Energy balances

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62 From the plots emerges how the electrical production of the system represent roughly the double of the energy required from the plant to operate, that means that around a half of the energy produced could be sold to the grid. Considering the thermal balance, the system could provide enough energy in the summer months (from June to September) while in the other months heat integration from auxiliary boilers is needed. However, since the heat production of the system is much higher than the one from the ICE in the actual configuration (10050 Mwh/year of the SOFC with respect to 7670 Mwh/year by ICE) the boilers that are already installed in the plant could provide the amount of heat to integrate the SOFC, without the need of any new installation.

Figure 32 Thermal balance of the plant with Mitsubishi SOFC

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FCE SOFC

So, it is possible to consider the electric and thermal output of the systems in terms of MWh/

year and comparing them month by month with the energy demand data provided by ACEA for the year 2021. In this way, for each month is possible to evaluate how the internal uses of the plant are covered and how much energy can be sold to the electric network.

For what concern the thermal energy, since the efficiency of the FC is not so high, it is possible to appreciate that part of the load has to be fulfilled by a back-up unit of gas boilers, which produce thermal power from the combustion of NG from the gas distribution network.

The energetic balance of the first model of FC considered (FCE SOFC 200) is graphically represented in the plots below.

Figure 33 Electric balance of the plant with FCE SOFC

Figure 34 Thermal balance of the plant with FCE SOFC

64 From the plots emerges how the electrical production of the system represent roughly 2.5 times the electric energy required from the plant to operate, that means that around 60% of the energy produced could be sold to the grid. Considering the thermal balance, the system could provide enough energy in the summer months (from May to September) while in the other months heat integration from auxiliary boilers is needed. However, since the heat production of the system is much higher than the one from the ICE in the actual configuration (11700 Mwh/year of the SOFC with respect to 7670 Mwh/year by ICE) the boilers that are already installed in the plant could provide the amount of heat to integrate the SOFC, without the need of any new installation.

FCE MCFC

In case of the MCFC system due to the lower efficiency it is possible to appreciate a lower energy output (both electric and thermal), however the system is able to produce roughly the double of the energy required by the plant at the moment, as emerges from the graph reported below.

The energy performances of the MCFC are slightly worse also when considering heat production, as can be noticed in the figure 39, with the system which is able to fulfill the thermal load only in June, July, and September.

Figure 35 Electric balance of the plant with FCE MCFC

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Figure 36 Thermal balance of the plant with FCE MCFC

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Considerations on first scenario and FC comparison

To complete the energetic analysis of the first scenario a comparison between the fuel cell is proposed. The behavior of each single system has been described in the previous sections, and now the goal is to determine which system could be the most suitable, at least from an energetic point of view.

For this purpose, in the following graph the electric and thermal production of each system is plotted, with reference to the plant load.

As highlighted in the figure 40, the best performances are obtained by the FCE SOFC system, followed by the Mitsubishi unit and then the FCE MCFC. As deeply explained in the next chapter, the higher efficiency of a systems affects in a positive way the return of the initial investment, so it is always a good choice to look for efficiencies as high as possible.

Figure 37 Comparison of electric performance of different FC units

Figure 38 Comparison of thermal performance of different FC units

67 For what concern the thermal output, the performances of the Mitsubishi SOFC and MCFC are very close, and are slightly lower compared to FCE SOFC, as emerges in the plot figure 41.

When analyzing heat production, some consideration can be made, because the system with the highest output is not always the better choice. In fact, considering the production trend captured in the figure 41, it is possible to appreciate how during summer month there is a surplus of heat produced with respect to the consumption of the plant, and this quota must be somehow managed. The easiest way could be represented by the dissipation of the exceeding heat but is the most inefficient way of handling it, not only because of the thermal energy wasted, but also because it would require the installation of a heat dissipator and its auxiliaries. As an alternative it is possible to consider if the heat could be sold to any industrial facility in the proximity of the ACEA plant, since we can imagine during the summer the thermal request from the residential sector is minimum.

On the other hand, a higher thermal output means that except in summer months, the heat demand of the plant is covered in a more efficient way, reducing sensibly the energy required from the auxiliary boilers and so the gas consumption. This could lead to a lower dependance of the plant on not renewable source. As many energetic issues, there is not a unique solution, but it represents a threshold problem that has to be deeply analyzed to find the better way to manage it.

As already discussed in the paragraph 3.1 in Europe one of the biggest limits to the expansion of biogas-based CHP units were exactly this: the lack of infrastructure (DH networks, industrial facilities) able to properly exploit the heat generated by CHP systems.

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Hybrid FC and upgrading solutions

In this section the performance of different layouts is showed, elaborating data obtained in the chapter about FC sizing. In the plots below are graphically reported the difference in the behavior of the FC unit in the different scenarios considered, and their ability to cover the internal demand of the plant.

Figure 39 Electric load coverage in the hybrid configuration

Figure 40 Thermal load coverage in the hybrid configuration

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