Best Practices for Energy Management in a Compounding Plant

Editor’s Note: for a recent story in Compounding World magazine, Dean Elliott, ENTEK’s Technical Processing Manager, contributed the following information on ways compounders can save energy in a compounding plant.

ENTEK prescribes to lean manufacturing, and we see three forms of energy waste in compounding that can be avoided with proper planning and procedures.

• Equipment Energy Loss
  • It’s important to spec the overall system correctly for your application. For example, if the extruder or downstream equipment is oversized or undersized, there is a potential for energy inefficiency (waste).
  • Water cooled motors cool more efficiently than air cooled motors – already utilizing internal cooling system, whereas an air-cooled motor relies on an external blower for cooling.
  • Running motors on VFD (variable frequency drive) increases efficiency (not running full speed when not necessary)
  • Efficient cooling system that operates with latent heat of vaporization of water [barrels are internally cooled] blanket each barrel and shroud over blankets to help retain heat in barrel. Each barrel is individually temperature controlled.
• Processing Energy Loss – Most of the energy generated is frictional heat which comes from the motor of the extruder. How do we minimize the use of that energy?
  • Screw design – be sure not to overdesign the layout (screws should not be too aggressive). This is measured by SEI (specific energy input). For example, if a good quality product requires 0.100 (kW.hr)/kg, a screw design that uses 0.13 (kW.hr)/kg is overdesigned by 30% which is a waste of energy.
  • Extruder operation –For example, running your screw speed too high with the screws too empty can increase your SEI unnecessarily like the example above. [measure by torque instead of speed to account for screw fullness]
  • The co-rotating twin-screw extruder is an inefficient pump [roughly 10-15% efficient]. This equates to energy loss in restrictive areas such as mixing zones and at the die. Using the most ideal pumping elements will minimize your SEI/reduce your wasted SE and increase your pump efficiency. When screws and barrels start to wear, the pumping efficiency is reduced. This can force the operator to run at higher screw speeds than necessary, or lower feed rates than desired.
  • Using your HMI to trend processing under Industry 4.0 helps maintain optimal running conditions and rapidly take corrective action against upset conditions.
  • Leaving the extruder powered on and/or the screws turning for long periods of time when not producing, there is wasted energy in the heating of the equipment. It also results in build-up of carbon which unnecessarily extends purging and clean out time and increases screw and barrel wear.
  • Underutilizing equipment – could cause capital equipment expense unnecessarily. Understanding the limiting factors of your process and addressing them sometimes requires a design change on an existing piece of equipment in place of buying a whole new system. For example, less expensive options include: improving your screw design by breaking up short aggressive mixing zones into longer less aggressive zones; improving moisture removal from the process by adding a vacuum stuffer or a larger vacuum pump or vacuum pump filtration system; adding a melt pump as a more efficient pump; increasing the hole diameter on the die and/or using a larger mesh screen size if quality allows.
• Maintenance Energy Loss – Following best practice maintenance protocols can prevent waste in many areas.
  • As mentioned above, wear of screws and barrels. It’s advisable to learn and understand the amount of wear your process can tolerate. Replacing screws and/or barrels prematurely or after needed can lead to waste.
  • Loss of a heater in a zone results in dependence upon frictional heat, which in turn effects your SEI.
  • Cooling system – blocked valves allow water to pass through constantly, which causes more heat to be required than necessary to maintain the setpoint
  • Heat control system – it’s important to maintain a properly tuned heat/cooling system so that heating and cooling can be used efficiently. Large temperature oscillation is wasted energy.