Orders in June: Optimized soot-blowing & Duct cleaning

June resulted in orders for cleaning duct on black liquor boiler and a smart soot-blowing system on a biofuel boiler.

Optimized soot-blowing

The upgrade of the soot-blowing system will reduce the time needed for performing soot-blowing and remove condensate in the soot-blowing steam. Condensate leads to wear of heat exchanger surfaces with resulting high costs.

Duct cleaning

The infrasound has several positive properties when it comes to preventing build-up of deposits in ducts:

  1. Large amplitude pulsation of the flue gas
  2. Vibrating the duct walls slightly
  3. Long cleaning range, covers also long ducts
  4. Low noise

Optimized soot-blowing and Duct cleaning

When cleaning e.g. an economizer using infrasound the cleaning effect comes from the extra turbulence created in the flue gas when the infrasound oscillates the flue gas back and forth. The same effect is present when keeping ducts clean. Infrasound cleaning uses low frequency, 20-30 Hz typically. The displacement amplitude of the oscillation is inversely proportional to the frequency, resulting in a large displacement amplitude. Compared to acoustic cleaning using higher frequencies the large amplitude of infrasound results in a more powerful way of removing ash particles that has settled on surfaces but has not yet sintered to hard deposits.

When operating an infrasound cleaner sound pressure waves are travelling back and forth in the flue gas duct. The result is a sound pressure typically varying between +200 Pa and -200 Pa around the actual pressure inside the duct. The pressure changes direction as many times as the frequency of the sound, 20-30 times per second. 200 Pa results in 200 N force (~20 kg) per square meter and the effect is a vibration of the duct walls. Typically the vibration velocity amplitude is 10-15 mm/s when operating the infrasound cleaner during 1-2 seconds. This effect, which is not harmful to the walls, is very helpful in preventing deposits in ducts, it has a similar effects as a rapping device working on a surface, with the difference the infrasound acts on the whole duct. The sound pressure created in the duct is calculated prior to the installation of the infrasound cleaner and the vibrations created are measured after starting up the system.

Benefits of using infrasound

Infrasound has a long wavelength, around 20 m, resulting in long cleaning range and the ability to reach around objects and through bends in the flue gas ducting. This is due to the fact that sound is screened off only by objects of size comparable to the wavelength. For most cases when cleaning e.g. an economizer this allows for cleaning of a whole back pass using just a single infrasound cleaner. For the same reasons it is possible the keep long ducts, straight or bent, using a single infrasound cleaner. This results in low costs for installation, operation and maintenance.

Leave a Reply