Stability of CWM in long-distance pipelines

The change in apparent viscosity of CWM occurring during long-period operat ions was measured using a loop rest facility in which a pipe of 200 mm insi de diameter was used. The apparent viscosity of CWM showed a tendency to in crease while CWM was circulated in the loop. It was hypothesized that the a gglomerated coal particles were dispersed, attributed to the high shear rat es created by the CWM fluid flowing through the pipe and the pump. The coal particles in the CWM, being pulverized, adsorbed greater amount of dispers ant. It was, thus, considered that the amount of dispersant in the liquid p hase was reduced to an extent too little to maintain the viscosity of the C WM at low levels. For the purpose to investigate this phenomenon, the rheological properties were examined experimentally in detail at high and low shear rates. High sh ear rates were produced by allowing CWM to flow into a small pipe at variou s velocities. Low shear rates were created by a rotary viscometer. As a res ult, the apparent viscosity of CWM increased far more quickly at higher she ar rates. Based on these findings, a model for rheological change of CWM was proposed . Increase in viscosity of CWM was predicted using this model, which exhibi ts the relation between shear rate and apparent viscosity. The apparent vis cosities of CWM calculated by this model were in good agreement with the me asured values. It became clear that an increase in apparent viscosity occur red in the flow of pipeline at low shear rates rather than during pumping o peration at high shear rates. Based on this model, the required initial amo unt of dispersant can be determined in order to maintain the apparent visco sity of CWM almost constant.