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What are induced draft fans? And how do they work?

Draft, is commonly referred to as the difference between the atmospheric pressure and the pressure existing within a flue gas passage or the furnace of a boiler system. When the flow of flue gas and air become influenced by the effect of a gradually decreasing pressure below atmospheric pressure, this is referred to as induced draft.

Induced draft fans or ID fans are used in systems such as steam boilers and thermal oil heaters to draw out and remove flue gases from combustion chambers, by creating a vacuum of negative air pressure (typically -10 mm Hg). This is achieved by using a blower to to suck air through the combustion chamber and the rest of the system, before discharging the air and flue gas through a stack or chimney.

In this way, not only do induced draft fans enable the regulation of pressure within systems such as boilers, but they work to facilitate the combustion process in boilers and other systems, by supplying the necessary air needed for the combustion of fuels.

What are common ID fan issues & problems?

Unlike forced draft fans, which do not operate within the high temperatures and acidic environments of exhaust gases, induced draft fans are continually exposed to harsh conditions which increase their susceptibility to developing ID fan issues, inefficiencies in their operation and ultimately ID fan failure.

  • ID fan imbalance

ID fan imbalance is caused when either particulates and fluid build up within hollow compartments of the ID fans or when an uneven layer of build-up accumulates on the fan’s blades. The delicate procedure of balancing involves the adding or removing of weight, in order to move the weight center towards the axis of rotation.

  • Excessive vibration

Even the smallest layer of dust can produce a significant ID fan imbalance which in turn can cause an increase in mechanical vibration. Whilst all fans must generate some level of vibration, if this vibration level reaches a certain amplitude, it can cause severe induced draft fan problems.

Induced draft fan issues caused by excessive vibration include: metal fatigue and damage to shaft bearings, the breakdown of lubricants in bearings, the loosening of fasteners and other ID fan components, mechanical breakdown and ultimately costly plant shut downs.

  • High maintenance & operating costs

Unlike forced draft fans, induced draft fans must handle a large volume of low density and hot air, meaning maintenance and operating cost are significantly higher. In order to keep these costs and energy consumption as low as possible, the ID fan system should run as close as possible to its best efficiency point.

ID fan imbalance or excessive vibration are both factors which would cause an ID fan to operate outside of its optimum efficiency parameters, meaning that not only will maintenance and operation costs increase, but the ID fans durability will decrease.

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ID Fan issues can cause an increase in maintenance and operating costs if not dealt with.

What are the disadvantages of traditional ID fan cleaning methods?

Rather than waiting to deal with an ID fan issue after the issue has manifested itself and began to have an affect upon the efficiency of a system- to save time and valuable money, it’s therefore important for that these issues are prevented from occurring in the first place.

An effective ID fan cleaning method, is a process that should maximise the efficiency of an induced draft fan, whilst maintaining the quality of its working form into the future. However, not only do traditional methods of cleaned induced draft fans, such as sand and water blasters, fail to provide a longterm solution to ID fan imbalance and excessive vibration but they can exasperate these issues further.

Invasive cleaning methods such as these can instead result in the deterioration of the ID fan’s structure, by loosening mechanical connections and propagating cracks and crevices, both factors of which would contribute further to fan imbalance and an increase in vibrations.

How can Acoustic Cleaners solve ID fan problems?

Primasonics Acoustic cleaning technology works by producing a range of high and low energy frequency sound waves, which penetrate ID fan build up with rapid pressure fluctuations. This causes the particles of the compacted materials to vibrate at a different rate to their environment, causing them to debond from each other and dislodge from the ID fan’s surfaces.

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The Primasonics Quattro Range.
  • Prevention

Unlike traditional ID fan cleaning methods, Acoustic Cleaning is a non intrusive technology, which provides a long-term ID fan cleaning solution. Not only do Acoustic Cleaners efficiently remove particulate build-up, but they also prevent build-up from manifesting itself in the future- thus proving to be both an effective and economical ID fan maintenance investment

  • Non- intrusive

Unlike traditional hopper and silo solutions, acoustic cleaners can tailor their frequency to deal appropriately with different ID fan issues, with Acoustic Cleaning technology uniquely designed to reflect sound from solid surfaces, therefore penetrating build-up only and not the ID fan structure.

Aiding the prevention of ID fan imbalance and excessive vibration, Acoustic Cleaners can therefore target both the impeller and internal fan casing, whilst ensuring that inaccessible parts of the fan are also continually cleared without applying stress to the ID fan structure.

  • Efficient

Furthermore, it is also possible to operate Acoustic Cleaners intermittently using a simple timer or connected to vibration sensors and sounded as part of a Monitored Preventative Maintenance (MPM) system.

Majors savings can therefore be achieved as not only do acoustic cleaners provide a solution to decreasing your energy consumption, but by eradicating ID fans build-up, acoustic cleaners effectively eliminate the cost of unscheduled fan shutdown and maintenance work.