Chapter 10- PROPULSION BOILERS 



Because the concentration of chloride ions is 

 relatively constant in sea water, the chloride 

 content is used as a measure of the amount of 

 solid matter that is derived through sea water 

 contamination. The results of the chloride test 

 are used as one indication of the need for blow- 

 down. Chloride content is expressed in equiva- 

 lents per million (emp).^ 



Hardness is a property that water acquires 

 because of the presence of certain dissolved 

 salts. Water in which soap does not readily 

 form a lather is said to be hard. 



Alkalinity is a property that the water ac- 

 quires because of the presence of certain im- 

 purities. On ships that make alkalinity tests, 

 the results are expressed in epm. 



Some ships are required to determine the pH 

 value , rather than the alkalinity, of the boiler 

 water. The pH unit does not measure alkalinity 

 directly; however, it is related to alkalinity in 

 such a way that a pH number gives an indication 

 of the acidity or alkalinity of the water. The 

 pH scale of numbers runs from to 14. On 

 this scale, pH 7 is the neutral point. Solutions 

 having pH values above 7 are define das alkaline 

 solutions. Solutions having pH values below 7 are 

 defined as acid solutions. 



Boiler water that is treated with phosphates 

 must be tested for phosphate content . Boiler 

 water that is treated with standard Navy boiler 

 compound is not tested for phosphates. Phos- 

 phate content is expressed in parts per million 

 (ppm). When the phosphate content of boiler 

 water is maintained within the specified limits, 

 the hardness of the water shovild be zero. There- 

 fore, hardness tests are not required for boiler 

 water when phosphate water treatment is used. 



The test for chloride content indicates some- 

 thing about the amount of solid matter that is 

 present in the boiler water, but it indicates only 

 the solid matter that is there because of sea 

 water contamination. It does not indicate any- 

 thing about other solid matter that may be dis- 

 solved in the boiler water. A more accurate 

 indication of the total amount of dissolved solids 



Equivalents per million can be defined as the number 

 of equivalent parts of a substance per million parts of 

 some other substance. The word "equivalent" here 

 refers to the chemical equivalent weight of a substance. 

 For example, if a substance has a chemical equivalent 

 weight of 35.5, a solution containing 35.5 parts per 

 million is described as having a concentration of 1 

 epm. 



can be obtained by measuring the electrical 

 conductivity of the boiler water, since this is 

 related to the total dissolved solid content . All 

 ships are now furnished with special electrical 

 conductivity meters for measuring the conduc- 

 tivity of the boiler water. The total dissolved 

 solid content is expressed in micromhos, a unit 

 of electrical conductivity. 



As a regular routine, the test for dissolved 

 oxygen is made only on feed water, although 

 occasional testing of water in other parts of 

 the system is recommended. A chemical test 

 for dissolved oxygen is made aboard ship. Since 

 this test cannot detect dissolved oxygen in con- 

 centrations of less than 0.02 ppm, more sensi- 

 tive laboratory tests are sometimes made as a 

 check on the operation of the deaerating feed 

 tanks. 



When tests of the boiler water show that the 

 water is not within the prescribed limits, chem- 

 ical treatment and blowdown are instituted. 

 Several methods of chemical treatment are now 

 authorized. Each method is designed to com- 

 pletely eliminate hardness and to maintain the 

 alkalinity (or the pH value) within the prescribed 

 limits. The method of boiler water treatment 

 specified for each ship is the method that will 

 best perform these two functions and, at the 

 same time, take account of the total concen- 

 tration of solids that can be tolerated in the 

 particular type of boiler. The type of water 

 treatment authorized for any particular ship is 

 specified by the Naval Ship Systems Command; 

 it is not a matter of choice by ship's personnel. 



Chemical treatment of the boiler water in- 

 creases, rather than decreases, the need for 

 blowdown. The chemical treatment counteracts 

 the effects of many of the impurities in the 

 boiler water, but at the same time it increases 

 the total amount of solid matter in the boiler 

 water and thus increases the need for blowdown. 

 Each steam boiler must be given a surface blow 

 at least once a day, and more often if the water 

 tests indicate the need. Bottom blows are given 

 at least once a week, usually about an hour after 

 the boiler has been secured. Bottom blows must 

 not be given while a boiler is steaming. Special 

 instructions for boiler blowdown are issued to 

 certain categories of ships. 



COMBUSTION REQUIREMENTS 



Certain requirements must be met before 

 combustion can occur in the boiler furnace. The 

 fuel must be heated to the temperature that will 



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