OT: Drax to be turned off whenever it's "too" windy or sunny

This is not new - we've been using coal plants as backup reserve for several years now.

I would guess (but I don't know) that the periods being talked about is of the order of days/weeks, not hours. In other words, the forecast says we're going to have a dunkelflaute next week, so crank up the boiler. It runs for two weeks and then goes back to 'idle'.

The other question is what 'idle' means. Can you keep the boilers on 'simmer', up to temp but not producing much steam? Then you throw some more logs on the stove ahead of when you need the steam. I don't know what the losses of an idling thermal plant are, but surface area to volume suggests you can retain heat in a large boiler for a long time. (such happened with steam locomotives, on a much smaller scale)

I'd guess that all this has been thoroughly tested during the years that coal plants were used during the winter only and, since Drax is really a coal plant wearing a green hat, it's no different.

Theo

Well it will probably constrain the nice juicy dividends that Drax have been paying me for a few years.

As a student, I 'worked' in a coal fired power station in 1959. I seem to remeber it took 4 days to get a set up to temperature. It's only hydro power that has an ON/OFF switch.

In message <gSD* snipped-for-privacy@news.chiark.greenend.org.uk>, Theo <theom+ snipped-for-privacy@chiark.greenend.org.uk> writes

The other issue is what does this do to the boiler. Keeping the boiler at working temperature means that it is subject to certain constant stresses, warming it up and cooling it down on a regular (FSVO) basis is quite likely to be a bad thing for it, meaning that the maintenance load on it increases in the long run. It could be that the payment structure covers that adequately.

Adrian

Not contradicting what you say in anyway, but they turn Drax down every night. (3GW in the day, 1GW over night). So clearly there is an ability to idle(ish), in a 24 hour cycle. i.e. Turning output up and down is probably distinct for changing temperature.

Where government is involved, *one* would be a considerable achievement.

And 'cheap' won't be the one.

There's certainly some truth in that, but I'd add further conditions of 'reliable and economic' for it to be done outside a laboratory. We saw laboratory models of wave and tidal power many decades ago, and while there are a few real-world implementations, they obviously have not yet been made genuinely reliable and economic. Scientists often do not realise what a hostile environment the great outdoors actually is, particularly on coastlines.

But when a new idea is touted as 'cheap' or 'will reduce household bills', you know absolutely certainly that if that were true, it would already be in use, nobody would be waiting for the government to subsidise it and there would not possibly be any reason to require it by law.

I'm assuming they're not swinging the boiler temperature very much. When it's 'idling' it's at say 98C, when it's producing steam it's at 100C. The more wood they throw at it the more steam them make, but it stays at 100C (unless they run out of water). OK it's high pressure steam so probably not

You'd only drop the temperature during the summer when you know it's not going to be needed, or during scheduled maintenance. That would reduce the number of cycles to a handful per year. Of course that depends on the losses when 'idling' being low enough to keep it on tickover.

Because you aren't heating it from cold, perhaps the time to raise it from

Theo

Maybe I'm misunderstanding you, but I would assume that steam in all modern fossil-fuel-burning power stations was highly superheated and supercritical, and much hotter than just above the BP of water, somewhere around 500 to 600°C.

A problem with rapid fluctuations in temperature, as would be the case if Drax were running in true rapid on-off mode would be the refractory brickwork in the vicinity of the burners in the boiler. Slow run up and run down allows gentler and more uniform expansion and contraction of the brickwork, putting much less stress on it, less spalling and longer lasting.

The company I used to work for has a Proteus gas turbine for emergencies. It only took a few minutes (about five IIRC) to go from start to full generation, and everyone within half a mile knew about it!

Brings back memories of testing a newly built 24MW, RB211 powered generator set, at full load, with all the acoustic enclosure doors wide open. We spent months getting ready, sorting problems, etc. and when we finally had a successful start at about 16:30, it was decided to keep going for the 8-hour run-test. By midnight, the local housing estate was not at all happy, but legally we were allowed 10 noisy nights per year.

Yes, because that's how you get efficiency, which IIRC is calculated as:

All measured in K. The T-cold is going to be as close to 100C (373K) as they can manage, the temperature of the steam as it exits the low-pressure turbine. T-hot is the steam temp as it enters the high-pressure turbine. So you can get close to 60%.

Then you shove the steam into a cooling tower.

Which is ideal - lots of nukes, constant power, make it cheap when demand is low, so people heat stored water, charge EVs, heat their homes then and even out the peaks. Any excess at these times can be used to produce Hydrogen for later use for transport, etc.

It seems they keep them on simmer, with the turbines still turning

Well, you extract the heat from the steam in the condenser, a vast structure beneath the low-pressure turbine, which warms water in a secondary circuit, which in turn is cooled in the towers.

During my thin sandwich degree course, I spent time at Eggborough power station. All that generation of power stations with 500 MW alternators had suffered from delays and faults requiring significant repair work - things were about 5 years late at the time. The previous designs had been 120 MW, and a number of aspects hadn't scaled well, resulting in premature and catastrophic failures.

One of my tasks involved taking the shipping rubber bands off a cabinet of relays, which were already well outside their stamped 5-year warranty date. I was intrigued by one relay whose function was, as condenser vacuum fell, to open the turbine hall roof vents, so that the anticipated blast (1) didn't take all the windows out.

(1) The low pressure turbine casings included a special explosion vent comprising a thin metal sheet normally sucked onto a mesh frame, with a sharp spike poised above it. If pressure becomes positive, the metal bulges and is pierced by the spike to vent to atmosphere

Chris

Another critical thing is to avoid water droplets in the steam, as they damage the turbine blades, so that’s another reason for T-hot being so high.

Yes, I remember back in the 1960s on a school 'industrial tour' we visited one of the main turbine generator manufacturers and they showed us blades that had been perforated by water droplets.

Not really. T-hot is high for Carnot efficiency, as Tim says. That isn't the worry for water droplets. The worry is that you want T-cold as low as possible. So they condense the steam with cooling. In my own layman understanding, condensation of steam creates low pressure (1 psia) which helps the flow through the turbines. The problem occurs in the final turbine nearest to the cold exhaust.

Massive. Someone who did a consultancy for Eirgrid was told it took

All other things being equal, yes we should BUT all other things are not equal

The politics and planning of getting big power stations built adds massive amounts to the cost and they cannot be built close to where demand is. This adds infrastructure cost and massive pylons across the landscape.

We have signed up to retain harmonisation with Euratom which was a huge mistake so there is no easy way to avoid the cost of meeting EU regulatory standards The point about SMRs is they may not be as ultimately efficient but they can be installed in 3 years, not 20. And close to where the power is needed.

Neither the tTories nor Labour have the guts to break away from the Eu regulations, so SMRS are the only way to lessen their impact at this point in time. and certainly having factory built modules means from planning to grid connections will be mighty fast - not much different to a gas power station

poisoning makes it tricky

The Natrium reactor is a far better idea. The working fluid is molten salt and they hold a huge store of it, so the heatbank can be tapped at various power levels to allow modulation above and below the reactor output.