Schlüsselwörter
(Englisch)
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Manure, agricultural, biogas, gas cleaning, fuel cell
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Kurzbeschreibung
(Deutsch)
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Mit diesem Projekt soll im Pilotmassstab währen 500 Stunden der Nachweis erbracht werden, dass Biogas aus der Güllevergärung ausreichend für die Hochtemperaturbrennstoffzellenanwendung gereinigt werden kann. Mit dieser Gülle-zu-Strom-Technologie soll eine signifikante Nutzung des bisher ungenutzten Güllepotentials ermöglicht werden. Die Erkenntnisse aus diesem Projekt fliessen direkt in zukünftige Biogas-Brennstoffzellen-Demoprojekte ein
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Kurzbeschreibung
(Englisch)
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This project will demonstrate a pilot scale gas cleaning system with removes contaminants from manure biogas to satisfy the requirements of high-temperature fuel cells. The use of fuel cells, which have high efficiencies even at small scales and part load, could serve to mobilise manure resources. Once validated in long-duration operation (500 hours) at a farm site, the gas cleaning concept can be used directly in future fuel cell demonstrations.
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Schlussbericht
(Englisch)
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This project aims to validate a robust sorption-based gas cleaning system, which removes the contaminants from manure-derived biogas to a degree that is suitable for high-temperature fuel cells, i.e. SOFC. Sulphur and siloxanes are critical compounds for SOFC
We present detailed results of our biogas sampling campaigns performed in 2018 at three Swiss agricultural biogas production sites to study the variation in trace contaminants affecting fuel cells and gas cleaning systems. As expected we could confirm the large variability of contaminants in the raw biogas mainly depending of the feedstock digested and the importance of removing organic sulphur.
Systems for biogas cleaning were assessed by a techno-economic survey of technically feasible options, including the consideration of supplier quotations. In a lab-based test bench using a synthetic biogas mixture, sorbents were evaluated for their capacity for dimethyl sulfide (DMS), as we consider DMS as one of the most difficult organic sulphur compounds to be removed.
A fully automated sulphur chemiluminescence detector (SCD) system was build and commissioned which allows online measurement of total sulphur at concentrations far below 0.5 ppmv. For SOFC application this concentration level is considered as the targed value for a cleaned biogas. This unique online SCD system is considered as critical for testing and evaluating gas cleaning concepts for SOFC application. This analytical system allows a fast testing of different designs and operation conditions tested at pilot scale or in the commissioning phase of demonstration plants.
Based on the sorbent selection in lab tests and on techno-economic considerations this project culminates in a pilot-scale field demonstration of biogas cleaning to a degree that should be suitable for SOFC. The best sorbent experiment performed until end of August 2019, was an experiment with SulfaTrap R7 & CuO-AC for the duration of 200 hrs. During the first 150 hrs of the experiment, no measureable sulphur breakthrough was observed after the second bed. Nevertheless further tests on sorbent materials are needed in order to prepare a scale up of a gas cleaning system. It is not yet fully clear, what the critical factors are for the observed limitation of sorbent capacity for organic sulphur. One hypothesis is that the measured capacity of sorbent material for DMS is dominated by physisorption.
This project has been extremely valuable to further improve the testing capabilities for gas cleaning systems. The application of cleaned biogas from agriculture in a SOFC is most likely one of the most difficult cases. One reason is that the cleaned biogas should not differ much from natural gas in term of gas quality, temperature and pressure. This would allow to use turn-key SOFC systems for biogas application, which have originally be designed for natural gas operation. However, this would also mean, that the biogas should be cleaned at room temperature and low pressure in order to keep the biogas cleaning system simple. From a chemical point of view of the gas cleaning increasing temperature and pressure are both advantageous for a better gas cleaning (technical, economic).
We expect that knowledge of this project will be transfer to other biogas value chains. This can be either for different end uses of the biogas, such as biogas cleaning for upgrading plants based on membrane or scrubbers as well as catalytic methanation. For each value chain a review of the specification of the end use system is needed as well as for the raw gas quality in order to select best option in sorption based gas cleaning. Given the high variance of raw gas qualities and required clean biogas qualities most likely for each value chains a dedicated gas cleaning system has to be designed. Whenever possible these gas cleaning solutions should be built on “standard building block”, which can be easily combined for specific applications.
Our project has confirmed that a fundamental understanding of all relevant processes in gas cleaning is critical for a smart design of gas cleaning systems and good collaboration between industry and academia is a key to success.
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