Technical Information

SIEMAG TECBERG has received an order for the supply, installation and commissioning of a centralised mine-cooling system from SDIC Xinji Energy Co. Ltd. in the province of Anhui in China. The system is to be set up at the new mine of Liuzhuang and comprises a central cooling unit on surface and a pressure exchanger – the Pressure-Exchange System (P.E.S.) developed by SIEMAG TECBERG, also known as three-chamber pipe feeder – with pumps and distributor equipment situated in the underground.

In order to increase production capacity, coal is being mined from strata located at ever-increasing depths where ground temperatures are much higher. In addition, much stricter demands are now being made on working conditions in Chinese mines, where temperatures exceeding 26 °C in working faces are no longer permitted.

To achieve the prescribed temperature in underground working areas, the air in the mine has to be cooled down. The cooling power for each working face is calculated taking into account the rock temperature (in this case approximately 40 °C at a depth of 760 m), the quantity and temperature of the air, the rated electrical power of the mining machinery and the heat it emits, as well as losses in the piping network. The overall cooling capacity depends on the number of working faces and driving faces in operation simultaneously. The calculations carried out for the Liuzhuang mine by DMT GmbH & Co. KG (formerly DMT-Gesellschaft für Forschung und Pruefung mbH) in Bochum, Germany, yielded a required cooling capacity of 22 MW for operations in three working faces with a daily production quantity of 10,000 tons of coal and 15 driving faces for the development of new mining fields.

During the first phase, the cooling capacity installed was 5.5 MW. SIEMAG TECBERG is supplying the central cooling unit including installation material as well as the first charge with the required water additives. The cooling system is assembled in a building constructed by the customer on surface. The cooling medium of water is cooled down to 3 °C by two turbo chillers and return cooling takes place in four evaporation-cooling towers. The water lost by evaporation is replaced with fresh water which is treated beforehand in a special water-treatment plant. The water-treatment plant is fitted with equipment for softening the water and adding chemicals as corrosion protection, hardness-stabilisers and biocides. In the primary circuit, the cold water is pumped to the underground through insulated shaft pipes at a rate of 300 m³/h by a 120 kW frequency-controlled chilled-water pump.

The secondary water circuit, which connects directly with the coolers in the working faces, is located in the underground. The primary water circuit with its operating pressure of approximately 80 bar in the underground is coupled to the secondary water circuit with approximately 30 bar by the Pressure Exchange System (P.E.S.). The use of the P.E.S. system has proved highly economical and efficient in many mine-cooling systems.

The circulation of water in the secondary circuit is powered by one pump equipped with two 250 kW motors. The distribution of the water in the underground is controlled by seven industrial PCs with connected control and measuring devices. The connection between the PCs themselves and between the PCs and the control systems on surface is via Ethernet-TCP/IP.

One of the greatest challenges of the project was the short delivery period of six months and the MA certification (Mining Products Safety Approval and Certification) for the equipment destined for use in the underground.

Centralised cooling systems in mines with chilling of coolant on surface is already common practice in Germany. In closed piping systems, the cold stored in water can be transported to underground air coolers economically and without significant loss while the pressure exchanger ensures a controlled volume flow and the transmission of the required chilling capacity to the secondary cooling circuit with a temperature increase of less than 0.5 °C.