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In learning English, learners are faced with various challenges, such as listening, speaking, reading and writing. Among them, writing is the most important and difficult one, and grammatical errors are the most common type of errors in English writing. The research and implementation of grammatical error detection and correction in English writing is of great significance to both English learners and English teachers. In this paper, we propose a sequence annotation model based on recurrent neural network to solve the problem of the influence of grammar errors and other noises in English writing corpus on sequence information extraction. Aiming at the grammatical errors in English writing, this paper proposes two methods of English grammatical error detection and correction. The experimental results show that the accuracy of RNN is higher than that of CAMB after 10 to 20 iterations, ranging from 0.848 to 0.916.

As a new form of education, the language education software based on AI (Artificial Intelligence) technology effectively improves the timeliness and interest of language teaching, and enrich and improve the English education system to a certain degree. Second language acquisition (SLA) theory integrates linguistics, language education, sociology, psychology and other disciplines, focusing on the study of people’s acquisition of foreign languages and the mechanism of language ability. This article is based on teaching practice materials and students’ English learning data, and uses the Noticing Hypothesis theory to try to solve the problems emerged from artificial intelligence teaching courses.

Down-fired boilers are commonly used to burn low-rank coals for power generation. However, they often have operational problems such as low char burnout and high NOx emissions. This paper comprehensively investigates how to mitigate such problems in a 300 MWe down-fired utility boiler burning a low-volatile coal by optimizing the staged-air windbox structure. First, experiments and simulations are conducted on a 1:1-scaled model of the staged-air windbox to study the cold air flow in the original and two new windbox structures for understanding the effect of different staged-air windbox structures. Then, combustion simulations are performed for the utility boiler to further study the influence of the newly designed staged-air windboxes on the boiler performance, based on which the optimization scheme of the staged-air windbox in the boiler is more reliably concluded. Finally, the utility boiler is retrofitted by using a newly designed staged-air windbox. Performance tests are made for the boiler before and after the retrofit. The new staged-air windbox is confirmed to greatly improve the performance of the utility boiler, e.g., NOx reduction by 20.7% and thermal efficiency increase by nearly 2 percentage points (from 88.76% to 90.48%) at full load. The idea of the new staged-air windbox design can be readily implemented into down-fired boilers of this kind for more efficient and environmentally friendly firing of low-rank coal for heat and power generation.

This study attempts to better understand the mechanisms of wind farm blockage effect by analysing momentum balance in realistic atmospheric flow over an idealised large offshore wind farm. The analysis is performed following the two-scale momentum theory, which predicts the importance of three different terms in the farm-scale momentum balance, namely the streamwise pressure gradient, Coriolis force and acceleration/deceleration terms. A numerical weather prediction (NWP) model is used as a realistic farm-scale flow model in this study to investigate how these three terms tend to change in time. Initial results suggest that the streamwise pressure gradient may be enhanced substantially by the resistance caused by the wind farm, whereas its influence on the other two terms appears to be relatively minor. These results suggest the importance of modelling the farm-induced pressure gradient accurately for various weather conditions in future studies of wind farm blockage.

Co-combustion of sludge with coal is a promising sludge disposal approach. In this study, three different combustion models, including different turbulent gas-phase combustion and char surface combustion sub-models, were employed to simulate the combustion and emission characteristics of co-combusting sludge with coal in a 100 MW tangentially coal-fired utility boiler. By comparison of the numerical results from different combustion models to a set of full-scale coal–sludge co-combustion field experiments, a precise and suitable computational fluid dynamic (CFD) model was finally developed. The comparison result demonstrated that the finite-rate/eddy-dissipation model together with the multiple-surface-reaction model, which have carefully considered the effect of high moisture content on the fuel ignition and char combustion processes, were competent in modeling the characteristics of coal–sludge co-combustion. On the basis of the developed numerical model, the ignition, char burnout, and NOx emission cha...

To reduce NOx emissions without introducing an obvious increase in the carbon content of fly ash, a novel combustion system was applied to a 600 MWe Foster Wheeler (FW) down-fired boiler. This approach mainly consisted of moving fuel-lean nozzles from the arches to the front/rear walls, rearranging staged air, and introducing separated overfire air (SOFA). The aim of this work was to evaluate the overall performance of the novel combustion system relative to different SOFA ratios (i.e., 15, 20, 25, and 30%) and different SOFA locations in the upper furnace (1.0, 2.0, and 3.0 m above the arches) using numerical simulations and experimental measurements. Both numerical and experimental results showed that, with increasing the SOFA ratio from 15 to 20%, NOx emissions were greatly reduced but the carbon content in the fly ash increased slightly. With a further increase from 20 to 30%, NOx emissions slightly decreased but the carbon content in the fly ash increased substantially. Considering both the environme...

In the present paper, computational fluid dynamic modelings were established to research a newly presented re-heat steam temperature deviation solution on the basis of FLUENT 6.3.26 considering a 700 MWe tangentially fired pulverised-coal boiler, which confronted with severe flue gas and re-heat steam temperature deviation. The model was solidly validated by grid independence test and comparison with the experimental data obtained from a series of on-site measurements. Upon reliable validation, the model was further used to investigate the forming mechanism of re-heat steam temperature deviation as well as the influence of burner tilt angle on it. The conclusions mainly include (1) Residual swirling flow in the upper furnace caused the flue gas velocity and temperature deviations in crossover pass. For a typical anticlockwise tangential firing system, the flue gas velocity and temperature were lower in left part of crossover pass. The deviation of flue gas further generated the convective heat transfer imbalance of final re-heater, therefore, the temperature deviation of re-heat steam was severe. (2) Tilting the burner upward can effectively reduce the intensity of residual flow as well as the flue gas deviation degree. The + 11° tilt angle of burner was relatively optimum considering the flue gas deviation and final re-heater overheating potential. Specifically, the intensity of residual swirl flow dropped 44% with burner tilting upward for + 11°. Practical operation of boiler demonstrated that the reheat steam temperature deviation was reduced from 22 °C to 10 °C in this case. (3) When the tilt angle of additional air (AA) was bias set, the flow field of upper furnace was changed. Consequently, the residual swirl flow intensity and the flue gas deviation were reduced considerably. On-site measurements indicated that the combination of tilting burner upward for + 11° and setting the bias of AA tilt angle for 10° can further reduce the re-heat steam temperature deviation to 4 °C.

A reduced-dimension space time adaptive processing (STAP) for airborne multiple-input multiple-output (MIMO) radar based on three iterations is proposed. The optimum filter for MIMO-STAP is described as a separable filter, and the optimal weight vector in high dimension can be iteratively solved by three lower dimension weight vectors. Consequently, the quite high sample support and computational complexity in optimal MIMO-STAP can be efficiently reduced. For short data records, the proposed method can achieve better clutter suppression performance. Simulation results demonstrate the effectiveness of the proposed method.

Sodium, calcium, sulfur and chlorine in the flue gas of coal-fired boilers are the main cause of ash deposition/fouling in heat exchangers. However, there are still many debates on the mechanism of ash deposition/fouling due to the lack of direct micro evidence. This paper aims to clarify the initial deposition/fouling characteristics of a high-alkali coal by computer-controlled scanning electron microscopy (CC-SEM). The results demonstrate that temperature has an influence on the deposition/fouling compounds. The crystalline compounds in the samples at 900 °C were mainly CaSO4 and Ca2Al2SiO7, while the compounds in the samples at 500 °C were mainly NaCl. Sulfur had a significant adsorption effect on sodium and calcium at 900 °C, while chlorine had a significant adsorption effect on sodium at 500 °C. A 3-layer microstructure of deposition/fouling was found after the samples were stripped by molecular force. Additionally, deposition/fouling could be divided into three stages: the formation of sodium salt precursors, the growth of loose structural aluminosilicates and the adhesion of particulates on the surface. Sulfates, especially Na2SO4 and CaSO4 formed a precursor for the initial deposition/fouling of high-alkali coal.

Gallium and Indium co-substituted Yb, Er:YAG was fabricated through the chemical co-precipitation method. The formation process and structure of the Ga3+ and In3+ substituted phosphor powders were characterized by the X-ray diffraction, thermo-gravimetry analyzer, infrared spectra, and X-ray photoelectron spectroscopy, and the effects of Ga3+ and In3+ concentration on the luminescence properties were investigated by spectrum. The results showed that the blue shift occurred after the substitution of Ga3+ and In3+ for Al3+ in matrix, and the intensity of emission spectrum was affected by the concentration of Ga3+ and In3+.