Materials Removal Facility Project
The system has performed as good if not better than expected. Employee training was critical in the recognition and handling of hazardous materials, types of recyclable corrugated to remove, and other burnable and non-burnable materials to extract during the initial pick. Bale tying and forklift training were also important as well as bale handling, stacking, and load-out procedures.
A representative from the selected market for the corrugated material arranged a visit to their plant for the MRF employees to familiarize them with their processing operations and the type and quality of material that can be accepted.
After startup the corrugated buyer visited the MRF to confirm what materials and quality were being selected. Since that time the buyer has been most pleased with the amount and quality of material shipped.
Initial Pick Up Station
The learning process for the initial pick station soon indicated that many items other than corrugated and non-burnable should be removed at that point and delivered directly to the WTE plant.
Some of these are baler twine, long pieces of film plastic, rope, etc. that caused operational problems passing through the MRF. If anything this initial pick platform could be expanded to remove other recyclable and problem items.
The trommel has operated successfully meeting bag opening and sizing functions almost as expected. Bag opening efficiency ranges above 85% meaning that some unopened bags pass through the system. These are usually very light containing mostly burnable materials.
There are some unburnable materials that remain in the unopened bags that end up being processed through the WTE plant, and eventually are disposed of in the landfill. So far these have not presented near the operational problems that existed when burning unprocessed MSW.
Design changes to the trommel teeth have improved the bag opening efficiency, and the trommel hole size selected for the small component (fines) was determined to be too large resulting in lost aluminum recyclables and fines tonnages greater than projected. However stack tests showed significant reduction in heavy metals emissions one of which, mercury, is a controlled substance.
Reducing the hole size might jeopardize this positive result, but would definitely reduce the amount of fines generated and lost aluminum recyclables. The decision was made to reduce the opening by covering up half of the three-inch diameter hole. Records will show that the fines tonnage was reduced by almost half and the heavy metals emission rates were virtually unaffected.
Magnetic separation is effective in removing almost all ferrous materials. However, many contaminants are also removed in the process requiring manual removal to satisfy market requirements. Attempts to improve this have had minimal results.
Recently another baler was purchased and set up with conveyors positioned under the magnets to accumulate and convey the ferrous products to the baler. A pick station is utilized to remove the contaminants.
Eddy current separation for removal of aluminum is excellent. It is estimated that almost 90% of all aluminum is removed in this station. This is important because aluminum is a very attractive financial market that produces high revenues.
The aluminum market expects minimal contamination and therefore the material is also hand picked prior to baling.
Final Pick Up Station
The final pick station platform is designed to capture materials that escape the initial pick and the mechanical separation process. It also has the capability to focus on the removal of other recyclables such as plastic, which is exposed after passing through the trommel.
The plastic market has been unattractive since startup, and Polk chooses to burn this high BTU material for steam production and sales. If the plastic market did develop and MSW tonnages continue to increase, the MRF has the capability to remove this material for revenues while maintaining plant throughput.
The final pick is only used periodically and to date cannot justify an added employee.