Study On The Compaction Of Coal Logs And The Mechanism Of Their Transportation In Hydraulic Pipeline

With the development of industry and economy, the demand of coal is increasing every year in China. The current coal transportation capacity is unable to meet the demand of coal. The capacity of coal transportation is insufficient in a long term. Coal transportation is into a bottleneck stage. As a new method of coal transportation, coal log pipeline technology is proposed to alleviate the problems of coal transportation. However, coal log pipeline technology still has some problems:the coal logs can not fully meet the requirements of hydraulic transportation, the research about the hydraulic characteristics of coal log train (a row of several coal logs) is not insufficient and the comprehensive evaluation of coal log pipeline technology is needed. Hence, studying the coal compaction suitable for pipeline transportation, the hydraulic characteristics of coal log train and the numerical simulation, and the comprehensive evaluation on the environmental impact, economic cost and energy consumption of coal log pipeline are conducive to promoting the development and practical application of coal log pipeline technology.Firstly, this paper studied the coal compaction process. According to the coal compaction process, a small hydraulic compaction machine has been transformed, achieving coal log compaction and demoulding automatically. The moldings for compacting coal were also designed for carrying out experimental study of coal log compaction. This paper also built a hydraulic transportation pipeline experiment system with 15 m length and 50 mm pipe inner diameter. The design of the pipeline was optimized.In coal log compaction, anthracite, bituminous coal and lignite were selected as the raw materials. The cationic emulsified asphalt and polyvinyl alcohol were selected as binders. The coal logs with the diameters of 45 mm and 135 mm were compacted. The key parameters to compact coal logs were put forward according to the experiment results. The coal types, compaction pressure, pulverized coal particle size and the binder types and adding amount on the effect of coal log compaction were studied. The structure, water resistance, wear resistance and compressive strength of coal logs were studied. The minimum requirements for coal logs to be transported smoothly were proposed. This paper made it clear that the necessary conditions of compaction pressure, pulverized coal particle size and binder adding amouts to meet pipeline transportation.In hydraulic transportation mechanism of coal log train, the pipe resistance loss and frictional resistance loss were studied using the hydraulic transportation experiment system. The velocities of a single coal log and coal log train were measured changing with water velocity using phototimers. The surface pressures of coal log train were measured at different flow rates. The drag and lifting forces were calculated and the effect of the two forces on the motion of coal log train was also analyzed. Then the drag and lifting coefficients were also calculated according the drag and lifting forces. The numerical simulation of the coal log moving in the pipe was performed using dynamic mesh method and Fluent software, displaying the motion of the coal log from resting on the pipe to starting and the movement passing through a turn. The calculated coal log velocity and pressure from simulation was also compared with the experiment results. The results agreed with the measurement results well. Finally, the changes of forces and influence from the simulation results were also analyzed.This paper studied the microstructure of anthracite coal logs, bituminous coal logs and lignite coal logs by scanning electron microscope. The pore structures and pore specific surface area of the three kinds of coal logs were measured using nitrogen adsorption method. The compaction process and the effects of compaction pressure and binder on the coal log structure were also analyzed and discussed from the results. The combustion characteristics of coal logs were detected and investigated using thermal analysis technology. The combustion characteristic parameters of coal logs were got and compared with those of raw coals. It was found that adding binder changes the coal contents and slightly changed the combustion characteristics of coal. The combustion performances of anthracite and lignite were improved and the combustion performance of bituminous coal was declined. The emission characteristics of coal logs were studied in the combustion atmosphere. Cation emulsified asphalt decreased the SO2 emission concentrations of anthracite and bitumite coal logs while it increased that of lignite coal logs. Polyvinyl alcohol reduced the SO2 emission concentrations of anthracite coal logs while it increased those of bitumite and lignite coal logs. Binders decreased the NOx emission of anthracite coal logs while they increased the NOx emission of coal logs made of lignite and bituminous coal.Finally, this paper established the evaluation systems of coal log pipeline, railway transportation for coal and truck transportation for coal. The detailed data about the three transportation scheme were colleted. The data lists of energy consumption, pollutant emissions and economic cost were made. The energy consumptions and environmental impacts of three transportation scheme were comprehensively evaluated and compared. It was found that the coal log pipeline outperformed the rest two schemes. The economic costs of three transportation schemes were evaluated using life cycle cost analysis method. It was found that the income of coal log pipeline technology was better than the rest two schemes and the investment cost is the lowest. The annual operating cost of coal log pipeline technology was higher than that of railway transportation and lower than truck transportation. The cost of binder accounted for a large proportion of annual operating cost. Finally, the key factors affecting the evaluation results-binder dosage, compaction pressure, pulverized coal particle size and the wear rate of coal logs in pipe were analyzed using sensitivity analysis, quantitatively analyzing the effects of the four factors on the ourput results.