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

In the system realizing waste heat utilization through thermal cycle, there is a mutual restriction relationship between the cycle thermal efficiency and the utilization rate of heat source, solving this problem is the key to build an efficient waste heat utilization system. Taking supercritical carbon dioxide cycle as an example, this paper constructs a new cycle, namely the partial expansion cycle, to broaden the waste heat absorption temperature range, so as to enhance the waste heat utilization rate. After coupling gas turbine exhaust, the waste heat utilization system’s power generation efficiency reaches 28.62%, the cycle thermal efficiency reaches 34.03%, and the heat source utilization rate reaches 84.11%. Moreover, to demonstrate the advantages of the partial expansion cycle, a waste heat utilization system is constructed based on the single regenerative Brayton cycle and the recompressed Brayton cycle. Furthermore, the three cycles are compared. Through calculation using the first and second law of thermodynamics, it is found that the power generation efficiency of the partial expansion cycle is higher than that of the other two classical cycles. Via analyzing the circulation process, it is found that the reason for the high efficiency of the partial expansion cycle is that the partial expansion structure broadens the endotherm temperature zone, makes the heat source utilization rate increase greatly, and thus improves the power generation efficiency.

The effects of blending ratio and heating rate on co-combustion characteristics of municipal sludge and camellia oleifera shell were studied by thermogravimetric analysis, and the combustion kinetics of the samples were modeled by two methods, Flynn-Wall-Ozawa (FWO) and Kissinger-Akahira-Sunose (KAS). Moreover, the flammability index and comprehensive combustion characteristic index of various samples were calculated, and the interaction between the mixed fuel components during the combustion process was analyzed. The results show that, the burnout temperature of the mixed fuel significantly reduced, and the combustion stability and comprehensive combustion characteristics were significantly improved after the sludge was mixed with camellia oleifera shell. With the increase of the mass blending ratio of camellia oleifera shell from 20% to 80%, the burnout temperature decreased from 590 ℃ to 532 ℃, the burnout degree gradually increased, the mass loss increased from 63.13% to 92.19%, and the flammability index and comprehensive combustion characteristic index increased by 1.66 and 2.32 times, respectively. The interaction between the components of sludge and camellia oleifera shell mixed combustion occurred, which showed an inhibition effect in the volatile combustion stage, while a promoting effect in the fixed carbon combustion stage. The average apparent activation energies of sludge calculated by the FWO method and KAS method were 122.32 kJ/mol and 118.08 kJ/mol, respectively, and the average apparent activation energies of the camellia oleifera shell were 166.46 kJ/mol and 164.94 kJ/mol, respectively. The average apparent activation energy of the mixed samples increased with the mass mixing ratio of camellia oleifera shell.

The P-U characteristic curve of a photovoltaic array exhibits multi-peak characteristics in partially shaded environments, leading to the inefficiency of conventional maximum power point tracking (MPPT) algorithm in tracking the maximum power. To address this issue, this paper proposes a two-layer control model for photovoltaic MPPT based on an improved tuned swarm optimization (TSO) algorithm. In the upper layer, the Levy flight strategy and polynomial mutation strategy are embedded into tuna algorithm, creating the Levy-polynomial mutation tuna swam optimization (LPTSO) to search for the global maximum power point. In the lower layer, the perturbation observation method is employed to locally track the global maximum power point, thereby reducing power oscillations in local shading environments. The two-layer control model is applied to the photovoltaic MPPT simulation system, and the simulation experimental results show that, for multi-peak MPPT control, the proposed model achieves significant improvements in convergence speed, tracking efficiency, power oscillations, etc. In conclusion, the proposed two-layer control model for photovoltaic MPPT effectively addresses the issue of maximum power tracking failure in partially shaded environments.

Renewable energy suffers some drawbacks such as instantaneity, instability, and the mismatch between supply and demand during the utilization. Thermochemical heat storage exhibits distinct advantages, including high heat storage density, elevated heat storage temperature, and negligible heat loss during the long-term storage. It has the capability to convert intermittent energy sources into stable moderate and high temperature heat energy to fulfill the needs of fluctuating output. The classification, basic mechanisms and characteristics of thermochemical heat storage within reaction temperature range of 400~1 100 ℃ are reviewed. Subsequently, the thermal storage performance of typical thermochemical heat storage materials, such as carbonates, hydroxides, oxides, metal hydrides, ammonia and methane are analyzed, and the structural targeted regulation and modification methods are investigated, alongside the introduction of typical demonstration projects. Following this, the reactor design and system integration of solid-gas and gas-gas reaction systems are discussed. In the last, the future research interests are deliberated and proposed in the development and industrial application of thermochemical energy storage materials.

In order to inhibit the flow separation on blade surface and improve the aerodynamic performance of the blade, the design scheme of installing vortex generator on the blade surface is proposed. Taking DU97-W-300 blade section with vortex generator as the research object, the orthogonal experimental design method is used to investigate the influences of height, length, installation angle, chord installation position, spacing and pitch of the vortex generator on the aerodynamic performance of the blade section, so as to determine the basic law of vortex generator parameter design. The results show that, the vortex generator parameters that affect the magnitude of aerodynamic performance of the blade are as follows: spacing, pitch, length, height, chord installation position, and installation angle of the vortex generator. The optimal vortex generator parameter combination law is: height of 0.75ξ (ξ is blade boundary layer thickness), length of 1.6ξ, installation angle of 20°, chord installation position is 10% blade chord length, spacing of 1.6ξ, pitch of 0.8ξ, which can increase the maximum lift coefficient of this blade by 40% and the maximum stall angle of attack by 9.5°.

Constructing a power system predominantly based on renewable energy sources imposes increasingly stringent demands on deep peak shaving capability and ultra-low-load operation of coal-fired power generating units, thereby presents more severe challenges to the safe operation of steam turbine units under low-load conditions. This paper employs numerical simulation methods, focusing on an in-depth analysis of the operational performance of the last stage of a steam turbine under low-load conditions, and explores various solutions for their working mechanisms and optimization effects under ultra-low-load conditions. It is found that, when the unit transitions from medium-low load to ultra-low load, vortex clusters such as gap vortices, backflow vortices, and separation vortices emerge near the last stage blades, with their extent gradually expanding as the load decreases. Reducing the back pressure of the unit and operating the low-pressure cylinder with cylinder-cutting are effective strategies to attenuate steam turbine vortex flow and enhance the last stage’s performance, with a combined application of these strategies yielding better results. For instance, under 20% turbine heat acceptance (THA) conditions, reducing the back pressure from 4.9 kPa to 2.5 kPa significantly diminishes the influence range of the last stage vortex cluster, increasing the rotor blade torque from −38 N·m to 73 N·m, thereby markedly improves the last stage performance. Under 10% THA conditions, employing a combination of reduced back pressure and low-pressure cylinder-cutting can completely eliminate the tip clearance vortex, with the radial lengths of the backflow vortices and separation vortices reducing by more than 50%. The optimized rotor blade torque increases by approximately 130 N·m, significantly enhancing the last stage performance.

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.

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.

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.