A novel thermoelectric system for enhancing power generation from waste heat

Today, we face some significant environmental and energy problems such as global warming, urban heat island, and the precarious balance of world oil supply and demand. However, we have not yet found a satisfactory solution to these problems. Waste heat recovery is considered to be one of the best solutions because it can improve energy efficiency by converting heat exhausted from plants and machinery to electric power. This technology would also prevent atmospheric temperature increases caused by waste heat, and decrease fossil fuel consumption by recovering heat energy, thus also reducing CO2 emissions. The system proposed in this research generates electric power by providing waste heat or unharnessed thermal energy to built-in thermoelectric modules that can convert heat into electric power. Waste heat can be recovered from many places, including machinery in industrial plants, piping in electric power plants, waste incineration plants, and so on. Some natural heat sources such as hot springs and solar heat can also be used for this thermoelectric generation system. The generated power is expected to be supplied to auxiliary machinery around the heat source, stored as an emergency power supply, and so on. The attributes of this system are (1) direct power generation using hot springs or waste heat; (2) 24-h stable power generation; (3) stand-alone power system with no noise and no vibration; and (4) easy maintenance attributed to its simple structure with no moving parts. In order to maximize energy use efficiency, the temperature difference between both sides of the thermoelectric (TE) modules built into the system need to be kept as large as possible. This means it is important to reduce thermal resistance between TE modules and heat source. Moreover, the system’s efficiency greatly depends on the base temperature of the heat sources and the material of the system’s TE modules. Therefore, in order to make this system practical and efficient, it is necessary to choose the heat source first and then design the most appropriate structure for the source by applying analytical methods. This report describes how to design a prototype of a thermoelectric power generator using the analytical approach and the results of performance evaluation tests carried out in the field.

Power generation from waste heat in a food processing application

BackgroundWith the increasing concerns on the energy shortage and carbon emission issues worldwide, sustainable energy recovery from thermal processes is consistently attracting extensive attention. Nowadays, a significant amount of usable thermal energy is wasted and not recovered worldwide every year. Meanwhile, discharging the wasted thermal energy often causes environmental hazards. Significant social and ecological impacts will be achieved if waste thermal energy can be effectively harnessed and reused. Hence, this study aims to provide a comprehensive review on the sustainable energy recovery from thermal processes, contributing to achieving energy security, environmental sustainability, and a low-carbon future.Main textTo better understand the development of waste thermal energy utilization, this paper reviews the sustainable thermal energy sources and current waste energy recovery technologies, considering both waste heat and cold energy. The main waste heat sources are prime movers, renewable heat energy, and various industrial activities. Different waste heat recovery technologies to produce electricity, heating, and cooling are analyzed based on the types and temperatures of the waste heat sources. The typical purposes for waste heat energy utilization are power generation, spacing cooling, domestic heating, dehumidification, and heat storage. In addition, the performance of different waste heat recovery systems in multigeneration systems is introduced. The cold energy from the liquified natural gas (LNG) regasification process is one of the main waste cold sources. The popular LNG cold energy recovery strategies are power generation, combined cooling and power, air separation, cryogenic CO2 capture, and cold warehouse. Furthermore, the existing challenges on the waste thermal energy utilization technologies are analyzed. Finally, potential prospects are discussed to provide greater insights for future works on waste thermal energy utilization.ConclusionsNovel heat utilization materials and advanced heat recovery cycles are the key factors for the development of waste high-temperature energy utilization. Integrated systems with multiply products show significant application potential in waste thermal energy recovery. In addition, thermal energy storage and transportation are essential for the utilization of harnessed waste heat energy. In contrast, the low recovery rate, low utilization efficiency, and inadequate assessment are the main obstacles for the waste cold energy recovery systems.

Quantification of global waste heat and its environmental effects

Thermodynamic performance comparison between ORC and Kalina cycles for multi-stream waste heat recovery

Forecasting Thermoelectric Power Generation through Utilization of Waste Heat from Building Cooling Systems based on Simulation

Developing a low-cost and high-performance thermally regenerative battery (TRB) is significant for recovering low-grade waste heat. A self-stratified TRB induced by the density difference between electrolytes is proposed to remove the commercial anion exchange membrane (AEM) and avoid ammonia crossover. The simulation and experiment results show the uneven distribution of NH3, verifying the feasibility of self-stratified electrolytes. For better power generation performance, nanoprism Cu covering Ni electrodes with a high specific surface area and a stable framework are adopted to provide more reaction active sites for fast charge transfer during discharge. A maximum power density (12.7 mW cm-2) and a theoretical heat-to-electricity conversion efficiency of 2.4% (relative to Carnot efficiency of 27.5%) are obtained in the self-stratified TRB employing nanoprism Cu covering Ni electrodes. Moreover, the cost-effectiveness, simple structure, and sustainable discharge operation indicate that it will be a potential choice for energy conversion from low-grade heat.

According to statistics, low-temperature waste heat below 300°C accounts for more than 89% of industrial waste heat. If the waste heat is not recycled, a large amount of low-temperature waste heat will be released into the atmosphere, thereby exacerbating global warming and posing a significant threat to human survival. Although the power generation efficiency of solid-state thermoelectric generation technology is lower than the organic Rankine cycle, it only requires a smaller construction area, which increases its market acceptance, applicability, and penetration. Especially in the pursuit of net-zero emissions by global companies, the importance of low-temperature waste heat recovery and power generation is even more prominent. The current thermoelectric conversion efficiency of commercial thermoelectric chips is about 5%. Power generation cost, thermoelectric conversion efficiency, and energy use efficiency are highly correlated with the commercialization of solid-state thermoelectric technology. This research shares five practical waste heat power generation cases commercialized by recycling three heat sources. It also points out the three significant challenges facing the commercialization of power generation from low-temperature waste heat recovery. This study analyzes 2,365 TEG patents submitted by 28 companies worldwide todetermine the basic technology for realizing waste heat recovery through TEG and explore the potentialcommercialization of related waste heat recovery products. The future challenge for the large-scale commercialization of solid-state thermoelectric technology is not technological development but financial incentives related to changes in international energy prices and subsidies that promote zero carbon emissions.

The reverse electrodialysis heat engine (REDHE) has emerged as a promising technique in the waste heat harvest field due to its ability to convert very low-grade waste heat (below 100°C) into power. A REDHE consists of a regeneration unit and a reverse electrodialysis (RED) cell unit, which are in charge of heat to the salinity gradient energy-conversion process and salinity gradient to the power conversion process, respectively. Despite the fact that a regeneration unit accounts for 60% to 70% of the energy destruction of the overall system, most of the research conducted on RED units has barely reviewed the regeneration units. Therefore, the evaluation of regeneration units is necessary. This work provides a review of the research progress made on regeneration units. In this paper, a systematic review of the operating fluids and regeneration methods employed in a regeneration unit is provided. Also, the effects of solvent and solute characteristics on the performance of a regeneration unit and the overall system and the working fluid selection principle are investigated. Additionally, the disadvantages of the methods employed in existing and future development directions are analyzed. Finally, other applications of the heat engine (apart from power production) are presented. Since the RED technology has been primarily used to recover blue energy, its operating fluid is the NaCl aqueous solution. However, the NaCl solution is not suitable for the REDHE technology. Specifically, it is not suitable for the regeneration process of a regeneration unit because the latent heat of water vaporization is huge, which leads to huge energy consumption in the regeneration module. Also, the power generation performance of the NaCl solution is poor, and the maximum power density is only 1/8 of that of the LiBr solution, resulting in the low efficiency of the overall system. Since the REDHE technology is used to recover low-grade heat energy, its regeneration unit adopts a low-temperature separation technology. The main regeneration methods used are distillation separation and membrane distillation separation. The distillation separation technology is the most mature, but it consumes more energy and has a high maintenance cost. On the other hand, the regeneration temperature of the membrane distillation technology is low, but the required technology is difficult to apply, and the cost of the membrane is high. It should be noted that the biggest difference between the REDHE and traditional separation technologies is that the former aims to build an optimal concentration gradient for the battery cells, rather than to perform the complete separation of components. For example, the seawater desalination process assumes that the separated water is pure water. For an RED cell, if the diluted solution is pure water, the battery performance will decline rapidly due to the decrease in the solution conductivity. Currently, more research work has been conducted on various separation technologies and less on the coupling of regeneration technology with power generation technology. Future research should focus on the coupling of the thermal separation module with the power generation module. Although the objective of the REDHE technology is to utilize the industrial waste heat, the heat-source temperature can be very low (down to 40°C), which means that the technology can also be used for low-grade heat recovery such as geothermal and solar energy. At the same time, although the technical efficiency of the REDHE is low, its power generation process is accompanied by electrode reaction and temperature change. This means that during power generation, the REDHE can also be used for sewage treatment, organic matter degradation as well as waste acid and alkali recovery.

Industrial waste heat is one of the most widely distributed and used potential of conventional recyclable energy in industrial production .However, for the low concentration and less energy of low quality waste heat resources, the mature traditional waste heat recovery technology is not suitable for this kind of the recycling of waste heat resources due to its recycling economy and feasibility of the restrictions. In this paper, the secondary utilization of low quality waste heat resources is studied, especially the control system research of low-temperature waste heat recovery power generation equipment by heat pipe waste heat recovery device matching with roots-type steam engine. Control system is managed by system hardware which with C8051F040 single-chip microcomputer as CPU, and fuses the signals of speed encoder and temperature sensor to realize real-time input, and realizes real time communication between touch screen and single chip microcomputer through RS232 bus. By testing, system works stably. Finally it is resulted that the recovery of low-temperature waste heat and the conversion of electric energy can be achieved by the test.

The waste heat of ships has the characteristics of large temperature gradient, huge recoverable amount and various properties. Traditional technologies such as thermoelectric power generation (TEG) and organic Rankine cycle (ORC) are difficult to take into account the different characteristics of the various types of waste heat from ships. In order to realize the efficient cascade utilization of various waste heat from ships, improve the efficiency and meet the stringent requirements of the new international carbon emission regulations, a cascade recovery system of ship waste heat based on TEG-ORC (thermoelectric power generation/organic Rankine cycle) is proposed in this paper. After designing of the TEG-ORC combined cycle experimental system, the simulation research has also been carried out. The effects of TEG bottom cycle scale, ORC working medium flow rate and evaporation pressure on system net output power, system power generation cost and bottom cycle ratio (QTEG/QORC ) are studied. The results show that the TEG-ORC combined cycle overcomes the limitation of single waste heat utilization method, realizes multi-stage utilization of ship waste heat, as well as improves the utilization of waste heat. Of course, the stability and safety of ORC bottom cycle operation are also promoted. The simulation results show that when the TEG bottom cycle scale is 22 pieces, ORC working medium flow rate is 0.44 kg/s, and ORC working medium evaporation pressure is 2.2MPa, the system economy is optimal. At this time, the system power generation cost is 0.26 $/kW·h, the system net output power is 2520.3 W, and the thermal efficiency is 23.33%.

PurposeResponding to natural resource depletion and carbon dioxide (CO2) emission problems, and also the stricter government’s energy regulations, the purpose of this paper is to develop a sustainable waste heat recovery optimal-profit-oriented management model especially targeting on the easily forgotten low- and medium-temperature waste heat in the industry. In the paper, a system is constructed to facilitate converting the low- and medium-grade waste heat in factories into electricity, and yields optimal profit.Design/methodology/approachThis paper integrates an efficient Organic Rankine Cycle (ORC) system from both sustainable energy reservation and cost effectiveness approaches with an optimization model that adopts particle swarm optimization (PSO) algorithm to determine proper installation locations and feasible generator sets. The system is constructed to facilitate converting the low- and medium-grade waste heat in factories into electricity, and yields optimal profit. The model considers the environmental factors: temperature, heat amount, equipment configuration of the number of ORC sets, and detailed investment cost constraints.FindingsThe results show that annual investment return rate, annual increase in electricity, power generation efficiency, and annual CO2 emission reduction are all highly improved, and investment recovery period is shortened. Also, the larger scale of the waste heat emission, the better the performance is achieved. Finally, the study also completes a sensitivity test under dynamic conditions of electricity price, generator sales price and factory budget constraints, and the results are consistently robust. More valuably, this paper demonstrates applications on two different manufacturing industries with various waste heat emission scales to prove the accountability.Originality/valueThe main contributions are in three aspects. First, it proves that applying PSO to a nonlinear mathematical model can help determine the optimal number and style configuration of generators for waste heat sources. Second, different from the prior research works focusing on power generation, this paper also deliberates the cost factors, cost of generators, costs of numerous peripheral components and future maintenance costs to ensure the factories not conflict with the financial limitations. Third, it is not only successfully applied in two industries with different scales, but also robust with various economic tests, electricity price change, generator sales price change, and investment budget adjustments.

Energy crisis and carbon emission are increasingly prominent issues in our society. As one of the clean energy sources, thermoelectric power generation is a promising alternative energy technology to convert heat into electricity. If there is a heat source, thermoelectric generators can provide electricity for watches, sensors, electronics, spacecraft, etc., and can also be used to recover waste heat, such as automobile exhaust heat, industrial waste heat, ship waste heat, etc. This paper begins with the basic principles of thermoelectric generators and an outlook of thermoelectric materials in different application scenarios. Then, the thermoelectric generator systems, which can be classified into different groups according to their different power generation levels, also the corresponding progress, challenges, and future development are presented. In addition to exploring high-performance thermoelectric materials, the system efficiency of thermoelectric generators is much dependent upon advanced structural design and thermodynamic optimizations. In the previous and present works, some new optimization methods are applied to improve the performance of thermoelectric devices and systems, these include such as the asymmetric design, phase change heat transfer, optimization for thermoelectric devices based on temperature distributions, also heat pipe and converging design for thermoelectric generator systems. These works help breakthrough in thermoelectric power generation from low-level power generation to relatively higher-level power generation. The current progress helps provide a comprehensive insight into thermoelectric power generation technology from micro power supplies to kilowatt systems.

Most of the exhaust temperature of ships is above 300℃, usually this part of waste heat would be directly discharged into the environment, not fully utilized. In order to improve the energy efficiency ratio of ship storage and transportation more effectively, domestic and foreign counterparts have done a lot of technical research on the recovery and utilization of ship waste heat, but most of them are based on a single application perspective. Emphasizing the application of multi-angle combined waste heat, driven by waste heat for CO2 supercritical power generation coupling trans-critical refrigeration system was proposed and designed. While the combined system recovered waste heat for power generation, the functions of refrigerating cooling and seawater desalination were realized by using the properties of CO2 working medium. Taking Fuyuan Yu 7861 ocean-going fishing boat as a design case, the relevant thermal calculation and equipment matching of CO2 supercritical power-transcritical refrigeration system driven by waste heat recovery were targeted. The results showed that the total power consumption of the system is 34.171KW, the waste heat power generation efficiency is 12.9%, the refrigeration performance coefficient is 2.368, the energy saving effect is remarkable, and the energy saving and emission reduction are realized.

As an emerging research direction in the field of highway transportation, fuel cell vehicles have attracted worldwide attention. In the process of fuel cell operation, about 50% of the energy is lost in the form of heat. If this part of waste heat can be recovered while ensuring the proper temperature inside the battery, the operation efficiency of the vehicle will be further improved. However, the recovery of low-grade waste heat is difficult and the recovery efficiency is low. This paper first reviews the feasible methods of using the waste heat of fuel cell, and proposes a fuel cell cooling system with a waste heat generation system. The power generation effect of thermoelectric generators under different temperature differences in the operating conditions of the car was simulated to verify the actual power generation effect of the thermoelectric generators. At the same time, in order to increase the temperature difference of the power generation system, the heat sink of the thermoelectric power generation system was subjected to multi-physics simulations under different structures. The simulation results show that thermoelectric generator has a certain energy generation ability under the operating conditions of the car. And the cylindrical radiator has the best comprehensive performance in terms of heat dissipation. This paper provides a new idea and related theoretical guidance for improving the energy efficiency of fuel cell vehicles.