Low-temperature Heat Recovery Research Articles

Flexible Thermoelectric Electrode with a New Nitrogen-Modified MXene/SWCNT Layered Structure for Efficient Low-Grade Thermal Energy Collection.

Confronting the global challenge of energy efficiency in the backdrop of environmental concerns, the innovation of a flexible thermoelectric electrode marks a significant stride forward, especially in the realm of low-temperature heat recovery. This investigation unveils a pioneering electrode material, a nitrogen-doped SWCNT/MXene bilayer thin film, which was meticulously engineered for thermoelectric systems. Surpassing the conventional Pt electrode with inherent inflexibility and prohibitive cost, our proposed electrode showcases excellent ductility alongside commendable thermoelectric properties. Our electrodes demonstrate significant advancement, achieving a thermopower output of 14.11 μW·cm-2 with the Seebeck coefficient escalating to 1.61 mV·K-1 even at a modest temperature differential of 40 °C. The results mark a substantial 32% enhancement in thermoelectric performance compared to the power output at 10.69 μW·cm-2 for a Pt electrode under similar conditions. This remarkable improvement underscores the superior efficiency and potential of our electrodes for practical thermoelectric application, offering a viable and cost-effective alternative to traditional Pt-based solutions. This innovation not only positions itself as a formidable contender to Pt electrodes but also signals a new dawn for efficient thermoelectric energy harvesting, underscored by the material's scalability and ready availability.

Performance evaluation of a flexible CO2-ORC and sorbent regeneration integrated novel dry gasification oxy-combustion power cycle for in-situ sulphur capture, CO2 capture and power generation

In this work, CO2-Organic Rankine Cycle (CO2-ORC) and sorbent regeneration integrated novel Dry Gasification Oxy-Combustion (DGOC) power cycle has been proposed. Integration of CO2-ORC, a low-temperature heat recovery cycle, further enhances the power cycle efficiency. This work presents the performance evaluation of proposed cycle in terms of optimum conditions of gasifier and regenerator, sulphur capture efficiency, quality of CO2 capture, net plant efficiency, exergy efficiency and economic aspect with different sorbents for in-situ sulphur capture at various operating pressures in the Aspen Plus simulation environment. Results show that optimum gasifier temperature increase with increase in operating pressure and trend is almost similar for all sorbents studied. Optimum regenerator conditions vary significantly with different sorbent and operating pressure. Maximum efficiency was obtained with CuO sorbent of about 39.85%. CuO has the maximum sulphur capture efficiency of 99.98% whereas Fe2O3 has the lowest Sulphur capture efficiency. Exergy analysis shows a similar trend, with CuO having the maximum exergetic efficiency. Economically combined cycle with MnO sorbent performs marginally better than other sorbents.

Design optimization and analysis of a multi-temperature partition and multi-configuration integrated organic Rankine cycle for low temperature heat recovery

With the development of society and economy, more and more attention has been paid to energy saving where low temperature heat plays an important role. As an effective means to utilize low temperature heat, the organic Rankine cycle attracts great attention, where interval partition number, the optimization of interval temperature, system configuration optimization, working fluid selection and matching with heat source have significant influence on system performance. It is challenging to optimize organic Rankine cycle system considering these issues simultaneously. This study proposes a multi-temperature partition and multi-configuration integrated organic Rankine cycle system model to improve low temperature heat utilization and a comprehensive comparison with basic organic Rankine cycle, recuperative organic Rankine cycle and regenerative organic Rankine cycle is conducted to assess thermal and economic performance with ten working fluids. A numerical optimization analysis compared with other literature and the result of traversal, is performed to ensure the accuracy of mathematical models under the same settings. A series of thermal analysis for organic Rankine cycle systems with multiple system configurations, working fluids selection, condition of heat source and so on are implemented considering internal temperature optimization with evaporation temperature and regenerative ratio. A solution strategy framework is established for the proposed system models. In order to verify the practicability of the proposed model, a case study is built with refinery diesel as the heat source. The result shows that thermal efficiency of the proposed system model has an increase of 4.95–14.01 % compared with the basic organic Rankine cycle and the one with single interval temperature has better performance with 4.95 % higher thermal efficiency and 1.45 % higher total annual cost. Thus, the proposed system model and its corresponding solution strategy can be applied for low temperature heat recovery.

Reactive cooling simulation of electronic components

Low-grade heat recovery is an indispensable solution towards high energy efficiency of power electronics. The fast pace of sustainable digitalisation calls for developing alternative solutions to create a sustainable loop for decreasing the energy footprint. However, heat transfer under low-temperature differences challenges effective heat recovery processes. Therefore, in this paper, reactive fluid performance in a practical heat exchanger is investigated using high-fidelity finite rate chemistry method, which is a key step to deploy the attractive Ericsson cycle for low-temperature heat-to-electricity conversion. Under fixed thermal efficiency, it is found that replacing non-reactive fluid by N2O4 reactive fluid can immediately boost electrical efficiency of an Ericsson cycle by at least 260%. The needed primary heat exchanger component in an integrated cooling and power electronic system can be 54.8% smaller in volume whilst enabling a 26% higher thermal performance, provided that the hot source temperature is low (<403 K). For thermal processes involving high temperature hot source, substantial limitation of chemical reaction rate on the effectiveness of an Ericsson cycle is identified. Remarkably, low temperature difference is not a limitation for reactive heat transfer that continuous endo-/exothermic reaction happening throughout a heat exchanger improves Nusselt number Nu = 7.5 by a factor of ∼ 1.3 than the corresponding value (Nu = 5.9) for non-reactive fluid. Turbulence is found beneficial for reactive heat transfer, suggesting the use of corrugated-type heat exchangers for better thermal exchange rates.

Hybrid PEM Fuel Cell Power Plants Fuelled by Hydrogen for Improving Sustainability in Shipping: State of the Art and Review on Active Projects

The interest in hybrid polymer electrolyte membrane fuel cells (PEMFC) fuelled by hydrogen in shipping has seen an unprecedented growth in the last years, as it could allow zero-emission navigation. However, technical, safety, and regulatory barriers in PEMFC ship design and operation are hampering the use of such systems on a large scale. While several studies analyse these aspects, a comprehensive and up-to-date overview on hydrogen PEMFCs for shipping is missing. Starting from the survey of past/ongoing projects on FCs in shipping, this paper presents an extensive review on maritime hydrogen PEMFCs, outlining the state of the art and future trends for hydrogen storage and bunkering, powertrain, and regulations. In addition to the need for a clear regulatory framework, future studies should investigate the development of an efficient fuel supply chain and bunkering facilities ashore. As for the onboard power system, health-conscious energy management, low-temperature heat recovery, and advancements in fuel processing have emerged as hot research topics.

Thermoelectric Generator Using Low-Cost Thermoelectric Modules for Low-Temperature Waste Heat Recovery

One of the most significant problems in industrial processes is the loss of energy according to the sort of heat. Thermoelectrics are a promising alternative to recovering this type of thermal energy, as they can convert heat into electricity, improving the industrial efficiency of the process. This article presents the characteristics of low-cost thermoelectric modules typically used for generation (SP1848-27145SA (TEG-GEN)) and refrigeration (TEC1-12706 (TEC-REF)), both utilized in this research for heat recovery. The modules were evaluated against various configurations, source distances, and distributed systems in order to determine optimal recovery conditions. The experiments were conducted both at the laboratory level and in a large-scale furnace of the traditional ceramics industry, and they revealed that even refrigeration modules are suitable for energy recovery, particularly in developing countries, whereas other generators are more expensive and difficult to obtain. These thermoelectric generators were tested for low-temperature heat recovery in regular furnaces, and the results are to be implemented elsewhere. Results show that even the thermoelectric refrigeration modules can be a solution for heat recovery in many heat sources, which would be particularly strategic for developing countries.

Enhanced heat transfer in a phase change energy storage with helical tubes

Solar collectors integrated with phase change materials (PCM) store heat energy for later use. However, the settling of PCM prolongs the melting duration in a vertical cylindrical container. Hence, selective methods are required to alleviate such solid PCM settling issues. A helical heat transfer tube (HTT) can improve melting by increasing the contact surface. The present research studies the charging and discharging of PCM using three helical coil HTT configurations: fully expanded, semi-compressed, and fully compressed. The fluid flow rate and inlet temperatures are 20 LPH and 80 °C, respectively. The simulation involves two-dimensional numerical modeling using Ansys Fluent software and the finite volume method with the enthalpy-porosity technique. The fully compressed HTT melt settled PCM inside the vertical cylindrical container faster. The experimental results show that using a fully compressed HTT reduced the melting time by 50 % compared with a fully expanded HTT of 160 min due to the effective melting of settled PCM. Its peak heat stored, energy efficiency, Nusselt, Stefan, and Rayleigh numbers are 356 kJ, 34.8 %, 75.34, 0.47, 2.8036 × 107, respectively. The compressed HTT is a practical design suggested for solar collectors and low-temperature heat recovery systems, which demand a fast heat storage rate.

Modeling of a transient low-temperature waste heat recovery in the plate heat exchanger in Flownex Simulation Environment

The paper analyses the feasibility of determining the parameters of a heat exchanger operating in the crop production and realising low-temperature heat recovery from biological processes. For the first time, the Flownex 8.7 Simulation Environment has been used for this purpose. The temperature of the waste water was between 20 and 30°C. On the basis of the simulations, the power of the heat exchanger is determined to be 1 MW. The heat exchanger can efficiently heat up cold water from a deep well (7-10°C) to an assumed temperature of 19.7°C. The results from the simulation calculations correspond to the results obtained under actual conditions within a range of up to 2%.

Performance improvement of an integrated system with high-temperature PEMFC, Kalina cycle and concentrating photovoltaic (CPV) for low temperature heat recovery

This study proposed a novel integrated system that including the high-temperature proton exchange membrane fuel cell (HT-PEMFC), Kalina cycle, concentrating photovoltaic (CPV), and the half-effect absorption refrigeration system. The waste heat discharged from HT-PEMFC was recovered to drive Kalina cycle for more power output, while the lower-grade waste heat of CPV was utilized by the half-effect absorption refrigeration cycle which provided the refrigerating capacity for Kalina cycle’ condenser cooling demand, and thus the power output of Kalina can be further improved. For examining the feasibility and evaluating the performance of the novel integrated system, a mathematical model for the proposed system was established. The results showed that the electrical efficiency of Kalina subsystem was increased by 1.217%, the exergy efficiency of PEMFC and CPV were increased by 23.99% and 9.39%, respectively, compared with the single supply system. Parameter analysis indicated that the efficiency of integrated system was improved with the increase of fuel cell operating temperature, photovoltaic operating temperature and the basic ammonia concentration, and was decreased with the increase of the Kalina separation pressure and PEMFC current density. It was also found that the total power generation efficiency of integrated system was 27.71%, which was increased by 5.03% compared with the single supply system.

Experimental study on heat energy recovery and utilization of coal gangue hill based on gravity heat pipe

The coal gangue hill is formed by the accumulation of waste in the coal mining process. A large amount of heat energy accumulates inside it, which makes it prone to spontaneous combustion, seriously pollutes the environment and wastes resources. In this paper, taking a gangue hill in a mining area as an example, a gravity heat pipe device is used to extract heat from the deep part of the gangue hill, and a mathematical model for heat extraction is established. And through experiments to explore the cooling effect of coal gangue at different depths, it is concluded that the cooling range of gravity heat pipe can reach about 15%. At the same time, to avoid the waste of geothermal resources, this paper uses the extracted heat twice and designs a thermoelectric power generation system based on the gravity heat pipe device to realize the purpose of resource utilization of the underground heat energy of coal gangue hills. The experimental results show that the thermoelectric conversion efficiency can reach 7.39%, and after the addition of the soaking plate, the thermoelectric efficiency is increased to 9.02%, which has a very important reference significance for promoting the treatment of coal gangue hills and the recovery and utilization of low-temperature geothermal heat.

Experimental investigation of a high-temperature heat pump for industrial steam production

Low-temperature flue gas heat recovery acts as an important way for energy saving and emission reduction in industry sectors. It is difficult to reuse low-temperature heat in the industrial production process, upgrading low-temperature heat using a heat pump is a promising approach to pursue. In this work, an experimental prototype of a high-temperature compression-absorption heat pump was conducted and investigated. Driving by low-grade waste heat and a small amount of electricity, using ammonia-water as a working fluid, this heat pump experimental prototype can produce high-temperature (more than 150 °C) process steam for industrial processes. The operation strategies of the experimental system are clarified and programmed into the control system. Two hours of automatic stable operation indicates the operation strategies are suitable for this high-temperature heat pump. The temperature and pressure of the produced steam are 154 °C and 0.53 MPa, respectively. The steam heat output of the heat pump experimental prototype reaches 70.15 kW, in which the electric heating share is 18.9% and the waste heat heating share reaches 81.1%. The experimental results indicate the hybrid heat pump is capable of recovering low-temperature (less than 170 °C) flue gas heat for process steam generation. This work provides a new approach to upgrade low-temperature waste heat for process steam production.

Cascade heat utilisation via integrated organic Rankine cycle and compressor-assisted absorption heat pump system

Absorption heat pumps have attracted increasing attention due to the recent interest in high-efficiency waste heat utilisation in buildings. By ways of the outstanding performance of organic Rankine cycle (ORC) for low-temperature heat recovery applications, this paper proposes a new hybrid system integrating an organic Rankine cycle and compressor-assisted absorption heat pump (OCAHP) to improve the operating range and overall performance of the heat pump via cascading heat utilization. A thermodynamic model of the OCAHP system is developed for the evaluation of its performance at different operating parameters. The results show that the system has an excellent performance even at an ambient temperature as low as −20 °C, and its primary energy efficiency is improved significantly compared to both conventional and compressor-assisted absorption heat pumps. The performance improvement is at least 10% over a wide ambient temperature range. Also, it has a greater potential to maintain high-performance operation at a low heat source temperature (below 100 °C) while still meeting the heating requirements. Furthermore, the system shows a good tolerance to the variation of hot water supply temperature. Under a hot water temperature of 60 °C, the primary energy efficiency of the OCAHP is up to 1.5. The above features have proved that the proposed system has a great potential to be used in practical applications and achieve energy efficiency enhancement in typical winter condition.

Optimisation of simple and regenerative organic Rankine cycles using jacket water of an internal combustion engine fuelled with biogas produced from agricultural waste

Internal combustion engines have a very important place in biogas production facilities to convert biogas energy to electricity. Unfortunately, although intense studies on improving internal combustion engine efficiencies by operational optimisation methods, serious progress is not achieved yet. However, there are many ways to improve the performance of these engines apart from structural optimisation methods. One of the most important ways is to utilize by integrating jacket water used to cool the biogas fuelled internal combustion engines into the new generation low-temperature heat recovery systems like organic Rankine cycles. In the present study, simple and regenerative organic Rankine cycles were optimised to improve the overall performance of an biogas fuelled internal combustion engine by using the jacket water which is released into the atmosphere after cooling the engine. Also, the energy, exergy and environmental aspect of these systems are evaluated. Finally, exergoeconomic analysis for both systems are conducted, and then payback periods of both systems are determined. As a result of the study, the maximum net power, thermal and exergy efficiencies of the simple organic Rankine cycle was calculated as 42.14 kW, 11.47 % and 63.27 % respectively, while the maximum net power, thermal and exergy efficiencies of the regenerative organic Rankine cycle are found as 45.3 kW, 12.34 % and 68.02 %. In addition, it is observed that the maximum power production obtained from the regenerative organic Rankine cycle corresponded to nearly 630 kg CO2/h emission reduction. The best payback period value is also calculated as 7.37 years in the simple organic Rankine cycle.

Experimental and numerical analysis on low-temperature off-design organic Rankine cycle in perspective of mass conservation

Experimental and numerical studies on the low-temperature heat recovery organic Rankine cycle operating in off-design conditions are conducted for the in-depth understanding of the system's underlying mechanisms in terms of mass conservation. Experimental data sets were obtained from a 1 kW lab-scale organic Rankine cycle test bed using R245fa as the working fluid. The effects of several boundary conditions, including charged mass, are thoroughly examined under low-temperature heat source within the range of 65–95 °C. Numerical models of the heat exchangers are developed by applying the discretization method to predict the captured mass inside the phase-changing components and validated within 5% error range. By the integration of experimental and numerical methods, unprecedented and critical results covering the pressure formation process, mass distribution, and liquid receiver modeling are derived from the analysis which could not be discovered through previous approaches. The unconventional thermodynamic state of the working fluid inside the liquid receiver is revealed in detail and a passive design is suggested for the liquid receiver model. An improved solver architecture is proposed for the complete development of a fully deterministic off-design organic Rankine cycle simulation model, where the reality-based logics obtained from the key findings are projected into the novel model.

Multi-generation energy system based on geothermal source to produce power, cooling, heating, and fresh water: Exergoeconomic analysis and optimum selection by LINMAP method

The current study deals with thermodynamic modeling and multi-objective optimization of a new multi-generation energy system using geothermal as the primary energy source. The proposed system includes a Kalina cycle, a refrigeration unit, thermoelectric module, steam turbine, and heating unit. The new aspects of the proposed system are using the thermoelectric system to low temperature heat recovery and using the benefit of the multi-product. The system exergy analysis shows that the reverse osmosis desalination unit with 449.1 kW has the highest exergy destruction rate in the system. Additionally, three components i.e., reverse osmosis unit, heating system, and steam turbine are responsible for 82.8% of exergy destruction of the system. Exergo-economic analysis revealed that the turbine and the thermoelectric module have the highest cost rates of 12.51 US$/h and 3.62 US$/h respectively. It also concludes that the sum of the cost rate of component and associated exergy destruction cost rate, a significant exergo-economic parameter, for the turbine and reverse osmosis unit are the highest values. Parametric analysis of the proposed system for geothermal source pressure, steam turbine backpressure, Kalina turbine backpressure, and ammonia mass fraction of basic solutions are carried out. The unit cost of product and exergy efficiency are objective functions for optimization. Multi-criteria optimization indicates that using the Linear Programming Technique for Multidimensional Analysis of Preference (LINMAP) method based on suggested design variables, can reduce the unit cost of the product to 0.107 US$/kWh, and the exergy efficiency can be increased up to 15.86%.

Waste-heat utilization potential in a hydrogen-based energy system - An exploratory focus on Italy

The target of the full decarbonisation by 2050 requires high penetration of renewables, with the development of overgeneration situations in the energy system. Hydrogen and electro-fuels could play a key role in hard-to-abate sectors and in grid balancing. By means of the developed NEMeSI model we study the Italian future energy mix, including several Power-to-X (P2X) options to accommodate high RES introduction. The model is set to solve a linear optimization problem, by optimizing the use of resources through the minimization of the supply costs. The use of excess power from renewables is evaluated in solutions such as hydrogen production and electro-fuels synthesis, coupled to Power-to-Heat and storage systems. The model studies the Italian case in a decarbonised scenario and provides an estimation of potential waste heat recovery from the P2X processes, differentiating from low to high temperature waste heat. Waste heat can be used for district heating purposes or for power generation via organic Rankine cycle. Both high and low temperature heat recovery show a potential in the order of tens of TWh, with a preference for power generation use.

Technology for Optimizing Flue Gas Pollutant Emission Reduction in Oil Field Heating Furnace Combustion

The energy consumption of the heating furnace is an important part of the energy consumption of the oilfield gathering and transportation system. The low energy efficiency of the heating furnace will directly lead to the increase of oilfield production costs. In response to the national energy-saving and emission-reduction policy, the oilfield has implemented energy-saving practices in heating furnace load adjustment, efficient combustion, excess air coefficient control, flue gas waste heat utilization, and furnace modification. It is clear that the energy efficiency of oilfield heating furnaces is still lower than foreign advanced levels. There is an urgent need for further energy conservation and efficiency enhancement. MVR low-temperature flue gas heat recovery technology, flame shape matching technology, nanofluid heat transfer enhancement technology, solar auxiliary heating technology and other new technologies that can be used for energy saving and consumption reduction of oilfield heating furnaces provide a reference for oilfield heating furnaces to tap the potential and increase efficiency.

Https://medwinpublishers.com/PPEJ/using-bayesian-networks-for-quantifying-domino-effect-probability-in-a-hydrocarbon-processing-area.pdf

Hydrogenation technology has many advantages in light and clean oil products, and has become the most reasonable and effective key technology in the refining industry. However, the hydrogenation reaction process is high temperature, high pressure and hydrogen operation, which consumes a lot of fuel and power, and the energy consumption of the unit is high. Through pinch analysis, the violators of pinch points are identified, and the heat exchange process of the existing hydrogenation unit is optimized and adjusted. Reasonably distribute the heat exchange load of mixed hydrogen oil and low-content oil, improve the final heat exchange temperature of mixed hydrogen oil, reduce the heating load and fuel consumption of heating furnace, strengthen the recovery of inefficient low-temperature potential heat, advance to the design of maximum energy recovery (MER), realize the optimization of cold utility and hot utility, and effectively reduce the energy consumption of hydrogenation unit after optimization. The optimization of heat exchange network of hydrogenation unit significantly improves economic and social benefits.

Thermodynamic analysis of a Carbon Carrier Cycle (CCC) for low temperature heat recovery

The aim of the paper is to study the thermodynamic behavior of a non-conventional power cycle, named Carbon Carrier Cycle (CCC), which is expected to obtain interesting performance with low temperature heat source. The CCC may be regarded as derived from an absorption machine, where an expander replaces the condenser, the throttling valve and the evaporator. The working fluid is a mixture of CO2 and a proper absorber. In the paper, the thermodynamic model of this kind of cycles is described, and the results obtained considering Acetone as the absorber are discussed. A first performance comparison is then conducted with a more conventional Organic Rankine Cycle (ORC).

Theoretical study on geothermal power generation using thermoelectric technology: a potential way to develop geothermal energy

ABSTRACT Thermoelectric power generation is an outstanding technology for high- and low-temperature heat recovery. Their packaging, lack of moving parts, direct heat to electrical conversion, and zero-emission are the main benefits for geothermal power generation. The design of a large-scale, ground-based, and segmented annular concentric cylindrical thermoelectric generators (CCTEGs) with produced geothermal fluid are proposed. A mathematical model for thermoelectric power generation is presented, which considers the heat transfer in the interior of a thermoelectric module and the electric current effect, and is solved with Engineering Equation Solver (EES) software. Numerical results show that about 136 kW of power output could be obtained with 500 m length of segmented annular CCTEG under the inlet fluid temperature difference of 130°C. For the same total flow rates and the same total CCTEG length, the in-series layout of segmented annular CCTEG is better than the in-parallel layout in power generation capacity. Flow rate and fluid temperature have a significant effect on the generated power. A higher flow rate ratio of cold fluid to hot fluid will result in higher power capacity. A desirable flow rate ratio of cold fluid to hot fluid is recommended to take as the flow area ratio of cold fluid flow conduit to hot fluid flow conduit when the critical potential increased power generation capacity is taken as 1.0 kW/kg.