Multi-objective optimization for efficient modeling and improvement of the high temperature PEM fuel cell based Micro-CHP system

Highlights

• The plant efficiency analyzed by considering the effect of degradation during the fuel cell and reformer.

• Electrical generation and the net electrical efficiency were selected as objective functions.

• The results were compared with two different configurations.

Abstract

Fuel cells due to different useful features such as high efficiency, low pollution, noiselessness, lack of moving parts, variety of fuels used and wide range of capacity of these sources can be the main reasons for their tendency to use them in different applications. In this study, the application of a high temperature proton exchange membrane fuel cell (HT-PEMFC) in a combined heat and power (CHP) plant has been analyzed. This study presents a multi-objective optimization method to provide an optimal design parameters for the HT-PEMFC based micro-CHP during a 14,000 h lifetime by considering the effect of degradation. The purpose is to optimize the net electrical efficiency and the electrical power generation. For the optimization process, different design parameters including auxiliary to process fuel ratio, anodic stoichiometric ratio, steam to carbon ratio, and fuel partialization level have been employed. For optimization, A new technique based on Tent mapping and Lévy flight mechanism, called improved collective animal behavior (ICAB) algorithm has been employed to solve the algorithm premature convergence shortcoming. Experimental results of the proposed method has been applied to the data of a practical plant (Sidera30) for analyzing the efficiency of the proposed ICAB based system, it is compared with normal condition and another genetic algorithm based method for this purpose. Final results showed that the difference between the maximum electrical power production under normal condition and ICAB based condition changes from 2.5 kW when it starts and reaches to its maximum value, 3.0 kW, after 14,000 h lifetime. It is also concluded that the cumulative average for the normal and the ICAB based algorithm are 24.01 kW and 27.04 kW, respectively which showed about 3.03 kW cumulative differences.

Introduction

When generating electricity has been directed from power plans to a location near the user, it is possible to use generating heat. About 9% of electricity is wasted on transmission lines. Therefore, a significant amount of energy savings can be achieved when electricity is generated at the site and a significant portion of the heat produced can be used. Another advantage of CHP is that energy security is increased and the vulnerability of the lines is reduced. High-efficiency hybrid cycle power plants convert about 50% of the available energy into electrical power. The micro-CHP units use the heat dissipation of the generator for heating and cooling to increase overall system efficiency [1].

Due to the small size of the CHP units, it is important to note that these units operate at a lower efficiency than the large central power plants. However, if generating heat is used effectively, the overall efficiency can be much higher than the central power plant that is only designed to generate electricity. Another disadvantage is relying on the availability of refined fuel. Large power plants are capable of converting raw refined fuels such as coal into useable power. Small generators need clean fuels like natural gas to work cleanly [2,3].

On the other side, the increasing requirement for energy and the limitation of natural energy resources have made fuel cell research as one of the interesting topics of the researchers. However there are still problems with fuel cells, it has advantages over other power generation equipment such as non-pollution, high energy conversion efficiency, silent operation and high reliability, and is hoped to be one of the main sources of energy in the future. Fuel cells have many advantages over other sources of energy production. That is why a clear perspective is possible for these systems. The micro-combined heat and power (micro-CHP) systems combined with fuel cells give better efficiency compared with ordinary micro-CHPs. Polymer exchange membrane fuel cells (PEMFCs) is a type of promising model of the fuel cells due to their high efficiency, low operating temperature, and fast start-up [4,5]. The PEMFCs are a kind of high efficiency converters with efficiency about 40%–50% in different power scales. Recently, there are several researches about PEMFCs [6,7]. For instance, Solsona et al. [8] introduced an experimental model for a low-temperature PEMFC system in the presence of humidifier. A control procedure was also utilized based on Nafion® membrane. The achievements were compared with empirical achievements.

Kumar et al. [9] proposed and studied on a practical model of PEMFC. The modality of the method was validated by ARX and ARMAX. MATLAB software was used for system identification. PI and PID controllers were adopted for handling the desired load current. Panagiotis et al. [10] introduced dynamical models by considering the electrical equivalent and the semi-empirical formulas for PEMFC. In addition, they proposed a transfer function based model for semi-experimental equations. In another research, Abbaspour et al. [11] introduced a reliable controller based on neural network for PEMFC modeling. The model considered the probability of happening serious damages between the partial pressure of hydrogen and oxygen in PEMFCs. The reason for using neural network was to consider the PEMFC nonlinearities in the problem. Napoli et al. [12] studied on the technical and the economical situation of the SOFC and PEMFC based micro-CHP plant. Results showed that a principal target among different conventional technologies is the investment cost. In 2015, A thermal and economical analysis was performed on a high temperature (HT-PEMFC) based CHP systems by Colella et al. [13]. The results declared that the average electrical power per-unit cost is so higher than the per-unit cost of heat recovery and electrical power.

Herdem et al. [14] performed analyzed on a HT-PEMFC based on gas fuelled methanol reformate system for mobile applications. The paper modeled methanol steam reformer system. Detailed parametric studies were performed, and the power is generated for portable power generation applications. Romdhane et al. [15]introduced an eco-dynamic model for a PEMFC based micro-CHP. The system included a micro-CHP system based on PEMFC. In the research, the eco-neighborhood efficiency of a site in North-West of France has been analyzed. The method has been validated and developed by empirical data.

The main purpose of this paper is to analyze the long-term efficiency of an HT-PEMFC based micro-CHP plant with performing multi-objective optimization. The main purpose is to employ net electrical efficiency and thermal generation as objectives function. Several parameters including auxiliary to process fuel ratio, steam to carbon ratio, anodic stoichiometric ratio, and fuel partialization are provided for design parameters. At final, to declare the advantage of the proposed method, the values of electrical production and the lifetime electrical performance have been compared.