Objective
Water used underground is mainly taken from subsoil waters and streaming water. The dust control techniques development involves more and more sophisticated installations which require a clean water supply. It is the case that underground, water generally presents characteristics which make it's use difficult.
The filters in use are effective for solid particles elimination, however there is no operational solution for flocculated products treatment. These elements are settling within mains, especially when the system is at rest, and cause jamming by spray resumption.
The research objective is to design and to implement underground an industrial water treatment process.
Water treatment was undertaken using a dispersant to prevent iron oxidation. This chemical is introduced into the spraying circuits by means of a dosing pump. As this chemical likewise acts on suspended matter, it's initial dosing is no longer sufficient when there are wide variations in suspended matter concentration.
The various analyses have demonstrated the presence of a quantity of ionized iron which cannot be ignored. In order to oxidize this kind of iron, aeration has been applied at the feeder basins in order to oxidize the free iron and thus to produce ferric iron. Oxidation of the iron from the steel of the conduits has been confirmed downstream from the basins.
In order to retain those particles having a tendency to flocculate, we have opted for a deep filtration system on a self-cleaning bed of sand. This type of filtration has the advantage of easy adaptation to variations in untreated water nature and also of providing a consistent range of filtrate quality.
A sand filter was tested in the spray and cooling circuit of a coal-shearer with a theoretical flow of 300 l/min. This machine is fitted with an on-board pressure booster.
Water analyses were carried out on samples taken from various points of the installation. The averages of the measurements taken over three months showed that the sand filter retains approximately 97% of the material in suspension and 95% of the iron oxides.
The presence of high levels of material in suspension (250 mg/l) in water during significant periods made it necessary to install a second filter in parallel. The cleaning functions and the operation of the two filters were automated in order to have one filter in operation and the other in cleaning. Cleaning of the filter was optimized by injection of air and pulsed water. In its final phase, the filter is equipped in doublelayer (anthracite and sand) which provides an advantage when dealing with water containing suspended materials of widely differing characteristics.
All of these improvements have made it possible to get such a water quality that the number of nozzles being replaced on the machines has been divided by 10.
A generation of sand filters of smaller dimensions (100 l/min.) has also been designed for use water circuits for road headers. The general application of this filter, which can be fitted on board the power station, is under way.
Underground Water Mains
A survey of the water distribution mains for the various underground units was carried out with the aim of identifying feeder sources.
To supply these mains, what is generally used is water collected underground, which then passes through the mains and the drainage basin.
Certain units are drinking water from the urban mains to supply machines which require water of high quality.
Water and Spray Nozzles Analyses
The various water analyses have identified significant iron contents and a high water hardness level. Bacteriological quality is not to be implicated considering the low, overall germ content.
The suspended matter quantities in water vary between 5 and 27 mg/l.
Analyses carried out by means of ICP plasma torch confirm the redominance of iron, calcium, manganese and silicon.
The build-up of scale in the nozzles results from the decomposition of the bicarbonates which then leads to the retention of iron oxides and other elements in suspension.
Analysis of the Phenomenon
It is proved that, irrespective of the solid particles or flocculants retained by filters, smaller elements than the filtration mesh, settle in the mains, accumulate and begin to move again with water consumption resumption.
What then occurs is an inrush of aggregates into the filters areas and into the spray equipment, thus causing jamming.
The various analyses carried out on water and deposits have demonstrated the presence of significant proportions of iron constituents. The iron content is increased by contamination caused by the pyrite products contained in the coal and minerals through which the water passes.
The ferrous salts oxidation gives rise to ferric hydrated oxides precipitations. These oxides settle in the spraying circuits as flakes, several hundreds of microns in size.
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57802 Freyming Merlebach
France