Liquid heaters and vaporizers – Indirectly heated – Separate fluid
Patent
1982-03-12
1984-07-31
Favors, Edward G.
Liquid heaters and vaporizers
Indirectly heated
Separate fluid
122438, 122504, F22B 116
Patent
active
044623402
DESCRIPTION:
BRIEF SUMMARY
The invention relates to an arrangement for preventing the formation of cracks at the inside surfaces of feedwater line nozzles which open into pressure vessels, particularly nuclear reactor pressure vessels or steam generators.
Such an arrangement is known for steam generators of nuclear reactors from German Published Non-Prosecuted Application 23 46 411.
If a cold medium is replenished to a system (vessel, pipeline) which is filled with a medium of elevated temperature, via a horizontal connection, i.e. a feedwater line nozzle, a stratification of colder and warmer medium comes about in the horizontal connecting piece, if the feeding takes place with a mass throughput which is small relative to the size of the connecting cross section. i.e. with low flow velocities. The same thing occurs if the medium is already present in the system to be fed in evaporated condition. The stratification comes about because the lighter (warmer) medium can flow back into the upper part of the flow cross section of the nozzle due to its buoyancy against the colder water to be fed-in. The temperature differences of the media lead to thermal stresses in the connecting nozzle or the connecting line which as a rule are already highly stressed by the internal pressure of the system, so that with a sufficiently large number of cycles of the feeding processes, material fatigue and thereby, the formation of cracks can occur. The phenomenon of temperature stratification could be demonstrated by temperature measurements on feedwater line nozzles of a steam generator for pressurized-water reactors.
In the known arrangement according to the German Published Non-Prosecuted Application mentioned at the outset, the feeding takes place with a flow conducted in the horizontal and/or downward-directed direction within the vessel. Although the feed nozzles are lined at their inner periphery with so-called thermosleeve tubes, the thermal stress problems mentioned at the outset can nevertheless still occur in subregions of the nozzles.
It is an object of the invention to develop the arrangement of the type mentioned at the outset in such a manner that for slow feeding of the feedwater line nozzle such as occurs under partial load or zero load operation of a plant, material fatigue and thereby, the crack formation at the nozzle are impossible with certainty, even with larger numbers of load changes of the feeding processes. According to the invention, the stated problem is solved by the feature that the feedwater is fed into the water/steam space of the pressure vessel through a substantially horizontal line section and a following rising line section up to the overflow edge at the end of the flow travel of the rising line section, from where the feedwater is admixed through a downwardly-directed line section, and optionally through a ring feedline connected thereto, with the medium in the water/steam space and in the descent space of the pressure vessel, so that temperature stratification due to flowback of warmer water in the nozzle is prevented. An advantageous further embodiment claim is that the line section which is substantially horizontal, is followed first, through a bend, by a substantially downwardly-directed line portion which leads into a collecting cup that has risisng flow paths up to the overflow edges. The advantages attainable with the invention are in particular that a reverse flow of the specifically lighter medium in the fed system against the heavier (still cold) medium still to be fed-in is prevented. Through the invention, not only all the problems of thermal stresses and crack formation which occur particularly under zero load and low load operation solved, but also those occurring during starting-up and shut-down operation.
In the following, the invention will be explained in greater detail with the aid of the drawing showing several embodiment examples, and the operation described. In schematic, simplified presentation, omitting the parts not required for an understanding of the invention,
FIG. 1 is a longitudinal sect
REFERENCES:
patent: 3661123 (1972-05-01), Romanos
Mayer Hans
Sterk Zvonimir
Favors Edward G.
Greenberg Laurence A.
Kraftwerk Union Aktiengesellschaft
Lerner Herbert L.
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