EP0978599A1 - Sewage disposal process at low depth working with a single vacuum source - Google Patents

Abstract

The drainage system consists of a network of gravity feed pipes (30 - 35) which follow the natural slope of the land and carry the water to a series of manholes (20 - 23) situated at low points and of sufficient volume to store the water for a set period. The water is drawn from the manholes through suction pipes (4) to a single pumping station (1) via a management system with valves (8) emptying each manhole in turn.

Description

The present method consists in making a network shallow sanitation, thanks to a device centralized pumping system which empties several separate low points, where several networks converge gravitational following the natural slope of the land.

These gravity networks can be made at low depth without additional cost linked to the multiplication of positions pumping, because there is only one suction station discharge from which several suction pipes leave towards the collection looks.

In the traditional conception of networks the topography is the determining factor and often penalizing for the realization of projects.

When the ground is flat, the network must deepen quickly to allow gravity flow and you have to build pumping stations to raise water and leave again by gravity.

When the terrain is rough, we have to deepen to cross the mounds or create a post if the pipeline gravity is too deep.

The discharge stations are very heavy in their current design: a tarpaulin must be made reception located below the gravity arrival itself already deep, so create an important and deep civil engineering, the pumps are immersed in the effluent and it is necessary provide the devices to ensure their guidance and lifting.

Currently we are therefore trying to limit the number of positions because their cost of production and maintenance is high.

In the current state of the art, there are several solutions to overcome depths and decrease the costs of gravity networks.

• Dans l'assainissement sous vide, de petits tronçons de collecteurs gravitaires amènent l'effluent dans des regards de collecte équipés de valves qui sont reliés par une canalisation maintenue sous vide à une Centrale de vide. La Centrale de vide est une installation importante qui est constituée d'une cuve maintenue en permanence sous vide par des pompes à vide et équipée également de pompes d'extraction du liquide en dehors de la cuve.
• Dans le système sous pression, chaque point de collecte est équipé d'un petit poste de relèvement, ce qui entraíne la multiplication des équipements mécaniques et électriques.
• Le système à air comprimé nécessite la réalisation d'une centrale d'air comprimé et d'un réseau d'air comprimé alimentant chaque aéro-éjecteur.

Sanitation under vacuum, under pressure, compressed air.

• In vacuum sanitation, small sections of gravity collectors bring the effluent into collection manholes equipped with valves which are connected by a pipe maintained under vacuum to a vacuum system. The vacuum system is an important installation which consists of a tank permanently maintained under vacuum by vacuum pumps and also equipped with pumps for extracting the liquid outside the tank.
• In the pressure system, each collection point is equipped with a small lifting station, which results in the multiplication of mechanical and electrical equipment.
• The compressed air system requires the creation of a compressed air unit and a compressed air network supplying each aero-ejector.

In all these techniques, the transfer is expensive and they therefore have an application essentially when the field difficulties make the traditional solution very penalizing (rocky, swampy terrain ...).

The advantage of this process is to reconcile the achievement shallow gravity networks, with inexpensive transfer networks for investment and operation.

In the process which is the subject of the Patent, the pipes gravitational are placed according to the slope of the ground, at about 1m40 deep; they therefore converge towards low points without crossing high points.

In each of these low points, a collection look is created (or suction) equipped with a high level, a level low and an alarm level connected by a cable to the remote management from the pumping station.

In the collection manholes, we immerse the end of a waterproof pipe that connects the collection manhole to the pump.

This waterproof pipe can be laid at the same time as the gravity line, it is of small section, identical to a discharge line, follows the profile of the land about 1 meter deep.

The end of the pipe which is in the manhole of collection is fitted with a valve, the opening and closing are controlled by high level indicators and low, the information is then also transmitted by a remote control cable to the remote management located at the station pumping.

All the suction lines converge towards the pumping station and are gathered when they leave in the same structure as that where the pump is located.

When connecting the pipeline to the pump, places a circuit isolation or opening valve.

Pumping is done by a self-priming pump and not submerged which creates an aspiration when it is started in the pipeline and discharges the wastewater to the outlet.

The pumping station is managed by a remote management which collects the high and low level information in each look of collection, which controls the opening or closing of valves and simultaneously valves as well as starting or stopping the pump.

This allows each collection manhole to be emptied separately at from a single pumping unit.

To obtain a good performance of the system, the pipes must remain in charge at all times and the operation is carried out in the absence of vacuum.

The reliability of the type of valve and valves is therefore very important.

The pump operates in discharge suction. She must therefore be adapted to create a good suction without risk of plugging and setting in motion the liquid parts and solids with a passage section sized to allow the passage of long fibers and fibers.

The size of the collection manholes will depend on the number of connected constructions. They should be able to provide sufficient effluent storage so that in case of system failure, the look does not overflow before the troubleshooting intervention triggered by the alarm.

The diameter of the suction pipes will be calculated as for backflow depending on the flow to be provided and pressure losses.

The process has limits related to atmospheric pressure: emptying of collection manholes by means of the atmospheric pressure of 1 bar (10 meters). The geometric height between the bottom of the collection cover and the pump does not exceed 7 meters for a satisfactory flow be obtained.

In developing the project, it will therefore be necessary to take into account topography and pressure losses and play on the section of pipes, if the pressure drops are too strong.

Also, the choice of the location of the post is very important and its altitude should be such that the elevation does not exceed 7 meters between the collection points and the pumping point.

• Dans un mode de fonctionnement, chaque réseau d'aspiration peut être relié directement à la station qui commandera l'ouverture et la fermeture de la vanne du circuit considéré et du clapet.
• Dans un autre mode de fonctionnement, plusieurs réseaux d'aspiration sont connectés sur une canalisation principale d'aspiration. La vanne commandant l'ouverture du circuit considéré, est alors située sur la canalisation secondaire au voisinage de son raccordement à la canalisation principale d'aspiration.

Different operating modes of the process can be realized:

• In one operating mode, each suction network can be connected directly to the station which will control the opening and closing of the valve of the circuit in question and of the valve.
• In another operating mode, several suction networks are connected to a main suction pipe. The valve controlling the opening of the circuit in question is then located on the secondary pipe in the vicinity of its connection to the main suction pipe.

In an example of application of the method described below, the the topography of the area to be served is shown on the figure 1. This diagram shows that there are two high points (odds 13.34 and 12.00) and four low points (odds 10.75, 8.18, 9.58 and 9.32).

Diagram 2 shows a possible embodiment of the process with a single pumping station (1) located in the crossroads at TN 11,80, with 4 collection tarps (20) (21) (22) (23) located in each of the low points or gravity networks (30) (31) (32) (33) (34) (35) arrive a depth of 1.40m.

These collection manholes (20) (21) (22) (23) are made up of concrete elements, for example Ø 160.

The collection manhole 20 receives the gravity network 30, ie 100 Population equivalent.

The collection manhole 21 receives the gravity networks 31 and 35, or 120 equivalent inhabitants.

The collection manhole 22 receives the gravity networks 32 and 39, or 100 Population equivalent.

The collection manhole 23 receives the gravity network 33, i.e. 70 Population equivalent.

In total, 390 equivalent inhabitants, which at the rate of 150 liters per day per inhabitant, gives a daily volume of 58.5 ^m3 or a peak flow of 14.6 ^m3 / hour or 4 liters / second.

The collection manhole (20) (21) (22) (23) or suction tank has a high level (10), a low level (11) and a alarm level (12) as shown in diagram N ° 3.

A waterproof pipe (4) (in HDPE for example), connects the tank at the discharge suction station (1) similarly a remote control cable (7).

This pipe (4) is submerged at the bottom of the tank suction (20) (21) (22) (23) and its end is provided a particularly reliable valve (5).

The pumping station (1) consists of a Ø 2000 manhole, in which there are two pumps (6) connected to the different suction networks (4). Each network has its own connection to the pump (6) of a valve (8), allowing opening or closing the circuit.

When the high level (10) is reached in one of the tanks suction (20) (21) (22) (23), information is transmitted by cable (7) to remote management, which controls the simultaneous opening of the valve (8) and the valve (5) and also starts the pump (6).

The tank (20) (21) (22) (23) empties until the level bottom (11) is reached; the valve (5) and the valve (8) are then close, and the pump (6) stops. This until the restart of one of the circuits.

In the embodiment example as described above, circuits operate separately but depending on the configuration of the terrain and in particular in networks arranged in length we can set up a pipe main suction to which would be connected secondary suction lines.

In the configuration used in the example if requested priority on two circuits, priority is given by the remote management to the one receiving the highest speed.

Calculation of the volume of the suction tanks (20) (21) (22) (23) is done as follows:

The effluent being stored in the tank (20) (21) (22) (23), the minimum volume in reserve must be equal to the volume corresponding to the flow rate stored between two pump starts (6) with a safety volume in the event of dysfunction. If Q is the daily flow, the peak flow is Q '= Q: 6 in m3 hour.

The volume V to be stored is equal to Q '/ Nx6 (N being the number of pumps and 6 the number of starts of the pump in one hour). TANK EQH Q daily Q POINT M3 / h Minimum V 20 100 100x150L = 15m3 2.5 0.21m3 21 120 120x0.15 = 18m3 3 0.25m3 22 100 100x0.15 = 15m3 2.5 0.21m3 23 70 70x0.15 = 9.5m3 1.6 0.18m3

For a tank of Ø 1600 S = 2.01 m2 so a height of 0.25 m is required: 2 = 12.5 cm minimum water in the tank.

We will admit a height of 20 cm between the top (10) and bottom levels (11), level 15 alarm (12), 10 cm above and a safety reserve of 40 cm above the alarm (12). The gravity arrival being at least 1m40, the total depth of the gaze will therefore be around 2m30. The cut of a look is shown in Figure 3.

The self-priming pump will operate by discharge suction.

It must ensure the flow rate corresponding to 390 Eqh, i.e. 4 liters per second with an HMT equal to the sum of the pressure drops in the increased suction and discharge of the geometric height of the repression and aspiration.

With a Ø 76.8 discharge, a discharge length of 530 m and a flow rate of 4 liters per second, the pressure drop is 4m82.

The piezo dimension at the exit, is therefore 8.02 m + 4.82 m = 12m84.

For the suction the departure of the pipe in the example considered is 2m30 below the level of the TN, we can draw up the table of dimensions piezo suction Collecting manhole TN rating Suction start TN-2.30 Distance Pressure loss Ø 76.8 Piezo suction rating 23 8.18 5.88 250m - 2.25 3.63 22 9.58 7.28 230m - 2.07 5.21 21 9.32 7.02 275m - 2.48 4.54 20 10.75 8.45 352m - 3.21 5.24

The most unfavorable case is that of look 23, the pump must therefore have an HMT of 12.84 - 3.63 = 9.21 for a flow rate of 41 / second.

For the suction to work well, the height must be geometric does not exceed 7 meters between the point and the pump located in the post at 10m50 about; which is well respected, so we can admit the Ø 76/8 as satisfactory for the realization of this project.

Claims (3)

Shallow drainage installation in which the emptying of several collection manholes (20) (21) (22) (23) located at the low point where the gravity waters of a watershed are concentrated, takes place from the same pumping station (1) operating by discharge suction characterized by the presence of a remote management which ensures the successive emptying of each of the manholes collection (20) (21) (22) (23) by alternately putting under suction partial and temporary the network concerned by a drain request punctual. Installation according to claim (1) in which each collection manhole (20) (21) (22) (23) is connected directly to the station pumping (1) by an independent suction pipe (4). Installation according to claim (1) in which each secondary suction line (4) coming from a collection manhole (20) (21) (22) (23) is connected to the pumping station (1) by a main suction line to which are connected several secondary pipes.

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