Proper treatment of make-up waste and boiler water is necessary to prevent scale, or other deposits, and corrosion within the boiler. The absence of adequate external and internal treatment can lead to operational upsets or total boiler failure. Where a choice is available, pretreatment external to the boiler is always preferred and more reliable than treatment within the boiler.

1. Boiler Water Treatment Chemicals
2. Boiler Water Treatment System
3. Boiler Water Treatment Basics
4. Boiler Water Treatment Manual Instructions
5. Drew Marine Boiler Water Treatment Manual Pdf

The treatments are divided along the lines of preboiler and condensate systems, and the boiler itself. The preboiler system is usually treated with pH adjustment chemicals, amines, and oxygen control chemicals, called scavengers.

Water Treatment Manual 5 1 Steam boiler systems 1.1 Introduction A boiler is a steel pressure vessel in which water under pressure is converted into steam by the application of combustion. In other words, it is simply a heat exchanger which uses radiant heat and hot flue gases, liberated from burning fuel, to generate steam and hot water. Page 1: Water Treatment Weil-McLain Easy-Fit This manual must only be used by a qualified heating installer/service technician. Before installing, read all instructions, including this manual, the Ultra Boiler Manual and all applicable Supplements. Basic Boiler Principles HOT WELL DEAERATOR EXTERNAL TREATMENT MAKE UP RETURNED CONDENSATE WATER AND HEAT FEEDWATER WATER AND SOLIDS SATURATED STEAM EVAPORATED WATER Continuous blowdown to remove dissolved solids in boiler water Intermittent blowdown to remove suspended solids in boiler water.

Obtain, and follow, instructions for feedwater treatment, prepared by a competent feedwater chemist. Do not experiment with homemade treatment methods or compounds.

Representative samples of feedwater and boiler water must be analyzed frequently to ensure they are in specification. The following terms and guidelines are to be used in conjunction with the advice of a water treatment specialist.

Recommended Guidelines for Boiler Water Treatment

Use proper water treatment to prevent the buildup of scale on the boiler. After scale has built up on the walls of the boiler it is almost impossible to remove it from the boiler. The introduction of acids in the pressure vessel is thoroughly discouraged, since virtually any solution that will chemically attack the scale will also attack the boiler metal.

pH

The pH value of the boiler water is a number between zero and fourteen. Values below seven are acidic, seven is neutral, and values above seven are alkaline.

The pH factor is the most important factor influencing scale formation and the corrosive tendencies of boiler water. The pH should be maintained between a minimum of 10.5 and a maximum of 11.0 to prevent acidic corrosion of boiler tubes and plates, and to provide for the precipitation of scale forming salts before scale is deposited.

Below a pH of 5.0 the water is acidic enough to dissolve the steel boiler plates. Under these conditions the steel gradually becomes thinner and thinner until its destruction. At a pH between 5 and 9.4 pitting of shell plates will occur at a rate depending on the amount of dissolved oxygen in the boiler.

Dissolved Oxygen

Dissolved oxygen is caused by the solubility of atmospheric oxygen in the supply water. Aeration of the city water supply is frequently used to remove other noxious gasses. Efficient aeration results in saturation of the water with oxygen.

The majority of corrosion problems are directly related to the quantity of dissolved oxygen in the boiler water. Elimination of the corrosive effect of dissolved oxygen can be accomplished both directly and chemically.

Direct or mechanical removal of dissolved oxygen is accomplished through the use of a deaerator or by heating the water to a temperature above 180 degrees F. Heating the water can be done with a preheater or sparge tube installed in the return system.

Chemical deaeration is done through the introduction of specific chemicals in the boiler to react with the oxygen. The dissolved oxygen content should be maintained at a minimum but at no time should it exceed 0.007 mg/l.

Sulfites

Sodium sulfite is generally used for the chemical removal of dissolved oxygen within the boiler water. To assure the rapid and complete removal of the oxygen entering the boiler feedwater system the concentration of sulfite in the boiler must be maintained at a minimum of 20 PPM (parts per million).

Solids

Solids can be broken up into two categories: suspended solids and dissolved solids. Suspended solids are those which can be removed by filtration while dissolved solids are in solution with the water. The best test for the determination of solids content of the boiler water is through a conductance test.

The conductance value of boiler water varies by the various ionized salts present. The conductance can be used to measure the total dissolved solids in the boiler water and to serve as an accurate means of the control of solids through the use of blowdown.

Another test which is sometimes used as a gauge of solids is to measure the chloride present in the boiler water. The ratio of chlorides in the boiler water to that of the feed water can be used as a means to determine the amount of blowdown required. The chloride test is unsuitable for feedwater with low incoming concentrations and the concentrations in the feedwater must be averaged over time for accuracy.

High boiler solids will lead to foaming, priming, surging and carry over. These problems can be overcome by proper, daily blowdown of the boiler.

Alkalinity

The alkalinity of boiler water should be sufficiently high enough to protect shell and plates against acidic corrosion, but not high enough to produce carryover. A minimum value for alkalinity for adequate protection is 200 PPM.

High boiler alkalinity, which is in excess of 700 PPM, should be avoided. Values higher than this can lead to embrittlement of the steel.

Phosphates

Phosphates are used to react with calcium hardness in the boiler water. In order for this reaction to take place it is important to maintain a pH at a minimum value of 9.50. It is desirable to keep the concentration of phosphates in the water to 30 - 50 PPM in order for complete reaction of the phosphates with the calcium hardness entering the boiler through the feedwater.

Hardness

The hardness of water is caused by calcium and magnesium ions which will vary greatly throughout the country depending on the source of the water.

In boilers the hardness of the water can cause the formation of scale and sludge or mud. The hardness must be removed in the makeup water to the return system. Total hardness should not exceed 50 PPM.

Oils

Every effort should be made to prevent oils from getting into the boiler water. Oil causes foaming, or combines with suspended solids to form a sludge which can cause the overheating of boiler plates. If oil does get into the boiler, the boiler should be taken out of service immediately and thoroughly cleaned.

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For industrial companies using a boiler for its facility, some type of boiler feed water treatment system is usually necessary to ensure an efficient process and quality steam generation. The most appropriate boiler feed water treatment system will help the facility avoid costly plant downtime, expensive maintenance fees, and boiler failure as a result of scaling, corrosion, and fouling of the boiler and downstream equipment.

But what is a boiler feed water treatment system and how does it work?

The complex answer to this question (which largely depends on the quality and quantity of makeup water needed for the boiler on an individual basis) is simplified and broken down for you below:

What is a boiler feed water treatment system?

A boiler feed water treatment system is a system made up of several individual technologies that address your specific boiler feed water treatment needs.

Treating boiler feed water is essential for both high- and low-pressure boilers. Ensuring the correct treatment is implemented before problems such as fouling, scaling, and corrosion occur, will go a long way in avoiding costly replacements/upgrades down the line.

An efficient and well-designed boiler feed water treatment system should be able to:

• Efficiently treat boiler feed water and remove harmful impurities prior to entering the boiler
• Promote internal boiler chemistry control
• Control return-line corrosion
• Avoid plant downtime and boiler failure
• Prolong equipment service life

What’s included in a basic boiler feed water treatment system?

Boiler Water Treatment Chemicals

As mentioned above, the exact components of a boiler feed water treatment system depend on the quality of water being drawn from in relation to the quality of water makeup needed for the specific boiler (according to the manufacturer’s recommendations), but in general, a basic boiler feed water treatment system typically includes some type of:

• Filtration and ultrafiltration
• Ion exchange/softening
• Membrane processes such as reverse osmosis and nanofiltration
• Deaeration/degasification
• Coagulation/chemical precipitation

Depending on the impurities present in your water, any combination of these treatments might best suit your facility and make up your treatment system, and depending on the needs of your plant and process, these standard components are usually adequate. However, if your plant requires a system that provides a bit more customization, there might be some features or technologies you will need to add on.

What does a boiler feed water treatment system typically remove?

A boiler feed water treatment system might be made up of the technologies necessary to remove problematic dissolved solids, suspended solids, and organic material, including any number of the following:

Boiler Water Treatment System

• Iron: either soluble or insoluble, iron can deposit on boiler parts and tubes, damage downstream equipment, and affect the quality of certain manufacturing processes
• Copper: can cause deposits to settle in high-pressure turbines, decreasing their efficiency and requiring costly cleaning or equipment change-outs
• Silica: if not removed to low levels, especially in high-pressure boilers, silica can cause extremely hard scaling
• Calcium: can cause scaling in several forms depending on the chemistry of the boiler feed water (e.g. calcium silicate, calcium phosphate, etc.)
• Magnesium: if combined with phosphate, magnesium can stick to the interior of the boiler and coat tubes, attracting more solids and contributing to scale
• Aluminum: deposits as scale on the boiler interior and can react with silica to increase the likelihood of scaling
• Hardness: also causes deposits and scale on boiler parts and piping
• Dissolved gasses: chemical reactions due to the presence of dissolved gases such as oxygen and carbon dioxide can cause severe corrosion on boiler pipes and parts

How does a boiler feed water treatment system work?

Specific treatment processes vary depending on the requirements of the boiler and quality/chemistry of the feed and makeup water, but a typical boiler feed water treatment system will usually include the following steps:

Makeup water intake

Makeup water, or the water replacing evaporated or leaked water from the boiler, is first drawn from its source, whether raw water, city water, city-treated effluent, in-plant wastewater recycle (cooling tower blowdown recycle), well water, or any other surface water source.

Coagulation and chemical precipitation

After all the large objects are removed from the original water source, various chemicals are added to a reaction tank to remove the bulk suspended solids and other various contaminants. This process starts off with an assortment of mixing reactors, typically one or two reactors that add specific chemicals to take out all the finer particles in the water by combining them into heavier particles that settle out. The most widely used coagulates are aluminum-based such as alum and polyaluminum chloride.

Sometimes a slight pH adjustment will help coagulate the particles, as well.

Filtration and ultrafiltration

The next step is generally running through some type of filtration to remove any suspended particles such as sediment, turbidity, and certain types of organic matter. It is often useful to do this early on in the process, as the removal of suspended solids upstream can help protect membranes and ion exchange resins from fouling later on in the pretreatment process. Depending on the type of filtration used, suspended particles can be removed down to under one micron.

Ion exchange softening

When pretreating boiler feed water, if there’s high hardness complexed with bicarbonates, sulphates, chlorides, or nitrates, a softening resin can be used. This procedure uses a strong acid cation exchange process, whereby resin is charged with a sodium ion, and as the hardness comes through, it has a higher affinity for calcium, magnesium, and iron so it will grab that molecule and release the sodium molecule into the water.

Boiler Water Treatment Basics

Dealkalization

After the softening process, some boiler feed water treatment systems will utilize dealkalization to reduce alkalinity/pH, an impurity in boiler feed water that can cause foaming, corrosion, and embrittlement. Sodium chloride dealkalization uses a strong anion exchange resin to replace bicarbonate, sulfate, and nitrate for chloride anions. Although it doesn’t remove alkalinity 100%, it does remove the majority of it with what can be an easy-to-implement and economical process. Weak acid dealkalization only removes cations bound to bicarbonate, converting it to carbon dioxide (and therefore requiring degasification). It is a partial softening process that is also economical for adjusting the boiler feed water pH.

Reverse osmosis (RO) and nanofiltration (NF)

Reverse osmosis (RO) and nanofiltration (NF) are often used down the line in the boiler feed water treatment system process so most of the harmful impurities that can foul and clog the RO/NF membranes have been removed. Similar processes of separation, they both force pressurized water through semipermeable membranes, trapping contaminants such as bacteria, salts, organics, silica, and hardness, while allowing concentrated, purified water through. Not always required in boiler feed water treatment, these filtration units are used mostly with high-pressure boilers where concentration of suspended and dissolved solids needs to be extremely low.

Deaeration or degasification

At this point in the boiler feed water treatment process, any condensate being returned to the system will mix with the treated makeup water and enter the deaeration or degasification process. Any amount of gasses such as oxygen and carbon dioxide can be extremely corrosive to boiler equipment and piping when they attach to them, forming oxides and causing rust. Therefore, removing these gases to acceptable levels (nearly 100%) can be imperative to the service life and safety of the boiler system. There are several types of deaeration devices that come in a range of configurations depending on the manufacturer, but generally, you might use a tray- or spray-type deaerator for degasification or oxygen scavengers.

Distribution

After the boiler feed water has been sufficiently purified according to the boiler manufacturer’s recommendation and other industry-wide regulations, the water is fed to the boiler where it is heated and used to generate steam. Pure steam is used in the facility, steam and condensate are lost, and condensate return is pumped back into the process to meet up with the pretreated makeup water to cycle through pretreatment again.

In conclusion

Boiler Water Treatment Manual Instructions

SAMCO has over 40 years of experience helping our customers design and custom-engineer boiler feed water treatment systems. If you have any questions, be sure to visit our website for more information about boiler feed water treatment here. We also have an article you might be interested in about how much a boiler feed water treatment system might cost you and who we recommend as qualified boiler feed water treatment companies for you to consider as you search for all the options available for your plant.

Drew Marine Boiler Water Treatment Manual Pdf

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