Overview
Cement production is an energy-intensive process. Hot exhaust gases from cement kiln pass countercurrently through downward-moving raw materials in preheater. SP boiler is designed for waste heat recovery from exhaust gas (-5000~-6000Pa, 320~400℃) from preheater. Dust content in exhaust gas is up to 80~100g/m3, with particle size distribution <10µm 90~97%, <2~3µm 50%. the majority of dust is cao, which contributes 44.22%, while sio2 is about 13.8%. Al2O3 is about 2.88%, while alkali metal like MgO, Na2O, K2O is a low percent.
These dusts are easy to settle down on SP boiler tubes and form loose deposits. Under the effect of electrostatic force, deposit layer could grow to 20~50µm, and then falls down from tubes under gravity. But SO3 in exhaust gas reacts with steam and forms sulphate, which will turn loose deposit into a compact state. Ash fouling will greatly bring down boiler efficiency and cause corrosion of tubes.
An effective and reliable online cleaning solution for SP boiler is vital for normal operation of whole cement line. Mechanical rapping system is used in the past, while sonic horn, also known as acoustic cleaner, is widely accepted now.
Mechanical Rapping System
A rapping system is normally used for waste heat recovery boiler. It lifts and releases heavy hammers to collide with anvils. That will generate shock force to break bonds between tube and deposit.
Disadvantages of rapping system is obvious. When shock force is strong, it will cause fatigue damage, and shaft where hammers are fitted is easy to distort. When shock force is weak, cleaning performance is not satisfying. Large amount of deposit, formed during cleaning intervals, will peel off from tubes when rapping system is activated, and part of the dust will enter high temperature fan and deteriorate its working condition. That is potential threat to stable operation of clinker calcination process.
Instead of massive cleaning in a short time, proactive cleaning is better option in consideration of influence on operation of high temperature fan. To prevent ash buildup on heating surface, maintain thermal efficiency and avoid performance degradation, acoustic cleaning is considered as optimal solution for SP boiler.
Acoustic Cleaning for SP Boiler
Acoustic cleaning is mature technology used for ash cleaning on world market. Sonic horn uses compressed air to generate oscillation of Titanium diaphragm in resonance chamber. Potential energy of compressed air is transformed into low frequency, high intensity sound wave, which transfer energy to particulates, causing it to vibrate and detach from tube surface.
Sonic Horn Advantages
- Thorough cleaning within effective range. Due to inflection, diffraction of sound wave, sonic horn can remove deposit without consideration of tube arrangement.
- Intermittent operation at short cleaning interval. Preventative cleaning to keep tubes clean and avoid dust entry into high temperature fan.
- Acoustic cleaning without physical damage to heating surface.
- Lower operation cost.
