JPS5825921B2 - steam generator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a steam generator comprising a tube plate pierced by holes to which the ends of a group of U-tubes are connected, said tubes carrying a first fluid flow and normally The second one consists of water.
Under the operating conditions of the generator, it is evaporated by the first fluid, which is externally surrounded by the fluid and exchanges heat through the tube wall.

More specifically, the invention relates to a U-tube steam generator comprising an outer casing or shell having a vertical axis and divided into two regions by a horizontally arranged tube plate.

A first region, located below the tube plate and through which the U-tube opens, is divided by an internal partition into an area for access of the first fluid and an area for the release of the second fluid.

The second region of the steam generator shell consists of an annular header for inlet of the second fluid and an internal cylindrical skirt.

The skirt surrounds the group of U-tubes and extends at the top above the group of tubes by a separate assembly connected to a duct for the discharge of the generated steam.

After passing through the lower end of the skirt between the tube plate and the skirt, the second fluid flows between the tube groups and then between the tubes in the direction of the vertical axis of the outer shell.

In a generator in which the second fluid is supplied through a peripheral part of a U-tube bank, said U-tube bank having a constant spacing, in particular in the grid of holes, and in which the tubes are connected to a tube plate. In particular, the second fluid is cooled by heat exchange with a hot first fluid or a second fluid in which the flow in said tube arm is directed from an inlet area below the tube plate and is directed to the tube plate and discharge area. Experience has shown that either the returning first fluid does not flow between the tube arms in the same way.

In particular, it is clear that cooling the U-tubes located in the middle, hottest part of the tube bank is often not sufficient.

The reason is that the second fluid reaches these tubes with greater difficulty than the surroundings.

Moreover, despite all the precautions taken, different impurities are always carried along with the second fluid, in particular mineral salts and iron oxides which form sludge upon evaporation by heat exchange.

These sludges contact the tube plate and tend to accumulate in the central portion of the tube bank.

The aforementioned sludge has the effect of reducing the cooling coefficient of the tube and, as a result of its decomposition in the steam, forms compounds that have a corrosive effect on the metal of the tube.

In particular, this localized evaporation of the second fluid tends to dry out the sodium sulfate that is normally included in the second fluid for purposes of reducing corrosion.

As a result, the sodium sulfate is converted into sodium hydroxide, which tends to damage the generator tubes within a short period of time.

Finally, the sludge derived from the second fluid and deposited on the tube plate is difficult to remove from the generator as a result of the presence of the tube bank, and this constitutes a major drawback.

The present invention relates to a steam generator in which the particular construction and arrangement of groups of U-tubes supported by tube plates overcomes the drawbacks of conventional designs.

This arrangement allows improved circulation of the second fluid within the tube bank region.

The hot first fluid through the tube bank regions is placed at a maximum distance from the peripheral region of the inlet of the second fluid by further providing a simple and efficient device installed in these regions and drawing out the sludge. It flows especially in the dark areas.

For this purpose, the generator has the following characteristics:

The arm spacing of the U-tube through which the high temperature first fluid flows is the low temperature first fluid.
The U-tubes are arranged within the tube plate with a spacing greater than the arm spacing of the U-tubes through which fluid flows.

Optionally, the U-tubes are arranged in parallel planes, with the tube arms through which the hot first fluid flows arranged in laterally spaced relationship contained within the plane of said tubes.

In other embodiments, the tubes are arranged in a radial plane;
Tube arms through which a hot first fluid flows are arranged in spaced relation in a central region of the tube plate surrounded by a peripheral region including arms through which a cold first fluid flows.

In one feature of the invention, the tube arm through which the hot first fluid flows has a lateral duct occupied by a duct having an opening in the vicinity of the tube plate for suction of the sludge formed in the second fluid. Define the passage.

In another feature of the invention, the lateral passage is provided with another second fluid that is flowed through plunger tubes arranged vertically between at least a certain number of U-tubes.

The plunger tube is associated at its end remote from the tube plate with a venturi for mixing with a reheated second fluid drawn from the upper region of the tube bank.

The present invention will be described in detail with reference to the accompanying drawings.

The same reference numbers in different drawings indicate the same parts.

The generator 1 mainly consists of a cylindrical shell 2 having a vertical axis and forming the outer casing of the generator.

The shell is closed at the lower end by a hemispherical end 3.

The shell 2 has at its opposite end an extension in the form of a second shell 4, which is closed by a top domed end 5.

The generator casing thus formed is internally separated by horizontal tube plates 6.

The tube plate 6 delimits two regions 8 and 7 arranged respectively above and below the tube plate.

The regions are provided for the flow of a first fluid and a second fluid separate from each other.

The second fluid consists of water to be evaporated in the generator by exchanging heat with the first fluid in a manner described below.

Regions 7 located below the tube plate 6 are separated by transverse bulkheads 9, as shown, which extend perpendicularly to the tube plate 6 and the plane of the drawing, and which extend within said region 7 into two in each case.
Areas 10 and 11.

Nozzle duct 1 for inflow and discharge of a first fluid into the zone
2 and 13 are open.

Said fluid is fed into the generator at a predetermined temperature and pressure and enters the upper region 8 of the shell through the tube plate 6, a group of U-tubes and their ends.

The U-tubes are supported by a tube plate and their ends extend through holes formed in the tube plate in suitably spaced relation.

Each U-tube 14 has two arms 15 and 16 respectively, which are joined at the top end by a bend 17.

The arm 15 through which the first fluid flows after entering the U-tube constitutes a 1° hot leg of said U-tube, while the portion 16 from which the first fluid exits the U-tube and returns to region 11 is connected to said U-tube. It constitutes one cold leg of the tube.

The second fluid enters the outer casing of the generator through duct 18.

The duct 18 opens into the shell 4 and has an extension in the form of an annular header tube 19 , which serves to distribute a second fluid, usually water, into the upper region 8 .

A cylindrical skirt 20 forms a single layer of U-tube 1 within said upper region 8.
4 and placed concentrically to the shell 2.

The lower end 21 of the skirt is placed at a short distance above the tube plate 6 without contacting it.

As a result, the second fluid guided from the main pipe 19 into the annular space defined between the skirt 20 and the shell 2 is passed under said skirt and the arm 1 of the U-tube
5 and 16 and flows outside the U-tube 14.

It is an advantage that the tube 14 is held in place and vibrations are particularly prevented by mounting a series of spacer plates 23 within the skirt 20.

Is the spacer plate 23 provided with an open portion?
Alternatively, it is preferably mounted as a diverting thread to maintain the different tubes in a given space without interfering with the upward flow of the second fluid.

The baffle plate has the advantage of producing an agitation action in the second emulsion and homogenization of the second temperature around either the hot or cold leg of the tube.

The second fluid flows through the tube 14 when the first fluid flows within the tube.
an upper shell 2 that is evaporated by contacting and exchanging heat with the first fluid and then forming an extension of the skirt 20;
4 and is collected by a cyclone device 25.

The generated steam is forced towards the top of the generator and is directed through passage 27 to end section 26.

Said area comprises an assembly 2 comprising a drying unit 29 of known type, such that the vapor-containing liquid is dewatered.
It has 8.

The dry vapor finally leaves the generator through an outlet 30 provided in the domed end 5, while the separated liquid is optionally collected in a bottom collector 31.

As shown in FIG. 2, which is a lateral cross-sectional view of the lower region of the steam generator, the group of U-tubes is such that the spacing of the hot legs at the point where the hot legs of the U-tubes enter the tube plate 6 is equal to the spacing of the cold legs in the tube plate. It is arranged so that it is larger than the interval.

In this case, due to this asymmetry in spacing, the bulkhead 9 formed in the region 7 under the tube plate has been displaced to the left in the drawing, and the hot leg 15 of the U-tube is larger than the region corresponding to the cold leg 16. It is designed to occupy space.

Under this condition, the second fluid entering from the space 22 between the skirt 20 and the shell 2 will flow to the lower end 21 of said skirt.
and into the tube bank 14 where it is distributed between the hot legs 15 of said tubes 14 in a more efficient manner.

In particular, the second fluid can reach any tube, especially the tubes arranged in the central part of the tube bank, without risking too rapid local evaporation.

This results in a general cooling of the tube bank and eliminates the risk of inhomogeneous evaporation of water.

Thus, drying out of the sodium sulfate, which is added to reduce corrosion of incorporated products, especially tubes, is prevented.

Furthermore, impurities contained in the second fluid and converted into solid sludge during operation collect on the upper surface of the tube plate 6 under gravity and are easily removed.

In fact, due to the spacing of the tube groups in the hot leg 15, there is sufficient lateral space or passage for the insertion of a withdrawal tube or duct 33 for suction of the sludge.

The sludge passes through leak-tight holes 34 in the shell 2;
It is then directed through pipe 35 to a cleaning unit (not shown).

Other sludge withdrawal pipes such as pipe 33a are connected to the cold leg 1 of the U pipe.
It can also be placed in the passage formed between 6 and 6.

Note that the presence of sludge in these areas is less critical than during the hot leg.

In the example shown in FIGS. 1 and 2, the U-tube group is arranged such that the entire assembly of tubes is located in a series of parallel vertical planes extending at right angles to the direction of the partition wall 9. In the example shown in FIGS.

In another embodiment shown in FIGS. 3 and 4, the U-tubes 14 are distributed in a radial plane, and the hot legs 15 of the tubes 14 are grouped together at sufficient intervals in the central region of the tube plate. The cold legs 16 are arranged in an annular region surrounding the central region with smaller spacing.

In this case, the partition wall 9a provided under the tube plate to define the population and discharge area for the first fluid is cylindrical, the first fluid is admitted into the central region 10a through the nozzle duct N2a, and the fluid is introduced into the peripheral region 11a and passes through nozzle ducts N3a and 13b.

In this embodiment, a tube is shown drawing out the sludge that has formed in the second fluid and collected on the upper surface of the tube plate, as shown at 36, the draw tube 36 being more horizontal, but at a higher temperature. It is adapted to extend vertically between the tubes in the head region and the cold foot region.

Finally, in another embodiment shown in FIG. 5, which is directly derived from the embodiment shown in FIG. 3, an injection system is provided between the groups of hot legs of the U-tube 14.

The injection system comprises a plunger tube 37 which is open at its lower end 38 in the vicinity of the tube plate 6, and in the upper part of which is provided a venturi 39.

The outer end of the supply pipe opens into the venturi.

The pipe carries a second emulsion drawn near the top of the tube bank into the venturi.

[Brief explanation of drawings]

FIG. 1 is a schematic longitudinal sectional view of a first embodiment of a steam generator. FIG. 2 is a cross-sectional view taken along the line ■--■ in FIG. FIG. 3 is a partial longitudinal sectional view of another embodiment of the generator. FIG. 4 is a sectional view taken along line IV-IV in FIG. 3. FIG. 5 is a partial cross-sectional view of another embodiment shown in enlarged dimensions. 1... Generator, 2... Shell, 3...
...Semicircular sphere end, 4...Second shell, 5...
...Dome-shaped end, 7, 8... Area, 6...
...Tube plate, 9...Transverse bulkhead, 10
．． 11... Area, 12, 13... Nozzle duct, 14... U pipe, 15, 16...
...Arm, 17...Bend, 19...
・Main pipe, 20...Skirt, 24...
Shell, 25...Cyclone device, 29...
...Drying unit, 27...Aisle, 30...
...exit, 31...assembly.

Claims (1)

[Claims] 1 having an outer casing divided into two compartments by a horizontal pipe plate having a vertical axis and having a plurality of holes to which the ends of a group of U-tubes are connected;
The conduit for circulating fluid opens into a first of said compartments located at the lower part of the pipe plate, said first compartment being separated by at least one intermediate wall from at least one area for receiving the first fluid to the first compartment. at least one region from which one fluid is discharged;
The compartment has a cylindrical internal skirt surrounding the U-tube group;
a second fluid is configured to enter between the tube plate and the skirt through a lower end of the skirt before circulating through an intermediate portion of the vessels of the tube group in a vertical axis direction of the outer shell; A steam generator characterized in that tube arms through which a high-temperature first fluid circulates are arranged inside a tube plate at a wider interval than the mutual spacing between tube arms through which a low-temperature first fluid circulates.