Evelyn:
I just dropped in to see how some of my old professional friends are doing in furnishing excellent, intelligent responses to other engineers with queries. Your thread interests me because we covered this same issue many times in the past in this forum. The helpful responses have not changed and they are all highly recommended.
In order to get a detailed, accurate recommendations on how to accomplish what you want to do I highly urge you to respond to Latexman with what he is requesting. If you do, you will obtain the kind of detailed recommendations and advice that you need to do your project safely and efficiently. Basically, what is needed is Basic Data, the exact type and size of tank you are planning to inert, the rates of glycerin fill, the availability of the proposed inert nitrogen in flow rate, its pressure and temperature.
The Forum members have to have the above data and information in order to ensure that what they recommend is SAFE engineering design that will not only work, but that will carry out exactly what you require. Some items of concern I would pass on to you are:
- The API 650 design has a maximlum pressure rating as well as a mazimum vacuum operation. Be aware that when you enclose this tank with an inert gas you are subject to a potential vacuum condition as well as over-pressure. You should hold one or several Hazops to ensure that all potential future issues and safety concerns are resolved before going forth.
- The maximum rates of glycerin inlet and outlet flows must be taken into consideration for the operation to be considered safe.
- There may be a difference between the inlet nitrogen temperature and that in the tank (50 C). What I have done in the past is that I introduced the nitrogen through a submerged pipe in order to allow it to go through the hot (or warm) liquid fluid in order to be preheated before entering the tank's vapor space. This stabilizes any pressure variations in the vapor space and over-feeding of nitrogen with subsequent vapor purging.
- Take careful consideration of your tank vacuum breaker and pressure relief. I consider the vacuum breaker as a major item to design carefully. Any sudden tank leak or major liquid outlet can cause a potential vacuum and tank collapse.
- Constant, available nitrogen supply must always be present.
- Always design for and alert all operating and maintenance personnel about the inherent dangers of nitrogen inside the tank during any mainenance or clean-out. The nitrogen feed line should be designed with a positive method of removing a section of pipe downstream of the nitrogen feed line block valve. Never trust that the nitrogen feed block valve is shut closed while doing internal maintenance.
- Nitrogen deaths due to asphyxiation have been far too numerous and can be halted if proper steps are taken.
I hope the above helps. Saludos.
My best regards to all my old friends.