ERK5-1999-00007 Holistic integration of MCFC technology towards a most effective systems compound using Biogas as a renewable source of energy

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Chemical Conversion : EESD (Energy, Environment and Sustainable Development) : Electricity : Thermochemical Conversion

Proposal No:	ERK5-1999-00007
Date Prepared:	February 2004
Source:	European Bio-Energy Projects (EUR 20808)

Introduction

Anaerobic digestion (AD) involves the breakdown of organic waste by bacteria in an oxygen-free environment. The biogas produced as a result is, as a renewable energy CO₂ neutral. By converting the chemical energy into electrical energy in a high temperature fuel cell, it is possible to increase the electricity output in comparison to conventional CHP). This does not only produce less CO₂ emissions per produced kWh (in comparison with classical CHPs) but it also has been proven that using biogas as fuel is followed by a drastic decrease of regional emissions of methane.

Furthermore, MCFC's have the lowest NO_x, SO₂ and VOC emission-levels compared to other conventional systems. Another feature of the high temperature fuel cell is that a part of the thermal energy, which is created in the electrochemical process, can be consumed directly at the location where it is released. This internal heat removal happens during the conversion of the methane into the electrochemical active species, hydrogen, which is an endothermal process and known as "Internal Reforming".

Until now, hardly any experience has been gained concerning the utilization of biogas in fuel cells. Innovative aspects are the development of the gas cleaning units for biogas, to remove especially H₂S, as well as endurance and performance information on MCFC - gas cleaning unit. Finally a novel technique, based on adapted Quality Function Deployment (QFD) for the holistic technology integration is used. QFD will enable the identification of optimal locations for the MCFC-Biogas plant compound in Austria, Spain and Slovakia.

The major innovative step is however the combination of MCFC's and Biogas technology. Therefore answers concerning:

• the gas upgrading (reliability, costs#),
• the endurance and performance of the MCFC system with slightly changing gas quality and composition and
• the integration of the technology in the market have to be analysed and/or improved.

Activities

The multidisciplinary and multisectorial approach of the project and the composition of the consortium promises successful teamwork.

Two gas cleaning units have been developed, one based on a biological and the other on a chemical principle, that reduce H₂ S in Biogas from 300 ppm (=state of the art) to under 10 ppm.

The expected endurance of MCFC's using Biogas as fuel is to be confirmed with two testbeds, each comprising a 300 W MCFC-lab size stack, manufactured by MTU, and their respective gas cleaning units. One of the testbeds (mobile) is coupled with the chemical gas cleaning unit and is being tested in three different locations with different gas qualities. The second testbed (stationary) is coupled with the biological gas cleaning unit and is meant to be used for long term tests.

Nontechnical barriers such as economic, logistic, legal and social aspects are being assessed in Austria, Spain, Germany and Slovakia for the technology integration of the systems compound.

Progress

After the first material analysis it can be said in a preliminary way, that Biogas does not harm the fuel cell in no way. It moreover increases its efficiency. The work performed on the technical side of the project was the development of both the chemical as well as the biological gas cleaning units with their subsequent analytical tests. This included the setting of common interfaces between the gas cleaning units, biogas plants and the MCFC unit.

Biological gas cleaning unit: Preliminary results show that the H₂ S concentration in the outlet biogas is always under 10 ppm with an inlet of approximately 400 ppm H₂ S.

The chemical biogas upgrading system has achieved together with the first MCFC test cycle also values of under 10 ppm.

Single cell tests have been performed in order to find out the impact of NH₃ on the cells. The observations were the following:

• A slight break through of ammonia was observed.
• The amount of ammonia, which broke through, depended on the applied load.
• The ammonia did not cause any additional corrosion on the cell components during the operation time of about 2000 h.

Additional tests should however be done in order to find explanations for the ammonia break through. The construction of the 2 testbeds proved to be more complicated than expected, in part due to the high safety standards set by the German TÜV.

The first test cycle was performed at SEABORNEs location, in Owschlag, Germany. The burn-out procedure was started on this stack in April 2002 at the facilities of MTU in Ottobrunn, Germany. Then the stack was cooled down and delivered to Seaborne, where it was reactivated at the end of May. After 2,500 h operation the tests were terminated. It is likely that the gas composition was not stable during the experimental run and the CH₄: CO₂-ratio was shifted towards higher amounts of the CO₂. Therefore the real electrical efficiency (DC) should be expected to be in the range between 35 and 52% (DC). Results on the test operation in Nitra will soon be available.

Impact and exploitation

The large potential for biogas coming from biogas producing facilities in both agricultural as well as industrial sectors shows a virgin area of core business for the involved sectors. The exploitation of the results is clearly focused on the promotion of the implementation of Biogas Plants using MCFC's. The gas upgrading systems are to be further developed and commercialized after the finalization of the project.