Thermal treatment of biomass
A biomass pyrolysis process is provided in which biomass feedstock is mixed with a heat carrier. The heat carrier at least partly comprises char. The ratio by weight of biomass to char is in the range 1:1 to 1:20. The process may be carried out by in a screw/auger pyrolysis reactor in which the solid feedstock components are conveyed along the reactor by a first screw. A second screw conveys at least a portion of the solid products of the biomass pyrolysis back to a heat transfer medium input port. Thus, the heat transfer medium includes char from the biomass pyrolysis.
1. A biomass pyrolysis process including the steps:
conveying by a first conveying means biomass feedstock and heat transfer medium from a biomass feedstock input port and heat transfer medium input ports through a pyrolysis zone of a biomass pyrolysis apparatus to produce at least solid and gaseous biomass pyrolysis products; and
conveying by a second conveying means at least a portion of the solid products from an output port of the pyrolysis zone back to the heat transfer medium input port, wherein the second conveying means conveys at least a portion of the solid products through the biomass pyrolysis apparatus and is disposed in thermal contact with the first conveying means at the pyrolysis zone within the biomass pyrolysis apparatus, and wherein the first and second conveying means are located with respect to each other so that one of them surrounds at least part of the other or so that they are adjacent to each other.
2. A biomass pyrolysis process according to claim 1 wherein the heat transfer medium includes solid heat carrier balls.
3. A biomass pyrolysis process according to claim 1 , wherein vapour and/or gaseous products of the biomass pyrolysis process are provided to an inlet of a biomass gasification process.
4. A biomass pyrolysis process according to claim 3 wherein the pyrolysis process is carried out at a pressure over atmospheric pressure of at least 50 mbar.
5. A biomass pyrolysis apparatus having:
a biomass feedstock input port;
a heat transfer medium input port;
a first conveying means for conveying the biomass feedstock and heat transfer medium through a pyrolysis zone of the apparatus;
an output port for solid products of the biomass pyrolysis; and
a second conveying means for conveying at least a portion of the solid products of the biomass pyrolysis back to the heat transfer medium input port, so that the heat transfer medium includes said solid products of the biomass pyrolysis,
wherein the second conveying means conveys at least a portion of the solid products through the biomass pyrolysis apparatus and is disposed in thermal contact with the first conveying means at the pyrolysis zone within the biomass pyrolysis apparatus, and wherein the first and second conveying means are located with respect to each other so that one of them surrounds at least part of the other or so that they are adjacent to each other.
6. A biomass pyrolysis apparatus according to claim 5 wherein the second conveying means is disposed annularly around the first conveying means.
7. A biomass pyrolysis apparatus according to claim 5 , further having an air and/or water inlet for introducing air and/or water into the second conveying means for reaction with the char conveyed by the second conveying means.
8. A biomass pyrolysis apparatus according to claim 5 wherein the heat transfer medium includes solid heat carrier balls.
9. A biomass pyrolysis apparatus according to claim 5 , further comprising a biomass gasification apparatus, wherein vapour and/or gaseous products of the biomass pyrolysis are provided to an inlet of the biomass gasification apparatus.
10. A biomass pyrolysis apparatus according to claim 9 , wherein the pyrolysis apparatus is adapted to carry out pyrolysis at a pressure over atmospheric pressure of at least 3 mbar.
11. A biomass pyrolysis process according to claim 1 wherein the second conveying means disposed annularly around the first conveying means.
12. A biomass pyrolysis process according to claim 1 wherein the pyrolysis zone of the biomass pyrolysis apparatus is a screw/auger kiln.
13. A biomass pyrolysis process according to claim 1 wherein said solid products of pyrolysis include char, and wherein the heat transfer medium at least partly comprises char.
14. A biomass pyrolysis process according to claim 13 wherein the ratio by weight of biomass to char is 1:1 to 1:20.