Additional Power Production Research Articles

Improvement potential detection of integrated biomethane liquefaction and liquid air energy storage system

Biomethane (BM) is highly competitive bio-energy alternatives for lowering the dependency on fossil fuels globally. The form of BM that is most suitable for storage as well as shipping to far-flung areas of the world is liquefied biomethane (LBM). However, due to the significant power consumption by compressors used in BM liquefaction process (like natural gas), it is a cost- and energy-intensive operation. Additionally, because biomethane is created at atmospheric pressure, unlike ordinary natural gas, liquefaction requires more power consumption because the pressure at which BM is produced is much less than corresponding critical pressure. Therefore, an integrated system of liquid air energy storage (LAES) system discharging end and a biomethane liquefaction process is introduced that is both economical and efficient in terms of energy use. The sub-cooling and liquefaction processes of biomethane are aided by the cold-exergy of liquid air at the time of regasification mode of LAES, which eventually lowers the refrigeration cycle duty of LBM process. On the other hand, gaining the additional advantage, the expansion stage of liquid air is aided by the thermal exergy of a compressed mixed refrigerant (MR). On the basis of conventional exergy analysis, composite curves analysis, advanced exergy analysis, and sustainability index, the impacts of novel integration of LBM and LAES are estimated in this study. Conventional exergy analysis determines that 15.9 % of exergy destruction is decreased in the proposed LBM-LAES system having additional power production of 4529 kW using gas turbine. Results based on advanced exergy analysis conclude that avoidable, endogenous and exogenous portions of exergy destructions are decreased by 28.9 %, 39.9 % and 43 %, respectively; which implies the significant improvement potential. Composite curves analysis depicts that the efficiency of primary cryogenic heat exchanger is improved in the proposed integrated scheme. Additionally, the overall sustainability index is increased from 1.55 to 2.13 for LBM-LAES process.

Potentials of thermocapacitive heat engine for photovoltaic/thermal (PV/T) applications

Effective thermal management can significantly boost the photovoltaic module (PVM) performance due to the suppression of PVM temperature. In this paper, a thermally-driven thermocapacitive heat engine (TCHE) is proposed to harvest the long wavelengths of sunlight transmitted through PVM with the help of solar selective absorber for the aim of additional power production. The performance potentials of the conceptualized hybrid system are evaluated based on the models of PVM and TCHE considering multiple irreversible effects. Calculative results indicate that maximum power density and maximum energy efficiency of the PVM-TCHE hybrid system are, respectively, 38.74% and 38.56% higher than those of the single PVM, showing that TCHE is an effective thermal management approach for PVM. In addition, the influences of various design variables and operation conditions are studied to find clues for further improving the overall performance. Sensitivity analyses show that a larger operating temperature of PVM, diode ideality factor, ion concentration of electrolyte or charge cut-off voltage positively benefits the performance, while a larger ambient temperature or warm-up time worsens the performance. The charge during the charging process and discharging process can be optimally allocated.

Comparative thermodynamic analysis of an improved ORC process with integrated injection of process fluid

In contrast to water-steam Rankine cycles, the ORC process uses organic working fluids. For working fluids of the dry class, a recuperator heat exchanger is frequently installed to increase the cycle efficiency. This paper analyses an improved ORC process with these features: A liquid working fluid stream is injected into the vapour flow between the high-pressure and the medium-pressure stage of the turbine. Furthermore, the recuperator is replaced by a spray condenser. The main objective is to increase efficiency with moderate changes in the process layout. A thermodynamic comparison of the improved process with a state-of-the-art ORC process is carried out by simulations and optimisations. A significant efficiency gain for the improved ORC process is obtained by a combination of the aforementioned features, mainly because of an increase of the mass flow in the economiser of the vapour generator (better heat utilization) and a corresponding mass flow in the medium stage of the turbine (additional power production). As a use case, waste heat utilization from a clinker cooler at a temperature level of 275 °C was simulated. The improved process would lead to a significant increase in the overall net efficiency by up to 14%, compared to a state-of-the-art ORC process.

Comprehensive Life Cycle Assessment Analysis of an Italian Composting Facility concerning Environmental Footprint Minimization and Renewable Energy Integration

The present paper aims to investigate the environmental impacts of a real municipal solid waste management facility operating in Italy including two power units, i.e., a combined heat and power system and an internal combustion engine, fed by the biogas produced from anaerobic digestion and waste disposal in sanitary landfill. The Life Cycle Assessment study is carried out in Simapro 9.1.1.7 and, in addition to the base case scenario, the implementation of additional renewable energy and circular economy solutions is evaluated. More precisely a PV plant on the roof of the anaerobic digesters section and the use of plastic and paper residues in a gasification process for additional heat and power production are considered. The main outcomes of the simulations demonstrate the following: (i) the benefits in terms of energy and fuel savings provided by the two power units; (ii) the environmental impact reduction due to the compost obtained from the anaerobic digestion of the organic waste as potential fertilizer; (iii) a potential power capacity of 2 MW through the gasification of the plastic and paper residues. With reference to the latter, despite bringing an increase of the carbon emissions (+48%) compared to the base case, it could contribute to reach higher environmental standards for MSW composting facilities.

Synergistic integration of molten hydroxide direct carbon fuel cell and Stirling heat engine for efficient and clean coal use

To reuse the exhaust heat produced by molten hydroxide direct carbon fuel cells (MHDCFCs), a new combined system mainly composed of an MHDCFC, a regenerator, and a Stirling heat engine (SHE) is theoretically integrated for fuel-to-power efficiency enhancement. Mathematical formulas of the performance indicators for the combined system are derived based on the first and second laws of thermodynamics, from which the feasibility and effectiveness of the combined system are evaluated from both energetic and exergetic viewpoints. Moreover, the optimum working regions of the combined system are further specified by using a multi-objective function paying equal attention to both efficiency and power output. Results show that SHEs can be effectively acted as bottoming cycles for MHDCFC for additional mechanical power production. Numerical calculations indicate that the maximum power density and its corresponding energy efficiency and exergy efficiency of the proposed system are, respectively, about 97.6%, 97.1% and 99.2% greater than that of the single MHDCFC. Furthermore, extensive parametric studies show that increasing working temperature, volume ratio, hot-side working substance temperature or mean pressure is beneficial for the overall system performance, while increasing reactor compartment width may degrade the overall system performance.

Molten Carbonate Fuel Cells for 90% Post Combustion CO2 Capture From a New Build CCGT

This paper presents the findings of the techno-economic assessment undertaken by Wood for the UK Government Department for Business, Energy and Industrial Strategy on the large-scale deployment of Molten Carbonate Fuel Cells (MCFCs) for post-combustion CO2 capture integrated with a new build combined cycle gas turbine power plant for the generation of low carbon electricity. The findings are compared with a state of the art proprietary amine scrubbing technology. Based on a new build power plant to be installed in the North East of England, with a power train comprising two trains of H-class gas turbines each with a dedicated steam turbine, the configuration presented utilises MCFCs between the gas turbine exhausts and their heat recovery steam generators and cryogenic separation for unconverted fuel recycle and CO2 purification. It was found that the proposed configuration could achieve 92% CO2 capture from the overall power plant with MCFCs while achieving 42% of additional new power production with only 2.6 %-points of thermal efficiency penalty compared to a conventional proprietary amine benchmark. While the total project capital cost increased by 65%, the high overall thermal efficiency and additional power generated resulted in a Levelised Cost of Electricity almost identical to the benchmark at £70/MWh (US$97/MWh). A number of areas are identified for potential further improvement in this scheme. It is concluded that use of MCFC technology, which also has the capability to be tailored for hydrogen production and combined heat and power services, shows significant potential to be competitive with, or exceed, the cost and technical performance of current state of the art technologies for post-combustion CO2 capture.

Designing sustainable bioenergy from residual biomass: Site allocation criteria and energy/exergy performance indicators

This work aims at developing a comprehensive methodology defining the influence of the proper feedstock management, number and location of gasification-power plants, and process configuration based on the thermodynamic performances of the proposed system under different scenarios. The feedstock was citrus peel from local citrus processing factories. A three-step model was adopted: best site criteria decision tool, location-allocation analysis by minimising energetic transport costs, energy/exergy and emissions analysis. This model was applied to three process scenarios. In the first, we considered a wet biomass (65% water content) dried at a local plant using cogenerated heat; in the second, the biomass dried prior to transportation (15% water content) used to power the combined heat and power plant. The cogenerated heat fed an Organic Rankine Cycle (ORC) unit. In the third, the cogenerated heat is used for district heating.The scenario analysis showed that the regional potential for producing renewable electricity from citrus peel gasification is 66.7–74.6 GWh. Results showed that the Energy Return on Investment (EROI) is <1 only when the feedstock is transported dry (15% water content), and the cogenerated heat is used for additional power production in an ORC unit. The highest EROI values (24–47) are obtained when the feedstock is transported wet and dried using the cogenerated heat. A sensitivity analysis reveals that the optimal number of plants is three with a reduction of the energetic transport cost of 46% compared to a single plant. The maximum global energy and exergy efficiencies were 39% and 16%, respectively. The exergy-based renewability indicator showed that the proposed bioenergy system could be considered renewable in only one of the three process scenarios.

Techno-economic analysis of a modified concentrating photovoltaic/organic Rankine cycle system

ABSTRACT The combination of concentrating photovoltaic (CPV) and organic Rankine cycle (ORC) systems not only leads to a reduction of photovoltaic (PV) operating temperature, but also leads to an additional electric power production. Increase in the temperature of the PV decreases its operating efficiency, while increases the ORC efficiency. Therefore, there is an optimum temperature in which the total electricity produced by the combined system will be maximum. In this study, a modified CPV/ORC system is simulated and the optimum operating temperature of the PV panel is determined for different PV efficiencies. The most striking result is that increase in the PV nominal efficiency will result in the selection of a lower temperature for the PV optimum temperature. The results indicate that for the PV panels with efficiencies of 10%, 14%, 18%, and 22% the PV optimum temperature are 145.0°C, 139.8, 132.3, and 121.2°C, respectively.

Review and techno-economic assessment of fuel cell technologies with CO2 capture

The concept of using Fuel Cells (FCs) within large scale power generation cycles for CO2 capture has been studied over the last decade. Two types of FCs, Solid Oxide Fuel Cells (SOFCs) and Molten Carbonate Fuel Cells (MCFCs) have emerged as promising CO2 capture systems, with the added advantage of additional power production. Although promising, neither SOFCs nor MCFCs are commercially available for CO2 capture applications, primarily due to low technological maturity, lack of large demonstration projects, and significant associated costs.In this work, the aim is to provide a comprehensive literature review of Fuel Cell technologies with CO2 Capture and a techno-economic analysis of five selected cases utilising SOFCs and MCFCs as CO2 capture systems in power plants. Economic parameters were homogenised to enable a fair comparison between the technologies. Results show that Cases 1 and 5 which consider MCFCs as CO2 concentrator’s in Natural gas and super critical pulverised coal cycles respectively give the best LCOE performance. The LCOE is comparable to current state-of-the-art CO2 capture technologies applied to large-scale power plants.

Review of Fuel Cell Technologies with CO2 Capture

In 2016, the IEA estimated that CO2 emissions from the production of energy represented 42% of the total global emissions. To limit the increase of the Earth’s temperature to 1.5oC above pre-industrial levels in the framework of the Paris agreement, more than 1,950 GWe must be decarbonised within the power sector. Currently, the most advanced CO2 capture (CC) technologies applied to large-scale power plants are post- and pre-combustion capture and oxyfuel combustion. However, the main drawback of these technologies is the energy penalty, and consequent efficiency loss, which leads to a high Levelized Cost of Electricity (LCOE). As a result, novel energy systems, which promise high efficiency and low CO2 emissions, such as fuel cell (FC) hybrid power cycles with CC, merit research, development and detailed analysis of their potential economics. The objective of this paper is to review the techno-economic status of Molten Carbonate Fuel Cell (MCFC) and Solid Oxide Fuel Cell (SOFC) technologies for CC application. This includes their development status, optimal configurations, economic analysis, challenges to reach commercial operation and time frame to develop as candidates for future deployment at commercial scale. SOFCs and MCFCs have emerged as potential technologies in CC systems, with the added advantage of providing additional power production. Although promising, neither SOFCs nor MCFCs are commercially available for CC applications, primarily due to their low technological maturity and high associated costs of the FCs. The current authors have identified gaps in the literature that requires a unique study, containing a number of potential configurations, with an updated and homogeneous approach to assess the techno-economic performance of SOFCs and MCFCs as CC systems in power plants.

A feasible way to handle the heat management of direct carbon solid oxide fuel cells

A novel integrated system consisting of an external heat source, a direct carbon solid oxide fuel cell (DC-SOFC), a vacuum thermionic generator (VTIG) and a regenerator is proposed to handle the heat management of the DC-SOFC. The electrochemical/chemical reactions, ionic/electronic charge transport, mass/momentum transport and heat transfer are fully considered in the 2D tubular DC-SOFC model, which shows that the overall heat released in the cell is always different from the heat required by the internal Boudouard reaction. Three different operation strategies of the proposed system are presented, and accordingly, analytical expressions for the overall power output and efficiency for the proposed system are specified. The results show that the VTIG could effectively recover the waste heat for additional power production at a large operating current density, and the maximum power density and efficiency of the proposed system could reach more than 8100 W m−2 and 60% at 30,000 A m−2 and 1173 K, respectively. The effects of the operating current density, the operating temperature and the distance between the carbon layer and anode of the DC-SOFC, and the size, anode temperature and work function of the VTIG on the performance of the proposed system are discussed through comprehensive parametric studies.

Performance improvement of a direct carbon solid oxide fuel cell through integrating an Otto heat engine

A novel system consisting of an external heat source, a direct carbon solid oxide fuel cell (DC-SOFC), a regenerator and an air standard Otto cycle engine is proposed to improve the performance of the DC-SOFC. Considering the electrochemical/chemical reactions, ionic/electronic charge transport, mass/momentum transport and heat transfer, a 2D tubular DC-SOFC model shows that the overall heat released in the cell can be smaller than, equal to or larger than the heat required by the internal Boudouard reaction. Three different operating modes of the proposed system are identified, and accordingly, analytical expressions for the equivalent power output and efficiency of the proposed system are derived under different operating conditions. The modeling results show that the Otto heat engine can effectively recover the waste heat from the DC-SOFC for additional power production especially at large operating current density. Comprehensive parametric studies are conducted to investigate the effects of the different operating conditions of DC-SOFC on its performance and heat generation. The effects of compression ratio, internal irreversibility factor and power dissipation of the Otto heat engine on the system performance improvement are also studied.

Performance Analysis of Small Size Compressed Air Energy Storage Systems for Power Augmentation: Air Injection and Air Injection/Expander Schemes

ABSTRACTTwo small size second-generation compressed air energy storage (CAES) systems have been investigated. Both plants are based on a 4600 kW Mercury recuperated gas turbine (GT) and on an artificial air storage system. In CAES air injection (CAES AI) plant, the stored compressed air is mixed with the air flow exiting the GT compressor and fed after a recuperative heating to the GT combustion chamber. A topping air expander is included in the CAES air injection/expander (CAES AI/E) plant scheme. Preliminary evaluations have been carried out to assess the maximum achievable GT power augmentation taking safety of operations and plant life duration into consideration. Plant performance has been evaluated during the overall operational cycle (charging, storage and discharging phases). CAES AI plant allows a 30% maximum extra power delivery (some 1500 kW) in respect to the nominal design GT power. The introduction of the topping air expander in CAES AI/E plant allows an additional power production of some 300 kW. Both plants have shown storage efficiency improvements by reducing the discharge period duration. Satisfactory values around 70% have been found in the best operating conditions.

Introducing and analysis of a hybrid molten carbonate fuel cell-supercritical carbon dioxide Brayton cycle system

A hybrid system is proposed, which integrates a molten carbonate fuel cell, and a supercritical carbon dioxide Brayton cycle. This case deals with waste heat recovery from catalytic burner exhaust gas using a Brayton cycle as a bottoming cycle for additional power production due its very high temperature, which yields high electrical and overall efficiencies. After designing and simulating the process energy and exergy analyses are performed. The greatest exergy destruction is observed in the reformer while the lowest exergy efficiency is attributable to the fuel cell. The main advantage of this kind of hybrid system, in addition to efficiency improvement and cost reduction, is its ability to reduce harmful emissions and negative impacts on the environment.

Exergy analysis and optimisation of a marine molten carbonate fuel cell system in simple and combined cycle configuration

In this paper we present the exergy analysis and design optimisation of an integrated molten carbonate fuel cell (MCFC) system for marine applications, considering waste heat recovery options for additional power production. High temperature fuel cells are attractive solutions for marine energy systems, as they can significantly reduce gaseous emissions, increase efficiency and facilitate the introduction of more environmentally-friendly fuels, like LNG and biofuels. We consider an already installed MCFC system onboard a sea-going vessel, which has many tightly integrated sub-systems and components: fuel delivery and pre-reforming, internal reforming sections, electrochemical conversion, catalytic burner, air supply and high temperature exhaust gas. The high temperature exhaust gasses offer significant potential for heat recovery that can be directed into both covering the system’s auxiliary heat requirements and power production. Therefore, an integrated systems approach is employed to accurately identify the true sources of losses in the various components and to optimise the overall system with respect to its energy efficiency, taking into account the various trade-offs and subject to several constraints. Here, we present a four-step approach: a. dynamic process models development of simple and combined-cycle MCFC system; b. MCFC components and system models calibration via onboard MCFC measurements; c. exergy analysis, and d. optimisation of the simple and combined-cycle systems with respect to their exergetic performance. Our methodology is based on the thermofluid and chemical reactions modelling of each component, via our in-house ship machinery systems modelling framework, DNVGL COSSMOS. For the major system components spatially distributed exergy balances are considered in order to capture the coupling of the local process phenomena and exergy destruction with component design characteristics. Exhaust heat recovery is considered using a steam turbine combined-cycle module integrated with the rest of the MCFC system. Both the simple and combined cycle MCFC systems are optimised with respect to their overall exergetic efficiency subject to design, technical, operational and space constraints. The exergy analysis identified and ranked the sources of exergy destruction and the subsequent optimisation yielded significant improvement potential for both systems. The simple MCFC system optimisation yielded an exergy efficiency improvement of 7% with 5% more power produced. Heat recovery in the combined cycle MCFC resulted in 40% more power produced, with a 60% overall exergy efficiency (relative increase of 45%). Both MCFC systems outperform conventional dual-fuel engines with respect to efficiency, having also a positive impact on CO2 emissions with a relative reduction of about 30%.

Design and Optimization of Compact Heat Exchangers to be Retrofitted into a Vehicle for Heat Recovery from a Diesel Engine

Higher depletion rate and increasing price of fossil fuels have motivated many researchers to harness energy from the waste heat from internal combustion engines, and thus improve the overall efficiency. Among the waste heat recovery methods, the bottoming Rankine cycle is the most promising. In this technique, the recovered heat is used to produce additional power using turbine. In order to maximise the additional power production, an effective heat exchanger design is necessary. The main focus of the current research was to design heat exchangers which needed to be pancake-shaped to be retrofitted into a vehicle. The heat exchanges chosen were shell and U-tube type. CFD simulations were carried out to optimize the design of the heat exchangers and calculate the additional power that could be achievable by using this optimized pancake-shaped heat exchangers.

Performance evaluation of an SOFC based trigeneration system using various gaseous fuels from biomass gasification

Thermodynamic analyses of an internal reforming solid oxide fuel cell (IR-SOFC) system are carried out using three different practical gasifier products. Syngas products from bubbling fluidized bed (BFB), circulating fluidized bed (CFB), and dual fluidized bed (DFB) gasifiers are considered and comparatively studied. Fuels from the ThermoChem bubling fluidized bed gasifier (TRI), CUTEC circulating fluidized bed gasifier and SilvaGas&Taylor dual fluidized bed gasifiers are also considered. Some parametric studies are conducted to evaluate effects of fuel and air utilization factors, recirculation ratio, stack temperature, reference-state conditions, etc., on the system performance. An SOFC based integrated system is then proposed in order to utilize relatively high temperature waste heat from SOFC unit by producing power, water heating, and space cooling. The proposed system consists of (a) an internal reforming SOFC unit, (b) an organic Rankine cycle (ORC) working with Toluene, (c) an absorption chiller cycle, and (d) a water heating unit connected to an ORC condenser. Energy and exergy efficiencies of subunits and overall system are comparatively evaluated considering irreversibilities of the system components for the best fuel performance. The TRI fueled SOFC system shows the best energy and exergy efficiencies with lowest exergy destructions throughout the trigeneration system. Energy and exergy efficiencies of the SOFC system are determined as 42.2% and 36.5%, respectively. 24.6 kW of additional power production from ORC cycle, 69.9 kW of heating energy production from water heating, and 22.1 kW of cooling load from AC cycle are obtained by the system integration. Furthermore, the system integration for exhaust gas utilization enhances the energy and exergy efficiencies up to ∼78% and ∼50%, respectively.

A thermodynamic analysis of waste heat recovery from reciprocating engine power plants by means of Organic Rankine Cycles

Organic Rankine Cycle (ORC) is a Rankine cycle using organic fluid as the working fluid instead of water and steam. The ORC process is a feasible choice in waste heat recovery applications producing electricity from relatively low-temperature waste heat sources or in applications having a rather low power output. Utilizing waste heat from a large high-efficiency reciprocating engine power plant with ORC processes is studied by means of computations. In addition to exhaust gas heat recovery, this study represents and discusses an idea of directly replacing the charge air cooler (CAC) of a large turbocharged engine with an ORC evaporator to utilize the charge air heat in additional power production. A thermodynamic analysis for ORCs was carried out with working fluids toluene, n-pentane, R245fa and cyclohexane. The effect of different ORC process parameters on the process performance are presented and analyzed in order to investigate the heat recovery potential from the exhaust gas and charge air. A simplified feasibility consideration is included by comparing the ratio of the theoretical heat transfer areas needed and the obtained power output from ORC processes. The greatest potential is related to the exhaust gas heat recovery, but in addition also the lower temperature waste heat streams could be utilized to boost the electrical power of the engine power plant. A case study for a large-scale gas-fired engine was carried out showing that the maximum power increase of 11.4% was obtained from the exhaust gas and 2.4% from the charge air heat.

Waste heat recovery from the exhaust of a diesel generator using Rankine Cycle

Exhaust heat from diesel engines can be an important heat source to provide additional power using a separate Rankine Cycle (RC). In this research, experiments were conducted to measure the available exhaust heat from a 40kW diesel generator using two ‘off-the-shelf’ heat exchangers. The effectiveness of the heat exchangers using water as the working fluid was found to be 0.44 which seems to be lower than a standard one. This lower performance of the existing heat exchangers indicates the necessity of optimization of the design of the heat exchangers for this particular application. With the available experimental data, computer simulations were carried out to optimize the design of the heat exchangers. Two heat exchangers were used to generate super-heated steam to expand in the turbine using two orientations: series and parallel. The optimized heat exchangers were then used to estimate additional power considering actual turbine isentropic efficiency. The proposed heat exchanger was able to produce 11% additional power using water as the working fluid at a pressure of 15bar at rated engine load. This additional power resulted into 12% improvement in brake-specific fuel consumption (bsfc). The effects of the working fluid pressure were also investigated to maximize the additional power production. The pressure was limited to 15bar which was constrained by the exhaust gas temperature. However, higher pressure is possible for higher exhaust gas temperatures from higher capacity engines. This would yield more additional power with further improvements in bsfc. At 40% part load, the additional power developed was 3.4% which resulted in 3.3% reduction in bsfc.

Feasibility Study for Self-Sustained Wastewater Treatment Plants—Using Biogas CHP Fuel Cell, Micro-Turbine, PV and Wind Turbine Systems

This paper studies the application of renewable energy sources in wastewater treatment plants to achieve self-sustain- ability of power. The data of wastewater treatment plant in the rural city of Toukh-EGYPT are presented as a case-study. The primary objective is to provide an entirely renewable standalone power system, which satisfies lowest possible emissions with the minimum lifecycle cost. Mass balance principle is applied on the biodegradable components in the wastewater to evaluate the volume of digester gas that is produced from sludge through anaerobic digestion process. Using digester gas as a fuel lead to study combined-heat-and-power technologies, where fuel cell is selected in order to abide by the low emissions constraint. The study assessed the electrical power obtained from fuel cell and the utilization of the exhausted heat energy for additional electrical power production using a micro-turbine. After covering the major part of load demand, the use of other renewable energy sources was studied. The strength of both solar and wind energy was determined by the case-study location. Hybrid optimization model for electric renewable (HOMER) software was used to simulate the hybrid system composed of combined-heat-and-power units, wind turbines and photovoltaic systems. Simulation results gave the best system configuration and optimum size of each component beside the detailed electrical and cost analysis of the model.