DEMOSOFC is the first industrial size biogas fed fuel cell [1] plant in Europe and it is installed at the SMAT Collegno wastewater treatment plant premises.
Solid Oxide Fuel Cells (SOFC) are fed with biogas produced as a by-product of the wastewater treatment process. The fuel cell technology can guarantee the production of electricity and heat with high conversion efficiencies and near-zero-emissions to atmosphere (NOx, SOx, PM).
At the end of January 2020, data from the operation of the plant – started in October 2017 – have been analyzed in order to evaluated the energy and environmental benefits of the proposed solution.
During the analyzed operating period, the plant worked for more than 10’000 hours considering the two SOFC modules currently installed. The average power produced in the same period – 2 years and half – is 40 kW electrical (imagine that the electric meters installed in residential buildings have a maximum power of 3 kW, so average DEMOSOFC power was equal to around 13 meters).
The total electrical production – which was been completely self-consumed by the wastewater treatment plant – is equal to more than 450 MWh of electricity, which corresponds to the annual consumption of around 113 families of 4 people [2]. This electrical production has generated an economic saving higher than 60’000 € [3] (energy self-consumed and not bought from the grid) while the heat recovery from the SOFC exhaust gases has generated a saving of around 18’000 € [4] (expressed as natural gas not bought from the grid). These savings are currently ‘limited’ by the reduced number of operating hours, due to the experimental nature of this system. If the plant was operated like an industrial site and worked for 95% of the total time at an average power of 150 kW electrical, with a constant 55% electrical efficiency (industrial scenario) , the saving for the wastewater treatment plant would have been around 350’000 € only for the electricity production.
NOx emissions, measured onsite, are lower than the detection limits of the instruments used: NOx < 20 mg/m3. If we consider a safety value of the emission equal to the detection limit (even if the real emissions are probably much lower) and we compare this number with the emissions from the biogas-fed internal combustion engines (standard competitive technology) installed in the SMAT Castiglione plant, the saving generated – in the analyzed operating period when the plant was running – is 565 kg di NOx, which is equal to the emissions from around 327 city cars in one year[5]. The reduction in NOx emissions of the SOFC technology compared with the internal combustion engines is higher than 87%.
For what it concerns the CO2 emissions, the higher electrical efficiency [6] of the SOFC system (50%) compared with an internal combustion engine (40%) leads to a reduction in the emissions for every kWh of electrical energy produced. Considering the entire DEMOSOFC operating period until the end of January 2020, the SOFC system generated a saving in CO2 emissions of 34% (which would have been released if the energy was produced with a traditional engine). If we consider the same city car, which travels for a total yearly distance of 15’000 km, the production of CO2 is equal to 2 tons/years [7]. The saving generated by the DEMOSOFC site has been thus equal to around 17 city cars equivalents.
According to the above mentioned industrial scenario, it is interesting to observe the potential impact of these systems on a larger scale. If we consider the same industrial scenario presented above, the expected NOx saving could be measured in 3.3 tons or 2172 equivalent city cars. For what it concerns the CO2 emissions, the saving could be quantified as 273 tons, which is the equivalent produced by 137 city cars, while the electric production would be around 2725 MWh, equivalent to 681 families average consumption.
consumption.
Click here to view the complete info-graphic of the results!
[1] A fuel cell is an electrochemical cell that converts the chemical energy of a fuel (often hydrogen) and an oxidizing agent (often oxygen) into electricity through a pair of redox reactions, without any combustion.
[2] Average yearly consumption for a 4-member family: 4000 kWh/year.
[3] Average price of electricity from the grid equal to 0,13 €/kWh.
[4] Average price of natural gas from the grid equal to 0,06 €/kWh.
[5] Gasoline euro 5, with an emission rate equal to 100 mg NOx /km, and an annual distance traveled of 15’000 km.
[6] Defined as the ratio between the electrical power produced (in kW) and the inlet power available in the fuel (equal to the mass flow of fuel multiplied by its heat of combustion).
[7] Considering an emission factor equal to 114 g CO2/km.
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