scholarly journals Enhancing the Energy Efficiency of Wastewater Treatment Plants through Co-digestion and Fuel Cell Systems

2017 ◽  
Vol 5 ◽  
Author(s):  
Marta Gandiglio ◽  
Andrea Lanzini ◽  
Alicia Soto ◽  
Pierluigi Leone ◽  
Massimo Santarelli
Keyword(s):  
Energy Efficiency ◽  
Wastewater Treatment ◽  
Fuel Cell ◽  
Wastewater Treatment Plants ◽  
Cell Systems

Modeling and Performance Simulation of a Reformer and Fuel Cell System for Electricity Generation From Digester Gas Using PEM Fuel Cells

2017 ◽  
Author(s):  
Sebastian Roa Prada ◽  
Oscar Eduardo Rueda Sanchez
Keyword(s):  
Power Generation ◽  
Wastewater Treatment ◽  
Fuel Cells ◽  
Fuel Cell ◽  
Electricity Generation ◽  
Wastewater Treatment Plants ◽  
Pem Fuel Cell ◽  
Pem Fuel Cells ◽  
Cell Systems ◽  
Power Recovery

Wastewater treatment plants help removing organic matter from wastewater, and at the same time, generate digester gas as a useful byproduct. Digester gas is rich in methane, which can be used to generate electricity. Fuel cell systems are the cleanest technology for power recovery from digester gas, since all other technologies generate electricity by burning all the digester gas. The most commonly used type of fuel cell for power generation from digester gas in wastewater treatment plants is the molten carbonate fuel cell. This type of fuel cell can tolerate the impurities usually found in digester gas, such as CO2 and H2S; however, this kind of fuel cell systems is more suitable for large wastewater treatment plants. This prevents the use of fuel cells for power generation from digester gas in wastewater treatment plants serving medium and small size cities, or even farms. This research attempts to explore solutions to make fuel cell technologies technically and economically feasible for medium and small size wastewater treatment plants. The most suitable type of fuel cells for small applications is the Proton Exchange Membrane, PEM, fuel cell. The main challenge in using PEM fuel cells for power recovery from digester gas is that they are highly sensitive to impurities in its hydrogen gas supply. Therefore, in order to use PEM fuel cells in this application, energy must be spent in cleaning the digester gas before it enters the PEM fuel cell and reformer system. Energy is also required in the form of heat by the reformer system to produce the hydrogen needed by the fuel cell. Both the energy used in the cleaning of the digester gas and the hydrogen generation process comes from burning part of the digester gas. This reduces the amount of digester gas available for hydrogen production and electricity generation, respectively. The approach followed in this investigation seeks to develop a Simulink® model of the reformer and fuel cell so that the modeling tools of Matlab® can be used to simulate the performance of the system under different operating conditions. A sensitivity analysis is carried out to identify critical operating parameters affecting the performance of the overall system. The results obtained in this work provide guidelines for future studies of performance optimization and optimal control using the tools available in Matlab®, in order to get maximum electricity generation from digester gas using PEM fuel cell systems.

Exergy and Economic Analysis of Two Different Fuel Cell Systems for Generating Electricity at Waste Water Treatment Plants

2012 ◽  
Author(s):  
Nicholas Siefert ◽  
Gautam Ashok
Keyword(s):  
Wastewater Treatment ◽  
Fuel Cell ◽  
Microbial Fuel Cell ◽  
Current Density ◽  
Exergy Analysis ◽  
Wastewater Treatment Plants ◽  
Pem Fuel Cells ◽  
Sale Price ◽  
Cell Systems ◽  
Anode Electrode

Generating electricity at wastewater treatment plants is a promising near-term application of fuel cell systems. The scale of most wastewater treatment plants is such that there is a good match with the scale of today’s fuel cell systems. This paper presents an exergy analysis and an economic comparison between two fuel cell systems that generate electricity at a wastewater treatment plant. The first process integrates an anaerobic digester (AD) with a solid oxide fuel cell (SOFC). The SOFC was modeled using publicly-available data from the tests on the Rolls-Royce pressurized SOFC. The second process has the wastewater sent directly to a microbial fuel cell (MFC). An MFC is an electrochemical cell in which bacteria convert acetate, sugars and/or other chemicals into protons, electrons and carbon dioxide at the anode electrode. The MFC was modeled as a PEM fuel cell as used for vehicle applications, but with a few changes: (a) anaerobic bacteria, such as geobacter, grow directly on the surface of the anode electrode, (b) there is no anode gas diffusion layer (GDL), (c) iron pyrophyrin, rather than platinum, is used as the catalyst material on the anode, in addition to the bacteria, and (d) the Nafion electrolyte is replaced with a bipolar membrane in order to minimize the transfer of non-proton cations, such as Na+, from the anode to the cathode. The rest of the equipment in the MFC is the same as those in commercial vehicle PEM fuel cells in order to use recent DOE cost estimates for PEM fuel cell systems. In both cases, we generated V-i curves of SOFC and MFC-PEM systems from data available on a) PEM & SOFC electrolyte conductivity and b) anode and cathode exchange current densities, including the effect of platinum levels on the cathode exchange current density of PEM fuel cells. A full exergy analysis was conducted for both systems modeled. The power per inlet exergy will be presented as a function of the current density and the pressure of the fuel cell. Using various Department of Eneregy (DOE) cost estimates for fuel cell systems, we perform parametric studies for both the MFC and AD-SOFC systems in order to maximize the internal rate of return on investment (IRR). In the MFC case, we varied the platinum loading on the cathode in order to maximize the IRR, and in the AD-SOFC case, we varied the current density of the SOFC in order to maximize the IRR. Finally, we compare the IRR of the two systems modeled above with the IRR of an anaerobic digester integrated with a piston engine capable of operating on biogas, such as the GE Jenbacher. Using an electricity sale price of $80/MWh, the IRR of the AD-SOFC, the microbial fuel cell and the AD-piston engine were 9%/yr, 10%/yr and 2%/yr, respectively. This economic analysis suggests that further experimental research should be conducted on both the microbial fuel cell and the pressurized SOFC because both systems were able to generate attractive values of IRR at an electricity sale price close to the average industrial price of electricity in the US.

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