Heat Recovery Rate Research Articles

Implementation of Regenerative Thermal Oxidation Device Based on High-Heating Device for Low-Emission Combustion

In this paper, a heating device is implemented by considering two large factors in a 100 cmm RTO design. First, when the combustion chamber is used for a long time with a high temperature of 750–1100 °C depending on the high concentration VOC gas capacity, there is a problem that the combustion chamber explodes or the function of the rotary is stopped due to the fatigue and load of the device. To prevent this, the 100 cmm RTO design with a changed rotary position is improved. Second, an RTO design with a high-heating element is implemented to combust VOC gas discharged from the duct at a stable temperature. Through this, low-emission combustion emissions and energy consumption are reduced. By implementing a high heat generation device, the heat storage combustion oxidation function is improved through the preservation of renewable heat. Over 177 h of demonstration time, we improved the function of 100 cm by discharging 99% of VOC’s removal efficiency, 95.78% of waste heat recovery rate, 21.95% of fuel consumption, and 3.9 ppm of nitrogen oxide concentration.

A REVIEW on PRIMARY ENERGY RATIO VALUES of GAS ENGINE DRIVEN HEAT PUMP SYSTEMS

This study reviews the primary energy ratio values of gas engine driven heat pump systems in order to compare gas engine driven heat pump systems among themselves or with heat pump systems using different energy sources in terms of efficiency values. A comprehensive literature review of studies investigating primary energy rates of gas-driven heat pump systems have been presented. The primary energy ratios obtained in the studies on gas driven heat pump systems were determined and tabulated. In addition, waste heat recovery rates in these systems were also investigated. Studies in the relevant field are grouped as experimental and theoretical. Additionally, the differences in the examined system structures are stated and primary energy ratios are presented. Primary energy rates of systems with and without heat recovery were examined. There is no compilation study on the subject in the literature. The calculation methodology used and the obtained values for calculating the primary energy rates of gas-driven heat pumps are presented. Thus, the energy efficiency and environmental evaluations of the examined systems are presented in the light of the literature. In addition, which refrigerants were used in the studies conducted in the literature are presented. Recommendations are provided on choosing alternative and sustainable refrigerants.

Thermo-hydro-mechanical fully coupled model for enhanced geothermal system and numerical solution method based on finite volume method

Enhanced geothermal system (EGS) has been widely used to improve the production performance of geothermal reservoirs. Extracting the heat energy from geothermal reservoirs involves complex multi-physical process, referred to as the thermal–hydro–mechanical (T–H–M) coupling. To optimize the production schedule, numerical simulator is an important tool for EGS development. However, the numerical solution method based on FVM is rare in the literature. To address this gap, in this study, we derive the mathematical equations of fully coupled T–H–M model. Then, the solution method based on FVM is established. Next, the its accuracy is verified against two cases. Last, the proposed method is applied to an EGS model to simulate the heat extraction process. The evolutions of pressure, temperature, and fracture aperture are analyzed. The effects of controlling parameters of the extraction efficiency are discussed. Results indicate that increasing the injection rate will reduce the lifespan of EGS but accelerate the energy extraction. Increasing the injection temperature can promote the heat extraction to limited extent. Increasing the matrix permeability can significantly improve the extraction efficiency. Enlarging the fracture spacing can enlarge the heat recovery rate. In addition, reducing the fracture permeability can avoid thermal shortcut and improve the production performance.

Energy efficiency analysis of ammonia-fueled power systems for vehicles considering residual heat recovery

Ammonia shows great potential as a zero-carbon fuel for vehicles. However, both the internal combustion engine (ICE) and the proton exchange membrane fuel cell (PEMFC), the currently available vehicle engines, require hydrogen decomposed from ammonia. On-board hydrogen production is an energy-intensive process that significantly reduces system efficiency. Therefore, energy recovery from residual heat is essential to promote overall efficiency, but ICE and FC require different amounts of hydrogen, and produce residual heat of dissimilar quality and quantity. To thoroughly understand the relationships among system configuration, rate of residual heat recovery and system efficiency, this paper takes three typical ammonia-fueled power systems, which employs only ICE, only PEMFC and both ICE and PEMFC as engine(s), respectively, as examples to set up system efficiency model and conduct simulation under various operating conditions. Results show there is a mismatch between the produced residual heat and the heat required for ammonia decomposition for systems using only ICE or PEMFC. For system using both PEMFC and ICE, the residual heat can be recovered to a maximum extent by way of parameters matching and dynamic power management between engines. This system has the highest efficiency and widest high efficiency region among the three analyzed typical configurations.

Enhancement effect of semicoke waste heat on energy conservation and hydrogen production from biomass gasification

Key approaches to alleviating global warming and curbing fossil fuel depletion involve various industrial energy-conservation technologies and carbon dioxide (CO2) emission reduction methods. The production of hydrogen (H2)-rich gas from inexpensive and readily available biomass, as an alternative energy source, is becoming increasingly promising. However, this application faces challenges such as high energy consumption and low gas quality. In this study, the waste heat released by semicoke production from lignite gasification and CO2 from exhaust gas were utilized to gasify biomass. This approach aims to save energy in biomass gasification and use CO2 in exhaust gas to improve the H2 content in biogas. A simulation was conducted to recover semicoke waste heat by combining a suspension tube with CO2 flow to generate steam and high-temperature CO2, which were then simultaneously sent into a gasifier to produce H2 through biomass gasification. The results revealed that the rate of semicoke waste heat recovery exceeded 90 %. The yield of steam and the rate of waste heat recovery improved with increasing mass flow rate of semicoke and then slightly decreased with increasing steam pressure and CO2 mass flow rate. The yield of H2 increased with the semicoke mass flow rate and steam pressure. The rate of energy conservation ranged from 15 % to 239 %, peaking at a CO2 mass flow rate of 0.09 kg/s. Compared with the case without waste heat recovery, the economic benefits increased from 12 to 28 times.

An insightful multicriteria model for the selection of drilling technique for heat extraction from geothermal reservoirs using a fuzzy-rough approach

Geothermal energy stands out as an exceptional renewable resource for power generation, offering a consistent power production without the intermittency issues. Despite its potential to deliver a consistent supply of electricity on demand, geothermal adoption is hindered due to substantial costs. Utilising the most effective drilling method can alleviate this challenge by boosting efficiency and reducing operational costs. The primary goal of this study is to identify the best drilling method for extracting heat from geothermal reservoirs. This optimised approach facilitates better access to geothermal reservoirs, leading to increased heat recovery rates and improved project viability. Traditional methods often fall short in evaluating optimal drilling alternatives due to uncertainties. To address this, our research introduces an innovative paradigm that integrates novel T-Spherical Hesitant Fuzzy Rough (T−SHFR) set, method for the removal effects of criteria with a geometric mean and ranking alternatives with weights of criterion hybrid Multiple Criteria Decision-Making (MCDM) techniques. By leveraging the novel T−SHFR concept, our approach allows for a comprehensive assessment of various factors. This holistic evaluation ensures an exhaustive comprehension of the decision-making environment. The study reveals that reservoir characteristics play a significant role in selecting a sustainable drilling alternative. Furthermore, directional drilling appears as the most promising method with higher energy yields followed by slim hole drilling. The robustness and credibility of these findings are established through sensitivity and comparative analyses, indicating the potential applicability of this MCDM method to analogous challenges in different contexts. The findings of the ranking techniques were validated using Spearman's rank correlation coefficient, which revealed a positive and notable correlation. This research will empower stakeholders to make informed decisions, thereby enhancing the overall efficiency and sustainability of geothermal energy projects.

Cooling Air Velocity on Iron Ore Pellet Performance Based on Experiments and Simulations

During the pellet cooling process, cooling air velocity is crucial for optimizing the cooling rate, evaluating the utilization rate of cooling heat energy, and improving pellet performance. As the simulated cooling air velocity increased, the gas temperature at the cooling endpoint decreased from 87 °C to 51 °C, and the solid temperature decreased from 149 °C to 103 °C. The total enthalpy of the recovered gas initially reduced and then increased while the heat recovery rate gradually increased. During the experiment, the inhomogeneity of pellet quality gradually increased with the rise in cooling air velocity. The effect of cooling air velocity on pellet properties is primarily reflected in the formation of cracks and low-melting liquid phases (FeO and fayalite). As the cooling air velocity increases, the softening onset temperature of the pellet decreases significantly. The melting zone decreases from 193 °C to 105 °C, and the permeability of the adhesive zone increases.

Comparative Study of Heat Transfer Simulation and Effects of Different Scrap Steel Preheating Methods

The materials charged into a converter comprise molten iron and scrap steel. Adjusting the ratio by increasing scrap steel and decreasing molten iron is a steelmaking raw material strategy designed specifically for China’s unique circumstances, with the goal of lowering carbon emissions. To maintain the converter tapping temperature, scrap must be preheated to provide additional heat. Current scrap preheating predominantly utilizes horizontal tunnel furnaces, resulting in high energy consumption and low efficiency. To address these issues, a three-stage shaft furnace for scrap preheating was designed, and Fluent software was used to compare and study the preheating efficiency of the new three-stage furnace against the traditional horizontal furnace under various operational conditions. Initially, a three-dimensional transient multi-field coupling model was developed for two scrap preheating scenarios, examining the effects of both furnaces on scrap surface and core temperatures across varying preheating durations and gas velocities. Simulation results indicate that, under identical gas heat consumption conditions, scrap achieves markedly higher final temperatures in the shaft furnace compared to the horizontal furnace, with scrap surface and core temperatures increasing notably with extended preheating times and higher gas velocities, albeit with a gradual decrease in heating rate as the scrap temperature rises. At a gas velocity of 9 m/s and a preheating time of 600 s, the shaft furnace achieves the highest waste heat utilization rate for scrap, with scrap averaging 325 °C higher than in the horizontal furnace, absorbing an additional 202 MJ of heat per ton. In the horizontal preheating furnace, scrap steel exhibits a heat absorption efficiency of 35%, whereas in the vertical furnace, this efficiency increases notably to 63%. In the vertical furnace, the waste heat recovery rate of scrap steel reaches 57%.

Energy and Exergy Analysis of an Improved Hydrogen-Based Direct Reduction Shaft Furnace Process with Waste Heat Recovery

The traditional production mode using coal as the main energy source is not conducive to the sustainable development of the iron and steel industry (ISI). The hydrogen-based direct reduction shaft furnace (HDRSF) process is a feasible technical route for promoting the green development of the ISI. However, there is a lack of comprehensive analysis with respect to the energy utilization and process flow of the HDRSF method. To address these issues, a systemic material–energy–exergy model of HDRSF is established. An improved HDRSF process incorporating waste heat recovery is also proposed, and energy consumption intensity and exergy intensity are used as assessment metrics. This study’s findings indicate that the proposed waste heat recovery can considerably lower gas demand and energy consumption intensity, but exergy intensity has little effect. The reducing gas demand drops from 2083 m3 to 1557 m3, the energy consumption intensity drops from 2.75 × 107 kJ to 1.70 × 107 kJ, and the exergy intensity drops from 1.08 × 107 kJ to 1.05 × 107 kJ when the reducing gas temperature is 900 °C, H2:CO = 1:1; meanwhile, the recovery rate of waste heat reaches 40%. This study can serve as a reference for actual HDRSF process production.

Thermal-economic performance evaluation and bi-objective optimization of organic Rankine cycles using pure and mixed working fluids for waste heat recovery

To further enhance the recovery rate of low temperature waste heat, the low temperature flue gas in the sinter annular cooler is chosen as the heat source of organic Rankine cycle (ORC) system in the current study, and the system thermal-economic performance evaluation are conducted. The thermal-economic performance models of ORC system are established firstly, and the butane and isopentane are selected to constitute the mixed working fluid. Then the changes of system performance with the mass fraction of isopentane (MR601a) and ORC crucial parameters are evaluated comprehensively, and the bi-objective optimization is applied to ascertain the optimal ORC crucial parameters under various MR601a. The results indicate that the MR601a of 0.6 can obtain the maximum glide temperature. The higher the evaporating temperature is, and the lower the condensing temperature is, the larger the exergy efficiency is, while the smaller the levelized energy cost is. There is an optimal superheat degree to make the ORC system achieve the better overall performance under various MR601a. The exergy efficiency of butane is the maximum with a respectable waste heat recovery rate of 64.18 %, while the levelized energy cost of isopentane in the whole conditions is the minimum with the better economic performance.

Comprehensive Utilization and Control Measures of Iron and Steel Slag

With the increase of steel production, the amount of steel slag piled up is on the rise. The article analyzes the current situation of blast furnace slag utilization, elaborates on the current treatment technology of blast furnace slag, and points out that in the future, the utilization of blast furnace slag will develop towards the direction of developing high value-added products, and the sensible heat recovery rate of blast furnace slag is expected to increase. Analyze the current application status and treatment process of converter slag. The comprehensive treatment technology of converter slag is limited by multiple factors, and it is proposed to control converter slag from the production source through "slag recycling".

Functional analysis of multi-scale fractures within a single fracture cluster in multi-horizontal wells

Defining the fracture function at each scale in the reservoir helps to analyze and optimize the thermal recovery properties of the reservoir. This study aims to reveal the functionalities of fractures at different scales by simulating one single fracture cluster coupled in multi-scale fractures. The geometric layout and parameter characteristics of the main fractures, branch fractures, and micro-fracture domain are investigated to speculate on their functions and influence on heat extraction performance. The results display that the main fractures and micro-fracture domain serve as the predominant channel for fluid flow. The branch fractures exert control over the flow transition from the main fractures to the micro-fracture domain, thereby influencing the generation of preferential flow. Micro-fracture domain is the primary way of fluid filtration loss. When the thickness of micro-fracture domain increased from 0 m to 20 m, the production flow rate increased from 2 kg/s to 4.2 kg/s, and the water loss ratio increased from 1 % to 4.9 %. However, expanding the micro-fracture domain can significantly enhance production flow rate and heat recovery rate at the expense of increased water loss ratio. Notably, preferential-flow-induced thermal breakthrough will not occur prematurely in this process. The permeability of branch fractures exerts the most substantial influence on the overall heat extraction, owing to its greatest impact on reservoir lifespan. These findings would provide valuable insights for optimizing fracturing morphology in multi-horizontal wells.

Evaluation of wavy wall configurations for accelerated heat recovery in triplex-tube energy storage units for building heating applications

Efficient thermal energy storage (TES) is crucial for integrating intermittent renewable energy sources and managing fluctuations in energy supply and demand. Among TES methods, latent heat TES (LHTES) using phase change materials (PCMs) is highly promising due to its high energy storage density and nearly isothermal operation during phase transitions. However, the inherently low thermal conductivity of PCMs hinders heat transfer rates, negatively impacting charging and discharging performance. This study investigates novel wavy channel geometries for the PCM container in a triplex-tube LHTES unit to enhance heat transfer and improve solidification rates during the discharge process. A comprehensive computational model based on the enthalpy-porosity method is developed to simulate the PCM (paraffin wax RT35) solidification inside wavy channels with sinusoidal, zigzag, and step-function profiles. The effects of channel geometry, heat transfer fluid (HTF) velocity, and inlet temperature on solidification rate and heat recovery are systematically evaluated. Results demonstrate that the step-function geometry significantly accelerates solidification compared to straight channels, reducing discharge time by 65.1 % and increasing heat recovery rate by 147.9 %. Decreasing waviness width from 15 mm to 5 mm further reduces solidification time by 70.1 %, while increasing waviness height from 5 mm to 15 mm leads to a 74.4 % reduction. Moreover, increasing HTF flow from Re = 250 to 1000 enhances heat recovery by 92.3 %, and lowering inlet temperature from 20 °C to 10 °C improves it by 76.9 %. The findings provide valuable insights for designing efficient LHTES units with wavy channel geometries for renewable energy integration and thermal management applications.

Realizing rapid cooling and latent heat recovery in the thermoelectric-based battery thermal management system at high temperatures

To realize rapid cooling of the battery at high temperatures and effective latent heat recovery from phase change materials (PCMs), a thermoelectric-based battery thermal management system (BTMS) is proposed. Additionally, a transient multiphysics numerical model is developed to predict the system's thermal performance, and the concept of the latent heat recovery rate of PCMs is introduced. Results show that the introduction of thermoelectric coolers (TECs) significantly enhances the system's efficiency in cooling the battery at high temperatures (Stage 1) and recovering PCM latent heat (Stage 2). The overall thermal performance can be further improved by utilizing PCMs with a higher mass fraction of expanded graphite (EG) or increasing the TEC input current. Moreover, after the end of Stage 2, the power supply for TECs is interrupted, and the system enters Stage 3, which only relies on PCMs to control the battery temperature. The duration of Stage 3 increases with the EG mass fraction, achieving a peak of 3830 s at an EG mass fraction of 12%. Considering the thermal performance and power consumption of the system, the optimal solution is determined as an EG mass fraction of 12% and a TEC input current of 4 A. In this situation, the required time for Stage 1 and Stage 2 is 170 s and 620 s, with the latent heat recovery rate of PCMs up to 361.94 J/kg/s. The findings will provide new insights for the development of the thermoelectric-based BTMS.

Large-scale physical simulation of injection and production of hot dry rock in Gonghe Basin, Qinghai Province, China

Based on the independently developed true triaxial multi-physical field large-scale physical simulation system of in-situ injection and production, we conducted physical simulation of long-term multi-well injection and production in the hot dry rocks of the Gonghe Basin, Qinghai Province, NW China. Through multi-well connectivity experiments, the spatial distribution characteristics of the natural fracture system in the rock samples and the connectivity between fracture and wellbore were clarified. The injection and production wells were selected to conduct the experiments, namely one injection well and two production wells, one injection well and one production well. The variation of several physical parameters in the production well was analyzed, such as flow rate, temperature, heat recovery rate and fluid recovery. The results show that under the combination of thermal shock and injection pressure, the fracture conductivity was enhanced, and the production temperature showed a downward trend. The larger the flow rate, the faster the decrease. When the local closed area of the fracture was gradually activated, new heat transfer areas were generated, resulting in a lower rate of increase or decrease in the mining temperature. The heat recovery rate was mainly controlled by the extraction flow rate and the temperature difference between injection and production fluid. As the conductivity of the leak-off channel increased, the fluid recovery of the production well rapidly decreased. The influence mechanisms of dominant channels and fluid leak-off on thermal recovery performance are different. The former limits the heat exchange area, while the latter affects the flow rate of the produced fluid. Both of them are important factors affecting the long-term and efficient development of hot dry rock.

Quantifying flow regime impacts on hydrodynamic heat transfer in rough-walled rock fractures

Hydrodynamic heat transfer in rock fractures is crucial for many geophysical processes and engineering activities, notably in harnessing geothermal energy. Despite extensive research, characterizing hydrodynamic heat transfer in rock fractures, complicated by their geometric heterogeneity, remains a formidable challenge. To address this challenge, we experimentally investigated the hydrodynamic heat transfer in rock fractures with diverse geometric features at steady-state elevated temperatures. We found that both heterogeneous fracture geometry and elevated temperatures promote the transition of fracture flow from a linear to nonlinear regime. This flow regime transition enhances the heterogeneity of heat transfer intensity within the fracture and exacerbates the increase in heat transfer efficiency with flow rate. At a fortyfold increase in flow rate, the heat transfer coefficient in the most heterogeneous fracture rises by approximately 72 times, compared to about 28 times in the least heterogeneous one. Leveraging experimental data, we developed parametric models linking heat transfer coefficients, outflow temperature, and heat recovery rate to flow rate and geometric features, yielding a theoretical formulation for the maximal heat recovery rate. By introducing the concept of an energy conversion rate, we quantitatively evaluated the effect of nonlinear flow resistance on heat extraction feasibility, revealing that energy conversion rates in highly heterogeneous fractures can be up to 452 times lower than in less heterogeneous ones. This highlights the pivotal role of flow resistance in heat extraction feasibility. Our findings are instrumental for understanding and predicting the hydrodynamic heat transfer within fractured geothermal reservoirs and analogous hydro-thermal systems.

Dual harvesting from exhaust gas of diesel generators using thermoelectric generators and cold water tank

The present work concerns a dual harvesting concept applied to exhaust gas of Diesel generators using thermoelectric generators and cold water tank. To proceed, a simplified thermal modelling is developed and appropriate parametric analysis of power generation with the TEGs and heat recovered is conducted in function of the Diesel generator power and the TEG thermal conductivity and thickness. It was shown that powers up to 534 W can be generated with the TEGs and heat recovery rates up to 4463 W can be obtained for a Diesel generator power of 125 kW. Also, it was shown that the temperature difference across the TEGs and the power generated increase exponentially when the Diesel generator power and ratio of thickness to thermal conductivity of TEGs increase.

Numerical modelling and experimental validation on the discharging performance of paraffin/graphite matrix composite with various configurations of bulk density and wall temperature

Graphite material in the form of expanded has proven to be an effective material to remedy the low thermal conductivity of paraffin storage medium. The present work focuses on the solidification performance of carbon-based approach via graphite matrix composite with phase change to eliminate the bottleneck of low thermal conductivity issue of phase change materials for thermal energy storage applications beyond the current literature. Paraffin/graphite matrix composites with various bulk density values of 0 kg/m3 (Case 1), 23 kg/m3 (Case 2), 50 kg/m3 (Case 3), 100 kg/m3 (Case 4), and 143 kg/m3 (Case 5) under various operating conditions of wall temperature (Twall: 15 °C, 25 °C, 35 °C, and 45 °C), which mimic real applications' fluid temperature, are performed numerically in detail. The numerical model was validated with experimental outputs performed by the authors. Numerical results show that paraffin/graphite matrix composites have a great potential for the solidification/discharging process to recover the heat stored in the charging/melting period. Uniform and rapid solidification behaviour is achieved with the paraffin/graphite matrix composite in terms of conduction-dominated heat transfer via abundant thermal bridges compared to the pure paraffin case. Higher bulk density values and lower cold surface temperatures present superior performance in solidification rate and thermal energy recovery rate. However, the effect of the bulk density is slowed down with the beyond of certain value of bulk density (100 kg/m3). For 100 kg/m3 (Case 4) at Twall = 15 °C, the heat recovery rate is enhanced by 31.17 times and 3.84 times compared to the 0 kg/m3 and 23 kg/m3. The heat recovery rate of 100 kg/m3 is improved by 350.8 % for Twall = 15 °C in comparison with Twall = 45 °C. The total solidification rate (t = 17.5 min) increased by 90.94 % and 62.94 % for 100 kg/m3 at Twall = 35 °C compared to 0 kg/m3 and 23 kg/m3, respectively.

Heat and water recovery from gaseous stream using a flat-sheet ceramic membrane as a transport membrane condenser

Ceramic-membrane technology has been employed to recover waste heat and vapor from moist gases. In addition to the hydrophilicity, pore size, and porosity of separation materials, a membrane condenser can achieve a high recovery rate. In this study, a transport membrane condenser (TMC) was successfully constructed using a flat-sheet ceramic membrane (FCM) with a large pore size of 45.54 μm. The membrane characteristics, including the mean pore size, pore size distribution, and porosity, were investigated to determine their recovery mechanism. Their water and heat fluxes, recovery rates, and thermal resistance were compared under several experimental conditions. The inlet conditions significantly affect the TMC recovery performance. Higher recovery fluxes were obtained at lower water temperatures, higher gas temperatures, and higher gas flow rates. However, when the Reynolds number of water increased, the heat flux increased rapidly, and the recovered water decreased slightly. The highest TMC water recovery rate was 84.1%. In addition, to further analyze the separation mechanisms, a two-dimensional model was developed using ANSYS Fluent code. The simulation results were compared with the experimental data to verify the accuracy of the numerical method. The comparison results showed a high degree of consistency.

Integration of hydrothermal liquefied sludge as wastewater for anaerobic treatment and energy recovery: Aqueous phase characterization, anaerobic digestion performance and energy balance analysis

For the hydrothermal liquefaction (HTL) process as the final method for waste activated sludge, the liquid by-product of the process, i.e., the HTL aqueous solution, poses the greatest bottleneck due to its large volume and contaminant levels. In this study, the effects of hydrothermal liquefaction pretreatment (HTL) on the performance of anaerobic digestion and energy balance of the waste-activated sludge (WAS) aqueous phase were investigated. The results showed that HTL could greatly increase the hydrolysis of WAS and enhance the protein, polysaccharide and volatile fatty acid contents in the aqueous phase. The anaerobic digestion showed that the optimal gas and methane production efficiency was achieved at 160 °C. Positive net energy gain was obtained in each process (ΔE) and the optimal HTL heat recovery rate was obtained at 160 °C. HTL was found to improve the hydrolyzing bacterial community in anaerobic digestion but had little effect on the archaeal community.