Plants can reduce the waste of expensive hygienic manufacturing materials by using equipment that offers powerful product-recovery capabilities.
by Paul Cardon
October 25, 2017

Eccentric disc pumps can operate with such high efficiency that they can pump air when no fluid is present, which creates a vacuum effect on the suction side and a compressor effect on the discharge side of the pump. Once the product runs out in the feed tank, the eccentric disc technology continues to pump air in a very constant, non-abrupt, non-pulsating manner, so that the surface tension on any remaining fluid is not broken. This produces a plug effect, which pushes out the product “plug” as a whole.

eccentric disc pumpsImage 3. Eccentric disc pumps are so efficient and versatile that they are able to pump air even when no fluid is present, which enables them to completely and safely clear both suction and discharge lines during hygienic-pumping processes.

Because eccentric disc pumps transition to the purging process by using the air that is already in the feed tank, product purity is rarely an issue. In certain applications, the operator purifies the air or gas blanketing the product to protect purity. This method of product recovery is much safer and cleaner than pigging or a basic air/gas-blowing process. It also eliminates the risks and costs associated with sourcing air or gas compressors or high-pressure bottles.

The typical amount of product recovered with an eccentric disc pump is more than 95 percent on the suction side of the pump and typically 60 to 80 percent or more on the discharge side. There are additional benefits of using eccentric disc pumps in product-recovery applications, including:

  • The pumps can recover product from tank bottoms as well as inlet and outlet lines.
  • They can recover product from small lines where pigging is not possible.
  • They can recover product through a line outfitted with ordinary valves, heat exchangers, magnetic traps, flow meters and other accessories.
  • Product recovery is seamless, as no line interruptions will occur between normal production and the product-recovery phase.
  • For the majority of the process, air mixing is not a concern, as most of the product recovered by an eccentric disc pump comes in the form of a product plug with no air mixed in. A simple flow switch can be used to shut down the pump before the air purge reaches the product’s destination.

Limitations of Other Pump Types

Compared to eccentric disc pumps, twin screw, lobe and ECP pumps lack line-cleaning capabilities, and manufacturers often have to use them in conjunction with pigging systems that use a projectile to push out the residual product. While well-installed pigging systems deliver the highest recovery rates, they can only be used in lines that are built without the interruptions of ancillary components, such as heat exchangers, valves, filters and flow meters. Operators must also take great care to ensure that purified compressed gas or air is used to push the pig, which can prove a challenge for maintaining product purity.

Twin screw, lobe and ECP pumps also wear constantly, which increases their internal clearances over time, resulting in product slip that reduces flow capacity and volumetric efficiency as operating pressures and fluid viscosities change.

These pump types are also designed with two shafts that have to be sealed, which doubles the number of areas where leaks can occur. Twin screw, lobe and ECP pumps are also not dry self-priming and can run dry for only a short period of time unless they have flushed double-mechanical seals. These pumps will also experience diminished performance when handling low-viscosity materials.

The Direct Route to Savings

The use of eccentric disc pumps as a cost-saving measure is a breath of fresh air for managers and engineers at hygienic plants, who may have run into a cost-reduction wall. Many operators have pursued pump efficiency for cost savings, but there is very little room to improve motor efficiency with today’s designs.

eccentric disc pumpsImage 4. Eccentric disc pumps

Installing a higher efficiency positive displacement pump might yield electricity cost savings of only $200.

Savings of $32,000 a year on product recovery, as suggested in the example system, does a lot more to move the needle. In the model cost scenarios discussed here—$200 for the pump energy savings and $32,000 for the product recovery savings—the savings is 160 times higher with product recovery. Put another way, the product-recovery savings accumulated in one year with this example will pay for 32 years of energy to operate the pump.

Example System

  • Product per foot (2.5-inch line diameter): 0.23 gallons
  • Weight per gallon: 8.3 pounds
  • Discharge distance: 100 feet
  • Total weight: 191 pounds
  • Product recovered at 70% rate: 134 pounds
  • Price per pound: $1.00
  • Cost savings/day: $134
  • Cost savings per week
    (5 days): $670
  • Cost savings per month
    (4 weeks): $2,680
  • Cost savings per year
    (12 months): $32,160

Conclusion

Lobe, ECP and twin screw pumps are popular, but their lack of line-clearing capabilities means optimized product recovery will never be realized.

Eccentric disc pumps deliver high utilization (or yield) of high-value products and ingredients that would otherwise remain in suction or discharge process lines during changeovers or at the end of production runs. This substantially eliminates waste with a corresponding—and significant—increase in profits.

To read other Efficiency Matters articles, go here.

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