The Inspecta Automatic Purge System, designed, engineered and manufactured in South Africa, is a cost-effective, ambient-air purge system to remove the fly ash build-up within Inspecta pipe-sets, for leak detection in power stations. And it does not require either compressed air or an additional power source to operate.
The INSPECTA Automatic Purge System in application.
Instrotech designed the successful Acoustic Steam Leak Detection System (Inspecta ASLD) and has developed a fully automatic purging system which can be easily retrofitted to existing Inspecta installations. The new automatic system eliminates routine manual purging of the pipe-sets and maintains the leak detection system at peak performance, without manual intervention.
Installed in most Eskom power stations, Inspecta ASLD systems use acoustic detection technology which detects tube leaks less than 2 mm in diameter in the large boiler structures. The coal used by Eskom has a very high ash content, so a considerable amount of fly ash remains after combustion. The fly ash swirls around inside the boiler and quickly blocks the ‘listening’ pipe-sets that contain the sensitive leak-detection microphones. Unless the systems are cleaned frequently, either manually or automatically, their ability to detect the leaks early is significantly degraded.
Cost savings case study
The Inspecta ASLD has been shown to detect steam tube leaks reliably and accurately. To achieve this, the system must be correctly calibrated and the listening pipe-sets kept clear of any obstruction that would reduce their sensitivity. Experience has demonstrated that if there is any obstruction that reduces the sensitivity by more than 10%, it will result in a measurable degradation of the Inspecta ASLD and a delay in the detection of a tube leak.
Figure 1 illustrates that to optimise the performance of the leak detection system, the pipe-sets, particularly those located in the combustion areas of the boiler, should be cleared of fly ash build-up every one and a half to two hours. It is not practical to do this consistently and reliably using a manual purging system.
Figure 1 shows the rate at which sound level deteriorates over time due to fly ash build-up.
If the fly ash is allowed to build up over a period of five to six hours, this will result in a serious degradation in the sensitivity and effectiveness of the leak detection system. Under such degraded conditions, tube leaks may only be detected after progressing for some time. Such delays may well result in extensive secondary tube damage and, in turn, extend the downtime required to repair the damaged boiler.
Comparative cases of early detection and delayed detection of tube leaks highlight the positive impact that an effective leak detection system can have in reducing the consequent extent of damage and the costs of downtime for repairs.
In the case where a leak was detected promptly and the boiler shut down before significant secondary tube damage had occurred, an outage time of two days was needed before the boiler was brought back online.
In the case where detection of the tube leak was delayed and the boiler shut down two hours after the boiler cited in the first case, it is assumed that the tube leak happened quickly and created significant secondary damage, so more than 40 tubes were damaged. EPRI information (EPRI 2003) confirms that the boiler outage time increases steeply as secondary damage increases. In this case, it took 11 days to repair the boiler – which resulted in 11 days of lost electricity production.
(Note: EPRI, the Electric Power Research Institute, is based in Washington DC in the USA and has offices around the world.)
Retrofitting the automatic air purge system
The Inspecta APS system can be installed into an existing Inspecta ASLD configuration simply by replacing the existing Inspecta pipe-set with an Inspecta APS-enabled pipe set. All existing plant wiring remains the same.
If there is a delay in the detection of a fast-progressing tube leak by just a few hours, the downtime to repair the boiler can increase by more than five times compared to a leak that is detected earlier.
Installing Inspecta APS on a boiler ensures the pipe-sets are automatically kept clear of fly ash, so the sensitivity of the Inspecta steam leak detection system is not compromised. This, in turn, enables the system to detect small tube leaks reliably at an early stage.
Operating automatically, the system has the advantage of removing the potential risk of human error from routine maintenance because it does not require any human intervention to function.
Inspecta APS is purpose-designed to work in the extreme environmental conditions of a power station boiler house and the system incorporates AI-driven adaptive performance.
If early leak detection is achieved by installing Inspecta APS, and consequently reduces downtime for leak repairs in a large generation unit by only one day, the savings in electricity production loss exceed the cost of the system tenfold.
For more information visit: www.instrotech.co.za
