FOULING, SCALING AND CORROSION
Fouling reduces the consumption of water and heat transfer. It may be caused by the collection of garbage outside the pump suction grid in the pits, the growth of algae in lighted areas, and mucus in the shadows or dark areas of water systems. The material can clog pipes or other parts of the system after he escaped and migrated to the flow of water. Zoom also reduces the consumption of water and heat transfer. Deposition of dissolved minerals on the surface of the equipment causes scaling. This is especially so in hot places, where the heat transfer is the most important. Corrosion is caused by impurities in the water. In addition to the reduction in water flow and heat transfer he also damage the equipment. In the end, corrosion reduce the effectiveness of the work. This can lead to expensive repairs or even replacement of equipment.
Impurities at least five confirmed sources. One of the earth's atmosphere. Water projected in the air, whether natural precipitation or water, pouring out through cooling tower, picks up dust, as well as oxygen and carbon dioxide.
Similarly, synthetic atmospheric gases and dust affect the purity of water. Industrialized area exposed to such impurities are embedded in the water supply system.
Decaying plant life, the source of water impurities. Rotting plants produce carbon dioxide. Other products of vegetable decay, causing an unpleasant odor and taste. By-products of vegetable collapse of nutrition for the goo growth.
These three sources of pollution pollute the water with a material that makes it possible for him to pick up more impurities from the fourth source of minerals. Minerals in the soil beneath the surface of the earth, probably, are the main source of pollution in the water. Many minerals are present in the subsurface soil. They are more soluble in the presence of impurities from the first three sources mentioned above.
Industrial and domestic wastes are fifth in principal source of water impurities. Municipal waste affects the bacterial count. Therefore, it is of interest to health officials, but not the paramount importance of scale and corrosion point of view. Industrial waste, however, can greatly increase the corrosive properties of water. This may indirectly cause a higher than normal content of mineral substances.
Correction or generation of finely divided material that has the appearance of mud or silt causes of fouling. This sludge, as a rule, consist of mud and debris from the air. Sludge is introduced with the make-up water. Leaves and dust together in the wind and washed out of the air and rain. This debris settles in tanks or in other parts of the cooling system. Growth of plants, and also contaminates. Bacteria or algae in the water leads to the formation of large masses of algae and slime. They can clog the system of water pipes and filters. Paper, bottles and other debris also cause pollution.
Scaling
There are three ways to prevent formation of scale. The first is to eliminate or reduce hardness minerals from the feed water. Control of factors that cause hardness salts to become less soluble important. Hardness minerals are defined as water-soluble compounds of calcium and magnesium. The majority of the compounds of calcium and magnesium are much less soluble than the corresponding sodium. By replacing calcium and magnesium part of these minerals with sodium solubility of sulphates and carbonates has improved to such an extent that scaling is no longer a problem. This feature of water softening. The second method of prophylaxis of the scale, controlling water conditions that affect the solubility of scale-forming minerals. Five factors that affect the rate of formation of scale:
- Temperature
- TDS (total dissolved solids)
- Hardness
- Alkalinity
- pH
These factors to some extent be controlled by proper design and operation water-cooled equipment. Proper temperature levels are maintained, ensuring a good flow velocity of the water and adequate cooling tower. Consumption of water recirculating systems should be about 3 gallons per minute per ton. The lower level in the flow stream to allow the water to stay in contact with hot surfaces condenser for a long time and pick up more heat. Temperature drop on the tower should be from 8 to 10 degrees Fahrenheit (from 4.5 to 5.5 degrees C) for compression refrigeration system and 18 to 20 degrees F (10 to 11 degrees C) in most of the absorption systems. This cooling effect, due to evaporation, depends on the tower features and uncontrolled atmospheric conditions.
Airflow through the tower and degree of water gap of two factors that determine the amount of evaporation that will occur. Because the heat energy required for evaporation, the amount of water into steam and lost from the system determines the amount of heat. That is, the number of BTU heat recovery factor. One pound of water in cooling towers temperature, requires 1050 BTU be converted from liquid to vapor. Therefore, the higher the weight of water evaporated from the system, the stronger the effect of cooling or lowering of the temperature throughout the tower.
Total dissolved solids, hardness and alkalinity effect on three interrelated factors: evaporation, makeup, and bleeding or blowing rates. Water, when it evaporates, the system remains in its pure form, leaving behind all dissolved substances. The volume of water evaporative cooling takes place at a relatively constant figure due to the use of float valves.
Fresh makeup water brings with dissolved material. This is added, that has been left behind by evaporated water. Theoretically, if we assume that all the water leaves the system due to evaporation and system volume remains constant, the concentration of dissolved material will increase to infinity. For this reason, bleeding or purging is used.
There is a limit to the number of any material that can be dissolved in water. When this limit is exceeded, the introduction of additional material will cause any sludge or scale form. Control the speed at which the dissolved material is removed controls the degree to which this material is concentrated in the circulating water.
Identification
Descaling depends on the chemical reaction between the scale and chemical cleaning. Identifying the scale is important. Of the four scales are most often found only carbonate strongly reactive with cleaning chemicals generally regarded as safe for use in cooling equipment. At other scales requires pretreatment-ment, which makes them more active position. This advance preparation depends on the type of scale to be removed. Attempts to remove the scale of the problem without proper pre-treatment may waste time and money.
The scale of the identity can be in one of three ways:
- Experience
- Field tests
- Laboratory analysis
Except iron scale, orange, it is very difficult, if not impossible, to determine the scope of appearance. The experience gained cleaning systems in this area over a long period of time. Thus, the procedure for pre-treatment and the number of scale remover required to remove the type of scale are most often found in the area, become common knowledge. Unless radical changes in the feed-water quality occur, type of scale discovered remains practically unchanged. Experience further enhanced by using two different methods.
In field tests, which are very simple in execution, determine the reactivity of scale with a cleaning solution. By adding 1 tablespoon of liquid scale remover or 1 teaspoon of solid scale remover 1/2 litre of water is preparing a small amount of cleaning solution. A small piece of scale, then deleted in the cleaning solution.
Speed of reaction, as a rule, will determine the type of scale. Reaction between the scale remover and carbonate scale results in a buoyant upward. The scale eventually dissolve or disintegrate. However, if the scale sample hard or flint composition and little or no gurgles in acid is observed, the heat should be applied. Sulfate scale will dissolve in 140 degrees F (60 degrees). Small samples should be used within approximately one hour. If the scale of the sample contains a high percentage of silica, little or no reaction will be observed. Iron scale easily distinguished appearance. Testing with a clear decision, as a rule, is not required.
Since this process of identification, rather elementary and combinations of all kinds of scale often there are, obviously, more accurate methods may be needed. Such methods are most easily carried out in a laboratory. Many chemical manufacturers provide this service. Scale samples that cannot be identified in the field may be sent by mail in these laboratories. Here's a complete breakdown and analysis of the scale of the problem will be performed. Detailed cleaning recommendations will be given to the sender.
Most scales have primarily carbonate, but they may also contain a different number of sulfates, iron, or silicon. Thus, the number of scale remover required for cleaning should be designed specifically for the type of scale now. In the presence of sulfate, iron, or silica also affects other purification procedures...
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