Water / Wastewater - UK Focus v
A Massive Step Change in Open Channel Flow Measurement Technology
RS Hydro have installed the fi rst ISCO LaserFlows in the UK, in a market which has been requiring a high accuracy non-contact open channel area velocity fl ow meter for decades.
In the UK, and in fact globally, investment in metering instrumentation within the wastewater industry is set to increase dramatically as smart networks, improved operational performance, carbon foot printing and environmental legislation all act to drive companies to reduce costs and improve performance. The industry has seen countless projects implemented to achieve very specifi c goals but are ultimately fl awed from the outset because the data they depend on is of low or unverifi ed quality. It’s also all too easy to blame an instrument or infrastructure but as the old saying goes, ‘an instrument is only as good as the person who installs it.’ Experts would go as far as saying that a second class instrument will out-perform a fi rst class product if the person installing it has the best training and experience in the market place. The critical issue of training and repeatability of correct installation is not the main subject of the discussion here but rather the technological approach to providing accurate fl ow data in open channel wastewater applications. The idea of this discussion always attracts professionals throughout the fl ow measurement industry but until now has been an application which is plagued with strict regimes of maintenance, H&S aspects, high capital cost of installation and a necessity to have an unrelentingly high standard.
Technologies Available...
The cost of installing or repairing a concrete fl ume or structure will make Metering and Environmental Managers shiver but in the wastewater industry it has been more or less a necessity of life that has to be carried out cost-effectively and by professional engineering companies. It is not uncommon for such a scheme to cost over £100,000 with signifi cant downtimes and knock-on effects. The de- facto standard is to use ultrasonic level measurement in a stilling well 3-5 hmax
channel with a uniform geometry. Even with ADCP (acoustic doppler current profi lers) fl ow meters, velocities are typically only measured in one thin vertical window;
(3) Radar based surface velocity systems which have been around for over 10 years and offer the ability to install sensors where it is too expensive or not possible to install fl umes, area velocity or full-bore pipe technologies. However, they offer lower accuracies due to the fact that they can only measure surface velocity and they require a known and stable sub-surface profi le. A typical installation involves manual profi ling of the fl ow to ascertain a fl ow profi le;
(4) Electromagnetic or ultrasonic (transit time) pipe fl ow meters where the pipe is always fully surcharged except for a couple of manufacturers who have managed to adapt these technologies to measure partially fi lled pipes. Beyond standard clamp on or electronmagnetic, hybrid technologies can be expensive but often only applicable to very niche applications.
Options 1 and 2 require regular maintenance (typically daily or weekly) so with potential risks, increasing regulatory requirements and fi nite resources is using a brush to clean sensors in a channel still practical or indeed necessary? In a world where there seems to be less time to do these regular jobs, ‘the man and a brush’ approach really needs to be abandoned.
That day has now come with the availability of highly accurate reliable, non-contact area velocity meters in the form of the LaserFlowTM
from
Teledyne ISCO which has been launched to solve all of the issues associated with open channel fl ow measurement.
upstream of the fl ume structure. Although this may appear fairly simple to achieve it is only one signifi cant point in a whole list of requirements that must be near perfect to ensure that such fl umes meet the Environment Agency’s MCERTS standard for the self- monitoring of effl uent fl ow discharges to water courses and sewers. A good installation is only part of a company’s commitment to ensure that any such measurement system is accurate 24/7/365.
Rob Stevens and James Chapman RS Hydro
Tel: 01527 882060 Web:
www.rshydro.co.uk
Ask any professional metering or environmental manager, and it is the holistic approach to whole of life cost, performance, maintenance, reliability and performance that will be the backbone of a good metering system. Unfortunately this approach is compromised by a lack of appropriate technology or fi nancial funding. To date, any solution is either very expensive and accurate, or inexpensive with high maintenance and lower accuracy. To date many of these decisions have been based on a limited range of technological solutions which have principally been limited to:
(1) Conventional fl umes using ultrasonic, pressure or radar level technologies to derive fl ow from level;
(2) Area velocity sensors which are wetted and typically mounted in the middle of a
www.envirotech-online.com IET March / April 2014
Introducing the LaserFlow The LaserFlowTM
combines an ultrasonic level sensor with a
45-degree refl ector plate and a military grade 3R laser velocity sensor. The integrated ultrasonic sensor (or alternatively external sensor) provides continual level measurement whilst the laser focuses at a point below the surface and measures the refl ected energy from up to 10,000 spectral readings per measurement
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