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In Short,
The Purpose of Water Treatment:
1. To remove the accumulation of any hard-adherent scale from the water side (tubes or walls) of boilers, hot water tanks, steam cookers, etc.
2. To prevent the formation of scale.
3. To inhibit corrosion.
Butler Cathodic Protectors have been tested and approved for toxicity by the New York City Board of Standards and Appeals. By-products of BUTLER CATHODIC PROTECTORS are non-pollutant.
BUTLER CATHODIC PROTECTORS give a two-fold protection against scale and corrosion. Galvanic current flows from anode to cathode and results in:
1. Cathodic Protection
2. Electrochemical reaction on the Butler anode which automatically releases metallic ions into the electrolyte.
The resulting chemical reaction between the zinc and/or magnesium and the other ions from the Butler anodes with the mineral salts completes the cycle.
BUTLER CATHODIC PROTECTORS are easily installed and removed.
Since 1938 BUTLER CATHODIC PROTECTORS have been meeting the objectives for water treatment automatically and effectively without the frequent and costly attention required by chemical treatment. Frequent additions of chemicals or boiler water tests are completely eliminated. The only maintenance required is regularly scheduled blowdown.
BUTLER CATHODIC PROTECTORS are galvanic cells consisting of a sacrificial anode of either zinc or magnesium alloy enclosed by its own cathode. When the Butler sacrificial anode is enclosed by its own helical-wound silver plated cathode and submerged in the boiler water (the electrolyte), it becomes an automatic chemical ion dispenser. This assures a constant flow of ions from the sacrificial anode to the boiler water. When the sacrificial anode is in positive contact with the tubes or metal of the boiler it also becomes a high-conductivity cathodic protection anode. This combined activity gives the boiler both chemical treatment and cathodic protection.
BUTLER CATHODIC PROTECTORS have been used in hot water and steam generators and potable hot water tanks since 1938. The original design and alloys for the anodes were established by consulting research scientists from Tulane University in New Orleans, Louisiana.
The number and type of BUTLER CATHODIC PROTECTORS required for each boiler are determined from a scientific formula which takes into consideration the size and type of boiler or vessel, operating pressure and temperature, the percentage of makeup and the pH and hardness of the raw water. The determining factors for hot water tanks is the capacity and quantity of water used. BUTLER CATHODIC PROTECTORS are available for boilers and tanks (hot water to 150 psig).
Technical Explanation:
Most feed water for boilers is composed of varying quantities of the following salts: NaCl (sodium chloride), NaHCO3 [sodium bicarbonate], CaSO4 [calcium sulfate] and small amounts of other impurities. After the BUTLER CATHODIC PROTECTORS are installed (submerged in the water and connected with positive contacts between tubes and anodes), several reactions take place as follows:
An electric current is generated and flows through the solution (electrolyte) from the anode to the boiler tubes. The current produces electrochemically, from the Butler alloy anode, zinc or magnesium ions as well as trace amounts of other metal ions. These metallic ions combine chemically with the various salts present in the boiler water in their ionized state and a series of complex zincates and other metallic complexes are formed. These zinc and other metallic complexes stay in suspension, preventing hard scale from forming on the boiler tubes and walls. Positive ions migrate toward the cathode and negative ions toward the anode.
Scale Protection:
At the anode, zinc salts of Zn(Cl)2 [zinc chloride], Zn(OH)2 [zinc hydroxide], and Zn2SO4 [zinc sulfate] are formed, plus other metalloid compounds. A smaller amount of ZnCO3 [zinc carbonate] will be formed because of the lower pH maintained around the anode. However, at the cathode, H+ [hydrogen] ions are neutralized, leaving an excess of OH- [hydroxide] ions in the immediate vicinity which tends to increase the pH. With increasing pH or alkalinity, the CO22 [carbon dioxide] together with the HCO3 [bicarbonate] is converted to CO3 [carbonate], resulting in CaCO3 [calcium carbonate]. This becomes a flocculent precipitation of calcium carbonate because of the peptizing effect of the zinc hydroxide complex present.
At low current densities, CaCO3 [calcium carbonate] is precipitated as hard, dense, tightly adherent film. However, at higher current densities created by the BUTLER CATHODIC PROTECTORS and because of the vigorous evolution of H2 [hydrogen], the chemical reaction between CaCO3 [calcium carbonate] and Zn(OH)2 [zinc hydroxide], deposits will be more porous and flaky. Consequently, they will slough off and must be removed by periodic blowdown of the boiler. The presence of oxygen increases the corrosion rate of zinc, producing both the zinc ions and the hydroxide ions necessary for the formation of the zinc cationic complex. At the same time, however, oxygen is removed very effectively from the solution.
Corrosion Protection:
There are several types of corrosion in boilers. There is electrolytic corrosion and/or oxygen corrosion and the type of corrosion which results from a dilute acid solution or chemical substance in the feedwater. Occasionally there is a combination of all three. The Butler method of water treatment can and does inhibit all three types of corrosion, either singularly or collectively, by use of both cathodic protection and chemical reactions in the water. Electrolytic corrosion is caused by current leaving the boiler metal at different points due to the differences in the electrical potential of the various surfaces. This corrosion process can be stopped if the current is reversed and forced onto the iron surfaces. This current reversal is done with higher-conductivity sacrificial anodes as cathodic protection. Oxygen corrosion is also controlled by cathodic protection and chemical ion reactions as explained in preceding paragraphs. Corrosion from acid water is prevented by raising the pH to the alkaline passive side. This function is performed also by the combination of cathodic protection and chemical reactions as explained above. Butler also uses BUTLER CATHODIC PROTECTORS with magnesium alloy anodes for corrosion prevention.
Zeolite Water Softeners:
Zeolite Water Softeners are not a complete water treatment for boilers. Artificially (zeolite) softened water exposes the boiler, and related vessels and piping to severe corrosion.
There is a considerable difference of opinion, even among the various softener manufacturers, as to whether sodium zeolite softening makes a change in the pH (acid-alkaline ratio) of the water. The raw untreated water may be the deciding factor. However, low pH water passing through a zeolite softener may not only be damaging to the mineral but be responsible for highly corrosive conditions in the water lines and boilers. All natural waters contain calcium and magnesium bicarbonate. Except for the very elaborate expensive softening systems, softeners do not give zero hardness water, therefore there remains the distinct possibility of some scale formation in boilers.
Zeolite softeners convert calcium bicarbonate to sodium bicarbonate. Under the temperature and pressures found in boilers, the sodium bicarbonate breaks down to form sodium carbonate and carbon dioxide. Carbon dioxide is a gas which carries into the headers, steam lines and return condensate lines. In the presence of moisture, it forms carbonic acid which attacks these lines. This carbon dioxide is in addition to the carbon dioxide already dissolved in the water. Moreover, there is no control of silica or dissolved oxygen in such zeolite treating. In addition, there is always the possibility that the softener will not be checked and serviced as regularly as is required. Therefore, supplemental treatment to control pH, corrosion and scale is absolutely necessary. If zeolite softened water is a necessity, BUTLER CATHODIC PROTECTORS will provide a safe pH, will protect against corrosion and will prevent scale formation.
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