Method for reducing the oxygen content in steam generator wall tubes

Abstract

In a method for reducing the oxygen content in the flow volume of tubes of erected and installed tube wall regions or tube wall segments of a steam generator or steam boiler of a power station fired, in particular, with carbon-containing fuel, a solution is to be provided which eliminates or at least diminishes the problem of the incorporation of atmospheric oxygen into the boiler water which arises when tubes of the steam generator wall are being filled with boiler water and/or when boiler water is being discharged from these tubes. This is achieved in that an inert gas or an inert gas mixture is introduced into tubes of the tube wall regions or tube segments, through which boiler water or steam formed from this flows when the power station is in operation, before filling with boiler water or steam, in a way whereby gaseous oxygen present in the respective flow volume of the tubes, particularly in the form of atmospheric oxygen, is displaced, and/or an inert gas or an inert gas mixture is introduced during a discharge of boiler water or steam from the respective flow volume of the tubes, in a way whereby the free volume occurring is filled.

Claims

1. A method for reducing stress corrosion cracking of tubes of erected and installed tube wall regions or tube wall segments of a steam generator tube wall of a boiler of a power station fired by carbon containing fuel by reducing the oxygen content in the flow volume of the tubes of the erected and installed tube wall regions or tube wall segments before filling the boiler with water for a first time when the boiler is started for a first time, wherein the tubes of the tube wall regions or tube wall segments are composed of one of the steels T22, T23, or T24, the method comprising: introducing an inert gas or an inert gas mixture into the tubes of the tube wall regions or segments of the steam generator tube wall of the boiler of the power station fired by carbon containing fuel, through which boiler water or steam formed from this boiler water flows when the power station is in operation, before filling the tubes of the tube wall regions or segments of the steam generator tube wall of the boiler with boiler water for the first time when the boiler is started for the first time, such that the inert gas or the inert gas mixture displaces atmospheric oxygen which is present as a gaseous oxygen in the respective flow volume of the tubes of the tube wall regions or segments of the steam generator tube wall of the boiler at a time point before the tubes are filled with boiler water for the first time when the boiler is started for the first time.

2. The method according to claim 1, wherein a free flow volume within the tubes, which is present before the tubes of the tube wall regions or segments of the steam generator tube wall of the boiler are filled with boiler water for the first time when the boiler is started for the first time, is filled completely with the inert gas or the inert gas mixture.

3. The method according to claim 1, wherein the inert gas or inert gas mixture is provided in the form of an inert gas cushion.

4. The method according to claim 3, wherein the inert gas cushion has a pressure higher than atmospheric pressure.

5. The method according to claim 3, the tubes of the tube wall regions or segments of the steam generator tube wall of the boiler are brought into fluid-conducting flow connection with the inert gas cushion.

6. The method according to claim 1, wherein nitrogen is used as the inert gas or in the inert gas mixture.

Description

DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS

(1) According to the invention, therefore, the flow volume filled with atmospheric oxygen when the tubes are being filled and/or the free volume forming during the discharge of boiler water in the flow volume of the tubes of a steam generator wall is filled with an inert gas or an inert gas mixture which in each case is introduced into the tubes at this time point. When the steam generator is being filled with boiler water, the inert gas or inert gas mixture displaces the air in the respective flow volume of the tubes and protects these tubes and consequently the steam generator wall against stress corrosion cracking which can otherwise arise by atmospheric oxygen being incorporated into the boiler water. Similarly, when a steam generator is being shut down and the boiler water is being discharged, an inert gas or inert gas mixture is introduced into the free flow volume forming in each case in the tubes during the discharge of the boiler water. In this case, too, no atmospheric oxygen is introduced into the flow volume of the tubes which could otherwise possibly be incorporated into the boiler water. Also, the inert gas volume introduced prevents a reaction of the atmospheric oxygen with the tube inner walls which otherwise possibly takes place in the standstill phase of the steam generator.

(2) In particular, an inert gas or an inert gas mixture is used as the inert gas or inert gas mixture, and therefore, in a refinement, the invention provides for introducing in each case an inert gas or an inert gas mixture. It is in this case especially preferable to use nitrogen as inert gas.

(3) In an expedient refinement, the invention provides for preventing a follow-up flow or inflow of air when boiler water or steam is being discharged from the respective flow volume of the tubes.

(4) It is especially advantageous to employ the method according to the invention when the discharge of boiler water or steam from the respective flow volume of the tubes is carried out when the steam generator is being shut down. There is otherwise the serious danger here that atmospheric oxygen is sucked into the flow volume of the tubes.

(5) According to a further refinement of the invention, it is especially expedient and advantageous if the free volume within the tubes which is present before the tubes are filled with boiler water or steam and/or occurs when boiler water or steam is being discharged from the tubes is filled completely with the inert gas or the inert gas mixture.

(6) In order to simplify the introduction of inert gas or an inert gas mixture into the tubes, the invention provides, furthermore, for the inert gas or inert gas mixture to be provided in the form of a gas cushion having, in particular, an increased gas pressure.

(7) In this case, according to a development of the invention, it is also advantageous for the introduction of the inert gas or inert gas mixture if the tubes are brought into fluid-conducting flow connection with the inert gas cushion.

(8) In order to prevent the situation where atmospheric oxygen penetrates into the flow volume of the tubes when a steam generator is being shut down and when venting valves are being opened, the invention provides, furthermore, for an inert gas or an inert gas mixture to be introduced with the opening of venting valves. In this case, it is then expedient and advantageous, furthermore, if the tubes and/or the venting valves are brought into fluid-conducting flow connection with the inert gas cushion via connected venting lines.

(9) Finally, the invention is distinguished in that nitrogen is used as inert gas.

(10) It is especially advantageous to employ the method according to the invention in the case of tube wall segments or tube wall regions, the tubes of which are composed of one of the steels T22, T23 or T24 (designation according to ASTM 213 Standard).