handling H2SO4 1

[ww2]

Dear specialist
I have been honoured with the commissioning task of a H2SO4 injection to a cooling tower system. It consist of a peristaltic pump taking suction on a 10000l H2SO4 drum and a, about 500m 1 ½” stainless line, ending in the cooling tower base. The transport line has low point drains. The line has been hydraulically tested months ago and maybe most of the water has been removed. The suggestions made are to start with a mock operation and run it on water. I am not so positive to this suggestion and more concerned about the removal of the water. Can someone out there give me some advice?
koekoek

 

[abcmex]

1) It would be advisable to have drains on the low points. Someday you may get the honor to decommission the line and it will be much more complicated to purge the sulfuric acid than the water.
2) It may be better to get the water out of the pipe. It may react with the acid. You may use the purges (see 1) and later dry air.
3) I hope your acid is concentrated enough to avoid corrosion in your stainless pipe.
4) Be sure that the backflow (water into the acid line) is not possible.
RGS

 

[cub3bead]

My experience with H2SO4 and stainless steel pipe has not been stellar and not very successful. I hope that it what you have installed is schedule 80 and that it is all welded. If you have any threaded connections they will be the first point of failure. Threads take about 0.065” off the pipe wall thickness.

Low point drains are nice but you need to consider the safety and environmental risks associated with them. You also need to consider the type of valve used. My preference is for TFE lined plug valves; positive shut off and superior corrosion resistance.

The water has to come out of the line before you introduce the acid. The dilution of H2SO4 with water releases a tremendous amount of heat and the resulting dilute acid accelerates corrosion of the pipe. You can attempt to purge it with dry air (-40°F) until the exiting dew point reaches the entering dew point but be prepared for this to take a while. The fastest way I have found to purge acid lines is to first pass dry steam through the line until the line is above the boiling point of water and then start the dry air purge to cool the line. Leave the line pressurized until you are ready to pack the line with acid.

Are you diluting the acid at the tower before you put in the basin? Concentrated H2SO4 has a sp.gr. of 1.84 so it will sink to the bottom of the tower basin and can attack the concrete floor of the basin before it mixes with the recirculating cooling water.

Abcmex is right about preventing water from backing into the acid delivery pipe.

You mentioned that you are using a peristaltic pump for this installation. What type of hose is used? If you have flooded pump suction and the hose cracks you could have a major acid spill to deal with when the acid drains out of your storage tank.

 

[ww2]

Thank you guys for your advice.
About the piping material I wrongly used stainless steel as a common name for alloy steels. In fact the material used is Hastelloy ASTM BE22, UNS N10665. Hope you'll agree on this quality.
Steaming the line before drying with instrument air seems to be a good idea but in this case it will cause the line to expand about 1m.
The remark on the flooded pump is most useful the storage drum to the pump suction is pressurized up to two barg. I’ll have to think of something
again tanks a lot

 

[Fzob]

A suggestion to dry the line.

Alternate between pulling a vacuum and then pressuring with dry N2. Do this about three times and then start checking the dew point of the N2 exiting the pipe.

The lower the vacuum you can pull, the better and quicker the line will dry out.

 

[ww2]

Thank you Fzob, I will take this in consideration. I ‘m not aware of a contractor having the necessary tools to supply the service of pulling a vacuum. But I’ ve never asked.

 

[jherbert]

hi,

every refrigeration contractor in your area
'should' have a vacuum pump on his truck/van.

good luck