Isothermal gas impregnation of biomass

Abstract

A method of treating biomass (2), such as lignocellulosic material or cellulosic material, comprising the steps of: i compressing the biomass to a first pressure and at a first temperature, ii. transferring the biomass into a treatment chamber (20) containing a treatment gas at a second pressure lower than the first pressure and a second temperature being not more than 5°C higher than the first temperature, and iii. transferring the biomass from the treatment chamber into a hydrolysis unit (50), wherein the biomass has the second temperature, or a temperature not more than 5°C higher than the second temperature, when entering the hydrolysis unit. A corresponding system is also provided.

Description

[0001] ISOTHERMAL GAS IMPREGNATION OF BIOMASS

[0002] TECHNICAL FIELD

[0003] The present invention relates to a method of treating biomass and a corresponding system therefor.

[0004] BACKGROUND

[0005] Processes for producing pulp and similar products generally include an treatment step, also known as an impregnation step, in which biomass, e.g. lignocellulosic material or cellulosic material, is impregnated with an impregnation fluid comprising the chemicals, such as sodium hydroxide (NaOH), and sodium sulfide (Na2S), which break the bonds between lignin, hemicellulose, and cellulose, to provide the latter as the main constituent of the produced pulp.

[0006] Efficient impregnation requires that the impregnation chemicals efficiently wet and contacts the biomass. The use of impregnation liquids however leads to the need for additional equipment to prepare and handle the impregnation liquid, both when adding the impregnation liquid to the biomass, but also when, as is typical, impregnation liquid is removed from the biomass before subsequent process step. In contrast, gas impregnation processes, which use a gas to impregnate the biomass, suffer from a decreased efficiency due to the limiting gas-liquid solubility.

[0007] There is accordingly a need for a method of treating biomass which overcomes the abovementioned drawbacks and limitations. There is further a need for a corresponding system for treating biomass.

[0008] SUMMARY

[0009] At least one of the abovementioned needs or at least one of the further needs which will become evident from the below description, are according to first and second corresponding aspects of the present invention obtained by a method of treating biomass, such as lignocellulosic material or cellulosic material, comprising the steps of: i. compressing the biomass to a first pressure and at a first temperature,

[0010] II. transferring the biomass into a treatment chamber containing a treatment gas at a second pressure lower than the first pressure and a second temperature being not more than STD higher than the first temperature, and iii. transferring the biomass from the treatment chamber into a hydrolysis unit, wherein the biomass has the second temperature, or a temperature not more than STD higher than the second temperature, when entering the hydrolysis unit, and a system for treating biomass such as lignocellulosic material or cellulosic material, comprising: i. a first compressing device configured to compress biomass to a first pressure and at a first temperature and to transfer the biomass into a treatment chamber,

[0011] II. a treatment chamber connected to the first device to receive compressed biomass, the treatment chamber being filled with a treatment gas at a second pressure lower than the first pressure and a second temperature being not more than 5 higher than the first temperature, iii. a second compressing device configured to transfer the biomass from the treatment chamber into a hydrolysis unit, and iv. a hydrolysis unit connected to the second compressing device.

[0012] The present invention is accordingly based on the recognition by the present inventors that treatment of biomass using gas overcomes the problems associated with liquid based treatment. Further, surprisingly, it was noted that an increase in temperature during the impregnation should be avoided as such temperature increase was shown to significantly increase the vapor pressure of any liquid present in the biomass, such increased vapor pressure significantly lowering the solubility of the treatment gas in the liquid, thus significantly lowering the efficiency at which the treatment gas was dissolved in the liquid in the biomass and thus brought into contact with the biomass.

[0013] Accordingly, by limiting the temperature increase during the treatment in the treatment chamber, in particular by not heating the treatment chamber or the gas in the treatment chamber, i.e. performing the method as an isothermal process, the treatment gas could be efficiently used to treat the biomass. Expressed differently, no external heat energy, such as by heating the treatment chamber or heating the treatment gas, is added to the treatment chamber or the treatment gas.

[0014] The method of treating biomass may alternatively be considered a method of pretreating biomass, a method of impregnating biomass, or a method of hydrolysing biomass. Correspondingly the system may alternatively be considered a system for pretreating biomass, a system for impregnating biomass, or a system for hydrolysing biomass. The biomass may be any type of plant material or plantbased material. The term lignocellulosic material is used herein to mean materials containing lignin, cellulose, and hemicellulose. One example of such materials is wood, others include other agricultural or forestry wastes such as bagasse and wheat straw. When lignocellulosic material is treated in a treatment vessel by the injection of fluid, it will typically further comprise a quantity of the fluid. The term lignocellulosic material further encompasses lignocellulosic material in slurry form, such as mixtures or slurries containing lignin, cellulose, and hemicellulose and fluid. The term cellulosic material is used herein to mean materials containing cellulose.

[0015] Compressing the biomass has the dual purpose of decreasing the liquid content of the biomass, as well as establishing a pressure difference between the biomass and the second pressure in the treatment chamber. Specifically, it was found that during the inevitable expansion of the biomass upon entering the treatment chamber, the treatment gas is efficiently diffused into the biomass.

[0016] The first pressure is preferably at least 1 bar higher than the second pressure. The first temperature is preferably in the range of 5-70 TT such as 10-70qC, or 5-25 TD, more preferably room temperature, e.g. 15-25 Tl Alternatively the first temperature may be in the range of 20-65 TD, such as 30-65 TD, preferably 55-65 °C. It is preferred that no additional heating of the biomass, beyond any heating caused by the compression, is applied to the biomass during the compression. Additionally, the biomass may be cooled such that the first temperature does not surpass 35 TD, more preferably does not surpass 25 O. The first pressure is preferably at least 1 bar higher than ambient pressure, e.g. preferably at least 1 bar higher than 1 .01325 bars.

[0017] The first compressing device may be any device configured to compress the biomass. The first compressing device may for example comprise a pump, such as a piston pump, or a screw. The biomass is transferred into the treatment chamber by the same first compressing device as compresses the biomass. The treatment chamber may be any chamber capable of holding the treatment gas. The treatment chamber may have one opening or connection for receiving the biomass, one opening or connection for receiving the treatment gas, and one opening or connection for allowing the biomass to the leave the treatment chamber.

[0018] The first compressing device may alternatively comprise a piston, alone or in combination with a screw conveyor, for compressing the biomass and transferring it into the treatment chamber. US4119025 and US4947743 for example show apparatuses which combine a screw conveyor and a piston and which may be used as the first compressing devices. The second pressure is lower than the first pressure. This ensures that the biomass expands upon entering the treatment chamber. The second pressure is preferably at least 1 bar lower than the first pressure. The second temperature is not more than STD higher than first temperature. While it is preferred that the second temperature is the same or lower than the first temperature, the compression of the biomass may lead to a slight increase in temperature in the treatment chamber within the STD. Additionally, heat energy may be released as the treatment gas dissolves in water present in the biomass. The treatment chamber may be cooled in order to prevent that the second temperature is more than STD above the first temperature. More preferably, the second temperature is not more than 4qC, most preferably not more than 3TD, for example not more than 2qC, higher than the first temperature.

[0019] The treatment gas may be any gas capable of acidifying the biomass. Suitable gases include carbon dioxide (C02) and sulphur dioxide (S02).

[0020] As specified, the biomass is transferred from the treatment chamber into a hydrolysis unit. Accordingly, the biomass, at the second temperature, is transferred to the hydrolysis unit in which it may be hydrolyzed at increased temperature and pressure. When entering the hydrolysis unit the biomass has the second temperature, or at least a temperature not more than STD higher than the second temperature. Accordingly, there is no separate or further heating of the biomass material between leaving the treatment chamber and entering the hydrolysis unit. An increase in temperature, within the not more than STD above the second temperature, may for example arise due to the transferring of the biomass. For example, transferring the biomass from the treatment chamber in the hydrolysis unit using the second compression device, e.g. the second compression screw as further described below, may lead to a minor, i.e. not more than STD, increase in the temperature of the biomass. By ensuring that the temperature of the biomass entering the hydrolysis unit has the second temperature, or at least a temperature not more than 5oqC higher than the second temperature, evaporation of the treatment gas from the biomass is prevented or at least reduced.

[0021] The dosage, or ratio, of treatment gas to dry substance of biomass may preferably be 1 -5 wt%. Expressed differently, 10-50 kg of treatment gas may typically be added to the treatment chamber per ton of dry matter of biomass that is transferred into the treatment chamber. The second compressing device may be any device configured to transfer the biomass. The second compressing device may for example comprise a pump, such as a piston pump, or a screw. Alternatively, the second compressing device may be replaced by a valve.

[0022] The hydrolysis unit is a unit configured to hydrolyze the biomass. The hydrolysis unit may comprise a steam explosion unit. The hydrolysis unit may be a BioTrac™ hydrolysis unit.

[0023] Preferably the biomass is compressed using a first compressing screw or plug screw feeder, whereby the first compressing screw or plug screw feeder is operated so as to compress the biomass to form a plug capable of preventing the treatment gas escaping the treatment chamber through the first compressing screw of plug screw feeder.

[0024] Correspondingly it is preferred when the first compressing device comprises a first compressing screw or plug screw feeder, whereby the first compressing screw or plug screw feeder is configured to compress the biomass to form a plug capable of preventing the gas escaping the treatment chamber through the first compressing screw of plug screw feeder. This is advantageous in that a compressing screw or plug screw feeder both compresses the biomass and transfers it into the treatment chamber. The compressing screw or plug screw feeder typically comprises a conical screw narrowing in diameter towards one end, whereby biomass transported by the screw is pressed between the screw and a surrounding enclosure more and more until the biomass exits a nozzle at the narrow end of the screw and enclosure. A hopper may be connected to the screw and enclosure at the opposite end of the screw and enclosure to allow the biomass to enter into the space between the screw and the enclosure.

[0025] Preferably the first compressing device further comprises a device configured to break up the biomass upon entering the treatment chamber. This is advantageous in that it assists the diffusion of the treatment gas into the biomass. The device configured to break up the biomass may comprise a conical ram or spike arranged so as to engage biomass entering the treatment chamber.

[0026] If desired, the biomass in the treatment chamber may be agitated or transported within the treatment chamber to further assist diffusion of the treatment gas into the biomass and / or to transport the biomass from one end of the treatment chamber to another end.

[0027] Preferably the second compressing device comprises a second compressing screw or plug screw feeder, whereby the second compressing screw or plug screw feeder is configured so as to compress the biomass to form a plug capable of preventing the treatment gas escaping the treatment chamber through second first compressing screw of plug screw feeder. The second compressing screw or plug screw feeder may be configured as described above in relation to the first compressing screw or plug screw feeder. Preferably the second compressing device further comprises a device configured to break up the biomass before entering the hydrolysis unit. This is advantageous in that it improves the hydrolyzation of the biomass. The device configured to break up the biomass before entering the hydrolysis unit may be configured as described above in relation to the device configured to break up the biomass upon entering the treatment chamber.

[0028] Preferably the treatment gas is S02. This is advantageous in that S02provides a good acidifying effect on the biomass.

[0029] Preferably the second temperature is no more than 1 °C higher than the first temperature. This is advantageous in minimizing the temperature increase of the biomass in the treatment chamber prevents a decrease of the treatment efficiency. More preferably the second temperature is the same as the first temperature. Expressed differently it is preferred that the process is isothermal.

[0030] Preferably the biomass is heated in the hydrolysis unit. This is advantageous in that it increases the efficiency of the hydrolysis. At the same time, it is noted that there is no heating, beyond what heating may be provided by the second compressing screw or plug screw feeder, of the biomass as it passes between the treatment chamber and the hydrolysis unit.

[0031] Accordingly, it is preferred that the treatment chamber is devoid of any heating element or other means of heating the treatment chamber. Thus, by not heating the biomass before it enters the hydrolysis unit the treatment is made more efficient and there is more versatility in selecting the hydrolysis unit.

[0032] The method may further comprise spraying water into the treatment chamber.

[0033] Correspondingly, the treatment chamber may comprise one of more nozzles for spraying water into the treatment chamber.

[0034] This is advantageous in that it increases the moisture content of the biomass and may also lower the temperature in the treatment chamber, thereby further increasing the efficiency of the impregnation. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] A more complete understanding of the abovementioned and other features and advantages of the present invention will be apparent from the following detailed description of preferred embodiments in conjunction with the appended drawings, wherein:

[0036] Fig. 1 shows an embodiment of a system for treating biomass according to the second and first aspects of the present invention.

[0037] Fig. 2 shows the difference between the first and second temperatures, i.e. second temperature-first temperature, in relation to different first temperatures for different ratios of added kg S02per ton dry substance of biomass in the treatment chamber.

[0038] Fig. 3 shows the efficiency of impregnation with S02in relation to different first temperatures for different ratios of added kg S02per ton dry substance of biomass in the treatment chamber.

[0039] All the figures are schematic, not necessarily to scale, and generally only show parts which are necessary in order to elucidate the respective embodiments, whereas other parts may be omitted or merely suggested. Any reference number appearing in multiple drawings refers to the same object or feature throughout the drawings, unless otherwise indicated. One or more superscript ‘ appended to a reference number indicates that the feature so reference is a variant of the feature assigned that reference number.

[0040] DETAILED DESCRIPTION

[0041] Fig. 1 shows an embodiment of a system 10 for treating biomass 20 according to the second and first aspects of the present invention. System 10 comprises a treatment chamber 20 holding a treatment gas SO2, a first crew plug feeder 30 receiving the biomass 2 to compress it and transfer it into the treatment chamber 20, and a second screw plug feeder 40 transferring the biomass 2 from the treatment chamber 20 to the hydrolysis unit 50. The treatment chamber 20 further comprises a transport screw 22 for transporting the biomass from one end of the treatment chamber 20 to the other so as to ensure a suitable residence time for the biomass 2 in the treatment chamber 20. Each of the first and second screw plug feeders 30 and 40 comprise a tapering screw 32, 42, an enclosure 34, 44, a nozzle 36, 46, and a device for breaking up the biomass, 38, 48. The first screw plug feeder 30 further comprises a secondary outlet or nozzle 36b for allowing liquid in the biomass to escape during the compression. In use the biomass is compressed to a first pressure and at a first temperature, such as room temperature. The compressed biomass enters the treatment chamber 20 in which is provided the treatment gas S02 at a second pressure that is lower than the first pressure and at a second temperature that preferably is the same as the first temperature, i.e., as shown there is no heating applied to the treatment chamber 20. Upon entering the treatment chamber 20 through the nozzle 36 the biomass 2 expands due to the difference in temperature. The expansion is further aided by the device 38 which is implemented as a spike or ram that engages the biomass 2 to break it up. The biomass 2 entering the treatment chamber 20 has a low content of liquid as liquid is pressed out of the biomass in the first screw plug feeder 30 and leaves it through the secondary nozzle or outlet 36b.

[0042] In the treatment chamber 20 the biomass 2 is treated by the treatment gas for a suitable time as determined by the speed of the transport screw 22. Once the biomass 2 has reached the end of the treatment chamber 20 it enters the second crew plug feeder 40, is compressed, and exits through the nozzle 36 to be further broken up by the device 38 before the biomass passes into the hydrolysis unit 50.

[0043] Thus, as shown, by not heating the biomass or the treatment chamber 20 or gas therein an efficient impregnation may be obtained. Further, by not providing any heating between the biomass exits the treatment chamber 20 and enters the hydrolysis unit 50, the process is made more efficient and there is more versatility in selecting the hydrolysis unit 50.

[0044] If desired, water may be sprayed into the treatment chamber 20 as indicated by arrow 52. The water may be sprayed into the treatment chamber 20 via one or more nozzles. The spraying of water provides for increasing the moisture content of the biomass material and reducing the temperature of the biomass thereby further increasing the efficiency of the impregnation.

[0045] EXAMPLE

[0046] A number of test runs were made to evaluate inter alia the difference in temperature between the second temperature and the first temperature, and the efficiency of impregnation. Generally, the test runs were made with 10 ton / h of wood chips being transferred into the treatment chamber. The first temperature generally was from 0-70 °C. The change in temperature, i.e. second temperature-first temperature, as well as the impregnation efficiency, was evaluated for different dosages, i.e. ratios, of added kg SO2 per ton dry substance of biomass in the treatment chamber and for different first temperatures. The following dosages were tested: 15 kg, 25 kg and 35 kg S02 per ton dry substance of biomass. The dosages correspond to 1.5 wt%, 2.5 wt% and 3.5 wt%, respectively of S02. Generally, an increase in temperature, i.e. a second temperature being higher than the first temperature, may be due to heat energy released as the S02d in any dissolves in water present in the biomass. In contrast, a decrease in temperature, i.e. a second temperature being lower than the first temperature, may be due to heat loss from the treatment chambering being larger than the heat energy released as the S02 dissolves in water present in the biomass.

[0047] As seen in Fig. 2, the difference in temperature ranges from about +3°C, i.e. the second temperature being STD higher, to -2.5 °C, i.e. the second temperature being 2.5 TD lower, than the first temperature. Accordingly, as described herein, the second temperature in no case was more than STD higher than the first temperature. As further seen in Fig. 2, the difference in temperature generally decreases from a positive difference to a negative difference as the first temperature increases. Generally, for all dosages, the difference in temperature was approximately +1 TD when the first temperature was GOTT Thus, as preferred, the second temperature may preferably be no more than 1 °C higher than the first temperature. However, as shown in Fig. 3, the efficiency of the impregnation is inversely dependent on the first temperature where the efficiency is the highest for all dosages the lower the first temperature. Thus, the highest efficiency was obtained for the first temperature being 0°C.

[0048] Generally, from Fig. 2 and Fig. 3, it can be concluded that for first temperature of at the most 20qC, the efficiency of impregnation was similar for all dosages of S02. At higher first temperatures, e.g. above 20 TD, the lower dosages of S02yielded progressively higher efficiency.

[0049] FEASABLE MODIFICATIONS

[0050] The invention is not limited only to the embodiments described above and shown in the drawings, which primarily have an illustrative and exemplifying purpose. This patent application is intended to cover all adjustments and variants of the preferred embodiments described herein. Thus the present invention is defined by the wording of the appended claims. Thus, the equipment may be modified in all kinds of ways within the scope of the appended claims. It shall also be pointed out that all information about / concerning terms such as above, under, upper, lower, etc., shall be interpreted / read having the equipment oriented according to the figures, having the drawings oriented such that the references can be properly read. Thus, such terms only indicate mutual relations in the shown embodiments, which relations may be changed if the inventive equipment is provided with another structure / design. It shall also be pointed out that even thus it is not explicitly stated that features from a specific embodiment may be combined with features from another embodiment, the combination shall be considered obvious, if the combination is possible.

[0051] Throughout this specification and the claims which follows, unless the context requires otherwise, the word “comprise”, and variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated integer or steps or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

Claims

Claims1 . A method of treating biomass (2), such as lignocellulosic material or cellulosic material, comprising the steps of: i. compressing the biomass to a first pressure and at a first temperature,II. transferring the biomass into a treatment chamber (20) containing a treatment gas at a second pressure lower than the first pressure and a second temperature being not more than S'XD higher than the first temperature, and ill. transferring the biomass from the treatment chamber into a hydrolysis unit (50), wherein the biomass has the second temperature, or a temperature not more than S'XD higher than the second temperature, when entering the hydrolysis unit.

2. The method according to claim 1 , wherein the biomass is compressed using a first compressing screw or plug screw feeder (30), whereby the first compressing screw or plug screw feeder is operated so as to compress the biomass to form a plug capable of preventing the treatment gas escaping the treatment chamber (20) through the first compressing screw of plug screw feeder.

3. The method according to any preceding claim, wherein step ill comprises breaking up the biomass upon entering the treatment chamber (20).

4. The method according to any preceding claim, wherein the biomass is transferred from the treatment chamber (20) into the hydrolysis unit (50) using a second compressing screw or plug screw feeder (40), whereby the second compressing screw or plug screw feeder is operated so as to compress the biomass to form a plug capable of preventing the treatment gas escaping the treatment chamber through second first compressing screw of plug screw feeder.

5. The method according to any preceding claim, wherein step: ill comprises breaking up the biomass before entering into the hydrolysis unit.

6. The method according to any preceding claim, wherein the treatment gas is SO2.

7. The method according to any preceding claim, wherein the second temperature is no more than 1 °C higher than the first temperature.

8. The method according to any preceding claim, wherein the second temperature is the same as the first temperature.

9. The method according to any preceding claim, wherein the biomass is heated in the hydrolysis unit (50).

10. A system (10) for treating biomass (2) such as lignocellulosic material or cellulosic material, comprising: i. a first compressing device (30) configured to compress biomass to a first pressure and at a first temperature and to transfer the biomass into a treatment chamber (20),II. a treatment chamber connected to the first device to receive compressed biomass, the treatment chamber being filled with a treatment gas at a second pressure lower than the first pressure and a second temperature being not more than 5TD higher than the first temperature, ill. a second compressing device (40) configured to transfer the biomass from the treatment chamber into a hydrolysis unit (50), and iv. a hydrolysis unit connected to the second compressing device.

11. The system according to claim 10, wherein the first compressing device comprises a first compressing screw or plug screw feeder (30), whereby the first compressing screw or plug screw feeder is configured to compress the biomass to form a plug capable of preventing the treatment gas escaping the treatment chamber through the first compressing screw of plug screw feeder.

12. The system according to any of the claims 10-11 , wherein the first compressing device further comprises a device (38) configured to break up the biomass upon entering the treatment chamber.

13. The system according to any of the claims 10-12, wherein the second compressing device comprises a second compressing screw or plug screw feeder (40), whereby the second compressing screw or plug screw feeder is configured so as to compress the biomass to form a plug capable of preventing the treatment gas escaping the treatment chamber through second first compressing screw of plug screw feeder.

14. The system according to any of the claims 10-13, wherein the second compressing device further comprises a device (48) configured to break up the biomass before entering the hydrolysis unit.

15. The system according to any of the claims 10-14, wherein the treatment chamber is devoid of any means of heating the treatment chamber.

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