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Has anyone considered the removal of to much water from an ammonia plant.
With a hanson or similar type still removing excess water automatically, could to much water be taken out causing stress corrosion cracking?
When making ammonia they add water to avoid stress corrosion .
Anhydrous Ammonia - Refrigeration
Product Type: Liquid
Ammonia is easily liquefied and is stored and shipped as a liquid under pressure. It is used in organic preparations, for neutralization, a nutrient in biological processes and in commercial refrigeration systems. Refrigeration Grade Ammonia has less than .01% water, and per Department of Transportation requirements must be transported in a Non Quench Tested vessel due to welds being degraded over time.
Water is bad!!
It sounds like you are speaking about an auto-purger to remove noncondensables! Hopefully when your plant was built they pressure tested with nitrogen to avoid allowing water to get into your system!
If you are speaking of non condensable gases, there is a simple test that you can do to make sure that your purger is doing its job correctly! You should measure the temperature in the condensers return line(make sure that your temp probe is well insulated) this should correspond with your temp/pressure chart! Make sure that you take your temp/pressure reading from the same point in the pipe! I hope that this has answered your question!
The Hansen purger can remove small amount of water from ammonia. But if you have large amounts, you have a lot of work to do.
If you have a screw system, the oil will pick up lot of the water and (it will look milky) and the standard paper element oil filters will swell and restrict flow rather quickly.
You can call your ammonia supplier and buy a test kit to check for the water and an idea of the quantity of water. He should also tell you the make of a company to help clean it up.
The problem is the ammonia has a great affinity for water and they mix to form "aqua-ammonia". You can use a distilling process and boil the ammonia from the mixture and leave the water behind.
IIAR has several good papers on water contamination in ammonia systems.
ken
I am bought new tank, plant sunshine, connected pipe on suction and admission gear, filled tank liquid ammonia, evacuation ammonia and ammoniac water down launched. One man worked two months with 10 tons ammonia and OK.
Hansen's new purger can be purchased with a water still. In America we have some Manufacturers that make larger stills for permanent installation. If it is a specific failure like a shell and tube condenser or plate and frame failure then Air gas rents a large still that can remove a large amount of water. Removing water is not as critical as non condensibles but it should be removed as much as possible.
Hello Ranger,
The replies of Poodzy and Zolimer are the most important things you have to know.
1/ Water is bad.
2/ Hope that no water is used to pressure test the system.
There are some questions yet to answer.
How did the water get in?
How much water is in? (like TXiceman suggested)
There are permanent units to put into the system to get the water out but if the system is small and there is a lot of water in I would suggest to just take out the old NH3, vacuum the system, flush with nitrogen gas and then vacuum again and fill with new NH3.
So, good luck and let us know what happened.
Greets.
And here's another reason why you want the water to go out.
ENERGY CONSUMPTION
The basic guideline is:
1% water gives a reduction of 2% in Capacity.
1% water will increase power consumption with 1%
Greetings,
Bart
Water can be removed without dumping the charge. Stills are very simlpe and easy to install.
Thanks for replies but what i am mainly interested in is to much water removed and the effects.
I dont believe anhydrous ammonia would/should have anything less than 1% water. If you remove to much water by using an efficient still you could run danger of stress corrosion cracking of components.
Water is put in for this reason if i understand it correctly.
Hello Ranger,
You are correct about the minimum of water in NH3. less then 2 % is acceptable. Stress corrosion can occur if the system is not designed wordt the correct type is steel. Here in the netherlands we have to use materials with a 3.1.B certificate due to regulations. If it is not know what kind of material is used then an NH3 analyses every 6 years is sufficiant to show the water ammount in the system. But again those are the local rules in the Netherlands. They are called the PGS 13. (NH3 Law)
Greets,
Bart.
AAAHHHH typing error.
line with stress corrosion ...... must be read as:
if the system is not designed with the correct type of steel.
greets.
There have been some discussions on the stress corrosion cracking here in the US. One vessel manufacturer in particular has issued some information where they suggest the use of PWHT (post weld heat treatment) to normalize the steel to reduce the stresses due to fabrication.
In part, the water content has something to do with this, as does the steel itself. According to this manufacturer, they also feel the oxygen content plays some small part in this to. They have noted a sample of evidence that shows the the cracking occurs in the vapor space of the vessels also. This leads back to the need for refrigerated purgers.
Somewhere along the line, it seems the problems of stress corrosion cracking has become more prevalent in recent memory and I'm not sure why...
Could it be because standards are getting higher and we are more educated.
Years ago we didnt check vessel/pipework for corrosion and deterioration,or anything .
With more stringent safety regs etc we were forced into it (in Australia ).
All knowledge has come from other industries like petro chemical , which has been doing it for years.
The more you know the more you have to worry about.
Hi everyone,
you believe as though have you got water in ammonia 1% ? Water bad- OK, but as remove, to out of action and let out ammonia..... and let in new? much problems and dollars
Not enough water in a system to prevent stress cracks.. Never seen a system like that.
The excess water will collect in the coldest spot.
Nature of vapor pressure.....If your running a multiple stage with one stage below atmosphere...rest assured you have plent of water to avoid stress cracks.
Better check your chemistry. Water and ammonia will mix and become what is commonly know as aqua ammonia. Otherwise how does an ammonia absorption system operate. The ammonia and water form a solution that behave with very well defined properties for the mixture.
So the water doe not pocket as you stated.
Ken
Problem
What is SCC?
- The combined effects of mechanical stress and corrosion on vessels can result in a special type of failure known as Stress Corrosion Cracking (SCC).
- It is not possible to repair vessels once they have suffered SCC.
- SCC has the potential to cause a catastrophic failure.
Stress corrosion cracking is a phenomenon which can occur in carbon steel and other metals exposed to a combination of mechanical stress and corrosion. In a pressure vessel, SCC appears as numerous fine cracks on the interior surfaces of the vessel, usually where the head and shell are welded together. This can also occur in any area where pitting of the material is present.
During normal operation in ammonia refrigeration systems the applied stress levels alone are not high enough to initiate stress corrosion cracking. However, welding stress levels in high strength materials or welds which are harder than the base material, together with the applied stresses of the industrial refrigeration system, can be enough to initiate SCC if oxygen is present. With as little as a few ppm oxygen in liquid ammonia or a few thousand ppm in gaseous ammonia, SCC can occur.
In the ammonia refrigeration industry, the upper portion of the high-pressure receiver is one of the most likely vessels to develop SCC. This is because it is the area of the system that sees the highest pressure and is the most likely to have high concentrations of non-condensable gases such as oxygen. Cracking is less likely to occur in low temperature vessels because oxygen must be present to act as a catalyst.
How to prevent SCC?(Gartner Refrigeration)
- Post weld heat treating (PWHT) will substantially reduce the probability of SCC in vessels exposed to air contaminated ammonia. It relaxes residual and thermal stresses that occur during welding and tempers the heat affected areas. For most pressure vessels in the refrigeration industry the material used to fabricate the shell is ASTM/ASME SA-516-70 rolled carbon steel. To PWHT this material per ASME code requires heating the vessel to 1100° F and holding it at that temperature one hour per inch of thickness. It is then cooled in the furnace at the slowest possible rate.
- Purging the refrigeration system can also reduce the possibility of SCC because it eliminates the non-condensables, such as oxygen, which accelerate the process. These impurities may enter the system while charging, from leaky valve stems, during piping repairs, or inadequate evacuation of the air prior to charging. In addition to reducing the possibility of SCC, a good purging system will have the benefit of lowering the condensing pressure and improving system efficiency.
- Water concentrations of 0.2% can inhibit cracking. Unfortunately, even such small amounts of water are generally not tolerated in refrigeration applications.
- Catastrophic failures can be avoided by carefully inspecting the vessels on a regular basis. For ammonia systems that are in excess of 10,000 pounds and require Process Safety Management (PSM), these inspections are part of the mechanical integrity program. Methods to detect SCC include radiographic and ultrasonic testing, wet magnetic particle method (ASME SE-138), and an acoustic emission test. These tests can be performed without internal access to the vessel, but do require the removal of insulation.
TXiceman, you are very correct. Water and Ammonia mix quite well to create Aqua Ammonia. I will have to say that this mixture will collect and concentrate in the coldest vessel. This is not a theory it is a fact. just do a few plant pump outs and you will see it happen. Also when you install a still on a system the liquid supply to it will always be from the bottom or the pump discharge of the coldest vessel. You really only need to know two things about SCC. Buy post weld heat treat for all your vessels and install and MAINTAIN a good non-condensible purger.
keepitcool,
By the nature of the ammonia and water, the colder the solution, the more ammonia it will hold...warm it up and it will gas off or hold less ammonia.
Worked on a process years ago that used absorption to reclaim the spent ammonia that was to wet to use in the refrigeration cycle. The ammonia was concentrated by chilling the solution and it was stored and sold to a fertilizer company as a waste product.
Ken
Hi guys,
We have built our own water removal plant or still. We have removed 2500 litres of water thus far in 2.5 months. We reckon there is another 4-5000 litres left. The plant has a total NH3 charge of abou 60 tonnes NH3. With a 10-12% water concentration.
Water greatly effects capacity, the compressors need to run at a lower suction pressure to give the same capacity without the water... Electricity bill goes through the roof and all the hidden costs add up on service life on equipment.
grantd.
Hello Grant, I am in Italy and deal with quite a few Ammonia compressors that have alot of water and rust in theri systems. This mix is being brought back into the compressors and contaminating the oil and causing sludge and varnish and in the end bearing damage due to the fine rust particles. i am interested in understanding more about your "Water Removal Still". This escalade of events happened more since many clients changes from the mineral oil to a synthetic oil. I beleive the problem is the Ammonia sìystem and not the oil but some how we need to remove the water and rust form the system. This is quite a big system with over 20 x 330 kw screw compressors running.
Ciao, Lonestar
Phillips refrigeration has a ammonia still using hot gas and we rent electric heat stills. The Hansen purger water removal is minor. THE ACCEPTABLE AMOUNT OF WATER in an ammonia refrigeration system IS .02% or less not 2%. Your ammonia needs to be 99.98% pure to be refrigerant grade. Anything less is fertilizer. As little as 300ppm will cause corrosion. Permanent electric and hot gas stills are being installed to plants running in vacuums. We use an indirect heat source to heat ammonia causing ammonia to boil off and the water to be left behind. We take batches of liquid ammonia at the coldest point.
Do you have oil pots? They do the same job as stills.Quote:
Originally Posted by mrfreezeit
Greetings everyone, We all agree that any water in a ammonia system is BAD. We have a very simple still system in use at our plant. We have a glycol chiller with a dry suction line. the oil pot is oversized and wrapped with electric heating cables. we fill the oil pot half way on the sight tube,close the inlet valve leaving the suction outlet open, turn on the heat cables and let it alone for about 72 hours allowing the ammonia to boil off leaving oil and water behind. We then bleed off the oil pot and then start the process over again. We have been doing this for several years and all tests and oil analysis show a acceptable amount of water in the system. this is a fairly simple operation if you have a vessel or chiller with a dry suction line.
Hi all, just to add, though very late, that Grasso has drier & York too that removes water & dirt from the system. Grasso Drier is expensive & should be around US$20K.
Hello Grant
Which plant in Durban are you working on? I'm originally from Durban been gone around 8 years.
Both Grasso and Hansen make a water removal device the Hansen cannot be used here though and the Grasso is price prohibitive at around £17k too much for a single invoice. I have wanted to build my own as this can be hidden in my maintenece budget. Did you have any plans or did you copy someone else? Is yours automated. I need a few ideas to start can you help?
To get the ammonia out of the system you could use a component called ammonia purifier. This is basically functions reverse of the air purger .i.e You boil the ammonia by heating with hotgas or electric power. After ammonia boils water remains on the bottom of the exchanger vessel.
It is possible to get quite large amount of water in this way depending on the exchanger capacity.
It is possible t
actually he is correct, water will collect in the coldest vessel, this is because when ammonia gas is pulled from the top of a vessel it virgins the ammonia (kind of like salt being left behind when you boil saltwater) the water remains in the vessel. it also mixes with any oil and causes a thick crusty buildup on the inside of a low side vessel if it is below -20 degrees F.Quote:
Originally Posted by TXiceman
destilling ammonia is very easy and very effective I have removed about 500 l of water froma system with 8000 kgs of ammonia with a simple high- pressure liquid heated still.
It's important to destill slowly at a evaptemp. at 5C or so.
In the beginning you get a lot of water very quickly but as the content decreases the process slows down considerably.
If anybody has any big problems pm me might even travel if the problem is complex enough.
hello there!:pQuote:
Originally Posted by GrantD
i work for a company that manufactures ice blocks. we use grasso compressors. we notice that during startup the compressor has low condensation (30 degrees celsius) and suction temperatures (-21 degrees celsius). after two days, the suction temperature rises by 2 degrees celsius but the condensation temperature remains the same. the suction temperature does not anymore recede to its low level despite the fact that we decrease harvest of ice blocks from brine. we use manual gas purger but we do not have water purger. we have made adjustments on our expansion valve but nothing good happened.
does this phenomenon have something to do with the presence of water in ammonia?
any prompt reply is highly appreciated. thank you
If your plant is designed correctly and u make sure that all vessels are stress relieved and that all piping used are of hi carbon steel and the welding contractor uses the correct welding materials, u do not have to worry about SCC. This will take about 60 years to really have a serious risk an by that time the plant will either be DE-commissioned or the vessels and piping will have been replaced as a safety measure.
Coming back to water in ammonia plants. This have always been a bad thing as mentioned above by all.
To remove water is also the easy as mentioned above and these systems can be build by yourself for a fraction of the cost as in buying one.
Lonestar haze the results of not removing water as his plant haze reached critical state as the water have bonded with the oil creating a emulsion. by removing the water now he can only stop the forming of emulsions, but now he have to remove the emulsion from his plant, and this is a tricky one.
I had this in one of our plants and it took me two years to clean it out and a lot of work and money.
To get the plant back to a satisfactory stage took about two months and then came getting out the emulsion that formed.
thanks. do you a have design or can you refer a website that presents a design for building a water separator from ammonia? more powerQuote:
Originally Posted by Lodiev
MMC Kulde in Norway has an automatic water separator for rent or sale that can be integrated into the system with flanges.
it will separate water from the system as long as the system is running and will give a warning when it is time to drain water.
http://www.mmc.no