scholarly journals 4E Analysis of a Fuel Cell and Gas Turbine Hybrid Energy System

2020 ◽  
Vol 11 (1) ◽  
pp. 7568-7579
Keyword(s):  
Fuel Cell ◽  
Cell Voltage ◽  
Energy System ◽  
High Energy ◽  
Exergy Efficiency ◽  
Combined Cycle ◽  
Net Energy ◽  
Exergy Destruction ◽  
Molten Carbonate ◽  
Ambient Temperatures

Exergy analysis of the expansion turbine hybrid cycle of integrated molten carbonate fuel cells is presented in this study. The proposed cycle was used as a sustainable energy curriculum to provide a small hybrid power plant with high energy efficiency. To generate electricity with the system mentioned above, and externally repaired fusion carbon fuel cell was used located at the top of the combined cycle. Moreover, the turbine and steam turbine systems are considered as complementary and bottom layers for co-generation, respectively. The results showed that the proposed system could reach net energy of up to 1125 kilowatts, while the total exergy efficiency (including electricity and heat) for this system is more than 68%. Moreover, the energy supplied and exergy efficiency derived from the proposed cycle are stable versus changes in ambient temperatures. Besides, the effect of increasing the current density on the cell voltage and the total exergy destruction was considered. Also, the new approaches of the exergoeconomics and exergoenvironmental analysis are implemented in this system. The results show that the hybrid system can decrease the exergy destruction costs more than 16%, and the environmental footprint of the system more than 23.4%.

Part Load Strategies of a Multi-MW Molten Carbonate Fuel Cell Gas Turbine Hybrid System

2007 ◽  
Author(s):  
Georgia C. Karvountzi ◽  
Paul F. Duby
Keyword(s):  
Fuel Cell ◽  
Gas Turbine ◽  
Hybrid System ◽  
Cell Voltage ◽  
Combined Cycle ◽  
Molten Carbonate Fuel Cell ◽  
Molten Carbonate ◽  
Part Load ◽  
Full Load ◽  
Carbonate Fuel Cell

The goal of this study is to define the operating envelope of a 20MW molten carbonate fuel cell (MCFC)-gas turbine hybrid system, under part load conditions. The first part of the paper reviews our baseline fuel cell hybrid system model that predicts overall system LHV efficiency around 69% at full load. The second part of the paper consider several strategies: 1/ run fuel cell at full load and bypass gas turbine; 2 /run fuel cell at full load and gas turbine at part load; 3/ run fuel cell at OCV and gas turbine at full load; 4/ run fuel cell at part load and gas turbine at full load; and 5/run both fuel cell and gas turbine at part load. The best system part-load performance was achieved when the fuel cell operates at part load while the gas turbine is at full load. The highest operational flexibility is achieved when we part load both the fuel cell and the gas turbine. Depending on system targets and deliverables such as fuel cell voltage and fuel utilization or gas turbine firing temperature some of these modes may not be economical. A comparison with the performance of a conventional combined cycle 20MW power plant under part load was performed. The MCFC hybrid system showed better efficiency and better cost of electricity (COE) under part load operation than the gas turbine combined cycle part loaded.

scholarly journals Exergy Analysis of Polymer Electrolyte Fuel Cell Systems Using Methanol

2003 ◽  
Author(s):  
Akimitsu Ishihara ◽  
Shigenori Mitsushima ◽  
Nobuyuki Kamiya ◽  
Ken-Ichiro Ota
Keyword(s):  
Fuel Cell ◽  
Polymer Electrolyte ◽  
Steam Reforming ◽  
Waste Heat ◽  
Material Balance ◽  
Cell Voltage ◽  
Exergy Efficiency ◽  
Exergy Loss ◽  
Polymer Electrolyte Fuel Cell ◽  
The Difference

An exergy (available energy) analysis has been conducted on a typical polymer electrolyte fuel cell (PEFC) system using methanol. The material balance and enthalpy balance were calculated for the PEFC system using methanol steam reforming, and the exergy flow was obtained. Based on these results, the exergy loss in each unit was obtained, and the difference between the enthalpy and exergy was discussed. The exergy loss in this system was calculated to be 178kJ/mole MeOH for the steam reforming process of methanol. Although the enthalpy efficiency approached unity as the recovery rate of the waste heat from the cell approached unity, the exergy efficiency remained around 0.45 since the cell’s operating temperature of 80°C is low. It was also found that the cell voltage should exceed 0.82V in order to obtain the exergy efficiency of 0.5 or higher. A direct methanol fuel cell (DMFC) was analyzed using the exergy and compared with the methanol reforming PEFC. In order to obtain the exergy efficiency higher than that of PEFC with steam reforming, the cell voltage of the DMFC should be 0.48V or greater at the current density of 600mA/cm2.

scholarly journals Mathematical absurdities in the California net energy system

2019 ◽  
Vol 3 (3) ◽  
pp. 1018-1028
Author(s):  
Carl A Old ◽  
Ian J Lean ◽  
Heidi A Rossow
Keyword(s):  
Linear Models ◽  
Energy System ◽  
High Energy ◽  
Ordinary Least Squares ◽  
Mitochondrial Metabolism ◽  
Energy Utilization ◽  
Parameter Estimates ◽  
Net Energy ◽  
High Energy Phosphate ◽  
Laws Of Thermodynamics

Abstract Net energy systems, such as the California Net Energy System (CNES), are useful for prediction of input:output relationships not because of fidelity to the laws of thermodynamics, but because they were designed to predict well. Unless model descriptions of input:output relationships are consistent with the laws of thermodynamics, conclusions regarding those relationships may be incorrect. Heat energy (HE) + recovered energy (RE) = ME intake (MEI) is basic to descriptions of energy utilization found in the CNES and is consistent with the laws of thermodynamics; it may be the only relationship described in the CNES consistent with the first law of thermodynamics. In the CNES, efficiencies of ME utilization for maintenance (km) and gain (kg) were estimated using ordinary least squares (OLS) equations. Efficiencies thus estimated using static linear models are often inconsistent with the biochemistry of processes underlying maintenance and gain. Reactions in support of oxidative mitochondrial metabolism are thermodynamically favorable and irreversible; these reactions yield ATP, or other high-energy phosphate bonds, used for what is generally termed maintenance. Synthesis of biomass (gain) is less thermodynamically favorable; reactions do not proceed unless coupled with hydrolysis of high-energy phosphate bonds and lie closer to equilibrium than those in support of oxidative mitochondrial metabolism. The opposite is described in the CNES (km > kg) due to failure of partitioning of HE; insufficient HE is accounted for in maintenance. Efficiencies of ME utilization (km and kg) as described in the CNES are variable. Further neither km nor kg are uniformly monotonic f (ME, Mcal/kg); for ME (Mcal/kg) <0.512 or >4.26, km are inconsistent with thermodynamically allowed values for efficiencies (>1.0); kg are a monotonically positive f (ME) concentration (Mcal/kg) for ME <3.27 Mcal/kg. For ME <1.42 Mcal/kg, kg are not in the range of thermodynamically allowed values for efficiencies (0 to 1.0). Variable efficiencies of ME utilization require that the first law may not be observed in all cases. The CNES is an excellent empirical tool for prediction of input:output relationship, but many CNES parameter estimates evaluated in this study lack consistency with biology and the laws of thermodynamics.

Highly Efficient Conversion of Ammonia in Electricity by Solid Oxide Fuel Cells

2006 ◽  
Vol 3 (4) ◽  
pp. 499-502 ◽  
Author(s):  
N. J. J. Dekker ◽  
G. Rietveld
Keyword(s):  
Fuel Cells ◽  
Fuel Cell ◽  
Energy Density ◽  
High Pressures ◽  
Cell Voltage ◽  
Electrical Current ◽  
High Energy ◽  
Solid Oxide ◽  
High Energy Density ◽  
Oxide Fuel

Hydrogen is the fuel for fuel cells with the highest cell voltage. A drawback for the use of hydrogen is the low energy density storage capacity, even at high pressures. Liquid fuels such as gasoline and methanol have a high energy density but lead to the emission of the greenhouse gas CO2. Ammonia could be the ideal bridge fuel, having a high energy density at relative low pressure and no (local) CO2 emission. Ammonia as a fuel for the solid oxide fuel cell (SOFC) appears to be very attractive, as shown by cell tests with electrolyte supported cells (ESC) as well as anode supported cells (ASC) with an active area of 81cm2. The cell voltage was measured as function of the electrical current, temperature, gas composition and ammonia (NH3) flow. With NH3 as fuel, electrical cell efficiencies up to 70% (LHV) can be achieved at 0.35A∕cm2 and 60% (LHV) at 0.6A∕cm2. The cell degradation during 3000 h of operation was comparable with H2 fueled measurements. Due to the high temperature and the catalytic active Ni∕YSZ anode, NH3 cracks at the anode into H2 and N2 with a conversion of >99.996%. The high NH3 conversion is partly due to the withdrawal of H2 by the electrochemical cell reaction. The remaining NH3 will be converted in the afterburner of the system. The NOx outlet concentration of the fuel cell is low, typically <0.5ppm at temperatures below 950°C and around 4ppm at 1000°C. A SOFC system fueled with ammonia is relative simple compared with a carbon containing fuel, since no humidification of the fuel is necessary. Moreover, the endothermic ammonia cracking reaction consumes part of the heat produced by the fuel cell, by which less cathode cooling air is required compared with H2 fueled systems. Therefore, the system for a NH3 fueled SOFC will have relatively low parasitic power losses and relative small heat exchangers for preheating the cathode air flow.

Efficiency Analyses of a Coal Gasification Molten Carbonate Fuel Cell With a Gas Turbine Combined Cycle Including CO2 Recovery

2008 ◽  
Author(s):  
F. Yoshiba ◽  
E. Koda
Keyword(s):  
Fuel Cell ◽  
Gas Turbine ◽  
Coal Gasification ◽  
Combined Cycle ◽  
Molten Carbonate Fuel Cell ◽  
Molten Carbonate ◽  
Coal Gas ◽  
Co2 Recovery ◽  
And Storage ◽  
Carbonate Fuel Cell

The efficiency of an integrated coal gasification system equipped with a molten carbonate fuel cell, a gas turbine and a steam turbine (IG/MCFC) is calculated. Coal is conveyed to a gasifier furnace by CO2 and changed to coal gas by adding oxygen; a methyldiethanolamine (MDEA) method is applied to initiate a cleanup procedure of the coal gas. A water-gas shift converter is employed to heat up the coal gas. The cathode gas of the MCFC is composed of CO2 and O2 with a composition of 66.7/33.3 (noble cathode gas composition). The magnitude of the system’s electrical power output is assumed to be that of a 300 MW class. The calculated net efficiency of the 2.2 MPa pressurised system reached a 60.1% high heating value (HHV) without CO2 recovery. The 2.2 MPa pressurised system, however, has a short lifetime limited by the shortening of electrodes. For this reason, a further 0.15 MPa pressurised system (low pressurised system) efficiency is recorded which has a more promising shortening time of the electrodes. The net efficiency of the low pressurised system is 51.9% HHV without CO2recovery. Since the coal is gasified using oxygen and the cathode gas of the MCFC is composed of CO2/O2, the system’s exhaust gas only includes CO2, thus the system is ready for the recovery and storage of carbon dioxide (Carbon Capture and Storage ready, CCS ready). For the purpose of estimating the net efficiency with CO2 recovery, a liquid form of CO2 with a pressure of 10MPa is assumed. Using the 2.2 MPa pressurised system, the net efficiency including the consumption of CO2 compression and liquefaction is evaluated at 58.2% HHV. Another simple CO2 closed system configuration without gas turbine is proposed; the net efficiencies of the 2.2 MPa and the 0.15 MPa system including the consumption of CO2 liquefaction are determined at 56.4% and 50.3% HHV, respectively. According to the calculation results, a high efficiency system with CO2 recovery is possible by applying the noble cathode gas in the IG/MCFC systems.

Molten Carbonate Fuel Cells for Retrofitting Postcombustion CO2 Capture in Coal and Natural Gas Power Plants

2018 ◽  
Vol 15 (3) ◽  
Author(s):  
Maurizio Spinelli ◽  
Stefano Campanari ◽  
Stefano Consonni ◽  
Matteo C. Romano ◽  
Thomas Kreutz ◽  
...  
Keyword(s):  
Fuel Cells ◽  
Fuel Cell ◽  
Natural Gas ◽  
Co2 Capture ◽  
Power Plants ◽  
Combined Cycle ◽  
Co2 Separation ◽  
Molten Carbonate ◽  
Promising Alternative ◽  
Molten Carbonate Fuel Cells

The state-of-the-art conventional technology for postcombustion capture of CO2 from fossil-fueled power plants is based on chemical solvents, which requires substantial energy consumption for regeneration. A promising alternative, available in the near future, is the application of molten carbonate fuel cells (MCFC) for CO2 separation from postcombustion flue gases. Previous studies related to this technology showed both high efficiency and high carbon capture rates, especially when the fuel cell is thermally integrated in the flue gas path of a natural gas-fired combined cycle or an integrated gasification combined cycle plant. This work compares the application of MCFC-based CO2 separation process to pulverized coal fired steam cycles (PCC) and natural gas combined cycles (NGCC) as a “retrofit” to the original power plant. Mass and energy balances are calculated through detailed models for both power plants, with fuel cell behavior simulated using a 0D model calibrated against manufacturers' specifications and based on experimental measurements, specifically carried out to support this study. The resulting analysis includes a comparison of the energy efficiency and CO2 separation efficiency as well as an economic comparison of the cost of CO2 avoided (CCA) under several economic scenarios. The proposed configurations reveal promising performance, exhibiting very competitive efficiency and economic metrics in comparison with conventional CO2 capture technologies. Application as a MCFC retrofit yields a very limited (<3%) decrease in efficiency for both power plants (PCC and NGCC), a strong reduction (>80%) in CO2 emission and a competitive cost for CO2 avoided (25–40 €/ton).

Power Cycle Integration and Efficiency Increase of Molten Carbonate Fuel Cell Systems

2005 ◽  
Vol 3 (4) ◽  
pp. 375-383 ◽  
Author(s):  
Petar Varbanov ◽  
Jiří Klemeš ◽  
Ramesh K. Shah ◽  
Harmanjeet Shihn
Keyword(s):  
Fuel Cells ◽  
High Temperature ◽  
Fuel Cell ◽  
Gas Turbines ◽  
Waste Heat ◽  
Combined Cycle ◽  
Molten Carbonate Fuel Cell ◽  
Steam Turbines ◽  
Molten Carbonate ◽  
Carbonate Fuel Cell

A new view is presented on the concept of the combined cycle for power generation. Traditionally, the term “combined cycle” is associated with using a gas turbine in combination with steam turbines to better utilize the exergy potential of the burnt fuel. This concept can be broadened, however, to the utilization of any power-generating facility in combination with steam turbines, as long as this facility also provides a high-temperature waste heat. Such facilities are high temperature fuel cells. Fuel cells are especially advantageous for combined cycle applications since they feature a remarkably high efficiency—reaching an order of 45–50% and even close to 60%, compared to 30–35% for most gas turbines. The literature sources on combining fuel cells with gas and steam turbines clearly illustrate the potential to achieve high power and co-generation efficiencies. In the presented work, the extension to the concept of combined cycle is considered on the example of a molten carbonate fuel cell (MCFC) working under stationary conditions. An overview of the process for the MCFC is given, followed by the options for heat integration utilizing the waste heat for steam generation. The complete fuel cell combined cycle (FCCC) system is then analyzed to estimate the potential power cost levels that could be achieved. The results demonstrate that a properly designed FCCC system is capable of reaching significantly higher efficiency compared to the standalone fuel cell system. An important observation is that FCCC systems may result in economically competitive power production units, comparable with contemporary fossil power stations.

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