Choose an ultrasonic flowmeter when you cannot cut into the pipe and want nothing in contact with the leachate. Choose an electromagnetic flowmeter when you want a standard, in-line meter and can modify the pipework to take it. At a landfill ammonia stripping plant, the operator wanted to change the inlet and discharge flowmeters on one line from ultrasonic to electromagnetic, to match its other lines.
The challenge: one plant, two kinds of meter
An ammonia stripping plant measures leachate flow at its inlet and discharge. On one line the meters were ultrasonic. On the other lines at the same landfill they were electromagnetic. Running two types means two sets of spares and two sets of know-how, so the operator wanted to standardise.
The approach: swap the meter, then check the pipework
How the two types differ
| Ultrasonic | Electromagnetic | |
|---|---|---|
| In the pipe? | Non-invasive: no part inside or in contact with the leachate | Yes: a lined tube with electrodes touching the liquid |
| Pipework change | None needed | Flanged: pipe must be cut and adapted |
| Liquid needs to be | Able to carry sound | Electrically conductive |
An electromagnetic meter passes the liquid through a magnetic field and reads a voltage across two electrodes. It therefore needs a conductive liquid, and leachate usually qualifies.
What the swap involved
The proposed meters were DN80 electromagnetic flowmeters, with flanges. Each has an in-line length of 200 mm, so the pipework must be modified to make room. The supplier suggested the client check that it had the space. If space is tight, a wafer-pattern unit may fit instead, which sits between existing flanges.
Installation was not included. Delivery was about 10 to 12 weeks. The first version quoted two meters, one each for the inlet and the discharge. A revised version quoted one. The scope depends on what the client decides to change.
Materials
A related quotation for another line of the same plant specified a DN80 electromagnetic meter with a 316 stainless steel body, an ebonite lining and Hastelloy C4 electrodes, with a local display. The lining and electrodes are the parts wetted by leachate, so those are the materials to choose with care. A separate quotation for another line went the other way, supplying an ultrasonic flowmeter with a separate converter.
Why it works
Choosing the type is about the installation more than the physics. Ultrasonic meters win when pipework is hard to modify or access is limited, and they avoid contact with a fouling liquid. Electromagnetic meters win on standardisation and on a straightforward in-line design. Leachate monitoring is part of the duties on landfill operators; see the Environment Agency’s landfill operator guidance.
What to consider for your own project
- Measure the space. A 200 mm in-line meter needs a straight, accessible section.
- Check conductivity before choosing an electromagnetic meter.
- Specify wetted materials for the lining and electrodes.
- Count the installation. Pipework changes cost more than the meter in some cases.
- Standardise where you can. One type of meter means one set of spares.
For other parts of the same plant, see our post on replacing obsolete instrumentation and controls.
FAQ
Does an electromagnetic flowmeter work on leachate?
Yes, if the leachate is electrically conductive, which it normally is. Choose the lining and electrode materials for the liquid.
Can I fit an electromagnetic meter without cutting the pipe?
No. It sits in the line between flanges, so the pipework must be modified, unless a wafer-pattern unit fits the existing space.
What is the advantage of ultrasonic?
Nothing is in contact with the liquid, and the pipe does not need to be cut.
How long does it take to supply a meter?
About 10 to 12 weeks in this case.
Choosing a flowmeter?
Tell us your pipe size and liquid and we will recommend a meter type.