Water Hydraulic Systems supply the shields with pressure in underground mining. In the mining process the systems spray, cool and increase the safety in the longwall.
Published in the RAG-"Steinkohle" Employee Magazine, Issue 03|2016
Pictures: © RAG, Hauhinco
Water hydraulics is an important element in a modern coal mine. Water hydraulics are used in the high pressure supply of the longwall as well as in the spraying systems and in the cooling systems of the drive motors. Hauhinco, located in Sprockhövel, Germany has been supplying water hydraulic systems to RAG mines since the 1960s. At both mines Prosper-Haniel and Ibbenbüren one central water hydraulic pump station is in use for multiple longwalls. "Due to safety reasons, water hydraulics is compulsory in underground mining, as the fluid medium is non-flammable", explains Holger Hoffmann, Managing Director of Hauhinco. "In addition water hydraulics are more environmental friendly than oil hydraulics. Water also has better control characteristics due to less compressibility." At the hearts of the systems are plunger pumps that depending on the input power are equipped with three or five plungers. The plunger which runs in a cylinder draws the fluid through an inlet valve. The medium is then pushed out by the plunger through an outlet valve. Thus experts refer to this type of pump as a displacement pump. Each pump is equipped with a bypass valve, which sends water back to the tank when less or no usage is required.
With the beginning of the fully automated extraction method the RAG began using water hydraulic high pressure stations for walking-pit support systems. Hydraulic controlled shields replaced the pillars for the support of the overlaying rocks in the longwall and made the underground work easier as miners did not have to relocate pillars by hand anymore. With the help of automated shield supports this step is done autonomously. After the shearer or the plow has extracted the coal, the shield cylinders then retract allowing the shield to move forward. Once in place the shield canopy cylinders then extend supporting the new roof. Advancing cylinders in the shield then push the pan line forward up against the new coal face. The high pressure pump station supplies the cylinders with hydraulic fluid. A typical station usually consists of multiple three or five plunger pumps each equipped with an electric motor, emulsion tanks, high pressure and return filter, hosing, hydraulic accumulators, control modules, explosion-proof measuring devices as well as equipment for the data transfer and visualization above ground.
A water-spray and cooling pump station supplies the shearer water spray or the coal plow water spray and the cooling systems for the drive motors with the necessary pressure and volumetric flow rate. "The water spray at the shearer or the plow minimizes the dust development during the mining process, by binding dust in the water", explains Hoffmann. "Moreover it cools the electric motors during the extraction process." In a plow operation spray-nozzles are integrated in the shield canopy, in a shearer operation nozzles are also integrated in the shearer drum. Most of the times the water spray takes place three shields before and after the extraction in the plow and shearer area. Besides a three plunger pump, a station consists of a water tank, a filter unit, electric controls and the hosing. Each High Pressure and Water Spray Pump Station has a spare pump, which is used when regular checkups are carried out at another pump. The maintenance of the pumps itself is done above ground. The employees at the control room monitor which pumps are running at what volume and at what pressure. Optical waveguides transmit the data from the control in the longwall to the control room above ground.
The largest water hydraulic pump stations in underground coal mining are in two Russian mines and one American mine, each pump unit weighing more than two tons. Each pump generates a pressure of up to 360 bar at 635 liters per minute and 400 Kilowatt input power.
Published with the kind permission by the RAG Aktiengesellgesellschaft.