There are several benefits of using sulfuric acid in water treatment, including environmental benefits. By treating and purifying water using sulfuric acid solutions, industries can ensure the safe disposal of wastewater and the reduction of environmental pollution. In an era where water scarcity is a significant concern and water pollution is ever-increasing, it is essential to ensure effective water treatment processes are in place to maintain public health and safety

Impact of low sulphuric acid availability

Most plants specify 93% sulphuric acid for the treatment. Approximately 1,600 to 1,900 gallons of acid are used daily by a typical factory that serves 140,000 people. The most widely utilized piping materials for injecting and transporting acid are polyvinylidene fluoride (PVDF) and carbon steel.

PVDF thermoplastic pipe, which has outstanding chemical resistance to the majority of acids, is commonly utilized since carbon steel has several disadvantages, such as maintenance requirements, which make it less appealing to plant owners. Typically, it is offered as a double-contained or single-wall piping system.

Over the past several years, many water treatment plants in the southeastern and midwestern United States have faced troubles with existing piping systems that used sulphuric acid as a chemical dosing method. Reduced availability of low concentration acid (93%) has resulted in pipeline damage, leaks, joint failures, chemical spills, and downtime.

Thermoplastic materials have been used by piping manufacturers in response, although applications of sulfuric acid will eventually cause stress cracks in these pipes. Using AGRU’s Halar® piping systems, which are more resistant to sulfuric acids than other plastics, is one way to address this issue.

Polymers can withstand sulfuric acid

Care must be taken when choosing materials for diffusers or injectors that can withstand sulfuric acid across during dilution process.

PVC

PVC is a good low cost material that can chemically withstand all concentrations of sulfuric acid. PVC has relatively low temperature resistance (a maximum working temperature of 140 ºF), and should not be used for the diffuser components such as the injector or quill that are near the dilution or diffusion of the acid, as the heat of reaction can damage the pipe.

CPVC

CPVC is a good low cost material that can also withstand all concentrations of sulfuric acid. With a maximum service temperature of 200 ºF, CPVC can withstand some heat of dilution, for injectors or diffusers that are adding small amounts of acid.

Kynar (polyvinylediene fluoride)

Has excellent resistance for all acid concentrations up to 93%. With a higher working temperature of up to 225 ºF, it can make an excellent choice for many dilution or chemical diffusion projects. It is not recommended for 98% sulfuric acid as it will exhibit some degradation over time.

PTFE/ Teflon

The only material that can withstand all concentrations of sulfuric acid at the temperatures that can be created during the dilution of sulfuric acid is PTFE (Teflon) or other fluoropolymers such as PFA. The best piping material is a Teflon lined steel piping system which has a maximum working temperature of about 350°F.

This material is expensive, and may not be needed in many cases. Additionally, the lengths of pipe cannot be made too long, and there may be many flanged piping connections. Inyo Process can supply Teflon quills can be supplied in a variety of styles, including all Teflon and Teflon lined Hastelloy or FRP wrapped Teflon for added stiffness.

CTFE/ Halar

Can be used for sulfuric acid. Has a lower maximum temperature (approximately 250°F) than teflon, and is typically more expensive, with limited shapes and pipe fitting available. Can be welded, however it will discolor to a brown or yellow when used with concentrated sulfuric acid.

Epoxy Resin Fiberglass

Epoxy Resin Fiberglass has good resistance to sulfuric acid. As an example, Hetron 922, which is often used in potable water systems is resistance to 70% sulfuric acid up to about 180 ºF. Like many polymers, care must be taken to ensure that concentrated acid is not spilled on the fiberglass in the piping, as the spot temperatures will degrade the epoxy and cause failure.

Metals that can withstand sulfuric acid

Carbon Steel

Concentrated sulfuric acid pipes frequently use carbon steel. Since it will rapidly deteriorate in the presence of acid and water, it is not advised or thoroughly discussed .

Stainless Steel

There is some resistance of stainless steel to sulfuric acid. 316L S.S. is frequently and successfully used as pipe material surrounding the quill (don’t use stainless steel for the quill).

It is outside the purview of this website to choose the right kind of stainless steel or to forecast the resistance or lifespan of stainless steel material. Only two alloys—Alloy 20 and Hastelloy C-276—will be covered.

Alloy 20

One of the so-called “Super” stainless steels, Alloy 20 (20Cb-3), was created to have the highest resistance to acid attack. Its overall resistance to chloride stress corrosion cracking and general pitting attack is attributed to the presence of nickel, chromium, molybdenum, and copper. Columbium stabilizes the alloy to reduce the amount of carbide precipitation that occurs during welding.

It is quite easy to construct and has high mechanical qualities. If concentrated sulfuric acid is allowed to react with water and reach high temperatures of about 150ºF, corrosion can occur on an Alloy 20 quill. This is especially true if the concentration even momentarily reaches the 30-80% zone, which is easily accomplished. Compared to teflon, lengthier quills may be supplied because of the metal substance without bending or breaking.

Hastelloy C-276

Hastelloy C-276 is a good choice for nearly all concentrations of sulfuric acid as long as temperatures are managed. At higher temperatures, corrosion rates will likely be unacceptable. Corrosion can occur on a Hastelloy quill if concentrated sulfuric acid is allowed to react with the water and reach the high temperatures of approximately 150ºF, particularly if the concentration even temporarily reaches the 30-80% region, which can easily occur

Tantalum, platinum, gold & zirconium

Tantalum, platinum, gold & zirconium have good resistance to sulfuric acid. They will not be discussed in detail, as these exotic metals are typically cost prohibitive for all but the most demanding high temperature applications.

Ceramics

There are a number of ceramics and glass that also exhibit good resistance to sulfuric acid particularly at elevated temperatures. They too will not be discussed in detail, as there are few components that are commercially available for chemical diffusion.

Conclusion

It is crucial to take into account a material that offers minimal upkeep and, more crucially, chemical resistance to all grades of sulfuric acid in water treatment, that could be utilized throughout a facility’s lifespan.

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