Sulfuric Acid Tank Overflow Liquid Trap
Sulfuric Acid Tank Overflow Liquid Trap
(OP)
We have a 98% sulfuric acid tank of mid 1980's construction on site that was recently inspected. The tank is a vertical tank with a cone roof of about 40m3 capacity. The roof has a 1" vent pipe that goes through a dessicant trap. The tank also has a 3" overflow pipe off the tank wall. The overflow connection has a goose-neck trap at the bottom that was filled with an inert liquid (I think this was a silicon oil) to ensure normal venting goes through the vent line rather than the overfill line. When the gooseneck in the overfill line was inspected it was found liquid in had reacted with the acid vapour and set solid. Obviously this would have resulted in a very dangerous situation if the tank had ever been overfilled in error, possibly causing catastrophic failue. As a result no liquid has been put into the gooseneck yet. Apart form raising this issue my question is does anyone know what is a safe inert liquid that can be used in the gooseneck in future?





RE: Sulfuric Acid Tank Overflow Liquid Trap
water?
most traps like this simply corrode away that is safer than a plugged one
RE: Sulfuric Acid Tank Overflow Liquid Trap
RE: Sulfuric Acid Tank Overflow Liquid Trap
RE: Sulfuric Acid Tank Overflow Liquid Trap
You don't way what the tank is constructed of. I imagine it must be SS or CS with plenty of corrosion allowance. A one inch vent seems undersized.... corrosion products can build up and begin to restrict flow, plus there is the issue of overflow vent plugging.
Although I don't agree with everything in this source, you may benefit from perusing this website dedicated to sulfuric acid: http://www
Good luck!
RE: Sulfuric Acid Tank Overflow Liquid Trap
The tank and pipwork is CS. I'll check out the website and also get the lab to check if glycerine is compatable with 98% sulfuric acid.
RE: Sulfuric Acid Tank Overflow Liquid Trap
RE: Sulfuric Acid Tank Overflow Liquid Trap
This is constructed but not running yet.
RE: Sulfuric Acid Tank Overflow Liquid Trap
Suggest you use a conservation vent from Groth, Protectoseal/Varec to limit environmental interchange with the tank atmosphere. These can be fitted with a dessicant cartridge on the inlet port so that any atmospheric air going into the tank is dried to approx -40 dewpoint, thus preventing corrosion. All conservation vents are available in various polymers to resist chemical effects.
API has procedures for sizing conservation vents on tanks. Thes require the fill rate, the drain rate, and the exposed area above ground. The highest inflow rate occurs on a hot day when the tank gets drenched by a sudden cold rain shower.
RE: Sulfuric Acid Tank Overflow Liquid Trap
RE hydrogen control, the vent MUST be the highest point and not restricted - makes for an interesting vent cover challenge. I used to use a hydrogen recombiner catalyst, but it is no longer manufactured, and the "replacement" is many thousands of US$ per kg, and probably need less than 200g.
RE: Sulfuric Acid Tank Overflow Liquid Trap
Also be aware that by setting the depth of the seal loop on a vent, you are, in effect, setting the operating pressure and vacuum limits that this old tank will see.
The 1" vent to the dessicant trap doesn't sound right to me unless you have a very small tank .....what are your dimensions and capacity ? How fast can the tank be filled ?
I agree with the commnents above regarding the prefernce for a nitrogen blanket..... especially if you already have a system in place for other tanks.
A suggestion: I believe you should carefully look at the top-centerline of acid tank nozzles where there has been much flow over the years ( inlets, outlets) at the 12 o'clock position there may be hydrogen grooving damage. we have found this on tanks in the past.
Good luck and send us any pictures available of the project...
regards..
-MJC
RE: Sulfuric Acid Tank Overflow Liquid Trap
RE: Sulfuric Acid Tank Overflow Liquid Trap
That puts you back to the conservation vent. There are various resins available so picking one for sulfuric acid vapors compatibility is not too tough. The vacuum vent acts as a failsafe and will keep you from damaging the tank if the N2 system is down and someone pulls fluid from the tank.
RE: Sulfuric Acid Tank Overflow Liquid Trap
Good luck,
Latexman
RE: Sulfuric Acid Tank Overflow Liquid Trap
RE: Sulfuric Acid Tank Overflow Liquid Trap
RE: Sulfuric Acid Tank Overflow Liquid Trap
Could you replace the CS gooseneck material with something that is widely corrosion resistant (some kind of lined steel or maybe something like tantalum) and then use 98% H2SO4 to fill the trap? Obviously that removes chem compatibility issues.. and if the overflow pipe material is corrosion resistant, then it wouldn't matter if the acid slowly becomes more dilute. Just a thought
RE: Sulfuric Acid Tank Overflow Liquid Trap
although this might work out for small and temporary installs, by mixing metals, you now introduce galvanic issues (that can be worked around, but takes it's own maintenance), and part of the problem is avoiding both volatility of sulfuric acid, and avoiding stratification by absorption of atmospheric water vapor (leading to dilution and stratification, which aggravate corrosion). The economics of tantalum is a challenge on larger scale installs. The best piping system would be PVDF (Kynar), which is becoming cost competitive on larger scales.