This paper presents an exergy-based sustainability analysis of manufacturing roof tiles from plastic waste in Uganda. Exergy analyses measure the sustainability of industrial processes. This work focuses specifically on the developing country context and on utilizing waste material. A summary of the current plastic waste situation in Uganda, the environmental and health issues associated with plastic waste, current means of recycling plastic waste into new products, and an analysis of the Ugandan roofing market are presented. The motivation for this study is to examine the resources utilized to improve overall exergy efficiency, reduce production costs, and reduce negative environmental impacts. The company, Resintile, is the only manufacturer of roof tiles from plastic waste in Uganda. Their tiles comprised mainly of sand and plastic waste are manufactured in an industrialized process involving drying, extrusion, and pressing. The exergy consumed at each stage including transportation is presented. The extruder consumes the majority of the exergy, but wrapping insulation around the barrel could save over 3 MJ, and a heat engine could provide over 7.5 MJ of usable exergy. The total exergy consumed to produce one batch of seventy-five tiles is over 122 MJ, the potentially recoverable exergy is over 5 MJ (4.3% of consumed exergy), and the realistic recoverable exergy is nearly 10.7 MJ (8.7% of consumed exergy). The realistic can be greater than the potential by adding a heat engine to the sand drying process to generate usable exergy rather than merely recover consumed exergy. Resintile’s plastic roof tiles save a net 86.3 kg of CO 2 from entering the atmosphere per batch of tiles and adoption of the suggested improvements to the manufacturing process would save an additional 3.8 kg of CO 2 per batch.

In this paper, a novel coal gasification technology used for Integrated Gasification Combined Cycle (IGCC) power plants is proposed, in which a regenerative unit is applied to recover syngas sensible heat to generate steam and then the high temperature steam is used to gasify coke from pyrolyzer. Through such a thermochemical regenerative unit, the sensible heat with lower energy level is upgraded into syngas chemical energy with higher energy level, and therefore a higher cold gas efficiency (CGE) is expected. The Aspen Plus Software is selected to simulate the novel coal gasification system. Then the exergy and Energy-Utilization Diagram (EUD) analyses are applied to disclose the plant performance enhancement mechanism. It reveals that 83.2% of syngas sensible heat can be recovered into steam agent and so the CGE is upgraded to 90%. And with the enhancement of CGE, the efficiency of an IGCC plant based on the novel gasification system can be as high as 51.82%, showing a significant improvement compared to 45.2% in a Texaco coal gasification based plant. At the same time, the exergy destruction of gasification process is reduced from 132.5MW to 98.4MW through thermochemical reactions. Lift of accepted energy level ( A ea ), and decrease of released energy level ( A ed ) and heat absorption ( ΔH ) contribute to the exergy destruction reduction in the gasification process. Additionally, since oxygen agent is no longer used in the IGCC, 34.5MW exergy loss in the air separation unit is avoided. Thereby the novel coal gasification technology proposed in this paper has a good thermodynamic performance and may provide a quite promising way for high efficient and clean coal utilization.

The guayule ( Parthenium argentatum ) plant is a source of natural rubber and a possible high-energy biofuel. Herein guayule bagasse, the residual biomass after latex extraction, which accounts for 90% of the processed plant material, is modeled in a fast pyrolysis biorefining process. The simulation uses PRO/II ® software and is based on data and processes used successfully in a bench scale facility. The unique 200-ton per day plant includes fast pyrolysis utilizing the tail gas reactive process followed by atmospheric separation, hydrodeoxygenation and final product separation, resulting in products similar to traditional fuels, i.e., gasoline, jet fuel and diesel. Approximately 10% of the biomass is converted to liquid fuels with 10% of this converted to gasoline, 34% jet fuel and 56 % diesel. These yields are compared to alternative feedstock and methods. The simulation results are utilized in an exergetic assessment. The depletion of exergy from its natural state (cumulative exergy demand, CExD) is considered as a measure of sustainability of the refining process. Breeding factors, measures of exergy production (the ratio of chemical exergy of the output products to the process exergy inputs), are determined. Results show, for the entire biorefining process, favorable breeding factors can possibly exceed 10, thus suggesting a favorable method of exergy production.

Mixing of fresh (river) water and salty water (seawater or saline brine) in a control fashion would produces an electrical energy known as salinity gradient energy (SGE). Two main conversion technologies of SGE are membrane-based processes; pressure retarded osmosis (PRO) and reverse electrodialysis (RED). In PRO, semipermeable membranes placed between the two streams of solutions allow the transport of water from low-pressure diluted solution to high-pressure concentrated solution. RED requires two alternating semipermeable membranes that allow the diffusion of the ions but not the flow of H 2 O . Lifetime and power density of the semipermeable membrane are two main factors affecting on deployment of PRO and RED. Semipermeable membranes with lifetime greater than 10 years and power density higher than 5 W/m 2 would lead to faster development of this conversion technology. An exergy analysis of an SGE system of sea-river can be applied to calculate the maximum potential power for electricity generation. Seawater is taken as reference environment (global dead state) for calculating the exergy of water since the seawater is the final reservoir. Once the fresh water is mixed with water of the sea or lake it becomes unuseful for human, agricultural or industrial uses loses all its exergy. Aqueous sodium chloride solution model is used in this study to calculate the thermodynamic properties of seawater. This model does not consider seawater as an ideal model and provides accurate thermodynamics properties of sodium chloride solution. As a case study, exergy calculation of Iran’s Urmia Lake-GadarChay River system. The chemical exergy analysis considers sodium chloride (NaCl) as main salt in the water of Lake Urmia. The sodium chloride concentration is more than 200 g/L in recent years. Based on the exergy results the potential power of this system is 329 MW. This results indicates a high potential for constructing power plant for salinity gradient energy conversion.

Solar thermal energy is considered one of the most promising renewable energy resources, especially for high intensive solar radiation locations, such as Saudi Arabia. Therefore, there is a need to assess the performance of one potential dominant solar thermal energy technology that can be applied in Saudi Arabia, which is Solar Chimney Power Plant (SCPP). SCPP is guided through natural draft utilizing solar radiant energy to impart ascending thrust to the flow of air and therefore, transforming the radiant energy to run the turbine. This paper presents the exergy analysis of the assumed model of the SCPP and presents its performance for Dhahran, Saudi Arabia, as an illustrative of the exergy model developed. The modeling was validated against published data. The tower height is 195 m and the collector diameter is 240 m. The tower can produce, on average, around 123kW during daytime and has, on average, air mass flow rate of around 160 kg/s. The exergetic efficiency was found to be around 0.45%.

Absorption Power Cycles (APCs) provide an interesting field within power cycles. The multicomponent mixture with variable temperature across boiling is employed as a working fluid. This has a potential for decreasing exergy loss associated with heat transfer during phase change processes (boiling and condensation). Absorption process has also an effect of lowering exhaust pressure of a turbine. The APCs hold a potential for heat recovery applications at very low temperatures, where constant temperature of boiling and condensation largely limits performance and economic effectiveness of Organic Rankine cycles (ORCs). Theoretical calculations show superiority of APC over extensive range of considered ORC working fluid. The advantage of APC further increases when air cooled condenser needs to be used instead of wet cooling tower. With the same boundary conditions for all cycles the APC provides higher utilization efficiency and power output at source temperatures below approximately 120 °C, for temperatures as low as 60 °C the net power output can be surpassed even more than three times. The proposed APC employs aqueous solution of salts considered generally for absorption cooling (Lithium Bromide, Lithium Chloride, Calcium Chloride) as a working fluid. Unlike ammonia used in mixture with water in Kalina APC or often ORC working fluids, used salts are non-toxic, environmentally friendly and pure water in expander simplifies its design. After summary of theoretical research from thermodynamics point of view are discussed principles, aspects and issues for design of single components of the cycle. Results of sizing are presented on two examples with 100 °C heat source. First one is 20 kW e unit using hot air as a heat source and air cooled condenser, second one is 500 kW e unit with heat source being pressurized water and using wet cooling tower heat rejection. Results show possibility of building relatively efficient system for even small power output with turbine isentropic efficiency nearly 80 % for the 20 kW e unit, but relatively large heat exchangers.

Two significant goals in solar plant operation are lower cost and higher efficiencies. This is both for general competitiveness of solar technology in the energy industry, and also to meet the US DOE Sunshot Initiative Concentrating Solar Power (CSP) cost goals [1]. We present here an investigation on the effects of adding a bottoming steam power cycle to a solar-fossil hybrid CSP plant based on a Small Particle Heat Exchange Receiver (SPHER) driving a gas turbine as the primary cycle. Due to the high operating temperature of the SPHER being considered (over 1000 Celsius), the exhaust air from the primary Brayton cycle still contains a tremendous amount of exergy. This exergy of the gas flow can be captured in a heat recovery steam generator (HRSG), to generate superheated steam and run a bottoming Rankine cycle, in a combined cycle gas turbine (CCGT) system. A wide range of cases were run to explore options for maximizing both power and efficiency from the proposed CSP CCGT plant. Due to the generalized nature of the bottoming cycle modeling, and the varying nature of solar power, special consideration had to be given to the behavior of the heat exchanger and Rankine cycle in off-design scenarios. Variable guide vanes (VGVs), which can control the mass flow rate through the gas turbine system, have been found to be an effective tool in providing operational flexibility to address the variable nature of solar input. The effect VGVs and the operating range associated with them are presented. Strategies for meeting a minimum solar share are also explored. Trends with respect to the change in variable guide vane angle are discussed, as well as the response of the HRSG and bottoming Rankine cycle in response to changes in the gas mass flow rate and temperature. System efficiencies in the range of 50% were found to result from this plant configuration. However, a combustor inlet temperature (CIT) limit lower than a turbine inlet temperature (TIT) limit leads two distinct Modes of operation, with a sharp drop in both plant efficiency and power occurring when the air flow through the receiver exceeded the (CIT) limit, and as a result would have to bypass the combustor entirely and enter the turbine at a significantly lower temperature than nominal. Until that limit is completely eliminated through material or design improvements, this drawback can be addressed through strategic use of the variable guide vanes. Optimal operational strategy is ultimately decided by economics, plant objectives, or other market incentives.

Concentrated Solar Power using supercritical CO 2 (S-CO 2 ) Brayton cycles offers advantages of similar and even higher overall thermal efficiencies compared to conventional Rankine cycles using superheated or supercritical steam. In this paper, a S-CO 2 Recompression Brayton cycle is integrated with a central receiver. The effect of pressure drops in heat exchangers and solar receiver surface temperature on the thermal and ex-ergetic performance of the recompression Brayton cycle with and without reheat condition is studied. Energy, exergy and mass balance are carried out for each component and first law and exergy destruction are calculated. In order to obtain optimal operating condition, optimum cycle pressure ratios are obtained by maximising the thermal efficiency. The results showed that under low solar receiver pressure drops and solar receiver temperature approach, the S-CO 2 Recompression Brayton cycle has more thermal and exergy efficiencies than the no reheat case. Pressure drop reduces the gap between reheat and no reheat case, and for pressure drops in the solar receiver of 2.5% or higher, reheat has significant impact on thermal and exergy performance of the cycle studied. The overall exergy efficiency showed a bell shaped, reaching a maximum value between 19.5–22.5% at turbine inlet temperatures in the range of 660–755 °C for solar receiver surface temperature approach among 100–200 °C.

The performance of CAES is evaluated for various configurations, with and without thermal energy storage. First, a conventional compressed air energy storage process is modeled using a time series iterative forward differencing method to simulate the round trip efficiency, exergy storage, cavern temperatures and pressures, and the gas expander exit temperature of a CAES plant. The computational model was validated experimentally by comparing trended data of the compression cycle of a 280 HP Gardener-Denver tandem horizontal two-stage compressor to computational results. It was found that the process of cooling the compressors resulted in a large exergy loss and the inefficiencies of the expanders lead to higher temperature gas being exhausted back to ambient pressures. Second, Advanced Adiabatic Compressed Air Energy Storage (AACAES) was simulated to study the effectiveness of storing the thermal energy removed from the compressors to be added to the compressed air as it enters the expanders at a later time. Third, the concept of increasing the capacity of the thermal energy storage systems to allow recharge with concentrated solar heat was explored. It was found that the thermal efficiency of converting the solar thermal energy to power would be high (> 60%). Further, the expander exhaust temperature and exergy are high (> 500 K), implying that additional waste heat energy recovery will be possible. Taken together, the results of this study show that an integrated, high efficiency, on-demand, water-free, solar energy delivery system is possible if combined with an AACAES system.

Hybrid photovoltaic/thermal (PV/T) systems are continually being investigated, in particular the use of such systems in concentrating collectors as part of the ARPA-E FOCUS program. While many combined thermal and electrical models exist, most are limited to 0-D energy balance approaches or 1-D approaches where temperature variations through insulation, glazing and substrates are considered. Here, we develop a 2-D model for a concentrating PV/T system where the model accounts for temperature variations along the length of the collector. The proposed configuration consists of a GaAs cell laminated to an aluminum extrusion. The working fluid, a transparent high temperature heat transfer fluid with suspended nanoparticles, flows through the extrusion where it actively cools the PV cell before passing in front of the cell acting as an optical filter. The model includes PV cell efficiency, temperature, and bandgap dependence, a detail often neglected in prior works. This paper focuses on PV efficiency along the length of the system and outlet fluid temperature for both counter and parallel flow arrangements. Of particular interest here is the wavelength used in the design of the fluid filter and how changing the design impacts the exergetic efficiency and percent of exergy created as heat.

The FSPOT-X Project, focused on maximizing exergy generated from AM1.5 sunlight, targets an overall system efficiency of >35%. The objective hybrid power system will deliver grid-ready AC power while simultaneously providing thermal energy storage for dispatchable electrical power generation in post sunset conditions. The challenging system-level requirements flow-down critical temperature differential and thermal transport requirements to multiple system components and their interfaces. By integrating and demonstrating multiple technologies, the FSPOT-X hybrid power system seeks to efficiently convert photons to electrons maximizing heat transfer efficiency across system element interfaces. These include: I1) capturing all incident sunlight from the solar concentrator in a receiver cavity to maximize energy generation from the CPV cells, I2) extracting PV thermalization heat from the receiver and into the reflux chamber, I3) moving heat from the reflux chamber through the thermal transfer interface, I4) using the thermal transfer interface to shift heat into the TAPC’s hot heat exchanger, I5) storing excess unused heat in phase change material, and I6) disposal of waste heat at the system level. For each of these thermal interfaces, effective and efficient technical means are being used and applied in order to maximize overall system efficiency for delivery of a next generation cost-effective and market-ready solar power system.

All current commercial CSP plants operate at relatively low thermodynamic efficiency due to lower temperatures than similar conventional plants and due to the fact that they all employ Rankine conversion cycles. We present here an investigation on the effects of adding a bottoming steam power cycle to a hybrid CSP plant based on a Small Particle Heat Exchange Receiver (SPHER) driving a gas turbine as the primary cycle. Due to the high operating temperature of the SPHER being considered (over 1000 Celsius), the exhaust air from the primary Brayton cycle still contains a tremendous amount of exergy. While in the previous analysis this fluid was only used in a recuperator to preheat the Brayton working fluid, the current analysis explores the potential power and efficiency gains from instead directing the exhaust fluid through a heat exchanger to power a Rankine steam cycle. Not only do we expect the efficiency of this model to be competitive with conventional power plants, but the water consumption per kilowatt-hour will also be reduced by nearly two thirds as compared to most existing concentrating solar thermal power plants as a benefit of having air as the primary working fluid, which eliminates the condensation step present in Rankine-cycle systems. Coupling a new steam cycle model with the gas-turbine CSP model previously developed at SDSU, a wide range of cases were run to explore options for maximizing both power and efficiency from the proposed CSP combined cycle gas turbine (CCGT) plant. Due to the generalized nature of the bottoming cycle modeling, and the varying nature of solar power, special consideration had to be given to the behavior of the heat exchanger and Rankine cycle in off-design scenarios. The trade-offs of removing the recuperator for preheating the primary fluid are compared to potential overall power and efficiency gains in the combined cycle case.

In previous work the authors have demonstrated that when hydrogen is combusted in stoichiometric proportions at 1 atm and 1200 K, and singlet oxygen comprises 0–20% of the oxidizer, an optimal range of exergetic efficiency exists. The maximum exergetic efficiency occurs at approximately 10%. Over this range, roughly 60% of the total exergy destruction occurs prior to ignition. This is a significant result because it suggests that the exergetic efficiency of combustion might be improved at a fundamental level by chemical means, thereby inherently increasing the efficiency of fuel use for a desired energy application. The objective of the study presented in this paper is to analyze the reaction mechanisms for combustion with varying percentages of singlet oxygen, to determine which reaction pathways most influence the observed trends in exergy destruction and exergetic efficiency. This was accomplished by performing both sensitivity and rate-of-production analyses of the hydrogen-oxygen combustion mechanism. The results of the analysis show that the presence of singlet oxygen governs the rate of production of hydroxyl and other key radicals. These key radicals directly affect the phenomenological processes associated with chemical induction and thermal induction during ignition. Therefore, the observed optimum exergetic efficiency correlates to the quantity of singlet oxygen in the inlet charge that minimizes exergy destruction by fostering chemical reactions due to radical formation to a greater extent than thermal heat release. The results of this analysis are noteworthy and provide new insight regarding how the exergetic efficiency of combustion may be optimized by introducing singlet oxygen, thereby altering the reaction pathways to enhance energy conversion in a fundamental way that could have important implications for improved fuel use.

In this work, four different arrangements of solar cooker box-type with internal reflectors results, for irreversibility and second law efficiency are presented. The solar cooker has two glasses in its cover to diminish the losses of heat radiation and convection, which in turn creates the hot house effect inside the cooker. The interior of the cooker has flat mirrors placed at different angles to reflect the solar radiation toward recipient with water. The obtained results are based on the heated water temperatures. These are obtained by means of numerical simulation, which in turn allows the comparison under identical conditions for the cookers. The results reveal that the energy reaching the cookers, less than 5%, is used in the water heating process. Most of the available energy is “stored” into the cooker glass cover, which shows the need for further work on improving cover materials in order to diminish such a situation.

This paper examines the economic benefits of various operation strategies for a thermal energy storage (TES) system in a solar thermal power plant. A thermodynamic model developed to evaluate different design options has been utilized to calculate system performance and assess the impact of operation strategies, storage capacity, and market prices on the value of TES. The overall performance is also investigated through several parametric studies, such as solar multiple, geographic location, and choice of HTF. The influence of these parameters has been evaluated in consideration of exergy destruction due to heat transfer and pressure drop. By incorporating exergy-based optimization alongside traditional energy analyses, the results of this study evaluate the optimal values for key parameters in the design and operation of TES systems, as well as highlight opportunities to minimize thermodynamic losses. Annual performance for each case is characterized both by nominal and part-load efficiency. Levelized cost of electricity (LCOE) is calculated for all cases, illustrating a set of optimal parameters that yield a minimum LCOE value.

Finding optimal operating conditions of solar-based power and cooling systems is always a challenge. Performance of these systems is highly dependent on several important parameters, which not only impact the long-term efficiency but also its technical and economic feasibility. This paper studies the operation/configuration problem of an ammonia-water power and cooling cycle using an exergetic analysis. Thermodynamic performance of the combined cycle was addressed by using analysis of variance and multiple linear regression analysis. Modeling was done in Matlab ® , using Refprop 9.0 to calculate the thermodynamic properties of the ammonia-water mixture. Convergence issues were observed on the thermodynamic properties estimation carried out by Refprop when the stream had high ammonia mass fraction. To solve this issue an averaging algorithm was implemented online to estimate such properties using pure ammonia data and high, but stable, ammonia concentration data. After this implementation, small differences between current and reference model were seen. Optimum operating conditions were obtained using response surface technique. The response variable used was the ratio between exergetic efficiency and exergy destruction. Results showed that the response variable is mainly influenced by the ammonia concentration, pressure ratio, turbine efficiency and temperature gradient in the heat exchanger. Finally integration of the power/cooling cycle with a solar field was performed using two types of concentrated solar collectors: Linear Fresnel Collector (LFC) and Parabolic Trough Collector (PTC). The analysis showed that LFC technology can be a viable alternative for small scale applications combined with power/cooling systems.

WINDGRABBER™ (WG) is a novel new roof or pole top mounted wind turbine system proposed for product commercialization up to 50 kWe. WG is projected to be cost-attractive in an environmentally friendly manner. The WG system uses the available energy in the wind via (1) a passively yawed air impact inlet air scoop, (2) a flow tube, (3) an air turbine and (4) a multiphased air inlet with an air impact - drag type outlet section. The WG wind turbine system preferentially utilizes a combination enclosed - radial out-flow, cross-flow, reaction-impulse air turbine of squirrel cage configuration, using either a single or double axial flow inlet of centrifugal fan design with backwardly curved, air foil air blades mounted on the discharge end of a flow tube. The WG wind turbine design is based on the air power instead of the wind power equations, combined with duct resistance, wind impact and wind drag calculations, to determine system wind energy conversion effectiveness with respect to the Betz limit, as well as overall system efficiency. Low pressure drop screens may be provided at the various inlets and outlets to protect birds and small mammals from being drawn into rotating components. A currently proposed Phase I – CAE modeling for conceptual design verification, system optimization and 300 watt pilot plant test program, followed by a Phase II – design improvement and scale up to 3,000 watt prototype demonstration program and followed by a Phase III cost reduction, product improvement and scale up to a 5,000 watt commercial demonstration program is currently being considered by BCK Consulting, L.L.C. (BCK) and West Texas A & M University (WTAMU). The history of WG , up to and including its latest developmental status, will be discussed in this paper with projections offered regarding its future product commercialization prospects. Please see ASME paper ES2010-90062 presented previously [Ref.1].

Today’s rate of fossil fuel consumption rapidly depletes fuel reserves and leads to a number of adverse environmental effects. Although the scope of these effects has yet to be fully realized, it is clear that the development of alternative energy sources is very important. A relatively new form of alternative energy known as reverse electrodialysis (RED) appears to be one of the promising energy sources of the future. This technology harvests the energy stored in the salinity gradient between two different liquids, and converts it directly into electric power. This power is generated by pumping water through an array of alternating pairs of cation and anion exchange membranes called cells. Various academic sources calculate the available energy to be 1.5 MJ for every cubic meter of sea and river water mixed, making all river basins a potential location for power production. Small prototype systems using 50 cells with areas of 100 cm 2 were assembled by a group in the Netherlands, but larger stacks remain to be tested. An understanding of the feasibility of RED as a possible energy source relies on testing of cells with larger membrane area and different numbers of membrane pairs. An experimental system was designed with cells 61 cm × 16.5 cm, which will increase the output by nearly a factor of 10. Along with having much larger dimensions than previous systems, the design has an adjustable number of cells in the stack, allowing users obtain test results at a variety of settings. Comparing the output of systems with few cells to systems with many cells will help us to optimize the stack size in terms of hydrodynamic losses. Initial testing of the system resulted in a positive result. The tests showed that the system produced power, and the 1.98 volts measured was 83% of the predicted value. Leakage of the electrode rinse solution contaminated the membranes, and prevented more testing. Once the electrode rinse system is redesigned, more testing will be done.

In this work, energy and exergy analyses are applied to a thermal energy storage system employing a storage medium in the two-phase or supercritical regime. First, a numerical model is developed to investigate the transient thermodynamic and heat transfer characteristics of the storage system by coupling conservation of energy with an equation of state to model the spatial and temporal variations in fluid properties during the entire working cycle of the TES tank. Second, parametric studies are conducted to determine the impact of key variables (such as heat transfer fluid mass flow rate and maximum storage temperature) on both energy and exergy efficiencies. The optimum heat transfer fluid mass flow rate during charging must balance exergy destroyed due to heat transfer and exergy destroyed due to pressure losses, which have competing effects. Similarly, the optimum maximum storage fluid temperature is evaluated to optimize exergetic efficiency. By incorporating exergy-based optimization alongside traditional energy analyses, the results of this study evaluate the optimal values for key parameters in the design and operation of TES systems, as well as highlight opportunities to minimize thermodynamic losses.

The present work provides a feasibility analysis of a hybrid distributed generation system to meet the energy needs for residential communities in four locations in Mexico. Tuxtla Gutierrez (Oaxaca), Puerto Escondido (Oaxaca), Guaymas (Sonora) and Mexicali (Baja California Norte) were the four locations selected to assess the potential available energy resources in meeting cost-effectively and sustainably the electricity and thermal loads of small communities in Mexico. Electricity and thermal loads are obtained for the four locations by using calibrated building energy models for residential buildings in Mexico. Based on the feasibility analysis, it is found that while hybrid systems can reduce significantly CO 2 emissions, they are not cost-effective to implement in all locations due to the relatively cheap electricity costs from the only federal utility company in Mexico.