Acid Sparge And Acid Sparging. When you want to introduce acid directly into a liquid below its surface a sparge pipe is used. It is necessary to select materials that are compatible with the chemicals and the process. This article explains the issues to address when selecting the sparge pipe materials for injecting acid into a process reactor and what to consider when designing and installing the sparge pipe into such vessels or tanks.
Keywords: acid sparge pipe, acid sparging, chemical injection, chemical dosing, acid dosing.
Situation:
If it is necessary to dose strong acid into a reactor or vessel containing a liquid it ought to be done in a way that limits the reaction intensity. Some acids when contacting water release a great deal of energy as heat and steam. In such situations it is best to inject the acid under the liquid surface. This reduces the violence of the reaction and less acid carry-over occurs in the vapours venting from the vessel.
Materials of Construction:
Depending on the acid involved high alloy steel sparges are suitable. You may find that the internal of the pipe is eroded/corroded away in the region of the interface level where the acid mets the tank contents.
When a high alloy sparge does not last long enough one other option is to install a fully Teflon-lined pipe. The lining is both inside and out, right over the top and underneath the fixing flange, fully containing the metal pipe core. The core of the sparge should be of a metal where if the Teflon sheath is holed, and product made contact with the metal, the corrosion rate would be slow and the sparge would still deliver a reasonable operating life.
Installation:
The sparge pipe can be installed through the top of the reactor vessel, mounted on it’s own flange. It can also be installed through the wall of the vessel. The hole in the mounting flange should be made substantially larger than the lined sparge to insure the Teflon is not damaged by forcing the sparge through a tight hole during installation.
To prevent a vacuum forming in the sparge during during vessel pump-out a vacuum breaker is fitted.
To reduce the likelihood of blocking the inside of the sparge from product, a compressed air injection point, with isolation and non-return valves, is also installed in the acid line just above the sparge pipe.
Within the reactor the sparge pipe is located in-place in the vapour space just above maximum fill height. Three braces, two from the roof and one from the wall, arr attached to a lined pipe reducer. This prevented the sparge swinging about from the violence of the reaction and the agitation caused by a mixer. The reducer was rubber lined to prevent it cutting into the Teflon liner and exposing the pipe inside. A sketch of the sparge locating collar is shown below.
With the right installation, design and material selection you should have a long-term success.
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