Search Results (398)

In the transition to sustainable energy consumption, waste heat recovery and storage systems become key to advancing Europe’s energy efficiency and reducing carbon emissions, especially by harnessing thermal energy from low-temperature sources like wastewater. This study focuses on optimizing a heat recovery system that uses heat pipes for effective heat extraction and coconut oil as a phase change material for efficient thermal storage. A total of 12 numerical simulations were conducted to analyze the outcomes of varying operational parameters, including the diameter of the heat pipe, condenser size, secondary agent flow rate, coil length, and primary agent inlet temperature. The numerical findings indicate that reduced flow rates, in combination with smaller condenser diameters and increased primary agent temperatures, greatly improve the efficiency of heat absorption and transfer. Following a 4 h test period, the most successful outcome resulted in a melting fraction of 98.8% and a temperature increase of 18.95 °C in the output temperature of the secondary agent. In contrast, suboptimal conditions resulted in only a 2.21 °C rise and a 30.80% melting fraction. The study highlights the importance of component sizing and optimization, noting that strategic modifications and appropriate phase change materials can lead to highly efficient and scalable systems. Full article

Cement production is one of the most energy-intensive industries. During the clinker formation and cooling processes, excess heat is lost to the atmosphere. For this reason, using waste heat to generate useful energy is considered the most promising approach to sustainable cement production. Many cement plants still face challenges in energy efficiency due to historically low energy prices and subsidies in Uzbekistan, which have deterred the adoption of waste heat recovery (WHR) technologies. This study conducts a techno-economic analysis of WHR technologies for a cement plant with an annual capacity of 1 million metric tons (Mt). It evaluates potential energy savings and economic benefits, identifying key waste heat sources, such as preheater flue gas and clinker cooling air, with a total recoverable waste heat of 60.52 MW. The implementation of WHR systems can significantly enhance energy efficiency and reduce operational costs. Results show that WHR can reduce clinker production costs by 3.81% and the levelized cost of clinkers by 7.49%, while cutting annual indirect CO₂ emissions by 63.26%. Given the legislative support and recent energy price liberalization, the first WHR projects are expected to start in 2025 in Uzbekistan. This analysis offers valuable insights for adopting WHR technologies to improve sustainability and competitiveness in Uzbekistan’s cement industry. Full article

Internal combustion engines (ICEs) are one of the significant sources of wasted energy, with approximately 65% of their input energy being wasted and dissipated into the environment. Given their wide usage globally, it is necessary to find ways to recover their waste energies, addressing this inefficiency and reducing environmental pollution. While previous studies have explored various aspects of waste energy recovery, a comparative analysis of different bottoming configurations has been lacking. In this research, an extensive review of the existing literature was conducted by an exploration of four key bottoming cycles: the steam Rankine cycle (SRC), CO₂ supercritical Brayton cycle, inverse Brayton cycle (IBC), and air bottoming cycle. In addition, these four main bottoming systems are utilized for the waste energy recovery of natural gas-fired ICE with a capacity of 584 kW and an exhausted gas temperature of 493 °C. For the efficient waste heat recovery of residual exhausted gas and heat rejection stage of the main bottoming system, two thermoelectric generators are utilized. Then, the produced power in bottoming systems is sent to a proton exchange membrane electrolyzer for hydrogen production. A comprehensive 4E (energy, exergy, exergy-economic, and environmental) optimization is conducted to find the best main bottoming system for hydrogen production. Results showed that the SRC-based system has the highest exergy efficiency (21.93%), while the IBC-based system results in the lowest efficiency (13.72%), total cost rate (25.58 $/h), and unit cost of hydrogen production (59.91 $/GJ). This combined literature review and research article underscore the importance of finding an economically efficient bottoming cycle in the context of waste energy recovery and hydrogen production. Full article

The traditional production mode using coal as the main energy source is not conducive to the sustainable development of the iron and steel industry (ISI). The hydrogen-based direct reduction shaft furnace (HDRSF) process is a feasible technical route for promoting the green development of the ISI. However, there is a lack of comprehensive analysis with respect to the energy utilization and process flow of the HDRSF method. To address these issues, a systemic material–energy–exergy model of HDRSF is established. An improved HDRSF process incorporating waste heat recovery is also proposed, and energy consumption intensity and exergy intensity are used as assessment metrics. This study’s findings indicate that the proposed waste heat recovery can considerably lower gas demand and energy consumption intensity, but exergy intensity has little effect. The reducing gas demand drops from 2083 m³ to 1557 m³, the energy consumption intensity drops from 2.75 × 10⁷ kJ to 1.70 × 10⁷ kJ, and the exergy intensity drops from 1.08 × 10⁷ kJ to 1.05 × 10⁷ kJ when the reducing gas temperature is 900 °C, H₂:CO = 1:1; meanwhile, the recovery rate of waste heat reaches 40%. This study can serve as a reference for actual HDRSF process production. Full article

Solving strategic IMO tasks for the decarbonization of maritime transport and the dynamics of its controlling indicators (EEDI, EEXI, CII) involves the comprehensive use of renewable and low-carbon fuels (LNG, biodiesel, methanol in the mid-term perspective of 2030, ammonia, and hydrogen to achieve zero emissions by 2050) and energy-saving technologies. The technology of regenerating secondary heat sources of the ship’s power plant WHR in the form of an Organic Rankine Cycle (ORC) is considered one of the most promising solutions. The attractiveness of the ORC is justified by the share of the energy potential of WHR at 45–50%, almost half of which are low-temperature WHR (80–90 °C and below). However, according to DNV GL, the widespread adoption of WHR-ORC technologies, especially on operating ships, is hindered by the statistical lack of system prototypes combined with the high cost of implementation. Developing methodological tools for justifying the energy efficiency indicators of WHR–ORC cycle implementation is relevant at all stages of design. The methodological solutions proposed in this article are focused on the initial stages of comparative evaluation of alternative structural solutions (without the need to use detailed technical data of the ship’s systems, power plant, and ORC nodes), expected indicators of energy efficiency, and cycle performance. The development is based on generalized results of variation studies of the ORC in the structure of the widely used main marine medium-speed diesel engine Wärtsilä 12V46F (14,400 kW, 500 min⁻¹) in the operational load cycle range of 25–100% of nominal power. The algorithm of the proposed solutions is based on the established interrelationship of the components of the ORC energy balance in the P-h diagram field of thermodynamic indicators of the cycle working fluid (R134a was used). The implemented strategy does allow, in graphical form, for justifying the choice of working fluid and evaluating the energy performance and efficiency of alternative WHR sources for the main engine, taking into account the design solutions of the power turbine and the technological constraints of the ORC condensation system. The verification of the developed methodological solutions is served by the results of comprehensive variation studies of the ORC performed by the authors using the professionally oriented thermoengineering tool “Thermoflow” and the specification data of Wärtsilä 12V46F with an achieved increase in energy efficiency indicators by 21.4–7%. Full article

Data centers (DCs) require continuous cooling throughout the year and produce a large amount of low-grade waste heat. Free cooling and waste heat recovery techniques are promising approaches to reduce DC energy consumption. Although previous studies have explored diverse waste heat utilization strategies, there is a significant gap in combining waste heat recovery with lake water cooling in DCs. Therefore, this study proposed a system integrating lake water cooling with waste heat recovery for DCs. To evaluate the energy-saving performance of the suggested system, the influence of waste heat recovery locations and volumes has been investigated. An analysis of the improvement in system parameters is also conducted. The study’s findings highlight that targeted recovery of waste heat from sources like chilled water or air in server rooms can significantly reduce the cooling energy demand of the system. The results show that recovering heat from the return air of IT equipment can yield a remarkable power usage effectiveness (PUE) and coefficient of performance (COP) of 1.19 and 10.17, and the energy consumption of the cooling system is reduced to 10.06%. Moreover, the outcomes reveal the potential for substantial energy savings of up to 26.05% within the proposed system by setting the chilled water and air supply temperatures to 16 and 20 °C, respectively. Full article

Waste car tires are a significant burden on the environment. One way to manage them is through energy recovery by burning them in the furnaces of combined heat and power plants or cement plants, which from an environmental point of view is not a favorable solution. Another way to use waste tires is to produce liquid fuels, which can be used as pure fuels or components added to conventional fuels. Therefore, it is necessary to conduct research aimed at evaluating the physical and chemical properties of tire-derived fuels relative to conventional fuels. It is also important to determine the impact of feeding engines with synthetic fuels, regarding their operational and environmental performance. In this article, the physicochemical properties of typical diesel fuel, synthetic fuel derived from waste tires (WT) and its blends with diesel fuel (DF) in shares of 5, 10, 15, 20 and 25% v/v were studied. Tests were also conducted on an internal combustion engine with a common rail injection system (CR IC) engine to determine operational and emission parameters. The results showed, among other things, a deterioration relative to diesel fuel of such parameters as cold filter plugin point (CFPP) and flash point (FP). At the same time, a favorable effect of synthetic fuel addition was noted on hydrocarbon (HC) and nitrogen oxide (NOx) emissions. Full article

The opportunities related to the adoption of synthetic gaseous fuels derived from solid biomass are limited by the issues caused by the peculiarities of the syngas. The aim of this paper is to analyze several possible layouts of hybrid energy systems, in which the main thermal source is the organic fraction of municipal solid wastes. The case of a small community of about 1000 persons is analyzed in this paper. The examined layouts coupled an externally fired micro gas turbine with a waste heat recovery system based on both an Organic Rankine Cycle and supercritical CO₂ gas turbines. A thermodynamic analysis has been carried out through the use of the commercial software Thermoflex 31, considering the losses of each component and the non-ideal behavior of the fluids. The results of the numerical analysis highlight that the introduction of a waste heat recovery system leads to an increase of at least 16% in the available net power, while a cascade hybrid energy grid can lead to a power enhancement of about 29%, with a considerable increase also in the energetic and exergetic global efficiencies. Full article

This article proposes a heating method based on heat pump technology to address the large amount of low-grade waste heat generated by a certain type of ultra-high voltage direct current (UHVDC) converter valve. Thermal performance calculations for two systems, a basic vapor compression heat pump system (BVCHPS) based on thermal expansion valve throttling and an ejector-enhanced heat pump system (EEHPS) are analyzed. The research results show that the EEHPS exhibits superior COP and exergy efficiency when generating hot water above 80 °C using a heat source below 50 °C. Additionally, mathematical modeling analysis identifies optimal structural parameters such as nozzle throat diameter, throat area ratio, and nozzle outlet diameter for the ejector in its design state. The low-temperature waste heat recovered from the UHVDC converter valves can be further used in engineering applications such as heating, refrigeration, seawater desalination, and sewage treatment. Full article

The global energy crisis, forced by fossil fuel shortages and supply chain disruption, stimulates EU policymakers to find alternative energy replacement. Modifying the present polyisoprene footwear production plant into a hybrid system by combining different energy sources raises energy efficiency. The proposed hybrid system incorporates classical and solar-based technology, resulting in energy optimization by utilizing waste heat recovery. By installing an economizer for feeding water preheating using flue gas recovery, it results in the volume of the flue gases lowering from ${\mathrm{v}}_{{\mathrm{FG}}_{\mathrm{P}}}=1.7969{{ \mathrm{m}}^3}_{\mathrm{FG}}/{\mathrm{kg}}_{\mathrm{P}}$ to ${\mathrm{v}}_{{\mathrm{FG}}_{{\mathrm{ECO}}_{\mathrm{P}}}}=1.597 {{\mathrm{m}}^3}_{\mathrm{FG}}/{\mathrm{kg}}_{\mathrm{P}}$, or by 11.13%, while the flue gases’ temperature is lowered from 204 °C (477.15 K) to 50.99 °C (324.14 K). Further improvement in combining feed water and air preheating results in natural gas savings of 12.05%, while the flue gases’ exhaust temperature is decreased to 30.44 °C (303.59 K). The third option, using condensate heat recovery and feeding water preheating using flue gases, showed natural gas savings as much as 17.41% and exhaust flue gases cooling to 112.49 °C (385.64 K). The combination of condensate heat recovery, combustion air and feed water preheating results in the volume of the flue gases being lowered by 20.42% and natural gas savings by 20.24%, while the flue gases’ temperature is reduced to 45.11 °C (318.26 K). The proposed solar application in polyisoprene production predicts the hybrid system showing fuel savings ranging from 77.96% to 87.08% in comparison to the basic process. The greatest fuel savings of 87.08% is shown in a solarized polyisoprene footwear production plant with combustion air and feed water preheating combined with the condensate return system. Integrating the solar heat into the regular industrial process of polyisoprene production showed great potential and showed environmental sustainability through energy optimization in polyisoprene production. Full article

The disposal of wood waste at facilities for incineration in Sweden is the only applied management practice today. Energy production from biomass has gained attention for its potential to recover energy and reduce greenhouse gas emissions. However, besides being a valuable source for energy generation, wood waste can be effectively recycled into new products. Specifically, recycling wood waste into particleboard is the widely practiced method in Europe, while its benefits have not been explored in the country so far. The objective of this study is to assess the environmental, social, and economic sustainability of producing particleboard and generating energy from wood waste in Sweden. This research investigates four alternative systems for wood waste disposal. The first system involves the production of heat, the second system involves heat and power by wood waste, while the third and the fourth systems, in addition to energy recovery, include partial recycling of wood waste in particleboard production. A life cycle sustainability assessment covering all three pillars (environment, social, and economic) of sustainability was conducted to compare these systems. The results show that adding recycling schemes to incineration in wood waste management practices strengthens the sustainability for all three aspects, and hence, these management methods can be considered as complementary methods rather than competing methods. When all sustainability categories are considered, alternative three (heat recovery and recycling) comes forward as the best option in 11 out of 16 impact categories. Full article

The installation of food waste disposers has been prohibited in South Korea, due to conflicts with governmental policies that are focused on resource recovery from food waste and concerns about potential damage to the city’s sewer system. However, there is a growing demand for such systems in the country. This study proposes a system for the collective recovery of solid resources from food waste tailored for apartment complexes in South Korea, using an innovative solid–liquid separation technology. In the pilot experiment, 49.60% of the solids fed into the system were recovered as solid matter, confirming its practical applicability. Ultimately, a solid resource collective recovery system suitable for the high-rise apartment residence style of South Korea was developed and applied to an actual apartment complex. The final-stage solids were discharged from the system and processed through bio-drying, subsequently exhibiting a combustible material content of 67.06%, higher heating value (HHV) of 4843 kcal/kg, and lower heating value (LHV) of 3759 kcal/kg; moreover, they have the potential to be repurposed as biomass–solid refuse fuel (bio-SFR), compost, feed, and substrate for biogas production. The proposed food waste disposal system not only aligns with governmental policies, but also facilitates the recovery of high-quality resources from food waste, while providing a sustainable waste management solution. Full article

Heat is involved in many processes in the food industry: drying, dissolving, centrifugation, extraction, cleaning, washing, and cooling. Heat generation encompasses nearly all processes. This review first presents two representative case studies in order to identify which processes rely on the major energy consumption and greenhouse gas (GHG) emissions. Energy-saving and decarbonating potential solutions are explored through a thorough review of technologies employed in refrigeration, heat generation, waste heat recovery, and thermal energy storage. Information from industrial plants is collected to show their performance under real conditions. The replacement of high-GWP (global warming potential) refrigerants by natural fluids in the refrigeration sector acts to lower GHG emissions. Being the greatest consumers, the heat generation technologies are compared using the levelized cost of heat (LCOH). This analysis shows that absorption heat transformers and high-temperature heat pumps are the most interesting technologies from the economic and decarbonation points of view, while waste heat recovery technologies present the shortest payback periods. In all sectors, energy efficiency improvements on components, storage technologies, polygeneration systems, the concept of smart industry, and the penetration of renewable energy sources appear as valuable pathways. Full article

This article introduces a novel multiple-cycle generation system for efficient heat recovery at high and low temperatures. The system is modeled and optimized using the M2EP analysis method (mass, energy, exergy, and performance) and the particle swarm optimization algorithm. The multigeneration system produces electricity, cold, domestic hot water, and biogas by utilizing Kalina cycles, diffusion–absorption refrigeration machines, and high-performance heat exchangers by harnessing waste heat from cement kiln exhaust gases. The Kalina cycle is employed for electricity generation, wherein the H₂O+NH₃ mixture, heated by hot water, circulates through heat exchangers. Downstream of the Kalina cycle, the refrigeration machine generates cold by evaporating the strong solution of the H₂O+NH₃ mixture. Hydrogen circulates in the diffusion–absorption refrigerator (DAR) circuit, facilitating the exchange between the evaporator and the absorber. The domestic hot water and biogas production systems operate at lower temperatures (around 45 °C). The simulation results for the Kalina cycle indicate an electrical energy production of 2565.03 kW, with a release of usable energy (residual gases) estimated at 7368.20 kW and a thermal efficiency of 22.15%. Exergy destruction is highest at heat exchanger 1, accounting for 26% of the total. A coefficient of performance of 0.268 and an evaporator temperature of 10.57 °C were obtained for the DAR cycle. The absorber contributes the most to energy exchanges, comprising 37% of the entire circuit. Summarizing the potential for valorizing waste heat from cement kilns, this article lays the foundation for future research. Full article

The objective of this paper was to study the sCO₂ cycle as a waste heat recovery system for a 180 kW biogas engine. The research methodology adopted was numerical simulations through two models built in different programs: Aspen HYSYS and GT Suite. The models were used to optimize the design and thermodynamic parameters of a CO₂ cycle in terms of system power, system efficiency, expander, and compressor efficiency. Depending on the objective function, the sCO₂ cycle could provide additional power ranging from 27.9 to 11.3 kW. Based on the calculation performed, “Recuperated cycle at maximum power” was selected for further investigation. The off-design analysis of the system revealed the optimum operating point. The authors designed the preliminary dimensions of the turbomachinery, i.e., the rotor dimension is 16 mm, which will rotate at 100,000 rpm. Full article