Water treatment system to use AMD water to increase savings

30th April 2010 By: Carla Thomaz

Water treatment systems supplier Water Engineering Systems Unlimited (Wesu) is looking at using acid mine drainage (AMD) and effluent water to replace potable water used in cooling towers and gland service water.

Wesu MD Zvi Wagner tells Mining Weekly that water used in cooling towers, refrigeration plants and gland water for slurry pumps deposits scale, fouling and biolife on heating system equipment, which scales and corrodes the heating systems. To tackle these destructive processes, potable water is used and treated with hazardous chemicals at a huge cost, he says.

Wagner explains that Wesu uses a ScaleBio filter technology to eliminate scale corrosion and biolife in water systems and heat exchangers, making them work more effectively. The technology uses a partial electrolysis technique to balance the water based on its chemical parameters and the engineering parameter of the system. He notes that by replacing potable water with AMD water, the return on investment could be as low as four months, saving the South African mining industry a fortune, and reducing the potential AMD crisis.

In evaporative systems, such as cooling towers, traditional chemical treatment dictates that the total dissolved solids (TDS) will be controlled in a cooling tower's sump water, sometimes referred to as basin or dam. To control the TDS, high TDS water is blown down or drained from the sump and replaced with low TDS water. Low TDS water is potable water. Wesu's inducing of electrical currents into the water means that its system does not require massive blow down to reduce the TDS and, as it can operate at very high TDS levels. As a result, it does not require potable water to keep the cooling system clean from scale. Wagner adds that this allows for effluent, process water, salinated water and AMD water to be used instead of expensive and scarce potable water.

Wagner reports that the electrolysis technique the company uses calculates the exact amount of scale that will be deposited in any system, based on the chemical parameters of the water and the engineering parameters of the system. A water treatment system is then designed to manufacture this scale a thousand times faster than it deposits naturally in the system, and to remove it from the water. Once removed, he explains, there is no scale left to deposit in the system and, with the water being brought to its kinetic equilibrium, no scale or corrosion will occur.

To manufacture the scale, Wesu has designed a reactor based on partial electrolysis that injects a minute amount of electrical power and accelerates the chemical reactions between the minerals naturally contained in any water, which results in scale deposition in the system. At the same time, small amounts of biocides are produced preventing the formation of biolife.

The Wesu electrolysis systems have been installed and are operating in South African gold, platinum, copper and base metal mines, as well as chrome smelters. Wagner adds that the applications vary from cooling towers on compressors to submersible arc furnaces, internal cooling for arc furnaces and the treatment of slime dam water that is returned to the mine. Future projects will include refrigeration plants, gland water systems, and reconditioning open cast cement quarry drain water to replace scarce and expensive potable water.

Wagner adds that Wesu's ecofriendly electrolysis technology is saving the South African mining industry a fortune as it is well known fact that 1.2 mm of scale increases energy consumption by 43% and pressure in the heat exchanger's tubes by 70%, which means that pumps have to work harder to deliver the same amount of cooling water. By keeping the heat exchanger clean, no increase in pressure is experienced and fewer pumps are required to circulate the water, which translates to less electricity consumption. Further, the system keeps the environment safe through the reducion of carbon emission and avoiding unnecessary effluent.

The system does not require a highly skilled labour force as the system is self-maintaining, self-operating and self-monitoring, as the plant manager of one of the oldest gold mines in South Africa says after two years of experience with the WESU systems. Further, Wagner notes that Wesu provides a full and comprehensive operation, maintenance and spare parts Wesu system plan for up to 20 years.