In natural gas-steam combined cycle power plants, the connection section between the gas turbine and the waste heat boiler is characterized by a sharply expanded channel confined by plates with large inclination angles, which often results in unsatisfactory flow pattern and consequently leads to a reduction in deNO_x efficiency in the downstream. Installation of triple layers of deflectors is proposed to improve the flue gas flow uniformity. Computational fluid dynamics modeling approach is adopted to investigate the influences of the deflector parameters including installation arrangements, installation angle and density on the flue gas flow characteristics in the flue duct. A large vortex is clearly observed in the connection section with a vorticity up to 20 m^–1, when no deflector is installed. Installing a single layer of deflector with varying installation angles is able to decrease the size of the vortex, while installation of double layers of similar deflectors leads to a satisfactory flow pattern in the connection section. A more preferable flue gas flow pattern in the whole boiler channel is obtained by a setup of triple layers of deflectors. The optimal lengths projected horizontally are 2.25 m, 1.36 m and 0.70 m for the three-layer deflector plates, and the distances between two plates are 1.20 m, 1.40 m and 1.00 m separately. The installation angle is between 15° and 30° with uniform incrementation for the first deflector, and between 15° and 60° with uniform incrementation for the second deflector. A relative velocity standard deviation of 2.1% is obtained at outlet cross-section with the triple deflectors. The research results can provide theoretical guidance for the design of flue gas flow equalization devices

The microwave attenuation method is one of the common methods for online measurement of carbon content in fly ash in recent years. However, due to the differences in sampling locations and sampling devices of the fly ash, there is a large uncertainty in particle size of the fly ash, which results in a large error in the measurement of carbon content in fly ash. The existing carbon content fitting models are all based on the relationship between the attenuation of the characteristic frequency signal by fly ash and the carbon content of fly ash, which has problems such as large error and poor adaptability. In order to solve these problems, this paper proposes to use the time-domain main peak attenuation of the signal instead of the attenuation of the signal at the eigenfrequency as a method for online fitting of the carbon content in fly ash. To correct the error caused by the uncertainty of fly ash particle size, the effects of fly ash with different particle size ranges on the measurement of ash level and fly ash carbon content are compared on the basis of the study on ash level and carbon content measurement. The results show that, the peak attenuation of the signal in the time domain is used to calculate the carbon content, and the results are in good agreement with the actual values. For the same mass of ash samples in the waveguide, the particle size of the fly ash does not have any significant effect on the measurement accuracy of the ash level. When the microwave method is applied to measure the carbon content in the fly ash in the waveguide, for the same mass of ash samples, the attenuation of the fly ash on the microwave signal inside the waveguide decreases gradually with the particle size of the fly ash. Thus, the measured value of carbon content increases as the particle size of the fly ash decreases.

In order to improve the flow field structure of rain area in cooling tower and further increase the ventilation, on the basis of the existing flat plate type wind guide plate, this paper proposes a streamline wind guide plate with low wind resistance that can be arranged in the rain area. Under the design condition, by taking the conventional cooling tower and the reformed tower with flat plate-type air guide plate arranged at each height as the reference objects, the influences of the low wind resistance streamline air guide plate on ventilation, flow field structure and temperature distribution of the whole tower are analyzed, at five different arrangement heights (1/6, 1/3, 1/2, 2/3, 5/6 air intake height). The results show that, with the rise of the height of the air guide plate arrangement, the air distribution in each region of the tower has changed, which has a significant effect on the packing heat exchange in inner zone, so that the cooling performance of the whole tower improves at first and then declines. When arranging the streamlined wind guide plate at 2/3 height of the air inlet, the ventilation increment and the average temperature reduction at the bottom of the filler area reaches the optimal value, and the improvement effect of the cooling tower performance is the best. Compared with the conventional cooling tower, the circulating water temperature drop and the ventilation increases by 2.65% and 2.78%, respectively. In addition, the circulating water temperature drop increases by 1.2% after the tower is retrofitted with a low wind resistance streamlined air guide, compared with the flat plate with an optimal arrangement height.

Against the actual problems that the wet cooling tower is easy to hang ice at the bottom of the packing and the upper edge of the inlet in winter, a three-dimensional numerical model of the cooling tower based on the constant heat load is established. The anti-freezing characteristics of the cooling tower in severe cold weather without anti-freezing device are explored, and the variation characteristics and influencing factors of key parameters such as the water temperature distribution of packing bottom and the air mass flow at tower top outlet are analyzed. The results show that, the lower the ambient temperature, the greater the influence of the unit load on the average water temperature and the lowest water temperature at the bottom of the packing. The main factors affecting the change of the difference between the average water temperature and the lowest water temperature at the packing bottom include unit load, wind velocities and water distribution mode. Among them, the influence of water distribution mode is greater, followed by unit load, and the influence of wind velocities is less. The air mass flow at tower top outlet is positively correlated with the unit load and negatively correlated with the ambient temperature. When the ambient temperature is the same, the air mass flow at tower top outlet of the outer ring with underwater is less than that of the full tower. The water temperature inside the lower part of the windward side and the outside of the leeward side is the lowest, and the freezing risk is the greatest. When the wet cooling tower is running in winter, the anti-freezing device should be arranged on the windward side and the leeward side.

With the rapid development of artificial intelligence, virtual reality and augmented reality technology, it is possible to realize real-time monitoring of operation state of air cooling island of direct air cooling unit by using digital virtual technology. Firstly, a three-dimensional model of the air-cooled island is established, and the operating state parameters of the air-cooled island are obtained by numerical calculation. The air-cooled island operating state database and display and query software are developed. Secondly, based on the concept of digital twin, a meteorological station is set up in the power plant to obtain real-time change data of ambient temperature, wind speed and wind direction, and the operating conditions of the unit are used as software input parameters. Finally, the operation state of the air-cooled island is calculated and displayed in three dimensions. The real-time display technology for air operation state of air cooling system based on digital twin avoids the investment and maintenance of a large number of measuring points on site, which lays a foundation for the development of intelligent power stations.

Raw water pretreatment can be divided into three stages: coagulation, sedimentation and filtration. The flocculation process directly affects the structure of alum and the turbidity of effluent. At present, the method of measuring the turbidity of the effluent is usually used to control the dosage of coagulant, but due to the time lag, it can not quickly reflect the coagulation effect and adjust the dosage of the feedback. With the rapid development of computer technology, the application of alum image processing technology can realize rapid, accurate and real-time detection of flocs state, so as to control the dosage more accurately and improve the coagulation effect. From the perspective of computer vision technology, this paper summarizes the technical characteristics of alum image acquisition and processing in flocs, introduces the method of real-time tracking and calculating the characteristic parameters of alum structure, such as equivalent particle size, fractal dimension, etc., and some test results are also provided. Through these parameters the best coagulation effect can be judged, which provides the basis for coagulation control and dosing.

The HT700 superalloy was joined by rotational friction welding (RFW) method, and the welded specimens were subjected to post weld heat treatment (PWTH). The microstructural evolution and mechanical properties of the joints were systematically investigated by optical microscopy, scanning electron microscopy, transmission electron microscope, micro-hardness, and tensile tests at both room temperature and 750 ℃. The results show that, the as-welded joint shows three typical zones across the weldline: weld center zone (WCZ), thermomechanically affected zone (TMAZ), and heat affected zone (HAZ), in which the microstructure gradually changes from equiaxed fine grains (WCZ) and deformed coarse grains (TMAZ) to equiaxed grains (HAZ) that are similar to the base material. The dynamic recrystallization and dissolution of strengthening phases have occurred in the WCZ during RFW, in which γ′ strengthening phase dissolves to a larger extent than M23C6 or MC carbides. The microstructure of the as-welded joint including the grain size, shape, and the distribution of precipitates gradually changes from the weldline to the parent alloy. Consequently, the as-welded joints exhibit relatively poor mechanical properties due to the dissolution of γ′ which becomes even worse at 750 ℃ because of the grain-boundary sliding. After PWHT, the as-welded microstructure can be homogenized by grain growth and the re-precipitation of strengthening phases, which is responsible for the remarkable improvement in tensile strength at both room and high temperature after PWHT. And the high-temperature ductility of PWTH joints has been improved to a certain extent. This study gives new insights into the high-quality welding of the HT700 superalloy.

ZnFe₂O₄ oxygen carrier (OC) doped with different additives (Sr, Ce, La and Al) was prepared by sol-gel method to investigate the influence of different additives on performance of the ZnFe₂O₄ oxygen carrier. Chemical looping hydrogen generation (CLHG) experiments were carried out in a fixed bed reactor. It was found that the performance of ZnFe₂O₄ was greatly improved by doping different metals, and the hydrogen production of per unit mass OC from high to low is La>Sr>Al>Ce. The physicochemical properties of different amount of La-doped ZnFe₂O₄ were further analyzed by combining X-ray diffraction, H₂-temperature-programmed reduction, Brunauer-Em-mett-Teller method and other characterization methods. The data indicated that the ZnFe₂O₄ modified by La with 12% mass fraction has the highest reaction activity. La dropping can increase the specific surface area of the OC, reduce the reduction temperature, increase the migration rate of lattice oxygen, promote the formation of oxygen vacancies, and is beneficial to the increase in hydrogen production in the chemical looping process.

To solve the problems of fouling, slagging, and high-temperature corrosion in an ultra supercritical 1 000 MW unit boiler fueled by Zhundong coal, engineering verification test of nano-high-entropy ceramic coating in separated over fire air (SOFA) area of the boiler rear water wall was carried out, based on the coal characteristics, slagging condition and corrosion type of the boiler. Several methods such as macrographic check, scanning electron microscope (SEM), X-ray diffraction (XRD), Raman spectrum, friction coefficient and surface energy test were applied to observe the change of nano-high-entropy ceramic coating before and after experiments, thus to reveal the possible slag resistance and corrosion resistance mechanisms of nano-high-entropy ceramic coating. The results show that, the coating remained intact after 11 months’ boiler operation, with no obvious slagging and corrosion pits on the surface and no significantly thinning of the pipe wall. Nano-high-entropy ceramic coating can better solve the problems of fouling, slagging and high-temperature corrosion on the boiler water wall, which provides a guarantee for safe operation of the boiler fueled by Zhundong coal.

Transformer insulating oil will gradually deteriorate during the operation of power equipment, resulting in a significant reduction in the electrical, physical and chemical properties of transformer oil. In this paper, the adsorption phase reaction technology is used to solidify hydrophilic SiO₂ nanoparticles on microcrystalline cellulose (MCC), to prepare modified cellulose dust collector materials with high adsorption performance, to purify and treat dirty transformer oil by combining with electrostatic adsorption technology. For the SiO₂ modified cellulose dust collector material, it can be concluded through the oil purification effect test that, the best preparation condition is dissolution and drying for 12 h, and adding 6 g ethyl orthosilicate (TEOS) as a silicon source. Then, the modified cellulose dust collector material prepared above conditions is placed in the electrostatic oil purification reactor. After synergistically purified by the two methods, the transformer oil’s main operational indicators such as moisture reduces from 32.0 mg/L (the initial value) to 23.5 mg/L or less, and other key indexes including medium loss factor, acid value and volume resistivity have reached the national standard of operational oil. It shows that the electrostatic technology combined with modified cellulose adsorbent material can effectively adsorb the impurity particles in the oil.