Circulating water treatment by electrolysis
Scale is a hard deposit of predominantly inorganic material on heat transfer surface caused by the precipitation of mineral particles in water. As water evaporates in a condenser, cooling tower or an evaporative condenser, pure water vapour is lost and the dissolved solid concentration increases in the remaining water. If this concentration cycle is allowed to continue, the solubility of various solids will eventually be exceeded. The solids will then settle in pipelines or on heat exchange surfaces, where it frequently solidifies into a relatively soft, amorphous scale. In the circulating water systems, the carbonate scale and magnesium salt scale account for more than 60 per cent of the total (by specific gravity) scale. Dust and dirt account for over 30 per cent and other kinds of scale, such as sulphate scale, phosphate scale, ferric scale, etc account for less than 10 per cent of the total scale when they are all added up.
These scales are scattered in carbonate scale and dirt, therefore, if we can remove these two main scales, the problem of scaling in circulating water can be solved. Scale, in addition to causing physical blockage of piping, equipment, and the cooling tower, also reduces heat transfer and increases the energy use. For example, the thermal conductivity of copper is 2674 BTU/[hr (ft2)(F/in)], while the common cooling water scale calcium carbonate has a thermal conductivity of 6.4 BTU/[hr (ft2) (F/in)]. A calcium carbonate scale of just 1.5 ml thickness is estimated to decrease thermal efficiency by 12.5 per cent. In compression refrigeration systems, scale translates into higher head pressures, hence an increase in power requirements and costs. For example, 1/8ö of scale in a 100 tonne refrigeration unit represents an increase of 22 per cent in electrical energy compared to the same size unit free of scale.
Corrosion is defined as the destruction or loss of metal through chemical or electrochemical reaction with its surrounding environment. Mild steel is a commonly used metal in the cooling water system that is most susceptible to corrosion. Other metals in general, such as copper, stainless steel, aluminum alloys also do corrode but the process is slow. However, in some waters and in presence of dissolved gases, such as H2S or NH3, the corrosion to these metals is more severe and destructive than to mild steel. Corrosion is a three-step electrochemical reaction in which free oxygen in the water passes into a metal surface at one point (referred to as the cathode) and reacts with water and electrons, which have been liberated by the oxidation of metal at the anode portion of the reaction at another spot on the metal surface. The combination of free electrons, oxygen and water forms hydroxide ions. The hydroxide ions then combine with the metal ions, which were liberated at the anode as part of the oxidation reaction, to form an insoluble metal hydroxide. The result of this activity is the loss of metal and often the formation of a deposit. Corrosion causes blockages or wear in the pipes, valves, strainers, pumps, shafts, seals, etc. It also causes reduced water flow, lower heat transfer and higher costs.
Types of corrosion
General attack: Exists when the corrosion is uniformly distributed over the metal surface. The considerable amount of iron oxide produced contributes to fouling problems.
Pitting attack: Exists when only small area of the metal corrodes. Pitting may perforate the metal in short time. The main source for pitting attack is dissolved oxygen.
Galvanic attack: Can occur when two different metals are in contact. The more active metal corrodes rapidly. Common examples in water systems are steel and brass, aluminium and steel, zinc and steel and zinc and brass. If galvanic attack occurs, the metal named first will corrode.
Bacterial and microbiological
There are many species of microorganisms (algae, protozoa, and bacteria) that can thrive in cooling systems under certain circumstances. Their growth is helped by favourable water temperature and pH, the oxygen picked up by the spray water, sunlight, and organics that provide food. Generally, microbial organisms form colonies at points of low water velocity that leads to uncontrolled microbiological accumulations. The deposits are transferred throughout the piping system, which interfere with heat transfer surfaces and restrict flow through piping, strainers, spray nozzles, and control valves. The deposits are also concern for threatening infectious agents like the bacteria Legionella Pneumophillus.
What is the solution to these circulating water problems? We want to have a treated water with no hardness and correct pH value and freedom from microbiological contaminations. The solution is developed in the form of a machine which removes the hardness by electrolysis of water.
Principle of operation
By specific low-voltage and high-frequency electrolysis technology, water can be softened without the use of chemicals. It electrolyses water into weak micro molecule reductive water and active water, enhancing water´s solubility and ability of dissolving scale. The specific electric field changes the crystallization of CaCO3, Mg(OH)2 and other scale, inhibiting the formation of scale. The active micro molecule water, electrolysed by the specific low voltage and high frequency by patented technology, gradually dissolves the scale existing in the inner walls of pipes, heat exchangers, cooling tower etc. The sucking baskets suck scale and rust onto their nets, making the process of removing scale and rust visible. Meanwhile, the active micro molecule water generates a protective membrane in those equipment, preventing the corrosion of pipes and equipment. Its sucking baskets will produce lots of O3, OH, and H2O2 during electrolysis. These products have excellent sterilisation efficiency, so that they can kill algae and bacteria effectively.
Advantages of Expedio green water treatment method:
- Removes total hardness, alkalinity, dirt and silt from the circulating water.
- Increases COC, lowers blow down of water and make up water requirements.
- Reduces water wastage.
- Prevents algae and bacterial growth.
- Oxidises the present scales in the systems and removes them.
- Eliminates use of chemicals for softening and pH correction.
- Eco-friendly and energy saver.
- Lower operation and maintenance cost.