Q. How does pulverizerupgrades enhance over-all system performance?

Ans. Pulverizers are criticalelements in reducing operating costs, meeting emission controlrequirements and beget boiler system flexibility especially whenfuel-switch is involved.

Q. For reduced emission weshould install low-NOX burners. What has the pulverizer to do withthis?

Ans. In fact installinglow-NOX burners (LNBs) to reduce emissions will increaseloss-on-ignition (LOI). This means an increase in unburned coalcarried over to ash. This LOI cannot be reduced unless coal finenessis improved.

Q. How does fuel flexibilityinfluence the capacity and performance of coal pulverizers?

Ans. If there is a fuel-switchto a lower volatile coal there will be an increase in the amount ofunburnt carbon in the ash unless coal fineness is improved. And thatincreases the load on the pulverizer.

Switching to a low-cost orlow-sulphur coal can limit pulverizer capacity if the new coal ismore difficult to grind, i.e. having low grindability or has a lowerheating value. Lower-heating-value coals increase coal mass flowratethrough the pulverizer for the same heat input to the boiler.

Q. What is the harm if theload on the pulverizers is raised?

Ans. New plant operating modesmay require lower loads on the pulverizer where vibration and unevenpulverizer operation become important.

Q. So how can we upgrade thepulverizer without taxing it with excessive load?

Ans. one method is to installa dynamic pulverizer system (FIG.1) having an extended range ofperformance brought about by multistage rotating classifiers.

Another pulverizer designupgrade is to replace the stationary primary air throat (ring) withrotating elements resulting in reduced pressure-drop, extendedcomponent wear life and easier replacement facility.

Q. Fuel switch frequentlycalls for greater pulverizer turndown capability. how can this beaccommodated in pulverizer upgrade?

Ans. the answer to thisproblem is installing a variable load system for the grindingelements.

Manual or automatic speedadjustment of the dynamic classifier optimizes coal fineness as afunction of the pulverizer through put. it makes immediateaccommodation of fuel changes possible and permits superior millturndown without the excessive vibration that occurs when the coalload in the mill is insufficient to maintain a stable coal layerbetween the grinding elements.