Document Z8yV2axwmjDe7KbQ6RMd7aBa8

734 CHAPTER 55 1959 Guide Table 1 .... Mineral Analyses Typifying Composition of Waters Available and Used industrially in the USA location or Area*'* Unit ID 12) 13) 14) (5) (6) 17) 16} 19) Calcium................ Magnesium.......... Sodium.................. Potassium............ Ca Mg Na K 6 5 36 62 92 96 3 155 400 1 2 8 18 34 27 2 46 1,300 2 6 7 44 8 183 215 78 11,000 111 1 18 10 3 400 Bicarbonate........ Sulfate.................. Chloride................ HCOj SO, Cl 14 13 no 202 339 334 549 210 150 10 2 22 135 84 121 11 38S 2,700 2 10 13 13 10 280 22 117 19,000 Dissolved Carbonate Hardness... . Non-Carbonate Hardness.......... CaCO, CaSO 12 11 98 165 287 274 5 7 18 40 58 54 94 35,000 8 172 125 0 295 5,900 * All nlun sue parte per million of the unit cited to aeareet whole dumber (aee Betemee )._ b Number* utdkete location or area aa follow*: <1} cvt-vni aupply--New Ycck City (I) Swamp Water (Colored) Black Creek, Middleburg, Florida (I) Nta(ara River (Filtered) Nta^ra Falls, New York (4) Mlteumi River (Untreated) Avenfe (5) Well Waters--Public Sopply--Dayton, Ohio--30-40 ft (V) Well Water--Maywood, DViiu.iU 3090 ft (7) WeQ Water--SmithSeld. Va.--330 It (8) Well Wats--RuOTeeil, N. Mexico (9) Ocean Water--Avene* of dissolved gases such as carbon dioxide, oxygen, and sulfur dioxide,- that tend to make them corrosive. Dissolved gases are the main factors affecting condensate corrosiveness, but they may also be present in water con taining mineral impurities to an extent that will make the water corrosive. Mineralized Waters All the waters found in streams, wells, lakes, and the ocean are mineralized. The same is true of all municipal supplies even though they may have been treated. For a given' area, ground waters are likely to be more highly mineralized than are surface waters. Conversely, surface waters are more likely to be contaminated with municipal sewage and trade wastes. Virtually all mineralized waters also contain biologi cal organisms. Mineralogical Characteristics. The character and amount of extraneous inorganic materials--including deleterious gases--dissolved and suspended therein, describe the miner alogies! characteristics of any water. Revealing such infor mation is the function of a mineralogical chemical analysis. The analyses in Table 1 diwlnse the composition of the public water supplies used by about 45 percent of the total population of the cities, in the United States, having more than 20,000 inhabitants.* All values recorded are in terms of parts per million* * Pert* per mOliao ere hereinafter abbreviated ppa. A part per million sitnifice a unit weight of material per million unit weighte of the eolation. Table 2 .... Conversion Factors for Water Analyses To Coavarf Into Multiply by Grains per U. S. gallon...................... Grains per Imperial gallon................ Grams per liter...................................... Mg per liter............................................ ppm ppm ppm ppm 17 14)i 1000 1 This is the approved standard terminology for reporting the results of mineral analyses * Values reported in the other terms commonly used may be converted into the standard form by using the factors listed in Table 2. Data for dissolved gases or pH values have been omitted in Table 1 because even waters of the same mineral contents may vary widely in these respects. Unpolluted natural waters usually have pH values within the range 5 to S, de pending upon their free CO* contents. Polluted waters, which include those derived from wells or swamps in marshy ground, may have pH values well below 5. Biological Characteristics. The slime-forming organisms are mostly lower plants, grouped by botanists into the phylum thallophyta. This group is distinguished by the absence of leaves, roots, or stems from the mosses, ferns, and seed plants which comprise the three other phyla of the plant kingdom. The thallophyta (see Table 3) are divided into algae, which can synthesize chlorophyll for the production of sugar, and the fungi which lack chlorophyll, and must therefore secure already synthesized carbohydrates. All thallophyta are of universal distribution and many of them are dime-forming. Of the five divisions of algae, only three (the green, the blue-green, and the diatoms) are found in fresh water. Of the five divisions of fungi, all may occur in fresh water, the principal slime formers being indicated in Table 3. The methods of analysis commonly used in the sanitary examination of a water have, as their principal object, to identify and count pathogens. Most slime-forming organisms are not pathogens. When a water is subjected to a biochemical analysis for the purpose of evaluating its slime producing characteristics, tests, widely different from sanitary bacteriological tests, must be made. Tests upon the water itself are seldom satisfactory, and true indications of the sliming characteristics of a water'can Phyla Table 3 .... Principal Slime Formers Kongii Diririon of Pfiyta . Algae Single celled, sometimes forming slimy sheets. Many celled in either sheets or fronds. Fungi Bacteria (Schizomycetes) frequently forming slimy surface coatings. Slime Molds (Myxomycetes) forming slimy sheets as one stage of their life history. Sac fungi (Ascomycetes) of which one division, the yeasts, occasionally form slimy aggregates. The alga-like fungi {Pkycomyeeles) and the stalked fungi (Basidomycetes) rarely form slimes but their filaments may hold together the slimes of other organisms. Corrosion and Water-Formed Deposits, Causes and Prevention 735 only .be .determined by the analysis of deposits on surfaces having a temperature, that approximates the operating tem perature range of the final design equipment. The results of such tests are commonly used for selecting proper pre ventive measures. Slime and algae micro-organisms are capable of rapid multiplication and, if not controlled, can cause shut-down or permanent damage to equipment. They can be controlled by chemical treatment of the water or in certain cases by mechanical cleaning of the surfaces affected. The chemicals used are usually toxic, and should therefore be handled only by trained personnel having a full understanding of the quantity required and their effect on operators as well as surfaces. Chemical treatment is usually preferred to mer.ha.nir.al cleaning particularly where surfaces are inaccessible for cleaning or where a shut-down of the operation is necessary for mechanical cleaning. Condensates All condensates are caused by the cooling of vapor. Con densates resulting from the cooling of water vapor in air are dews, sweats, ram, and snow, while those formed in steamcondensing apparatus are termed condensates or return water. In the heating and ventilating field, the biological charac teristics of condensates are likely to be of concern only where the condensate is used as cooling water in recirculating systems. The deleterious gas contents of condensates, how ever, very often' create serious corrosion troubles. The data in Table 4 typify the chemical composition of Table 4 .... Data Typifying the Deleterious Gas Content of Different Atmospheres Air Norm of Gat fo""*. Rural %by Volume Partial pressure pda Metropofitoo %b. Volume Partial Pretwre pdo Oxygen........ Carbon Dioxide... Sulfur Dioxide... O, CO, so. 21 3.143 0.03 -<T004 None None 21 006 0.003 3.143 0.009 0.004 Rue Gate, Blfum. Coal Fuel Oib Natural Gas Nome of Gat Uiemicof Partial Partial pret pres %by Volume wre % by Volume sure % *>, Volume Partial pres sure psia pdo psia Oxygen........ Carbon Dioxide... Sulfur Dioxide... o, CO. so. 2 0.299 7 1.048 10 1.497 15 2.245 13 1.946 10 1.497 0.07 0.010 0.03 0.004 0.0001 0.0015 Fig. 1 .... Solubility of Gases at Partial Pressure of 1 Psi the atmosphere in rural and metropolitan areas, and of stack gases when various types of common fuels are used. The curves in Fig. 1 disclose the solubility of the major deleterious gases present in such atmospheres in otherwise pure water, when the partial pressure of the gas is one psia. The most common deleterious gases entrained by steam are oxygen and carbon dioxide. In rare instances, hydrogen sulfide, sulfur dioxide, or ammonia are present. In most steam-condensing equipment/' * the non-condens able gases entrained with steam accumulate so that the amount present in the vapor space is several hundred times higher than in the incoming steam and the amount dis solved in the condensate may therefore approach, or even exceed for short periods, the amount entrained by the steam. CAUSES AND PREVENTION OF SCALES AND SLUDGES Scales may be formed on surfaces of equipment in contact with water, and sludges in the body of the water, by the separation from the water of dissolved or suspended solids. According to the nature of a particular piece of equipment and the method of its operation, such separation may be promoted by one or more than one, of several factors: a. The concentration of solids may be increased by the evaporation of water. b. The dissolved solids may be rendered less soluble in the water by changes in temperature. - c. Conditions may favor the decomposition of unstable compounds with the formation of less soluble compounds. Figs, 2 and 3 show that the solubilities of both calcium carbonate and calcium sulfate decrease with the rising temperature within a moderate range of temperatures. Sur faces transferring heat into water, such as condensers and