Session: 19-02: Symposium to Honor Professor Jane Davidson II

Paper Number: 169856

169856 - Solar Steam With Thermal Energy Storage for Renewable Fuel Production 

Abstract: 

With an award from the U.S. Department of Energy that provided a part of the funding for the project, Sunvapor designed, built, and commissioned an industrial solar steam generation system with thermal energy storage in Brawley, CA, USA. The primary purpose of the project is to demonstrate the operation of an industrial solar steam system that includes several hours of thermal energy storage (TES) so that it may serve as a reference for larger industrial steam-consuming plants for which there is sufficient available land and a goal of deep decarbonization. The project also serves as a reference case for solar steam integration into a renewable fuels production process.  

Deep (i.e., greater than 30%) solar decarbonization of industrial facilities that consume energy mostly in the form of process heat substantially twenty-four hours a day, demands thermal energy storage. Commercial adoption of solar steam with TES requires sufficient land to produce a surplus of heat generation and favorable economic conditions. Since the advent of fracking, the price of a unit of natural gas has remained historically low in the USA. Cap & Trade and the Low Carbon Fuel Standard (LCFS) are incentive mechanisms that support the decarbonization of fuel production facilities in California. Sunvapor and Oberon Fuels signed a Heat Purchase Agreement under which Sunvapor, as the owner of the solar steam facility, delivers solar steam to Oberon’s rDME® fuel production process. Oberon’s process converts renewable feedstock to dimethyl ether (DME) which serves as a renewable substitute for propane, among other things. The carbon intensity (CI) score of the process is limited by the use of natural gas to generate steam. Solar steam lowers the CI score, leading to Cap & Trade and LCFS credits.

The catalytic dehydration process to produce DME specifies saturated steam at a pressure of 17.2 barg and corresponding temperature of 208°C. Sunvapor has designed and built a Bullet Steam Accumulator^TM (BSA^TM) that delivers steam at these conditions to the reactor column’s reboiler. The BSA^TM is a certified ASME Section 1 Unfired Steam Boiler heated indirectly by a heat transfer fluid that flows through an array of linear segmented mirror collectors. The array has a capacity of approximately 100 kW. The BSA^TM is sized to discharge steam at a capacity of 150 kgh^-1 for seven hours. With this storage capacity, the fuel production facility is able to experience the benefits of solar steam delivered long after sunset.

The integration of a new solar boiler into a fuel production facility is presented here along with results of the performance of the system. These results include thermal efficiency, demonstrated steam storage capacity and the observed steam quality at design discharge rates and are compared to design predicted values. Mixing of the liquid water storage media while charging to uniformly heat and thus utilize the water mass is also key to performance, and test results demonstrating the ability to achieve rapid and complete mixing will also be presented along with estimates of the storage utilization efficiency factor. The limitations inherent to the pilot scale system will be described, and the utility of the pilot to an upscaled commercial system will be addressed.

Presenting Author: Brandon Hathaway Sunvapor, Inc.

Presenting Author Biography: Brandon Hathaway has studied Mechanical Engineering as an undergrad at Rose-Hulman Institute of Technology, followed by graduate studies at the University of Minnesota where he specialized in reactor development and testing for solar thermochemical processes while achieving a PhD in Mechanical Engineering. In a follow-up postdoctoral position, he acted as Research Scientist at the Solar Energy Lab at the University of Minnesota, before joining Sunvapor, Inc. as the Director of Engineering, overseeing both commercial deployment as well as research and development of solar thermal technologies for industrial processes.