The pressures to achieve improved reliability and performance of cooling water systems while reducing costs have always existed. When left uncontrolled, corrosion and deposition can lead to unscheduled maintenance and turnarounds, production bottlenecks, and significant capital expenses. Further without effective processes and treatment to control microbiological growth, businesses could expose their employees and community to health risks.
Today, this is all compounded by an ever-increasing need to reduce water consumption and be a better environmental steward.
The WWI Advanced Cooling Solution is an innovative offering that can help you monitor, control and maintain your cooling systems with greater efficiency, reliability, and predictability. It lowers your total cost of ownership and minimizes the environmental impact of your operation.
The Advanced Cooling Solution combines the revolutionary monitoring and control capabilities of True Sense with the unparalleled, patented chemistry of WWI *, remote information management that is wireless enabled for speed of implementation, along with the most complete portfolio of filtration and products for side stream softening, filtering, and wastewater reuse.
Shortage OF Sulfuric Acid/Alternative By Water World International
There is a severe global sulfuric acid shortage WWI , driven by several factors including high phosphate fertilizer demand and H2SO4 plant outages WWI s across the globe. Prices in some areas have more than doubled. Supply is dwindling. WWI Water & Process Technologies can help those who use sulfuric acid in their cooling towers with the following programs:
Conversion to AEC Alkaline Cooling Technology. WWI 's AEC alkaline technology allows you to operate at higher calcium carbonate super saturation levels, in many cases up to an LSI of +2.85 under standard industrial conditions of lower flow velocities and higher heat loads, and an LSI of +3.00 in conditions of lower stress, such as reduced heat load and higher flow velocities.
Are you under acid allocation? It may be possible to eliminate acid from your operations completely by operating at a higher pH and reducing cycles of concentration (if necessary). Contact WWI for details on how to make this program work for you.
Putting Reverse Osmosis (RO) in front of your demineralizer or softener. Doing so can reduce or even eliminate both acid and caustic costs, improve water quality, reduce wastewater WWI neration, and eliminate chemical handling hazards. Contact WWI to calculate the cost-effectiveness of replacing your primary cation/anion demineralizers with RO and/or EDI.
Even in the best of times, sulfuric acid is a potential hazard in your plant. With the recent sulfuric acid shortage ,WWI and the spike in price, now might be a good time to consider making a change WWI .
Boiler Water treatment
There is a definite legal and moral responsibility on the part of the management to ensure reliable, continuous and efficient operation of the steam boiler and to ensure that no damage to equipment or physical hazard occurs.
Water, we have seen, contains many impurities and the design and operation of modern steam boilers is such that proper feed water treatment is an absolute necessity.
Boiler Scale and Deposits
Boiler scale is caused by impurities being precipitated out of the water directly on heat transfer surfaces or by suspended matter in water settling out on the metal and becoming hard and adherent. The evaporation in the boiler causes impurities to concentrate.
In untreated boiler water, the formation of scale is like a "back to nature" movement. As minerals are deposited out from water they from many types of crystalline and rock-like structures. The most common scale in boilers is due to carbonate deposits caused by hardness.
Carbonate scale is usually granular and sometimes very porous. A carbonate scale can be easily identified by dropping it in a solution of hydrochloric acid. Bubbles of carbon dioxide will effervesce from the scale.
Sulphates scales are harder and more dense. A sulphate deposit is brittle and does not effervesce when dropped in acid. Silica scales resemble porcelain. This scale is very brittle, is not soluble in acid, and dissolves slowly in alkali.
Iron deposits are very dark colored. The are either due to corrosion or iron contamination in the water. They are soluble in hot acid giving a dark brown solution.
Problems Caused by Scale
The biggest problem caused by scale is overheating and failure of boiler tubes. The thermal conductivity of porous boiler scale is similar to insulating brick. The scale acts as an insulating layer and prevents an efficient transfer of heat through the tubes to the circulating water. The reduction in thermal conductivity means lower boiler efficiency which in turn leads to overheating and may result in the softening, bulging or even fracturing of the boiler tubes. Boiler scale can also cause plugging or partial obstruction of circulating tubes in a water tube boiler, which again causes starvation and overheating of the tubes.
Another important aspect is that corrosion may occur under the boiler scale. In general, boiler scale causes
a. increased fuel bill by decreasing the operating efficiency
b. thermal damage
c. unscheduled down-time
d. increased cleaning time and cleaning costs
e. reduced working life of a boiler.
Corrosion
Corrosion is one of the most serious problems in boiler operation. Dissolved oxygen and carbon dioxide are the two gases which are mainly responsible for this.
What is corrosion? Stated simply, corrosion is the reversion of a metal to its ore form. Iron, for example, reverts to iron oxide as the result of corrosion.
Corrosion takes many forms, it may produce general attack over a large metal surface or it may result in pinpoint penetration of metal. Corrosion often occurs in standby boilers due to the exposure of wet metal to the oxygen in the air.
CORROSION DAMAGE IS IRREVERSIBLE.
Magnetite
Boiler steel is often protected from the effects of corrosion by a thin layer of magnetite. This thin film is found to be most stable in the pH range 11-12 and provided the film remains intact, the underlying steel will not corrode. Dissolved oxygen constitutes the main danger to this protective sheath. An additional advantageous property of a magnetite film is its excellent thermal conductivity, i.e. heat transfer efficiency is promoted by magnetite.
Caustic Cracking
This is a special type of corrosion, often referred to as caustic embrittlement. Boiler metal failure is characterized by continuous mostly inter-granular cracks. For this type of cracking to occur
a. the metal must be under stress
b. the boiler water must contain caustic, and
c. there must be a leakage of steam or boiler water.
This is a particular problem in riveted boilers and the rolled tube ends in modern boilers are also vulnerable areas of attack.
Carryover
Carryover describes the contamination of the steam with boiler water. It can be due to FOAMING when bubbles are formed on the surface and are carried out with the steam. High concentration of solids in the boiler water cause foaming, as well as soil and other contamination of the feed water.
Carryover can also be due to PRIMING when slugs of boiler water are thrown over the steam. This is often caused by excessive steam demand or rapid increase in load. In severe cases of priming top tubes can be exposed and subject to overheating. The effects of carryover can be quite serious. The steam will be contaminated; water hammer may occur; slugs of boiler water can damage machinery; dissolved or suspended solids in the boiler water will deposit in the steam and condensate system.
POOR WATER GIVES POOR STEAM
In conclusion, water impurities cause scale and steam contamination, dissolved gases in water cause corrosion. These impurities lead to scale formation and result in inefficient operation, increased fuel cost and boiler damage. To protect a boiler from thermal damage and from the irreversible damage caused by corrosion, effective boiler water treatment is an absolute necessity.
Boiler Losses due to scale
Thickness of Scale |
Increase in fuel consumption due to scale |
|
|
0.5 mm |
2 % |
1 mm |
4 % |
2 mm |
6 % |
4 mm ( 0.125” ) |
10 % |
8 mm ( 0.25” ) |
20 % |
16 mm ( 0.5” ) |
40 % |
30 mm (1” ) |
80 % |
Boiler Water Treatment (Internal /External) Treatment prevents all:
- Corrosion;
- Fouling;
- Steam Contamination;
- Caustic Embrittlement.
External treatment
The water treatment facilities purify and deaerate make-up water or feed water. Water is sometimes pretreated by evaporation to produce relatively pure vapor, which is then condensed and used for boiler feed purposes. Evaporators are of several different types, the simplest being a tank of water through which steam coils are passed to heat the water to the boiling point. Sometimes to increase the efficiency the vapor from the first tank is passed through coils in a second tank of water to produce additional heating and evaporation. Evaporators are suitable where steam as a source of heat is readily available. They have particular advantages over demineralization, for example, when the dissolved solids in the raw water are very high.
Certain natural and synthetic materials have the ability to remove mineral ions from water in exchange for others. For example, in passing water through a simple cation exchange softener all of calcium and magnesium ions are removed and replaced with sodium ions. Since simple cation exchange does not reduce the total solids of the water supply, it is sometimes used in conjunction with precipitation type softening. One of the most common and efficient combination treatments is the hot lime-zeolite process. This involves pretreatment of the water with lime to reduce hardness, alkalinity and in some cases silica, and subsequent treatment with a cation exchange softener. This system of treatment accomplishes several functions: softening, alkalinity and silica reduction, some oxygen reduction, and removal of suspended matter and turbidity.
Chemical treatment of water inside the boiler is usually essential and complements external treatment by taking care of any impurities entering the boiler with the feed water (hardness, oxygen, silica, etc.). In many cases external treatment of the water supply is not necessary and the water can be treated only by internal methods.
Internal treatment
Internal treatment can constitute the unique treatment when boilers operate at low or moderate pressure, when large amounts of condensed steam are used for feed water, or when good quality raw water is available. The purpose of an internal treatment is to
1) react with any feed-water hardness and prevent it from precipitating on the boiler metal as scale;
2) condition any suspended matter such as hardness sludge or iron oxide in the boiler and make it non-adherent to the boiler metal;
3) provide anti-foam protection to allow a reasonable concentration of dissolved and suspended solids in the boiler water without foam carry-over;
4) eliminate oxygen from the water and provide enough alkalinity to prevent boiler corrosion.
In addition, as supplementary measures an internal treatment should prevent corrosion and scaling of the feed-water system and protect against corrosion in the steam condensate systems.
During the conditioning process, which is an essential complement to the water treatment program, specific doses of conditioning products are added to the water. The commonly used products include:
- Phosphates-dispersants, polyphosphates-dispersants (softening chemicals): reacting with the alkalinity of boiler water, these products neutralize the hardness of water by forming tricalcium phosphate, and insoluble compound that can be disposed and blow down on a continuous basis or periodically through the bottom of the boiler.
- Natural and synthetic dispersants (Anti-scaling agents): increase the dispersive properties of the conditioning products. They can be:
- Natural polymers: lignosulphonates, tannins
- Synthetic polymers: polyacrilates, maleic acrylate copolymer, maleic styrene copolymer, polystyrene sulphonates etc.
- Sequestering agents: such as inorganic phosphates, which act as inhibitors and implement a threshold effect.
- Oxygen scavengers: sodium sulphite, tannis, hydrazine, hydroquinone/progallol-based derivatives, hydroxylamine derivatives, hydroxylamine derivatives, ascorbic acid derivatives, etc. These scavengers, catalyzed or not, reduce the oxides and dissolved oxygen. Most also passivate metal surfaces. The choice of product and the dose required will depend on whether a deaerating heater is used.
- Anti-foaming or anti-priming agents: mixture of surface-active agents that modify the surface tension of a liquid, remove foam and prevent the carry over of fine water particles in the steam.
The softening chemicals used include soda ash, caustic and various types of sodium phosphates. These chemicals react with calcium and magnesium compounds in the feed water. Sodium silicate is used to react selectively with magnesium hardness. Calcium bicarbonate entering with the feed water is broken down at boiler temperatures or reacts with caustic soda to form calcium carbonate. Since calcium carbonate is relatively insoluble it tends to come out of solution. Sodium carbonate partially breaks down at high temperature to sodium hydroxide (caustic) and carbon dioxide. High temperatures in the boiler water reduce the solubility of calcium sulphate and tend to make it precipitate out directly on the boiler metal as scale. Consequently calcium sulphate must be reacted upon chemically to cause a precipitate to form in the water where it can be conditioned and removed by blow-down. Calcium sulphate is reacted on either by sodium carbonate, sodium phosphate or sodium silicate to form insoluble calcium carbonate, phosphate or silicate. Magnesium sulphate is reacted upon by caustic soda to form a precipitate of magnesium hydroxide. Some magnesium may react with silica to form magnesium silicate. Sodium sulphate is highly soluble and remains in solution unless the water is evaporated almost to dryness.
There are two general approaches to conditioning sludge inside a boiler: by coagulation or dispersion. When the total amount of sludge is high (as the result of high feed-water hardness) it is better to coagulate the sludge to form large flocculent particles. This can be removed by blow-down. The coagulation can be obtained by careful adjustment of the amounts of alkalis, phosphates and organics used for treatment, based on the fee-water analysis. When the amount of sludge is not high (low feed water hardness) it is preferable to use a higher percentage of phosphates in the treatment. Phosphates form separated sludge particles. A higher percentage of organic sludge dispersants is used in the treatment to keep the sludge particles dispersed throughout the boiler water.
The materials used for conditioning sludge include various organic materials of the tannin, lignin or alginate classes. It is important that these organics are selected and processed, so that they are both effective and stand stable at the boiler operating pressure. Certain synthetic organic materials are used as anti-foam agents. The chemicals used to scavenge oxygen include sodium sulphite and hydrazine. Various combinations of polyphosphates and organics are used for preventing scale and corrosion in feed-water systems. Volatile neutralizing amines and filming inhibitors are used for preventing condensate corrosion.
Common internal chemical feeding methods include the use of chemical solution tanks and proportioning pumps or special ball briquette chemical feeders. In general, softening chemicals (phosphates, soda ash, caustic, etc.) are added directly to the fee-water at a point near the entrance to the boiler drum. They may also be fed through a separate line discharging in the feed-water drum of the boiler. The chemicals should discharge in the fee-water section of the boiler so that reactions occur in the water before it enters the steam generating area. Softening chemicals may be added continuously or intermittently depending on feed-water hardiness and other factors. Chemicals added to react with dissolved oxygen (sulphate, hydrazine, etc.) and chemicals used to prevent scale and corrosion in the feed-water system (polyphosphates, organics, etc.) should be fed in the feed-water system as continuously as possible. Chemicals used to prevent condensate system corrosion may be fed directly to the steam or into the feed-water system, depending on the specific chemical used. Continuous feeding is preferred but intermittent application will suffice in some cases.
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