Methods for controlling pretreatment of biomass

1. A method for controlling the total solids contents of biomass discharged from a plug screw feeder into a pretreatment digester, the plug screw feeder comprising a throat section having a number of drain openings, the digester being connected to a damper which contacts the biomass material as it enters the digester, the damper being driven forward by a piston which exerts a force on the damper to create a back pressure against the biomass, the method comprising:

measuring the flow rate of biomass introduced into the plug screw feeder;

measuring the total solids content of biomass introduced into the plug screw feeder;

measuring the flow rate of a effluent slurry discharged from the plug screw feeder;

calculating the total solids content of the biomass discharged from the plug screw feeder into the pretreatment digester based on the flow rate and total solids content of biomass introduced into the plug screw feeder and the flow rate of the effluent slurry discharged from the plug screw feeder; and

adjusting at least one of (1) the number of open drain openings in the plug screw feeder throat section, (2) the force exerted on the damper by the piston, (3) the rotational speed of the plug screw feeder and (4) the total solids content of biomass introduced into the plug screw feeder based on the calculated total solids content of the biomass discharged from the plug screw feeder.

2. The method as set forth in claim 1 further comprising:

measuring the total solids content of the effluent slurry discharged from the screw plug feeder; and

calculating the total solids content of the biomass discharged from the plug screw feeder into the pretreatment digester based on the total solids content of the effluent slurry discharged from the plug screw feeder.

3. The method as set forth in claim 1 wherein a flushing fluid is directed at the drain openings to flush fines from the drain openings, the flushing fluid forming a part of the effluent slurry discharged from the plug screw feeder, the method comprising measuring the flow rate of the flushing fluid.

4. The method as set forth in claim 3 wherein the flushing fluid is directed at the drain openings at an angle with the drain openings to not impede the flow of liquid being discharged from the openings.

5. The method as set forth in claim 4 further comprising adjusting a mass ratio of acid to dry biomass discharged from the plug screw feeder by changing the total solid content of the biomass discharged from the plug screw feeder.

6. The method as set forth in claim 1 comprising contacting a biomass feedstock with an aqueous acid solution to prepare an acid-impregnated biomass stream, the aqueous acid solution having an acid concentration of less than about 5 wt %.

7. The method as set forth in claim 1 comprising introducing biomass discharged from the plug screw feeder and steam into the pretreatment digester.

8. The method as set forth in claim 1 comprising controlling the total solids content of the biomass discharged from the plug screw feeder into the pretreatment digester to be between about 40 wt % to about 60 wt %.

9. The method as set forth in claim 1 comprising controlling the total solids content of the biomass discharged from the plug screw feeder into the pretreatment digester to be between about 45 wt % to about 55 wt %.

10. The method as set forth in claim 1 comprising:

controlling a concentration of acid in the effluent slurry;

controlling the temperature of the pretreatment digester; and

controlling an average residence time of biomass in the pretreatment digester.

11. The method as set forth in claim 1 wherein the flow rate of biomass introduced into the plug screw feeder is a mass flow rate and the flow rate of the effluent slurry discharged from the plug screw feeder is a mass flow rate.

12. The method as set forth in claim 1 wherein the flow rate of effluent slurry discharged from the plug screw feeder is a volumetric flow rate.

13. The method as set forth in claim 1 comprising analyzing biomass downstream from the pretreatment digester and adjusting the total solids content of the biomass discharged from the plug screw feeder into the pretreatment digester based on the analysis.

14. The method as set forth in claim 13 wherein at least one of the pH, total solids content, liquid fraction composition and solid fraction composition of the biomass downstream from the pretreatment digester is analyzed.

15. A method for producing a pretreated biomass feedstock, the method comprising:

contacting a biomass feedstock with an aqueous acid solution to form an acid-impregnated biomass stream;

dewatering the acid-impregnated biomass stream to produce a effluent slurry and dewatered biomass;

controlling a concentration of acid in the effluent slurry;

introducing the dewatered biomass and steam into a pretreatment digester;

controlling a total solids content of dewatered biomass introduced into the pretreatment digester;

controlling the temperature of the pretreatment digester; and

controlling an average residence time of biomass in the pretreatment digester.

16. The method as set forth in claim 15 wherein the concentration of acid in the effluent slurry is controlled by adjusting a concentration of acid in the aqueous acid solution.

17. The method as set forth in claim 15 wherein the effluent slurry is discharged from a plug screw feeder which feeds biomass to the pretreatment digester.

18. The method as set forth in claim 15 wherein the effluent slurry is discharged from a drain screw or screw press which is used to dewater the biomass.

19. The method as set forth in claim 15 wherein the total solids content of dewatered biomass introduced into the pretreatment digester is controlled by adjusting at least one of (1) the number of open drain openings in a throat section of a plug screw feeder which feeds biomass to the pretreatment digester, (2) the force exerted on a damper which is connected to the digester which contacts the biomass material as it enters the digester, (3) the rotational speed of the plug screw feeder and (4) the total solids content of biomass introduced into a plug screw feeder which feeds biomass to the pretreatment digester.

20. The method as set forth in claim 15 comprising calculating the total solids content of dewatered biomass introduced into the pretreatment digester.

21. The method as set forth in claim 15 wherein the aqueous acid solution has an acid concentration of less than about 5 wt %.

22. The method as set forth in claim 15 wherein the pH of the effluent slurry is controlled to be between about 1 and about 2.

23. The method as set forth in claim 15 wherein the total solids content of the biomass introduced into the pretreatment digester is controlled to be between about 40 wt % to about 60 wt %.

24. The method as set forth in claim 15 wherein the total solids content of the biomass introduced into the pretreatment digester is controlled to be between about 45 wt % to about 55 wt %.

25. The method as set forth in claim 15 wherein the temperature of the pretreatment digester is controlled to be from about 160° C. to about 195° C.

26. The method as set forth in claim 15 wherein the average residence time of biomass in the pretreatment digester is controlled to be at least about 1 minute.

27. The method as set forth in claim 15 comprising analyzing biomass downstream from the pretreatment digester and adjusting at least one of (1) the concentration of acid in the effluent slurry, the (2) total solids content of dewatered biomass introduced into the pretreatment digester, (3) the temperature of the pretreatment digester and (4) the average residence time of biomass in the pretreatment digester based on the analysis.

28. The method as set forth in claim 27 wherein at least one of the pH, total solids content, liquid fraction composition and solid fraction composition of the biomass downstream from the pretreatment digester is analyzed.