By Steve Wilson / December 20, 2016 / www.mississippiwatchdog.com
According to a new report from an independent monitor, the $7 billion Kemper Project clean coal power plant narrowly avoided a serious accident in October when 1,750 degree synthesis gas backed up into the coal feed system.
The engineering firm URS — which was hired by the Mississippi Public Service Commission as its on-site independent monitor — said in the report that the Oct. 13 incident happened because a pin fell out of the actuator of a large rotary valve that protects the coal feed system, which supplies lignite to the plant’s two gasifiers, from depressurizing. That allowed syngas to back up into components not designed for that level of heat.
The loss of the pin kept the valve in the open position.
Former gasifier island project manager Brett Wingo said the incident could have resulted in a catastrophic explosion that might have burned down the gasifier and released poisonous hydrogen sulfide gas, which can cause on-site deaths in high concentrations from as little as one breath. He said an explosion would’ve been more likely had the gasifier been running at its designed operational pressure of 650 pounds per square inch. During recent testing, the gasifier has been running at 350 pounds per square inch.
URS said Mississippi Power repaired the valve by welding what is known as a keystock on it to keep the pin from falling out and leaving it in an open position.
“Describing a pin ‘falling out’ as something benign, natural or normal, like it’s acceptable, is absurd,” Wingo said. “Either the pin was not installed or properly secured during installation and/or not properly inspected prior to operation or during operation. Pins don’t just ‘fall out,’ not on critical applications like this.”
Mississippi Power officials didn’t return a request for comment.
The incident occurred just a few weeks before Tom Fanning, the CEO of Mississippi Power’s corporate parent the Southern Company, assured investors on Oct. 31 that Kemper would meet its start date.
“As we moved through the startup process and we’ve knocked over these dominoes that you normally expect with the startup process, I think it has gone beautifully,” Fanning said that day. “I think we’re going to be able to demonstrate ‘used and useful’ very easily. This plant is going to work. It is working.”
On Nov. 3 the company announced its previous commercial operation date for the plant running on lignite would be pushed back to Dec. 31. The company says it won’t meet that target either.
To understand why the incident was so dangerous, one must understand how Kemper turns lignite coal mined on site into electricity.
As designed, lignite coal, after being pulverized and dried to a specific moisture content, enters the coal storage silo atop the gasifier from a conveyor. It then moves down to the lock vessel, where it is pressurized with nitrogen to slightly above gasifier pressure, which is 650 pounds per square inch. From there, it drops into the dispense vessel, where it remains pressurized at gasifier pressure and goes to the high pressure coal feeder, where it is fed into one of the facility’s two gasifiers to be converted into synthesis gas.
The dispense vessel and high-pressure coal feeders always remain at gasifer pressure, while the lock vessel cycles between atmospheric pressure and gasifier pressure. When the lock vessel is ready for another batch of coal, it must vent harmless nitrogen and some coal dust into the storage silos before it can accept more. When the valve failed, the lock vessel vented syngas into the silo area instead.
From there, the syngas is supposed to flow from the gasifier through the gas cleanup system — which removes anhydrous ammonia, sulfuric acid and 65 percent of the carbon dioxide from the syngas stream — and to the facility’s electricity-generating turbines.