Technical Field

The invention relates to a gravity sewer device for overcoming watercourses or similar underground obstacles, so-called inverted siphons consisting of one or more inlet shaft chambers with an automatic flushing bell, connected to a descending leg of a sewer conduit, crossing an ascending leg of a sewer conduit and an outlet shaft, wherein the automatic flushing bell ensures the filling and emptying of the working volume of the shaft, and the waste water is periodically discharged under increased pressure and at high speed into the sewer conduit of the inverted siphon.

Background Art

The most commonly used method and technical equipment for overcoming watercourses or similar underground obstacles is the inverted siphon. When the term "liquid" is used below, this means in particular wastewater or rainwater, however, various other admixtures do not affect the scope of the definition of this term.

The standard arrangement of the sewer inverted siphon is shown in Fig. 1. The wastewater flows through the gravity conduit 1 at the flow rate Q(0) into the upper inlet chamber 2, which forms the transition from the sewer conduit to the inverted siphon. The inverted siphon itself consists of the descending conduit leg 3, a horizontal, reap, slightly inclined part forming the crossing 5 under the watercourse 4 or a similar underground obstacle, and the ascending conduit leg 6. The inverted siphon leads to the lower outlet shaft chamber 7, which must always be located lower than the upper inlet chamber. The wastewater flows out of the shaft chamber 7 through the gravity conduit 8 at the flow rate Q(0).

From the point of view of physics, the inverted siphon works on the principle of connected vessels and Bernoulli's equation.

From a practical point of view, the usable diameters of the inverted siphon conduits cannot be minimized, particularly due to their possible clogging and subsequent blockage.

After more than a hundred years of operational experience, standardized technical and hydraulic requirements for inverted siphons have been standardised around the world: minimum profile (inner diameter) of inverted siphon DN200, slope of the crossing conduit at least towards the outlet conduit leg, slope of the outlet leg 1:5, however, it must not be greater than 1:3, the velocity of the water flow in the inverted siphon shall not fall below v(ef)=0.75 m.s ^-1 for mixed rainwater and sewage and v(ef)=1.0 m.s ^-1 for sewage water.

These technical and hydraulic conditions determine the use of inverted siphons for cros ^' sing watercourses or similar underground obstacles for sewerage systems with a continuous flow of more than Q(0)=25 1.s ^-1 , which corresponds to internal diameter DN200 with effective flow velocity v(ef)=0.75 m.s ^-1 .

In the case of smaller sewerage systems, the use of an inverted siphon is excluded; instead, a discharging station with a discharge conduit is usually used for crossing, where the wastewater is pumped down the slope only to ensure the passage of the sewage conduit.

Many inventors have tried to solve the problem of low flow velocity and clogging of inverted siphons.

Their solutions can be divided into two basic groups. The first group consists of solutions that work with the creation of a narrowed point of entry into the inverted siphon and controlled suction of air so as to create a so-called air cushion in the legs of the inverted siphon. This reduces the cross-section of the inverted siphon conduit, which increases the flow rate. The disadvantage of the group of solutions with the air cushion is their technical complexity and thus operational unreliability. Representative of this group of solutions is, for example, JP2006063645A, whose authors are Koda Yoshiharu and Odaka Shiro.

The second group comprises solutions that work with periodic filling of the inlet chamber of the inverted siphon, where the outlet chamber of the inverted siphon has a mechanical conduit closure. It opens in a controlled or automatic manner depending on the state of the water level in the inlet chamber or the water pressure in the outlet chamber. In this group of solutions, the inverted siphon conduit is always filled with water, i.e., without any air cushion. This group is also problematic due to the technical complexity, so it is used mainly for large-diameter inverted siphons.

Representative of the second group of solutions is, for example, CA2529352A1, whose authors are Steinhardt J. M. and Stiehl O.

The objective of the invention is to eliminate the disadvantages of the prior art and to create a simple and operationally reliable sewer system which will be able to function even at a very low flow rate Q(0) without the risk of the crossing conduit clogging under a watercourse or similar underground obstacle.

Summ ary of the Invention

The shortcomings of the prior art are substantially eliminated and the objective of the invention is fulfilled by the self-flushing inverted siphon according to the invention.

It belongs to the second group of technical solutions of the inverted siphons and works without any air cushion, with a constant cross-section of the conduit and periodic emptying of the inlet chamber of the inverted siphon.

This invention uses a known solution of the Miller flush bell, disclosed in US727990A, US710703A and US761316A.

For the purposes of this invention, the Miller flush bell for use in inverted siphons has been innovatively modified according to exemplary solutions 1 and 2 so as to be able to work in a system of the new technical solution of a self-flushing inverted siphon, which is a modification of the Miller flush bell, hereinafter referred to as the automatic flushing bell 17.

For the purposes of the present invention, the Miller flush bell has been further innovatively modified according to exemplary solutions 3 and 4, which is a variant of the automatic flushing bell, hereinafter referred to as the automatic flushing bell 20.

The self-flushing inverted siphon according to the invention forms a section of a gravity sewer, which crosses a watercourse or a similar underground obstacle, is graphically shown in Fig. 2 and compared with the classic design of the inverted siphon in Fig. 1. It consists of one or more inlet shaft chambers 9 connected to the descending leg 12 of the sewage conduit, the crossing 13, the ascending leg 14 of the sewage conduit and the outlet shaft 7, wherein the automatic flushing bell 17 or 20 is located in the inlet shaft chamber 9. The gravity sewer of the inlet 1 is connected to the inlet of the inlet shaft chamber 9, which is equipped with a space for trapping sand and coarse sediments 10, a bar screen or a screen basket 11. The gravity sewer of the outlet £ is connected to the outlet shaft 7.

The wastewater flows at the flow rate Q(0) through the gravity conduit 1 into the upper inlet chamber 9, equipped with a sand trap 10 and a floating impurities catcher 11.

The automatic flushing bell 17 (alternatively as variant 20), which includes a siphon conduit 15 and a vent pipe 16, provides periodic alternation between two phases, water accumulation and transfer, when the water level in the storage space of the chamber 9 oscillates between H1 and H2, where the filling velocity (flow rate) is Q(0), and the transfer velocity (resp. flow rate) is Q(l).

The difference in the H2-H1 level height limits is the driving force for the water transfer and must be chosen with respect to the length of the inverted siphon and local flow resistances in the conduit so that the effective velocity v(ef) does not fall below 1.0 m.s ^-1 ; the approximate value for correlation calculation can be considered H2- H1=0.5 m.

The design of the accumulation volume of the main part of the inlet chamber 9 must be carried out in accordance with the total volume of the sewage conduit of the inverted siphon. It must be at least 1.5 times greater than the inverted siphon volume. it has proven to be an advantageous solution to use an automatic flushing bell 17 or 20 for the conduit dimensions and the difference between the upper and lower water level height limits H2-H1: internal diameter DN100 for H2-H1 from 0.2 to 0.6 m internal diameter DN150 for H2-H1 from 0.6 to 0.7 m internal diameter DN200 for H2-H1 from 0.7 to 1.0 m

It proved to be an advantageous solution to design the difference in the H2-H1 level height limits so that the effective flush rate of the inverted siphon v(ef) does not fall below 1.0 m.s ^-1 , then consider H2-H1 as a reference value for the correlation calculation of the inverted siphon conduit with inner diameter DN100, and then consider H2-H1*0.5 m. A calculation example is given in Example 1.

An advantageous solution has proven to be to design the accumulation volume of the main part of the inlet chamber to be at least 1.5 times greater than the volume of the inverted siphon conduit.

The use of non-corroding materials, e.g., polypropylene, polyethylene, stainless steel AISI 316L, has proven to be a preferred solution for the automatic flushing bell 17 or 20 according to this invention, while materials such as HOPE or cast iron commonly used for pressure conduits can be used for the inverted siphon conduit.

The use of the automatic flushing bell 20 has proven to be another separate advantageous solution.

Units and equations used g gravitational acceleration on the Earth's surface [m.s ^-2 ] v(k) final velocity [m.s ^-1 ] v(0) filling velocity at the inlet [m.s ^-1 ] v (ef) effective velocity [m.s ^-1 ]

Q(k) final flow rate [l.s ^-1 , m ³ .s ^-1 ]

Q(0) average flow rate at the inlet [l.s ^-1 , m ³ .s ^-1 ]

Q(1) average flow rate of water being transferred [l.s ^-1 , m ³ .s ^-1 ]

P(hy) hydrostatic water pressure [Pa, kPa] p (A) atmospheric pressure [Pa, kPa]

P(PL) pressure loss in the conduit [Pa, kPa] ς local flow resistance in the conduit [Pa, kPa]

T temperature [°C]

L length [m]

S cross-section area [m 2, cm2], t time [s, hour]

P water density [kg.m ^-3 ] v kinematic viscosity [mm ² .s ^-1 ]

[mm] where the empirical equation [1] is used in the laminar flow region, [2] in the transient region and [3] in the turbulent flow region. The automatic flushing bell 17 is defined as a complete constant device for switching with a constant level described in Examples 1 and 2, the bell 17a being a part of it in the form of a single-stage inverted bell, described in said examples and shown in detail in Fig. 3.

The automatic flushing bell 20 is defined as a complete device for switching with a variable and controlled level described in Examples 3 and 4, the bell 17b being a part of it in the form of a two-stage inverted bell, described in said examples and shown in detail in Fig. 4.

Overview of Figures in the Drawings

The invention will be further explained in the exemplary embodiment according to the accompanying drawings, in which:

Fig. 1 shows a standard technical solution of a sewer inverted siphon under a watercourse;

Fig. 2 shows a technical solution of a self-flushing inverted siphon according to the invention, with an automatic flushing bell 17, described in Example 1;

Fig. 3 shows the individual parts of the automatic flushing bell 17 for the description of its function in Example 2;

Fig. 4 shows the individual parts of the automatic flushing bell 20 for the description of its function in Example 3;

Fig. 5 shows schematically the function of a sequencing batch reactor using the automatic flushing bell 20, the solution being described in Example 4; Fig. 6 shows the dependence of the pressure loss of the inverted siphon conduit from Example 1 and the flow rate according to the Colebrook-White equations.

Example 1:

Self-flushing inverted siphon

The inverted siphon for overcoming a watercourse or similar underground obstacles according to the invention, a self-flushing inverted siphon, is shown in Fig. 2.

The self-flushing inverted siphon consists of an upper inlet chamber 9, to which a gravity sewage pipe 1 is connected. The upper inlet chamber is equipped with a space for collecting sand and coarse sediments 10, with bar screens or a screen basket 11. In the main part of the inlet chamber there is situated an automatic flushing bell 17.

The siphon conduit 15 of the automatic flushing bell 17 is connected to the descending leg 12 of the sewage inverted siphon conduit, then to the crossing conduit 13 of the watercourse 4, the ascending leg of the sewage conduit 14_ from where it then leads into the lower outlet sewer shaft 7. The gravity sewage conduit 8 is connected to the sewer shaft 7.

Wastewater flows at the flow rate Q(0) through the gravity conduit 1 into the upper inlet chamber 9, equipped with a sand trap 10 and a floating inpurities catcher 11. The automatic flushing bell 17, which includes a siphon conduit 15 and a vent pipe 16, provides periodic alternation between two phases, water accumulation and transfer, when the water level in the storage space of the chamber 9 'oscillates between H1 and H2, where the filling velocity (flow rate) is Q(0), and the water transfer velocity (flow rate) is Q(l). The difference in the H2-H1 level height limits must be chosen with respect to the length of the inverted siphon and local flow resistances in the conduit so that the effective velocity v(ef) does not fall below 1.0 m.s ^-1 ; the approximate value for correlation calculation can be considered H2- H1=0.5 m.

The design of the accumulation volume of the main part of the inlet chamber 9 must be carried out in accordance with the total volume of the sewage conduit of the inverted siphon. It must be at least 1.5 times greater than the inverted siphon volume.

Fulfilment of these two basic conditions, observance of the effective velocity in the flushing phase and at least 1.5 times the volume of the flushed water compared to the total volume of the inverted siphon, create preconditions for trouble-free operation of the self-flushing inverted siphon.

To understand the essence of the invention, an exemplary calculation is performed. is a notation of Bernoulli's equation for the outflow of water from the tank through one conduit, from which, if the filling velocity v(0) is ignored (it is many times lower than the outflow velocity at the end of the conduit v(k), we get to the following for the outflow rate: v(k)=V(2.g.H), where g is gravitational acceleration 9.81m.s ^-2 and H is the level height difference in the storage tank between the upper and lower-level height limits H2-H1.

When using the continuity equation, the flow rate at the end of the conduit amounts to:

Q(k) = v(k).S, where S is the cross-section of the conduit.

If, for example, the inverted siphon has a total length L=17 m, the sum of the local flow resistances of the inverted siphon conduit is ζ=3.0 m, water temperature T=20°C, density o=998 kg.m ^-3 , kinematic"

2 -1 viscosity y=l.004 mm .s and the starting height between the upper and lower level height limits is H=0,7 m, then for DN100 conduit (cross-section S = 78.5 cm ² ) the theoretical outflow velocity is v(k)-3.71 m.s ^-1 and the flow rate Q(k)=15.55 l.s ^-1 . This is a purely theoretical value.

For practical calculation, it is necessary to consider Reynolds numbers for different flow rates and conduit roughness.

If we use computational Colebrook-White(*) equations, we get the curve of dependencies of pressure losses and flow velocity, shown in Fig. 6, for the characteristic behaviour of the particular inverted siphon.

For H=0.7 m and time T=0 it holds that the hydrostatic pressure p(hy)=6.853 kPa, the theoretical outflow velocity v(k)-3.71 m.s ^-1 , the actual velocity for the given specific case v(ef)=1.9 m.s ^-1 when meeting the condition p(hy)=p(PL), where p(PL) is the pressure loss at the given operating point of the WP1 diagram. The level height in the upper chamber of the inverted siphon starts to decrease to the level at which the real velocity v(ef)=1.0 m.s ^-1 is ensured. This is at the operating point of the WP2 diagram, which corresponds to H=0.2 m.

The working area of a specific inverted siphon is therefore between points WP1 and WP2. The values enable you to approximate the mean outflow velocity, the average flow rate and subsequently to calculate the emptying time of the inlet chamber of the inverted siphon.

Example 2

Automatic flushing bell with constant switching level

The siphon principle, explained by the theory of connected vessels and Bernoulli's equation, was already known in ancient Greece.

Since then, many technical applications and products have been developed using this principle.

The examples given here as an innovative solution according to the invention use the form of a siphon bell, published in 1891 by Mr. S. W. Miller and disclosed in US727990A under the name "SIPHON".

Fig. 3 shows the complete assembly of the automatic flushing bell 17, which consists of the original siphon conduit 15 with the bell 17a fitted.

Innovatively, the assembly was supplemented with a side closing pipe 18 for adjusting the level height H3 and a vent pipe 16.

By this, a variant of the "Miller - Semerid" automatic flushing bell is formed - an automatic flushing bell 17 in a complete assembly for use in a self-flushing inverted siphon.

The principle of operation is as follows:

The tank is filled with water from the water level H1 (lower-level height limit) at the same rate inside and outside the bell 17a, until the water level H3 is reached.

At this level, the rising water covers the side closing pipe 18, the tank continues to fill up to level H2, with different velocities inside and outside the bell 17a, the water level in the storage tank is open to the atmosphere, the water level inside the bell 17a is not. The rise in water between H3 and H2 causes an increase in the air pressure inside the bell 17a, which causes the water to drop towards the siphon 15. When the water in the siphon 15 drops to the H5 level, the H2 level is just reached in the storage tank as the upper-level height limit.

The filling and accumulation phase ends, the water transfer phase begins.

The overpressure in the tank causes the water to be forced into the conduit 25, the excess air escapes into the atmosphere through the pipe 16, the water column and the "siphon effect" start are connected, the tank starts being emptied.

The emptying of the tank continues until the lower-level height limit H1 is reached, which is defined by the edge of the bell 17a. At this moment, air is sucked in by the bell 17a and the column of expelled water in the siphon conduit 15 is interrupted.

A new period, the filling and accumulation phase, begins, from the water level height H1 in the tank. Automatic flushing bell with variable and controlled switching level

The automatic flushing bell 17 in Example 2 is suitable for applications where fixed setting of the switching level H2 is sufficient.

In Example 3 and in Fig. 4 a separate innovative modification is described, which results in a variant according to the second embodiment, i.e., an automatic flushing bell 20 with the variable switching level Hx:

The bell 17b having a cylindrical and a conical part (the bell 17a only has a cylindrical part) is mounted on a siphon conduit 15 with a vent pipe 16 and is supplemented by a side closing tube 18.

In place of the bell's spherical cap 21a or the bend in the siphon conduit 21b, there is a pipe of small diameter 26a, resp. 26b, on which the solenoid valve 22a, resp. 22b is mounted.

The conical portion of the bell 17b may have a deflector 24 at the bottom, which is a baffle plate with directing lamellae to increase the absorption capacity of the automatic flushing bell and change the direction of water 27 being sucked in. The suction direction 27 is shown in detail on the deflector 24 in Fig. 4.

The principle of operation is as follows:

The tank is filled with water starting from the water level height H1 (lower-level height limit) at the same rate inside and outside the bell 17b, until the water level height H3 is reached, and after the side closing tube 18 has been covered, the tank continues to be filled. Once the level Hx has been reached, it is possible to open the decompression valve 22 (variants 22a, 22b) at any time up to the level H2. By opening this valve, air is released from the space of the bell 17{> and the siphon conduit 15, thus connecting the water continuum. The siphon effect starts immediately, the filling phase ends, and the tank starts being emptied.

With the automatic flushing bell 20 (Example 3), in contrast to the automatic flushing bell 17 (Example 2), it is possible to change the switching level Hx to the H2 level in accordance with current needs.

Example 4

Water discharge for sequencing batch reactor

The automatic flushing bell 20 in Example 3 can be used as a separate technical solution of the invention for discharging water from a sequencing batch reactor, which is shown in Fig. 5:

The tank 1_9 is equipped with a discharging station 29 for replenishing water in the tank 19, further with a blower 28 for supplying compressed air for the aeration device 31, by means of the device for controlled discharge of separated clean water the automatic flushing bell 20, described in Example 4.

For normal operation, the sequencing batch reactor is supplemented by a control system 30 with connected digital inputs il to i3 for sensing the water level H7, H8 resp. H9, which is ensured by means of a level sensor 23. The control is performed in a combination of volume and time mode via digital outputs ol to o3, when the output ol switches on, resp. switches off the blower 28, the outlet o2 switches on/off the discharging station 29, and the outlet o3 carries out decompression in the bell 17b of the automatic flushing bell 20 through the solenoid valve 22, so that the outlet o3 opens the solenoid valve 22, thereby releasing air from the bell space 17b and siphon conduit 15, and subsequently the water continuum is connected. This then triggers the siphon effect when the filling phase ends, and the tank starts being emptied.

The automatic flushing bell 20 in the sequencing batch reactor is always supplemented with a deflector 24 to increase the absorption capacity, to provide water suction 27 direction control and prevent suction of settling particles 24 in the automatic flushing bell 20, and is described in Example 4 and shown in Fig. 4, including the P'- P sectional view in the detailed ground plan.

The principle of operation of the sequencing batch reactor with the automatic flushing bell 20 is as follows:

3 basic phases alternate in the reactor in one cycle: phase F1 - filling and simultaneous biological reaction (pump station 29 and blower 28 are on), phase F2 - sludge sedimentation (blower 28 is off) and phase F3 - decantation and water discharge.

For phases F1 and F3, the volume control of the automatic flushing bell 20 can be successfully used, phase F2 must be strictly time controlled. Usually, a 60-minute sedimentation period is used in one cycle, where sedimentation means switching off the blower 28 and interrupting water discharging from the pumping station 29.

With the proposed modification of the automatic flushing bell 20, it is not a problem to include time control: If the water level is anywhere between H8 and H9, the control system 30 switches off the blower 28 via the digital output ol for the required 60-minute period, then the control system 30 opens the solenoid valve 22 via the digital output o3 for 10 to 15 seconds. This depressurizes the automatic flushing bell 20 at point 21, via line 26 through the solenoid valve 22 from point 21, which connects the water column inside the bell 17b and at the same time the F3 phase begins, the clean water being discharged until the H7 level is reached. The entire three-phase cycle of the sequencing reactor then starts again.

Industrial utilisation

The devices according to the invention can be particularly used in the field of wastewater transport and treatment.

List of reference marks

1 - gravity sewer conduit, inverted siphon inlet

2 - shaft, upper inlet chamber of the inverted siphon

3 - descending leg of the sewage conduit of the inverted siphon

4 - watercourse or other obstacle to be overcome by the inverted siphon

5 - sewage conduit crossing a watercourse

6 - ascending leg of the sewage conduit of the inverted siphon

7 - lower output shaft of the inverted siphon

8 - gravity sewer conduit, inverted siphon outlet

9 - upper inlet chamber of the inverted siphon with an automatic flushing bell installed

10 - space for accumulation of sand and coarse sediments

11 - bar screen or screen basket

12 - descending leg of the sewage conduit of the inverted siphon

13 - sewage conduit crossing a watercourse

14 - ascending leg of the sewage conduit of the inverted siphon

15 - siphon conduit of the automatic flushing bell

16 - siphon conduit deaeration

17 - automatic flushing bell according to the first embodiment 17a - bell as a part of the equipment 17

17b - bell as a part of the equipment 20

18 - side closing pipe of the automatic flushing bell

19 - tank of the sequencing batch reactor

20 - automatic flushing bell according to the second embodiment

21 - connection of the pipe to the automatic flushing bell 20

22 - valve for controlled decompression of the bell 17b for Examples

3 and 4

23 - water level sensor H7, H8 and H9 for the control system 30

24 - deflector to increase absorption capacity and direct the flow of water

25 - discharge conduit of the automatic flushing bell 3/7, 20 26 - decompression pipe for venting air through the valve 22

27 - flow direction, water suction into the bell 17b

28 - blower for the sequencing batch reactor, Example 4

29 - pumping station for the sequencing batch reactor, Example 4

30 - control system for the sequencing batch reactor, Example 4

31 - aeration device for the sequencing batch reactor, Example 4 il, i2, i3 - digital inputs of the control system 30 ol, o2, o3 - digital outputs of the control system 30

A height of the bell 17a in Fig.3 [mm]

B distance between the edge of the bell 17a and the bend of the siphon pipe [mm]

D inner diameter of the bell 17a (Fig. 3) or 17b (cylindrical part) [mm]

D1 inner diameter of the bell 17b (lower conical part) [mm] DN conduit inner diameter [mm]

B structural height [m] H1 lower height limit [m] H2 upper height limit [m]

H3 water level when the side pipe 16 is covered [m]

H4 lower edge of the discharge conduit 25 [m]

H5 upper edge of the siphon conduit 15 [m] H6 upper level of the deaeration pipe 16 [m]

H7 lower water level for the sequencing batch reactor [m] H8 bell cap level 17b (Example 4) [m]

H9 maximum water level for the sequencing batch reactor [m]

H water level in the tank, in general [m]

H2-H1 distance between lower and upper-level height limits [m]

Hx water level when opening the decompression valve 22 [m]