginal agricultural areas. However, Miscanthus inflorescences do not provide nectar or pollen, so diversification measures are required to increase the biodiversity supporting ecosystem services of Miscanthus-dominated regions. The co-cultivation of perennial flower-rich wild plant species (WPS) could function as biodiversity hotspots in these regions. Furthermore, Miscanthus and the WPS biomass have already showed high suitability for combustion. However, it is still unknown how a substrate mix of Miscanthus and WPS performs qualitatively. This study assesses the effects of mixing the biomass from WPS and Miscanthus on the calorific value and the overall combustion characteristics. Plant material from a long-term field trial in Southwest Germany was used for analyzing both higher heating value, ash melting behavior, lignocellulosic composition and relevant macro and trace elements. The biomass yield was not considered in this study.Scientific innovation and relevance: The innovation of this study lies within the concept of improving the overall ecosystem service performance of Miscanthus cultivation at farm scale, especially with regard to biodiversity friendliness, through agricultural diversification. The results are relevant because they show the possibility to improve both ecosystem services and biomass quality by combining different types of plant biomasses. This will demonstrate the potential synergies between ecosystem services and economic feasibility in biomass production. Results and conclusions: As expected, the addition of WPS biomass did not affect the calorific value of Miscanthus biomass, but it improved the overall combustion characteristics of Miscanthus biomass. The latter was indicated by both an improved ash melting behavior and an increase of the calculated critical temperature (when 100% of ash is molten). For example, the addition of 30% common tansy (Tanacetum vulgare L.) dry matter biomass to Miscanthus dry matter biomass resulted in an increase of the critical temperature from 1000 °C to 1200 °C. These results indicate that the addition of biomass from WPS like common tansy could reduce maintenance costs of incineration plants and thus compensate for lower biomass yield levels compared with Miscanthus. Consequently, this study provides an example for how to improve overall ecosystem services of biomass production at farm scale without impeding economic feasibility, and thereby contributing to the development of a sustainable bioeconomy

Fate of ilmenite as oxygen carrier during 1 MWth chemical looping gasification of biogenic residues

Chemical looping gasification (CLG) is a novel gasification technology, allowing for the efficient conversion of different solid feedstocks (e.g. biogenic residues) into a high-calorific syngas. As in any chemical looping technology, the oxygen carrier (OC), transporting heat and oxygen from the air to the fuel reactor, is crucial in attaining high process efficiencies. To investigate the fate of the OC during CLG in an industrial environment, ilmenite samples, collected during >400 hours of chemical operation in 1 MWth scale using three different biomass feedstocks, were analyzed using different lab techniques. In doing so, changes in OC particle morphology and composition induced by CLG operation were determined. Moreover, the most important physical and chemical characteristics of the utilized OC were measured. The ensuing dataset allowed for an in-depth evaluation of the CLG technology in semi-industrial scale in terms of OC lifetime and durability. It was found that in the absence of agglomeration, the cycled OC exhibits an oxygen transport capacity of 2.6 wt.-%, a particle density of 3400 kg/m3 and particle diameters between 60 and 250 µm in steady-state conditions. Moreover, it was found that OC loss via particle attrition determines the lifetime of the OC inside the 1 MWth CLG system. On the other hand, feedstock-related agglomeration, observed during CLG operation with wheat straw, was shown to impede OC circulation between AR and FR and thus prevent efficient CLG operation. In summary, the present study thus not only highlights that generally long-term CLG operation in industry-like conditions is feasible, but also provides important insights into measures to improve OC lifetime and durability inside an industrial chemical looping system, such as an optimization of cyclone efficiency or tailored pre-treatment of the utilized feedstock