Exergy analysis of a hydrogen and water production process by a solar-driven transcritical CO 2 power cycle with Stirling engine

Abstract

 A novel cogeneration plant including Stirling engine to produce water and hydrogen. A dynamic RO model including recovery turbine for different permeate flow rate. About 8% reduction in exergy destruction in the system using ideal Stirling engine. More electrical power production, higher than both LNG and CO 2 power cycle. Electrolyzer-based ZLD approach by employing electrolyzer beside RO desalination. ACCEPTED MANUSCRIPT AbstractThis study attempts to go beyond the conventional framework of the integrated solar transcritical CO 2 power cycle works, aimed at further utilization of available exergy as much as possible. This paper proposed a novel system for hydrogen and fresh water production in which a Stirling engine used instead of a condenser, for the places with abundant access to solar radiation and sea, and least to freshwater sources. This proposal leads to further utilization of streams' exergy through the system instead of wasting to the environment, and further power production by the engine followed by the higher products. The electrolyzer employed beside Reverse Osmosis (RO) desalination system, and takes full advantages of highly concentrated brine stream of desalination, eliminating the wastewater rejection through proposed system leading to attaining a near-ZLD approach in fresh water and hydrogen production. This reduces the adverse impacts of desalination's wastewater on the environment. A thermodynamic and exergy analysis is carried out to compare the superiority of this study and investigate the effect of some key parameters on the overall performance of the system as well. The results showed that replacing the condenser by a Stirling engine reduces the exergy destruction through heat transfer from CO 2 to an LNG unit. Exergy destruction was reduced from 16.7% to 8.8% for the above configuration for an ideal Stirling engine that exploits it to produce extra power which its minimum is at least 9 kW and 15 kW higher than CO 2 and LNG power productions.Moreover, Entering RO brine stream, wasting 2.58 kW exergy, to the electrolyzer leads toNaClO and H 2 production besides removing brine stream. In a power plant, sodium hypochlorite is used for disinfection of cooling systems and hydrogen can be used as a source of energy in fuel cells. An examination of some thermodynamic factors showed that higher ACCEPTED MANUSCRIPT 2 CO 2 turbine inlet pressure has an optimum value in producing fresh water and hydrogen, while the higher CO 2 turbine inlet temperature slightly reduces the productions rate. The more recovery ratio also causes a sharp reduction in hydrogen production, whereas it has an optimum amount of fresh water production at recovery ratio equals to 0.47.

Experimental investigation of solar‐assisted transcritical CO 2 Rankine cycle for summer and winter conditions from exergetic point of view

“…In another study, they modified the system by replacing the condenser with a Stirling engine. 29 Similar to this study, Ahmadi et al 23 carried out a thermodynamic analysis of solar-powered tCO 2 -RC integrated with thermal energy storage tank and LNG system. Flat plate collectors were proposed for solar heat recovery.…”

Thermodynamic and economic analysis of performance evaluation of all the thermal power plants: A review

“…In a study, Rankine cycle working with ammonia‐water was compared to regenerative Rankine power generation cycle by applying second law of thermodynamics and exergy analysis . Exergy topological approach was applied in an organic Rankine cycle and in micro‐organic Rankine heat engines in order to represent an approximation of the exergy destruction by utilizing various working fluid . They carried out their research on the simulation and exergy analysis of a 600 MWe and 800 MWe Oxy combustion pulverized coal‐fired power plant.…”

“…79 Exergy topological approach was applied in an organic Rankine cycle and in micro-organic Rankine heat engines in order to represent an approximation of the exergy destruction by utilizing various working fluid. 11,[80][81][82][83][84][85][86] They carried out their research on the simulation and exergy analysis of a 600 MWe and 800 MWe Oxy combustion pulverized coal-fired power plant. Blanco-Marigorta et al 87 identified the location, magnitude and the thermodynamic reasons for inefficiencies in a solar thermal power plant using exergy analysis.…”

A review on solar‐assisted gas turbines

“…Solar energy is one of the most popular renewable energies which is evolving noticeably in recent years due to its availability and ease of exploitation . Solar energy are applied for different purposes such as heating, desalination and electricity generation as shown in Figure .…”

“…8,9 Annual growth rate of renewable energies for the world between 1990 and 2014 was 2.2% which had higher rate than total primary energy supply (1.9%). 10 Solar energy is one of the most popular renewable energies [11][12][13] which is evolving noticeably in recent years due to its availability and ease of exploitation. [14][15][16] Solar energy are applied for different purposes such as heating, 17 desalination 18 and electricity generation as shown in Figure 1.…”