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Technological solutions for improving combustion efficiency, safety concerns

7th June 2013

By: Zandile Mavuso

Creamer Media Senior Deputy Editor: Features

  

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According to sources, more than 12 steam boilers in South Africa fail catastroph- cally each year as a result of undetected low water-level conditions, says specialist combustion optimisation company Boiler Combustion Technologies (BCT).

To this end, the Leveltect sensor has been developed to address safety concerns regarding steam boilers.

“Low water levels in steam boilers cause damage that equates to hundreds of thousands of rands, causing weeks of disruption and risking serious injury to employees, or even fatalities. Water-level-control devices most commonly in use depend on a float and magnetic switch arrangement to control water levels and, ultimately, cut power to the boiler whenever critically low water levels occur. To reduce the risk of damage, two water-level-control devices are normally provided for every boiler – one to control the pump and audible alarm, the other to cut power to the boiler fans and stoker,” says BCT director Jean le Roux.

He further adds that the root cause in 90% of such failures is attributable to equipment failure and human error. The integrity of the water-level-control system of most boilers depends on mechanical devices that are subject to wear, fatigue, fouling and neglect, which may cause them to fail. Although the water-level-control devices are normally duplicated on every boiler to reduce the probability of simultaneous failure, both employ the same technology with the same inherent weaknesses and proneness to failure.

Furthermore, these devices still depend on human diligence and alertness to ensure their continued integrity or to detect their failure before the water level of a boiler drops to a critical level.

BCT’s Leveltect sensor ensures that a boiler has a separate watchdog instrument, which can monitor the presence of water in the gauge glass. It contains no moving parts and requires no maintenance other than the regular testing of its integrity. It can be used to switch pumps, sound sirens or cut power to the boiler at a certain water level. It is not affected by dirt and can withstand temperatures up to 200 ˚C.

“The Leveltect level switch eliminates that last remaining concern about the safety of steam boilers. The noninvasive plug-and-play technology requires no access to the internal parts of the boiler. There is no need to stop boiler operation during installation and it can be connected to the existing water-level-control system with the boiler in operation. The technology also sells for much less than other conventional water-level-control devices,” says Le Roux.

BCT

also states that before 2000 most packaged shell boilers used electro-mechanical controls. Electronic automation of coal-fired steam boilers became popular during the late 1990s and triggered a revolution in the control of coal-fired steam boilers.

Combustion optimisation systems are instrumental in ensuring best energy savings for steam generating plants. However, improving the efficiency of the combustion process in a coal-fired steam boiler entails far more than just running fans and stokers on variable-speed drives or having a programmable logic controller regulating the combustion process. The key to efficient combustion lies in the accurate control of excess air at all times.

Apart from combustion optimisation systems, BCT also offers their patented Autobed guillotine automation systems to users of steam boilers. With a turn-down ratio of about 3:1 a conventional coal-fired boiler control system can control down to about 30% of the boiler’s maximum steaming capacity.

“BCT has managed to overcome this constraint by developing and patenting the Autobed control system for the automation of guillotines. “The objective of the control system is to find the best coal-bed depth for the steaming load imposed on a boiler. This ensures a continuous long fire on the grate, improving air distribution through the coal bed and enhancing combustion efficiency. This technology also allows continuous load control down to 10% of boiler maximum continuous rating and is specifically recommended in instances where boilers are oper- ated at low steaming loads for extended periods,” adds Le Roux.

The company often finds that boiler operation is still based on beliefs developed over decades of using cheap energy and control systems of a previous era, as well as high levels of human intervention. Closer control of the air-fuel ratio of combustion can significantly improve the efficiency of combustion, saving users of steam boilers up to 15% on coal use. It also presents opportunities for a substantial reduction in electricity consumption of boiler fans, typically by 40% to 60%, compared with damper-based combustion control systems.

“With the proposed carbon tax, which will most probably be levied from 2015, coal users face another huge energy cost challenge. It is estimated that carbon tax could add an additional 15% to the price of coal, which makes optimisation of combustion a non-negotiable issue”, he concludes.

Edited by Tracy Hancock
Creamer Media Contributing Editor

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