low flow acid feeding system

[sweetfood]

I need to pump in less than 0.5 gpm of sulfuric acid to high pressure system which runs around 170 psi. Looking into using a small low flow high pressure metering pump. Looking into using a small low flow high pressure metering pump. It needs good accuracy. I handled quite bit of hazardous chemical but not this small flow rate. Has anyone had to design this type of system? I need some inputs.

 

[bimr]

You should think about using a sidestream to inject the acid.

Make sure you utilize a 3 valve block and bleed so that water is not forced back into your acid tank.

You may consider diluting the acid stream so that you can pump a larger volume to improve accuracy.

 

[moltenmetal]

This is a good applicaton for a small, seal-less hydraulic double diaphragm pump such as those made by American Lewa, Pulsafeeder, ProMinent etc. 1/2 gpm is a fair bit of flow, so this won't be a small pump. 170 psig is a bit too high for the all-plastic direct driven diaphragm pumps, so you're probably looking at either stainless steel or alloy 20 (presuming this is concentrated sulphuric acid). Corrosion resistance of both these materials to clean, non-diluted room temperature acid is quite good.

Are you pumping from a tank, a tote or a drum? Suction-side details differ depending on where you're drawing from. The pump vendors can provide advice but you do need to adjust to your particular circumstances using your own commonsense.

Anywhere you could potentially get dilution due to suck-back during shut-downs or loss of pump prime etc., you're going to have a corrosion problem. Remember- water WILL "climb" the injection point right up to your injection check valve, and this dilution will make heat and extremely corrosive dilute acid. Your injection point should either be above liquid level (if injecting into a vessel) or made of suitable non-metallic or non-metallic lined components to handle the diluted acid and the heat of dilution.

 

[sweetfood]

Thanks for all of your inputs. It is a strong acid at 93% concentration and it is in its main storage tank. I was actually looking at Hydro-cell double diaphragm metering pump to do this, but that didn't get many people excited for some reason. Diaphragm pump gets a bad name. It is going to side stream which runs at high pressure and location was decided based on the chemical reaction the operation wants to achieve. I start thinking about using mag drive gear pump with VFD and add a flow meter to control its flow. I am not sure if we can get the accuracy we need by doing this though....

 

[moltenmetal]

I would a million times prefer a diaphragm metering pump to a gear pump for this application. Not only do you get better positive displacement behavior out of them, they last longer too. Although sulphuric acid is relatively viscous, it is not a particularly good lubricant...depending on the gear pump gear and wear plate materials you could be looking at wear/corrosion leading to frequent maintenance. At 1/2 gpm it might be OK- at lower flows than that, gear pumps are garbage unless you're pumping oil.

Why do the diaphragm pumps get a bad name? They're not very mechanically efficient, but they do work for long periods without maintenance. The flow is pulsile but you can get dual or triple heads or use pulse dampeners with good success. We use them in far more severe services than this. Haven't used Hydracell much, but we have used them on occasion without problem. American Lewa, Pulsafeeder, Bran + Luebbe, ProMinent Orlita etc. we've used very frequently with very good success.

 

[sweetfood]

Pulsation was one of reasons that some people didn't want to go with diaphragm pump. How much of pulsation does dual head pump generate? Is it noticeable enough that pulsation dumper is required? I like the idea of metering pump if I can convince people.