Automatic Purge System for Power Stations

January 12, 2023  399  399   

Instrotech designed the successful Acoustic Steam Leak Detection Systems (Inspecta ASLD) and has now developed a fully automatic purging system that’s easily retrofitted to existing Inspecta installations. The installation of this 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 that detects tube leaks less than 2mm in diameter in the large boiler structure. The coal used by ESKOM is very high in ash content, so there is a considerable amount of fly ash remaining after combustion. This fly ash swirls inside the boiler and quickly blocks the ‘listening’ pipe-sets that contain the sensitive leak-detection microphones. Unless the systems are frequently manually or automatically cleaned their ability to detect the leaks early, is significantly degraded.

Cost Savings Case Study

The proven Inspecta ASLD has been shown to reliably detect steam tube leaks. To achieve this accuracy, the system must be correctly calibrated and the ‘listening’ pipe-sets kept clear of any obstruction that will reduce the sensitivity of the system. Experience has shown 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.

Fig 1.

Fig. 1 shows that to optimise effective leak detection operation, the pipe-sets, located in particularly the combustion areas of the boiler, should be cleared of fly ash buildup every 1.5 to 2 hours. It is not practical to reliably achieve this using a manual purging system.

If the fly ash is allowed to build up, over a period of 5 to 6 hours, this will result in a serious degradation in the leak detection sensitivity of the Inspecta ASLD. Under these degraded conditions, tube leaks may only be detected after progressing for some time. The resulting delay in detecting a tube leak may well result in extensive secondary tube damage and significantly extend the downtime to repair the damaged boiler.

In Case 1. Early detection of a Tube Leak, the leak was detected promptly, and the boiler shut down before significant secondary tube damage had occurred, resulting in an outage time of 2 days before the boiler was brought back online.

In Case 2. A Delayed Detection of a Tube Leak was detected and the boiler shut down 2 hours after case 1.
It is assumed that a tube leak occurred rapidly and created significant secondary damage, so that upwards of 40 tubes were damaged. From EPRI information (EPRI 2003), the boiler outage time increases steeply as secondary damage increases. It took 11 days to repair the boiler which resulted in 11 days of lost electricity production.

Inspecta APS retrofitting

The Inspecta APS system can be installed into the current Inspecta ASLD configuration by simply replacing the existing Inspecta pipe-set with an Inspecta APS enabled one. 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 may increase by more than 5 times compared to a leak that is detected earlier.

Installing Inspecta APS onto a boiler ensures the pipe-sets are automatically kept clear of fly ash, ensuring that the sensitivity of the Inspecta steam leak detection system is not compromised. This, in turn, will enable the system to reliably detect small tube leaks at a very early stage.

Benefits of the Inspecta APS

• Complements the existing Inspecta ASLD system.
• Easily retrofitted to Inspecta ASLD plant sensor network. The Binder connector fitted, is compatible with the Inspecta HA-3 sensor. An option exists to fit power station-specific connectors if required.
• Significantly increases the effectiveness of the Inspecta ASLDsystem by automatically maintaining optimum performance levels.
• Improved early leak detection means that boiler outage times can be significantly reduced.
• Inspecta APS removes the routine maintenance human factor. It is automatic and does not require any human intervention to function.
• The system is purpose-designed to work in the extreme environmental conditions of a power station boiler house.
• AI-driven adaptive performance

If early leak detection is achieved by installing Inspecta APS, and consequently reducing 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 by ten-fold.