Sewage booster station

Abstract

 A booster station (5) of sewage water, in which the startings and stoppings of pumps (6) installed in it are controlled by means of pressure prevailing on the suction side of the pumps or in frequency converter drives by means of frequencies. The invention is implemented such that the pumps (6) of the booster station (5) have a common inlet pipe (7) of the suction side which branches from a previous pumping station or an equivalent incoming inlet pipe (4).

Description

[0001] This invention relates to a booster station of sewage water, in which the startings and stoppings of pumps installed in it are controlled by means of pressure prevailing on the suction side of the pumps or by means of frequencies in frequency converter drives.

[0002] Recently, the treatment of sewage has been started to concentrate on larger and more effective treatment plants, whereby smaller ones have been closed down. Furthermore, buildings farther and farther from the treatment plant have been started to be taken within the drainage system. As a result of these changes, there has occurred a need to make so-called transfer sewers which can be extremely long. Long pressure lines with a cost-effective flow velocity cause great flow losses, whereby the pumps are required a great lifting height usually with relatively small volume flows. If there also exist bottom and top dead centres in the pressure line, air or gas in the water stays in the top dead centre and, when the pump operates, it transfers between the top dead centre and the bottom dead centre causing an additional lifting height requirement. Thus, a situation has arrived in which the sewage pump is required a very great lifting height compared to the volume flow. Then, a centrifugal pump should flow-technically be a multistage pump which includes several impellers connected in series. Such sewage pumps are not manufactured due to clog-proofness required of them.

[0003] In a known arrangement, the transfer sewer contains several pumping stations suitably located successively and each pump station has a suction basin in which the level controls the startings and stoppings of the pump. Disadvantages of such an arrangement are, inter alia, the odour problem causing inconvenience to the environment of the pumping station, which is caused by sewage water in the suction basin in connection with open air. This is particularly emphasised with long pressure lines in which the retention times of water are long, whereby hydrogen sulphide is able to build up in the wastewater. Another problem is that the suction basin increases the manufacturing costs of the pumping station, particularly if the pumps are wished to be in a separate dry space. Additionally, the suction basin or the whole pumping station has to be in practice below the ground surface, which can limit their location and/or cause digging and possibly quarrying costs. Furthermore, hydrogen sulphide or some other gas built up in the suction basin of the pumping station causes a decline in the oxygen content, which endangers the work safety of maintenance persons.

[0004] Another known arrangement is to connect the pumps of the same pumping station in series. A disadvantage of this is, inter alia, that the reliability of pumping operation decreases, because if one of the pumps is out of order, pumping does not operate at all. A further disadvantage is that the subsequent pump has to operate with high inlet pressure, whereby the leak possibility and leak speed of its shaft seals are increased. Furthermore, the pumping station has to have a separate dry space for the subsequent pump, which increases the building costs of the pumping station.

[0005] Additionally is known an arrangement in which there is no suction basin in the booster station and in which in the previous pumping station there are two pumps which have their own pressure pipes for the suction pipes of the pumps of the booster station. Then, the startings and stoppings of the pumps occur according to pressures prevailing in the suction pipes. When pumping sewage, a system of two alternating pumps is used and the pumps are selected such that the output of one pump is always sufficient. This way, pumping is ensured also in a case of one pump being out of order or being serviced. In this known arrangement, the reliability of pumping however suffers, because if in one line one of the pumps is e.g. locked or damaged and one pump similarly in the other line, pumping does not operate and the reliability of operation is halved.

[0006] The object of this invention is to provide a novel kind of a sewage booster station which does not pertain disadvantages occurring in known prior art. The booster station according to the invention is characterised by the pumps of the booster station having a common inlet pipe on the suction side which pipe branches from a previous pumping station or an equivalent incoming inlet pipe.

[0007] An advantageous embodiment of the booster station according to the invention is characterised by that in the inlet pipe between the inlet pipe and the pumps is located a pressure measuring sensor suitable for sewage water.

[0008] Another advantageous embodiment of the booster station according to the invention is characterised by that the starting and stopping of the pumps are controlled by means of pressure prevailing in the inlet pipe.

[0009] A further advantageous embodiment of the booster station according to the invention is characterised by that the pumps of the previous pumping station are selected such that the lifting height of the pumps is greater than the requirement with its own pipeline curve and desired volume flow.

[0010] As advantages of the invention, it can be mentioned that disadvantages of known prior art have been eliminated. The booster station according to the invention requires no suction basin. An additional advantage of the arrangement according to the invention is that the pumps can be selected more freely as long as the lifting height requirement of the previous pump is fulfilled, because its lifting height can also be greater than the minimum requirement for the lifting height. It is then possible to select the pumps such that they provide as good as possible total efficiency. Furthermore, it is possible to select suitable pump types. When required, it is also possible to select in the booster station a large number of different pumps. It also enables pressure pipes incoming from several previous pumping stations.

[0011] Next, the invention is described in more detail by referring to the accompanying drawings in which

Fig. 1 shows a cross-sectional view of two successive booster stations.

Fig. 2 shows the booster station 5 of Fig. 1 in a larger scale.

Fig. 3 shows a top view of the booster station of Fig. 2.

Fig. 4 shows a booster station installed above ground.

Fig. 5 shows pipeline curves of the pumps.

[0012] In a first pumping station 1, there is a suction basin 2 in which there are e.g. a submersible pump or pumps 3 which pump sewage through a pressure pipe 4 to a booster station 5. In the booster station according to the invention, there thus is no suction basin in connection with air space.

[0013] The starting and stopping of a pump or pumps 6 of the booster station 5 are controlled by means of pressure prevailing in an inlet pipe 7. Another possibility is to control the starting and stopping with remote control in accordance with the starting and stopping of the pumps 3 of the previous pumping station. When using frequency converters in the pumping stations, the frequency of the booster station is controlled by means of pressure prevailing in the inlet pipe 7. When further using frequency converters in the pumping stations, the frequency of the pumps 6 of the booster station 5 is controlled in accordance with the previous pumping station with remote control.

[0014] In the inlet pipe 7 between the inlet pipe 4 and the pump or pumps 6 is located a pressure measuring sensor 8 suitable for sewage water. As a result of possible clogging of the pumps or pipeline of the previous pumping station or some other reason lowering the pressure, minimum pressure is defined for the pressure of the pressure sensor 8 in which pressure the pumps 6 will stop (to avoid cavitation) and possibly the minimum pressure in which the pumps 3 will stop with remote control.

[0015] As a result of possible clogging of the pump 6 or its pressure pipe or some other reason, maximum pressure is defined for the pressure of the pressure sensor 8 when the pump is operating in which the pump 6 will stop, or maximum pressure in which the pump 3 will stop with remote control.

[0016] In the embodiment example of Fig. 4, the booster station 5 is located above the ground surface.

[0017] The pumps 6 are selected such that the lifting height of the previous pump is greater than the requirement with its own pipeline curve and desired volume flow Q and the lifting height of the pump 6 of the booster station is the common lifting height of the pipeline curves of both pumping stations with the same Q, the lifting height of the pump 3 of the previous pumping station deducted. The selected lifting height of the pump 3 can also be about 15-30% greater than the requirement with its own pipeline curve.

[0018] It is possible to locate the pressure sensor 8, which enables also the measurement of underpressure, on the side of the pipe 7, whereby no solid matter heavier or lighter than water will accumulate in it. The pressure of the pressure sensor 8 is monitored, whereby changes occurring in the pumps 3 and 6 and their pressure pipelines will be observed in time.

[0019] It is also possible that pressure pipes of several previous pumping stations arrive in the booster station. It is also possible that the previous pumping station is in accordance with the invention.

[0020] The lifting height requirement for the previous pump ensures that sufficient inlet pressure is provided to the subsequent pump to avoid cavitation. In practice, the minimum pressure can be set a little on the side of underpressure when considering the NPSH_r value (suction capacity) of the pump. Lifting height inaccuracy is caused by the tolerances of the Q/H curves of the pumps and the calculation inaccuracy of the pressure pipe. It is also good to have safety margin in case the previous pump wears faster.

[0021] By the pressure of the pressure sensor 8, it is also possible to monitor the changes of the subsequent pump and pipeline for if the pressure increases it means that changes have occurred in the subsequent pumps or pipeline.

[0022] The lifting height (H₁) of the pumps of the previous pumping station is selected with desired volume flow Q such that it is in the design stage between about 1.2 times a calculated lifting height (H₃) of its own pipeline and about 0.95 times a total lifting height (H₄) of the pumps of both pumping stations and the lifting height of the pump of the booster station is selected such that it is greater than or equal to (H₄)-(H₁). Then, it can be ensured that, due to the +/- tolerances of the pump curves and/or the calculation inaccuracy of the pipeline curve, pressure in the suction pipe can be increased sufficiently compared to the static state in order for the pumps of the booster station to start and operate without the danger of cavitation. Furthermore, the lifting heights of the pumps of the previous pumping station can in practice decrease due to momentary clogging or water containing air, particularly if the incoming water falls in the previous pumping station. If there are top dead centres in the pressure line of the previous pumping station where air or some other gas can remain or accumulate, it increases the lifting height requirement, whereby pressure can decrease in the suction pipe. It can also decrease due to the wear of the pumps of the previous pumping station. Then, safety margin is provided with the selection coefficient of H₁. The selection possibility of the pumps of the above-mentioned first pumping station enables the selection of pump models good and suitable of their efficiencies.

[0023] The invention also enables combining pressure pipes incoming from several previous pumping stations in a distributor pipe. If required, there can be several pumps connected to the distributor pipe in the booster station. The stoppings and startings of the pumps occur in accordance with the pressure of the distributor pipe.

[0024] If e.g. the pump of the subsequent pumping station is damaged or clogged, a maximum value has been set for the pressure of the distributor pipe which stops the pumps of both the booster and the previous pumping station with remote control. Then, the pumps will not remain rotating in vain in the pumping station badly or at all.

[0025] Also pressure measurement can be installed and certain maximum pressure can be set for the pumps of the previous pumping station, e.g. 30 s after starting, which stops the pump if the subsequent pump is damaged or gets locked.

[0026] In the frequency converter drives, the frequencies can be set mutually suitable such that the total efficiency on the whole frequency range can be maximised.

[0027] The booster station can be located either under or above ground.

[0028] It is well known by those skilled in the art that the invention does not limit to the embodiment examples described above, but it may vary within the scope of the enclosed patent claims.

Claims

1. A booster station (5) of sewage water, in which the startings and stoppings of pumps (6) installed in it are controlled by means of pressure prevailing on the suction side of the pumps or in frequency converter drives by means of frequencies, characterised in that the pumps (6) of the booster station (5) have a common inlet pipe (7) of the suction side which branches from a previous pumping station (1) or an equivalent incoming inlet pipe (4).

2. A booster station according to claim 1, characterised in that in the inlet pipe (7) between the inlet pipe (4) and the pumps (6) is located a pressure measuring sensor (8) suitable for sewage water.

3. A booster station according to claim 1 or 2, characterised in that the starting and stopping of the pumps (6) are controlled by means of pressure prevailing in the inlet pipe (4, 7).

4. A booster station according to any one of claims 1-3, characterised in that pumps (3) of the previous pumping station (1) are selected such that a lifting height (H₁) of the pumps (3) is greater than the requirement with its own pipeline curve and desired volume flow.

5. A booster station according to claim 4, characterised in that the lifting height (H₁) is selected such that it is in the design stage between about 1.2 times a calculated lifting height (H₃) of its own pipeline and about 0.95 times a total lifting height (H₄) of the pumps of both pumping stations.

6. A booster station according to claim 5, characterised in that the lifting height of the pumps (6) is selected such that it is greater than or equal to (H₄)-(H₁).

7. A booster station according to any one of claims 1-6, characterised in that in a distributor pipe (7) of the pumps (6) of the booster station (5) are combined inlet pipes incoming from several previous booster stations.

8. A booster station according to any one of claims 1-7, characterised in that the previous booster station(s) is/are also in accordance with the invention.

9. A booster station according to any one of claims 1-8, characterised in that the booster station (5) is located above ground.

10. A booster station according to any one of claims 1-8, characterised in that the booster station (5) is located under ground.

Drawing