Thermodynamic Irreversibility Research Articles

Comparative analysis of four gas-fired, carbon capture-enabled power plant layouts

Emission of carbon dioxide from fossil fuel-fired thermal power plants is a major concern for energy providers all around the world. In this context, carbon capture from thermal power plants and the energy penalty incurred in the process are important issues. The present work reports on a detailed analysis of gas-fired power plant layouts with in-built carbon capture, i.e. the flue gas from these power plants contains mainly carbon dioxide and water vapour. Four layouts, two of which are based on pressurized oxyfuel combustion and two on chemical looping combustion (CLC), have been considered. Based on detailed mass balance, energy and thermodynamic analyses of the power plant layouts, the net efficiencies for each plant have been computed. After accounting for thermodynamic irreversibilities and CO2 compression to 110 bar, these have been found to vary between 31 and 52 % for the four plants. Despite the technological maturity of oxyfuel combustion, it is concluded that CLC-based plants would be future-ready in the sense that they can readily accommodate CCS with only 2 % loss in overall thermal efficiency for CO2 capture.

Thermodynamic analysis of an idealised solar tower thermal power plant

In the real solar tower thermal power system, it is widely acknowledged that the thermodynamic irreversibility, such as convective and radiative loss on tower receiver, and thermal resistance in heat exchangers, is unavoidable. With above factors in mind, this paper presents an ideal model of the solar tower thermal power system to analyze the influence of various parameters on thermal and exergy conversion efficiencies, including receiver working temperature, concentration ratio, endoreversible heat engine efficiency and so forth. And therefore the variation of maximum thermal conversion efficiency in terms of concentration ratio and endoreversible heat engine efficiency could be theoretically obtained. The results indicate that raising the receiver working temperature could initially increase both thermal and exergy conversion efficiencies until an optimum temperature is reached. The optimum temperature would also increase with the concentration ratio. Additionally, the concentration ratio has a positive effect on the thermal conversion efficiency: increasing the concentration ratio could raise the conversion efficiency until the concentration ratio is extremely high, after which there will be a slow drop. Lastly, the endoreversible engine efficiency also has significant influence on the thermal conversion efficiency, it will increase the thermal conversion efficiency until it reaches the maximum and optimum value, and then the conversion efficiency will drop dramatically.

Steady state simulation and exergy analysis of supercritical coal-fired power plant with CO2 capture

Integrating a power plant with CO2 capture incurs serious efficiency and energy penalty due to use of energy for solvent regeneration in the capture process. Reducing the exergy destruction and losses associated with the power plant systems can improve the rational efficiency of the system and thereby reducing energy penalties. This paper presents steady state simulation and exergy analysis of supercritical coal-fired power plant (SCPP) integrated with post-combustion CO2 capture (PCC). The simulation was validated by comparing the results with a greenfield design case study based on a 550MWe SCPP unit. The analyses show that the once-through boiler exhibits the highest exergy destruction but also has a limited influence on fuel-saving potentials of the system. The turbine subsystems show lower exergy destruction compared to the boiler subsystem but more significance in fuel-saving potentials of the system. Four cases of the integrated SCPP-CO2 capture configuration was considered for reducing thermodynamic irreversibilities in the system by reducing the driving forces responsible for the CO2 capture process: conventional process, absorber intercooling (AIC), split-flow (SF), and a combination of absorber intercooling and split-flow (AIC+SF). The AIC+SF configuration shows the most significant reduction in exergy destruction when compared to the SCPP system with conventional CO2 capture. This study shows that improvement in turbine performance design and the driving forces responsible for CO2 capture (without compromising cost) can help improve the rational efficiency of the integrated system.

The second law of thermodynamics under unitary evolution and external operations

The von Neumann entropy cannot represent the thermodynamic entropy of equilibrium pure states in isolated quantum systems. The diagonal entropy, which is the Shannon entropy in the energy eigenbasis at each instant of time, is a natural generalization of the von Neumann entropy and applicable to equilibrium pure states. We show that the diagonal entropy is consistent with the second law of thermodynamics upon arbitrary external unitary operations. In terms of the diagonal entropy, thermodynamic irreversibility follows from the facts that quantum trajectories under unitary evolution are restricted by the Hamiltonian dynamics and that the external operation is performed without reference to the microscopic state of the system.

Entropy generation due flow passing over the porous block in the cavity

Flow over porous structures finds applications in heat transferring devices due to attainment of high heat transfer rates. Thermodynamic irreversibility can be used as a measure of quality of the porous body in the thermal system. In the present study, flow over a porous block situated in a square open–ends cavity and rate of entropy generation due to heat transfer and fluid friction are considered. The effects of the block aspect ratio and porosity on volumetric entropy generation rate are examined numerically. In the simulations, four aspect ratios and three porosities of the block are accommodated. The total area of the block is kept constant for all the aspect ratios considered in the simulations. A uniform heat generation (105 W/m²) is considered in the block resembling the heat generating device, such as encapsulated electronic device, and air is used as working fluid in the cavity. It is found that volumetric entropy generation rate in the cavity reduces with increasing aspect ratio and porosity of the block. Entropy generation rate due to heat transfer is considerably higher than its counter part due to fluid friction because of low Reynolds number flow at cavity inlet and small natural convection current generated in the cavity.

Reversible Heat Engines: Bounds on Estimated Efficiency from Inference

We consider work extraction from two finite reservoirs with constant heat capacity, when the thermodynamic coordinates of the process are not fully specified, i.e., are described by probabilities only. Incomplete information refers to both the specific value of the temperature as well as the label of the reservoir to which it is assigned. Based on the concept of inference, we characterize the reduced performance resulting from this lack of control. Indeed, the estimates for the average efficiency reveal that uncertainty regarding the exact labels reduces the maximal expected efficiency below the Carnot value (\(\eta _\mathrm{C}\)), its minimum value reproducing the well known Curzon–Ahlborn value: \(1-\sqrt{1-\eta _\mathrm{C}}\). We also estimate the efficiency before the value of the temperature is revealed. It is found that if the labels are known with certainty, then in the near-equilibrium limit the efficiency scales as \(\eta _\mathrm{C}/2\), while if there is maximal uncertainty in the labels, then the average estimate for efficiency drops to \(\eta _\mathrm{C}/3\). We also suggest how the inferred properties of the incomplete model can be mapped onto a model with complete information but with an additional source of thermodynamic irreversibility.

Thermally developing combined electroosmotic and pressure-driven flow of nanofluids in a microchannel under the effect of magnetic field

In the present study, the heat transfer characteristics of thermally developing magnetohydrodynamic flow of nanofluid through microchannel are delineated by following a semi-analytical approach. The combined influences of pressure-driven flow, electroosmotic transport and magnetic field is taken into account for the analysis of the complex microscale thermal transport processes. Solutions for the normalized temperature distributions and the Nusselt number variations, considering the simultaneous interplay of electrokinetic effects (electroosmosis), magnetic effects, Joule heating and viscous dissipation are obtained, for constant wall temperature condition. Particular attention is paid to assess the role of nanofluids in altering the transport phenomena, through variations in the effective nanoparticle volume fractions, as well as the aggregate structure of the particulate phases. It is observed that magnetohydrodynamic effect reduces advective transport of the liquid resulting in gradual reduction of heat transfer. Increase in nanoparticle volume fraction shows decrease in heat transfer. Similar effects are observed with increase in aggregate sizes of the nanoparticles. The effect of the nanofluids on system irreversibility is also studied through entropy generation analysis due to flow and heat transfer in the microchannel. Total entropy generation is found to be dominant at the thermally developing region of the microchannel, whereas it drops sharply at the thermally developed region. Presence of nanoparticles in the base fluid reduces the total entropy generation in the microchannel, thereby indicating decrease in thermodynamic irreversibility with increasing nanoparticle volume fraction.

Thermal stress analysis and entropy generation rate due to laser short pulse heating of a metallic surface

An analytical solution is developed for thermal stress in exponentially time decaying laser short-pulse heating of a metallic surface. Because the heating duration is short, a nonequilibrium heating model incorporating the electron kinetic theory approach is used to formulate the temperature distribution during the laser heating pulse. Thermomechanical coupling is introduced in the analysis to formulate the thermal stress field. Thermodynamic irreversibility is considered and the entropy generation rate due to heat transfer and thermal stress field is formulated during the heating process. It is found that temperature decays gradually in the surface region and becomes sharp as the distance increases towards the solid bulk. Thermal stress is compressive in the irradiated region. Thermodynamic irreversibility due to heat transfer dominates thermodynamic irreversibility because of the thermal stress field.

A thermodynamic irreversibility based design method for multi-contaminant hydrogen networks

This paper presents a new method for the design of hydrogen networks with multiple contaminants. The proposed method is based on the principle that minimizing thermodynamic irreversibility of the satisfying process will result in minimum utility consumption of the hydrogen network. Therefore, the entropy change which indicates the thermodynamic irreversibility of the satisfying process is minimized for each sink to obtain the minimum utility consumption. A new concept, virtual concentration, which is drawn from the thermodynamic analysis of the satisfying process, is proposed to measure the purity of the hydrogen streams with multiple contaminants. Source streams with the nearest virtual concentration as the sink are used to satisfy the sink to reduce the entropy change of each satisfying process. The detailed design procedures are proposed to obtain the hydrogen network distribution. The exact flow rate of each source stream is achieved by solving the mass balance equations. Three literature examples are illustrated to show the effectiveness of the proposed approach.

Adsorption/desorption of a dye by a chitosan derivative: Experiments and phenomenological modeling

Abstract The literature for adsorption of solutes from the liquid phase to solids or gel adsorbents under batch conditions is vast. The corresponding literature on the fundamentals of the process and its modeling from empirical to physical (phenomenological) models is also very extensive. This is not true for the process of desorption, despite its importance for the adsorption process to acquire economical viability. The literature for batch desorption is very small compared to that of adsorption and the corresponding theoretical/modeling studies are almost absent. In order to study the dynamics of batch adsorption/desorption process, a novel adsorbent–adsorbate combination of a chitosan-based derivative and a reactive dye is considered. Adsorption and desorption equilibrium experiments at optimal pH values were performed for three temperatures. Kinetic experiments were performed at three temperatures and three values of initial dye concentration in the solution (for adsorption) and in the adsorbent particle (for desorption). Typical analysis for equilibrium and kinetic data is presented. In addition, a phenomenological kinetic model is developed and fitted to the data assuming complete reversibility of the adsorption/desorption process. The model is extended to simulate batch adsorption/desorption cycles, which are typically studied experimentally in the literature. It is shown that the reduction of the adsorption efficiency during the cycles is not necessarily due to thermodynamic irreversibility of the process but may be due to the total solute mass conservation requirement.

System Integration and Flowsheet Optimization of 1000 MW Coal-fired Supercritical Power Generation Units

For traditional power generation process, energy losses are often caused by heat-and-mass transfer between the boiler and turbine subsystems, especially the heat transfer process with fairly high temperature difference in boiler. Generally, such energy losses are often unavoidable, if heat-and-mass transfer processes occur only in an independent way within certain subsystem or equipment but not in a cascade-integrated way. In this paper, new integration approach was proposed in order to reasonably utilize the heat at different temperature levels from the overall system perspective. Compared with isolated designs of the boiler and turbine subsystems, this approach comprehensively considers the match of heat transfer processes in air preheater and feedwater regeneration subsystem, and takes the principle of feedwater availability in the feedwater preheating process into account. The heat utilization process is reconstructed among the streams of flue gas, air, steam, feedwater and condensate water in a more coupling way. As a consequence, the thermodynamic irreversibility within air-preheating process and feedwater-regenerating system is sharply reduced. The heat-transfer characteristics and energy-saving effect of the integrated system was quantitatively analyzed. The results show that the power output of the novel integrated system is 21.74 MW higher than that of the conventional system. Moreover, the cost of electricity (COE) and the coal consumption rate can be decreased by 1.2% and 5.09g/kWh, respectively. This paper provides useful information for the energy-saving effects and design optimization of heat transfer process in thermal power generation.

The thermodynamic irreversibility of a mechanical system possessing the property of recurrence

The transition from one thermodynamic state to another by a mechanical system possessing the property of recurrence is investigated. It is established that the concept of a state in phenomenological thermodynamics corresponds to the concept of an attainability set in mechanics. It is shown that the presence of states that are reversible within the framework of classical mechanics, does not contradict the irreversibility of thermodynamic states.

Exergoenvironmental analysis of hybrid electric vehicle thermal management systems

Abstract The exergetic efficiency of the thermal management system (TMS) in hybrid electric vehicles (HEVs) has great importance since the supply of available energy onboard is limited, and that the efficiency is closely tied to the overall environmental impact of the vehicle. Thus, it is imperative to have a good understanding of the thermodynamic irreversibilities and environmental impact associated with the system and its components. In this paper, exergoenvironmental analysis is conducted on hybrid electric vehicle thermal management systems. In the exergy analysis part, the balance equations are written for each system component of the TMS to determine exergy destruction rates and exergy efficiencies of the system and its individual components. In the environmental analysis part, a life cycle assessment (LCA) is carried out (using Eco-indicator 99 points) and environmental impact correlations are created in order to obtain the environmental impact of each relevant system components and input and output streams. Consequently, exergoenvironmental variables are calculated, and exergoenvironmental evaluation is performed to determine the most environmentally friendly system components and provide information about trends and possibilities for design improvements. Based on the analysis, it is found that the electric battery has the highest environmental impact in the system due to the copper used in the anodes and gold used in the integrated circuits which accounts for over 40% and 26% of the overall impact respectively.

Refining carbon flux paths using atomic trace data

Pathway analysis tools are a powerful strategy to analyze 'omics' data in the field of systems biology. From a metabolic perspective, several pathway definitions can be found in the literature, each one appropriate for a particular study. Recently, a novel pathway concept termed carbon flux paths (CFPs) was introduced and benchmarked against existing approaches, showing a clear advantage for finding linear pathways from a given source to target metabolite. CFPs are simple paths in a metabolite-metabolite graph that satisfy typical constraints in stoichiometric models: mass balancing and thermodynamics (irreversibility). In addition, CFPs guarantee carbon exchange in each of their intermediate steps, but not between the source and the target metabolites and consequently false positive solutions may arise. These pathways often lack biological interest, particularly when studying biosynthetic or degradation routes of a metabolite. To overcome this issue, we amend the formulation in CFP, so as to account for atomic fate information. This approach is termed atomic CFP (aCFP). By means of a side-by-side comparison in a medium scale metabolic network in Escherichia Coli, we show that aCFP provides more biologically relevant pathways than CFP, because canonical pathways are more easily recovered, which reflects the benefits of removing false positives. In addition, we demonstrate that aCFP can be successfully applied to genome-scale metabolic networks. As the quality of genome-scale atomic reconstruction is improved, methods such as the one presented here will undoubtedly be of value to interpret 'omics' data.

Assessment of the Flue Gas Recycle Strategies on Oxy-Coal Power Plants using an Exergy-based Methodology

While oxy-combustion CO2 capture was foreseen to have higher improvement potential than post-combustion a decade ago, research has not been carried out at the same pace since then and today, the latter exhibits higher technological maturity along with low energy penalty thanks to advanced process integration and solvents formulation. Thus, significant efficiency improvement is needed for the oxy-combustion route to be competitive with post-combustion for carbon capture on coal-fired power plants. In order to achieve such improvements, process integration at system level is required to assess the true energy savings potential of oxy-combustion. In this study, an exergy-based methodology is performed to compare various flue gas recirculation strategies on a state-of-the-art 1100 MWe gross oxy-fired power plant. Exergy analysis at unit operation level allows the identification of the location and the magnitude of the thermodynamic irreversibilities occurring in the process, leading to an enhanced understanding of the studied system. In addition to the reference case in which the secondary recycle is fully depolluted and dehydrated; three alternative flue gas recirculation options have been investigated. Among the studied strategies, recirculation of the secondary flow prior the regenerative heat exchanger with a high temperature particle removal device leads to the highest net plant efficiency. This option not only allows the minimal exergy losses in the boiler but also minimizes the flowrate going through the downstream depollution devices. The net plant efficiency obtained for this architecture is 38.0%LHV, which represents a 3% increase compared to the reference oxy-combustion plant. Comparing this figure to an air-fired power plant modeled with the same set of hypotheses, the energy penalty is 8.1%-pts.

Entropy generation in a solar collector filled with a radiative participating gas

Heat losses in solar energy collectors are associated with thermodynamic irreversibility, which causes entropy generation. These losses can be reduced through EGM (entropy generation minimization) techniques. Using computational fluid dynamics, entropy generation associated with viscous dissipation, heat conduction and convection, and thermal radiation is studied for a solar collector filled with a radiative participating gas. The EGM methodology shows that gas filled solar collectors have an optimum optical thickness and an optimum tilt angle where the heat losses are minimized. These optimum conditions for gas filled collectors cannot accurately be determined using conventional performance parameters. Solar collectors filled with radiative participating gases are also found to be suitable for the tropics.

An Assessment of the Bottoming Cycle Operating Conditions for a High EGR Rate Engine at Euro VI NOx Emissions

This paper investigates the application of a Bottoming Cycle (BC) applied to a 10-litre (L) heavy duty Diesel engine for potential improvements in fuel efficiency. With the main thermodynamic irreversibility in the BC due to the temperature difference between the heat source and the working fluid, a proper selection of the working fluid and its operating condition for a given waste heat is the key in achieving high overall conversion efficiency. The paper reviews a fluid selection methodology based on thermodynamic/thermo-physical and environmental/safety properties. Results are presented using seven pure, dry, isentropic and wet working fluids (synthetic, organic and inorganic) operating with expansion starting from the saturated vapour, superheated vapour, supercritical phase, saturated liquid, and two-phase. Efficiency improvements by recovering Charge Air Coolers (CAC) and Exhaust Gas Recirculation (EGR) cooler heat on two engine platforms were calculated. The first platform operating at Euro 6 engine out NOx emissions levels and the second platform operating with Euro 5 engine out NOx emissions coupled with a 80% efficient selective catalytic reduction system. Performance and heat rejection data for the 10L platforms were derived from experimental measurements on an advanced 2L single cylinder research engine which was used to determine the trade-off between thermal efficiency and regulated/unregulated emissions. Results indicate a potential improvement of 5.1% and 6.3% in engine power for a cruise (B50) and high load (C100) condition, with a technically feasible BC operating at subcritical mode with minimum superheat.

Entropy production along nonequilibrium quantum jump trajectories

For classical nonequilibrium systems, the separation of the total entropy production into the adiabatic and nonadiabatic contributions is useful for understanding irreversibility in nonequilibrium thermodynamics. In this paper, we formulate quantum analogues for driven open quantum systems describable by quantum jump trajectories by applying a quantum stochastic thermodynamics. Our main conclusions are based on a quantum formulation of the local detailed balance condition.

An Economics-Based Second Law Efficiency

Second Law efficiency is a useful parameter for characterizing the energy requirements of a system in relation to the limits of performance prescribed by the Laws of Thermodynamics. However, since energy costs typically represent less than 50% of the overall cost of product for many large-scale plants (and, in particular, for desalination plants), it is useful to have a parameter that can characterize both energetic and economic effects. In this paper, an economics-based Second Law efficiency is defined by analogy to the exergetic Second Law efficiency and is applied to several desalination systems. It is defined as the ratio of the minimum cost of producing a product divided by the actual cost of production. The minimum cost of producing the product is equal to the cost of the primary source of energy times the minimum amount of energy required, as governed by the Second Law. The analogy is used to show that thermodynamic irreversibilities can be assigned costs and compared directly to non-energetic costs, such as capital expenses, labor and other operating costs. The economics-based Second Law efficiency identifies costly sources of irreversibility and places these irreversibilities in context with the overall system costs. These principles are illustrated through three case studies. First, a simple analysis of multistage flash and multiple effect distillation systems is performed using available data. Second, a complete energetic and economic model of a reverse osmosis plant is developed to show how economic costs are influenced by energetics. Third, a complete energetic and economic model of a solar powered direct contact membrane distillation system is developed to illustrate the true costs associated with so-called free energy sources.

Exergy Analysis of Oxidative Steam Reforming of Methanol for Hydrogen Producton: Modeling Study

Abstract Hydrogen production by oxidative steam reforming of methanol in a fixed bed catalytic reactor was modeled and simulated. The addition of O2 to feed reduced the temperature in the reformer. 99.86% conversion was obtained at 550 K and S/C molar ratio of unity in steam reforming while it is at 540 K in oxidative steam reforming. Although H2 and CO yields were decreased in oxidative steam reforming in comparison to steam reforming, the reductoin H2 yield was note significant whereas reduction in CO was appreciably high. The thermal and exergy efficiencies were favored by reforming temperature and S/C molar ratios. However, variation in S/C molar ratio showed negligibly small effect on efficiencies. The reforming temperature had a notable influence on the efficiencies. The exergy destruction was found to be lower at higher temperature and S/C molar ratio. Thus, oxidative steam reforming of methanol at 540 K and S/C molar ratio of unity utilizes sufficient amount of input energy in the form of useful work and thermodynamic irreversibilities in the reactor are quantitatively small.