Application of high-pressure compressor in nickel mining

New Caledonia, Australia is one of the world's largest laterite nickel deposits. Currently, near the Goro District, a large nickel mine extraction industrial zone is under construction. The industrial zone will have complete supporting facilities, including factories, power supply, ports, streets, etc., with about 800 staff.

The ore reserves in the Goro District are about 50 million tons, of which the annual output of nickel ore is about 60,000 tons, which is mainly mined by Vale in Brazil. Vale's nickel mining business covers the world, and huge costs have been invested in the purchase, production and construction of environmental protection facilities for nickel projects in Goro District.

Modern craft

The high-pressure acid leaching method used in the extraction of nickel laterite is a modern technology and has not been widely used. However, compared with the traditional electric furnace smelting method, this technology has lower energy consumption and is more environmentally friendly.

The mixture of nickel raw material and water is sent by a diaphragm pump into an autoclave for acid leaching (about 5 meters in diameter and about 30 meters in height), which is filled with sulfuric acid and compressed air. Nickel sulfate and sulfuric acid are fused to form a nickel-sulfur solution. After further treatment, pure nickel can be obtained.

The compressed air pressure in the autoclave is about 60-80 bar, and the temperature is about 200-250°C. The function is to assist the reaction in the autoclave, keep the pressure in the autoclave constant, and avoid excessive wear of the seals caused by power interruption. In addition, it can also assist in cleaning the autoclave.

Selection of air compressor system

In the nickel mine project in the Goro area, customized several sets of high-pressure compressor systems for Vale.

Taking into account the local natural conditions, these compressor systems are all designed in a container style, equipped with exhaust vents and sand filter devices to protect the equipment from sand, dust and high temperature. In addition, in terms of noise reduction, the cabinet uses a special sound reduction design. When the equipment is running, the noise intensity is about 73 dB(A) (measured at a distance of 1 meter according to the standard DIN 45635).

For three autoclaves with a gas capacity of 300m3/h, selected three I 25.0-45 compressors, each with a displacement of 114 m3/h and a final pressure of 90-350bar. This type of compressor has a 4-stage compression and adopts an air-cooled design, which is suitable for long-term continuous operation. It performs particularly well under high temperature and sandy weather conditions.

Advanced design concept

Each compressor configured in the nickel extraction project is equipped with an independent O&K controller for full monitoring of equipment operating data. O&K is used to record the running time, operating conditions, pressure, temperature and other data of the display equipment, automatically shut down the equipment when the equipment fails, and transmit the fault signal to the advanced monitoring center.

The compressor equipment serving the acid leaching process should meet the different gas volume requirements of the autoclave on the one hand, and on the other hand, it should also avoid short-term shutdowns during operation to ensure the long-term operating efficiency of the equipment. Therefore, each compressor equipment is equipped with 12 80-liter gas cylinders with a storage pressure of 300 bar. This configuration can avoid multiple shutdowns in a short period of time. Before entering the autoclave, the compressed air in the cylinder needs to be reduced to the rated pressure by a pressure reducing device.

The decompression device reduces the compressed air in the cylinder to the 60-80 bar required for the autoclave reaction, and monitors the entire decompression process. In addition, considering that condensation may occur when the compressed air is reduced from 300 bar to 60 bar, the final stage of the equipment is equipped with a high-pressure refrigeration dryer to dry the compressed air. The maximum working pressure of the high-pressure refrigeration dryer can reach 300 bar, and the dew point of the air after drying is approximately + 3 °C. A filter is additionally arranged downstream of the pressure reducing device to filter and discharge condensate during the compression process.