The probe reveals that the snag in the coal evacuation system occurred at 2pm on Wednesday. An NTPC official confirmed that the generation in the unit was brought down from 400MW to 190MW after the snag had been detected.
The NTPC set up a three-member committee of experts to examine the causes that led to the blast in the boiler.
The 500MW 6th unit of NTPC Unchahar thermal power plant was running on less than half the total sanctioned load for more than an hour when its boiler turned into a ball of fire and ash on Wednesday, according to a preliminary probe.
The investigation suggests NTPC engineers got a hint of a snag in the unit much before the high pressure inside the furnace opened up a section of boiler to let out flue gases and simmering ash. The probe reveals that the snag in the coal evacuation system occurred at 2pm on Wednesday, while the boiler burst at 3.30pm.
Ravindra Singh Rathi, regional executive director of NTPC northern region, confirmed that the generation in the unit was brought down from 400MW to 190MW after a snag had been detected in the ash evacuation system around 2pm on the fateful day.
“The snag in the coal evacuation system often happens. It, however, gets fixed. This time, too, the machine was kept in an operational mode while the snag was getting fixed,” he told on Friday.
Rathi said that the operational load of the unit was also brought down so that lesser coal was pumped into the furnace. “That would have also lessened the ash load. The situation, however, aggravated after boulders of ash got stuck in the evacuation system, raising the pressure inside the furnace,” he said. Some of boulders also flew back into the furnace disturbing the combustion and eventually increasing the pressure alarmingly.
Rathi said the incident as a case study for ensuring safety of power plants in the country. The NTPC set up a three-member committee of experts to examine the causes that led to the blast in the boiler. The committee, headed by NTPC executive director (operations) S K Roy, will have general manager A K Sanaiyar and GM (engineering) Udyan Kumar as its members.
The committee will take help of experts from the Bharat Heavy Electricals Limited (BHEL), which specialises in manufacturing heavy electrical equipment, including boiler and turbines for thermal power station.
The boiler at NTPC’s Unchahar unit was, too, provided by the BHEL. The committee, Rathi said, will examine the design, operation and maintenance of the blast-affected unit. “We need to start from the scratch,” Rathi said.