Chances are the pork sausage on your breakfast plate came from the grocery store frozen. And if it’s one of the big-name brands, chances are equally good that it was not processed by the company whose name is on the package but by a “co-packer” — a company that specializes in that particular product.
One of the larger co-packers in the Midwest produces tons of frozen pork sausage every day in a continuous process that includes blending the meat and spices, stuffing the casings or forming the patties, cooking the sausages, and finally freezing the ready-to-eat product. That final critical step is accomplished in a sophisticated waterfall pouch chiller using a food-grade propylene glycol/water mixture at -5 °F (-21 °C).
Because the glycol/water mixture can come into physical contact with the product, and because nothing is perfect—including packaging—the chiller is equipped with bottom-mounted screens to catch any bits of sausage or packaging materials that may get into the liquid and keep them out of the heat exchangers. This function is critical to the process because the glycol/water mixture must be maintained within a narrow temperature range to meet strict food safety regulations.
If the screens get clogged, the flow of glycol/water through the heat exchangers is reduced, and the temperature in the processing area rises. If the temperature exceeds food safety guidelines, then the entire batch of sausage and the potentially contaminated glycol/water mixture would have to be entirely discarded or “reworked” if the damage was minor.
“That happened two or three times a year on average,” explained Jeff Simpson, a Fluid Process and Industrial Wastewater Engineer at Crane Engineering in Kimberly, Wisconsin. “The cost of replacing the process fluid alone was about $20,000 per incident.”
Over and above that, maintenance costs were running in the $40,000 to $60,000 range per year, and they still weren’t preventing the over-temperature incidents.
“The customer was walking a fine line between the cost of labor and downtime to clean the screens and sumps and the cost of lost production while the chiller was out of operation while they were being cleaned. They needed a better solution, so they invited us to their facility to review the process and make a recommendation.”
While the situation called for a more effective filtration system, handling the 1,000 GPM (227 m³/h) flow of glycol/water through the system presented an unusual challenge. That challenge was made even more difficult by the user’s request for a solution that did not require the system to be shut down for filter maintenance.
The standard alternatives were either a multi-filter system with enough capacity to handle the flow while one of the filters was off-line for maintenance — or a self-cleaning filter. While the self-cleaning filter offered significant cost benefits, the volume of glycol/water that had to be filtered was greater than the capacity of then-available standard models.
“We decided to pursue the self-cleaning alternative,” Simpson continued, “and to prove the concept, we installed an Eaton DCF-800 self-cleaning filter on a side stream. That particular filter is rated for 60 GPM (13.5 m³/h), and in several months of operation at maximum flow, it never clogged or required any maintenance.”
The DCF filter consists of a cylindrical stainless-steel housing that holds a filter element. Fluid enters inside the element and flows through it to the outlet, depositing any contaminants on the inside wall of the element.
A spring-loaded cleaning disc moves up and down, wiping the filter element clean and depositing the contaminants at the bottom of the housing, out of the flow path. This configuration prevents a re-suspension. Standard cleaning frequency can be based on time, differential pressure, manual selection, or any other application-specific criteria. Because it remains in service while being cleaned, the DCF filter satisfied the customer’s no-maintenance-downtime requirement.
“With the concept proven, the next hurdle was finding a self-cleaning filter with enough capacity to handle the full 1,000 GPM (227 m³/h) flow of glycol/water in the system,” Simpson said.
Crane was able to procure one of the first of the new Eaton DCF-3000 filters produced and installed it in the co-packer’s chiller circuit. All components in contact with the product are made of stainless steel and the filter is rated at 1,100 GPM (250 m³/h) while filtering up to 100 microns. It stands a little over 8-ft (2.40 meters) tall and weighs approximately 720 lbs (325 kilograms) when fully flooded. It can be equipped with slotted wire strainer elements ranging from 50 to 1,140 microns to meet a broad range of application requirements.
The unit installed on the co-packer’s chiller uses a 75-micron strainer to provide minimum flow restriction. The output is then routed through an Eaton FLOWLINE stainless-steel bag filter housing with a ten-micron needle-felt bag filter for the final cleaning before entering the heat exchanger. DW