Mixing Tanks & Systems
There are many choices when it comes to selecting a mixing tank or vessel material. This article will review the parameters typically used in selecting an appropriate tank and a summary of some producer’s recommendations for various materials of construction.
There are two main types of mixing tanks, plastic and metal. Poly mixing tanks include High Density Polyethylene (HDPE), Polypropylene (PP), Polyvinylidene (PVDF) and Teflon (PTFE). Metal tanks are usually 304 Stainless Steel, 316L Stainless Steel, Hastelloy C and other exotic metals. We will be focusing on selecting tanks for sanitary or food grade applications which require approval from the FDA.
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The main parameters considered in mixing tank or vessel selection are contents, corrosion resistance, volume, temperature, location and other conditions. Plastic mixing vessels offer advantages over steel mixing tanks including cost, weight, rapid fabrication time compared to stainless steel and the ability to see liquid level. Metal tanks are more resistant to cracking and temperature effects but they require polishing of the base metal and welds and so the cost to manufacture is typically much higher than plastic tanks. If you need pressure or vacuum rating, then it’s an easy choice for a stainless steel mixing tank. Certain critical heating and cooling applications also would point to a jacketed stainless process vessel. Poly tanks in PP and PVDF are USP VI rated, so they are very common for use in DI and RO ultrapure water systems and biopharma mixing applications such as buffer prep, media prep, chrome slurry agitation, etc.
White Mountain Process www.wmprocess.com offers mixing and blending packages (mixer and tank system) in stainless steel or poly materials.
Polyethylene / Polypropylene / PVDF / PTFE / 316Lss / Hast C – and other materials of construction. FDA + USP VI poly tanks and Industrial/Sanitary/BioPharma metal and stainless mixing vessels.
White Mountain Process is a supplier of stainless and poly mixing tanks and mixing vessels to support the industrial mixers and agitators we specialize. With focus on the biopharm and sanitary mixer users, we offer all stainless sanitary polished tanks, sanitary high viscosity blending equipment and biotech ready tanks and vessels. We also offer FDA and USP VI plastic tanks and plastic tank mixer packages including stainless tank stands.
Typical sanitary mixing vessels include mechanical polish and electropolishing with cGMP documentation packages.
White Mountain Process specializes in custom fabricated sanitary mixing impellers in many configurations. Mixer and tank polishing, passivation, and electropolishing are services offered, as well as agitator impeller repairs and retrofits.
TYPES OF POLY VESSELS AND METAL VESSELS FOR AGITATION
POLY MIXING TANKS
POLYETHYLENE – PE TANK
FDA Resin White Translucent FDA 21 CFR177.1520 Linear PE tanks offer very good chemical resistance and stress-crack resistance. The operating temperature is from 140 F (60 C) down to -94 F (70 C). HDPE has good impact resistance and can be used for sanitary conditions. These tanks are typically used for caustics, metal finishing, plating and brine. Strong oxidizing agents, aromatic hydrocarbons and solvents should be avoided. PE we offer is an FDA approved resin.
Fluorinated PE tanks are often used for ultra pure water storage where ozone is used for sterilization. Cross linked PE is not typical for sanitary use so we generally do not offer that.
POLYPROPYLENE – PP MIXTANK
USP VI Resin White
Non Cytotoxic, USP VI and FDA 21 CFR177.1520
PP tanks offer very good chemical resistance and excellent stress-crack resistance. It’s operating temperature is from 220 F (104 C) down to 32 F (0 C). It only has a fair impact resistance and can be used for sanitary applications. PP mixing tanks are good for many organic chemicals and etching chemicals. Strong oxidizing agents and aromatic or chlorinated hydrocarbons should be avoided.
KYNAR – PVDF PROCESS VESSEL
USP VI Resin
Great corrosion resistance and high temp, very high purity
Non Cytotoxic, USP VI and FDA 21 CFR177.1520
PVDF tanks offer superior resistance to inorganic acids, strong oxidizing agents and halogenated compounds. PVDF tanks also offer excellent resistance to stress-crack but only fair resistance to impacts. It has a temperature operating range of 230 F (110 C) down to -40 F (-40 C)
TEFLON – PTFE BLENDING VESSEL
PTFE tanks offer superior chemical and corrosion resistance. PTFE also has a wide range of temperatures from 260 C down to -270 C. PTFE is an excellent material for sanitary applications as it is inert but also is more costly. PTFE is not as strong as other plastics but can be obtained with fillers to increase its physical strength.
Mixer shaft/impeller are available with USP VI Teflon and ETFE coating.
METAL MIXING TANKS
304SS – STAINLESS STEEL TANK AND MIXER
304 Stainless Steel is used for pharmaceutical and chemical industries due to its high corrosion resistance. 304 SS tanks can be used at wide temperature ranges and have high physical strength but are more costly than most plastic tanks due to the higher material costs and the labor required to grind smooth the surface and especially welds.
316LSS – STAINLESS STEEL VESSEL AND AGITATOR
316L SS alloy has a higher corrosion resistance than 304 SS and has a higher operating temperature range. This material is resistant to strong acids so is used for more aggressive applications such as digesters, tanks and evaporators.
HASTELLOY – GRADE B AND C AGITATED TANK
Hastelloy C is a nickel-chromium-molybdenum-tungsten alloy with superior corrosion resistance and is highly resistant to pitting and cracking. Hastelloy C can be used in a wide variety of applications including corrosive chemicals at elevated temperatures, flue gas scrubbers and nuclear fuel reprocessing. This alloy has a high cost for construction and polishing.
The information above is an overview of different manufacturer’s specifications and guidelines. Specific manufacturer’s will have detailed information on their particular materials of construction and should be consulted to make your final determination for material selection. Please contact wmprocess.com 800-737-9619 for any questions.
GENERAL MIXING TANK OPTIONS
- Open top mixtank
- Dust tight tank with lid, mixer will have sealed transition to vessel
- Portable mixing tank on castors, can be poly or stainless
- Closed tank with sealed agitator, typically a mixer lip seal or mechanical seal – any pressure or vacuum application would be stainless steel or metal tank
- Multishaft / Multimotion agitation
- Sanitary and/or Biopharma ready
- More sophisticated automated blending system