Patent Application
20130326935
The present invention relates to a system and corresponding process for the recovery of useful materials such as gasses and oils from biomass.
Biomass feedstock has been subjected to various processes, including combustion for the generation of power and heat, typically using processes similar to those employed with fossil fuels, e.g., with the biomass being burned in a boiler to produce high pressure steam.
In recent decades, biomass has been increasingly used for the production of useful solids (e.g., charcoal), liquids (e.g., tar and other organics), and gaseous products—by means of various processes that involve the thermal degradation of biomass in the absence of air or oxygen. See, for example, Biomass pyrolysis: a state-of-the-art review. B. V. Babu, Biofuels, Bioprod. Bioref. 2:393-414 (2008), the disclosure of which is incorporated herein by reference.
Applicant itself is a world leader in the production of food and chemical processing equipment and systems that include thermal processing, polymer processing, drying, agglomeration, size reduction, compaction, briquetting, liquid/solid separation, mixing and blending for the food, chemical and polymer markets. Included within such equipment are Applicant's Solidaire® Drying System, which can be used for various purposes, e.g., to process heat-sensitive materials ranging from free-flowing solids to wet cakes and slurries.
What is clearly needed are improved procedures for the treatment of biomass to provide useful products, such as biofuels, and particularly in a manner that improves performance and corresponding economics, e.g., by minimizing concerns due to such things as conversion efficiency, feedstock variability, changes in feedstock upon storage, and the energy needed for mechanical size reduction.
The present invention provides a system, including components thereof, as well as a process for using such a system to treat biomass in order to obtain commercial products (e.g., bio-products such as bio-oils and bio-fuels). The process can comprise a plurality of processing steps, including preferably a plurality of pyrolysis steps, which in turn can provide and facilitate the recovery of corresponding gasses/vapors and other products. The invention further provides useful intermediates and final products derived from the system and corresponding process described herein. The system and corresponding process provide an optimal combination of low capital cost, energy balance, yield, scale and scalability, and the ability to be customized for use with various feedstock and under varying conditions.
In a preferred embodiment, a process of this invention includes the following steps:
a) providing an initial source of biomass, the biomass having initial characteristics, including particle size, water content, and content of polysaccharide based polymers (e.g., hemicellulose, cellulose, and lignin content);
b) optionally and preferably, pretreating the initial biomass source in order to provide it with desired characteristics, e.g., including changing its particle size in order to accommodate further processing;
c) optionally and preferably, drying the initial biomass source to reduce its moisture content, under conditions in which gasses and/or vapors can be captured and subjected to one or more processes selected from the group consisting of: (i) recycling the gas/vapor into the system, in order to faciliate pretreatment (e.g., drying) of biomass, (ii) condensing and recovering the gas/vapor or components thereof, and (iii) thermal oxidation, venting or otherwise disposing of the gas/vapor;
d) providing a first pyrolysis device adapted to heat the optionally pretreated, dried biomass under controlled conditions;
e) introducing the optionally pretreated biomass into the first pyrolysis device, and operating the device under conditions suitable to preferentially affect the relative content of polysaccharide based polymers, preferably, by providing a first pyrolysis product having substantially reduced hemicellulose content as compared to the initial biomass, while substantially retaining the cellulose and/or lignin content, while driving off volatiles in the form of one or more gasses or vapors;
f) obtaining a first pyrolysis product (e.g., intermediate), comprising a carbon enriched material having an altered content of polysaccharide based polymers (e.g., substantially less hemicellulose content than the initial biomass, while substantially retaining and optionally enriching cellulose and/or lignin content as compared to the initial biomass),
g) providing a second pyrolysis device, adapted to further pyrolyze the first pyrolysis product in order to provide one or more second pyrolysis gasses/vapors (e.g., condensable or non-condensable fuel) and byproduct (e.g., ash, char);
h) introducing the first pyrolysis product into the second device, and operating the second device under conditions suitable to:
The invention further provides individual system components, as well as corresponding chemical intermediates and final products, that are considered novel in their own right. For instance, the system provides a first pyrolysis device adapted to treat biomass in the manner provided herein in order to provide a first, e.g., intermediate, product by pyrolysis, while recovering one or more corresponding gasses and/or vapors. The system further provides a second pyrolysis device adapted to treat biomass, and particularly to treat an intermediate as described herein, in order to provide a byproduct for further processing or recovery, while also recovering one or more corresponding gasses and/or vapors. The gasses and/or vapors recovered from either or both pyrolysis steps themselves can contain useful chemicals, e.g., corresponding to the breakdown of hemicellulose and cellulose/lignin, respectively. The ability to preferentially distinguish as between the breakdown products and corresponding gasses/vapors derived from the first and second pyrolysis steps can provide a useful, and economically efficient means for recovering corresponding chemical compounds therefrom.
In turn, the invention provides a system that includes the functional combination of first and second pyrolysis devices as described herein. The devices can be provided separately, or in any suitable combination, e.g., as regions or zones of the same device, or as the same device (including individual portions thereof) operated under different corresponding conditions.
The devices and corresponding steps can also be provided in any suitable physical and/or temporal combination, e.g., they can be combined or coupled directly, where both are physically positioned in a manner that permits the first pyrolysis product to be directly or indirectly delivered to the second device. In turn, if the intermediate can remain at or near the first reaction temperature, its exotherm can be used to provide some or all of the energy necessary in the second pyrolysis device, thereby conserving costs, and ideally improving yield, etc. By contrast, the first and second pyrolysis steps can be provided in such a manner that they are separated or remote in either time and/or location, e.g., such that the intermediate product is recovered, optionally permitted to cool down, and later subjected to the second pyrolysis step at a remote time and/or location.
In turn, the devices and corresponding steps can be provided in such a manner that one or more of the gas/vapor components derived from either the first and/or second pyrolysis steps, are functionally recycled into the overall system, e.g., to permit the recycling/combustion of heated gasses from the first pyrolysis device in order to facilitate the pretreatment (drying) of biomass. In such an embodiment, the system can further comprise a flow circuit and corresponding controls, permitting the recirculation of one or more gas/vapors, for use in various other parts of the system, or ancillary systems.
The present invention further provides a first pyrolysis (e.g., intermediate) product, that preferably provides substantially reduced hemicellulose content as compared to original biomass content, while comparatively retaining the cellulose and/or lignin content.
A system of the present invention can be used to separate the pyrolysis process into a plurality of stages, in order to optimize the product and processing characteristics associated with each, while minimizing the capital expenses and operating expenses for the system itself. The stages can include one or more steps selected from the group consisting of feedstock preparation, drying, size reduction, heating/reacting, further reacting, gas/solid separation, combustion/liquefying of the gases, agglomeration, further (e.g., fast) pyrolysis/gasification, and solid cooling. A preferred system, in turn, can be customized for use with various feed stocks, under varying conditions, and for a corresponding array of end uses. Separation and selection of the equipment for each unit operation/biomass can be optimized, and is particularly justified for large capacity systems.
In turn, the invention further provides one or more commercial chemicals (e.g., pyrolysis reaction products) derived from one or more gasses and/or vapors produced using a process as described herein.
A particularly preferred embodiment of the system will be further described with reference to attached
A preferred process of the invention will be further described with reference to the plot of
Target biomass can be obtained from any suitable source. Examples of suitable biomass include, but are not limited to, wood (e.g., wood chips, forestry residues, agricultural waste wood), grasses (e.g., switchgrass), algae, and agricultural plants or residues (e.g., corn, and more preferably corn stover). The suitable biomass is preferably readily available, low cost, and easy to harvest and transport to a processing center, and preferably have a reasonably high calorific value and low moisture.
One preferred example of a suitable feedstock is corn stover, which originates from the top half of a corn stalk and typically needs to be ground up in order to be both transported and conveyed effectively. Conventional grinders for use in the field include those known as haybusters, which can be used with different screen sizes, to produce correspondingly different biomass products. For instance, corn stover can be ground to a form that is very light in bulk density, e.g., less than 5 lbs/cubic ft. In turn, the ground corn stover can be dried in a flash/dispersion dryer. Similarly, forest residuals and wood ships are often ground in conventional machines (available, for instance, from West Salem Machinery), in order to provide chips that are less than about 1 inch (25 mm) in size. At such a size, the chips could be dried in a direct fired rotary dryer, such as those manufactured by M-E-C Company, since they are not suitable for pneumatic conveying as required in a flash dryer.
Preferably, a process of the present invention includes the step of drying biomass prior to pyrolysis. Optionally, and preferably, such drying can be accomplished using gases produced from thermal oxidation of low value gases produced during pyrolysis. The combustion gas can be mixed with gas recirculated from the drying process to reduce the inlet temperature to the direct dryer. Preferably, this gas can have reduced oxygen content, thereby reducing the risk of combustion, and effectively removing oxygen upstream of the pyrolysis processes. It is typically preferred to limit the size reduction prior to drying, to correspond with that required by the dryer, since size reduction of raw biomass can tend to be very costly, particularly when reducing it to fine particle size. In use, a dryer can preferably preheat the dried biomass to approximately 150 C-250 C, (e.g., about 200 C), which is just below pyrolysis temperature. This reduces the heat duty to pyrolyzer. Direct dryers for biomass are effective due to low capital cost, low maintenance, ability to use high temperature combustion gases, scale up to large capacities, and energy efficiency.
In a preferred method of this invention, the optionally pretreated biomass is delivered into the first pyrolysis device under conditions suitable to heat the biomass to a desired temperature within a short residence time, and in the substantial absence of oxygen. For instance, a preferred process and device can be used to heat the biomass to a temperature between about 250 and about 500 C, more preferably between about 300 and about 400 C, and even more preferably between about 340 and about 360 C. In turn, the biomass is heated for a suitable time, e.g., from about 1 C/second to about 60 C/second, more preferably between about 3 C/seconds to about 30 C/seconds, and even more preferably between about 5 C/seconds and about 20 C/seconds. Preferably, the biomass is heated for a heating time (tpyr1,h as described with regard to
The extent of the first pyrolysis is preferably sufficient to substantially reduce the hemicellulose content as compared to original content, while comparatively retaining the cellulose and lignin content. In turn, the first pyrolysis can drive off volatiles (e.g., hemicellulose breakdown products) in the form of a gas and/or vapor, which can be handled in any suitable manner, and preferably to recover useful chemical compounds therefrom. This first pyrolysis can also remove undesirable volatiles that would be undesirable in the downstream process such as acetic acid, sulfur, oxygen.
Preferably, a first pyrolysis device for use in a system of the present invention provides an optimal combination of capacity, operating cost, heat transfer, conversion of celluloses and lignins to valuable organic compounds, and removal of undesirable volatiles.
For instance, a device such as the Solidaire Drying System (available commercially from Bepex International) can handle large particles effectively and can effectively perform size reduction of the pyrolyzed material by attrition of the outer surface of the particle. In turn, such a device can provide an optimal combination of various attributes, including the rate of heat increase, scalability, and usefulness with a wide variety of materials. This can result in a fine, thoroughly treated end product, despite a large feed particle. Applicant has found that the ability of a Solidaire type device to handle a wide range of biomass materials, in combination with these and other features, makes it particularly useful in a process of the present invention. Although it is best to design a system to handle a specific biomass material, the flexibility of the system is also important as feedstock availability and costs fluctuate significantly. Since the feedstock cost is a significant component of the cost of producing the product, the ability of the system to handle multiple biomass materials is critical.
A typical Solidaire unit includes a cylindrical, heated housing and a high speed rotor with adjustable paddles. The material moves in a thin, dense, annular spiral from inlet to discharge. The adjustable paddles allow for its use with a wide range of material properties, which makes the device particularly useful for the wide range of biomass available. The adjustable paddles can convey materials with poor flowability, as well as adapt to variations in the conveyance of materials whose flow characteristics change in the course of the reaction. In turn, such a device provides a very high heat transfer coefficient, by virtue of the movement of material (convection) in the form of a dense layer in contact with the heat transfer surface (conduction), resulting in both rapid and even treatment of the material. As the heat transfer occurs indirectly through the vessel wall, the device can minimize the use of inert gases required in other devices. Minimizing or eliminating the need for inert gas, as provided in a preferred embodiment of this invention, can improve the collection efficiency of the volatiles and reduces the cost of the gas treatment system.
A first device of this type is particularly well suited for use with biomass such as corn stover, which consists of the leaves and stalks of maize (Zea mays) plants left in a field after harvest and consists of the residue, often including the stalk; the leaf, husk, and cob remaining in the field following the harvest of cereal grain. Stover makes up about half of the yield of a crop and is similar to straw. Corn stover is itself typically a light, fluffy, non-flowable material that can be hard to process using conventional approaches.
A preferred Solidaire type device is described, for instance, in U.S. Pat. No. 5,271,163, Pikus, the disclosure of which is incorporated herein by reference. The '163 patent describes, inter alia, a method and apparatus for treating flowable material wherein an elongated cylindrical housing is provided with an inlet for introducing material to the housing at one end thereof. The elongated cylindrical housing can comprise a vessel of the type described in U.S. Pat. No. 3,425,135, the disclosure of which is also incorporated herein by reference. An agitator is provided for rotation within the housing. The agitator includes a plurality of paddles which extend from the periphery of the agitator adjacent its axis of rotation and then outwardly toward the inner wall surface of the cylindrical housing.
The vessel is jacketed so that heating or cooling medium may be circulated adjacent the inner wall surface or electrically heated by conduction or radiation. In turn, different sections of a vessel, or vessels connected in series, can be maintained at different temperatures to provide differing treatments for material introduced to the vessel or vessels.
In a preferred method of this invention, following the first pyrolysis step the resulting intermediate product can be used in any suitable manner, but is preferably delivered to the second pyrolysis device under conditions suitable to further heat the biomass to a desired temperature within a short residence time. For instance, a preferred second pyrolysis step and device can be used to heat the biomass to a temperature between about 350 and about 1000 C, more preferably between about 400 and about 800 C, and even more preferably between about 550 and about 650 C. In turn, the biomass is heated at a suitable heating rate, e.g., from about 1 C/second to about 200 C/seconds, more preferably between about 3 C/seconds to about 100 C/seconds, and even more preferably between about 5 C/seconds and about 50 C/seconds. Preferably, the biomass is heated for a heating time (tpyr2,h as described with regard to
The extent of the second pyrolysis is preferably sufficient to substantially breakdown (e.g., decompose and depolymerize) the remaining cellulose and lignin content. In turn, the second pyrolysis can drive off corresponding volatiles in the form of a gas and/or vapor, which can be handled in any suitable manner, and preferably in order to recover useful chemical compounds therefrom. The resulting solid byproduct (e.g., ash or char) can itself be recovered and used in any suitable manner.
A second pyrolysis device of the present system can be of any suitable type, e.g., in the form of a second device, or as separate compartments of a single device, or as the same device (or portions thereof) operated under corresponding, different conditions.
Examples of a second pyrolysis device include a Solidaire type device, of the type described above, as well as other devices that have been described for use in the pyrolysis of biomass, and are capable of being adapted for use in a system of this invention. Examples of such devices include, but are not limited to, devices selected from the group consisting of a Solidaire type paddle drying device, bubbling and circulating fluidized bed reactors, rotating cone reactors, auger reactors, ablative reactors, vacuum reactors, and free fall reactors.
A preferred process and system of this invention can be used to preferentially recover volatiles from the first and second pyrolysis steps, respectively, in order to preferentially recover corresponding chemical compounds therefrom.
Representative products to be derived from the biomass are described, for instance, in Synthesis of Transportation Fuels from Biomass: Chemistry, Catalysts, and Engineering, Chem. Rev. 106:4044-4098 (2006), the disclosure of which is incorporated herein by reference. The products to be derived from the pyrolysis of hemicellulose and cellulose include acids (e.g., formic, acetic, propanoic), esters (e.g., methyl formate, butyrolactone, angelicalactone); alcohols (e.g., methanol, ethanol, ethylene glycol); ketones (e.g., acetone), aldehydes (e.g., formaldehyde, acetaldheyde, ethanedial, glycolaldehyde, acetol); sugars (e.g., anhydroglucose, cellobiose, fructose, glucose); furans (e.g., fufurol, HMF, furfural); phenols (e.g., phenol, diOH-benzene, dimeth-phenol); lignin; and guaiacols (e.g., isoeugenol, eugenol, methyl guaiacol, syringols).
The bio-oil contains acids (some of the major components include acetic, propanoic), esters (methyl formate, butyrolactone, angelica lactone), alcohols (methanol, ethylene glycol, ethanol), ketones (acetone), aldehydes (acetaldehyde, formaldehyde, ethanedial), miscellaneous oxygenates (glycolaldehyde, acetol), sugars (1,6-anhydroglucose, acetol), furans (furfurol, HMF, furfural), phenols (phenol, diOH benzene, methyl phenol, dimethyl phenol), guaiacols (isoeugenol, eugenol, 4-methyl guaiacol), and syringols (2,6-diOMe phenol, syringaldehyde, propyl syringol). The multicomponent mixtures are derived primarily from depolymerization and fragmentation reactions of the three key building blocks of lignocellulose: cellulose, hemicellulose, and lignin. The guaiacols and syringols are formed from the lignin fraction, whereas the miscellaneous oxygenates, sugars, and furans form from the cellulose and hemicellulose biomass fraction. The esters, acids, alcohols, ketones, and aldehydes probably form from decomposition of the miscellaneous oxygenates, sugars, and furans.
The pyrolysis of pure cellulose produces mainly levoglucosan in yields of up to 60%, which is believed to be formed by a mechanism involving intramolecular condensation and sequential depolymerization of the glycosidic units.
Given the present application, those skilled the art will appreciate the manner in which various factors can affect the recovery of compounds as between the first and second pyrolysis steps, e.g., based upon such factors as the feedstock itself (including moisture content, Nitrogen content and biochemical makeup), the conditions of first and second pyrolysis, respectively, (e.g., temperatures, heating rate and times, heat transfer rate, extent of vapor dilution) the efficiency of solids removal, and including also the exposure of air during storage of the bio-oil or other chemical compositions recovered from either or both pyrolysis.
| Number | Date | Country | |
|---|---|---|---|
| 61658021 | Jun 2012 | US |
