High Ratio Fabric Filters with 12 m Long Bags for Large Coal Fired Power Plants
P. Wieslander1, S. Francis2, and A. Vajpeyi3
1Alstom Environmental Control Systems, Alstom Power Sweden AB, Sweden
2Alstom Power Inc, USA
3Alstom India Ltd, India
Abstract- For many years, electrostatic precipitators (ESPs) have been used to collect particulate emissions from coal fired boilers. Today, with the need to produce the lowest cost electricity with the lowest possible emissions, coal fired boilers need to have flexibility to burn a wide variety of coals and at the same time achieve very low emissions. In this case the size, cost and arrangement of the ESP becomes very large and plants are now considering the use of high ratio fabric filters (HRFFs) to meet these requirements. While HRFFs have been used to collect particulate emissions from coal fired boilers for many years, designing the filters to meet the required emissions from large 800 to 1100 MWe boiler systems is a more challenging task than for smaller boilers (100 to 600 MWe). The most effective means to reduce the steel weight and footprint of HRFFs is to increase the bag length, while maintaining, or even reducing, the bag-to-bag pitch. Alstom has more than 20 years experience of 8 m long bags, on-line cleaned, and more than 5 years successful experience of 10 m long on-line cleaned bags in coal fired boiler applications. Alstom has now developed a HRFF design with 12 m long bags, and reduced bag-to-bag pitch, for large coal fired boilers, as a continuation of the HRFF design with 10 m long bags successfully launched in 2008. This paper presents information on key issues that need to be considered when designing and evaluating a HRFF with 12 m long bags for a large coal fired boiler installation. Aspects of gas/dust flow distribution to the individual compartments of the filter as well as the concerns regarding large flow/loading into the bag nest in each compartment will be discussed. A very efficient, newly developed, cleaning system has been incorporated in the filter to clean the bags properly without increasing dust emissions, and allowing the system pressure drop to be kept as low as possible. Included is also information on several HRFF reference installations in the 800 - 1000 MWe boiler range, as well as data on coal fired boiler reference installations in Australia and South Africa with successful long-term operation on abrasive fly ash at inlet loads similar to those from firing domestic Indian coals. The reduction in HRFF first cost with 12 m as compared to 10 m long bags, and tighter bag row pitch, is estimated at around 10%.
Keywords- Fabric filter, fly ash, power plant, coal firing, flow modelling, pulse cleaning