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[en] Highlights: • An effective method is proposed to balance the speed and accuracy of evolution. • Step size adjustment strategies can improve the efficiency of heat recovery in HENS. • The proposed method possesses strong global search ability in optimization process. The major difficulty in the heat exchanger network synthesis (HENS) is dealing with the simultaneous optimization of large-scale continuous and integer variables. Heuristic algorithms are used in HENS due to their efficient global search ability and the step size (ΔL) constitutes one of the critical concepts in it. In this paper, by analyzing the influence of ΔL in Random Walk Algorithm with Compulsive Evolution (RWCE), it was pronounced that evolution speed got faster when ΔL increased in the early stage and evolution accuracy was higher by ΔL declination, in the late stage. Hence, five new different ΔL adjustment functions were proposed. This case-study concluded that ΔL adjustment functions in an upward parabola declination could maintain high speed in the early stage and improve the accuracy of solutions in late stage respectively. However, during the late stage, the minor ΔL led to the decline of the global search ability and it was difficult to jump out of the local minimum. Furthermore certain individuals in the population were randomly given a relatively large ΔL in late stage. Thus, an integrated RWCE algorithm with ΔL adjustment strategy was presented and demonstrated satisfying global and local search ability.
[en] Highlights: • A new Utility Exchanger Network (UEN) synthesis and design procedure is introduced. • UEN design was studied based on Unified and Conventional Total Site Targeting methods. • Calculated heat recovery and utility targets achieved after UEN design for Unified method. • The number of exchangers in the UEN reduced based on the Unified method. Total Site Heat Integration (TSHI) targeting and optimisation methods have been well developed while few studies deal with detailed Utility Exchanger Network (UEN) design. The UEN is the network of heat exchangers that connect a site’s centralised utility system to provide the required process heating and cooling while also facilitating inter-process heat recovery, i.e. TSHI. This paper presents a new UEN design procedure based on the recently developed Unified TSHI targeting method. The Unified method applies more strict constraints on the UEN network, compared to Conventional methods, allowing series utility exchanger matches for a non-isothermal utility if the exchangers in series are from the same process. This constraint reduces the dependency of the individual processes that constitute the Total Site. In UEN design procedure based on the Unified method, calculated utility targets can be archived after UEN design and the number of exchangers reduces compared to the Conventional methods’ design procedure. Also, different Exchanger Minimum Approach Temperature in the UEN synthesis may have an influence on network design and the exchanger configuration but the identical heat recovery and utility targets are achieved after UEN design based on both design procedures.
[en] Highlights: :• A 2D CFD model was built and verified to compute the performance of a steam Ejector • Analyzed performances of a steam ejector with its primary structure parameters • Studied multifactor effects on ejector performance based on orthogonal test method • Verified performances of the optimized ejector under various operating conditions One-dimensional theoretical methods are always utilized for analysis of performances of a steam ejector but they commonly have certain limitations. Numerical simulation and analysis were carried out by means of CFD method to the flow field inside a steam ejector for recovery of waste heat; moreover, the single-factor analysis was performed to see how the ejector was affected by those single-factors such as the diameter of the nozzle outlet, the distance between the nozzle outlet to the inlet of the mixing chamber and diameters of the contraction section of the mixing chamber and the diffuser chamber, respectively, while other conditions are fixed. Multi-factor analysis was then carried out to investigate the performances of the ejector and its structures were optimized by means of the five-factor and four-level orthogonal tests to gain the sensitivity for each factor to performances of the ejector. Results indicate that the optimized ejector has much better performances and the diameter of the nozzle outlet is the most sensitively influencing factor on performances of the ejector. This study may provide a new way of thinking for optimization of structure parameters of any steam ejector and have certain values for design and application of steam ejectors.
[en] An LPE (low-pressure economizer) based waste heat recovery system for a CFPP (coal-fired power plant) is investigated thermodynamically. With the installation of LPE in the flue before the FGD (flue gas desulfurizer), the heat contained in the exhaust flue gas can be recovered effectively and the water consumption can be reduced in the FGD resulted from the temperature dropped flue gas. The impacts on the related apparatuses after installing LPE in a CFPP are analyzed and the internal relationships among correlated parameters are presented. The efficiencies of LPE installed in a CFPP evaluated by the first law, the second law and the thermal equilibrium efficiencies are also compared and analyzed. A detailed case study based on a 350 MW CFPP unit is presented and the variations of the thermal performance after the installation of LPE are investigated. The results show that the second law and the thermal equilibrium efficiencies are increased which can be indicators to evaluate the performance of the LPE system while the first law efficiency is decreased after installing LPE. Results also show that the saving of SCE (standard coal equivalent) is 3.85 g/(kW·h) for this CFPP unit under full load after installing LPE. - Highlights: • An evaluation method of the LPE (low-pressure economizer) system is established. • Impacts on the original thermal system by installing LPE are investigated. • A theoretical guideline is provided to improve the thermal system efficiency by LPE. • A detailed case is presented to demonstrate the energy saving of the LPE system
[en] Highlights: • SVM and BP-ANN is adopted to predict the performance of ORC system. • Different division methods for data set are proposed for comprehensiveness. • SVM-LF and BP-ANN proves to be qualified in performance prediction. • The limitation and prediction characteristic of SVM using RBF is revealed. • A 50 kW ORC experimental system is built to offer experimental data. Low temperature power generation system based on organic Rankine cycle (ORC) has been a popular candidate for low grade heat utilization and recovery. To find a way to predict the performance of the ORC system, the exploration and analyses of the Support Vector Machine (SVM) and Back Propagation Artificial Neural Network (BP-ANN) were carried out. For comparison, both Gauss Radial Basis kernel function (SVM-RBF) and linear function (SVM-LF) have been employed in SVM. Additionally, for the sake of comprehensiveness, two division methods for data set called “random division method” and “blocked division method” were studied. Finally, SVM-LF and BP-ANN demonstrated better stability and higher accuracy for both two division methods and for different testing sets while SVM-RBF showed good results for random division method and disappointing results for blocked division method.
[en] The current tendency in energy domain is to reduce fuel consumption in favor of sustainable energy approaches. In this frame, the present work suggests an efficient way of heat recovery from boilers using concentric tube. The motivation behind the suggested concept is that it could be considered the cheapest, easiest to construct and simplest to use among all the existing heat recovery systems. In other words, the goal is to suggest a technique that could be utilized by a wider range of users regardless their technical level. Another advantage of the proposed concept is that is can be applied even on small scale boilers. With this in mind, a numerical tool is also developed allowing to make pre-studies to optimize the geometric parameters such as diameters and length, as well as to perform post-studies that allows to optimize operational parameters such as flow rates and fluids configurations. Furthermore, an experimental study is carried-out to validate the numerical results of the adopted heat exchanger. It was shown that water can be heated up to 100 °C depending on the flow rate and that the recovered heat increases through a rational function.
[en] Highlights: • A simulation model is proposed to investigate the HDH evaporation system performance. • The effects of the operational parameters on the evaporation capacity and specific steam consumption (SSC) are discussed. • An optimization program for minimum SSC was developed. • A pilot HDH evaporation system was built, and the experimental results are consistent with the theoretical results. In this paper, a theoretical and experimental investigation on HDH evaporation system performance was performed. A fixed size HDH system was constructed, and for the purpose to obtain the optimal operating parameters, a mathematical model was proposed to investigate the effect of the operating parameters on the evaporation rate and specific steam consumption (SSC). The evaporation rate is proportional to three operating parameters. SSC decrease with the increase of heat recovery ratio (HRR) in regenerator. Moreover, the operating parameters of the system were optimized to obtain minimum SSC using the GlobalSearch algorithm. The minimum SSC is 0.338–0.398 kg per kg of evaporated water at different evaporation capacities. And the value of minimum SSC increases with an increase in the evaporation limit. Furthermore, the experimental results were compared with the optimized results, and they are in good agreement. Considering both the evaporation rate and SSC, the recommended operating parameters are: mg = 502.53 kg/h, ml = 3556.93 kg/h, Tlie = 83.59 °C.
[en] Oil and gas platforms in the North Sea region are associated with high power consumption and large CO2-emissions, as the processing and utility plants suffer from significant changes in production rates and performance losses over the field lifespan. In this paper, a generic model of the overall offshore system is described: its thermodynamic performance is assessed by performing an exergy accounting and rules of thumb for oil and gas platforms are derived. Simulations are built and conducted with the tools Aspen Plus®, Dynamic Network Analysis and Aspen HYSYS®. 62–65% of the total exergy destruction of an offshore platform is attributable to the power generation and waste heat recovery system, and 35–38% to the oil and gas processing. The variability of the feed composition has little effect on the split of the thermodynamic irreversibilities between both plants. The rejection of high-temperature gases from the utility and flaring systems is the major contributor to the exergy losses. These findings suggest to focus efforts on a better use of the waste heat contained in the exhaust gases and on the ways in which the gas compression performance can be improved. - Highlights: • North Sea oil and gas platforms are investigated and a generic model is developed. • Exergy analysis of these offshore facilities is performed. • Most of the total exergy destruction is attributable to the utility systems producing the electrical power required onsite. • Rejection of the exhaust gases from the utility systems is the major exergy loss of this system. • The highest thermodynamic performance is reached with low well-fluid content of water and gas
[en] Low-grade waste heat source accounts for a large part of the total industrial waste heat, which cannot be efficiently recovered. The ORC (Organic Rankine Cycle) system has been proved to be a promising solution for the utilization of low-grade heat sources. It is evident that there might be several waste heat sources distributing in different temperature levels in one industry unit, and the entire recovery system will be extremely large and complex if the different heat sources are utilized one by one through several independent ORC subsystems. This paper aims to design and optimize a comprehensive ORC system to recover multi-strand waste heat sources in Shijiazhuang Refining and Chemical Company in China, involving defining suitable working fluids and operating parameters. Thermal performance is a first priority criterion for the system, and system simplicity, technological feasibility and economic factors are considered during optimization. Four schemes of the recovery system are presented in continuous optimization progress. By comparison, the scheme of dual integrated subsystems with R141B as a working fluid is optimal. Further analysis is implemented from the view of economic factors and off-design conditions. The analytical method and optimization progress presented can be widely applied in similar multi-strand waste heat sources recovery. - Highlights: • This paper focuses on the recovery of multi-strand waste heat sources. • ORC technology is used as a promising solution for the recovery. • Thermal performance, system simplicity and economic factors are considered