Jammed Cyclones In Preheating Process
Cyclones are basically used to clean up the dust-laden gases leaving simple dry process kilns. If, instead, the entire feed of raw meal is encouraged to pass through the cyclone, it is found that a very efficient heat exchange takes place: the gas is efficiently cooled, hence producing less waste of heat to the atmosphere, and the raw mix is efficiently heated. This efficiency is further increased if a number of cyclones are connected in series. The number of cyclones stages used in practice varies from 1 to 6 (usually 5) and the temperature of material is around 900 Deg C.
A penalty paid for the efficiency of suspension preheaters is their tendency to block up. Salts, such as the sulfate and chloride of sodium and potassium, tend to evaporate in the burning zone of the kiln. They are carried back in vapor form, and re-condense when a sufficiently low temperature is encountered. Because these salts re-circulate back into the raw mix and re-enter the burning zone, a recirculation cycle establishes itself. A kiln with 0.1% chloride in the raw meal and clinker may have 5% chloride in the mid-kiln material. Condensation usually occurs in the preheater, and a sticky deposit of liquid salts glues dusty raw meal into a hard deposit, typically on surfaces against which the gas-flow is impacting. This can choke the preheater with a large build-up to the point that air-flow can no longer be maintained in the kiln. It then becomes necessary to manually break the build-up away.
Reliable methods of monitoring flow through the pre-heater tower cyclone represents best practice. Reducing the amount of hot metal within a blocked system reduces the volume of material personnel are exposed to if internal inteventional is required. Reduce volume also has the advantage of generally reducing the overall exposure time to the personnel and also time the pre-claimer is shut down to unblock the cyclone.
Conventionally blockages in the cyclone are detected using contact free nucleic, isotopic probes e.g. Gamma Ray radiometric measuring system for continuos measurement of build-up. However the personnel nuclear radiation safety issues & Government permission requirements make the Radiometric solution difficult to maintain and safety dispose off after the isotope’s life is over !
The idea is to stop the jamming /choking of cyclones because of the build up, hence the manufacturer recommends to utilise the Matsushima make non-contact Microwave barrier switches model Transmitter MWBS-TR-02 & Receiver- MWBS-RC-02 provided in Air Cooled Enclosure with Vortex cooler to enable mounting in the high temperature outside the cyclone. Microwave passes through refractory, therefore no hole is to be made in the refractory of the cyclone and only a small hole in the steel shell (later closed with castable) is sufficient to detect, without contact, the undesired accumulation of material which blocks the line between transmitter and receiver. The system with a Max. distance detection of 100m and small detection area of dia. 25Mm has a Sensitivity setting with digital switch system enables exact and stable setting for alarm in case of blockage.
- Min. downtime of Pre-calciner
- Stability & High-efficiency
- Energy Utilisation
Early detection of blockage through the MATSUSHIMA MWBS leads to taking timely corrective action of maintenance with minimum risk to knock out the still small build up; which in turn will lead to better stability through utilisation of Petcoke beyond the current capacity improving the plant efficiency leading to improved quality of the product cement.