CRITICAL OBSERVATIONS DURING SHUT DOWN AUDIT OF A 330 MW PULVERIZED COAL FIRED BOILER By K.K.Parthiban, B.Tech ( IIT-M), M.E Thermal Engineering- RECT Trichy
Introduction Boiler maintenance cost can be reduced, if every failure & shortcoming are analysed and addressed. In a power plant, engineers are stressed and hard-pressed for early restart of the unit and hence they do not have time to analyze the failures. However, employing specialists for unit inspection during shut down would help to identify defects in boiler & reasons for past failures. Actions could be taken to stop repetitive failures. In future, unscheduled outages can be avoided. Performance of the plant can be greatly improved. There have been cases wherein two or three annual shut down audits have led to much better understanding of the boilers. There have been cases where the plant engineers stopped calling us when they became clear of what to inspect in the annual shut downs. The value Photo 1: Distant view of the unit addition of a shutdown audit by experienced boiler consultants can be known only if it is experienced. We bring below the value addition by us in a tower type PF boiler outside India. Features of the unit The boiler is a once through unit with a centrifugal separator. The furnace is made of spiral wall rifle tube construction. All the tube banks of superheaters, reheaters and economizers are horizontally arranged in a single pass directly above the furnace. The screen tubes are arranged above the furnace. The screen outlet tubes act as support tubes for all the tube banks except for the low temperature economiser. The tower type configuration is a bold configuration selected by the designers. It certainly improves the free board for better burn out of the coal particles. The lateral pitch of bank assemblies decrease, as the gas moves up. Thus, required gas side velocities are maintained for good heat transfer. The low temperature economiser is constructed out of square finned tube. The unit is provided with two rotary airheaters. Gas recirculation fans are provided for startup purpose and for low load operation. 5 mills are provided. Electrostatic precipitator is provided for dust capture. Condensate polishing units are provided for ensuring the feed water / return condensate quality. Detailed observations at shut down We bring out our observations in the unit which was inspected by us. We feel this technical paper would help the unit operators to understand about methodical approach to be taken for inspection of the boiler and correlate to the failures being experienced in the unit. We have compiled below the important observations in this unit.