New build: power plant explosion

[GreatWhitehunter]

I actually recently interviewed at this plant.( I'm a Intrument and controls Tech) The boiler on these combined cycle plants sometimes have duct burners to increase steam temps. The actual purging is done by starting the gas turbine with an electric starting motor or diesel engine and some are static starts(means they motor the generator). The turbine runs at about 25% speed for 15-20 min which purges the turbine,exhaust duct and boiler to the stack where natural draft takes over. I'm willing to bet the root cause will involve a contractor on site. It seems that most of the incidents that occur in this industry are largely because of them. One thing that really made me concerned was the lack of structure in the emergency response. I've work in plants all over tha world and there are usually at least two sign in check points before working on these sites. So in an event like this prompt verification of who's onsite and accounted for can happen quickly.

Matt

 

[Kernopelli]

I actually recently interviewed at this plant.( I'm a Intrument and controls Tech) The boiler on these combined cycle plants sometimes have duct burners to increase steam temps. The actual purging is done by starting the gas turbine with an electric starting motor or diesel engine and some are static starts(means they motor the generator). The turbine runs at about 25% speed for 15-20 min which purges the turbine,exhaust duct and boiler to the stack where natural draft takes over. I'm willing to bet the root cause will involve a contractor on site. It seems that most of the incidents that occur in this industry are largely because of them. One thing that really made me concerned was the lack of structure in the emergency response. I've work in plants all over tha world and there are usually at least two sign in check points before working on these sites. So in an event like this prompt verification of who's onsite and accounted for can happen quickly.

Matt

I gather from what's been posted here, it sounds as if they were trying to light off one of the boilers and after repeated attempts they might have decided it was a gas supply issue and were purging supply lines(?).

We have the same sign in/out procedures as you have described and it is taken seriously. Failure to adhere to this procedure will result in a trip to the employee review board and results in discipline that can lead to termination. I think you will probably be right about a contractor being at fault. I would say that so far it sound as if the safety oversight personnel must have dropped the ball as well. Maybe they were contracted too and there was no independent or state/federal oversight present at the time of the incident?

I have seen contractors do some brilliant things and some do crazy things but corrections doesn't tolerate some things/ behaviors from contractors that is common on most job sites. There is a very low tolerance for the typical Billy Bad Boy/ Mr Independent/I'm Gonna Intimidate You" mentality worker that comes in. If he starts pulling that "Nobody's gonna look at me, talk to me or tell me anything or I'm going to flip out on them" stuff, he's gone. The first time they do they're escorted to the front gates and told never to come back. We do not try to tell them their trade but we don't have to put up with a lot of the crap that happens on a lot of job sites and that's a good thing.

So have you heard back from your interview? Will this sway your decision if you are offered a job at this plant? I don't know the details surrounding this position or what your current employment status is but these are usually excellent jobs. Despite this incident I might have a hard time saying no to a new plant offering me this opportunity.

 

[JB4310]

I wonder if the on site safety oversight were just winging it or if they were using analyzers to test the concentrations?

The one guy I saw interviewed said they were told the "meters" read safe levels.

They are treating the site as a crime scene and are not ruling out negligence, not sure if they mean criminal type?

I live 35 miles away and didn't know anything about it (the plant being built), was supposed to have been a great boost the power grid once on line.

.

 

[GreatWhitehunter]

These type of boiler are usually very safe. The proper name is HRSG or Heat Recovery Steam Generators and are usally three stages:High Pressure,Intermediate Pressure, Low Pressure (HP,IP,LP). I'm not 100% sure these units had Duct burners are most of the newer plants have great heat rated and don't need them. So the if that was the case here it would indicte in proper purge times from the Gas Turbine. I also see alot of operators changing Logic and constants in the controls system. Hopefully this isn't one of those situations. These HRSG don't have any open flames in them(unless they had the duct burners I mentioned) just tubes with water in them so there are alot of gaps in the stories I'm hearing. I won't be taking a postion at this plant since I already took another at a close plant.

The site log was also strictly enforced at every plant I've work at also.
I believe they gave a one strike rule and after that you were out. I'm thinking some unauthorized cutting and welding may have been going on. It's unlikely that extreme line pressures were the cause. Most safely relief valves are checked and rechecked before they leave the shop. One think I heard mentioned was the workers being overworked. This is a major problem since the energy market was de regulated in early 2000. These indepentant power companys are extremely greedy and often time put the stock holders interest above safety. They all preach safety but at the end of the day it's all dollars and cents.

Matt

 

[Egon]

Didn't some of the news statement say it was gas from a purged line that accumulated in buildings that was the original problem.

The boilers were not involved directly.

 

[DanD78]

I work with two 380 pound per hour, 1300 psi coal fired boilers. To get the boilers on coal we use natural gas fired duct burners to heat the bed up before adding coal. When we get a gas flame fail the boiler goes through a programed purge cycle before another attempt can be made to lite the gas. During this purge cycle the purged air goes up and out the stack. I would assume a gas fired turbine would have the same type of purge out the exhuast. Our steam goes to a 60 mega watt turbine and sends extracted 150 and 15 lb steam out to the plant. The steam that is not extracted by the process goes to a condensor to reclain the condensate for reuse as feed water.

I would hope they were smarter than to purge the gas lines out the end of a pipe with out a flair. There never seems to be any follow up on accidents like this unless it shows up in a power house magazine.

Dan

 

[JB4310]

I'm not sure if they ever got the turbines running yet, they were purging lines, now they are saying it seems to have started by a welders torch outside in a courtyard, that would be consistent with what the guy said who got blown out, he said it seemed like it came thru the building, like from the outside.

There's a big controversy going on now, with them treating it like a crime scene they still haven't let federal investigators in to do their work. One fed guy said he could see employees of the contractor working inside but they were being kept out, supposedly to preserve evidence.

JB.

 

[GreatWhitehunter]

These units are quite different from traditional boiler. The is usually no flame in the these HRSG's (unless duct burners are present) and are just capturing heat from the gas turbine's hot exhaust gas. The gas turbines were ready for simple cycle and were being tested( like sea trails for a ship). The story I'm hearing now is that the contractors were reporting the smell of natural gas throughout the day before the accident. It makes sense that the gas must have been trapped in the building since NG is quickly rises(unlike Propane) and could not get to atmosphere to disapate. If the operations staff is at fault for this accident they need to get ride of all of them and the management and start over. I know a local outfit that specializes in repairs and testing of these plant after these type of situations. So there'll at least be more work to stimulate the econony. Though the sacrifice of human life was not justified.

Matt

 

[gsganzer]

I design pollution control systems for combustion turbines HRSG's, boilers and the such and have commissioned about 200- 300 of them. I've also done the controls for the HRSG/Boiler itself, including the drum level control, gas valve control, de-superheater control.

I've been in a number of plants where we've had close calls because of someone being inexperienced with the commissioning process. I've been doing this for about 20 years and I can tell you that the quality of the people doing this type of work has gone downhill. My comfort level when doing commissioning is not what it used to be and I find myself double checking everything that someone else claims has been completed. "Independent verification" is my new mantra. Not to preach, but there seems to be a problem with the current batch of 20-something-year-olds where they do everything half-***** and don't understand consequences for failing to follow protocol.

I don't have the details on this explosion, but there's two possibilities when the term "purge" has been used.
1. Gas train purging. This is when they perform some gas blows of the gas metering system and/or gas compressor system to flush debris out of the lines and establish gas to the system. Typically all "hot work" is shutdown during this process and the gas blows are done out a vent when possible. Its typical for this operation to be done by a very select and organized group during lunch hours, when all activity is shut down and the personnel are at a minimum. The entire site is aware of gas blows.
2. The burner management system (BMS) requires that the duct be purged (4X air exchanges) prior to an ignition attempt. I've seen multiple instances where there was a fluke in the system after repeated attempts to light off. This resulted in the accumulation of gas in the duct that ignited. This should never happen if all of the controls have been properly tested and signed off prior to the real deal.

I most likely worked with the folks at the CT site at one time or another. You always have to be safe and watch out for your own back.

 

[dmccarty]

Wow. This is another thread that shows the greatness of TBN. I learned more about the accident reading TBN than reading the media reports. Which is sad really. I wonder if that might be why the old mainstream media is loosing money.

Thanks,
Dan