pH control with 50% H2SO4 - Pump/Piping/Setup 1

[TiCl4]

We have a new application that requires gross pH control (6.0-9.0 pH on product specification). We will be installing a 17,500 gal processing tank (Derakane 411) that will receiving waste acrylic polymer (<2% solids) and recovering it via ultrafiltration.

The waste stream is collected from wash-downs in the plant from all areas, and sometimes goes high in pH due to caustic spills/leaks or other issues (yes, I'm working to mitigate the effect from this). pH can also naturally be high from the amount of aqueous ammonia used in production or from the naturally higher (9-10) pH of some of our products.

I've chosen sulfuric acid for neutralization based on mostly on its relatively low cost. Based on data from a previous pilot run, small flows will be intermittently needed (1-2 gpm) for short periods of time. Additionally, the installation is expected to move in the next year due to a building relocation. My plan is as follows:

I plan to buy 50% sulfuric in IBCs and use those IBCs as the storage "tank" for the pH control. This is chosen to avoid having personnel handle the transfer of sulfuric from drums/IBCs to another storage tank. The sulfuric will be stored in a semi-climate controlled area - expect ambient temperatures to go from 40 F to 100 F. I plan to draw from the top of the IBC using an all plastic, air-driven diaphragm pump with air supply regulated to 20 psig. The pump will be mounted at a height greater than the IBC height. The air-exhaust will be fitted with a shroud that will, in the event of diaphragm failure, collect spraying acid. This shroud will be gravity returned to the IBC to avoid spills. The discharge piping material will be 1" Hastelloy C276, schd 80, with C276 stub-ends and CS 150# lap-joint flanges. The suction piping will be the same, but tubing will be used to draw the material from the tote (the pump is 1/4" inlet/outlet). I had planned to use PTFE tubing, but I think I remember from past experience that it doesn't have very good bite with ferrule connections. Any suggestions there? I had planned to use the flexible tubing to avoid having to break/remove piping every time an IBC is changed out.

I have also looked at various plastic pipes for chemical resistance (PVC-U, i.e. Trovidur), but my experience with this site is that plastic pipe will get broken or will leak at some point. C276 appears to be adequate based on the information provided by Haynes (link below), and I prefer the mechanical strength advantage, especially in pulsating service with a diaphragm pump.

Any thoughts/feedback on that plan? Any and all suggestions will be most welcome!

https://www.parrinst.com/wp-content/uploads/downloads/2011/07/Parr_Hastelloy-Corrosion-Info.pdf

 

[EdStainless]

Even though I am a metals guy I would seriously look at using FRP for these lines.
If you do them in metal there is no real reason for 276.
Alloys such as 20, 904L, AL-6XN, and even 825 all have very similar corrosion rates near ambient temp in pure 50% sulfuric.

Any particular reason that you aren't using 25% acid? The high alloy SS grades will last nearly forever at this concentration.

CPVC or PVDF should work fine at 50% also.
You could look at a lined plastic tubing.

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P.E. Metallurgy, Plymouth Tube

 

[TiCl4]

EdStainless - thank you for the quick reply!

I shied away from FRP due to two concerns. The first is that I have no idea how well FRP would handle the vibration/pressure waves from the diaphragm pump - my only experience with FRP is in flue gas scrubbing systems and HCl piping with centrifugal pumps - not a high vibration environment. I know we could put pulsation dampeners on the pumps, but I've never seen an FRP pulsation dampener. The other concern is that we do not have anyone on-site who can work with FRP (our facility is a medium-small facility, ~120 people), so if something happens, we cannot repair it without calling an outside contractor. We have an experienced welder who can work with most metal types for repairs.

If going FRP, what kind of FRP are we talking? I don't know too much about it.

I chose 50% sulfuric simply because we already buy that as a raw material in IBCs. Going to 25% will double the required flow rate of the neutralizing acid, but the pump can go up to 5 gpm, so I don't see any issues with that. It will also double the changing of IBCs, but again, not a big issue. We do not have any piping codes that address 904L. I can dig through the codes, but do you know off-hand what material class it falls under in ASME B16.5 and what ASTM standards address the piping? If not, I'll go dig it up.

Another question - I'm not settled on sulfuric as a neutralizing agent. I chose it because of its cost advantage over other acids, but I do not want to install something that is a higher hazard/risk/headache just to save a couple of bucks (the cost impact of going to another acid would be relatively minor). HCl would be not much better, I think, because of its vapor pressure causing nuisance vapors from the IBC. The same goes for acetic acid. Any suggestions for another means of neutralization?

I understand sulfuric acid is widely used for neutralization, and I'm looking for guidance for best practices for piping/handling it in small volumes/flow rates (2-4 gpm), or for another method for safe (and relatively cheap) neutralization.

 

[EdStainless]

As you know there are a number of resin systems that are very resistant to Sulfuric, the novalac vinyl ester epoxies are the first that come to mind. This resin is just used in the liner, with the structural bulk of the pipe made from less expensive resin. I would think that you would have spool sections with flanges custom fabricated so that they are easy to assemble on site.

Alloy 20 is really the workhorse Sulfuric alloy. The specs are: Pipe and Tube; ASTM B729, ASTM B829, ASTM B468, ASTM B751, ASTM B464, ASTM B775, ASTM B474. B464 and B468 are the most common for welded pipe and tube.
The nice thing about 25% is that there are many high alloy SS grades that work well in the as-welded condition in this service.
I can't think of anything that I would rather use, nitric being the only other real option and the list of alloys is about the same.

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P.E. Metallurgy, Plymouth Tube

 

[Iomcube]

If availability isn't the issue I would recommend using HCl rather than H2SO4 for gross pH control. From a safety point of view 35% HCL far better than 50% H2SO4

 

[EdStainless]

If you want to go HCl the system will be 100% non-metallic that is for sure.
I would look into 20-25% Sulfuric.

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P.E. Metallurgy, Plymouth Tube

 

[TiCl4]

Thank you all for your recommendations and insight! This thread can be considered closed.