Niansu Hu

Investigation of sulfur forms and transformation during the co-combustion of sewage sludge and coal using X-ray photoelectron spectroscopy

X-ray photoelectron spectroscopy was used to investigate the characteristics and evolution of sulfur (S) in mixtures of bituminous coal and sewage sludge (SS) and their chars during isothermal combustion. Five groups of mixtures with SS content of 0%, 10%, 20%, 30% and 100%, were examined at different burn-off ratios (beta) of 0, 30%, 50%, 70% and 100%. The S in the coal mainly exist as the forms of mercaptan (S1), sulfide (S2), thiophene (S3), sulfoxide (S4), sulfone (S5) and sulfate (S6). During the coal combustion process, the content of S1 and S2 decreased, while that of S3 and S5 increased in the early stage and decreased in the late stage. The S4 content increased throughout the entire process of combustion. Small amount of S6 was detected, showing a fluctuated pattern. The trend of S1, S2, S5 and S6 in SS was alike with that in coal, whereas S4 decreased at the end of combustion. The changing process of S3 in SS was opposite to that of coal, while the composition of S in the mixtures resulted from the mixing of coal and SS. The transformation of each functional group during co-combustion were correlated with their transformation characteristics during the mono-combustion of coal and SS, and no obvious interaction was observed, which demonstrated that the coal-origin and SS-origin sulfur in mixtures kept their own characteristics in the combustion. SS may accumulate on the solid surface as alpha increase, resulting its significant influence on the evolution of each form of S. When alpha was low, most of the S-contained functional groups presented the characteristics of coal. The percentage of coal-origin functional groups declined as alpha increased. The transforming trends of most functional groups were similar with that of SS when alpha reached 30%.

Development of steady-state electrical-heating fluorescence-sensing (SEF) technique for thermal characterization of one dimensional (1D) structures by employing graphene quantum dots (GQDs) as temperature sensors.

A fluorescence signal has been demonstrated as an effective implement for micro/nanoscale temperature measurement which can be realized by either direct fluorescence excitation from materials or by employing nanoparticles as sensors. In this work, a steady-state electrical-heating fluorescence-sensing (SEF) technique is developed for the thermal characterization of one-dimensional (1D) materials. In this method, the sample is suspended between two electrodes and applied with steady-state Joule heating. The temperature response of the sample is monitored by collecting a simultaneous fluorescence signal from the sample itself or nanoparticles uniformly attached on it. According to the 1D heat conduction model, a linear temperature dependence of heating powers is obtained, thus the thermal conductivity of the sample can be readily determined. In this work, a standard platinum wire is selected to measure its thermal conductivity to validate this technique. Graphene quantum dots (GQDs) are employed as the fluorescence agent for temperature sensing. Parallel measurement by using the transient electro-thermal (TET) technique demonstrates that a small dose of GQDs has negligible influence on the intrinsic thermal property of platinum wire. This SEF technique can be applied in two ways: for samples with a fluorescence excitation capability, this method can be implemented directly; for others with weak or no fluorescence excitation, a very small portion of nanoparticles with excellent fluorescence excitation can be used for temperature probing and thermophysical property measurement.

Nonisothermal TGA Study on the Combustion Reaction Kinetics of Biomass

The combustion reaction kinetics of two Chinese straws were investigated by a differential thermal balance , volume fraction of reactive gas was N2: O2 = 80:20 and heating rate was 30degC/min. Reaction of samples were mainly composed volatile and fixed carbon combustion phase, ranges of them were 425 K - 650 K and 650 K - 810 K in round numbers according to TG, DTG and DTA curves. Reaction kinetic parameters were calculated with Coats-Redfern method. Ranges of activation energy in volatile combustion phase were 20 kJ.min -1 or so, fixed carbon combustion phase were different, they were 145 kJ.min -1 and 66 kJ.min -1 . Results showed that the order of reaction of volatile combustion phase and fixed carbon combustion phase were zero and second, respectively. The reaction initial temperatures of two samples ranged from 420 K - 460 K and reaction final temperatures ranged from 780 K - 810 K.

Sewage Sludge Drying Based on Heat Pump

A suit of low temperature test dryer for sewage sludge drying based on heat pump was put forward in this paper. Principle and characteristic of this equipment was introduced. Sewage sludge drying mechanism were briefly summaried from literatures. Factors such as drying air temperature and flow speed that effect sewage sludge drying process were discussed. Drying temperature and flow speed both contribute positively to drying speed in initial drying section while contributing little in the evening section of drying process. Change of superficial morphology during the drying process was analyzed. Economy of this low temperature dryer based on heat pump was discussed. Results show that the operation cost is equal to the operation cost of the dryer with coal as heat source, while is less than half of the dryer with electricity or natural gas as heat source.

Target Value Surface and Energy Loss Surface in the Steam Turbine Unit Performance Monitoring System

In order to optimize the performance of the steam turbine unit performance monitoring system, improve the reliability, stability and accuracy of the system, a new idea to establish target value surface and coal consumption growth surface in different load is presented. Take an imported supercritical steam turbine unit, which capacity is 600 MW, as an example to expound the design idea, the mathematic model and the construction process of these two types of surfaces.

Mathematical Modeling of Drying Characteristics of Sewage Sludge

Drying characteristics of sewage sludge were investigated using hot air of a temperature range of 50~80degC and an air velocity range of 0.60~1.48 m/s at a laboratory scale dryer. Several mathematical models available in the literatures were fitted to the experimental data by multiple nonlinear regression analysis. Four statistical parameters: coefficient of determination (R 2 ), reduced chi-square (chi 2 ), root mean square error (RMSE) and mean relative deviation modulus (P) were used to evaluate the fitting of these models to experimental data. The Page model gave the better predictions than others. Then a modified model based on Page model was developed and the new model could fit the drying characteristics of sewage sludge well with R 2 over 0.9993 at widely drying conditions.

Blade Stress Analysis of Control Stage in Different Governing Mode

Using different governing modes in the process of large steam turbine load variations will make the thermal characteristic and force of unit get complicated, especially affect the thermal characteristic and force change of the control stage notability the most. This article researched the governing mode problems of the domestic-type 600 MW steam turbine, analyzed different characteristics in different governing modes of control valve, calculated the control stage blade force in different loads and governing modes, and the blade force variations on the main steam pressure change in the same load, based on large amount of field test data. By calculating and analyzing, we found that, the blade force of sequential valve governing mode is significantly higher than the single valve governing mode in domestic-type 600 MW steam turbine. For the same load, the higher the main steam pressure, the smaller the main steam flow, the greater control stage blade force is. Therefore, in the process of unit actual operation, it should try to avoid the risk of working conditions of control stage blade stress in order to ensure the safety of unit operation when the governing modes are switching or the control valve opening is changing to regulate the load.

Fault Simulation and Diagnosis of Generator Cooling System Based on a Simulation Platform

The simulation model of generator cooling system is an important part of the simulation model of thermal power unit, whose dynamic property has a direct effect on the simulating efficacy of the thermal power unit. Fault diagnosis technology based on simulation platform is applied to generator cooling system fault diagnosis, which provides certain ground work for setting-up fault diagnosis system for generator cooling system and application of DCS data fault diagnosis technology to power plant.

Optimization of Steam Governing Arrangement for 600MW Sub-critical Steam Turbine Unit

Take a domestically-made imported 600 MW subcritical steam turbine unit as an example to carry on the research on steam governing performance of the regulation valve, get the bending stress ratio of the 1st stage blades and turbines imbalance steam force by calculating, and then confirm the operating safety of the unit under different steam governing arrangements. Through the analysis of the calculation result, the optimization for a units steam governing arrangement is presented. The result of the calculation can offer the feasible theory and optimization basis for the valves governing adjustment, provide some reference for the optimizing steam governing performance of other types of steam turbines.

Applied Research of a Cooperative Evolution Model in Operation Optimization of the Thermal Power Plant

The on-line optimal control of operation is difficult to achieve with routine optimization methods because of the nonlinear thermal system and the changing frequently conditions in start-up, stop and load change of the large-scale thermal power plant. Based on the research of three typical evolution optimization methods which are evolution strategies, genetic algorithm and evolution programming in evolution optimization theory, the author analyzed the feasibility to solve the parallelism of on-line optimal calculation for thermal system by using evolution optimization methods, the existed problems in on-line optimal application of thermal system by using evolution optimization methods in the world at present. By understanding the relationship between the sub-population scales, the evolutional efficiency of layered cooperative evolution genetic algorithm and the thermal system characteristic, the author proposed the sub-population evolution layer model and the population evolution layered cooperative model. Furthermore, the author addressed the adaptive adjusting algorithm of sub- population scale, presented the adjusting standard and method of sub-population scale. The feasibility and efficiency of this model are verified by simulation experiments in 300MWXPDS simulator at Wuhan University.