•Proton exchange membrane fuel cell thermal management solutions.•Fuel cell heat recovery for heating/cooling and power applications.•Low-grade heat recovery solutions for proton exchange membrane ...fuel cells.•Proton exchange membrane fuel cell heat recovery for self-serving the system.
The present paper provides a comprehensive review of heat recovery opportunities for proton exchange membrane fuel cells. A significant amount of heat is generated by these fuel cells while operating that is equivalent to ~45 to 60% of the total energy content of hydrogen entering the cells. The generated heat must be removed effectively from the stack by using a properly-designed cooling system in order to prolong its lifetime and maintain its performance. Applying proper thermal management strategies and capturing opportunities for fuel cell heat recovery can add significant values to a fuel cell system in terms of size, costs, and its overall energy efficiency. The heat generated by proton exchange membrane fuel cells can be captured and used for a range of combined heating/cooling and power applications: i.e. combined heat and power, combined cooling and power, or combined cooling heat and power solutions. The heat generated by a fuel cell stack also provides opportunities for its integration with organic Rankine cycles, thermoelectric generators, and thermally regenerative electrochemical cycles for power cogeneration applications. Furthermore, the heat recovered from a fuel cell can be used for self-servicing the system such as enhancing the hydrogen discharge rate of metal hydride canisters (supplying hydrogen to the stack) or preheating inlet air and hydrogen to improve performance of the fuel cell. The present paper also helps identify the research gaps in this area and provides direction on future studies on thermal management and integrated heat recovery solutions for proton exchange membrane fuel cells.
•The aluminium industry is highly energy intensive, has significant environmental impact and release a large proportion of energy as waste heat.•The production energy required, energy losses and ...energy content of the waste heat is quantified.•The environmental impact of each aluminium production stage is described with focus on the refining, primary and secondary industries.•Equipment used within each process step with potential for waste heat recovery is described.•Waste heat can be reused utilising heat recovery technologies to reduce energy consumption among other benefits.
Aluminium is becoming more frequently used across industries due to its beneficial properties, generally within an alloyed form. This paper outlines the entire production process of aluminium from ore to the finished metallic alloy product. In addition, the article looks at the current state of the art technologies used in each discrete process step. Particular interest is directed towards casting technologies and secondary recycling as the relative proportion of recycled aluminium is increasing dramatically and aluminium is much more energy efficient to recycle than to produce through primary methods. Future developments within the industries are discussed, in particular inert anode technology. Aluminium production is responsible for a large environmental impact and the gaseous emissions and solid residue by-products are discussed. In addition to the environmental impact, the industry is highly energy intensive and releases a large proportion of energy to atmosphere in the form of waste heat. One method of reducing energy consumption and decreasing the environmental impact of emissions is by installing waste heat recovery technology. Applied methods to reduce energy consumption are examined, with a latter focus on potential applications within the industry for waste heat recovery technologies.
Recovering wasted heat is sustainable and cost-effective approach to secure energy supply in cities. This paper extended the Stackelberg game model to investigating the supply chain of the waste heat ...recovery market. Three models were proposed to investigate the optimal decision-making for different supply chain participants. With a validation case, the results suggested that the joint decision can reach the optimal outcomes and cost. Mobile heating strategy has advantages over coal-fired boilers, electric boilers, natural gas boilers in terms of costs and environmental protection. With a typical consumption of the recovered waste heat 342 GJ/day for water heating (from 25 °C to 60 °C) can save 11.672t standard coal and 79,800 RMB per day. In addition, improving thermal energy quality of waste heat recovery can generate higher profit and attract more potential customers.
•Developing supply chain models for waste heat recovery quality were built.•Decision models for supply chain were compared.•Mobile heating has advantages in costs and environment protection.
Low-grade heat accounts for >50% of the total dissipated heat sources in industries. An efficient recovery of low-grade heat into useful electricity not only reduces the consumption of fossil-fuels ...but also releases the subsequential environmental-crisis. Thermoelectricity offers an ideal solution, yet low-temperature efficient materials have continuously been limited to Bi
Te
-alloys since the discovery in 1950s. Scarcity of tellurium and the strong property anisotropy cause high-cost in both raw-materials and synthesis/processing. Here we demonstrate cheap polycrystalline antimonides for even more efficient thermoelectric waste-heat recovery within 600 K than conventional tellurides. This is enabled by a design of Ni/Fe/Mg
SbBi and Ni/Sb/CdSb contacts for both a prevention of chemical diffusion and a low interfacial resistivity, realizing a record and stable module efficiency at a temperature difference of 270 K. In addition, the raw-material cost to the output power ratio in this work is reduced to be only 1/15 of that of conventional Bi
Te
-modules.
•Utilization of waste heat in a biogas cogeneration power plant was analyzed.•Techno-economic optimization of the waste-heat recovery unit was conducted.•Rankine cycle and organic Rankine cycle using ...toluene were compared.•The overall electrical efficiency of the biogas power plant was increased by 3%.•A 6.8-year payback period of the investment was obtained.
In a typical biogas cogeneration plant, a part of the exhaust gas energy is used for heating buildings within the plant. However, a certain amount of this energy remains unused. This study examined the utilization of this waste-heat through the Rankine cycle and organic Rankine cycle. A multiobjective thermo-economic optimization procedure of a waste-heat recovery unit installed at the exit of an engine before the engine cooling fluid–exhaust gas heat exchanger is proposed herein. The optimization procedure includes sizing all heat exchangers in the waste-heat recovery unit based on the measured Colburn and friction factors. The thermo-economic optimization was performed to investigate the maximal power output and the minimal payback period while preserving the function of the heating system. The procedure was applied to a biogas power plant with two engines (mass flow rate of the exhaust gases from each engine was 1.77 kg/s at a temperature of 410 °C). The electrical efficiency of this system was 42.1% and the measured overall yearly energetic efficiency was 66.7%. Optimization shows that the waste-heat recovery unit based on Rankine cycle is more economical than the unit based on the organic Rankine cycle using toluene. The electrical efficiency of the entire power plant increased by 2.97% and the payback period of the investment was 6.8 years, while the Levelized Cost of Electricity was 0.0419 $/kWh. The proposed method could be used to analyze the investment profitability of waste-heat utilization in other cogeneration plants.
In this forward-looking perspective, the current technologies for low-temperature waste heat recovery are first analyzed from two aspects: (i) the local waste heat recovery technology and (ii) global ...optimization of energy flow network. Based on the analysis, barriers for the further promotion of waste heat recovery are outlined, and they include the lack of global optimization methodology, distributed waste heat recovery system with high costs, and mismatches between waste heat source and demand. To address these issues, perspectives on three aspects are provided. First, advanced graphical analysis and optimization methodology integrating the heat exchange and energy conversion can promote the user-friendly optimization. Second, concentrated waste heat recovery and supply can save the investment, installation area and operation costs, thereby making the waste heat recovery cost-effective. Third, thermal storage, thermal transportation and high temperature heat pump can better couple the waste heat source and user demand from time-scale, spatial scale and energy grade, respectively. Visions for the future are combined with technical details to provide comprehensive perspectives for the next-step waste heat recovery.
•Technologies for low-temperature waste heat recovery are analyzed.•Optimizing method for combined heat exchange and conversion network is discussed.•Concentrated waste heat recovery and supply is a cost-saving option.•Technologies for the waste heat source and user demand coupling are discussed.
•Analysis of thermoelectric generators for waste-heat recovery in a real industry.•Use of two computational models to design a thermoelectric generation system.•Optimized design could generate up to ...45 kW from a hot gas flow.•Levelized cost of electricity of around 15 c€/kWh using this technology.
One of the options to reduce industrial energy costs and the environmental impact is to recover the waste-heat produce in some processes. This paper proposes the use of thermoelectric generators at a stone wool manufacturing plant to transform waste-heat from a hot gas flow into useful electricity. A combination of two computational models, previously developed and validated, has been used to perform the optimization from a double point of view: power output and economic cost. The proposed thermoelectric generator includes fin dissipaters and biphasic thermosyphons as the hot and cold side heat exchangers respectively. The model takes into account the temperature drop along the duct where the gases flow, the electric consumption of the auxiliary equipment, and the configuration and geometry of the heat exchangers. After the simulations a maximum net power production of 45 838 W is achieved considering an occupancy ratio of 0.40 and a fin spacing of 10 mm. The installation cost is minimized to 10.6 €/W with an occupancy ratio of 0.24. Besides, the Levelised Cost of Electricity, LCOE, is estimated for a thermoelectric generator for the first time. It is necessary to use standar methodologies to compare this technology to others. The LCOE estimated for the proposed design is around 15 c€/kWh within the ranges of current energy sources, proving, in this way, the capabilities of waste-heat recovery from industrial processes at reasonable prices with thermoelectric generators.
•Increasing demand for energy and environmental issues are biggest global challenges.•Harnessing renewable energies and WHR can effectively address these issues.•ORC is reliable technology that ...efficiently convert these heat sources into power.•ORC application, working fluids, expanders, modelling and optimization are reviewed.
The ever-increasing demand for energy, scarcity of traditional energy sources and severe environmental issues are, perhaps, the biggest global challenges that need immediate actions. In this regard, harnessing the renewable energies and waste heat recovery are considered as potential solutions that can effectively address these issues. Organic Rankine cycle (ORC) is proved to be reliable technology that can efficiently convert these low to medium-grade heat sources into useful power. This paper is a comprehensive review of literature about the ORC that contains the ORC configurations, ORC applications, ORC working fluid selection and modelling and experimental study of the ORC expansion devices.
In this work, organic Rankine cycle (ORC) integrated with Latent Thermal Energy Storage (LTES) system for engine waste heat recovery has been proposed and investigated to potentially overcome the ...intermittent and fluctuating operational conditions for vehicle applications. A melting-solidification model has been established to investigate and compare the performance of twelve Phase Change Materials (PCMs) under different heat source conditions. Among the twelve PCMs, LiNO3-KCl-NaNO3 is identified as the optimal PCM for engine exhaust heat recovery. The performance of the ORC system integrating with different volume of LTES using LiNO3-KCl-NaNO3 under dynamic heat source simulating vehicle conditions is studied. Results illustrate the fluctuation of engine exhaust heat can be potentially overcome by using the proposed solution. The condition of 100 L LTES provides 30.4% larger total output work than that of 50 L LTES, while it is merely 1.5% larger than that of 90 L LTES. The performance of three different LTES-ORC scenarios are compared and results show ORC combining with double LTES delivers 17.2% larger total power output than that of single LTES (100 L) under the same operational conditions.
•ORC integrated with double LTES for engine waste heat recovery is proposed.•Twelve inorganic-salt PCMs are screened and the optimal one has been identified.•System output performance under different LTES volume is studied.•Three different scenarios integrated with single or double LTES are compared.
•Novel flue gas heat recovery system based total heat exchange is proposed.•Dew point temperature of flue gas from the boiler increases to around 60 °C.•Average boiler efficiency is 106% and average ...heat recovery efficiency is 88%.•Wheel rotation speed and backwater temperature are important factors in operation.
Waste heat recovery from flue gas is an efficient way to increase the thermal efficiency of a gas-fired boiler. This paper proposes a novel flue gas waste heat recovery system, which comprises a condensing heat exchanger and an enthalpy wheel. The flue gas firstly flows through the condensing heat exchanger for heating boiler water, and then flows through the enthalpy wheel. The wheel, covered with desiccant material, acts as a medium for further heat and moisture transfer from the flue gas to the oxidizing air, resulting in an increase in the dew point temperature of the flue gas. Experimental results show that the average boiler efficiency reaches 106% and the average total recovery efficiency reaches 88%. The dew point temperature of the flue gas discharged from the boiler increases to around 60 °C, higher than that of conventional flue gas (around 55 °C). Consequently, more latent heat is recovered in the condensing heat exchanger by virtue of the proposed system. A mathematical model is established for further analysis based on the experimental results. The rotation speed of the enthalpy wheel and backwater temperature are key factors influencing the system performance.
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