DIGESTER AND DIGESTION PROCESS

Abstract

A digestion apparatus is provided that include a vessel, a closure, and a fluid-transporting system. The vessel has a digestion chamber therein and an opening that provides access to the digestion chamber. The closure is adapted to interface with the vessel opening to form a fluid-tight seal against a digestion pressure and temperature within the chamber. The fluid-transporting system is adapted to direct fluid out of the digestion chamber back into the digestion chamber through an inlet port. The apparatus may include improved fluid heating, sample holding, safety and/or circulation options. Also provided are digestion methods that may use the digestion apparatus.

Description

BACKGROUND OF THE INVENTION

The invention relates generally to improved digestion technology, e.g., apparatuses and processes for digesting samples. In particular, the invention relates to digesters that provide improved fluid heating, sample holding, safety and circulation options.

There is a substantial current need for improved apparatuses for carrying out chemical reactions at elevated temperatures and/or pressures. Such apparatuses include, for example, digestion apparatuses that are used to produce pulp and/or intermediate fibrous materials from a wide variety of cellulosic materials.

In general, digestion apparatuses are designed to carry out cellulosic digestion in batch or continuous processes in a rapid manner to result in a high yield. In a conventional batch cooking sulfite process, for example, a digester is filled with wood chips and charged with fresh cooking liquor. The digester is then sealed, and heated to cooking temperature by direct or indirect heating. Once cooked, a substantial portion of the lignin and carbohydrates may be degraded and/or leached from the pulp. Spent cooking liquor (black liquor) and the pulp are separated after cooking.

The laboratory digester is one of the most widely used instruments in the pulp and paper industry. The digester allows a user to experiment with a wide range of chemical compositions to optimize the full-scale cooking process. Laboratory digesters are available in a wide range of volumes and may provide critical insight into the chip cooking process for scale-up and/or optimization efforts.

A number of laboratory digesters are commercially available. For example, M/K Systems, Inc. (Peabody, Mass.) manufactures a high-pressure, vertically circulating, batch-process digester that runs pulp-digesting processes on a laboratory scale in a precisely controlled manner. Typically available in either single or dual vessel models, the digester provides excellent control over the cooking profile, homogeneous temperature distribution due to excellent systemic flow control and excellent liquor mixing. In addition, the digester is suitable for both alkaline and acid digesting process with various types of wood chips and fiber sources. Furthermore, the digester is designed to operate at high temperatures at elevated pressures.

Certain models of digesters from M/K Systems are constructed with features that improve fluid-transportation efficiency, higher pressurization, and space utilization. In addition, other features, e.g., a variety of different sample holding options, lead to improved digestion performance. U.S. Pat. No. 7,811,416 and U.S. Patent Application Publication No. 20100329943, both to Kallmes, describe such features and other improvements to digester technologies.

Nevertheless, there exist further opportunities to provide alternatives and improvements to sample digestion technologies. For example, improvements have been made in the areas of heating, fluid flow characteristics, flow path design, and sample holding options. Such improvements may be useful to overcome shortcomings associated with prior art cellulose digestion processes. In turn, the improvements may address previously unmet and long-felt needs to improve process capacity, precision, efficiency, and safety. In other words, the improvements may allow materials to be digested even more precisely, with enhanced safety, at higher temperatures and/or pressures, and with greater throughput and operator convenience.

SUMMARY OF THE INVENTION

The invention provides a digestion apparatus that include a vessel, a closure, and a fluid-transporting system. The vessel has a digestion chamber therein and an opening that provides access to the digestion chamber. Optionally, the digestion chamber may have a lower tapered portion. The closure is adapted to interface with the vessel opening to form a fluid-tight seal against a digestion pressure and temperature within the chamber. The fluid -transporting system is adapted to direct fluid out of the digestion chamber back into the digestion chamber through an inlet port.

Some embodiments of the inventive apparatus include a fitting is provided having at least five fitting ports in fluid communication with each other. As least one fitting port fluid is interfaced with the vessel, closure, and/or fluid-transporting system. Typically, at least three fitting ports define substantially coplanar fitting passageways and at least two of the substantially coplanar fitting passageways are not parallel to each other. For example, the fitting may have exterior surfaces that define a prism having a square or rectangular base. Optionally, a one-way valve may be interfaced with a fitting port and an additional vessel interfaced with the one-way valve.

In addition or in the alternative, the fluid-transporting system may be adapted to direct fluid out of the digestion chamber into at least one of first and second flow paths. The first flow path is effective to return fluid through an inlet port into the chamber. The second flow path forms a bypass loop located outside the chamber that is effective to allow fluid to circulate therein. A valve may be provided for selectively closing one of the first and the second flow paths.

A plurality of heaters may be provided. In some instances, a first heater in the form of a heat exchanger may be provided for heating fluid outside the chamber for introduction into the digestion chamber, and a second heater may be provided for heating the vessel and/or chamber.

A condenser may be interfaced with the fluid transporting system and/or chamber. In such as case, a pressure-relieving means may be provided that allows for fluid released therefrom to drain into the condenser. The pressure-relieving means may include a rupture disk or a pressure relief valve.

In some instances, the fluid-transporting system may be adapted to direct fluid out of the digestion chamber back into the digestion chamber through a flow path that extends, in order, through a submerged outlet port, a filter, a pump, a conduit and an inlet port, wherein the conduit is located in the flow path immediately before the inlet port. The conduit may define a flow path that exhibits no bend having a radius of curvature less than about 1 centimeter when the flow path has a diameter of about 1 centimeter. Similarly, the flow path from the outlet port and the pump may exhibit no bend having a radius of curvature less than about 2 centimeters when the pump is positioned in an offset manner below the outlet port and the flow path exhibits a diameter of about 1 centimeter. Such systems and variations thereof may define a flow path that ensures substantial laminar digestion fluid flow through the inlet port. Optionally, the filter and the pump independently and fluidly communicate with a downstream drain valve that when opened allows fluid to drain simultaneously from the filter and the pump.

A rinse line may be provided in fluid communication with the inlet port via a one-way valve (or check valve), allowing the user to connect low pressure water to the high pressure system. The one way valve may be installed such that low pressure water can enter the digester, but the valve may be closed to pressure exiting the digester. The rinse line may be used in combination with a means for distributing fluid as a safety and performance improvement feature.

A container may be provided within the digestion chamber. In some instances, the container may comprise a plurality of compartments for holding a plurality of samples. For example, the container may comprise a basket and one or more dividers. In some instances, horizontal divider(s) may define the compartments within the basket. The horizontal divider(s) may define compartments of substantially identical shape and size and/or may be removable from the basket. The horizontal porous divider(s) allow the user to cook a plurality of different samples within the same vessel, as liquor flows from the top section to lower sections. Additionally, one or more vertical non-porous dividers may be used to allow a plurality of samples to be cooked simultaneously within the same basket.

The invention also provides digestion methods. For example, a method is provided that involves first placing a sample within a digestion chamber of a vessel. Then, a fluid may be circulated and optionally heated to a desired temperature within a bypass loop located outside the chamber. Then, the fluid may be directed out of the bypass loop through an inlet port into the chamber toward the sample. The fluid downstream from the sample may then be out of the chamber and back into the chamber through the inlet port, optionally without returning fluid downstream from sample to the bypass loop. Optionally, the vessel and/or chamber is heated to a desired vessel and/or chamber temperature before the fluid is introduced into the inlet port and the chamber. In any case, fluid transported out of the chamber may be systemically re-circulated, e.g., repeatedly heated outside the chamber, directed through an inlet port into the chamber toward the sample, and, after contacting the sample, transported out of the chamber.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts in schematic cross-sectional view a single vessel embodiment of a digestion apparatus of the invention.

FIG. 2 depicts in schematically cross-sectional view the fluid-transporting member shown as a component of the digestion apparatus of FIG. 1 in the form of an elongate tube having perforations along its length.

FIG. 3 is a photograph of a container that includes a basket and a removable dispersion weight.

FIGS. 4A and 4B, collectively referred to as FIG. 4, are photographs of a basket container with a detachable mesh bottom. FIG. 4A shows the container with the bottom attached. FIG. 4B shows the container with the bottom detached.

FIGS. 5A and 5B, collectively referred to as FIG. 5, schematically depict an unitary cube plumbing fitting having six ports. FIG. 5A depicts the fitting in perspective view. FIG. 5B depicts the same fitting in cross-sectional view along the plane indicated by dotted line A.

FIG. 6 is a photograph of a digestion apparatus of the invention similar to that depicted in FIG. 1.

FIG. 7 are photographs of an upper portion of an exemplary digestion apparatus of the invention. FIG. 7A highlights laminar fluid flow through an inlet port that extends through a flange. FIG. 7B highlights the plumbing associated with the flow path upstream from the inlet port.

FIGS. 8A and 8B, collectively referred to as FIG. 8, schematically depict containers having a plurality of compartments of substantially identical shape and size. FIG. 8A depicts a container having a cross-shaped divider therein that vertically separates four compartments. FIG. 8B depicts a container having three horizontally separated compartments.

FIG. 9 is a close-up photograph that shows the location of an inline V-filter below the vessel of an exemplary digestion apparatus similar to that depicted in FIG. 1.

FIG. 10 is a close-up photograph that shows a conduit that forms a portion of the curved flow path between the digestion vessel and the pump of an exemplary digestion apparatus similar to that depicted in FIG. 1 except with an offset pump placement.

FIG. 11 provides a simplified depiction of digestion apparatus similar to those shown in FIGS. 1 and 6.

FIGS. 12A -12C, collectively referred to as FIG. 12, depict various vessel designs for the inventive digestion apparatus. FIG. 12A depicts a vessel design with a flat base. FIG. 12B depicts a vessel design with a conical base. FIG. 12C depicts a vessel design with a rounded base.

DETAILED DESCRIPTION OF THE INVENTION

Definitions and Overview

Before describing the present invention in detail, it is to be understood that the invention is not limited to specific digestion fluids or apparatus setups, as such may vary. It is also to be understood that the terminology used herein is for describing particular embodiments only, and is not intended to be limiting.

In addition, as used in this specification and the appended claims, the singular article forms “a,” “an,” and “the” include both singular and plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a vessel” includes a plurality of vessels as well as a single vessels, reference to “fluid” includes a fluid as well as a mixture of fluids, and the like.

Furthermore, terminology indicative or suggestive of a particular spatial relationship between elements of the invention is to be construed in a relative sense rather an absolute sense unless the context of usage clearly dictates to the contrary. For example, the terms “over” and “on” as used to describe the spatial orientation of a first item relative to a second item does not necessarily indicate that the first item is located necessarily above the second item. That is, the first item may be located above, at the same level as, or below the second item depending on the device's orientation. Similarly, an “upper” surface of an item may lie above, at the same level as, or below other portions of the item depending on the orientation of the item.

In this specification and in the claims that follow, reference will be made to a number of terms that shall be defined to have the following meanings, unless the context in which they are employed clearly indicates otherwise:

The terms “cellulose, “cellulosic” and the like are used herein in their ordinary sense and refer to a complex carbohydrate or polysaccharide that includes a plurality of monomeric glucose units (C₆F1₁₀O₅). As is well known in the art, cellulose constitutes the chief part of the cell walls of plants, occurs naturally in fibrous products such as cotton and linen, and is the raw material of many manufactured goods such as paper, rayon, methanol, and cellophane.

The term “chamber” is used herein to refer to enclosable or enclosed space. For example, a “digestion chamber” within a vessel may refer to a partially or fully enclosable or enclosed space within the vessel in which digestion may take place.

The term “closure” is used herein to refer to an item that closes. For example, a closure may take the form of a lid, plug, cap, or the like to close an opening of a vessel.

The terms “digest,” “digestion,” and the like are used herein in their ordinary sense in the field of chemistry and refer to softening, disintegration, and/or decomposition of a material such as cellulose) by means of heat, chemical action, and/or the likes. Thus, the term “digestion fluid” refers to a liquid and/or gaseous substance, that is capable of flowing, that changes its shape at a steady rate when acted upon by a force, and that aids in the softening, disintegration and/or decomposition of a material. Similarly, the term “liquor” as used herein refers to a solution or other fluid used to carry out cellulosic digestion. In any case, the terms “digester” and “digestion apparatus” are typically interchangeably used.

The term “fitting” is used herein in its ordinary plumbing sense and refer to items having ports that may be used to connect pipe, tubing, or other conduit sections, to adapt plumbing supplies to different sizes or shapes (e.g., gender), and for other purposes, such as regulating or measuring fluid flow. Exemplary two-port fittings include, “elbows,” “couplings,” “unions,” “reducers,” etc. Exemplary three-port fittings include “tees” and exemplary four-port fittings include “crosses.” Other commonly available fittings include “caps,” “plugs,” “nipples,” and “barbs.”

The term “flow path” as used herein refers to the route or course along which a fluid travels or moves. The term may have a synonymous meaning with the term “line” when used in a plumbing context.

The term “fluid-tight” is used herein to describe the spatial relationship between two solid surfaces in physical contact such that fluid is prevented from flowing into the interface between the surfaces.

The term “in order” is generally used herein to refer to a sequence of events. When a fluid travels through a flow path that extends “in order” through items X and Y, he fluid travels through item X before traveling through item Y. “In order” does not necessarily mean consecutively. For example, a fluid traveling in order through items X and Y does not preclude the fluid from traveling through item Z after traveling through item X before traveling through item Y.

The term “pressurized” as used herein refers to subjecting a fluid under a force per unit area greater than that which otherwise surrounds the fluid.

The term “substantially identical” as used to describe a plurality of items is used to indicate that the items are identical to a considerable degree, but that absolute identicalness is not required. For example, when perforations are described herein as of a “substantially identical size,” the perforations' size may be identical or sufficiently near identical such that any differences in their size are trivial in nature and do not adversely affect the performance of the perforations' function. The terms “substantial” and “substantially” are used analogously in other contexts involve an analogous definition.

The term “vessel” is used herein in its ordinary sense and refers to a hollow or concave item, typically sealable, for holding fluids or other contents.

In general, the invention relates to an apparatus for digesting a cellulosic material or other sample. The apparatus includes a vessel containing a digestion chamber accessible through a vessel opening. A closure is also provided to interface with the vessel opening against a predetermined digestion pressure and temperature within the chamber. A container inside the digestions chamber may be provided for holding a sample. (The term “container” is generally used synonymously with “sample holder.”) A fluid-transporting system is adapted to direct digestion fluid through an inlet port and an optional fluid distribution means toward any sample in the container.

The inventive apparatus may include a number of novel and nonobvious features that provide a number of previously unavailable digestion or other processing options. For example, a fitting may be provided having at least five fitting ports in fluid communication with each other. Such a fitting may be used to provide greater process flexibility, e.g., by allowing the fluid-transporting system to direct fluid out of the digestion chamber into a main flow path and a bypass loop. In turn, the bypass loop may allow for enhanced heating process options. A small portion of the system liquor may be directed outside of the vessel through the bypass loop, which could be accomplished by installing a valve to close the exit of the vessel and closing liquor which normally is fed back into vessel. After the heater has been raised to an acceptable temperature, the liquor return line and vessel-exit valve could be opened, allowing traditional flow, essentially starting the cook with a pre-heated heater.

Similarly, the container may be divided into a plurality of compartments. For example, the container may comprise a basket with a removable porous horizontal divider that defines compartments of substantially identical shape and size within the basket. The compartments may hold different samples so that they may undergo processing under same digestion conditions, one or more samples serving as a control for comparison with one or more other samples. Removable vertical dividers can also be installed, allowing the user to cook multiple different materials within the same cooking basket.

Additional safety and/or performance enhancing features may be included. In some instances, a pressure-relieving means may be provided that allows for fluid released therefrom to drain into a condenser interfaced with the fluid transporting system and/or chamber. In addition or in the alternative, a rinse line may be provided in fluid communication with the inlet port via a one-way valve. The rinse line may be used in combination with a means for distributing fluid as a safety and process control feature.

As another example, the fluid-transporting system, to enhance digestion efficiency, may be constructed to direct fluid out of the digestion chamber back into the digestion chamber through, in order, a submerged outlet port, a pump, a conduit and an inlet port. The conduit may define a flow path that exhibits no bend having a radius of curvature less than about 1 centimeter when the conduit has a diameter of about 1 centimeter. Such systems and variations thereof may define a flow path that ensures substantial laminar digestion fluid flow through the inlet port.

The materials used to form the components of the inventive apparatus are selected with regard to physical and chemical characteristics that are desirable for proper functioning of the apparatus. For example, all materials used to construct the various components of the inventive apparatus should be chemically inert and physically stable with respect to any substance with which they come into contact when used to carry out sample digestion (e.g., with respect to pH, etc.).

Single Vessel Digestion Apparatus, Generally

An exemplary simplified single vessel apparatus of the invention is schematically depicted in FIG. 1. As with all figures referenced herein, in which like parts are referenced by like numerals, FIG. 1 is not necessarily to scale, and certain dimensions may be exaggerated for clarity of presentation. As shown in FIG. 1, the apparatus 10 includes a single cylindrical vessel 20 having a curved sidewall 21 bounded by a generally planar top surface 22 and a platen base 24. Sidewall 21 is generally perpendicular to each of the top surface 22 and the platen base 24. Optionally, a flange 25 extends outwardly from the top of vessel 20 perpendicular to sidewall 21, thereby defining in part the top surface 22 of the vessel 20. An opening 26 at the top surface 22 provides access to digestion chamber 30 within vessel 20. Typically, the opening 26 is sized and shaped allow facile transport of a container 60 containing materials into and out of the chamber. Optionally, the size of the opening has a cross sectional area equal to or greater to the cross-sectional area of any other portion of the chamber 30 along an axis perpendicular to the opening. Also optionally, markings (not shown) may be present on an interior surface of the sidewall 21 to as to provide a visual fill-marking that indicates the level to which digestion fluid may be filled for optimal performance.

As shown in FIG. 1, a groove 27 is located on the top surface 22 of the vessel 20. While the groove 27 is shown as generally circular in shape, alternative embodiments of the invention may include grooves of any of a number of cross-sectional shapes. Seated within groove 27 is elastic ring 28 having a shape that generally conforms to the groove 27. Optionally, one or more additional concentric grooves and rings (not shown) may be provided on surface 22 as well. Further optionally, sealing gasket materials may be used in the place of elastic rings and/or grooves (also not shown).

Also provided is a closure 40 in the form of a lid having substantially parallel upper and lower planar surfaces indicated at 42 and 44, respectively. Lid 40 may be placed over opening 26 such that lower surface 44 faces top vessel surface 22 and that elastic ring 28 is interposed between surface 44 and 22. When the lid 40 is urged together with flange 25 applied using clamps (not shown), the ring 28 may be compressed between surface 22 and 44. As a result, a fluid-tight seal may be formed between the lid 40 and the vessel 20. As lid 40 may weigh on the order of 10 kg, operators of the digestion apparatus may appreciate a handle or other means (not shown) for facile manipulation, reorientation, and/or movement the lid. Optionally, such a handle may be thermally isolated such that the operator may not need to use heavy gloves when using the handle to manipulate, reorientation or moving the lid.

A container 60 may be placed within the digestion chamber 30 through opening 26 located in top planar surface 22 of the vessel 20. When sealed within the digestion chamber 30, the container 60 may serve to hold a cellulosic material therein for digestion by digestions fluids within the chamber. As shown, the container 60 formed from a cylindrical basket having an opening 62 at its top through which cellulosic materials may be loaded into the container 60. The container 60 has a shape and size generally similar to that of the chamber 30 to reduce dead space within the chamber 30 in which no cellulosic digestion may be digested. Optionally, a handle 64 may be attached to the opposing points on the sidewalls near the top of the container 60 to allow a user a convenient means for maneuvering the container 60 in and out of vessel 20.

The container 60 typically also has a bottom 66 containing one or more holes 68 through which digestion fluid may flow. As shown, the bottom may be formed from a wire mesh, but any perforated bottom may generally be used with the invention as long as the holes 68 are appropriately sized and located. For example, the one or more holes 68 are typically sized to ensure that cellulosic material within the container 60 remains within the container before, during, and after exposure to digestion fluid within the chamber 30. Often, the holes are arranged in an array. Optionally, the sidewalls of the container 60 may also contain holes of appropriate size and arrangement.

Further optionally, as shown in FIG. 4, the bottom 66 of the container may be detachable from the sidewalls. In some instances, a plurality of modularly interchangeable bottoms with different mesh sizes and/or hole arrangements may be provided so that they can be used with the same container. That way, the container may better retain samples therein at all stages of digestive state while allowing for appropriate or optimal digestion fluid flow therethrough, as discussed below.

In some instances, the container may vary in volume according to a change in digestive state of any cellulosic material contained therein. For example, a perforated fluid-dispersion weight 70 in the form of a disk having generally opposing parallel upper and lower surfaces indicated at 72 and 74, respectively. The weight also contains an array of holes 76 extending through surfaces 72 and 74 that provides a plurality of flow paths through which fluids may travel. In other words, the weight 70 is effectively rendered porous for digestion fluid flow-through. The disk 70 is shaped and sized to allow it to be placed in movable relationship with container 60. Optionally, a handle 78 attached to upper surface 72 may be provided to allow for facile handling of the weight 70. An exemplary basket and dispersion weight suitable for use with the invention is shown in FIG. 3. Optionally, the container may allow for an extension component to increase the container's capacity.

In operation, cellulosic material may be placed within the container 60, and the porous weight 70 may be placed over the cellulosic material with lower surface 74 facing the cellulosic material and the bottom 66 of basket 60. As a result, the effective volume of the basket 60 for containing cellulosic material is bounded by the basket 60 and the weight 70. As the digestive state of the cellulosic material in the basket changes, the spatial relationship between the basket and the weight may change as well. As a result, the container 60 may effectively vary in volume according to the cellulosic material in the basket. Typically, as cellulosic material is digested, the mechanical strength of the material is decreased. The weight 70 will tend to compress or compact the cellulosic material as its physical integrity degrades, thereby reducing the effective volume of the basket.

The apparatus also includes a fluid-transporting system for transporting digestion fluid within the digestion chamber. The fluid-transporting system serves to direct digestion fluid through a port and the container toward any cellulosic material in the container. In some instances, the fluid-transporting system may be adapted to direct digestion fluid from a supply exterior to the digestion chamber toward the cellulosic material therein in the container. In addition or in the alternative, the fluid-transporting system may be adapted to direct digestion fluid from a supply within the chamber toward the cellulosic material.

As shown in FIG. 1, the fluid-transporting system may include a plurality of components that are interfaced with the digestion vessel 20 and/or chamber 30 via a plurality of ports (inlet port, outlet or other types of ports) through the vessel 20 and the lid 40. For example, a liquor inlet port 102 traverses through the vessel flange 27. A liquor outlet port 108 is located in the base 24 of the vessel 20. Additional components of the apparatus shown in FIG. 1 external to the vessel 20 that may be considered components of the fluid-transporting system include, for example, fitting 300, pump 110, flow meter 310, conduits 320, 322, 324, 326, 328, and valves 109, 112. Fitting 300 provides fluid communication between port 108 and conduit 320. Pump 110 provides a driving force to provide fluid flow, and flow meter measures fluid flow in the fluid-transporting system. Drain 200 fluidly communicates with the branching conduit 322 via drain valve 118.

Filter 121 may be used to ensure that the fluid-transporting system does not become clogged from digested material that may escape from the sample holder. As shown in FIGS. 1 and 9, a filtering means is provided in the form of a commercially available inline V-filter 121 with a coil hollow filtration (indicated by dotted lines in FIG. 1), with filter mounted inline with the liquor flow such that liquor flows from the vessel, over the hollow wire mesh and into the pump. Another line of the V-filter may be used to drain off fine particular matter, e.g., stray fibers, after a digestion process is completed, thereby avoiding the need to clean out the pump of contaminants which could interfere with pump's proper functioning. The filter 121 is downstream from outlet port 108 and upstream from pump 110. The filter may serve to capture stray fibers and the like, thereby preventing them from reaching the pump.

Furthermore, additional components within the chamber 30 may also be interfaced to the fluid-transporting system as well. For example, a means for distributing fluid may be located downstream from the inlet port. As shown in FIG. 1, a digestion fluid distributing means 130 in the form of fluid-conveying member or dispersion nozzle may be connected to liquor inlet port 102 via conduit 124. As shown, the nozzle 130 may be mounted to lid 40, but such mounting is not required. The nozzle 130 is oriented such that emerging fluid is directed toward the basket 20 and the weighted disk 70 located therein. As shown in FIG. 2, the dispersion nozzle 130 formed from a straight elongate tube 131 having a lumen 132 extending from an open proximal inlet port terminus 133 to a closed distal terminus 134. A plurality of circular perforations 135 of substantially identical shape and size may be arranged in a single equidistant linear array along the length of the tube. The perforations 135 extend through the wall of the tube 131. The proximal terminus 133 constructed to be attachable directly to a port or indirectly via a conduit to the port. U.S. Pat. No. 7,811,416 and U.S. Patent Application Publication No. 20100329943 describes other possible nozzle designs.

A plurality of flow paths is shown. A drain flow path allows fluid drain from the lower portion of the chamber 30, in order, through outlet port 108, valve 109, fitting 300, conduit 320, filter 121, pump 10, conduit 322, valve 118, drain 200, and out of apparatus 10. Circulatory flow path allows fluid from the chamber 30, in order, through outlet port 108, valve 109, fitting 300, conduit 320, filter 121, pump 10, conduits 322, conduit 324, flow meter 310, conduit 326, control valve 112, conduit 328, inlet port 102, conduit 124, nozzle 130, opening 62 or basket 60, holes 76 of weight 70, and holes 68 in the bottom 66 of the basket 60, and back into the bottom of the chamber 30.

The apparatus 10 typically also includes a heat exchanger 140 and a temperature detector 150 for measuring fluid, e.g., liquid, temperatures in the fluid-transporting system as well. The heat exchanger may be used to heat and/or cool fluid in the fluid-transporting system. For example, a cooling jacket may be placed around a heater to form the heat exchanger. When water is fed through inputs of the cooling jacket and the heater is turned off, the jacket effectively converts heater into a component of a cooler. The placement of the heat exchanger 140 and the detector 150 may be selected to ensure their optimal performance, e.g., to provide uniform heating and rapid detection response. For example, the heat exchanger and temperature detector may generally be placed anywhere along the circulatory flow path, as long as the heat exchanger and temperature detector do not interfere with each other's performance. As shown, the temperature detector 150 is interfaced with fitting 300 and the heat exchanger 140 is located between conduits 322 and 324, i.e., downstream from the pump 110 and upstream from the flow meter 310. As discussed below, band heaters wrapped around the vessels may be used as a secondary or primary source of heating for the digestion apparatus.

Additional vessel ports or “nipples may be present. Typically, a vessel may have three or four ports to facilitate access by interrogative instrumentation and other accessories. For example, a first pressure interface port 104 is shown disposed near the top of sidewall 21. A second pressure interface port 106 is disposed through lid 40. Pressure interface ports may be used to provide an interface with components that act in response to pressures present in the chamber 30. For example, the pressure release valve 116 is connected with the second pressure interface port 106, which allows vapor communication between the pressure release valve 116 and the chamber 30. The pressure release valve allows for controlled venting of the chamber 30 to ensure control over pressure therein.

Similarly, port 94 is also shown disposed through lid 40. Sensor 92 within port 94 provides a means for measuring vapor temperature and/pressure within the chamber 30. Optionally, as shown in FIG. 7B, sensor 92 may disposed through other parts of the digestion apparatus, e.g., the flange 25.

The rupture disk 114 is shown connected with the first pressure interface port 104, which allows vapor communication between the rupture disk 114 and the chamber 30. The rupture disk 114 has a first surface 115 in vapor communication with chamber 30 via interface port 104 and an opposing second surface 117 that faces a conduit 202 that fluidly communicates with a condenser 400. The disk 114 serves as a safety mechanism to ensure that any excessive pressure buildup in the chamber 30 does not lead to explosive or catastrophic failure of the apparatus 10. For example, a rupture disk may be provided that ruptures at a predetermined pressure limit that is slightly higher than a peak desired processing pressure. Thus, when the peak desired processing pressure is 300 pounds per square inch (PSI), rupture disks that vent at 310 PSI may be used.

The digestion apparatus may vary in construction. For example, FIG. 6 is a photograph of an exemplary digestion apparatus. From casual inspection, it should apparent that the digestion apparatus of FIG. 6 is similar to but not identical to that depicted in FIG. 1.

FIG. 11 shows that the inventive apparatus may include other components as well. For example, a liquor insertion tank 700 may be provided. As shown, a flow path may be created from the liquor insertion tank 700 to the pump 110, via, in order, line 702, valve 404, and conduit 320. Such a flow path allows the pump draws in liquor rather than wait for liquor to creep in via head pressure alone.

FIG. 11 also show how two different flow paths are created at V-filter 121. A first flow path begins at conduit 320, and a second flow path begins at conduit 321. It has been observed that, when the flow paths terminate at different drain valves, operators often forget to open both valves for proper cleaning and maintenance. Thus, a combined drain line represents another novel and nonobvious aspect of the invention. As shown in FIG. 11, the first flow path extends through conduit 320 and pump 110 before reaching conduit 322 and drain valve 118, whereas the second flow path extends through conduit 321 to reach conduit 322 and drain valve 118 in a manner that bypasses pump 110. In other words, both conduits 320 and 321 fluidly communicate with drain valve 118. The combined drain line ensures that whenever the pump is cleaned and drained via drain valve 118, the filter 121 is drained via drain valve 118 as well.

Exemplary Digestion Process And Parameters, Generally

In operation, the digester 10 shown in FIG. 1 may be used to effect digestion of cellulosic and other samples in the manner described below. While the inventive digestion process is generally described below as comprising a plurality of steps to be carried out in succession, one of ordinary skill in the art will recognize that at least some of these steps may be carried out in an overlapping or simultaneous manner. The order in which the steps are carried out may vary as well.

As an initial matter, the digester may be used to digest any material. However, materials that are of substantial or high cellulosic content are generally preferred. Exemplary cellulosic materials include, wood chips, raw cotton, hemp, flax, bamboo, methanol preparation, numerous biomaterial preparations, etc. However, the digester may be optimized for use with a particular material. For example, the holes 68 in the bottom 66 of basket 60 may be of a sufficiently large size to as to allow for uninhibited fluid through flow but of a sufficiently small size to ensure containment of material loaded therein. A sample may be placed through opening 62 into basket 60, followed by porous weight 70. Care should be taken to ensure that the weight 70 is positioned in a manner that that allows for it to move and compress or compact the sample as the bulk volume and mechanical strength of the material decreases through digestion. This may involve placing the weight 70 such that its lower surface 74 faces and is substantially parallel to the bottom 66 of basket 60. A user may then use the handle 64 to maneuver the basket 60, bottom 66 first, into the chamber 30 through chamber opening 26.

Digestion fluid may then be introduced into the chamber 30. Depending on the digestion chemistry desired by the user, any of a number of digestion fluids may be used. For example, the digestion fluid may be basic or acidic in nature and have a pH ranging from zero to 14. The acidity/alkalinity may be measured and/or recorded by using a pH meter. Similarly, the fluid may include oxidizing and/or reducing agents selected according to the sample in the basket 60. In any case, it is typically desirable to ensure that the drain valve 118 is closed before the digestion fluid is introduced into the chamber 30. Additionally, strong oxidizing agents such as ozone can also introduced through a one-way check valve into the vessel and/or fluid transporting system. The one-way check valve ensures fluid flow in one direction: the vessel pressure cannot exit out, while fluids can be introduced into the system. As discussed elsewhere herein, one-way check valves may be installed into the vessel closure or into the multi-connector below the vessel.

In some instances, the digestion fluid may be introduced into the chamber via opening 26. In such a case, the system power may be off. However, digestion fluid in some embodiments may be introduced into the chamber through the liquor inlet port 102 from a source (not shown) through pumping action effected optionally by pump 110.

The volume of digestion fluid added may vary according to the design of the inventive apparatus and other factors such as the volume and chemistry of the sample to be digested. Exemplary volumetric ratios of digestion fluid to sample may range anywhere from 1:2 to 2:1 to 5:1 to 10:1. In addition, a sufficient amount of digestion fluid may be introduced into the chamber 30 so that at least a portion of the sample and the outlet port 108 are submerged. Optionally, the weight 70 may be submerged as well. However, it is generally desirable to avoid introducing an excessive volume of digestion fluid into the chamber 60 so as to interfere with the workings of rupture disk 114 and the pressure control valve 112. These components typically require space to be allocated for vapor compression. Accordingly, it may be undesirable to submerge the first and second interface ports, 104, 106, respectively.

Before the chamber 30 is sealed, it may be desirable to operate the pump 110 in a purely circulatory manner without either the nozzle 130 or the conduit 124 connected to liquor inlet port. Typically, fluid from the chamber 30 may be directed to displace any gas within conduits in the second fluid flow path using the pump 110 at a low speed to distribute digestion fluid systemically throughout the apparatus. As a result, overall fluid level in the chamber 30 may be lowered and trapped gas bubbles within the flow path, e.g., in the outlet port 108, the circulation pump 110, conduit 120, control valve 112, or inlet port 102 that contribute to irregular fluid flow may be displaced. In short, such pumping action effectively primes and/or warms up the apparatus for smooth sample digestion in a controlled operation.

Once the apparatus has been primed and/or warmed up, conduit 124 may be attached to nozzle 130 and the inlet port 102, and the chamber 30 may be sealed in a fluid-tight manner against a predetermined digestion pressure and temperature within the chamber. Depending on the conditions required to carry out a desired sample digestion operation, the predetermined pressure and temperature may vary. Typically, sample digestion requires both heat and elevated pressure. Exemplary pressures suitable for effecting industrial cellulosic digestion are typically on the order of 50 to about 500 PSI, though higher pressures are often preferred over lower pressures. Thus, the predetermined pressure may be no less than about 100 to about 180 to about 200 to about 300 PSI. Exemplary temperatures suitable for digest cellulosic materials in practice are typically about 50 to about 300° C. Thus, the predetermined temperature may be no less than about 100 to about 200° C.

For the apparatus 10 shown in FIG. 1, lid 40 may then be placed over the vessel opening 26 so as to form the fluid-tight seal against the predetermined digestion pressure and temperature within the chamber. Lid 40 may be placed over opening 26 such that lower surface 44 faces top vessel surface 22 and that elastic ring 28 is interposed between surface 44 and 22. Optionally, vacuum grease or some other sealing compound may be applied to the elastic ring 28 and/or portions of surfaces 44 and 22, which may come into contact with the elastic ring. Clamps 50 are then secured to the lid 40 and flange 25 to compress ring 28 so as to form a fluid-tight seal.

Other means may be used to provide a fluid-tight seal as well. Typically, a fluid-tight seal involves the immobilization of the lid 40 to the vessel flange 25. When corresponding holes are present in the lid and vessel flange (not shown), bolts may be extended through the corresponding holes to urge the lid and flange together. In some instances, alternative or additional external means may be used to urge the pieces together (such as clips, tension springs or associated fastening apparatus). Other means such as male and female couplings or friction fittings may be advantageously used as well. Releasable adhesives such as those in the form of a curable mass, e.g., as a liquid or a gel, may be placed between the substrates and subjected to curing conditions to form an adhesive polymer layer therebetween. Additional releasable adhesives, e.g., pressure-sensitive adhesives or solvent-containing adhesive solutions may be used as well.

Once the chamber 30 is sealed, the heat exchanger 140, in heating mode, and the pump 110 may be used to cook the sample in the basket 60 in a controlled pressurized environment. Optionally, steam may be introduced into the digester before cooking. The heat exchanger 140 may be used to heat any digestion fluid in contact therewith and may be controlled using feedback from the temperature detector 150 and/or sensor 92. Depending on the desires of the user, the heat exchanger 140 may be controlled on the fly or follow a preprogrammed cooking profile. Since the volume in the chamber 30 remains constant while the temperature therein increases, pressure in the chamber 30 increases as well. Optionally, steam or another gas may be introduced into or extracted from the chamber 30, e.g., via control valve 112, while the chamber 30 is sealed so as to ensure that the pressure in the chamber 30 is maintained within in an optimal range for sample digestion without compromising safety.

Simultaneously, the pump may direct digestion fluid to baste the sample in the basket while the material is cooked. Because the bottom of the chamber is filled digestion fluid, that fluid represents a supply, which may be used to baste the sample in the basket. In operation, the pump 110 draws fluid from the supply at the bottom of the chamber through outlet port 108 via valve 109 into the pump 110. Then, fluid is forced through the conduit 120, control valve 112, inlet port 102, conduit 124, toward the nozzle 130.

Notably, the position of pump 110 may affect the operation of the fluid-transporting system. As shown in FIGS. 1 and 6, pump 110 may be placed directly below outlet port 108. It has been experimentally demonstrated that a digestion apparatus having a pump located directly below the apparatus' outlet port tends to perform better than a similar digestion apparatus having a similar fluid-transporting system design that uses an offset pump location. An offset pump placement tends to lead to cavitation and other problems absent in fluid transporting systems with a pump placement shown in FIGS. 1 and 6.

However, it is possible to avoid cavitation and other problems associated with an offset pump placement. For example, it has been observed cavitation and similar pump problem occur when fluid is fed to the pump in an inadequate manner, e.g., with an unsteady, irregular and/or nonlaminar flow. To reduce such flow for an offset pump placement, sharp turns, e.g., those associated with 90° elbow and tee shaped fittings should generally be avoided in the flow path from the outlet port 108 and the pump 110. Instead, as shown in FIG. 10, a conduit 320 forming gently curving flow path of appropriate cross-sectional area may be employed to deliver substantially gas free liquid to a pump 110 located with an offset placement relative to the outlet port of the digestion vessel. Additional digestion fluid transportation issues as they relate to apparatus performance are discussed below.

Digestion fluid is directed through the open proximal inlet port terminus 133 at a flow rate and pressure effective to allow the digestion fluid to occupy the entire lumen 132 or substantially the entire lumen 132. Consequently, pressurized digestion fluid is sprayed out of the perforations 135 at a velocity higher than that would be achieved from gravitation forces alone. Fluid emerging from the nozzle 130 is distributed toward the sample through the holes 76 of weight 70. Instead of merely flowing toward the sample under gravitational and surface forces, the nozzle 130 effectively concentrates fluid flowing therefrom into focused streams that increases the rate at which digestion fluid penetrates the sample. As a result, use of the nozzle 130 effectively increases sample digestion efficiency over the digestion efficiency that would be achieved without the nozzle.

Sample so sprayed in a digestion chamber typically exhibits a higher degree of digestion than sample exposed to digestion fluid under the same conditions but under gravitational forces alone.

As a result of exposure to elevated temperature, elevated pressure, and continuous exposure to circulated (refreshed) digestion fluid, the sample in the basket 60 may be digested to a desired degree. As the sample is digested, its physical integrity will become increasingly compromised. As a result, the weight 70 will typically move toward the bottom 66 of the basket 60 and compress or compact the sample therebetween. Once the desired degree of digestion is achieved, the heat exchanger run in cooling mode to cool off the apparatus. Alternatively, the heat exchanger and/or pump may be turned off to allow the apparatus to cool. Once cooling has taken place, the apparatus may be drained and cleaned.

It should be noted that a number of process digestion processes may be monitored while they are taking place. For example, it is generally desirable to ensure that the fluid flows within the fluid-transportation system at a substantially constant pressure and/or flow rate. Spikes in pressure and/or flow rate may indicate a less than optimal digestion performance.

In addition, vapor and liquid temperatures may be independent monitored. Such independent temperature monitoring involves employing different temperature monitoring/detection means at different locations of the digestion apparatus. Generally, the vapor temperature may be measured using a sensor that does not come into directed contact with the liquor, e.g., in a location above the liquor circulation path. Such a sensor may, for example, be placed in the closure, flange, or upper sidewall of the chamber. In contrast, the liquid temperature is typically measured using a sensor that does come into direct contact with the liquor. Such a sensor, for example, may be placed at the lower portion of the chamber or in the fluid-transporting system.

In any case, as shown in FIG. 1, the circulating liquor temperature may be monitor using detector 150 while the vapor temperature may be measured using temperature sensor 92. It should be noted that it may be desirable to carry out a digestion process in a manner that ensures that the measured vapor temperature does not exceed the measure temperature of the circulating liquor. When the measured vapor temperature spikes above the measured liquor temperature, such spiking may be attributable to localized generation of superheated vapor, an artifact of uneven heating and inhomogeneous digestion reactions. Accordingly, a signal generator be employed to generate a signal when the measured vapor temperature exceed the measure digestion fluid temperature. Such a signal may be used to alert a digester operator to suboptimal digestion process conditions or to control various components of the digestion apparatus, e.g., open or close valves, increase or decrease power to heaters, etc.

Unitary Fitting with a Plurality of Fitting Ports

Space utilization of digestion apparatuses is an important issue because many digestion processes may take hours or days. Because laboratory spaces are often limited, there may be only enough space for one digester for a particular laboratory. In such instances, a digester of a particular size having the capacity to process a larger sample volume per run may be preferred to a digester of the same size but having the capacity to process a smaller sample volume per run. For example, it is generally desirable to use a sample container having a larger volumetric capacity within the digestion chamber than a smaller sample container. In addition, it is generally desirable to provide minimize the volume occupied by fluid and/or plumbing outside the vessel chamber of the digestion apparatus.

Nevertheless, there is an increasing need to interface more accessories and fixtures with digestion apparatuses to improve performance and enhance safety. As shown in FIG. 1, such accessories and fixtures may include, for example, sensors 92 such as pH meters, detectors 150, valves 116, and pressure relieving means such as rupture disks 114. Often, it is impracticable to drill additional ports in the vessel and/or closure after the vessel and/or closure has been manufactured.

Persons of ordinary skill in the art would recognize that a unitary fitting having numerous ports may be used to replace an assembly of fittings each having fewer ports than the unitary fitting. For example, a cross may be replaced with an assembly of two tees. Similarly, the six-port cube-shaped fitting 300 shown in FIG. 5 may sometime be functionally duplicated by assembling four tees, each having three ports. However, the fitting in FIG. 5, as is the case with other unitary fittings in general, will typically occupy less volume than an assembly of fittings each having fewer ports. In turn, the number of connections and tubing may be reduced, thereby resulting in significantly less liquor outside of the cooking vessel itself

Accordingly, a unitary fitting having a large number of fitting ports in fluid communication with each other in combination with digestions apparatuses represents a novel and non-obvious improvement relative to the prior art. Such a fitting generally allows for the digestion apparatus to retain a higher proportion of fluid within the vessel, e.g., in contact with the sample or container (sometimes referred to as the cooking substrate). The fitting may also minimize the out-of-vessel cooking liquor by reducing the number of connectors and excess tubing.

FIG. 5 depicts a unitary cube-shaped fitting 300 have six ports 302 that traverse each substantially planar exterior surface of the fitting. Such a fitting may be used with the fluid-transporting system associated with digestion apparatuses. As shown in FIGS. 1 and 6, the fitting 300 may have ports interfaced with one or more of the following—outlet port 108, detector 108, conduit 402, conduit 320, and valve 500.

Optionally, the fitting may have another port (not shown) interfaced with a one-way valve to allow for fluid transfer between chamber 30 of vessel 20 and an additional vessel (not shown), e.g., via a pressure difference between the vessels, to form a dual vessel apparatus. For example, certain embodiments of the invention may include two or more vessels. For such and other embodiments with two more chambers, a liquor transfer option may be provided to allow a user a convenient means to transfer liquids and vapor from a higher-pressure vessel to a lower pressure vessel. Typically, such transfer takes place when system and/or pump power are off Valves between flow paths connecting the vessels are opened, and fluid transfer may continue until pressure is equalized between the vessels or until a valve is closed in the flow path.

In addition, the locations of the ports through which inter-vessel fluid transfer can vary. For example, fluid may exit a fitting port located below and in fluid communication with a first vessel at a high pressure, travel through a connector hose, and enter a second vessel at a low pressure via a port that traverse through a closure atop the second vessel or a flange of the second vessel. Similarly, fluid may exit a first vessel at a high pressure via a port that traverses through a closure atop the vessel or a flange of the second vessel, travel through a connector hose, and enter a second vessel at a lower pressure via a fitting port located below and in fluid communication with a second vessel. To facilitate ease of use, the connector hose may be flexible.

In any case, a fitting having numerous fitting ports may be interfaced via at least one of the port to the vessel, closure, and/or fluid-transporting system. More generally, the fitting may have at least three fitting ports define substantially coplanar fitting passageways. Sometimes, at least two of the substantially coplanar fitting passageways may not be parallel to each other. In some instances no substantially coplanar fitting passageways is a parallel to another.

The exterior surfaces of such a fitting may vary. For example, the fitting may have exterior surfaces that define a prism. As depicted in FIG. 5, the fitting may have a square base. However, bases of other shapes, e.g., rectangles, pentagons, hexagons, octagons, etc. may be used as well.

Heating Options

The invention also includes a number of heating options that represent an improvement over previously known vertically circulating digesters. One area involves preheating. In general, previously known digesters do not allow for a preheating option. As discussed above, the digestion process typically begins when the sample and digestion fluid are loaded at room temperature into the digestion chamber of the vessel. Once the closure is interfaced with the vessel opening to form a fluid-tight seal against the chamber, the fluid transporting system and the heat exchanger is activated so that digestion fluid is directed fluid out of the digestion chamber into a flow path where the fluid may be heated by a heat exchanger before reintroduction into the chamber. Accordingly, the sample must initially soak in the digestion fluid at room temperature before the fluid heated to a desired cook temperature. That is, sample soaking and heating steps of a digestion process are effectively coupled to each other and may not be carried out independently from each other.

In contrast, the invention provides a number of options that a digestion process to with decoupled sample heating and sample soaking steps. As a first heat-soak decoupled option, the digestion apparatus may have a fluid-transporting system that may direct fluid out of the digestion chamber one or more different flow paths. For example, the fluid-transporting system may direct fluid into at least one of first and second flow paths. The first flow path may be a main circulatory flow path that is effective to return fluid through an inlet port into the chamber. The second flow path may form a bypass loop located outside the chamber that is effective to allow fluid to circulate and be heated therein. Typically, a valve is included for selectively closing one of the first and the second flow paths. Similarly, a heater may be provided for heating fluid in a section shared by the first and second flow paths.

In operation, a sample is placed within the digestion chamber. The fluid may be first circulated within the bypass loop and then directed out of the bypass loop through an inlet port into the chamber toward the sample. Finally, the fluid downstream from the sample may be directed out of the chamber and back into the chamber through the inlet port, typically without returning fluid downstream from sample to the bypass loop. Optionally, fluid may be heated within the bypass loop to a predetermined and/or desired temperature effective to allow the fluid to digest the sample before being directed back into the chamber. Closing valves to stop fluid from exiting the chamber and closing the re-entry valve maintains flow inside the bypass loop. This heats the system faster.

Turning to FIG. 1 for example, fitting 300 provides a means for forming the first and second flow paths as described above. The first flow path may serve as a main circulatory flow path that extends in order through chamber 30, outlet port 108, valve 109, fitting 300, conduit 320, filter 121, pump 110, branching conduit 322, heat exchanger 140, conduit 324, flow meter 310, branching conduit 326, valve 112, branching conduit 328, inlet port 102, conduit 124, and nozzle. Valves 404, 118, 500, and 602 are closed to ensure that fluid traveling through the first flow path is not diverted. In contrast, the second flow path may form a bypass loop that extends through fitting 300, conduit 320, filter 121, pump 110, branching conduit 322, heat exchanger 140, conduit 324, flow meter 310, branching conduit 326, and valve 500. Valves 109, 404, 118, and 112 may be closed to ensure that fluid remains in the bypass loop. Preferably, drain valve 118 may be located downstream from pump 110.

In addition or in the alternative, the digestion apparatus may be constructed to comport to a second heat-soak decoupled option in which a plurality of heaters and/or heat exchangers are included. For example, a first heater may heat fluid outside the chamber for introduction into the digestion chamber, and a second heater may directly heat the vessel and/or chamber. When, as shown in FIG. 1, the second heater 90 is a band heater wrapped around the vessel, the second heater may indirectly heat fluid inside the chamber. In contrast, when the second heater is located with the chamber, the heater may directly contact fluid within the chamber to effect heating.

In any case, it should be noted that a band heater that is wrapped around the vessel may serve as a secondary heater. Such a band heater may also replace an inline heater exchanger. The band heater may heat the vessel directly, the vessel representing the largest source of metal in the system, which in turn heats the liquor in the vessel.

In operation, a sample is placed within a digestion chamber of a vessel, and the chamber and/or vessel is heated with substantially no fluid therein. That is, the sample may not be initially submerged within fluid in the chamber as the chamber and/or vessel is heated. Once the chamber and/or vessel is heated, e.g., to a predetermined or desired temperature, fluid may be directed through an inlet port into the chamber toward the sample. Then, fluid downstream from the sample may be directed out of the chamber, optionally for reintroduction into the chamber toward the sample.

The above-described heat-soak decoupled options may be employed independently from or in conjunction with each other. For example, fluid may or may not be introduced through the inlet port until the vessel, chamber and/or fluid is heated to a desired temperature.

In any case, any of a number of heaters and detectors may be used with the invention. For example, the heater include an electrically powered resistive heating element and/or use gaseous, liquid, or solid combustion technologies known in the art that carries out heat transfer through conduction, convection and/or radiation. Exemplary temperature detectors suitable for use with the invention include thermocouple, photodiode, and other technologies known in the art. An optional programmable controller (not shown) may be provided that uses signal from the detector to control output from the heater so as to ensure that the chamber's temperature and pressure conforms to a desired profile. Such controllers are widely available and may be obtained from numerous commercial vendors, e.g., Omega (Stamford, Conn.).

Rinse Line

As alluded to above, laboratory digestion apparatuses are often used to prepare samples for experiments involving cellulosic materials associated with the pulp paper industry. Sample preparation would typically involve first carrying out a digestion cooking process. Such a process may begin by placing a sample at room temperature in a container. Then the container may be placed in the digestion chamber of a vessel, and the digestion chamber may be filled with digestion fluid. Once the chamber is sealed with a closure, the digestion fluid may be heated and circulated in a matter such that a steady stream is directed through an inlet port into the chamber toward the sample. As a result, the chamber itself will become hot and pressurized during the cooking process.

Eventually, heat will cease to be applied. However, components of the digestion apparatus typically remain hot, e.g., at a temperature that exceeds about 100° C., for an extended period. In addition, the vessel typically remains pressurized until the vessel has cooled. As a result, only after the digestion apparatus has cooled to a manageable temperature, e.g., less than about 100° C., would an operator attempt to remove the sample container from the digestion chamber. In some instances, the apparatus may take hours to cool, though a heat exchanger may be used to cool the digestion fluid as it continues to circulate in the digestion apparatus.

Typically, the cooking process does not represent the final step in sample preparation. Instead, after the sample container is removed from the digestion chamber, the container is typically placed in a sink and rinsed with cold water. The rinsing step is typically carried out to further cool the sample and to remove any unwanted residue, e.g., digestion fluid or unwanted reaction product such as lignin and carbohydrates.

Thus, in another embodiment, the inventive digestion apparatus may include a rinse line. As shown in FIG. 1, the rinse line 600 may be provided fluid communication with the inlet port 102 via a one-way check valve 602 and branching conduit 328. The check valve 602 allows a rinse fluid such as low pressure water to be introduced into the digestion chamber 30 while preventing digestion fluid such as liquor or vapor under high pressure from leaving the digestion apparatus via the rinse line.

In operation, the rinse line may be used after a desired digestion cooking process has taken place. Instead of waiting for the digestion apparatus to cool, an operator may drain the digestion apparatus of digestion fluid while the apparatus remains hot. Then, the rinse line 600 may be used to introduce cold water or some other fluid through the inlet 102, conduit 124 and nozzle 130 to rinse the sample in the digestion chamber 30.

The rinse line 600 provides a number of processing advantageous over previously known digestions apparatuses without a rinse line. As an initial matter, sample cooking and rinsing steps had to be carried out separately, i.e., in the digestion apparatus, and in a sink, respectively. In contrast, the addition of a rinse line allows the operator to carry out the sample cooking and rinsing steps in the same digestion vessel chamber without the need to relocate the sample. This is advantageous because hot digestion fluid residue may be present on the cooked sample and the container, thereby representing a safety hazard. Additionally, the rinse line can also clean off portions of the digester system such as rupture disks, increasing their longevity. When left un-cleaned, residual acidic/alkaline contaminants on the rupture disk may lead to undesired corrosion, thereby causing the disk to vent at below-design pressure conditions.

In addition, the rinse line provides a means to halt sample cooking while the digestion apparatus is cooled. In previously known digestion apparatuses, as discussed above, an operator must allow the digestion apparatus to cool to a manageable temperature before removing the sample container from the digestion chamber for rinsing. As the apparatus cools, the sample may continue to cook. In contrast, the rinse line may be used effectively to quench the sample and optionally remove digestion fluid therefrom. Rapid quench-cooling the sample enhances cooking precision.

Pressure Relieving Means and Condenser

As alluded to above, a condenser may be used with digestion apparatuses. A condenser is a device or unit used to condense a substance from its gaseous to liquid state, typically by cooling the substance. In so doing, the substance releases its latent heat which is typically transferred to the condenser coolant. Exemplary coolants include water and air.

In the context of the present invention, condensers are typically used to facilitate functions such as digestion fluid extraction and/or vapor sampling temperature liquor during the cooking cycle. As shown in FIG. 1, when valve 404 is opened, an external condenser 400 may fluidly communicate via conduit 402 and 406. As a result, fluid from chamber 30 may be cooled by condenser 400 before being extracted therefrom via conduit 408 by opening valve 410.

Also as alluded to above, digestion apparatuses are often constructed with components that serve as pressure relieving means. For example, pressure release valves may allow for controlled venting of the digestion chambers to ensure control over pressure therein. Similarly, rupture disks may serves as a safety mechanism to ensure that any excessive pressure buildup in the chamber does not lead to explosive or catastrophic failure. In any case, the operation of pressure relieving means is typically accompanied by the release or discharge of hot pressurized digestion fluid. Such fluid may represent an operational hazard.

To reduce the dangers associated with pressure relieving means, the invention provides a digestion apparatus as generally described herein in combination with a condenser interfaced with the fluid transporting system and/or chamber. The condenser may be placed downstream from the pressure-relieving means to allow for fluid released therefrom to drain into the condenser. For example, as shown in FIG. 1, the condenser is interfaced with the rupture disk 114 via conduit 202. As discussed below (not shown), vent valve 116 may also be interfaced via a detachable flexible hose upstream from condenser 400 as well. As a result, the condenser may cool the released fluid for ease of handling.

Pressure relieving means in combination with condenser may sometimes be used improve certain digestion processes. For example, cellulosic and other samples often outgas as they are brought to a cooking temperature in a digester. Such outgassing may compromise the performance of the digester. In some instances, outgassing may contribute to the irregularity of digestion fluid flow. In addition or in the alternative, outgassing may contribute to undesirable overpressurization within the vessel chamber. In turn, desired digestion reactions may be hindered or their rates compromised.

To avoid such outgassing problems, some operators have resorted to a problematic technique that involves preheating a sample and digestion fluid within an open digester. Instead sealing the vessel before applying heat, the lid is left off the digestion vessel until the after the sample has had some time to outgas as the temperature is ramped up. This is problematic for a number of reasons. First, as heat is applied to the sample and digestion fluid, the sample is not the only source of vapor generation. Vapors of the digestion fluid may be produced, e.g., via evaporative processes, as well. Because such vapors may be caustic, acrid and/or noxious in nature, the practice of such a technique requires, at a minimum, a ventilation hood or some other means to draw such vapors away from the operator. Splatter and other heat related dangers associated with an open-digester precook also make this technique undesirable.

In some embodiments, a pressure relieving means may be provided to address outgassing problems without resorting to preheating a sample in an open vessel. For example, a vent valve may be used to allow outgassed vapor to be released from a sealed vessel. Typically, such a vent valve is interfaced with the chamber at a location not susceptible to submersion by sustained contact with, or pooling by digestion fluid. Thus, such a vent valve may be interfaced with a port located above the inlet port and/or fluid distribution means. Optionally, the vent valve may be interfaced with a port extending through the vessel closure.

In operation, a sample is placed within the vessel, and the digestion chamber is sealed. As heat and digestion fluid is directed toward the sample, sample outgassing may increase the chamber pressure. Thus, the vent valve may be opened to relieve such pressure buildup. In some instances, the valve may be opened manually. Alternatively, the valve may be opened automatically in a periodic, as-needed, and/or predetermined manner according to the temperature and/or pressure of the chamber. In any case, a flow path, e.g., in the form of flexible tubing, may be provided between the vent valve and the condenser to avoid a dangerous and uncontrolled spray of hot digestion fluid as the vent valve is opened. Optionally, quick disconnect fitting technology, i.e., technology designed for use with components that are moved often and without disrupting system fluid pressure or compromising safety, may be used so as to avoid uncontrolled flow of digestion fluid as the when tubing is being connected or disconnected from digestion chamber, e.g., at the vent valve, and/or from the condenser.

The invention may include one or more condensers. When a plurality of condenser is employed, each condenser may serve a different purpose. For example, distinct condensers may be used for sampling and safety purposes. Each of a plurality of pressure relieving means may be made to communicate with different condensers.

Digestion Fluid Transportation

Among other inventive facets described herein, the manner in which digestion fluid is transported represents another novel and nonobvious aspects of the invention for a number of reasons. As alluded to above, irregular digestion fluid flow is generally an undesirable event that may be mitigated via pump priming. In addition, as discussed in U.S. Pat. No. 7,811,416 and U.S. Patent Application Publication No. 20100329943, digestion fluid distribution means such as nozzles have been observed to increase the velocity and dispersion of white liquor and/and other fluids in digestion apparatuses to increase penetration of such fluids into sample fibers. It has now been discovered that irregular fluid flow may be particularly detrimental to the performance of vertically circulating digestion apparatuses in general as well as such digestion distribution means in particular.

The fluid-transporting system may be constructed to reduce irregular fluid flow. As shown to FIG. 1, vertically circulating digestion apparatuses 10 are constructed with a fluid-transporting system that uses a pump 110 to direct fluid from a drain 109 at a lower elevation through a flow path that travels upward to an inlet port 102 at a higher elevation. As such, the flow path must typically exhibit at least one bend.

It has been discovered that the bend 329 in the flow path immediately preceding the inlet port 102 can be a source of irregular flow. Sharp bends tend to contribute to irregular fluid flow to a greater degree than more gradual bends. While not wishing to be bound by theory, it appears that gas bubbles tend to accumulate at such an elevated bend. Bubbles have been observed to disrupt laminar fluid flow.

FIG. 7 provides photographs of an upper portion of an exemplary digestion apparatus of the invention fluid-transporting system having an experimental verified improved fluid flow. As shown in FIG. 7A, fluid 700 emerging from the inlet 102 may be maintained in laminar flow. FIG. 7B highlights the plumbing associated with the flow path upstream from the inlet port. Notably bend 329 in the flow path immediately preceding the inlet 102 is gradual rather than sharp in nature.

Thus, in another embodiment, the invention provides a digestion apparatus as generally described herein with an improved fluid-transporting system adapted to direct fluid out of the digestion chamber back into the digestion chamber. The fluid-transporting system defines a flow path that ensures substantial laminar digestion fluid flow through the inlet port. For example, the flow path may extend through, in order, a submerged outlet port, a pump, a heat exchanger, and a conduit that immediately precedes an inlet port. When the conduit has a diameter about 1 centimeter, the conduit may define a flow path that exhibits no bend having a radius of curvature less than about 1 centimeter. Preferably, the flow path may exhibit no bend having a radius of curvature less than about 2 centimeters. Persons of ordinary skill in the art should be able to scale flow path diameters and radii of curvature accordingly upon routine experimentation in view of the disclosure contained herein.

Another contributory source of irregular fluid flow can be found in how fluid is fed from the vessel to the pump. As discussed above, it is typically desirable to provide the pump with a well-developed inlet flow so that the pump meets its potential. One way this may be done, as shown in FIG. 1, by placing the pump such that its inlet is located directly below the outlet port 108 of the vessel 20 and a substantially linear downward flow path is formed from the outlet port 108 to the pump 110.

However, as discussed above, an offset pump placement may be used. For example, the flow path between the outlet port 108 and the pump 110 should avoid sharp turns, e.g., those associated with 90° fittings. Instead, as shown in FIG. 10, a conduit 320 forming gently curving flow path of appropriate cross-sectional area may be employed to provide a well-developed and substantially bubble free flow to the impeller of pump 110 located with an offset placement relative to the outlet port of the digestion vessel. For example, the flow path exiting from the chamber 30 from the vessel outlet port 108 may begin in a substantially vertically downward direction but enter the pump 110 in a substantially horizontal direction.

As discussed above, a pump may not perform or be as reliable as expected due to a faulty intake plumbing layout. When poorly developed flow enters the pump, mechanical problems arising from cavitation and vibration may occur. Similarly, premature seal, bearing and impeller failure may also occur. As a result, the operation of digester may be accompanied with high maintenance costs, high power consumption, and less-than-specified head and/or flow, as well as imprecise cooks due to lack of liquor flow.

Thus, in yet another embodiment, digestion apparatus as generally described above is provided. The fluid-transporting system is adapted to direct fluid out of the digestion chamber back into the digestion chamber through a flow path that extends, in order, through a submerged outlet port, a pump, and an inlet port. The flow path between outlet port and the pump may have a diameter of about 1 centimeter and exhibit no bend having a radius of curvature less than about 2 centimeters. Optimally, any bend present in the flow path may exhibit a radius of curvature of at least about 4 centimeters. Persons of ordinary skill in the art should be able to scale flow path diameters and radii of curvature accordingly upon routine experimentation in view of the disclosure contained herein.

When the pump is constructed to receive fluid from a horizontal flow path segment, the pump may be located below the submerged outlet port in an offset manner. The pump should be offset from the outlet port at a sufficient distance to avoid pump cavitation problems. For example, it has been experimentally demonstrated that for a particular digestion apparatus that employs a flow path having a horizontal segment of about 8 centimeters in length immediately preceding the pump, the apparatus's pump tends to exhibit cavitation problems at about 185° C. when digestion fluid of a particular viscosity is circulated. In contrast, the same digestion apparatus filled with the same digestion fluid may be operated at a substantially higher temperature, e.g., above about 210° C., when the horizontal segment is increased in length to about 50 centimeters.

To have a well-developed flow pattern, then, it may be preferable to have a substantially straight and horizontally oriented flow path segment of a length of at least about 15 to 20 times the diameter of the pump's intake port. Preferably, the straight horizontal segment of the flow path immediately preceding the pump is of a length of at least about 50 to about 65 times the diameter of the pump's intake port.

Multicompartment Container

In another embodiment, the invention provide an apparatus generally described herein except that it includes a container within the digestion chamber, the container comprising a plurality of compartments for holding a plurality of samples. Such a container may be used to ensure that a plurality of different samples can be processed under similar or identical conditions during the same experimental run. As a result, some of the samples may serve as an “experimental control” while the other(s) may serve as an “experimental variable.”

FIG. 8 schematically depicts different containers having a plurality of compartments of substantially identical shape and size. FIG. 8A depicts a container 60 in the form of a basket having a cross-shaped divider 61 therein resting on the basket's bottom 66. The divider 61 that vertically separates the basket into four compartments, 63A, 63B, 63C, and 63D. Optionally, the divider may be removable from the basket.

FIG. 8B depicts a container 60 having three horizontally separated compartments 63A, 63B, and 63C. Each compartment 63A, 63B, and 63C has a corresponding bottom 66A, 636, and 66C made from a mesh or other porous material. The mesh material is typically selected to ensure that samples contained in the compartments do not fall through the mesh, and may vary, e.g., in wire and hole size.

Thus, additional container constructions are possible. For example, the number of compartments may be increased or decreased as needed. In addition, the dividers may be rigid or flexible. In some instances, porous sacks, pouches, and the like may be used to compartmentalize different samples within the container.

Tapered Vessel Chamber

As discussed above, the fluid-transporting system may be constructed to reduce irregular fluid flow associated with the digestion apparatus of the invention. It has now been discovered that the construction of digestion vessel and chamber may also affect fluid flow. In particular, it has been discovered that vessels forming a digestion chamber that exhibits a tapered lower portion may be advantageously used to effect fluid transfer.

FIG. 12 depicts various vessel designs for the inventive digestion apparatus. Each vessel 20 of FIG. 12 has an upper sidewall 21 that defines a substantially cylindrical portion of a chamber 30. However, the vessels exhibit different base constructions. FIG. 12A depicts a vessel design with a flat base 24. FIGS. 12B and 12C depict a vessel designs with tapered bases 24. In particular, FIG. 12B depicts a vessel design associated with a chamber having a lower portion that exhibits a substantially conical geometry, and FIG. 12C depicts a vessel design associated with a chamber having a lower portion that exhibits a substantially hemispherical geometry.

As shown, container 60 is located within chamber 30. Optional feet 65 is provided to raise the bottom of container 60 from the base 24 of the vessel of FIG, 12A. Alternatively, as shown in FIGS. 12B and 12C, the container may rest on the taper base 24 of vessel 20.

In operation, as fluid is introduced into the chamber 30, the fluid flows downward, pooling at a lower portion 31 of the chamber 30. In turn, the pooled fluid may flow out of the chamber 30 via outlet port 108 and drawn through conduit 320 toward pump 110. Depending on how fluid is introduced into the chamber 30 and how fluid flows through sample material in the container 60, fluid pooled at the lower portion 31 of the chamber may exhibit turbulence, and/or other phase and/or compositional variations such as bubbles and particular matter in liquor.

It has been experimentally verified that the vessel design shown in FIG. 12C provides improved fluid flow to the pump relative to the vessel design 12A. For example, digestion apparatuses with the improved design may be run at higher temperatures, pressures, and/or flow rates. While not wishing to be bound by theory, the improved design may provide well developed flow to the pump in different ways. For example, it is possible that the taper design provides funnel-type functionality to provide improved liquid channeling performance. In addition, it is possible the tapered geometry tends to increase the depth of pool fluid, thereby reducing the effect of surface turbulence and associated bubble generation (particularly when liquors containing surfactants are used) on fluid flow to the pump.

Thus, in a further embodiment, a digestion apparatus is provided as generally described above. However, the digestion chamber exhibits a tapered lower portion. For example, the tapered lower section may have a substantially conical or hemispherical geometry. The fluid-transporting system may be adapted to direct fluid out of the digestion chamber back into the digestion chamber through a flow path that extends, in order, through a submerged outlet port at the tapered base, a pump, a conduit and an inlet port. In such a case, the fluid-transporting system defines a flow path from the outlet port to the pump in a manner that ensures substantially steady pressure for fluid emerging from the pump.

Variations on the Invention

Variations of the present invention will be apparent to those of ordinary skill in the art in view of the disclosure contained herein. For example, the inventive apparatus may be designed to run on a number of different power sources. Direct current power sources, e.g., battery powered and/or alternating current power sources, e.g., 110V, 230V, 380V, single phase, may be used to power various components of the inventive digester. Additionally, the fittings described above may use all male, all female, or a combination of male and female connections.

In addition, the invention may be used to carry out chemical reactions other than digestion and/or may serve as a part of a process that uses the sample digested. For example, the invention may be used to carry out chemistries associated with the conversion of sample materials such as carbohydrates, polysaccharides, and cellulosic materials into products such as alcohols, acrylates, ketones, etc. As another example, the fluid-transporting system of the invention may be adapted to circulate yeast or other solutions that may be required to produce alcohol, optionally through fermentation. Similarly, when it is desirable to prevent oxidation of alcohols in the inventive apparatus, inert gas and/or vacuum technologies may be used to ensure that any chambers containing alcohol are free from the presence of oxygen or other oxidizing agents.

Accordingly, plumbing components may vary as well. In general, plumbing components must be selected to withstand chemistries associated with the digestion process. Thus, for example, digesters designed for digestion processes employing highly corrosive digestions fluids at elevated temperatures may require the use of stainless steel tubing and valves. However, the invention does not necessarily require rigid plumbing components. Flexible tubing may be used in a number of situations. For example, flexible tubing may be used to connect the digesters of the invention to water and digestion fluid supplies or to effect controlled drainage of fluid from the digester. An optional flow meter also can help control the flow rate in the bypass line or main circulation line.

It is to be understood that, while the invention has been described in conjunction with the preferred specific embodiments thereof, the foregoing description merely illustrates and does not limit the scope of the invention. For example, while the foregoing description focuses on the invention in a batch-processing context, the invention may also be of use in a continuous processing context. By incorporation fluid extraction and/or injection technologies, the inventive apparatus may be adapted to simulate continuous processes as well.

In any case, additional variations of the invention may be discovered, e.g., upon routine experimentation, without departing from the spirit of the present invention. For example, the inventive apparatus may be constructed to contain or exclude specific features and components according to the intended use of the apparatus, and any particular embodiment of the invention, e.g., those depicted in any drawing herein, may be modified to include or exclude element of other embodiments. Alternatively stated, different features of the invention described above may be combined in different ways. Other aspects, advantages, and modifications within the scope of the invention will be apparent to those skilled in the art to which the invention pertains.

All patents and patent applications disclosed herein are incorporated by reference in their entirety to an extent not inconsistent with the above disclosure.

Claims

1. A digestion apparatus, comprising: good a vessel having a digestion chamber therein and an opening that provides access to the digestion chamber;a closure adapted to interface with the vessel opening to form a fluid-tight seal against a digestion pressure and temperature within the chamber;a fluid-transporting system adapted to direct fluid out of the digestion chamber back into the digestion chamber through an inlet port; anda fitting having at least five fitting ports in fluid communication with each other, at least one fitting port interfaced with the vessel, closure, and/or fluid-transporting system.

2. The apparatus of claim 1, wherein at least three fitting ports define substantially coplanar fitting passageways.

3. The apparatus of claim 2, wherein at least two of the substantially coplanar fitting passageways are not parallel to each other.

4. The apparatus of claim 2, wherein no substantially coplanar fitting passageways is a parallel to another.

5. The apparatus of claim 1, wherein the fitting has exterior surfaces that define a prism.

6. The apparatus of claim 5, wherein the prism has a square or rectangular base.

7. The apparatus of claim 1, further comprising a one-way valve interfaced with a fitting port.

8. The apparatus of claim 7, further comprising an additional vessel interfaced with the one-way valve.

9. A digestion apparatus comprising: a vessel having a digestion chamber therein and an opening that provides access to the digestion chamber;a closure adapted to interface with the vessel opening to form a fluid-tight seal against a digestion pressure and temperature within the chamber;a fluid-transporting system adapted to direct fluid out of an outlet port of the digestion chamber, past a heater, through an inlet port, and into the chamber;a condenser interfaced with the fluid transporting system and/or chamber; anda pressure-relieving means for relieving any excessive pressure buildup in the digestion chamber, the pressure-relieving means allows for fluid released therefrom to flow to the condenser.

10. The apparatus of claim 9, wherein the pressure-relieving means includes a rupture disk and/or a pressure relief valve.

11. The apparatus of claim 9, wherein the pressure-relieving means extends through the closure.

12. The apparatus of claim 11, wherein the pressure-relieving means includes a valve.

13. The apparatus of claim 9, wherein the pressure-relieving means fluidly communicates with the condenser via flexible tubing.

14. The apparatus of claim 13, wherein the flexible tubing is connected to the pressure-relieving means and/or the condenser via quick disconnect fitting.

15. A digestion apparatus, comprising: a vessel having a digestion chamber therein and an opening that provides access to the digestion chamber;a closure adapted to interface with the vessel opening to form a fluid-tight seal against a digestion pressure and temperature within the chamber; anda fluid-transporting system adapted to direct fluid out of the digestion chamber back into the digestion chamber through a flow path that extends, in order, through a submerged outlet port, a pump having an intake port of an intake port diameter, and an inlet port,wherein and the pump is located below the submerged outlet port in an offset manner and the flow path between outlet port and the pump exhibits a substantially horizontal segment of a length that is at least about 20 times the intake port diameter.

16. The apparatus of claim 15, wherein the length of the substantially horizontal segment is at least about 50 times the intake port diameter.

17. A digestion apparatus, comprising: a vessel having a digestion chamber that exhibits a tapered lower portion and having an upper opening that provides access to the digestion chamber;a closure adapted to interface with the vessel opening to form a fluid-tight seal against a digestion pressure and temperature within the chamber; anda fluid-transporting system adapted to direct fluid out of the digestion chamber back into the digestion chamber through a flow path that extends, in order, through a submerged outlet port at the tapered base, a pump, a conduit and an inlet port,wherein the fluid-transporting system defines a flow path from the outlet port to the pump in a manner that ensures substantially steady pressure for fluid emerging from the pump.

18. The digestion apparatus of claim 17, wherein the tapered lower section has a substantially conical geometry.

19. The digestion apparatus of claim 17, wherein the tapered lower section has a substantially hemispherical geometry.

20. A digestion apparatus, comprising: a vessel having a digestion chamber therein and an opening that provides access to the digestion chamber;a closure adapted to interface with the vessel opening to form a fluid-tight seal against a digestion pressure and temperature within the chamber;a fluid-transporting system adapted to direct fluid out of the digestion chamber past a heater through an inlet port into the chamber; anda rinse line in fluid communication with the inlet port via a check valve.

21. The apparatus of claim 20, further comprising a means for distributing fluid located downstream from the inlet port.

22. The apparatus of claim 21, wherein the means for distributing fluid comprises a fluid-conveying member having a plurality of perforation through which fluid may flow.

23. The apparatus of claim 22, wherein the fluid-conveying member comprises a tube having a lumen extending from an open proximal terminus attached to the port to a closed distal terminus and the perforations fluidly communicates with the lumen.

24. A digestion apparatus, comprising: a vessel having a digestion chamber therein and an opening that provides access to the digestion chamber;a closure adapted to interface with the vessel opening to form a fluid-tight seal against a digestion pressure and temperature within the chamber;a fluid-transporting system adapted to direct fluid out of the digestion chamber past a heater through an inlet port into the chamber;a first temperature sensor that monitors vapor temperature in the chamber at or near the closure; anda second temperature sensor that monitors fluid temperature within the fluid-transportation system and/or in a submerged portion of the chamber.

25. The apparatus of claim 24, further comprising a signal generator that generates a detectable signal when the first temperature sensor detects a vapor temperature that exceeds a fluid temperature detected by the second temperature.