Heat removal and recovery in biomass pyrolysis
View Patent ↗Pyrolysis methods and apparatuses that allow effective heat removal, for example when necessary to achieve a desired throughput or process a desired type of biomass, are disclosed. According to representative methods, the use of a quench medium (e.g., water), either as a primary or a secondary type of heat removal, allows greater control of process temperatures, particularly in the reheater where char, as a solid byproduct of pyrolysis, is combusted. Quench medium may be distributed to one or more locations within the reheater vessel, such as above and/or within a dense phase bed of fluidized particles of a solid heat carrier (e.g., sand) to better control heat removal.
1. A pyrolysis method comprising:
(a) combining biomass and a solid heat carrier to provide a pyrolysis reaction mixture;
(b) subjecting the pyrolysis reaction mixture to pyrolysis conditions to provide a pyrolysis effluent;
(c) separating, from the pyrolysis effluent, (1) a solids-enriched fraction comprising a solid char and a recycled portion of the solid heat carrier and (2) a solids-depleted fraction comprising gaseous and liquid pyrolysis products; and
(d) directly contacting in a reheater the solids-enriched fraction with (1) an oxygen-containing combustion medium to combust at least a portion of the solid char and reheat the recycled portion of the solid heat carrier and (2) a quench medium to limit the temperature of the recycled portion of the solid heat carrier, wherein at least a portion of the quench medium is introduced to the reheater in a liquid state within a dense phase bed of the heat carrier.
2. The pyrolysis method of claim 1 , wherein the biomass selected from the group consisting of hardwood, softwood, hardwood bark, softwood bark, corn fiber, corn stover, sugar cane bagasse, switchgrass, miscanthus, algae, waste paper, construction waste, demolition waste, municipal waste, and mixtures thereof.
3. The method of claim 1 , wherein, in step (a), the biomass and the heat carrier are combined below a pyrolysis reaction zone.
4. The method of claim 3 , wherein the pyrolysis reaction zone is within an upflow, entrained bed reactor.
5. The method of claim 1 , wherein the quench medium comprises water.
6. The method of claim 1 , wherein the oxygen-containing combustion medium comprises air.
7. The method of claim 1 , wherein the solid heat carrier is sand.
8. The pyrolysis method of claim 1 , wherein the pyrolysis conditions include a temperature from about 400° C. (752° F.) to about 700° C. (1292° F.) and a pyrolysis reactor residence time of less than about 2 seconds.
9. The pyrolysis method of claim 1 , wherein at least a portion of the oxygen-containing combustion medium is introduced within the dense phase bed of the heat carrier to form a fluidized bed.
10. The pyrolysis method of claim 9 , wherein the quench medium is introduced to the reheater at a plurality of positions in the reheater.
11. The pyrolysis method of claim 9 , wherein a further portion of the quench medium is introduced within a dilute phase of the heat carrier.
12. The method of claim 1 , wherein a flow of the quench medium to the reheater is controlled in response to a temperature measured in the reheater.
13. The method of claim 12 , wherein the flow of the quench medium to the reheater is controlled in response to a temperature measured in the dense phase bed.
14. The method of claim 12 , wherein the flow of the quench medium to the reheater is controlled in response to a temperature measured in a dilute phase of the heat carrier.
15. The method of claim 11 , wherein said further portion of the quench medium is directed downwardly toward the surface of the dense phase bed.