Patent Application
20130248760
The invention generally relates to pre-treatment of biomass using steam explosion methods, thermal mechanical pulping processes, and others to condition the biomass particle before torrefaction or gasification.
Medium density fiberboard is made with dry wood chips and uses fibers of trees in the fiberboard. Other processes require multiple steps of grinding the wood chips, drying the chips, re-grinding the chips, moisturizing the fibers, densifying the fibers, and then densifying the wood chips (such as in the form of pellets). These processes are complex, capital intensive and require large amounts of energy. Some other typical processes need to dry the chips of biomass and then grind the chips to very small dimensions before sending them to a subsequent heating/processing unit. This drying and grinding takes a lot of energy and capital costs. These processes produce small fibers but ones that are many times the size of the fine powder particles produced in the biomass particle and none have been used a biomass gasification reaction. Likewise, some processes have produced fuel compositions from ethanol but not through torrefaction or biomass gasification.
A biomass composition of matter to be used in a torrefaction process or a biomass gasification reaction. The biomass in a particle form is created in a pretreatment step that occurs prior to the torrefaction process or the biomass gasification reaction. A bulk structure of the biomass is 1) stripped apart to at least partially separate an outer layer of lignin in the biomass from the cellulose fibers, 2) internally blown apart to create fragments of the fiber bundle, and 3) any combination of the two in the pretreatment step. The biomass in particle form has a length to thickness aspect ratio on average of less than 300 to 1, a thickness on average of less than 100 microns thick and a length on average of less than 3000 microns.
The multiple drawings refer to embodiments of the disclosure. While embodiments of the disclosure described herein are subject to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and will herein be described in detail.
While the disclosure is subject to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and will herein be described in detail. The disclosure should be understood to not be limited to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the disclosure.
In the following description, numerous specific details are set forth, such as examples of specific chemicals, named components, connections, types of heat sources, etc., in order to provide a thorough understanding of the present invention. It will be apparent, however, to one skilled in the art that the present disclosure may be practiced without these specific details. In other instances, well known components or methods have not been described in detail but rather in a block diagram in order to avoid unnecessarily obscuring the present disclosure. Thus, the specific details set forth are merely exemplary. The specific details may be varied from and still be contemplated to be within the spirit and scope of the present disclosure.
In general, a number of example processes for and apparatuses associated with a pre-treatments of biomass are described. The following drawings and text describe various example implementations for biomass particle created by the pre-treatments of biomass. In an embodiment, a method creates a biomass composition of matter to be used in 1) a biomass gasification reaction where larger organic molecules making up the biomass are decomposed into smaller molecules to create syngas components, including hydrogen (H2) and carbon monoxide (CO), as a product of the biomass gasification reaction, 2) a torrefaction process, or 3) any combination of the two. Biomass in a particle form is created in a pretreatment step that occurs prior to the biomass gasification reaction or torrefaction process. The biomass initially has a bulk structure including organic polymers of lignin that surround a plurality of cellulose fibers in a fiber bundle. The bulk structure of the biomass is 1) stripped apart to at least partially separate an outer layer of lignin in the biomass from the cellulose fibers, 2) internally blown apart to create fragments of the fiber bundle, and 3) any combination of the two in the pretreatment step that uses at least moisture, pressure, and heat to liberate and expose the cellulose fibers to be able to react in a two stage sequence during the biomass gasification reaction or torrefaction process rather than react in a repeating cycle of multiple layers of lignin followed by the cellulose and hemi-cellulose. The produced biomass in particle form has a length to thickness aspect ratio on average of less than 300 to 1, a thickness on average of less than 100 microns thick and a length on average of less than 3000 microns.
One skilled in the art will understand parts and aspects of many of the designs discussed below within this illustrative document may be used as stand-alone concepts or in combination with each other.
A pretreatment step may create a biomass composition of matter, such as those examples shown in
The biomass in chip form 151 initially has a bulk structure including organic polymers of lignin that surround a plurality of cellulose fibers in a fiber bundle. The bulk structure of the biomass may be 1) stripped apart to at least partially separate an outer layer of lignin in the biomass from the cellulose fibers, 2) internally blown apart to create fragments of the fiber bundle, and 3) any combination of the two in the pretreatment step. The pretreatment step, such as Thermo Mechanical Pulping (TMP), Steam Explosion Process (SEP) or similar process, may use at least moisture, pressure, and heat to liberate and expose the cellulose fibers to be able to react in a two stage sequence during the biomass gasification reaction or torrefaction process rather than react in a repeating cycle of multiple layers of lignin followed by the cellulose and hemi-cellulose. The biomass in particle form 153 may have a length to thickness aspect ratio on average of less than 300 to 1, a thickness on average of less than 100 microns thick, and a length on average of less than 3000 microns.
In an embodiment, woody biomass can arrive at the pretreatment process in the form of chips 151 that can range in size from 0.5 to 3″ in length. (See chip 351 in
The pretreatment system advantageously strips apart and/or internally blows apart the fibers in the fiber bundle from each other leaving the lignin that was in the middle lamella (See
Note, the lignin-coated fibers could be first processed using torrefaction and or extractive removal, and then followed by biomass gasification, or gasified directly or only torrefied.
Thus in an embodiment, the biomass particle 153 created in the pretreatment step includes both 1) chunks of pure lignin, from the outer layer of lignin surrounding any hemi-cellulose and cellulose in the cellulose fibers, that have been separated from the cellulose fibers as well as 2) cellulose fibers now freestanding from the fiber bundle. The freestanding cellulose fibers generally will have some lignin still attached to the surface of the fiber. The biomass particle when fed into the biomass gasifier is allowed a more rapid exposure to directly react the cellulose and hemi-cellulose as well as substantially eliminating having to react layer after layer of lignin surrounding the cellulose and hemi-cellulose, followed by another layer of lignin surrounding cellulose and hemi-celluloses, etc. that would have to be sequentially reacted through if the pretreatment step did not at least partially separate the lignin from the cellulose fibers. The produced particles of biomass 153 are fed downstream to the biomass gasifier for the rapid biomass gasification reaction in a reactor of the biomass gasifier because they create a higher surface to volume ratio for the same amount of biomass compared to the received biomass in chip form 151, which allows a higher heat transfer to the biomass material and a more rapid thermal decomposition and gasification of all of the molecules in the biomass.
Referring to
The pretreatment step of Thermo Mechanical Pulping process can make the biomass in particle form. Thus, Thermo mechanical pulping is one method that actually separates the fibers from each other in the fiber bundle leaving the lignin and hemi-cellulose at least partially intact on the outside of the cellulose fiber.
Referring to
In general, the Thermo Mechanical Pulping process can use two or more stages to pretreat the biomass for subsequent supply to the biomass gasifier. The stages are configured to use a combination of heat, pressure, moisture, and mechanical agitation that are applied to the biomass to degrade bonds between the lignin from the cellulose fibers, and then mechanically strip fibers from the fiber bundle to separate an outer layer of lignin in the biomass from the cellulose fibers. The stages then supply the biomass particles in a pulp form from an outlet stage of the Thermo Mechanical Pulping process to one of a densification unit, a torrefaction unit 712, a dryer, or a biomass gasifier 714.
In an embodiment, the multiple stages of Thermo Mechanical Pulping are configured to loosen and strip fibers from the lignin in the biomass. The two or more stages may include a steam tube stage 706 and a refiner unit stage 708. The steam tube stage 706 has the input cavity to receive biomass in chip form 751 and a steam supply input to apply steam into a vessel containing the biomass in chip form 751 to elevate temperature in the vessel to between 130 to 200 degrees C. at a pressure between 70 and 110 PSI. In an embodiment, chips 751 are pretreated with steam in the steam tube's pressure vessel 706 at about 160° C. and about 90 psi for approximately 2 minutes. These conditions are sufficient to soften the lignin. The biomass in chip form 751 with softened lignin is then fed from the steam tube stage 706 to the refiner unit stage 708, which is at the same pressure as the steam tube stage 706. In the refiner unit 708, a mechanical separator is configured to further to cooperate with the steam to separate the plurality of cellulose fibers in the fiber bundle into biomass in particle form 753 consisting of 1) individual strands of fibers 2) a group of no more than three individual fibers in the group of fibers 2), and 3) any combination of both. A conveying system coupled to a collection chamber at an outlet stage of the refiner unit stage supplies particles of biomass in pulp form. A majority of the initial lignin and cellulose making up the biomass received in the receiver section of the thermally decomposing stage remains in the produced particles of biomass but is now substantially separated from the fibers in pulp form.
Generally, biomass may contain a cellulose core with a coating of hemi-cellulose and lignin.
Cellulose is a principal chemical constituent of the cell walls of higher orders of plants. Cellulose is a complex carbohydrate, such as (C6H10O5), occurring in the form of polymer chains, primarily Glucose molecules joined together end to end. Cellulose contains linear polysaccharides in the cell walls. The multiple groups of glucose molecules form a chain held firmly together side-by-side and forming microfibrils with high tensile strength. Lignin and hemi-cellulose can also be found between the microfibrils bonding them together and contributing to the strength of the fiber. Microfibrils can be grouped together to form fibrils and the fibrils can be grouped together to form the cellulose fibers. Lignin and hemi-cellulose can be found between each of these components providing additional strength to the fiber. The cellulose molecules form the fibers. Note, the SEP explosion pretreatment step can even separate some of the microfibril bonds making a frayed strand of fiber.
Hemi-cellulose is a group of carbohydrates found in or bonded to the cell wall, in more or less intimate association with cellulose. This group of carbohydrates generally includes those less-resistant substances in the cell wall, which though insoluble in hot water can be removed with either hot or cold dilute alkalis or readily hydrolyzed into sugars and constituent acids by means of hot dilute acids. It may be produced from ‘other’ products of photosynthesis:
Thus, the hemi-cellulose may be an amorphous group of branched polysaccharides that surrounds the cellulose fibers and is a linkage between the cellulose fibers and the lignin. The cellulose is typically a homogeneous polymer while the hemi-cellulose is typically a heterogeneous chemical group of polymers.
Lignin is a complex and high molecular weight polymer built upon phenyl propane units, such as (C10H1203), bound together by ether and carbon-carbon bonds. Lignin surrounds and occurs between cell walls making up the fibers acting as a binding agent to hold cells together. Lignin adheres between the outer layers of the cellulose fibers giving structural rigidity to the biomass made up bundles of cellulose fibers and holds those cellulose fibers together.
Referring to
Referring to
In an embodiment, the thermally hydrating stage has low pressure steam applied to the biomass received in chip form 651 in order to soften and elevate a moisture content of the biomass so at least the cellulose fibers and surrounding lignin of the biomass in the steam explosion stage can be internally blown apart in the next stage. The biomass in chip form 651 in the thermally hydrating stage is heated to greater than 60° C. using the low pressure steam, and in the steam explosion stage, the softened and hydrated biomass is exposed to 160 to 850 PSI and temperature between 160-270° C. for a sufficient time period to create high pressure steam/fluid inside the partially hollow cellulose fibers and other porous areas in the bulk structure of the biomass material. In an embodiment, chips of biomass are heated to temperatures over 200° C. and pressures over 23 bar (325 psi). The higher the pressure tends to create smaller fragments of lignin and cellulose fibers. In addition, when mechanical agitation is applied to the biomass as the biomass proceeds through the SEP process 608, this factor also tends to create smaller fragments of lignin and cellulose fibers when the biomass composition exits the steam explosion stage.
The pressure at an exit in the steam explosion stage is dropped rapidly in less than three seconds by extruding the bulk structure of the biomass into a tube at normal atmospheric pressure to cause an internal explosion, which internally blows apart the biomass into minute fine particles of biomass 653.
As shown in the diagram on the bottom of the figure, the biomass in fine particle form 653 formed after the pretreatment step of the steam explosion process is a fragment of one to several cellulose fibers adhering to each other with having some lignin on the fiber while other areas of the individual cellulose fibers have no lignin adhering to the surface of the cellulose fiber. Note, the biomass composition formed after the pretreatment step is generally individual cellulose fibers or even several cellulose fibers clumped together; however, merely a portion of the cellulose fibers remain intact, which makes the mass of each biomass particle smaller. The biomass composition formed after the SEP pretreatment step is multiple fragments of the individual cellulose fibers or even several cellulose fibers clumped together. The flow characteristics of these fragments of biomass in particle form 653 is more like that of grains of sand rather than like fiber stalks.
The biomass produced into the moist fine particle form 653 from the stages may have average dimensions of less than 50 microns thick and less than 500 microns in length. In an embodiment, the average dimensions of the particles of biomass produced from the steam explosion process are approximately 5 to 100 microns thick preferably 5-50 microns thick with a length of less than 200 microns (outliers may be up to 500 microns long), and the produced biomass in a particle form 653 has a length to thickness aspect ratio on average of less than 10 to 1. An aggregate amount of biomass in particle form 653 produced after the SEP pretreatment step has an increased exposed surface area of at least 20 times the surface area compared to a surface area of a same amount of biomass in chip form 653 supplied to an input stage of the SEP pretreatment step. The thickness of a single cell of biomass depending on the plant species is around 20 to 40 microns thick. Thus, the steam explosion process is generally blowing apart each cell in the biomass creating a small thickness of 5 to 20 microns thick for the resulting fine particles of biomass produced from the SEP.
Note, the lower the pressure in the steam explosion reactor vessel, such as (6 bar), the bigger the particles of biomass are formed almost like fiber particles; and likewise, the higher the pressure in the steam explosion reactor vessel, such as (16 bar), the smaller the particles of biomass are formed almost like fine grains of sand or finely ground up coffee grounds.
The increased surface area of the resulting fine particles of biomass formed as a product of the SEP also can improve the downstream biomass gasifier's performance. The SEP produces a higher amount of surface area for a same starting quantity of biomass than the TMP process on the biomass. The higher amount of surface area makes a higher throughput of biomass material attainable through the same biomass gasifier design. The reaction rate of biomass particles passing through the biomass gasifier in the biomass gasification reaction seems to be a mathematical function of the surface area of those fine particles biomass. A steam oxidation of the biomass occurs in the biomass gasification reaction. The steam oxidation of the biomass affects the reaction rate of the biomass particles in the biomass gasification reaction. Thus, a higher throughput is attainable with the increased reaction rate due to the greater surface area of the produced fine particles of biomass from SEP. The higher throughput results in any of 1) a lower residence time is needed in the biomass gasifier for a same amount of SEP biomass particles compared to a TMP biomass particle size; and alternatively, 2) a higher quantity of SEP biomass particles can be reacted in the biomass gasifier compared to a TMP biomass particle size for a same amount of residence time in the biomass gasifier.
Those produced moist fine particles of biomass 653 can be subsequently fed to a feed section of the biomass gasifier 614, the torrefaction unit 612, a densification unit, a dryer, or any combination of these. Note, the produced moist fine particles of biomass 653 can be directly fed to a feed section of the biomass gasifier 614 after passing through a dryer/low temperature 300 degree C. torrefaction unit and obtaining the desire moisture content for the biomass gasifier.
The internally blowing apart the bulk structure of biomass in a fiber bundle into pieces and fragments of cellulose fiber, lignin and hemi-cellulose results in all three 1) an increase of a surface area of the biomass in fine particle form compared the received biomass in chip form 651, 2) a creation of the two step reaction in the biomass gasification reaction of any of lignin adhering cellulose fiber as well as any loose chunks of lignin and then a reaction of the cellulose fibers as opposed to a multistep cycling reaction of lignin and then the cellulose fibers followed by lignin and more cellulose fibers, and 3) a change in viscosity of the resulting produced biomass in fine particle form 653 to flow like grains of sand rather than like fibers.
TMP and SEP are two methods discussed for producing the biomass in particle form 653, 753. Other methods for producing these chunks of lignin and lignin-coated fibers are generally regarded as high yield pulping processes. One of these includes what is known as CTMP—Chemi-thermo mechanical pulp. In this process sodium sulfite is added to help loosen the lignin. Grinding the chips in a stone mill may also be used. These fibers are known as stone ground wood.
Moisture values in the incoming biomass in chip form 651 can vary from about 15% to 60% for biomass left outside without extra drying. Chips of biomass may be generated by a chipper unit 604 cooperating with some filters with dimensions to create chips of less than about one inch and on average about 0.5 inches in average length and a ¼ inch in thickness on average. (See for example
Both the steam explosion unit 608 and the TMP process 706, 708 are configured to receive two or more types of biomass feed stocks, where the different types of biomass include 1) soft woods, 2) hard woods, 3) grasses, 4) plant hulls, and 5) any combination that are blended. The steam explosion process or TMP turns them into a homogenized feedstock that is subsequently collected and then fed into the biomass gasifier 614, 714 or torrefaction unit 612, 712. The torrefaction unit 612, 712 and biomass gasifier 614, 714 are designed to be feedstock flexible without changing out the physical design of the feed supply equipment or the physical design of the biomass gasifier or torrefaction unit via at least particle size control of the biomass particles produced from steam explosion stage or TMP process.
Thus, in an embodiment, the thermally hydrating stage may receive the biomass in chip form 651 including leaves, needles, bark, and wood. The thermally hydrating stage applies the low-pressure saturated steam to the biomass at a temperature above a glass transition point of the lignin in order to soften and elevate the moisture content the biomass so the cellulose fibers of the biomass in the steam explosion stage can easily be internally blown apart from the biomass in chip form 651. In an embodiment, the chips of biomass are heated to greater than 60° C. using the steam. The low pressure steam supply input applies low-pressure saturated steam into a vessel containing the chips of biomass at an elevated temperature of above 60 degrees C. but less than 120 degrees C. at a pressure around atmospheric PSI, to start a decomposition, hydrating, and softening of the received biomass in chip form 651. The low pressure supply input may consist of several nozzles strategically placed around the vessel. The chips stay in the thermally hydrating stage long enough to saturate with moisture.
The thermally hydrating stage feeds chips of biomass that have been softened and increased in moisture content to the steam explosion stage, which is at a pressure 10 to 40 times the pressure as is present in the thermally hydrating stage and an elevated temperature, such as a temperature of 160-270° C., 223° C. preferably. The pressure may be at 180-850 Pound per Square Inch (PSI) (400 PSI preferably). The steam explosion stage further raises the moisture content of the plug of biomass to at least 40% by weight and preferably 50 to 55% moisture content by weight. The % moisture by weight may be the weight of water divided by a total weight consisting of the chips of biomass plus a water weight. In the steam explosion stage, the softened and hydrated chips of biomass are exposed to high temperature and high-pressure steam for a sufficient time period, such as 3 minutes to 15 minutes, to create high pressure steam inside the partially hollow cellulose fibers and other porous areas in the bulk structure of the biomass material. (See for example
Note, the Steam Explosion Process (SEP) on the biomass chips uses no mechanical refiner to separate fibers; rather, the biomass chip is internally exploded in SEP. Also, no chemical acid additives are added in SEP, such as added acid; and thus, a yield of 88% or greater may be achieved.
After the thermally hydrating stage, the softened biomass in chip form 651 are any combination of 1) crushed and 2) compressed into a plug form, which is then fed into a continuous screw conveyor system, which these provide a mechanical agitation to the biomass to be combined with the high pressure steam explosion used in this SEP process. The continuous screw conveyor system moves the biomass in plug form into the steam explosion stage. The continuous screw conveyor system also uses the biomass in plug form to prevent blow back backpressure from the high-pressure steam present in the steam explosion stage from affecting the thermally hydrating stage. Other methods could be used such as 1) check valves and 2) moving biomass in stages where each stage is isolatable by an opening and closing mechanism.
The steam explosion stage can operate at pressures up to 850 psi. The plug screw feeder conveys the chips along the steam explosion stage. High-pressure steam is introduced into the plug screw feeder in a section called the steam mixing conveyor. The high pressure supply input may consist of several nozzles strategically placed around the steam mixing conveyor. Retention time of the biomass chip material through the steam explosion stage is accurately controlled via the plug screw feeder. In the steam explosion stage, the biomass in plug form is exposed to high temperature and high pressure steam at at least 160 degree C. and 160 PSI from the high pressure steam input for at least 5 to 15 minutes and preferably around 10 minutes until moisture penetrates porous portions of the bulk structure of the biomass and all of the liquids and gases in the biomass are raised to the high pressure.
The continuous screw conveyor system feeds the biomass in plug form through the steam explosion stage to an exit.
In an embodiment, a small opening forms the exit, such as ½ to ¾ inch opening, and goes into a tube that is maintained at around atmospheric pressure and any internal fluids or gases at the high pressure expand to internally blow apart the biomass. The pressure at the exit in the steam explosion stage is dropped rapidly by extruding the bulk structure of the biomass at between 160 to 850 PSI into a tube at normal atmospheric pressure to cause an internal “explosion” rapid expansion of steam upon the drop in pressure or due to the “flashing” of liquid water to vapor upon the drop in pressure below its vapor pressure, which internally blows apart the biomass in chip form 651 into minute fine particles of biomass 653. In another embodiment, the steam explosion reactor portion of the steam explosion stage contains a specialized discharge mechanism configured to “explode” the biomass chip material to a next stage at atmospheric pressure. The discharge mechanism opens to push the biomass from the high-pressure steam explosion reactor out this reactor discharge outlet valve or door into the feed line of the blow tank.
Thus, the pressurized steam or super-heated water out of the steam explosion reactor in this stage is then dropped rapidly to cause an explosion, which disintegrates the chips of biomass into minute fine particles. (See for example
The moisture and biomass chips get extruded out the reactor discharge to a container, such as the blow line, at approximately atmospheric pressure. The size of the exit orifice effects factors such as exit velocity, a depressurization time constant, and even whether every fiber exiting mechanically interacts with an edge of the orifice or has enough space to violently interact with the other mass around that fiber but not too much to space such as a 3 inch exit orifice to allow many fibers to exit without violently interacting with a neighboring fiber or edge of the exit orifice line. Thus, the size of the exit orifice is controlled relative to the size of the fibers passing through that exit orifice. The high-pressure steam or water conversion to vapor inside the partially hollow fibers and other porous areas of the biomass material causes the biomass cell to explode into fine particles of moist powder. The bulk structure of the biomass includes organic polymers of lignin and hemi-cellulose that surrounds a plurality of cellulose fibers. The bulk structure of the biomass is internally blown apart in this SEP step that uses at least moisture, pressure, and heat to liberate and expose the cellulose fibers to be able, as an example, to directly react during the biomass gasification reaction rather than react only after the layers of lignin and hemi-cellulose have first reacted to then expose the cellulose fibers. The high temperatures also lowers the energy/force required to breakdown the biomass' structure as there is a softening of lignin that facilitates fiber separation along the middle lamella.
The morphological changes to the biomass coming out of SEP reactor can include:
The created moist fine particles may be, for example, 20-50 microns thick in diameter and less than 100 microns in length on average. Note, 1 inch=25,400 microns. Thus, the biomass comes from the chipper unit 104 as chips up to 1 inch in length and 0.25 inches in thickness on average and go out as moist fine particles of 20-50 microns thick in diameter and less than 100 microns in length on average, which is a reduction of over 2000 times in size. The violent explosive decompression of the saturated biomass chips occurs at a rate swifter than that at which the saturated high-pressure moisture in the porous areas of the biomass in chip form can escape from the structure of biomass.
Note, no external mechanical stripping of the fiber bundles is needed in SEP rather the process uses steam to explode cells from inside outward and potentially uses some mechanical agitation of the biomass to create smaller fragments as a resultant product. Use of SEP on the biomass chips produces small fine particles 653 of cellulose and hemi-cellulose with some lignin coating. (See
The produced fine particles of biomass are fed downstream to the biomass gasifier 614 for the rapid biomass gasification reaction in a reactor of the biomass gasifier 614 because they create a higher surface to volume ratio for the same amount of biomass compared to the received biomass in chip form 651, which allows a higher heat transfer to the biomass material and a more rapid thermal decomposition and gasification of all the molecules in the biomass.
The produced particles of biomass loses a large percentage of the moisture content due to steam flashing in the blow line and being vented off as a water vapor. The produced particles of biomass and moisture are then separated by a cyclone filter and then fed into a blow tank. Thus, a water separation unit is inline with the blow line. A collection chamber at an outlet stage of the steam explosion stage is used to collect the biomass reduced into smaller particle sizes and in pulp form and is fed to the water separation unit. Water is removed from the biomass in fine particle form in a cyclone unit or a flash dryer.
A moisture content of the fine particles of biomass 653 is further dried out at an exit of the blow tank by a flash dryer that reduces the moisture content of fine particles of biomass 653 to 5-20% by weight preferably and up to 35% in general. A goal of the fiber preparation is to create particles of biomass with maximum surface area and as dry as feasible to 5-20% moisture by weight of the outputted biomass fine particle. The flash dryer merely blows hot air to dry the biomass particles coming out from the blow tank. The flash dryer can be generally located at the outlet of the blow tank or replace the cyclone at its entrance to make the outputted biomass particles contain a greater than 5% but less than 35% moisture content by weight.
The resulting particles of biomass differs from Thermal Mechanical Pulping (TMP) in that particles act more like crystal structures and flows easier than fibers which tend to entangle and clump.
The reduced moisture content of 5% to about 35% by weight of the biomass in fine particle form is fed by a conveying system, as an example, to a torrefaction unit 612 to undergo torrefaction or pyrolysis at a temperature from 100 to 700 degrees C. for a preset amount of time.
A conveyor system supplies the biomass in particle form to a torrefaction unit 612 to process the biomass at a temperature of less than 700 degrees C. for a preset amount of time to create off gases to be used in a creation of a portion of the syngas components that are collected by a tank and may be eventually fed to the methanol synthesis reactor.
The fine particles of biomass 653 out of the blow tank and flash dryer has a low moisture content already due to the steam flashing, further air drying, and are a composite of fragments of cellulose fibers with a lignin coating, pieces of lignin, cellulose, and hemi-cellulose, etc. The biomass gasifier 614 has a reactor vessel configured to react the biomass in moist fine particle form with an increased surface area due to being blown apart by the steam explosion unit 608. The biomass gasifier 614 has a high pressure steam supply input and one or more heaters, and in the presence of the steam the biomass in fine particle form 653 are reacted in the reactor vessel in a rapid biomass gasification reaction between 0.1 and 5.0 second resident time to produce at least syngas components, including hydrogen (H2) and carbon monoxide (CO). When the biomass in fine particle form 653 produced are supplied in high density to the biomass gasifier 114, then the small particles react rapidly and decompose the larger hydrocarbon molecules of biomass into the syngas components more readily and completely. Thus, nearly all of the biomass material, lignin, cellulose fiber, and hemi-cellulose, completely gasifies rather than some of the inner portions of the chip not decomposing to the same extent as that fine particle. These fine particles compared to chips create less residual tar, less carbon coating and less precipitates. Thus, breaking up the integrated structure of the biomass in a fiber bundle tends to decrease an amount of tar produced later in the biomass gasification. These fine particles also allow a greater packing density of material to be fed into the biomass gasifier 614. As a side note, having water as a liquid or vapor present at at least 10 percent by weight may assist in generating methanol CH3OH as a reaction product in addition to the CO and H2 produced in the biomass gasifier 614.
The torrefaction unit 612 and biomass gasifier 614 may be combined as an integral unit.
In the alternative, the moist blown apart particles of biomass may be fed in slurry form from the output of the steam explosion reactor directly, or after drying, to a densification unit. The densification unit may densify the biomass from form into pellets of biomass, which those pellets are then fed into the biomass gasifier 614. This direct feed and conversion of biomass from form to pellet form saves multiple steps and lots of energy consumption involved in those eliminated steps. Alternatively, the pellets may be transported to facilities for further processing to liquid fuel, heat/power, animal feed, litter, or chemicals.
In an embodiment, the biomass gasifier 614 is designed to radiantly transfer heat to particles of biomass flowing through the reactor design with a rapid gasification residence time, of the biomass particles of 0.1 to 10 seconds and preferably less one second. The biomass particles and reactant gas flow through the radiant heat reactor. Primarily radiant heat from the surfaces of the radiant heat reactor and particles entrained in the flow heat the particles and resulting gases to a temperature in excess of generally 700 degrees C. and preferably 1300° C. to produce the syngas components including carbon monoxide and hydrogen, as well as keep produced methane at a level of ≦1% of the compositional makeup of exit products, a resultant stable ash formation, complete amelioration of tar to less than 500 milligrams per normal cubic meter, and the production of the hydrogen and carbon monoxide products. In some embodiments, the temperature range for biomass gasification is greater than 800 degrees C. to 1400 degrees C. In some embodiments, the temperature range for biomass gasification is greater than 700 degrees C. to 1450 degrees C. In some embodiments, the temperature range for biomass gasification is greater than 1000 degrees C. The biomass in particle form used as a feed stock into the radiant heat reactor conveys the beneficial effects of more effective heat transfer of radiation to the biomass particles and increased gasifier yield of generation of syngas components of carbon monoxide and hydrogen for a given amount of biomass fed in, and improved process hygiene via decreased production of tars and C2+ olefins compared to chips of biomass. A control system for the radiant heat reactor matches the radiant heat transferred from the surfaces of the reactor to a flow rate of the biomass particles to produce the above benefits.
The biomass in particle form produced for fuel production breaks apart a larger piece of biomass into the particle sizes to increase an exposed surface area of the particles compared to the larger piece of biomass. The particle sizes compared to the larger piece of biomass increases surface area, improves flow characteristics because it flows more like grains of sands/coffee rather than like fibers, results in less tar and char formation in downstream torrefaction or gasifier process and rather decomposes more completely into constituent gases including CO, H2, CO2 and ash.
Another possible biomass gasifier 614 implementation has a high temperature steam supply input and one or more regenerative heaters. In the presence of the steam, the particles of the biomass broken down by the pretreatment step are reacted in the reactor vessel in a rapid biomass gasification reaction at a temperature of greater than 700 degrees C. in less than a one second residence time in the biomass gasifier to create syngas components, including hydrogen (H2) and carbon monoxide (CO). The biomass gasifier 614 can typically feed to a methanol (CH3OH) synthesis reactor.
An example Particle Size Analysis to determine the particle size can be a Digital Image Processing Particle Size and Shape Analysis System such as a Horiba Camsizer XT particle size analyzer. Such a system uses one or more cameras to provide rapid and precise particle size and particle shape distributions for dry powders bulk material in the size range, for example, from 30 μm to 30 mm. The measurements from the digital image processing system allows a correlation to existing data from techniques as diverse as sieving and sedimentation, which in some instances may also be used to measure particle size. In an embodiment, the particle size of the steam exploded wood chips is measured using a Horiba Camsizer XT particle size analyzer. The sample to be measured is mixed in a resealable bag by kneading and agitating the material in the bag by external manipulation. After mixing, a sample amount, such as approximately 3 cm̂3, is loaded into the sample hopper of the instrument. The target is to run and analyze enough sample size, such as at least 2 million particles from each sample, so the sample volume is only important insofar as it corresponds to an adequate number of particles. Example settings on the instrument can be as follows 0.2% covered area, image rate 1:1, with X-Jet, gap width=4.0 mm, dispersion pressure=380.0 kPa, xFe_max [and xc_min, accordingly]. Feed rate is controlled to yield a target covered area so that the computer can process the images quickly enough. The camera imaging rate is fixed, and both “basic” and zoom images are obtained for every run. A single value for average particle size, such as the diameter is less than 50 microns, may be the objective measurement standard. In an embodiment, a three point value for both Fe-max and xc-min is more complete. So that's like a 6 point value. The particle size distribution (PSD) may be defined as Fe-Max D10, D50, D90 and Xc-min D10, D50, D90. The measurement then can use multiple values such as input 6 values to determine the measurement. Other similar mechanisms may be used.
Calculations can be made using Fe max and xc min on a volume basis. Two models can be used to analyze the particle images: xc-min, which yields results comparable to those obtained by physically screening/sieving samples, and Fe-max, which is similar to measuring the longest dimension of a given particle with a caliper. Raw data, frequency plots, binned results, and particle images are obtained for all samples. D10, D50, and D90 may be calculated on a volume basis, as is the average aspect ratio. D90 describes the diameter where ninety percent of the distribution has a smaller particle size and ten percent has a larger particle size. The D10 diameter has ten percent smaller and ninety percent larger. A three point specification featuring the D10, D50, and D90 is considered complete and appropriate for most particulate materials. In an embodiment, the particle size distribution PSD may be defined as D50 (μm) Model Fe-max.
The examples in Table 1 were produced with a Steam Pressure of 16 bar and a reaction time of 10 minutes.
As discussed, the decomposition of the large carbohydrate and other organic molecules in the biomass gasification reaction occurs due exposure of the biomass composition to elevated heat of greater than 700 degrees C., but not to an internal flame other combustion source. Thus, an external heater heats the biomass in particle form. The exposure of the cellulose fibers to be able to directly react during the biomass gasification reaction rather than merely reacting only in a repeating cycle of the layer of lignin first reacting to then expose the cellulose fibers, and then a next layer of lignin followed by cellulose fibers reacting causes a biomass gasification reaction product of resultant stable ash formation, a complete amelioration of tar to less than 500 milligrams per normal cubic meter, and a yield of at least 90% of the biomass to hydrogen, carbon dioxide, and carbon monoxide gaseous products.
The biomass gasifier feeds a gas clean up section to clean ash, sulfur, water, and other contaminants from the syngas gas stream exiting the biomass gasifier 614. The syngas is then compressed to the proper pressure needed for methanol synthesis. The syngas from the catalytic converter may connect upstream or downstream of the compression stage.
The synthesis gas of H2 and CO from the gasifier is sent to the common input to the one or more methanol synthesis reactors. The methanol produced by the one or more methanol synthesis reactors is then processed in a methanol to gasoline process.
The liquid fuel produced in the integrated plant may be gasoline or another such as diesel, jet fuel, or some alcohols.
The TMP process can use chips of wood, needles, bark, leaves, fiber crops, or waste paper. Wood pulp comes from softwood trees, such as spruce, pine, fir, larch and hemlock, and hardwood trees, such as eucalyptus, aspen and birch. Wood and other plant materials used to make pulp contain three main components (apart from water): cellulose fibers (used in other technologies for paper making), lignin (a three-dimensional polymer that binds the cellulose fibers together, which is chemically removed in the paper making field) and hemi-celluloses, (shorter branched carbohydrate polymers). The biomass contains cellulose fibers and hemi-cellulose that are held together with lignin. The aim of pulping is to break down the bulk structure of the fiber source, be it chip form, stem form, or other plant parts, into the small groups of fibers or even into individual constituent fibers.
The TMP unit can be configured to receive two or more types of biomass feed stocks, where the different types of biomass include 1) soft woods, 2) hard woods, 3) grasses, 4) plant hulls, and 5) any combination that are blended and thermo mechanically processed into a homogenized torrefied feedstock within the TMP unit 708 that is subsequently collected and then fed into the biomass gasifier 714. The torrefaction unit 712 assists in making a biomass feed system that is feedstock flexible without changing out the physical design of the feed supply equipment or the physical design of the biomass gasifier via at least particle size control of the biomass particles produced from refiner unit stage 708.
The thermo mechanical pulping process breaks down a bulk structure of the received biomass, at least in part, by applying steam from the steam supply input to soften the lignin and make it easier to degrade bonds between the lignin and the hemi-cellulose from cellulose fibers of the biomass. Strength of the fibers is further impaired with the gasification's use of thermo mechanical pulping because the fibers are separated to potentially individual fibers and also cut to small dimensions. A lack of concern exists to maintain the strength of the fibers in the woody biomass chips compared to the paper pulping industry. The traditional TMP process tries to maintain the strength of the fibers to make particle board, newspapers, etc. In the current application of using the fibrous biomass in pulp form as a chemical reactant feedstock, the steam in connection with the mechanical force can be used to weaken the fibers and the fibers can then be cut to small dimensions because the fibers, lignin, and cellulose will eventually be thermally decomposed into syngas components. This process of TMP for gasification is less costly than producing paper with TMP because the gasification process does not require full length strong fibers as required for making paper or the traditional extra steps used to keep the strength of the fibers.
The Thermo Mechanical Pulping process also reduces the amount of energy required to produce particles of biomass compared to mechanical treatment alone. A major issue in the paper industry is that mechanical pulp mills use large amounts of energy, mostly electricity to power motors that turn the grinders. Steam treatment significantly reduces the total energy needed to make the pulp and eases the separation of the fibers. Thus, many advantages exist to the gasification of woody and other fibrous biomass to strip apart the fibers from the lignin.
There are a number of different mechanical processes that can be used to separate the wood fibers. For example, manufactured grindstones with embedded silicon carbide or aluminum oxide or metal discs called refiner plates can be used to grind the biomass chips. Thus, the chips are steamed while being refined by the grindstones or metal discs to create the pulp. These chips of biomass have a large moisture content, are thermally heated from the steam, expanded by the elevated temperature and pressure, and then a mechanical force may also be applied to the wood chips in a crushing, shearing, vibrating, or grinding action, which generates additional heat and shredding action, which aids in separating the individual fibers from each other and the lignin.
The TMP unit reduces the biomass into smaller particle sizes that should be more easily and rapidly gasified. Fibers are long tubular strings of material, whereas chips are irregular spheres. The fibers compare to angel hair spaghetti, whereas chips are more like ravioli. Torn and shredded fibers may be preferred for the gasification process because they create a higher surface to volume ratio for the same amount of biomass. The higher surface area of the fibers traveling through the biomass gasifier 714 compared to a chip allows higher heat transfer to the biomass material and a more rapid thermal decomposition and gasification of all the molecules in the biomass. Thus, nearly all of the biomass material lignin, fiber, and cellulose completely gasify rather than some of the inner portions of the chip not decomposing to the same extent to that the crusted shell of a char chip decomposes.
A collection chamber at an outlet stage of the refiner unit stage 708 is used to collect the biomass reduced into smaller particle sizes and in pulp form, which should be more easily and rapidly gasified. The produced particles of biomass in pulp form include fibers in the form of long tubular strings of material that are torn and/or shredded. The biomass particles separated into fibers are preferred for the biomass gasification reaction in the biomass gasifier 714 because they create a higher surface to volume ratio for the same amount of biomass compared to chips of biomass, which allows higher heat transfer to the biomass material and a more rapid thermal decomposition and gasification of all the molecules in the biomass. The refiner unit stage 108 has a knife stage in the fiber separation unit that initially separates the fibers from the chips and may chop the fibers of the biomass to shorter lengths of 1-3 mm and then a high pressure steam fiber separation stage furthers the blowing apart of the loosely grouped fibers in the particles of biomass. The refiner unit produces fiber particles that on average are approximately 20-50 μm thick and 1-3 mm in length. In another embodiment, the fibers may have an equivalent spherical diameter of less than 3 mm.
The biomass gasifier 714, torrefaction unit 712, and chipping unit 704 may operate similar as described in
While some specific embodiments of the disclosure have been shown the invention is not to be limited to these embodiments. For example, the recuperated waste heat from various plant processes can be used to pre-heat combustion air, or can be used for other similar heating means. Regenerative gas burners or conventional burners can be used as a heat source for the furnace. Alcohols C1, C2 and higher as well as ethers that are formed in the torrefaction process may be used as a high value in boosting the octane rating of the generated liquid fuel, such as gasoline. Biomass gasifier reactors other than a radiant heat chemical reactor may be used. The Steam Methane Reforming may be/include a SHR (steam hydrocarbon reformer) that cracks short-chained hydrocarbons (<C20) including hydrocarbons (alkanes, alkenes, alkynes, aromatics, furans, phenols, carboxylic acids, ketones, aldehydes, ethers, etc, as well as oxygenates into syngas components. The disclosure is to be understood as not limited by the specific embodiments described herein, but only by scope of the appended claims.
This application claims the benefit of and is a continuation in part of US application titled “Pretreatment of biomass using thermo mechanical methods before gasification,” Ser. No. 13/429,847, filed on Mar. 26, 2012 as well as US application titled “Pretreatment of biomass using steam explosion methods,” Ser. No. 13/531,318 filed on Jun. 22, 2012.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 13429847 | Mar 2012 | US |
| Child | 13618528 | US | |
| Parent | 13531318 | Jun 2012 | US |
| Child | 13429847 | US |
