Method and apparatus for conveying a cellulosic feedstock
A method and apparatus for preparing a cellulosic feedstock are disclosed. Embodiments of the method comprise passing the cellulosic feedstock through an optional impregnation chamber to an outlet of the impregnation chamber, passing the cellulosic feedstock from the outlet of the impregnation chamber to a holding tank having an inlet and an outlet, and conveying the cellulosic feedstock downwardly and laterally as it travels through the holding tank. Embodiments of the apparatus comprise at least one sidewall defining a passage. The passage has an upper portion and a lower portion, and the lower portion has a greater cross-sectional area than the upper portion. At least one inlet is provided adjacent the upper portion, and at least one outlet is provided adjacent the lower portion, at an elevation below the inlet.
1. A holding tank for a cellulosic feedstock comprising:
at least one sidewall defining a passage having an upper portion and a lower portion, the lower portion having a greater cross sectional area than the upper portion;
at least one inlet adjacent the upper portion;
at least one outlet adjacent the lower portion, at an elevation below the inlet; and
at least one discharge member adjacent the at least one outlet wherein the at least one discharge member comprises a base, an open top that is at least as large as, and is in vertical registration with, the at least one outlet, and at least a first discharge member outlet that is laterally positioned and conveys the cellulosic feedstock laterally across the outlet,
wherein (i) the at least one discharge member comprises a first pair of screw conveyors, each conveyor in the first pair rotating about respective first and second generally parallel axes, (ii) the screw conveyors have a first pitch adjacent the first discharge member outlet, and a second pitch narrower than the first pitch distal to the first discharge member outlet, (iii) the axes are generally horizontal and (iv) the cellulosic feedstock is essentially a solid.
2. The holding tank of claim 1 , wherein the sidewalls comprise a first sidewall and a second sidewall opposed to the first sidewall, the first and second sidewalls diverging relative to each other from the upper portion to the lower portion.
3. The holding tank of claim 2 , wherein the sidewalls comprise a third sidewall and a fourth sidewall opposed to the third sidewall, the third and fourth sidewalls extending between the first and second sidewalls, the third and fourth sidewalls diverging relative to each other from the upper portion to the lower portion.
4. The holding tank of claim 1 , wherein the at least one discharge member comprises at least one screw conveyor mounted above the base.
5. The holding tank of claim 1 , wherein the screw conveyors are rotated in the same direction and feed material from above towards the first discharge member outlet.
6. The holding tank of claim 1 wherein the screw conveyors each have a first flight and a second flight, the first flight having the first pitch and the second flight the second pitch.
7. The holding tank of claim 6 , wherein each screw conveyor comprises a third flight intermediate the first and second flights, the third flight having an intermediate pitch that is wider than the first pitch and narrower than the wider pitch.
8. The holding tank of claim 1 , wherein the discharge member further comprises a second pair of screw conveyors.
9. The holding tank of claim 8 , wherein the second pair of screw conveyors urges material from above towards a second discharge member outlet that is laterally positioned and spaced away from the first discharge member outlet.
10. The holding tank of claim 8 , wherein the second discharge member outlet is in a different direction to the first discharge member outlet.
11. The holding tank of claim 8 , wherein second pair of screw conveyors are rotatable about parallel axes.
12. The holding tank of claim 11 , wherein each screw conveyor in the second pair rotates in the same direction.
13. The holding tank of claim 12 , wherein the screw conveyors of first pair rotate opposite to the screw conveyors of second pair.
14. The holding tank of claim 11 , wherein the axes are generally horizontal.
15. The holding tank of claim 1 , further comprising a heating jacket provided on at least a portion of the at least one sidewall.
16. The holding tank of claim 1 , further comprising a heating jacket provided on the at least one sidewall.