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Nitrogen Blanketing For A Tank Used To Store Distilled Palm Fatty Acid

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#1 ramanujam


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Posted 30 January 2008 - 12:10 PM

hi all,
I am undertaking a project where in i have to apply a nitrogen blanket in a storage tank which is being used to store distilled palm kernel fatty acid(DPKFAD). The problem being faced now is that the colour of the DPKFAD is becoming darker ie. it is going upto 30 units against the value of 10-12 units when it is being pumped into the tank, mostly because of the reaction taking place between DPKFAD and atmosphere. The stoage tank has a capacity of 50 tonnes. At any point of time only half the tank is filled with DPKFAD.
I would like to know at what rate should nitrogen be purged into the tank and will there be any benefit by applying a nitrogen blanket.

#2 Art Montemayor

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Posted 30 January 2008 - 01:27 PM

Your application is probably one of the highest priority applications for Nitrogen Blanketing in the Food Industry. I would certainly do all that is possible to install a Nitrogen Blanket in your oil storage tanks.

The rate (flow rate, that is) at which Nitrogen is injected into the storage tank's upper section is determined by how fast you normally pump out the oil product. The Nitrogen Blanket is a semi-static system in that it should (theoretically) remain on top of the stored liquid at a constant pressure and temperature. However, we all know that the stored liquid is really a transient fluid - it may be stored for a while, but it is destined to be pumped out for distribution and sales. When that happens, the conditions of pressure are changed for the Nitrogen Blanket since it has to expand to occupy the space vacated by the exiting liquid. A pressure sensing device signals a Nirtogen make-up valve to inject inert gas to keep the increased volume at the pre-designated storage pressure.

Upon subsequent re-filling of the storaage tank with fresh production oil, the Nitrogen blanket is forced to compress due to the increased liquid inventory. This compression raises the Nitrogen pressure and any excess pressure above the designated set storage pressure has to be removed from the tank in order to avoid an over-pressure in the tank. The usual manner is to vent the excess tank nitrogen to the atmosphere and suffer the loss as a storage cost.

The tank liquid storage cyle continues to repeat itself .............

Therefore, in order to determine the flow rate at which you have to be able to feed Nitrogen into the tank, you must consider the maximum tank pump-out flow rate and add a small contingency factor to make sure you can match the required flow rate without causing a sudden partial vacuum condition inside the tank - which would be very bad for the tank.

I hope this explanation helps you understand how the system works and how it is usually designed.

#3 proinwv


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Posted 30 January 2008 - 02:28 PM

Art has given you a good reply and may I add to it saying that to accomplish this you will need to have appropriate P/V venting installed to protect the tank within its MAWP & MAWV and also include a gas blanketing valve to provide the N2. Additionally you should consider an emergency vent for protection. API 2000 is a good resource for all of the above, but since the oil is not highly volatile, a simple volume replacement is a good guide for the venting/blanketing requirements, but I would add a % above this for a FS.

#4 ramanujam


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Posted 31 January 2008 - 02:31 PM

Thanks for the reply Art.

What i would also like to know is will the colour of the DPKFAD remain the same ie. at around 10-12 units and not revert to its original colour ie. around 30 units by blanketing the tank with nitrogen?

The DPKFAD is being used for soap manufacturing( white coloured soap cake). The company for which i am undertaking this project is using a lot of bleaching agent to reduce the colour. What has been observed is, by reducing the amount of bleaching agent(hydrogen peroxide) used, the soap becomes milder and the odour is much better.

#5 Art Montemayor

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Posted 31 January 2008 - 02:56 PM


I suspected there were important incentives in the prospect of applying Nitrogen Blanketing. That's why I mentioned that I considered this a high priority application.

Unfortunately, I can't give you a specific yes or no on what you are asking as to any color variance due to Nitrogen blanketing. However, what I would recommend is that you make a small, quick pilot plant experiment to demonstrate whether the desired effect can be achieved by blanketing with nitrogen. All it takes is a relatively small quantity of dedicated hot oil and a small amount of nitrogen regulated from a nominal 250 cubic feet capacity high pressure cylinder. I would employ a 55-gallon drum that can be conveniently available. I would try storing the oil hot and for pre-estimated storage times that you deem important for your use - such as 1 day, 1 week, or even a month. If done and controlled properly, I suspect you will find that the oil is preserved much as you would like it to be. This kind of impirical and real-life factual test data is very convincing and gives you a good base to justify the capital costs required to achieved the expected profitable results.

I don't think the cost of running such an experiment would be much - something in the hundreds of dollars, which I visualize would be quickly recovered in the future with a higher quality and more desirable end product .

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