The treatment of desulfurization ash (DA) by high-temperature can solve the increasingly environmental risk caused by the accumulation desulfurization ash on the one hand, and realize the reuse of Ca and S on the other. However, the understanding of the high-temperature reduction decomposition process of desulfurization ash is still vague. In this study, a multivariate and multiphase reaction mathematical model of the complex system of desulfurization ash, carbon, and gas is established by using the principle of minimum free energy. The modeling results show that the reductive decomposition of DA has four stages, and the decomposition products are different in each stage. This result confirms that the optimal thermodynamic conditions to obtain only CaO as a decomposed product are a temperature greater than 1400 K and a C/S molar ratio of 0.5. Further, the processes of CaO and CaS production are parallel competitive reactions, but are regulated by different factors at different stages. A micropositive pressure equilibrium reaction crucible was designed for laboratory DA decomposition experiments. The correctness of the calculation result of the minimum free energy mathematical model is proved by the high temperature reductive decomposition experiment. When the temperature and C/S molar ratio are 1500 K and 0.5, the DA decomposition rate can reach 100%. The main reaction product is spherical CaO, the minimum S content is approximately 1.5%, and the desulfurization rate can reach approximately 70%. The present strategy is highly promising for application in industrial DA recycling processes.
The additional frequency control of wind turbines is an effective method to solve the problem of low inertia in power systems with high proportions of new energy. The primary frequency regulation of auxiliary wind power inertia systems based on rotor kinetic energy can not only make the wind turbine run at the maximum power point but also has the lowest cost and better economy of the auxiliary frequency regulation module. The wind power inertia output control scheme based on rotor kinetic energy control is constructed by considering the frequency response characteristics of synchronous generator sets and loads. The calculation model of the minimum inertia demand of the power system is established using the rate of change of frequency and the maximum frequency offset as constraints. Combined with the real-time operating conditions of the wind turbine, the speed regulation limit of the wind turbine rotor kinetic energy control is obtained to avoid wind turbine off-grid due to excessive frequency regulation. To prevent frequency secondary drop of the system during the speed recovery process, the steady speed recovery of the wind turbine is controlled by setting the rate of speed change. The feasibility of the strategy for the regulation of the auxiliary primary frequency proposed in this study was verified in an example based on a two-region, four-machine system. When a disturbance sets the sudden load power to 150 MW, under the kinetic energy control of the wind turbine rotor, the system frequency change rate and the maximum frequency offset are increased; in particular, the maximum frequency offset is reduced by 0.348 Hz, which further illustrates the flexibility and plasticity of the rotor kinetic energy control of the wind turbines. The results of this study provide a theoretical basis for adding additional frequency control to existing wind turbines.
Context: Gastrointestinal polyps are common gastrointestinal diseases that involve localised hyperplastic masses derived from gastrointestinal mucosa. Aims: To investigate the risk factors of delayed post-polypectomy bleeding (DPPB) after the treatment of gastrointestinal polyps with snare-assisted endoscopic sub-mucosal dissection (ESD) and to construct a nomogram model to predict the risk of DPPB. Settings and Design: A total of 226 patients who underwent snare-assisted ESD for gastrointestinal polyps from May 2018 to November 2020 were divided into DPPB group ( n = 10) and non-DPPB group ( n = 216). Subjects and Methods: The correlations of clinical data and endoscopic data with DPPB were compared. Univariate analysis was performed to screen the influencing factors of DPPB. Multivariate logistic regression analysis was used to screen the risk factors of DPPB, which was employed to construct a nomogram prediction model. Statistical Analysis Used: SPSS 16.0 software was utilised for statistical analysis. Numerical data were expressed as percentage ( n [%]), and Chi-square test was performed for univariate analysis. The significant factors ( P < 0.05) in univariate analysis were included in multivariate logistic regression analysis, and the variables with statistical significance ( P < 0.05) were considered as independent risk factors. The factors were used to construct a nomogram model for predicting the risk of DPPB. Bootstrap method was employed to perform repeated sampling 1000 times for internal verification. The consistency index (C-index) was used to evaluate the discrimination of the model, and C-index ≥0.70 represented a good discrimination. Two-tailed P < 0.05 indicated that a difference was statistically significant. Results: Univariate and multivariate logistic regression analyses revealed that hypertension, polyp location, polyp diameter, polyp morphology and intra-operative bleeding were the independent risk factors for DPPB ( P < 0.05). The C-index of the nomogram model for predicting the risk of DPPB was 0.791, indicating a good discrimination. The calibration curve showed that the mean absolute error between predicted and actual DPPB occurrence risks was 0.014, indicating a high accuracy. Conclusions: Hypertension, polyp location, polyp diameter, polyp morphology and intra-operative bleeding are the independent risk factors for DPPB, and the nomogram model established based on these factors for prediction has good discrimination and accuracy. Therefore, it is recommended to perform targeted intervention for high-risk groups to reduce the incidence of DPPB.
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