Waste Heat Power Research Articles

Superior thermoelectric cooling performance by suppressing bipolar diffusion effect and enhancing anisotropic texture in p-/n-type Bi2Te3 based compounds

Thermoelectric technologies can be used for waste heat power generation, and for solid-state cooling without environmentally hazardous refrigerants or moving parts. Thermoelectric cooling materials like the Bismuth Tellurides have been intensively investigated for several decades, but to date, thermoelectric cooling device applications have been limited to niche markets, because of their low cooling efficiency and high power consumption. Here, we demonstrate a thermoelectric module with significantly enhanced cooling performance and low power consumption, with fast cooling, using state-of-the-art p-/n-type Bi2Te3 based thermoelectric materials. Small grain size and anisotropic texture were achieved an exceptional high performance in the p-type Ag0.0006Bi0.46Sb1.5Te3.07 and n-type (CuI)0.002Bi2Te2.7Se0.3 compounds through rapid solidification and hot extrusion processes, resulting in significantly improved thermoelectric performance over a wide temperature range (zTmax = 1.45 for the p-type and 1.40 for the n-type compounds). The observed temperature-dependent thermoelectric properties in the n-type (CuI)0.002Bi2Te2.7Se0.3 compound could be explained in terms of Rashba band splitting rather than the multiband Boltzmann transport equations. We suggest that the enhancement of thermoelectric performance is due to the increase in chemical potential by Ag- (p-type) and CuI-doping (n-type) which suppresses bipolar diffusion, while the anisotropic texture and micro grains decreases lattice thermal conductivity. The thermoelectric module using these state-of-the-art thermoelectric materials demonstrated a reduction in power consumption by 38% and an increase of cooling speed by 170% compared with commercial single crystal-based TE devices, which is promising for practical applications.

Performance analysis of ORC low temperature waste heat power generation system

For 90~180°C low temperature waste heat resources, three different types of organic working fluids, benzene, isopentane and R245fa are selected from the perspectives of safety, environmental protection and physical properties of working fluid. The mathematical models of the system are established through MATLAB and REFPROP and the influence of the evaporation temperature on the performance of the ORC low temperature waste heat power generation system is studied. The results show that the thermal efficiency and net output power of the system increase with the increase of evaporation temperature; the evaporation pressure of CFC-type working fluids is relatively low; the net output power and thermal efficiency of HFC and HC-type working fluids are generally relatively low. The evaporator has the largest irreversible loss in the system, followed by the condenser and expander while the working fluid pump has the smallest irreversible loss.

Reforming of converter gas with coke oven gas for thermochemical energy storage and carbon dioxide emission reduction

During traditional processing and utilizing of converter gas, a common by-product gas of steel production, the recycling of waste heat is insufficient, carbon emission is high, and the added value of the gas is low. The reforming of converter gas with coke oven gas is proposed to utilize the gas more efficiently. The reforming recycles the waste heat of the gas by thermochemical energy storage technology and converts CH4 and CO2 into H2 and CO, which improves the recovery rate of the waste heat and gas added value, and reduces the direct emission of CO2. Thermodynamic equilibrium calculation and regression analysis were used to investigate the effects of the temperature, pressure, and mole fraction of coke oven gas on the results of the reforming. The results show that atmospheric pressure and the temperature range of 850 °C–1000 °C are suitable for the reforming, at which the conversion rates of CH4 and CO2 are more than 90% and 75%, respectively. The ratio of H2 to CO is determined by the mole fraction of coke oven gas. Then, the reforming process was investigated by experiments which simulated the reforming process in converter flue. The experimental results show that the in-suit catalysis of converter dust can significantly improve the conversion rates of CH4 and CO2 and the conversion rates can reach a high level at about 1000 °C. Then, the waste heat utilization of the reforming was investigated, and it was concluded that 35–40% of the waste heat is converted into chemical energy in the reforming. After the waste heat power generation of the product gas, the total recovery rate of waste heat is 60–65%. Finally, the amount of coke oven gas reformed by a fixed amount of converter gas without additional heating was calculated. The results show that when the preheating temperature of coke oven gas is 500 °C the range of 850 °C–900 °C is appropriate for the reforming, at which the conversion rate of CO2 is approximately 50% and about 40% of the waste heat was converted to chemical energy. For a steel plant with an annual output of 20 million, the direct emission of CO2 can reduce by 2.13 × 108 Nm3, and waste heat of 3.24 × 106 GJ can be converted into chemical energy.

Strategy for introducing sewage sludge energy utilization systems at sewage treatment plants in large cities in Japan: A comparative assessment

The sewage sludge recycling strategy in Japan is shifting to a phase focusing on energy utilization. At present, the treatment of dewatered sludge depends on high-temperature incineration at 850 °C, and it is necessary to switch to energy conversion technologies to recover energy. Sewage treatment plants equipped with digestion tanks can recover energy by decomposing some of the volatile solids in the sludge, but decreasing the volatile solid content of the dewatered sludge in the solid matter also decreases the efficiency of the dewatered sludge conversion process. Therefore, in this study, we developed a tool for evaluating sewage sludge energy conversion systems based on a precise heat balance analysis. We also focused on how the presence or absence of digestion affects each energy conversion technology. The targeted sewage sludge energy conversion technologies were three incineration systems that included waste heat power generation (power generation from low-pressure steam and high-temperature water, power generation from high-pressure steam, and power generation from low-pressure steam and sludge drying) and two solid fuel conversion systems (dry granulation and low-temperature carbonization). The evaluation indices were energy balance, greenhouse gas emissions, and total project cost. The results showed that 1) not using digestion is a superior option in the incineration with waste heat power generation systems, and 2) using digestion is superior in the solid fuel conversion systems.

Research on big data analysis model of multi energy power generation considering pollutant emission—Empirical analysis from Shanxi Province

With the development of the integrated energy Internet, energy structure optimization and emission reduction have led to higher requirements for developing various energy sources to enable coordinated and sustainable development. However, data-mining methods are rarely used to study the coordination of multi-energy generation in published research results. In this study, from the perspective of power industry emissions, coordinated generation of various energy sources, and balance of power generation and consumption, a data-mining algorithm was used to analyze the development of thermal power, hydropower, wind power, waste heat, gas, and other power sources. The chi-square automatic interaction detection tree (CHAID), logistic regression, and two-step clustering methods were applied. The results show that: a) CO2 and SO2 emissions were mainly affected by thermal power generation, whereas NOx emissions were jointly affected by thermal power, garbage power, and gas-fired power, and the emissions of various pollutants increased with an increase in power consumption. The optimal power-generation scheme under minimum emission can be obtained. b) There was a strong correlation between thermal power generation and residential electricity consumption, and renewable energy (wind energy, photovoltaic, hydropower) exhibited the highest correlation with the electricity consumption of the tertiary industry, which indicates that renewable energy generation can be promoted by managing electricity consumption in the tertiary industry. c) When the electricity demand of all users was small, the proportion of renewable energy power generation increased; in contrast, the thermal power generation was larger. This indicates the importance of improving the sustainable and stable power supply of renewable energy. This study provides a data analysis model for the coordinated development of multiple energies, which will contribute to the decision-making basis for controlling power emissions, improving the utilization rate of renewable energy, and optimizing the energy structure.

Screening of Energy-Saving Technologies for Cement Production Based on Boston Consulting Group Matrix

Based on the analysis of the development situation of China’s cement industry and the BCG Matrix method, this paper classifies and screens 31 energy-saving technologies in China's cement production, and puts forward guiding suggestions for the application of energy-saving technologies for cement enterprises. The screening results show that the “Energy-efficient powder separation technology” and “New low-calcium cement clinker and production technology” are “double-high” technologies with excellent on both screening indicators. The investment energy saving rates are 17.5 tce/10,000 yuan (tons of standard coal equivalent per 10,000 yuan) and 10 tce/10,000 yuan. The promotion ratio increments are 35% and 25%. “Cement clinker energy-saving nitrogen reduction firing technology”, “Fan drive mode adopts high voltage frequency conversion speed control technology”, “Pure low temperature waste heat power generation technology for cement kiln” are “single-high” technologies with excellent on one of screening indicators. The investment energy saving rates are 0.3tce/10,000 yuan, 4.1tce/10,000 yuan, 3.9tce/10,000 yuan respectively. The promotion ratio increments are 19%, 35%, 31.5% respectively.

Proposal and comprehensive analysis of an innovative steam generation system by deep recovery of low-grade waste heat

The waste heat generated by industrial processes is often not fully recycled, resulting in a significant amount of wasted energy and thermal pollution. Meanwhile, low-pressure steam plays an important role in industry as many processes consume a large amount of steam. An innovative steam generation system based on the deep recovery of low-grade industrial waste hot water is proposed. The waste hot water first flashes out low-pressure steam, and then drives an organic Rankine cycle to generate mechanical work, which is used to compress the low-pressure steam. A techno-economic model is established. The thermodynamic indicators are calculated under preliminary optimization conditions, and a comparative analysis between the proposed system and other waste heat utilization systems is carried out under the same heat source conditions. The techno-economic analysis shows that the proposed system is better for recycling wasted hot water. The steam generation mass ratio, exergy efficiency, and cost per ton of recycled steam are 2.50%, 44.31%, and 7.67 $/ton, respectively, under the optimized conditions. When the heat source temperature is 100 °C, the exergy efficiency of the proposed system is 37.01% and 60.59% higher than that of the steam generation heat pump system and waste heat power generation system, respectively. Advanced exergy analyses are conducted to determine the actual potential improvement for system components, with the avoidable exergy destruction of the expander showing the largest. This paper proposes an efficient and cost-competitive approach for the deep recovery of low-temperature hot water for producing industrial steam.

Economic performance evaluation of the wind supercharging solar chimney power plant combining desalination and waste heat after parameter optimization

In this paper, the economic analysis model of solar chimney power plant combining seawater desalination and waste heat (SCPPDW) and wind supercharging solar chimney power plant combining seawater desalination and waste heat (WSCPPDW) was established. Based on net present value (NPV) method, the economic performance of two systems and that of WSCPPDW after optimization were studied. It was found that the addition of wind supercharging device increased the net income (NET) and NPV by 42.8% and 102.5%, respectively. With the increase of time, the annual NET of two systems increased, and the annual NPV firstly increased and then decreased. The annual NET and NPV of WSCPPDW were always larger than those of SCPPDW, which were negative in the first four years, but those of WSCPPDW were only negative in the first year. After sequentially optimizing the turbine rotational speed, nozzle length, chimney outlet radius and mixing section length, the power and freshwater output of WSCPPDW were improved by 455.8% and 11.7%, respectively. And the total net income (TNET) and total net present value (TNPV) were increased by 183.4% and 442.8%, respectively. The declining inflection point of annual NPV was brought forward by 10 years compared to that of initial WSCPPDW.

Fire Monitoring System for Power Batteries on Ship

In recent years, due to the influence of policies such as environmental protection and reduction of harmful gas emissions, clean energy such as lithium batteries, hydrogen-oxygen fuel cells, and waste heat power generation technologies are being applied on ships. As the application level of new energy continues to expand, its safety issues have attracted more and more attention from society. The system collects the air pressure, temperature, humidity, flame heat radiation, and smoke information inside the ship’s power battery box, and uses the STM32 processor to determine whether the ship’s power battery has a fire hazard. This system can effectively avoid the thermal runaway of the power battery, detect the thermal runaway at an early stage and actively respond to reduce losses, and protect the life and property safety of passengers on board.

Improved room-temperature thermoelectric characteristics in F4TCNQ-doped CNT yarn/P3HT composite by controlled doping

Abstract High room-temperature thermoelectric performance is important for low-grade waste heat power generation as there are plenty of heat thrown away uselessly in our daily life, most of which are below 100 °C. However, most of the thermoelectric materials are limited to high temperature application. In this work, room-temperature thermoelectric power factor of carbon nanotube (CNT) yarn is improved by controlled doping, which is achieved by making composite with poly 3-hexylthiophene −2, 5-diyl (P3HT) followed by doping with 2, 3, 5, 6-tetrafluo-7, 7, 8, 8-tetracyanoquinodimethane (F4TCNQ). The temperature-dependent Seebeck coefficient based on power–law model suggests that P3HT shifts the Fermi energy of CNT yarn towards the valence band edge, and reduces the ionic scattering and carrier relaxation time. As a result, the Seebeck coefficient is increased while the variation of Seebeck coefficient with temperature is reduced, and hence, the room-temperature thermoelectric power factor is improved. With controlled doping, the power factor of CNT yarn/P3HT composite reaches to 1640–2160 μW m−1K−2 at the temperature range of 25–100 °C, which is higher than that of CNT yarn alone.

Optimization design of thermal system for industrial waste heat power generation

In order to improve the utilization rate of industrial waste heat and improve the fine design level of waste heat power station, this paper constructs the mathematical model of waste heat boiler and steam turbine, and puts forward the optimization design method of thermal system of waste heat power generation project. By using typical cases, it is proved that there is the optimal design pressure of HRSG, which makes the power generation of the system maximum, and provides a method to improve the power generation of HRSG.

Research on the Robustness of the Roots Waste Heat Power Generation System

Research on the Robustness of the Roots Waste Heat Power Generation System

Improving energy efficiency through the use of waste heat products in the production of building materials

Concern for the sustainable management and recycling of solid waste is becoming more visible in all sectors of the economy. This study explores the possibility of using coal ash residue (waste from Kazan CHPP-2) as a substitute for fine-grained aggregate in sulfur concrete. The trend towards an increase in the level of utilization of waste heat power engineering is an important task. The chemical composition, microstructure and mechanical properties, including density, water absorption, compressive strength and thermal conductivity of sulfur concrete, including coal ash with partial and complete sand replacement, were investigated and the results were compared with those for standard cellular concrete. The authors studied modern heat-insulating materials and materials from industrial waste products. The article analyzes the estimated thickness of the insulating material depending on the type of structure. Outside walls made of sulfur concrete, in addition to high strength properties, have high thermal and economic performance.

Research on Algorithm Fusion for the Control of a Roots-Type Waste Heat Power Generation System

At present, the recovery of low-quality waste heat is a major problem in energy utilization. To solve this problem and improve energy efficiency, this research group designed a low-quality waste heat power generation device with a roots-type power machine as the core component. However, the power generation device produces a large hysteresis in power generation regulation. While the hardware can be improved, the design of the measurement and control system is also critical. In view of the problems existing in low-quality waste heat power generation devices, this research group introduced an internal model controller into the control system and designed an internal model controller and filter through the analysis of each module. In addition, to improve the performance of the controller, this research group applied the deep learning method to optimize the control system and used the prediction function of the deep learning method to further improve the stability of the device. The simulation and experimental results show that the control strategy can make this device for the recovery of low-quality waste heat respond quickly to fluctuations in the gas source and improve the hysteresis problem.

PERFORMANCES OF HIGH POROUS CELLULAR CONCRETE

The widespread use of cellular concrete for enclosing structures forces researchers to develop ways to im-prove their performance and durability. Compositions of aerated and foam concrete with the use of waste heat power engineering have been developed. The optimal formulation ratios have been identified that con-tribute to the creation of a rigid interpore matrix and water-repellent pore protection. The regularities of the synthesis of aerated concrete and foam concrete were established, which consist in optimizing the processes of structure formation through the use of a polymineral cement-ash binder and a pore-forming agent. The mix composition intensifies the process of hydration of the system, which leads to the synthesis of a poly-mineral highly porous heterodispersed matrix. The increased activity and granulometry of aluminosilicates predetermine an increase in the number of contacts and mechanical adhesion between particles during com-paction, strengthening the framework of the interpore partitions. The mechanism of the influence of the composition of the concrete mix on the microstructure of the composite is established. The calculated sound insulation of airborne noise shows sufficient characteristics for using aerated concrete blocks as enclosing structures. One of the main advantages of aerated concrete is its low thermal conductivity, which is especial-ly important from the point of view of ensuring the energy efficiency of buildings and structures. Even in spite of the high values of open porosity of the developed aerated concrete, the rigid frame makes it possible to achieve almost 2 times higher frost resistance characteristics than that of the reference specimen

Prospect of Waste Heat Utilization in Cement Plant

The prospect of waste heat utilization in cement plant is very broad. In this paper, it is briefly summarized, and then the production system and equipment selection of waste heat power plant and the technical implementation analysis are discussed. It is hoped that this paper can have certain reference value for specific projects of the same type of waste heat utilization.

Thermodynamic Performance Analysis of a Waste Heat Power Generation System (WHPGS) Applied to the Sidewalls of Aluminum Reduction Cells.

To recover energy from the waste heat of aluminum reduction cells, a waste heat power generation system (WHPGS) with low boiling point working fluid based on Organic Rankine Cycle was proposed. A simplified model for the heat transfer around the walls of aluminum reduction cells and thermodynamic cycle was established. By using the model developed and coded in Matlab, thermal performance analysis of the system was conducted. Results show that the electrolyte temperature and the freeze ledge thickness in the cell can significantly affect the heat absorption of the working fluid in the heat exchange system on the walls. Besides, both the output power and the thermal efficiency of the power generation system increase with the system pressure. The output power and thermal efficiency of the system can also be affected by the type of working fluid used in the system. Working fluids for the best system performance under different output pressures were determined, based on the performance analysis. This WHPGS would be a good solution of energy-saving in aluminum electrolysis enterprises.

An experimentally validated control strategy to optimize power generation quality for waste heat recovery system

Roots-type engine is suitable for small power generation system fuelled by waste heat. The disorderly fluctuations of the waste heat source upstream of the power generation process and changes in external environmental factors cause the working parameters of the device to change, which makes the speed of roots engine unstable, and the output power quality of the system is not good. For this problem, this paper starts from the control structure and control strategy to improve the adjustment speed and anti-interference ability of the control system. In this contribution, the model transformation of the dynamic work unit of waste heat power generation device from engineering to theoretical model is performed, the temperature of working gas and the speed of output shaft of roots engine are determined as control objects, and the internal mode control strategy is introduced to optimize the controller of the system. Simulation results are in good agreement with the measurements, which verify that the optimized control system can effectively improve the following ability and anti-interference of the system, and shorten the response time.

An exergoeconomic–environmental analysis of an organic Rankine cycle system integrated with a 660 MW steam power plant in terms of waste heat power generation

ABSTRACT This study aimed to assess the thermodynamic performance of an Organic Rankine Cycle (ORC) unit for power generation operated by the industrial waste heat of exhaust gas of a steam power plant. For conducting exergoeconomic and environmental analyses, real data measured from a coal-fired power plant operating under subcritical conditions at the highest capacity of 660 MW was utilized. The main goal of this study is to increase the performance of the subcritical power plant to reach the performance of the supercritical steam power plant by converting waste heat into electricity. As a working fluid, R600, R245fa, R236ea and R236fa working fluids were chosen for the present system. The influences of flue gas temperature, evaporator pinch point temperature and the steam power plant unit load on the power plant performance were determined. According to the results obtained, ORC exergy efficiency reached the highest value of 42.26%, and a net power output of 4.7 MW was achieved, thereby rising overall exergy efficiency by 0.3%. Calculations illustrate that the exergy efficiency enhances with a steam power plant unit load. Conversely, this exergy efficiency decreases with an increase in flue gas temperature and evaporator pinch point temperature. In addition, the power output generated by the ORC unit is increased with increasing flue gas temperature and steam power plant unit load. But, this net power output is reduced with rising the evaporator pinch point temperature. The novelty of this work is the flue gas of steam power station can confirm to be a suitable source of low-temperature heat for conversion into electrical energy, thereby enhancing the general performance of the process and lowering environmental impact.

Thermodynamic Optimization of a Waste Heat Power System under Economic Constraint

A novel thermo-economic performance indicator for a waste heat power system, namely, MPC, is proposed in this study, which denotes the maximum net power output with the constraint of EPC ≤ EPC0, where EPC is the electricity production cost of the system and EPC0 refers to the EPC of conventional fossil fuel power plants. The organic and steam Rankine cycle (ORC, SRC) systems driven by the flue gas are optimized to maximize the net power output with the constraint of EPC ≤ EPC0 by using the Non-dominated Sorting Genetic Algorithm-II (NSGA-II). The optimization process entails the design of the heat exchangers, the instantaneous calculation of the turbine efficiency, and the system cost estimation based on the Aspen Process Economic Analyzer. Six organic fluids, n-butane, R245fa, n-pentane, cyclo-pentane, MM (Hexamethyldisiloxane), and toluene, are considered for the ORC system. Results indicate that the MPC of the ORC system using cyclo-pentane is 39.7% higher than that of the SRC system under the waste heat source from a cement plant with an initial temperature of 360 °C and mass flow rate of 42.15 kg/s. The precondition of the application of the waste heat power system is EPC ≤ EPC0, and the minimum heat source temperatures to satisfy this condition for ORC and SRC systems are obtained. Finally, the selection map of ORC versus SRC based on their thermo-economic performance in terms of the heat source conditions is provided.