Emptying of Concentrated nitric acid tank(98% HNO3) 2

[panteo]

Hope someone can provide some urgent advice on this.

We are storing 98% nitric acid in large aluminum storage tanks. (1,500 ton, 2,000 ton)
You can see the picture of the CNA storage tanks at the following web page.

http://www.antlove.com/cna_tank.htm

Next year, we have to empty and clean the tank for internal inspection specified in domestic law.
According to the law, the welding seam of bottom plate must be tested using non-destructive method.
The problem is that emptying and cleaning of the tanks is very dangerous for the personnel and harmful to the aluminum tanks.
If we try to clean aluminium tank with water, it will form weak nitric acid inside the tank and will corrode the tank very fast, since aluminium tank is not suitable for Nitric Acid less than 90% concentration.

Many thanks in advance,

Jae-Hyuk Im

 

[hacksaw]

drain the tank, you have to vacuum pump the residue and then flush the residue. the trick is rapid dilution, but then you have to completely dry the interior.

soulds like an incomplete basis for tank design (including provision for annual inspections) was used. I'd have a serious conversation with the licensed engineer that developed the design.

 

[Montemayor]

panteo (Chemical):

I believe some information and basic project scope is missing from your description. That is why hacksaw's comments are so important and probing.

I have been involved and part of world-scale capital projects; LNG project development was one of them. I know, by personal experience, the detailed and meticulous lengths to which our project teams had to go into to obtain the confidence and approval of the financial lending institutions. If you participated in the early formation of your project's life, I'm sure you are familiar with what I am referring to. You cannot even consider spending early project engineering development monies if you don't have a SOLID and WORKABLE scope of work. It is obvious to me that your Nitric Acid complex is a world-scale project. It is, I would suspect, financed by international lending institutions - usually organized as consortiums in order to dilute the individual risks on the project's return. Otherwise, the total capital investment (hundred's of millions of dollars, I would guess) would have to be put up by private investors (not likely these days) or your government (not likely either, unless a gun is put to their heads). Projects of this magnitude are usually justified using Project Financing - whereby the loan is serviced by the project's revenue in the early years. That is why the financiers are pulling the strings and running the show from the very early onset -- they want to ensure that they will be PAID! In other words, the project's successful generation of positive revenue must be ensured before any money is loaned for that effort.

What hacksaw is driving at is very true. There must be a detailed scope of work on every section of your project - especially those sectors that knowingly are identified as "underpinnings" due to their need to go into a turn-around (and cause a definite halt on the project's revenue!). Project engineers at the planning, conceptual, preliminary and Final design stages have had to generate details on every piece of equipment - especially the storage tank area. Why Aluminum (with it's "Achille's heel" for dilute Nitric Acid) was picked as the Material of Construction has to be documented and explained in detail. I am willing to wager that an engineering study was probably done to justify the selection of Aluminum over other materials. And in doing so, the project managers had to identify in detail what the risks and revenue losses the project could suffer in case of material or human failure. This is the normal way this type of project is undertaken and designed. Multi-million dollar projects like this are not done on the back of an envelope or on the "feelings" or trust of a design engineer. Too much is at risk and this simply is not acceptable.

The above is meant to explain that the answer(s) has to be in the documented detailed design of your plant. Normally, this is spelled out in detailed operating and maintenance manuals - that in your case, would take many tomes - and occupy a library room within your admininstration building. I do not believe you could expect to find a reasonable answer elsewhere - especially in this forum. We simply are missing a multitude of basic data in a situation where multi-million dollar risks are at hand.

Your plant fotos are very informative and interesting. Where is your plant located and what is the base load for your CNA product - Nylon, fertilizer, or explosives?

I wish you safety and success in your upcoming turn-around.


Art Montemayor
Spring, TX

 

[unclesyd]

Unless the tank has a proper bottom drain it will be hard to vacuum the tank due to NOX fumes and all materials having to be S/S or TEFLON lined. The tanks also maybe approaching 28'in height. Depending on the heel left in the, as “panteo” states, tank dilution is the biggest problem. If you try to dilute you still have to be pumping out any liquid below the draw off line. This material generates a great deal of heat while being diluted making the corrosiveness of this solution to Al very high as he states. You would still have to get below 7% Acid to add any neutralizing material. Depending on the state of the acid, white, red ,fuming it can very quickly generate a tremendous amount of fumes and possibly over pressure the tank

We have emptied 67% nitric acid S/S tanks from the top using a jet pump and also a submergible air driven pump. The drains were plugged with Pt dust.

Can you remove the draw off line and use this flange as a entry point for a small line then use a jet or pump to pull out most of the acid? Your liquid would be below this point.

If you can get to point where you will have add water I would use a rotating tank cleaning nozzle to keep the walls clears. We use this method on all HNO3 tanks.

panteo, What are the rules for NOX fumes in Korea? What type of venting used, partial vacuum, slight pressure?

Art, panteo
Like hacksaw said “I’d be looking for a tank designer, et all. You wouldn’t want to know how many times that I’ve engaged in discussions about tank drains and the need thereof. Al is the preferred material of construction for storing very strong Nitric Acid. NASA as well as the Russians have done a lot work on storage of these acids, but I bet they provided someway to drain them.

 

[Montemayor]

unclesyd (Materials):

I do not agree with your suggestion of "looking for a tank designer" - presumably to take to task for designing a flawed tank or to threaten with litigation. This is an engineering problem at the moment for the sake of planning what to do - as panteo states - for the next turn-around that is coming up next year.

My point is that the solution is to be found in the plant's basic design manuals (if one exists) . If it is not to be found there, then management has a hard decision to make - not the operating and maintenance engineers. I believe this is also what hacksaw was alluding to. Certainly experienced and capable tank designers may be called in as consultants (even the original E&C company!) to resolve what is termed as an urgent problem. The answer may be to replace the Aluminum tanks with Stainless ones ( Stainless alloys are impervious, I believe, to to all Nitric Acid concentrations) or to develop credible and reliable procedures for emptying the existing tanks. But certainly, the size of the tanks (& the plant) identify this as a serious, world-scale plant site and not your average, storage tank problem. If the business decisions made on this project were flawed initially, then you will find that new business decisions will have to be made to insure that this doesn't happen again. The answer, whatever it may be, will be a very, very expensive engineering answer if the basic tank design was flawed. And plant management should be advised of the true situation.

There are engineering solutions and answers to the problem if safe procedures are not found in the plant's operating manuals; however, the solutions must prove to be safe, dependable, and timely. I believe that we all recognize that the potential cost will be very expensive - and that is why management must be alerted for their impending decision should acceptable emptying procedures for these tanks not be found.

Art Montemayor
Spring, TX

 

[unclesyd]

Art,
I think you presumed too much in my statement, “I’d be looking for a tank designer, et all”. The meaning was not for litigation or retribution, but for some insight as to the whys and wherefore no drain was provided by design and hopefully some assistance to “panteo” with the problem of emptying and cleaning of the tank for inspection. One problem with getting assistance is that "panteo's" tank is one of the larger ones around for this concentation acid. My experience is with 65% acid from a 1500 ton/day plant(name plate).

The statement that all stainless is impervious to all concentrations concentrations is not correct. The selection of stainless for tank fabrication is a a complex process. And when you get close to 95% or higher concentrations, the fuming grades included the choice of tank material gets even harder. Nitric acid will corrode stainless steel tanks. I don’t think the reason for “panteo’s aluminum tank for saving money.

Now getting to “panteo’s” problem.

How much time are you going to have to turn around the tank and what time of the year will the outage be?

Will you have enough time, clearing or allowing the fumes to abate, to allow another hole to be cut in the shell? The hole would only have to be large enough to get a tube for a jet or pump thru. A 35,000 psi water cutting system could be used for the cut. A good system will only put about 1.5 gpm at the max. I don’t think dilution would be a problem. This system has worked very well on S/S tanks and is quite fast.

As Art would say start planning to put a bottom drain in the tank.

 

[panteo]

Thanks for your concern.
I'm working at Fire and Safety division of Huchems fine chemical corporation in Rep' of Korea.
The company's website is

http://www.huchems.com

Huchems corp. is the Korea's largest producer of Concentrated Nitric Acid(CNA: 98%, white) with a capacity of 104,300 MTPA.
We have two CNA plants designed by CHEMICO(33,000MTPA) and PLINKE(71,300MTPA).
The plants were built in 1979 and 1990. We have two CNA storage tanks made of aluminum.
The capacity of the thanks are 1,360 and 1,019KL each.
As our production quantity is little short of demand, we have to buy some CNA from the other domestic companies.
We use the CNA to produce DNT(Di-nitro-toluene).
Since CHEMICO company is no longer exist in the Earth, I contacted PLINKE for this problem.
Unfortunately, most of PLINKE's clients have smaller tanks, built horizontal with dished ends.(Max.150ton)
I searched "Basic Design and Maintenance" documents regarding the facility but found nothing helpful.
The Korean law, revised in 1999, states that the storage tanks for dangerous chemicals of over 1,000 KL capacity must be inspected internally every 10 years.
There has been no need for the internal inspection of the CNA storage tanks according to the previous law.
So, there has been no internal inspection for the CNA storage tanks.

In 1992, due to severe corrosion of the tank, we replaced the cone roof of the old CNA tank(1,019KL) while maintaining minimum storage level(some 8 tons). We installed a new suction piping through the level gauge valve(LT) for the temporary pump. There is no bottom drain valve in these tanks.
There was lots of red fumes generated at that time.
Ten years ago, the rules were rather loose. The roof change work can not be allowed under current rules.
For over 25 years, nobody carried out the internal inspection of the CNA tanks in the company.
In 1997, we emptied 65% nitric acid tank(2,306KL, S/S) and carried out internal inspection. The environment regulations are very tough nowadays. I doubt that we can treat the lots of acidic waste water to allowable level with same cost.(lots of total nitrogen(TN) in the waste water)

We will have only 10days for the cleaning and inspection for one tank till July next year.

I think it's very good idea to make a drain hole in the shell.
(A 35,000 psi water cutting system sounds like very interesting to me)

Many tanks in advance.

 

[panteo]

Please take a look at the following web-page.

http://www.antlove.com/cna_tank.htm

I posted a drawing of the tank drain piping done in 1992.

 

[unclesyd]

panteo,

How large is the heel?
Do you have any place in the system where you can pump the diluted acid?
We have also shipped weak nitric to other people who can use it?
Store it in leased trailers and dispose of it over time to stay within your limits of you waste disposal.

A lot of work on Nitric Acid in the US was done by NASA. As mentioned in previous post the Russians have done a lot work on all the Nitric Acids.

If you have trouble finding a vendor with hyper-pressure cutting, check with someone in the Petroleum industry. Along with that note, this type cutting is used the highway industry to cut concrete. Get one that has tank experience.

I’ll bet that you got the corrosion on the roof of your tank from a compound called Nitrosyl Chloride.

 

[hacksaw]

to what extent can the tank imspection be performed exernally and with remote inspection under you new rules?

 

[panteo]

Unclesyd,
There is no place in the system for the diluted acid.
I suppose there is lots of aluminum nitrate in the bottom of the CNA tank.
It seems like a good idea to lease trailers.
It's not easy to find a enough space for a temporary storage tank around the CNA tank area.
How is "Nitrosyl Chloride" formed inside the tank?
Do you mean "NASA" is "National Aeronautics and Space Administration"?

 

[panteo]

Hachsaw,
The new rules specify the followings.
1) The welding seams of the bottom plate must be inspected using non-destructive test method.(15% of all welding seams)
2) The thickness of the bottom plate must be checked.
3) Inspectors must enter the tank for vacuum box test.
The new rules does not allow us carrying out the external inspection and remote inspection.

 

[unclesyd]

panteo,

You are correct on NASA. They have what is called Tech-Briefs, you might find a lead there.

Nitrosyl Chloride is formed in Nitric Acid service when you have Chlorides present. It is extremely hard to purge from a system as it regenerates itself after it reacts. It is the primary reactant in Aqua Regia. Prior to the analytical techniques available today we used to purge the NO absorption tower. If I remember correctly the purge point was the twenty first theoretical tray. It tends to accumulate in the vapor space. Our primary source was from the NO Absorber cooling cools leaking. We had a terrible problem with MIC.

Hacksaw,
You question on remote inspection is essentially none, but people are still trying to perfect instruments.
On a hot day in August in Florida I certainly would like to have had remote inspection tools for tank bottoms, especially if we found some thing. Panteo’s problem is like a lot of others, myself included, in the industry have faced, older tanks were not design for easy entry and inspection except for a few enlightened companies. As “panteo” states new rules, vessel entry permits, fume abatement, etc., have changed everything even if tank entry was considered in design. His problem is trying to make the tank safe to enter for his inspection.

Tank bottom inspection done properly as “panteo” is trying to do is one hell of job and is the subject of much discussion, sometimes heated. WNA or in fact all higher concentrations of HNO3 are hard to handle under today’s rules and regulations.

Panteo's acid disposal problem is a potential bad headache. Acid storage tank heals one time were pumped to a pit filled with crushed limestone. Makes a lot of fumes, not permitted anymore, but some very good tomato fertilizer.

 

[ghopkins]

Panteo,

The tanks are large, but could a vacuum condition ever exist? Vacuum rated flat bottoms can be expensive in such large tanks. For example, if the PVRV is rated for -8" WC, then maybe the drain was located 8" (or equivalent given SG of HNO3) above bottom so it won't "implode" and never see a full empty condition. I would hope that this is the only reason why a full bottom drain wasn't included in the original design. The idiocy of such a design, if this is the reason, is also apparent given the hazards of the material and obvious need to inspect the tank. But maybe the need for inspection wasn't so "obvious" at the time of the design, since it sounds like the inspection rules at one time were non-existant.

Regardless, make sure the bottom can't lift off the foundation in a vacuum condition while being completely empty.

ghopkins

 

[hacksaw]

Rail cars make for storage if you have enough of them and a rail access.

I hope that you are making a case for eventual tank replacement or modification. Inspection and inspectability is such a key part of risk management these days.

 

[panteo]

ghopkins,
Thank you for your good advice.
Our CNA tanks are equiped with breather valves, set +-11.7"WC(+-300mmAq). We've never experienced vacuum condition in the tank, but we will be cautious on vacuum in any situation.