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  • 2017 Volume 37 Issue 10
    Published: 15 October 2017
      
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  • Calculation Optimization for Enhanced Heat Transfer in Boiler Furnace Based on Multi-section Models
    MA Kai, HAN Wentao, YAN Weiping, GAO Zhengyang, LI Chaofan, LI Wenke, ZHENG Gang
    2017, 37(10): 773-779.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    Calculation method was investigated for enhanced heat transfer in boiler furnace after retrofit of the water walls. According to the staged combustion technology currently adopted by power boilers and the difference in heat transfer characteristics, the thermodynamic calculation based on one-dimensional multi-section models was improved, i.e. dividing the furnace into 8 sections, including 2 sections for the burner area. Based on the change of heat absorption of water wall tubes before and after heat transfer enhancement, the effective coefficient of water wall tubes after retrofit was obtained by iterative calculation, which was then substituted into the formula of sectional calculation, thus obtaining the heat load and outlet temperature of each section after retrofit. The thermal calculation of a 600 MW supercritical coal-fired boiler was performed by programming. Results show that by the optimization method, the effective thermal coefficient of water wall tubes after heat transfer enhancement is calculated to be 0.051-0.092 higher than before, with the outlet temperature of furnace reduced by 45.55 K, which is beneficial to the reduction of heat surface slagging at furance outlet.
  • Chemical Kinetics Simulation on High-temperature Morphology of Alkali Sodium in Zhundong Coal
    JI Jieqiang, CHENG Leming, LIU Yanquan, WANG Qinhui, LUO Zhongyang
    2017, 37(10): 780-787.
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    Chemical kinetics software Chemkin was applied to perform analog calculation on morphology distribution of gas-phase sodium at high temperatures in Zhundong coal with high alkali content during combustion process, and the calculation results were subsequently compared with reference data, so as to study the effects of following factors on the distribution of high-temperature morphology of alkali sodium, such as the temperature, excess air coefficient (α) and pressure, etc., and to analyze the sensitivity of relevant products. Results show that the calculation results agree well with actual measurements, proving the model to be correct; temperature significantly influences the conversion of sodium-containing gas-phase products; the component distribution of sodium-containing gas-phase products is remarkably influenced by α in the case of α<1, which is slightly influenced by pressure.
  • Heat Transfer Characteristics Around Single Coal Particles Entrained by Flue Gas Under the Action of High Intensity Acoustic Field
    XU Weilong, JIANG Genshan, AN Liansuo, LIU Yuechao
    2017, 37(10): 788-795.
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    Heat transfer characteristics around single coal particles entrained by flue gas under the action of high intensity acoustic field were studied based on two-dimensional, unsteady and laminar equations for mass, momentum and energy conservation and transport, so as to analyze the temperature field, local Nusselt, surface-averaged Nusselt and space-and time-averaged Nusselt numbers around the coal particles at the sound pressure level (SPL) varying in 145-167 dB and at frequencies of 50 Hz, 1 000 Hz and 5 000 Hz, respectively. Results show that at 50 Hz, the flow field around coal particles is mainly affected by curvature effects, and the Nusselt number increases with the rise of amplitude of oscillation velocity; with the rise of frequency, the effect of flow acceleration increases, and phase lag would appear between the thermal boundary layer and the oscillating flow field at 5 000 Hz; the combined effects of curvature and flow acceleration result in the maximum difference of 2.82% in the space-and time-averaged Nusselt number at different frequencies, i.e. little difference of Nusselt number; the space-and time-averaged Nusselt number is 1.78 times of that without acoustic field at 167 dB and 5 000 Hz.
  • Effects of Bearing Dynamic Coefficient on Shafting Vibration of the 1 000 MW Steam Turbine with Single Supports
    BIN Guangfu, YAO Jianfei, WANG Gang, CUI Yahui
    2017, 37(10): 796-800.
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    To solve the problem of exssive shafting vibration appearing at bearings 3, 4 and 5 for IP/LP rators in a 1 000 MW steam turbine with single supports, a dynamic finite element model was set up, so as to analyze the sensitivity of vibration of all bearings to the unbalance excited on the coupling connecting two low-pressure rotors. Moreover, the dynamic coefficient of bearing 4 between two LP rators was altered by changing its inlet oil temperture, thus to study the effects of dynamic coefficient on the steady state response of the shafting. Results show that the dynamic coefficient of bearing 4 has the greatest influence on the vibration of bearing 5, followed by bearing 4, which are for supporting of LP rator 2; whereas the dynamic coefficient of bearing 4 has little influence on the vibration of bearing 1 and 2 for the HP rator. The excessive shafting vibration could be reduced by improving the inlet oil temperature of bearing 4 in actual applications.
  • Analysis on Structure and Loss of Secondary Flow in Stator Cascades of an ORC Radial Inflow Turbine
    WANG Zhi, YIN Libing, LIU Yimiao, JIAO Qingya, QU Haitao
    2017, 37(10): 801-807.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    To improve the aerodynamic performance of stator cascades in radial inflow turbines, three-dimensional viscous numerical simulation was carried out for the flow of organic working fluid in a radial inflow turbine. The forms of various vortices on lower and upper end walls and in the stator cascade passage were analyzed in detail. Meanwhile the distribution of total pressure loss coefficient along the axial and radial directions was presented. Results show that there exists a horizontal flow between the pressure surface and suction surface, but no passage vortex is formed, which is not an important vortex structure for secondary flow in stator cascades of ORC radial inflow turbines. The total pressure loss mainly appears in later 0.4 cascade passage in axial chord direction, near lower and upper end walls in blade height direction, close to the suction surface in circumferential direction.
  • Effects of Bowed Blade Design on Water Erosion and Movement of Secondary Water Droplets
    YAO Hong, ZHOU Xun, YU Xiaojun, WANG Zhongqi
    2017, 37(10): 808-813.
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    To reduce the erosion damage over last stage blades of industrial steam turbines caused by water droplets, an active control method was developed based on the liquid-steam two-phase flow to study the movement characteristics of secondary water droplets and the water droplet erosion. By comparing the effects of stator blades in different bendings on the movement characteristics of secondary water droplets, the influencing mechanism was obtained, thus proposing the method to use bowed blades to control the impact range and intensity of secondary water droplets. Results show that a negatively bowed stator blade can reduce the speed of secondary water droplets in the mid span of the blade, which is also effective on the movement of water droplets on the stator surface; the negatively bowed stator blade improves the speed of secondary water droplets on endwalls of the stator, which is beneficial to the secondary droplets passing through the rotor blade passage, and to the reduction of secondary droplets impulse on the rotor blade; the negatively bowed stator blade can greatly reduce the degree of water erosion at the top of rotor blade on the suction side by changing the velocity distribution of secondary water droplets; a bowed stator blade with-25° angle can reduce the high erosion area at the top of rotor blade by more than 90%.
  • Multivariable Predictive Control of a Pulverizing System Based on Outlet Temperature Optimization of the Coal Mill
    GAO Yaokui, HU Yong, ZENG Deliang, LIU Jizhen
    2017, 37(10): 814-820.
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    To reduce the latent heat of vaporization and the ignition heat required for pulverized coal combustion, and to improve the stability and economy of the boiler combustion within a wide load range, a multivariable predictive control scheme was designed for the pulverizing system based on outlet temperature optimization of the coal mill, which considers both the safety of milling equipment and the optimization of mill outlet temperature for energy saving purposes. Simulation results show that the multivariable predictive control scheme improves the outlet temperature of coal mill and reduces the coal powder moisture under the premise of safe operation of the milling equipment, better ensuring the safe, stable and economical operation of the coal-fired power unit.
  • Automatic Fault Diagnosis and Prediction of Wind Turbines
    XIANG Jianping, JIANG Nannan, Simon Jonathan Watson
    2017, 37(10): 821-828.
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    A Morlet wavelet-based compensated algorithm was proposed to calculate the accurate amplitudes of faulty signals. The specific way is to compute the time range and frequency values of the faulty signals at first, and then to compensate the amplitudes calculated for above faulty signals according to the center frequency values of Morlet wavelet coefficients to further obtain the accurate amplitudes. A Simulink model was used to demonstrate the feasibility and generalization of the algorithm. At the same time, the algorithm was used to analyze the electric power signals of a test rig and large turbines. Results show that this algorithm can automatically find the amplitude trend of faulty components in a time sequence, and indicate the residual service life of wind turbines after faults are generated. Based on the information of the residual service life, the maintenance and repairing plan for wind turbines, especially offshore ones, can be developed to lower the cost of wind power in operation and maintenance.
  • Fault Detection of Industrial Processes Based on Multivariate Statistical Process Monitoring
    NIU Yuguang, WANG Shilin, LIN Zhongwei, LI Xiaoming
    2017, 37(10): 829-836.
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    A novel fault detection method based on sparseness-constrained non-negative matrix factorization (SCNMF) was proposed for complex industrial processes. The specific way is to use alternating constrained least squares (ACLS) with sparseness constraint on coefficient matrix H to solve the non-negative matrix fracterization (NMF) problems, then to enhance the initialization stage of SCNMF by non-negative double singular value decomposition (NDSVD), and finally to apply the presented method to the fault detection in various boiler processes of a 1 000 MW unit. Results show that the SCNMF is superior to conventional NMF on both the convergence and the sparsity, and its monitoring performance is also better than NMF and principal component analysis (PCA).
  • An Improved Particle Swarm Optimization Algorithm for Fault Diagnosis of Nuclear Power Equipment
    LIU Rui, LI Tieping, ZHOU Guoqiang, TIAN Xinlu
    2017, 37(10): 837-841.
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    An improved particle swarm optimization (IPSO) algorithm was proposed for fault diagnosis of nuclear power systems. By using the known symptom sets of nuclear power faults, and with the probabilistic causal model, the IPSO algorithm was introduced to solve the fault sets with maximum a posteriori probability; based on traditional PSO algorithm, the principle of good point set was used to initialize the range of PSO; by adaptive adjustment of inertia weight, the premature convergence of PSO was avoided, and the convergence speed was accelerated. Finally, the validity of the method was demonstrated by examples. Results show that the probabilistic causal model based on IPSO algorithm is not limited by fault samples, which therefore has good versatility, with high precision in fault diagnosis and high speed in optimization.
  • Effect of a New Anti-abrasion Device on Wear Reduction of the Economizer
    PEI Bin, YANG Dongwei, YU Hongling, JIN Jing
    2017, 37(10): 842-847.
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    Ansys Fluent software was used to study the changes of flue gas flow field in an economizer, so as to determine the local area where the tube bundles had been worn by too high velocity of flue gas, following which, a new anti-abrasion device was proposed and its effectiveness was simulated by numerical method. Results show that after the anti-abrasion device is installed, the maximum flue gas velocity has been reduced to 8 m/s, resulting in obvious reduction of local abrasion in the tube bundles.
  • Characteristic Study on Calcium and Sodium Based Spray-dry Desulfurization of Coke Oven Gas
    ZHOU Hao, CHEN Jianzhong, ZHOU Mingxi, CHENG Ming, NI Jiandong, YANG Yun, XU Jian, CHEN Huohu
    2017, 37(10): 848-854.
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    Desulfurization tests were conducted on the simulated coke oven gas with low humidity and high temperature in a spray drying absorber, so as to study the desulfurization characteristics of agents Na2CO3 and Ca(OH)2 at high inlet gas temperatures and far approach to adiabatic saturation temperature (AAST), and to analyze the effects of following factors on the desulfurization efficiency, such as the stoichiometric ratio (SR), inlet gas temperature, AAST and gas temperature drop, etc. Results show that as the stoichiometric ratio increases, the desulfurization efficiency of Na2CO3 grows faster than that of Ca(OH)2, and when the stoichiometric ratio of Na2CO3 to SO2 and Ca(OH)2 to SO2 gets up to 1.1 and 1.5, respectively, the desulfurization efficiency tends to be stable. The spray-dry desulfurization efficiency decreases exponentially with the increase of AAST. Keeping the outlet gas temperature constant, the desulfurization efficiency can also be improved by raising the inlet gas temperature. Increasing the gas temperature drop is also beneficial to the desulfurization efficiency.
  • Design Optimization and Performance Analysis of a Hybrid Solar CCHP System
    YOU Shengshui, ZHANG Fengyuan, WU Yuandan, YU Lijun
    2017, 37(10): 855-860.
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    To reduce the consumption rate of fossil fuels, a hybrid combined cooling, heating and power (CCHP) system with the utilization of solar energy was designed, of which the working principle and operation strategy were analyzed. Taking a commercial building in Shanghai as an example, the electric chiller ratio and PV arrays area ratio were optimized by genetic algorithm to achieve multi benefits of the hybrid CCHP system, including energy, economic and environmental benefits. Meanwhile, the effects of solar system on the comprehensive performance of hybrid CCHP system were analyzed with the separate production (SP) system as a reference object. Results indicate that the comprehensive performance of hybrid CCHP system is much higher than traditional SP and CCHP systems. The optimal PV arrays area ratio of hybrid CCHP system depends on its electric chiller ratio, and when the electric chiller ratio is reasonably set, optimum comprehensive performance can be obtained for the hybrid CCHP system.