Enabling flexible CHP operation for grid support by exploiting the DHN thermal inertia. (15th June 2022)

• Record Type: Journal Article
• Authors: Garcet, J.; De Meulenaere, R.; Blondeau, J.
• Is Part Of: Applied energy. Volume 316(2022)
• Publication Date: 2022-06-15
• Subjects: CHP -- DHN -- Frequency reserve -- Flexibility -- Dynamic modelling; Power (Mechanics) -- Periodicals; Energy conservation -- Periodicals; Energy conversion -- Periodicals; 621.042
• DOI: 10.1016/j.apenergy.2022.119056
• Languages: English
• ISSNs: 0306-2619

Abstract

Abstract: As a result of the increased penetration of intermittent renewable energy sources, Combined Heat and Power (CHP) units are being looked upon as one of the sources that might provide for the ever growing need for electrical flexibility. However, CHP units are often considered as must-run units on the grid for their main purpose is generally to cover the heat demand of an adjoining District Heating Network (DHN). This paper demonstrates how a CHP–DHN system may be used as a frequency reserve without excessively compromising the lifetime of the CHP, using either a specific storage tank or the DHN's thermal inertia in order to compensate for the resulting heat imbalance. In the latter case, it is shown that a buffer tank, although smaller than a specific Thermal Energy Storage (TES), is required due to restrictions for acceptable DHN temperature gradients. In both approaches, the size of the tank has been mapped out considering frequency reserve's duration and capacity. The results show that a simplistic static model of the DHN is sufficient for the design of a specific TES, while a detailed dynamic simulation is required when the DHN is used as storage, to prevent overestimating the flexibility of the CHP–DHN system. This research could be used to assess the potential for improving CHP–DHN systems flexibility, using them as frequency reserves, and to design the required storage or buffer tanks. Highlights: A control strategy to use a CHP-DHN system as a frequency reserve is proposed. Dedicated storage tanks and/or DHN thermal inertia are used. The DHN can be used as heat storage, but a buffer tank is required. A detailed dynamic DHN model is needed to determine the DHN flexibility. The flexibility of the CHP–DHN system was determined for 370 MW CHP.