The disclosed embodiments relate generally to the art of cellulosic material digesters, and more particularly to a continuous tube reactor to extract fermentable sugars, lignin and pulp from cellulosic material.
In a typical continuous pulp digester, the wood chips and the white liquor are fed into the upper end of a vertically aligned digester, with the interior of the digester defining a cylindrical digesting chamber maintained at a relatively high pressure (e.g. 200 PSI) and high temperature (e.g. approximately 380.degree. F.). The mixture of chips and white liquor moves slowly and downwardly through the digester so that the total dwell time within the digester is generally between about two to four hours. During the period that the wood chips are in the digester, the white liquor reacts with the material in the wood chips to break down certain organic compounds in the wood chips so as to “delignify” the pulp.
At several locations along the length of the digester, portions of the liquid are extracted, either to be re-circulated back into the digester, sent to an evaporator, or possibly to be processed elsewhere in the system. To retain the wood chips that are being processed in the digester, the liquid is extracted through sets of screens which are generally placed in sets at vertical locations circumferentially around the digester.
Accordingly, a system and method for continuous tube reactor is disclosed.
One embodiment comprises a continuous digester comprising a cellulosic material feed section including a pre-steam and impregnation zone, a sugar extraction zone, a lignin extraction zone and a cooking zone, the continuous digester to impregnate the cellulosic material with a mild acid solution and continuously digest the cellulosic material to extract fermentable sugars, lignin, and pulp. Another embodiment comprises a method for receiving cellulosic material in a continuous digester, removing air from the cellulosic material, impregnating the cellulosic material with a mild acid, hydrolyzing hemicellulose in the cellulosic material to fermentable sugars, extracting the fermentable sugars from the cellulosic material, cooking the cellulosic material to extract lignin from the cellulosic material, washing the cellulosic material in a hot alcohol wash, a hot water wash, and a cold water wash, and discharging pulp.
This Summary is provided to introduce concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. Furthermore, the claimed subject matter is not limited to implementations that solve any or all disadvantages noted in any part of this disclosure.
Disclosed embodiments illustrate aspects of a continuous tube reactor. In some embodiments, a continuous tube reactor 100 converts higher grade cellulosic feedstock (material) in a relatively continuous process to fermentable sugars for ethanol production, to relatively chemical free lignin for products conventionally made from fossil base material, and to pulp for paper making and other products. In some embodiments, a continuous tube reactor converts lower grade cellulosic material into lignin and fermentable sugars.
In some embodiments, a continuous tube reactor may use a multi-stage chemical “cracking” process to split cellulosic feedstock into three commercial end-products, fermentable sugars for ethanol production, lignin for plastics and other conventionally fossil-fuel-base products, and pulp for paper making. Additionally, this cracking process may be accomplished with a single pressure vessel and may use existing auxiliary equipment. In this way, a continuous tube reactor may provide transformational harvesting and use of sustainable renewable cellulosic materials, transformational production of alternative fuels, transformational production of pure lignin and products thereof, and transformational production of pulp, as will be described in more detail in the following detailed description with reference to the attached figures.
With reference to the example embodiment illustrated in
In the present embodiment, all process auxiliary tanks, blow tank for pulp discharge, sugars and lignin concentrators, lignin recovery centrifuge, air compressor, and vacuum evaporation equipment and condensers for ethanol recycling are mounted on a 32 ft long goose-neck trailer. This allows a pilot-scale continuous tube scale reactor to be transported and re-assembled within a relatively short time, such as a week or two from a pulp mill, saw mill or ethanol plant to another to allow multiple end-users to experiment with their own feedstock, laboratories, and in case of ethanol facilities, with their own fermentation and distillation processes.
For high-grade woody cellulosic feedstock some embodiments of a continuous tube reactor may have six process zones for unbleached pulp, including a zone to hydrolyze hemicelluloses to fermentable sugars and extract them, three cooking zones to dissolve and extract lignin in three stages, a three-stage wash zone consisting of hot alcohol wash, hot water wash, and cold water wash, and a pulp discharge zone. In some embodiments, for bleached pulp production one or more bleaching zones may added between cooking zones and an end wash zone.
In one example embodiment, cellulosic material may be converted to fermentable sugars, lignin and pulp in one single pass through a horizontal tubular pressure vessel using a solution comprising 60% ethanol and 40% water for a transportation and process liquid. For example, an embodiment process liquid may be a mixture of around 60% ethanol and 40% water at 350°-400° F. and a process pressure of 300 psig. In this example, each of the process zones may have several process liquid inlet/extraction rings to provide heat and process liquid input and dissolved organic matter extraction as well as process consistency and porosity control within the entire length of the reactor, as will be explained more fully in the following detailed description.
In the present embodiment continuous tube reactor 200, the continuous tube reactor will process almost all of the feedstock into lignin 234 and fermentable sugars without any pulp production except that a small percentage of the feedstock is left at the end of the reactor in a fibrous stage to facilitate a cross-flow extraction process of dissolved sugars and lignin. In this way, part of the residual fibrous matter can be recycled back to the reactor feed end, if desired, or all of it can be burnt to produce steam 212 and power 220 for the plant. Some of the residual fibrous matter has to be always burnt to get rid of the inorganic salts and ashes in the feedstock.
As can be seen in
Organic vapors from evaporation and blow tank will be burned in a conventional bio-fuel boiler 210 as well as the organic extractives from the impregnation liquid. In this way, small amounts of fresh make-up water may be used since much of the moisture in the feedstock can be recycled through evaporation, as shown in
The continuous tube reactor 300 eliminates the recovery boiler 438, causticising 448 and lime kiln 452, which are generally responsible for ¾ of the emissions and greenhouse gases of a Kraft process 400 mill. In this way, by combining the cooking, washing and bleaching processes into one continuous process inside multiple, relatively small diameter continuous tube reactors 300, all the process liquids may be circulated counter-currently upstream until being extracted to an evaporation plant, and the emissions and greenhouse gases may be dropped to less than 10% of a Kraft process 400 mill's values.
Additionally, a continuous tube reactor 300 uses very clean ethanol for cooking liquor instead of sodium and sulfur-containing Kraft process 400 chemicals, further allowing for reduced evaporation plant emissions. Also, a Kraft process 400 mill operates by burning lignin and other dissolved organic matter to recover costly cooking chemicals from ashes through causticising and lime kiln processes.
With reference to
As further shown in
Now looking at 720 and 750 in
Therefore, having a lower porosity is advantageous for displacing the liquid contained within the digester with new fresh liquid from one peripheral location along the tube reactor.
In one form, a biasing system include pumping water behind trailing plug 932, whereby the pressure over the surface area creates a force which pressurizes the water between the leading and trailing plugs. In this way, leading piston 930 may remain intact as long as fill water in the reactor section 950 and washing section 980 is not relieved through a relief valve.
In the embodiment illustrated in
After the feedstock porosity is adjusted to a defined level, the feedstock/water mixture may be heated to a temperature and then pre-impregnated with a water and chemical solution. After a time the leading piston and all the feedstock material between the leading and trailing plugs may then be allowed to travel forward by setting the relief valve at the end of the washing section 980 to relieve at a desired pressure. The speed of the travel of feedstock may be controlled by the water input volume per unit of time behind the trailing plug 932
There are four process zones in the reactor section 950 as shown in example embodiment 900, with each process zone ending with a packing/extraction section. In general, the packing/extraction section has a series of rings including an initial packing ring and several subsequent countercurrent displacement rings described further herein. At the beginning of the first process zone, named mild acid hydrolysis zone 956, the porosity of the feedstock is first lowered to a level by extracting some liquid out with a so-called packing ring. The volume of extraction may be controlled by measuring it with a positive displacement pump or cylinder.
After the packing ring, the initial impregnation fluid may be extracted with a mild acid hydrolysis liquid, such as an acid hydrolysis liquid containing 60% alcohol, 1% sulfuric acid, and 39% water, by way of example. The extraction may be accomplished by a measured amount of mild acid hydrolysis liquid being pumped into the last of the several displacement rings with a positive displacement pump or cylinder. In some embodiments, several of these pumps or cylinders may be “ganged” to operate together so that the liquid that is displaced within the first extraction ring will flow into the inlet side of the next pump or cylinder to be delivered to the second displacement ring and so on. In this manner the fresh ingoing liquid will counter-currently “wash” out the liquid to be extracted; however, the porosity remains relatively constant throughout the entire extraction section since all input/output liquid volumes are same by virtue of all displacement pumps or cylinders being of same volume.
This newly input mild acid hydrolysis liquid converts the feedstock hemicelluloses to sugars, which are then extracted in a similar manner at the end of the process zone after a packing ring has first reduced the porosity again by a desired value corresponding to the amount that the feedstock has shrunk during its travel through the processing zone. Again a packing ring may be followed by four or more displacement rings which in a countercurrent flow pattern extract the processed sugars to a sugar concentrator tank to be further processed in a conventional manner through fermentation to ethanol.
Some embodiments may utilize three subsequent process zones with their own packing and extraction sections following the above sugar extraction section. In these embodiments, these process zones may be a first lignin extraction zone, a second lignin extraction zone, and a third lignin extraction zone, and numbered 974, 942, and 978 respectively. In a preferred embodiment, the process liquid in these zones is 60% ethanol and 40% water.
After de-lignification, there may be an additional packing ring followed by a four-ring hot alcohol countercurrent displacement wash, another four-ring counter-current hot water wash, and finally a four-ring counter-current cold-water wash. Thereafter, a discharge section 988 may discharge the feedstock to a blow tank utilizing the pressure within the system to bias the material outward.
With the foregoing description in place, there will now be a more detailed discussion of lowering the porosity. In general, throughout the system, the porosity values may change given the various states of the feedstock. As the feedstock is processed through the various zones its particle size and shape is reduced and the particles soften due to the organic matter being dissolved from the feedstock. To avoid porosity increase the feedstock may be packed at the end of each process zone to maintain proper and uniform displacement liquid cross-flow.
In general, with each positive displacement piston within an embodiment, there may be a pressure drive system upstream of the system that provides sufficient pressure for passing the feedstock and the intermediate pistons through the tube reactor assembly. In order to control the porosity in the manner described above, the feed drive may provide a certain displacement of a known quantity of fluid.
In an example embodiment, the feed drive is a positive displacement device which positively displaces a prescribed amount of fluid into the system. Along the way, various packing rings in the system controls the porosity through the entire tube reactor. Basically, in order to pack the feedstock and lower the porosity, the intermediate packing rings will be extracting liquid at intermediate stages. In other words, at the very end portion of the system there is a pressure-relief-valve-based extraction whereby if (for example) one unit of water is pumped in by the feed pump or cylinder behind the trailing plug and one unit of water is removed at a packing ring, then the particles of the feedstock before that particular packing ring will move closer to one another (wherein the trailing piston will advance forward), and effectively the porosity of the feedstock in that section is lowered.
In this way,
Therefore, referring now back to
However, the pump assembly provides operation of multiple drive pistons in a positive displacement manner that inject and withdraw a prescribed amount of fluid to maintain the fluid content within the system. Fluid can thus be extracted at prescribed intervals based on either gauges or known properties of the feedstock to adjust the porosity as described above. In general, a pump assembly having, for example, a single piston can be utilized for extracting fluid from a packing ring 662 as shown in
It will further be understood that the configurations and/or approaches described herein are exemplary in nature, and that these specific embodiments or examples are not to be considered in a limiting sense, because numerous variations are possible. The specific routines or methods described herein may represent one or more of any number of processing strategies. As such, various acts illustrated may be performed in the sequence illustrated, in other sequences, in parallel, or in some cases omitted. Likewise, the order of any of the above-described processes is not necessarily required to achieve the features and/or results of the embodiments described herein, but is provided for ease of illustration and description.
The subject matter of the present disclosure includes all novel and nonobvious combinations and subcombinations of the various processes, systems and configurations, and other features, functions, acts, and/or properties disclosed herein, as well as any and all equivalents thereof.
This application claims the priority of U.S. Provisional patent application Ser. No. 61/180,067, filed May. 20, 2009.
Number | Date | Country | |
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61180067 | May 2009 | US |