(471a) Systematic Process Design Strategies for Efficient and Synergistic Integration of Solar Thermal Hydrogen, Electricity and Fresh Water Production Processes

Authors: 
Gençer, E., Purdue University
Tawarmalani, M., Purdue University
Agrawal, R., Purdue University
There is an ever-increasing demand for food, energy and water (FEW) due to population growth and change in consumption habits. For the past century, energy, chemicals, fertilizers and even fresh water via desalination or water treatment have been supplied by using fossil fuel resources. However, with decaying fossil fuel reserves and increasing greenhouse gas (GHG) emissions, the grand challenge is to sustainably meet FEW needs without compromising the current level of civilization. Development and implementation of renewable energy conversion processes by systems approach are essential to ensure a smooth transition to a sustainable economy. Among these alternatives, solar energy is particularly prominent because of its tremendous potential [1]. High conversion efficiency and integrated energy storage systems are indispensable to overcome intermittent and dilute nature of harnessing solar energy [2-3]. Recently proposed hydricity concept, synergistic solar thermal hydrogen and electricity coproduction, presents a potential solution for continuous and efficient power supply and also an exciting opportunity to envision and create a sustainable economy to meet all the human needsâ??namely, food, chemicals, transportation, heating, and electricity [1].

Here, we introduce an integrated process design strategy based on the hydricity concept for the coproduction of fresh water, hydrogen and electricity from concentrated solar thermal energy. Process simulations for the proposed integration are performed in an integrated Matlab and Aspen Plus platform [4]. The operating conditions of various units and topological structure of the integrated process are determined via sensitivity analysis and optimization in Matlab. Detailed process simulations of thermal desalination processes are validated by comparison with performance data from the current operating desalination plants. The resultant desalination processes are further integrated with solar thermal electricity and hydrogen processes to coproduce electricity, hydrogen and fresh water. Standalone and integrated solar conversion processes are evaluated based on the process energy efficiency and exergy efficiencythat refers to the fraction of incident solar exergy that is directly recovered as the net exergy output, which is defined as the sum of electricity and the hydrogen exergy output. We have identified exergetically inefficient steps and implemented new process designs to improve the thermal efficiency of standalone solar desalination processes.

The integration of solar thermal power generation, solar thermal hydrogen production and thermal desalination techniques reduces exergy losses associated with each one of the standalone processes and thus provide a synergistic strategy. The implementation of the proposed process synthesis strategy results in efficient solar thermal process designs, which coproduce i) baseload power, ii) fresh water, and iii) hydrogen. Depending on the targeted end-use, hydrogen can be used as an energy career, transportation fuel, feedstock for the production of chemicals, fuels or fertilizers for food production. Coproduced products can supply all FEW needs unveiling a sustainability roadmap.

[1] Gençer E, Mallapragada DS, Marechal F, Tawarmalani M, Agrawal R. Round-the-clock power supply and a sustainable economy via synergistic integration of solar thermal power and hydrogen processes, Proceedings of the National Academy of Sciences (PNAS), 112(52), 15821-15826, 2015.

[2] Gençer E, Al-musleh E, Mallapragada D, Agrawal R. Uninterrupted Renewable Power through Chemical Storage Cycles. Current Opinion in Chemical Engineering, 5, 29-36, 2014.

[3] Gençer E, Agrawal R. A commentary on the US policies for efficient large scale renewable energy storage systems: Focus on carbon storage cycles, Energy Policy, 88, 477-484, 2016.

[4] Gençer E, Tawarmalani M, Agrawal R, Integrated solar thermal hydrogen and power coproduction process for continuous power supply and production of chemicals, Computer Aided Chemical Engineering, 37, 2291-2296, 2015.