(537a) Modeling and Optimization of a Novel Solar Parabolic Trough Plant Used for Industrial Process Heat That Utilizes Flexible Heat Integration

Industrial process heat is generally provided by natural gas and other fossil fuels and represents a large portion of energy usage worldwide. In 2014, in the U.S. manufacturing sector, 5,303 TBtu of fuel (natural gas, fuel oil, coal, etc.) was consumed for process heat and an additional 3,080 TBtu was consumed to produce steam generation for process heat [1]. This shows a large opportunity for solar thermal heat to supplement traditional heat sources in manufacturing applications and industrial process heat applications as a whole.

In this study, a novel solar industrial process heat (SIPH) plant with flexible heat integration (FHI) is modeled and simulated over a year using weather data for Salt Lake City, Utah. The novel SIPH plant highlights how solar thermal power could effectively be used in an industrial setting with a dynamic and optimized response to changing solar conditions.

A detailed dynamic parabolic solar trough model is constructed and validated with the National Renewable Energy Laboratory’s System Advisor Model. The dynamic model is then used to simulate the dynamic behavior of the proposed SIPH plant, which contains two process fluids (high temperature and low temperature) that each require 13.5 MWt to meet their heating needs. Two solar thermal heat exchangers are used to heat up the two process fluids. Natural gas furnaces are used after each heat exchanger to ensure that the process heating needs are always met when solar isn’t available or conditions aren’t ideal (see Figure 1).

The proposed SIPH plant is simulated for a baseline case where the plant has no available degrees of freedom and the heat transfer fluid (HTF) flows through each heat exchanger in series. The plant is also simulated using FHI, a concept studied in solar thermal power plant applications [2-4]. FHI has had no previous studies for use in SIPH applications, making this the first of its kind. The concept of flexible heat integration is to allow for flexible heat collection temperatures and flexible heat delivery based on changing solar conditions. FHI is implemented in this application in a novel way by allowing the SIPH plant to have two manipulated variables: the HTF setpoint, and a valve that controls the ratio of HTF flow going to the high temperature and low temperature heat exchangers. This design allows solar heat to be collected at lower temperatures when solar conditions aren’t ideal and then allows for the heat to be exchanged in a flexible way to maximize solar potential. By running the system at steady state at varying solar conditions, a heuristic optimization routine is created that changes the two manipulated variables to minimize natural gas usage based on changing solar conditions. This optimization routine is then implemented with FHI in a yearlong simulation to show the potential of an optimized SIPH plant that utilizes FHI. Results show that the plant utilizing FHI increases solar share and reduces natural gas usage and greenhouse gas emissions. This study shows an opportunity for the potential of FHI in SIPH plants, which can help bring more renewable energy to industrial process heating.

[1] “Static Sankey Diagram Full Sector Manufacturing (2014 MECS),” U.S. Department of Energy, 2014. https://www.energy.gov/eere/amo/static-sankey-diagram-full-sector-manufa....

[2] K. Ellingwood, K. Mohammadi, and K. Powell, “A novel means to flexibly operate a hybrid concentrated solar power plant and improve operation during non-ideal direct normal irradiation conditions,” Energy Convers. Manag., vol. 203, no. August 2019, p. 112275, 2020, doi: 10.1016/j.enconman.2019.112275.

[3] K. Rashid, S. M. Safdarnejad, and K. M. Powell, “Process intensification of solar thermal power using hybridization, flexible heat integration, and real-time optimization,” Chem. Eng. Process. - Process Intensif., vol. 139, no. January, pp. 155–171, 2019, doi: 10.1016/j.cep.2019.04.004.

[4] K. Ellingwood, K. Mohammadi, and K. Powell, “Dynamic optimization and economic evaluation of flexible heat integration in a hybrid concentrated solar power plant,” Appl. Energy, vol. 276, no. April, p. 115513, 2020, doi: 10.1016/j.apenergy.2020.115513.