Ferrous bicarbonate

In LP boilers with little returning condensate the requirement for MU is correspondingly high and may be relatively cool and partially oxygenated. Here it is not uncommon to observe the transport of ferrous bicarbonate [Fe(HC03)2] into the boiler (especially where no neutralizing amine is supplied) and the subsequent development of iron sludge, which settles on the top of combustion tubes and to the bottom of the boiler. 

Under conditions of water loss and poor waterside control, it is fairly common for iron sludges and foulants formed elsewhere to settle in the boiler. Trying to identify the source of this problem is complicated when the transport of soluble iron salts such as ferrous bicarbonate Fe(HC03)2 into the boiler takes place. A further complication occurs... 

Reduced operating capacity due to iron fouling of the resin, which occurs because soluble iron (in the form of ferrous bicarbon-... 

Precipitated iron also acts as a binder and forms deposits with other materials. The source of iron originates either from contaminated condensate or from MU water, where it is present in the form of ferrous bicarbonate [Fe(HC03)2]. 

Ferrous bicarbonate [Fe(HC03)2] Transport into FW line and boiler. Common in smaller boilers with a high percentage of cold water MU water. 

The resulting ferrous bicarbonate is not particularly stable in condensate, being affected by heat, pH, and the partial pressure of C02 in the steam-C02 condensate mix. Various secondary reactions subsequently take place, resulting in the formation of ferrous ox ferric oxides, hydroxides, and carbonates throughout the condensate system. 

Ferrous bicarbonate may be transported to a point where little or no amine is available, which then provides the source for various secondary corrosion reactions. Corrosion mechanisms and deposition formation often take place at points in the system well downstream of the original points of steam condensation and initiation of corrosion. 

Ferrous bicarbonate is a mild base and, as corrosion proceeds, the ratio of bicarbonate to carbonic acid increases to produce a corresponding increase in pH. The high pH is therefore not necessarily... 

The nascent hvdrogen reduces anv nitrates or nitrites to ammonia. Atmospheric oxygen converts the ferrous salt into colloidal feme hydroxide, a reaction that is facilitated by cascade aeration. As it coagulates and settles, the ferric hydroxide punfies the water in an analogous manner to that described for aluminium hydroxide above. The process is rather expensive, however, and for this reason some American towns have added ferrous sulphate direct to their waters. This is less satisfactory as the salt is not oxidised so readily as ferrous bicarbonate m addition to this, sulphuric acid is introduced into the water. 

Ferrous hydrogen carbonate or ferrous bicarbonate, FeH2(C03)2, exists in solutions obtained by dissolving ferrous oxide or carbonate in water charged with excess of carbon dioxide. On exposure to air carbon dioxide is evolved, and a precipitate is obtained consisting essentially of ferric hydroxide.2... 

In the second reaction, no electrons are involved. In this case, take the convention that if no electrons are involved, either consider the positive or, alternatively, the negative oxidation states as the reference species. For this reaction, initially consider the positive oxidation state. Since the ferrous iron has a charge of +2, ferrous bicarbonate has 2 for its number of reference species. Alternatively, consider the negative charge of bicarbonate. The charge of the bicarbonate ion is -1 and because two bicarbonates are in ferrous bicarbonate, the number of reference species is, again, 1x2 = 2. From these analyses, we adopt 2 as the number of reference species for the reaction, subject to a possible modification as shown in the paragraph below. (Notice that this is the number of reference species for the whole reaction, not only for the individual term in the reaction, hi other words, all terms and each term in a chemical reaction must use the same number for the reference species.)... 

III. Chalybeate waters which contain salts of iron in greater ]iroportion than 4 parts in 100,000. They contain ferrous bicarbonate, sulfate, crenate, and apocrenate, calcium carbonate, sulfates of potassium, sodium, calcium, magnesium, and aluminium, notable quantities of sodium chlorid, and frequently small amounts of arsenic. They have the taste of iron and are usually clear as they emerge from the earth. Those containing ferrous bicarbonate deposit a sediment on standing, by loss of carbon dioxid, and formation of ferrous carbonate. 

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