The increased presence of renewables in the energy sector is a positive step towards mitigation of greenhouse-gas emissions and portfolio diversification. However, the inherent intermittency of sources like solar and wind, poses a challenge to other actors in the market. Such is the case of conventional power plants like combined cycles gas turbines (CCGT), which have to adapt to varying loads and prices on the electricity grid. The integration of such renewables generates the need for these plants for being more flexible in terms of ramping-up periods and higher part-load efficiencies. Flexibility becomes even more important for combined heat and power (CHP) plants since these have to serve simultaneously both, the electricity market and the heat market.

A new layout has been investigated by integrating low-temperature thermal energy storage and a heat pump in a traditional CCGT-CHP plant layout. The present study develops a model for optimizing the short-term dispatch strategy of such novel layout with the objective of maximizing its operational profit. To tackle complexity, the problem was formulated as a mixed-integer linear problem with a sliding time window, solved with the optimization tool CPLEX, run in the software JULIA. The constraints and boundary conditions considered in the study include, i.a. hourly demand and price of electricity and heat, ambient conditions and CO~2~ emission allowances. To asses the techno-economic benefit of such novel layout, a year of operation was simulated for a CCGT-CHP plant in Turin, Italy. Furthermore, different layout configurations and critical size-related parameters were considered. Finally, a sensitivity analysis was made to assess the performance under different market scenarios.

The results show that it is indeed beneficial, under assumed market conditions, to integrate a heat pump in a CCGT-CHP plant and that it remains profitable to do so under a variety of market scenarios. The best results for the assumed market conditions were found when including a 15 MWth capacity heat pump in the 400 MWel CCGT-CHP. Such project would yield a net present value of 1.22 MEUR and an internal rate of return of 3.04%. An increase was shown also in flexibility with 0.14% of the electricity production shifted while meeting the same heating demand. On the other hand, it was found that the thermal energy storage increases the added flexibility, but does not make up for the extra investment under the boundary conditions considered (i.e. weather and market).


Techno-Economic Optimization of a Combined Cycle Combined Heat and Power Plant With Integrated Heat Pump and Low-Temperature Thermal Energy Storage

Division / Sponsor:
International Gas Turbine Institute (IGTI)

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2020/volume/84058

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