Oxygen, carbon dioxide and nitrogen are removed from additional or top-up water as well as returned condensate, without thermal degassing (usually temperatures between > 85°C and > 95°C, i.e. oxygen levels between around 2.2 mg/L and 0.86 mg/L) or with thermal pressure degassing (temperatures between > 100°C and 110°C, i.e. oxygen level of < 0.02 mg/L and < 1mg/L carbon dioxide). This water is referred to as boiler feed water and it comes very close to the standards of the VdTÜV (Association of Technical Inspection Agencies), VGB, TRD 611 (Technical Rules for Steam Boilers) and DIN (German Industry Norms) for the prevention of pitting and surface corrosion in boiler areas with water contact.
The Technical Rules for Steam Boilers (TRD) have been issued to provide rules for technology according to the Steam Boiler Code. The TRD supply users with general instructions for boiler operation. Steam and hot water generators may only be used with "appropriately treated feed water", according to the rules TRD 611, TRD 612, information sheets by VdTÜV (Association of Technical Inspection Agencies)/the energy efficiency association AGFW (TCh 1466/FW 510), guidelines by the technical inspection association TÜV and the VGB, DIN EN 12953-10:2003, DIN EN 12952-12:2003 and DIN EN 285. This refers to water that allows for corrosion and coating free boiler operations and that complies with mandatory requirements.
For boiler feed water, which is usually a mixture of additional water and condensate, to meet requirements, the condensate must also be of appropriate quality.
The risk of corrosion caused by oxygen and carbon dioxide is particularly high, where steam is used through a number of condensation stages in different parts of the plant. This is why it is wise to perform steam / condensate treatment.
Hot water recirculation systems are used increasingly to supply heat to building complexes, industrial and municipal users. Heating takes place either directly via combustion plants or indirectly via heat exchangers.
The requirements for filling and top-up water for these plants are compiled in the guidelines issued by the German Technical Inspection Association TÜV and the Association of German Engineers VDI.
Hygienic and toxicological aspects are important, in addition to fundamental principles of water chemistry.
We generally distinguish between a saline and a low-salt operating mode for circulating water.