Air Preheater Enhancements

Air preheaters play an integral part in the efficient operation of power plants. Over time, the performance requirements change, typically from different fuels and operating cycles. Howden have an experienced team of engineers and site specialists who can provide a complete air heater enhancement service.

It is generally very cost effective to upgrade, or enhance, an air preheater in order to improve the existing boiler performance. The two most common methods are to increase thermal performance, and to reduce leakage.
In many cases it is possible to increase the heat recovery in an air heater by installing higher performance elements and/or by increasing the overall depth, by better use of space within the rotor and thus improve the overall efficiency of the boiler.

Many designs of air preheater are prone to leakage drift (the significant increase in leakage over a period of time). This can affect boiler operation in a number of ways, such as increasing fan power, increasing velocities in the precipitators, reducing the flow of hot air to the mills, or shrinking the draught fan margins. By fitting our advanced Howden VN sealing system, these problems can be reduced or eliminated.

The benefits of upgrading air preheaters to our latest technology include:

• Reduced draught fan power and consequent increase in saleable power output.
• Lower gas velocities permitting increased precipitator efficiency and reduced dust emission from the stack.
• Reduction of the temperature dilution effect of air leakage, reducing corrosion attack downstream of the air preheater.
• Reduction of leakage, making more air available at the coal mills to ensure that sufficient pulverised fuel can be transported to the burners (particularly when firing wet coals), and thus any shortfall in station MW output is recovered.
• Reduction of leakage which in turn lessens flow through the FD and ID fans, and which can eliminate MW output shortfall caused by overloading of the fans.
• Before retrofitting FGD plant downstream of the boiler, it is worth remembering that excess air preheater leakage can lead to an unnecessary increase in plant size.
• Improving the sealing system can therefore result in a reduction in the size of FGD plant required, with consequent cost savings.