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Treating Water for Boiler Use Many Harmful Impurities—Sea Water—Condenser Leakage and Makeup Feed — Treatment of Water at Source or at Boiler By L. F. Wilson Lieutenant-Commander, United States Naval Reserve tically all water supplies carry im- purities to a greater or lesser ex- tent. In the operation of either steam or internal combustion power units, close attention to, and full understand- ing of the water conditions is of great- est importance for efficiency and even for safety. Conditions of water im- purity can only be corrected with a purpose of use in mind. It cannot be purified completely by any process, ex- cept distillation, which is not practical in the quantities required for steam power purposes. For human consumption, the organic impurities are those to which greatest attention must be given. For steam purposes, it is the mineral impurities in solution which cause the boiler oper- ator to worry. The United States navy, as everybody knows, operates steam vessels all over the world on salt as well as fresh water. It is not so generally known that the navy is one of the largest operators of stationary plants, however. In large vessel operation every effort is made to return to the boilers as much condensate as possible so that the “make up” water require- ment will be small. To this end the condensers are of the “closed” type and are watched carefully for leaks. In fresh water the proportion of raw water used is not of so much im- portance. Depending upon the nature and proportion of impurities, it is sometimes desirable to operate with raw water proportions up to 100 per cent. In the latter cases condensers are useless. The perfect boiler water would not be pure water but would be one carrying a small amount of dissolved carbonate of lime or mag- nesia. I: IS pretty well known that prac- Common Impurities in Water Supplies Water may be alkaline, neutral or acid; it is generally found to be alkaline. Waters are usually acid when drawn from coal mines or from the vicinity of coal beds. These waters may carry sulphuric acid, which is produced by the oxidation of the pyrites or sulphide or iron, which is always found with coal. In the order of their most frequent occurrence, the more common im- purities in the natural water supplies 26 are named and described as follows: 1. Calcium Carbonate (CaCOs)— Carbonate of lime or chalk is the most common form in which lime occurs in water. It is but slightly soluble in chemically pure water, but when carbonic acid is present it is found in water in the form of bi- carbonate of lime, which is quite soluble. Bicarbonate of lime when carried into a boiler is decomposed by the heat. The carbonic acid is driven off with the steam and normal carbonate of lime is formed, which is practically all precipitated in the boil- er when the temperature reaches 230 degrees Fahr., corresponding to very low boiler pressures. 2. Calcium Sulphate (CaSO,)—Sul- phate of lime or plaster of paris is a common constituent of natural water and is responsible for the hardest kind of boiler scale. Scale formed from sulphate of lime sometimes is as hard as porcelain. It is almost entirely precipitated when the boiler pressure reaches 165 pounds (375 de- grees Fahr.), precipitation being in the form of heavy crystals which at once fasten themselves to the sides of the boiler, forming a scale of great hardness. Sulphate of lime attaches itself to the heating surfaces of the boiler much more firmly than does carbonate of lime. 3. Sodium Chloride (NaCl)—Com- mon salt is a very common impurity varying in amounts from less than one grain to very excessive quantities. It has corrosive action to a consider- able extent. This element also causes foaming and priming due to its cumu- lative properties under the influence of heat and pressure inside the boiler. It greatly increases the surface ten- sion of the water and tends decidedly to cause foaming and priming. 4, Carbonic Acid (CO,)—This sub- stance is found in most natural waters and is the same as the gas which we know in soda and seltzer waters, and is responsible for the presence of many of the mineral impurities, as it holds them in solution in the water. It has corrosive action, manifesting itself in the form of pitting. 5. Sodium Sulphate (Na,SO,)— Glaubers salts are sometimes natur- ally present but are more often con- centrated in boilers artificially as the MARINE REVIEW—July, 1929 result of the reaction between sodium carbonate (soda-ash) and calcium sulphate when soda-ash is used as a treatment. The sodium sulphate is perfectly soluble and its properties are acid which is evidenced in pitting and grooving of heating surfaces. More recently it has been quite definitely proven that this impurity induces electrolytic corrosion by act- ing as_an electrolyte. 6. Magnesium Carbonate (MgCOs) —Magnesia acts in exactly the same manner as carbonate of lime, its bi- carbonate being soluble and its normal carbonate being practically insoluble. Magnesium carbonate is used as lag- ging for boilers and is an excellent noneconductor of heat, but when in the form of boiler scale, it is on the wrong side of the shell. 7. Magnesium Chloride (MgCl.)— This substance is a very objectionable mineral when present in boiler water, it being very corrosive in its action, causing pitting and grooving in boil- ers. 8. Magnesium Sulphate (MgSO,)— Is both corrosive and scale forming. It is a very common constituent of well waters and causes harmful action inside the boiler. 9. Calcium Chloride (CaCl,)—Is sometimes found in mineral water, in which it is very soluble. It does not of itself form scale, but a transfer of acids takes place and calcium sulphate -is formed when other sulphates are present. Its action is chiefly cor- rosive. 10. Silica (SiO,)—Is a very com- mon constituent of the southern water supplies of the United States, forming tough incrustations quite impervious to heat and difficult to counteract after they have once formed upon the inside of a boiler. 11. Sodiwm Carbonate (Na.CO;)— Is spoken of as soda-ash when in commercial form and causes consider- able trouble, particularly in high pres- sure boilers, by causing foaming and lifting of the water. It is not par- ticularly corrosive unless present in excessive amounts. It is used as a treatment for calcium and magnesium sulphate. 12. Iron—Is generally present as a bicarbonate except in the vicinity of coal mines, where it appears frequent-