WO2017143420A1

WO2017143420A1 - Method and apparatus for pretreating biomass

Info

Publication number: WO2017143420A1
Application number: PCT/BR2017/050037
Authority: WO
Inventors: Luciano ZAMBERLAN; Rodrigo Felicio FARIA
Original assignee: Raízen Energia S/A.
Priority date: 2016-02-22
Filing date: 2017-02-22
Publication date: 2017-08-31

Abstract

The present invention is directed to a method and apparatus for pretreating biomass, in particular sugarcane residues, prior to feeding it to a biofuel producing facility, wherein, in a first stage, biomass is mixed with liquid and kept wet. Wet biomass is then fed to a second, washing stage, wherein all solids are submerged in the liquid and stirred. The mixture is fed to a third, separation stage, wherein the solids are transported into a fourth stage by a conveyor with screens to separate ash from the biomass. The clean biomass is finally fed to the fourth, de-watering stage, which removes excess water from the biomass, delivering a higher solids concentrated biomass.

Description

METHOD AMD A A ATUS FOR PRETTRF.ATTMfi RTOMASS

FIELD OF THE INVENTION

[0001] The present invention is directed to a method and apparatus for pretreating biomass, in particular sugarcane residues, prior to feeding it to a biofuel producing facility .

BACKGROUND OF THE INVENTION

[0002] There is a great interest in the bioconversion of biomass,. such as material comprising lignocellulosic residues, into fermentable sugars. These sugars can be used in turn as chemical feedstock for the production of a biofuel, which is a clean-burning renewable energy source . Accordingly, there is a need in the industry for clean- burning renewable fuels.

[0003] Sugarcane ethanol is produced by the fermentation, of sugarcane juice and molasses. As a biofuel, it is cleaner and has a lower carbon footprint than petroleum derived fuels, while maintaining a competitive production cost. Therefore, sugarcane ethanol has emerged as a leading renewable fuel for the transportation sector, particularly in Brazil.

[0004] In processing raw sugarcane for the production of ethanol, the cane stalks are first fed into a crushing roller and then into a series of roller-type mills which squeeze the cane and force the sugar-containing j ice from the broken cells for further processing and refining treatment. Sugarcane residues (bagasse, straw and leaves) may be used in various ways . [0005] These by-products of the production of sugar and ethanol are generated in great volumes and, for example, many modern sugarcane ethanol facilities include thermoelectric power plants,, which burns sugarcane residues and provide energy for facility. Sugarcane residues may also be further processed for breaking down Iignoceliulosic material and generating further fermentable sugars for the prod ction of ethano1.

[0006] The development of such technologies for second generation (2G) ethanol has overcome several obstacles over the last few years, but there is still some problems that need to be solved before such processes achieve economic feasibility. Several of these problems now appear when scaling up production processes. For instance, the ash content in sugarcane bagasse, while relatively small, greatly contributes for damaging valves and equipment used in industrial scale 2G ethanol processes due to abrasion.

[0007] Therefore, before feeding sugarcane residues into a 2G ethanol process there is a need for separating mineral impurities from organic matter or, at least, decreasing ash content in sugarcane residues.

[0008] Prior art teaches apparatuses and methods for pretreating biomass, in particular sugarcane biomass, in order to remove unwanted material, such as pith fractions and other non-fibrous material.

[0009] For example, US 4,237,582, teaches a system consisting of a vertical depither, U-shaped washer, and a second vertical depither, arranged one above the other, so that bagasse and other vegetable fibers fall by gravity from unit to unit. A first depither is disposed above the inlet of a U-shaped washer which in turn has a second depither disposed below the outlet end of the U-shaped washer. Vegetable fiber fragments are metered into the first depither by means of a pin feeder. The fragments are broken down by the hammers in the upper part of the first depither and substantially depithed through the remainder of the first depither. The depithed fiber falls directly from the first depither into the inlet to the U-shaped washer. The removed pith falls into a separate outlet. The fiber is propelled through the washer, which removes any water- soluble matter. The washed fiber is drained at the exit end of the washer and allowed to drop into the second depither, where it is further depithed with the exiting fiber being conveyed to a digester, while the pith from the second depither is combined with that of the first depither and is conveyed to storage or use.

[0010] While useful for obtaining a high quality depithed fiber of optimum length and strength characteristics for the paper industry, such a system has an unacceptable loss of biomass for biofuel production, which does not require depithing .

[0011] US 5,173,122, in turn, teaches an apparatus for washing sugarcane billets, comprising a container for receiving the sugarcane billets and water sprays. As the container is rotated, the billets are re-oriented (in order to expose all portions of them to the sprayed water) and moved from the charging end of the container toward its discharge end. The container is generally cylindrical and rotatably driven by a motor about its longitudinal axis.

[0012] While such apparatus washes thoroughly the sugarcane billets and is suitable for use in a high- throughput operation, it does not efficiently washes sugarcane bagasse, because the dirt is not only on the surface of the sugarcane (as it. happens with billets) , but entangled within the mesh of bagasse fibers.

[0013] As noted, none of the prior art. technologies is suitable for use in an industrial scale 2G ethanol process. Therefore, there is still a need for a method and apparatus for pretreating biomass, in particular sugarcane residues, which reduces ash content, of biomass while keeping loss of organic matter as low as possible.

SUMMARY OF THE INVENTION

[0014] In one embodiment of the present invention, a method is provided for pretreating biomass, in particular sugarcane residues, prior to feeding it to a biofuel producing facility, wherein, in a first stage, biomass is mixed with liquid and kept wet . Wet biomass is then fed to a second, washing stage, wherein all solids are submerged in the liquid and stirred. The mixture is fed to a third, separation stage, wherein the solids are transported into a fourth stage by a conveyor with screens to separate ash from the biomass. The clean biomass is finally fed to the fourth, de-watering stage, which removes excess water from the biomass, delivering a higher solids concentrated biomass.

[0015] In another embodiment of the present invention, an apparatus is provided for pretreating biomass, in particular sugarcane residues, prior to feeding it to a biofuel producing facility, the apparatus comprising (i) first wetting means, in which biomass is mixed with liquid and kept wet; (ii) a second, washing zone, comprising a tank wherein all solids are submerged in the liquid and stirred by rotating baffles; (iii) a third, separation zone, comprising a conveyor with screens at the bottom to separate the ash from the biomass, and feeding the clean biomass to a fourth zone; and (iv) the fourth, de-watering zone comprising de-watering means to remove excess water from the biomass and deliver a higher solids concentrated biomass,

[0016] The method and apparatus for treating biomass according to the invention is designed for optimum ash removal efficiency, preferably 10 to 90%, while maintaining a high recovery of biomass and operating at a high throughput, preferably 1 to .30 TPH of dry bagasse feed,

[0017] Surprisingly, the conveyor system with screens at the bottom provides for improved, more efficient separation of sedimented particles of different sizes, while allowing for a continuous washing method. Further, the compact design of the apparatus according to the invention with integrated de-watering means provides for clean biomass with higher solids content, suitable for biofuel production processes.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] FIG. 1 is a flow diagram of a method

the present invention.

[0019] FIG. 2A is a simplified side view

apparatus according to the invention.

[0020] FIG. 2B is a simplified top plan view

apparatus according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0021] The present invention is directed to a method and apparatus for pretreating biomass, in particular sugarcane residues, reducing its ash content, prior to feeding it to a biofuel producing facility. [0022] In the context of the present invention, biomass is intended to mean organic matter that can be converted to fuel and is therefore regarded as a potential energy source.

[0023] Sugarcane residues is intended to mean the remainder of sugarcane plant after sugar containing juice has been extracted from sugarcane stalks for the production of sugar and ethanol , Sugarcane residues comprise bagasse and straw, i.e. the tops and leaves of sugarcane stalks.

[0024] Sugarcane bagasse is the dry, fibrous residue of sugarcane, consisting of lignocellulosic fibers together with pith, which consists of broken cells and other non- fibrous material. A typical composition of bagasse is: cellulose 33-53%; hemicellulose 18-23%; lignin 24-34%; ash 1-20%. The relative amount of these components depends on the sugarcane variety, the age and size of the stalks.

[0025] Ashes are comprised of inorganic compounds found in the pulp structure (which composition depends on the plant species, soil, the type of fertilizer etc.) and also of inorganic material dragged with harvesting {either mechanized or manual) . The main components of ash are silica, potassium, calcium, phosphorus, magnesium and other inorganic, material .

[0026] In the context of the present invention, biofuel is intended to mean a fuel, either gaseous, solid or liquid, such as ethanol, that is produced from renewable resources, especially plant biomass, vegetable oils, or treated municipal and industrial wastes . Preferably, biofuel is ethanol and more preferably, second generation (2G) ethanol. A biofuel producing facility is preferably a 2G ethanol prod cing faci.1ity . [0027] In the context of the present invention, pretreating is intended to mean a process wherein raw material is conditioned for optimizing performance of subsequent processing step (s) . Pretreating may include additional conditioning of the raw material. Preferably, pretreating is washing biomass to reduce its ash content, particularly by removing silica.

[0028] In one embodiment of the present invention, a method for pretreating biomass is provided, as illustrated by FIG. 1, comprising the steps of: wetting biomass; submerging and stirring biomass within liquid; transporting solids by a conveyor with screens to separate ash from biomass; and de-watering clean biomass.

[0029] In the first step 10, biomass is mixed with liquid and kept wet. Preferably, biomass is sugarcane residues which are mainly bagasse. Yet, the method according to the present invention is also suitable for pretreating other kinds of biomass, such as residues from miscanthus, switchgrass, sorghum etc. or biomass from other sources.

[0030] Liquid used for wetting biomass in the first step 10 is preferably water or an aqueous solution, which may optionally include other solvents. In one particular embodiment according to the present invention, the first step 10 is conducted within a screw conveyor, which provides a uniform wetting of the biomass while feeding wet biomass to subsequent step 12.

[0031] In the second step 12, wet biomass is fed to a washing stage, wherein all solids are submerged in the liquid and stirred. Preferably, the washing stage is a tank with liquid, preferably water or an aqueous solution which is substantially the same used in the previous step 10. In one particular embodiment according to the present invention, biomass is submerged and stirred by using one or more rotating baffles .

[0032] Stirring in the second step 12 must be vigorous enough to detach adhered ash, particularly silica

(especially sand or silt), from the biomass. Yet, stirring should be gentle enough to keep biomass substantially afloat, while ash is allowed to settle. Preferably, stirring is performed in a range of 0,2 to 1 hp/dry TPH of bagasse.

[0033] In the third step 14, the mixture of biomass with liquid is fed to a separation stage, wherein the solids are transported into the subsequent stage by a conveyor with screens to separate ash from the biomass. Preferably, the conveyor is a belt screen, with an opening size ranging from 0.5 to 5 mm. Preferably, the conveyor includes blades spaced apart which retain biomass, while transporting it upwards out of the liquid.

[0034] Transporting in the third step 14 must be slow enough to allow ash, particularly silica, to pass through the screen and be separated from biomass.

[0035] In the fourth step 16, the clean biomass is fed to a de-watering stage, which removes excess water from the biomass, delivering a higher solids concentrated biomass. Preferably, de-watering is performed by a screw press. Preferably, clean biomass contains 10 to 90% less ash content with respect, to untreated biomass.

[0036] Although the method according to the present invention was described above with each step occurring separately and in a sequential manner, the first and the second steps 10, 12 may partially overlap as represented by the dashed double arrow in FIG. 1. Optionally, the first and the second steps 10, 12 occur simultaneously, with dry biomass fed directly to the washing stage.

[0037] In a preferred embodiment according to the present invention, the second and the third steps 12, 14 partially overlap as represented by the dashed double arrow in FIG. 1, although the first and the second steps 10, 12 occur- separately and in a sequential manner.

[0038] In another embodiment of the present invention, an apparatus for pretreating biomass is provided, as illustrated by figures 2A and 2B, the apparatus comprising

(i) first wetting means 20, in which biomass is mixed with liquid and kept wet; (ii) a second, washing zone, comprising a tank 30 wherein all solids are submerged in the liquid and stirred by at least one roller with baffles 24; (iii) a third, separation zone, comprising a conveyor with screens at the bottom 26 to separate the ash from the biomass, and feeding the clean biomass to a fourth zone; and (iv) the fourth, de-watering zone comprising de-watering means 22 to remove excess water from the biomass and deliver a higher solids concentrated biomass.

[0039] In a preferred embodiment according to the invention, the apparatus comprises a tank 30 with a first, deeper section and a second section with a positive inclination a. Preferably, a varies from 5° to 60°.

[0040] The first wetting means 20 is preferably a screw conveyor, which provides a uniform wetting of the biomass while feeding wet biomass to the washing zone. Preferably, biomass is sugarcane residues which are mainly bagasse. Yet, the apparatus according to the present invention is also suitable for pretreating other kinds of biomass, such as residues from miscanthus, switchgrass, sorghum etc, or biomass from other sources,

[0041] The first wetting means 20 is preferably adapted for using water or an aqueous solution for wetting biomass. Optionally, the first wetting means is adapted for using other solvents as well.

[0042] In a preferred embodiment according to the invention, the washing zone includes two, optionally three, four or five, rollers with baffles 24 for submerging all solids in the liquid and stirring. Preferably, the tank 30 is filled with water or an aqueous solution which is substantially the same used in the wetting means 20.

[0043] The movement of the one or more rollers with baffles 24 must be vigorous enough to detach adhered ash, particularly silica (especially sand or silt) , from, the biomass. Yet, such movement should be gentle enough to keep biomass substantially afloat, while ash is allowed to settle. Preferably, the one or more rollers with baffles 24 consist of rollers with curved blades disposed in a helical manner around them,

[0044] In a preferred embodiment according to the invention, the first, deeper sectio of the apparatus includes one or more openings at the wall of one or more tapered lower sections 38 for removing the accumulated ash.

[0045] In a preferred embodiment according to the invention, the separation zone comprises a conveyor with screens at the bottom 26 extending from the first, deeper- section of the apparatus to the second, section with positive inclination a. Preferably, the conveyor 26 is a belt screen, with an opening size ranging from 0.5 to 5 mm. Preferably, the conveyor: includes blades 28 spaced apart which retain biomass, while transporting it upwards out of the liquid.

[0046] Preferably, the belt conveyor 26 is driven by first and second driving means 34, .36 at each end. Operation of the first and second driving means 34, 36 must be slow enough to allow ash, particularly silica, to pass through the conveyor screen 26 and be separated from biomass.

[0047] In a preferred embodiment according to the invention, the clean, biomass leaves the conveyor 26 and through an outlet 32, being then fed to the de-watering zone comprising de-watering means 22. Preferably, clean biomass leaves the outlet 32 with 10 to 90% less ash content with respect to untreated biomass.

[0048] Preferably, the de-watering means 22 is a screw press which removes excess water from the biomass, delivering a higher solids concentrated biomass.

EXAMPLE

[0049] Ashes present in sugarcane bagasse samples were determined to correspond to 8 to 35% in dry weight basis. A prototype apparatus according to the invention was constructed and several test, runs were conducted, wherein batches of 4 to 9 m³ of sugarcane were fed to the apparatus at different material rate flows, ranging from 2 to 6 tons per hour (TPH) .

[0050] Test runs resulted in ash removal efficiency varying from 10-90% for all adherent ash in bagasse. Also a low loss of cellulosic biomass was achieved (5% on average, as compared to an. average loss of 20% obtained, by using traditional pretreating methods and apparatuses) . [0051] While the principles of the present invention have been described in connection with certain specific embodiments, it should be clearly understood that these are made only by way of illustration and are not intended to limit the scope of the invention defined by the claims. It should also be understood that certain modifications to the presently claimed invention may be made by the skilled in the art without departing from the spirit and scope of the present invention.

Claims

1. A method for pretreating biomass comprising the steps of: (i) wetting biomass; (ii) Submerging and stirring biomass within liquid; (iii) transporting solids by a conveyor with screens to separate ash from biomass; and (iv) de-watering clean biomass.

2. The method of claim 1, wherein biomass is selected from residues of sugarcane, miscanthus, switchgrass or sorghum.

3. The method of claim 2, wherein biomass is sugarcane residues, optionally sugarcane bagasse.

4. The method of claim 1, wherein step (i) is carried out with an aqueous solution.

5. The method of claim 1, wherein step (i) is carried out within a screw conveyor.

6. The method of claim 1, wherein step (ii) is carried out in a washing stage comprising a tank with an aqueous solution .

7. The method of claim 6, wherein step (ii) is carried out by using one or more rotating baffles.

8. The method of claim 1, wherein step (iii) is carried out over a belt screen, with an opening size ranging from 0.5 to 5 mm and blades spaced apart to retain biomass.

9. The method of claim 1, wherein step (iii) is carried out within a screw press.

10. An apparatus for pretreating biomass comprising: (i) first wetting means, in which biomass is mixed with liquid and kept wet; (ii) a second, washing zone, comprising a tank wherein all solids are submerged in the liquid and stirred by at least one roller with baffles; (iii) a third, separation zone, comprising a conveyor with screens at the bottom to separate the ash from the biomass, and feeding the clean biomass to a fourth zone; and (iv) the fourth, de- watering zone comprising de-watering means to remove excess liquid from the biomass.

11. The apparatus of claim. 10, wherein the first wetting means is a screw conveyor.

12, The apparatus of claim 10, wherein the liquid is a water solution.

13, The apparatus of claim 10, wherein the tank has first, deeper section and a second section with a positive inclination .

14. The apparatus of claim 13, wherein the positive inclination varies from 5° to 60°.

15, The apparatus of claim 10, wherein the first, deeper section of the apparatus includes one or more openings at the wall of one or more tapered lower sections for removing the accumu1ated ash .

16. The apparatus of claim 1Q, wherein the at least one roller with baffles consists of a roller with curved blades disposed in a helical manner around them.

17, The apparatus of claim 10, wherein the washing zone comprises two to five rollers with baffles.

18. The apparatus of claim 10, wherein the at least, one roller with baffles operates in a range of 0,2 to 1 hp/dry TPH of bagasse.

19. The apparatus of claim 10, wherein the separation zone comprises a belt screen extending from the first, deeper- section of the apparatus to the second section with a positive i c1 i ation .

20. The apparatus of claim 10, wherein the separation zone comprises a belt screen with an opening size ranging from 0.5 to 5 mm and blades spaced apart to retain biomass.

21. The apparatus of claim. 10, wherein the de-watering means is a screw press.