In heating plants, up to 25 MWth, a cost-efficient and compact way to recuperate the energy in the hot flue gas is utilizing 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 tube. For the manual cleaning, the boiler must be taken offline and normally an oil-fired boiler is used to compensate for the production loss. Manual cleaning is 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 the 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 constitutes 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.

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

A standard 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 500 liters must be installed close to the infrasound cleaner.

References from previous installations

Heat Management has plenty of references and case studies for this boiler type. Typical results for the references are a reduced number of stops for manual cleaning, reduced average load on flue gas fan, and reduced average flue gas outlet temperature.

Learn more about our previous installations

General installation of infrasound cleaner