Feasibility study: A regional optical sorter for mixed glass

Glass sorting technology Minnesota's once-stable market for container glass has become more uncertain, and prices paid for glass have significantly changed.

To address concerns of the regional and statewide recycling industry, the MPCA contracted with Tim Goodman & Associates to conduct an optical sorting feasibility study for glass. The study had three primary objectives:

  • Determine the preliminary technical and economic feasibility of developing a regional glass beneficiation facility that would mechanically remove contaminants from the mixed glass stream and color-sort the glass utilizing optical scanning technology.
  • Identify and research alternative regional markets for clean glass (mixed or color-separated) in order to provide a broader range of market options for MRFs around the state.
  • Assist MPCA staff in establishing a dialog with glass recycling industry players regarding the development of a regional glass beneficiation facility.

PDF icon Feasibility Study - A regional optical sorter for mixed glass (June 2007: 500Kb)

Key findings

  • Over 90% of the mixed glass potentially available for processing at the facility is generated at four MRFs located in the Minneapolis/St. Paul Metro Area. This amounts to approximately 53,000 tons annually of pre-beneficiated, mixed glass. 
  • Based on estimated contamination levels, processing loss due to particle size, optical sorter operational efficiencies, and an assumed breakout of glass into the three colors of flint, amber and green, this 53,000 tons would yield approximately:
    • 24,018 tons of flint cullet;
    • 8,662 tons of amber cullet; and
    • 8,766 tons of predominantly (80%) green cullet.
  • Cullet can be used at levels as high as 80% in the manufacturing of new glass containers. For every 10% of cullet used in the manufacturing process there is:
    • A 60°C drop in furnace temperature allowing a furnace to be operated at a lower temperature resulting in prolonged furnace life;
    • Up to a 3% reduction in fossil fuels leading to a 3% reduction in CO2 emissions;
    • A 6% reduction in NOx emissions; and
    • A 17% reduction in CO2 emissions associated with raw material conversion.
  • Due to the high capital and operating costs associated with a regional glass beneficiation facility, it should be located close to major suppliers of mixed glass, major glass markets, and a well developed transportation network. By these standards the most logical location for a facility would be in the metro area. 
  • The longer haul distances and smaller quantities of mixed glass generated at MRFs in Greater Minnesota make it unlikely that any significant amounts of glass would be delivered to a glass beneficiation facility in the metro area from these facilities.
  • Though Anchor Glass Container is the major market for recycled glass in the state, several other markets are available to MRFs in Greater Minnesota.
    • Glass Advantage (West Fargo, ND) – Blasting media manufacturer.
    • Raguse Manufacturing (Wheaton, MN) – Blasting media manufacturer.
    • Road construction aggregate replacement – Localized throughout Minnesota.
  • The processing line for glass beneficiation should include a mechanical processing component that would first remove contaminants from the mixed glass stream and an optical scanning system that would color-separate the glass into flint, amber and green streams or flint and a mixed amber/green (gramber) stream.
  • In total, the estimated capital cost of a dedicated glass beneficiation facility designed for up to 60,000 tons of mixed glass feedstock is estimated at approximately $5.5 to $6.5 million. This cost can be broken out as follows:
    • The capital cost for the glass processing equipment (mechanical processing and optical sorting) needed to process up to 60,000 tons annually of mixed glass is estimated at $3.25 million for a three-color sort system (flint, amber and green); and $2.75 million for a two-color sort system (flint and amber/green).
      • The capital cost for two wheel loaders and a truck scale is estimated at approximately $400,000.
      • Land and building costs are highly variable based on location, acreage, use of an existing building versus Greenfield development, utilities, availability, and real estate market conditions at the time a facility is constructed. Depending on these variables the cost of real estate, including a new or existing building, is estimated to be between $2.3 and $2.9 million.
  • The estimated annual operating costs (including debt service payments) ranges between $2.1 and $2.3 million.
  • Based on low, medium, and high revenue scenarios, estimated annual revenue from cullet sales (either to Anchor Glass or as road construction aggregate) ranges between $1.2 and $1.7 million.
  • Depending on the same variables mentioned above, the estimated tipping fee, after applying revenues from cullet sales, would be between $12 and $24/ton.
  • Though some refinement of numbers are needed, it appears that if the overall costs come down to a per-ton tipping fee in the $12 - $16/ton range, a glass beneficiation facility could be economically attractive for some of the larger mixed glass generators in the metro area.


Primary author: Tim Goodman of Tim Goodman & Associates (St. Louis Park, Minn.)