Energy From Thorium Discussion Forum

It is currently Jan 23, 2018 7:04 am

All times are UTC - 6 hours [ DST ]




Post new topic Reply to topic  [ 33 posts ]  Go to page Previous  1, 2, 3  Next
Author Message
PostPosted: Aug 17, 2015 2:44 pm 
Offline

Joined: Jul 14, 2008 3:12 pm
Posts: 5057
I highly doubt any retrofit market. These big giant district heating grids are only interesting for enormous new build residential areas, where economy of standardization and mass manufacturing and standard installation can be effectively leveraged. If you have to manage custom houses in the thousands, it is going to be totally pointless in costs.

Quote:
In a nuclear system we have little reason to go for a lower delivery temperature than 70C as any savings from drawing heat at a lower temperature than 130C are eaten by increased pumping power getting the heat from the plant to the city where it willl be used.


I don't think so, pumping water is very different than gas/steam. It is low pressure so you can just go for big pipes for the long mains lengths.

Quote:
New construction would likely have said heat exchanger - although we would have to do a cost judgement as the heat exchanger might have a higher capital cost than a cylinder which is after all a consumer item.


Brazed plate HXs are consumer items. All combi boilers have them (hundreds of millions in the world). Not to mention airconditioning and ventilation HX market.

I would worry about water quality if you are thinking of pumping potable heated water many km. Likely this ends up with all stainless and other high grade materials of construction for all piping, increasing the cost of the infrastructure.


Top
 Profile  
 
PostPosted: Aug 17, 2015 2:54 pm 
Offline

Joined: Jun 19, 2013 11:49 am
Posts: 1495
Cyril R wrote:
I highly doubt any retrofit market. These big giant district heating grids are only interesting for enormous new build residential areas, where economy of standardization and mass manufacturing and standard installation can be effectively leveraged. If you have to manage custom houses in the thousands, it is going to be totally pointless in costs.


At which point District Heat cannot compete on any sort of basis, we can't get any kind of economy of scale one estate at a time - it has to be a huge refit programme.
Regulations in Britain essentially require the current gas boiler be placed against an outside wall - which means that there is no new internal piping to consider as all the pipes are brought to the outer wall where they acn be connected to our system. One with a hot water cylinder need not have any equipment inside the house at all - the heat meter would be placed on the outsdie of the wall as all meters tend to be on houses in Britain. You simply plumb the hot water system directly into the existing hot water cylinder heating loop (hot water cylinders tend to be heated indirectly by a boiler through a coil) and into the central heating loop. A pressure reducing valve is most likely necessary but that and the heat meter are the only two pieces of equipment.

Digging up the road is the major cost - and it has been done before - for things like cable television if nothing else, and given the huuge price of a heat pump some sort of zero carbon future is likely to require this, as the alternative is several thousand pound pumps for every house.
Cyril R wrote:
I don't think so, pumping water is very different than gas/steam. It is low pressure so you can just go for big pipes for the long mains lengths.

Indeed, which is what I am proposing - but dropping to 95C tap from the steam turbine from 130C reduces generation loss by about 35MWe/GWt - but cuts the heat content of the water drastically, from a delta-T of 65C to about 40C. Which increases the amount of pumping power required by 65% - which is roughly 30MWe.
So we've gained nothing and must spend more on larger pipes and more powerful pumps - and probably better heat exchangers at the district heating end, a five or six degree loss becomes a much bigger deal since storage starts to get more expensive at that point.
Cyril R wrote:
Brazed plate HXs are consumer items. All combi boilers have them (hundreds of millions in the world). Not to mention airconditioning and ventilation HX market.


Combi boilers are also rather more expensive than a hot water cylinder - which can be picked up for under £200.
The question is how much of the cost of a combi boiler is the heat exchanger and how much is the rest.
Cyril R wrote:
I would worry about water quality if you are thinking of pumping potable heated water many km. Likely this ends up with all stainless and other high grade materials of construction for all piping, increasing the cost of the infrastructure.

I am talking about the pipework inside the house.
People have contracted legionella because water in the pipes was infected because it had not been heated enough to be sterilised due to combi boiler/electric water heater malfunctions.


Top
 Profile  
 
PostPosted: Aug 17, 2015 4:08 pm 
Offline

Joined: Jul 14, 2008 3:12 pm
Posts: 5057
Quote:
At which point District Heat cannot compete on any sort of basis, we can't get any kind of economy of scale one estate at a time - it has to be a huge refit programme


If so it had better be a fully standard unit - manifold, controls, valve, and HX all standard for all houses.

Quote:
dropping to 95C tap from the steam turbine from 130C reduces generation loss by about 35MWe/GWt - but cuts the heat content of the water drastically, from a delta-T of 65C to about 40C. Which increases the amount of pumping power required by 65% - which is roughly 30MWe.


If you double the diameter it cuts to 7 MWe. Bleeding lower down the turbine might also be cheaper (i don't really know the economics of this).

Quote:
Combi boilers are also rather more expensive than a hot water cylinder - which can be picked up for under £200.
The question is how much of the cost of a combi boiler is the heat exchanger and how much is the rest.


Brazed plate HX are about $40 for 70 kWt units if purchased in bulk. Retail through repairmen is another matter. (can be more like conmen).

Quote:
I am talking about the pipework inside the house.
People have contracted legionella because water in the pipes was infected because it had not been heated enough to be sterilised due to combi boiler/electric water heater malfunctions.


The UV systems are pretty cheap. You gotta worry about potable water in long pipe lengths, then your long pipe potable water system is risky. What if someone doesn't use the hot water tap for a day and it is stagnant and cools into legionella range? If I come home from work and drink your system's water, that seems pretty risky to me. Last thing you want is all that stagnant pipe length (unless you have perfect and fabulously expensive insulation).


Top
 Profile  
 
PostPosted: Aug 17, 2015 4:21 pm 
Offline

Joined: Jun 19, 2013 11:49 am
Posts: 1495
Cyril R wrote:
If so it had better be a fully standard unit - manifold, controls, valve, and HX all standard for all houses.

I imagine manifold, controls, meter and valve can be entirely standardised no matter what the system.
The HX is slightly more complex - but a standard output domestic hot water heat exchanger can be provided that can put into houses that currently use demand heaters like a combi boiler.
Cyril R wrote:
If you double the diameter it cuts to 7 MWe. Bleeding lower down the turbine might also be cheaper (i don't really know the economics of this).

I had considered this - unfortunately the 48MWe pumping power requirement assumes a 48 inch pipe for a gigawatt loop.
I did a quick look and the largest diameter steel pipe manufacturers can supply off-the-shelf is only 60 inches, and even that is relatively rare.
Above that you are into plastic pipes that might have trouble with high temperatures and the 25 bar necessary to stop the water boiling under certain transient conditions.
Cyril R wrote:
Brazed plate HX are about $40 for 70 kWt units if purchased in bulk. Retail through repairmen is another matter. (can be more like conmen).

In that case we can certainly replace combi boiler houses with no need to fit a water cylinder - which is good. The control valves will be the problematic part in that case.
Cyril R wrote:
The UV systems are pretty cheap. You gotta worry about potable water in long pipe lengths, then your long pipe potable water system is risky. What if someone doesn't use the hot water tap for a day and it is stagnant and cools into legionella range? If I come home from work and drink your system's water, that seems pretty risky to me. Last thing you want is all that stagnant pipe length (unless you have perfect and fabulously expensive insulation).

The pipes would only contain heated potable water inside each individual house in any case.
Many houses in Britain currently have a hot water cylinder which is heated indirectly by a coil through which water from the boiler is circulator - the minimum capital cost system would simply plumb that coil into the district heating system.
The problem with stagnant water downstream of the hot water cylinder is not so problematic because the water has to spend a significant period of time at a high enough temperature to kill the legionella - the water in the pipes down stream of it is effectively sterile.

If the HX can heat the water above about 60 degrees then it can't sustain a legionella culture because even if it stands in the pipe it will be hot enough long enough to kill any legionella before it cools down to stagnant temperatures.
This is not the cae in proposed very low temperature systems like those being constructed in Denmark where the district heating supply is only at 55C to start with - so they handle this problem by eliminating the water down stream of the heat exchanger using short, smallest-possible-bore pipework. The water might be infected with legionella but even if it is there is not a high enough bacterial count to actually infect anyone or produce any significant toxin loads, as that water is flushed from the pipework in the first couple of seconds of faucet use.

EDIT:

I put in for a quote for a long length of heavily insulated flexible pipe containing 2 20mm-OD service pipes - will see if it comes back and that should give us a price for lower population density areas where only a few houses would connect to a main.

Found some documents that seem to suggest that the 203,000 cubic metre storage pit being built at Vojens in Denmark has a specific cost of only €15/cubic meter - which is extremely low - that would put our cost of storage at only $275/MWh.

Which is really starting to get rather silly.


Top
 Profile  
 
PostPosted: Aug 19, 2015 9:08 pm 
Offline

Joined: Jun 19, 2013 11:49 am
Posts: 1495
Apparently companies manufacture pipes up to 3.65m [144"] in (outer) diameter with up to inch thick steel walls.

Unfortunately such pipes are used for construction primarily and are thus made of A36 mild steel. I don't know if its practical to make them out of pipeline steels.
31 bar is the maximum transient pressure in that scenario enumerated above - that gives a hoop stress of 220MPa. Normal peak operating pressure is about 22 bar.

The minimum specification Yield stress of A36 is ~220-250MPa and the UTS is something in the vicinity of 550MPa.

Is this acceptable?


Top
 Profile  
 
PostPosted: Aug 20, 2015 3:31 am 
Offline

Joined: Sep 02, 2009 10:24 am
Posts: 507
I'm not really convinced of the energy payback.

If we have 2GW of heat, producing 1GW of electricity, that can be used, with existing distribution, and new - cheap - air source heat pumps, to provide at least 3GW of heat in homes.

With large - but still standard - domestic hot water tanks, heat can be stored over a day, assuming air to water heat pumps. With a new build, I'd store the hot water at about 40-50C, using underfloor heating. Potable water would be raised to this temperature with a heat exchanger and then boosted to 65C with an electric heater.

If we dig up every road to take water out at 90C, and put on place expensive heat exchangers, we drop the plant efficiency but reduce the demand. If we took the entire 2GW of heat, we have less heat than with the electric heat pumps and much greater cost.

Can it work by reducing the efficiency and taking out some heat, but still producing mostly electrical power?


Top
 Profile  
 
PostPosted: Aug 20, 2015 9:06 am 
Offline

Joined: Jun 19, 2013 11:49 am
Posts: 1495
alexterrell wrote:
I'm not really convinced of the energy payback.

If we have 2GW of heat, producing 1GW of electricity, that can be used, with existing distribution, and new - cheap - air source heat pumps, to provide at least 3GW of heat in homes.

But we don't have 2GW of heat producing 1GW of electricity.
We have 2GWt producing something like 250MWe of electricity which can be delivered 50 miels from the plant for another 100MWe - so 2GWt producing 350MWe.

alexterrell wrote:
With large - but still standard - domestic hot water tanks, heat can be stored over a day, assuming air to water heat pumps. With a new build, I'd store the hot water at about 40-50C, using underfloor heating. Potable water would be raised to this temperature with a heat exchanger and then boosted to 65C with an electric heater.

The only cheap air source heat pumps are air to air machines.
Air To Water pumps cost thousands of pounds each - and will struggle to provide adequate space heat in cold weather.
Since Britain is not a permafrost zone the pipes buried in the ground are protected from the low temperature and thus their heating performance is not significantly degraded by cold weather.

alexterrell wrote:
If we dig up every road to take water out at 90C, and put on place expensive heat exchangers, we drop the plant efficiency but reduce the demand. If we took the entire 2GW of heat, we have less heat than with the electric heat pumps and much greater cost.

I am not proposing for the water in the road to be 90C - and space heating would not need heat exchangers.
I am proposing a fairly standard 70C out, 40C return system that is a direct cycle for space heating.
Only domestic hot water needs a heat exchanger, and only assuming you do not simply use an existing hot water cylinder.

Additionally heat can be stored for orders of magnitude less cost than electricity - so I can use heat produced last week during a demand lull to cover the peak demand tonight.
alexterrell wrote:
Can it work by reducing the efficiency and taking out some heat, but still producing mostly electrical power?

That is pretty much what I am proposing.....


Top
 Profile  
 
PostPosted: Aug 20, 2015 10:16 am 
Offline

Joined: Sep 02, 2009 10:24 am
Posts: 507
OK, can you give some numbers?

Granted, we're not using 50% efficient Thorcon modules, but a PWR, which let's assume can produce 1GW of electricity from 3GW of thermal output.

Whether we have Air-Air, Air-Water, Ground-Water heat pumps, we have a COP of 3 to 4. Lets be conservative and assume 3.

Currently the LWR chucks out water at about 30C - not useful for anything except swimming pools and greenhouses.

If we want the LWR to chuck out water at 90C, how much electrical power can we get? Do we assume the rest is thermal?


Top
 Profile  
 
PostPosted: Aug 20, 2015 10:21 am 
Offline

Joined: Jun 19, 2013 11:49 am
Posts: 1495
alexterrell wrote:
OK, can you give some numbers?

Granted, we're not using 50% efficient Thorcon modules, but a PWR, which let's assume can produce 1GW of electricity from 3GW of thermal output.

Whether we have Air-Air, Air-Water, Ground-Water heat pumps, we have a COP of 3 to 4. Lets be conservative and assume 3.

Currently the LWR chucks out water at about 30C - not useful for anything except swimming pools and greenhouses.

If we want the LWR to chuck out water at 90C, how much electrical power can we get? Do we assume the rest is thermal?


There is this paper (linked in the OP). I assume a pressurised water loop operating at the 130C draw temperature (~120C line temperature) to make it easier to move the heat.


Top
 Profile  
 
PostPosted: Aug 21, 2015 10:53 pm 
Offline

Joined: May 05, 2010 1:14 am
Posts: 130
Would there be any advantage in using sub-60 C water, but running it past a couple of recently-used fuel assemblies to knock out any Legionaire's bugs?


Top
 Profile  
 
PostPosted: Aug 22, 2015 6:54 am 
Offline

Joined: Jun 19, 2013 11:49 am
Posts: 1495
Even if you were able to get political permission for radioactive decontamination - you would only be able to do that at a central location which would require a separate potable rated hot water distribution system.

That will be rather expensive as it means a third and probably fourth pipe in the system (to bleed off some hot water for return to the plant, sterilisation and reheating so the mains stay hot).


Top
 Profile  
 
PostPosted: Aug 22, 2015 4:04 pm 
Offline

Joined: Feb 28, 2011 10:10 am
Posts: 348
I am with Alex Terrell on this. I think that heat pumps are more useful for heating (and cooling) needs, especially with regard to the current stock of housing that needs to be retrofitted and adapted. Building a district heating system does not come cheap. However, Sweden is an interesting example and has invested a lot in district heating systems since the 1960s. See the links in my post "Energy policy in Sweden":

viewtopic.php?f=13&t=4413

The U.S. DOE has done an interesting study last year: "Mini-Split Heat Pumps Multifamily Retrofit Feasibility Study" (see attachment), which concludes that multi-split heat pumps are viable as alternative for multifamily buildings, which are perhaps the most challenging building types to equip with heat pumps.


Attachments:
minisplit_multifamily_retrofit.pdf [1.42 MiB]
Downloaded 118 times
Top
 Profile  
 
PostPosted: Aug 22, 2015 4:24 pm 
Offline

Joined: Jun 19, 2013 11:49 am
Posts: 1495
An air to water heat pump is enormously expensive, struggles with cold weather and doesn't solve the peak load issue.
Heating loads will be concentrated in certain parts of the day in certain parts of the year and will spike demand to enormous levels.

It is doubtful it would be worthwhile fitting one for hot water - a hot water cylinder with a night rate immersion cylinder will almost certainly come out cheaper.

District heating does not come cheap - but it lasts far longer than a heat pump will.

District heating will have a lower heat cost since the effective COP for DHW use is still >5.

EDIT:
camiel wrote:
The U.S. DOE has done an interesting study last year: "Mini-Split Heat Pumps Multifamily Retrofit Feasibility Study" (see attachment), which concludes that multi-split heat pumps are viable as alternative for multifamily buildings, which are perhaps the most challenging building types to equip with heat pumps.


That study is for forced air heating - which is not common in the UK and is known to have far lower retrofit costs.... if you have a forced air system already. Air to Air Heat pumps with COP of 5 are available for something like £120/kW.

Estimates on an air to water split heat pump are £6-10k including installation.

EDIT #2:

Further research on pipe suitable for the heat transfer loop has led me to stumble across PVDF (with the rather odd name polyvinylidenefluoride) which is useful for pipes up to about 140C apparently.
Whilst it has a terrible temperature derating factor of about 0.4 at 120C this could allow for something other than steel to be used on submains off the main loop. It also has a far lower thermal conductivity than steel. Bad news is that has a price of something like $10/lb so might be too expensive. But material cost does not seem to be a major factor in the cost of the network so it might be useful.

If we cut the loop from 120C/55C to 120C/45C (since we are feeding 70/40C systems after all) that would increase the heat transfer power of the system to 1150MWt for a similar pump power.


Top
 Profile  
 
PostPosted: Aug 23, 2015 9:32 am 
Offline

Joined: Jul 14, 2008 3:12 pm
Posts: 5057
Plastic sucks. Don't use it. Lean Duplex stainless is the obvious choice here. I recommend 2304 duplex for this application.


Top
 Profile  
 
PostPosted: Aug 23, 2015 10:15 am 
Offline

Joined: Jun 19, 2013 11:49 am
Posts: 1495
Isn't stainless going to be enormously expensive?
And large scale transmission connections are going to need absolutely enormous capacities: ~4-5GWt.
100" or more.

EDIT:

A lot of work in Sweden has revolved around reducing capital costs of installations - with the objective of getting the distribution pipework and connection to the house for less than ~€4000.
They have succeeded in surprisingly low density environments. (20-30m of mains per dwelling in some cases).


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 33 posts ]  Go to page Previous  1, 2, 3  Next

All times are UTC - 6 hours [ DST ]


Who is online

Users browsing this forum: No registered users and 1 guest


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
Powered by phpBB® Forum Software © phpBB Group