Efficiency Enhancement of an Ammonia-Based Solar Thermochemical Energy Storage System Implemented with Hydrogen Permeation Membrane

Abstract

The ammonia-based solar thermochemical energy storage (TCES) is one of the most promising solar TCESs. However, the solar-to-electric efficiency is still not high enough for further commercialization. The efficiency is limited by the high ammonia decomposition reaction temperature, which does not only increase the exergy loss through the heat recuperation but also causes a large re-radiation loss. Nonetheless, lowering the reaction temperature would impact the conversion and the energy storage capacity. Thanks to the recent development of the membrane technology, the hydrogen permeation membrane has the potential to enhance the conversion of ammonia decomposition under the moderate operating temperature. In this paper, an ammonia-based solar thermochemical energy storage system implemented with hydrogen permeation membrane is proposed for the first time. The system model has been developed using the Aspen Plus software implemented with user-defined Fortran subroutines. The model is validated by comparing model-generated reactor temperatures and conversions profiles with data from references. With the validated model, an exergy analysis is performed to investigate the main exergy losses of the system. Furthermore, the effects of the membrane on system efficiency improvement are studied. The results show that exergy loss in the charging loop is dominant, among which the exergy losses of Heat Exchanger Eh,A, together with that of the re-radiation Er, play important roles. Compared with the conventional system, i.e., the system without the membrane, the Eh,A and Er of the proposed system are more than 30% lower because the hydrogen permeation membrane can improve ammonia conversion at a lower endothermic reaction outlet temperature. Consequently, the proposed system, presumably realized by the parabolic trough collector at ~400 °C, has a theoretical solar-to-electric efficiency of ηste, which is 4.4% higher than the conventional ammonia-based solar thermochemical energy storage system. Last but not least, the efficiency is 3.7% higher than that of a typical parabolic trough solar power plant, which verifies the thermodynamic feasibility of further commercialization.

Optimal Design of an Absorbent-Enhanced Ammonia Synthesis Process for Solar Thermochemical Energy Storage

“…Total Capital Investment. The labor and material cost (LM) for the process unit j is defined as follows 11) where the factor LM* j consists of labor and material costs for all the ancillary materials, and C f,j is a fixed cost parameter representing the cost of instruments and control system. The corresponding physical module (PM) cost is calculated using the following equation 64 PM LM 0.15FOB…”

“…Various chemicals have been explored as potential candidates for gas and solid–gas TCES systems, including ammonia, hydrides, carbonates, oxides, hydroxides, and methane. , Among these, the ammonia-based concept was first proposed in the mid-1970s by Carden and has since undergone over four decades of development, particularly at the Australian National University (ANU) . This makes it one of the most extensively researched TCES concepts to date. − The utilization of ammonia in TCES systems holds significant promise due to its carbon-free nature, aligning with green energy initiatives. This storage system offers several advantages.…”