Need to datalog Hydrochloric Acid Fumes pressure? 2

[Blazer406]

I need to be able to datalog the pressure in the top of a 6500 gal 37% HCL tank to see what the pressure does as the tank is being loaded by a tanker truck.

We used some labview items back in college, but that has been years ago.

The pressure transducer needs to be capable of corrosive fumes and be very low pressure and accurate.... 0" - 20" water column.... or close.

The more simple and cost effective the better.

It would be nice to go outfit this sensor in the field and hook into a laptop and log it during the loading cycle....

 

[cloa]

This is not Mechanical Engineering- you want the Chemical process engineeering forum.

 

[Blazer406]

I'll try over there.... but I am a ME and we dip our toes into many corners of engineering..... so I respectfully disagree..... datalogging pressure transducers is ME stuff to me.

 

[SnTMan]

Blazer406, possibly you are not familiar with Omega Engineering:

http://www.omega.com/

Regards,

Mike

 

[Blazer406]

Yes, I used to have one of their big catalogs......there is so much stuff on there....it is mid boggling on what I actually need. I was hoping someone that is current on what is actally commercially available... recommend a particular sensor and the hardware to interface with it and a PC.... I want to get a popular model that is reasonably priced if that makes sense.

I am perfectly capable of choosing a sensor that will work and a datalogger that will work.... but because of my lack of up-to-date experience with this.... I'm subject to spending 4x what I need to to get the job done and buy some system that nobody ever buys because the software sux.....

I'm just gun shy about purchasing the wrong thing....

Thanks for the suggestion.

 

[SnTMan]

Well I know it's a wild idea, but maybe you could call them

Regards,

Mike

 

[Blazer406]

I am looking at:

Datalogger - a Dataq Instruments EL-USB-4 USB single channel 4-20 mA current loop data logger. $75.25
stores up to 32,000 readings. Can log at 1 per sec or up to 1 per 12hrs.... once you configure it and start it... you just let it collect unti you are through and plug it back into the laptop to retrieve the data..... comes with software.

Sensor - a Setra model 201 very low differential gauge pressure transducer in a 0-50" WC range. It is specifically for corrosive gasses or liquids. I don't hvae a clue how much this is?? $$

What I am not sure is the wiring of the setup. It appears I will need some source of regulated power.... looks like 24VDC.....and a very short piece of cable.... not sure if I need a shielded cable or not...

 

[moltenmetal]

In future, please red-flag your double posts to avoid wasting people's time.

"Designed for corrosive gases or liquids", in cheap pressure transmitter lingo means, "can be used with something other than dry air, because it actually has an isolating diaphragm between the measurement sensor and the process connection". The cheaper ones don't- they have a $10 piezoresistive sensor without an isolating diaphragm, sometimes merely siliconed to the process connection.

The Setra sensor you're looking at is made of stainless steel, with a stainless isolating diaphragm- neither of which have a hope of resisting wet HCl.

My suggestion: put down the Omega catalog. You need to speak to Rosemount, Endress + Hauser, Yokogawa, ABB etc. for a proper, industrial pressure transmitter in materials of construction which will have a hope in hell of surviving long term. These are large tanks, not a carboy in a lab. You need to do this right.

The added complication will be that you need quite a low pressure range, whereas almost all of the transmitters which are made of materials resistant long term to wet HCl rely on the use of remote diaphragm seals. These seals need to be physically large to make low pressure measurements accurately, as a result of basic physics.

You might get away with a Hastelloy C transmitter without a remote diaphragm seal, depending on how you install it and how hot the transmitter gets in service. Some brands offer tantalum diaphragms which will last a lot longer, but tantalum is not an option for the lower housing. You MIGHT also be able to get away with a PFA or PVDF/viton diaphragm isolator, which will be resistant, although I don't know how stable either of these will be over your 0-20 " wg range over the long term. Both are subject to permeation by HCl vapour.

 

[Blazer406]

Thanks for the info.... I didn't intend to double post.....but it was suggested to post over on the Chemical forum..... which hasn't got much attention anyway.

In my situation, we are only using this very short term.... we are tweaking our fume scrubber design and vent line size. We need to see what internal pressures we are seeing during a load cycle. Then the (pressure measuring system) system will be taken down, cleaned if necessary, and put in the desk drawer.

Sounds crazy, but I have thought about using some clear silicon or tygon tubing and make a manometer..... staked down on a sloped board....say a slope of 1" per foot.... graduated.....put some water in the manometer with a little food coloring.....and set up a video camera (with a time stamp) and watch the manometer during a load cycle.... cheap and effective.....

 

[moltenmetal]

OK, understand your application better- it's a one-off and short term.

Pressures aren't high, so you could implement a manometer if you did it carefully- but I would suggest that you don't use water as the manometer fluid as it will absorb and dissolve HCl vapour, turning rapidly into acid. Mineral oil would probably be safer- it should be nonreactive for a short-term test.

If you have a line pop off, even a tubing line, HCl vapours at 20" wg will be spewing out and causing quite a bit of harm to people who are not properly kitted out in PPE, so you need to make sure that everything you use in that manometer is up to the job. Tygon tubing will be HCl resistant, as will PVC fittings etc., but not some of the other plastics. Take care and keep people safe.

 

[Blazer406]

I believe the pressures are usually less than 10" WC, but at the end of the load as the operator blows down the tank and the last bit of acid leaves the tanker headed toward the storage tank, the large burst of air that enters the HCL storage tank could be driving up the pressure above 10" WC....even with a 6" vent line size.