Hot Utility Research Articles

Advanced temperature control in ethanol fermentation using a PSO-PID controller with split-range control strategy

Global energy demand is experiencing a notable surge due to growing energy security. Renewable energy sources, like ethanol, are becoming more viable. In the present study, the application of a PSO-PID (Particle Swarm Optimization – Proportional Integral Derivative) controller with a split-range control strategy was suggested for the regulation of temperature within the fermentation system. To optimize performance, a POS-PID controller with a split-range arrangement utilizing two control valves for hot and cold utilities was constructed. The study began by examining the open-loop dynamic response of the system to inlet temperature and concentration disturbances during ethanol production fermentation. Subsequently, a transfer function model was developed through linearization at the steady-state operating point. The split-range controller structure, implemented by optimizing the PSO-PID controller parameters using PSO, effectively demonstrated temperature control in simulations of a nonlinear model. In this investigation, the ethanol fermentation system was modeled as a CSTR using a modified Monod equation for microbial growth kinetics. Various dynamic behavioral disturbances were explored and verified in the model with plant data in this study. The simulation model results were validated through plant data. The proposed method showed superior closed-loop performance with respect to errors, with the actuators proving to be effective than other reported methods for temperature control.

Evaluation of dimethyl carbonate production process from CO2 by rigorous simulation and detailed optimization

AbstractThe CO2‐derived dimethyl carbonate (DMC) synthesis process becomes greatly attentive but suffers high energy consumption in DMC distillation process. In this work, the DMC‐MeOH azeotropes separation process by pressure swing distillation and extractive distillation was compared, and key operating parameters, including the total number of trays and the feeding position of the mixture liquid, were optimized with the minimum total annual cost (TAC) as the objective function. On the basis of this optimization, economic evaluation of different distillation processes was conducted, and it was found that extractive distillation was more economical than pressure swing distillation. The application of the dividing‐wall distillation process upgraded by extractive distillation can significantly reduce the minimum annual total cost by 37.4% and 10.7% compared to the original pressure swing distillation and extractive distillation process, respectively. The optimization of relevant heat exchange network based on pinch technology resulted in energy consumption reduction by 27.2% and 25.9% for its hot and cold utilities, respectively. Carbon life cycle assessment (LCA) on the DMC distillation process revealed over 50% of energy as well as carbon emissions from steam consumption, whose reduction can significantly minimize CO2 emissions, energy consumption, and ultimate cost. © 2024 Society of Chemical Industry and John Wiley & Sons, Ltd.

Optimization of heat management and utilization in batch processes

Batch plants boast operational flexibility in manufacturing process and resource sharing, making batch processes suitable to fluctuating-demand or small-scale production. However, given time dependence of operational behavior, batch processes are more demanding in energy integration than continuous processes, a task which is especially important amid the global net zero-emission current. It is, therefore, imperative to develop sustainable design strategies for intermittent processes. The study introduced a targeting method and developed an innovative over-time heat integration technique to optimize energy utilization in batch processes, involving use of heat transfer media for heat recovery over various time intervals and a heat makeup strategy to heat the media over different periods, in order to enhance heat-energy utilization efficiency. The technique is applicable to both fixed and unspecified batch schedules, the latter of which involves simultaneous design of production schedule and heat recovery systems, increasing flexibility and improving heat energy utilization. Case studies are conducted to demonstrate the proposed method. With the heat makeup technique, energy efficiency can be significantly enhanced, achieving energy savings of 51% and 93.1% in hot and cold utility, respectively. Meanwhile, the simultaneous design of production schedule and heat integration can boost savings up to 53% and 99%. Results have proven the benefits of the technique, including significant reduction of energy consumption and carbon emission, contributing to clean production, environmental protection, and sustainable development.

Combining Exergy and Pinch Analysis for the Operating Mode Optimization of a Steam Turbine Cogeneration Plant in Wonji-Shoa, Ethiopia.

In this research, the simulation of an existing 31.5 MW steam power plant, providing both electricity for the national grid and hot utility for the related sugar factory, was performed by means of ProSimPlus® v. 3.7.6. The purpose of this study is to analyze the steam turbine operating parameters by means of the exergy concept with a pinch-based technique in order to assess the overall energy performance and losses that occur in the power plant. The combined pinch and exergy analysis (CPEA) initially focuses on the depiction of the hot and cold composite curves (HCCCs) of the steam cycle to evaluate the energy and exergy requirements. Based on the minimal approach temperature difference (∆Tlm) required for effective heat transfer, the exergy loss that raises the heat demand (heat duty) for power generation can be quantitatively assessed. The exergy composite curves focus on the potential for fuel saving throughout the cycle with respect to three possible operating modes and evaluates opportunities for heat pumping in the process. Well-established tools, such as balanced exergy composite curves, are used to visualize exergy losses in each process unit and utility heat exchangers. The outcome of the combined exergy-pinch analysis reveals that energy savings of up to 83.44 MW may be realized by lowering exergy destruction in the cogeneration plant according to the operating scenario.

Techno-economic and environmental feasibility study of MILD combustion in domestic utility boilers under partial load operation

This paper aims to achieve the benefits of MILD combustion, such as enhanced thermal efficiency with simultaneous NOx reduction in existing conventional domestic hot water utility boilers which encounter partial heat loads. For this purpose, a system based on waste heat recovery and flue gas recirculation (FGR) is introduced to perform techno-economic and environmental studies under continuous fluctuations of heat load demand in a typical building at various climate conditions. Technical investigations on several types of utility boilers revealed that MILD combustion could be implemented only in modulation boilers, which can serve combustion stability requirements in turndown conditions due to partial load demands. Up to 6 % fuel saving, which aligns with a commensurate decrease in CO2 emissions and a minimum 75 % reduction in NOx emissions, is foreseeable by manipulating optimal FGR for each specific boiler in various climate conditions. Finally, economic investigation demonstrated that the payback period for the proposed revamped system is less than one year for most climates.

Improving the Economic Efficiency of Heat Pump Integration into Distillation Columns of Process Plants Applying Different Pressures of Evaporators and Condensers

The electrification of process industries is one of the main challenges when building a low-carbon society since they consume huge amounts of fossil fuels, generating different emissions. Heat pumps are some of the key players in the industrial sector of the carbon-neutral market. This study proposes an approach to improve the economic feasibility of heat pumps within process plants. Initial energy targeting with grand composite curves was used and supplemented with the detailed design of an evaporator and a compressor for different condensation and evaporation pressures. The trade-off between the capital cost of the heat pump and the electricity cost was investigated, and optimal configurations were selected. This case study investigates the gas fractioning unit of a polymer plant, where three heat pumps are integrated into distillation columns. The results demonstrate that the heat recovery is 174 MW and requires an additional 37.9 MW of electricity to reduce the hot utility by 212 MW. The selection of the evaporation and condensation pressures of heat pumps allows 21.5 M EUR/y to be saved for 7 years of plant operation. The emission-saving potential is estimated at 1.89 ktCO2/y.

STREAMS HEAT INTEGRATION IN THE SEPARATION PROCESS OF THE FURFURAL-WATER HETEROAZEOTROPIC MIXTURE BY USING TWO STRETCHING COLUMNS

The process of azeotropic mixtures rectification takes place in many branches of the chemical industry. This process requires significant energy consumption both for heating and evaporation of process streams, and for vapor condensation and cooling of products. The consumption of external energy essentially depends on the methods of separation processes organization. Pinch analysis is one of the modern methods for designing chemical-technological systems with the aim of optimal use of external energy sources by maximizing the heat integration of system process streams, taking into account the limitations of a particular manufacture, the requirements of environmental safety and environmental protection. In this paper the heat integration of the heteroazeotropic furfural-water mixture separation process by two columns was considered. In each column the azeoptrope is a light-boiling one, and one of the mixture components is a low-boiling one. The heat and material balances of the rectifying plant were calculated and the table of its streams was formed, that is, the data of the chemical-technological system were extracted. From the total set of heat streams, the subset was selected for heat integration. Composite curves for the selected heat streams subject to heat integration were built and their relative position on the temperature-enthalpy diagram was analyzed. This analysis showed that for a certain value of the minimum temperature difference in the heat exchange equipment Тmin, there is a threshold problem. The problem was formulated for a value of Тmin slightly less than the threshold value that led to a slight increase in the consumption of external energy carriers. Options for further improvement of the network of heat exchangers were considered, and the occurrence of a cycle through the pseudopinch was identified. It gave possibility to remove a heat exchanger with a low load and redistribute this load among to other ones. Restoring Тmin in this case is impossible, because a strict restriction on the absence of hot utilities is accepted. Significant savings in external utilities load have been demonstrated. For retrofit modern Alfa Laval heat exchange equipment was selected for all the necessary positions.

Energy integration of hydrodealkylation (HDA) of toluene

The chemical industry is constantly making advancements. Previously, large equipment was used to transfer heat, but now the industry has modernized. Energy Integration is a trending area of study that can be applied in several sectors to redesign processes. Energy Integration refers to any technique in chemical engineering that results in smaller, environmentally friendly, and more energy-efficient appliances. The goal of energy integration is to improve energy transfer and reduce the equipment's capacity for heat transfer. Pinch analysis has been used in this study to explain the energy integration of Hydrodealkylation (HDA) of the toluene process by finding the best alternative for the Heat-Exchange Network (HEN). Pinch technology offers a systematic approach to reducing energy use across all sites and activities. By using pinch technology, it is possible to determine the proper alterations to the fundamental process parameters that can result in energy savings. In this study, the DWSIM, a chemical process simulator, has been used to simulate the flowsheet of the HDA process. Data obtained from the flowsheet have been used in the pinch analysis to find the best alternative for the heat exchanger network. Heat exchange from hot utility to cold utility has been done in this study, and a proper HEN has also been elaborated. The heating and cooling requirements for the HDA case study have been estimated using pinch analysis. It is estimated that the hot utility (HU) requirement is 64.19 kW and the cold utility (CU) is 202.83 kW. The detailed analysis suggests a 20–30 % reduction in energy consumption.

Energy, exergy, and economic analyses and optimization of a deethanizer tower of a petrochemical plant

Abstract The distillation tower’s reboiler is one of the largest energy consumers in petrochemical facilities, and reducing its energy consumption is a crucial issue. This study proposes two optimal methods, namely Direct Vapor Recompression (DVR) and External Vapor Recompression (EVR), to reduce the consumption of cold and hot utilities in a petrochemical deethanizer tower. The Pars petrochemical in Iran is taken as a case study, and the proposed methods are compared with the base case using energy, exergy, and economic approaches, simulated through Aspen HYSYS software in the steady-state design conditions. Exergy analysis reveals that the EVR and DVR methods reduce the exergy destruction of the deethanizer tower by about 70.06 % and 67.29 %, respectively, compared to the base case. Moreover, the EVR method allows for complete recycling of low-pressure vapor, reducing the total exergy destruction rate from 0.871 to 0.261 GJ/tethane. The feed separation cost for the base case, DVR, and EVR are estimated to be around 28 $/kgfeed, 21.57 $/kgfeed, and 21.14 $/kgfeed, respectively. The EVR method results in reduced utility and ethane separation cost rates from 5.153 to 3.274 $/tethane and 17.64 to 15.78 $/year. Overall, the findings suggest that both DVR and EVR methods are effective in reducing the energy consumption and costs associated with deethanizer tower operations. Moreover, real-time optimization techniques can be developed to monitor and adjust the deethanizer tower’s operating parameters, such as feed flow rate, reboiler duty, and reflux ratio.

A heuristic method to introduce hot feed into chemical process for energy saving with minor structure modification

Hot feed is a relatively inexpensive strategy to improve the energy utilization in chemical plants. Since hot feed is often an afterthought, retrofitting the heat exchanger network (HEN) with hot feed becomes a key step to decide the energy saving. This paper proposes a heuristic method to introduce hot feed into the existing HEN with minor structure modifications. The concept of heat flow path is extended to fit the hot feed problem. The possible changes of heat exchangers in a path are analyzed in details referring to the heat flow direction. Based on this, the bottleneck and the maximum shift capability of each path can be determined quantitatively. Rules for the creation and selection of new paths are presented to achieve more hot utility saving. A wax oil hydrogenation unit is analyzed to illustrate the proposed method, where heat carried by hot feed can be fully used to save the hot utility. The proposed method obtains more hot utility reduction (3349.0 kW versus 783.8 kW) by the hot feed strategy and a simpler retrofitting scheme than a previous method based on the grand composite curve. Besides, this method can show clear insights in the HEN retrofit with hot feed and it is easy for industrial application.

Waste heat recovery potential in the thermochemical copper–chlorine cycle for hydrogen production: Development of an efficient and cost-effective heat exchanger network

With the finite nature of fossil fuel resources and related environmental issues, it is necessary to replace fossil-fuel-based hydrogen production methods with more sustainable ones. For the clean production of hydrogen, the copper-chlorine (Cu–Cl) thermochemical cycle is a favorable choice. However, internal waste heat recovery of the cycle is essential to improve the efficacy of the system. In this paper, the waste heat recovery potential of the four-step Cu–Cl cycle is investigated, to support the design of a new cost-effective and high-performance heat exchanger network. Pinch analysis is executed to find the optimum rates of cold and hot utilities for this cycle. Three heat exchanger network cases are investigated which include case 1, without heat recovery; case 2, with 16 heat exchangers; and case 3, with 11 heat exchangers. The effect of varying design parameters on the energy system's efficiency and cost-related parameters are also explored here. Based on the pinch analysis results, the minimum heating and cooling and the maximum recoverable heat, on a normalized basis, are 333.3 kJ/mol H2, 76.9 kJ/mol H2, and 134.4 kJ/mol H2, respectively. Moreover, for cases 1, 2, and 3 the thermal efficiencies are calculated as 33.3%, 41.1%, and 40.5%, respectively. Additionally, it is observed that, when the thermal energy of the cycle is supplied from a solar power tower plant, the levelized cost of hydrogen for case 1 is 9.6 $/kg H2, for case 2 is 7.9 $/kg H2, and for case 3 is 7.8 $/kg H2.

A near-zero carbon emission methanol production through CO2 hydrogenation integrated with renewable hydrogen: Process analysis, modification and evaluation

Carbon dioxide hydrogenation to produce methanol has the potential to liberate humanity from its reliance on fossil fuels, while simultaneously reducing carbon dioxide and developing the economy. This paper focuses on the effect of catalyst type and the process conditions such as temperature, pressure, H2/CO2 feed ratio, and space velocity on CO2 conversion and CH3OH selectivity. The net generated CO in the reaction system results in the loss of CO2 and H2 to the purge gas, which reduces the utilization efficiency of carbon and hydrogen. The specially designed catalysts and processes with recycling can improve CO2 conversion and CH3OH selectivity, and the CO flow rate difference can be close to zero in the total recycling condition. Starting from these ideas, the two kinds of near-zero carbon emission processes with total recycling (respectively named total recycling process after flash separation and named total recycling process after stripping separation) are proposed. The utilization efficiency of carbon and hydrogen are similar in the two processes, but hot and cold utilities in the latter are 17.96% and 15.11% lower than in the former, respectively. Through the process integration between reaction heat and double-effect distillation, the energy consumption is further reduced in the total recycling process after stripping separation. The utilization efficiency of CO2 is 99.88% in the total recycling process after stripping separation with double-effect distillation of the light split/reverse configuration, and the proposed process just requires cold utility.

Synergistic Chemical Looping Process Coupling Natural Gas Conversion and NOx Purification

We present a novel low-temperature chemical looping combustion scheme for simultaneous natural gas conversion into a sequestration-ready CO2 stream and NOx purification. The scheme employs nickel oxide (NiO) supported on ZrO2 as the oxygen carrier. In the process, CH4 reduces the oxidized carrier to Ni/ZrO2 in a co-current moving bed reactor, which is then oxidized back to NiO/ZrO2 by the NOx-laden flue gas in a fluidized bed reactor, completing the oxygen carrier loop. Thermodynamic studies demonstrate that the presence of CO2 does not significantly affect NOx purification performance at different flue gas flow rates. The operating temperatures of the reactors are selected based on NOx-temperature programmed oxidation (TPO) and CH4-temperature programmed reduction (TPR) experiments. Results show that the process can optimally operate at temperatures close to the combustion plants’ flue gas temperature of 400–500 °C, reducing the need for hot utilities. The study conducts comprehensive isothermal and autothermal analyses of the process to evaluate the effects of temperature and carrier flow rate on CH4 conversion, CO2 selectivity, carbon deposition, and NOx conversion. For the autothermal analysis, the CH4 reactor operates adiabatically, while the NOx reactor operates isothermally. Comparative studies with the conventional NOx selective catalytic reduction (SCR) process indicate an exergy efficiency and effective thermal efficiency (ETE) improvement of 9 and 18 percentage points, respectively. The findings suggest that this low-temperature chemical looping process is a promising solution for flue gas NOx treatment, utilizing cheaper natural gas as the reductant and eliminating environmental concerns, such as ammonia or urea slippage. Overall, this study contributes to the development of more efficient and sustainable methods for reducing NOx emissions.

Improved energy recovery from the condensed steam as part of HEN retrofit

The conventional approach to heat exchanger network (HEN) retrofit involving design techniques based on Pinch Technology (PT) is extended to include minimization of energy losses resulting from steam-condensate expansion. The authors proposed a new approach to minimize energy losses in utility system, thermally coupled with the combined heat and power (CHP) plant, using condensate subcooling phenomena. Moreover, applying condensate subcooling can counteract the drawbacks of commonly used multi-stage condensate expansion which increase operability and reduces investment and maintenance costs. A case study illustrates the suitability of improved condensate management as a HEN retrofit measure. The study object is a Methyl-Tert-Butyl Ether (MTBE) plant processing 18 t/h isobutylene and consuming 4386 kW of hot utility (steam) in the HEN. A study of the maximum possible heat recovery using PT indicates that the combined heat recovery from hot process streams and condensate can be increased by 510 kW compared to the existing state. At the same time, it is possible to generate additional power of 120 kW in the CHP plant that supplies energy to the MTBE plant. The locations of heat exchangers are accounted for in HEN reconfiguring. A new scheme of steam and condensate system is presented.

Simulation and redesigning the methanol production cycle using coil-wound liquefied natural gas heat exchangers

The current research uses Aspen Software to find the best way to run the petrochemical methanol complex. This was done by using pinch technology and arranging the heat exchanger network. First, a process flow diagram of the Kaveh industrial plant was used to simulate different plant parts. Then retrofit the plant’s heat exchanger network to minimize capital costs and improve energy efficiency. Plotting the composite curve of the streams, the type, and the quantity of hot and cold utilities came next., and the most economical minimum temperature difference, etc. The best capital cost decreased by around 70%, while the utilities increased by about 50%, and the payback money lasted for 6 months. The methanol cycle was redesigned using coil-wound heat exchangers to improve operational flexibility because of high-temperature streams.The capital costs decreased by around 10%, and utility costs were saved with the liquefied natural gas heat exchangers.

Utility targeting in heat exchanger network with parametric uncertainties

For almost a half-decade, the methodology of Pinch Analysis (PA) and heat integration (HI) has been used to optimize the requirements of external utilities. Though much has been done, optimizations under uncertain conditions still need more work, discussion, and practical implementation. In most of the HI problems, it has been observed that variation in the minimum driving force affects the shape of the source and sink profile eventually the heat exchanger network (HEN) design. Due to changing operating conditions, human errors, and sometimes poor maintenance, it has been experienced that the process plants along with their equipment and vessels do not operate at the desired value upon which they are expected to run. The parameters with variations and uncertainties due to disturbances in the process plants need to be addressed for the desired product output. In this work, the concept of PA has been unified with robust optimization (RO) to target the utility requirements in HEN optimization where the uncertainties in the heat capacity flow rate F and supply temperatures Tin of the source streams are considered. The developed nominal forms of mathematical programming are converted into the deterministic robust counterpart equivalents to incorporate the uncertainties whose set of variations is known. RO is an optimization technique where the information of accurate probability distribution needs not be known; rather, it works in a defined set of uncertainty ensuring the feasibility of the solution. Using two examples from the literature, the developed models have been solved and results for the solutions against the range of uncertainties in parameters have been established. The produced data demonstrates, in the case of uncertain inlet temperature the rise in total utilities is 115% and 225% in examples 1 and 2 for worst case is calculated. Plots of budget parameter Γ vs the utility requirement have also been compared with results. Application of this model will further assist the plant engineers/managers in deciding the requirements of hot utilities and cold utilities under the parametric uncertainties as needed.

Experimental investigation and multi-objective optimization of boiler-recuperator systems to reach MILD combustion characteristics

The article aims to achieve the benefits of MILD combustion in a conventional hot water utility boiler by performing a simple revamping and generalizing results to the industrial utility boilers. For this purpose, experimental and numerical investigations were performed on preheating and diluting of combustion air using a recuperator and a flue gas recirculation (FGR) line in a pilot-scale boiler equipped with a conventional premixed burner. Experimental results of maximum preheating and optimal dilution led to increased thermal efficiency and simultaneous NOx reduction in the pilot-scale boiler, which are characteristics of MILD combustion. Thermodynamic modeling and optimization were conducted to determine the optimum air dilution for different industrial utility boilers equipped with various recuperators. Multi-objective optimization provides a set of optimal solutions for fuel flow rate, excess air and FGR to improve system efficiency and reduce NOx emission. It was found that the optimal FGR decreases with increasing boiler efficiency. For instance, in a system equipped with 50 % recuperator effectiveness, the optimal FGR reduces from 0.6 to 0.24 when boiler efficiency increases from 60 % to 90 %, respectively. These optimal FGRs ensure that the system efficiency is maximized while reducing NOx emissions to less than 30 ppm. The novelty of present study is investigating wide range of FGRs for various boiler-recuperator systems and demonstrating that maximum possible preheating together with optimum FGR can provide advantages of MILD combustion to any conventional utility boilers.

Structure optimization of task-specific ionic liquids targeting low-carbon-emission ethylbenzene production

The production of ethylbenzene from dry gas is a representative of an energy-intensive process in oil refineries, and the distillation process accounts for the major energy consumption and carbon emissions. Due to the increasing energy and environmental challenges, there is a strong demand for new technologies or intensified process designs that enable us to have energy-efficient and sustainable process operations. In this work, an ionic liquid (IL)-based energy-efficient extractive distillation (ED) process with low carbon emission is proposed for the distillation process of ethylbenzene production from dry gas. First, the structure of task-specific ILs is optimized through the computer-aided IL design (CAILD) method with a novel design objective. An ammonium-based IL ethylammonium trifluoromethanesulfonate ([C2H8N][TfO]), that has the best objective performance, is identified by solving a mixed-integer nonlinear programming (MINLP) problem. The energy, environmental (carbon emission), and economic performance of this [C2H8N][TfO]-based ED process in the ethylbenzene production is then thoroughly evaluated on the basis of optimized process operations in Aspen Plus. For demonstration purposes, a case study for the separation process of an industrial-scale ethylbenzene production in a Chinese refining industry is performed. When compared to the conventional process that is currently used in the petrochemical industry, our proposed [C2H8N][TfO]-based ED separation process has 40 % energy (hot utility) savings and a 11 % cost reduction. Notably, the IL-based ED separation process has 40 % lower carbon emissions versus the conventional process, indicating its great potential for sustainable operation in the production of ethylbenzene from dry gas.

Style: A new optimization model for Synthesis of uTility sYstems with steam LEvel placement

Moving industrial production to a more sustainable basis requires a step change in the efficiency of site steam and cogeneration systems, coupled with a switch away from fossil fuels to renewable energy sources. This paper presents the first step in the development of an optimization framework capable of identifying a roadmap to move utility systems to a more sustainable basis. Previous approaches to the design and optimization of steam and cogeneration systems have simplified the problem to the extent that many important practical issues have been neglected, restricting the scope of the options included. The use of grossly simplified models has been prompted by the mathematical difficulties of optimizing such complex energy systems. To overcome limitations in previous work and provide a sound basis for future developments, this paper proposes a new superstructure-based optimization model for the optimization of utility systems, accounting for optimum steam level placement. The latter is important for improving systems efficiency and reducing energy consumption. The optimization problem involves the selection of more realistic operating conditions of the steam mains (superheat conditions and pressure). The model accounts for water preheating, as well as superheating and de-superheating for process steam generation and use. Hot oil circuits are also included as hot utility option to overcome potential steam temperature and/or pressure limitations at high temperatures, and with it provide more flexibility in the framework. The general problem requires making several continuous and discrete decisions, where non-linearities and non-convexities from underlying physics and binary decisions exacerbate the complex nature of the problem, yielding a nonconvex Mixed Integer Non-Linear Programming (MINLP) formulation. However, MINLP formulations can become computationally intractable to solve. Thus, to guarantee tractability and fast conversion, the STYLE model develops a novel successive Mixed Integer Linear Programming formulation. The STYLE methodology is applied to two case studies to illustrate the advantages of the synthesis method and the benefits of optimizing steam levels for the reduction of overall energy consumption at industrial sites. The proposed approach addresses major shortcomings inherent in previous research and provides a foundation for future work to explore the next generation of sustainable utility systems.

Investigation of process stream systems for targeting energy-capital trade-offs of a heat recovery network

The process industries consume a huge amount of heat energy contributing to environmental impact. Energy recovery is a key instrument of energy-saving that can be implemented via a heat exchanger network. Pinch-based approaches presume analysis of energy targets of industrial processes to find the optimal ΔTmin for heat exchanger network design. Classical Pinch Analysis do not account for the stream splitting in the super targeting procedure while parallel branches are usually needed. The splitters and mixers contribute a lot to the capital cost of the heat exchanger network. Current work proposes the update of super targeting procedure accounting stream splitting and mixing in a Pinch problem. The original algorithm of Composite Curves construction is proposed to analyse the distribution of process streams and stream splitting in subsystems above/below the Pinch before the design of the heat exchanger network. It was then used in a super targeting procedure to precise the capital cost and, as a result, the optimal ΔTmin. The process stream distribution and stream splitting are analysed in a whole range of ΔTmin. Identifying all possible starting points for heat exchanger network design. Two new criteria were proposed to estimate the topological complexity of network pre-design and the specific ratio of stream splitting. The case study analyses the ethylene oxide process and calculation of trade-off between capital and energy costs were performed and optimal ΔTmin = 16 °C. The result was compared with two known approaches, which account for the number of heat exchangers without stream splitting. Total annual costs and optimal ΔTmin was also calculated for different energy prices to show a possible deviation of starting point for heat exchanger network design. The range of optimal ΔTmin from 9 to 54 °C resulted in the range of hot utility prices from 42 to 291 $/kWy, and the emission targets will be from 14,380 to 77,919 tCO2/y. The methodology can be used for the pre-design of the heat exchanger network to better precise the optimal ΔTmin, capital cost targets, and check the optimum changing for different energy prices.