(463e) Integrated Process Design for Efficient Solar Thermal Hydrogen and Power Production

Authors: 
Gençer, E., Purdue University
Tawarmalani, M., Purdue University
Agrawal, R., Purdue University

For the past century, energy sector has been predominantly dependent on fossil energy resources. However, concerns regarding limited fossil fuel reserves and increasing greenhouse gas (GHG) emissions from fossil fuels accelerate advancements and implementation of renewable energy conversion processes such as wind turbines, photovoltaic devices, and concentrated solar power plants. Among these alternatives, solar energy conversion processes are particularly prominent since solar energy is the only energy source that can alone meet all human energy needs with its tremendous potential. Yet intermittencies and land availability constraints for solar energy collection are the grand challenges for solar energy conversion technologies and demand high conversion efficiency and synergistically integrated energy storage solutions. Recently, it has been shown that chemical energy storage cycles that utilizes solar heat and electricity to synthesize a carbonaceous material, provides efficient and energy dense storage options for uninterrupted large scale energy supply to the grid [1-2]. Furthermore, the potential of solar energy usage in biofuel production has been investigated [3]. The common aspect of these studies is the dependence on the production of solar hydrogen. Analysis of theoretical and achievable sun-to-hydrogen efficiency for solar thermal hydrogen production revealed that the solar thermal hydrogen production has a great potential to efficiently produce hydrogen [4].

Here, we introduce a novel integration strategy for the coproduction of hydrogen and electricity from concentrated solar thermal energy [5]. The integration of solar thermal power production and solar thermal hydrogen production techniques reduces the exergy losses associated with either of the systems and thus provide an efficient solution. Solar power production processes are evaluated based on the process exergy efficiency that 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. Process simulations for the proposed integration are performed in an integrated Matlab and Aspen Plus platform. The operating conditions of various units and topological structure of the integrated process are determined via sensitivity analysis and optimization using genetic algorithm in Matlab.

The integrated coproduction process provides a synergistic process that minimizes exergetic losses and increases production efficiency. The novel features of the integrated process and the modeling approach are presented. Two solar thermal hydrogen production techniques: (i) single step membrane, and (ii) two-step metal oxide cycle are presented as a case study to demonstrate the benefit of the proposed integration strategy. Efficient coproduction of hydrogen and electricity presents a continuous power supply solution that can achieve high sun-to-electricity efficiencies when combined with the proper hydrogen power cycle and also creates other opportunities since hydrogen has numerous uses in chemical industry, biofuel production, and transportation sector.

[1] Al-musleh EI, Mallapragada DS, Agrawal R. Continuous power supply from a baseload renewable power plant. Applied Energy, 122, 83-93, 2014.

[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] Mallapragada DS, Tawarmalani M, Agrawal R. Synthesis of augmented biofuel processes using solar energy. AIChE Journal, 60(7), 2533-2545, 2014.

[4] Mallapragada DS, Agrawal R. Limiting and achievable efficiencies for solar thermal hydrogen production. International Journal of Hydrogen Energy, 39(1), 62-75, 2014.

[5] 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.