The Problem of Sludge

The Problem with Sludge

The build-up of Magnetite (iron oxide) negatively impacts many types of equipment in diverse contexts. Typically the "sludge" in hydronic systems is wrongly attributed simply to dirt. In fact the sludge is made up primarily of iron oxided combined with other contaminants.

 

The Vulnerabilities of Modern Boilers and Pumps

Older boiler systems had wider channels in them. The issues with the harmful aspects of magnetite were not as pronounced and tended to just dissipate over time. Modern boilers and ECM pumps are much more highly complicated and fine tuned than the older systems. The channels inside of them are much narrower. The buildup of magnetite and scale reduces efficiency and causes components to overheat. If left untreated these can cause holes to burn inside the boilers and pumps which are difficult and sometimes impossible to fix. 

Variable-speed motors inside ECM pumps have strong magnets inside them, which can attract magnetite. The combination of high-efficiency boilers with narrow waterways and ECM pumps with magnets may add up to potential multiple failure points, where iron-oxide sludge and nonmagnetic debris, such as lime-scale, can collect and cause potentially expensive damage if installed on old systems. 

Sludge and Scale Formation in Boilers

In a boiler, water is continuously converted into steam. Due to this continuous evaporation of water, the concentration of soluble matters increases progressively. Then the salts separate out from the solution in the order of their solubility, the least soluble ones separating out first.

 

Sludge

If the precipitate is loose and slimy it is called sludge. Sludge is formed by substances like MgCl2, MgCO3, MgSO4 and CaCl2. Sludge has greater solubilities in hot water than cold water.

 

Scale

1) If the precipitate forms hard and adherent coating on the inner walls of the boiler, it is called scale.  2) Scale is formed by substances like Ca (HCO3)2, CaSO4 and Mg (OH) 2. 1.5.2

Scale has low thermal conductivity, so the rate of heat transfer from boiler to inside water is greatly decreased. In order to provide a supply of heat to water, excessive or over-heating is done. This causes increase in fuel consumption and increases the burden on the boilers, the pump and all related systems.

Magnetite Sludge
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