Coal ash to blame for Indian boiler explosion

• 6 years ago (2017-11-03)
• David Flin

Asia 847 Coal 274

---

The explosion at NTPC’s Unchahar power plant, in which the death toll currently stands at 39, may have been caused by the malfunctioning of fans designed to maintain pressure inside the boiler. NTPC officials have issued a statement in which they said that a large amount of ash concentrated in the boiler furnace, and a problem with getting the ash removed could have led to extremely high pressure, causing it to leak. NTPC experts said that this possibly led to a sudden surge in the pressure inside the boiler, possibly to up to 40 times above normal levels, causing the boiler to explode.

Virendra Singh Rathi, Regional Executive Director (North) of NTPC, confirmed that the committee set up to investigate the cause of the blast would probe the possibility of improper functioning of fans. He said that while one fan pumps air into the furnace, the other extracts air. “There should be a balance in the air movement inside the boiler for proper pressure. In the case of any imbalance, the system trips and fans start reducing the pressure. It does not seem to have happened in this case. We are waiting for the final enquiry report.”

NTPC’s initial inquiry found that the ash duct evacuating the bottom ash was not functioning properly. A large piece of coagulated ash appeared to have been involved, causing imbalance in the combustion and subsequently the pressure. The pressure increased from a normal five mm water columns (mmwc) to around 250 mmwc. Rathi said: “That opened up the economiser hopper, installed on one side of the boiler. Soon, hot flue gases started to emanate, and hit the workers who were working in that area.”

In addition to the 30 dead, around 100 workers suffered burns, and 20 of them are said to be in a very critical condition. Some survivors spoke of a rattling in the unit, and then a blast, causing intense heat.

The 1550 MW plant, with six generating units, is being investigated as to whether safety measures were in place, and whether alarm systems were working.