Rotating Air Preheater Concept - Heat ManagementRotating Air Preheater Concept Heat Management have identified Rotating air preheaters as an application where infrasound cleaning system

Rotating Air Preheater Concept

Heat Management have identified Rotating air preheaters as an application where infrasound

cleaning system is highly effective and profitable. We have therefore developed an evaluation and

installation concept for simplifying a buyer’s journey towards a cleaner and more efficient rotating

air preheater.

3D drawing of an infrasound cleaner installed on a Ljungström APH

How can online infrasound cleaning of rotating air preheaters

(RAPH) reduce operation and maintenance costs?

The operation and maintenance costs of conventional steam soot blowers for rotating air preheater are relatively high as they consume valuable steam for operation and only provide a local cleaning effect - causing regular stops for manual cleaning. In addition to this steam may also cause considerable wear on the air preheater elements. Altogether, steam soot blowers are relatively costly to operate and maintain. Below describe the technical advantages that infrasound soot cleaning technology can provide and the simple standardised installation concept.

Ways of saving:

One or two of the points below is normally enough to motivate an installation of an infrasound cleaning system. Investment payback rarely exceed 1 year, installation included.

• Saving steam Steam soot blowing in Ljungström APHs is typically operated for 30-90 minute per

day. Steam lost due to soot blowing has negative impact on the overall electrical

power production. Lost steam also has to be replaced with the same amount treated

and re-heated feed water. Even the larger Infrasound generators consume

compressed air for less than 1000 euro per year. The cost saving in replacing steam

usage with infrasound is significant.

• Higher APH thermal efficiency The infrasound cleans the elements efficiently, also the ones that are difficult to reach

with e.g. steam soot blowing. This is due to the fact that infrasound is not screened

by objects such as air preheater elements and therefore has the same intensity in the

complete air preheater sector. This means that the infrasound soot cleaning

technology has the major advantage of providing a global cleaning effect. The steam

soot blowers only provide a local cleaning effect leading to areas that are not kept

clean and therefore will have reduced heat transfer rate.

Infrasound cleaning equipment operates up to 30 times per 60 minutes never

allowing soot particles to sinter. The frequent cleaning intervals keeps the APH

constantly clean, not allowing for efficiency reductions during pause times as in the

case with steam soot blowing. The absence of this temperature increase alone can

normally motivate an installation of Infrafone.

• Higher availability Infrasound generators have few moving parts, none of them are inside the gas

stream. Maintenance can be performed during full operation of the boiler and only

takes a few hours. This together with the high cleaning efficiency allows the APH to

have a very high level of availability. Heat Management guarantees 99.5% availability

on the product.

• Less wear Infrasound is a very delicate cleaning method that, with short intervals, covers the

entire rotor with oscillating infrasound. This allows a good cleaning efficiency without

the risk of destroying APH elements which often sooner or later happens with more

aggressive methods like steam soot blowing and explosive cleaning. Less wear allows

less cost for changing baskets and also reduces the risk for unplanned maintenance

stops.

• Lower differential pressure A cleaner APH has lower pressure drop resulting in less power consumption for ID/FD fans.

Upper picture shows a basket from an

APH equipped with Infrasound generator,

lower picture from APH with steam soot

blowers.

Standardized installation:

To minimize the total investment cost for installing an infrasound cleaning system we have developed a standardized installation concept specially for rotating airpreheaters. The concept is scalable and can applied for different sizes of infrasound generators and APHs.

• Installation location A good installation location is generally at the bottom corner, at gas side, of the APH. Since the rotor is turning, one infrasound

generator will be enough to clean the entire rotor, even if half of the rotor is located at the cold side. This installation location also

normally allow that existing platforms can be utilised which makes the installation cheaper.

• The infrasound generator The power range of infrasound generators varies between 350 and 10000W. The length is always around 5 meters (15 ft), the

diameter however is proportional to the acoustic output. The unit design is very flexible but in the case with rotating APHs it´s

normally enough with one ~30° bent to allow the unit top to end up at an existing platform. Vibration dampers are used to allow

for a quiet and energy efficient installation. Total weight is around 300-1300 kg (660-2900 lb). The delivery consists of 5-6 parts that

later are connected with flanges. Installation normally takes 4-5 days.

• Operation and maintenance 6-8 (87-116psi) bar compressed air is used to produce the infrasound. Consumption is around 5-30 Nm3/h (177-1060 ft3/h)

depending on size. A 1-2 m3 (35-70 ft3) buffer tank is installed to avoid any negative fluctuations on the compressed air systems.

Electricity is only used to feed the control cabined (15W). The included PLC has capacity operate completely standalone but it´s

recommended to connect alarm, sound pressure trends and enable/disable signal to the DCS.

Maintenance is easily performed and can be done during operation of the boiler. Spare parts for full preventive maintenance cost

around 1-3000 euro/year.