Thermodynamic analyses of a solar-based combined cycle integrated with electrolyzer for hydrogen production

In the current study, a combined steam and gas turbine system integrated with solar system is studied thermodynamically. In addition, an electrolyzer is added to the integrated system for hydrogen production which makes the current system more environmental friendly and sustainable. This system is then evaluated by employing thermodynamic analysis to obtain both energetic and exergetic efficiencies. The parametric studies are also conducted to investigate the effects of varying operating conditions and state properties on both energy and exergy efficiencies. The present results show that while gas turbine can generate 312 MW directly, 151.72 MW power is generated by steam turbine using solar collectors and exhausted gases recovered from the gas turbine. Furthermore, by adding electrolyzer to the integrated system, a total of 131.3 g/s (472.68 kg/h) hydrogen is generated by using excess electricity which leads to more sustainability system.     

Energetics and diffusion of hydrogen in hydrogen permeation barrier of α-Al2O3/FeAl with two different interfaces

To provide insights into the interface structure of hydrogen permeation barrier of α-Al₂O₃/FeAl and its effect on stability and diffusion of hydrogen isotopes, the thermodynamics and kinetics of H diffusion in α-Al₂O₃ (001)/FeAl (111) slab with Al/O and Al/Fe/O interfaces have been studied by the density functional theory. Hexagonal alumina layers above the FeAl plane in interface region are predicted. The interfacial binding involves cation–anion and metal–metal interactions. H-surface interaction on the α-Al₂O₃/FeAl slab resembles that on pure α-Al₂O₃ (001) slab, and the H interstitials in the α-Al₂O₃ part of the slab with the Al/O interface are significantly less stable than in bulk of α-Al₂O₃ slab, whereas that with the Al/Fe/O interface are slightly more stable. H diffusion into the α-Al₂O₃ part of both slabs must overcome a larger barrier of about 1.66–2.02 eV at surface-to-subsurface step, as pure α-Al₂O₃ case. For the bulk path, the migration of H atom can occur more readily in the α-Al₂O₃ part of the slab with the Al/O interface compared to that with the Al/Fe/O interface. Thus α-Al₂O₃/FeAl barrier with interface region of the Al, Fe mix-oxide is predicted to be much effective at protection against H permeation of the underlying steel.     

The metal–carbon–fluorine system for improving hydrogen storage by using metal and fluorine with different levels of electronegativity

In order to improve the capacity of hydrogen storage using activated carbon nanofibers, metal and fluorine were introduced into the activated carbon nanofibers by electrospinning, heat treatment, and direct fluorination. The pore structure of the samples was developed by the KOH activation process and investigated using nitrogen isotherms and micropore size distribution. The specific surface area and total pore volume approached 2800 m²/g and 2.7 cc/g, respectively. Because of the electronegativity gap between the two elements (metal and fluorine), the electron of a hydrogen molecule can be attracted to one side. This reaction effectively guides the hydrogen molecule into the carbon nanofibers. The amount of hydrogen storage was dramatically increased in this metal–carbon–fluorine system; hydrogen content was as high as 3.2 wt%.     

Hydrogen production by Escherichia coli growing in different nutrient media with glycerol: Effects of formate,pH, production kinetics and hydrogenases involved

The Escherichia coli BW25113 or MC4100 wild type parental strains growth and H₂ production kinetics was studied in batch cultures of minimal salt medium (MSM) and peptone medium (PM) at pH of 5.5–7.5 upon glycerol (10 g L^?1) fermentation and formate (0.68 g L^?1) supplementation. The role of formate alone or with glycerol on growth and H₂ production via hydrogenases (Hyd) was investigated in double hyaB hybC (lacking large subunits of Hyd 1 and 2), triple hyaB hybC hycE (lacking large subunits of Hyds 1-3) and sole selC (lacking formate dehydrogenase H) mutants during 24 h bacterial growth. H₂ production was delayed and observed after 24 h bacterial wild type strains growth on MSM. Moreover, it reached the maximal values after 72 h growth at the pH 6.5 and pH 7.5. Biomass formation of the mutants used was inhibited ～3.5 fold compared with wild type, and H₂ production was absent in hyaB hybC hycE and selC mutants upon glycerol utilization on MSM at pHs of 5.5–7.5. Formate inhibited bacterial growth on MSM with glycerol, but enhanced and recovered H₂ production by hybC mutant at pH 7.5. H₂ evolution was delayed at pH 7.5 in PM, but observed and stimulated at pH 6.5 upon glycerol and formate utilization in hyaB hybC mutant. H₂ production was absent in hyaB hybC hycE and selC mutants upon glycerol, formate alone or with glycerol fermentation at pH 6.5 and pH 7.5; formate supplementation had no effect. The results point out E. coli ability to grow and utilize glycerol in MSM with comparably high H₂ yield: as well as they suggest the key role of Hyd-3 at both pH 6.5 and pH 7.5 and the role of Hyd-2 and Hyd-4 at pH 7.5 in H₂ production by E. coli during glycerol fermentation with formate supplementation. The results obtained are novel and might be useful in H₂ production biotechnology development using different nutrient media and glycerol and formate as feedstock.     

Life cycle greenhouse gases emission analysis of hydrogen production from S–I thermochemical process coupled to a high temperature nuclear reactor

A methodology for assessing the environmental impact of products and services is the life cycle analysis (LCA); which is a versatile tool to define the inclusion process and the scope of the production system, for different scenarios and selective comparison of environmental burdens. For the LCA developed in this work, the S–I thermochemical cycle coupled to a high temperature gas nuclear reactor was selected. The defined system function is the production of hydrogen using nuclear energy and the functional unit is 1 kg of hydrogen at the plant gate. The product system was defined by the following steps: (i) extraction and manufacturing of raw materials (upstream flows), (ii) external energy supplied to the system, (iii) nuclear power plant, and (iv) hydrogen production plant. Particular attention was placed to those processes where there was limited information from literature about inventory data, like the TRISO fuel manufacture, and the production of iodine from caliches, which is supplied to the thermochemical process for hydrogen generation. The environmental impact assessment focuses on the emissions of greenhouse gases as comparative parameter related to global warming. The results showed low emissions when electric power was supplied from nuclear energy. When the electric power supply was changed to a mix of fossil fuels, the emissions were significantly higher.     

Energy,exergy, economic and environmental (4E) analysis of using city gate station (CGS) heater waste for power and hydrogen production: A comparative study

This paper deals with energy, exergy, economic, and environmental (4E) analysis of two new combined systems for simultaneous power and hydrogen production. The combined systems are integrated from a city gate station (CGS) system, a Rankine cycle (RC), an absorption power cycle (APC), and a proton exchange membrane (PEM) electrolyzer. Since the pressure of natural gas (NG) in transmission pipeline is high, this pressure is reduced at CGS to a lower pressure. However, this NG has also ample potential to be recovered for multiple productions, too. In the proposed systems, the outlet energy of NG is used for power and hydrogen production by employing RC/APC and PEM electrolyzer. The power sub-cycles are driven by waste heat of CGS, while PEM electrolyzer is driven by this waste heat along with a portion of CGS-Turbine output power. A comprehensive thermodynamic modeling and parametric study of the proposed combined systems are conducted from the 4E analysis viewpoint. The results of two proposed systems are compared with each other, considering a fixed value of 1 MW for RC- and APC-Turbines power. Under the same external conditions and using steam as working fluid of RC, the thermal efficiency of the combined CGS/PEM-RC and -APC systems are obtained 32.9% and 33.6%, respectively. The overall exergy efficiency of the combined CGS/PEM-RC and -APC systems are also calculated by 47.9% and 48.9%, respectively. Moreover, the total sum unit cost of product (SUCP) and CO₂ emission penalty cost rate are obtained 36.9 $/GJ and 0.033 $/yr for the combined CGS/PEM-RC and 36 $/GJ and 0.211 $/yr for the combined CGS/PEM-APC systems, respectively. The results of exergy analysis also revealed that the vapor generator (in both systems) has the main contribution in the overall exergy destruction.