(489e) Heat Integration of Renewable Electricity-Driven Power-to-Heat Technologies Under Time-Varying Electricity Price

Growing commitments to reduce greenhouse gas emissions from fossil fuels, along with the declining cost of renewable energy, has resulted in the increasing utilization of renewable energy in process industries. Electricity’s share of the world’s final energy consumption is projected to be doubled and reach 40% by 2050, due to the increase in renewable-based generation capacity [1]. On the other hand, it is reported that approximately one-third of the U.S. total energy consumption is used in the industrial sector, most of which is related to the combustion of fossil fuels to supply heat to various industrial processes [2]. Thus, to ensure a sustainable future energy economy, there exists a unique opportunity for the utilization of renewable electricity to satisfy process heat demand through Power-to-Heat (PtH) [3].

In specific industrial applications, some well-established PtH technologies have been widely used, such as induction heating [4], resistance heating [5], electrode heating [6], and heat pumping [7], which can be significantly different in operating temperature, efficiency, and energy consumption. To drive progress towards electrification and decarbonization of heating systems, one promising option is the use of highly energy-efficient heat pumps, which upgrade low-grade heat to high-grade one by consuming renewable electricity. It can be economically attractive if a large amount of low-grade heat is available and the temperature increase is relatively modest. Moreover, electrode boilers can be used to replace conventional boilers to generate steam, and electric heaters can be used to directly supply heat to the processes. Although utilizing these electric heating systems has considerable advantages over the traditional fossil fuel-dependent ones (e.g., high energy efficiency and low emissions), there are barriers to their wider use in process industries, mainly due to the associated high capital and energy cost [8]. Thus, it is necessary to use optimization-based techniques to determine the cost-effective design and operation of the PtH units, particularly in the context of intermittent renewable electricity generation. Some work has been done to investigate the introduction of PtH technologies to industrial processes and energy systems [9, 10]. However, the insights derived from most of the previous studies are limited to specific designs and considerations of the systems, and thus, a more generic optimization framework is required to rigorously quantify the benefits of electrification and evaluate its applicability.

Motivated by these considerations, we proposed a novel multiscale optimization framework for integrating the design and operation of heat exchanger network (HEN), renewable-based power generating units, PtH units, and energy storage units under time-varying electricity price. Hot and cold streams from industrial processes are given; specifically, hot steams with different pressures generated from fossil fuels as well as cooling water can be used to heat up and cool down the industrial streams. In addition, multiple types of PtH units, including heat pumps, electric heaters, and electrode boilers are also available for heat supply. Power can be obtained through investing in distributed renewable-based power generating units and/or purchasing from the grid. Investment in both electricity storage, e.g., lithium-ion battery storage, and thermal energy storage, e.g., sensible heat storage, is considered. A superstructure is developed to account for all the possible ways of integrating hot and cold process streams, utility streams, PtH units, power generating units, and energy storage units. The proposed multiscale model includes investment decisions in the process units and hourly operating decisions introduced to the model through representative days using the k-means clustering algorithm [11] which corresponds to power and heat flowrates. The objective of the proposed optimization model is to minimize the annualized capital costs of process units plus the annual operating costs of the utilities. The advantage of the proposed framework is that it can be used to effectively screen different options for the supply of both heat and power, so as to identify the most cost-effective and energy-efficient design of an enhanced electrified heat recovery system; further, this framework is general enough and thus can be adapted and integrated with the synthesis of any industrial processes. To illustrate the effectiveness of the proposed multiscale framework, a few case studies are performed to showcase the comparison of the techno-economic feasibility of electric heating systems with conventional utility systems.

[1] McKinsey and Company, Global energy perspective 2022. 2022.

[2] U.S. Energy Information Administration, Annual energy outlook 2022 with projections to 2050. 2022.

[3] Bloess, A., Schill, W. P., and Zerrahn, A., Power-to-heat for renewable energy integration: A review of technologies, modeling approaches, and flexibility potentials. Applied Energy 2018, 212, 1611-1626.

[4] Lucía, O., Maussion, P., Dede, E. J., and Burdío, J. M., Induction heating technology and its applications: past developments, current technology, and future challenges. IEEE Transactions on Industrial Electronics 2013, 61(5), 2509–2520.

[5] U.S. Department of Energy, Improving process heating system performance: a sourcebook for industry. 2015.

[6] Hechelmann, R. H., Seevers, J. P., Otte, A., Sponer, J., and Stark, M., Renewable energy integration for steam supply of industrial processes—a food processing case study. Energies 2020, 13(10), 2532.

[7] Arpagaus, C., Bless, F., Uhlmann, M., Schiffmann, J., and Bertsch, S. S., High temperature heat pumps: Market overview, state of the art, research status, refrigerants, and application potentials. Energy 2018, 152, 985–1010.

[8] Thiel, G. P., and Stark, A. K., To decarbonize industry, we must decarbonize heat. Joule 2021, 5(3), 531–550.

[9] Bühler, F., Zühlsdorf, B., Nguyen, T. V., and Elmegaard, B., A comparative assessment of electrification strategies for industrial sites: Case of milk powder production. Applied Energy 2019, 250, 1383–1401.

[10] Hechelmann, R. H., Seevers, J. P., Otte, A., Sponer, J., and Stark, M., Renewable energy integration for steam supply of industrial processes—a food processing case study. Energies 2020, 13(10), 2532.

[11] Li, C., Conejo, A. J., Siirola, J. D., and Grossmann, I. E., On representative day selection for capacity expansion planning of power systems under extreme operating conditions. International Journal of Electrical Power & Energy Systems 2022, 137, 107697.