Smoke tube boilers

In heating plants up to 25 MWth a cost-efficient and compact way to recuperate the energy in the hot flue gas, is by means of a smoke tube boiler. As the name suggests in a smoke tube boiler, the flue gas passes inside tubes, surrounded by a water mantle cooling the smoke tubes. The boilers are normally mounted vertically and generally have three tube passes with between 300 and 800 tubes inside the boiler, ranging from hot in the center to cold in the outer parts. 

On-line cleaning of smoke tube boilers is challenging and must be combined with manual cleaning as well. Traditional cleaning methods include compressed air blowing from the top of the boiler as well as manual cleaning of each individual tube. For the manual cleaning, the boiler must be taken offline and normally an oil-fired boiler is used to compensate the production loss. The manual cleaning is a dangerous work that can take up to one day and cost both man hours and oil consumption.  

Most commonly, the fouling of a smoke tube boiler starts in the bottom turning chamber, where there is no automatic cleaning and where the compressed air blowing from the top does not reach. The fouling mechanism includes accumulation of so called “beard” at the inlet of the smoke tubes. As the beard grows, it is sucked into the tubes and eventually clog them. Since each tube constitute for 0.5 % of the heat transfer area of the pass, heat transfer is quickly deteriorated resulting in losses in thermal efficiency. Using long range infrasound, the smoke tubes are kept open in the bottom, avoiding said losses and prolonging the time between outages for manual cleaning. Figure 1 below show an example of “bearding” in a vertical smoke tube boiler. 

Download case study on how the sawmill Moelven Edanesågen AB uses infrasound cleaning for their smoke tube boiler!

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Fig 1. Vertical smoke tube boiler, with upper smoke tubes (top) and fouling in the bottom turning chamber (bottom)

Cost efficient supply of a powerful infrasound cleaner

Heat Management has developed a standard infrasound cleaner for this purpose, which does not require a full acoustic model and which has a generic design, for each installation. The result is the cost efficient supply of a powerful infrasound cleaner for all smoke tube boilers. The infrasound cleaner is operated with a 24 V DC solenoid valve and runs on compressed air (6-8 bar), for two seconds every four minutes and a sound pressure sensor gives the acoustic output of the infrasound cleaner, between 25 and 40 kPa. Air consumption ranges from 6 to 9 Nm3/h, depending on the size (MWth) of the boiler. A buffer tank of 750 liter must be installed close to the infrasound cleaner.

General installation of infrasound cleaner

Allmän installation av infraljudsotare

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Watch this interview with Stig-Erik Larsson, Dryer- and Boiler Operator at Edane saw mill