Please use this identifier to cite or link to this item:
|Investigation on Transportation Characteristics of Pulverized Coal Slurry
|Mohapatra, Saroj Kumar
|Hydrotransportation;Coal water slurry;Particle size distribution;Rheology;Computational Fluid Dynamics;Twisted pipes
|Coal contributes a major fraction of the installed capacity. It is estimated that around 44 – 45% of the coal reserves are young, which contain high moisture and high ash coals. Presently, the coal water suspension has successfully replaced diesel in a variety of applications viz. low speed marine engines, diesel fired furnaces and stoves. In some places, the washed/pulverized coal is directly transported from the mine to the powerplant using the slurry pipelines. These systems are reliable, clean/dust free, and economical. Besides, these systems have very few chances of failure and are mostly used in the regions, where the mines are not accessible by rail/road transportation. In such applications, the coal fraction in the CWS can range from 10- 60% (upper limit decided by the rank of coal; higher the rank, higher can be the upper limit) depending upon the factors like availability of coal, pumping power, the rank of coal, throughput required, etc. The high rank coal reserves are limited and getting depleted at an escalating rate to meet the demands of growing population. This concern has compelled the scientific community to use the young high ash coals. The coal water slurry fuel is one promising way to use low quality coal as an economical liquid fuel. Due to poor physico-chemical and surface properties of such coals, these systems appear to be unsustainable. This research presents a sustainable solution to use the existing low-quality coals efficiently without any modification in the already installed systems. The Indian coal possessing high moisture and oxygen functional groups was successfully treated using hydrothermal and microwaves irradiation, resulting in the improvement of morphological, physical, chemical and rheological characteristics. These changes are due to the elimination of the Hydroxyl (-OH-) and Carboxyl (-COOH-) groups, which are observed to contribute the most to the hydrophilicity of the coal particles. The morphological investigations reveal the breaking up of the bigger particles into fines upon microwave irradiation. The treated coals exhibit physico-chemical and surface properties similar to high rank coals but still possess high ash that does not pose any issue with the normal operation of the system. The hydrotransport of the industrial powders and bulk solids such as minerals, mineral tailings, coal and ash is considered to be an efficient mode of transportation. The pipelines ranging from a few meters to few kilometers in length are used for such transportation purposes. The pipe fittings such as converging section, diverging section and elbow are an integral part of these pipelines. The complex solid-liquid flow of coal water slurry through conical converging sections and diverging sections is simulated using the computational fluid dynamics approach. Nine different geometries of the sections are analyzed in the present study. The length of the section is the key variable in the geometric variations and ranges from 0.05m to 0.6m. The influx velocity at the entrance of all the sections is varied in the range of 0.5 m/s to 5 m/s. The mass concentration of the solids dispersed inside the liquid phase is varied from 10 to 60%. The results generated by the computational fluid dynamics tool are in good agreement with the experimental data. The design of the section is evaluated based on results obtained for three characterization parameters viz. pressure recovery coefficient, head-loss across the diverging section and volumetric efficiency. The 0.3m long diverging section is found to be the optimum design for best pressure recovery, maximum volumetric efficiency and lowest head-loss. If not well addressed, the issue of particle settling in such pipelines can lead to blockage and even bursting of the pipeline due to the continued deposition of the solids. The present study proposes the introduction of a twisted pipe section of a suitable length and geometry, that produces enough turbulence in the flow, sufficient for the re-dispersion of the already settled particles and check their further deposition. To achieve this objective, 5 different geometries (each having 4 different lengths) of twisted pipes are designed and used to model the dynamics of the particles’ flow through them and in their downstream region. A low influx velocity (where maximum settling is expected) of 0.5 m/s is selected for all the cases and the influx solids’ mass concentration ranges from 40-60%. The results generated by the commercial CFD software are in good agreement with the experimental data. The parameters viz. mixing index, pressure loss, and specific energy consumption are evaluated to choose the best design of the twisted pipe section. The 0.2m long 3 lobes twisted pipe section is found to deliver the suspension of highest homogeneity at the cost of a slight increase in pressure loss and specific energy consumption. The present solution ensures the mitigation of particles’ settling and the other related issues
|Appears in Collections:
Items in DSpace are protected by copyright, with all rights reserved, unless otherwise indicated.