Methodology for thermal design of novel combined refrigeration/power binary fluid systems

Refrigeration cogeneration systems which generate power alongside with cooling improve energy utilization significantly, because such systems offer a more reasonable arrangement of energy and exergy “flows” within the system, which results in lower fuel consumption as compared to the separate generation of power and cooling or heating. This paper proposes several novel systems of that type, based on ammonia–water working fluid. Importantly, general principles for integration of refrigeration and power systems to produce better energy and exergy efficiencies are summarized, based primarily on the reduction of exergy destruction. The proposed plants analyzed here operate in a fully-integrated combined cycle mode with ammonia–water Rankine cycle(s) and an ammonia refrigeration cycle, interconnected by absorption, separation and heat transfer processes. It was found that the cogeneration systems have good performance, with energy and exergy efficiencies of 28% and 55–60%, respectively, for the base-case studied (at maximum heat input temperature of 450 °C). That efficiency is, by itself, excellent for cogeneration cycles using heat sources at these temperatures, with the exergy efficiency comparable to that of nuclear power plants. When using exhaust heat from topping gas turbine power plants, the total plant energy efficiency can rise to the remarkable value of about 57%. The hardware proposed for use is conventional and commercially available; no hardware additional to that needed in conventional power and absorption cycles is needed.     

Gradient-Structured Ceramics with High Energy Storage Performance and Excellent Stability

Owing to the high power density, eco-friendly, and outstanding stability, the lead-free ceramics have attracted great interest in the fields of pulsed power systems. Nevertheless, the low energy storage density of such ceramics is undoubtedly a severe problem in practical applications. To overcome this limitation, the lead-free ceramics with gradient structures are designed and fabricated using the tape-casting method herein. By optimizing the composition and distribution of the gradient-structured ceramics, the energy storage density, and efficiency can be improved simultaneously. Under a moderate electric field of 320 kV cm⁻¹, the value of recoverable energy storage density (W_rec) is higher than 4 J cm⁻³, and the energy storage efficiency (η) is of ≥88% for 20-5-20 and 20-10-20. Furthermore, the gradient-structured ceramics of 20-10-0-10-20 and 20-15-0-15-20 possess high applied electric field, large maximum polarization, and small remnant polarization, which give rise to ultrahigh W_rec and η on the order of ≈6.5 J cm⁻³ and 89–90%, respectively. In addition, the energy storage density and efficiency also exhibit excellent stability over a broad range of frequencies, temperatures, and cycling numbers. This work provides an effective strategy for improving the energy storage capability of eco-friendly ceramics.     

Modern and appropriate technologies for the reduction of gaseous pollutants and their effects on the environment

Harmful effects on environment such as global warming and climate change may result from the gases emanating from fossil fuel combustion. Jordan and most Middle East countries use fossil fuels exclusively. Therefore, new technologies which could accommodate the demand for cleaner effluents, such as: combined cycles, fluidized bed combustion, magneto hydrodynamics, fuel cells, nuclear power, natural gas, renewable energy, and energy conservation have been considered. CO₂ being the most produced gas, many technical methods of reducing and reusing CO₂ have been suggested such as: Injection in oceans, storage in caverns, injection in depleted oil and gas fields, pumping during oil recovery, storage as CO₂ ice, elimination by fixation using water algae, and increasing plantation especially forestation. These methods are being used at different degrees in the Middle East countries. Reduction of formation and harmful effects of other gaseous pollutants is also discussed, with some concentration on the transportation sector, energy efficiency and fuel cells, which have special importance for the developing countries.     

Looking beyond lithium-ion technology – Aqueous NaOH battery

The objective of this work is to investigate a water based sodium battery technology. The new concept proposed here for an aqueous rechargeable battery is replacing lithium hydroxide with a sodium hydroxide electrolyte in the patented technology developed at Murdoch University. Alternative energy storage system using abundantly available sodium as the aqueous electrolyte coupled with Zn anode and environmentally friendly MnO₂ cathode are investigated and found feasible. Sodium intercalation and de-intercalation mechanism is identified in MnO₂|NaOH|Zn cell yielding 225 against 142 mAh/g for LiOH counterpart. The preliminary studies of the aqueous NaOH battery showed improved energy density and voltaic efficiency.     

Air-stable,earth-abundant molten chlorides and corrosion-resistant containment for chemically-robust,high-temperature thermal energy storage for concentrated solar power

A dramatic reduction in man-made CO₂ emissions could be achieved if the cost of electricity generated from concentrated solar power (CSP) plants could become competitive with fossil-fuel-derived electricity. The solar heat-to-electricity conversion efficiency of CSP plants may be significantly increased (and the associated electricity cost decreased) by operating CSP turbines with inlet temperatures ≥750 °C instead of ≤550 °C, and by using thermal energy storage (TES) at ≥750 °C to allow for rapidly dispatchable and/or continuous electricity production. Unfortunately, earth-abundant MgCl₂–KCl-based liquids currently being considered as low-cost media for large-scale, high-temperature TES are susceptible to oxidation in ambient air, with associated undesired changes in liquid composition and enhanced corrosion of metal alloys in pipes and tanks containing such liquids. In this paper, alternative high-temperature, earth-abundant molten chlorides that are resistant to oxidation in ambient air are identified via thermodynamic calculations. The oxidation resistance, and corrosion-resistant containment, of such molten chlorides at 750 °C are then demonstrated. Such an air-tolerant strategy, involving chemically-robust, low-cost TES media paired with effective containment materials, provides a critical advance towards the higher-temperature operation of, and lower-cost electricity generation from, CSP plants.     

Photovoltaic–Pyroelectric Coupled Effect Induced Electricity for Self‐Powered Photodetector System

Ferroelectric materials have demonstrated novel photovoltaic effect to scavenge solar energy. However, most of the ferroelectric materials with wide bandgaps (2.7–4 eV) suffer from low power conversion efficiency of less than 0.5% due to absorbing only 8–20% of solar spectrum. Instead of harvesting solar energy, these ferroelectric materials can be well suited for photodetector applications, especially for sensing near‐UV irradiations. Here, a ferroelectric BaTiO₃ film‐based photodetector is demonstrated that can be operated without using any external power source and a fast sensing of 405 nm light illumination is enabled. As compared with photovoltaic effect, both the responsivity and the specific detectivity of the photodetector can be dramatically enhanced by larger than 260% due to the light‐induced photovoltaic–pyroelectric coupled effect. A self‐powered photodetector array system can be utilized to achieve spatially resolved light intensity detection by recording the output voltage signals as a mapping figure.     

Exergy recuperative CO2 gas separation in pre-combustion capture

The integrated coal gasification combined cycle (IGCC) can achieve higher power generation efficiency than conventional pulverized coal combustion power plants. However, a CO₂ capture process prevents improving power generation efficiency of IGCC, because CO₂ separation from gas mixtures requires huge amounts of energy. Therefore, in this study, we analyzed the CO₂ separation process in the pre-combustion capture process using a process simulator (PRO/II) in the steady state, and proposed a new process using a modularity based on self-heat recuperation (SHR) technology to decrease energy consumption. Pre-combustion capture was applied in the IGCC plant, which involved coal gasification and CO-shift conversion with CO₂ capture. The results show that the energy consumption for the CO₂ separation process using SHR was decreased by two-thirds. This means that the power generation efficiency can be improved by SHR compared with conventional IGCC with a CO₂ capture process.     

Life cycle assessment of membrane-based carbon capture and storage

Many investigations have conducted life cycle assessments (LCA) of the most commonly discussed routes of carbon capture and storage (CCS): post-combustion with amine wash separation; oxyfuel using cryogenic air separation and pre-combustion by integrated gasification combined cycle (IGCC) using physical separation. A research alliance developed corresponding separation systems using different types of membranes to allow a more energy efficient separation process: polyactive polymeric membranes for post-combustion, ceramic membranes for oxyfuel and metallic membranes for IGCC separation. By conducting an LCA, the study examines the actual greenhouse gas emissions and other environmental impacts of the new membrane separation technologies, together with concepts implementing the more common technologies. The reference systems represent today’s state-of-the-art supercritical coal fired power plant in Germany, together with a more advanced ultra-supercritical plant operating at 700 °C without CO₂ capture. The results demonstrate that among the three reference power plants the IGCC is the superior concept due to the highest efficiency. Regarding climate change, the IGCC power plants with CO₂ capture are still the best concepts. When other environmental impacts are considered, the capture technologies are inferior. The membrane concepts show the overall better results in comparison to the conventional capture technologies. The environmental impacts for membrane applications add a new range of findings to the field of CCS LCAs. Now the results for several different approaches can be compared directly for the first time.     

Novel plasma generating systems for advanced materials processing

Material processing using nano-technology is now advancing towards a more precise and controllable “smart” stage and plasma systems with high performance are being required for advanced thermal processing. One such unique plasma generator, a high speed plasma accelerator is capable of generating high energy plasma flows of required composition within a large range of plasma parameters. Another gas tunnel type plasma system also exhibits high energy density and high efficiency. Its application to the plasma spraying of ceramics proved that the characteristics of these ceramic coatings are superior to conventional ones. Various types of plasma accelerators are described here with emphasis on a MagnetoPlasma Compressor of Compact Geometry (MPC-CG) which was used to investigate plasma flow interaction with solid silicon surfaces. Different types of submicron structure were obtained due to the compression plasma flow action? The plasma produced by a gas tunnel type plasma source was used for the surface modification of Titanium, TiN films being formed in a relatively short time of 5 s. Plasma sprayed ZrO₂/Al₂O₃ coatings were also investigated, and the results showed that the ZrO₂/Al₂O₃ composite system has the possibility for the development of high functionally graded thermal barrier coating (TBC), which exhibits excellent mechanical properties and oxidation resistance.     

立体停车位液压系统控制策略及节能控制技术研究

针对目前立体停车位均采用阀控液压动力系统,存在系统效率低、能耗大等问题,将伺服电机直驱定量泵的节能技术应用于立体停车位的液压系统中.采用滑模变结构算法与模糊控制算法相结合的模糊滑模控制算法作为立体停车位各个工况切换的控制策略,相比于工业中常用的模糊PID控制算法,模糊滑模变结构控制能够对系统设定流量需求进行快速响应,在多个工况切换时,波动小、稳定速度快.同时对使用节能技术的立体停车位运行时的功率、能耗及系统效率进行测试,结果表明使用伺服电机直驱定量泵的液压节能系统与使用传统阀控液压系统相比,能耗降低了31.2%,系统效率提高了33.2%,具有较好的节能效果.     

Neutron measurements at nuclear power reactors [55]

Staff from the Pacific Northwest National Laboratory (operated by Battelle Memorial Institute), have performed neutron measurements at a number of commercial nuclear power plants in the United States. Neutron radiation fields at light water reactor (LWR) power plants are typically characterized by low-energy distributions due to the presence of large amounts of scattering material such as water and concrete. These low-energy distributions make it difficult to accurately monitor personnel exposures, since most survey meters and dosimeters are calibrated to higher-energy fields such as those produced by bare or D₂O-moderated ²⁵²Cf sources. Commercial plants typically use thermoluminescent dosimeters in an albedo configuration for personnel dosimetry and survey meters based on a thermal-neutron detector inside a cylindrical or spherical moderator for dose rate assessment, so their methods of routine monitoring are highly dependent on the energy of the neutron fields.Battelle has participated in neutron assessments at a number of LWR facilities to characterize neutron radiation fields and to evaluate the responses of plant dosimeters and survey instruments. In these studies, the tissue equivalent proportional counter was used for measuring neutron dose and dose equivalent rates, and multisphere spectrometers were used to measure energy distributions. The use of these instruments in LWR work locations is usually difficult because of extreme environmental conditions such as high temperatures.These studies have confirmed the presence of low-energy neutron fields in most work locations. The studies have also found that albedo dosimeters used at power plants typically overrespond significantly when using a calibration based on californium exposures. Survey instruments also respond highly in typical LWR environments.     

Thermal stress numerical study in granular packed bed storage tank

Thermal energy storage (TES) systems are central elements of various types of power plants operated using renewable energy sources. Packed bed TES can be considered as a cost-effective solution in concentrated solar power plants. Such a device is made up of a tank filled with a granular bed through which a heat-transfer fluid circulates. However, in such devices, the tank might be subjected to an accumulation of thermal stresses during cycles of loading and unloading due to the differential dilatation between the filler and the tank walls. The evolution of tank wall stresses over thermal cycles, taking into account both thermal and mechanical loads, is studied here using a numerical model based on the discrete element method. Simulations were performed for two different thermal configurations: (i) the tank is heated homogeneously along its height or (ii) with a vertical gradient of temperature. Then, the stresses resulting from the two different loadings applied on the tank are compared as well the kinematic response of the internal granular material. The kinematics of the granular material are analyzed at the particles scale (i.e. discrete elements), with a focus on the effect of particle/particle and wall/particle friction. Results show that a faster rearrangement of the packing occur when a thermal gradient is moving along the tank, leading to higher values of stresses applied on the tank walls. In addition to this, the behavior of the packed bed is dependent on the friction levels in the tank, whether the friction between particles themselves or the friction at the contact of particles with the shell. The influence of the slenderness ratio of the tank is investigated as well. Moreover, a reduction of 20% of thermal applied stresses can be obtained when inclined wall boundaries are used. The combination of an homogeneous configuration with low levels of friction (using lubricants) in thermocline storage tanks with inclined fixed boundaries can decrease significantly the induced stresses applied on the wall.     

Methodology for implementing power plant efficiency standards for power generation: potential emission reduction

Some methods of generating power such as power generation through coal, natural gas, oil result in inevitable emissions of greenhouse gases. While power generation is necessary due to its increasing demand, it is important for power companies to generate their power in an efficient manner to reduce its effect on the environment. One of the most effective ways of tackling inefficiency issues is through the implementation of efficiency standard. While there exist a lot of studies addressing the topic of energy efficiency standards, there are very few papers that deal specifically with efficiency standard for power generation plant. This paper presents methodology for the implementation of power plant efficiency standard; as mandatory or voluntary regulatory instrument, that may be implemented by the government to control greenhouse emissions from power plants. It is hoped that through its implementation, power companies shall become more conscious of their efficiency and emission quality, hereby encouraging the adoption of more efficient energy sources and latest available technologies. In this paper, methods of calculating greenhouse intensity value and its corresponding allowable ranges have been demonstrated. Case study on a 10-year-old base-load multi-fuel-fired power plant in Malaysia has shown that the power plant is in conformance to the power plant efficiency standard, with an actual greenhouse intensity of 859.4461 kgCO₂/MWh sent-out, well within the allowable range of greenhouse intensities for that power plant which is between 760 and 890 kgCO₂/MWh sent-out. It has also been demonstrated that older power plants are allowed to have higher values of greenhouse intensity. Benefits of utilising natural gas and operating the power plant at full load have also been shown.

     

Exergy efficiency improvement in hydrogen production process by recovery of chemical energy versus thermal energy

Exergy analysis is recently being employed as one of the preferred methods to improve the design performance of a system and to achieve overall sustainability. Exergy is mainly composed of physical or thermo-mechanical and chemical components and a single stream can possess one or more forms of exergy. Where there is exergy lost in unused chemical streams or wasted energy, the recovery of exergy would reduce losses and increase the second law efficiency of the process. In many chemical process plants such as hydrogen (H₂), ammonia, nitric acid, etc., there is a potential to recover waste or excess heat by process heat exchange or by generating utilities. For a process like steam–methane (CH₄) reforming (SMR), exergy efficiency can be improved by recovering the available excess heat partially or fully in the form of chemical energy or thermal energy. This paper presents the generalised system analysis to show that the recovery of exergy in the form of chemical energy is better than in thermal energy form due to fewer losses and higher efficiency. The concept is illustrated with the example of a simple combustion system with excess heat in which saving fuel proves to be more exergy efficient than generating utility. The approach is applied to an industrial case study of H₂-producing SMR plant with two modified cases of steam generation and recycling portion of unconverted CH₄ as feed. In the case study, heat exchanger network is treated as a separate process component and a simple methodology is proposed to calculate the exergy losses for the same. The results of the case study prove that the recovery of chemical energy is more efficient than that of thermal energy from an exergy perspective.     

Production of green energy from co-digestion: perspectives for the Province of Cuneo, energetic balance and environmental sustainability

In Italy and many European countries, energy production from biomass is encouraged by strong economic subsidies so that biomass energy plants are getting large diffusion. Nevertheless, it is necessary to define the environmental compatibility taking into account global parameters as well as environmental impacts at regional and local scales coming from new polluting emissions. The environmental balances regarding new energy plants are of primary importance within very polluted areas such as Northern Italy where air quality limits are systematically exceeded, in particular for PM₁₀, NO₂, and ozone. The paper analyzes the renewable energy scenario relating to manure anaerobic digestion and biogas production for the Province of Cuneo, N–W Italy, and the environmental sustainability of the possible choices. The study is focused on energy producibility, heat and power, nitrogen oxides and ammonia emissions, GHG (greenhouse gases) balances dealing also with indirect releases of CH₄ and N₂O, as well as emissions due to energy crops production. The most important conclusion that can be drawn is that the production of renewable energy from anaerobic digestion could cover up to 13 % of the Province electricity consumption, but sustainability in terms of CO₂ emissions can be reached only through an overriding use of agricultural waste products (manure and by-products instead of energy crops) and cogeneration of thermal energy at disposal; the application of the best available techniques to waste gas cleaning, energy recovery, and digestate chemical–physical treatments allows positive emissive balances.     

Investigation on gradient thermal cycle for power and refrigeration cogeneration

In order to improve energy utilization efficiency of low grade heat, a novel gradient thermal cycle for power and refrigeration cogeneration is proposed. The cycle is cascaded with two stages based on different thermal driven temperature. The first stage is pumpless Organic Rankine Cycle (PRC) while the second stage is two-stage sorption refrigerator. R245fa is selected as the working fluid of PRC, whereas CaCl₂-BaCl₂-NH₃ working pair is chosen for two-stage sorption refrigerator. Different heat source temperatures from 80°C to 95°C are adopted for analysis and comparison. Results indicate that the highest average power output and cooling effect are able to reach 204 W and 0.91 kW under the condition of 95°C heat source temperature and 10°C refrigeration temperature. For different heat source temperatures, total energy and exergy efficiency of the gradient thermal cycle for power and refrigeration cogeneration range from 9.49% to 9.9% and 10.9% to 11.8%, respectively. For gradient thermal cycle exergy efficiency of heat utilization ranges from 24% to 18.8% which is 126.5% and 70.9% higher than the PRC and two-stage sorption refrigerator, respectively, when the heat source temperature is 80°C.     

Co-production of power and urea from coal with CO<Subscript>2</Subscript> capture: performance assessment

Coal-based power plants are largest emitter of CO₂ as a single sector. To use fossil fuels (including coal), CO₂ capture and storage is a visible option. But large energy requirement for this process and risk associated with storage of CO₂ demand alternative solutions including recycling of captured CO₂. In this paper, a co-production of power and urea is proposed using coal with captured CO₂. Detailed ASPEN Plus^® model is developed for this plant. As shift reaction for producing H₂ has significant effect on output parameters, analysis is done for two different values of shift reaction, i.e., 90 and 95 % conversion. Plant consumes substantial auxiliary power (~19 % for the base case). Auxiliary power becomes a minimum for about 25 % captured CO₂ utilization for 95 % shift conversion. An economy factor is also defined to estimate the economic advantage of utilizing captured CO₂. Results show that economic advantage is obtained for CO₂ utilization beyond ~5 % for 95 % water gas shift reaction and it is beyond ~10 % for a 90 % shift reaction.     

Photoresponsive Smart Coloration Electrochromic Supercapacitor

Electrochromic devices have been widely adopted in energy saving applications by taking advantage of the electrode coloration, but it is critical to develop a new electrochromic device that can undergo smart coloration and can have a wide spectrum in transmittance in response to input light intensity while also functioning as a rechargeable energy storage system. In this study, a photoresponsive electrochromic supercapacitor based on cellulose‐nanofiber/Ag‐nanowire/reduced‐graphene‐oxide/WO₃‐composite electrode that is capable of undergoing “smart” reversible coloration while simultaneously functioning as a reliable energy‐storage device is developed. The fabricated device exhibits a high coloration efficiency of 64.8 cm² C^?1 and electrochemical performance with specific capacitance of 406.0 F g^?1, energy/power densities of 40.6–47.8 Wh kg^?1 and 6.8–16.9 kW kg^?1. The electrochromic supercapacitor exhibits excellent cycle reliability, where 75.0% and 94.1% of its coloration efficiency and electrochemical performance is retained, respectively, beyond 10 000 charge–discharge cycles. Cyclic fatigue tests show that the developed device is mechanically durable and suitable for wearable electronics applications. The smart electrochromic supercapacitor system is then integrated with a solar sensor to enable photoresponsive coloration where the transmittance changes in response to varying light intensity.     

A technical and economic evaluation of CO<Subscript>2</Subscript> separation from power plant flue gases with reclaimed Mg(OH)<Subscript>2</Subscript>

A method of inexpensively and reliably separating CO₂ from flue gases by means of using magnesium hydroxide (Mg(OH)₂) has been studied. Mg(OH)₂ may be easily reclaimed from power plants using magnesium enhanced flue gas desulfurization systems (ME-FGD). The CO₂ scrubbing system may be operated as either a once-through system which produces magnesium carbonate for sequestration of carbon, or as a regenerable system where a concentrated CO₂ gas stream is created for further processing.The experimental results indicate that CO₂ is absorbed into solutions containing reclaimed Mg(OH)₂ by mean of a first order reaction, where the activation energy of this reaction was measured to be 7.7 kcal/mol. Continuous flow experiments were performed in a bubble reactor with simulated flue gas containing 15%_V CO₂ in contact with a solution of Mg(OH)₂. Experiments have shown that up to 70% of CO₂ separation may be achieved in this system. For a system based on a typical 500 MW power plant and reclaiming the magnesium hydroxide from a ME-FGD, experiments have shown that from 7–17% of the CO₂ from the gas stream may be continuously removed through the regenerable system.The energy requirements for CO₂ separation were also evaluated for a regenerable system based on equilibrium data in the liquid phase. A liquid solution equilibrium solver, MINEQL+, was used to determine the equilibrium values. The economic evaluation is based on a 500-MW power plant burning a high sulfur coal. The calculation considered up to a 22 °C temperature difference between the absorption step and the regeneration system. These calculations show that approximately 40 to 68 MW of energy are required to separate 7% of the CO₂ from the flue gas stream. The energy required depends on the temperature and pH difference between the absorption and desorption step, and the liquid-to-gas ratio in the absorber. The details of the energy calculations are given in the paper.