Smoke tube boiler
The smoke tube boiler is a type of boiler where flue gas is passing on the inside of many tubes, which creates many challenges for a fouling prevention system. Often the boilers cannot be operated the full operational year.
General info
Smoke tube boiler cleaning
In heating plants and saw-mills, 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 often mounted vertically and have a few tube passes with several hundreds of tubes inside the boiler.
On-line cleaning of smoke tube boilers is challenging and must often 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 often be taken offline and an oil-fired boiler can be necessary to compensate the production loss. The manual cleaning is a dangerous work that can take much time 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 constitutes 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.
References on Smoke tube boilers
SCA Bollstabruk, Sweden
SCA Bollstabruk has two identical 12MWth grate boilers in operation year-round, with an exception of an annual revision stop when the heat demand can be met with one boiler.
Statkraft, Kungsbacka, Sweden
Statkraft Kungsbacka has two 14MWth smoke tube boilers, supplying the city of Kungsbacka and surrounding areas with district heat. The boilers are in operation for the whole year, except during revision and when the need for heat can be fulfilled with only one boiler.
Ljungträ AB, Köping, Sweden
Ljungträ AB is a sawmill in Köping, Sweden, who’s main business is to saw, sell and distribute fir. The sawmill has a 3 MWth Danstoker boiler which required manual cleaning every time the flue gas temperature raised above 230-240 °C.
Stenvalls Trä, Piteå, Sweden
Stenvalls Trä in Lövholmen, is a sawmill in Piteå, Sweden. The boiler and the economiser are used to heat water for the drying process and fulfil other heat needs. The boiler is in operation for the whole year and must be stopped up to 3 times for manual cleaning. Each stop for manual cleaning results in a 48hr production loss and required compensation firing with oil.
