Waste Heat Usage Research Articles

Covering District Heating Demand with Waste Heat from Data Centres

Currently, the huge potential of data centre waste heat for the decarbonization of the heating sector is often ignored. Here, a feasibility study is presented for covering the heat demand of two districts of Frankfurt (Germany) mainly by data centre waste heat. Contrary to many existing projects, the waste heat shall supply existing buildings, the total heat demand is very high (144 GWh/a) and it should be covered almost exclusively by waste heat usage. In this study, the potential and demand are estimated, a heating supply concept is presented and evaluated regarding costs, heat pump capacity, and storage size. As a result, the utilisation of data centre waste heat is not only possible, but it’s the most promising way for decarbonizing the heating sector in this area. With high-capacity heat pumps (37 MWth), gas boilers (20 MWth) and a storage for daily peaks, 97.5 % of the heat demand can be covered by waste heat usage. It is economically favourable compared to decentralized heat pumps for all types of buildings and with the proposed concept, CO2-emissions in the network area are reduced by 78 % on average. Laws to oblige the waste heat usage of data centres are recommended.

Machine learning and multilayer perceptron enhanced CFD approach for improving design on latent heat storage tank

Solid-liquid phase change heat storage is an important method to solve the mismatch of the generation and usage of waste heat, which is conducive to decarbonization and energy conservation. However, there always exists inhomogeneity for the melting and temperature of the phase change material (PCM) in solid–liquid phase change heat storage. Changing the shape of the heat storage tank will change the distance of heat transfer to the phase change material, thus changing the heat storage performance. Therefore, this paper designed ten shapes of trapezoidal tank with different proportions of upper and lower radius. And the heat storage performance of ten cases were investigated through the designed numerical model, whose accuracy is convinced through comparison with experimental results. Many indexes are proposed to evaluate the properties of the latent heat thermal energy storage (LHTES) from the view of whole region, uniformity among subregions, and the storage heat performance of integrity. Except for drawing mass fraction, temperature, and streamline contours, the temperature proportion and the average velocity are proposed to quantitatively evaluate the temperature distribution and convection intensity. The results showed that the cases with larger upper radius are shorter than cases with larger lower radius. In addition, the shortest melting time is 17210 s, which is about 39.2% shorter by 11080 s than that of basic case. The evaluation from the view of uniformity also indicated that properly increasing the PCM amount is beneficial for improving the melting uniformity. The most uniform temperature and mass fraction are case 5 and case 4, respectively, with 12.92% and 38.28% improvement. Finally, one multilayer perceptron (MLP) network model is built to predict the melting fraction and total heat storage. After training, one model with a deviation lower than 10% between simulation and prediction is set up.

A novel bi-evaporator cooling system via integration of absorption refrigeration cycle for waste energy recovery from an ejector-expansion trans-critical CO2 (EETRCC) cycle: Proposal and optimization with environmental considerations

In this paper an integrated refrigeration system is designed, in which the waste heat from an ejector-expansion trans-critical CO2 (EETRCC) cooling scheme is used for the generation of cooling not only above but also below the temperature of zero degrees Celsius. Waste heat usage was accomplished via employment of an absorption refrigeration system in conjunction with a CO2trans-critical refrigeration cycle. The absorption refrigeration cycle generates excess cooling above zero temperature utilizing the waste heat from ejector expansion system. Appropriate thermodynamic models are employed for feasibility assessment of integrated refrigeneration system, along with economic considerations to estimate produced cooling price. The results revealed significant better performance of novel integrated framework compared to standalone EETRCC cycle. In the best-case scenario, the levelized cost of cooling for the former is obtained as 105.3 $/GJ and, while the latter produces cooling with a levelized cost of 120.9 $/GJ. Also, it has been concluded that, when the temperature of the second evaporator is raised, the exergy efficiency of the system drops by 3 %, which results in increment of unit cost of the cooling by 6.34 %. In addition, highest exergy destructions are found to be 27.53 kW in the gas cooler and 15.57 kW in the generator.

Feasibility and performance analysis of a novel air separation unit with energy storage and air recovery

The high-purity air output by expansion during energy release is discharged into the ambient for liquid air energy storage (LAES) technology, resulting in a large loss of material resources. Currently, LAES research focuses mostly on enhancing thermally driven power generation while disregarding the use of its discharging air. To address this issue, we proposed a novel air separation unit (ASU) with energy storage and air recovery (ASU-ESAR) based on the matching characteristics of air separation and LAES technologies in refrigeration temperature and material utilization. Except for storing liquid air on large-scale by employing ASU and directly recovering cold energy of liquid air, ASU-ESAR has the benefit and novelty of fully recycling high-purity air outputted during energy release, as well as its low temperature and high pressure energy, into ASU. Its process design and feasibility studies are carried out. Energy conservation efficiency, economic benefits, and its influences on China's power grid and emission reductions are assessed. Without any waste heat usage, an electrical round-trip efficiency of 55.82%–58.72% is presented. Taking Shanghai, China as an example, ASU-ESAR's electricity costs are reduced by 5.77%–7.65% when compared to conventional ASU, and the payback period for LAES system with a power capacity of 70.70–74.38 MWh/day is 2.2–2.9 years. The average peak-valley ratio (PVR) of China's power grid might fall by 13% once ASU-ESAR is implemented across the industry, and the yearly CO2 emissions could be reduced by 12.53-27.71 Mt. Its application can achieve a win-win situation of electricity cost savings in ASU operations as well as energy savings and emission reductions on the power generation side.

Life Cycle Assessment of Direct Air Carbon Capture and Storage with Low-Carbon Energy Sources.

Direct air carbon capture and storage (DACCS) is an emerging carbon dioxide removal technology, which has the potential to remove large amounts of CO2 from the atmosphere. We present a comprehensive life cycle assessment of different DACCS systems with low-carbon electricity and heat sources required for the CO2 capture process, both stand-alone and grid-connected system configurations. The results demonstrate negative greenhouse gas (GHG) emissions for all eight selected locations and five system layouts, with the highest GHG removal potential in countries with low-carbon electricity supply and waste heat usage (up to 97%). Autonomous system layouts prove to be a promising alternative, with a GHG removal efficiency of 79-91%, at locations with high solar irradiation to avoid the consumption of fossil fuel-based grid electricity and heat. The analysis of environmental burdens other than GHG emissions shows some trade-offs associated with CO2 removal, especially land transformation for system layouts with photovoltaics (PV) electricity supply. The sensitivity analysis reveals the importance of selecting appropriate locations for grid-coupled system layouts since the deployment of DACCS at geographic locations with CO2-intensive grid electricity mixes leads to net GHG emissions instead of GHG removal today.

Concept for Realizing High Output Power Density Thermionic Energy Convertor by Field-Assisted Thermionic Emission Using a Direct-Tunneling Metal–Insulator–Graphene Cathode

The usage of waste heat is an effective way to satisfy the great demand for energy in modern human society. A thermionic energy convertor (TEC) can directly produce electricity from thermal energy with high efficiency. However, high working temperature is one of the major challenges in TEC. In this work, a concept based on field-assisted thermionic emission (FTE) has been proposed to solve this problem. Basically, the field-assisted thermionic energy convertor (FTEC) uses a metal-insulator-graphene (MIG) structure as the cathode to produce direct-tunneling FTE current for the conversion. The fundamental performance of FTEC has been theoretically studied. The penetration field within the MIG structure that controls both the FTE current and the hot electron energy is the key for the performance optimization. By engineering the MIG cathode band structure to balance the above mentioned effects of the penetration field, the ideal efficiency of ~10% and the corresponding output power density of ~5 W/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> can be obtained simultaneously under 700 K. Further comparison between FTEC and conventional TEC indicates that the output power density can be improved by at least four orders of magnitude under a mild temperature (600-700 K). These results provide a universal approach for realizing compact high output power density TEC and its combined system.

Evaluation of the industrial waste heat potential for its recovery and integration into a fourth generation district heating system

The transition towards 4th generation district heating systems are widely studied in last years. In this research, the economic reasonability of recovered industrial waste heat usage in the district heating system is investigated. Research is based on a case situation with an actual district heating system and nearby located factory with possible waste heat. This article contains a description and characteristics of selected district heating system and potential waste heat source, the overall methodology for the thermal energy potential and recovery calculations of waste heat flow. Taking into account losses in transmission, 67.5 MWh of heat can be transferred to the heat supply network every month, covering 4–12 % of the system load during the heating season. This would reduce the CO2 emissions from the heating system by 5–10 % monthly.

Novel technological solutions for eco-protective water supply by economical and sustainable seawater desalination

Development of novel and economical technological solutions for enviro-sensitive seawater desalination enabling the abolishment of marine ecosystem deteriorations due to brine discharges has a vital and indispensable importance for sustainable water supply worldwide. The encouragement of environmental decision policies that focus on reducing energy footprints by novel water and wastewater treatment plants is also prioritized as a very prominent reality for their widespread acceptability and realization in new age. In this respect, eleven innovative systems differentiated into two main groups, namely with and without brine discharge, were developed for exposing their techno-economical sustainability capabilities in enviro-protective seawater desalination. Depending on experimental performances, the systems arranged with different configurations of membrane distillation and forward osmosis at three heat recovery choices for natural gas or waste heat usage were individually simulated in real scale. The field simulations revealed that a more economical seawater desalination was provided by waste heat than that by RO, MD, and MED regardless of carbon tax liability. Zero brine discharge was assured using external fresh water with no additional cost at 31% loss per drinking water. This study finally claims that the developed systems can be successfully and cost-effectively implemented for eco-protective water supply from seawater in semi-arid, sub-tropical, temperate, and weak-temperate countries.

The Potential of a Cascaded TEG System for Waste Heat Usage in Railway Vehicles

This work focuses on the conceptual design and optimization of a near series prototype of a high-power thermoelectric generator system (TEG system) for diesel-electric locomotives. The replacement of the silencer in the exhaust line enables integration with already existing vehicles. However, compliance with the technical and legal frameworks and the assembly space requirements is just as important as the limited exhaust back pressure, the high power density and the low life cycle costs. A special emphasis is given to the comparison of cascaded two-stage Bi2Te3 and Mg2Si0.4Sn0.6/MnSi1.81 modules with single-stage Bi2Te3 modules, both manufactured in lead-frame technology. In addition to the numerous, partly competing boundary conditions for the use in rail vehicles, the additional degree of freedom from the cascaded thermoelectric modules (TEM) is considered. The problem is investigated by coupling one-dimensional multi-domain simulations with an optimization framework using a genetic algorithm. The achievable electrical power of the single-stage system is significantly higher, at 3.2 kW, than the performance of the two-stage system (2.5 kW). Although the efficiency of the two-stage system is 44.2% higher than the single-stage system, the overall power output is 22.8% lower. This is because the lower power density and the lower number of TEM more than compensates the better efficiency. Hence, the available installation space, and thus the power density, is a critical constraint for the design of TEG systems. Furthermore, for applications recovering exhaust gas enthalpy, the large temperature drop across the heat exchanger is characteristic and must be considered carefully within the design process.

Selection of cooling fluid for an organic Rankine cycle unit recovering heat on a container ship sailing in the Arctic region

As Arctic sea ice coverage declines it is expected that marine traffic could increase in this northern region due to shorter routes. Navigating in the Arctic offers opportunities and challenges for waste heat recovery systems (WHRS). Lower temperatures require larger heating power on board, hence a larger demand for waste heat usage, to cover services and maintaining on board spaces temperatures. However, a lower heat rejection temperature increases the WHRS thermal efficiency. The air temperature for the Arctic route selected is colder than that of the seawater, opening the opportunity of having air as coolant. This paper explores the use of two different coolants, air and seawater, for an organic Rankine cycle (ORC) unit using the available waste heat in the scavenge air system of a container ship navigating in Arctic Circle. Using a two-step single objective optimisation process, detailed models of air and seawater heat exchangers are evaluated as the WHRS condensers. The results suggest that an ORC unit using R1233zd(E) as its working fluid coupled with seawater as its coolant is the preferable option to reduce CO2 emissions. Using the ambient air as the coolant while a less effective option could be cheaper to install.

Interpreting regional and local diversities of the social acceptance of agricultural AD plants in the rural space of the Moravian-Silesian Region (Czech Republic)

Agricultural anaerobic digestion plants have recently become a typical part of rural landscape in the Czech Republic due to massive governmental subvention programmes. Yet, their potential as an effective tool how to response to global climate changes at a local level is rather underused (maize used as a primary input mainly, usage of waste heat is limited, etc.). This situation is caused by misguided subvention policies. The aim of this contribution is first to analyse the agricultural anaerobic digestion plants in the rural space of the Moravian-Silesian Region, and second, to deepen the knowledge on the perception of the digestion plants among the population of municipalities in which such facility was constructed. A questionnaire survey has been carried out in three model municipalities (n = 369) located in the Moravian-Silesian Region. Several recommendations and notes for public administration and potential investors concerning the location of future anaerobic digestion plants projects and settings of supportive programmes have been defined.

Investigation and Prognosis of Waste Heat Occurrence during the Extrusion Process of Tubular Profiles

Extrusion is a fundamental procedure of polymer processing and is used to produce tubular profiles, foils, cable coatings, etc. Rising energy prices increase the pressure for extruder manufacturers and operators to cut costs. Nowadays, extruder manufacturers are forced to develop more energy-efficient extruders. One possibility to reach that goal is to reuse the occurring waste heat during the extrusion process. Operators could use the waste heat within their own company to reduce their primary energy costs. The prediction of energy consumption and usage of waste heat for new extrusion lines as well as existing extrusion lines with new products within the planning stage is very important. Additionally the energy recovery for new extrusion lines has to be projected within planning stage. The research approach is to enable the construction of energy recovery for future production based on theoretical view and the energy monitoring of real extrusion lines. Therefor a program was developed to forecast the amount of waste heat. The energy monitoring included the energy consumption of the main consumers and the waste heat amount of cooling chambers and barrel cooling for three different single grooved barrel extruders. The energy monitoring results show that some of the temperature of the cooling chambers qualifies for reutilization. The barrel cooling waste heat can be fully reused. The program calculates the cooling of the tubular profile with finite element difference wherein the heat transfer is calculated in the radial direction. The thermal state of the tubular profile can be simulated at every position within the extrusion line. Furthermore the thermal output into the coolant can be calculated. The calculated and collected data are satisfactory more often than not. Based on the energy monitoring results concepts for the usage of waste heat were elaborated. Thereupon measures for the usage of waste heat were implemented and validated.

Energy efficiency for industries through synergies with urban areas

Generally waste heat, waste water and waste streams are available as industrial energy resources in industrial plants and their roof areas for solar energy use. In Austria, until now, only waste heat has been used in small parts for heat supply of towns. The application of waste heat has so far been largely taken for internal heat recovery only. A holistic approach considering all available energy resources by the industry in synergetic connection with the surrounding urban areas is yet to feature. Only a few projects in terms of waste heat usage for district heating have been implemented. At international level, the utilization of industrial energy has also hardly been considered in a synergistic combination with the municipal authorities. Numerous legal requirements (Directive for Integrated Pollution Prevention and Control, law for energy efficiency) determine conditions for industrial companies in terms of their environmental performance and energy savings etc. To a large extent, the production processes are already optimized due to the application of quality management systems and other tools. With the help of other energy efficiency methods it is hardly possible to achieve the required energy efficiency savings without influencing the production process. Therefore, the energetic linking of industrial companies and urban areas through the usage of industrial energy, to cover the energy demand of the towns offers an energy efficiency measure for industries without biasing their economic behaviour. Additionally, this approach represents an opportunity for energy enhancing independency of specific regions. The potentials for synergies were examined based on four project regions in Austria with a population between 7000 and 12,000 inhabitants and a more or less strong penetration of industrial companies. It was found that in total, up to 35% of the total energy demand of the surveyed towns could be covered. This means also a saving of the primary energy demand for the towns in the same extent. For electricity, coverage of up to 46%, and for heat, coverage of up to 32%, are possible. That means that nearly no oversupply of the towns occurs and all accumulating industrial energy can be taken by the towns. The recovery and exploitation of the so far unemployed industrial energy leads to a significant increase of efficiency for the industrial companies.

Cleaner energy for cleaner production: modelling, simulation, optimisation and waste management

Energy supply and its efficient use in production are key to ensuring the healthy functioning of the world economies. Based on that, to ensure sustainability, the supply and use of energy have to apply the principle of minimising negative environmental impacts and even improving the environment through net-regenerative development. In this context, ensuring cleaner energy is the cornerstone for cleaner production, especially for reducing the emissions of greenhouse gases and other pollutants, which are directly related to the types and loads of the energy sources used. This introductory article presents a review of the main lessons recently learned in the area of more efficient energy use, cleaner fuels and biofuels, cleaner production, CO2 capture, optimisation and waste management. This article provides the readers with ideas and technologies that can be incorporated into real world solutions and can serve as the foundations for future research. With firm realisation of the importance of these issues, the 17th conference “Process Integration, Modelling and Optimisation for Energy Saving and Pollution Reduction – PRES” was held in Prague, Czech Republic, to provide a platform for discussing ideas and devising solutions for cleaner energy supplies that are used more effectively and efficiently. This was followed by comprehensive research that resulted in several high quality scientific contributions published in the Journal of Cleaner Production. The wide topical coverage and the high quality provided excellent directions for future collaborative research of the PRES family – including process level emission minimisation, self-sufficient regions, and industrial symbiosis for optimizing usage of waste heat and waste material flows.

Hierarchical prioritization of innovative treatment systems for sustainable dairy wastewater management

Multiple criteria decision making is an effective approach that can be successfully used for revealing eco-innovative solutions in industrial wastewater treatment by prioritizing various promising technologies. Besides, eligible researches on emerging membrane processes viz., forward osmosis and membrane distillation are gaining widespread interest in scientific communities focused on reclamation, recovery and reuse of industrial wastewaters. In this study, the preferability of four innovative systems compared to a traditional system was hierarchically prioritized for environmentally benign treatment and utilization of dairy industry wastewater using the most common tool in multi-criteria decision making analysis, analytical hierarchy process. The analyses were attributed to the preferences classified with regard to the technical, economic and environmental aspects of the alternatives. Despite the existence of both greatest importance of energy consumption and higher energy requirements of novel solutions, major prominent features to be provided by real-scale applications of innovative systems were determined as more valuable multiple outcomes in environmental protection and economic profit. The sensitivity analysis to evaluate how the variations in the predefined weights of attributes influence the preference priorities indicated that the decision prioritization analysis on the novel technology selection was sufficiently sensitive to all the main evaluation criteria. This study proved that novel membrane technologies have more preferable features in dairy wastewater treatment by further whey utilization and waste minimization and more effective industrial water reuse, especially in case of waste heat usage in membrane distillation. Finally, sustainable dairy wastewater management in a more desirable manner than now could be accomplished by means of technically highly efficient, economically cost-effective and environmentally eco-innovative achievements.

The relationship among CPU utilization, temperature, and thermal power for waste heat utilization

This work addresses significant datacenter issues of growth in numbers of computer servers and subsequent electricity expenditure by proposing, analyzing and testing a unique idea of recycling the highest quality waste heat generated by datacenter servers. The aim was to provide a renewable and sustainable energy source for use in cooling the datacenter. The work incorporates novel approaches in waste heat usage, graphing CPU temperature, power and utilization simultaneously, and a mineral oil experimental design and implementation.The work presented investigates and illustrates the quantity and quality of heat that can be captured from a variably tasked liquid-cooled microprocessor on a datacenter server blade. It undertakes a radical approach using mineral oil. The trials examine the feasibility of using the thermal energy from a CPU to drive a cooling process. Results indicate that 123 servers encapsulated in mineral oil can power a 10-ton chiller with a design point of 50.2kWth.Compared with water-cooling experiments, the mineral oil experiment mitigated the temperature drop between the heat source and discharge line by up to 81%. In addition, due to this reduction in temperature drop, the heat quality in the oil discharge line was up to 12.3°C higher on average than for water-cooled experiments. Furthermore, mineral oil cooling holds the potential to eliminate the 50% cooling expenditure which initially motivated this project.

Development and Optimization of a TEG-system for the Waste Heat Usage in Railway Vehicles

The fuel consumption of diesel electric locomotives is the crucial factor for the vehicle's life cycle costs (LCC) and its CO2 emissions. Assuming that most components in railway vehicles are technically quite mature, innovative solutions like thermoelectric generators (TEG) need to be considered. This work shows the development and optimization of high power TEG for diesel electric locomotives, complying with the challenges of low LCC, high power density and sufficient thermo-mechanical stability. Therefore, a flexible and double-sided bondable Bi2Te3 based module is introduced and optimized with regard to the power density and mechanical strength. The module is virtually integrated into a waste heat exchanger which is also geometrically optimized to achieve a high power output without exceeding a maximum exhaust gas back pressure. The introduced optimization process finds a mechanical durable module with increased power density for the particular application, although the results of the TEG analysis show, that the system efficiency is still low but increasable by certain changes in the system design.

The pulse tube engine: A numerical and experimental approach on its design, performance, and operating conditions

The pulse tube engine is a simple heat engine based on the pulse tube process. Due to its simplicity it has a high potential to be applicable in waste heat usage and energy harvesting purposes. In this work, mathematical and experimental design tools are developed to study a pressurized laboratory scale pulse tube engine. The mathematical model is based on the transient numerical solution of the governing differential equations for mass, momentum and energy. The Modelica environment of SimulationX is used to solve the equations numerically and the model is employed to design the experimental test engine with helium as working fluid. The transient behavior of the pulse tube engine's underlying thermodynamic properties is studied numerically and experimentally under different design parameters as well as for different heat input temperatures, filling pressures and operating frequencies. The measured engine characteristics are compared with the calculated predictions. Internal and external power losses are quantified. Design studies for a further development of the pulse tube engine are performed experimentally. The developed numerical tool provides a rational framework for up-scaling the current laboratory model to industrial scale.

Theoretical and Experimental Investigations of the Pulse Tube Engine

The pulse tube engine is a simple prime mover based on the pulse tube process. It has high potential to be applicable in waste heat usage. In the present work a simulation model is used to design a pressurized experimental pulse tube engine employing helium as working fluid. The measured engine characteristics are compared with the calculated predictions. Using the model and the experimental test rig, the engine performance is studied for different heat input temperatures, filling pressures, and operating frequencies. The energy conversion process, based on a broken thermodynamic symmetry and a thermal lag occurring in the pulse tube, is proven theoretically. Fundamental characteristics and application limitations of the pulse tube engine are disclosed experimentally. The obtained engine behavior provides suggestions for its further development.

Power generation from waste heat in a food processing application

In this paper, the potential of recovering waste heat from the fryer section and exhaust stream sent to the stack of a typical potato crisps or chips manufacturing plant and using the heat to drive an Organic Rankine Cycle (ORC) system for power generation has been presented. Five different ORC system Options (A, B, C, D and E) were considered. The first two options (A and B) make use of the waste heat from the foul gas and exhaust to stack respectively for power generation using a single ORC system each while the third option (option C) makes use of a novel dual heat source single ORC system where the low temperature waste heat from the foul gas is used to provide preheating and the high temperature waste from the exhaust to the stack used to provide the evaporation. Option D also shows a dual heat source ORC system where the high temperature waste heat to the exhaust stack is used to provide the preheating while the lower temperature foul gas is used for the evaporation (reverse of option C in terms of waste heat usage) while option E makes use of a reheat cycle where the waste heat from the foul gas is used to provide the reheating of the working fluid exiting the turbine. In terms of waste heat usage, the combination of options A and B can be compared with options C, D and E. The simulation result shows that in terms of net power generation, cooling water requirement, and working fluid (R245fa) requirement, the combination of Options A and B gives the best power generation result and this is similar as the result produced by Option C. Following option C is option E which gave a better result than option D. The entropy generation analysis showed that the entropy generation is inversely proportional to the power output. It was also observed that the net power generation for the ORC configuration adopted in this paper (option C) meets the average daily power requirement of the crisps manufacturing process as well as 98.58% of the daily peak power requirement. ► We model and optimised different ORC configurations for power generation from waste heat in crisps manufacturing plant. ► We carried out second law analysis of the different configurations. ► We selected the configuration which will be most economical for power generation from waste heat in crisps manufacturing plant.