Optimal integration of Power-to-Gas and district heating through waste heat recovery from electrofuel production

Abstract

The growing penetration of renewable energies, which have a fluctuating nature, requires the enhancement of energy system flexibility. This can be achieved through sector integration, which encompasses the conversion of energy into the most convenient vectors. In this regard, a promising option is represented by Power-to-Gas (PtG) technologies. They allow the direct conversion of surplus renewable electricity into fuels (e.g. green hydrogen or methane) and its long-term storage, operating as seasonal storage. The potential of PtG systems can be unlocked if the waste heat produced by exothermic components (e.g. electrolyzer and methanation reactor) is recovered and fed, for instance, into a district heating network (DHN) to be supplied to an end-user. However, since the operation of PtG systems may be discontinuous, a full integration of the fuel, electrical and heating sectors is possible only with advanced management and control tools. This work presents a control strategy based on Model Predictive Control, with the aim of operating the production of methane from a PtG system and the supply of waste heat to a DHN with minimal cost. The case study comprises an electrolyzer, a methanation reactor, storage tanks for hydrogen and methane, a boiler and a heat pump for upgrading the temperature level of the recovered heat. The controller feasibility is demonstrated through a Model-in-the-Loop simulation platform and its performances are compared to that obtained with a conventional controller. The novel controller enables a 54 % increase in operating margin and more than halves carbon dioxide emissions. A better exploitation of renewable energy is also obtained (+ 4.6 %), as well as an increase in the share of heat recovered from the PtG plant.