Evolutionary based multi-criteria optimization of an integrated energy system with SOFC,gas turbine,and hydrogen production via electrolysis

The aim of this study is to exploit the waste heat of a biomass-based solid oxide fuel cell (SOFC)–model (a)–in a gas turbine (GT) to enhance the power generation/exergy efficiency (model (b)). Moreover, surplus power which is generated by the GT is transferred to a proton exchange membrane electrolyzer (PEME) for hydrogen production (model (c)). Parametric study is performed to investigate the influence of the effective parameters on performance and economic indicators. Eventually, considering exergy efficiency and total product cost as the objective functions, the proposed models are optimized by multi-objective optimization method based on genetic algorithm. Accordingly, the optimum solution points are gathered as Pareto frontiers and subsequently favorable solution points are ascertained from exergy/economic standpoints. Results of parametric study indicate that model (b) is the best model as it has higher exergy efficiency and lower total product cost. Moreover, model (c) may be a more suitable model compared to the model (a) because of higher exergy efficiency and capability of hydrogen production. The results further show that, at the best final solution point, the exergy efficiency and total product cost of the model (b) would be 33.22% and 19.01 $/GJ, respectively. Corresponding values of exergy efficiency and total product cost of the model (c) are 32.3% and 20.1 $/GJ. Moreover, the rate of hydrogen production of the model (c) is 8.393 kg/day, at the best solution point. Overall, the integration methods are promising techniques for increasing exergy efficiency, reducing total product cost and also for hydrogen production.     

High and rapid hydrogen release from thermolysis of ammonia borane near PEM fuel cell operating temperatures: Effect of quartz wool

Ammonia borane (NH₃BH₃, AB), containing 19.6 wt% hydrogen, is a promising hydrogen storage material for use in proton exchange membrane fuel cell (PEM FC) powered vehicles. We recently demonstrated that using quartz wool, the highest H₂ yield (2.1–2.3H₂ equivalent) values were obtained by neat AB thermolysis near PEM FC operating temperatures, along with rapid kinetics, without the use of either catalyst or chemical additives. It was found that quartz wool minimizes sample expansion and facilitates the production of diamoniate of diborane (DADB), which is a key intermediate for the release of hydrogen from AB. It was also found that only trace amount of ammonia (<10 ppm) is produced during dehydrogenation reaction and spent AB products are found to be polyborazylene-like species, which can be efficiently regenerated using currently demonstrated methods. The results indicate that our proposed method is the most promising one available in the literature to-date for hydrogen storage, and could be used in PEM FC based vehicle applications.     

Wind/hydrogen hybrid systems: Opportunity for Ireland’s wind resource to provide consistent sustainable energy supply

Ireland with its resource of wind has the potential to use this natural resource and sustain the country’s power needs for the future. However, one of the biggest drawbacks to renewable energy generation, particularly wind-generated electricity is that it is an intermittent and a variable source of power. Even at the “best” sites wind varies dramatically from hour to hour and minute to minute. This leads to two main problems:     

Separation of hydrogen from hydrogen/ethylene mixtures using PEM fuel cell technology

This article is a study of the feasibility of electrochemically separating hydrogen from hydrogen/ethylene mixtures. Experimental results are presented for the performance of the anode of a proton exchange membrane (PEM) fuel cell that is used to separate hydrogen/ethylene mixtures. Experiments were performed using a single cell PEM fuel cell. The experimental results show that, to a large extent, the ethylene reacts with the hydrogen in the anode chamber to form ethane. In spite of this reaction, it is still possible to separate a significant portion of the hydrogen and options for improving the separation efficiency are discussed. A zero-dimensional mathematical model of the hydrogen separation and hydrogenation process has been developed and it has been shown that this model gives generally good agreement with the experimental results.     

A 5 kWt catalytic burner for PEM fuel cells: Effect of fuel type,fuel content and fuel loads on the capacity of the catalytic burner

For proton exchange membrane fuel cell systems (PEMFC) integrated with fuel processors, the calorific value of reformate gases produced during the start-up phase must be recovered. An appropriate exhaust after treatment system has crucial importance for PEMFC systems. Catalytic combustion is a promising alternative regarding its total oxidation capability of low calorific value gases at low temperatures, thereby reducing environmentally hazardous emissions. The aim of the study is to develop an after treatment system using a catalytic burner with a nominal capacity of 5 kW_t, which is also adaptive to partial loads of PEM fuel cell capacity. Fuel type, fuel composition and fuel loads are important parameters determining the operating window of the catalytic burner. Precious metal based catalysts, as proved to be the most active catalysts for the oxidation of hydrocarbons, can withstand temperatures of about 1073 K without exhibiting a rapid deactivation. This is the main barrier dictating the operating window and thereby determining the capacity of the burner. In this work, 1.5% natural gas (NG) alone was found to be the upper limit to control the catalyst bed temperature below 1073 K. In the case of catalytic combustion of hydrogen–NG mixture, 7% of hydrogen with NG up to 0.6% could be totally oxidized below 1073 K. Within the experimented ranges of fuel loads, between 2.5 kW_t and 5.5 kW_t, the temperature of the catalyst bed was seen to increase with increasing the fuel load at constant fuel percentages. It has been observed that fuel type was another parameter affecting the exhaust gas temperature.     

Alkali free hydrolysis of sodium borohydride for hydrogen generation under pressure

The present study is related with the production of hydrogen gas (H₂), at elevated pressures and with high gravimetric storage density, to supply a PEM fuel cell on-demand. To achieve this goal, solid sodium borohydride (NaBH₄) was mixed with a proper amount of a powder reused nickel–ruthenium based catalyst (Ni–Ru based/NaBH₄: 0.2 and 0.4 g/g; ≈150 times reused) inside the bottom of a batch reactor. Then, a stoichiometric amount of pure liquid water (H₂O/NaBH₄: 2–8 mol/mol) was added and the catalyzed NaBH₄ hydrolysis evolved, in the absence of an alkali inhibitor. In this way, this research work is designated alkali free hydrolysis of NaBH₄ for H₂ generation. This type of hydrolysis is excellent from an environmental point of view because it does not involve strongly caustic solutions. Experiments were performed in three batch reactors with internal volumes 646, 369 and 229 cm³, and having different bottom geometries (flat and conical shapes). The H₂ generated was a function of the added water and completion was achieved with H₂O/NaBH₄ = 8 mol/mol. The results show that hydrogen yields and rates increase remarkably increasing both system temperature and pressure. Reactor bottom shape influences deeply H₂ generation: the conical bottom shape greatly enhances the rate and practically eliminates the reaction induction time. Our system of compressed hydrogen generation up to 1.26 MPa shows 6.3 wt% and 70 kg m⁻³, respectively, for gravimetric and volumetric hydrogen storage capacities (materials-only basis) and therefore is a viable hydrogen storage candidate for portable applications.     

A solar thermal cooling and heating system for a building: Experimental and model based performance analysis and design

A solar thermal cooling and heating system at Carnegie Mellon University was studied through its design, installation, modeling, and evaluation to deal with the question of how solar energy might most effectively be used in supplying energy for the operation of a building. This solar cooling and heating system incorporates 52 m² of linear parabolic trough solar collectors; a 16 kW double effect, water-lithium bromide (LiBr) absorption chiller, and a heat recovery heat exchanger with their circulation pumps and control valves. It generates chilled and heated water, dependent on the season, for space cooling and heating. This system is the smallest high temperature solar cooling system in the world. Till now, only this system of the kind has been successfully operated for more than one year. Performance of the system has been tested and the measured data were used to verify system performance models developed in the TRaNsient SYstem Simulation program (TRNSYS). On the basis of the installed solar system, base case performance models were programmed; and then they were modified and extended to investigate measures for improving system performance. The measures included changes in the area and orientation of the solar collectors, the inclusion of thermal storage in the system, changes in the pipe diameter and length, and various system operational control strategies. It was found that this solar thermal system could potentially supply 39% of cooling and 20% of heating energy for this building space in Pittsburgh, PA, if it included a properly sized storage tank and short, low diameter connecting pipes. Guidelines for the design and operation of an efficient and effective solar cooling and heating system for a given building space have been provided.     

Design optimization of rib/channel patterns in a PEMFC through performance heterogeneities modelling

In this paper, an approach coupling an along the channel and rib-channel models has been developed to perform a design optimization of PEM fuel cell bipolar plates rib/channel patterns. Overall performance mainly results from a competition between current collection and oxygen supply. The allows proposed to investigate the effect of geometry and operating parameters on the resulting equilibrium and optimum. Moreover, heterogeneities issued from the crushing effect by the rib on the GDL are accounted.The electrochemical parameters used in the model are fitted to experimental measurements before being used in the optimization process. Results at the channel/rib scale show the competition between the oxygen supply from the gas channel to the catalyst layer and the current collection by the ribs. This understanding is possible thanks to the access to local conditions (such as the oxygen concentration) given by the model which are difficult to reach with experimental measurements. In-plane and through plane heterogeneities of current density distribution in the catalyst layer are exhibited.Design optimization is performed on the channel width/total width ratio on the cathode side. The model suggests an optimal channel design by varying its width along the flow while the standard design considers a contant ratio. This optimal channel is shown to be mainly dependent on the stoichiometry ratio of oxygen.     

Photocatalytic hydrogen production for PEMFC supply: A new issue

Photocatalysis was used to produce hydrogen via alcohol dehydrogenation with a Pt/TiO₂ catalyst. An experiment of coupling was realized between a photocatalytic hydrogen production reactor and an air-breathing PEM fuel cell. The photocatalytic hydrogen consumption rate achieved an optimum value for a loading of 1 wt% of platinum. Three different alcohols were compared. Their hydrogen production efficiency and the maximum current for the PEM fuel cell were compared and were ranged as: methanol ≥ ethanol > 2-propanol. The photocatalytic production was successfully used to feed the PEM fuel cell and reached a current of 0.202 A corresponding to a current density of 8.1 mA cm⁻². No poisoning effect occurred for 100 h of working.     

Design of a cost-effective on-grid hybrid wind–hydrogen based CHP system using a modified heuristic approach

An economic model and optimization procedure is developed in this paper for grid-connected hybrid wind–hydrogen combined heat and power systems for residential applications in northeastern Iran. The model considers various significant factors: energy production cost, electrical trade with local grid, electrical power generation from the wind/hydrogen energy system, thermal recovery from the fuel cell, and maintenance. Also, various tariffs for purchasing and selling electrical energy from the local grid are considered for the hybrid system operation. The optimization objective is to minimize the system total cost subject to relevant constraints for residential applications. To achieve this aim, an efficient optimization method is proposed based on particle swarm optimization. The proposed algorithm performance is compared with that for the imperialist competition algorithm. The results show that the hybrid system is the most cost-effective for the residential load, and the results of the proposed algorithm are more promising than those for the alternative algorithm.     

Conceptual design of an integrated thermally self-sustained methanol steam reformer – High-temperature PEM fuel cell stack manportable power generator

We have investigated the concept of an integrated system for small, manportable power units. The focus of this study is the direct thermal coupling of a methanol steam reformer (MSR) and a high-temperature proton exchange membrane fuel cell (HT PEMFC) stack. A recently developed low-temperature (LT) MSR catalyst (CuZnGaO_x) was synthesized and tested in a designed reforming reactor. The experimental data show that at 200 °C the complete conversion of methanol is achievable with a hydrogen yield of 45 cm³ min^?1 g_CAT^?1. An experimental setup for measuring the characteristics of the integrated system was designed and used to measure the characteristics of the two-cell HT PEMFC stack. The obtained kinetic parameters and the HT PEMFC stack characteristics were used in the modeling of the integrated system. The simulations confirmed that the integrated LT MSR/HT PEMFC stack system, which also includes a vaporizer, can achieve a thermally self-sustained working point. The base-case scenario, established on experimental data, predicts a power output of 8.5 W, a methanol conversion of 98.5%, and a gross electrical efficiency (based on the HHV) of the system equal to 21.7%. However, by implementing certain measures, the power output and the electrical efficiency can readily be raised to 11.1 W and 35.5%, respectively.