TRAGIC INCIDENCE AT UNCHAHAR THERMAL POWER STATION. LIKELY CAUSE

Shocking news of Boiler explosion at Unchahar power station was very painful to all power engineers who are actively associated with Power station. Death of more than 30 persons is extremely deplorable and I do not remember any such deadly incident recently with all modern instruments and control at place. 

I have seen most of the videos ,interviews already published in you tube and other channel and all are blaming ash pipe choking of boiler bottom ash , air heater ash hopper /eco bottom hopper. In a video now available in you tube shows flames are coming out from 

second pass just below the economiser coil . 

Formation of clinker or ash pipe line choking is very common in any coal based thermal power station and it got cleaned through clinker grinder or any other mechanical means. This will not create disturbance at this magnitude. As it was told furnace pressure went to + 350 mm water column. This is also unlikely to shoot upto +350 mm in a zip . It will increase slowly . The furnace is balanced draft furnace therefore positive pressure is not desirable otherwise hot flue gas will come out through peep hole in the furnace. There is alarm and trip with high furnace pressure . It also 

trip the boiler means all fuel input will be stopped however fan will

be running for purging . But Operator will get time to react and save boiler. 

The Boiler is new and been commissioned very recently. It is likely full oil support was there during explosion. Some body mentioned that both boiler was tripped and operators were trying to bring the boiler in operation. Number of workers present means there are small pending jobs which may not be required for operation but required to be completed before final handing over to customer.

It is unlikely during tripping fuel valve any corner was  in stay put and pumping oil in the furnace and oil is pooled inside the furnace as bottom ash hopper is choked there is no escape . Once the boiler is again lighted up after purging and coal fired then this oil was get burn causing rapid disturbance at the furnace . Nature of smoke , flame indicates the same . It is understood that disturbance was very rapid otherwise NTPC engineers and operators are competent  enough to save the situation. It is evident from the incident that none got time to react and it is only possible if there is oil pool inside the furnace. 

Truth will come out after through inspection and analysis. I like to

mention there was an explosion in Kahalgaon boiler due oil pool as during a power failure oil valves are in stay put condition and put oil inside the furnace without fire. Therefore after statutory purging also oil vapour will be in the furnace  and some of them will get deposited in eco coil /airheater busket etc. Then after fire un control combustion will take place  in the furnace and causing explosion. 

Once such type explosion happens buck stay will fail and it will rip open the water walls , a portion of the duct wall etc. The boiler furnace is supported from the top so the mass will be  vibrating violently as it is supported from top and all other pressure parts supports are from the top.

We will waiting for the analysis and pray to GOD such incident should not happen.