Design and optimization of electrochemical cell potential for hydrogen gas production

© 2020 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences This study deals with the optimization of best working conditions in molten melt for the production of hydrogen (H2) gas. Limited research has been carried out on how electrochemical process occurs through steam splitting via molten hydroxide. 54 combinations of cathode, anode, temperature and voltage have been investigated for the optimization of best working conditions with molten hydroxide for hydrogen gas production. All these electrochemical investigations were carried out at 225 to 300°C temperature and 1.5 to 2.5 V applied voltage values. The current efficiency of 90.5, 80.0 and 68.6% has been achieved using stainless steel anodic cell with nickel, stainless steel and platinum working cathode respectively. For nickel cathode, an increase in the current directly affected the hydrogen gas flow rate at cathode. It can be hypothesized from the noted results that increase in current is directly proportional to operating temperature and applied voltage. Higher values were noted when the applied voltages increased from 1.5 to 2.5 V at 300°C, the flow rate of hydrogen gas increased from 1.5 to 11.3 cm3 min−1, 1.0 to 13 cm3 min−1 in case of electrolysis @ stainless steel and @ graphite anode respectively. It is observed that the current efficiency of stainless steel anodic cell was higher than the graphite anodic cell. Therefore, steam splitting with the help of molten salts has shown an encouraging alternate to current methodology for H2 fuel production

Graphitic Carbon Nitride as a Catalyst Support in Fuel Cells and Electrolyzers

Electrochemical power sources such as polymer electrolyte membrane fuel cells (PEMFCs) require the use of precious metal catalysts, which are deposited as nanoparticles onto supports in order to minimize their mass loading and therefore cost. State-of-the-art/commercial supports are based on forms of carbon black. However, carbon supports present disadvantages including corrosion in the operating fuel cell environment and loss of catalyst activity. Here we review recent work examining the potential of different varieties of graphitic carbon nitride (gCN) as catalyst supports, highlighting their likely benefits, as well as the challenges associated with their implementation. The performance of gCN and hybrid gCN-carbon materials as PEMFC electrodes is discussed, as well as their potential for use in alkaline systems and water electrolyzers. We illustrate the discussion with examples taken from our own recent studies.This project has received funding from the European Union’s Graphene Flagship under Horizon 2020 research and innovation programme grant agreement No. 696656 – GrapheneCore1 and from the EPSRCEP/L017091/1. C.M. acknowledges the award of a Royal Society University Research Fellowship by the UK Royal Society

Special Issue on “Dynamic Modeling and Control in Chemical and Energy Processes”

Recent energy policies have enforced the need to minimize GHG emissions [...

Design and Simulation of a Feedback Controller for an Active Suspension System: A Simplified Approach

The concept of controlling vehicle comfort is a common problem that is faced in most under- and postgraduate courses in Engineering Schools. The aim of this study is to provide a simplified approach for the feedback control design and simulation of active suspension systems, which are applied in vehicles. Firstly, the mathematical model of an active suspension system (a quarter model of a car) which consists of a passive spring, a passive damper and an actuator is provided. In this study, we chose to design and compare the following controllers: (a) conventional P, PI and PID controllers that were tuned through two conventional methodologies (Ziegler–Nichols and Tyreus–Luyben); (b) an optimal PID controller that was tuned with a genetic algorithm (GA) optimization framework in terms of the minimization of certain performance criteria and (c) an internal model controller (IMC) based on the process transfer function. The controllers’ performance was assessed in a series of realistic scenarios that included set-point tracking with and without disturbances. In all cases, the IMC controller and the optimal PID showed superior performance. On the other hand, the P and PI controllers showed a rather insufficient behavior that involved persistent errors, overshoots and eventually, uncomfortable ride oscillations. Clearly, a step-by-step approach such as this, that includes modeling, control design and simulation scenarios can be applied to numerous other engineering examples, which we envisage to lead more students into the area of automatic control

Optimal operation of power systems utilizing renewable and alternative energy sources

The exaggeration of fossil fuel reserves in conjunction with the simultaneous increase in greenhouse gas emissions has recently aspired scientific community towards the study of environmental and energy related issues. The main idea of the thesis is to systematically develop optimal operation methods applied in innovative integrated systems that will suitably exploit renewable and alternative energy sources. The proposed RES-integrated system exploits solar and wind energy with the use of photovoltaic systems and wind turbines, respectively. The produced power is used to meet the electrical needs of a fixed load and a lead-acid accumulator is implemented to absorb excess energy peaks that further provides to the system in periods of low power production. In order to boost the autonomous system operation, a water electrolyzer and a fuel cell are also incorporated. In cases of a subsystem operation failure (e.g. hydrogen deficit), a diesel engine is responsible to meet the energy needs as a back-up unit. The integrated system based on methanol, involves the power production by a fuel cell towards meeting the energy criteria of a variable load. The necessary hydrogen is produced by methanol steam reforming in a plug flow reactor. Due to the inevitable CO production, a preferential oxidation reactor is employed as a prerequisite for ensuring CO concentration levels below 50ppm. The utilities subsystems comprise two heat exchangers and a burner that provides heat by using the effluent of the fuel cell anode and an additional methanol supply as a main fuel. [...]Η ραγδαία μείωση των αποθεμάτων ορυκτών καυσίμων και η ταυτόχρονη αύξηση των εκπομπών των αερίων του θερμοκηπίου, ενέπνευσαν την ερευνητική κοινότητα στην μελέτη των αλληλένδετων ενεργειακών και περιβαλλοντικών προβλημάτων. Βασικό μέλημα της διατριβής αποτελεί η ανάπτυξη και η μελέτη της βέλτιστης λειτουργίας, δύο καινοτόμων ολοκληρωμένων συστημάτων που βασίζονται στην αξιοποίηση ανανεώσιμων (Α.Π.Ε.) και εναλλακτικών πηγών ενέργειας. Η ολοκληρωμένη μονάδα αξιοποίησης ηλιακής και αιολικής ενέργειας, απαρτίζεται από φωτοβολταϊκά συστήματα και ανεμογεννήτριες που αποδίδουν ισχύ προς κάλυψη των ενεργειακών αναγκών ενός σταθερού φορτίου. Συσσωρευτής μολύβδου-οξέος χρησιμοποιείται για την απορρόφηση της περίσσειας ισχύος και την απόδοση της σε περιόδους ελλειμματικής παραγωγής. Η ενίσχυση της αυτονομίας του συστήματος, εξασφαλίζεται με την ενσωμάτωση μίας μονάδας ηλεκτρόλυσης και μίας κυψέλης καυσίμου. Σε περιπτώσεις προβληματικής λειτουργίας (π.χ. ελλείμματος υδρογόνου), αξιοποιείται μία ντηζελογεννήτρια που λαμβάνει τον χαρακτήρα υποσυστήματος εκτάκτου ανάγκης. Η ολοκληρωμένη μονάδα αξιοποίησης μεθανόλης περιλαμβάνει την απόδοση ισχύος από κυψέλη καυσίμου προς κάλυψη των ενεργειακών αναγκών ενός μεταβαλλόμενου φορτίου. Το απαιτούμενο υδρογόνο παράγεται από την καταλυτική επεξεργασία μεθανόλης σε αντιδραστήρα αυτόθερμης αναμόρφωσης. Λόγω όμως, της ανάγκης παραγωγής υδρογόνου υψηλής καθαρότητας, υλοποιείται και αντιδραστήρας επιλεκτικής οξείδωσης που επιφορτίζεται με το ρόλο της μείωσης του CO σε επίπεδα χαμηλότερα των 50ppm. Συμπληρωματικά υποσυστήματα της ολοκληρωμένης μονάδας αποτελούν δύο εναλλάκτες θερμότητας, καθώς και ένας φούρνος που αποδίδει θερμότητα με βάση το ρεύμα των απαερίων της κυψέλης καυσίμου, καθώς και της επιπλέον παροχής μεθανόλης. [...

Dynamic Modeling and Control of a Coupled Reforming/Combustor System for the Production of H2 via Hydrocarbon-Based Fuels

The present work aims to provide insights into the dynamic operation of a coupled reformer/combustion unit that can utilize a variety of saturated hydrocarbons (HCs) with 1–4 C atoms towards H2 production (along with CO2). Within this concept, a preselected HC-based feedstock enters a steam reforming reactor for the production of H2 via a series of catalytic reactions, whereas a sequential postprocessing unit (water gas shift reactor) is then utilized to increase H2 purity and minimize CO. The core unit of the overall system is the combustor that is coupled with the reformer reactor and continuously provides heat (a) for sustaining the prevailing endothermic reforming reactions and (b) for the process feed streams. The dynamic model as it is initially developed, consists of ordinary differential equations that capture the main physicochemical phenomena taking place at each subsystem (energy and mass balances) and is compared against available thermodynamic data (temperature and concentration). Further on, a distributed control scheme based on PID (Proportional–Integral–Derivative) controllers (each one tuned via Ziegler–Nichols/Z-N methodology) is applied and a set of case studies is formulated. The aim of the control scheme is to maintain the selected process-controlled variables within their predefined set-points, despite the emergence of sudden disturbances. It was revealed that the accurately tuned controllers lead to (a) a quick start-up operation, (b) minimum overshoot (especially regarding the sensitive reactor temperature), (c) zero offset from the desired operating set-points, and (d) quick settling during disturbance emergence

Dynamic Modeling and Control Issues on a Methanol Reforming Unit for Hydrogen Production and Use in a PEM Fuel Cell

Abstract: The presented research work focuses on the mathematical description and control analysis of an integrated power unit that uses hydrogen produced by methanol autothermal reforming. The unit consists of a reformer reactor where methanol, air and water are co-fed to produce a hydrogen rich stream through a series of reactions. The hydrogen main stream is fed to a preferential oxidation reactor (PROX) for the reduction of CO at levels below 50ppm with the use of air. In the end, the PROX outlet stream enters the anode of a PEM fuel cell where power production takes places to serve a load demand. The operation of the two reactors is described by a combination of partial differential equations (mass and energy balances) and non-linear equations (kinetic expressions of the reactions), while the power production in the fuel cell is based on the inlet hydrogen flow and on operational characteristics. A simple case sceanrio is employed when a step change on methanol flowrate is imposed. Main target is to identify and analyze the changes occuring in the main variables of concern (H 2 , CO and temperature levels) that affect the overall system operation. Based on the results, an insight on the challenging control scheme will be applied in order to identify possible ways of setting up a reliable and robust control structure according to the developed mathematical model