Liquid Sulfur Tanks / Ventilation

[cgair]

We are a Refinery/Upgrader in Regina, Saskatchewan, Canada. We currently have 2 - 608,000USGAL (40050 long tons) liquid sulfur storage tanks that are 95' diameter by 14' high. Each tank is vented to atmosphere through two 10" steam jacketed roof vents spaced 5' apart on the outer perimeter of the tank roof. Over the past few years, we have periodically experienced problems with smoldering and heavy clouds of vapour (suspected SO2 with H2S) from the vents after truck and rail car loading from the tanks. I am looking for any specific ventilation design for liquid sulfur storage. i.e. vent configuration, amount of ventilation required, or any details that someone can share.

 

[PurdueGuy]

cgair,

Assuming you have a PV vent:

You may want to check the PV Vent parameters and resize the valve to double check

I.E. Vaccuum Setpoint, Pressure setpoint, flowrate (SCFH) in/out, etc.

Anderson Greendwood Varec makes a great sizing program to make calculations much easier and accurate.

 

[cgair]

PurdueGuy,

I'm sorry, I should have been more clear, the storage tanks are both open to atmosphere. They do not have PV vents. And the tanks are 4,050 long tons (608,000USGAL), not 40,050 long tons.

Additional information - Our sulfur has H2S. We figure that we may have a buildup of pyrophoric iron sulfide in the tank. When we pump from the tank, oxygen is introduced and the iron sulfide ignites and smoulders. It has been suggested to increase the ventilation in the tank such that there will be enough air sweep to avoid an explosive H2S mixture and to ensure that an oxidizing atmosphere is continuously present to develop a protective iron oxide film in the tank vapour versus iron sulfide. With the two vents side by side on such a large diameter tank, there is virtually no air circulation.

Does anyone have any experience, input or information regards to this matter?

 

[ENC]

Well the matter you are describing requires some study. However, generally the displaced air during filling is vented and the new air is introduced during discharge from the tank. This is a typical problem with most of the above ground storage tanks (AST). To make the processes more controlable a positive control system should be introduced. This is typically handled with an industrial ventilation system that will keep the system atmosphere below the LEL ( lower explosive limit) and out the the fire triangle range. If you need addition help email me at fjstanton@cs.com

The best of luck.

 

[jeffscott]

I am aprocess engineer in calgary. I have designed several sulphur degassing systems storage systems for above ground tanks.

The danger is fire and explosion. Most of the systems use an air purge that returns the air and vapours back to the sulphur plant reaction furnace or incinerator stack. The first systems were steam or air eductors. Blowers are now in use.

The trick is to keep the H2S concentration below 20% of LEL.

This is really quite a easy to solve problem if the money is available

 

[mstainbrook]

You mentioned you thoguht you had some SO2 venting. (caused by burning of sulfur due to ignition of the iron?) You don't think your "smoldering" is an ongoing fire?

IF you add more air creating a positive air purging system won't this add Oxygen to the fire?

I'm curious to see is you have had an SO2 detector/sensor indicate/measure the ammounts of SO2 present?

mstainbrook
stainbrook@angelfire.com
IT/Controls/Environmental Equip Eng

 

[hacksaw]

we used snuffing steam to purge the air and put out fires.

you can't leave it on permanently because of the risk of acid formation.

H2S is always a problem. Every solution invites a dozen new problems.With steam jacketed vents you may be worsening the problem because of the chimney effect, but realize that you may not have a choice in winter. What steam pressure are you using?

At one time closed vents were talked about, but techical limitations of collecting the vapors and preventing condensation corrosion were over whelming.

Use of non-contact level systems (radar) helps to a degree.

 

[greg87]

Are you saying that sometimes, at the very end of the unloading cycle you get this rush of vapor? How are the rail cars and tankers unloaded? Can you stop the transfer short of completely unloading the trucks?