ASouth African-designed acoustic tube leak-detection system will be commis- sioned at Unit 3 of State-owned power utility Eskom’s 1 000 MW Komati coal-fired power station, in Mpumalanga, next month.

This installation forms part of more than 100 acoustic tube leak-detection systems that have been installed locally, with process control and instrumentation equipment distributor Instrotech having supplied seven units at the eight-unit 1 600 MW Camden power station, near Ermelo, in Mpumalanga, alone.

Electronics and electrical engineering group Siemens, with the assistance of Instrotech, will undertake the commissioning of the Inspecta Fast Fourier Transform (FFT) Acoustic Tube Leak Detection System, supplied by Instrotech, in 2011.

Instrotech MD Paul Mason says, while the system only takes between six and eight weeks to manufacture, significant amounts of boiler pipe work and cabling need to be installed on site before the Inspecta FFT system can be installed and commissioned.

“The most complex part of the installation is fitting and welding the metal pipe work to the boiler wall. Fortunately, this is undertaken by specialist contractors that are contracted by Siemens,” notes Mason.

The installation and commissioning of the Inspecta FFT central processor unit and the field sensors are relatively straightforward, says Mason. This process usually takes between one and three days, depending on the size of the boiler and the number of sensors.

Instrotech designed and developed the Inspecta FFT Acoustic Tube Leak Detection System at the request of Eskom, which generates 93% of its electricity from coal, to detect boiler tube leaks in coal-fired utilities, oxygen plants and gasifiers.

The first Inspecta FFT system was installed at Eskom’s 3 600 MW Mpumalanga-based Duhva and Matla power stations in 1985, with the first international system supplied to Germany in 1993. These contracts were followed by installations in India and China in 1995 and in Australia, Malaysia and Turkey in early 2000, says Mason.

He adds that, since the first system was commissioned in 1985, all Eskom coal-fired power stations have procured at least one Inspecta FFT Acoustic Tube Leak Detection System.

The conventional method of detecting boiler tube steam leaks is by ear; however, the steam leak would have already caused significant damage to the boiler and surrounding pipes when detecting leaks using this method.
In comparison, the computer-based acoustic tube leak-detection system uses FFTs to generate audio spectrums and analyse plant conditions.

When a leak is detected by a change in the sound patterns, alarms are activated and the fault localised. Mimic diagrams enable plant operators to identify the affected area and plot the progress of the leak for planned shutdowns.

The sound in the boiler is continually monitored by specially designed audio sensors, which can detect leaks of less than 2 mm in diameter in a 600 MW boiler.

The sensor is a miniature industrial pressure transmitter, enclosed in a sealed acid- and dust-proof capsule, which is essential in the harsh environments in which boilers operate.

The Inspecta FFT system interfaces with supervisory control and data acquisition or distributed-control systems, which ensures that all the results are available on a network and can be shared by whoever has access to it.

This also supports the system’s long-term trend feature, which is useful for analysis.

The Inspecta FFT system consists of a self-contained hardware package, a Eurocard central processor unit, with programmable memory, and an interface card with a high-speed analog-to-digital converter and isolated input/output circuits for interfacing with field wiring and an operator’s console.

The field equipment consists of up to 32 audio sensors that are strategically positioned around the power station’s boiler. The audio sensors, with integrated head amplifiers cast in aluminium field housings, with an Ingress Protection rating of 65, are designed to withstand the harsh conditions found at power station boilers, notes Mason.

Further, pipework sets are installed between the boiler wall and the audio sensors. The pipe work sets work as a wave, which channels the audio signals from inside the boiler to the audio sensor. The pipe set also protects the audio sensors from the extreme heat generated in the boiler.

Autopurge actuators are an additional option used to ensure the wave guides remain free of fly ash. This is important to ensure the highest-quality signal reaches the audio sensor.

The benefits of using the Inspecta FFT detection system includes the early detection of tube leaks, the avoidance of unscheduled outages, early steam-leak detection and an increase in boiler-tube life, operating performance, power station uptime, operating profits and personal safety.

The Inspecta FFT Acoustic Tube Leak Detection System can be customised to meet a customer’s specific operating requirements, notes Mason.

Owing to Instrotech’s understanding of local conditions, the company offers faster, more effective and more efficient support and maintenance services and spares, compared with foreign alternatives that do not have local support offices, he says.

Besides being installed at Eskom’s Camden, Komati, Duhva and Matla power stations, the Inspecta FFT Acoustic Leak Detection System has also been installed at its Grootvlei, Kendal, Kriel, Majuba, Tutuka and Hendrina power stations, in Mpumalanga, the Lethabo power station, in the Free State and the Matimba power station, in Limpopo.

Instrotech continues to supply Eskom with new systems, systems upgrades and spares, concludes Mason.