Boiler Mountings

Topics: Carbon dioxide, PH, Base Pages: 5 (1581 words) Published: January 12, 2013
Boiler Water Tests
Expression of Test Results - PPM (parts per million)
In water treatment, results are most commonly expressed in parts per million (ppm). Other terms commonly encountered are milligrams per liter (mg/l) and grains per gallon (gpg). For practical purposes, 1 ppm = 1 mg/l and 1 gpg = 17.1 ppm. The term “ppm” is unitless; that is, as long as the same units are used on both sides of the relationship, any units can be used. For example, 1 ppm can be used to express all of the following; one ounce per million ounces, one pound per million pounds or one ton per million tons. However, one ppm is not one pound per million gallons because the units are not the same on both sides of the relationship. 1 pound per 1000 gallons = 120 ppm

An item that is 99.9% pure contains 1000 ppm of impurities. A boiler that makes up 4000 gal/day of water having 100 ppm of hardness, has a potential of accumulating over 1000 pounds of scale per year. Alkalinity Test

In natural waters, alkalinity is most commonly the result of bicarbonate and carbonate ions; in treated waters, alkalinity may also be contributed by hydroxide, phosphate, silicate, and other treatment ions. The color changes of phenolphthalein indicator, which occurs at pH of 8.3 (P Alkalinity) and bromcresol green indicator, which occurs at pH 4.2 (Total Alkalinity) are the standard reference points for expressing alkalinity. For boilers operating up to 300 psig, the accepted alkalinity range is 200 ppm to 700 ppm, with P being 60% to 80% of Total Alkalinity. Balances alkalinities are no guarantee of clean, trouble-free boilers. However, this is one of the important factors, together with others, that must be properly controlled if the boiler is to be kept clean. Chloride Test

Chloride ions, unlike other ions that enter the boiler, are extremely soluble and do not precipitate or decompose when subjected to boiler conditions. Therefore, chlorides are used as a measure of boiler water concentrations (i.e. how many times the mineral content--which stays in the boiler when steam is produced--of the raw water has been concentrated or built up in the boiler. The chloride test is used (often in conjunction with the conductivity test) to regulate boiler blowdown. Blowdown is necessary to keep boiler solids (both dissolved and precipitated) from building up to the level where they might cause scale and carryover. Boiler water chlorides limits are set on the ideas that:

1. The boiler should get good fuel efficiency , and,
2. Based on both makeup and treatment dissolved solids, the total boiler water dissolved solids should not go so high that carryover, scaling and corrosion are a potential problem. The chloride test is also useful in determining the percentage of condensate return and in finding out if the condensate is contaminated by process water in-leakage or carryover. Conductivity Test (Boiler and Condensate)

Conductivity is a measure of the ability of water to conduct electric current. The ability to conduct electricity is related to the amount of dissolved (ionizable) solids in the water. Conductivity is generally read in units called micromhos, using a sample which has been neutralized with gallic acid to the phenolphthalein (P) end point. The reason for neutralization is that ions which exist above the P end point contribute disproportionately to the conductivity. The reason for using gallic acid is that it is only slightly ionized and excess gallic acid does not contribute markedly to conductivity. For boilers up to 300 psig, the accepted limit for total dissolved solids (measured gravimetrically, not conductimetrically) is 3500 ppm. About 85% of the time, this results in a conductivity (neutralized) of 4500 micromhos. The limit is set to minimize carryover and excessive scaling/corrosive tendencies. Conductivity can also be used as a quick test for condensate contamination. For this purpose a multiple...
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