Heat Recovery Section Research Articles

A geothermal-based freshwater/cooling system assisted by heat recovery sections: 3E analysis and techno-economic optimization using genetic algorithm

The proposed system uses a dual-loop organic Rankine cycle, a reverse osmosis desalination unit, an absorption cooling unit, and a thermoelectric generator to produce electricity and freshwater for urban areas. A thorough assessment of the system's thermodynamic and economic performance has been conducted, with a parameter-based investigation to assess the effect of key variables on the system performance. The parametric study indicates that rising the geothermal mass flow rate enhances the energy efficiency, but lowers the energy efficiency and affects the cooling requirements. Moreover, the optimum inlet temperature in turbine 1 increases the desalination efficiency up to 105.02 kg/s at 115 °C, and higher temperatures reduce the performance and system efficiency. Adjusting the temperature difference at the pinch point at Evaporator1 is crucial for system efficiency, with trade-offs between freshwater output, expenses, and exergy efficiency. The capability of the system to produce up to 6,048,000 L of potable water daily signifies a monumental leap towards meeting the water demands of nearly 42,000 individuals, based on European consumption standards. Lastly, the application of genetic algorithms in the optimization process results in an exergetic efficiency of 32.79 % and a cost rate of 58.05 $/h, demonstrating the system's enhanced operational effectiveness.

A Modeling Analysis of Wastewater Heat Recovery Effects on Wastewater Treatment Plant Nitrification

A global shift towards renewable energy production, driven primarily by the challenges posed by climate change, is currently underway. In this context, the utilization of heat recovery from municipal wastewater emerges as a promising green technology. Notably, the advantage of implementing energy recovery in sewers, as opposed to wastewater treatment plants (WWTPs), lies in the higher temperature of the wastewater and its proximity to potential heat users. Despite these benefits, concerns arise regarding the potential adverse effects on biological wastewater treatment processes downstream of the heat recovery section, particularly during colder seasons. This paper seeks to assess the impact of a heat recovery system along the sewer network on the efficiency of biological wastewater treatment processes. The methodology involves a modeling analysis of a real sewage network in Italy. Under typical northern Italy climate conditions, the results demonstrate the feasibility of heat recovery in sewers for WWTPs designed with a sludge residence time under aerobic conditions (SRTaer) greater than 13 days. In such cases, the nitrification process remains relatively unaffected. However, for lower SRTaer values, a case-specific feasibility assessment is recommended to evaluate the overall process efficiency comprehensively.

A potential coupling of reforming and electrolysis for producing renewable hydrogen from landfill gas

Organic sold waste disposed of in landfills undergoes a mostly anaerobic process which generates a mixture of methane (CH4), carbon dioxide (CO2) and other various gases such as nitrogen, oxygen, sulphides, and non-methane organic compounds (NMOC), known as landfill gas (LFG). Being composed mostly of CH4 and CO2, landfill gas is a potent greenhouse gas (GHG). As a result, various waste treatment interventions are required to minimize the potential catastrophic damage to the environment from direct greenhouse gas emissions from landfills. One effective solution is combustion to generate electricity exploiting methane’s flammability properties. Biomass-based power plants have been present for decades. However, the combustion process is accompanied by a remarkable production of thermal energy which is typically not exploited and therefore lost to the ambient. The current work presents an energetic solution to manage organic waste by employing green hydrogen production. To do so, a hybrid layout based on a cogeneration unit (CHP) fed with landfill gas is considered. The electrical power produced by the CHP is used to produce hydrogen through low-temperature water electrolysis. Furthermore, due to the significant waste heat available in the system, excess thermal power is employed for the methane steam reforming process through a heat recovery section. Hydrogen produced from the reforming section is green since the input is from landfill gas, which is considered renewable. The levelized cost of hydrogen produced from such a hybrid layout is obtained and compared with non-renewable sources in this field. In addition, the annual H2 production rate is calculated for a capacity factor equal to 70%. The results show an annual Hydrogen production of about 167 t/y. LCOH at the stack of about 2 €/kg is reported.

Performance evaluation of a solar multi-stage humidification dehumidification desalination plant with heat recovery section

In this study, a solar multi-stage humidification-compression desalination plant with heat recovery section was experimentally studied. Since honeycomb cellulose pads are more efficient than the conventional packings, in this plant, the humidifier was filled with cellulose pads. The influence of several operating parameters on the plant performance was experimentally studied. The experiments were conducted by one-at-a-time method and the plant was optimized using the response surface methodology based on a central composite design. The results showed that increasing the temperature of the inlet water to the humidifier and the compressor pressure ratio while reducing the water-to-air mass flow ratio enhanced the gained output ratio (GOR), performance ratio (PR), and recovery ratio percentage (RR%). Besides, to improve the specific energy consumption (SEC), the temperature of the inlet water to the humidifier and water-to-air mass flow ratio should be increased while the compressor pressure ratio should be decreased. The salt concentration in the feed does not have a significant influence on the system performance. The production cost was estimated at 1.3–8.53 $·m−3 in the proposed system, which, is capable to produce demineralized water.

High-temperature green hydrogen production: A innovative– application of SOEC coupled with AEC through sCO2 HP

This study evaluates a potential coupling between AEC and SOEC through a CO2 heat pump unit that works in super-critical conditions. In such a way, thermal power requested by SOEC can be provided by recovering heat loss from AEC via the CO2heat pump. The coupled configuration is characterized by renewable electric input. Hence, the power is provided for electrolysis without more external thermal resources. The energy, economic and environmental impacts of such intervention have been determined and compared with SOEC in solo mode. The layout is created and simulated in a MATLAB SIMULINK environment.The simulation results show a potential improvement in the total energy efficiency of the whole system without an external heat resource, up to 68%, which is higher than 65% of SOEC itself, thanks to the heat recovery section that is correlated with sCO2 HP contribution. LCOH varies widely depending on SOEC size from around 2.59 €/kgH2 up to 9.27€/kgH2.

Development of a Test Bench for Biogas-fueled Internal Combustion Engines Working in Cogeneration Mode for Residential Applications

The aim of this paper is the presentation of a test bench developed and installed at the Laboratory of the University of Bologna: the test bench has been developed for internal combustion engines, working as cogeneration units and fueled with biogas. In this perspective, the test bench purpose is to experimentally test and optimize the operation of cogenerative internal combustion engines on varying the boundary conditions, in terms of both biogas composition and electric and thermal load. Other main components are the anaerobic digester, a multi-fuel internal combustion engine, the electric load and a heat exchanger for the heat recovery from the exhaust gases and connected to a water circuit representing the thermal user. The test bench has been equipped with the opportune measurement devices, as well as with a specifically developed data acquisition system. First experimental tests, carried out on varying the methane content within the CH4-CO2 blend and the electric load allowed to optimize the test bench in terms of heat recovery section and air supply to the engine.

Upgradation of agricultural straw pyrolysis through co-processing with PE waste and by-product detoxification

Co-pyrolysis of biomass and waste PE is not only an effective way to mitigate waste PE pollution, but it is also an economical method of obtaining bio-crude with high quality. However, the incomplete conversion and toxicity of by-products (char and aqueous phase) are restricting its industrialization, which is not noticed. Therefore, this study aimed at a new integrated process that is composed of co-pyrolysis, steam reforming of by-products, and heat recovery sections. Compared with traditional biomass pyrolysis, the liquid products of co-pyrolysis were heterogeneous, which is suitable for products separation. The new system reduced the energy consumption in product separation by 2389 MJ and 437.26 kWh per ton of raw materials. The O content of bio-crude was decreased from 37.97 % to 4.82 %. Compared with existing hydrogen production processes, the yield of H2 in this study was 69.4 kg/ton, and production efficiency was 71 %. For environmental assessment, biomass collection and product treatment were found as the main environmental influence factors, and the main influencing factors included pesticides, fertilizers, electricity, diesel, and exhaust gas. During seven cases, the co-pyrolysis has significantly reflected the decreasing impact of exhaust gas and electricity consumption on GWP (decreasing about 40 %-60 %). Besides, the distributed co-pyrolysis model significantly reduced the diesel consumption during biomass transportation and reduced the impact on ODP by about 60 %.

Assessment of using energy recovery from a sustainable system including a pyramid-shaped photovoltaic cells and batteries to reduce heating energy demand in the ventilation section

Buildings should reduce their carbon dioxide emissions by 95 % from 2020 to 2050. The cooling and heating system of the building is one of the most important parts of the building in CO2 production. In this study, thermal analysis of a building that was heated and cooled using the radiant pipe within the floor was investigated in the climate region of Riyadh (latitude 24.7, longitude 46.73). The floor of the building with an area of 200 m2 with a thermal resistance of 0.713 m2.KW was located over a parking space. To decline the heat loss or heat gain of the floor, phase change material (PCM) at the thickness of 3, 6, 9 and 12 cm was installed inside the floor. Owing to installing PCM of A25 with a melting point temperature (MPT) of 25 °C, heat transfer through the roof declined by 15.8 % (at a thickness of 3 cm) to 46.7 % (at a thickness of 12 cm). Several PCMs such as A23(MPT = 23 °C), A24, A25, A26, A27 and A29(MPT = 29 °C) were examined. In heating mode, A23by recording the energy demand reduction of 345.4 kWh was the best while in cooling mode, A25 was the best by recording the energy saving of 476 kWh. Moreover, in the heat recovery section, the use of heat from batteries and solar cells to preheat the ventilation air lead to an energy consumption reduction of 1.8 %.

Performance of dual multistage flashing - recycled brine and solar power plant, in the framework of the water-energy nexus

Water is an essential source for life, and due to rapid growth in the population, the demand for clean water is increasing, while the freshwater reservoirs and aquifers are continuously depleting, creating water scarcity. By using desalination techniques, ocean water can be converted into useable water. In this study, a Multistage flashing- Brine recirculation (MSF-BR) model is used as a technique to produce desalinated water. A mathematical model is developed to investigate the performance ratio of the MSF plant driven by solar energy by using a poly PV array type. This solar power plant can provide 6.52 kg/s superheated steam for the system of thermal desalination. The solar power plant is made up of 72 poly-Si panels with 34 strings each. This facility has a capacity of 30 MW; 15 MW is utilized to produce 6.52 kg/s of superheated steam, which is used to power the MSF-BR desalination plant, while the rest is fed into the grid. The MSF-BR plant is made up of twenty-four stages, twenty-one of which are in the heat recovery section (HRS) and the remaining three in the heat rejection section, which is designed to be the most efficient. The top brine temperature is 110 C, the distilled water is 63.314 k/s, and the blowdown brine salinity concentration is around 69,439.54 ppm, according to the MSF-BR performance. Also, with a heat transfer area of 14,559.8 m2 for HRS and 1,663.8 m2 for the rejection section and a stage length of 1.37 to 2.648 m from the first to the last stage, the optimum gain was achieved.

Modelling and simulation of industrial multistage flash desalination process with exergetic and thermodynamic analysis. A case study of Azzour seawater desalination plant

Abstract Despite the fact of being intensive energy consumption, MSF is a mature technology that characterised by a high production capacity of high-quality water. The multistage flash (MSF) desalination process is one of the prominent thermal desalination used in the industry of seawater desalination to produce high quantity and high quality of freshwater. However, this process consumes large amount of energy and faces thermal limitations due to its high degree of exergy destruction at several units of the process. Therefore, the research of MSF is still existed to elevate the performance indicators and to resolve the concern of high energy consumption. To rectify these limitations, it is important to determine the units responsible in dissipating energy. This study aims to model an industrial MSF process validated against real data and then investigate the exergy destruction and thermodynamic limitations of the process. As a case study, Azzour MSF seawater desalination plant, located in Al Khiran in Kuwait is under the focus. A comprehensive model is developed by analysing several published models. Specifically, the calculation of exergy destruction has embedded both physical and chemical exergies that identified as a strong point of the model developed. As expected, the highest exergy destruction (55.5%) occurs within the heat recovery section followed by the brine heater with exergy destruction of 28.26% of the total exergy destruction. This study identifies the sections of the industrial process that cause the highest energy losses.

Performance evaluation of a multi-stage humidification compression with heat recovery based on mathematical modeling

A solar multi-stage desalination plant based on humidification compression with a heat recovery section was proposed in this study. Unlike conventional multi-stage plants, in this plant, water was reheated in the energy recovery section before entering the next humidifiers. The plant consisted of three packed columns (humidifiers), a polytropic compressor and three heat exchangers for energy recovery. A mathematical model was established to evaluate the impact of several operating parameters on the plant performance. The model was numerically solved, and a good conformity was found between the experimental data and numerical results. Average absolute error values of 2.12%, 0.25% and 0.38% were found for the outlet air humidity, outlet water temperature and outlet air temperature, respectively. In addition, the gained output ratio (GOR) and performance ratio (PR) for the proposed plant were found to be higher than those of conventional plants. In addition, higher inlet water temperature and lower pressure ratio and water-to-air mass flow ratio enhanced the GOR. On the other hand, the variation of pressure ratio had no significant influence on the PR, but higher inlet water temperature and lower water-to-air mass flow ratio increased the PR.

Decision support system for a heat-recovery section with equipment degradation

In the framework of Industry 4.0, decision support systems (DSS) are an essential part in the process of converting information into managerial actions. This paper proposes a specific DSS to improve the daily operation of an industrial heat-recovery section (a network of heat exchangers) in a fiber-production factory. In this process, the aim is to optimize the resource utilization in real time while satisfying a set of production constraints. The operational decisions to be taken by the network operators is to set up the heat-source allocation to heat exchangers. Furthermore, the heat transfer decreases over time due to fouling in the exchangers, so an additional decision to take is which exchanger to clean and when. The proposed model-based DSS builds upon a rigorous mathematical representation of the network, integrating continuous operation with the discrete decisions on maintenance. Then, a mixed-integer nonlinear optimization, solved in real time, drives the analysis and choice phases to fulfill product specifications according to an economic criterion. In this way, the proposed DSS not only provides the user with a right allocation of heat sources to exchangers, but also suggests which of them are potentially beneficial to be cleaned.

Efficiency analysis of 50 kWe SOFC systems fueled with biogas from waste water

Solid oxide fuel cell systems (SOFCs) are able to convert biogas from e.g. waste water plants highly efficiently into electricity and heat. An efficiency study of industrial sized solid oxide fuel cell systems installed at a waste water treatment plant is presented. The site consist of a biogas cleaning unit, two Convion C50 SOFC systems and a heat recovery section. The electric and total efficiencies of the systems are analyzed as a function of the electric net power output. The two systems achieved consistently high electric (50–55%) and total (80–90%) efficiencies in an electric net power output range between 25 kW and 55 kW. The study also shows that the high system efficiencies are independent of the CH 4 content in the biogas. The results indicate that fuel cell systems are able to perform power modulation according to the power demand, while achieving constant high efficiencies. This is a clear benefit in comparison to micro turbines and combustion engines which are normally used for converting biogas into electricity and heat. • Solid oxide fuel cell systems fueled with waste water treatment biogas. • Constant high system efficiencies by variating electric net power output. • System efficiencies are independent from the CH 4 present in the biogas.

Modelling and real-time optimisation of a heat-exchanger network

This work proposes a hybrid mathematical model and an optimisation-based tool to support the management of a heat-recovery section (formed by several heat exchangers) in a fibre-production factory. The purpose of the network is to heat different products using several hot sources, employed as utilities. Furthermore, concerns about the degradation of the equipment due to fouling are explicitly taken into account. Hence, the goals are to allocate the hot sources to heat exchangers and to suggest which heat exchanger should be cleaned to achieve optimal economic operation. Experimental models for the overall heat-transfer coefficients with respect to the flows have been identified, and production constraints are considered too. The problem is formulated such that it can be solved in a real-time optimisation fashion via mixed-integer non-linear programming. The approach has been tested through plant historical situations.

Air Distribution and Air Handling Unit Configuration Effects on Energy Performance in an Air-Heated Ice Rink Arena

Indoor ice rink arenas are among the foremost consumers of energy within building sector due to their exclusive indoor conditions. A single ice rink arena may consume energy of up to 3500 MWh annually, indicating the potential for energy saving. The cooling effect of the ice pad, which is the main source for heat loss, causes a vertical indoor air temperature gradient. The objective of the present study is twofold: (i) to study vertical temperature stratification of indoor air, and how it impacts on heat load toward the ice pad; (ii) to investigate the energy performance of air handling units (AHU), as well as the effects of various AHU layouts on ice rinks’ energy consumption. To this end, six AHU configurations with different air-distribution solutions are presented, based on existing arenas in Finland. The results of the study verify that cooling energy demand can significantly be reduced by 38 percent if indoor temperature gradient approaches 1 °C/m. This is implemented through air distribution solutions. Moreover, the cooling energy demand for dehumidification is decreased to 59.5 percent through precisely planning the AHU layout, particularly at the cooling coil and heat recovery sections. The study reveals that a more customized air distribution results in less stratified indoor air temperature.

Numerical simulation of a three-layer porous heat exchanger considering lattice Boltzmann method simulation of fluid flow

The present study investigates the thermal characteristics of a proposed porous heat exchanger (PHE). This heat exchanger consists of three sections, one high-temperature (HT) section and two heat recovery (HR) sections. Product of combustion as a high-temperature gas mixture enters to HT section in which enthalpy of gas flow is converted to thermal radiation, while in HR sections, the reverse phenomenon occurs. Simulation of fluid flow in porous medium generated by random and regular monodisperse and polydisperse particles is done using combination of the lattice Boltzmann method and smoothed profile method. Because of high-temperature variation in this system, effect of temperature on thermo-physical properties is also considered which has not been studied in previous research studies. Since the gas and solid phases are in non-local thermal equilibrium, separate energy equations are used for these phases. To obtain the radiative term in the solid energy equation, the radiative transfer equation is solved numerically by the discrete ordinates method. The influence of particles array and their sizes on the efficiency of the PHE system is studied. Finally, the effects of various parameters like optical thickness and scattering coefficient on the performance of PHE system are investigated.

Process development and exergy cost sensitivity analysis of a hybrid molten carbonate fuel cell power plant and carbon dioxide capturing process

An integrated power plant with a net electrical power output of 3.71 × 105 kW is developed and investigated. The electrical efficiency of the process is found to be 60.1%. The process includes three main sub-systems: molten carbonate fuel cell system, heat recovery section and cryogenic carbon dioxide capturing process. Conventional and advanced exergoeconomic methods are used for analyzing the process. Advanced exergoeconomic analysis is a comprehensive evaluation tool which combines an exergetic approach with economic analysis procedures. With this method, investment and exergy destruction costs of the process components are divided into endogenous/exogenous and avoidable/unavoidable parts. Results of the conventional exergoeconomic analyses demonstrate that the combustion chamber has the largest exergy destruction rate (182 MW) and cost rate (13,100 $/h). Also, the total process cost rate can be decreased by reducing the cost rate of the fuel cell and improving the efficiency of the combustion chamber and heat recovery steam generator. Based on the total avoidable endogenous cost rate, the priority for modification is the heat recovery steam generator, a compressor and a turbine of the power plant, in rank order. A sensitivity analysis is done to investigate the exergoeconomic factor parameters through changing the effective parameter variations.

Performance optimization of a multi stage flash desalination unit with thermal vapor compression using genetic algorithm

In the present study, a multi stage flash desalination system with brine recirculation and thermal vapor compression (MSF-BR-TVC) is analyzed. From four different configurations of MSF-BR-TVC systems, the one with two ejectors the receives secondary vapor from two successive middle stages of the heat recovery section is studied in more detail due to its higher performance ratio which is 9.90. In this configuration, the compression ratio for the first and second ejectors are 4.55 and 4.06, respectively. Also, the mixing number for these two ejectors are 2.62 and 2.33. Then, an optimization process based on genetic algorithm is carried out to evaluate the effect of most important parameters on the performance ratio. It is observed that optimum performance ratio of 12.80 is achieved for the heat steam, last stage and top brine temperatures of 90.18°C, 39.75°C and 89.97°C, respectively. Although such performance ratio is the highest value in the range of decision variables, it leads to a large, uneconomical specific heat transfer area. To resolve this issue, two-objective optimization is performed using NSGA II method. The two objectives are selected as performance ratio and specific heat transfer area with the latter considered as cost function due to its direct connection with cost. Two-objective optimization using NSGA II leads to a Pareto front curve. Selection of each point on this curve depends on the designer’s decision, namely priority of the performance ratio or the specific heat transfer area. Moreover, the effect of the number of total stages on the optimum performance ratio for the selected MSF-BR-TVC is investigated. Results show that increasing the total number of stages from 20 to 30 increases the optimum performance ratio from 9.97 to 15.27.

Dynamic modelling of Heat Exchanger fouling in multistage flash (MSF) desalination

Fouling on heat transfer surfaces due to scale formation is the most concerned item in thermal desalination industry. Here, a dynamic fouling model is developed and incorporated into the MSF dynamic process model to predict fouling at high temperature and high velocity. The proposed dynamic model considers the attachment and removal mechanisms in the fouling phenomena with more relaxation of the assumptions such as the density of the fouling layer and salinity of the recycle brine. While calcium sulphate might precipitate at very high temperature, only the crystallization of calcium carbonate and magnesium hydroxide are considered in this work. Though the model is applied in a 24 stages brine recycle MSF plant, only the heat recovery section (21 stages) is considered under this study. The effect of flow velocity and surface temperature are investigated. By including both diffusion and reaction mechanism in the fouling model, the results of the fouling prediction model are in good agreement with most recent studies in the literature. The deposition of magnesium hydroxide increases with the increase in surface temperature and flow velocity while calcium carbonate deposition increases with the increase in the surface temperature and decreases with the increase in the flow velocity.

Optimization for energy consumption in drying section of fluting paper machine

Non-linear programming optimization method was used to optimize total steam and air consumption in the dryer section of multi-cylinder fluting paper machine. Equality constraints of the optimization model were obtained from specified process blocks considering mass and energy balance relationships in drying and heat recovery sections. Inequality constraints correspond to process parameters such as production capacity, operating conditions, and other limitations. Using the simulation, the process parameters can be optimized to improve the energy efficiency and heat recovery performance. For a corrugating machine, optimized parameters show the total steam use can be reduced by about 11% due to improvement of the heat recovery performance and optimization of the operating conditions such as inlet web dryness, evaporation rate, and exhaust air humidity, accordingly total steam consumption can be decreased from about 1.71 to 1.53 tonnes steam per tonne paper production. The humidity of the exhaust air should be kept as high as possible to optimize the energy performance and avoid condensation in the pocket dryers and hood exhaust air. So the simulation shows the supply air should be increased by about 10% to achieve optimal humidity level which was determined about 0.152 kgH2O/(kg dry air).