Temperature Measurement


Eye on the flame

September 2009 Temperature Measurement

The difference between good and bad combustion means a great deal for thermal power plant operators.

Durag looks at how monitoring technology can be used to achieve better burning.

The quality and efficiency of firing systems and the associated operational availability of boiler plants and steam generators is essentially dependent on the optimal mixture and dosing of fuel and combustion air in the entire combustion zone.

Disturbances of the local fuel/air ratio can result in localised combustion areas with high combustion temperatures and high formation of thermal NOx. Other problems include the creation of localised combustion areas with incomplete combustion, associated with the production of high levels of CO. High flue gas losses can also result, along with high amounts of unburned carbon or loss of ignition.

Challenges

To achieve an optimal control of the combustion process, it must be possible to adjust two firing parameters individually. These are the uniform distribution of fuel according to the design data and, control of the combustion air distribution over the combustion zone.

Receiving good basic information from the actual situation inside the firing zone is essential in order to be able to achieve these targets. Therefore an online/realtime analysis of the actual firing situation is mandatory and has to deliver information regarding the local position of the main combustion zone, flame temperature distribution, local flame propagation, ignition point and the presence of any local fouling.

Solution

The furnace camera sensor of the Durag video and thermography system supplies online information directly from the combustion chamber to assist the operator in optimising the combustion process. The system provides a realtime video image as well as a realtime online thermographic analysis of the temperature distribution inside the combustion chamber.

The Durag system is an optical pyrometer based on advanced video data processing technology. A high quality picture with a wide angle of view and a small sensor diameter is obtained with a boroskope lens. The CCD camera is mounted in the cold part of the lance, thus allowing sensitive equipment to be mounted outside of the combustion chamber, allowing continuous use at high temperatures. An additional sapphire lens and air flushing are used to protect the boroskope tip from slag and ash particles.

In addition to the video image the system provides methods for the thermal analysis of the spatial temperature distribution inside the combustion chamber. Other capabilities include the ability to perform continuous temperature analysis with continuous display of the absolute temperature profile through the combustion chamber and the detection of the actual thermal position of the combustion zone.

For automatic closed loop control measures, all the data generated by the thermographic systems can be transferred to the main process control system at the customer site through a standardised data interface. Typically, one or two furnace cameras are enough to visualise and analyse the entire combustion chamber.

In the control room the setup requires the installation of one video monitor for every sensor or for every sensor group for online visualisation of the combustion process and one PC with a graphic monitor (maximum processing of two sensors possible) for thermography and temperature analysis.

Applications and results

The online data from the thermographic system supports the analysis of the combustion process: it provides the tools and ability to improve combustion quality by taking the necessary control measures. This can include the correction of undefined and incorrect positioning of the main combustion zone through adjustment of the fuel/air ratio for individual burners. The system can also be used to minimise the amount of unburned carbon in the ash and to minimise flue gas losses and increase the efficiency level by adjusting the excess air at constant combustion.

Using optimal furnace control reduces the maintenance requirements and furnace out-of-service conditions due to local overheating and undefined situations in the water and steam systems (avoiding water tube ruptures). It also has the benefit of minimising the boiler’s start-up time through a controlled temperature profile.

According to Durag using the thermographic temperature analysis data to aid operation of the boiler typically results in return on investment achieved in less than one year.

For more information contact Mike Andrews, OEN Enterprises, +27 (0)11 675 4447, mike@oenenterprises.co.za, www.oenenterprises.co.za



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