Recent developments in applied thermal engineering: Process integration, heat exchangers, enhanced heat transfer, solar thermal energy, combustion and high temperature processes and thermal process modelling

Applied Thermal Engineering 105 (2016) 755–762

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Applied Thermal Engineering journal homepage: www.elsevier.com/locate/apthermeng

Editorial

Recent developments in applied thermal engineering: Process integration, heat exchangers, enhanced heat transfer, solar thermal energy, combustion and high temperature processes and thermal process modelling a r t i c l e

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a b s t r a c t Energy supply and its efficient use are key to ensuring energy security and the health of the economies. The engineering of thermal and related processes for supply, recovery and use of heat and power plays an important role in achieving this. In this context, energy recovery and minimising energy waste are the cornerstones for achieving the broader objectives, especially accounting for the overwhelming share of energy losses in the chain from sourcing, through conversion steps and final use, that could reach over 60%. This article presents a review of the main lessons recently learned in the area of more efficient energy use and energy saving. It provides the readers with ideas and methods that can be incorporated into real world solutions and can serve as the foundations for future research. Many of these results are based on the outcomes and follow up articles resulting from the 18th conference ‘‘Process Integration, Modelling and Optimisation for Energy Saving and Pollution Reduction – PRES’15” that was held in Kuching – the state of Sarawak – Malaysia. This can serve as a platform for discussing further ideas and devising solutions for cleaner energy supply and use. The wide topical coverage and the high quality of the contributions are expected to provide incentives and directions for future collaborative research of the PRES family – including process level emission minimisation, self-sufficient regions, and industrial symbiosis for optimising usage of waste heat and waste material flows. Ó 2016 Published by Elsevier Ltd.

1. Introduction Energy saving and pollution reduction can be improved by Process Integration as shown by Linnhoff et al. [1] at the end of the previous century and as later being extended by Smith [2]. More recent developments have been presented in 2013 [3] incorporating process intensification, further providing a comprehensive text in 2014 [4]. From the thermodynamic point of view, the energy consumption of a system can be reduced by improving the reversibility of the system, which can be realised by reducing the overall driving force. For example, while carrying out Heat Integration for a chemical plant, the utility consumption can be reduced by decreasing the overall driving force of the system, represented by the Minimum Allowed Temperature Difference (DTmin) values. However, when the driving force in the overall system is reduced, the equipment size increases. In parallel, in the course of decreasing the driving force, some equipment might become the ‘‘bottleneck” of the system, limiting further energy saving. The bottleneck can be eliminated by amending the topology to achieve equipment intensification, which determines the overall driving force. Consequently, the total cost of an energy system can be optimised by taking into account the trade-offs between the decrease http://dx.doi.org/10.1016/j.applthermaleng.2016.06.183 1359-4311/Ó 2016 Published by Elsevier Ltd.

of the driving force and the increase of the equipment size. In Process Integration and Intensification, engineers should also develop suitable mathematical models to support the need for advanced computation when solving practical problems. Besides the discussed issues, added by Leo to connect the discussion above and below. Fields of engineering related to energy supply and use face challenges previously not met. This is because of several trends in the World Economy which have recently combined:  Continuing rise of the worldwide energy use.  The current decrease in the nominal prices of the main fossil fuel sources and the still fragile recovery of the main world economies driving the development.  The ever growing environmental pollution via all impacts related to the use of energy – Greenhouse Gases, aqueous pollution, as well as land pollution. These impacts are usually not quantified, but there are indirect indications that the disasters facilitated by them involve a financial burden that more than offsets the current nominal decrease in the fossil source prices.  The closed vicious cycle of increasing energy demands and pollution amplified by the low fossil fuel prices.

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Fig. 1 shows the historical development and trend projections for energy generation and use in the United States [5]. It is obvious that it is projected to phase out the usage of coal as a main source of energy, especially for heating and power generation in the USA, which is one of the countries using substantial amount of coal presently. On the other hand, besides the renewables, the major increase of energy consumption is going to be covered by natural gas, which has lower specific GHG emissions, however a still substantial amount. Policy assumptions tend to be especially complicated. In the USA, policies at the federal, state, and local levels can all affect energy supply, demand, and prices. Often these policies have timelines or other attributes that are revised by subsequent legislation or interpreted by executive departments. Some policies can interact in ways that are difficult to foresee. Based on this reasoning, the philosophy and long term strategy of PRES conferences has been formulated and followed for almost 20 y: the cleanest energy is energy saved, not produced. Even the so called 0 % emission renewables still have some GHG emissions [6]. However, from the viewpoint of thermal engineering they are some other important factors in the game [7]. Above-normal ambient temperatures during the 2015–16 winter were a key factor in lowering heating demand and winter fuel expenditures. Compared with the 2014–15 winter, propane and heating oil demand decreased by 16 % and 18 %, and residential electricity demand decreased by 6 %. The 2015–16 winter season (October through March) was 15 % warmer than last winter, driven in part by one of the strongest El Niño events in decades – see Fig. 2. However, the lower winter heating means mostly higher energy consumption for cooling by air-conditioning during the rest of the year. Those numerous impacts and challenges are included into the main topics of the conference series ‘‘Process Integration, Modelling and Optimisation for Energy Saving and Pollution Reduction – PRES”, which has played an increasingly active role in finding answers to key sustainability issues. Every year, hundreds of people from both academic and industrial sectors, from all over the world, attend this conference to exchange research ideas, opinions and experiences. It has become one of the most prestigious conferences in the field of improving energy and materials efficiency in industry and other sectors of the economy. The first venue of the PRES series was organised under the CHISA umbrella in 1998, in the central part of Europe, Prague. Since then, the conference was held in a number of other venues, including Hungary, Italy, Canada, Greece, Malaysia and the Czech Republic. In 2015, the 18th conference, PRES’15 was held in Kuching, Sarawak, Malaysia, organised by the University of Nottingham

US Energy production (2010-2040) [109 kJ/y] 50

Fig. 2. Heating degree days in US between October 2015 and March 2016 [7].

Malaysia Campus, and Universiti Technologi Malaysia. The conference attracted 394 abstracts from more than 880 authors from 56 countries. Of these 452 papers were selected by the PRES’15 International Scientific Committee, of which 170 papers were presented as Oral presentations and 203 Posters. On the top of it they were 3 Invited Plenary and 27 Key-Note lectures. The topics of PRES’15 include: Process Integration for sustainable development, Energy saving technology, CO2 minimisation and mitigation, Combined Heat & Power, Combined cycles, Heat exchangers as equipment and integrated items, Integration of renewable, biomass and energy conversion technologies, Integrated and multifunctional operations, Operational research, supply chain and technology management, Pulp and Paper, Clean technologies and Low-emissions technologies, Sustainable processing and production, Waste minimisation, processing and management, Thermal treatment of waste including waste to energy, Dynamic, flexible and sustainable plant operation, Industrial and experimental studies, Industrial application & optimal design, e-learning, e-teaching and e-knowledge, CFD and numerical heat transfer, Sustainable biofuel production, Sustainable Green Palm Oil Transformation, and the Green Asia Move. Selected papers from PRES conferences have been published in Applied Thermal Engineering during the whole conference history, building a decades-long strong collaboration. Applied Thermal Engineering published the first Special Issue (SI) for selected papers that appeared in PRES’99 in 2000 [8]. Since then, it has been followed by SI’s of PRES 2000 [9], PRES’01 [10], PRES 2002 [11], PRES’03 [12], PRES 2004 [13], PRES’05 [14], PRES 2006 [15], PRES’07 [16], PRES 2008 [17], PRES’09 [18], PRES 2010 [19], PRES’11 [20], PRES 2012 [21], PRES’13 [22], PRES 2014 [23].

US Energy consumption (2010-2040) [109 kJ/y] 50

history projection

Natural gas

40

history projection

Petroleum and other liquids

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30

20

Coal

Renewables Nuclear

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Natural gas

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Crude oil and lease condensate

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Coal

Renewables

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Nuclear

Other Other 0 2010

0 2020

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2040

2010

2020

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Fig. 1. Energy production and consumption in US between 2010 and 2040 [5].

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Besides Applied Thermal Engineering, a few other well-known journals have also been publishing Special Issues for PRES conferences: Energy – PRES’11 [24], PRES 2012 [25], PRES’13 [26], PRES 2014 [27]; Journal of Cleaner Production - PRES’01 [28], PRES 2002 [29], PRES’03 [30], PRES 2004 [31], PRES’09 [32], PRES’11 [33], PRES 2014 [34]; Cleane Technologies and Environmental Policy – PRES 2006 [35], PRES’09 [36], PRES 2010 [37], PRES’11 [38], PRES 2012 [39], PRES’13 [40] and PRES 2014 [41]; Heat Transfer Engineering [42], Resources, Conservation and Recycling [43] and Waste Management [44]. 2. The main topics of this special issue This Special Issue of the Applied Thermal Engineering includes 18 selected manuscripts, which deal with various aspects of the journal topics. The papers have been organised into the following groups: Heat exchange, Process Integration, solar thermal energy, combustion and high-temperature processes, enhancement of heat transfer, and process modelling. The editors believe that the papers will be of interest to readers.

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semi-definite programming. The proposed alternative robust MPC design method was implemented with software called MUP. Extensive case studies of heat exchanger control were used to demonstrate the effectiveness of the alternative robust MPC. This proposed strategy was compared with similar approaches in the literature. Experimental results showed that the proposed robust MPC ensured energy savings and improved control performance for heat exchanger operation. The third paper in this subsection, entitled ‘‘Thermo-hydraulic design of single and multi-pass helical baffle heat exchangers” [47] is authored by Picón-Núñez, García-Castillo, and AlvaradoBriones from the Department of Chemical Engineering, University of Guanajuato, Mexico. They present a shortcut sizing approach for single and multi-pass heat exchangers with helical baffles. The authors introduce an alternative approach to determining the correction factor of the logarithmic mean temperature difference as a function of the number of heat transfer units. It has been shown that multi-pass arrangements resulted in complex internal heat flow paths, which were modelled with a simplified method. The model is solved to determine the outlet temperatures where the correction factor was determined. The method is illustrated with a few case studies taken from the literature.

2.1. Heat exchange 2.2. Process Integration The heat exchanger is key equipment type and is widely used in many energy-intensive industries. Heat transfer enhancement, a new type of heat exchanger, control of heat exchanger and design of new heat exchangers are discussed in the following papers. The first article in this subsection is entitled, ‘‘Two types of welded plate heat exchangers for efficient heat recovery in Industry” [45], which is authored by Arsenyeva, Tovazhnyanskyy, Kapustenko, Khavin, Yuzbashyan, and Arsenyev, from Kharkiv Polytechnic Institute, National Technical University, Kharkiv, Ukraine and AO SPIVDRUZHNIST-T LLC, Kharkiv, Ukraine. This paper presents design theory of welded Plate Heat Exchangers (PHEs), aiming to enhance the heat recovery and efficiency of energy consumption. Two approaches were applied in estimating the thermal and hydraulic performance of the unit: by properly selecting the plate corrugation pattern and by adjusting the number of passes for heat exchanging streams. The optimisation problem is observed for targeting the minimal heat transfer area under the requirements of proper operating conditions. The number of plates with different corrugation geometries in one pass are the optimising variables. A mathematical model of PHE has been developed to obtain the value of the objective function in a space of optimising variables. The optimisation procedure was applied for heat exchangers in a preheat train of a crude oil distillation unit of an oil refinery, based on the obtained design parameters with the effect of flow movement arrangement in the unit and its influence on shear stress and fouling formation. The comparison of Plate-and-Shell and Compabloc types of welded PHE is discussed as well. The second paper in this subsection is titled ‘‘Experimental Investigation of Alternative Robust Model Predictive Control of a Heat Exchanger” [46]. It has been authored by Juraj Oravec, Monika Bakošová, Alajos Mészáros and Nikola Míková from the Slovak University of Technology in Bratislava, Slovak Republic. They investigated advanced control of heat exchangers. This is an important task for control engineers because these devices play key roles for many energy-intensive processes in many industries. This study presents novel robust model-based predictive control (MPC) for heat exchangers. The influence of uncertain parameters was considered in the design of the robust model-based predictive controller. The constraints of the optimisation problem of the control system were formulated in the form of linear matrix inequalities. The convex optimisation problem could be solved using

Process Integration is a powerful tool for reducing energy consumption and emissions. In this Special Issue, 5 papers discussed the application of Process Integration to various problems. The first paper in this group is entitled ‘‘Integration of Diesel Plant into a Hybrid Power System Using Power Pinch Analysis [48]”, which was authored by Rozali, Wan Alwi, Ho, Abdul Manan and Klemeš, from the Department of Chemical Engineering, and Process Systems Engineering Centre (PROSPECT), Universiti Teknologi Malaysia; Faculty of Chemical and Energy Engineering, Universiti Teknologi Malaysia, and Pázmány Péter Catholic University, Budapest in Hungary. The authors used Pinch Analysis to integrate diesel plant into a hybrid power system. One option for energy supply generation is diesel power system. However, these systems often encounter difficulties of emission control and high cost of the diesel fuel. Some of these difficulties can be overcome by incorporating renewable energy (e.g. wind turbines, and solar PV) along with the existing diesel station. Hybrid systems mentioned above provided clean and reliable power supply, and could be more cost-effective compared to sole diesel systems. This paper assessed the feasibility of retrofitting an existing diesel power plant into a hybrid power system (HPS) with Power Pinch Analysis (PoPA). An HPS configuration was developed with PoPA methodology, which could provide near-optimal solar and wind electricity supplies, and minimise the cost of the system. Results of the above example showed that an HPS that combined solar and wind system with diesel power generation could save significant quantities of diesel fuel at a reasonable cost. The second paper in this sub-section is titled with ‘‘An efficient optimisation algorithm for waste Heat Integration using a heat recovery loop between two plants [49]”, which has been authored by Chang, Chen, Wang, and Feng from China University of Petroleum, Beijing, China, and Xi’an Jiaotong University, China. In this paper, the authors show that a heat recovery loop (HRL) is an indirect approach for waste Heat Integration between plants. They propose that the mathematical model for HRL design gives rise to a complex and nonlinear problem, resulting in a non-convex Mixed Integer Nonlinear Programming (MINLP) model. It was difficult to solve the problem without any specific strategy because computational results could easily be trapped in local optimum solutions. The main reason for the above problem was that operation cost,

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the capital cost of heat exchanger networks, piping and pumping costs were considered simultaneously. This paper proposed an optimisation algorithm, which can solve the above complex problem effectively. By using convex reformulation and piecewise wise relaxation, the complex problem could be reformulated as a convex MINLP model. In the model, the objective function was convex and all constraints were linear. It was observed that the computational loads were reduced significantly and better solutions could be obtained for the HRL design with the method proposed. As the main application of this work concentrated on low-grade heat recovery, hot water was selected as the intermediate fluid to carry out waste Heat Integration between plants. An industrial case study was used to show the effectiveness of the proposed approach. The third paper in this subsection is entitled ‘‘Two-step hybrid approach for the synthesis of multi-period heat exchanger networks with detailed exchanger design” [50], which was authored by Short, Isafiade, the late Fraser from University of Cape Town, Rondebosch, South Africa and Zdravko Kravanja from University of Maribor, Slovenia. A novel methodology is presented for multiperiod heat exchanger network synthesis. The synthesis method proposed can be used to obtain optimal designs by systematically generating a lot of candidate networks, by using detailed individual heat exchanger designs and their evaluation over all periods. In the optimisation procedure, a modified multi-period mixed integer non-linear programming (MINLP) was developed based on the stage-wise superstructure (SWS) model to include correction factors. The above strategy could be used to reduce the overall cost of the designed network. Shortcuts and detailed models of the individual exchanger were used in turn to reduce calculation effort. The designs obtained accurately represented the actual network. A case study was investigated to show the benefits of the proposed approach. The fourth paper in this group is entitled ‘‘An Improved Model for Heat Integration of Intermittent Process Streams in Multipurpose Batch Plants” [51], which has been authored by Lee from the Department of Chemical Engineering and Biotechnology, National Taipei University of Technology teamed up with Seid and Majozi from the School of Chemical and Metallurgical Engineering, University of the Witwatersrand, Johannesburg, South Africa. The paper presents a mathematical technique for simultaneous Heat Integration (HI) and process scheduling in multipurpose batch plants. The authors suggest taking advantage of the intermittent continuous behaviour of process streams during transfer between processing units. The presented formulation aims at maximising the coincidence of availability of hot and cold stream pairs with feasible temperature driving forces for heat recovery. Unlike other contributions in the literature, time is treated as one of the key optimisation variables instead of a predefined parameter. Applying the proposed model to a case study, the authors report improvements of up to 50 % in utility cost savings and more than two-thirds in product revenue, with optionally achieving more than 80 % profit increase if adding three additional heat exchangers. The fifth paper in this group is titled ‘‘The improved heat integration of cement production under limited process conditions: A case study for Croatia” [52], which has been authored by Boldyryev, Mikulcˇic´, Mohorovic´, Vujanovic´, Krajacˇic´ and Duic´. Mikulcˇic´ is from Holcim Croatia d.o.o., Croatia while the other authors are from the University of Zagreb, Croatia. According to the authors, the cement industry sector is energy intensive and has one of the highest CO2 emissions. The cement industry sector is calling for CO2 emission reduction and the potential for renewable energies to be integrated. In the work, the authors summarised some literature works that deal with increasing energy efficiency and reducing CO2 emission. However, according to the

authors, the developments in the literature are rarely supplemented with proper applications of the methodology, especially for HEN generation. The cement industry is lacking applications of Process Integration approaches owing to its specific process condition and some limitations. In this work, the authors explored the possibility of the pathways towards maximisation of heat recovery. The concept designs of HEN are analysed and developed using methodology that is based on principal of Pinch Analysis. Authors demonstrated that considerable amounts of energy can be saved in the cement production. In the case study used by authors, the heat recovery in the existing process is improved. Both external heating and cooling are reduced by 30 %. The retrofit on the existing HEN requires € 256,000 with a payback period of 3.4 months. It is achievable by improving the existing process heat transfer equipment. Further improvements demonstrated by the authors are waste heat utilisation and power generation by hot gases. This covers the site demands and reduces the use of primary energy resources and minimises CO2 emissions. The discussed methodology can be used for energy analysis. The results obtained can provide efficient retrofit recommendations, new concept designs, and energy planning and strategies. The authors concluded that there should be more discussion and investigation on technical aspects for successful implementation. 2.3. Solar energy Solar energy is a kind of sustainable energy. The research on solar energy received much attention recently. In this subsection, two papers addressed the topics related to solar energy. The first paper in this sub-section is titled ‘‘An experimental and analytical study on the feasibility of SMA spring driven actuation of an iris mechanism” [53], which has been authored by Rajan, Abouseada, Manghaipathy and Srinivasa, from Texas A&M University at Qatar, Doha, Qatar, and Ozalp, Majid and Salem from KU Leuven, Belgium, and Texas A&M University, College Station, USA. In this paper, the authors address the fact that a variation in incoming solar energy affected adversely the inside temperature of a solar reactor and lowered its efficiency. They believed that it was important to develop a mechanism which could keep semiconstant temperatures inside the reactor from sunrise to sunset. The authors present an iris mechanism that reduced or enlarged its circular opening by using Nickel–Titanium Shape Memory Alloy (SMA) springs. SMA springs could keep the memory of their shapes at certain temperatures. Therefore, it was possible to exert different forces that may then be transferred to the variable aperture mechanism, by controlling the temperature of the spring. In this article, a variation of the force exerted by an SMA spring, when temperature changing, was experimentally examined. The viability was tested as well for an SMA spring’s use in actuating an iris mechanism aperture. A 7 kW solar simulator was used in experiments at varying power levels, to simulate conditions under fluctuating solar radiation. The authors found that SMA springs might be a good option as a replacement of the actuation mechanism driven by a motor. The second paper in this subsection is titled ‘‘Thermo-economic comparisons between solar steam Rankine and organic Rankine cycles” [54], authored by Desai and Bandyopadhyay from the Indian Institute of Technology Bombay, Powai, Mumbai. In this paper, the authors stated that among all concentrated solar power technologies, plants with a parabolic trough collector and steam Rankine cycle were the most matured and established technology. The Organic Rankine cycle was a promising option for a modular scale power plant with low-temperature heat sources. The following factors would play an important role in the decision for selection between steam Rankine and organic Rankine cycles: solar collector field characteristics and cost, steam Rankine cycle effi-

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ciency, and power block cost. They propose a novel method for selecting the working fluid with a graphical representation, named working fluid selection diagram, by considering the condition of equality of the levelised cost of energy. The solar collector field selection diagrams and proposed working fluid could be used for a quick suggestion about the optimal configuration of a concentrated solar power plant, without detailed simulations. In contrast with the proposed method, most of the methods proposed in literature required multiple simulations for selecting various design parameters and optimum configuration of the plant. This paper shows that R113 and iso-hexane achieved a levelised cost of energy close to the parabolic trough collector based plant with steam Rankine cycle. The authors also studied effects of different parameters on a selection of the optimal configuration of a concentrating solar power plant. In the conceptual design of a concentrated solar power plant, the following issues were very important: the analytical procedures developed for selecting the solar collector field and working fluid of the power generating cycle. The methods proposed in this paper could be applied at the initial design stage to reduce the search space related to various design parameters and to compare the alternative configurations. 2.4. Combustion and high-temperature processes Combustion plays an important role in heat energy utilisation. The research on combustion is always interesting for thermal engineers. High-temperature processes are also very important in thermal engineering. In this sub-section, four papers discuss these issues. The first paper in this subsection is titled ‘‘Novel approach to proper design of combustion and radiant chambers” [55], which was authored by Jegla, Kilkovsky´ and Turek, from Institute of Process Engineering, Brno University of Technology, Czech Republic. In this paper, a design of combustion and radiant chambers has been addressed. Many process and power equipment items, such as fired heaters, power boilers, or incinerator furnaces, have combustion and radiant chambers. The authors point out that operating problems, which many of these combustion chambers suffered from, were typically due to the design procedures using data of insufficient accuracy regarding the calculated local heat transfer data in individual parts of the chambers equipped with modern low-NOx burners. The design engineers had to devise more accurate design procedures for the respective equipment, because of these problems. This paper discussed the main results based on a several-year-long research effort. A novel and up-to-date approach was presented as a basic outline to properly design combustion and radiant chambers with inbuilt heat transfer surfaces. The presented novel method significantly improved the quality of the resulting combustion chamber designs. The three most important components of the method are: (a) determination of the actual burner heat flux distribution with experimental step, (b) identification of the actual fuel burnout profile, and (c) utilisation of the respective fuel burnout profile in the design of the combustion chamber and its inbuilt heat transfer surfaces. The new method thus replaced the currently used design methods based on the ‘‘well stirred” models. The second paper in this sub-section is ‘‘Scale-adaptive simulation on the reactive turbulent flow in a partial combustion lance: Assessment of thermal insulators” [56], which has been authored by Law, Gimbun, from Universiti Malaysia Pahang, Pahang, Malaysia. This paper presented a scale-adaptive simulation (SAS) of a partial combustion lance (PCL) in order to evaluate the effect of thermal insulation on the performance of syngas combustion. Standard k–e (SKE) and Reynolds stress models (RSM) were used in the simulation. The models for combustion reaction were nonpremixed and partially premixed flame models, and an eddy dissi-

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pation model (EDM). Radiative heat transfer was calculated with discrete ordinates (DO) and spherical harmonics (P-1) methods. The results suggested that SAS provided a good prediction for reactive turbulent flow. In this work, the best agreement between simulation results with experimental data was about 5.3 %, for syngas combustion using non-premixed flame with a DO approach. It was shown that the peak outlet temperature could be increased by about 20.4 % with the installation of an insulator. The third paper in this group was entitled ‘‘Sinter strength evaluation using process parameters under different conditions in iron ore sintering process” [57], authored by Cheng, Yang, Zhou, Liu, Wang from Xi’an Jiaotong University, China. The authors made conclusions from [58] and addressed an internal connection between the process parameters and real sinter quality in the sintering process. The authors stated that few investigations were reported on bridging the process parameters and real sinter quality for engineering applications. They pointed out that only process parameters (flow resistance, heat condition of sintering bed and off-gas composition) could be obtained with the numerical method in the existing studies. Actual sinter strength and reducibility cannot be captured because of a lack of reliable models and the limitation of the computing resource. The paper focused on this problem, which was necessary for parameters optimising in both numerical simulation and on-line control equipment of sinter quality. The melt quantity index (MQI), peak temperature and duration time of melting temperature (DTMT), were used in this paper. The authors also explained its physical significance as the effective ‘‘energy” for melting phase formation. Then the corresponding relation between MQI and sinter yield was confirmed by the authors’ experimental data and the reproduced data taken from literature. According to the authors, the MQI was recommended as a wise indicator of real sinter strength. The effects of a few operating parameters (fixed carbon content, sintering pressure and fuel reactivity) on sinter strength were studied by measuring the MQI, sintering speed and air flow rate. In addition, the influencing mechanism of two important operating parameters (heat utilisation and combustion efficiencies) on MQI was proposed. The authors pointed out that the monitoring of the above parameters would provide a strong support for the transparency of the sintering process ‘‘black-box” and optimisation procedure of operating parameters. A conceptual design for the on-line control of sinter strength was proposed based on the present results in this paper as well. The fourth paper in this subsection is entitled ‘‘Effect of mixture flow stratification on premixed flame structure and emissions under counter-rotating swirl burner configuration” [59], which was authored by Chong from Universiti Teknologi Malaysia, and UTM Centre for Low Carbon Transport in Cooperation with Imperial College London, Universiti Teknologi Malaysia; Lam from University Malaysia Terengganu, and Hochgreb from University of Cambridge, UK. An investigation has been performed of the flame structure and emission performance of stratified swirl methane/air flames by using a double-annulus counter-rotating premixed swirl burner. Stratification of the flow and mixtures were established by changing mixture equivalence ratios between the inner and outer annuli and the bulk air flow rates. Two distinct flame fronts were stabilised at an outlet of the burner, separated by a shear layer caused by velocity differences. Higher swirl flow in the inner annulus generated an elongated and enlarged area of flame reaction zone due to increased flame intensity, as the flame shape strongly relied on the magnitude of velocity exiting the annulus. Mixture and flow stratification affected local emissions. For example, 91 % and 49 % higher emission rates of NO and CO were observed respectively for a richer mixture stratification within the inner channel at 70:30 flow split, compared to a premixed arrangement, in spite of generally aiding flame stability. It

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was shown that enrichment of the outer annulus at 70:30 split flow resulted in only slightly increasing of NO and CO emissions by 3 % and 9 % compared with a homogeneous mixture. 2.5. Enhancement of heat transfer Enhancement of heat transfer is an interesting research topic and received much attention from engineers. In this sub-section, two papers discussed this topic. The first paper in this sub-section has been authored by Kukulka, Smith, Li from State University of New York College at Buffalo, Buffalo, USA, VipertexTM, Buffalo, USA, and Zhejiang University, Hangzhou, China. The title of their paper was ‘‘Comparison of condensation and evaporation heat transfer on the outside of smooth and enhanced 1EHT tubes” [60]. This paper presented experimental results that evaluated the outside condensation and evaporation heat transfer taking place on a 12.7 mm (0.5 in.) OD horizontal copper tube. Evaporation conditions included mass flux ranging from 10 to 40 kg/m2 s; with inlet quality of 0.1 (±0.05); outlet quality of 0.8 (±0.05); and nominal evaporation temperature of 5.85 °C. Condensation conditions considered in this paper included mass flux values in the range from 5 to 50 kg/m2 s; at saturation temperature of 44.85 °C; with inlet quality of 0.8 (±0.05); and outlet quality of 0.1 (±0.05). For enhanced tubes, heat transfer predicting procedures available were limited (within the degree of confidence necessary to perform analysis) since any work that had been done was limited to specific geometry and operating conditions that had been based upon tests from which the predicting procedures had been derived. The authors compared smooth tubes with the newly developed VipertexTM 1EHT (Enhanced Heat Transfer) enhanced surface tube. The results showed that average evaporation heat transfer coefficients for R22 and R410A on the 1EHT tube were one to four times greater than those of a smooth tube. The performance of condensation heat transfer on the outside of a 1EHT tube was less than a smooth tube due to the pattern/ drainage characteristics of that model of the tube for the flow conditions considered. This supports the findings of the previously published results see e.g. [61]. In order to enhance heat transfer performance, three-dimensional enhanced surfaces were incorporated on the surface of tubes. It was found that under many conditions, enhanced surface tubes could transfer more energy and give the opportunity to advance the design of many heat transfer products. The enhanced heat transfer tubes has been widely used in a variety of industries in order to reduce cost and decrease footprint. Vipertex 1EHT tubes were a new type of enhanced heat transfer tube with multiple enhancement patterns. Since this design was unique, it was necessary to investigate the heat transfer characteristics of this novel enhanced heat transfer tube and compare its features to that of other tubes. The second paper in this sub-section has been authored by Tarighaleslami, Walmsley, Atkins, Walmsley, and Neale, from University of Waikato, Hamilton, New Zealand, with the title of ‘‘Heat Transfer Enhancement for site level indirect heat recovery systems using nanofluids as the intermediate fluid” [62]. This paper has been based on the approach published some time ago by [63] and being steadily extended. The authors studied the implementation of nanofluids as a Heat Transfer Enhancement technique in Process Integration. Water was replaced by various nanofluids as the heat transfer media in an industrial Heat Recovery Loop (HRL). Nanofluids were prepared by distributing a nanoparticle through a base fluid, which included water, ethylene glycol or oils. It showed that suspended nanoparticles slightly affect the thermal and physical properties of the base fluid in the experiments. The heat transfer characteristics of the fluid were improved by adding the primarily nanoparticles, which increased Reynolds number and thermal conductivity. A case study was investigated for a large

dairy factory in New Zealand. The results show that by applying various HRL design methods and a nanofluid as an intermediate fluid, heat recovery was increased without adding extra heat exchanger area and infrastructure. For example, when 1.5 vol% CuO/water nanofluid was used as an intermediate fluid and by using a constant temperature storage control strategy, heat recovery from liquid–liquid heat exchangers increased between 5 % and 9 %. It should be pointed out that the impact of using a nanofluid for the air–liquid exchangers was limited by the air-side heat transfer coefficient. When using a nanofluid as process streams in a retrofit situation of a condenser, the total available duty from the process stream significantly nullifies the heat transfer benefit. This indicates that using a nanofluid in the HRL design phase could decrease heat exchanger area for liquid–liquid matches significantly. Results also show that the increasing of pressure drop and friction factor in the above system were negligible. 2.6. Thermal process modelling Process modelling is very important in process design, operating, and optimisation. The research on process modelling receives much attention from the researchers. The first paper in the sub-section is entitled as ‘‘Multicomponent Devolatilization Kinetics and Thermal Conversion of Imperata cylindrical” [64], which was authored by Oladokun, Ahmad, Amran Abdullah, Nyakuma, Bello, Al-Shatri from Universiti Teknologi Malaysia and University of Maiduguri, Maiduguri, Borno State, Nigeria. A conversion of biomass resource, imperata cylindrica, into clean energy was studied. Imperata cylindrica can be taken as a biomass energy source because it can be converted to clean energy through thermochemical processes such as pyrolysis, gasification and combustion. The paper benefits from the work published recently by [65]. To carry out further process development, a mathematical model for chemical kinetics has been developed and validated on the basis of thermal degradation studies with a thermogravimetric analyser at the following conditions: temperature range of 30–1,000 °C, four heating rates of 5 °C, 10 °C, 15 °C, and 20 °C min 1, and Nitrogen was used as medium. The methods of model-free and model fitting multicomponent were used to determine the pre-exponential factors (ko), activation energies (Ea) and fractional contribution (n). A novel approach was introduced for determination of biomass (cellulose, hemicellulose and lignin) compositions by extending the model fitting multicomponent method to identify components that correspond to each biomass composition within the pyrolysis temperature range. The parameters obtained by model-free methods of FlynnWall-Ozawa and Kissinger-Akahira-Sunose were as follows: average activation energies 164.93 kJ mol 1 and 163.44 kJ mol 1, and the average pre-exponential factor of 1.04  1025 min 1 and 4.65  1018 min 1. By using the multicomponent model obtained, a simulation was carried out for 3–14 pseudocomponents. The best quality of fit (0.75 %) was for ten pseudocomponents at the heating rate of 15 °C min 1 with the activation energy of 101.56 kJ mol 1. The results were comparable to that obtained with a model free method. The results obtained in this paper indicate that the pseudo-component reaction modelling method could be used to predict the experimental devolatilisation rate and biomass composition. The second paper in this subsection is titled ‘‘Biomass Characteristics Index with Calorific Value: A Numerical Approach to Palm Bio-energy Estimation” [66], which has been authored by Tang, Lam, Aziz, Morad from University of Nottingham Malaysia Campus, and Jalan Broga, Semenyih, Selangor from Universiti Teknologi Malaysia. The authors have used the approach stipulated by [67] and realised that oil palm industry produced a huge amount of

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valuable crude palm oil and a large amount of plantation waste or biomass. The waste produced could be utilised as fuel. In order to obtain an estimation of the energy output from the biomass, this paper made a comprehensive study of bulk density and moisture content of the biomass. In a conventional approach, these properties were obtained with empirical methods on an individual sample basis. However, the conventional empirical methods had the following drawbacks: (1) requiring a lot of experimental results to draw biomass properties’ curve (2) data variation affecting the accuracy of the analysis result. These drawbacks would limited properties estimation procedure and further affect the optimum biomass utilisation. To solve the above problem, it was necessary to search for a direct representation of the properties. They proposed a Biomass Characteristics Index (BCI) for representing the relationship between bulk density and moisture content. A numerical framework was developed to calculate the BCI. This index was used to estimate the biomass bulk density and moisture content before calculation of the calorific value. A regression graph was plotted to show the relationship among the values with different appearance shapes of biomass. The result showed that different size and shape of biomass had a different BCI. The classification of biomass based on its specific BCI can predict the related bulk density and moisture content. Therefore, the method proposed in this paper reduced the hassle, especially in terms of time constraint to obtain the values with a conventional empirical method. This would increase the operational management efficiency of utilisation of overall biomass 3. Conclusions It can be seen that the papers in this Special Issue discuss the following topics: saving energy by Process Integration, heat exchanger design and control, heat transfer enhancement, solar energy, combustion and high-temperature processes, and process modelling. The editors believe that the articles in this SI of Applied Thermal Engineering will be of interest to readers from a broad range of the scientific and engineering community. PRES conferences have been successfully held 18 times. The next one, the 19th PRES’16 Conference is going to be held in August 2016 in Prague, The Czech Republic, jointly with CHISA 2016. Another Special Issue for PRES 2016 should be presented in the foreseeable future. The Editors are looking forward to seeing another successful conference and more fruitful special issues. On the website of PRES 2016 one can find more information about this coming conference. The PRES International Scientific Committee is looking forward to meeting all ATE readers at PRES 2016 in Prague! References [1] B. Linnhoff, D.W. Townsend, D. Boland, G.F. Hewitt, B.E.A. Thomas, A.R. Guy, R. H. Marsland, User Guide on Process Integration for the Efficient Use of Energy, IChemE, Rugby, England, 1982 (last edition 1994). [2] R. Smith, Chemical Process Design and Integration, John Wiley & Sons Ltd., Chichester, UK, 2005. [3] J.J. Klemeš, P.S. Varbanov, Process intensification and integration: an assessment, Clean Technol. Environ. Policy 15 (3) (2013) 417–422. [4] J.J. Klemeš, P.S. Varbanov, S.R. Wan Alwi, Z. Abdul Manan, Process Integration and Intensification: Saving Energy, Water and Resources, Series: De Gruyter Textbook, De Gruyter, Berlin, Germany, 2014, 254p. [5] EIA, EIA’s Annual Energy Outlook is a projection, not a prediction, US Energy Information Administration, 2016, accessed 25.05.2016. ˇ ucˇek, J.J. Klemeš, P.S. Varbanov, Z. Kravanja, Significance of environmental [6] L. C footprints for evaluating sustainability and security of development, Clean Technol. Environ. Policy 17 (18) (2015) 2125–2141. [7] EIA, Strong El Niño helps reduce U winter heating demand and fuel prices, US Energy Information Administration, 2016, accessed 25.05.2016. [8] J. Klemeš, F. Friedler, Editorial, Appl. Therm. Eng. 20 (15–16) (2000) 1335. [9] J. Klemeš, Editorial, Appl. Therm. Eng. 21 (13–14) (2001) 1281–1282.

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Zhi-Yong Liu School of Marine Science and Engineering, Hebei University of Technology, Tianjin, China Petar Sabev Varbanov Jirˇí Jaromír Klemeš Faculty of Information Technology and Bionics, Pázmány Péter Catholic University, H-1083 Budapest, Hungary E-mail addresses: [email protected] (P.S. Varbanov), [email protected] (J.J. Klemeš) Jun Yow Yong Faculty of Information Technology, University of Pannonia, Egyetem utca 10, H-8200 Veszprém, Hungary E-mail address: [email protected]