Heat Recovery Method Research Articles

Review: CFD Analysis Comparison of Tapered Helical and Square Coil Heat Exchanger Bu Using Different Types of Nanofluid with Oil as Its Base Fluid in Aluminium and Copper Tube

Abstract: The recovery of waste heat has been a topic of concern for large-scale industrial companies for several decades. This recovery not only makes an operation more environment friendly, but it also helps to cut costs. In addition to this, it can reduce the amount of resources needed to power a facility. Many industries have implemented different methods of waste heat recovery. One popular choice is using a heat exchanger. This paper presents the study of two different types of nano-fluids in two materials off heat exchangers ie.aluminium tapered helical coil heat exchanger and copper tapered helical coil heat exchanger. In this present paper the efforts are made to understand that how to compare the heat transfer rate in Copper and aluminium tapered helically coiled tube heat exchanger using different types of Nano fluid by studying research papers of various authors. Keywords: Tapered Helical Coil, Tapered Square coil, Nano-fluid, Heat Exchanger, CFD, Pressure Drop, Temperature Distribution, Aluminium and copper.

Ammonia absorption performance of a liquid desiccant dehumidification system applied in laboratory rodent room

• Henry’s law constant of ammonia in common liquid desiccants is investigated. • The ammonia transfer model in pack modules of liquid desiccant system is proposed. • Liquid desiccant dehumidification system with LiBr solution is verified to get better ammonia performance than other desiccants. • The improved system significantly decreases the ammonia concentration of supply air compared to regular liquid desiccant dehumidification system. Laboratory rodent room usually adopts full fresh air system with large ventilation rates and causes energy waste for heat-cold offset process. Liquid desiccant system is identified as an energy saving approach in humidity control field. This paper presents the ammonia absorption performance of a liquid desiccant dehumidification system applied in laboratory rodent room while considering air dehumidification requirements. Prior to the simulation process of the system, Henry’s law constant ( H C ) of ammonia, one method to assess the solubility, in LiBr, LiCl, and CaCl 2 solutions are tested at the salt concentration range of 20–50 wt% and at the temperature range of 10–50 °C. The ammonia concentration of supply air ( C sa ) in the LiBr condition is apparently smaller than that in LiCl and CaCl 2 conditions of a liquid desiccant dehumidification system. In addition, C sa apparently increases with the increasing number of mass transfer units of ammonia ( NTU a ) and solution flow rate. The simulation results show that most ammonia is introduced by heat recovery process. An improved system structure is proposed to reduce ammonia transfer. Using the proposed heat recovery method, C sa is decreased by more than 70% over the initial system.

Thermoelectric Power Generators: State-of-the-Art, Heat Recovery Method, and Challenges

Electricity plays a significant role in daily life and is the main component of countless applications. Thus, ongoing research is necessary to improve the existing approaches, or find new approaches, to enhancing power generation. The thermoelectric generator (TEG) is among the notable and widespread technologies used to produce electricity, and converts waste energy into electrical energy using the Seebeck effect. Due to the Seebeck effect, temperature change can be turned into electrical energy; hence, a TEG can be applied whenever there is a temperature difference. The present paper presents the theoretical background of the TEG, in addition to a comprehensive review of the TEG and its implementation in various fields. This paper also sheds light on the new technologies of the TEG and their related challenges. Notably, it was found that the TEG is efficient in hybrid heat recovery systems, such as the phase change material (PCM), heat pipe (HP), and proton exchange membrane (PEM), and the efficiency of the TEG has increased due to a set of improvements in the TEG’s materials. Moreover, results show that the TEG technology has been frequently applied in recent years, and all of the investigated papers agree that the TEG is a promising technology in power generation and heat recovery systems.

Thermodynamic analysis and optimization of auto-thermal supercritical water gasification polygeneration system of pig manure

A large amount of livestock manure is produced every year around the world, which requires harmless utilization to reduce environmental pollution and produce energy. As a promising and pollution-free technology in recent years, Supercritical water gasification (SCWG) can utilize pig manure with high moisture to produce hydrogen. In this paper, a novel process modeling an auto-thermal SCWG polygeneration system of pig manure was established with thermodynamic analysis, coupled with in-situ hydrogen separation and waste heat recovery method. Simultaneously, the environmental significance was analyzed through Life cycle assessment (LCA), and the GWP was 1.73 kgCO2-eq/kgH2 under optimal conditions with CCS. The results showed that the system with in-situ hydrogen separation would produce more H2 to improve energy efficiency. Adding a waste heat recovery unit could reduce the exergy loss of 89.14% of the cooling unit, which had the largest exergy loss in the system. In this study, there were 5081Nm3/h of H2 and 16377 kW of hot steam produced when the SCWG system was auto-thermal (620 ℃, 25 MPa, 650 t/d dry manure and 10 wt% reactor concentration), where the energy efficiency of the system could reach 79.85% that had a 3.6–35.64% increase to the previous SCWG systems. In addition, the optimal operating parameters of this polygeneration system were obtained, which the exergy efficiency could reach 54.25%. A lower complete gasification temperature and a larger in-situ H2 separation ratio were conducive to achieving higher H2 yield when the optimal ratio of preheated water to dry material was 8.

High performance solar receiver–reactor for hydrogen generation

This paper reports on the numerical analysis of a volumetric solar receiver-reactor for hydrogen production, using the 2-step reduction–oxidation cycle. A detailed parametric sweep covering hundreds of various parameter combinations is performed for a large solar reactor, using a transient physical model. We generate performance maps which are currently cost prohibitive via experimental or high–fidelity simulation studies. The following performance metrics are evaluated: solar to fuel efficiency, hydrogen yield, conversion extent and specific hydrogen yield. We show that the relations between the different performance metrics are complex, leading to different optimal points depending on the metric pursued. The daily hydrogen yield for a single reactor varied between 0.89 kg for an absorber thickness of 30 mm, and up to 1.04 kg for a 60 mm thick receiver, with solar to fuel efficiency values of 3.84% and 3.81% respectively. For a case with 45 mm thick receiver, an intermediate hydrogen yield of 0.94 kg is calculated, while exhibiting the highest efficiency (4.05%). The efficiency can be further increased to 5.86% by using a simple heat recovery system, and reach an upper limit of 21.16% with a more sophisticated heat recovery method.

Sludge preheating and viscosity reduction by waste heat from the exhaust gas of sludge paddle dryer

A method of waste heat recovery and utilization was explored by incorporating a heat recovery system into an existing industrial-scale sludge drying system with handling capacity of 440 kg dry solid (DS) per hour. The recovered heat was used to preheat sewage sludge (and carrier gas) to lower sludge viscosity and flowing resistance during sludge transportation in pipeline, as well as the heat consumption during drying. 5.3% decrease of heat consumption in drying, 48% decrease of sludge flowing resistance, and 15% decrease of spraying water consumption in spray tower were fulfilled. Theoretical modeling of heating and flowing behavior of sewage sludge in pipeline, and cooling behavior of hot wet air in a type-III spiral plate heat exchanger were also conducted. The results showed that wall slip phenomenon occurred between sludge and inner surface of sludge pipe during sludge flowing process, which had marked influence on sludge preheating in pipeline.

Waste Heat and Wastewater Recovery in Textile Processing Industry: A Case Study of Adopted Practices

Textile wet processes dispose of huge amounts of water and energy in the form of hot wastewater and exhaust gas emissions. A significant amount of water and energy can be conserved by adopting various waste heat and water recovery methods, such as the use of heat exchanger, recycling hot wastewater, steam condensate, and cooling water recovery and reuse. In this study, various waste energy and water conservation methods are summarized to highlight their importance for water and energy conservation. For practical consideration, a detailed assessment of such practiced methods was done in one textile processing industry. The obtained results revealed that a high amount of energy and water could be conserved by adopting various waste heat and water recovery methods, with the advantage of reducing environmental pollution while minimizing the consumption of energy and water.

Slowing down the heat in thermoelectrics

AbstractHeat transport has various applications in solid materials. In particular, the thermoelectric technology provides an alternative approach to traditional methods for waste heat recovery and solid‐state refrigeration by enabling direct and reversible conversion between heat and electricity. For enhancing the thermoelectric performance of the materials, attempts must be made to slow down the heat transport by minimizing their thermal conductivity (κ). In this study, a continuously developing heat transport model is reviewed first. Theoretical models for predicting the lattice thermal conductivity (κlat) of materials are summarized, which are significant for the rapid screening of thermoelectric materials with low κlat. Moreover, typical strategies, including the introduction of extrinsic phonon scattering centers with multidimensions and internal physical mechanisms of materials with intrinsically low κlat, for slowing down the heat transport are outlined. Extrinsic defect centers with multidimensions substantially scatter various‐frequency phonons; the intrinsically low κlat in materials with various crystal structures can be attributed to the strong anharmonicity resulting from weak chemical bonding, resonant bonding, low‐lying optical modes, liquid‐like sublattices, off‐center atoms, and complex crystal structures. This review provides an overall understanding of heat transport in thermoelectric materials and proposes effective approaches for slowing down the heat transport to depress κlat for the enhancement of thermoelectric performance.image

Thermodynamic and thermoeconomic analysis of a novel power and hydrogen cogeneration cycle based on solid SOFC

To enhance the performance of the thermodynamic systems, reduce the pollutants emission to the environment, and decline the fuel utilization, waste heat recovery methods are in high interest. In this paper, a new configuration of an integrated solid oxide fuel cell and gas turbine combined with a biogas reforming cycle is presented for the cogeneration of power and hydrogen. The thermal energy discharged from the SOFC-GT system is used to supply the energy required for the reforming reaction in the biogas reforming cycle for hydrogen production. Comprehensive thermodynamic and thermoeconomic modeling has been performed using EES software. Also, a parametric study has been performed to demonstrate the effect of different parameters on the main performance metrics of the devised system. The results revealed that the energy efficiency and exergy efficiency of the proposed combined system have increased compared to the SOFC-GT system by 23.31% and 28.19%, respectively. The net output power and hydrogen production rate are obtained by 2726 kW and 0.07453 kg/s, respectively. From the exergy viewpoint, the afterburner causes a considerable amount of exergy destruction for the system by approximately 26% of the total exergy destruction rate. Besides, the sensitivity analysis revealed that by increasing the inlet temperature of the fuel cell, the cell voltage reaches a maximum value at a temperature of 679 K and then decreases. Moreover, the total exergy destruction rate and SUCP of the cogeneration system is calculated by 1532 kW and 9400 $/GJ, respectively.

Development of a novel dual heated cascade supercritical carbon dioxide cycle and performance comparison with existing two configurations for waste heat recovery

As an efficient method for the waste heat recovery of gas turbine, supercritical carbon dioxide (S-CO2) power cycle has gained much attention, due to the high efficiency and compact structure. Thus, in this work, a novel S-CO2 power cycle is developed for the waste heat recovery via the modification of dual heated cascade cycle with an intercooler (intercooling cycle). Compared with the dual heated cascade cycle (original cycle) and the intercooling cycle, the novel cycle has independent pressures at different heaters and turbines. To analyze the system performance, thermodynamic models are established and a genetic algorithm (GA) is applied to optimize the decision variables with the maximization of net work. These variables include two turbine inlet temperatures, a middle pressure, a low pressure, and a split ratio. Thereafter, thermodynamic parameters of the considered three cycles are obtained under different waste gas temperatures. For the recovery of 600°C waste gas, the novel cycle has the highest net work 3957.87 kW, while the lowest net work 3735.32 kW is obtained by the original cycle. For the effects of decision variables, a higher high-temperature turbine inlet temperature means a lower net work, while the increase of low-temperature turbine inlet temperature results in small increases of cycle performances. On the other hand, under the constraints of the pinch point, with the increase of low and middle pressures, the net work of the novel cycle increases. A higher net work is usually obtained at a lower split ratio. Furthermore, at different waste gas inlet temperatures, the highest cycle efficiency is always derived by the proposed cycle. For the net work, the proposed cycle has the highest value in the temperature range 600°C–750°C.

Performance analysis of ceramic membrane tube modules for water and heat recovery in coal-fired power plants

Ceramic membrane separation technology is a promising method for water and heat recovery from exhaust flue gas in thermal power plants. Matching among function, load and structure of membrane modules is critical to design and operation of such recovery processes. In this paper, an analytical model based on membrane separation mechanism is proposed to evaluate the water and heat recovery performance in a ceramic membrane module. A series of calculation considering both structural parameters and load conditions in a power plant is conducted. Results show that under the conditions of different flue gas temperature and water vapor volume fraction, the membrane module has three working modes corresponding to different condensation processes. For flue gas with high temperature and low humidity, the temperature rise of cooling water can reach up to 40 °C when the mass flow rate ratio of cooling water to flue gas is less than 50%. For flue gas with low temperature and high humidity, low cooling water temperature could promote water recovery process. Keeping the mass flow rate ratio higher than 200% can maintain the water recovery rate not less than 60%. The optimal water and heat recovery rate is obtained by optimizing the size and structure of the membrane module within limited volume. This study provides a basis for structure optimization and operation regulation of ceramic membrane modules for water and heat recovery purpose.

Innovative arrangements of multiple organic Rankine cycles to effectively generate power from the medium-to-low grade of heat source

Organic Rankine cycle (ORC) is an important method for waste heat recovery. However, there is a remarkable irreversible loss between ORC and heat source/sink, which reduces the performance in energy utilization. In this work, an innovative concept of multi-ORCs arrangement has been proposed for improving the energy utilization. The concept is something like playing the jigsaw puzzle. We have tried the best to fill the temperature gap between heat source and heat sink by multiple ORCs. According to the T-s diagram, the heating temperature of the working fluids paralleling to the temperature of heat source should be considered primarily. Based on the first and exergy laws, multi-ORCs arrangements and system thermo-economic analysis have been carried out for the given single-phase (hot air with 300 °C) and two-phase (saturated steam with 185 °C) heat source, respectively. For single-phase heat source, the net output/LCOE of three-ORCs and four-ORCs arrangements are 6789 kW/0.063 USD/kWh and 6627 kW/0.072 USD/kWh, respectively; for two-phase heat source, they are 5976 kW/0.069 USD/kWh and 6174 kW/0.068 USD/kWh respectively. This means that the performance improvement depends on the reasonable selection of working fluids and reasonable arrangement of the ORCs, and the thermodynamic and economic issues should be simultaneously considered. The research findings provide a new means for the ORC system optimization.

EVALUATING THE COST-BENEFIT OF A WASTE HEAT RECOVERY ENERGY SYSTEM WITH EXERGOECONOMICS

While it is certain that life cannot exist without energy, it is impossible to think of the use and efficiency of energy systems outside economic conditions and constraints. For energy producers and consumers, the determination of the cost of unit energy or electricity is basically a result of the combined evaluation of the first law of the thermodynamics and economy. However, the result of this approach is incapable of determining the source, location and magnitude of the unutilized energy. From this point of view, the concept and analysis of the exergy resulting from the use of the first and second law of thermodynamics is a method used both to fulfil the aforementioned deficiencies and to reveal the amount of exergy destroyed in any process. Moreover, the combination of exergy analysis with economic analysis, by pricing the exergy destruction, which is a result of the inefficiencies of the system and components examined, leads the investor in how much the inefficiencies in the system and components cost, and how this economic burden can be reduced. In summary, the cost of exergy destruction can be considered as financial burden that need to be reduced for more efficient and economic systems. The waste heat recovery method is used to reduce the amount of fuel the main system consumes by recovering the excess energy released into the atmosphere via generating more energy. In this study, a waste heat energy system has been examined with exergy and exergoeconomical analyzes in order to obtain information that can improve both efficiency and economy, and the components that should be focused on and the contributions of these components to the whole system have been determined based on the results obtained. The study showed that exergoeconomic analysis is one of the methods that can be used to gain more information about systems for energy costing and economic optimization.

Comparative technical and economic analysis of innovative methods for waste heat recovery from flue gases for boiler type BKZ 220-100

Two alternative schemes for waste heat recovery from flue gases of boiler type BKZ 220-100 in the Stepnogorsk TPP (Kazakhstan) are presented. The technical solutions are innovative because they create conditions for deep heat recovery even when using battery emulsifiers to purify the gas flow. A characteristic feature of the schemes is the purification of a small part (10-15%) of the stream by means of a bag filter and the mixing of the stream with the main gas flow consisting of moist gases after a battery emulsifier. An analysis and assessment of the technical and economic feasibility of the implementation of the two alternatives has been carried out.

Characterization of a new total heat recovery system using CaCl2 as working fluid: Thermal modeling and physical analysis

• A new type of heat pump system is proposed. • The variation trend of three working medium in absorber is analyzed. • The rise of flue gas temperature can reduce the harmful substances by more than 50%. • The advantages of the system compared with LiBr absorption heat pump are analyzed. This paper introduces a kind of open cycle absorption heat wet flue gas heat recovery system, which use CaCl 2 as the working medium. The system will use the wet heat recovery method and combined with an efficient heat pump system for flue gas as a heat source generator. Through direct contact with the solution in the absorber, the flue gas is going to carry out gas, liquid heat transfer between heat exchanger, realization of sensible heat and latent heat step by step. As the key part of the system, absorber is established by one-dimensional steady-state heat transfer and mass transfer model. This paper uses the finite difference method to model the discrete numerical methods, and analyzes the characteristics of heat and mass transfer in the absorber. We obtain the concentration curves of the three kinds of working medium's temperature and flow along the height direction. We also analyze the influence of CaCl 2 solution parameters changes on the absorption process, parsing the reason of the temperature change by analyzing the three working medium's energy flow trend. We found that the temperature change of flue gas is non-monotonic, which decreases gradually in the range of absorption tower height 0–0.9 m, and then increases gradually. The reason for this change is that sensible heat exchange and latent heat exchange exist between flue gas and solution. Although such a change has an impact on the efficiency of the system, it prevents the "white smoke" from condensing in the air, which effectively protects the environment. Compared with conventional LiBr absorption heat pump, the system constructed in this paper has certain advantages in latent heat recovery, flue gas heat energy utilization, energy conservation and emission reduction and economy.

Development and validation of a TRNSYS type to simulate heat pipe heat exchangers in transient applications of waste heat recovery

Heat pipe heat exchangers (HPHEs) are being more frequently used in energy intensive industries as a method of low-grade waste heat recovery. Prior to the installation of a HPHE, the effect of the heat exchanger within the system requires modelling to simulate the overall impact. From this, potential savings and emission reductions can be determined, and the utilisation of the waste heat can be optimised. One such simulation software is TRNSYS. Currently available heat exchanger simulation components in TRNSYS use averaged values such as a constant effectiveness, constant heat transfer coefficient or conductance for the inputs, which are fixed during the entire simulation. These predictions are useful in a steady-state controlled temperature environment such as a heat treatment facility, but not optimal for the majority of energy recovery applications which operate with fluctuating conditions. A transient TRNSYS HPHE component has been developed using the Effectiveness-Number of Transfer Units (ɛ-NTU) method and validated against experimental results. The model predicts outlet temperatures and energy recovery well within an accuracy of 15% and an average of 4.4% error when compared to existing experimental results, which is acceptable for engineering applications.

Assessment of energy potential for heat recovery in the EU industry

Thermal processes account for 70% of the EU industry final energy, with 30% thereof being wasted through losses. This fact has been a motivating factor toward applying various technologies and methods for waste heat recovery. Already such technologies exist and are applied in many industrial sectors, while some “new” technologies have also been tested or suggested. It is therefore useful to obtain insight information into such processes, together with their temperature ranges and, hence, assess the potential market for each industrial sector. Here such an attempt is made, based on existing literature. Estimates on the total energy that can be recovered through the EU industry are given and a special case study on the important Iron and Steel industry is presented. This kind of information can be useful for the improvement of existing and the development of “new” technologies or techniques.

Energy and Exergy Evaluations of a Combined Heat and Power System with a High Back-Pressure Turbine under Full Operating Conditions

High back-pressure technology is a promising method for the waste heat recovery of exhaust steams in combined heat and power systems. In this research, a 300 MW coal-fired subcritical combined heat and power system was selected as the reference system, and modeled in EBSILON professional. Then, energy-based and exergy-based performances of the high back-pressure system and traditional combined heat and power system were compared under full operating conditions. Moreover, a novel exergy-based evaluation method, which considers the energy level of the heating supply, was proposed and applied to evaluate the two systems. Results show that: In design conditions, both the heating capacity and power output of the high back-pressure system were higher than those of the extraction condensing system, which led to 17.67% and 33.21% increments of the gross thermal efficiency and generation efficiency, respectively. Compared with the extraction condensing system, the exergy efficiencies of the high back-pressure system were 7.04–8.21% higher. According to the novel exergy-based evaluation, the exergy efficiencies for the generation of the high back-pressure system and extraction condensing system were 46.48% and 41.22%, respectively. This paper provides references for the thermodynamic performance evaluation of the combined heat and power system.

Simulation of primary breakup of molten slag in the gas quenching dry granulation process

Gas quenching dry slag granulation process is an energy-saving environmental protection method for waste utilization and waste heat recovery of molten slag, and the molten slag is broken up by supersonic airflow into droplets in this process. This paper performed the numerical investigations on the breakup behavior of slag by the coupled level-set and volume of fluid (CLSVOF) methodology and gain a deep insight into the breakup mechanism of the primary breakup and influence of gas Weber number (We) and liquid Reynolds number (Re) on the primary breakup. The results indicated that the primary breakup include flat film breakup and spherical cap film breakup, the both are typical perforation breakup; Aerodynamic force cause K-H (Kelvin Helmholtz) instability, K-H surface waves are the root cause of film breakup; The wavelength and the film thickness decrease with increasing We which is conducive to reducing the ligament diameter; The wavelength and the film thickness decrease first and then increase with increasing Re which is optimum in the range of 1068–1280; The empirical formula of the ligament diameter is obtained. The ligament diameter decrease with increasing airflow velocity and slag density and increase with increasing slag mass flow rate and slag viscosity.

An assessment of the influence of local conditions on the economic and environmental sustainability of drain water heat recovery systems

Energy crisis caused by the population growth, increasing demand, and the limited availability of fossil fuels has led to wastewater-based heat recovery emerging as an alternative energy source. As wastewater-based resource recovery systems are location-specific, a holistic view of their sustainability requires a comprehensive analysis of the effect of local conditions on these systems. This study evaluated the role of climate and population density on the economic and environmental sustainability of drain water heat recovery systems (DWHRS) and compared it to that of a medium-scale district heating system. The DWHRS installed in a cold location showed about 2–2.6 times higher energy recovery and 4 times higher greenhouse gas emissions than that in a hot place. The economic impact was predominantly influenced by the cost of electricity, while the environmental sustainability was found to decrease with a decrease in the ambient temperature and solar radiation. Lower population density increases economic sustainability and lowers environmental sustainability of the system. The DWHRS is more sustainable than the medium-scale district heating system in low population density regions irrespective of the climatic conditions. However, in cold places with a high population density, the trade-off between the economic and environmental sustainability must be evaluated to decide whether to install a small- or medium-scale system. Therefore, it is essential to perform a detailed location-specific analysis before deciding the optimal type of heat recovery system for the location under consideration. The model can be utilized as an evaluation tool to quantify the sustainability of the DWHRS and help consumers decide the most suitable method of waste heat recovery.