Use of SiO2 coatings in water-carrying cooling systems

Abstract

The invention relates to the use of coatings of nanoscale SiO.sub.2 particles in water-carrying cooling systems to prevent abrasive corrosion and depositions as well as to a method for the production of such a coating.

Claims

1. Method for the coating of cooling water lines in cooling systems of water-cooled thermal power plants comprising the following steps (a) cleaning the cooling water lines with water under high pressure; (b) applying an epoxy resin amine hardener system as a primer coat; and (c) applying an aqueous coating composition that comprises nanoscale SiO.sub.2 particles having a size of less than 10 nm, which consolidate on the surface to form an SiO.sub.2 layer of <500 nm.

2. Method according to claim 1, characterized in that the cleaning is carried out at a pressure of up to 2500 bar.

3. Method according to claim 1, characterized by the application of a primer coating at a pressure of up to 500 bar.

4. Method according to claim 1, characterized by the application of the coating composition at a pressure of up to 10 bar.

5. Method according to claim 1, characterized in that the cleaning of the cooling water lines as well as the application of the primer coating and the application of the coating composition is carried out by means of a nozzle which is designed for use in reverse travel operation, the spray angle of which ranging between 60° and 120° to the longitudinal direction of the cooling water lines to be treated.

6. Method according to claim 1, characterized in that at least one primer coat is applied, the film thickness being in the range of between 80 μm and 2000 μm.

7. Method according to claim 1, characterized in that the film thickness of the SiO.sub.2 layer lies in the range of between 50 and 300 nm.

Description

(1) The invention also relates to a method for applying the coating proposed by the invention to cooling water lines, said method comprising the following steps: (a) Cleaning the lines with water under high pressure, (b) if considered necessary or expedient, the application of a primer coat, and (c) application of an aqueous sol-gel consisting of nanoscale SiO.sub.2 particles which consolidate on the surface to form an SiO.sub.2 layer.

(2) As a rule, the coating is applied by spraying.

(3) Cleaning of the lines with water is carried out under high pressure, with pressures of up to 2500 bar being used. For example, publication WO 2012/045466 A1 proposes and describes a cleaning system provided with a backward jetting nozzle which is operated in reverse travel mode and has a spraying angle of between 60° and 120° to the longitudinal direction of the coolant tube. Such a nozzle, which can be used not only for cleaning purposes but also for the application of coating materials, offers the advantage that the material removed by the cleaning process is discharged with the water stream, resulting in the coating process not being disturbed and the coat not being damaged by the movements of the nozzle and application hose.

(4) A single layer of the material used in accordance with the invention which is applied in a single work step is sufficient.

(5) The application of a priming coat is primarily useful for the treatment of older coolant tubes that already show signs of corrosion and pitting. For the primer coating, that may consist of and be applied in one or several layers, the material described hereinbefore based on an epoxy resin-amine hardener system is particularly appropriate. The film thicknesses of the primer coating are as indicated above for the tube coating.

(6) Application of the aqueous sol-gel takes place by spraying to produce the SiO.sub.2 layer, for which purpose the nozzle described above can be used, said nozzle, however, being operated at considerably lower pressures. Normally, the application pressure for the primer coating is up to 500 bar, but for the application of the sol-gel only up to about 10 bar.

(7) Details of the coating device and the coating process are described in publication WO 2012/045466 A1, the teaching of which is expressly included here.