Session: 17-01 Industrial & Cogeneration

Paper Number: 151724

Design of Multi-Level Pumped Thermal Energy Storage Systems For Coupled Industrial Heat Supply 

Industry represents a substantial share of global energy consumption, accounting for approximately 38% of total final energy use, both direct and indirect [1] and it is expected to rise by 10% between 2022 and 2027 [2]. Many large industrial sites generate their own electricity via on-site industrial power plants. One significant advantage of these industrial power plants is their ability to operate in cogeneration mode, producing both electricity and heat. Cogeneration is considered highly efficient as it captures and utilizes the heat generated during electricity production. This setup allows industries to secure a reliable power supply tailored to their energy demands, but it also locks them into a carbon-intensive energy model since most industrial power plants rely on fossil fuel combustion. Current prevailing renewable technologies directly produce electricity without generating useful heat. Currently, renewables can only supply around 11.5% of industrial heat and this is projected to only increase to 13% between 2022-2027 [2]. This lag in renewable heat supply poses a significant challenge for grid compatibility and heat usage for decarbonizing industrial operations.

A promising synergy exists when considering pumped thermal energy storage (PTES) systems. These systems can help shift industries towards renewable electricity while maintaining the benefits of cogeneration. PTES systems enable storage of excess renewable energy in the form of thermal energy during periods of low demand which can be converted back into electricity later. Coupling PTES thermal reservoirs with industrial heat users can provide heat over wide ranges of temperatures. In this way, PTES will support the integration of renewable energy for the power grid while mimicking the efficiency of traditional industrial cogeneration plants by providing both power and heat.

In a previous study, we identified the synergy between industrial heat users and PTES systems and investigated multi-vector operation of PTES systems [3]. The study was built on a PTES design utilizing supercritical CO₂ Brayton cycle with hot molten salt, and cold-water as thermal reservoirs. The current study builds on these previous findings by implementing the PTES system in a heat exchange network of an industrial process and investigating the resulting economic and emission impacts.

One area of investigation was identified as covering variable temperature ranges to reduce the exergy losses associated with using molten salt reservoirs as a heat source for medium to low temperature heat users in the 300 to 100 °C range. As an alternative we investigated modifying the charging cycle operation to lower temperatures utilizing thermal oils as the storage medium as well as bypassing the cold storage heat exchangers. This way, there are two different temperature levels that can be supplied. The model that was developed previously was augmented to include the secondary cycle and the state-of-charge management algorithm was modified to manage the additional thermal reservoirs. The operation of the PTES system was coupled with a benchmark process used to implement heat exchange network optimization studies [4]. We study the implications of changing operating conditions on the turbomachines and evaluate the resulting performance of the combined solution through various indicators: CO₂ emission reduction compared to fossil fuel supplied heating, utility cost reduction. Various scenarios are used to demonstrate the robustness of the proposed strategy, such as changing fossil fuel prices, different fuels and varying renewable supply and demand. The study shows that with the addition of these thermal reservoirs in an industrial setting, the overall CO₂ emissions can be mitigated, and renewable energy can be reliably used.

 

[1] IEA, World Energy Outlook 2023, Paris https://www.iea.org/reports/world-energy-outlook-2023

[2] IEA, Renewables 2022, Paris https://www.iea.org/reports/renewables-2022

[3] A. Albay, Z. Zhu, and Mehmet Mercangöz, “State-of-Charge (SoC) Management of PTES Coupled Industrial Cogeneration Systems,” ASME Turbo Expo 2024: Turbomachinery Technical Conference and Exposition, Jun. 2024, doi: https://doi.org/10.1115/gt2024-128921.

[4] T. F. Yee and I. E. Grossmann, “Simultaneous optimization models for heat integration—II. Heat exchanger network synthesis,” Computers & Chemical Engineering, Oct. 1990, doi: https://doi.org/10.1016/0098-1354(90)85010-8.

 

 

Presenting Author: Alp Albay Imperial College London

Presenting Author Biography: Alp Albay is a PhD student at Imperial College London Chemical Engineering Department, working on modelling and control of processes intended for industrial decarbonization.

Authors:

Alp Albay Imperial College London
John Adeyemi Imperial College London
Sharven Mahendren Imperial College London
Mehmet Mercangöz Imperial College London