CELLULOSIC MICROPOWDER PRODUCTION SYSTEM

Abstract

An improved process is provided for reducing cellulosic biomass into air suspendable micropowder. Although the process is particularly suitable for processing empty fruit bunches of oil palms, it is adaptable to most cellulosic biomass. The incoming biomass has a water content of around 50% and is reduced to centimeter scale pieces by a chipper or similar device. These pieces are then processed by a tandem line of four pairs of grooved rollers each successive roller having a larger number of grooves. This process squeezes moisture from the biomass and reduces the material into millimeter scale pieces. After an optional drying stage, the material is fed into a terrace line of three or four essentially smooth rollers which squash the material and reduce the particle size into a micrometer scale. Finally, the material is suspended in an air stream and fractionated by a cyclone and bag filter system.

Claims

1. A process for efficiently and rapidly reducing the particle size and moisture content of cellulosic biomass comprising the steps of: feeding centimeter scale cellulosic biomass pieces into a squeezer tandem roller line comprising a series of paired rollers having interdigitated surface grooves with successive roller pairs having a larger number of grooves thereby squeezing moisture from the biomass and reducing the squeezed biomass to millimeter scale particles; conducting the squeezed biomass into a terraced squasher roller line comprising a series of paired rollers arranged so that the first roller pair is above the successive roller pair with the surfaces of the rollers being essentially smooth and with each roller pair having a scraper plate to scrape biomass material from the roller surface thereby reducing the squashed biomass into submillimeter scale particles; and suspending the squashed biomass in an air stream which passes into a filter system which directs larger biomass particles back to the squasher roller line for additional processing and passes smaller micrometer scale particles as end product.

2. The process according to claim 1, wherein the squeezer roller line comprises four successive roller pairs.

3. The process according to claim 2, wherein the successive squeezer roller pairs have about 24 grooves, about 40 grooves, about 47 grooves and about 95 grooves, respectively.

4. The process according to claim 1, wherein the surfaces of the terraced squasher rollers are marked with shallow grooves with a depth less than about 2 mm.

5. The process according to claim 1, wherein the terraced squasher roller line comprises three sets of paired rollers.

6. The process according to claim 1, wherein the filter system comprises a cyclone filter and a bag filter.

7. The process according to claim 1 further comprising a step of drying the millimeter scale particles prior to the step of conducting the squeezed biomass into a terraced squasher roller line

Description

BRIEF DESCRIPTION OF THE FIGURES

[0009] FIG. 1 is a diagram of an earlier biomass system based on mechanical disruption of air suspended particles.

[0010] FIG. 2 is a photographic representation of the tandem line “Squeezer” consisting of four pairs of rollers.

[0011] FIG. 3 is series of photographs showing the surface of the “Squeezer” rollers; FIG. 3A: 24 grooves; FIG. 3B: 40 grooves; FIG. 3C 47 grooves; and FIG. 3D 95 grooves.

[0012] FIG. 4 is drawing showing the terrace arrangement of three pairs of “Squasher” rollers.

[0013] FIG. 5 is photograph of the surfaces of a pair of “Squasher” rollers showing the shallow surface grooves.

[0014] FIG. 6 is a diagram of the overall process line.

DETAILED DESCRIPTION OF THE INVENTION

[0015] The following description is provided to enable any person skilled in the art to make and use the invention and sets forth the best modes contemplated by the inventor of carrying out his invention. Various modifications, however, will remain readily apparent to those skilled in the art, since the general principles of the present invention have been defined herein specifically to provide a system for rapidly and efficiently reducing biomass to cellulosic micropowder.

[0016] The instant system replaces the inventor's own prior system shown in FIG. 1. In that system biomass chips 64 from a hopper were fed into a cutter 52 which reduced biomass to centimeter sized pieces 68. These were fed into a first rotary beater device 44 which kept the particles suspended. After many hours of operation the biomass was reduced to millimeter sized particles which were blown into a second mill 30 where they were suspended by propellers 35 and eventually reduced to particles in the submillimeters scale. These particles were fractionated with a baffle system to harvest the finished micropowder 60 in a container 42 while returning larger particles to the propellers 35 for additional treatment. While effective at making micropowder this system was slow (100-250 kg per hour or 2.5-5.0 tons per day), and necessarily consumed a considerable amount of energy to operate the mechanisms. The various grinding mills are generally operated by electric motors. The longer the process takes, the more energy is consumed by the motors. The faster the processing occurs, the less the overall energy consumption.

[0017] The present improved process system is inspired by the traditional cane mill where the sugar rich cell sap is rapidly extracted from chipped sugar cane by passing the plant material through the nap of large counter-rotating rollers not unlike a giant version of an old fashioned clothes wringer. The sugar cane is first chipped by a knife cutter to reduce the size of the pieces. The cane may also be crushed to breakdown the stem structure. Then this material is rapidly passed through a series of paired rollers to extract the juice. It is known in the art of sugar cane processing that there is a balance between speed and effectiveness of juice recovery. If plant material is fed into the series of rollers too rapidly, the thickness of material between the rollers will be too great. This thickness reduces the efficiency of juice recovery and having a greater number of rollers in series does not solve this problem because the plant material will be too thick at each successive roller pair. If the entering amount of sugar cane is reduced sufficiently, an layer of bagasse of optimal thickness will be formed between the rollers and essentially all the juice will be extracted by the series of in line rollers. Using a larger number of roller pairs will increase the effectiveness of extraction, to some degree, provided a critical thickness of the rolled material is not exceeded. Of course, there is no point in using a suboptimal amount of chipped sugar cane because this merely reduces the throughput and wastes operational energy.

[0018] Typical raw cellulosic biomass has appreciable moisture content—often around 50% by weight. Unlike juice in a sugar cane mill, the moisture is not the desired product of the operation; in fact, excess moisture can make processing into micropowder difficult. The new process uses a series of four paired rollers (tandem milling line), similar to sugar cane mill rollers, to reduce the moisture level of the biomass by “squeezing” the moisture out. Cellulosic biomass feedstock comes in a variety of forms with variable water content. For example, wood is processed by cutting it into small pieces (e.g. wood chips). Although water content varies with condition, wood often also has a water content of around 50% by weight.

[0019] Empty Oil Palm Fruit Bunches (EFB) are useful cellulosic biomass feedstock available in tropical regions. There are large plantations of Oil Palms (Elaeis guineensis) in Southeast Asia, particularly in Indonesia and Malaysia. These plantations produce Crude Palm Oil (CPO) from the fruits and seeds of the Oil Palm. The farmer harvests Fresh Fruit Bunches (FFB) from the palms. The FFB are heated and cooked by steam and then shaken to release the fruits which are pressed to produce CPO. The EFB are the cellulosic fruit branches left after the fruits are all removed. Although EFB are not “wood” in the botanical sense, they are fairly tough fibrous structures and have a typical 50% water content. The EFB are disrupted by a shredder to yield small fragments with a centimeter to millimeter size scale. Traditionally, this material is returned to the plantation to form mulch that adds organic material to the soil where it gradually decomposes. However, there is so much EFB added back to the plantation soil that adding EFB to the soil may actually result in environmental pollution.

[0020] In the inventive process the shredded EFB are treated by a squeezer roller train or line (FIG. 2). In the example, the rollers are constructed from cast iron and weigh about 110 kg each. The line contains four tandem (paired) grooved rollers (eight rollers total) as shown in FIG. 2. At each stage the plant material is squeezed between a pair of grooved rollers with each successive stage having a larger number of grooves. The rollers have a width of approximately 40 cm, and the preferred proportion is to have the roller diameter be about one half of the roller length. The first roller pair (FIG. 3A) has approximately 24 triangular (in cross-section) circumferentially disposed parallel grooves. The second roller pair (FIG. 3B) has approximately 40 triangular (55° apical angle) grooves while the third roller pair (FIG. 3C) has approximately 47 grooves and the fourth roller pair (FIG. 3D) has approximately 95 grooves. The grooves increase the effective surface area of the rollers as well as the area of the layer of squeezed plant material. In addition, when the plant material is pressed over the apices of the juxtaposed and interdigitated grooves, the resulting flexing of the material separates the cells at their junctures with each other (i.e., the middle lamella which glues adjacent plant cells together) and ultimately causes the cell walls themselves to pull apart to some degree. The successively smaller grooves encourage this process.

[0021] The first pair of rollers is operated by an 18 kW electric motor; the successive roller pairs are operated by 13.2 kW motors. Thus, the line consumes about 57.6 kW per hour to process about 12-20 tons of biomass so that the energy input is fairly modest. The “Squeezer” line reduces the water content to the 15-20% range while reducing the particle size into the millimeter or smaller size range. Much of the “squeezed” moisture actually drips from the rollers and can be captured and conducted away.

[0022] Next, the processed biomass enters the “Squasher” terrace line. This consists of three or four pairs of counter-rotating rollers arranged in a descending line as shown in FIG. 4. Each roller pair has a dedicated scraper plate to peel the appressed layer of biomass off the roller surface and to guide the biomass into the roller nap of the successive roller pair. As shown in FIG. 4 the surface of the Squasher rollers is essentially smooth with a series of shallow grooves (less than about 2 mm in depth) embossed into the surfaces. The Squasher roller breaks up the biomass structure by applying pressure. A thin layer of biomass is pressed between the two rollers so that there is efficient transfer of mechanical energy to the biomass structures thereby disrupting them. In addition, forcing the biomass into the shallow grooves helps hold the biomass in place (improving energy transfer) and also causes shear at an edge so that the biomass is cut in a way somewhat like the cutting forces operating within a pair of scissors. In addition, the shallow grooves encourage release of the biomass from the roller surface. At each level of the terrace, the scraper plate detaches and mixes the appressed biomass and supplies it to the next stage. As the biomass is processed by the Squasher, it is reduced to a maximum particle in the tens of micrometer size range with a large amount of material in the micrometer size range. Moisture level is reduced to 3-5% which results in considerable clumping and interaction of the micropowder due to static electricity. This can be controlled by a small water vapor or steam spray that discharges the static electricity.

[0023] The Squasher rollers are essentially smooth with only very shallow surface grooves which help ensure that crushed biomass can be readily removed from the rollers' surfaces. The axle and bearings of the upper roller of each pair are configured so that the roller can move in an upward or downward direction in response to the amount of biomass supplied to the roller. As the roller moves up and down, it adjusts to press the biomass tightly into a sheet partially adhering to the roller. The rollers rotate at a low speed usually in the range of 6-10 rpm. The overall capacity and effectiveness of the line depends on the roller size (surface area) and weight. An adjustable spring arrangement can be used to increase pressure over that supplied by the roller weight.

[0024] Finally, the micropowder exciting the Squasher line is fractionated and collected by a cyclone and bag filter combination. The cyclone uses centrifugal forces to remove the larger particles while the bag filter catches the small particles that have been adequately processed. Any particles that are too large can be recycled into the Squasher for additional processing. FIG. 5 shows a diagrammatic representation of the entire system. An optional air drying storage area is provided between the Squeezer and Squasher lines. In the storage area circulation of air and even heat application can be used to reduce the moisture level of the biomass as is necessary. Other well-known means for controlling the moisture level of the biomass (such as fluid bed drying and roll drying) can also be used. The micropowder exiting the terrace line Squasher is stored in a mixing container where an impeller stirs the powder to prevent clumping and ensure suspension of the micropowder in the air stream running into the cyclonic separator and the bag filter. Properly sized micropowder accumulates at the bag filter and is removed by being suspended in an air stream and can then be used either for direct combustion or for hydrolysis into sugars for making liquid fuels.

[0025] The following claims are thus to be understood to include what is specifically illustrated and described above, what is conceptually equivalent, what can be obviously substituted and also what essentially incorporates the essential idea of the invention. Those skilled in the art will appreciate that various adaptations and modifications of the just-described preferred embodiment can be configured without departing from the scope of the invention. The illustrated embodiment has been set forth only for the purposes of example and that should not be taken as limiting the invention. Therefore, it is to be understood that, within the scope of the appended claims, the invention may be practiced other than as specifically described herein.