• Publication Date: 06/01/2021
  • Organization(s):
    Sturtevant Inc.
  • Article Type: Case Histories
  • Subjects: Screening and classifying, Size reduction

Case History

Air classifier mill helps Wisconsin cheese and whey producer utilize valuable by-product.

Wisconsin Whey Protein, based in Darlington, WI, is a manufacturer of cheese, whey protein, and lactose products for the food, infant, medical, health, and wellness industries. In 2017, the company expanded its Darlington cheese and whey processing facility and added a new edible lactose plant to make use of the whey permeate the company produces as a by-product of its whey protein concentrate and whey protein isolate production. Whey permeate (also called dairy product solids, deproteinized whey, or modified whey) contains approximately 80 percent lactose and is a primary source of lactose for a variety of industries, including the beverage, confectionary, bakery, dairy, infant formula, and pharmaceutical industries.

Wisconsin Whey Protein’s sister company, Stainless Technologies, was charged with sourcing or fabricating and installing all the processing equipment for the new lactose plant. One of the final processing steps in lactose production is milling the dried lactose powder to achieve the optimal particle size distribution for the product’s intended application. For the milling equipment, Stainless Technologies turned to Sturtevant, a supplier of particle size reduction equipment based in Hanover, MA. Sturtevant has been supplying milling equipment for more than 130 years to a wide range of industries, including aggregates, animal feed, chemicals, cosmetics, fly ash, foods, pharmaceuticals, and pigments.

Stainless Technologies had previously worked with the supplier on another large lactose project for a different cheese company in Wisconsin. After reviewing the various options for fine grinding mills on the market, the company decided that Sturtevant was the best fit for this project as well and purchased one FCM 650 air classifier mill, along with several auxiliary items. The FCM 650 is a midsized, high-speed impact mill with an internal air classifier and features a pressure-­shock-resistant mill chamber and a 75-kilowatt (100-­horsepower) main drive motor.

The FCM 650 is a midsized, high-speed impact mill with an internal air classifier and features a pressure-shock-resistant mill chamber and a 75-kilowatt (100-horsepower) main drive motor. Milling.

“We were looking for a food-grade unit that could easily adapt to different mesh sizes,” said Mark Dachel, general manager of Stainless Technologies. “We decided to work with Sturtevant because we felt their machine met our needs and allowed for flexibility as market demands changed.”

In operation, material enters the mill’s grinding chamber through a feed inlet and is then impacted by a series of spinning pins or blocks, which reduce the material into fine particles. To exit the grinding chamber, fine particles must pass through a classifier, which is a cage of blades spinning like a turbine wheel, that acts as a screen. The classifier wheel only lets particles that are small enough pass through and rejects larger particles, causing them to remain in the grinding chamber for additional size reduction. The fine particles that exit the mill are collected in a baghouse receiver. Mill operators can easily adjust the output’s particle size distribution without needing to shut down the mill by increasing or decreasing the classifier wheel’s speed. Other system parameters also adjust easily, allowing for tight particle size control.

“We specify equipment based on the customer’s capacity and target particle size requests,” said Tomas Johansson, director of Sturtevant’s FCM mills division. “We also take into consideration material characteristics such as hardness and abrasiveness.”

The mill was designed to produce a particle size of 90 percent less than mesh 200 (d90 = 75 microns) at a capacity of 4,000 to 5,000 lb/h and an alternative particle size of 95 percent less than mesh 325 (d95 = 44 microns) at a capacity of 1,400 to 1,800 lb/h.

“Combustibility of the milled material must also be taken into account,” said Johansson. “Our FCM mills are 10-bar (145-psi) pressure safe to contain a possible dust explosion and are ATEX certified. Typically, the product receiver will have a suppression system, but for some applications, the system can instead be inerted with nitrogen to mitigate the combustion risk of very fine ground organic materials.”

The mill receives the lactose powder directly from a dryer via a pneumatic conveying system and baghouse receiver. After milling, the powder is transported to packaging equipment for final packaging in 25-kilogram bags or 900-­kilogram totes.

The mill receives the lactose powder
directly from a dryer via a pneumatic
conveying system and baghouse
receiver. Milling.

Equipment that handles materials intended for human or animal consumption must be regularly washed down and cleaned, which requires a quick-clean design and stainless steel product contact parts. Since the equipment was intended to mill lactose, the supplier designed the mill to meet USDA 3-A sanitary standards for independent washing and sanitizing of product contact parts. The mill features a Type 304 stainless steel rotor and liner and Type 440 stainless steel heat-treated mill blocks.

The mill features a Type 304 stainless steel rotor and liner and Type 440
stainless steel heat-treated mill blocks. Milling.

“To achieve pharmaceutical-­grade lactose, we recommended that a separate parts washing and sanitizing unit be installed near the mill per our drawings,” said Johansson. “The mill’s grinding chamber dome is easy to remove, and with an extra set of product-­contact parts, the dirty set of parts can be cleaned in the washing and sanitizing unit while the clean set is easily installed in the mill, allowing the process to continue after minimal downtime.”

While operators currently handwash the mill components, the company is actively working with the supplier to install a washer and tank system for automated washing.

Stainless Technologies worked directly with Johansson’s team from the initial project planning through commissioning and training. Sturtevant provided engineering services, designed the 3D layout, produced the piping and instrumentation diagram (P&ID), and consulted on the installation of the PLC and human-machine interface controls. The project took approximately a year to complete from initiation to facility startup and commissioning.

“Startup was smooth, and the plant started producing lactose immediately,” said Dachel. “The team from Sturtevant was supportive and instrumental to the project’s success.”


For further reading

Find more information on this topic in articles listed under “Size reduction” in our article archive.

Sturtevant • Hanover, MA
781-829-6501 • www.sturtevantinc.com

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