Densified fuel pellets
A biomass-based fuel pellet, such as a fuel pellet which includes thermoplastic polymeric material and a substantial amount of cellulosic material, e.g. cellulosic material derived from biomass source(s), is provided. The fuel pellet commonly includes about 5 to 15 wt. % of the thermoplastic polymeric material and at least about 75 wt. % cellulosic material. Optionally, the fuel pellet may comprise a lignin additive. Many embodiments of the fuel pellets are suitable for use in a coal-fired furnace and/or in other industrial boiler applications.
1. A densified fuel pellet formed by a process comprising:
compacting a mixture which includes
a) about 5 to 15 wt.% molten thermoplastic polymeric material;
b) at least about 75 wt.% cellulosic material;
wherein the fuel pellet has a minimum dimension of at least about 1 cm and a heat value of at least about 9,500 Btu/lb (as is basis).
2. The densified fuel pellet of claim 1 wherein the thermoplastic polymeric material has a melting point of about 120 to 150° C.
3. The densified fuel pellet of claim 1 wherein the fuel pellet has a moisture content of no more than about 3 wt.%.
4. The densified fuel pellet of claim 1 wherein the fuel pellet has a sulfur content of no more than about 0.5 wt.%.
5. The densified fuel pellet of claim 1 wherein the fuel pellet has a ash content of no more than about 8 wt.%.
6. The densified fuel pellet of claim 1 wherein the fuel pellet has a pellet durability index of at least about 80.
7. The densified fuel pellet of claim 1 wherein the fuel pellet has a specific gravity of about 1.0 to 1.2 g/cm 3 .
8. The densified fuel pellet of claim 1 wherein a batch of the fuel pellet has a bulk density of about 20 to 45 lb/ft 3 .
9. The densified fuel pellet of claim 1 wherein the fuel pellet has a specific gravity which is at least about 150% of the mixture's specific gravity.
10. The densified fuel pellet of claim 1 wherein the fuel pellet has a heat value of 9,500 to 12,000 Btu/lb (as is basis).
11. The densified fuel pellet of claim 1 wherein the cellulosic material is in particulate form having a maximum dimension of no more than about 20 mm.
12. The densified fuel pellet of claim 1 wherein the cellulosic material in the mixture has an initial moisture content of no more than about 15 wt.%.
13. The densified fuel pellet of claim 1 wherein the thermoplastic polymeric material comprises polyethylene, polypropylene, or a mixture thereof
14. The densified fuel pellet of claim 1 wherein compacting the mixture comprises extruding the feed mixture.
15. The densified fuel pellet of claim 1 wherein the thermoplastic polymeric material comprises a mixture of high density polyethylene and low density polyethylene.
16. The densified fuel pellet of claim 1 wherein the fuel pellet has a cylindrical shape with a diameter of at least about 1.5 cm; and the fuel pellet has a pellet durability index of at least about 95.
17. The densified fuel pellet of claim 1 wherein a batch of the fuel pellet has a bulk density of about 20 to 45 lb/ft 3 ; and the fuel pellet has a heat value of 9,500 to 12,000 Btu/lb (as is basis).
18. The densified fuel pellet of claim 1 wherein the fuel pellet has a density a heat value of 9,500 to 12,000 Btu/lb (as is basis); specific gravity of about 1 to 1.2 g/cm 3 ; a moisture content of no more than about 3 wt.%; a sulfur content of no more than about 0.5 wt.%; and an ash content of no more than about 5 wt.%.
19. The densified fuel pellet of claim 18 wherein the molten thermoplastic polymeric material comprises high density polyethylene, low density polyethylene or a mixture thereof.
20. The densified fuel pellet of claim 1 densified fuel pellet comprising:
a) about 5 to 10 wt.% of the molten thermoplastic polymeric material; which comprises high density polyethylene, low density polyethylene or a mixture thereof;
b) at least about 85 wt.% of the cellulosic material;
wherein the fuel pellet has a pellet durability index of at least about 95; a specific gravity of about 1 to 1.2 g/cm 3 ; a moisture content of no more than about 3 wt.%; a sulfur content of no more than about 0.3 wt.%; and an ash content of no more than about 2 wt.%.
21. The densified fuel pellet of claim 1 wherein the molten cellulosic material includes cereal straw, corn stover, sugarcane bagasse, switchgrass, sawdust, pulp mill rejects or a mixture thereof.
22. The densified fuel pellet of claim 1 wherein the thermoplastic polymeric material comprises high density polyethylene, low density polyethylene or a mixture thereof; and the fuel pellet has a heat value of about 9,500 to 12,000 Btu/lb (as is basis) and a PDI of at least about 90.
23. The densified fuel pellet of claim 22 wherein comprising:
a) about 5 to 10 wt.% of the molten thermoplastic polymeric material; and
b) at least about 85 wt.% of the cellulosic material.