The present invention is related to a turbine suited for integration into a community sewer system for channelling wastewater from a building or a group of buildings, comprising a housing and a rotor provided with an axle and a number of blades or impellers. The invention is also related to a method for cleaning the rotor of such a turbine. BACKGROUND ART

Generating electricity using a turbine fitted into the sewer system of a building is known. Patent US4246753 discloses a turbine of this type, comprising a housing (12) and a rotor provided with a plurality of blades (30). Wastewater acquires kinetic energy in the drainpipe and enters the housing through an inlet conduit (22), strikes the blades and causes the rotor to rotate, and exits the housing through an outlet conduit (40) to the sewer. The inlet and outlet conduits are vertical, and their diameters are approximately equal to the diameter of the drainpipe. The rotational energy of the rotor may be transformed into electrical energy via a generator (52). A clean water supply line (64) may feed injectors (48) and (50) in order to clean the blades with a pair of pressurized water jets.

The fact that this turbine is simply fitted in the drainpipe, without being adapted to the somewhat irregular nature of wastewater flow and the relatively small volume thereof, may substantially limit the energy efficiency of the turbine.

SUMMARY

One aim of the invention is to improve the energy efficiency of a turbine of the type described in the preceding section.

According to an aspect of the invention, at least one blade, and preferably all of them, comprises a cut-out at its distal end, i.e. at the end opposite to the rotor hub (which is the proximal end of the blade). If a rotating blade lacks such a cut-out, the blade is initially hit by the water jet on its rear side (i.e. counter to the blade's rotational sense), whereby the water jet initially opposes the blade's forward rotation, although the blade's inertia causes it to keep moving forward until the jet hits the front side thereof (in the same sense as the blade's rotational sense). Therefore, for a brief initial period, the water stream not only does not accelerate the blade but actually slows it down. With the cut-out this is not the case because, as the impact occurs a little later and with the blade a little further advanced, the initial impact is produced on the front side of the blade. The cut-out may be U- shaped and may have a depth of between a third and a fifth of the length of the blade.

The blades may be curved. For instance, at least one blade may be arcuated in the longitudinal direction or in the transversal direction or in both directions. At least one blade may also be corrugated, and the waves may preferably be parallel to the transversal direction. Any of these shapes contributes to taking more energy from the water stream, which is something particularly important given the irregular nature of said stream. According to another aspect of the invention, the turbine comprises a housing provided with a substantially cylindrical part, the axis of which is substantially parallel to the rotor axle, and a plurality of conduits for the entry of the wastewater into said housing, each of which in turn comprises an inlet for connecting the conduit to a drainpipe of the sewer system and a nozzle for connecting the conduit to said cylindrical part, such that the diameter of the nozzle is not bigger than a third of the diameter of the inlet, preferably not bigger than a fourth of the diameter of the inlet. In this way, two major improvements are achieved: multiple water jets enter the turbine and the water enters it at a higher speed. Furthermore, the use of multiple conduits makes it easier for these to be attached to multiple drainpipes, which may even have different directions, and it also facilitates the turbine's installation by allowing it to be placed wherever most convenient, which isn't necessarily where the drainpipe is located, and with any orientation (horizontal, vertical or inclined).

In one embodiment, at least two conduits may be attached to the cylindrical part of the housing along a direction substantially parallel to the rotor axle; in other words, the conduits may be attached to the cylindrical part along an axial direction, whereby multiple jets may simultaneously hit the same blade (in which case, the latter may have multiple corresponding cut-outs). In another embodiment, or in combination with the previous embodiment, at least two conduits may be attached to the cylindrical part of housing along a direction substantially perpendicular to the rotor axle; in other words, the conduits may be attached along a circumference of the cylindrical part, whereby each water jet could hit a different blade at any time (or at least most of the time).

The nozzle's axis may form an angle of between 45° and 60° with the tangent to the cylindrical housing part at the point of intersection of the cylindrical housing with the nozzle axis. This may enhance the advantageous effect of the cut-out.

In one embodiment, the diameter of the turbine may be less than 90 centimetres; in this manner, the turbine is relatively easy to install. With such a relatively small size, it may be preferable for the turbine rotor to comprise between 12 and 14 blades.

The turbine may comprise a pipe to supply clean water to the housing, as well as a pressure switch, a first electrovalve and a second electrovalve arranged in said pipe, the second electrovalve being downstream from the first electrovalve. This allows the blades to be cleaned automatically or according to a program.

According to one aspect of the invention, in one method for cleaning the turbine rotor the pressure switch may maintain both the first and the second electrovalves closed if it detects that the pressure upstream from the first electrovalve is less than or equal to the water pressure downstream from the second electrovalve, thus preventing wastewater from entering the clean water system. To initiate a cleaning session, said method may comprise the following steps:

- opening the first electrovalve while keeping the second one closed;

- opening the second electrovalve while holding the first one open. This makes it even more difficult, if not impossible, for wastewater to enter the clean water system. To end the cleaning session, said method may comprise the following steps:

- closing the second electrovalve while holding the first one open;

- closing the first electrovalve keeping the second one closed.

Analogously, it becomes even more difficult, if not impossible, for wastewater to enter the clean water system.

Additional objects, advantages and features of embodiments of the invention will become apparent to those skilled in the art upon examination of the description, or may be learned by practice of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Particular embodiments of the present invention will be described in the following by way of non-limiting examples, with reference to the appended drawings, in which: figure 1 shows a turbine with three circumferentially attached channelling conduits;

figure 2 shows the blades of a turbine as in figure 1 ;

figure 3 is a schematic view of the blades of such a turbine;

figure 4 shows an arcuated and corrugated blade;

figure 5 shows a turbine with two axially attached channelling conduits; and figure 6 shows the connection of the turbine of figure 5 to two drainpipes, one vertical and one horizontal.

DETAILED DESCRIPTION OF EMBODIMENTS

A turbine according to the invention may comprise several intake conduits and/or some blades provided with a cut-out at its distal end. The turbine illustrated in figures 1 and 2 comprises a generally cylindrical housing 10, which in turn comprises a cylindrical part 11 with two side walls 12. The turbine also comprises a number of blades 20 mounted on a hub (not shown) secured to a rotating axle 25 which passes through the turbine's side walls and may be mechanically coupled to an electric generator (not shown). The assembly comprising the blades, the hub and the axle constitutes the turbine's rotor.

The turbine further comprises a plurality of conduits 30 (in figure 1 there are three and in figure 5 there are two) for channelling wastewater from drainpipes 50 into the housing 10. As seen in figure 6, the conduits 30 form a narrowing between the drainpipes 50 and the turbine's housing 10, such that the water enters the housing 10 at a higher speed; the narrowest part of the conduit 30 (which connects to the cylindrical part 11 of the housing 10) is a nozzle 31 , and the widest part of the conduit 30 (which connects to the drainpipe 50) is an inlet 32. The ratio between the diameters of the inlet 32 and the nozzle 31 may be between 3 to 1 and 5 to 1 , or even bigger. For example, the diameter of the inlet 32 may be 300 mm and the diameter of the nozzle 31 may be 70 mm. The turbine also includes an outlet drainpipe 35 which is connected to the sewer.

The turbine may be attached to several drainpipes 50 in the building via the conduits 30, although a single drainpipe may be attached to several conduits. The drainpipes 50 may have any direction. Naturally, the turbine may be installed in any wastewater channelling system, such as a sewer or a sewage treatment plant or a channelling system for more or less dirty water. The housing 10 may comprise an inspection hole 33 on the cylindrical part 11

(fig. 5).

The blades 20 may be flat or may be arcuated, either in the longitudinal or transversal directions (or in both). As seen in figure 4, one blade 20 is transversally arcuated and presents a half-round shape, and it is longitudinally arcuated too (also seen in figure 3) and corrugated, with the waves parallel to the transversal direction, i.e. one wave following the other in the longitudinal direction. As seen in figures 2 and 4, each blade 20 comprises a U-shape cut-out 22 at its distal end. The blade may have a length of, for example, 40 cm, and the depth of the cut-out 22 may be about 10 cm at the deepest point and the width may be about 8 cm at the distal end of the blade. The number of blades may be 14. The cut-out 22 is in correspondence to the nozzle 31 of the conduit 30, such that the water jet exits the nozzle in such a way that it first hits the blade (which is rotating) at the base of the cut-out and on the front side of the blade, whereby, from the very beginning, the water jet hits the blade favourably in the sense of rotation thereof.

In sum, the shape of the blades is selected to take more of the energy carried by the water stream. Although not shown in the figures, the blades may not be symmetrical. The shape of the blades is independent from the arrangement of the conduits 30, except in the correspondence between the nozzle 31 and the cut-out 22.

In the embodiment of figures 1 and 2, the three conduits 30 are attached circumferentially (i.e. in a direction perpendicular to the axle 25) in order to hit three separate blades simultaneously. In the embodiment of figure 5, the two conduits 30 are attached axially (i.e. in a direction parallel to the axle 25) in order to hit the same blade with twice the force. In this latter case, the blades may be provided with two cut-outs 22 in correspondence to the nozzles 31 of the conduits.

Naturally, whether the conduits 30 are attached circumferentially or attached axially (or both ways), there may be any number of intake conduits, and the configuration and size of the turbine may be adapted to the number and the arrangement of the conduits.

Between the inlet 32 and the outlet drainpipe 35 there may be a shunt (also called "bypass", not shown) to ensure that, in the event of an incident in the turbine, the wastewater flows out of the building without interruption.

The turbine supports wet sewage input, not just wastewater, and the solid waste present in the wet sewage is substantially shredded after its interaction with the blades 20, which promotes its evacuation. The turbine may comprise a pipe (or multiple pipes) for channelling clean water (not shown) in order to clean the blades 20 and the interior of the housing 10. Said pipe is attached to a clean water supply line and comprises a pressure switch and two electrovalves (not shown) arranged in series. The cleaning process is as follows:

- The electrovalves are closed; when a cleaning session is to be carried out (which may be programmed or automatic), the first electrovalve is opened

(upstream) but the second electrovalve (downstream) remains closed; then, the second electrovalve is opened.

- The electrovalves are open; when the cleaning session is to be ended, the second electrovalve is closed first and then, the first electrovalve is closed.

In this manner, wastewater is prevented from entering the clean water supply line. For added safety, the pressure switch keeps both electrovalves closed if the pressure in the clean water supply line is less than or equal to the pressure inside the turbine, or perhaps even if it is only slightly bigger.

The turbine may be manufactured using various materials, for example stainless steel or PVC.

Although only a number of particular embodiments and examples of the invention have been disclosed herein, it will be understood by those skilled in the art that other alternative embodiments and/or uses of the invention and obvious modifications and equivalents thereof are possible. Furthermore, the present invention covers all possible combinations of the particular embodiments described. Reference signs related to drawings and placed in parentheses in a claim, are solely for attempting to increase the intelligibility of the claim, and shall not be construed as limiting the scope of the claim. Thus, the scope of the present invention should not be limited by particular embodiments, but should be determined only by a fair reading of the claims that follow.

In particular, any suitable use of the turbine can be envisaged, such as in buildings, purifying plants, sewage systems, ships, etc. The electricity generated by the turbine can be applied to separate hydrogen from water, and said hydrogen can stored to feed a fuel cell.