Nuclear CHP as a solution

Martyn1981

zeupater wrote: »

Hi
So, if the belief is that underground water mains rupture very rarely because they are designed & engineered using modern materials with pressure safety margins well above what the infrastructure is ever likely to achieve ... maybe, but add the variable of temperature and everything changes ...

HTH
Z

Not sure about that Z. If distributed heat pipes ever fail then we'd have seen such a thing in New York, we'd see fictional and real programs showing steam/water vapour clouds coming out of the ground and manholes. And when I visited (a long time ago) I'd have been fascinated to see them for real.

But, of course, we've never seen anything like that ...... have we?

ABrass

GreatApe wrote: »

1 district heating cannot work

Not all houses are in districts.

2 why nuclear heat can not work. Both in fact exist. There are over 400 commercial nuclear reactors that do generate heat and convert it to electricity. and there are district heating grids in existence which seem to be affordable

This is your problem in a nutshell. You are conflating the ability to generate electricity using steam in typically but not uniformly PWR systems with extensive management, maintenance, security and using enriched materials, again typically uranium, with a low cost universally distributed low grade heat distribution system.

Can you use your Bugatti Veyron to collect your neighbourhood bins? Yes, not a great value for money approach.

Those are big, expensive and need to be heavily managed. Could you put one in every large urban center and use the low grade waste heat from the PWRs to provide urban heating? Yes but it'd cost a fortune, we dont' want or need that many nuclear reactors and you'd still need all the cooling equipment to dispose of waste heat during the summer. Plus backups for when the nuclear reactors are down for maintenance, they typically only get 90% up time.

Where you wander off into cloud cuckoo land is trying to do it on the cheap using waste and *magic*. You can't run PWR style reactors using the waste, that's why it's waste. You'd be using radioactive decay in a pool to warm water to an unknown value, then running it through a heat exchanger. That means you need to keep fiddling with the pool to keep the right level of reaction and hope that the mix you've dumped in isn't highly corrosive at higher temperatures.

Unless you've got a lot of working you haven't shared this is crayon on the wall level of design.

Regarding heat loss this would not be a huge problem especially for the bulk pipes.
Their surface area to mass is low so there would be no large heat loss and with insulation the heat loss would be very acceptable.

For a 75cm pipe with 10cm mineral wool insulation carrying hot water it would have a heat loss of about 80 watts per meter in the open (less in the ground)

That is a pipe carrying 500 MW of heat
So for 10 miles it would have a loss of 1.3 MW out of 500MW it is which is less than 0.3% heat loss

Even if your nuclear heat station is 40 miles away you have a loss of just 1.04%

As I've said previously and proven now, the heat loss in the bulk pipes would be negligible only about 1%. There is also a return pipe but the loss there is less due to the return water being cooler but whatever let's pretend it's the same loss so we are at 2% if you pipe it from a nuke 40 miles away

The heat loss in the second and third legs of moving this hot water around would be more but still most of your heat is not lost it is used. I'd hazard a guess of less than 10% possibly as low as 6% overall that beats transmission losses on electricity and perhaps even methane losses in the natural gas wells/grids

Pulling numbers our of thing air isn't impressive, show your working.

This has all been suggested before, it was a rubbish idea then too.

zeupater

Martyn1981 wrote: »

Not sure about that Z. If distributed heat pipes ever fail then we'd have seen such a thing in New York, we'd see fictional and real programs showing steam/water vapour clouds coming out of the ground and manholes. And when I visited (a long time ago) I'd have been fascinated to see them for real.

But, of course, we've never seen anything like that ...... have we?

Hi

The point being conveyed is that as temperature increases the pipework material specification has to be improved to cope with the additional wear/degradation and pressure performance reduction.

The examples given related to water mains explained that although pressure is maintained at ~0.7bar, the pipework specification at standard (/typical) operating temperatures calls for ~12bar capability to provide system resilience. Although this is the case, relatively minor changes in ground conditions in summer & winter provide considerable stress to the underground infrastructure with ground movement and temperature related expansion & contraction of pipework increasing the chance of failure ... moving on, running water-main type pipework at ~70C reduces the pressure rating to around 2bar(reducing safety margin) & the material loses hardness & wears more quickly (reducing lifespan) so there's little opportunity to increase pressure above 1bar or temperature above 70C unless more suitable materials are specified.

The point raised about flow rate at 2m/s is extremely valid. Think about water flow as being wind-speed and the inside diameter of the pipe as being the swept area of a wind turbine ... when the wind-speed doubles you increase the available kinetic energy for the blades to capture by a factor of 8! ... within a pipeline solution it's exactly the same, increasing pressure to increase flow rate (pressure drop dependant) must logically increase the pumped energy input by a factor of 8 (increasing operating costs) and that 8x increase in energy inflicts 8x more damage (wear) to the inner wall of the pipe even if laminar flow is maintained.

Relating to laminar flow ... as the flow rate increases, the likelihood of induced turbulence increases, this being more inline with the rate of increase of energy availability than flow rate. Smooth (laminar) flow can easily be disrupted by bends in the pipework (flow on the outside of a bent pipe radius is longer than on the inside, thus disrupting flow), but the main contributor would be where supply connections are made as this causes a change in downstream flow - the likelihood of laminar flow becoming turbulent flow can reliably be modelled, as can the distance between an 'object' in the flow and where turbulence is expected and at what point cavitation would be expected where severe bends, connections, pipe diameter changes & valves occur which have an effect on pressure over relatively short distances at high velocity flow rates ...

Regarding New York ... that's a pretty decent example of what we're talking about .... from looking at this previously (some years ago!) it seems that the steam we see from this CHP system (the largest?) is the result of around 100miles of pipework under the streets of a pretty limited geographical area. The issue is that it's not only in a very densely populated urban environment, but the number of customer connections is in the low thousands, with the majority of heat being delivered to large commercial premises and large multi-occupancy buildings as opposed to domestic properties & small-scale residencies ... last time I looked the average annual maintenance cost per connection was somewhere around $1000, but the real issue is that the infrastructure was mostly laid down to service the area at around the same time that the area was undergoing major development (ie contemporaneous as opposed to retro-fit), therefore the disruption & costs were heavily reduced.

Okay, so the steam distribution system exists, it costs a lot of money to connect to & maintain that connection and is therefore mainly targetted at large commercial or multi-occupancy premises in order to make a profit .... so what's the overall thermal efficiency of the network (metered units of heat input to metered units sold)? ... around 60%, which is pretty acceptable considering it's distributing waste heat from power generation sources within the urban environment being served, but the question still revolves around the cost & efficiency losses involved when heat sources linked to a national heat-grid don't coincide with areas of dense population?

The previously roughly estimated costs for heat distribution (£Trillions!) were based on three elements ... a national heat transmission grid based on major underground works (large diameter tunnels) roughly on motorway & major trunk road miles (as they connect centres of population), a distribution grid using the cost/mile of laying water mains in rural areas (therefore very low) based roughly on total road miles (including pumping stations) & individual property connections based on a per property connection for standard water supply plus the cost of insulated twin-core heat-main .... the basis was 70C heat provision at approx 1bar of pressure to connect a metered supply directly to existing 'wet' heating systems, mainly using existing technology multi-wall plastic piping (apart from main service tunnel supplies!) .... so, if we're going to look at distributing superheated steam in metal pipes with welded connections at around the same pressures as New York (10bar/~140psi(?)) along with pressure reduction & blending valves for each connected property, apart from simply multiplying the previous figure by a significant factor (x5?, x10?), I'm not even going to have a stab at the cost .... it's simply a non starter ....

... CHP/Cogen is a solution to heating using what would otherwise be the waste energy by-product from local electricity generation and because thermal transmission is relatively inefficient & hugely expensive it's likely to stay that way for a very long time, which effectively rules out the use of large scale nuclear in a co-gen capacity, whether from existing or new sites as planning conditions would deem that they are placed far away from high density population centres, which are the very areas where the energy demand exists .... the whole population of North Somerset won't make much impact on ~6GW of heat from HPC even in deepest winter, bordering on absolutely none in summer!


Phew!! ... that was longer than expected ...

HTH
Z

zeupater

Hi All

Further to above, I've dug around a bit to find the original document that I read some years ago ....

Consolidated Edison - Steam Long Range Plan

.... I thought it was interesting when I first read it and it's worthy of having a decent look through as it probably addresses most of the issues which may surface on the high-pressure Co-gen side of the discussion on a kind of 'from the horse's mouth' viewpoint ...

... hope my memory of what it said is pretty much in-line with what it actually says ... :cool:

HTH
Z

zeupater

ABrass wrote: »

... Pulling numbers our of thing air isn't impressive, show your working ...

Hi

... I'd like to see those calculations too, especially the velocity of superheated steam in a 750mm id pipe with an initial pressure of (say) 10bar/160C with energy loss/delivery resulting in a non-condensed temperature fall restricted to (say) 40C to minimise condensed pumping provision whilst still delivering 500MW.t ...

Are we talking about walking pace, bicycle, F1, Fighter Jet or going on escape velocity? ... even more, how do we achieve that kind of velocity at an initial 160C with the energy available from a mere 10bar of differential pressure? ...

... you may not be "a nuclear scientist, nor an engineer" and therefore not have a clue on how access/calculate the answer, but almost any engineer worthy of taking part in the discussion would ... I've just done the calculation & it definitely far exceeds 2m/s, not that you'd hear it coming before it hit your twelfth generation Apple computer and smashed it to smithereens though! ....


:wave: ... waves at all engineers and/or scientists up for a basic calculation .... :think: ... nearest ones to my answer (if it's right! .. ) can also bang their heads on a brick wall in astonishment & disbelief .... :wall:


HTH
Z

#Edit - Just for fun, for those more interested in the issue, what happens in a fluid system if the distance related localised pressure anywhere in the system drops below 2bar before the temperature has reduced by ~40C ?? .... :whistle:

GreatApe

Calculations

500MW pipe with water at 90 centigrade 50 centigrade return
Need a flow rate of approx 3 tons per second

To achieve that 3 tons per second you need to vary pipe size, pressure and how frequently you place a pumping station. The higher the pressure the lower the distance between pumping stations the smaller the pipe.

https://www.copely.com/tools/flow-rate-calculator/

For instance you can achieve 3 tons per second with
80cm pipe 10 bar pressure and pumping station every 3km OR if you want lower pressure you could increase the size of the pipe to 1m diameter and lower the pressure to 3 bar OR if you don't want so many pumping stations you could do 100cm pipe 10 bar pressure when Ch allows pumping stations every 10km.

Let's go with 75cm pipe 10 bar pressure and pumping every 2km
I'm not saying this is optimal solution t may well be better to use lower pressure and more distance between pumping stations with 100cm pipe instead of 75cm pipe but just for arguments sake 75cm pipe it is


Use this site to figure out your heat loss
https://checalc.com/calc/inshoriz.html
75cm pipe with 10cm rockwool insulation is 80 watts heat loss per meter

So if your pipe is 50km in length you would have 4MW heat loss for a pipe carrying 500MW of heat which is less than 1% loss. The return pipe would be less heat loss since it would be returning at 50 centigrade rather than 90 but let's keep it simple and say that return pipe is also a 4MW loss you have 8MW for 500MW = 1.6% loss for transporting 50km distance

Very acceptable

A 10GW heat reactor would need 20 such pipes taken to 20 different councils
500MW is probably sufficient for an area with a population of 400,000

Someone asked what the speed would be.
In this example of 75cm pipe it would be below 6.8m/s
If using 1.2m pipe it would be 2.6m/s

You wouldn't even have to bury this pipe you could have it overground most of the distance with 1 meter tall heddgerow either side hiding it's presence

GreatApe

Keeping it simple if you have a bundle of five pipes going into London to feed say 10 million projected population and 10GW peak demand

2GW per pipe. 50km distance to heat reactor
160cm pipes 8 bar pressure 5km between pumps does the trick
Call this the backbone

Once in London. London is 1,600 sqKm so each pipe feeds 320 sqKm roughly equivalent of 6 boroughs
From the backbone each if these 5 nodes feeds 6-7 London boroughs with three pipes per borough
Assume 300k population and 300MW demand so 100MW per pipe and average 5km distance
58cm pipes 5 bar pressure 5km distance 100MW power.
Call this primary distribution

Now you are in a borough of average size 50 sqKm and 300,000 population however say one third of the palace is green so the density is 9,000 persons per SQKM and we want to connect up 33 pipes to 1sqkm grids. 1sqkm has 9,000 people and needs 9MW of power over there pipes. Average pipe distance 2.5km
15cm pipe 4 bar 2.5km distance 3MW power
Call this the secondary distribution

Now we are in a sqKm with 9,000 population
Let's divide this grid into 9 squares of population 1000
Power need is 1MW average distance 350 meters send over three pipes
5cm pipe 3 bar pressure 350 meter distance 0.33MW power
Let's call this the district

This is an area of population 1,000 with about 250 homes or flats

Let's split this into lines connecting 50 homes 200 people power 200KW
35mm pipe 2 bar pressure 50 meter distance.
Let's call this street/block heating grid

The very last leg is individual properties they need 2.5KW average but let's give over 25kw so they can run showers directly. 20mm pipe is more than sufficient

ABrass

You may not be aware but reactors don't scale up linearly beyond a certain point. Making the bigger makes them slower to cool down and more prone to melt down if they lose coolant. That's why you tend to see reactors I'm the 1GW range. 5GW is around three times bigger than the largest in the world.

On a slight tangent, the fact that you use water as both a moderator and a coolant has serious negatives. It's one of the downsides to the PWR design and the main reason think that sodium or pebble bed reactors are a good idea.
Most people don't realise that most nuclear incidents are steam incidents, the radiation just gets carried away as a side effect.

GreatApe

ABrass wrote: »

You may not be aware but reactors don't scale up linearly beyond a certain point. Making the bigger makes them slower to cool down and more prone to melt down if they lose coolant. That's why you tend to see reactors I'm the 1GW range. 5GW is around three times bigger than the largest in the world.

I'm talking thermal power

The EPRs being built in the UK are 1.6GW electrical but 4.5GW thermal each so those are the examples I was using I just rounded to the closest GW and said 5GW each

But it might be better to use a reactor like the one at sizewell b. 1.2GW electrical 3.5GW thermal
Three of those might be better than two EPRs for cost and redundancy. Two EPRs being 9GW while three sizewell b's would be 10GW. Sizewell B was built in 8 years and for £5.3 billion (in today's money). A heat only reactor should be significantly cheaper. Say half the price so you get 3.5GW thermal output for £2.6 billion price tag Or some £750/KW thermal. A very good price!

100GW thermal would probably be right for UK heating needs so £75 Billion cost and the reactors will last 60-100 years.

On a slight tangent, the fact that you use water as both a moderator and a coolant has serious negatives. It's one of the downsides to the PWR design and the main reason think that sodium or pebble bed reactors are a good idea.

LWRs work just fine

Most people don't realise that most nuclear incidents are steam incidents, the radiation just gets carried away as a side effect.

Not really
It's the decay heat what got Fukushima

Once you turn the reactor off there is still 7% of the heat output from decaying
This rapidly falls since the half life is so low. but what it means is if you lose primary cooling the reactor will heat up and up until it bursts. This is why there are 3-4 different cooling methods so if one fails the others kick in. The flooding due to the earthquake knocked all three out. However new designs like the AP 1000 have a passive cooling when power is lost so this should by avoided

Also heat only reactors should be even safer because they are lower temperature lower pressure and you actually want to lose heat from the vessel. You could have the reactor itself in a pool and size it such that when you shut it off the pool heats up. If for some reason all the 20 or so independent pipes for district heating have failed this pool will heat up and start to boil. You then have this containment building. The boiling water condenses onto the walls and then flows back into the pool where it boils again evaporates condenses on the walls and flows back to the pool and so on. So the containment structure itself acts as a heat sink and heat radiator it's a really cleaver solution

Also heat only reactors would be sized such that the pool they sit in it sufficient for the decay heat.
That is to say the energy needed to boil that water away is more than the decay heat of the reactor.
This is possible with heat o my because all you want to do is generate heat
So you want to lose heat from the reactor vessel unlike electricity generation where you don't want to lose much heat from the vessel you want to heat water to turn turbines and have as little lost through the vessel and pipes.

zeupater

ABrass wrote: »

You may not be aware but reactors don't scale up linearly beyond a certain point. Making the bigger makes them slower to cool down and more prone to melt down if they lose coolant. That's why you tend to see reactors I'm the 1GW range. 5GW is around three times bigger than the largest in the world.

On a slight tangent, the fact that you use water as both a moderator and a coolant has serious negatives. It's one of the downsides to the PWR design and the main reason think that sodium or pebble bed reactors are a good idea.
Most people don't realise that most nuclear incidents are steam incidents, the radiation just gets carried away as a side effect.

Hi

I see the source as being related to distribution of heat as opposed to it's initial creation as that's where the major cost & disruption lies.

If we're following the thread title & talking CHP, the major nuclear generation provision will continue to be located exactly where it currently is and if the nuclear fleet needs expansion it would almost certainly be on current sites & previously decommissioned ones.

This provides access to a pretty easy basic calculation of average transmission distance because we know the potential sites and their distance to major population centres ... for example Sizewell to central London would be ~120miles and Dungeness being ~80miles and elsewhere Wylfa to Liverpool would be ~80 miles, with Manchester being ~120 & Birmingham ~150... it must now be noted that all of these locations are just examples of distances to major population centres and that heat delivery from network branching would require significantly more miles of transport.

So, let's take 180km (~110miles) as being the typical requirement for backbone network heat delivery to a customer ... that's 360km of pipework including the return line and this carries just 500MW of heat which represents ~0.25% of peak demand .... So the total heat transmission backbone pipe requirement based purely on 10bar delivery in 750mm diameter pipes scales up to ~150000km ... whichever way you look at it, this represents a significant investment prior to entering the branch network (delivery to street) & individual property connections.

On individual connections, there's a pretty good case study on a reasonably sized CHP development in Chichester which would provide an example of what's involved ... Graylingwell Park ... works out at about £10k/connected property for the local heatmain piping plus property connections, but that doesn't include the cost & disruption of digging up existing roadways, paths, driveways etc & making good afterwards as it's a total development project involving disused buildings and new build ... looks pretty expensive to me even in a relatively high density development (9 properties/acre), not much change from £500billion on that level of density, so wait until you get to a semi-rural level of population density ....

As you say, Fukushima was a steam pressure event and planning for that kind of failure is exactly why reactors are built well away from population centres and it is this safety consideration that creates the requirement for massive investment in heat transmission, which is why it's effectively unaffordable as a solution ...

By the way, did I mention the energy required to pump 500MW of heat at 10bar in a 750mm pipeline is approx 5MW for the first 2km with an additional O.5MW being required every additional 2km ... this represents about 100MW per 360km return, so around 40GW of electricity in total ... odd really, isn't that pretty much the same as we currently use? ... oh well, I suppose that the ongoing & incidental costs of maintaining 10 bar pressure & high flow rates would have been a consideration in the theoretical stage, so I doubt that it would be overlooked for some reason, mind though - the idea of doubling current generation capacity just to save doubling generation capacity would be interesting to some ...

HTH
Z