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PostPosted: Feb 28, 2013 3:30 pm 
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Yes, I went back and found two docs that I think you had posted earlier in relation to the Heller system. Based on those publications they do look like the best performing dry cooling system, but probably slightly more expensive capital wise, it's a little hard to tell, even if so a small improvident in performance can soon justify a most additional capital cost.

Under normal conditions a straight DC condenser does work out because the TDS (total dissolved solids) loading in the cooling water overwhelms the water treatment plant, but the Heller system obviously works and works pretty for an air cooled system.


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PostPosted: Feb 28, 2013 5:20 pm 
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Lindsay wrote:
Yes, I went back and found two docs that I think you had posted earlier in relation to the Heller system. Based on those publications they do look like the best performing dry cooling system, but probably slightly more expensive capital wise, it's a little hard to tell, even if so a small improvident in performance can soon justify a most additional capital cost.

Under normal conditions a straight DC condenser does work out because the TDS (total dissolved solids) loading in the cooling water overwhelms the water treatment plant, but the Heller system obviously works and works pretty for an air cooled system.


I wonder if it has advantages for even a once through seawater cooling system. The efficiency advantage there would be tiny if present at all, but it would be very useful to get rid of seawater contamination into the working fluid. It would remove one of the biggest downsides of a once through seawater cooling condenser.


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PostPosted: Feb 28, 2013 6:26 pm 
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Cyril R wrote:
I wonder if it has advantages for even a once through seawater cooling system. The efficiency advantage there would be tiny if present at all, but it would be very useful to get rid of seawater contamination into the working fluid. It would remove one of the biggest downsides of a once through seawater cooling condenser.

Advantages over once through: I don't believe so in terms or performance, once through cooling systems have the smallest auxiliary load of any cooling option because they only move water and not air, and the condenser performance is usually pretty good because the water temperature is at or less than wet bulb temperature of ambient air* which a fully wet tower can get close to, but not attain.

I can see the Heller system doing very good things in cold climates as control over freezing would be so much easier than in a fully wet cooling tower or a fully dry air-cooled condenser.

I note that the presentation that I took this from seems to use mechanically induced draft fans on wet systems and natural draft on Heller, an interesting detail, not quite apples with apples, but understandable.

Attachment:
Heller Performance.jpg
Heller Performance.jpg [ 50.38 KiB | Viewed 1770 times ]

* I'd need to check this claim


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PostPosted: Mar 01, 2013 3:56 am 
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Advantages over once through: I don't believe so in terms or performance, once through cooling systems have the smallest auxiliary load of any cooling option because they only move water and not air, and the condenser performance is usually pretty good because the water temperature is at or less than wet bulb temperature of ambient air* which a fully wet tower can get close to, but not attain.


Agree, but I was thinking more in terms of eliminating the seawater ingress issue. With once through seawater cooling, you have vacuum in tubes and seawater at natural (higher) pressure. Lots of tubes means a big potential for leaks. The Japanese have had big problems with this, I think you referred to it as "condenseritis" which I thought was very funny.

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I can see the Heller system doing very good things in cold climates as control over freezing would be so much easier than in a fully wet cooling tower or a fully dry air-cooled condenser.


Yes, and I live in a cold climate so might be biased here to think this is better than a wet cooling tower. According to the graph you've posted, the advantage of the full dry Heller over the full dry forced flow ACC becomes bigger in cold climates, but oddly seems to perform very similar (in terms of power output) in a hot climate. So there must be "something" about the Heller system that gives it a big advantage in colder climates. Any idea what that something is?


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PostPosted: Mar 01, 2013 4:48 am 
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Cyril R wrote:
So there must be "something" about the Heller system that gives it a big advantage in colder climates. Any idea what that something is?

I don't know but I think that for any given water temperature the condenser pressure in the DC is lower therefore in cold places where freezing of cooling water is a constraint, the Heller system provides a lower condenser pressure. Although that in itself is no silver bullet, the STG has to be able to exhale that much larger volume of steam efficiently so you need longer last stage buckets or worst case a single LPT with double flow exhaust may not provide enough exhaust area so then you have to go to a double LPT to achieve the desired exhaust area, but the cost of your machine, the condenser/s and even the turbine hall just went up if you are forced to double LPT from a single or to a triple from a double.

No free lunches here.


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PostPosted: Mar 01, 2013 4:57 am 
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Cyril R wrote:
Agree, but I was thinking more in terms of eliminating the seawater ingress issue. With once through seawater cooling, you have vacuum in tubes and seawater at natural (higher) pressure. Lots of tubes means a big potential for leaks. The Japanese have had big problems with this, I think you referred to it as "condenseritis" which I thought was very funny.

I think that in that regard the Heller system may have an advantage there, but a well designed condenser with good water/condensate treatment and corrosion resistant structural materials should have a long and trouble free life. NZ's only coal fired power station which has once through river water cooling, has had a number of their condensers replaced, so it can be done and that is probably a lot cheaper than building an entire Heller system. I think that the old ones that came out were admiralty brass (guessing here), the new ones were 100% stainless steel. Stainless is great for condensate and feedwater systems.


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PostPosted: Mar 02, 2013 12:56 am 
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One advantage of spraying water into steam to condense it is that you can do this in a small volume (small compared to an air-cooled condenser). So I'd imagine you could put the spray bars inches from the back disk of the low pressure steam turbine, and entirely avoid the gigantic exhaust duct.

It's going to be hard to avoid a 90+ kPa head loss in this system, though. The steam being condensed is at 5 kPa or so. The spray water mixing with it is coming from a heat exchanger, on the other side of which is ambient-pressure air, fresh water, or sea water. So that spray water wants to be at a bit over ambient pressure. Recovering energy from that flow before sending it into the sprays is possible... you could have the DC condenser chamber at least 9 meters above a seawater/condensate HX, for example. An air cooled condensate HX seems unlikely to be small enough vertically to be below anything.

With the condensate flow necessary, it's so easy to lose a lot of energy. For instance, I don't think you can get back the energy lost from the drops falling through the steam. If the drops in the DC condenser fall just 5 meters, you lose 0.0023 watts per watt rejected.


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PostPosted: Mar 02, 2013 4:43 am 
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Lindsay wrote:
Cyril R wrote:
Agree, but I was thinking more in terms of eliminating the seawater ingress issue. With once through seawater cooling, you have vacuum in tubes and seawater at natural (higher) pressure. Lots of tubes means a big potential for leaks. The Japanese have had big problems with this, I think you referred to it as "condenseritis" which I thought was very funny.

I think that in that regard the Heller system may have an advantage there, but a well designed condenser with good water/condensate treatment and corrosion resistant structural materials should have a long and trouble free life. NZ's only coal fired power station which has once through river water cooling, has had a number of their condensers replaced, so it can be done and that is probably a lot cheaper than building an entire Heller system. I think that the old ones that came out were admiralty brass (guessing here), the new ones were 100% stainless steel. Stainless is great for condensate and feedwater systems.


Brass is unsuitable, way too soft. It will just erode from suspended insolubles in the cooling water. Stainless steel is great for river and lake water, but seawater is a different ballgame. Standard austenitic and ferritic steels are typically not suitable for long term submersible operation in warm seawater. They will suffer pitting and crevice corrosion. There are a limited number of super stainless steels developed specifically for this purpose, primarily the 44 series (UNS designation). The Gravelines nuclear plants in France use this material, worked well. These resist pitting corrosion from warm seawater. More commonly titanium condenser tubing is used. This stuff is inert in seawater, but it costs and arm and a leg and the delivery time is long. Also leaks with river water are low consequence as the cleanup systems can deal with the small concentrations of salts. With seawater a leak could quickly overwhelm the capacity of the cleanup trains. I'm guessing that an indirect system could use thinner titanium tubing, with no vacuum stress in the tubes, yet avoid seawater ingress.


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PostPosted: Mar 02, 2013 4:54 am 
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iain wrote:
One advantage of spraying water into steam to condense it is that you can do this in a small volume (small compared to an air-cooled condenser). So I'd imagine you could put the spray bars inches from the back disk of the low pressure steam turbine, and entirely avoid the gigantic exhaust duct.

It's going to be hard to avoid a 90+ kPa head loss in this system, though. The steam being condensed is at 5 kPa or so. The spray water mixing with it is coming from a heat exchanger, on the other side of which is ambient-pressure air, fresh water, or sea water. So that spray water wants to be at a bit over ambient pressure. Recovering energy from that flow before sending it into the sprays is possible... you could have the DC condenser chamber at least 9 meters above a seawater/condensate HX, for example. An air cooled condensate HX seems unlikely to be small enough vertically to be below anything.

With the condensate flow necessary, it's so easy to lose a lot of energy. For instance, I don't think you can get back the energy lost from the drops falling through the steam. If the drops in the DC condenser fall just 5 meters, you lose 0.0023 watts per watt rejected.


It is a heat rejection system. There's no point in trying to recover energy from it. Its function is to dump heat. There is virtually no friction loss in the DC condenser, so you're better off in maintaining vacuum than condensing in hundreds of miles of pipes. Much better to push noncompressible liquid than compressible steam.

According to the Heller presentation, the net present value of the heller system is better than the ACC system. It is also better than a wet cooling tower for a cold climate and the efficiency is the same in such a climate. This is also what other literature sources suggest. So it is already a quite efficient system and the cost is reasonable.


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PostPosted: Mar 02, 2013 6:10 am 
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Cyril R wrote:
Brass is unsuitable, way too soft. It will just erode from suspended insolubles in the cooling water. Stainless steel is great for river and lake water, but seawater is a different ballgame. Standard austenitic and ferritic steels are typically not suitable for long term submersible operation in warm seawater. They will suffer pitting and crevice corrosion. There are a limited number of super stainless steels developed specifically for this purpose, primarily the 44 series (UNS designation). The Gravelines nuclear plants in France use this material, worked well. These resist pitting corrosion from warm seawater. More commonly titanium condenser tubing is used. This stuff is inert in seawater, but it costs and arm and a leg and the delivery time is long. Also leaks with river water are low consequence as the cleanup systems can deal with the small concentrations of salts. With seawater a leak could quickly overwhelm the capacity of the cleanup trains. I'm guessing that an indirect system could use thinner titanium tubing, with no vacuum stress in the tubes, yet avoid seawater ingress.
www.copperinfo.co.uk wrote:
The data in Table 25 indicates that, while the erosion corrosion resistance of Admiralty brass in seawater is inferior to that of Aluminium brass, the substantially higher water speed required to produce erosion corrosion in fresh water results in Admiralty brass being perfectly suitable for fresh water cooled condensers and heat exchangers. It is therefore the alloy most commonly used for fresh water heat exchange service and is to be preferred to Aluminium brass for this purpose since Aluminium brass is liable to pitting corrosion in some fresh waters.
http://www.copperinfo.co.uk/alloys/brass/downloads/117/117-section-7-brasses-for-corrosion-resistance.pdf

I think that the materials selection for condensers is a bit trickier than one might think, which is why some condensers start leaking, and there's more going on that just the cooling water, some of these materials do not like being constantly washed in high pH high purity condensate that can clean off passive layers that protect against further corrosion, so there is definitely quite a bit to it. I claim no special expertise in this area, I just know that the materials selection must be made with care and must fully accommodate all site conditions in order to be durable and reliable.
Cyril R wrote:
There are a limited number of super stainless steels developed specifically for this purpose, primarily the 44 series (UNS designation).
Sounds right to me, I don't know the detail, but to my knowledge SS for condenser use has some specific properties not found in many standard stainless steels.


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PostPosted: Mar 02, 2013 7:18 am 
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The data in Table 25 indicates that, while the erosion corrosion resistance of Admiralty brass in seawater is inferior to that of Aluminium brass, the substantially higher water speed required to produce erosion corrosion in fresh water results in Admiralty brass being perfectly suitable for fresh water cooled condensers and heat exchangers. It is therefore the alloy most commonly used for fresh water heat exchange service and is to be preferred to Aluminium brass for this purpose since Aluminium brass is liable to pitting corrosion in some fresh waters.


This is comparing one inferiour option with another. Neither aluminium nor admiralty brass are suitable for long term warm seawater from a corrosion viewpoint, and both substrates are softer than stainless steels. Plus, copper and aluminium alloys are subject to a large number of failure modes in seawater (galvanic corrosion, intergranular corrosion, etc.), so they have been supplanted by better options.

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I think that the materials selection for condensers is a bit trickier than one might think, which is why some condensers start leaking, and there's more going on that just the cooling water, some of these materials do not like being constantly washed in high pH high purity condensate that can clean off passive layers that protect against further corrosion, so there is definitely quite a bit to it.


Absolutely, I was involved in a material selection project for seawater condenser tubing recently, and was amazed at the complexity of (what appeared to me) a simple task. Even the biological layer that forms from algae and whatnot is a big variable in different temperature regimes, being either helpful or detrimental to corrosion. Seawater being a conductive electrolyte whereas the condensate is an insulater makes this even more tricky. An accidental 10 degree rise in seawater from some transient in the plant could ruin most metals! After consulting a metallurgist, it was clear that for the highest reliability, the top choice was basically limited to either titanium alloy or super stainless steels designed for seawater service (S44 series). As the titanium tubing had too long a delivery time for the project, we went for the 44 series, the French have really good experience with this so is a low risk option. Even then care was needed in welding and rolling the tubes. Seawater condensers are surprisingly tricky and nasty things. Lake or river water looks comparatively benign, but its geographic availability is low.

One of the biggest advantages of dry cooling is that you no longer have whole seawater or river water corrosion problems. The Heller system for example uses an all aluminium heat rejection HX for the air cooler. This means really great thermal conductivity, but would be unthinkable for seawater, and possibly not acceptable even for river water.


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PostPosted: Mar 02, 2013 3:06 pm 
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iain wrote:
I don't think you can get back the energy lost from the drops falling through the steam. If the drops in the DC condenser fall just 5 meters, you lose 0.0023 watts per watt rejected.


Cyril R wrote:
It is a heat rejection system. There's no point in trying to recover energy from it.


I wasn't clear. If the steam coming out of the low pressure turbine is at 5 kPa, and the condensate coming from the HX is at 100 kPa, and you are pumping 67 m^3/s of condensate in order to dump 1.4 GW with a 5 C drop (condensate in to condensate out) in that HX... then you are using 6.3 megawatts of pumping power. As I said, you can cut that down a bit by locating the HX at least 9 meters below the condenser. If the condenser was really short, less than a meter, then you could reduce the pumping power significantly from that.

But if the condenser has the drops falling 5 meters, then you won't reduce the pumping power.

Maybe it's not a very big loss. I'm talking about 3 MW or so in a 1 GW(e) plant.

I am a bit confused about one thing though. Let's say the turbine exhaust is at 35 C and 5.62 kPa, and let's say the condensate returning from the HX is at 30 C. Vapor pressure at 30 C is 4.24 kPa.

I can imagine a crossflow DC condenser with the drops falling down, slowed by splash bars, and the steam flowing up. By the top, the steam has cooled to 30 C. So then what happens? Is the idea that the steam is at 30 C but >5 kPa, supersaturated, and in intimate contact with the water surface, and that causes rapid condensation? The rate of condensation matches the rate of turbine mass flow.

BTW, I get 579 kg/s turbine mass flow for 1.4 gigawatts of waste heat at 35 C dumped via condensation. This seems small but it's over 14,000 m^3/sec of steam, which seems unimaginably big. That's a 12 meter diameter duct, with steam going at 100 m/s. Just the kinetic energy of the steam moving this fast is 3 megawatts, and that's going to be unrecoverable as well. I'd want to take this steam out of the turbine radially rather than axially to get more surface area, but then that leaves me with a vertical axis low pressure turbine sitting in the middle of a DC condenser, and I've never seen a picture of anything like that.

Am I missing something here?

-Iain


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PostPosted: Mar 02, 2013 5:15 pm 
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Ok, so your idea is to take advantage of the gravity head to prevent loss of pressure. That's clever. Perhaps they already do this.

That mass flow figure looks about right. As for the velocity, I think the steam is actually moving even faster than that. Probably >200 m/s. Possibly >300 m/s.

They call it a jet condenser for a reason. 8)


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PostPosted: Mar 03, 2013 1:45 am 
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579 kg/s of steam moving at 250 m/s is 18 megawatts and still requires a 7.5 meter diameter duct. That's huge! Of course, that would be for a single low pressure turbine taking all the steam from the high pressure turbine off a 2.5 GW(th) reactor. Maybe nobody builds them that big for a reason, and that's why there are usually two or three low pressure turbines.

Radial steam exhaust seems a lot nicer: a 8 meter diameter centrifugal turbine last stage could have an exit 4 meters long, and have a considerably lower exit velocity, more like 140 m/s. That picks up 12 megawatts of extra power from the turbine right there.

These jet condensers have fascinating interior conditions.

For one thing, getting the 67,000 kg/s of condensate up to hundreds of m/s is not going to happen. Even 100 m/s is 335 MW. So that means the supersaturated steam is going to have huge relative velocity to these water droplets.

This steam is not very dense: 40 g/m^3. Into each cubic meter we inject 4.8 kg of condensate, 120 times as much condensate by mass. If that condensate is in drops 2 mm diameter, they have a combined cross section of 0.9 m^2.

Going back to the axial exhaust, the steam has 1.3 kPa of dynamic pressure, maybe 6 kPa of total pressure, and 450 Pa of aero drag from the droplets. This last number suggests the scale length of the jet condenser will be measured in meters. It's kind of amazing to think of a 7.5 m diameter blast going at 250 m/s stopped in a few meters by a waterfall.


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PostPosted: Mar 03, 2013 7:46 am 
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For one thing, getting the 67,000 kg/s of condensate up to hundreds of m/s is not going to happen. Even 100 m/s is 335 MW. So that means the supersaturated steam is going to have huge relative velocity to these water droplets.


Yes, one of the design considerations is as high as reasonable steam velocity (to stabilize the jet) and as low as possible spray velocity (to reduce pump power). Huge relative velocities are a given, considering the orders of magnitude difference in densities. I don't see any problems here, I'm imagining the radial steam smashing into an axial water spray from above, so full crosscurrent flow.

Quote:
This steam is not very dense: 40 g/m^3. Into each cubic meter we inject 4.8 kg of condensate, 120 times as much condensate by mass. If that condensate is in drops 2 mm diameter, they have a combined cross section of 0.9 m^2.


It would pay to try to get as tiny droplets as possible, and as high a droplet density as possible. We can do a lot better than 1 m2/m3. Shouldn't be too hard to get over 100 m2/m3 droplet surface area. The greater the droplet surface area the lower the needed velocity; producing smaller droplets would have a pressure drop (pump power) penalty, but this has to be much better than the way pump power scales with velocity.

Here's something I haven't figured out yet: how much condensing work is done by the feedwater heaters (ie drain liquid mass flow)? All the condensing work the feedwater heaters take up, the main condenser wouldn't have to condense. I found only one reference (to the SCWR work) and that condenser only had a mass flow rate of 42.5% of the reactor steam production. So that helps a lot.


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