GB2482138A

GB2482138A - Sewage flow metering

Info

Publication number: GB2482138A
Application number: GB1012161.4A
Authority: GB
Inventors: Roberto Zimmerman
Original assignee: Individual
Current assignee: Individual
Priority date: 2010-07-20
Filing date: 2010-07-20
Publication date: 2012-01-25
Also published as: GB201012161D0; IL214216A; IL214216A0

Abstract

The present invention relates to the metering of sewage water flowing in gravitational conduits under gravitational flow regime. In order to select a suitable site for installing measuring gear, a candidate site is selected in which records of sewage flow are collected sequentially on the time flow, and wherein for each data record two fields are recorded, one of which is level and the other one of which is velocity or flow rate. A scatter plot may be drawn relating velocity and level and an analysis of goodness of fit made. If the site is determined to be suitable, the permanent measurement gear is installed, including a level meter such as a bubbler.

Description

SEWAGE FLOW METERING METHOD

FIELD OF THE INVENTION

The present invention relates to the metering of sewage water flowing in gravitational conduits under gravitational flow regime.

BACKGROUND OF THE INVENTION

Some sewage water conduits are subjected to monitoring as regards the rate of flow. The monitoring is essential for the management of sewage and the proper maintenance of sewage conduits is a part of the wastewater management scheme implemented by local authorities.

In order to monitor the flow rate of sewage water flowing in gravitational flow conduits, several methods employing metering devices are presently in use, A well accepted monitoring set -up includes the installment of the what is known as a primary measuring device which is a prebuilt flow constrictor which the running sewage water are channeled into. Weirs are very simple devices, with open top and simple section dimensions thorough their length. Flumes are more compound as will be explained next. For example, a flume referred to as "Parshall flume!! is applied as an insert in sewage conduit, collecting all the liquid flowing into a relatively narrow open neck of known dimensions. The Parshall flume has an intake funnel and a discharging funnel, for respectively collecting and discharging downstream the sewage into and from the open neck region. The level of the liquid built up at a determined area along the intake funnel is correlated to the discharge rate of the flume.

Although it may be used for monitoring fresh water streams, the Parshall flume is considered well suited for sewage flow notably because of its tolerance of solids flowing in the sewage. The Parshall flume is superior to a weir in that the sewage is channeled to a narrow constrictor that forces the sewage water to a faster flow, thereby preventing the build -up of sediment.

Without using a primary measuring device, a flow measurement setup model known as "Area-Velocity Flow!! study, also known as the AV flow study is a well known setup for analyzing the flow parameters in a specific site along a flow channel. A device is installed in or above the stream to constantly measure the velocity!!V!! of the liquid, in the conduit. Concomitantly, the level of the liquid surface above the invert of the conduit, is also measured in order to calculate the "wet cross section area" ("A") of the stream. The flow rate ("0") is the result of the multiplication of the value "A" by the value "V".

The flow rate can be measured by employing any of the available techniques, but a common one is an ultrasonic Doppler transmitter, which measures the reflection of energy (echoes) from bubbles or particles contained in the stream. The flow rate, of the stream is simultaneously measured by any one of available methods, typically a vertically sensing ultrasonic sensor that measures the reflection of energy transmitted upwards. In such a measurement, the lower the level, the higher a pulse of energy transmitted is reflected

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a chart describing the sequence of events taking place as an optional site for installing is being sampled as a candidate monitoring site.

Fig. 2 is a chart describing the sequence of events taking place as the goodness of fit of the function between measured variables is assessed.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

In accordance with the present invention, a monitoring system for sewage lines operating under gravitational flow regime is maintainable using a minimal component gear assembly, providing some conditions are met, in a specific point along the line of sewage. In order to explain how a proper site is selected for installation of the measurement gear in accordance with the present invention, reference is made to Fig. 1 which describes site specific data collection routine (SSDCR) 12. First, in step 24, a location on a sewage line of particular significance is selected, typically reflecting a maintenance advantage such as ease of access or protection from potential threats of damage. In step 26 measurement gear is installed. This would account for what is known as !!area velocity flow!! measurement as explained above. Next, in step 28, flow rate, measured and level of fluid of the stream are sampled simultaneously, with sampling values recorded. For each sample one data record is produced wherein with two variables recorded, From the sample records, a graph is made, wherein all variables of one kind are plotted on one axis and the variables of the other kind are plotted on the other axis at step 30, typically, at each point in time in which sampling was carried out. Then, in step 32 data distribution is calculated after a sufficient amount of data has been collected and volume flow calculated. Data distribution is a statistical method for assessing the goodness of fit and formulating the relationship between variables. In this case, the two variables of the system measured, are velocity and level. It is noted that the volume flow rate is calculated as described above, and since it is linearly correlated with the velocity rate, the two variables can be used in the same manner to produce the distribution graph. It is further noted that the production of a graph describing the actual distribution of data is typically made by a computerized program, and the actual graph may not be made visible at all. In computerized methods a tabular data sheet is made in which for each record two fields of data are recorded. Another step, not shown is data cleansing in which a data records are assessed for extreme deviation, and typically is such cases the data may be removed.

In a practical example, accordance with the present invention, a scatter plot is drawn, depicting the sampled data as time progresses. On the Y axis the velocity or the calculated volume flow, in for example in meters or feet per second, or cubic meters or cubic feet, respectively. On the X axis the level of the stream is depicted typically in meters or feet.

Once the information has been collected and assembled in a layout susceptible to statistical analysis, a function between the two variables measures is determined typically by applying computerized analysis methods.

Referring to Fig. 2 the procedure for confirming the site as suitable for installing the measurement gear is described and explained in steps. Having collected enough data, a function between the two variables is determined, in step 62.

Then in step 64, the goodness of fit is calculated, such that a statistical assessment of the validity of the relationship between the two variables is assessed. Then at step 66, thresholding of the goodness of fit is made. For example, for linear regression a value lower than r2 = 0.75 may be regarded as insufficient for establishing a valid relationship between the variables. If the value representing goodness of fit is regarded as insufficient, the gear is dismantled and another site may be chosen for assessing in step 68. If, on the other hand the thresholding of the value representing the goodness of is above a certain predefined threshold, the site is confirmed in step 72, and a permanent gear for measuring the volume flow rate is installed.

It was found out experimentally that relatively simple and inexpensive level measurement appliance is sufficient for the application, i.e. measuring the volume flow rate when the two procedures carried out sequentially approved of a specific site. Typically a bubbler level measuring unit is applied. The bubbler is essentially a pipe anchored to the bottom of the conduit while a pressurized gas such as air is driven through. A pressure transducer is located inside a pressure chamber to sense the gas and simple mathematical relationship exists between the pressure and the water level. Such a bubbler can be purchased from Seba Hydrometrie of Gewerbestrasse 61 a 87600 Kaufbeuren, Germany, but other providers are available.

Finally, once a site has been tested and approved as described above, a level meter is installed at the site, to record level changes and the resulting flow metering is interpreted by automatically implementing the function at step 62.

Claims

CLAIMS1. A method for monitoring flow rate of sewage in conduits running under gravitational flow regime, said method comprising the steps of: * carrying out a site specific data collection routine (SSDCR) in a selected candidate site in which records of sewage flow are collected sequentially on the time flow, and wherein for each data record two fields are recorded, one of which is level and the other one of which is velocity or flow rate; * determining a function between the two variables of said records; * analysing the goodness of fit of the records with respect of said function; * installing a permanent measuring gear in said candidate site if the goodness of fit analysis has been successful And wherein said permanent measuring gear is a level meter.
2. A method for assessing the suitability of a site as in claim 1, wherein said permanent measuring gear is a bubbler level meter.
3. A method for assessing the suitability of a site as in claim 1, wherein said analysing the goodness of fit of the records is a linear regression analysis.