APPROXIMATE CLASSIFICATION OF IMPURITIES FOUND IN FEED WATERS
THEIR EFFECT AND ORDINARY METHODS OF RELIEF
+-----------------------+--------------+-----------------------------+
| Difficulty Resulting | Nature of | Ordinary Method of |
| from Presence of | Difficulty | Overcoming or Relieving |
+-----------------------+--------------+-----------------------------+
| Sediment, Mud, etc. | Incrustation | Settling tanks, filtration, |
| | | blowing down. |
| | | |
| Readily Soluble Salts | Incrustation | Blowing down. |
| | | |
| Bicarbonates of Lime, | Incrustation | Heating feed. Treatment by |
| Magnesia, etc. | | addition of lime or of lime |
| | | and soda. Barium carbonate. |
| | | |
| Sulphate of Lime | Incrustation | Treatment by addition of |
| | | soda. Barium carbonate. |
| | | |
| Chloride and Sulphate | Corrosion | Treatment by addition of |
| of Magnesium | | carbonate of soda. |
| | | |
| Acid | Corrosion | Alkali. |
| | | |
| Dissolved Carbonic | Corrosion | Heating feed. Keeping air |
| Acid and Oxygen | | from feed. Addition of |
| | | caustic soda or slacked |
| | | lime. |
| | | |
| Grease | Corrosion | Filter. Iron alum as |
| | | coagulent. Neutralization |
| | | by carbonate of soda. Use |
| | | of best hydrocarbon oils. |
| | | |
| Organic Matter | Corrosion | Filter. Use of coagulent. |
| | | |
| Organic Matter | Priming | Settling tanks. Filter in |
| (Sewage) | | connection with coagulent. |
| | | |
| Carbonate of Soda in | Priming | Barium carbonate. New feed |
| large quantities | | supply. If from treatment, |
| | | change. |
+-----------------------+--------------+-----------------------------+
It is evident that the whole subject of boiler feed waters and their
treatment is one for the chemist rather than for the engineer. A brief
outline of the difficulties that may be experienced from the use of poor
feed water and a suggestion as to a method of overcoming certain of
these difficulties is all that will be attempted here. Such a brief
outline of the subject, however, will indicate the necessity for a
chemical analysis of any water before a treatment is tried and the
necessity of adapting the treatment in each case to the nature of the
difficulties that may be experienced.
Table 14 gives a list of impurities which may be found in boiler feed
water, grouped according to their effect on boiler operation and giving
the customary method used for overcoming difficulty to which they lead.
Scale--Scale is formed on boiler heating surfaces by the depositing of
impurities in the feed water in the form of a more or less hard adherent
crust. Such deposits are due to the fact that water loses its soluble
power at high temperatures or because the concentration becomes so high,
due to evaporation, that the impurities crystallize and adhere to the
boiler surfaces. The opportunity for formation of scale in a boiler will
be apparent when it is realized that during a month's operation of a 100
horse-power boiler, 300 pounds of solid matter may be deposited from
water containing only 7 grains per gallon, while some spring and well
waters contain sufficient to cause a deposit of as high as 2000 pounds.
The salts usually responsible for such incrustation are the carbonates
and sulphates of lime and magnesia, and boiler feed treatment in general
deals with the getting rid of these salts more or less completely.