Energy From Thorium Discussion Forum

It is currently Sep 23, 2018 12:40 pm

All times are UTC - 6 hours [ DST ]




Post new topic Reply to topic  [ 78 posts ]  Go to page Previous  1, 2, 3, 4, 5, 6  Next
Author Message
PostPosted: Feb 02, 2010 3:14 am 
Offline
User avatar

Joined: Dec 08, 2009 6:07 pm
Posts: 162
Location: Albuquerque NM USA
Legionnaires' disease was first diagnosed about 1976 when some people at a Legionnaires' convention became ill and some died. Almost certainly the disease had been around for many decades prior to that, but had not previously been diagnosed. Since then, it has been diagnosed numerous times in several different countries.

The most common source of Legionnaires' disease seems to be droplets from cooling towers. In an attempt to prevent it, regulations in many areas require periodic inspections to ensure that the bacteria that causes Legionnaires' disease is not present in cooling towers. However, it seems unlikely that the problem can be totally eliminated.

It may be that the risk of Legionnaires' disease could be used to support the argument for direct once-through water cooling from the ocean or other body of water, but that could backfire if the regulating authority would permit only dry air cooling.


Top
 Profile  
 
PostPosted: Feb 02, 2010 6:02 am 
Offline

Joined: Jul 14, 2008 3:12 pm
Posts: 5045
FRE wrote:
Legionnaires' disease was first diagnosed about 1976 when some people at a Legionnaires' convention became ill and some died. Almost certainly the disease had been around for many decades prior to that, but had not previously been diagnosed. Since then, it has been diagnosed numerous times in several different countries.

The most common source of Legionnaires' disease seems to be droplets from cooling towers. In an attempt to prevent it, regulations in many areas require periodic inspections to ensure that the bacteria that causes Legionnaires' disease is not present in cooling towers. However, it seems unlikely that the problem can be totally eliminated.

It may be that the risk of Legionnaires' disease could be used to support the argument for direct once-through water cooling from the ocean or other body of water, but that could backfire if the regulating authority would permit only dry air cooling.


Where did you read this? The recirculating wet cooling technique uses a lot of anti-biofouling and anti-bacteria chemicals, sometimes also corrosion inhibitors - in fact so much that disposal of the increasingly concentrated brine becomes a disposal problem. Can't imagine that Legionaires' disease stands much of a chance in that environment.


Top
 Profile  
 
PostPosted: Feb 02, 2010 10:49 am 
Offline

Joined: Jul 28, 2008 10:44 pm
Posts: 3063
Offhand, I would expect that the exclusionary zone plus some trees should do a pretty good job of keeping the power plant quiet at the boundary of the property.


Top
 Profile  
 
PostPosted: Feb 02, 2010 11:05 am 
Offline

Joined: Jul 14, 2008 3:12 pm
Posts: 5045
There's a bunch of new techs that can be applied to a forced air cooling system. In particular carbon or metal foam based high surface area radiators, and tubercle vortex high efficiency, silent low RPM blades for the fans.

Lars has good ideas using trees on the periphery. Some people had similar ideas for a biomass plant cooling tower. Who says cooling towers have to be ugly : 8)

Image

Image


Top
 Profile  
 
PostPosted: Feb 02, 2010 1:46 pm 
Offline
User avatar

Joined: May 24, 2009 4:42 am
Posts: 823
Location: Calgary, Alberta
Beautiful, every home should have one.

Legionella is not a trivial problem, it requires careful management of a well designed system. One of the core issues is that Legionella occurs naturally in most environments in the air and soil, so there is this constant source of infection being ingested by the cooling tower. Most towers will carry some Legionella, the trick is to manage the biocide regime to maintain a low bacteria count in the circulating water. Warm concentrated fresh water fertilised by dust and contaminants from the air is a perfect breeding ground for Legionella, but by keeping the system physically clean and dosed regularly with biocide, bio-film dispersants and the like, it can be maintained with a low bug count. This is important to maintain a safe environment for plant staff and the community around the power station.


Top
 Profile  
 
PostPosted: Feb 02, 2010 2:11 pm 
Offline
User avatar

Joined: Dec 08, 2009 6:07 pm
Posts: 162
Location: Albuquerque NM USA
Cyril R wrote:
FRE wrote:
Legionnaires' disease was first diagnosed about 1976 when some people at a Legionnaires' convention became ill and some died. Almost certainly the disease had been around for many decades prior to that, but had not previously been diagnosed. Since then, it has been diagnosed numerous times in several different countries.

The most common source of Legionnaires' disease seems to be droplets from cooling towers. In an attempt to prevent it, regulations in many areas require periodic inspections to ensure that the bacteria that causes Legionnaires' disease is not present in cooling towers. However, it seems unlikely that the problem can be totally eliminated.

It may be that the risk of Legionnaires' disease could be used to support the argument for direct once-through water cooling from the ocean or other body of water, but that could backfire if the regulating authority would permit only dry air cooling.


Where did you read this? The recirculating wet cooling technique uses a lot of anti-biofouling and anti-bacteria chemicals, sometimes also corrosion inhibitors - in fact so much that disposal of the increasingly concentrated brine becomes a disposal problem. Can't imagine that Legionaires' disease stands much of a chance in that environment.


It's information that I've acquired over a number of years.

When the first diagnosed cases of Legionnaire's disease occurred, the health authorities had no idea what the source was. After considerable sleuthing, it was discovered that a near-by cooling tower was breeding the (newly discovered) bacteria. Subsequent investigation determined that it was a very common bacterium and that it was commonly found in cooling towers. Probably cooling towers become infected from bacteria carried by dust. The result was that regulations were enacted all over to ensure that cooling towers would not breed the organism that caused the outbreak, but the regulations have not been totally effective. Not everyone exposed will become ill, but when people do become ill, it is often fatal unless promptly treated with antibiotics. Elderly people are much more likely to become ill than younger people. It may be that minor exposure seldom results in illness because the body would have more time to fight it off before the bacteria have time to multiply too greatly.

A few years ago, when I was doing some research on more efficient air conditioning systems for homes, I learned that small cooling towers were available for home air conditioning systems, the purpose being to increase efficiency by reducing the high-side pressure. I was concerned because I doubt that they'd be as well managed as industrial cooling towers, so there could very well be a health risk associated with them.

Here in the South-West, many homes use evaporative coolers. I've wondered about the risks of those, but because there is no aerosol, probably bacteria in the coolers never become air-borne, so probably the risk is low.

In any case, cooling towers for power plants are a potential hazard that must be recognized and carefully monitored.


Top
 Profile  
 
PostPosted: Feb 02, 2010 3:21 pm 
Offline
User avatar

Joined: Dec 08, 2009 6:07 pm
Posts: 162
Location: Albuquerque NM USA
USPWR_SRO wrote:
Lindsay wrote:
Beautiful, every home should have one.

Legionella is not a trivial problem, it requires careful management of a well designed system. One of the core issues is that Legionella occurs naturally in most environments in the air and soil, so there is this constant source of infection being ingested by the cooling tower. Most towers will carry some Legionella, the trick is to manage the biocide regime to maintain a low bacteria count in the circulating water. Warm concentrated fresh water fertilised by dust and contaminants from the air is a perfect breeding ground for Legionella, but by keeping the system physically clean and dosed regularly with biocide, bio-film dispersants and the like, it can be maintained with a low bug count. This is important to maintain a safe environment for plant staff and the community around the power station.


Source please?


Probably if you were older, you would not be asking for the source.

When the original outbreak of Legionnaires' disease occurred at a Legionnaires' convention, I was at an unrelated convention in San Francisco. For days, the outbreak was followed by newspapers all over the country. I remember it very well, as will most people who were old enough at the time (about 1976) to be aware of such things; people born after about 1966 would be less likely to be aware of it. That means that people younger than about 44 probably would not remember the original outbreak since they would have been younger than 10 years old at the time. I also remember when it was discovered that a near-by cooling tower was infected and was emitting an aerosol that drifted over the immediate area. It was immediately realized that the same hazard could exist in other cooling towers, so heath personnel all over the country started taking samples from cooling towers and discovered that many were infected. Regulations soon followed in an only partially successful attempt to ensure that all cooling towers would be managed in such a way that the risk would be eliminated.

A google search will provide plenty of information from multiple sources.


Top
 Profile  
 
PostPosted: Feb 02, 2010 4:42 pm 
Offline

Joined: Apr 24, 2008 4:54 am
Posts: 490
Location: Columbia, SC
Older?

I am 47 years old. I remember well the legionaires convention outbreak. I was in high school.

I wanted a source linking that to power plant cooling towers. Thats the first time I had ever heard of a link between them. Links to HVAC cooling plants yes.....but not to power plant cooling towers. News to me.


Top
 Profile  
 
PostPosted: Feb 02, 2010 5:05 pm 
Offline

Joined: Jul 28, 2008 10:44 pm
Posts: 3063
Here is a start (http://en.wikipedia.org/wiki/Cooling_tower) .

"French researchers found that Legionella spread through the air up to 6 kilometres from a large contaminated cooling tower at a petrochemical plant in Pas-de-Calais, France. That outbreak killed 21 of the 86 people that had a laboratory-confirmed infection."

This was a cooling tower from a petrochemical plant but it seems reasonable to assume the same issue must be addressed in all wet cooling towers. It may be an easily solved issue but it caught me by surprise. I wonder if dry cooling with occasional assist from wet cooling has such a problem.


Top
 Profile  
 
PostPosted: Feb 02, 2010 5:47 pm 
Offline
User avatar

Joined: Dec 08, 2009 6:07 pm
Posts: 162
Location: Albuquerque NM USA
USPWR_SRO wrote:
Older?

I am 47 years old. I remember well the legionaires convention outbreak. I was in high school.

I wanted a source linking that to power plant cooling towers. Thats the first time I had ever heard of a link between them. Links to HVAC cooling plants yes.....but not to power plant cooling towers. News to me.


I hadn't heard about the problem with power plant cooling towers either but, since they use the same principals of physics as HVAC cooling towers, I would expect the problems to be the same. In any case, I wouldn't want to be very close to any type of cooling tower.


Top
 Profile  
 
PostPosted: Feb 02, 2010 7:36 pm 
Offline
User avatar

Joined: May 24, 2009 4:42 am
Posts: 823
Location: Calgary, Alberta
USPWR_SRO wrote:
Source please?


Source, personal experience as the manager of a 125 MW CCGT Cogeneration plant. Managing Legionella is an issue for anyone running a fresh water cooling tower setup. The worst offenders are not usually the big utility towers, it tends to be the smaller wet towers associated with air conditioning equipment. There was an outbreak of legionnaires disease in Christchurch, NZ some years ago which was eventually traced back to the hospital (NOT GOOD)

I don't know if Legionella is an issue in seawater based cooling towers, but it certainly is for fresh water based ones, due the steady warm conditions and lot of bug food, minerals etc from the air. I don't have any documents to point you to, but there will probably be many describing best practise and biological monitoring for cooling towers if you did a google search.

Where I used to work they would take dip slides once a week which grow the bugs visually, and then perhaps once a month take water sample and have it analysed at a lab. If the bug count comes back as being higher than a certain threshold, then some form of shock dosing of chlorine or other biocide is done and the bugs further analysed to determine is Legionella is present and in what number. Normally one just looks at total bug count and manages to that.

Edit: FRE I would not be concerned about being close to a well run tower at a power station, but a small wet tower on an office or apartment block next door, that is definitely more likely to be a problem, normally because people don't manage small towers, they just use them.


Top
 Profile  
 
PostPosted: Feb 02, 2010 10:19 pm 
Offline
User avatar

Joined: May 24, 2009 4:42 am
Posts: 823
Location: Calgary, Alberta
Lars wrote:
Lindsay,
Is this a problem that should impact the selection of the cooling system or is it one that just requires proper operations?
That is, should we shy away from wet cooling due to this problem or is it perfectly manageable?

Wet cooling towers are an extremely effective and economic means of rejecting heat to the environment and even the most efficient thermal power cycles have significant heat rejection requirements. Full wet or hybrid wet and dry towers are ideal for this purpose.

Regarding Legionella and other bacteria that are prone to grow in these towers, those issues are easily managed by initial good design combined with regular monitoring and appropriate biocide treatments. It is very easy to get this right, but it does require some regular attention.

The only black mark (if you can call it that) against hybrid wet/dry towers is that they consume water, on all other counts they are very benign and cost effective. I personally do not like dry cooling systems and would try to avoid using them if possible.


Top
 Profile  
 
PostPosted: Feb 02, 2010 10:57 pm 
Offline
User avatar

Joined: May 24, 2009 4:42 am
Posts: 823
Location: Calgary, Alberta
Thanks for that. Yes, direct once through cooling is nice if you can get it, get those nice low condenser pressures, especially on a LWR where the condensers have a lot of work to do.

I have just found this reference for anyone who would like to read more, it is put out by the NZ version of OSHA. There some further links within that web page. Enjoy.
http://www.osh.govt.nz/publications/series/hb-20-legionnaires.html


Top
 Profile  
 
PostPosted: Feb 03, 2010 1:54 am 
Offline
User avatar

Joined: Dec 08, 2009 6:07 pm
Posts: 162
Location: Albuquerque NM USA
Even if it is perfectly manageable, it might be best to leave doubt in the minds of those objecting to once-through cooling. That might make it possible to avoid cooling towers and use once-through cooling instead. They might be induced to fear the health risks of the cooling tower more than the possible environmental damage caused by once-through cooling.

That might be seen as stooping to their level.


Top
 Profile  
 
PostPosted: Apr 15, 2010 2:50 pm 
Offline

Joined: Mar 07, 2007 11:02 am
Posts: 911
Location: Ottawa
Just been reviewing this thread again, so much great information. I am lost on many of the fine engineering details but am still trying to sort out a preference. From my viewpoint I still think it is a pretty even race between all candidates of He multi-reheat, Supercritical CO2, Nitrogen and good old steam Rankine (likely ultra supercritical but maybe even just superheated steam).

I thought I`d add a quick summary and ask a couple more questions. Please chime in if you disagree with things (and why).

First is just good old steam. The big advantage is it is a well known system and off the shelve (with modifications needed). I`d also add that while the compact nature of gas turbines tend to make them look so much cheaper than steam, when you find reports comparing He or S-CO2 to steam the gas cycles don`t seem to come out all that much cheaper AND the authors are not including huge R&D costs of either He or S-CO2. Here is a good short paper that does some cost comparisons between S-CO2, He and Steam. They would not be comparing to the best multi-reheat helium cycles but still interesting.

Attachment:
300kwePCU.pdf [1.72 MiB]
Downloaded 289 times


The disadvantages to steam are that tritium control becomes a bigger issue and that the high melting point of typical intermediate coolant salts means feedwater return heating is a problem. ORNL had solutions in place for both issues and in the mid 70s tests with NaF-NaBF3 looked quite good for trapping tritium. There are other solutions to tritium as well, such as changing carrier salts to not produce it or adding a third coolant loop (nitrate salts or He gas, see ORNL TM 5325 and ORNL TM 3428). Feedwater heating was to be by steam injection which would add cost and complexity to the standard Supercritical Steam Rankine (Based on the Bull Run Coal Plant).

In general I think most of us tech nerds turn our noses up at steam but I am certainly far from convinced this is still not the way to go, especially for the first number of plants so we are not asking investors to also fund turbine development (which is what many people are saying killed the South African Pebble Bed project). I`d also add that every major group promoting molten salt systems (French TMSR/MSFR, Russian MOSART, Japanese FUJI) still assume a steam cycle.

Multi-Reheat He.

Has clear advantages if you can keep your inlet He temp high enough. If you keep the salt to its traditional 700 C limit you need pretty big heat exchangers to try to get your final He temp as close to this as possible. I couldn`t find it right now but I think Per`s system only has about a 35 C drop from peak primary salt temp to peak He temp (compared to a steam temp of 565 for MSBR and tiny IHXs). Helium (and any gas) also makes the tritium issue easy to deal with and provides a "soft" linkage between turbines and reactor (good for stable reactor control). Helium also seems fairly easy to integrate dry cooling by raising the waste heat rejection temperature. Can anyone give an idea of efficiency loss in this case since I often see 30 C as the quoted rejection temp?

Supercritical S-CO2

Seems to have clear advantages if we can`t get peak gas temperature up near 700 C or higher. Excellent efficiencies between 500 and 650 and extremely compact equipment. However, the need to get rid of heat near the critical point seems to rule out dry cooling, can someone confirm this (it has been mentioned on and off). I would guess that even more R&D would be needed than He but that is only a guess.

Nitrogen

I need to learn much more here but by Rod Adam`s and Per`s exchange it would seem that Nitrogen has some clear advantages if your total power output is lower. Can someone provide some numbers here? What would be the ideal output for Rod`s systems? If they can compete on a capital cost per MWe output I don`t see a big problem with having more turbines per plant. The R&D input certainly seems to be lower and to me this is a huge advantage. Very hard to convince people that we need hundreds of millions to develop our reactors and at the same time hundreds of millions to match gas turbines to them.

Anyhow, let me know what you think. I personally think it still a very close race...

David LeBlanc

P.S. I didn`t mention, but if you have a peak salt temp around 700 C there is actually very little difference in the potential thermal or net efficiency of He, S-CO2 and Steam (not sure about N2).


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 78 posts ]  Go to page Previous  1, 2, 3, 4, 5, 6  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:  
cron
Powered by phpBB® Forum Software © phpBB Group