Design and demonstration of 3 CHP plants using two 5 kW solid oxide fuel cells (SOFC) working with landfill gas and biogas from anaerobic digestion

PROJECT DESCRIPTION

BACKGROUND

Some sectors of the agro-food industry generate a significant amount of waste containing high organic content. Environmental problems associated with decomposing organic waste and manure include surface and groundwater contamination and air pollution caused by methane, as well as ammonia and unpleasant odours. Landfills already produce a third of the methane emissions contributing to climate change. The European landfill directive therefore aims to reduce the disposal of biodegradable waste in landfills (the main source of the methane they produce) and to push landfills to set up installations for the collection and recovery of the methane biogas that landfills generate.

OBJECTIVES

The project objectives centred on demonstrating the environmental and economic benefits of a combined heat and power system based on solid oxide fuel cells (SOFC) fed with biogas. Overall aims anticipated identifying new approaches capable of providing safer, cleaner, energy-efficient and more cost-effective means of disposing of wastes from municipal and agro-food industry sources.

RESULTS

Project outcomes successfully demonstrated the potential of the new technologies. Biogas was sourced from anaerobic digestion of slaughterhouse wastes and from different landfill emissions, where plants were set up at waste disposal sites to co-generate electricity and heat for use by the installations themselves. The methodology adapted SOFC technology, that is normally used with natural gas, and results showed that such equipment can be effective at producing electricity from biogas. In addition, the project also demonstrated the suitability of a system for purifying biogas prior to its burning in the SOFC.

Two prototype systems were built during the project and each contained: a biogas conditioning and purification system with a security air conditioning (AC) filter specifically designed and constructed for the characteristics of the biogas and the gas requirements of the fuel cell; a SOFC; and a regulation control system of the equipment.

One prototype was tested using biogas generated by anaerobic digestion of livestock manure and the other prototype was tested in two different landfill locations. Data from these different operational environments was analysed to identify optimal parameters in different conditions for the new technology. The beneficiary believes further testing is required to properly optimise the systems. However, the LIFE tests provided valuable information about the new technology’s power generation potential. For example, tests indicated electrical and thermal efficiencies of between 24.5 - 29% from the SOFC using a 75% methane content biogas. This compares well with the SOFC outputs from natural gas but the project concluded that landfill gas with a methane content of less than 50% was not sufficient to power the SOFC. Tests also confirmed the importance of analysing biogas composition carefully before using it in the SOFC and the additional security filter was essential to ensure a constant flow of biogas with a consistent methane content.

Efficiency results of between 90% and 100% were demonstrated by the biogas generated from livestock waste using a biotricklling filter. Different H2S concentrations (80-100 to 2 500 H2S ppms) were tested producing variable results in terms of the technology’s cost-effectiveness and key factors included the time reaction of bacteria when fed with very variable H2S concentrations.

Key conclusions from the BioSOFC project are:

The technology offers a viable alternative option for biogas use, although optimisation is still needed.

A serious analysis of the biogas impurities, concentration of CH4, stability, flow, pressure, etc. must be done before establishing the CHP system because all the benefits obtained in the SOFC might not compensate the previous treatment, especially in landfills.

The high investment needed is a current barrier since it is still a technology under development with many features to be improved: lifetime must be increased, durability of the stack, robustness, size of the system and also the availability of the system itself.

Even if the operational costs are minimum and the incomes via electricity selling and savings by the use of the heat generated are included in the calculations, the technology does not yet reach the point of being feasible economically.

Although technological advances, particularly in fuel cell materials and construction, will reduce costs, the reduction necessary to become competitive requires unit mass production.

SOFC has a niche market in the small scale applications, i.e for domestic and residential use, hotels, etc. Under 65 kW there is no competing technologies (microturbines or internal combustion engines), therefore, the use of SOFC would be an alternative once the barriers of the investment costs and the size of the equipment are overcome. For higher power, conventional technologies, although not as environmentally friendly, are economically feasible.

For a marketable product further co-financed projects – RTD and demonstration – have to be carried out in the near future.