Question:

Boiler uses different burning fuels, which is closely related to the soot blowers’ quantity and arrangements. The ash content of the fuel is an important factor that directly affects the types and quantity of the soot blowers, especially the units that use lignite. When the sodium in the ash reaches the overall content 4~5% or more, steam soot blowing will not work. Some coal-fired lignite has a minimum Na2O in the ash content,which is 1%; the maximum can up to 12%, which causes increasing slagging on the water-cooled wall.The slag thickness can reach about 50~150mm, and the slag layer gradually increase until the water-cooled wall covering the whole furnace. As the heat absorption in the furnace reduce, the smoke temperature at the exit of the furnace is greatly increased. Finally, the convection tube bundle is blocked and the furnace is forced to be shut down.

Case study:

China’s Inner Mongolia Yuanbaoshan Power Plant installed 3x660MW coal-fired boiler, because the boiler uses local high-alkali lignite, the ash content of Na2O is quite higher, the slagging thickness on the water-cooled wall is more than 100mm. Therefore, the company uses the RLD/FSB40W hydraulic soot blower which produced by our company. This soot blower is installed on the water-cooled

wall.See Figure 1 for details.

(Figure 1: Water soot blowers for boiler No2 in Yuanbaoshan Power Station, from Relyde.)

 Technical parameters of hydraulic soot blower:

• Model: RLD/FSB40W
• Travel: 400mm
• Blowing medium: ≤40°C chemically treated water
• Blowing pressure: 0.8~1.5 Mpa
• Blowing rotation of lance tube: 2.81 / 8.6 rpm
• Moving speed: 56/173mm / min
• Water consumption: 50~100 kg / min
• Nozzle diameter: Φ5.0~7.0 mm
• Output power R2 sped of Motor: 0.13 / 0.37 KW 2850/950 rpm
• Dimensions: 1010x416x780mm
• Weight: ≈180 kg

Blowing principle and process:

The hydraulic soot blower is driven by a two-speed motor. When the motor starts, it runs at high speed. The cam moves forward quickly with the threaded pipe. When it approaches the cone roller, the motor is switched from the variable speed controller to a low speed. At this time, the cam rotates slowly under the roller. The control valve is opened, the pressure water is sprayed through the nozzle of the blowing gun head to blow the water-cooled wall. Then, the cam continues to move forward, the front stroke switch is touched, the motor is quickly reversed, and the threaded tube is quickly rotated back to the starting position. Also, it willpress the rear stroke switch and stop the action (see Figure 2 for details).The valve is followedtothe detachment of the cam roller, therefore, the soot blower completes a whole cycle. Due to the use of the taper roller, the opening volume of the control valve is gradually increased as the nozzle of the soot blower moving forward, follows by the gradually increase of the blowing area. Thus, the hydraulic soot blower can have good blowing effects without damaging the surface of the water-cooled wall.
The blowing path of the nozzle is like the Archimedes line (see Figure 3 for details).

(Figure 2: Drawing of water soot blower)

(Figure 3：The blowing track for water soot blower)

Operational control:

Every time it blows, it will blow off large thick pieces of coke which generally around 100 mm to improve efficiency. According to different slagging thickness, you should use different blowing pressures. For example, to target the slag layer which the thickness is below 50mm, the purging pressure should is controlled at 0.8~1.1Mpa, as for the 50~150mm, and the purging pressure should be 1.1~1.5Mpa. The bowing effect is very obvious, and there is no physical damages on the water-cooled wall.

In conclusion:

For coal-fired boilers with strong slagging, the correct use of hydraulic soot blowers is a very effective blowing device for maintaining boiler operation, according to following advantages;

• For coal-fired boilers with severe slagging, the use of a hydraulic soot blower is much more effective than the steam or air compressed soot blower.
• Reasonable use of the hydraulic soot blower will not cause wear on the heated surface of the on the water-cooled wall than steam soot blower.
• The cost of a hydraulic soot blower is lower than that of a steam soot blower or anair compressed soot blower.