Systems and methods for processing mixed solid waste
Described are methods for processing mixed solid waste. The method includes providing a mixed solid waste stream including dry organic material comingled with wet organic and/or inorganic material. The mixed waste is shredded and then separated using size separation and density separation. The shredder has a cut size and rotation speed that produces less than 20% by mass of particles smaller than 2 inches from the mixed solid waste. The shredded mix solid waste is then separated by density and a portion of the stream is recovered as a recyclable or converted to a high value product.
1. A method for processing mixed solid waste, comprising:
providing a mixed solid waste stream including dry organic material comingled with wet organic and/or inorganic material;
shredding the solid mixed waste using a shredder with a cut size and rotation speed that produces less than 20% by mass of particles smaller than 2 inches;
separating the shredded material by size to produce an over fraction and an under fraction;
separating the over fraction in a density separator to produce a heavy stream and a light stream; and
converting the light stream or the heavy stream or a downstream portion thereof to a fuel and/or recovering one or more recyclable products therefrom.
2. The method of claim 1 , wherein the shredder has a plurality of cutters positioned on a rotor, wherein the cutters engage a cutting surface upon rotation of the rotor.
3. The method of claim 2 , wherein the rotor is spun at a speed less than 500 rpm.
4. The method of claim 2 , wherein the cutting surface is formed in cutouts in a fixed cutting bar that serves as a counter knife.
5. The method of claim 3 , wherein the cutouts have a longitudinal diameter of at least 8 inches.
6. The method of claim 1 , wherein the rotor has a diameter of at least 15 inches.
7. The method of claim 1 , wherein the shredder is a dual shaft shredder having counter rotating rotors.
8. The method of claim 1 , wherein less than 1 wt % of the mixed waste stream is separated as a recovered product using manual labor.
9. The method of claim 1 , wherein the mixed waste stream includes at least 15% dry organic waste and at least 30% wet organic waste.
10. The method of claim 1 , wherein at least 10 wt % of the mixed waste stream is dry organic waste selected from the group consisting of 3-D plastic, film plastic, paper, cardboard, rubber, textiles, and wood.
11. The method of claim 10 , wherein at least 10 wt % of the mixed waste stream is a wet organic waste selected from the group consisting of food waste, animal waste, yard waste and green waste.
12. The method of claim 1 , wherein the shredder has a throughput of at least 2 metric tons per hour per single line of mixed solid waste.
13. The method of claim 1 , wherein the screening and density separation produce a first stream enriched in wet organics and a second stream enriched in dry organics.
14. The method of claim 1 , wherein the wet organics are converted to a fuel or product using a first conversion technique selected from wet digestion, dry digestion, anaerobic digestion, aerobic digestion, or composting.
15. The method of claim 14 , wherein the first conversion technique produces biogas.
16. The method of claim 15 , wherein the biogas is converted to a liquid fuel or electricity.
17. The method of claim 13 , wherein the separation of the wet organic from the dry organic materials yields a dry organic material having less than 25% moisture content and the dry organic material is converted to a refuse derived fuel.
18. The method of claim 13 , wherein the dry organic waste is enriched in plastics, the second conversion technique comprising sorting the dry organic material by separating 3-dimensional plastics from 2-dimensional plastics to yield a 3-dimensional recyclable plastic product.
19. The method of claim 1 , wherein the mixed waste stream includes at least 20% by weight of low value material selected from the group consisting of wet organics, green waste, food waste, grit, fines less than 1 inch, asphalt, concrete, textiles, wood, rubber, film plastic, PVC, foil, rock, used consumer products, low value glass, composite materials, and combinations of these.
20. The method of claim 1 , wherein the mixed waste stream includes inorganic waste, the method further comprising:
separating at least a portion of the inorganic waste from the wet organic waste material and the dry organic waste material to increase purity of the wet organic and dry organic waste streams; and
recovering at least a portion of the dry organic material as a recyclable product.