The problems here to be faced are many. A proper water treatment program should do the following:
  1) Prevent an adherent sludge from forming on the tubes, etc.
  2) Prevent a scale condition.
  3) Prevent general corrosion of the boiler surfaces.
  4) Prevent localized corrosion due to dissolved oxygen.
  5) Prevent corrosion of the condensate return lines.

Before we begin, let us remember the part about the solubility of calcium carbonate - 11 PPM. With this fact in mind, you will understand why a hard scale can be formed in a steam boiler. In this case we cannot stop the calcium from forming an insoluble deposit, but we can change the physical properties to make it easier to blow down. The best known method is to prevent the calcium carbonate from adhering to under water surfaces. We have found that by adding certain organics such as our product to the boiler water, we can make the condition of the calcium phosphate and magnesium hydroxide quite non-adherent - thus making it easy to blow down property and keep the boiler clean.

Maintaining a pH of the boiler water at 9-11 by using our product prevents general Corrosion - of interior boiler water surfaces.

Pitting -

This type of corrosion is localized and is almost always caused by dissolved oxygen in the boiler water. This corrosion usually occurs at the water line or near it - or at a point where the feed water enters the boiler, in the case of a fire tube boiler. One of the best treatments is the use of D.M Concentrate. This material is an oxygen scavenger - it will absorb oxygen.

Return Line Corrosion -

This type of corrosion is caused by carbon dioxide in the steam condensing in the condensate to produce a dilute solution of carbonic acid. Although the pH is only around 4.5 to 5.0, there is severe corrosion usually at the bottom of the pipe where the condensate flows. There are two treatments: one is the use of a filming amine such as our product. This amine forms a film on the metal, thus acting as a protective coating. The second, and far the more accurate, is the use of neutralizing amine. Such as our product In this process the carbonic acid is neutralized to a pH of 7.8 to 8.4 at which point little corrosion occurs.

Chemical Feeding Systems

A- Low Make-up Systems. (Less than 10% city water). In these systems it is possible to add the chemical to the condensate tank by pump or manually. It is also possible to add by means of by-pass feeder on the feed water line.

B- Moderate Make-up (10-% to 25% of city water). Here the D.M Concentrate and the C.T.N.C are fed to the condensate tank but the Neutratherm amine should be fed to the boiler by means of a chemical pump.

C- High Make-up (over 25% of city water). As in above, however, this system should have a water softener as the chemical costs are high and a lot of steam capacity BTU's are lost due to the necessary blow-down, e.g. 25% blow-down is required for a 100% make-up of city water... where only an 8% blow-down is required for a 100% soft water make-up.

Water Impurities

Natural water contains a variety of impurities, which can drop out of solution when heated, leaving behind deposits, which interfere with proper boiler performance, inhibiting heat transfer and water flow. Water is an excellent solvent, dissolving gases from the air, gases from organics in the soil, suspended matter from the earth, and minerals, chiefly calcium carbonate, magnesium carbonate, calcium sulfate, magnesium sulfate, silica (sand), sodium chloride, sodium sulfate, and small quantities of iron, manganese, fluorides, aluminum, etc. Waters which contain a large proportion of calcium and magnesium are considered "hard to wash with", hence the name hard water. The amount of hardness in natural water can vary from several parts per million to over 500 parts per million. Since calcium and magnesium compounds are relatively insoluble in water, when heated, they tend to precipitate (fall out) of solution, causing scale and corrosion. Since deposits insulate the pipes, they prevent the efficient transfer of heat, causing overheating. If the overheating is severe enough and long enough, the metal fails. Boiler tube deposits can also cause plugging or partial obstruction of boiler tubes, also causing overheating. Corrosion can occur under the deposits, potentially leading to leaks in the tubes.

Natural waters also contain varying levels of oxygen and carbon dioxide, which act as oxidizers, causing both weakening and failure of metal and corrosion byproduct, which add to the boiler deposits.

Thermidaire offers oxygen-scavenging chemicals D.M Concentrate to eliminate oxygen from the system and pH boosters, such as C.T.N.C or C.T.B, to maintain the water in the 9-11. Daily testing by the boiler attendant allows the amount of chemical to be adjusted as needed. Condensate system corrosion is caused by carbon dioxide and oxygen carried into the system by the steam. Condensate corrosion is controlled by neutralizing amines, which neutralize the corrosive effect of the gases found in the return condensate piping and filming amines, which form a protective film on the interior surfaces of the return condensate piping. Neutratherm (Neutralizing amine) or Thermafilm (Filming amine) contains a variety of amine formulas, selected by your Thermidaire representative to compliment your particular water and its problems.

When possible, it is best to obtain boiler feed water from ground-water, as this water is more consistent in composition and contains less suspended matter than surface supplies, which are modified by rainfall and erosion.

A 1/9-inch deposit of scale on the waterside surface increases fuel consumption by 16%; while a 1/8-inch deposit of scale on the waterside increases fuel consumption by 20%. By measuring the difference between the stack temperature and the temperature of the water can indicate the amount of scale that may be present, assuming that the combustion side of the boiler is operating efficiently.

How Does A Boiler Work?

A boiler is water containing vessel which transfers heat from a fuel source (oil, gas, coal) into steam which is piped to a point where it can be used to run production equipment, to sterilize, provide heat, to steam-clean, etc.

The energy given up by the steam is sufficient to convert it back into the form of water. When 100% of the steam produced is returned to be reused, the system is called a closed system. Examples of closed systems are closed steam heating, hot water heating, and "one-pipe" systems.

Since some processes can contaminate the steam, so it is not always desirable to feed the condensate back into the boiler. A system that does not return the condensate is called an open system.

The two main types of boilers are:

Fire tube - the fire or hot gases are directed through the inside of tubes within the boiler shell, which are surrounded by water. The tubes are arranged in banks so that the gases can be passed through the boiler up to 4 times before passing out the stack. This system exposes the maximum heat transfer surface to the water. Fire tube boilers are also known as shell boilers and can produce up to approximately 750 hp or 25,000 lbs. of steam per hour. 80% of boilers in use are of this configuration.

A subtype of this boiler is the packaged boiler, shipped complete with fuel burning equipment, mechanical draft equipment, automatic controls and accessories and is designed to function automatically with a very minimum of attention. It is particularly important to prevent scale formation in this type of boiler.

Water tube - the fire or hot gases are directed to and around the outside of tubes containing water, arranged in a vertical position. Water tube boilers are usually rectangular in shape and have two or more drums. The separation of steam and water takes place in the top drum, while the bottom drum serves as a collection point for sludge. This system is usually used when more than
750 hp or several hundred thousand lbs. of steam per hour are needed.  There are other designs with special configurations, adapting them to particular applications.

Boiler Ratings and Boiler Load

The oldest method of rating boilers, still used to rate small boilers, is by horsepower (hp). One horsepower is defined as the ability to evaporate 34.5 lbs. of water into steam at 212 deg. F and above. Large boiler capacity is generally given in lbs. of steam evaporated per hour, under specified steam conditions. Maximum continuous rating is the hourly evaporation that can be maintained for 24 hours

To convert horsepower (hp) into lbs. of steam: Multiply hp x 34.5
Example: 100 hp x 34.5 = 3450 lbs. of steam per hour

To convert lbs. of steam to hp: Divide steam per hour by 34.5
Example: 8625 lbs. of steam ÷ 34.5 = 250 hp boiler

Another measure is the BTU (British thermal unit). 33,472 BTU equals 1 hp

To convert BTU into hp, divide the BTU rating by 33,472
Example: 8,368,000 BTU ÷ 33,472 = 250

Boiler load - The horsepower, lbs. of steam per hour, or BTU is the rating indicating the maximum capacity of a boiler. When a boiler operates at its maximum rated capacity, it is referred to as maximum load. If the load varies from hour to hour, it operates at a varying load. Load and load variations can influence the amount of chemicals required for treatment and the treatment controls required.

Treatment Options

If you do not treat the water used by your boiler, boiler shutdowns for expensive cleaning will be required to remove the buildup of scale. If the corrosion is sufficient, you may also need to replace your pipes.

Boiler water carryover, the contamination of the steam with boiler water solids, can occur if conditions of excessively high suspended and dissolved solids are present in the water. If the steam is used to sterilize, as in a hospital or food process plant, the solids can cause critical problems by depositing out at the point where the steam is used. In many industrial plants, steam is used directly on the product produced, so that deposit carryover can cause the shutdown of the plant, until the problem can be remedied. Maintaining the cycles of concentration at a low level and using antifoam chemicals can prevent this problem.

You can combine chemical treatment with the removal of solids known as blowdown. Softening agent chemicals, which react with calcium and magnesium to produce a non-adherent, very mobile and readily dispersed sludge, are added to the water to maintain the water at "0" hardness. Either manually wasting boiler water to the drain (bottom blowdown) and/or surface or skimmer blowdown removes the non-adherent sludge. The water wasted is replaced with fresh water, which further dilutes the amount of solids. The combination of this process of dilution and adding chemicals keep the system in control.

Regulating blowdown.

The two tests used to regulate the frequency and volume of blowdown are chloride level and specific conductance. The boiler attendant, who regulates blowdown to keep the solids within limits prescribed by your Thermidaire service representative, should run these tests daily. Since chloride does not react with the chemicals in the water treatment, the cycles of concentration can be calculated by testing this substance. Example: If the makeup chlorides are 20 PPM and boiler water chlorides are 100 PPM, the boiler is at 5 cycles of concentration. If makeup chlorides are at 30 PPM and the boiler water is at 120 PPM, the boiler is at 4 cycles of concentration.

The second test used for regulating blowdown is specific conductance. A conductivity meter is used to measure the conductivity of the "make up" water as compared to the conductivity of the boiler water. The ratio of the two figures is the "cycles of concentration". Example: If the makeup water conductivity is 300 umhos and boiler water conductivity is 2100 umhos, 2100 ÷ 300 equals 7 cycles of Concentration. Corrosion control is maintained by monitoring pH and/or alkalinity. Test strips and meters are available to measure pH

Does the Boiler Need Treatment when it is Out-of-Service?

Unless idle boilers are stored properly, they can corrode badly. Wet lay-up of a boiler is possible as long as the ambient temperature remains above freezing. Before wet storage, the boiler should be inspected, cleaned if necessary, and refilled to the normal water level with dearated feed water. Add the correct dosage of treatment and apply heat for one hour. If the super heater is drainable or the boiler does not have a super heater, allow the boiler to cool slightly after firing. Then, before a vacuum has a chance to form, completely fill the unit with deaerated feed water. After filling the boiler completely, connect a surge tank. This supply will compensate for volumetric changes due to temperature variations. Leave the drain between the non-return and main steam stop valves open wide. Tightly close all other drains and vents.

Test the boiler water once a week from the shutdown boiler, and add extra treatment, as necessary, to maintain minimum levels. When chemicals are added, use an external pump to circulate the boiler water or reduce the water level to the normal operating level and steam the boiler for a short time. Then follow the above directions to lay it up again. If the super heater cannot be drained, fill it with deaerated water and treat it in the same proportion as the boiler.

For dry lay-up, the boiler should be drained, cleaned and dried out. Place an absorbent material, such as hydrated lime or silica gel in trays inside the boiler and seal it to prevent air from seeping into the boiler. Periodic replacement of the drying agent may be required during a long storage period.

What is the Plant Control Test Log?

The plant control test log is the book of forms in which to record the daily tests that are performed to monitor the system and adjust its treatment. Your Thermidaire service representative will prescribe the parameters that should be maintained to keep your system in proper control and will then examine these logs when he makes his regular service visit. If boiler load varies, slight adjustments may be made by the boiler attendant to keep the chemical treatment within the limits set by the Thermidaire representative.

Ask your Thermidaire service representative for one