Direct fired systems haveexhibited half the explosion frequency of bin storage systems.Because flue gas is used as the pneumatic transport medium in binstorage systems, the plants may assume an inert gas is present.However, load changes, leakage in the system, or malfunctioningdampers can increase oxygen concentrations to levels suitable forexplosions.

The experiments show that thesize relationship of pulverizer, classifiers, crushers, and fans tocoal pipes is crucial in explosion origin and growth. The relativesizes determine whether or not a detonation can occur as well as themagnitude of the resultant forces. Detonation evolution requires achange in volume and must originate in a pulverizer system componentother than a coal pipe. While a fire is located in a coal pipe, itcannot trigger a detonation. However, if the fire moves and enters apiece of equipment of different size and venting characteristics,then the probability of an explosion increases. The relocation of afire to other components of pulverizer systems such as theclassifier. Crusher. Fan, or pulverizer can create a detonation.

pulverizer mills

In a pulverizer mill that usesthe impact principal, the coal remains in suspension during theentire pulverizing process. FIG.26 shows an impact pulverizer designwhere all moving parts rotate on a single shaft that is held in placeby two bearings mounted externally on separate bearing pedestals.This design has no metal-to-metal contact between pulverizingelements and requires no adjustments to compensate for wear. Thepulverizer operates with only a small inventory of coal and thereforeprovides fast response rates and short startup and shutdown times.

Raw coal and primary air enterthe crusher-dryer section (see Fig.26) where hammers propel the coalagainst a grid. The grid openings reduce the coal size to 1/4 in orless. Tramp iron and other no crushable foreign materials arerejected to an area for easy removal. When the coal passes throughthe grid section of the crusher-dryer, it enters the pulverizingsection, where rapid attrition takes place. Attrition, the impact ofcoal on coal, as well as on moving and stationary parts, reduces coalparticles to the proper size for combustion.

As shown in Fig.27, fan wheelswith abrasion-resistant alloy blades are mounted on the pulverizershaft. Coal is transported by this integral fan from the pulverizingsection directly to the burners. This pulverizer design does notrequire a separate primary air fan because of this integral fan. Thecoal feed from the coal bunker and the primary airflow are regulatedby adjusting the feeder speed and the primary air discharge damper.(Refer to Fig.2) these types of pulverizers are designed forcapacities ranging from about 4 to 27 tons/h.