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- ItemIndustrial waste heat utilization in the European Union—An engineering-centric review(MDPI, 2024-04-27) Turek, Vojtěch; Kilkovský, Bohuslav; Daxner, Ján; Babička Fialová, Dominika; Jegla, ZdeněkEfficient utilization of waste heat from industrial processes can be a significant source of energy savings for production plants as well as the driver of sustainable operation and emissions abatement. Industrial waste heat usually is contained in liquid or gaseous outlet streams. Alt-hough the possible ways to utilize waste heat are discussed by a wide variety of papers, these either provide only a general overview of utilization options and opportunities or focus on a narrow range of industrial processes. The aim of the present paper is to discuss practical aspects of waste heat utilization in the European Union so that the reader gains perspective on (i) thermal classification of waste heat, (ii) liquid and gaseous waste streams and their temperatures typical for industrial use cases, (iii) technical, economic, physical, and environmental aspects barring full utilization of the contained heat, (iv) waste heat sources in various industries, and (v) standard-ized equipment and technologies applicable to industrial waste heat utilization, including their advantages, disadvantages and weak points.
- ItemMachine Learning Method for Changepoint Detection in Short Time Series Data(MDPI, 2023-10-05) Smejkalová, Veronika; Šomplák, Radovan; Rosecký, Martin; Šramková, KristínaAnalysis of data is crucial in waste management to improve effective planning from both short- and long-term perspectives. Real-world data often presents anomalies, but in the waste management sector, anomaly detection is seldom performed. The main goal and contribution of this paper is a proposal of a complex machine learning framework for changepoint detection in a large number of short time series from waste management. In such a case, it is not possible to use only an expert-based approach due to the time-consuming nature of this process and subjectivity. The proposed framework consists of two steps: (1) outlier detection via outlier test for trend-adjusted data, and (2) changepoints are identified via comparison of linear model parameters. In order to use the proposed method, it is necessary to have a sufficient number of experts’ assessments of the presence of anomalies in time series. The proposed framework is demonstrated on waste management data from the Czech Republic. It is observed that certain waste categories in specific regions frequently exhibit changepoints. On the micro-regional level, approximately 31.1% of time series contain at least one outlier and 16.4% exhibit changepoints. Certain groups of waste are more prone to the occurrence of anomalies. The results indicate that even in the case of aggregated data, anomalies are not rare, and their presence should always be checked.
- ItemIndirect Convective Solar Drying Process of Pineapples as Part of Circular Economy Strategy(MDPI AG, 2019-07-24) Azouma, Yaovi Ouézou; Drigalski, Lynn; Jegla, Zdeněk; Reppich, Marcus; Turek, Vojtěch; Weiß, MaximilianThis study investigates the industrial-scale application of a simple convective solar drying process of pineapples as part of a circular economy strategy for developing countries. A renewable energy concept is presented, which follows the circular economy aims by effectively employing a simple system for biogas production and a two-stage drying system. Both these systems meet the requirements for implementation in the specific conditions of developing countries, of which Togo, where pineapple is a major crop, is taken as an example. With respect to earlier findings available in the literature, the paper focuses on the solar drying process, which is critical to the proposed strategy. A portable solar dryer working in indirect heating mode was built and later also modified to enhance its performance. Three main factors influencing the convective drying process, namely, drying time (270 min, 480 min), solar radiation intensity (650 W/m2, 1100 W/m2), and slice thickness (6–8 mm, 12–14 mm), were considered. The statistical Design of Experiments (DOE) method was applied to reduce the number and scope of experiments. In the best case, the moisture content was reduced from 87.3 wt % in fresh samples to 29.4 wt % in dried samples, which did not meet the quality requirements for dried fruit. An additional conventional post-solar drying procedure would, therefore, still be necessary. Nonetheless, the results show that in the case of pineapple drying the consumption of fossil fuels can be decreased significantly if convective solar pre-drying is employed.
- ItemThe energy performance of vacuum evaporators for liquid digestate treatment in biogas plants(PERGAMON-ELSEVIER SCIENCE LTD, 2018-03-01) Vondra, Marek; Máša, Vítězslav; Bobák, PetrVacuum evaporation is an efficient method for reducing the volume of liquid digestate (LD) from biogas plants (BGP). Furthermore, thickening LD in BGP contributes to the efficient utilization of waste heat and also reduces fossil fuel consumption that is needed for transporting LD. However, the utilization of vacuum evaporation must be reasonable, and a comprehensive study should precede the integration of evaporation technology in a particular BGP. For this purpose, this study compares selected parameters of three types of industrial evaporators which may be suitable for LD thickening. Furthermore, this study provides a mathematical model that describes the mass and energy balances of the chosen evaporators and is able to evaluate their energy performance for a given set of input variables. It was concluded that the forced-circulation evaporator has the highest energy requirements and also requires a high cooling performance. This type of evaporator will be interesting for the plant owners only if the cost of power generation is extremely low. In terms of consumption of energy and cooling duty, the multi-stage flash evaporator is the most efficient and it also requires the least heat transfer area. The falling-film evaporator provides only slightly worse performance.
- ItemAnalysis of Fired Equipment within the Framework of Low-Cost Modelling Systems(MDPI AG, 2019-02-07) Babička Fialová, Dominika; Jegla, ZdeněkFired equipment suffers from local overloading and fouling of heat transfer surfaces, products are not of the required quality, and operating costs are increased due to the high pressure drop of process fluids. Such operational issues are affected by the non-uniform distribution of fluid flow and heat flux variability. Detailed numerical analyses are often applied to troubleshoot these problems. However, is this common practice effective? Is it not better to prevent problems from occurring by using quality equipment design? It is, according to the general consensus. Still, the experience of designing fired apparatuses reveals that the established standards do not reflect the real maldistribution sufficiently. In addition, as found from the given overview of modelling approaches, the radiant chamber and the convection section are usually analysed separately without significant continuity. A comprehensive framework is hence introduced. The proposed procedure clearly defines the interconnection of traditional thermal-hydraulic calculations and low-cost modelling systems for radiant and convection sections. A suitable combination of simplified methods allows for the reliable design of complex equipment and fast identification of problematic areas. The utilisation of selected low-cost models, i.e., the second phase of the systematic framework, is presented regarding the example of a steam boiler.