METHOD FOR COOLING BIOMASS

Abstract

The present invention relates to an improved method and device for treating biomass in which thermally treated biomass is discharged from a pressurized prehydrolysis reactor unit and dewatered before it is cooled with cold liquid. The cooled slurry of biomass is then enzymatically treated.

Claims

1. A method for treating biomass comprising: (a) feeding biomass to a pressurized prehydrolysis reactor unit; (b) thermally treating the biomass in the pressurized prehydrolysis reactor unit; (c) discharging the thermally treated biomass from the pressurized prehydrolysis reactor unit to produce a discharged thermally treated aqueous slurry of biomass; (d) dewatering the discharged thermally treated aqueous slurry of biomass; (e) feeding the dewatered thermally treated aqueous slurry of biomass into a cooling unit; (f) cooling the dewatered thermally treated aqueous slurry of biomass by mixing the dewatered thermally treated aqueous slurry of biomass with a liquid having a lower temperature than the dewatered thermally treated aqueous slurry of biomass in the cooling unit; and (g) treating the cooled aqueous slurry of biomass with an enzyme.

2. The method according to claim 1, wherein the discharged thermally treated aqueous slurry of biomass is dewatered in a dewatering unit to separate a dewatered thermally treated aqueous slurry of biomass and a filtrate of a hot aqueous solution.

3. The method according to claim 2, wherein at least part of the filtrate of a hot aqueous solution is fed into a heat exchanger unit to produce a filtrate of a cold aqueous solution.

4. The method according to claim 3, wherein at least part of the filtrate of a cold aqueous solution is fed into the cooling unit of step (f) to cool the dewatered thermally treated aqueous slurry of biomass.

5. The method according to claim 2, wherein a part of the filtrate of a hot aqueous solution is separated and fed into the pressurized prehydrolysis reactor unit.

6. The method according to claim 1, wherein the thermally treated biomass has a temperature of from 120° C. to 220° C. and is discharged from the pressurized pretreatment unit through steam explosion to produce a discharged thermally treated aqueous slurry of biomass having a weight amount of biomass of from 25 to 60 wt %.

7. The method according to claim 6, wherein the discharged thermally treated aqueous slurry of biomass is dewatered to a weight amount of biomass in the dewatered thermally treated aqueous slurry of biomass of from 30 to 60 wt %.

8. The method according to claim 1, wherein the thermally treated biomass has a temperature of from 50° C. to 140° C. and is discharged from the pressurized pretreatment unit through dilution discharge to produce a discharged thermally treated aqueous slurry of biomass having a weight amount of biomass of from 5 to 25 wt %.

9. The method according to claim 8, wherein the discharged thermally treated aqueous slurry of biomass is dewatered to a weight amount of biomass in the dewatered thermally treated aqueous slurry of biomass of from 30 to 70 wt %.

10. The method according to claim 1, wherein the liquid for cooling the dewatered thermally treated aqueous slurry of biomass in the cooling unit in step (f) has a temperature of from 10° C. to 40° C.

11. The method according to claim 1, wherein dewatered thermally treated aqueous slurry of biomass is cooled in the cooling unit in step (f) to a temperature of 40° C. to 80° C.

12. The method according to claim 1, wherein the cooled aqueous slurry of biomass in step (g) has a weight amount of biomass of from 15 to 25 wt %.

13. A device for treating biomass comprising: a biomass feeding system; a pressurized prehydrolysis reactor unit for thermally treating a biomass and for discharging a thermally treated aqueous slurry of biomass; a dewatering unit for separating the discharged thermally treated aqueous slurry of biomass into a dewatered thermally treated aqueous slurry of biomass and a filtrate of hot aqueous solution; a cooling unit; wherein: the biomass feeding system is adapted to feed the biomass to the pressurized prehydrolysis reactor unit and to feed the discharged thermally treated aqueous slurry of biomass from the pressurized prehydrolysis reactor unit through the dewatering unit to the cooling unit, and the cooling unit comprises: at least one feeding port for the dewatered thermally treated slurry of biomass; at least one feeding port for a liquid having a lower temperature than the dewatered thermally treated aqueous slurry of biomass; means for mixing the dewatered thermally treated slurry of biomass and the liquid; and at least one feeding port for an enzyme for treating the cooled aqueous slurry of biomass downstream of the at least one feeding port for the dewatered thermally treated slurry of biomass and the at least one feeding port for a liquid having a lower temperature than the dewatered thermally treated aqueous slurry of biomass; and at least one discharge port for discharging the enzyme treated slurry of biomass from the cooling unit.

14. The device for treating biomass according to claim 13 further comprising a heat exchanger unit for cooling the filtrate of a hot aqueous solution to produce a filtrate of a cold aqueous solution.

15. The device for treating biomass according to claim 14 further comprising a filtrate feeding system adapted to feed the filtrate of a hot aqueous solution from the dewatering unit to the heat exchanger unit and optionally to the pressurized prehydrolysis reactor unit, and to feed the filtrate of cold aqueous solution from the heat exchanger unit to the cooling unit.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0091] FIG. 1 shows in the upper part a schematic plane of a device for executing a method for treating biomass as known in the art and In the lower part a schematic plane of a device for executing a method for treating biomass according to the invention.

DETAILED DESCRIPTION OF THE DRAWING

[0092] FIG. 1 shows in the upper part a device for treating biomass as known in the art and in the lower part a schematic plane of a device for executing a method for treating biomass according to the invention.

[0093] Biomass is thermally treated a pressurized prehydrolysis reactor unit by heating and pressurizing with steam for a certain time. The biomass thereby can be heated by heating means of the pressurized prehydrolysis reactor unit (not shown) and pressurized by steam generation from steam generation means of the pressurized prehydrolysis reactor unit (not shown).

[0094] The thermally treated biomass can be discharged from the pressurized prehydrolysis reactor unit though steam explosion. The discharged thermally treated aqueous slurry of biomass discharged through steam explosion has a temperature, depending on the temperature in the pressurized prehydrolysis reactor unit, of from 160° C. to 220° C., usually around 180° C. and a weight amount of biomass of 30 to 40 wt %. Alternatively, the thermally treated biomass can be diluted before it is discharged from the pressurized prehydrolysis reactor unit. In the latter case, biomass can either have a temperature below 100° C., such as around 80° C. during discharging, wherein no flashing occurs during discharging, or the biomass can have a temperature above 100° C., such as around 120° C., during discharging and a flashing without steam explosion occurs during discharging. Due to the dilution the weight amount of the biomass in the discharged thermally treated aqueous slurry of biomass is significantly lower than after steam explosion. However, also the temperature is significantly lower. The discharged thermally treated aqueous slurry of biomass discharged through dilution discharge has a temperature of from 80° C. to 120° C., usually around 80° C. or around 115° C. and a weight amount of biomass of 10 to 15 wt %.

[0095] In the device and method according to the prior art as shown in the upper part of FIG. 1 the discharged thermally treated aqueous slurry of biomass is cooled in two steps firstly by with mixing cold water in a cooling unit. In order to avoid a too high degree of dilution of the biomass below a desired weight amount for enzymatic hydrolysis of 17 to 20 wt % in the slurry of biomass, only limited amounts of cold water can be mixed into discharged thermally treated aqueous slurry of biomass which is not sufficient to cool the slurry to a temperature range suitable for downstream enzymatic hydrolysis of around 40° C. to 60° C. For slurry discharged through dilution discharge the amount of cold water is thereby even more limited due to the already low weight amount of biomass in the slurry. Consequently, in order to further reduce the temperature of the aqueous slurry of biomass it is fed into a heat exchanger which cools the slurry without further diluting the biomass in the slurry. However, heat exchangers have the drawback of low cooling efficiency and can easily plug which can cause disruption of the process and additional costs.

[0096] In the device and method according to the present invention as shown in the lower part of FIG. 1 the discharged thermally treated aqueous slurry of biomass is firstly dewatered in a dewatering unit before fed into a cooling unit. In the dewatering unit a filtrate of hot aqueous solution is separated from the slurry of biomass to such an extent that the dewatered thermally treated aqueous slurry of biomass has a weight amount of biomass of 50 to 60 wt % after steam explosion discharge or, alternatively, of about 40 wt % after dilution discharge.

[0097] The filtrate of hot aqueous solution is cooled in a heat exchanger to a temperature of 15 to 35° C. and mixed in the cooling unit with the dewatered thermally treated aqueous slurry of biomass. In the case that the filtrate of cold aqueous solution is not sufficient to cool the slurry of biomass to the desired temperature of around 40° C. to 60° C. additional cold water can be added to the cooling unit.

[0098] Exceed filtrate of hot aqueous solution separated from the dewatering unit, which is not used for cooling the biomass slurry, can be separated before feeding into the heat exchanger and recycled into the pressurized prehydrolysis reactor unit (not shown).

[0099] The slurry of biomass cooled to around 40° C. to 60° C. has a weight amount of biomass of around 20 wt % which are the desired temperatures and weight amounts for ensuring optimum enzymatic hydrolysis conditions and lower energy consumption in the downstream processes as lower amounts of liquid have to be removed from the slurry.