CA2737359A1

CA2737359A1 - Installation for removing heat from flowing water

Info

Publication number: CA2737359A1
Application number: CA2737359A
Authority: CA
Inventors: Urs Studer
Original assignee: Lyonnaise des Eaux France SA
Current assignee: Suez Eau France SAS
Priority date: 2008-09-16
Filing date: 2008-09-16
Publication date: 2010-03-25
Also published as: EP2329211B1; KR101176833B1; CN102203536A; KR20100084603A; WO2010031193A1; EP2329211A1

Abstract

The invention relates to an installation (1) for removing heat from a fluid flowing in a pipe, wherein the installation comprises at least one heat exchanger (2.1, 2.2, 2.3) which has direct contact with the fluid flowing in the pipe. The heat exchanger forms a vessel (5), which comprises a circulating heat transfer medium, and feed and discharge lines (8) for the heat transfer medium from and to a heat pump. The installation is characterized in that the design thereof is such that a heat exchanger surface formed by the same envelops an interior (3) of the pipe.

Description

INSTALLATION FOR REMOVING HEAT FROM FLOWING WATER
The invention relates to an installation for removing heat from a flowing liquid, for example wastewater or a cooling water in an industrial plant, or for discharging heat to such a flowing liquid, by means of a heat-exchange medium. The heat transferred to the heat-exchange medium is then withdrawn therefrom by a heat pump and used for heating buildings, for the conditioning of hot water or the like (or the heat is supplied to the heat-exchange medium using a heat pump operated in the reverse direction, and the heat is then discharged to the flowing liquid, wherein the heat pump can then be used for cooling buildings; under certain circumstances, a plant can perform both functions (cooling/heating), depending on the operating state).
Such installations are known, for example, from European laid-open specification 1 591 740 and from German patent 197 19 311.

The approaches disclosed in said documents have proved to be economical in many situations. However, there are applications in which the expenditure for installing the heat exchangers in a wastewater pipe is too high and/or in which the efficiency is too low. One example of such a situation is the removal of heat from wastewater conducted in pressure pipes (or another liquid conducted in the pressure pipe). By way of example, such pressure pipes are customary in areas which are relatively flat and do not have adequate sloping. Furthermore, they have also appeared in connection with the abolition/merging of sewage plants, on account of which wastewater is conducted from the site of an abolished sewage plant to the site of another sewage plant having a higher capacity, which is often possible only by means of pumps. A further application of pressure pipes are industrial plants which require, for example, cooling water.

Even if such specific requirements are not present, it is of course always desirable for the efficiency to be high.
Consequently, it is an object of the invention to provide an installation for removing heat from wastewater or a cooling liquid or another liquid (or for discharging heat thereto) which overcomes the disadvantages of the prior art and, in particular, shows progress in terms of the efficiency and the installation costs, in particular with respect to special applications.

According to a first aspect of the invention, provision is made of an installation for removing heat from a liquid flowing in a pipe and/or for discharging heat thereto, wherein the installation comprises at least one heat exchanger with at least one vessel, which contains a circulating heat-exchange medium, and also feed and discharge lines for the heat-exchange medium from and to a heat pump, wherein the at least one heat exchanger is configured such that a heat-exchange surface formed thereby envelops the pipe interior and is in direct contact with the liquid conducted in the pipe interior.

The fact that the heat-exchange surface envelops the pipe does not mean that the heat exchanger has to be present uninterruptedly along a periphery line of the pipe. Instead, it means that the heat-exchange surface is present both in the lower region and in the upper region, i.e. covers more than half the periphery line.
Worded slightly more generally, the following condition may be true: in a heat-exchanger region, the heat-exchange surface extends on both sides of each surface containing the centroid axis. It is preferred that, in this heat-exchanger region, parts free of the heat-exchange surface along the periphery line occupy, by way of example, in total at most about 150 , at most 90 or even at most about 600 or less, i . e . the entire azimuth angle range covered -by the heat-exchange surface is preferably at least 210 , at least 270 or at least 300 .

Owing to this relatively simple measure, the efficiency is increased considerably compared to the prior art.
The heat exchanger preferably has a plurality of segments which each span an azimuth angle range and extend in the axial direction over a certain length, for example over 0.5 m to 4 m. The number of segments which together span the pipe interior is preferably between 2 and 4, for example 3.

The provision of a plurality of segments which span an azimuth angle range is particularly advantageous in terms of assembly. The segments can each be produced and transported separately and assembled on site to form the heat exchanger which envelops the pipe and/or mounted on a carrier pipe. The assembly of the segments may involve welding.
It is likewise preferable for a surface of the heat exchanger to form a circumferential pipe, i.e. the heat exchanger itself forms a pipe.

If such a pipe formed by the heat exchanger is constructed from a plurality of segments, these can be welded along axially extending lines or possibly adhesively bonded or soldered or joined together sealingly in some other way.
It is very particularly preferable for said pipe formed by the heat exchanger (referred to as "heat-exchanger pipe" hereinbelow) to be mechanically so stable that it forms the entire wastewater pipe, i.e. no additional pipe which surrounds the heat exchanger is required.
This preferred approach has two significant advantages:
firstly, the actual wastewater pipe is not needed, which reduces the production costs considerably.
Secondly, it is also no longer necessary to assemble the heat exchanger in the pipe - this too is advantageous in terms of costs.
The heat exchanger can be formed such that the heat-exchanger pipe forms a pipe referred to here as "outer"
pipe, i.e. the heat-exchange medium flows inside the pipe formed by the heat exchanger. Alternatively - in a manner which is particularly suitable for thin pipes, in particular also pipes with small cross-sectional areas - the heat-exchanger pipe can also be an "inner pipe", such that heat-exchange medium flows outside the pipe. In this case, the wall thickness of the pipe is preferably not too large, such that the heat transfer through the pipe is sufficiently good.

In embodiments in which the heat-exchanger pipe is relatively thin, a carrier pipe, for example in the form of a plastic pipe, may also be present for mechanical reinforcement. Owing to the fact that the heat exchanger itself also forms a circumferential pipe, no sealing is required between the carrier pipe and the heat exchanger, and this makes production more economical and operation less awkward.

The installation according to the first aspect of the invention additionally preferably has supply pipes for supplying a plurality of heat-exchanger units in parallel with the heat-exchange medium. Each of these heat-exchanger units has a heat-exchange medium inlet connected to the first supply pipe, a heat-exchange medium outlet connected to the second supply pipe and a heat-exchange medium path therebetween. By way of example, the path can be defined by channels for the heat-exchange medium or by chicanes or the like and is generally formed such as to ensure the greatest possible heat transfer from the liquid (wastewater etc.) in the pipe to the heat-exchange medium, i.e. the path over which the heat-exchange medium has to travel should cover the greatest possible region of the heat-exchange surface.
According to a preferred embodiment, the supply pipes are arranged above the pipe. Specifically, it has been found that the ventilation of the heat exchangers can be an important issue, and the ventilation can be achieved more easily if the supply pipes are above the actual heat exchangers.

By way of example, said heat-exchanger units, which are supplied in parallel, can correspond in certain length portions to the segments already mentioned above.

Therefore, a further preferred concept of the invention is that of providing an installation for removing heat from a liquid flowing in a pipe (and/or for discharging heat thereto), which comprises a plurality of heat-exchanger segments that are supplied in parallel with heat-exchange medium and envelop different azimuth angle ranges of the pipe, i.e. are distributed along a periphery line - this as an alternative to or in addition to the parallel supply, known per se, of heat-exchanger units connected in series in the pipe direction (axial direction).

Overall, an installation according to preferred embodiments of the invention can be constructed from a plurality of segments, of which groups of preferably 2-4 segments together envelop an (axial) region of the pipe, wherein a plurality of such groups of segments are connected in series in the axial direction, and wherein each of the segments is supplied in parallel with heat-exchange medium.

This approach is particularly favorable in particular in terms of assembly; the assembly can nevertheless be effected with prefabricated heat-exchanger segments, which are joined together in groups to form (axial) regions enveloping the pipe or are mounted on the carrier pipe, wherein at least one further such axial region is then joined together/mounted and joined to the first axial region. Finally, all the segments are connected to the supply pipes.

A second aspect of the invention relates to the heat transfer per se. This second aspect is independent of the first aspect and is also applicable to heat-exchanger installations which do not have a structure enveloping the pipe, but instead are installed in the interior of a wastewater pipe (usually made of concrete) , as per the teaching of documents DE 197 19 311 and EP 1 591 740, for example.

According to this second aspect, provision is made of an installation for removing heat from a liquid flowing in a pipe and/or for discharging heat thereto, wherein the installation comprises at least one heat exchanger with at least one vessel, which contains a circulating heat-exchange medium, and also feed and discharge lines for the heat-exchange medium from and to a heat pump, wherein the heat exchanger is produced at least in part, for example at least in the region of a heat-exchange surface, and preferably as a whole from a ferritic steel.
Specifically, it has surprisingly been found that ferritic steels - owing to their magnetic properties, to date they were known primarily for pots and pans for induction cookers and the like - are very suitable as heat-exchanger materials for the removal of heat from wastewaters. To date, ferritic steels have been regarded as unsuitable for applications such as that in the present case, since they were regarded as relatively soft and susceptible to corrosion. However, it has been found that, in particular given an appropriately sufficiently high content of chromium and, if appropriate, other materials such as molybdenum, the resistance to abrasion and corrosion is sufficiently high, despite a generally lacking or small content of nickel, for the ferritic steels to also be suitable for this application, which is very demanding in terms of the corrosion properties. In addition, the heat-conducting properties have proved to be very advantageous, and the weldability is also good.
Particular preference is given to ferritic steels having a chromium content of at least 12% or at least 14%, for example between 15% and 32%, and particularly preferably additionally having a molybdenum content of at least 0.5% (for example between 0.5% and 5%, in particular between 0.5% and 2%).

One example of a suitable ferritic steel is the steel 1.4521 (444) (Arcelor) containing 1% Si, 1% Mn, 17.5-19.5% Cr, 1.75-2.5% Mo and traces of C, N, Ti, P, Nb and also at most 1% Ni.

The use of ferritic steels - instead of austenitic steels as known from the prior art - for heat-exchanger systems for removing heat from wastewaters or other possibly corrosive liquids is particularly beneficial in combination with the approach to bring the heat exchanger into direct contact with the wastewater.
Owing to the good weldability, it is likewise beneficial to use ferritic steels in combination with the approach to construct the heat exchanger from a plurality of heat-exchanger elements welded to one another.

The text which follows explains exemplary embodiments of the invention in more detail with reference to figures. In the figures, identical reference signs denote identical or analogous elements:

figure 1 is a view of a heat-exchanger installation, in section perpendicularly to the pipe axis, which forms a pressure pipe, figure 2 is a schematic illustration of the structure, represented as a developed view, of a heat exchanger as shown in figure 1, figure 3 likewise schematically shows an installation having a plurality of groups of heat-exchanger segments connected in series in the axial direction, wherein each segment is supplied in parallel with heat-exchanger liquid with the aid of supply pipes, figure 4 shows an embodiment of a heat-exchanger installation as an alternative to figure 3, and figure 5 shows a further alternative embodiment.

The heat-exchanger installation 1 shown in figure 1 has three heat-exchanger segments 2.1, 2.2, 2.3, which together envelop a pipe interior 3. The segments are welded along axially extending weld seams 4 and together form a heat-exchanger pipe which functions as a pressure pipe. In the operating state, the pipe interior 3 is generally filled completely with liquid, for example with wastewater or a cooling water or any liquid.

In the interior of the heat-exchanger pipe, the heat-exchanger segments 2.1, 2.2, 2.3 each form a vessel 5, in which the heat-exchange medium circulates. In the present example, the vessel is formed between two parallel heat-exchanger plates 6.1, 6.2, of which the outer plate 6.1 preferably has a greater material thickness, and the outer plates 6.1 of the heat-exchanger segments together form the heat-exchanger pipe. Owing to webs 6.3 which function as chicanes, the vessel 5 forms a row of channels which lie next to one another and through which the heat-exchange medium flows in series, as shown more clearly hereinbelow in figure 2. Supply pipes 7.1, 7.2, 7.3 are present for the supply of the heat-exchange medium. The heat-exchange medium passes from the feeding supply pipe 7.2 into the vessels 5 or from the vessels back into the discharging supply pipe 7.3 via feed and discharge lines 8. In the view shown in figure 1, two feed and discharge lines 8 respectively are shown one directly after the other, and this is why it cannot be discerned clearly in figure 1 which feed and discharge line 8 leads to which segment 2.1. One example of an expedient, corresponding arrangement is described below with reference to figure 3, however.
The material of the heat-exchanger segments is, for example, stainless steel, in particular a stainless steel of the ferritic type as mentioned above, or else an austenitic steel. The thickness of the inner plate 6.2, which forms the heat-exchange surface, is for example between 1.5 mm and 5 mm, preferably between 2 mm and 4 mm, and the thickness of the outer plate 6.1 is between 3 mm and 9 mm, depending on the size of the pipe and the compressive strength to be achieved. The wall thickness of the webs 6.3 is rather noncritical;
by way of example, it may be between 1 mm and 4 mm. The outer plate, the inner plate and the webs are produced from the same material, for example, or from different materials which can be fastened to one another.

Figure 2 schematically shows the structure, represented as a developed view, of a heat exchanger as shown in figure 1. In the illustration chosen here, the outer edges in figure 2 correspond to the weld seam 4 shown at the bottom in figure 1. As can be seen, the webs 6.3 are arranged such as to produce a meandering path for the heat-exchange medium in each heat-exchanger segment.

Figure 3 shows an installation having a plurality of groups of heat-exchanger segments connected in series.
In the example shown, three such groups are depicted, i.e. a total of 9 heat-exchanger segments. It goes without saying that heat-exchanger installations having more or fewer heat-exchanger segments can also be realized according to that shown in figure 3.
The supply pipes 7.1, 7.2 and 7.3 are installed on the basis of the Tichelmann system known per se, i.e. the first supply pipe 7.1 serves to feed the heat-exchange medium to the site located furthest away from the heat pump, and the heat-exchange medium flows into the feeding and discharging supply pipes 7.2 and 7.3 in parallel (the Tichelmann system can also be realized analogously exactly inversely).

The arrows in figure 3 denote the direction in which the heat-exchange medium flows. The direction F in which the wastewater (or the other liquid) flows is also shown. Instead of flowing in direction F, the liquid can also flow in the opposite direction F'.
As can be seen, it is necessary, owing to the three heat-exchanger segments which envelop the pipe interior, for at least one feed line and one discharge line to intersect. This is readily possible owing to the available degrees of freedom. In principle, it would also be possible, as an alternative, to conduct a feed or discharge line on the underside under the pipe, but this would be less beneficial.

The embodiment shown in figure 4 differs from that shown in figure 1 in that the heat-exchanger pipe is formed by the inner heat-exchanger plates 6.2. The heat-exchange medium accordingly circulates outside the pipe. This embodiment is favorable particularly when the pipe as a whole has a rather small diameter and the pressures to be expected in the pipe are not very high, and therefore the wall thickness of the pipe does not have to be too large and, by way of example, does not exceed 4 mm. The same statements as those made in respect of the version shown in figure 1 apply with respect to the configuration of the heat-exchange medium path.
The heat-exchange surface is formed by the inner plate 6.2 in those regions in which the latter is in contact with the heat-exchange medium.

In principle, it is also possible for both the inner and the outer heat-exchanger plates 6.2, 6.1 of the heat-exchanger segments to each form a pipe which surrounds the pipe interior 3.

Figure 5 shows a further embodiment having a carrier pipe 11, for example made of plastic, extending on the outside of the heat exchanger 2.1, 2.2, 2.3. This gives the pipe as a whole the required mechanical stability and serves for improved bonding. In the embodiment shown in figure 5, too, the heat-exchanger segments 2.1, 2.2, 2.3 together form a pipe which surrounds the pipe interior 3. In the embodiment shown, it is the inner heat-exchanger plates 6.2 of the three segments which form the pipe.

However, the embodiment shown in figure 5 could also be configured such that the outer heat-exchanger plates 6.1 or both heat-exchanger plates 6.1, 6.2 form the pipe.

In addition, departing from the embodiment shown, the heat exchangers could also be inserted into the carrier pipe 11 such that they do not form any continuous surface, in which case certain regions of the carrier pipe 11 would then come into contact with the liquid conducted in the pipe interior 3.
A heat-exchanger installation according to the second aspect of the invention may be formed according to the first aspect, or it may have a different configuration, for example installed in the interior of a wastewater pipe (usually made of concrete), as per the teaching of documents DE 197 19 311 and EP 1 591 740, for example.
Many further embodiments of both aspects of the invention are conceivable. It is also possible for additional functionalities to be present, for example the means described in EP 1 591 740 for preventing the formation of slime.

Claims

1. An installation (1) for removing heat from a liquid flowing in a pipe and/or for discharging heat to a liquid flowing in a pipe, wherein the installation comprises at least one heat exchanger (2.1, 2.2, 2.3) in direct contact with the liquid flowing in the pipe, with at least one vessel (5), which contains a circulating heat-exchange medium, and also feed and discharge lines (8) for the heat-exchange medium from and to a heat pump, characterized in that the at least one heat exchanger is configured such that a heat-exchange surface formed thereby envelops a pipe interior (3) of the pipe.

2. The installation as claimed in claim 1, characterized in that an azimuth angle range covered by a heat-exchange surface occupies at least 270°.

3. The installation as claimed in claim 1 or 2, characterized in that the heat exchanger has a plurality of segments (2.1, 2.2, 2.3) which span azimuth angle ranges that are disjointed in relation to one another.

4. The installation as claimed in claim 3, characterized in that each of the segments has a feed and discharge line (8), in such a manner that the segments can be supplied in parallel with the heat-exchange medium.

5. The installation as claimed in one of the preceding claims, characterized in that a surface of the heat exchanger forms a circumferential pipe which comprises the pipe interior (3).

6. The installation as claimed in claim 5, characterized in that the pipe formed by the heat exchanger is mechanically so stable that it forms the entire wastewater pipe, and in that the installation is free of a pipe surrounding the heat exchanger.

7. The installation as claimed in claim 5 or 6, characterized in that the vessel (5) is arranged inside the pipe formed by the heat exchanger.

8. The installation as claimed in claim 5 or 6, characterized in that the vessel (5) is arranged outside the pipe formed by the heat exchanger.

9. The installation as claimed in one of the preceding claims, characterized by supply pipes (7.1, 7.2, 7.3) for supplying a plurality of heat-exchanger units in parallel with the heat-exchange medium.

10. The installation as claimed in claims 4 and 9, characterized in that the heat-exchanger units correspond to the heat-exchanger segments (2.1, 2.2, 2.3).

11. The installation as claimed in claim 10, characterized in that a plurality of groups of heat-exchanger segments connected in series with respect to an axial direction of the pipe are present, wherein each heat-exchanger segment can be supplied in parallel with the heat-exchange medium.

12. The installation as claimed in one of claims 9-11, characterized in that the supply pipes run above the pipe.

13. An installation, for example as claimed in one of the preceding claims, for removing heat from a liquid flowing in a pipe and/or for discharging heat to a liquid flowing in a pipe, wherein the installation comprises at least one heat exchanger in direct contact with the liquid flowing in the pipe, with at least one vessel, which contains a circulating heat-exchange medium, and also feed and discharge lines for the heat-exchange medium from and to a heat pump, characterized in that the at least one heat exchanger is produced at least in part from a ferritic steel.

14. The installation as claimed in claim 13, characterized in that the heat exchanger consists of ferritic steel at least in the region of the heat-exchange surface, and preferably the heat exchanger as a whole consists of ferritic steel.

15. The installation as claimed in claim 13 or 14, characterized in that the ferritic steel has a chromium content of at least 12%.