Compressed Air Best Practices - February 2009 - (Page 14)

| 02/09 Focus Industry POWER PLANTS | COMPRESSED AIR AUDIT OF THE MONTH Boiler Soot Blowing in Power Plants This demand for low pressure was satisfied with a 6,000 scfm base load compressor and 1,400 scfm of VSD driven trim unit. The remaining 6,730 scfm of high-pressure air (300 psig) demand was satisfied by running one of the 2,000 hp original units and a new, additional 1,500 hp smaller centrifugal with 25% turndown. The newer unit is then 20% more power efficient then the original with almost 15% more effective turndown. p Soot-Blowing Cycles and Considerations A cleaning cycle is a period of time in which required blowers are cycled in a pre-arranged sequence to clean given areas of a boiler over a period of time. Many variables are intermeshed in determining a cycle, some of which are: p p p p p p Size of boiler Time period for cleaning Type and quality of fuel used Type of blowing (stacked or single) Highest soot blower capacity requirement Personnel preference for a given time period The new 1,500 hp compressor was more power efficient than the older 1995 units due to better manufacturing and advanced design The smaller centrifugal with more effective turndown was applied to the demand at 75% flow, 80% power and generally “not running in blow off.” Previously, the three older units were all running normally with two in “blow off.” This improved the overall high pressure efficiency about 20% The low pressure was obviously producing at a much better, specific power. An improvement of 48% compared to the previous high-pressure air regulated down The total savings reduced the annual electrical energy cost by 43% or $1,387,638 per year. The total project cost was $1,462,700, a simple payback of a little over one year (12.6 to 12.2 months) p p Most of these items are variable and should be considered in detail before the system specifications are written. Some ways a blower cycle can be reduced or expanded after installation are to: p Increase or decrease linear travel rate of long retractable lances (soot blowers) Increase or decrease number of revolutions of the wall blowers Increase or decrease pressure at the nozzles/change or modify nozzles Operate parallel blowing systems when possible Speed up the control sequence where one blower starts extending out into the boiler before the prior one is fully retracted Modifications to the IR rods to allow use at lower pressure during refraction limit just enough for cooling Changes to control valves/regulators with less pressure loss p p p Other Soot-Blowing Operational Considerations: Tube Erosion When steam is used as a cleaning medium and a soot blower starts it’s blowing cycle, there normally is a temperature differential between the soot blower and the steam. When this happens, steam condenses and slugs of water are ejected from the soot blower nozzle. After repeated cycles, the slugs may erode the tubes in the boilers requiring plugging of the tubes and eventually replacement. Tube erosion can often be a more significant problem in a steam system than in a compressed air system. p p p p 14 www.airbestpractices.com http://www.airbestpractices.com

Table of Contents Feed for the Digital Edition of Compressed Air Best Practices - February 2009

Compressed Air Best Practices - February 2009 Contents From the Editor Utility-Air News Compressed Air Audit of the Month Air Standards Instrument Air in Nuclear Power Plants Seven Sustainability Projects for Industrial Energy Savings The Pneumatic Advantage Personal Productivity Resources for Energy Engineers Wall Street Watch Advertiser Index Classifieds

Compressed Air Best Practices - February 2009

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