Early warning system for boilers in power plants

Working in conjunction with Alsthom in Stuttgart, Procon Engineering have been awarded two important contracts to supply their "Boiler Leak Detection Systems" to both China and Turkey

Working in conjunction with Alsthom, the Lintvalve division of Procon Engineering are installing systems at the Waigaoqiao Power Plant in the Pudong New Area of East Shanghai, and the Can Power Station in Cannukule, Turkey.

Working in conjunction with the "old" CEGB (Central Electricity Generating Board), Lintvalve were the first company in the world to provide commercially available acoustic leak detection equipment, designing and installing the first systems back in 1974.

The technology provides important preventative maintenance and safety information for power generation plants.

The Lintvalve system detects leaks at the earliest stages and therefore allows structured maintenance to be carried out during routine planned shutdowns.

Without such permanent monitoring systems, small steam leaks inside boilers can go undetected for many months, typically resulting in serious damage and unwanted boiler shutdown.

Through hard won experience, Lintvalve have developed a system based around both airborne and structure borne sensors which "listen" for small changes in the noise pattern coming from a boiler.

The key to the success of any leak detection system is a combination of understanding which type of sensors to use, where to place them and how to interpret the results.

Depending on the application and type of boiler, sensors have been developed which can detect both airborne and structure borne signals.

The principle used in acoustic leak detection relies on the fact that when a gas or fluid, under high pressure, passes through a small orifice it expands.

The resulting turbulence causes sound pressure waves, which pass through the gaseous medium existing inside a utility boiler.

This turbulence will also create sound waves (vibrations) in the structure around the hole, which will travel through the metal structure.

Acoustic sensors can then be placed on and around the boiler to detect these sound waves.

These vibrations or sounds contain frequency components over a wide spectrum, typically from 100Hz - 500kHz or beyond.

The signal amplitude and the frequency distribution will principally depend upon the differential pressure and the hole size.

The actual frequency distribution reaching a sensor will depend very much upon the transmission medium (gas or metal) and the differing amount of attenuation at the different frequencies, and even the shape of the hole.

It is not possible to simply measure the vibrations or sound of a small leak over the whole frequency spectrum because the normal background vibrations and noises from the boiler operation contain much larger amplitude, low frequency (below 1kHz) signal components than a small tube leak.

Lintvalve have developed a special technique to discriminate the sound of a small tube leak from the background noise.

Proprietary signal conditioning processes the signal from the sensor to eliminate the majority of this unwanted background noise at low frequency.

It then becomes possible to discriminate the leak from the residual background noise levels.

The Waigaoqiao Power Plant is being upgraded to meet the spiralling power consumption of Shanghai.

The plant, which boasts China's largest power generators to date, is being fitted with two giant 900 MW turbine generators supplied by separate coal fired boilers.

28 acoustic airborne sensors are installed at strategic locations around each boiler and connected via amplifiers to independent data acquisition systems in the main control rooms.

These monitor and process the information coming back from each boiler and provide detailed information on their status.

The Can power station is the first environment friendly thermic power plant to be built in Turkey.

Leak detection sensors are being fitted to two circulating fluidised bed boilers, which drive the 160 MW turbine generators.

To overcome detection problems caused by heavy solids loading produced in the furnaces, Lintvalve have specified eight structure borne sensors and four acoustic sensors for each boiler.

Results from both boilers are fed into a single data acquisition system and a modem link allows the remote surveillance of the leak detection equipment.

Lintvalve have recently extended the scope of their expertise and equipment to include leak detection systems for peat and gas fired boilers.

As the Procon product specialist in this field, Joe Naylor, concludes: "We are confident that the application of leak detection systems will increase, especially as companies become more attuned to the importance and benefits of structured preventative maintenance programs.

The cost to install our system is very small compared with that of unwanted shutdowns and the equipment can be easily installed without disruption to the plant.

In the early days there was some reticence from boiler manufacturers regarding the benefits and most of our systems were fitted to existing boiler installations.

We are now seeing a reversal of that trend and an increasing amount of our work is done in conjunction with the boiler manufacturers for new installations".

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