CN108884956B

CN108884956B - Connection unit

Info

Publication number: CN108884956B
Application number: CN201780021350.8A
Authority: CN
Inventors: 保罗·皮亚琴蒂; 法布里齐奥·拉尼; 马西米利亚诺·博尔阿索
Original assignee: Meccanotecnica Umbra SpA
Current assignee: Meccanotecnica Umbra SpA
Priority date: 2016-03-30
Filing date: 2017-03-30
Publication date: 2021-06-15
Anticipated expiration: 2037-03-30
Also published as: CN108884956A; ITUA20162117A1; WO2017168361A1

Abstract

A connection unit for sealingly connecting two tubes traversed by an electric current and rotatable with respect to each other, comprising: a first end element connected to one of the tubes; a first intermediate pipe; an insulated joint disposed between the first end member and the first intermediate tube; a second tube connected to the other; a rotation joint connecting the first intermediate pipe to the second pipe in a sealed and relatively rotatable manner; a bypass circuit electrically connecting the first end member to the second tube; and a heating element in series with the bypass circuit and arranged in the rotary union.

Description

Connection unit

Technical Field

The invention relates to a junction for a concentrating solar energy device. In particular, the invention relates to a connection unit for sealingly connecting two tubes, which are traversed by an electric current and are rotatable relative to each other.

Background

Concentrating solar power plants (CSPs) comprise a plurality of parabolic mirrors (parabolic troughs) to concentrate solar power on respective receiving pipes through which a heat delivery fluid disposed in the focal point of the mirrors flows.

The high temperature reached by the heat transfer fluid allows the use of the accumulated heat to produce supersaturated steam through the heat exchanger, e.g., the supersaturated steam can rotate a turbine and produce electrical energy.

To increase the efficiency of the device, the mirror is configured to rotate following the apparent motion of the sun. During the day, the receiving pipe is therefore rotated integrally with the parabolic mirror and is connected to one another by means of a stationary ground pipe.

It is therefore necessary to provide a fluid tight joint between the rotating and stationary tubes. For this purpose, flexible pipes are generally used which also allow to accommodate the thermal expansion of the pipes.

However, these tubes are subject to fatigue resistance limits as they are subjected to cyclic bending, torsional stresses and high temperatures.

The efficiency of a CSP device is closely related to the maximum temperature reached by the heat transfer fluid. Therefore, the use of substances that are stable at high temperatures is of interest.

The use of diathermic oil as heat transfer fluid sets an upper limit for the operating temperature that may not exceed 400 ℃.

Substances have been tested that can withstand operating temperatures of 600 ℃ with the aim of increasing the efficiency of the device. Some of these substances, for example mixtures of molten salts, such as nitrates and nitrites, have further advantages over thermal oils because they are not flammable and do not contaminate.

However, these materials have a relatively high freezing temperature when compared to thermal oils, which may even reach values of 240 ℃. On the one hand, the use of these substances allows to increase the energy efficiency of the device, but on the other hand it entails additional technical requirements such as the need to prevent the solidification of the heat transfer fluid, which, in addition to forming inclusions in the tube, may also damage the structure of the tube during the melting step of the solid residue due to the simultaneous increase in volume from the solid phase to the liquid phase.

For these reasons, the tube is crossed by a low voltage and high amperage (about 400A) to maintain, by means of the joule effect, a temperature capable of preventing the solidification of the fluid.

Disclosure of Invention

It is an object of the present disclosure to provide a connection unit between a fixed tube and a movable tube of a CSP apparatus that allows solving the above-mentioned problems.

The above object is achieved by a connection unit according to the present invention.

Drawings

For a better understanding of the invention, reference will now be made to preferred embodiments, by way of non-limiting example, and with reference to the accompanying drawings, in which:

FIG. 1 is a perspective view of a connection unit made in accordance with the present invention;

FIG. 2 is a side view, in partial cross-section, of the unit of FIG. 1;

FIG. 3 is a partially cut-away perspective view of the unit of FIG. 1 with parts removed for clarity;

FIG. 4 is a section taken along line IV-IV of FIG. 2;

FIG. 5 is an enlargement of detail X of FIG. 3; and

fig. 6 is a perspective view of a second embodiment of the present invention.

Detailed Description

With reference to fig. 1 and 2, reference numeral 1 denotes as a whole a connection unit for sealingly connecting two coaxial, mutually rotating pipes 2, 3 (partially shown). In particular, the pipe 2 may be formed by a fixed ground pipe; tube 3 may be formed by a connecting tube connected to a receiving tube of a parabolic mirror of a CSP system (not shown) that employs a heat transfer fluid with a higher freezing temperature, such as NaNO₃+ KNO 3. The tube 3 is preferably a flexible tube.

The connection unit basically comprises:

a first end tube 4, the first end tube 4 being rigidly and sealingly connected to the tube 2;

a first intermediate pipe 5;

an insulating joint 6, the insulating joint 6 connecting the first end pipe 4 to the first intermediate pipe 5 and being interposed axially between the first end pipe 4 and the first intermediate pipe 5;

a second tube 7; and

a rotational joint 11, the rotational joint 11 sealingly connecting the first intermediate pipe 5 to the second pipe 7.

The connection between the unit 1 and the tube 3 is conveniently effected by means of a second end tube 8 and an electrically conductive joint 9, wherein the electrically conductive joint 9 connects the second intermediate tube 7 to the second end tube 8 and is interposed axially between the second intermediate tube 7 and the second end tube 8.

The

tubes

4, 5, 7, 8 are made of an electrically conductive metal material and are coaxial with each other and with the rotary joint 11.

The insulation joint 6 includes: a flange 15, the flange 15 being fixed to the first end pipe 4; a flange 16, the flange 16 being fixed to the first intermediate pipe 5; and an electrically insulating gasket 17 (for example mica), the electrically insulating gasket 17 being interposed between the two facing

flanges

15 and 16. The flange 15 comprises a radial conductive appendage 19, the function of which will be explained later. The

flanges

15, 16 may be conveniently welded to the respective tubes 4, 5 and are preferably removably connected by means of a plurality of bolts 20.

The conductive joint 9, similar to the insulating joint 6 but with a conductive gasket, comprises a flange 25 fixed to the second tube 7 and a flange 26 fixed to the second end tube 8. The flange 25 comprises a radial conductive appendage 27, the function of which will be explained later. The

flanges

25, 26 may be conveniently welded to the respective tubes 7, 8 and are preferably removably connected by means of a plurality of bolts 28.

The rotary joint 11 (fig. 2 and 3) substantially comprises a seal 30, the seal 30 being formed by a pair of

opposite sealing rings

31, 32, the pair of

opposite sealing rings

31, 32 having axial contact and being urged against each other by a respective metal bellows 33, 34 interposed axially between each

sealing ring

31, 32 and the respective intermediate pipe 5, 7.

The seal 30 is enclosed by a housing 35, the housing 35 comprising a bell-shaped element 36 fixed to a flange 37 of the first intermediate pipe 5 and an outer cylindrical portion 38 extending axially from the bell-shaped element 36 to the second pipe 7.

The casing 35 also comprises, on the opposite side of the seal 30 with respect to the bell element 36 and inside the cylindrical portion 38, a wall 39 fixed to a flange 40 of the second pipe 7 and facing the bell element 36.

A bearing 41 is provided between the cylindrical portion 38 and the wall 39 to allow relative rotation of the cylindrical portion 38 and the wall 39.

The housing 35 also encloses a heating element 42 which is clearly visible in fig. 3 and 4.

The heating element 42 comprises a C-shaped metal heating body 43 housing the seal 30 and fixed to the bell element 36 (fig. 5) by means of a plurality of axial screws 44 passing through the bell element.

Screw 44 is electrically insulated with respect to bell member 36 by an insulating bush 45 and an insulating washer 46.

The heating element 42 also comprises a pair of electrical terminals formed by

parallel appendixes

47, 48 and extending from the free end of the heating body 43.

The appendage 47 is electrically connected to the appendage 19 of the flange 15 by means of a shaped strip 49.

The appendage 48 is electrically connected to the appendage 27 of the flange 25 by means of a flexible cable 50.

The heating body 43 is provided with a vertical through hole 51 (fig. 4 and 5) arranged below the seal 30 to allow the passage of any micro-leaks that can leave the housing 35 through a discharge duct 52, the discharge duct 52 having a vertical axis and passing through the cylindrical portion 38 below the heating element 42.

Unit 1 operates as follows.

The seal 30 allows relative rotation between the

pipes

2 and 3 and ensures hydraulic sealing by virtue of the elastic thrust of the bellows 33, 34 on the

sealing rings

31, 32. In order to prevent freezing of the heat transfer fluid, a low voltage and high voltage electrical current, which must be transmitted from tube 2 to tube 3 through connection unit 1, flows through the device.

The current flows from the tube 2 to the first end tube 4 and from there to the heating element 42 by means of the flange 15, the appendage 19 and the band 48. Thus, the current flows through the cable 50 and the conductive joint 9 to the second end tube 8 and then to the tube 3. The above-mentioned elements thus form in their entirety a bypass circuit of the seal 30, to which the heating element 42 is connected in series.

The insulating joint 6 isolates the first intermediate pipe 5 from the first end pipe 4 and thus the seal 30 from the first end pipe 4. Thus, the sealing rings 31, 32 are not subject to the passage of electric current and are equipotential. This avoids arcing between the parts in relative motion.

The heating element 42, crossed by the current flowing through the device, is heated by means of the joule effect and heats the rotating joint 11, and in particular the region of the seal 30 and of the bellows 33, 34, which would otherwise be "cold" due to the bypassing by the current as previously described, thus preventing local solidification of the heat transfer fluid.

A closer examination of the unit 1 made according to the invention clearly shows its advantages.

The connection unit 1 solves the above-mentioned problems associated with the prior art.

In particular, unit 1 enables relative rotation between tube 2 and tube 3 in the presence of high temperature and current circulating in the tubes, and uses the current to heat the sealing area. Thus, on the one hand, solidification of the heat transfer fluid in the sealing region is prevented and, on the other hand, arcing between the components in relative movement is prevented. Torsional fatigue stresses of the mechanical elements of the unit can also be avoided.

The unit 1 can be mounted directly on the main line of a CSP system without additional connection means or thermal conditioning means, thus directly intercepting the current flowing along the device.

The unit is easy to install, requires no maintenance and can be easily removed to replace components in the event of a failure.

According to the variant shown in fig. 6, the second end tube 8 forms part of the unit 1 and is connected to the second tube 7 by an insulating joint 54 similar to the joint 6. In this case, the flange 25 of the second tube 7 is isolated from the flange 26 of the second end tube 8, and the accessory 27 for connecting the cable 50 extends from the flange 26 instead of from the flange 25. This solution provides a redundant electrical bypass that isolates the seal 30 from the current even in the event of a failure of the joint 6.

Finally, it is clear that the connection unit 1 can be subject to modifications and variations without departing from the scope of protection of the present invention.

In particular, the

joints

6, 9 and 11 can be made in different ways.

If first end tube 4 and second end tube 8 are present, first end tube 4 and second end tube 8 may be replaced by any of the elements that secure

tubes

2 and 3 to

joints

6 and 9.

Claims

1. A connection unit for sealingly connecting two tubes (2, 3) which are traversed by an electric current and are rotatable relative to each other, comprising:

-a first end element connected to one (2) of said tubes (2, 3);

-at least a first intermediate pipe (5);

-an insulating joint (6), said insulating joint (6) being arranged between said first end element and said first intermediate pipe (5);

-at least a second pipe connected to the other (3) of said pipes (2, 3);

-a rotary joint (11), said rotary joint (11) sealingly and rotatably connecting said first intermediate pipe (5) to said second pipe;

-a bypass circuit electrically connecting the first end element to the second tube; and

-a heating element (42), the heating element (42) being in series with the bypass circuit and being arranged in the rotary joint (11).

2. A connection unit as claimed in claim 1, characterized in that said rotary joint (11) comprises an outer casing (35) and a seal (30), said seal (30) being housed in said outer casing (35) and comprising a pair of sliding axial contact sealing rings (31, 32), said sealing rings (31, 32) being sealingly connected to said first intermediate pipe (5) and to said second pipe, respectively, and said sealing rings (31, 32) being held in mutual axial contact by elastic means.

3. The connection unit according to claim 2, characterized in that said elastic means are constituted by a pair of metal bellows (33, 34) which sealingly connect said sealing rings (31, 32) to said first intermediate pipe (5) and to said second pipe, respectively.

4. The connection unit according to claim 2, characterized in that the heating element (42) comprises a heating body (43) arranged around the seal (30).

5. The connection unit according to claim 1, characterized in that the insulating joint (6) comprises an electrically insulating element arranged between the first end element and the first intermediate pipe (5).

6. The connection unit according to claim 1, characterized in that the bypass circuit comprises a first conductor element connecting the electrical terminal of the first end element to the first electrical terminal of the heating element (42) and a second conductor element connecting the second electrical terminal of the heating element (42) to the electrical terminal of the second tube.

7. Connection unit according to claim 6, characterized in that said heating element (42) comprises a substantially C-shaped heating body (43), said first and second electric terminals being constituted by appendages (47, 48) extending from the ends of said heating body (43).

8. The connection unit of claim 6, wherein at least one of the first conductor element and the second conductor element is rigid.

9. The connection unit of claim 6, wherein at least one of the first conductor element and the second conductor element is flexible.

10. The connection unit according to claim 2, characterised in that the first end element comprises a first end pipe (4) provided with a flange (15), the first intermediate pipe (5) comprises a flange (16) facing and fixed to the flange (15) of the first end pipe (4), an insulating element being provided between the flange (15) of the first end pipe (4) and the flange (16) of the first intermediate pipe (5).

11. The connection unit of claim 6, wherein the second tube comprises a second middle tube and a second end tube connected by a second joint.

12. The connection unit of claim 11, wherein the second engagement portion is electrically conductive.

13. The connection unit of claim 11, wherein the second engagement portion is electrically insulative.

14. Connection unit according to claim 11, characterized in that the electrical terminal of the second tube is defined by an appendage (27) of a flange (25, 26) of the second joint.