Format And Type Fonts CCHHEEMMIICCAALL EENNGGIINNEEEERRIINNGG TTRRAANNSSAACCTTIIOONNSS VOL. 39, 2014 A publication of The Italian Association of Chemical Engineering www.aidic.it/cet Guest Editors: Petar Sabev Varbanov, Jiří Jaromír Klemeš, Peng Yen Liew, Jun Yow Yong Copyright © 2014, AIDIC Servizi S.r.l., ISBN 978-88-95608-30-3; ISSN 2283-9216 DOI: 10.3303/CET1439069 Please cite this article as: Göllei A., Görbe P., Magyar A., 2014, Examination, modelling and simulation of hydrogen generation cell for complex renewable energy system, Chemical Engineering Transactions, 39, 409-414 DOI:10.3303/CET1439069 409 Examination, Modelling and Simulation of Hydrogen Generation Cell for Complex Renewable Energy System Attila Göllei*, Peter Görbe, Attila Magyar Department of Electrical Engineering and Information Systems, University of Pannonia, H-8200 Veszprém, Hungary golleia@almos.vein.hu Nowadays, the growing need for energy from renewable sources and growing revulsion towards fossil and nuclear fuels turns sustainable and green energy in the foreground. Producing (electrical) energy from renewable sources hardly means difficulties but the storage of the energy not consumed immediately is a great engineering challenge. In the present paper a complex model has been developed by investigating renewable energy sources, converting currently unnecessary energy to Hydrogen for storage purposes and feeding the main grid. A measurement based model of a Hydrogen generating cell developed for simulation of complex energetic system is presented in this paper. The parameter estimation of the static model has been performed based on measurement data collected during the detailed examination of a demonstration cell. Series of experiments has been carried out on a HHO gas producing dry cell in order to find out if there are optimal electrolyte concentration, current value, or geometric parameter (distance between plates) values for this equipment. During the measurement KOH electrolyte solution was used while different signals has been measured, for example cell voltage, gas production value. As a result of the experiments, a cell operating in an optimal way has been developed. The novel element of this work is the temperature and concentration dependent Matlab Simulink model of the hydrogen generation cell. Using this model, a dynamic simulator of a complex domestic power plant using renewable energy source and H2 generation cell become available. Hydrogen generation enables the long range storage of spare electric energy collected but not consumed or injected into the low voltage grid. The generated Hydrogen can be consumed by vehicles for transportation purposes or it can be applied in fuel cells generating direct electrical energy for energy-deficient low voltage network situations. Energetic situations potentially occurring in practice have been simulated in the complex model. Several hours of simulations showed that the presented H2 generating cell model performed well. Producing H2 from excess energy is not a brand new invention. This is the alternative way to store and convert renewable energy for further utilization. The produced Hydrogen can be used to store, to use in power cell to convert back to electric energy or to use in Hydrogen propulsion vehicles. Among the numerous realized H2 producing applications the most important class is when the energy consumption and the quantity of produced H2 is controlled. When the power consumption and generation are continuous (and not necessarily deterministic) function of time, the H2 production depends solely on the excess energy of the grid. 1. Introduction Producing Hydrogen and Oxygen from water using electricity is a very simple electrochemical process that can be performed easily and in a very demonstrative way. Producing Hydrogen in large scale or industrial quantities calls for an optimized or a near-optimized cell model. In a highly energy demanding process only a few percent of variance in the efficiency could mean a significant energy surplus or shortage (Görbe et al, 2009). The so-called dry cell is used here to produce Hydrogen and Oxygen gas and henceforward the electrochemical parameters of this dry cell are discussed. The name could be misleading as this electrolyzing cell uses water just like any other electrolyzing unit. There are, though, some attributes of this cell that makes it easier to design and handle. With wet HHO cells, the whole unit is underwater, while in the case of dry cells, the plates are separated with rubber seals. These seals stop the water from leaking 410 + - G as outlet Water inlet Stainless steal plates Rubber sealing Figure 1: The setup of a HHO gas generator cell block from the cell, the electrical connections and the edges of the plates are not touching the electrolyte. These parts of the unit are staying dry, thus the name dry cell. To make sure the gas made from the electrolyte gets out of the cell and the solution to flow between the plates, there are holes on the top (for the gas) and bottom (for the electrolyte) on the metal slats. Applications for H2 production can be found in international literature. For example the procedure presented in (Koutsonikolasa et al., 2013). Although the described procedure is efficient and able to produce a high quantity of H2 it is not suitable for an application like domestic power plant. The accurate solution is the usage of SCADA management system (Ziogoua et al., 2013). The domestic applicability of this technology in the future depends on the cost of SCADA system installation basically. Applying HHO units has two main advantages: 1. The surface of the dry cell plates enables one to use smaller amount of electrolyte compared to wet cells. Therefore, the volume and weight of the cell is smaller. 2. As opposed to wet cells, where the connectors are underwater therefore their surface is slowly corroded by the electrolyte, the connectors of dry cells remain dry, i.e. they do not corrode. (Al-Rousan, 2010). 1.1 The HHO cell unit The setup of one block of the unit can be seen in Figure 1. Usually 5 cells make up one block, so 5 cells connected in series gives one gas-producing block. The block’s electrical connections are on the two plates on the ends. Four of the six electrode plates are neutral electrodes, as there is no voltage connected to them. The potential is divided between the neutral plates according to voltage division in series connections. It means, that voltage between two electrodes is one fifth of the voltage on one whole block. In the experiment, a unit with 3 blocks connected in parallel has been used. Besides the HHO cell, a water reserve tank to infuse the electrolyte into the cell was necessary. A tube between the gas outlet and the tank has also been installed since the gas produced is not pure, it comes out as bubbles, so there is electrolyte coming out in the tube that needs to be recycled into the system. Then, as the electrolyte drips back in the tank, the gas can escape into the bottle through another hose. The produced H2 volume and the production speed is measured with this bottle. A power supply (Manson SPS9600) has been connected to the electrical connections of the HHO unit, this way the current input was controlled during the experiment. 2. Matlab model of dry cell The model of the measured dry cell was implemented in Matlab Simulink using the SimPowerSystems Toolbox. Two unknown functional relationships, one between the generated H2 volume, the cell current and the KOH concentration and another one between cell voltage, cell current and KOH concentration were approximated using 4 th and 3 rd order polynomials, respectively using Matlab Surface Fitting Tool. As Table 1: Experimental results Electrolyte concentration (g/L) MMW (mL/min/W) Gas production (L/min) Power of unit (W) Electrolyte concentration (g/L) MMW (mL/ min/W) Gas production (L/min) Power of unit (W) 1 2.13 0.2 10.8 6 2.63 2.52 119.5 2 2.66 0.75 34.44 7 2.67 2.96 140 3 2.66 1.37 55.83 8 2.65 2.76 125 4 2.59 1.51 82.15 9 2.46 2.28 105.6 5 2.72 1.9 90.6 10 1.82 2.15 103.2 411 the fitted polynomials do not have a physical meaning, the model is applicable to any similar electrochemical H2 generation device with electrical two pole system (in the various linear and nonlinear physical and chemical models, different coefficients will be dominant). The voltage relationship is given by Eq(5), where icell denotes the cell current and cKOH stands for the KOH concentration. KOHcellcell KOHKOHcellcellKOHcellKOHcellcell ci + pi+p c + pc i + p i + p c + p i + ppciu 2 21 3 30 2 0211 2 20011000 ),(  (5) The volume of the generated H2 is given by the polynomial Eq(6). 3 13 22 22 3 31 4 40 3 03 2 12 2 21 3 30 2 0211 2 200110002 KOHcellKOHcell KOHcellcellKOHKOHcellKOHcellcell KOHKOHcellcellKOHcellKOHcell c i+ pc i+p c i + p i + p c +pc i+ pc i + p i+p c + pc i + p i + p c + p i + p) = p,c(iH (6) A Simulink block scheme of the cell model is depicted in Figure 2. This Simulink model was validated by exposing the system to the same circumstances as the original measuring layout as the original cell, i.e., a measurement procedure was implemented. In this layout we run a long range simulation (24h) with this model, lowering water and rising KOH concentration conditions. It can be seen, the generating hydrogen is reducing because of the rising KOH concentration, this, and the exact values are suiting to our measuring results exactly. The results are shown in Figure 3 and Figure 6, Table 2: Coefficients of polynomial relationship describing the cell voltage Coefficient Value Coefficient Value Coefficient Value p00 1.429 p10 0.2548 p01 -0.1226 p20 -0.008571 p11 -0.01191 p02 0.008257 p30 0.0001141 p21 -8.76e-05 p12 0.0009697 Table 3: Coefficients of the polynomial relationship for the generated H2 gas. Coefficient Value Coefficient Value Coefficient Value p00 -0.1695 p10 0.1687 p01 -0.01765 p20 -0.007486 p11 -0.03234 p02 0.03446 p30 -0.0001077 p21 0.00412 p12 -0.004094 p03 -0.004061 p40 -4.269e-06 p31 6.169e-05 p22 -0.0005518 p13 0.0009544 Figure 2: Matlab Simulink model of the HHO cell. The functional blocks implementing the polynomial relationships (5) and (6) are denoted with different background colour 412 Figure 3: Simulation of cell model with constant 5 A current for 1 d. As it was expected, as the amount of water decreases and the KOH concentration increase, the H2 generation speed decreases and the cell finally stops 3. Dry cell model in complex energy systems The H2 generating cell model developed in the previous section was investigated in Matlab Simulink simulation environment that simulates the energy flow conditions of a complex energy system consisting of a renewable source with a grid-synchronized inverter, a low voltage grid, an intermediate voltage controller (see Görbe et al. 2010) and a Lithium-ion battery. We replaced the lithium ion battery to this cell model. It reduces the potential energy flow modes, because this cell can only adsorb current for storing energy in developed Hydrogen, it can’t reverse the electrochemical process for electrical energy from Hydrogen. The structure of the system can be seen in Fig. 4, where it is apparent that the cell model is connected directly only to the grid-synchronized inverter module of the system. Figure 4: Matlab Simulink model of a complex energetic system with HHO cell model inside 413 Table 4: Parameters of the complex energetic system energy mode simulation Time 0-1 s 1-2 s 2-3 s 3-4 s 4-5s I Outer Load Peak 0A 50A 0A -20A 30A PV panel Grid Synchronized Inverter Nonlinear Electric Network Hydrogen generation cell + - PV panel Grid Synchronized Inverter Nonlinear Electric Network Hydrogen generation cell + - PV panel Grid Synchronized Inverter Nonlinear Electric Network Hydrogen generation cell + - PV panel Grid Synchronized Inverter Nonlinear Electric Network Hydrogen generation cell + - A B C D Fig. 5: Complex energetic system energy flow modes: A:Normal inverter mode, B: inverter and Hydrogen generator mode, C: Hydrogen generation only mode, D: Distortion reduction only mode The system depicted in Figure 4 operates in different discrete states according to the energy flow direction. Four cases can be defined: - Normal inverter mode: The energy flows from the renewable source to the grid only (Figure 5.A). - Normal inverter and Hydrogen generation mode: The energy flows from the renewable source to both the dry cell and the grid (Figure 5.B). - Hydrogen generation only mode: The energy flows from the grid to the dry cell only (Figure 5.C). - Distortion reduction only mode: The energy flows from the grid into the intermediate capacitance and from the intermediate capacitance into the grid. The energy balance is zero for any whole period, and the active power is zero. (Figure 5.D). Model verification was performed by changing the energy flow modes in subsequent time intervals, and this was implemented by changing the energy balance of the system with outer current loads (I outer load). The different values for the simulations as parameters can be seen in Table 4. The simulation results are shown in Figure 6, where Uconn is the effective value oft the voltage at the connection point, IHHO is the current value of the dry cell, H2 generated is the volume of the generated Hydrogen, KOH conc is the KOH concentration of the electrolyte and Water is the volume of the water inside the cell system. These values are plotted as a function of time. The results of the simulation show that the behaviour of the simulated electronic two-pole system is identical to that of the measured database. 4. Conclusion We developed a complex model investigating renewable energy sources, converting currently unnecessary energy to hydrogen for storage purposes and feeding the main grid. We built a measurement based model of hydrogen generating cell for simulation of complex energy system in MATLAB SIMULINK 414 Figure 6: Simulation results of a complex energetic system with Cell model short time range (5 sec) environment. We estimated the model parameters based on measurement data collected during the detailed examination of a demonstration cell. We carried out a series of experiments on a HHO gas producing dry cell to find the optimal electrolyte concentration, current value, etc. or changing the setup by alternating the distance between the plates with KOH electrolyte solution. We monitored it in several regards, for example cell voltage, gas production, mL/min/W value. The novel element is the temperature and concentration dependent Matlab Simulink model of the hydrogen generation cell. This is suitable for simulation purposes. We tested it in a simulation of a complex domestic power plant using renewable energy source and hydrogen generation cell. Hydrogen generation enables the long range storage of spare electric energy collected but not consumed or injected into the low voltage grid. The generated hydrogen can be consumed by vehicles for transportation purposes or it can be applied in fuel cells generating direct electrical energy for energy-deficient low voltage network situations. We simulated all the potential energetic situations in this complex energetic system model. The simulations showed that the presented hydrogen generating cell model performed well. Acknowledgement We acknowledge the financial support of this work by the Hungarian State and the European Union under the TAMOP-4.2.2.A-11/1/ KONV-2012-0072 project. References Al-Rousan A. A., 2010, Reduction of fuel consumption in gasoline engines by introducing HHO gas into intake manifold. International Journal of Hydrogen Energy 35, 12930-12935 Bonzel H.P., Bradshaw A.M., Ertl G., Eds., 1989, Physics and Chemistry of Alkali Metal Adsorption. 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Görbe P, Magyar A., Hangos K.M., 2010a, THD Reduction with Grid Synchronized Inverter’s Power Injection of Renewable Sources, 20th International Symposium on Power Electronics, Electrical Drives, Automation and Motion (SPEEDAM) ISBN:978-1-4244-7919-1, 1381-1386 Görbe P., Magyar A., Hangos K.M., 2010b, Power Conditioning with Electric Car Battery Charging from Renewable Sources, Hungarian Journal of Industrial Chemistry, 38(1) , HU ISSN: 0133-0276, 27-33 Koutsonikolas D.E., Kaldis S.P., Pantoleontos G.T., Zaspalisa V.T., Sakellaropoulos G.P., 2013, Techno- Economic Assessment of Polymeric, Ceramic and Metallic Membranes Integration in an Advanced IGCC Process for H2 Production and CO2 Capture, Chemical Engineering Transactions, 35, 715-720. 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