LTI offers a boiler cleaning service, both pre-operational and periodic, on all types of equipment: radiation boilers, such as those used in biomass plants or coal-fired power plants, recovery boilers, such as those used in cogeneration plants or combined cycle power plants, and heat exchange steam generators, such as those used in solar thermal power plants.
Presentation pdf boilers
Chemical cleaning removes residues accumulated during the construction or operation of various plants, such as oxides, incrustation, dust, among others. They also form a protective film on the pickled surface.
What boilers are like.
A boiler is a vessel in which water is continuously vaporised by the supply of heat energy.
Types of boilers.
There are different types of boilers:
According to their design:
Smoke tube boilers (low pressure)
Aquotubular (high efficiency but more corrosion and incrustations)
According to their construction:
Packaged (designed, built and tested before shipment).
The aim of the treatments is to reduce and avoid the three main problems associated with steam generation:
The origin of incrustations and deposits:
Contaminants present in the feed water
Internal system corrosion products
Contaminants introduced into the condensate as leaks
Scaling occurs on the hot metal surfaces of the boiler during the evaporation process.
Decreases heat transfer
Causes overheating of the metal to the point of breakage.
This results in:
- Reduced heat transfer efficiency
- Increased system maintenance, higher cost
Scaling is usually associated with:
Water hardness, increasingly of less importance when treating Ca and Mg in external feed water treatments.
Coordinated phosphate programme
Chelate solubiliser programme
Solubiliser programme with dispersants
The most common is caused by oxygen attack on metals, accelerated by high temperatures and low pH.
It can also occur when oxygen is removed by direct attack of the steel by water vapour at high temperature.
The treatments that are usually carried out are:
Sodium sulphite treatment:
Sodium sulphite + oxygen → soluble sodium sulphate.
Increases the concentration of solids in the boiler water.
Cobalt catalyst must be added to accelerate at low temperatures.
Residual sulphite value in boiler = 20-60 ppm, depending on pressure.
Hydrazine + oxygen → water + nitrogen
Passivates iron and copper surfaces.
Slow reaction up to 180°C (organic catalyst), but at 230°C decomposes.
Residual value of hydrazine in boiler = 0.1-0.3 ppm, depending on pressure.
Substitutes for hydrazine
Due to the possible carcinogenic action of hydrazine, other compounds have been used:
hydroquinone, carbohydrazide, erythorbic acid, deitylhydroxylamine….
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