For years, the Polish hard coal mining has been struggling with the problem of fire hazards in areas with coal residue, mainly in goafs. Currently, a common method of limiting this hazard is the fire prevention involving use of fine-grained hydromixtures based on power generation waste, mainly fly ashes. The hydromixture is introduced into the caving zone created by the advancement of exploitation face and its task is to fill in voids, limiting the possibility of access to the mine air oxygen to a minimum. The first part of the article presents theoretical fundamentals of determining the parameters of gravitational hydraulic transport of water and ash hydromixtures used in the mining pipeline systems. Each hydromixture produced based on fine-grained wastes is characterized by specified rheological parameters that have a direct impact on the future flow parameters of a given pipeline system. Additionally, the gravitational character of the hydraulic transport generates certain limitations concerning the so-called correct hydraulic profile of the system in relation to the applied hydromixture characterized by required rheological parameters that should ensure safe flow at a correct efficiency. This paper shows an example of optimisation of the composition of a selected fly ash-water hydromixture in relation to its capacity for hydrotransport in gravity pipeline installations, as well as the amount of excess water that will always drain from the location of feeding the hydromixture to the underground workings.
The study presents the manners of determination of the Darcy friction factor λ for a homogenous hydromixture of alum sludge of varied hydration and temperature for the laminar flow zone. The rheological evaluation of the hydromixture as a viscoplastic body has been conducted with use of measurements of viscosity. The curves of flow were approximated with use of the generalized Vočadlo model. The Darcy friction factor λ of the pipeline was determined with use of the non-dimensional criterion λ(Regen) and λ(Re, He).