Pulverizing System Research Articles

Shape Modification and Size Classification of Microcrystalline Graphite Powder as Anode Material for Lithium-Ion Batteries

Natural microcrystalline graphite (MCG) composed of many crystallites is a promising new anode material for lithium-ion batteries (LiBs) and has received considerable attention from researchers. MCG with narrow particle size distribution and high sphericity exhibits excellent electrochemical performance. A nonaddition process to prepare natural MCG as a high-performance LiB anode material is described. First, raw MCG was broken into smaller particles using a pulverization system. Then, the particles were modified into near-spherical shape using a particle shape modification system. Finally, the particle size distribution was narrowed using a centrifugal rotor classification system. The products with uniform hemispherical shape and narrow size distribution had mean particle size of approximately 9 μm, 10 μm, 15 μm, and 20 μm. Additionally, the innovative pilot experimental process increased the product yield of the raw material. Finally, the electrochemical performance of the prepared MCG was tested, revealing high reversible capacity and good cyclability.

Study of flue-gas temperature difference in supercritical once-through boiler

The 600 MW coal-fired once-through Boilers with opposed firing at a power plant are found to experience marked temperature variation and even overtemperature on the wall of the heating surface as a result of flue-gas temperature (FGT) variation in the boiler. In this study, operational adjustments were made to the pulverizing, combustion, and secondary air box systems in these boilers, in order to solve problems in internal combustion. The adjustments were found to reduce FGT difference and optimize the boiler’ combustion conditions. The results of this study can provide a reference for optimization of coal-fired boiler of the same type in similar conditions.

Failure Prediction of a Motor-driven Gearbox in a Pulverizer Under External Noise and Disturbance

Participants in the Asia Pacific Conference of the Prognostics and Health Management Society 2017 (PHMAP 2017) Data Challenge were given measured vibration signals from motor-driven gearboxes used in pulverizers. Using this information, participants were requested to predict failure dates and the faulty components. The measured signals were affected by significant noise and disturbance, as the pulverizers in the provided data worked under actual operating conditions. This paper thus presents a fault prediction method for a motor-driven gearbox in a pulverizer system that can perform under external noise and disturbance conditions. First, two fault features, an RMS value in the higher frequency zones (HRMS) and an amplitude of a period for high-speed shaft in the quefrency domain (QAHSS), were extracted based on frequency analysis using the higher and lower sampling rate data. The two features were applied to each pulverizer based on results of frequency responses to impact loadings. Then, a regression analysis was used to predict the failure date using the two extracted features. A weighted regression analysis was used to compensate for the imbalance of the features in the given period. In addition, the faulty components in the motor-driven gearboxes were predicted based on the modulated frequency components. The score predicted by the proposed approach was ranked first in the PHMAP 2017 Data Challenge.

Application of a method for calculating coal quantity feed into boiler for double inlet and outlet ball mill in the coordinated control system

Accuracy of the measurement of coal quantity feed into the boiler furnace has great influence on the combustion and coordinated control of power plant. According to the characteristics of double inlet and outlet mill pulverizing system, the method of calculating the amount of coal into furnace using the correlated variable was presented. On this basis, the coordinated control system was designed. Running results show that the method of calculating the fuel quantity accurately and effectively guarantee the stability of coordinated control system. It has a high adjustment quality.

Optimization control of a pulverizing system on the basis of the estimation of the outlet coal powder flow of a coal mill

This study aimed to master the operating characteristics of a pulverizing system, improve the output control precision of the system, and reduce the fluctuation amplitude of the main operating parameters of coal-fired units. A nonlinear dynamic model of a direct-fired pulverizing system that considers the effect of coal moisture on the energy balance of a coal mill was established. Then, an estimated signal of the outlet coal powder flow of the coal mill was constructed as a new output control target of the pulverizing system. Finally, an output control optimization method for the pulverizing system was designed on the basis of this signal. Simulation results showed that the model effectively reflects the dynamic characteristics of a pulverizing system. In addition, the results of simulation were concordant with those of online measurements. The control scheme reduced the internal disturbances in the coal feed rate, thereby improving the tracking capability and control precision of the pulverizing system's output and enhancing the disturbance suppression capability of the mill outlet temperature. Thus, the designed control scheme can ensure the safe and stable operation of coal-fired units.

Water extraction from high moisture lignite by means of efficient integration of waste heat and water recovery technologies with flue gas pre-drying system

The flue gas pre-dried lignite-fired power system (FPLPS) integrates the fan mill flue gas dryer with an open pulverizing system and yields an increase of the boiler efficiency. Particularly, the dryer exhaust gas contains a large amount of vapor removed from high moisture lignite, which exhibits great potential for waste heat and water recovery. Two available options are considered to realize the extraction of water from lignite: the low pressure economizer (LPE) for water-cooled units and the spray tower (SPT) integrated with heat pump for air-cooled units. This paper aims at evaluating the energy saving and water recovery potentials of the FPLPS integrated with both schemes. Results showed that the plant efficiency improvement of the FPLPS at base case varied from 1.14% to 1.47% depending on the moisture content of raw lignite. The water recovery ratio and plant efficiency improvement in the optimal LPE scheme were 39.4% and 0.20%, respectively. In contrast, 83.3% of water recover ratio and 110.6MWth heat supply were achieved in the SPT system. Both schemes were economically feasible with discounted payback periods of around 3years. Moreover, parametric analysis was conducted to examine the economic viability of both schemes with different lignite types and market factors.

Modeling and control of ball mill system considering coal moisture

This study analyzes the dynamic characteristics of duplex inlet and outlet ball mill direct firing pulverizing system. A mass and energy balance-based model is built by thermodynamic analysis. As a critical parameter in pulverized coal humidity control, coal moisture is considered in the mechanism model, and an extended Kalman filter is designed to estimate the coal moisture. A multivariable control system is designed using extended state space predictive controller. The dynamic characteristic of the mill can be effectively forecasted using the established model. The system can rapidly track unit load changes while reducing the disturbance caused by coal moisture and other outlets.

Exergy analysis of the flue gas pre-dried lignite-fired power system based on the boiler with open pulverizing system

This paper deals with an exergetic analysis of the flue gas pre-dried lignite-fired power system (FPLPS) based on the boiler with open pulverizing system (OPSB) to explore the energy-saving potential of the FPLPS. A steady-state simulation was performed to obtain thermodynamic properties of process streams in a 600 MW unit. Results indicated that the plant efficiency of the FPLPS was relatively 3.42% higher than that of the conventional lignite-fired power system (CLPS). The improvement benefited from the integration of the flue gas dryer with the OPS, in which the dryer exhaust gas was separated from coal powders and prevented from recycling in the furnace. Consequently, the exergy destruction in the combustion process was reduced by 2.32%-pts for increased flame temperature, and the exergy loss of the boiler exhaust gas was reduced by 0.68%-pts for decreased temperature. Moreover, the dryer exergy efficiency was only 20.20% due to considerable exergy destructions in the moisture evaporation and the mixing of drying agents. The proposed retrofitting option by extracting cold flue gas from the economizer outlet could increase the plant efficiency by 0.33% relatively. Finally, attempts were made to examine the influence of varying pre-drying parameters on system performances.

Preparation and Intestinal Immunostimulating Activity of Low Molecular Weight Alginate from Saccharina (Laminaria) Species in Japan.

We studied the structure of alginates extracted from five commercial Saccharina (Laminaria) species including three varieties (eight samples in all) harvested in Hokkaido, Japan. The algae used were Saccharina japonica, S. japonica var. diabolica, S. japonica var. ochotensis, S. japonica var. religiosa, S. longissima, S. coriacea, S. angustata, and S. sculpera (Kjellmaniella crassiforia). These alginates have molar fractions of mannuronic acid (FM) ranging from 0.68 to 0.76 and weight average molecular weights (Mws) ranging from 511,000 to 616,000. Alginate samples from both S. angustata (FM = 0.76) and S. longissima (FM = 0.68) showed intestinal immunological activity through Peyer’s patch cells of C3H/HeJ mice. Low molecular weight S. angustata alginate (FM = 0.75, Mw = 70,000) degraded using a wet pulverizing system showed higher activity than the native one.

Outlier factor based partitional clustering analysis with constraints discovery and representative objects generation

As a classical partitional clustering algorithm, k-means algorithm is sensitive to initial centroids and may malfunction when dealing with datasets which contain clusters with different scales and densities. To improve the effectiveness of k-means algorithm, an outlier factor based partitional clustering analysis method is presented in this paper. Outlier factor is usually used to indicate the degree of an object to be abnormal in the dataset. For the proposed method, it is used to find the core objects. And then the Must-link constraints is generated to put the neighboring core objects into the same cluster. First, a similar-density-array-based outlier factor is proposed to find the core objects in the dataset. Then the neighboring core objects are distributed into the same sub-cluster. The sub-clusters are treated as the representative objects and these representative objects are then clustered following the process of the traditional k-means algorithm. Finally, the non-core objects are assigned to their nearest clusters, respectively. The experiments are performed on four datasets from UCI Machine Learning Repository and a field dataset from a ball mill pulverizing system. The experimental results verify that the effectiveness of our algorithm is high.

Modeling on the Effect of Coal Loads on Kinetic Energy of Balls for Ball Mills

This paper presents a solution for the detection and control of coal loads that is more accurate and convenient than those currently used. To date, no research has addressed the use of a grinding medium as the controlled parameter. To improve the accuracy of the coal load detection based on the kinetic energy of balls in a tubular ball mill, a Discrete Element Method (DEM) model for ball kinematics based on coal loads is proposed. The operating process for a ball mill and the ball motion, as influenced by the coal quality and the coal load, was analyzed carefully. The relationship between the operating efficiency of a coal pulverizing system, coal loads, and the balls’ kinetic energy was obtained. Origin and Matlab were utilized to draw the variation of parameters with increasing coal loads in the projectile and cascading motion states. The parameters include the balls’ real-time kinetic energy, the friction energy consumption, and the mill’s total work. Meanwhile, a method of balanced adjacent degree and a physical experiment were proposed to verify the considerable effect of the balls’ kinetic energy on coal loads. The model and experiment results indicate that a coal load control method based on the balls’ kinetic energy is therefore feasible for the optimized operation of a coal pulverizing system.

Application Research of PID-GPC Algorithm in the Ball Mill System

Direct-fired pulverizing system with double inlets and outlets, as an important power generating equipment in the thermal power plant, is characterized by nonlinear, multivariable, strong coupling and large delay. Meanwhile, ball mill is a typical three-input and three-output system, and to model this system and accomplish its automatic control has become a hot spot in today's research on thermal power generation. This paper takes into account PID control, the most widely used basic control law in industrial process control, and based on the generalized predictive control algorithm, ap- plies the Proportional Integral Differential Structured Generalized Predictive Control Algorithm (PID-GPC) to the ball mill. This algorithm incorporates the advantages of the robustness and predictive control model of the traditional PID con- trol algorithm. The simulation of a 300MW large power unit ball mill pulverizing system running under the negative pres- sure, in a power plant in Longshan, Hebei Province, shows that such algorithm has better robustness than general feed- forward decoupling PID control and GPC control, and it's more suitable to be applied in the industry.

Optimization of a lignite-fired open pulverizing system boiler process based on variations in the drying agent composition

This paper evaluates three lignite-fired OPSB (open pulverizing system boiler) processes, named OPSB-A, OPSB-B and OPSB-C, corresponding to three options of drying agents used for the pulverizing systems. OPSB-B is similar to our previous work [18] on drying agent composition. Performances of the three OPSBs were calculated and compared with a 600 MW lignite-fired boiler as the reference. The results showed that the coal savings of OPSB-A and OPSB-C were 5.41% and 4.06% in comparison with the reference boiler, whereas for OPSB-B, the savings was 2.57%. Accordingly, emissions of each OPSB could be reduced in proportion to the coal savings. Among the three OPSBs, OPSB-C showed the best performance of water recovery from mill-exhausts because it had the highest mill-exhaust water dew point of 73.2 °C, whereas the exhaust dew points of OPSB-A and OPSB-B were 63.9 °C and 70.9 °C, respectively. Both OPSB-C and OPSB-B are beneficial for achieving a high mill-exhaust humidity ratio, which facilitates water recovery from the mill-exhaust, and a low oxygen content in mill-exhaust, which improves the operating safety of the pulverizing systems, whereas OPSB-A is relatively inferior in these respects. The OPSB-C process is recommended for engineering applications because of its favorable overall performances.

Modelling and control of pulverizing system considering coal moisture

The pulverizing system serves an important function in the safe and efficient operation of thermal power units. The effect of coal moisture and pulverized coal moisture on the pulverizing system was considered in establishing a mass and energy balance-based dynamic mathematical model of a coal mill. The parameters of the model were identified by using the genetic algorithm and later validated with measurements. An extended Kalman filter was designed to estimate and verify the internal states of the coal mill. Based on the dynamic mathematical model of coal mill, pulverized coal moisture was used as a feed-forward signal, and a feed-forward compensation controller was designed to optimize the coal mill outlet temperature. Simulation results showed that the dynamic characteristic of the mill can be forecasted effectively with the established model. Moreover, pulverized coal moisture was reduced with feed-forward compensation, thereby improving the efficiency of the boiler.

A Fuzzy Sequential Pattern Mining Algorithm Based on Independent Pruning Strategy for Parameters Optimization of Ball Mill Pulverizing System

This paper presents a fuzzy sequential pattern mining algorithm based on independent pruning strategy for parameters optimization of ball mill pulverizing system. Based on the Apriori-alike process, the proposed algorithm uses the independent pruning strategy to mine the fuzzy sequential patterns, which could enhance the efficiency of the algorithm. Then, the optimal values of the process variables are determined by a searching method with the mined sequential patterns. The improved fuzzy sequential pattern support and the fuzzy sequential pattern confidence are adopted to ensure the accuracy of the mined sequential patterns. Moreover, the sliding time window technique is used to ensure the completeness of mining results. The experimental results for parameters optimization of ball mill pulverizing system also verify that the proposed algorithm could determine the optimal values correctly and the running time is not long. In addition, the proposed algorithm has been put into practice successfully and the statistic data show that the pulverizing capability of ball mill pulverizing system is increased and the energy consumption would be reduced. DOI: http://dx.doi.org/10.5755/j01.itc.43.3.5180

Research on Optimal Control Model for Ball Mill Based on Genetic Algorithm

As the key equipment in coal-fired power plants, the optimal control problem of ball mill is an important factor affecting the efficient operation of the mill. In this paper, the output model, energy consumption model and unit consumption model of coal pulverizing system are built on the basis of analysis of ball mill running condition. The unit consumption model is used as the genetic algorithm fitness function. The outlet temperature, practical ventilation and coal load of ball mill are chosen as the optimization variables. The algorithm model is built to solve the multi-objective problem of ball mill.

Pulverizing System Simulation Model of a 300MW Oxy-Fuel Coal Fired Boiler

This paper focused on researching the pulverizing system of a 300MW oxy-fuel coal fired boiler, which took dehydrated recirculation flue gas as the drying medium. According to the working principle, the paper established the simulation model, and completed dynamic simulation tests basing on the IMMS platform. The dynamic simulation tests included the disturbances of the pressure of the flue gas inlet and the opening degree of the main flue gas valve. The results demonstrate that the model is precise, stable and it possesses good dynamic characteristic.

Energy Consumption Analysis of Pulverizing System in Coal-Fired Power Plant

Pulverizing system is the main energy-consumption equipment in coal-fired power plant, so it is of great significance to study energy-saving and optimization of pulverizing system. This paper first analyzes the situation and condition of pulverizing system in large-scale coal-fired power plant in China. According to analysis, coal mill and primary-air fan are the two main energy consumption facilities. Then their energy consumption characteristics, including power consumption and unit power consumption are studied. Subsequently, the energy-saving operation proposal for the pulverizing system is proposed.

Flow Measurement of Primary Air Containing Pulverized Coal with Simple Venturi Tube

The flow measurement of primary air is very important for thermal power plants to maintain the safe state of operation. For direct firing pulverizing system, the measuring is essentially affected by pulverized coal particles. Abrasion and occlusion would bring great trouble to the measurement. Many measuring methods are invalid under that circumstance. Lots of efforts have been made to find appropriate ways to measure the flow of primary air containing pulverized coal. Venturi tube had been successfully used to measure the flow of air. If a venturi tube is used to measure the flow velocity of primary air, the differential pressure goes higher with the increase of the concentration of pulverized coal in the primary air. The neglect of the affection of pulverized coal on the measuring would result in remarkable deviation. With the aids of coal flow rate, a method of using venturi tube to measure the velocity of primary air containing pulverized coal was established. The affection of pulverized coal on flow measuring of primary air cannot be ignored.

Research and Application of Medium-Speed Pulverizer Control Based on AGC Mode

Large delay is the main characteristics of medium-speed pulverizer system which used in subcritical and supercritical unit. By introducing and analyzing the operating principle and working process, considering energy saving and consumption reducing, and combined with the performance requirement of AGC (Automatic Generation control), recommend solutions were put forward. It can effectively solve AGC control problems of load and pressure control accuracy and ensure frequency stability of the grid, provide a reference for similar units.