FR2570683A1 - IMPROVEMENT TO FLOATING ROOF TANKS FOR LIQUIDS, IN PARTICULAR STORAGE TANKS USED IN THE ELECTRONUCLEAR FIELD - Google Patents

Abstract

THE INVENTION RELATES TO FLOATING ROOF TANKS FOR LIQUIDS, OF THE TYPE INCLUDING A CYLINDRICAL WALL 2, A FLOATING ROOF 3 AND A FLEXIBLE MEMBRANE 4 CONNECTING THE PERIOD OF THE FLOATING ROOF TO THE WALL. IN ACCORDANCE WITH THE INVENTION, THE TANK INCLUDES, FOR PROTECTION AGAINST OVERPRESSION AND OR DEPRESSION, WHEN THE ROOF 3 IS IN LOW POSITION, OR STUCK IN INTERMEDIATE POSITION, A VACUUM BREAKER TUBING 34 PUTTING IN COMMUNICATION THE INTERIOR OF THE HOUSING FORMING THE ROOF WITH THE LIQUID FROM THE TANK, THIS TUBING 34 BEING SIZED SO THAT ITS NATURAL PRESSURE CORRESPONDS TO A PREDETERMINED PRESSURE. APPLICATION IN PARTICULAR TO THE ELECTRONUCLEAR FIELD, FOR STORAGE TANKS ENSURING THE SUPPLY OF DEGAZED WATER FOR A NUCLEAR REACTOR PRIMARY CIRCUIT.

Description

_-1-_ 2570683

  The invention relates to roof tanks

floating for liquids.

  Such tanks are used in particular as storage tanks in the electro-nuclear field for liquids such as degassed demineralised water. In this field, high reliability is required for the design of tanks, in order to eliminate any

  risk of shutting down, or even worse,

  deterioration of essential constituents; it is also essential to have a safe operation, without risk of false operation. Moreover, when

  such floating roof tanks are used for

  water point to the primary circuit of a nuclear reactor, it is necessary to have an air-free storage which ensures a very strict quality for the stored liquid, the degassed water in front, in this particular application , have an oxygen content not exceeding 100 gg for

avoid any risk of oxidation.

  Traditionally, such roof tanks

  float have a cylindrical wall and a floating roof.

  both sealingly connected to said wall which surrounds it by a flexible membrane. To preserve this flexible membrane connecting the perimeter of the roof and the side wall of the tank, avoiding in particular the formation of folds and / or uncontrollable application against the wall of the tank under the effect of the pressure of the liquid contained in the tank, it is usually provided that the space defined by the membrane and the wall of the tank, space communicating with the outside, receives a liquid of

  backpressure essentially acting as a lubricant

  relying on the membrane during the movements of the roof

  and, incidentally, at least in some cases

  positions, a centering of said roof relative to the

cylindrical wall of the tank.

  -2- One of the problems with the design of

  Such floating roof tanks lie in their protection

  against overpressure or depression due to

  the roof when filling or emptying the liquid they contain, or at a depression at the end of emptying when the roof is in the down position on its stops. Indeed, when maneuvering the floating roof, the specialists are always afraid that a

  jamming of the roof in an intermediate position

  improve the tank by pressurization, and especially in depression; in addition, in the extreme low position, that is to say in general when the roof rests on low stops provided at the bottom of the tank, the roof box exerts, as during a wedging, a disturbing depression effect the

  final phase of the emptying of the tank.

  According to a known technique, there is provided a small mechanical valve on the roof, sometimes called a breathing valve, and set on a relatively low calibration in both directions (about 30 mbar

  for example); this valve, acting as a breaker

  empty, must ensure only the protection of the tank

  with a roof in the low stop position.

  This technique is not satisfactory because the mechanical breathing valve, being mounted on the bottom of the box forming the floating roof, is difficult.

  accessible in case of malfunction; the accessibi-

  is also important if we want to change the calibration

  valve, in depression and / or overpressure, or

  yield. to its maintenance: it is then necessary in practice to wait for the floating roof is in high position or rests on its low stops to have access to this valve, which is a certain disadvantage, even inconceivable for a

  rational use of the reservoir.

  The aim of the invention is to avoid the disadvantages of

  previous techniques mentioned above.

-3-

  An object of the invention is to provide a reservation

  see floating roof whose structure allows a pro-

  effective tank protection in the event of jamming of the roof, against a depression at the end of emptying the liquid it contains when the roof is in the low stop position. Another object of the invention is to radically simplify the design of the means serving as a function of

  to avoid as much as possible of having to access it

  der in use of the tank.

  Another object of the invention is to have the pos-

  the ability to easily adjust the tare of these means, and

  preferably both overpressure and depression.

  Another object of the invention is to have a simple structure and a reasonable manufacturing cost.

for the tank.

  A last object of the invention is to preserve

  at most the liquid stored in the reservoir of a con-

  tact with ambient air, especially for an ap-

  in the electro-nuclear field.

  A floating roof tank for liquids

  form to the invention is essentially characterized by the fact that the means on the roof and allowing

  protect the tank against overpressure and / or

  when said roof is in the lower position, or stuck in the intermediate position, are constituted by a vacuum breaking tubing mounted on the underside of the box forming the roof so as to put the interior of said box into communication with the liquid of the tank, said tubing being dimensioned so that its natural setting corresponds

at a predetermined pressure.

  Preferably, the vacuum breaking tubing is in the form of a stick whose vertical branch passes through the face.

  lower part of the caisson, and the portion of the vertical limb

  outer shim to roof box has a length --4--

  lower than the height of the lower stops provided for in

  inside the tank and on which the

roof in low position.

  The vertical branch of the stick has

  tagbly a lower portion and an upper portion in the extension of each other, said

  portions being delimited by the level occupied by the liquid

  from the reservoir, the lower portion having a

  length corresponding to a predetermined maximum depression

  undermined; the upper portion of the vertical leg and the curved portion of the butt define a height of

  liquid corresponding to a predetermined maximum overpressure

  when the tank is filled, so that the cassevide tubing has a natural setting as well

in overpressure than in depression.

  The vacuum breaking pipe advantageously has: a bore corresponding to both a maximum air flow rate for the emptying phase, and to a maximum liquid flow rate

for the filling phase.

  Other features and advantages appear

  more clearly in the light of the description and

  figures of the annexed drawing illustrating modes of

  1 is a vertical section of a floating roof tank according to the invention; - Figure 2 is a partial section of the tank whose roof is in the upper position; - Figure 3 is a partial section illustrating the detail of the counter-pressure liquid draining members; and

  FIG. 4 is a section along IV-IV of FIG.

  In Figure 1, a floating roof tank

  for liquids 1 has a generally cylindrical wall

  2, a floating roof 3 made in an open box on the top, and a flexible membrane 4 sealingly connected -5-

  the perimeter of the floating roof at the side wall of the

  see. It should be noted that the membrane 4 is here hung

  at 5 mid-height of the tank, but the invention applies

  also in the case of a membrane attached to the

  top of the tank. According to the usual technique, the space 6, open to the outside, defined by the

  membrane 4 and the tank wall 2 is suitable for receiving

  see a back pressure liquid basically serving

  of lubricant for the flexible membrane 4, avoiding in particular

  particularly the formation of folds during the various movements

  floating roof 3, and allowing incidentally, at least in certain positions, a centering of said roof by

relative to the tank wall.

  Figure 1 schematically illustrates a number of equipment that are usually provided on

  Floating roof tanks for liquids: these equipment

  These will be briefly recalled, since those skilled in the art are well accustomed to the presence of such equipment. It is thus planned, for the floating roof 3, six

  guide wheels 7 with spring 8, mounted according to a distribution

  regularity on the upper periphery of the roof and

  designed to be applied against the wall 2 of the tank in

  all roof positions; an advantageous measure

  is to provide a design of the floating roof with

  its guide wheels, which always remain inferior to the dia-

  meter of the tank, so as to make possible, although this is not desirable, a complete reversal of the roof without jamming by the wall of the tank. The roof

  floating 3 is also equipped with an analog inclinometer

  9 on which is connected a cable 10, equipped with a slack and provided with a counterweight, for returning the reading and alarms in the control room, which allows to follow

  the inclination of the roof in the event of

  intermediate, operating at the bottom or -6- emptying the tank. The floating roof 3 is also equipped, in the vicinity of the membrane-roof junction, with peripheral vents 11 connected by a vent collector 12 provided with a valve 13, and possibly with an air purge 14 in the center of the roof in case it does not present

  not enough conicity to collect the air peri-

  phérie. As for the tank itself, it is equipped

  manual venting below the level of the points of access

  hooking 5 of the membrane, with several vents also distributed on the periphery and connected by a manifold with an outlet pipe to a valve 16; it is also provided at a low level of the inlet pipes 17,

  outlet 18, and drain 19 for liquid tank.

  A circular bridge 20 at the top of the tank facilitates

  the visit of the roof and the membrane.

  The movement of the floating roof is limited by

  stops 21 and high 22, and indicating equipment

  alarms (not shown) are intended to verify the

  fication of extreme high and low levels in the room

control.

  The tank is equipped with means allowing

  to empty the. volume of counter-liquid

  pressure when the roof is in the up position. As well as

  this has been illustrated in FIGS. 1 and 2, these means comprising

  a drain plug 23 through the wall

  2 at the top of the tank and connected to a channel

  conventional draining arrangement 24 provided with a valve 25 and

  greater than said wall. To protect the tank against

  an excess of filling, it can be

  overflow fitting 26 in the form of a stick, provided with

  in part. superior of a trap-siphon conduit 27.

  This device allows a complete emptying of the. vo-

  a liquid of counterpressure by the natural effect of the pressure of the reservoir liquid which tends to radially push the flexible membrane 4, and thus to expel this liquid until all the part of the membrane which is lower than the drain hole is applied against the inner wall of the tank. It then suffices to actuate liquid counterpressure filling means, preferably arranged in the upper part of the

  at a level close to that of the means of

  ge, and constituted for example (Figure 1) by a pipe, a valve 31 and a volumetric counter 32 allowing

  the admission of a predetermined volume.

  Figures 3 and 4 illustrate a means of

  both to prevent clogging of the water outlet

  by the flexible membrane during the emptying of the counterpressure liquid; this means is for example formed in the form of a flat element 33 fixed on the side wall 2 and whose protruding position prevents clogging of the emptying outlet 23 while allowing the liquid to pass laterally.

  After having examined the operation of the

  see when the roof is in the up position, it fake exami-

  situation at the bottom, or in part intermedia-

  re in case of jamming because it is in these positions

  that the device of the invention intervenes.

  It is indeed very important to also ensure the protection of the tank when the roof is in position

  low, or stuck in the middle position, and in particular

  bond facilitate complete emptying of the tank liquid.

  The problem can also be posed

  during a jamming of the roof during filling

empty tank.

  In accordance with the invention, provision is made for a

  vacuum breaker bulge (34) mounted on the underside of the box forming the floating roof, so as to put the interior of said box into communication with the liquid of the tank. This tubing (34) is dimensioned so that its natural setting corresponds to a predetermined pressure and / or depression, as will be explained below. The vacuum breaking tubing (34) is in the form of a stick whose vertical branch passes through the underside of the box. To avoid any risk of damage to the stock when the floating roof 3 bears on the lower stops 21, the portion of this vertical branch protruding from the box must have a length less than

the height of said low stops.

  The waterline 28 divides the butt 34 into a lower portion and an upper portion on either side of said line. The bottom part contains

  therefore a plug of liquid which is the active part of the

  positive tank protection, allowing complete emptying when the roof is in the low position. In addition, this liquid stopper provides effective protection against regassing of the liquid contained in the reservoir. For the

  natural setting, it is sufficient to size the lower portion

  in order to directly have the operating pressure

  desired: for example, a lower portion

  30 cm will correspond to a maximum depression of 30 mbar.

  This device is therefore very simple, and it

  automatically, which represents a significant improvement

  sible with respect to so-called breathing valves

  prior techniques; it is therefore no longer

  necessary to provide for accessibility during the

  tank for maintenance or adjustment of the

said valve.

  In addition, this device can also operate overpressure when one is no longer in a situation of emptying the tank, but in filling situation of the empty tank. Indeed, at the beginning of filling the tank, the air trapped initially between the roof and bottom of the tank can be evacuated by the vacuum breaker tubing (34) and the air purges. If an overpressure then occurs, the previous liquid plug will rise in the tubing: it is then sufficient to size also

  the upper position (above the waterline)

  28) so that the natural setting corresponds to a predetermined maximum overpressure at filling: as

  previously, an upper portion defining a high

  30 cm maximum fluid level will correspond to an over-

maximum pressure of 30 mbar.

  The vacuum breaking tubing (34) can then advantageously operate, and this in a completely natural way, both depression and overpressure. In this case, the bore of said tubing must correspond both to a maximum air flow rate for a depression, in the emptying phase of the reservoir, and to a maximum flow rate of liquid

  for an overpressure in the filling phase of said reservoir

  see. For an application to the electro-nuclear domain, demineralised water will advantageously be used as a counter-pressure liquid; the design of the floating roof tank of the invention also makes it possible to avoid bringing the liquid of the tank into contact with the air, which avoids having to re-degassing this liquid (the open air communications by the trap-siphon of the overflow piping and the vacuum-breaking tubing in fact introduce only a negligible disturbance,

  because the siphon breaker, which is very far from its communi-

  cation with the reservoir at the bottom, and the vacuum-breaking tubing contain a lower cap of liquid which

forms an effective screen).

  It goes without saying that the invention is not limited to the particular embodiment which has been described by way of example, but on the contrary covers all the variants

  resuming, with equivalent means, the characteristics

contained in the claims.

Claims (6)

  1. Floating roof tank for liquids,   carrying a cylindrical wall (2), a floating roof (3) sealingly connected to said wall which surrounds it by a flexible membrane (4), this membrane defining with the wall of the tank a space (6) adapted to receive a counter-pressure liquid, and on-roof means for protecting the tank against   overpressure and / or depression when said roof is in   low level; QcU oincéken rosition primary, characterized in that the means of protection are constituted by a vacuum breaker tubing (34) mounted on the underside of the box forming the roof (3) so as to put in communication the interior of said box with the reservoir liquid, said tubing (34) being dimensioned so that its   natural setting corresponds to a predetermined pressure.   2. Floating roof tank according to the   cation 1, characterized in that the tubing breaks   void (34) is in the form of a stick whose vertical limb   wedge passes through the underside of the box.   Floating roof tank according to claim   cation 2, characterized in that the portion of the vertical branch outside the roof box has a length less than the height of the lower stops (21) provided inside the tank and on which   comes to rest the roof (3) in low position.   4. Floating roof tank according to one of the   claims 2 and 3, characterized in that the   vertical branch comprises a lower portion and an upper portion in the extension of one another, said portions being delimited by the level (28)   occupied by the liquid in the tank, the lower portion   having a length corresponding to one   predetermined maximum depression. -11-   Floating roof tank according to the   cation 4, characterized in that the upper portion   the vertical leg and the curved portion of the butt define a height of liquid corresponding to a predetermined maximum overpressure when filling the reservoir, so that the vacuum breaking tubing   (34) has a natural setting both in in depression.   Floating roof tank according to claim   cation 5, characterized in that the tubing breaks   vacuum (34) has a bore corresponding to both a maximum air flow rate for the emptying phase, and a   maximum flow rate of liquid for the filling phase.