Dino fueled power plant Q/A - Page 1
Forum section: electronics / general

author: dr.diesel
author_rank: Super Contributor
timestamp: November 14, 2013, 11:47:12 pm
content: Inspired by f_e's recent post. What would you like to know about a coal fired power plant, from the Sr. Engineer responsible for the control system?Cliffs:- (2) 550MW generators- 30,000 physical IO points- Old, huge, big and bigger- 10,000 HP 13.8kv VFD motors- Redundant everythingQ/A only, no videos as I dislike Turkish prisons, maybe a pict or two if I get brave.

author: marshallh
author_rank: Unknown
timestamp: November 15, 2013, 12:44:17 am
content: I'm not familar with those systems, but you could always tell stories..

author: ConKbot
author_rank: Super Contributor
timestamp: November 15, 2013, 03:38:04 am
content: What was the biggest "Oh %#&(@&#%" or butt pucker moment that you can safely tell us about?

author: free_electron
author_rank: Super Contributor
timestamp: November 15, 2013, 05:49:35 am
content: Do they shovel lumps of coal in a big burner ? I don't think so.Explain how it works. I read they grind the coal to a fine powder and basically use injectors , much like a diesel engine.How to trap fine particles i the exhaust. Do they use co scrubbers .

author: nctnico
author_rank: Super Contributor
timestamp: November 15, 2013, 09:54:57 am
content: You could visit a power plant. A reasonably modern one also makes plaster out of the exhaust gasses.

author: Stonent
author_rank: Super Contributor
timestamp: November 15, 2013, 10:44:42 am
content: So what are they using on a modern plant? Anthracite, lignite, bituminous?What about the technology behind it all? PLCs, SCADA?

author: dr.diesel
author_rank: Super Contributor
timestamp: November 15, 2013, 01:02:11 pm
content: Quote from: free_electron on November 15, 2013, 05:49:35 amThis is a good place to start, let's do:Coal in > Control System > Massive amounts of hot air/exhaust > Future > ?Coal comes from mines via train, already cleaned and washed, in chunks about the size of #5-4 gravel, 100 Tons per car. From here it is usually feed directly into the inside coal bunkers or off loaded onto the pile outside, which is just like it sounds, a great big huge pile of coal. Outside the pile gets rained/snowed on etc, the moisture causes many problems, most plants carry enough of a pile to last 45+ days worth. The supply is not as regular as you'd think. Coal on the pile is groomed/mixed/worked as each train car doesn't have the exact same type of coal, via a Cat 854G and D12 Dozer at my plant. (These are HUGE) Coal fired power plants range in size from 90MW on the low side to about 800MW at the top, per single unit. My plant can burn 10,000 tons per day with both units at full load.Coal from the bunkers is fed directly to the coal feeders, which control the amount of coal that is fed to the pulverizer, these comes in pairs. A typical 550MW single unit will have 6 feeder/pulverizers, with each pair separately controlled, providing coal to different elevations of the boiler. Once metered through the feeder gravity drops the chunked coal into the pulverizer, of which there are two main types:- Bowl Mill type. These mills have large hardened steel wheels that ride on the floor of the pulverizer, crushing/pinching the coal as it is trapped between the wheel and the floor. Coal will continue to be crushed in this manor until is is small enough to be blown out passing through the classifier veins.- Ball Mill type. These are far less common, but use hardened steel balls about the size of tennis balls. Imagine a 55 gallon drum on it's side, about the size of semi trailer, filled 1/2 full of these balls. Coal is fed in while this drum it's spinning, being crushed by the balls, again trapped unit small enough to be blown out through the classifiers.In either case above the coal exits the pulverizer in a fine powder, much smaller than fine salt or sand. The back side of the pulverizer has an exhauster fan that simply blows the fine powder up and into the boiler via a coal conduit, which is simply a 30" diameter tube routed up and in. The entrance into the boiler does have burner nozzle, which is only used to direct the coal flow up or down.Coal is blown in from each of the 4 boiler corners, at different elevations, all boilers are a rectangle standing up. While in operation, that is a physical fireball in the upper center of the boiler, with dark glasses on you can see it burning through observation ports in the boiler!A few specs:- Each Pulverizer/Exhauster is run via a 900HP, 4160v electric motor.- Forced Draft furnace has (2) 5000HP, 4160v fans blowing air in, (2) 10,000HP, 13,800v internal fans sucking air out, holding a 0.50" negative pressure inside the boiler.There is no single point of failure in these systems, any one or multiple of the above can trip off without tripping the entire unit. The control system is exceptionally robust, specifically tuned to deal with most circumstances.p.s. You could actually open doors at the upper elevations and shovel coil in if you wanted to!Questions, please ask. Up next, the control system..

author: dr.diesel
author_rank: Super Contributor
timestamp: November 15, 2013, 01:14:42 pm
content: Quote from: nctnico on November 15, 2013, 09:54:57 amYes, visiting a plant is possible, I've given many tours. I'll get to this towards the end, plants with scrubbers do make a waste that ends up in dry wall, but with the housing collapse most of it is just land filled.

author: orion242
author_rank: Unknown
timestamp: November 15, 2013, 01:16:30 pm
content: I got lucky a long time ago and got a tour through a coal plant.http://www.consumersenergy.com/content.aspx?id=1332I was amazed that the “boiler” was hung from ceiling because of expansion and the stresses evolved. This “boiler” was several stories tall at the plant I was in.What’s the normal steam pressure there? Have you seen how they check for leaks on fresh steam piping?I don't think getting tours in the US these days happens all that often with the ridiculous security.

author: dr.diesel
author_rank: Super Contributor
timestamp: November 15, 2013, 01:47:22 pm
content: Yes, the entire boiler, steam drum are hanging from the ceiling of the power house. From cold to hot the boiler will "grow" almost 2 full feet. In my case the steam drum weighs in at 490,000lb, who knows how much the boiler adds to that. Power house construction is like nothing most have ever seen, an absolute tank with monstrous I-BeamsEVERYWHERE! If you took a large steel bridge, stood it on end vertically, grouped about 100 of them together, that's what the inside looks like.Drum boiler pressure runs about 2700psi in the drum, 2400psi of throttle pressure to the turbine. Once through supercritical boilers have no drum and run pressures over 3500psi.Boiler leaks are usually pretty easy to find @2400psi, most of the time the tube just bursts taking the unit offline. Small leaks can usually be heard, but don't stay small for very long.As for the tours

author: orion242
author_rank: Unknown
timestamp: November 15, 2013, 03:03:17 pm
content: 2,700psi!! holy crap. I guess small leaks would be short lived at that pressure. I would have to guess closing a gate valve and finding a leaking valve packing makes for a bad day.The steam heating systems I occasionally work with typically run 5-15psi, “high pressure” systems maybe 100-300psi. On the last high pressure system, I saw these guys with paper wands waving them down a new run of piping. When I asked what the heck they were doing, it was to check for leaks. When the paper is cut in half, they know there is a leak…

author: dr.diesel
author_rank: Super Contributor
timestamp: November 15, 2013, 03:11:08 pm
content: Control systemThere are couple major players in this industry, each are specifically tailored to the power industry, the specifics are intentionally left out.The control system has a unique layout:- Organized into what's called drops. Each drop has two completely separate, but redundant controllers/processors, each individual controller has redundant networking, with redundant power supplies. The redundant controllers have redundant networking between the pair (one of which is separate from the above), this is how they stay in sync, you can turn controllers off back and forth without losing control.- All networking switches are redundant, you can unplug entire switches without losing control.- Each drops redundant power supplies are fed from separate 30kva UPSs, with a bank of batteries bigger than most garages. In the event the UPS faults, the load is automagically switched to AC, fast enough nothing is dropped. The UPS batteries are separate from the station DC bus, which is the last line of defense when all else fails. (which I've seen)- Each drop has cages of I/O cards. Each cage can hold just about any type of I/O and can be mixed. Common I/O types are digital in/out, 4-20ma in/out, serial, Ethernet, proprietary communication etc. Critical plant I/O is triple redundant, going to different drops in-case an entire drop is lost.- I/O is polled at specific intervals and varies depending on purpose. Normal non critical stuff usually once per second with turbine I/O at 100ms or faster.- Most I/O can be hot swapped, depending on what it's controlling.- Each drop is a standalone entity and will continue the best it can, when neighboring drops fail, even if portions of it's logic depend on I/O points from other drops. Some are programmed with heartbeats to detect certain conditions so the entire plant can be automatically taken down in the event of uncontrollable loss.- Controllers/Processors run a tailored version of VxWorks on Intel x86 hardware. These are programmed via Solaris Sparc workstations in a logical (think AND/OR gate) type symbols on "logic sheets". Imagine functional drawings of 74 series logic and you'll have a pretty good idea.- Logic can be modified on-the-fly, but is generally only done online in not critical areas to reduce the risk. Just in-case one of those once in a million, stars are aligned type of events happen.- The entire control system network is physically separated from the outside world, there is no hacking in taking control by some unknown person 5000 miles away. You'd have to drive to the plant, physically plug into a free network port, which would do you no good since free ports are disabled. To even get to this point you'd have to cut one of my fingers off (not telling which one) to open the biometic lock on the door.Obviously a brief overview of an incredibly complex beast. The control system drives 30,000+ physical I/O points, from small solenoids in 1/4" tubing, to 10,000HP electric motors, to 500kv switch yard breakers, including some 150,000+ internal data points. Note modern day coal/combine cycle plants will have 5x the physical I/O.Even with all of this redundancy and complexity there are hard wired sensors with direct control (outside of the control system) of specific breakers to instantly stop all fuel to the boiler, or stop the turbine in the event of a complete loss of the control system. The boiler can melt within just a few seconds of cooling water loss and the generator is filled with hydrogen gas, something we'd all prefer say together! I don't recall which plant it was, but this has happened here in the US many years ago, it blew the entire plant to pieces on a hydrogen generator explosion.Questions, please ask.

author: dr.diesel
author_rank: Super Contributor
timestamp: November 15, 2013, 05:51:27 pm
content: Quote from: orion242 on November 15, 2013, 03:03:17 pmThankfully the vast majority of tube leaks are towards the inside of the boiler, obviously because this is the side that is facing the heat. I'm sure there are different sizes but ours are about 1.5" OD with a wall thickness of 3/16" maybe 1/4" (sorry, not a boiler mechanical guy). When the tubes burst they typically "fish eye", sometimes flailing around like a wet noodle bending and banging all around.External bursts are quite rare, but do happen and are very dangerous.Fish eye burst example:

author: Stonent
author_rank: Super Contributor
timestamp: November 15, 2013, 05:54:37 pm
content: They should have a gift shop with bumper stickers. "I <3 Carbon"

author: dr.diesel
author_rank: Super Contributor
timestamp: November 15, 2013, 06:02:18 pm
content: Ha,Most of the fellow employees truly believe in a clean safe environment. I'll get to it in the next part but scrubbed plants are fairly clean (not accounting for the CO2), I don't know the percentage off the top of my head but most of the smoke looking exhaust is actually just steam off the Flue-gas desulfurization process.EDIT:Note not all plants in the US have scrubbers, most of these are being closed down in the next 2-3 years due to recent EPA regs. Almost all of this generating capacity is not being replaced, at this time anyhow.

author: Stonent
author_rank: Super Contributor
timestamp: November 15, 2013, 08:46:55 pm
content: Caterpillar got out of the truck engine business a few years back due to increased EPA regs. I guess despite being a very popular choice it wasn't worth it for them considering the EPA regs are much less stringent for tractors and backup generators. They started licensing out and selling engine blocks to Navistar aka (International). Nav was sure they could get the big engines EPA certified without a Urea injection system. But after several years of selling noncompliant engines Navistar couldn't get them clean and had to pay a 15k fine IIRC on each installed engine until they finally swallowed their pride (and shut down their plant in Dallas) and went to Cummins with their hat in their hand asking for help.In a way that I'm sure sounded like Mater from Cars (Larry the cable guy) Cummins said "Well there's your problem! You ain't got no selective catalytic reduction urea injection system! We've got a few of those for sale if you're interested! We'll even make you an adapter to fit your stinky old engine!'

author: Stonent
author_rank: Super Contributor
timestamp: November 15, 2013, 08:59:50 pm
content: Regarding grades of coal back in the early 1900s the coal industry had an advertising campaign for Anthracite. It had a young lady wearing a white dress putting coal into a stove and the tagline said "Anthracite keeps her dress white!"I'm sure her father was very relieved.

author: rollatorwieltje
author_rank: Unknown
timestamp: November 15, 2013, 09:04:27 pm
content: How does a big plant like that deals with a sudden blackout / disconnect from grid?I know plants can start venting when the turbine speed gets too high, but does that still work if you suddenly have to get rid of 500MW+ worth of pressurized steam?I live near a chemical plant that uses high pressure steam, when they had to vent due to some process error is was extremely loud and could be heard up to 10KM away. That was nowhere near 500MW worth of energy though.

author: Stonent
author_rank: Super Contributor
timestamp: November 15, 2013, 09:08:18 pm
content: I'm guessing some kind of clutch or governor if the turbines get out of control but that's just what I would design it may not be right.

author: rexxar
author_rank: Frequent Contributor
timestamp: November 15, 2013, 09:21:56 pm
content: What happens when one of the boilers goes down? Is there not so much demand that the other can keep up, or does it get overloaded? For that matter, what happens when the whole plant gets shut down, just black out the whole city, or does power come in from another station somewhere?

author: dr.diesel
author_rank: Super Contributor
timestamp: November 15, 2013, 09:24:37 pm
content: A full load unit trip is a bit exciting and usually causes some minor damage. The main turbine has two sets of hydraulically controlled valves, when something bad happens these valvesSLAMclosed, they have huge springs constantly pushing them closed at all times, you have to "hold" them open during normal operation. When this happens a MFT (Main Fuel Trip) is initiated cutting all fuel to the boiler, almost instantly the boiler/drum over pressurizes (cause the normal path through the turbine is now closed) and vents all of the excess steam straight up into the air from the roof of the power house. The cooling water pumps say active replacing the escaping water until the boiler cools down, which takes hours. The entire building shakes around when this happens and is very loud, can be heard for miles.When the generator breakers are closed it is pretty much impossible (there are ways, ie losing generator excitation) for it to over-speed, doing so would mean over powering the grid, which is not possible due to the massive load. There is no clutch between the turbine and generator. The generator it'self is the most protected piece of equipment at the plant, there are multiple redundant protective systems, to my knowledge a catastrophic over-speed has not happened in the US. At least not in the past 50 years.A bunch more could be said here, perhaps I'll add it to the list of write-ups.

author: Alana
author_rank: Frequent Contributor
timestamp: November 15, 2013, 09:38:48 pm
content: Why you use hydrogen as coolant in generators?

author: notsob
author_rank: Frequent Contributor
timestamp: November 15, 2013, 09:47:44 pm
content: from wiki/snipGenerator coolingWhile small generators may be cooled by air drawn through filters at the inlet, larger units generally require special cooling arrangements. Hydrogen gas cooling, in an oil-sealed casing, is used because it has the highest known heat transfer coefficient of any gas and for its low viscosity which reduces windage losses. This system requires special handling during start-up, with air in the generator enclosure first displaced by carbon dioxide before filling with hydrogen. This ensures that the highly flammable hydrogen does not mix with oxygen in the air.The hydrogen pressure inside the casing is maintained slightly higher than atmospheric pressure to avoid outside air ingress. The hydrogen must be sealed against outward leakage where the shaft emerges from the casing. Mechanical seals around the shaft are installed with a very small annular gap to avoid rubbing between the shaft and the seals. Seal oil is used to prevent the hydrogen gas leakage to atmosphere.The generator also uses water cooling. Since the generator coils are at a potential of about 22 kV, an insulating barrier such as Teflon is used to interconnect the water line and the generator high-voltage windings. Demineralized water of low conductivity is used.Generator high-voltage systemThe generator voltage for modern utility-connected generators ranges from 11 kV in smaller units to 22 kV in larger units. The generator high-voltage leads are normally large aluminium channels because of their high current as compared to the cables used in smaller machines. They are enclosed in well-grounded aluminium bus ducts and are supported on suitable insulators. The generator high-voltage leads are connected to step-up transformers for connecting to a high-voltage electrical substation (usually in the range of 115 kV to 765 kV) for further transmission by the local power grid.The necessary protection and metering devices are included for the high-voltage leads. Thus, the steam turbine generator and the transformer form one unit. Smaller units may share a common generator step-up transformer with individual circuit breakers to connect the generators to a common bus./endsnip

author: SeanB
author_rank: Super Contributor
timestamp: November 16, 2013, 08:39:50 am
content: There are a few power plants here in South Africa which get the coal from the mine by conveyor belt, about 30km of belting in sections linking the mine to the plant, and this grows with the mine moving along the seam.A storey from my dad was of a routine belt replacement ( about 5km of rubber belt needing replacement) that went wrong when a work lamp on a support tower fell into the belt and the leg started to cut a rip in the belt during start up. They had to truck in and fly in about 3km of rubber from all over to quickly replace the torn section, and this took another day of lost production to get the belting, splice it in at the multiple spots where the individual rolls were joined and realign it again. There were a few mine storemen called at 3AM to go to stores, get all they had in stock out and place it on a lowbed hired at 3AM and ship it to arrive "as soon as possible or even faster" either by truck for the closer ones or on a cargo flight hired just for the few tons of belt they could fit in the plane. They drew straws at the site as to who had to go to the mine manager and tell him they would need an extra day to change the belt.

author: TheWelly888
author_rank: Frequent Contributor
timestamp: November 16, 2013, 08:57:08 am
content: As a 15 year old schoolboy decades ago, I went on a school outing to visit a 3000MW coal fired power station. The turbine hall was the highlight of the trip, the sheer power of the 6x 500MW turbo alternators roaring away.Sadly that coal plant closed earlier this year as it was nearly life expired and too expensive to fit de-sulpherisation gear to the exhaust.

author: Frenchie
author_rank: Regular Contributor
timestamp: November 16, 2013, 08:57:47 am
content: Without divulging too much detail about my job, I'm a chemical engineer and I work with kilns that burn considerable amounts of coal (>1kT per day for the site). Couple of minor items missed on coal milling from a control standpoint.Coal moisture is actually a more significant issue than given credit. 'Dry' coal will still have ~20-30% entrained moisture which degrades the performance of roller/bowl mills. To get an efficient grind a lot of mills have an inlet pre-heater, a gas burner that takes the inlet air up to some 350-400 degrees C controlling on a mill exit temperature approx 65C. Control of the pre-heater is critical as insufficient heat leads to poor grinding efficiency and too high can do serious damage to the mill (can crack the grinding table, balls, etc)Left in free air and sunlight stockpiled coal will begin to oxidise (not burn) and start producing heat. Left unchecked it will get sufficiently hot enough that it can self ignite and combust in the pile. Managing a stockpile well requires careful contouring, compaction and monitoring and is a bit of an art-form in itself. Stockpile fires tend to be smoldering piles of very hot coal rather than roaring flames. Whether or not they actually cause an issue depends on how big they are, whether there's a safety issue and whether or not there's a local community to worry about odours (in our case, the nearest house is less than a kilometre away, so they are a problem).Because it's literally dug out from the ground, coal contains a large portion (20%) of non-combustibles ie what becomes fly-ash. In a power station or similar where the burning space is separate the stack pollution control (electrostatic precipitator*) will drop this out of the flue gas. In my case, the reaction occurs within the burning space and the flame is in intimate contact with the product. The chemical makeup of the ash component actually needs to be taken into consideration as a feed component and we adjust the balance of the feed to suit.Lastly, on a purely semantic issue, coal is from plant matter rather than dinosaurs, but I'm splitting hairs.* There's a topic that might be fun for me to go into more detail about but I'll let the dr.diesel get to it first.

author: SeanB
author_rank: Super Contributor
timestamp: November 16, 2013, 10:02:10 am
content: Correct on the cooking coal pile, you go past one at Newcastle in the KZN midlands, they use it burning or not in the power plant. Makes for a nice light at night when you drive past.

author: notsob
author_rank: Frequent Contributor
timestamp: November 16, 2013, 10:10:04 am
content: 1. Make sure you mention the cooling system, most people see a hyperbolic cooling tower on the news and think its a power station.2. Efficiencies of the individual units ( these are guesses) . boiler - high 90's %, transmission transformers - above 99 %, turbine itself - probably 3 stage ~ 30%

author: Harvs
author_rank: Super Contributor
timestamp: November 17, 2013, 05:22:44 am
content: What I'd like to know, in what is an established and running industrial control system, what's the main day to day work of a control engineer?

author: Frenchie
author_rank: Regular Contributor
timestamp: November 17, 2013, 06:04:56 am
content: Quote from: Harvs on November 17, 2013, 05:22:44 amBeing nagged a lot by me

author: dr.diesel
author_rank: Super Contributor
timestamp: November 17, 2013, 01:26:30 pm
content: Quote from: Harvs on November 17, 2013, 05:22:44 amDay to day can vary quite a bit:- Most fossil plants are old, so there is constant stream of old mechanical/analog/etc systems that need integrated into the main control system.- With 30,000 I/O points or end devices, many which are redundant and "dumb", there are always a handful that are broke or misbehaving. Finding these is not always easy.- Schematic drawing maintenance.- Future planning for upgrades. My single plant alone has had over $1B in upgrades of the past 10 years. With 1/2 of that more planned for the next few more.- I answer aLOTof questions, not only to plant personnel, but to governing bodies as well.An interesting fact, you'd think turbine/boiler control logic would be somewhat standard throughout the industry, or at least through one specific company or vendor, but it's not. This is one spot that is changing slowly, moving to a more standard, known scheme. The hold up is the cost and the downtime duration needed to make it happen. As the EPA closes more plants down we get less and less downtime for upgrades.I will note, the Unix/Linux computer systems require zero effort. We swap the hardware about 4-5 years and carry on.

author: dr.diesel
author_rank: Super Contributor
timestamp: November 17, 2013, 11:02:43 pm
content: Flue-gas desulfurization (FGD)The FGD process is basically a giant chemical reaction, a bit out of my area of expertise, so I stole this summary:Code:"Wet SystemsIn a wet scrubber system, flue gas is ducted to a spray tower where an aqueous slurry of sorbent isinjected into the flue gas. To provide good contact between the waste gas and sorbent, the nozzles andinjection locations are designed to optimize the size and density of slurry droplets formed by the system.A portion of the water in the slurry is evaporated and the waste gas stream becomes saturated withwater vapor. Sulfur dioxide dissolves into the slurry droplets where it reacts with the alkalineparticulates. The slurry falls to the bottom of the absorber where it is collected. Treated flue gas passesthrough a mist eliminator before exiting the absorber which removes any entrained slurry droplets. Theabsorber effluent is sent to a reaction tank where the SO2-alkali reaction is completed forming a neutralsalt. In a regenerable system, the spent slurry is recycled back to the absorber. Once through systemsdewater the spent slurry for disposal or use as a by-product.Typical sorbent material is limestone, or lime. Limestone is very inexpensive but control efficiencies forlimestone systems are limited to approximately 90%. Lime is easier to manage on-site and has controlefficiencies up to 95% but is significantly more costly (Cooper 2002). Proprietary sorbents with reactivity-enhancing additives provide control efficiencies greater than 95% but are very costly. Electrical utilitiesstore large volumes of limestone or lime on site and prepare the sorbent for injection, but this isgenerally not cost effective for smaller industrial applications."Our typical efficiency was 99% through the FGD, a bit higher than listed above, via limestone. No other emissions equipment or exhaust scrubbing is currently done, however, construction is currently underway for Selective catalytic reduction (SCRs).

author: dr.diesel
author_rank: Super Contributor
timestamp: November 17, 2013, 11:21:15 pm
content: Quote from: rexxar on November 15, 2013, 09:21:56 pmThe grid is a massive structure with many hundreds of generating stations basically "pouring" power in. Typically nuclear plants are what's called base loaded, they are usually generating at maximum capacity and pretty much stay there 24-7. This is because the nuclear generation process doesn't lend itself to throttling, I don't have any experience here, not sure why. That leaves the coal plants (many of which are base loaded, usually the big ones > 400MWs) and many other smaller coal (some as small as 90MW) and NG fired units generating at some point less than max. These are the plants that provide the "spinning reserve" when other plants are suddenly taken offline. One or two big plants tripping off only result in the others picking up usually a few percentage points of load, not a big deal but hasA MASSIVEeffect on MW pricing, which I can't really talk about.

author: nctnico
author_rank: Super Contributor
timestamp: November 18, 2013, 01:44:22 am
content: AFAIK coal plants are also 'slow adjusters'. Power plants with gas turbines OTOH can regulate quick and are used to level the grid.

author: senso
author_rank: Frequent Contributor
timestamp: November 18, 2013, 02:43:00 am
content: Is it true that those generators/turbines cant be just stopped while hot or they just get bent due to the heat?I'm asking this because I have a friend that works in a huge factory and he says they have 2 generators powered by a pair of gas turbines, and one day one turbine died and has the generator was hot, the shaft bended as it was hot enough to be "soft".

author: dr.diesel
author_rank: Super Contributor
timestamp: November 18, 2013, 11:24:07 am
content: Quote from: senso on November 18, 2013, 02:43:00 amYes!When a unit trips it takes ~45 minutes for the turbine to coast down from 3600RPM to 0, at which point it is instantly put on turning gear at 3RPM until it cools to < 400F. This cooling duration takes about 5 days.

author: dr.diesel
author_rank: Super Contributor
timestamp: November 18, 2013, 01:46:07 pm
content: Quote from: nctnico on November 18, 2013, 01:44:22 amIn normal operation the plants generation is controlled by a "load center" remotely. From there they tick the units up or down depending on grid conditions, most plants limit the load center ticking to 2-3MW per minute.Ultimately the plant has full control and with a push of a button the load center is disconnected. This happens quite frequently as minor plant upsets require the ticking to stop while the unit upset settles out.

author: SeanB
author_rank: Super Contributor
timestamp: November 18, 2013, 06:50:43 pm
content: Nuclear plants are run at full power as to drop power takes hours, as you have to insert control rods to slow down the reaction, which results in an increase in power for a very short period as the byproducts finish reacting before settling down at a lower level over a period of minutes to days depending on the composition of the fuel ( how it has changed between new and when it is in need of refurbishment), but you can run them at lower levels down to about 50% of rated power. Ramping up takes the same length of time. If you SCRAM the plant you need to provide full cooling water to the reactor for a period of days and dump the heat to a cooling tower or pond just to keep the water from flashing and the plant from overheating. Even shut down there is a lot of heat generated that needs to be removed via the cooling water system, along with the Helium that is created from Alpha decay. Generally you shut them down every half decade or so for refuelling and major maintenance.

author: nctnico
author_rank: Super Contributor
timestamp: November 18, 2013, 08:52:53 pm
content: I'm just wondering: are there any nuclear power plants which allow visitors?I've visited several coal/gas based power plants when I was a teenager. Back then security was way more relaxed than currently.

author: dr.diesel
author_rank: Super Contributor
timestamp: November 18, 2013, 09:20:59 pm
content: Quote from: nctnico on November 18, 2013, 08:52:53 pmI walked right in a nuclear plant in the early 90s! Today the average person wouldn't have a chance, unless desired so by the plant manager or higher up. Background checks would still have to be completed prior to the visit.

author: DenzilPenberthy
author_rank: Frequent Contributor
timestamp: November 21, 2013, 01:46:14 pm
content: Quote from: TheWelly888 on November 16, 2013, 08:57:08 amWould that be the Didcot Cloud Factory? I used to live near there and went to an open day there probably about 20 years ago. I found it absolutely fascinating!

author: TheWelly888
author_rank: Frequent Contributor
timestamp: November 21, 2013, 06:58:53 pm
content: Quote from: DenzilPenberthy on November 21, 2013, 01:46:14 pmYes.

author: SeanB
author_rank: Super Contributor
timestamp: November 21, 2013, 07:48:57 pm
content: Quote from: dr.diesel on November 18, 2013, 09:20:59 pmI did training at one. You would get close to strip searched going in and out. Weird was that they had a regular Municipal SVP bus route through there. Only time I ever met a regular bus driver with a Top Secret security clearance. I might still have some of the training manuals I got there, with a nice front cover of the facility with the massive grey Z building in the background.