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FEED WATER TREATMENT tor Boilers on Great Lakes Vessels is one with which every engineer is familiar. The loss due directly to the insulating properties of the scale alone amounts to a large sum yearly. This waste does not take in- to consideration many other losses also due to scale formation. Almost from the beginning of the operation of steam driven boats on the Great Lages various types of ma- terial have been used for the preven- tion of boiler scale. Up to a few years ago these materials were crude, in- effective and in many cases, harmful. The problem was approached in many different ways, with no consideration given to the proper application and control of the boiler water chemical equilibrium. As a result the patient and conscientious effort of the engi- neer came to naught. The purpose of this article is to make the chemical reactions experi- enced in boiler water treatment more clearly understood. The various phases of the reactions are divided in- to separate groups. Waters of the Great Lakes Our problem is greatly simplified because the waters of the several Great Lakes are of the same type and vary only in the amounts of chemical salts present. It will be noted from the accompanying table giving the chemical analysis of the waters of the Great Lakes, that there are two differ- ent types of salts which make up the hardness of the water. To identify the reactions, the hard- ness elements of the water are divided into two classes called permanent and temporary hardness. In addition to the elements that cause hardness there is another type of salts pres- ent, called sodium salts. Other salts mentioned will not be discussed un- til later as the three tvnes ~ ontionsd above are the only ones with which we need concern ourselves. What Temporary Hardness Is The temporary hardness salts as shown in the analysis in the accom- panying table consist of the carbon- ates and bi-carbonates of calcium and magnesium. Chemically they are expressed as follows: calcium bi-carbonate, Ca (HCO,),; calcium carbonate, Ca CO,; magnesium bi-carbonate, Mg (HCO,),; Magnesium carbonate Mg CO,. Ts: problem of boiler water scale This article was prepared by N. B. Graham. manager, marine department, Elgin Softener Corp., Elgin, Il. ORRECT treatment of water used in marine boilers is now generally recognized as a factor of great importance in good operation. It not only saves fuel cost, but will also prolong the life of the boiler and reduce repairs and replace- ments. In this article the chem- ical reactions experienced in boiler water treatment are de- scribed in a simple and clear manner as an aid to a practical understanding of the problem. These salts under boiler tempera- ture and pressure will decompose and form mud without the use of any treatment whatsoever. The reactions are as follows: Ca (HCO) = FO = heat which yields Ca CO... CO. <> 280 It will be noted that the product of this reaction is Ca CQ,, calcium car- bonate, which is nothing more or less than mud, CO,, carbon dioxide gas and H,O, water. The water we know is harmless. The gas is the primary component of carbonic acid. A large proportion of this gas is carried’ out of the boiler with the steam. Where condensation takes place such as in a surface condenser thiS gas will dis- solve in the condensate forming car- BY N. B. GRAHAM bonie acid and if not neutralized cor- rosion will result. Also, the residue of the gas in the boiler water not carried out by the steam must be neu- tralized or corrosion of the boiler met- al will take place. The mud is chemically inert and the harm it will do to a boiler is of a physical nature rather than of a chemical nature. This is brought about by the quantity of mud in the boiler being allowed to accumulate to such a degree that the mud itself will bake on the heating surface in the form of a soft scale. The action of the magnesium Di-car- bonate, Mg (HCO,), is the same as for calcium bi-carbonate with the excep- . tion that the magnesium hydroxide is the mud product formed. The equa- tion is as follows: Me (HCO,), +H,O + Heat which yields Me (OH), +2 CO, | Bo It will be noticed that in this re- action there are two molecules of car- bon dioxide gas formed while in the calcium bi-carbonate reaction only one molecule was formed. The mud in this case, magnesium hydroxide, Mg(OH),, while having a _ different physical structure has the same ac- tion in the boiler and must be handled in the same manner as tie calcium carbonate. What Permanent Hardness Is The permanent hardness of the lake waters is the salt of magnesium sul- phate, MgSO,. As the water is evapo- rated from the boiler, Salts are left oekind and the concentration of these salts continue to build up and increase in amount until the water becomes saturated or can hold no more. This Chemical Analyses of Great Lakes Waters Chemical Salts Present in Lake Waters - Grains per U. S. Gallon Lake Calcium Carbonate | 1.90 | 4.70 | 3.51 | 5.00 | 4.53 Magnesium Carbonate | 68 | 2.02 | 2.23 | 467 | 2.18 Calcium Sulphate [| Magnesium Sulphate | | eB ee ee Calcium Chloride ee Magnesium Chloride —_, +. -_ —__ Iron & Al Oxide Ol | We Silica fe i Sodium Salts 237 A es a a a a ee Total Solids 3.34 (bees ee a ee ee Alkalinity |. 8.60 | 7.10. 0 ae eee GBS Total Hardness eee ee a ae a 6.26 MARINE REVIEW—July, 1934 tT