Geothermal-Driven Ejector Refrigeration System

A mathematical model of a heat-driven ejector refrigeration system that uses geothermal energy as the heat source was established. Philippine low-enthalpy geothermal resources were investigated and became the bases in computing for the heat at the generator part of the ejector refrigeration system. Analysis and comparison of the performance of the cycle considering working fluids like ammonia (R717) and R134a as the refrigerants were conducted. The properties of those fluids were based on an available thermodynamic database of various refrigerants. The governing principles and conservation equations for energy, mass and momentum were successively applied to control volume of ejector components. The properties for both fluid and flow were solved iteratively for isentropic and irreversible processes wherein entropy generation and frictional losses were accounted for. This included simulation of flows in two-phase region. Input parameters were set like the generating temperature and condensing temperature. The range of 60 to 100 °C available geothermal fluid temperature could produce 50 to 90°C of generating temperature for the fluid refrigerant. This range of generating temperature yielded an evaporating temperature of 8 to 25 °C at a fixed condensing temperature of 40 °C. After numerical analyses, the determined coefficient of performance was at the range of 0.21 to 0.39, while nozzle and ejector efficiencies were from 94% to 99%. The geometric profiles of the ejector were also projected along with the varying generating temperature for both fluids. From the calculation, ammonia offers higher performance and efficiencies and lower evaporating temperatures suitable for larger cooling needs.

Design and Optimization of Free Piston Expander for Energy Harvesting

There is a growing opportunity and need for research that investigates alternate power sources. One such source is low temperature waste heat, or energy cast off to the environment as part of some larger process. Through the capture and use of this abundant energy source for power production, it is possible to enhance the overall operating efficiency of the larger system. This presents significant potential for sustainability increase and energy savings. One potential system that can operate from these sources is a low temperature, small-scale steam expander. Investigations of one such device called a Free Piston Expander (FPE) are presented in this work. In final form, the FPE will be a MEMS based device capable of operation as part of a complete low temperature steam system. In this present study, a millimeter scale device is constructed and tested to yield insight into critical operational parameters for future microfabricated designs. Construction of this testbed device is via concentric copper tubing, allowing an effective baseline study of these determining parameters. Parameters studied include device cross sectional area and shape as well as operational pressure. Once consistent parameters are determined, three separate variations of circular FPE design are further tested. These FPEs are designed to either constrain piston rotation or allow for rotational freedom during operation. Testing is performed on these devices for consistency in piston motion. Piston motion is characterized based on a single expansion and reaction of the piston.

Design and Operation of a Hybrid CCHP System Including PV-Wind Devices

CCHP systems based on internal combustion engines have been widely accepted as efficient distributed energy resources systems. CCHP systems can be efficient mainly because that the waste heat of engines can be recovered and used. If the waste heat is not used, CCHP systems may not be beneficial choices. PV-wind systems can generate electricity without fuel consumption, but the electric output depends on the weather, which is not reliable. A PV-wind system can be integrated into a CCHP system to form a higher efficient energy system. Actually, a hybrid energy system based on PV-wind devices and internal combustion engines has been studied by many researchers. But the waste heat of the engine is seldom considered in the previous work. Researches show that, 20∼30% energy can be converted into electricity by a small size engine while more than 70% is released. If the waste heat is not recovered, the system cannot reach a high efficiency. This work aims to analyze a hybrid CCHP system with PV-wind devices. Internal combustion engines are the prime movers whose waste heat is recovered for house heating or driving absorption chillers. PV-wind devices are added to reduce the fuel consumption and total cost. The optimal design method and optimal operation strategy are proposed basing on hourly analyses. Influences of the device cost and fuel price on the optimal dispatch strategies are discussed. Results show that all of the excess energy from the PV-wind system is not worth being stored by the battery. The hybrid CCHP system can be more economical and higher efficient in the studied case.

CO2 Capture Using Calcium Oxide Applicable to In-Situ Separation of CO2 From H2 Production Processes

A lab-scale CO2 capture system is designed, fabricated, and tested for performing CO2 capture via carbonation of very fine calcium oxide (CaO) with particle size in micrometers. This system includes a fixed-bed reactor made of stainless steel (12.7 mm in diameter and 76.2 mm long) packed with calcium oxide particles dispersed in sand particles; heated and maintained at a certain temperature (500–550°C) during each experiment. The pressure along the reactor can be kept constant using a back pressure regulator. The conditions of the tests are relevant to separation of CO2 from combustion/gasification flue gases and in-situ CO2 capture process. The inlet flow, 1% CO2 and 99% N2, goes through the reactor at the flow rate of 150 mL/min (at standard conditions). The CO2 percentage of the outlet gas is monitored and recorded by a portable CO2 analyzer. Using the outlet composition, the conversion of calcium oxide is figured and employed to develop the kinetics model. The results indicate that the rates of carbonation reactions considerably increase with raising the temperature from 500°C to 550°C. The conversion rates of CaO-carbonation are well fitted to a shrinking core model which combines chemical reaction controlled and diffusion controlled models.

Feasibility Study of a Supercritical Cycle as a Waste Heat Recovery System

Following the increasing interest of aero-naval industry to design and build systems that might provide fuel and energy savings, this study wants to point out the possibility to produce an increase in the power output from the prime mover propulsion systems of aircrafts. The complexity of using steam heat recovery systems, as well as the lower expected cycle efficiencies, temperature limitations, toxicity, material compatibilities, and/or costs of organic fluids in Rankine cycle power systems, precludes their consideration as a solution to power improvement for this application in turboprop engines. The power improvement system must also comply with the space constraints inherent with onboard power plants, as well as the interest to be economical with respect to the cost of the power recovery system compared to the fuel that can be saved per flight exercise. A waste heat recovery application of the CO2 supercritical cycle will culminate in the sizing of the major components.

Performance Impacts of Tailored Surface Geometry in Li-Ion Battery Cathodes

Analytical models developed to investigate charge transfer in Li-ion battery cathodes reveal distinct transport regimes where performance may be limited by either microstructural surface characteristics or solid phase geometry. For several cathode materials, particularly those employing conductive additives, surface characteristics are expected to drive these performance limitations. For such electrodes gains in performance may be achieved by modifying surface geometry to increase surface area. However, added surface area may present a diminishing return if complex structures restrict access to electrochemically active interfaces. A series of parametric studies has been performed to better ascertain the merits of complex, tailored surfaces in Li-ion battery cathodes. The interaction between lithium transport and surface geometry is explored using a finite element model in which complex surfaces are simulated with fractal structures. Analysis of transport in these controlled structures permits assessment of scaling behavior related to surface complexity and provides insight into trade-offs in tailoring particle surface geometry.

What Fraction of the Electrical Energy Produced in a Hybrid Solar-Fossil Power Plant Should Qualify as ‘Renewable Electricity’?

Hybrid power production facilities, based on the integration of renewable resources into conventional fossil-fuel-fired power plants have gained a growing interest during the past decades due to a world-wide continuous increase of shares of the renewable sources into the electricity generation market. In fact, in spite of the variable nature of most of the renewable sources, the hybrid configuration may provide a more economic, sustainable, and reliable use of the renewables in all load-demand conditions compared to renewable single-resource facilities. Nonetheless, the question of what fraction of the electricity produced in such facilities is to be considered as generated from renewables, still remains not fully addressed. This implies that there is space for some arbitrariness in the quantification of the share of the produced electricity to be qualified for the subsidies granted to renewable electricity, as normally prescribed by most of the policies that promote the applications of renewable primary energy resources. To overcome this problem, in this work we first define the classical Single-Resource Separate-Production Reference allocation method (SRSPR) usually considered by the regulators which is based on reference partial primary energy factors that must be chosen by some authority as representative of the performance of the (best available or representative average single-resource) power production technologies that use the same renewable resource and the same fossil fuel as the hybrid facility. Then we propose a Self-Tuned Average-Local-Productions Reference allocation method (STLAPR) whereby the electricity allocation fractions are based on the energy scenario of the local area of interest that includes the hybrid plant itself. We compare the two methods for a case study consisting on the renewable-to-fossil allocation of the power produced in an Solar-Integrated Combined-Cycle System (SICCS) with parabolic trough solar field. It turns out that the differences between the classical SRSPR and the STLAPR method become significant as the hybrid facilities take on a sizable fraction of the production of electricity in the local area.

Technologies for Waste Heat Recovery in Off-Shore Applications

In off-shore oil and gas platforms the selection of the gas turbine to support the electrical and mechanical demand on site is often a compromise between reliability, efficiency, compactness, low weight and fuel flexibility. Therefore, recovering the waste heat in off-shore platforms presents both technological and economic challenges that need to be overcome. However, onshore established technologies such as the steam Rankine cycle, the air bottoming cycle and the organic Rankine cycle can be tailored to recover the exhaust heat off-shore. In the present paper, benefits and challenges of these three different technologies are presented, considering the Draugen platform in the North Sea as a base case. The Turboden 65-HRS unit is considered as representative of the organic Rankine cycle technology. Air bottoming cycles are analyzed and optimal design pressure ratios are selected. We also study a one pressure level steam Rankine cycle employing the once-through heat recovery steam generator without bypass stack. We compare the three technologies considering the combined cycle thermal efficiency, the weight, the net present value, the profitability index and payback time. Both incomes related to CO2 taxes and natural gas savings are considered. The results indicate that the Turboden 65-HRS unit is the optimal technology, resulting in a combined cycle thermal efficiency of 41.5% and a net present value of around 15 M$, corresponding to a payback time of approximately 4.5 years. The total weight of the unit is expected to be around 250 ton. The air bottoming cycle without intercooling is also a possible alternative due to its low weight (76 ton) and low investment cost (8.8 M$). However, cycle performance and profitability index are poorer, 12.1% and 0.75. Furthermore, the results suggest that the once-trough single pressure steam cycle has a combined cycle thermal efficiency of 40.8% and net present value of 13.5 M$. The total weight of the steam Rankine cycle is estimated to be around 170 ton.

Effect of Different Italian Regulatory Frameworks on the Energetic Assessment of CHP Plants: A Comparative Design and Experimental Condition Analysis

Since a Combined Heat and Power (CHP) plant can offer high economic benefits when a certain energy savings value is obtained, it is very interesting to consider the requirements foreseen by legislation to meet this target. The paper deals with an energetic assessment of eleven industrial CHP power plants, based on different prime mover technologies installed and in operation in Italy. The analysis has been carried out considering not only the nominal design data of the plants, but also experimental ones, in order to highlight their real operational performances. The aim of the study was to compare the effects of two legislations on the calculation of the primary energy savings: the first is the Italian legislation that was in force when the power plants were designed, and the second is the current European Directive, which was issued a few years later when the plants were already in operation. The results of the study show as the subsidy mechanism introduced by the new legislation is stricter than the previous one, and could have a significant effect on the economic profitability of a cogeneration plant installation. More critical comments on the overall regulatory framework are presented in the paper.

Developing a Methodology for Measuring the Comparative Energy Efficiency of Elevators

Existing elevator systems are upgraded approximately every 20 years, providing an opportunity for energy reduction upgrades. This demands complicated analysis because elevators consume energy while at idle and in lifting modes. Traffic patterns, loads and building usage must also be considered in addition to energy recovering potentials. An objective and inclusive measurement methodology for measuring elevator energy efficiency is essential for a valid cost benefit analysis. The necessary requirements for a workable system and a usable first generation solution are presented.