METHOD AND ARRANGEMENT FOR CLEANING A SENSOR

Abstract

The invention relates to a method for cleaning a sensor in a wastewater monitoring arrangement comprising at least one sensor with a sensor surface, such as an optical sensor with a window, lens, or the like. In the monitoring arrangement, during a normal operation mode, a sample flow of wastewater is arranged to flow past the sensor surface and the sensor is arranged to provide measurement values that describe a quality parameter of the wastewater. The method comprising steps of: starting a sensor cleaning cycle by discontinuing the sample flow; starting a cleaning liquid flow; arranging the cleaning liquid flow towards the sensor surface; mechanically cleaning the sensor surface by an automatic cleaning device; discontinuing the cleaning liquid flow after a predetermined cleaning time and ending the cleaning cycle; and starting the wastewater flow again.

Claims

1. A method for cleaning a sensor in a wastewater monitoring arrangement comprising at least one sensor with a sensor surface, such as an optical sensor with a window, lens, or the like, in which monitoring arrangement, during a normal operation mode, a sample flow of wastewater is arranged to flow past the sensor surface and the sensor is arranged to provide measurement values that describe a quality parameter of the wastewater, the method comprising steps of: starting a sensor cleaning cycle by discontinuing the sample flow; starting a cleaning liquid flow; arranging the cleaning liquid flow towards the sensor surface; mechanically cleaning the sensor surface by an automatic cleaning device; discontinuing the cleaning liquid flow after a predetermined cleaning time and ending the cleaning cycle; and starting the wastewater flow again.

2. The method according to claim 1, wherein the cleaning liquid flow comprises at least one chemical cleaning agent, such as a detergent, at least during a part of the cleaning cycle.

3. The method according to claim 1, wherein pressurized gas, preferably pressurized air, is fed to the cleaning liquid flow.

4. The method according to claim 1, wherein the cleaning liquid has an elevated temperature of at least 50° C., preferably at least 70° C., more preferably at least 75° C.

5. The method according to claim 1, wherein a filter is arranged before the sensor, in a flow direction of the sample flow during the normal operation mode, for removal solid and particulate material from the sample flow.

6. The method according to claim 1, wherein a sample strainer is arranged before the sensor, in a flow direction of the sample flow during the normal operation mode, to break up solid and particulate material, such as rags, paper debris and the like, in the sample flow before the flow comes into a contact with the sensor surface.

7. The method according to claim 5, wherein during the cleaning cycle the cleaning liquid flow is arranged to flow towards the filter for backflushing the filter.

8. The method according to claim 1, wherein the cleaning liquid flow is arranged towards the sensor surface at a straight angle.

9. The method according to claim 1, wherein the cleaning cycle is activated at predetermined time intervals.

10. A method to monitor wastewater in municipal wastewater treatment; food industry; agriculture; livestock farming; paper, board or pulp industry; or metallurgical industry, the method comprising cleaning a sensor in a wastewater monitoring arrangement according to claim 1.

11. An arrangement for a wastewater monitoring, comprising at least one sensor with a sensor surface, such as an optical sensor with a window, lens, or the like, in which arrangement during a normal operation mode a sample flow of wastewater is arranged to flow past the sensor surface and the sensor is arranged to provide measurement values which describe a quality parameter of the wastewater, the arrangement comprising a first reservoir for a cleaning liquid, connections for leading the cleaning liquid from the first reservoir towards the sensor surface, and transfer means, such as a cleaning liquid pump, for transferring the cleaning liquid from the first reservoir to the sensor, optional means for heating the cleaning liquid to an elevated temperature; automatic cleaning device for mechanically cleaning the sensor surface; a control unit, which is in functional contact with at least the transfer means and the automatic cleaning device, and which is arranged to carry out a cleaning cycle according to claim 1.

12. The arrangement according to claim 11, wherein the arrangement comprises a second reservoir for a chemical cleaning agent, connections for leading the chemical cleaning agent to the sensor, and a second transfer means, such as pump, for transferring the chemical cleaning agent.

13. The arrangement according to claim 11, wherein the arrangement comprises means for feeding pressurized gas to the cleaning liquid flow.

14. The arrangement according to claim 11, wherein the arrangement comprises a filter, which is arranged before the sensor in a flow direction of the sample flow during the normal operation mode, for removal solid and particulate material from the sample flow.

15. The arrangement according to claim 11, wherein the arrangement comprises a sample strainer, which is arranged before the sensor in the flow direction of the sample flow during the normal operation mode, and which is arranged to break up solid and particulate material, such as rags, paper debris and the like, in the sample flow.

16. The arrangement according to claim 11, wherein the arrangement comprises at least one sensor providing direct or indirect measurement data on turbidity, conductivity, pH, chemical oxygen demand (COD), biological oxygen demand (BOD), total dissolved gas (TDG), content of specific heavy metals, content of various species of nitrogen, sulfur and/or phosphorous species.

17. The arrangement according to claim 11, wherein all parts of the arrangement are arranged inside a single box-like unit.

18. The method according to claim 6, wherein during the cleaning cycle the cleaning liquid flow is arranged to flow towards the sample strainer for backflushing the filter the sample strainer.

19. The method of claim 1, wherein the wastewater is municipal wastewater; food industry wastewater; agriculture wastewater; livestock farming wastewater; wastewater from paper, board or pulp mill; or wastewater from metallurgical industry.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0046] FIG. 1 illustrates an arrangement and method according to one embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0047] Some embodiments of the invention are explained more closely in the schematical non-limiting drawings.

[0048] The monitoring arrangement illustrated in FIG. 1 comprises two sensors 1, 2 arranged after each other in a sample flow of wastewater, which flow direction during normal operation is denoted with arrows 3. The first sensor 1 is a pH measuring sensor and the second sensor 2 is a sensor measuring sulphide content. During normal operation mode the sensor probes 1′, 2′ are arranged in contact with the sample flow which flows past their sensor surfaces (not shown). The sample flow may be taken as a small by-pass flow from a main flow of receiving waters. The flow is led through an actuated sample inlet valve 4 and filtered by using a filter 5 arranged before the sensors 1, 2. The filter 5 removes possible solid and particulate material from the wastewater before it is led to sensors, thus reducing the exposure of the sensor surfaces to abrasive material and minimising the risk for flow connection blockage of the arrangement. Alternatively, or in addition to filter 5, a sample strainer may be arranged before the sensors. After the passing the sensors 1, 2 the sample flow 3 is discharged through an actuated sample discharge valve 6. During the normal operation the sample inlet valve 4 and sample outlet valve are open and enable the wastewater sample flow past the sensors 1, 2.

[0049] When a cleaning cycle starts the sample discharge valve 6 is closed and the sample flow 3 is effectively discontinued. An actuated cleaning liquid valve 7 is opened and a flow of cleaning liquid, e.g. water, is started from a first reservoir 8 for a cleaning liquid. The first reservoir 8 may comprise means for heating the cleaning liquid. It has been seen that the use of heated cleaning liquid may significantly improve the cleaning results obtained. The cleaning liquid is led from the first reservoir 8 towards the sensor surfaces of the sensors 1, 2, where it effectively removes dirt, such as fat and grease attached to the sensor surfaces. The flow direction of the cleaning liquid is denoted with arrows 9.

[0050] After passing the sensor surfaces the cleaning liquid flow is arranged to flow towards and through the filter 5. In this manner the cleaning liquid flow effectively also backflushes the filter 5 and improves its functioning and lifetime.

[0051] It is possible to use also a chemical cleaning agent for cleaning the sensor surfaces. Chemical cleaning agent may be introduced into the cleaning liquid flow from a second reservoir (not shown) by using a second transfer means 10 for chemical cleaning agent. The desired chemical cleaning agent amount may be easily adjusted by adjusting the volume pumped by the second transfer means 10. The chemical cleaning agent is fed into the cleaning liquid flow and mixed with the cleaning liquid during the transfer to the sensors 1, 2.

[0052] In order to maximize the cleaning result pressurized gas, e.g. compressed air, is fed to the cleaning liquid flow. The arrangement comprises means 11 for providing pressurized gas into cleaning liquid flow by opening an actuated gas valve 12. When pressurized gas is fed to the cleaning liquid flow, it causes turbulent flow conditions at the sensor surfaces, which even more effectively remove attached dirt and impurities from the sensor surface.

[0053] The sensor surface is further mechanically cleaned by using an automatic cleaning device 13. In FIG. 1 the automatic cleaning device 13 is schematically represented, but in practice it may be a wiper, brush or the like, which is brought into contact with the sensor surface, and used to detach and/or remove dirt and/or impurities from the sensor surface.

[0054] During the mechanical cleaning the valves 4, 6, 7, 12 may be closed, i.e. no flows are occurring in the arrangement during mechanical cleaning.

[0055] After mechanical cleaning the sensor surface may be rinsed by opening the cleaning liquid valve 7 and the sample discharge valve 6 and allowing cleaning liquid to flow pass the sensors 1, 2 and out through the sample discharge. After sufficient rinsing the normal operation mode of the monitoring is resumed.

[0056] The arrangement may comprise a required number of pressure relief valves for preventing pressure build-up within the arrangement.

[0057] Even if the invention was described with reference to what at present seems to be the most practical and preferred embodiments, it is appreciated that the invention shall not be limited to the embodiments described above, but the invention is intended to cover also different modifications and equivalent technical solutions within the scope of the enclosed claims.