Session: 03-03: Energy Storage Separate from CSP: Thermal, Mechanical, Thermochemical

Paper Number: 137032

137032 - High-Fidelity and High-Performance Computational Simulations for Rapid Design Optimization of Sulfur Thermal Energy Storage 

Abstract: 

Industrial process heating (IPH) accounts for ~70% of US manufacturing energy use and is primarily produced by fossil fuel combustion. Approximately, 1500 TWht (~60%) of IPH demand is in the temperature range of 100-300℃. Industrial applications in this temperature range include drying, hydrothermal processing, thermal enhanced oil recovery, food and beverage, bioethanol production, etc. Cost-effective thermal energy storage (TES) that increases the utilization of waste and renewable heat (solar, geothermal, etc.) could provide significant energy savings and reliable heat sources, decrease emissions, and increase US manufacturing competitiveness through reductions in fuel consumption.

TES development has historically been dominated by technologies suitable for deployment with concentrating solar power (CSP). State-of-the-art thermal storage deployed commercially with power tower CSP plants uses a 60%/40% NaNO₃/KNO₃ molten salt and operates between temperatures of approximately 280°C and 570°C using a two-tank configuration.  However, these nitrate salts are unsuitable for operation outside of this temperature range due to a high freezing point of approximately 220°C, and limits on high-temperature salt stability and corrosion resistance of containment alloys. Other materials being investigated for TES include those based on: (1) sensible energy storage (various molten salt compositions, inert solid particles, rocks or pebble beds, sulfur, water, concrete, graphite, etc.), (2) latent energy storage in materials that undergo solid-liquid phase change at relevant temperatures (organic materials for low-temperature applications, inorganic salts and/or metals for high-temperature applications), or (3) thermochemical energy storage (hydrides, hydroxides, carbonates, metal oxides, etc.).  The application temperature and challenges pertaining to storage material and/or containment cost, energy density, long-term thermal and cyclic stability, and charge/discharge heat transfer effectiveness drive material selection for a given IPH or electricity generation application.

Sulfur is a cheap commodity at $80/ton compared to $1100 - 1300/ton for conventional salts. When using a metric of storage cost per kWh, sulfur costs around 2-3 $/kWh.  Previous sulfur TES development focused on high temperature (>600 ℃) concentrated solar power applications with sulfur encapsulated in pipes and flow of gaseous HTF (air) in the shell side. However, for lower-temperature IPH applications in the range of approximately 100-300°C Element 16 adopted a compact and scalable TES design with molten sulfur in the shell and HTF pipes submerged in the molten sulfur bath. The low-cost molten sulfur TES for dispatchable IPH has deployment potential for broad applications.

The spatial and temporal evolution of the HTF and sulfur temperature is critical to the TES system performance, and thus detailed modeling can improve understanding of the performance and facilitate design improvements. Using high performance computing and computational fluid dynamics (CFD) a low-cost molten sulfur thermal energy storage (TES) system for industrial process heating (IPH) applications was developed. The unique challenges in CFD modeling of sulfur TES are the sharp property changes of sulfur relevant to the working temperatures. Above 159 ℃, liquid sulfur undergoes polymerization, and the viscosity of sulfur rapidly increases by several orders of magnitude between 159°C and 188°C, followed by a decrease in viscosity beyond 188°C due to thermal bound dissociation. In addition, various concentrations of H₂S impurities can also modify sulfur viscosity.  This numerical challenge is especially relevant to transient simulation of the sulfur TES charging and discharging processes as the extreme property variations limit the applicability of traditional heat transfer correlations. Transient CFD simulations including the temperature-dependent sulfur properties and geometric complexity of the TES design were used to predict the effect of natural convection during charging and discharging on the heat transfer process, sulfur temperature uniformity, charge/discharge rates, and performance of the storage devices. The CFD model was validated with experimental results for a full charge and discharge cycle. The work will show 3D and 2D simulation comparisons aimed to facilitate rapid design iterations and a machine learning based design optimization approach.  

Presenting Author: Munjal Shah National Renewable Energy Laboratory (NREL)

Presenting Author Biography: Munjal Shah joined as postdoctoral researcher at the National Renewable Energy Laboratory in 2023 after completing his PhD in 2023. His expertise is in modeling using computational fluid dynamics, Finite element analysis, and Multiphysics analysis. He works on developing advanced solar receivers for particle-based concentrating solar thermal power and solar thermochemical fuel production. He also works on next generation leak detection using smart distributed monitoring for unintended hydrogen releases. His interests are in integration of renewable energy systems in Industry heat processes for decarbonization.

Authors:

Munjal Shah National Renewable Energy Laboratory (NREL)
Janna Martinek National Renewable Energy Laboratory (NREL)
Karthik Nithyanandam Element 16 Technologies
Michael James Martin National Renewable Energy Laboratory (NREL)
Zhiwen Ma National Renewable Energy Laboratory (NREL)