Renewable energy is one of the most promising solutions to energy shortage that may occur in the future particularly in remote areas. Solar cells suffer from the problem of high temperature, which reduces the electrical efficiency and operational life. In this study we investigate a new hybrid technique of cooling and voltage induction. A set of small generators installed on the back of a solar panel operating under the influence of heat and magnetic energy are called thermo-magneto-electric generators (TMEG). A modeling study was done using COMSOL Multiphysics5.2a (COMSOL) software as a package to simulate the physical states of the system. This study showed that a TMEG has the ability to improve the efficiency as a result of reducing the temperature. An induction voltage is also an output of the system and can be combined with the output of the solar panel composing the hybrid system.

This paper addresses modeling, design, and experimental assessment of a Gamma type low-temperature differential free-piston Stirling engine. The most advanced third-order design analysis method is used to model, simulate and optimize the engine. Moreover, the paper provides an experimental parametric investigation of engine physical parameters and operating conditions on the engine performance. The experimental test results are presented for a model validation, which shows about a 5% to 10% difference in the simulation results. The aim of this study is to design a Stirling engine capable of harvesting low-temperature waste heat effectively and economically and convert it to power. The engine prototype is designed to increase the engine performance by eliminating the main losses occurred in conventional Kinematic engines. Thus, elastic diaphragm pistons are used in this prototype to eliminate the surface friction of the moving parts, the use of lubricant, and to provide appropriate seals. In addition, flat plate heat exchangers, linear flexure bearing, a stainless-steel regenerator and a polyurethane displacer are outlined as the main components of the engine. Experiments successfully confirm the design models for output power and efficiency. Furthermore, it is revealed that the displacer-to-piston natural frequency ratio is an important design point for free-piston Stirling engines and should be addressed in the design for optimum power output.

A 150kW organic working fluid radial turbine designed for the low temperature waste heat with temperature of 150 ∼ 200°C using R600a as working fluid was selected. Under the condition of same inlet temperature and rotational speed, the mixture R600a(iso-butane) / R601a(iso-pentane) with different compositions was adopted for the CFD numerical simulation to obtain the aerodynamic performance and the detailed flow of the organic working fluid radial turbine. The results show that the mixture R600a / R601a can broaden the output power range and increase the efficiency of the radial turbine compared with the pure working fluid. The output power of the organic working fluid radial turbine increases from 54.03kW to 129.6kW as the R600a composition increases from 0.1 to 0.9. The optimal composition of R600a / R601a was obtained for relatively higher efficiency of the organic working fluid radial turbine. The results can provide a reference for the selection of working fluid for radial turbine of the low temperature heat source.

Recovering the waste heat of flue gas to reduce its temperature with avoiding low-temperature corrosion is an effective way to improve the economic efficiency of coal-fired power plant. A coupled high-low energy level flue gas heat recovery system was introduced in the paper. The inlet air temperature of air preheater and the temperature of turbine condensate can be increased by using this system. Thermal economy model of the system was built based on equivalent heat drop method. The system was successfully applied in 1000MW ultra-supercritical double reheat coal-fired unit in Laiwu Power Plant of China Huaneng Group, and the operation data showed the boiler flue gas temperature was not higher than 90° C, and the coal consumption was reduced by using the system. (CSPE)

With ever-increasing ambient temperatures many electric power plants that employ cooling lakes to reject their waste heat into the environment are struggling to maintain reasonable turbine backpressures during the hot summer months when electric load demand is often the greatest. Some consider adding mechanical draft cooling towers (MDCT) to further cool the condenser circulating water (CCW) prior to entering the main condenser, but the additional auxiliary power required to drive MDCT fans often consume the additional generator output resulting from the lower backpressure. Spray ponds offer significant advantages over MDCT including superior simplicity and operability, lower power requirements, and lower capital and maintenance costs. The Oriented Spray Cooling System (OSCS) is an evolutionary spray pond design. Unlike a conventional spray pond in which spray nozzles are arranged in a flat bed and spray upward, blocking the ambient air flow to the spray region as it travels down to the pond below, the OSCS nozzles are mounted on spray trees arranged in a circle and are tilted at an angle oriented towards the center of the circle. As a result, the water droplets drag air into the spray region while the warm air concentrated in the center of the circle rises. Both of these effects work together to increase air flow through the spray region. Increased air flow reduces the local wet-bulb temperature (LWBT) of the air in the spray pattern, promoting heat transfer and more efficient cooling. During the late 1970’s the author developed a purely analytical model to predict the thermal performance of the OSCS which was successfully compared with the OSCS at the Columbia Generating Station (CGS) in the mid 1980’s. This paper describes how the OSCS may be employed to supplement the cooling capacity of an existing cooling lake to reduce the temperature of the CCW prior to entering a power plant, resulting in lower main condenser pressures and more net plant output.

The shell-and-tube waste heat boiler is a common facility to recover and utilize the energy of flue gas in industries. To improve the ability and efficiency of the boiler, a steam dome is configured above the drum so as to arrange more heat exchange tubes. Simulation and analysis of vapor-liquid two-phase flow across tube bundles arranged in the drum are of vital importance to design and safety operation. Numerical simulation of boiling two-phase flow across tube bundles in the drum was carried out to analyze the shell side thermal-hydraulics. Commercial software ANSYS FLUENT 14.5 was adopted for modeling and computational calculations. The applied modeling approach was validated against experimental results with a good agreement. In order to analyze the vapor-liquid two-phase flow performance under various working conditions, the inlet velocity of downcomer tubes of 3m·s −1 , 4m·s −1 as well 5m·s −1 for saturated water were simulated, respectively. The pressure field, flow characteristic, void fraction distribution and heat transfer characteristic were analyzed to have a good knowledge of the boiler operation. The following conclusions have been drawn through analyzing simulation results. (1)The total pressure drop on shell side increased with increasing the inlet velocity of downcomer tubes of saturated water. (2)The velocity of saturated water decreased after flowing into the drum less than z = 0.1m as the flow area increasing, and then increased rapidly as the volume of the mixture two-phase flow increasing. (3)The integral average void fraction of the drum decreased as the mass flow rate of inlet saturated water increasing. (4)The HTC (heat transfer coefficient) of the heat exchange tubes varied with the flow direction, which is related to the vapor-water void fraction. The conclusions obtained above can be used as a reference for the design of the separated structure shell-and-tube waste heat recovery boiler.

An comparison of technical specification and updated operation results between two USC coal fired boilers namely RDK-8, Germany and WGQ-3, China has been considered under the global scenario related to the variation of industrial production structure, power demand cut down, more stringent carbon dioxide depression and larger quantity of renewable units engaged into the grid, in this respect a discussion and analysis have been carried out subjected to low grade heat recovering and harmful emission prevention from boiler flue gas and introduction carbon harmful emission prevention from boiler flue gas and their multiple benefits on energy saving and environmental protection, moreover the experience and gains in the field of flue gas heat recovering and mitigating pollution, including the proprietary technique (WGGH) by SPERI are briefly stated, thereby a conclusion of enlightenment for further development of these units is mentioned.

Energy and water are mutually dependent, limited resources that are critical to the development and economic stability of the United States. Energy production requires large volumes of water, and water treatment and distribution requires large amounts of energy. In 2010, water and wastewater treatment accounted for roughly 1.8% of total electricity use in the United States, which corresponded to 69 TWh per year or, in terms of power-generating capacity, over 7.8 GW. Population growth and climate change will result in increased demand on these limited resources, making them not sustainable at present use levels. In recent years, both forward osmosis (FO) and membrane distillation (MD) have garnered significant attention as next-generation water desalination and reuse technologies with the potential to significantly reduce the energy cost associated with wastewater treatment. Critical technical hurdles and lack of operational understanding, however, have limited development of these individual technologies beyond the laboratory scale. In FO, a draw solution that produces high osmotic pressure but is still easily separable is a major challenge limiting the applicability of this process. The use of MD has been limited by membrane flooding due to oily and surfactant like compounds in industrial wastewaters and the transfer of volatile compounds across the membrane. Combining these technologies in a hybrid process overcomes their individual limitations, while exploiting the benefits of each. Effectively the FO unit pretreats the resulting diluted FO draw solution that is sent to the MD for regeneration via low-grade heat and product water recovery. The regenerated (re-concentrated) draw solution is then recycled to the FO unit. A key advantage of MD is that it is not limited by feed-solution osmotic backpressure, making it ideal for regenerating high-osmotic-pressure FO draw solutions. This, in turn, leads to strong potential for the integrated FO/MD process to treat high-salinity wastewaters that are difficult to treat economically by conventional technologies. The product water leaving the MD unit will be extremely high quality and directly suitable for reuse. With funding from the U.S. Department of Energy, RTI, in collaboration with industrial partner Veolia, has developed an integrated FO/MD process from lab to small pilot scale. In this presentation, pilot-scale testing efforts of this process technology with real industrial wastewater will be presented. Process performance data obtained on full-size FO and MD membrane modules as well as lessons learned from piloting scale-up and best application areas for the technology will be discussed.

There are various finned tube heat exchanges with diverse thermo-flow performance being widely applied in the power plants. Wherein, the H-type finned tubes are widely used in the economizer to improve the waste heat utilization efficiency of the coal fired boiler. The experimental studies regarding the heat transfer and resistance characteristics of single H-type and double H-type finned tubes have obtained the thermo-flow performances under different conditions. In addition, the test facility of double channels is specially designed to ensure the test accuracy. Correlations for Euler number Eu , Nusselt number Nu and Performance evaluation index P ec with Reynolds number Re are presented by analyzing the thermo-flow performances of the used bundles. The results show that the single H-type finned tube performs better heat transfer characteristic and relatively worse resistance characteristic than the double H-type finned tube. Consequently, the double H-type finned tube is recommended in the practical application considering the higher manufacturing installation efficiency. (CSPE)

Cement industry consumes high energy levels with 4GJ per ton produced in average, 30% of it being electric and 70% thermal [1]. Cogeneration in this type of processes is not widespread; for only a few efforts have been made worldwide to implement methods that take advantage of waste heat stream, given that these contain 36% of the thermal input energy required to produce electricity [2]. Furthermore the implementation of a power generation alternative to feed limestone’s calcinations process is suggested. This paper is focused on the evaluation of thermal energy recovery strategies through the implementation of cogeneration systems, enabling an increase in efficiency and profitability producing electricity in before and after-processes of the cement production process. This will be achieved using methods of computer analysis implementing the ASPEN HYSIS™ software to simulate the behavior of the systems taking the rotary kiln operating conditions as main input or output variables. For the implementation of the system two important steps furnace operation will be taken. First one, related to combustion, is performed to produce the energy required in limestone’s processing entering this system, at this point the commercial gas turbine is used, coupled to a generator subsequently taking the power of oxygen-rich flow at the exhaust which is at a high temperature allowing a post-combustion using an afterburner. Finally, a second stage is evaluated at the downstream of the kiln, where a flow of charged waste gases counts with enough energy to perform an additional phase of power generation using an organic Rakine cycle (ORC).

Gas turbine power plants fueled by natural gas are common due to their quick start-up operation and low emissions compared with steam power plants that are directly fired. However, the efficiency of basic gas turbine power plant is considered low. Any improvement in the efficiency would result in fuel savings as well as reduction in CO 2 emissions. One way to improve the efficiency is to utilize exhaust gas waste heat. Two waste heat utilization options were considered. The first option was to run a steam power plant (i.e. combined cycle power plant) while the other option was to use a regenerator which reduces the size of the combustion chamber. The regenerator utilizes the waste heat to preheat the compressed air before the combustion chamber. In addition, the efficiency can be improved with compressor intercooling and turbine reheating. In this paper, four gas turbine power plant configurations were investigated and optimized to find the maximum possible efficiency for each configuration. The configurations are (1) basic gas turbine, (2) combined cycle, (3) advanced combined cycle and (4) gas turbine with regenerator, intercooler and reheater. The power plants were modeled in EES software and the basic model was validated against vendor’s data (GE E-class gas turbine Model 7E) with good agreement. Maximum discrepancy was only 3%. The optimization was carried out using conjugate directions method and improvements in the baseline design were as high as 25%. The paper presents the modeling work, baseline designs, optimization and analysis of the optimization results using T-s diagrams. The efficiency of the optimized configurations varied from 49% up 65%.

Electric power plants in the U.S. dissipate 4.3 billion gallons of water per day into the atmosphere through evaporative cooling. As freshwater resources become constrained, it will be essential for power plants to transition from evaporative cooling to dry air cooling. One of the major problems associated with dry air cooling is the large size and associated cost of the dry air heat exchangers due to the large surface area required to overcome the low convective heat transfer coefficient of air. This study investigates using low-grade waste heat available in the combustion exhaust gases (106°C inlet, 86 MW dry waste heat available) of a 565 MW Natural Gas Combined Cycle Power Plant (NGCC) to drive a supplemental high efficiency turbo-compression cooling (TCC) system that decreases the size of the dry air heat exchangers. In this system, both a recuperative Rankine cycle and a supercritical system were considered to drive a turbo-compressor. The low-grade waste heat is supplied to a flue gas heat exchanger in either the recuperative Rankine or supercritical cycle to generate power that drives a vapor compression cycle to supply supplementary cooling for the power plant condenser water. For the TCC system to operate at a high COP , both the turbine and compressor must operate at isentropic efficiencies exceeding 80%. This high efficiency has been demonstrated for centrifugal turbomachines for a wide variety of applications over small ranges of specific speed: from 45 to 100 for turbines, and from 80 to 140 for compressors. In the present study, a wide range of possible fluids was considered to perform a complete system level thermodynamic analysis combined with a turbo-compressor dimensional scaling analysis. The results of the analyses show that the total UA required for both the primary dry air coolers and the dry air condensers in the supercritical TCC system with a COP of 2 is 26% less than the UA required for dry air cooling alone (from 150.7 to 111.5 MW K −1 ). As a result, using the supercritical TCC cooling system has the potential to reduce the overall cost of dry air cooling relative to the state of the art.

Waste heat recovery has become very important in the last decennia. The Organic Rankine Cycle is the most popular technology to transform waste heat into mechanical work or electricity. While large and medium scale installations are widely available on the market for various temperature and power levels, small scale ORCs are still in a pre-commercial phase because of a relatively high specific price. To make small scale ORCs more attractive for potential customers, the price has to be drastically reduced which means reducing the manufacturing and assembling operations, the number of parts in assemblies and unification of these assemblies. In addition, the performance has to be increased by using advanced cycle architectures and the right fluids. Not only the right choice of the working fluid is important but also the expander built-in volume ratio (BVR) has to be optimal or improved. Neither a fixed volume ratio expander, nor a turbine can provide an optimal expansion of a working fluid in a wide range of operating conditions [1]. In automotive applications, for instance, a strongly fluctuating heat input will be introduced to an ORC unit. To estimate losses caused by non-optimal operation, a model of a volumetric expander has been developed and verified using the result of extensive test campaigns with a screw expander. The volume ratio of the expander mentioned cannot be physically changed, so under widely changing pressure ratio, caused by varying inlet waste heat and ambient temperatures, it operates mostly far from its design point. The model gives a possibility to vary the BVR in order to compare a fixed-volume ratio expander with a variable one. Benefits from replacement of this expander by an adaptive one are studied. Only steady states are taken into account since there is no dynamic model of this expander developed yet. As a consequence of the results obtained, a concept of a variable volume ratio expander is proposed.

Fossil fuels are continuously depleting while the global energy demand is growing at a fast rate. Additionally, fossil fuels based power plants contribute to environmental pollution. Search for alternate energy resources and use of industrial waste heat for power production are attractive topics of interest these days. One way of enhancing power production and decreasing the environmental impact is by recuperating and utilizing low grade thermal energy. In recent years, research on use of organic Rankine cycle (ORC) has gained popularity as a promising technology for conversion of heat into useful work or electricity. Due to simple structure of ORC system, it can be easily integrated with any energy source like geothermal energy, solar energy and waste heat. A computer program has been developed in engineering equation solver (EES) environment that analyzes and selects appropriate working fluid for organic Rankine cycle design based on available heat sources. For a given heat source, the program compares energy and exergy performance of various working fluids. The program also includes recuperator performance analysis and compares its effectiveness on the overall thermal performance of the Rankine cycle. This program can assist in preliminary design of ORC with respect to best performing refrigerant fluid selection for the given low temperature heat source.

Recovering waste heat from automobiles remains an inviting subject for research. Solid-state thermoelectric generators (TEGs) have been widely investigated for this purpose, but their practical application remains challenging. An alternative to TEGs are thermogalvanic cells. Temperature difference between hot and cold electrodes creates a potential difference. Once connected to a load, electrical current and power are delivered, converting heat into electricity. In this work, we investigate the feasibility of incorporating such systems into automobiles. We carry out the experiments under real-world conditions. A climate-controlled wind tunnel is built to provide equivalent conditions to the ambient air stream under the car. The demonstrated system achieved a power density on the order of mW m −2 . We compare the power generated to those of TEGs currently tested by GM, Honda, BMW and Ford. Further, a simple economic estimation is calculated to assess the $ per Watt cost of future practical thermogalvanic waste heat recovery system.

This paper presents the results for a feasibility study of a solar chimney which uses low-grade waste heat from compost in conjunction with solar energy transmitted via a transparent roof top. The feasibility study shows that the solar chimney’s turbine power increases with pressure ratio, the height of the chimney as well as the differential temperature in the chamber. This paper also outlines the thermodynamic modeling related to using waste heat from composting to increase the air temperature in the inlet chamber of a solar chimney. It is found that from this analysis that the average temperature in the chamber increases as a function of the chimney inlet chamber axial length. For a chimney 1150 ft (350 m) high and 24 ft (7.3 m) in diameter processing 8000 tons of composting material it is found that a power output of 38 kW can be harnessed at the turbine.

Low grade waste heat and water recovery using ceramic membrane, is an emerging technology which helps to increase the efficiency of boilers and gas or coal combustors in various industrial processes and conventional power plants. The tube wall of a Transport Membrane Condenser (TMC) based heat exchanger is made of a nano-porous material with high membrane selectivity which is able to extract condensate water from the flue gas in the presence of other non-condensable gases (i.e. CO2, O2 and N2). In this work, a numerical study has been carried out to investigate the effects of transversal pitches of the TMC bundle tubes on the performance of a TMC based cross flow heat exchanger. A simplified multi-species transport model is used to investigate the heat and mass transfer characteristics of a condensing combustion flue gas in a crossflow transport membrane tube bundle. Various transversal (0.4”–0.6”) and longitudinal (0.4”–0.8”) pitches were used. The numerical results revealed that the effect of transversal pitches on the outlet parameters are more pronounced.

Nearly all states now have renewable portfolio standards (RPS) requiring electricity suppliers to produce a certain fraction of their electricity using renewable sources. Many renewable energy technologies have been developed to contribute to RPS requirements, but these technologies lack the advantage of being a dispatchable source which would give a grid operator the ability to quickly augment power output on demand. Gas turbines burning biofuels can meet the need of being dispatchable while using renewable fuels. However, traditional combustion of liquid fuels would not meet the pollution levels of modern dry, low emission (DLE) gas turbines burning natural gas without extensive back-end clean-up. A Lean, Premixed, Prevaporized (LPP) combustion technology has been developed to vaporize liquid ethanol and blend it with natural gas creating a mixture which can be burned in practically any combustion device in place of ordinary natural gas. The LPP technology delivers a clean-burning gas which is able to fuel a gas turbine engine with no alterations made to the combustor hardware. Further, the fraction of ethanol blended in the LPP gas can be quickly modulated to maintain the supplier’s overall renewable quotient to balance fluctuations in power output of less reliable renewable power sources such as wind and solar. The LPP technology has successfully demonstrated over 1,000 hours of dispatchable power generation on a 30 kW Capstone C30 microturbine using vaporized liquid fuels. The full range of fuel mixtures ranging from 100% methane with no ethanol addition to 100% ethanol with no methane addition have been burned in the demonstration engine. Emissions from ethanol/natural gas mixtures have been comparable to baseline natural gas emissions of 3 ppm NO x and 30 ppm CO. Waste heat from the combustor exhaust is recovered in an indirect heat exchanger and is used to vaporize the ethanol as it is blended with natural gas. This design allows for startup on natural gas and blending of vaporized ethanol once the heat exchanger has reached its operating temperature.

This paper describes design and optimization of a Waste Heat Recovery Unit (WHRU) for a power cycle which uses CO 2 as a working fluid. This system is designed for offshore installation to increase gas turbine efficiency by recovering waste heat from the exhaust for production of additional power. Due to severe constraints on weight and space in an offshore setting, it is essential to reduce size and weight of the equipment to a minimum. Process simulations are performed to optimize the geometry of the WHRU using different objective functions and thermal-hydraulic models. The underlying heat exchanger model used in the simulations is an in-house model that includes the calculation of weight and volume for frame and structure for the casing in addition to the thermal-hydraulic performance of the heat exchanger core. The results show that the for a set of given process constraints, optimization with respect to minimum total weight or minimum core weight shown similar results for the total installed weight, although the design of heat exchanger differs. The applied method also shows how the WHRU geometry can be optimized for different material combinations.

In Iceland there is a super abundance of waste hot water from geothermal power plants. Some of this is re-purposed (sequentially used) for district heating and heated swimming pools. This vast underused energy source can also enable the growth of out of zone plants, enhance agricultural production by 20% and extend the growing season. The authors have developed and field tested an energy intensive shallow system of bottom heat using the existing heated sidewalk materials. Tomatoes that do not survive outdoors in Iceland have produced ripe fruit. A zucchinis harvest was documented and the test banana plant was still alive in September after the first frost. These plants all died in the control garden which had the same piping system, and identical soil types and depths. Heat transfer data, infrared analysis and plant growth data were gathered to preliminarily document and quantify the system’s viability and market potentials.