8 replies to this topic

[bhaskaran]

solvents storage more than 300 tanks is available with us.Each tank was blanketted by nitrogen.These tanks were connected with vent condenser with +10.c utility.Even after this facility we are using large amount of solvents through vent of condensers.can anyone suggest whether cold traps will work or how to solve these problem?

[Art Montemayor]

Bhaskaran:

This sounds like a very important and critical problem; however, your explanation and question(s) are hard to decipher. Your lack of spacing between sentences doesn’t help either. Allow me to describe what I understand is your problem(s) and you can correct me if I have the wrong interpretation:

You are producing/storing liquid solvents in more than 300 storage tanks. These storage tanks are blanketed with nitrogen and also have a vent condenser that is cooled with a 10 ^oC cooling fluid.

You are experiencing severe solvent losses in spite of the above storage methods.

Is the above a correct interpretation? If not, please correct me. Also, submit a sketch of your storage tank installation in the form of a P&ID, complete with tank characteristics – such as MAWP, capacity and type of tanks, and typical pressure settings on the tanks. Also, identify the solvents or at least state their vapor pressure characteristics. Also identify the cooling fluid and the type/size of vent condenser you are using. The more information you submit, the more accurate and detailed the related response.

Await your reply.

[proinwv]

Bhaskaran:

In addition to what Art said, please send more detailed information on your blanketing arrangement. In particular, how many tanks are served by one blanketing valve. What are the set points of the tank blanket valve as well as the PV vents. With 300 tanks, this is a complex arrangement and we need more information.

[bhaskaran]

Sir,

Let me explain my tank farm systems in brief. We are handling 15 solvents (Acetone, EA, THF, MDC, IPE, IPA, ACN, MEOH, DMF, DMAC, etc.) which are stored in 300 tanks with different combination in terms of mother liquor & recovered. All tanks are vertical roof type. Tanks of same solvents are grouped together. All tanks were blanketted with nitrogen since above solvents flash point are less. Each tank is having own nitrogen controll valve(PCV) with setting of 50-75 mm WC. Loading & unloading takes place regularly. Ambient temperature in chennai will be around 35 ^oC. Tank is having PRV/VRV. When tank gets pressurised to 200 mm WC, PRV will open & allow it to go to condenser. Condenser vent also having PRV with setting of 300 mm WC. Condenser is supplied by +10 ^oC chilled water. Area of condenser is 7.5 m². Chilled water line size is 1".


Problem:

i) Since solvent vapours are going along with nitrogen what utilty with what temperature is required ?
ii) How to calculate the area of condenser for above application?
iii) How to calculate the VOC from condenser vent? any calculation is available?
iv) Any special type of condenser is available in market for above application?

Please help.

Regards,
Bhaskaran.r

[Art Montemayor]

Bhaskaran:

Based on what you describe, you have a formidable problem, and one that is potentially hazardous and dangerous to human life and the environment and also very economically sensitive because of expensive solvent losses through venting. While I consider it fairly easy and straight-forward in resolving it successfully, it will take relatively large capital and engineering costs to bring this problem to a successful conclusion. It certainly can’t be resolved on this Forum. I firmly believe that it will take the application of expert engineering expertise and some capital investment to recover evaporated solvents and prevent an environmental or human contamination incident in the future. I am hoping that Paul Ostand will jump into this thread and add his valued expert opinion(s).

To answer your specific questions:

1. You are already going in the right direction with the application of a refrigerated utility to apply in a vent condenser on each tank. I would opt to use a cooling fluid at 2 – 3 ^oC in order to maximize the amount to recovered solvents. In other words, I think you are using a cooling fluid that is a little too warm. But that is a factor that can be studied and optimized later on.
2. The area of your condensers is calculated by doing an engineering study before hand and optimizing the way the vents are treated. Your operational and storage methods as well as requirements will determine this. If you are operating around-the-clock with your storage, then I would consider using one central condenser for strategically grouped tanks in order to reduce the quantity of condensers and reduce the capital cost of these and their installations. One condenser shell with multiple coils might be the right and optimum answer.
3. The Volatile Organic Compound (VOC) contents in the vented nitrogen stream can be calculated based on the corresponding dewpoint calculation. This calculation is done for each of the stored fluids. When you ask if any calculations are available, I presume that you are hoping for some free, off-the-shelf calculations that you can apply. This will never be the case. Calculations will have to be done for each tank.
4. There are a lot of vent condensers and designs in the marketplace that be successfully used in your applications. However, I believe that with the quantity of your tanks (300), it will be expedient and wise to apply a custom-designed vent condenser and installation in order to minimize the capital monies spent in this endeavor.

For a copy of my Excel workbook on Storage Tank pressure controls and Nitrogen Blanketing, go to:

http://www.cheresour...art=0#entry8246

And download the copy there.

[proinwv]

Bhaskaran:

Montemayor seems to have the basics covered in his previous post. And, I leave the chemical process engineering to him.

I am curious whether you are properly blanketing. What I mean is do you have good N2 control so that the tank pressure does not drop into the vacuum vent range. We don't want to be adding atmospheric air (and O2) to the vapor stream you are presently venting or contaminating your product in storage.

While it is too late for this, the most effective way to eliminate the vapor carryover would have been to use pressure vessels operating above the vapor pressures. I only mention this because I assume that these tanks cannot operate anywhere near those pressures.

[pawan]

I do not agree with the proposed solution as cost effectiveness of condensing solvents goes lower & lower specially in case of highly volatile solvents as U decrease utility temperature.

Rather I would suggest using one absorber column per solvent grouped together as all the tanks pertaining to one solvent must be operating at same pressure.

Bhaskaran can use either water as solvent or any other suitable absorbent based on many processes available in his plant. (I dont know).

I have done this for Ethanol & found cost effective compared to vent condensing system.
Also for calculation of vapor losses either U can use standard Tank Emission calculation sheet from EPA which is available from their site OR can use good thumb rules.

We have saved > 800 KL/Year of Ethanol by this method using one small absorber of ~700 mm Dia & ~ 6000 mm Ht using water as absorbent and recycling the dillute alcohol to distillry section.

I can help you in estimating losses & sizing of these absorbers.

Thanks

[bhaskaran]

Dear Mr.pawan,
Thanx for ur idea.Iam having basic questions on ur suggestion
i)When solvent is saturated with nitrogen how absorption column can be effective?
ii)What sort of tanks u are using earliar & how much was the loss earliar?by incorporating this column how much u have saved?

In what way u can help me in solving this problem.

This is my email id:bhaskaran@orchidpharma.com

Thanx & regards
Bhaskaran

[pawan]

Thanks Mr Bhaskaran for adding me to your friend list. I invite you to join my blog also.
I am going to post a complete article on this issue on my blog............

It was for ethanol conical roof + 50mmWC tanks.
We are able to recover ~80%.

Rest U can find out on my Blog
Thanks