Mälardalen University researchers have looked at how waste heat from hydrogen production could be used for the district heating (DH) network of Luleå, in northern Sweden.
For hydrogen production, they considered a proton exchange membrane (PEM) electrolyzer and an alkaline electrolyzer, with installed capacities of 100 MW each. A large-scale heat pump and a heat exchanger were added to the system to integrate the waste heat into the DH network. The system simultaneously provides cooling to the electrolyzer stack, thus reducing the operational costs of the electrolyzer.
“The results showed that 203 060 MWhth can be extracted from the PEM electrolyzer with a waste heat temperature of 79 C, while 171 770 MWhth can be integrated on the DH network annually,” the scientists explained.
The overall system efficiency of PEM- and alkaline-connected systems is 94.7% and 88.4%, respectively.
“The alkaline connected system primarily encounters higher losses in terms of heat than a PEM connected system which is why the efficiency is lower,” researcher Andrea Miljanovic told pv magazine. “For the alkaline connected system, this means that 88.4 % of the total input energy to the system is useful.”
The levelized cost of heat (LCOH) is SEK 0.218 ($0.021)/kWhth and SEK 0.23/kWhth for PEM- and alkaline-connected systems, respectively. For future scenarios with the fourth generation of DH networks, it is predicted that the LCOH can reach SEK 0.018/kWth for a PEM electrolyzer system, and SEK 0.017/kWth for an alkaline electrolyzer.
“Our results can be used as a guidance for other DH operators with different DH temperatures,” Miljanovic explained. “Our sensitivity results indicate that the LCOH is reduced when supply temperatures in the DH network are lower than the current ones in Luleå. This means that lower supply temperatures imply lower LCOH.”
Miljanovic said that lower supply temperatures mean that a smaller heat pump could be used.
“For a fourth generation of DH-network (with supply temperatures below 80 C) a heat pump would in fact not be required at all which reduces the LCOH significantly.”
She said that the LCOH of the produced heat is site-specific, as the experiment has been adapted to the DH network temperatures in Luleå.
“Our results can still be used as a guidance for other DH operators regardless of their DH-temperatures,” said Miljanovic.
The researchers described their findings in “Utilization of waste heat from hydrogen production: A case study on the Botnia Link H2 Project in Luleå, Sweden.” The study was conducted in cooperation with ABB Sweden and Luleå Energi for the Botnia Link H2 project.
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