HEIL COMPLETES 270,000 TPY TRASH PROCESSING SYSTEM FOR MONTENAY POWER

BROOKFIELD, WI (JUNE, 1998)…
HEIL ENGINEERED SYTEMS recently completed startup and testing of new processing equipment to handle approximately 270,000 tons per year of municipal trash from the Dade County, Florida (Miami area).  Dade County is a rapidly growing area with garbage (MSW) and trash (primarily yard waste containing additional bulky waste and construction/demolition material) tonnage growing beyond the capacity of the existing 3,000 tpd Miami Dade County Resources Recovery Facility (The Plant).  Additional landfilling of trash in the existing landfill was also considered undesirable.

A private, local Independent Power Producer (IPP) had constructed a solid fuel power plant and needed additional biomass-type fuel to supplement their seasonal consumption of sugar cane bagasse.

The Miami-Dade County Dept. of Solid Waste Management, Montenay International Corp. (operator of The Plant) and the IPP structured a contract to modify the plant to produce high quality fuel and soil products from the trash.  The fuel size requirements were:  13% maximum by weight passing a ¼" x ¼" screen and 95% minimum by weight passing a 4" x 4" screen.  The fuel quality requirements were: 3% maximum by weight plastic and rubber content; 2% maximum by weight painted and treated wood; and 5% maximum by weight non-combustible (inert) material.

The IPP also agreed to accept a soil product with similar sizing and quality requirements.  The separation of Dade Co. municipal trash into rejects, ferrous fuel, primary soil and secondary soil had never been attempted with the quality and throughput requirements of the project participants.

Prior to detailed process design, numerous samples of municipal trash were hand sorted, shredded, screened through various trommel screen openings, destoned and analyzed to determine whether fuel and soil requirements could be achieved in a full scale system at 110 tons per hour.  Several months of testing by Montenay Power and Heil produced the confidence necessary to modify the plant.

The major components of the 26 million-dollar project were as follows:

  • Construct a new truck scale facility to weigh incoming trash and outgoing product [rejects, fuel, primary soil and secondary soil (broken concrete, rocks, etc.)].
  • Construct a new tipping building for trash storage to allow the existing tipping floor to be used for the initial separation of large reject items via large front-end loader and small skid/steer loaders.  Modify and add new infeed conveyor systems to each of the three existing trash shredding lines to allow easier removal of rejects by hydraulic grapple crane and sorting personnel.
  • Construct air-conditioned enclosures for the sorting personnel located along each side of the new sorting conveyors.
  • Modify the three existing shredders by eliminating their compression feeders, adding explosion detection/suppression equipment and explosion vent stacks through the roof.
  • Construct a common conveyor system to handle the rejects removed from each of the three lines.
  • Construct a common system of trommels, destoners, conveyors, and dust collection equipment to separate the output of all lines (110 tph) into fuel, primary soil, secondary soil and oversize rejects.
  • Construct a building to enclose the separation system and another adjacent building with large concrete bunkers to store fuel, primary soil and secondary soil.
  • Construct a new electrical control system containing motor starters, programmable logic controllers, I/O racks, IBM compatible computers (redundant) and touch screens (redundant).
Except for the truck scale and buildings, Heil Engineered Systems designed, provided, installed and tested the processing systems as described above.  The project was developed over three years, was built in 1996 and successfully commissioned in 1997.  The existing shredding lines were modified in sequence to allow continued operation of the plant.
Several unique features were required due to the constraints of the existing facility:
  • A section of the shredder explosion vent stack had to be hydraulically raised and lowered to allow passage of an overhead bridge crane used for shredder maintenance.
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View of three Heil trommels taken during construction of the processing line.  The trommels are used to screen the shredded trash to produce biomass fuel and two soil products.

  • A 12' x 60' trommel was located directly above a    10' x 50' trommel due to lack of space.
  • Three trommels, two destoners, numerous conveyors, bypass diverters, dust collection equipment and a network of maintenance walkways had to be constructed in a 30' wide x 155' long x 72' high building due to the lack of space in the existing plant.

The process flow is as follows:

Trucks containing trash are tipped on a new tipping floor constructed for this project.  After rejects have been removed on the tipping floor, the remaining trash is pushed into an existing storage pit.  Trash is recovered from the storage pit by one of two existing overhead bridge cranes which then place the material into one of the three parallel refurbished processing lines.  Additional rejects are removed by one of three hydraulic grapple cranes located adjacent to the metal pan infeed conveyors.

Following the metal pan infeed conveyors are three elevated rubber belt-sorting conveyors where sorting personnel remove additional rejects.  The remaining trash is then processed through three shredders, each capable of 50 tph of throughput.  Ferrous material is removed from the shredded trash with magnetic separators and the remaining material from the three lines passes through the common screening/destoning system.

Since separation of the minus ¼" soil/organics from the shredded trash @ 110 tph cannot be efficiently accomplished in a single trommel screen, the screening is accomplished in two stages: first, trommeling to minus 1" and then trommeling the minus 1" fraction to ¼".  Previous testing indicated that most of the stones, crushed concrete, ceramics and some metals were located in the +¼"-1" fraction; therefore, the output of the second trommel is sent to the destoners for separation of these items.  Material larger than 1" from the first trommel is sent to the third trommel for oversize (+5") removal.  The "unders" from the third trommel and the light and medium fractions from the destoners are combined to become fuel.

The four material streams (fuel, overs, soil, and secondary soil) are transported via belt conveyors to storage bunkers where they are loaded into open-top trailers via front-end loader.  Direct feed to trailers via conveyor is also available.

Upon completion of system construction and checkout, a six day performance test was conducted to demonstrate system guarantees.  This testing involved processing approximately 1,500 tons per day for the six-day test.  A system mass balance was prepared for each test day as well as measuring system downtime to determine availability.  Product sampling was also conducted to determine fuel and soil quality.

The results of the performance testing are presented in Tables 1 and 2.  All contractual guarantees were met or exceeded by Heil.  The project was placed into commercial operation immediately following testing on April 12, 1997.

Heil Engineered Systems is a leading supplier of solid waste processing, materials recovery, compost preparation, fuel preparation, and fuel delivery systems to private firms and municipalities throughout the country.