Utilization Rate Of Waste Heat Research Articles

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%.

Study on cold start of fuel cell stack combined with liquid heating and fuel cell self-starting

Fuel cell vehicles have been paid more and more attention, while the low temperature cold start capability has become the main reason that hinders their large-scale commercialization, especially for the fuel cell bus. Generally, liquid heating (positive temperature coefficient thermistor (PTC) as the heat source) and fuel cell self-starting heating are the common cold start methods. However, these methods can bring about low start speed and high energy consumption. Therefore, a new cold start method combined with liquid heating and fuel cell self-starting is proposed to solve the problems. Besides, phase change material (PCM) is introduced to reduce energy consumption further. The PCM can absorb the waste heat of the fuel cell stack. Then the heat can be used for stack cold start by circulating liquid. In this study, a fuel cell bus cold start system simulating model is built. Based on this model, the fuel cell temperature and energy consumption during the cold start are analyzed. The results show that the method combined with liquid heating and fuel cell self-starting is superior to the liquid heating method. The cold start time and PTC consumption of the PTC-PCM-self-starting heating mode are 19.0 % and 19.2 % less than that of PTC-PCM heating mode. As for the combined heating method, dropping the self-starting temperature can not only increase the cold start speed but also reduce the proportion of electric heating. For every 1 °C decrease, the start-up time is shortened by 1 % on average, and the waste heat utilization rate is increased by 0.5 %. Although increasing the self-starting current can increase energy consumption, it will save more cold start time and reduce the proportion of electric heating. For every 1 A increase, the start-up time is shortened by 0.3 % on average, and the waste heat utilization rate is increased by 0.1 %. The PTC-PCM-self-starting heating method provides a way for fuel cell stack to start quickly and energy-efficiently in low temperature environment.

Efficient cascade waste heat utilization using thermoacoustic engine with variable temperature heat sources

Waste heat recovery is vital for greenhouse gas emissions reduction and meeting increasing power demands. Thermoacoustic engines present a promising solution. However, existing research predominantly focuses on single heating temperatures, which restricts their efficiency in harnessing heat sources with variable temperatures. To overcome this limitation, this work proposed a novel concept of thermoacoustic engine containing multistage heat exchangers capable of cascade waste heat recovery by incorporating bypass orifices to address this issue. By organizing decreasing temperatures of heat source across heat exchangers with decreasingly lower temperatures, multiple heat-to-power energy conversions can be achieved. Theoretical analyses demonstrate that the total exergy utilization efficiency of single-stage (37.7 %), two-stage (47.6 %), and three-stage systems (51.2 %) significantly increases when increasing the stage number up to three. Further increasing the stage number results in less efficiency improvement (only a 1.3 % increase in a four-stage system). Simulation results show that the three-stage thermoacoustic engine can achieve an acoustic power of 2.7 kW and a total exergy utilization efficiency of 51.2 % for recovering 12 kW variable-temperature heat sources. Coupling the engine with a linear alternator increases electricity production by 12 % with higher waste heat utilization rate compared to traditional single-stage thermoacoustic generators. The experimental results further underscore the capability of the proposed thermoacoustic generator to effectively utilize heat sources with variable temperatures.

Energy, exergy, economic, and environmental analysis of a high-temperature heat pump steam system

Industrial steam is widely recognized as a valuable form of heat currency, possessing considerable social and economic significance. As the industry shifts to low carbon emissions, there is an urgent need to reduce CO2 emissions from industrial steam generation. The analysis of a high-temperature heat pump steam system (HTHPSS), which recovers industrial waste heat to produce high-temperature steam at 170 °C, includes evaluations of its energy, exergy, economic, and environmental (4E) to determine whether it can replace a coal-fired boiler. The economic analysis considered the recovery value of waste heat and the effect of CO2 trading prices. Optimization calculations were performed to investigate changes in the waste heat temperature and condenser outlet temperature. The study also offers recommendations for operational conditions and optimization strategies for the HTHPSS. The results indicate a positive correlation between the system coefficient of performance (COP) and the waste heat utilization rate with waste heat temperature and condenser outlet temperature. The maximum COP value is 2.73. The total exergy efficiency initially increases and then decreases as waste heat temperature increases. It also decreases as the condenser outlet temperature increases, reaching a peak value of 43.26 %. The waste heat temperature needs to be at least 59 °C to generate a net profit, with a corresponding payback period (PBP) of 4.40 years. The minimum PBP is 0.03 years, independent of waste heat temperature. The annual emission reduction increases as waste heat temperature increases and decreases as condenser outlet temperature increases. These results indicate that a HTHPSS could replace a coal-fired boiler and offer guidance for design optimization.

Space numerical simulation of full oxygen combustion flame in glass melting furnace based on flue gas preheating

This study explores the innovative design of a glass-melting furnace, which incorporates a combustion lance and a flue on one side. The research validates the simulation that the high-temperature flue gas, produced by the pure oxygen combustion of natural gas, can utilize residual heat in a multi-stage process to preheat and burn the fuel natural gas via a jet heat pump. This process significantly reduces energy consumption, thereby decreasing construction costs and energy usage in industries related to glass furnace production. The research focuses on the flame space of a 600 t/day natural gas flat glass all-oxygen combustion furnace. Utilizing numerical calculation methods, a three-dimensional mathematical model of the all-oxygen lance flame space was developed. Numerical simulation methods were employed to examine the temperature field, airflow field, and the distribution pattern of the liquid flow field within the glass space in the furnace. The simulation results reveal that incorporating high-temperature flue gas into the fuel can markedly enhance the performance of the spray gun flame. Additionally, choosing spray gun outlet designs of varying widths can tailor the flame width to better meet the requirements of the glass melting system, thereby significantly improving the waste heat utilization rate of the flue gas. This offers more alternatives for the direct utilization of flue gas. When compared to traditional oxy-combustion glass melting furnaces, this innovative design substantially reduces construction costs and is more energy-efficient and environmentally friendly.

Performance Optimization Analysis of An Air-source Heat Pump with Multi-Stage Waste Heat Recovery

In this paper presents the effect of different outdoor ambient temperatures and heating temperatures on the performance of an air-source heat pump drying system with multi-stage waste heat recovery has been analysed by recording actual operating status of the system for a little longer-term period. The results show that COP of the heat pump with any heat recovery mode will increase with heating temperature reduction or ambient temperature rising like that does it without heat recovery. As outdoor ambient temperature increasing, the suitable heat recovery mode to enhance COP of the heat pump drying system changes from mode 1-3 to mode 1-2-3 and then to mode 1-2. Especially outdoor low-temperature ambient conditions in winter, 1-3 under would both enhance COP and improve the problem of evaporator frost. But the waste heat utilization rate ηT of whole system is lowest. Moreover, it can be supposed by comparing η with ηT that the first-stage heat exchanger unit of the heat recovery system and the energy transfer fluid circulating in the system would be potential for optimization to further enhance the performance of whole air-source heat pump drying system.

Optimization of combined cooling, heating, and power systems for rural scenario based on a two-layer optimization model

In the process of rural urbanization, the burden of energy and carbon emissions has increased. To alleviate these problems, this study proposes a combined cooling, heating, and power with a photovoltaic/thermally assisted ground source heat pump system to meet the load demand of rural users. A two-layer optimization model is constructed with the goal of optimal economy. The upper layer is a capacity allocation model simulated with MATLAB software and solved with an accelerated particle swarm optimization algorithm to obtain the optimal equipment parameters. The optimization variables are constrained by the operation strategy of the lower layer. The lower layer is the operation optimization model. The operation model is established on the TRNSYS platform, and the operation strategy is formulated. The charging and discharging time of its energy storage device is constrained by the local time-of-use electricity price system. Taking a rural house nearby Huaihe river in Huainan, China as an example, a combined cooling, heating, and power system is designed. And an annual simulation of the system is conducted and optimized based on the local parameters. The optimization results show that the economy and performance of the optimized system are improved. During the heating period, the average COP of the optimized system increased from 4.94 to 6.59, and its energy saving rate reached 7.18%. The operating income increased by 862.93 CNY and 2866.87 CNY, respectively, compared with the non-optimized system and the separate production system. And the optimized PV/T waste heat utilization system can provide 3254.70 kWh of heat. The utilization rate of waste heat reaches 72.26%, which realizes the full utilization of renewable energy.

A Smart Community Waste Heat Recovery System Based on Air Source-Sewage Source Compound Heat Pump

Compared with the traditional hot water production methods, heat pump systems have the unique advantages of high efficiency, energy saving, and eco-friendly, so they have a very good promotion and application prospect. The sewage source heat pump systems can recover the waste heat of high-temperature sewage produced in residential communities, for this reason, this study integrated the proven air source heat pump technology with the sewage source heat pump technology and conducted a research on the smart community waste heat recovery system based on the air-source/sewage-source Compound Heat Pump system (CHP system). In the paper, the design steps and equipment selection flow of the proposed system were given, the waste heat utilization rate of the proposed system was calculated, and the obtained experimental results verified the energy-saving effect of the proposed system, which had provided a reference for the application of the compound heat pumps in other occasions.

Study on a new cascade utilize method for ship waste heat based on TEG‐ORC combined cycle

AbstractIn order to achieve the efficient cascade utilization of various ship's waste heat, improve the energy efficiency of ships and meet the strict requirements of the new international carbon emission regulations, this article proposes a of TEG‐ORC (thermoelectric power generation/organic Rankine cycle) combined cycle, and designs the experimental system. Coupling characteristics of each bottom cycle are taken as the entry point in the combined cycle, using the method of system simulation, the influence of TEG/ORC bottom cycle ratio, evaporation pressure and flow rate of ORC working fluid flow on the key performance of system output power, system thermal efficiency, and waste heat utilization rate of main engine flue gas are studied. The results show that TEG‐ORC combined cycle can overcome the limitations of TEG or ORC, maximize the recovery amount of waste heat, improve the stability and safety of ORC bottom cycle, simulation results show that when the bottom cycle ratio (QTEG/QORC) is 0.52, the maximum output power and maximum thermal efficiency of the experimental system are 2933.7w and 24.68%, respectively. In this condition, the scale of TEG bottom cycle is 41 pieces, the ORC working fluid flow rate is 0.046 kg/s, and the ORC working medium evaporation pressure is 3 MPa.

Energy, economic, and environmental analysis of integration of thermal energy storage into district heating systems using waste heat from data centres

Data centres produce waste heat, which can be utilized in district heating systems. However, the mismatch between data centres’ heat supply and district heating systems’ heat demands limits its utilization. Further, high peak loads increase the operation cost of district heating systems. This study aimed to solve these problems by introducing thermal energy storages. A water tank and a borehole thermal energy storage system were selected as the short-term and long-term thermal energy storage, respectively. Energy, economic, and environmental indicators were introduced to evaluate different solutions. The case study was a campus district heating system in Norway. Results showed that the water tank could shave the peak load by 31% and save the annual energy cost by 5%. The payback period was lower than 15 years when the storage efficiency remained higher than 80%. However, it had no obvious benefits in terms of mismatch relieving and CO2 emissions reduction. In contrast, the borehole thermal energy storage increased the waste heat utilization rate to 96% and reduced the annual CO2 emissions by 8%. However, the payback period was more than 17 years. These results provide guidelines for the retrofit of district heating systems, where data centres’ waste heat is available.

Experiment and numerical simulation of sinter cooling in annular cooler

Based on the empirical constant value of the thermal physical parameters of sinter, this paper combines experimental measurement and finite element simulation to study the equivalent thermal conductivity of sinter and establish a heat transfer model suitable for the cooling process of sinter. The influence of the empirical value and the change value on the cooling process is analyzed by analyzing the thermal property parameters of the sinter. The effects of sinter size and inlet air temperature on the cooling process are investigated by using varying thermal physical parameters. The results show that the smaller the particle size is, the higher the inlet air temperature is, and the higher the waste heat utilization rate of the outlet heat exhaust gas is.

Modeling and analysis of an ammonia–water absorption refrigeration system utilizing waste heat with large temperature span

Waste heat sources such as flue gas generate large temperature span during recovery process. In order to improve the temperature match with such waste heat sources, a novel absorption refrigeration system with continuous-temperature-changing generation process is proposed. Internal heat recovery process is introduced to both the generator and absorber, and a premixer is added to take the place of the solution heat exchanger in traditional system. A numerical model of the system is built, in which the continuous-temperature-changing generation process is simulated based on a stripping column with heat input at each stage. New parameters are defined and optimized to strengthen the internal heat recovery process, and thus to improve system efficiency. Simulation results show that the system can operate under a large waste heat temperature span of 67.5 K, almost twice of the conventional system. With the evaporation temperature, waste heat inlet temperature, and cooling water temperature at −15 °C, 150 °C and 20 °C, respectively, a maximum COP of 0.93 and exergy efficiency of 49.7% is acquired while the waste heat temperature span is 60 K, showing that the system can acquire larger utilization rate of waste heat with higher system efficiency.

A Framework of Exergy Efficiency Analysis for Cogeneration Power Plant in Cement Production

As a major energy consumer, cement production industry generates a large amount of waste heat during the clinker production process. There are also lots of dust and sulfur dioxide and nitrogen oxide emission accompanying with the waste heat loss, which are aggravating the eco-environment. It is necessary to develop new energy-saving technologies and push the waste heat utilization in cement industry to improve the utilization rate of waste heat from cement. In this study, an exergy efficiency analysis was conducted for the cogeneration power plant in cement production process. The results showed that cement production system can achieve heat recovery effectively with the cogeneration system.

Analysis of an absorption cycle driven by temperature-distributed heat sources

An ammonia–water absorption refrigeration system with a novel generator structure driven by temperature-distributed heat sources to increase the utilization rate of waste heat is presented. The stripping section of the distillation column and generator were replaced by a generator with temperature-distributed heat sources. The heat sources were distributed throughout the entire process in the generator, so the mass and heat transfer were coupled at different temperatures, which increased the waste heat utilization at low temperatures. Compared with a traditional system, temperature–distributed heat sources increased the utilization temperature range. In the simulation of the system, the condition at cold end kept unchanged while the heating distributions and quantity inside the generator were changed. The performance of the new generator driven by temperature-distributed heat sources was analyzed while compared with a traditional system through the coefficient of performance, separation efficiency and waste heat utilization.

A novel design methodology for waste heat recovery systems using organic Rankine cycle

This paper discusses a comprehensive design methodology for optimization of organic Rankine cycle designs using a new design to resource method. The objective of the design to resource method is to obtain the best designs, which are the closest match to the resource and the most cost-effective. The design analysis is constrained by the available main components and heat resource. The ratio of net power output to the total heat exchanger area is used as the objective function. The new design methodology was implemented on an existing lab-scale as a case study. Experiments were conducted to obtain the data to identify the heat transfer coefficients of the real processes and validate the simulation model results. Design evaluations were carried out on the plant by using three Capstone gas turbine load conditions and four design alternatives. The results indicate that design 1has the highest objective function of all the alternatives. It is able to increase the objective function from 100% to 391% of the base case depending on the Capstone gas turbine load conditions. The results also reveal that the current small scale plant is more suitable to Capstone gas turbine load condition 1 with the highest waste heat utilization rate of 76.9%.

An improved CO2-based transcritical Rankine cycle (CTRC) used for engine waste heat recovery

CO2-based transcritical Rankine cycle (CTRC) is a promising technology for the waste heat recovery of an engine considering its safety and environment friendly characteristics, which also matchs the high temperature of the exhaust gas and satisfies the miniaturization demand of recovery systems. But the traditional CTRC system with a basic configuration (B-CTRC) has a poor thermodynamic performance. This paper introduces an improved CTRC system containing both a preheater and regenerator (PR-CTRC), for recovering waste heat in exhaust gas and engine coolant of an engine, and compares its performance with that of the B-CTRC system and also with that of the traditional excellent Organic Rankine Cycle (ORC) systems using R123 as a working fluid. The utilization rate of waste heat, total cooling load, net power output, thermal efficiency, exergy loss, exergy efficiency and component size have been investigated. Results show that, the net power output of the PR-CTRC could reach up to 9.0kW for a 43.8kW engine, which increases by 150% compared with that of the B-CTRC (3.6kW). The PR-CTRC also improves the thermal efficiency and exergy efficiency of the B-CTRC, with increases of 184% and 227%, respectively. Compared with the ORC system, the PR-CTRC shows the significant advantage of highly recycling the exhaust gas and engine coolant simultaneously due to the special property of supercritical CO2’s specific heat capacity. The supercritical property of CO2 also generates a better heat transfer and flowing performances. Meanwhile, the PR-CTRC possesses a smaller SP (0.010–0.020m) than that of R123 systems (0.055–0.070m). Therefore, the PR-CTRC system is suitable for the waste heat recovery of an engine, especially for recovering both high-grade and low-grade waste heat.

METHODS OF REDUCTION OF FUEL CONSUMPTION AS MEANS FOR CO2 EMITTED BY SEAGOING SHIPS MINIMISING

The subject of paper is to focus the problem of carbon dioxide emission from seagoing ships. The paper presents analysis of possibilities of fuel consumption minimizing and this way reduction of carbon dioxide emission from seagoing ships. However, The VI Amendment to MARPOL Convention concerning prevention against air pollution by seagoing ships did not take into consideration carbon dioxide emission, the importance of this problem was perceived by international organizations among others by IMO. As a result corrections in VI Amendment to MARPOL Convention were introduced thus forcing reduction of CO2 emission by seagoing ships. Among means reducing emission of carbon dioxide into atmosphere the following are mentioned: construction modifications of new built ships i.e. reduction of ship speed, optimization of main engine and propeller selection, optimization of ship hull shape, application of resistance reducing hull coatings, use of alternative (ecological) fuels and utilization of propulsion plant waste heat. In turn, for ships already in operation methods for fuel consumption and carbon dioxide reduction can be individual for each ship full monitoring of main engine operational parameters and measurement of waste heat utilization rate. According to opinion of paper authors, the minimizing of carbon dioxide reduction can be mainly achieved by utilisation of exhaust gases heat for electric power production in steam turbo alternators running in one- or two stage steam pressure systems. The analysis executed in the paper of one- and two stage steam system advantages shows that one stage steam system is more economically profitable in practice application.

Thermodynamic evaluation on the integrated system of VHTR and forward osmosis desalination process

In order to effectively tackle the two global issues, water shortage and energy demand, an integrated system of a very high temperature reactor (VHTR) and forward osmosis (FO) desalination system is proposed. The integration basically implies the coupling of the waste heat from VHTR with the draw solute recovery system of FO seawater desalination system which is the only energy consuming part of the whole FO process. By integrating the two novel technologies, several advantages can be achieved, such as production of fresh water using waste heat and environment protection through waste heat reduction. In order to thermodynamically analyze the integrated system, the FO system and the power conversion systems (PCSs) of VHTR are simulated and integrated using UNISIM program and OLI property package. As a result, the integrated system of FO–VHTR was calculated to have higher Gain Output Ratio (GOR) values ranging from 9.0 to 13.8, than the typical GOR values, ranging from 6 to 12, of multi-stage flash (MSF) and multi-effect distillation (MED). Furthermore, when the technologies were coupled to the same capacity VHTR, the proposed system was calculated to have a significantly higher waste heat utilization rate than the other systems. Accordingly, the water production of the FO–VHTR system was found to be at least 5 times larger than that of the MSF–VHTR system.