WO2022255921A1

WO2022255921A1 - Treatment vessel and method for facilitating discharge and/or removing blockage of lignocellulosic material

Info

Publication number: WO2022255921A1
Application number: PCT/SE2022/050509
Authority: WO
Inventors: Roger JANSSON; Jerk SÖDERMAN; Jonas SAETHERÅSEN; Magnus WILHELMSSON
Original assignee: Valmet Ab
Priority date: 2021-05-31
Filing date: 2022-05-25
Publication date: 2022-12-08
Also published as: SE2150688A1

Abstract

A treatment vessel (10) for treating lignocellulosic material comprises a main section (20) having a first end (24) and a second end (26), and an outlet section (40) tapering from a first end (44) joined to the second end (26) of the main section (20) towards a second end (46) having an outlet opening (48). At least one nozzle (60a) for injecting fluid is arranged on the inner circumference of the treatment vessel (10) and is positioned within a perpendicular distance (d1, d2) from a transition plane (T) defined by the junction between the first end (44) of the outlet section (40) and the second end (26) of the main section (20). A fluid conduit (70a) is connected to the nozzle (60a) and provided with a gas inlet (80a) for admitting a super-atmospheric gas having a super-atmospheric pressure into the fluid conduit (70a) in order for the gas to be mixed with the fluid in the fluid conduit. The fluid is a liquid.

Description

TREATMENT VESSEL AND METHOD FOR FACILITATING DISCHARGE AND/OR REMOVING BLOCKAGE OF LIGNOCELLULOSIC MATERIAL

TECHNICAL FIELD

The present invention relates to a treatment vessel and a method for facilitating discharge and/or removing blockage of lignocellulosic material.

BACKGROUND

Treatment vessels are commonly used within the field of producing pulp from a lignocellulosic material. Treatment vessels include pretreatment or impregnation vessels in which wood chips, representing a lignocellulosic material, are pretreated or impregnated with impregnation fluid to produce a chip slurry. Treatment vessels further include digesters in which the chip slurry is cooked in order to obtain pulp for later use in the making of pulp products such as paper. Additionally, treatment vessels include prehydrolysis vessels in which wood and non-wood materials such as wood chips and agricultural residues can be processed for producing fibers for pulp products such as paper.

Treatment vessels for treating lignocellulosic material typically comprise an inlet for entry of lignocellulosic material into the treatment vessel and an outlet for discharging treated lignocellulosic material and fluids from the treatment vessel. The inlet and outlet may be combined in a combined inlet and outlet, but are typically separate and placed at opposing ends of the treatment vessel. The outlet is provided at an outlet end of the treatment vessel which typically is dome shaped to withstand pressure. The outlet comprises an outlet opening through which the treated lignocellulosic material and any present fluid is discharged. As the treated lignocellulosic material and any present fluid is typically discharged into a discharge pipe, it is generally preferred to have an outlet opening that is significantly smaller in diameter than the inner diameter of the treatment vessel. This size reduction gives rise to several challenges when discharging the lignocellulosic material such as slow mass flow and blockages. Slow or stopped discharge of the lignocellulosic material from the treatment vessel limits the treatment capacity and treatment efficiency of the treatment vessel, and thus impact overall efficiency and cost of operating the treatment vessel and any preceding or following treatment step in the process of treating the lignocellulosic material. With severe blockages it may even be necessary to empty the treatment vessel manually, a procedure which leads to several hour or even several days of halted production.

In order to improve discharge of treated lignocellulosic material from the treatment vessel, it is known to provide a mechanically driven outlet bottom scraper that agitates the lignocellulosic material present in the vicinity of the outlet opening. As treatment vessels are further generally provided with inlets for treatment fluids, it is also known to increase the flow of fluid into the treatment vessel in the hope of resolving blockages.

The provision of an outlet bottom scraper is however not without disadvantages, as it increases the complexity and maintenance requirements of the treatment vessel. In the absence of an outlet bottom scraper, it however becomes very difficult to resolve situations where full or partial blockage of the outlet arises due to hanging or bridging of treated lignocellulosic material, i.e., where especially treated wood chips interact mechanically with each other to form blockages. Further, increasing the flow of fluid is ineffective in resolving blockages.

There is accordingly a need for a treatment vessel for treating lignocellulosic material and a corresponding method which are able to facilitate discharge and / or remove blockages without being complex or maintenance intensive.

SUMMARY

At least one of the abovementioned needs or at least one of the further needs which will become evident from the below description, are according to a first aspect of the present invention obtained by a treatment vessel for treating lignocellulosic material, the treatment vessel comprising: a main section having an interior volume for holding and treating lignocellulosic material, the main section having a first end and a second end, an outlet section having an interior volume in fluid communication with the interior volume of the main section, the outlet section tapering from a first end joined to the second end of the main section towards a second end of the outlet section, wherein an outlet opening for discharging lignocellulosic material from the treatment vessel is provided at the second end of the outlet section, at least one nozzle for injecting fluid into the treatment vessel, the nozzle being arranged on the inner circumference of the treatment vessel and being positioned within a perpendicular distance from a transition plane defined by the junction between the first end of the outlet section and the second end of the main section, wherein the distance is s of the diameter of the main section of the treatment vessel, a fluid conduit fluidly connected to the nozzle for providing the nozzle with a fluid, the fluid being a liquid, to be injected into the treatment vessel, wherein the fluid conduit is provided with a gas inlet for admitting a super-atmospheric gas having a super-atmospheric pressure into the fluid conduit in order for the gas to be mixed with the fluid.

The present invention is accordingly based on the recognition by the present inventors that the admittance of super-atmospheric gas into the fluid conduits bringing fluid into the treatment vessel, such fluid conduits and nozzles generally being used to inject various fluids for treating the lignocellulosic material, causes the formation of a fluid-gas-mixture that when injected in the treatment vessel is capable of resolving blockages of the lignocellulosic material, including blockages such as hanging or bridging of lignocellulosic material. Surprisingly, the effect of the fluid-gas- mixture is sufficient so that the conventional mechanically driven outlet bottom scraper can be dispensed with. Notably, the effect of the injected fluid-gas-mixture is not only obtained at the point of injection, additionally the gas bubbles of the fluid-gas-mixture rise through the treatment vessel to agitate and disperse lignocellulosic material throughout the treatment vessel. Further, as the gas bubbles rise though the treatment vessel, they expand due to the gradually decreasing hydrostatic pressure. The expansion of the gas bubbles increases their effective area thus rendering them capable of agitating increasingly larger areas of the treatment vessel. The effect of the admittance of super-atmospheric gas into the fluid conduit is further surprising, noting that it is generally undesired to admit gas such as air into treatment vessels as such gas or air may interfere with the treatment of the lignocellulosic material.

The treatment vessel is preferably selected from the group consisting of impregnation vessels for impregnating lignocellulosic material, digesters for cooking chip slurry to obtain pulp, and prehydrolysis vessels for treating agricultural residues at acid conditions. As the treatment vessel is generally placed vertically when used, the terms “first” and “second” used herein when relating to the treatment vessel or its constituent parts generally correspond to the terms “upper” and “lower”. The treatment vessel may be configured with a jacket for holding a heating or cooling medium in order to heat the treatment vessel. The treatment vessel is preferably made of metal such as steel.

Treating lignocellulosic material may comprise one or more of impregnating lignocellulosic material with an impregnation fluid in order to prepare the lignocellulosic material for later treatment, drying lignocellulosic material, heating lignocellulosic material, cooking lignocellulosic material, and/or hydrolyzing lignocellulosic material.

The term lignocellulosic material is used herein to mean materials containing lignin, cellulose, and hemicellulose. One example of such materials is wood, others include other agricultural or forestry wastes such as bagasse and wheat straw. The term lignocellulosic material further encompasses lignocellulosic material in slurry form, such as mixtures or slurries containing lignin, cellulose, and hemicellulose and fluid.

Typically, the lignocellulosic material comprises wood chips, such as a wood chip slurry.

When lignocellulosic material is treated in a treatment vessel by the injection of fluid, it will typically further comprise a quantity of the fluid when it is discharged.

The treatment vessel should preferably be suitable for treating the lignocellulosic material at a temperature of at least 70°C. Typically the lignocellulosic material is treated at a temperature of 70-165°C, such as 70-150°C, and the treatment vessel should preferably be suitable for treating the lignocellulosic material at these temperatures.

Additionally, or alternatively, the treatment vessel is preferably suitable for treating the lignocellulosic material with a fluid injected into the treatment vessel.

The main section is typically shaped as a cylinder. The main section may be defined as the section of the treatment vessel in which the circumference of the treatment vessel is constant along its center axis, i.e., as in a cylinder.

The main section has an interior volume for holding and treating the lignocellulosic material. The size of the interior volume depends on the dimensions of the main section. Typically, the treatment vessel, and thus the main section, may have a length (height) of 10 to 80 m, and a width (diameter) of 2- 17 m.

The first end of the main section may generally be considered an upper end of the main section. The first end would correspond to the circumference at the upper end of a cylinder. Typically, the treatment vessel comprises an inlet section joined to the first end of the main section and defining a first end of the treatment vessel. The inlet section may be dome shaped, cupola shaped, conical, or frustoconical. The inlet section may further comprise an inlet opening for admitting lignocellulosic material into the treatment vessel. The second end of the main section may generally be considered a lower end of the main section. The second end would correspond to the circumference at the lower end of a cylinder.

The outlet section may generally be dome shaped, cupola shaped, conical, or frustoconical. The outlet section may be considered to define a second end of the treatment vessel.

The outlet section may be formed integrally with the main section. Alternatively, the outlet section is manufactured separately from the main section and thereafter attached to the main section.

The interior volume of the outlet section is in fluid communication with the interior volume of the main section. Accordingly, the interior volume of the outlet section, the main section, and, if present, the inlet section, together define the interior volume of the treatment vessel The term tapering means that the circumference of the outlet section decreases from the first end towards the second end. In other words, the first end has the same circumference as the main section, whereas the second end has a smaller circumference.

The first end of the outlet section may generally be considered an upper end of the outlet section. The first end of the outlet section is joined to the second end of the main section, thereby forming a junction, joint, or border between the sections.

The second end of the outlet section may generally be considered a lower end of the outlet section.

The outlet opening is preferably an opening or aperture at the second end of the outlet section. Preferably, the outlet opening is centered at the second end of the outlet section. Thus, where the outlet section is dome shaped, cupola shaped, or frustoconical, the outlet opening is preferably provided at the vertex or apex or top of the dome, cupola of frustoconical outlet section. Where the outlet section is conical, then the outlet opening may additionally or alternatively be arranged in the wall or surface of the cone.

The outlet opening preferably comprises a circular aperture. A conduit for receiving the discharged lignocellulosic material may be connected to the outlet opening, or the lignocellulosic material may be allowed to fall from the outlet opening into a receiving vessel arranged below the outlet opening. The outlet opening is suitable for discharging lignocellulosic material from the treatment vessel by having a diameter and / or area suitable for allowing the lignocellulosic material to pass through the outlet opening.

The nozzle may in its simplest configuration comprise or consist of an opening in the wall of the treatment vessel. Typically, the nozzle comprises a body provided with a fluid channel extending from a first end of the body to a second end of the body, whereby the body is arranged in an opening in the wall of the treatment vessel for allowing fluid to pass through the fluid channel from outside the treatment vessel into the treatment vessel. The nozzle is arranged on the inner circumference of the treatment vessel. This corresponds to the nozzle being arranged on the inner surface of the treatment vessel. The nozzle may be arranged to protrude into the treatment vessel from the inner circumference or surface of the treatment vessel. Alternatively, and preferably, the nozzle is arranged and configured so that it is flush (i.e., does not protrude into the treatment vessel) with the inner circumference or surface of the treatment vessel. The nozzle is preferably configured, e.g. by being oriented or constructed, to inject fluid into lignocellulosic material in the treatment vessel. In other words the nozzle is preferably not configured to inject fluid along an inner wall of the treatment vessel.

The nozzle is positioned within a perpendicular distance from a transition plane defined by the junction between the first end of the outlet section and the second end of the main section.

The transition plane may be alternatively but equivalently defined as the plane formed by the circumference of the treatment vessel at the position where the circumference of the treatment vessel, which generally is constant along the main section, starts to decrease as the main section ends and the tapering outlet section begins.

The perpendicular distance is the shortest distance between the nozzle and a point in the transition plane. As the treatment vessel is generally placed vertically when used, the perpendicular distance thus corresponds to the vertical distance between the nozzle and the transition plane. Generally, the nozzle is accordingly positioned a distance above or below the transition plane.

The distance is Ms of the diameter of the main section of the treatment vessel. This corresponds to the nozzle being positioned from Ms of the diameter below the transition plane to Ms of the diameter above the transition plane.

The fluid conduit may comprise a rigid or non-rigid pipe or tube. Typically, the fluid conduit comprises a rigid pipe. Typically, at least a part of the length of the pipe is attached or otherwise supported adjacent the outer surface of the treatment vessel.

The fluid conduit is suitable for providing the nozzle with a fluid to be injected into the treatment vessel. The fluid is a liquid. The fluid may for example comprise an impregnation fluid, a cooking fluid, a base, an acid, or a combination of such fluids. The fluid is injected into the treatment vessel by the nozzle.

The fluid conduit is provided with a gas inlet. The gas inlet may comprise an opening in the wall of the fluid conduit. The gas inlet may alternatively comprise a pipe inserted into the fluid conduit through an opening in the wall of the fluid conduit. The gas inlet may alternatively comprise a junction or branching, or any other type of connection, allowing the gas to come into contact with the fluid. The super-atmospheric gas has a super- atmospheric pressure. The super-atmospheric pressure is a pressure above 1 atm absolute.

In all aspects of the present invention, the pressure of the super- atmospheric gas is preferably at least 1 bar, such as 1-3 bar, above the pressure at the nozzle to which the at least one fluid conduit is fluidly connected. The pressure at the nozzle is dependent on the hydrostatic pressure due to the height or level of lignocellulosic material above the nozzle, as well as any overpressure, e.g., due to injecting steam or other liquids or gases into the treatment vessel, and/or due to heating or cooking of the liquid and / or lignocellulosic material within the treatment vessel.

The pressure of the super-atmospheric gas is typically not above 15 bar absolute. When the treatment vessel comprises a plurality of nozzles, then the pressure of the super-atmospheric gas should preferably be at least 1 bar, such as 1-3 bar, above the pressure at the nozzle being subjected to the highest pressure, which nozzle is typically the nozzle placed at the lowest position in the treatment vessel.

The super-atmospheric gas may for example be selected from the group consisting of be air, nitrogen, and carbon dioxide. The super-atmospheric gas is preferably selected so that it does not condensate when contacted with the liquid.

When the gas is admitted into the fluid conduit it mixes with the fluid.

The mixing of gas and fluid results in a fluid-gas-mixture or a two-phase stream of fluid with gas bubbles in the fluid. The super-atmospheric gas adds kinetic energy, pressure, and turbulence to the fluid. The resulting fluid-gas-mixture or two-phase stream of fluid with gas bubbles in the fluid thus has a higher kinetic energy, pressure and turbulence compared to the fluid flow injected when no super-atmospheric gas is admitted into the fluid conduit.

When it is stated herein that a first component is fluidly connected to a second component, this is to be interpreted as the component being connected in such a way that a space is formed inside the first component and extends up to and at least partly inside the second component.

The gas inlet is preferably positioned at a position sufficiently upstream from the nozzle such that the gas is mixed with the fluid before the fluid- gas-mixture is injected from the nozzle into the treatment vessel. The gas may be considered mixed with the fluid as soon as the gas has formed bubbles in the fluid.

This is advantageous in that the fluid-gas-mixture has been shown to be more efficient in breaking up blockages and facilitating discharge than either of fluid or gas used separately. The fluid-gas-mixture corresponds to a two-phase stream of fluid with gas bubbles in the fluid.

The gas is mixed with the fluid before the fluid-gas-mixture is injected from the nozzle into the treatment vessel. In other words, the gas is mixed with the fluid while still within the at least one fluid conduit and before the gas and fluid reaches the nozzle.

The terms upstream and downstream as used herein refer to how fluid passes through the fluid conduit and the nozzle into the treatment vessel Thus, a downstream direction will be a direction from the fluid conduit via the nozzle into the treatment vessel.

The position sufficiently upstream corresponds to a position where admitted gas has sufficient time to mix with the fluid to produce a two- phase stream of fluid with gas bubbles in the fluid before the fluid-gas- mixture reaches the nozzle.

The gas inlet is preferably positioned at least 1/ 16 of the diameter of the main section upstream of the nozzle.

Practical examples have shown that this position of the gas inlet is generally sufficiently upstream of the nozzle for ensuring that the mixing of gas and fluid results in a fluid-gas-mixture or a two-phase stream of fluid with gas bubbles in the fluid before reaching the nozzle and being injected into the treatment vessel. As an example, the gas inlet should be positioned in the fluid conduit at a position at least 0.5 m upstream of the nozzle for an 8 m diameter treatment vessel.

The gas inlet is preferably positioned at the most 2 times the diameter of the main section upstream of the nozzle.

Practical examples have shown that this position of the gas inlet is generally sufficiently close to the nozzle so that the gas introduced into the at least one fluid conduit is capable of forming a fluid-gas-mixture or two- phase stream of fluid with gas bubbles in the fluid having sufficient impact and turbulence when injected for efficiently facilitating discharge of the lignocellulosic material and / or resolve or removing partial or full blockages of the lignocellulosic material. For a treatment vessel having a main section with 8 m diameter, the gas inlet should be positioned in the fluid conduit at a position at the most 16 m upstream of the nozzle.

The nozzle is preferably arranged on the inner circumference of the outlet section. This corresponds to the nozzle being arranged between the outlet opening and the transition plane. In other words, the nozzle is positioned below the transition plane when the treatment vessel is arranged vertically with the main section above the outlet section. Accordingly, in this configuration, the axial distance along the center axis of the treatment vessel between the nozzle and the outlet opening is less than the corresponding distance between the transition plane and the outlet opening.

Practical examples have shown that it is generally advantageous to arrange the nozzle below the transition plane as the narrowing cross- sectional area of the treatment vessel in this area, due to the tapering of the outlet section, makes blockages of lignocellulosic material more likely to occur here.

The nozzle is alternatively arranged on the inner circumference of the main section. This corresponds to the transition plane being arranged between the nozzle and the outlet opening. In other words, the nozzle is positioned above the transition plane when the treatment vessel is arranged vertically with the main section above the outlet section. Accordingly, in this configuration, the axial distance along the center axis of the treatment vessel between the nozzle and the outlet opening is greater than the corresponding distance between the transition plane and the outlet opening.

Practical examples have shown that it is may also be advantageous to arrange the nozzle above the transition plane as so as to break up blockages and bridging of lignocellulosic material also in the main section of the treatment vessel. The nozzle is preferably configured to inject the fluid in a direction forming a positive angle with the transition plane.

This allows the fluid-gas-mixture to efficiently agitate the lignocellulosic material within the treatment tank. This is readily achieved by using a nozzle configured to inject fluid perpendicularly to the surface in which it is arranged, and by arranging such a nozzle on the inner circumference of the tapering outlet section. Alternatively, or additionally, the nozzle may be further configured to inject the fluid in a different direction, provided that the orientation of the nozzle when arranged on the inner circumference of the treatment vessel, together with the direction of injection of fluid form the nozzle, achieve injection of the fluid in a direction forming a positive angle with the transition plane.

When the treatment vessel is arranged vertically with the main section above the outlet section, then the vector corresponding to the direction of the injected fluid has one component directed vertically upwards away from the second end of the outlet section, and the other component being directed horizontally into the treatment vessel.

Configuring the nozzle to inject the fluid in a direction forming a positive angle with the transition plane is especially advantageous when the nozzle is arranged on the inner circumference of the outlet section because this provides an effective agitation of lignocellulosic material in the outlet section where blockages are more likely to occur. The positive angle may for example be from 5 to 75°, preferably from 10 to 60°, more preferably from 15 to 50°, such as from 30 to 45°.

The nozzle is alternatively configured to inject the fluid in a direction forming a negative angle with the transition plane.

This allows the fluid-gas-mixture to impact on lignocellulosic material within the treatment tank and push or force the lignocellulosic material towards the outlet opening.

This can be achieved by using a nozzle configured to inject fluid at a direction deviating from the normal to the mounting plane of the nozzle. Such a nozzle, when arranged on the inner circumference of the main section, could be oriented to inject the fluid in a direction forming a negative angle with the transition plane.

Practical examples have shown that it may be advantageous to configure the at least one nozzle so as to inject the fluid in a direction forming a negative angle with the transition plane.

When the treatment vessel is arranged vertically with the main section above the outlet section, then the vector corresponding to the direction of the injected fluid has one component directed vertically downwards, towards the second end of the outlet section, and the other component being directed horizontally into the treatment vessel.

Configuring the nozzle to inject the fluid in a direction forming a negative angle with the transition plane is especially advantageous when the nozzle is arranged on the inner circumference of the main section because this may facilitate discharge by pushing lignocellulosic material past the transition plane into the outlet section. The negative angle may for example be from -5 to -75°, preferably from -10 to -60°, more preferably from -15 to -50°, such as from -30 to -45°.

The treatment vessel preferably comprises: a plurality of nozzles as described above and, a plurality of fluid conduits as described above.

This is advantageous because using a plurality of nozzles and a plurality of fluid conduits with gas inlets allows for greater agitation of the lignocellulosic material to thereby better facilitate discharge and resolve blockages.

Preferably the plurality of nozzles are arranged along the inner circumference of the treatment vessel with similar or identical distances between adjacent nozzles.

The individual nozzles of the plurality of nozzles may be configured to inject the fluid in the same direction and angles relative to the transition plane, or with individually different directions and angles.

Preferably each nozzle of the plurality of nozzles is fluidly connected to a corresponding fluid conduit of the plurality of fluid conduits. This allows the selective admittance of super-atmospheric gas into one or more of the fluid conduits, thereby causing the selective injection of the fluid-gas- mixture into the treatment vessel from one or more of the nozzles. It is for example contemplated that the order, timing, and gas pressure of admitting the super-atmospheric gas into the gas inlets of the fluid conduits corresponding to the nozzles may be selected so as to produce various patterns in the injection of the fluid-gas-mixture so as to vary the agitation of the lignocellulosic material effected by the fluid-gas-mixture. Thus, in addition to selectively admit super-atmospheric gas into all of the gas inlets for a specific time period, the admittance of gas may selectively for example be a) pulsed, b) be effected into one gas inlet at a time resulting in a sequential injection of the fluid-gas-mixture from each nozzle, c) be effected at random resulting in a random injection of the gas- fluid-mixture from the nozzles, d) be effected sequentially in subsets resulting in injection of the gas-fluid-mixture from different subsets of the plurality of nozzles, and / or e) vary in pressure during or between sequential admittances of the super-atmospheric gas into the gas inlets. Alternatively, two or more nozzles may be fluidly connected to the same fluid conduit in which the number of fluid conduits in the treatment vessel is less than the number of nozzles in the treatment vessel. A fluid conduit may for example comprise a branching point downstream of the gas inlet whereby defining a manifold whereby a number of nozzles are fluidly connected to the branches of the manifold. Further alternatively, a fluid conduit may comprise a plenum to which a number of nozzles are fluidly connected, whereby the gas inlet is positioned in the plenum or upstream of the plenum.

Also, in this configuration can the order, timing, and gas pressure of admitting the super-atmospheric gas into the gas inlets of the fluid conduits connected to the nozzles be selected as described above, however, taking into account that two or more nozzles may be fluidly connected to the same fluid conduit.

Preferably, the plurality of nozzles comprises: a first plurality of nozzles arranged on the inner circumference of the outlet section and being configured to inject the fluid in a direction forming a positive angle with the transition plane, and a second plurality of nozzles arranged on the inner circumference of the main section and being configured to inject the fluid in a direction forming a negative angle with the transition plane.

This is advantageous in that combines the advantages of arranging nozzles below the transition plane with the advantage of arranging nozzles above the transition plane. Further, the directions of injection of the nozzles combine to facilitate discharge and to resolve blockages of lignocellulosic material.

Further pluralities of nozzles may be arranged above, below, or between, the first and second plurality of nozzles.

At least one of the abovementioned needs or at least one of the further needs which will become evident from the below description, are according to a second aspect of the present invention obtained by a system for treating lignocellulosic material, the system comprising:

- a treatment vessel according to the first aspect of the present invention,

- a fluid container connected to at least one of the fluid conduits, and

- a source of super-atmospheric gas having a super-atmospheric pressure fluidly connected to the gas inlet of at least one fluid conduit, the source being configured to selectively allow super-atmospheric gas to enter the at least one fluid conduit.

This is advantageous as such a system is capable of treating lignocellulosic material and facilitating discharge and / or resolving blockages thereof without requiring a mechanically driven outlet bottom scraper.

The system is preferably a system for treating lignocellulosic material as described initially, and further preferably for treating lignocellulosic material at a temperature of at least 70°C as described also initially. The fluid container preferably comprises a fluid tank or other container holding fluid. The fluid container or the system may further comprise a pump for pumping fluid to the nozzle or nozzles, and / or a valve for controlling flow of fluid to the nozzle or nozzles.

The source of super-atmospheric gas may for example comprise a pressure vessel and/or a compressor. The source may be configured to selectively allow super-atmospheric gas to enter the at least one fluid conduit by being connected to the gas inlet, via for example, a pipe or tube.

The source of super-atmospheric gas preferably comprises:

- a pressure vessel for holding the super-atmospheric gas, and

- a valve fluidly interconnected between the pressure vessel and the gas inlet, the valve being configured to selectively allow super-atmospheric gas to pass from the pressure vessel into the at least one fluid conduit. This is advantageous in that a pressure vessel is a readily available source of super-atmospheric gas. The valve may be any type of valve for controlling flow of super-atmospheric gas. The valve may be configured to selectively allow super-atmospheric gas to pass from the pressure vessel into the at least one fluid conduit by having two positions, i.e., one open position establishing a fluid connection through the valve to allow super- atmospheric gas flow through the valve, and one closed position in which the fluid connection is broken to prevent super-atmospheric gas from flowing through the valve.

The pressure vessel should be capable of holding the super-atmospheric gas at a pressure at least 1 bar, such as 1-3 bar, above the pressure at the nozzle fluidly connected to the fluid conduit the super-atmospheric gas is admitted into.

The system may further comprise:

- a detector configured to detect at least a partial blockage of lignocellulosic material within the treatment vessel, - an actuator operationally interconnected with the source of super- atmospheric gas for causing the super-atmospheric gas to selectively enter the at least one fluid conduit when the actuator is activated, and

- a control unit operationally interconnected between the detector and the actuator and configured to activate the actuator when the detector detects at least a partial blockage.

This is advantageous in that it allows blockages, including partial blockages to be automatically resolved.

The detector may comprise any detector capable of detecting at least a partial blockage of lignocellulosic material. Preferably the detector is capable of selectively detecting a partial blockage as well as a full blockage. The detector may be configured to detect the blockage by being positioned outside or inside the treatment vessel, or by being positioned at or in the outlet opening. When the detector is positioned outside the treatment vessel it may detect a blockage using indirect methods such as radar and ultrasound. When the detector is positioned inside the treatment vessel it may detect a blockage by mechanically, electrically, or optically measuring flow of lignocellulosic material within the treatment vessel. the actuator may comprise any type of actuator such as an electric, pneumatic, hydraulic, or magnetic actuator. The actuator is operationally interconnected with the source of super-atmospheric gas so that the actuator is capable of operating the source to selectively cause the upper atmospheric gas to enter the fluid conduit. The actuator may have an activated mode and a deactivated mode.

The control unit may comprise any control circuit or computer capable of being configured to activate the actuator when the detector detects at least a partial blockage. The control unit may further be configured to activate the actuator for different durations, order, timing, and gas pressures. Where the treatment vessel comprises a plurality of nozzles and fluid conduits, then the system may comprise plurality of actuators for selectively admit super-atmospheric gas into the plurality of fluid conduits. Further, where the system comprises a plurality of treatment vessels, the system may comprise a detector and one or more actuators for each treatment vessel. Alternatively, each treatment vessel may be provided with its own control unit, detector, and one or more actuators.

The control unit may comprise a computer program product comprising instruction which, when executed by the control unit, performs the steps of the method according to the fourth aspect of the present invention described further below.

The detector is preferably configured to detect the flow and / or composition of lignocellulosic material being discharged from the treatment vessel through the outlet opening.

This is advantageous in that the lignocellulosic material being discharged from the treatment vessel is easy to obtain access to. The detector may for example be configured to detect the flow of lignocellulosic material. In these cases, the detector may for example comprise a flow measuring device contacting the lignocellulosic material, i.e., using an impeller, propeller, strain gauge, pressure meter, electromagnetic flowmeter, thermal flowmeter or other mechanical or electrical interface to physically measure the flow of lignocellulosic material. Alternatively, the detector may comprise a device measuring the flow of lignocellulosic in without contacting the same, such as material, for example using a doppler radar or ultrasonic doppler flow meter.

A decreased flow would then indicate a partial blockage, whereas a stopped flow would indicate a blockage.

The detector may additionally or alternatively be configured to detect the composition of lignocellulosic material. The detector may thus be configured to measure one or more of the dry matter content, viscosity, density, conductivity of the lignocellulosic material. Generally, a partial of full blockage of lignocellulosic material in the treatment vessel results in less lignocellulosic material and more fluid being discharged. Accordingly, the dry matter content and viscosity would be expected to decrease thereby indicating a partial or full blockage. Depending on the properties of the lignocellulosic material being treated, the density and conductivity of the discharged lignocellulosic material would also change, and thereby provide a further indicator of partial or full blockage of lignocellulosic material in the treatment vessel.

At least one of the abovementioned needs or at least one of the further needs which will become evident from the below description, are according to a third aspect of the present invention obtained the use of one or more treatment vessels according to the first aspect of the present invention or the system according to the second aspect of the present invention for treating lignocellulosic material.

By using one or more treatment vessels or the system, the treating of the lignocellulosic material can be made more efficient and reliable since the discharge can be facilitated and blockages resolved without needing to use a mechanically driven outlet bottom scraper. The lignocellulosic material is preferably treated as described initially, and further preferably treated at a temperature of at least 70°C as described also initially.

At least one of the abovementioned needs or at least one of the further needs which will become evident from the below description, are according to a fourth aspect of the present invention obtained by a method of facilitating discharge and / or removing blockage of lignocellulosic material treated in a treatment vessel according to the first aspect of the present invention or in the system according to the second aspect of the present invention, the method comprising the step of: i) admitting super-atmospheric gas having a super-atmospheric pressure into at least one fluid conduit through the gas inlet.

This method is advantageous in that it allows discharge to be facilitated and / or blockages to be resolved or removed without requiring a mechanically driven outlet bottom scraper.

The method may be performed using the system according to the second aspect of the present invention. The method preferably further comprises the step of: ii) determining a need to facilitate discharge and / or remove blockage of lignocellulosic material, and performing step (i) upon determining a need to facilitate discharge and / or remove blockage of lignocellulosic material in step (ii).

This is advantageous in that it allows blockages to be automatically resolved. The need to facilitate discharge and/or remove blockage of lignocellulosic material may preferably be determined using the detector of the system according to the second aspect of the present invention.

The need to need to facilitate discharge and / or remove blockage of lignocellulosic material may be determined continuously, or at interval.

Step (ii) in the method preferably comprises monitoring the flow and / or composition of treated lignocellulosic material discharged through the outlet opening.

This is advantageous in that the lignocellulosic material being discharged from the treatment vessel is easy to obtain access to. The flow and/or composition may be monitored as described above for the detector of the system according to the second aspect of the present invention.

The monitoring may be performed continuously, or at intervals.

The pressure of the super-atmospheric gas admitted in step (i) is preferably at least 1 bar, such as 1-3 bar, above the pressure at the nozzle to which the at least one fluid conduit is fluidly connected.

The higher the pressure of the super-atmospheric gas, the larger its impact on the fluid in the fluid conduit, and the greatest its agitating effect on the lignocellulosic material in the treatment vessel.

The pressure at the nozzle is dependent on the hydrostatic pressure due to the height or level of lignocellulosic material above the nozzle, as well as any overpressure in the treatment vessel, e.g., due to injecting steam or other liquids or gases into the treatment vessel, and/or due to heating or cooking of the liquid and / or lignocellulosic material within the treatment vessel. A further aspect of the present invention concerns a computer program product comprising instruction which, when executed by a computer of by the control unit and the system according to the second aspect of the present invention, performs the steps of the method according to the fourth aspect of the present invention.

Yet a further aspect of the present invention concerns the use of super- atmospheric gas, admitted into a fluid conduit fluidly connected to a nozzle for injecting fluid into a treatment vessel for treating lignocellulosic material, for facilitating discharge and / or resolve blockages of the lignocellulosic material.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the abovementioned and other features and advantages of the present invention will be apparent from the following detailed description of preferred embodiments in conjunction with the appended drawings, wherein:

Fig. 1 shows an embodiment of a treatment vessel and a system according to the first and second aspects of the present invention.

All the figures are schematic, not necessarily to scale, and generally only show parts which are necessary in order to elucidate the respective embodiments, whereas other parts may be omitted or merely suggested. Any reference number appearing in multiple drawings refers to the same object or feature throughout the drawings, unless otherwise indicated. Letter suffixes of reference numbers indicate single individual objects or features among the objects and features having the same number.

DETAILED DESCRIPTION Fig. 1 shows an embodiment of a treatment vessel 10 and a system 100 according to the first and second aspects of the present invention. The treatment vessel comprises a main section 20 having an interior volume 22 for holding and treating lignocellulosic material 2, the main section having a first (upper) end 24 and a second (lower) end 26. As shown here, the main section 20 is preferably circular cylindrical having a center axis A. A dome-shaped inlet section 30 is provided at the first end 24 to close the upper end of the treatment vessel 10 and comprises an inlet opening 32 for allowing lignocellulosic material 2 to enter the treatment vessel 10. An outlet section 40 having an interior volume 42 in fluid communication with the interior volume 22 of the main section is provided below the main section 20. The outlet section 40 is here shown to have a frustoconical form and tapers from a first (upper) end 44, which is joined to the second end 26 of the main section 20, towards a second (lower) end 46 of the outlet section 40. An outlet opening 48 for discharging 8 treated lignocellulosic material from the treatment vessel 10 is provided at the second end 46 of the outlet section 40. In use, lignocellulosic material, such as wood chips, enters the treatment vessel 10 through the inlet opening 32 to be held and treated within the treatment vessel 10. Such treatment generally involves the addition of fluid to the lignocellulosic material. This fluid may for example be an impregnation fluid for preparing the lignocellulosic material for later process steps. A first plurality of nozzles, one being designated the reference number 60a, for injecting fluid 4 into the treatment vessel 10 are arranged on the inner circumference of the treatment vessel 10, specifically on the inner circumference of the outlet section 40. Whereas the treatment vessel 10 may comprise a single nozzle 60a, it is preferred that the treatment vessel comprises a (first) plurality as shown in the figure. It is further preferred that the treatment vessel 10 also comprises a second plurality of nozzles, one being designated the reference number 60b, being arranged on the inner circumference of the treatment vessel 10, specifically on the inner circumference of the main section 20. Each nozzle 60a, 60b is positioned within a perpendicular distance d 1 , d2 from a transition plane T defined by the junction between the first end 44 of the outlet section 40 and the second end 26 of the main section 20. This is because the risk for blockages of lignocellulosic material is higher in the vicinity of the transition plane where the treatment vessel 10 starts to decrease in circumference and cross-sectional area as it extends to the second end 46 of the outlet section 40 and to the outlet opening 48. The distance dl, d2 is s of the diameter D of the main section 20. Accordingly, the nozzles 60a, 60b can be positioned up to s of the diameter D below to s of the diameter D above the transition plane. The nozzles are provided with fluid 4 for injection into the treatment vessel 10 by a plurality of fluid conduits 70a, 70b fluidly connected to the nozzles 60a, 60b.

Where conventionally a mechanically driven bottom outlet scraper would be positioned within the outlet section 40 adjacent the outlet opening 48, the fluid conduits 70a, 70b are instead provided with gas inlets 80a, 80b for admitting a super-atmospheric gas 6 into the fluid conduit 70a, 70b in order for the gas to be mixed with the fluid.

Accordingly, if discharge of the lignocellulosic material needs to be facilitated and / or if a partial or full blockage of lignocellulosic material occurs within the treatment vessel 10, then super-atmospheric gas can be admitted into the fluid conduits 70a, 70b. Once admitted, the super- atmospheric gas mixes with the fluid to form a fluid-gas-mixture corresponding to a two two-phase stream of fluid with gas bubbles in the fluid. The addition of the gas to the fluid imparts further energy and turbulence to the fluid flow, and the injection of the fluid-gas-mixture into the treatment vessel is capable of agitating and resolving blockages. This effect is obtained both in the vicinity of the nozzles 60a, 60b, but also higher up in the main section 20 as the gas bubbles expand as they rise through the treatment vessel to thereby further agitate the lignocellulosic material.

Preferably, and as shown in the figure, the nozzles 60a arranged on the inner circumference of the outlet section 40 are configured to inject the fluid in a direction forming a positive angle a with the transition plane T. Conversely, the nozzles 60b arranged on the inner circumference of the main section 20 are preferably configured to inject the fluid in a direction forming a negative angle b with the transition plane T.

The system 100 comprises the treatment vessel 10, a fluid container 110 containing fluid 4 and being connected to the fluid conduits 70a and 70b, as well as a source, here represented by pressure vessel 120 of super- atmospheric gas 6. The source 120 is fluidly connected to the gas inlets 80a, 80b of the fluid conduit 70a, 70b and is configured, here by being provided with valves 130a, 130b fluidly interconnected between the pressure vessel 120 and the gas inlets 80a, 80b, to selectively allow super- atmospheric gas 6 to enter the fluid conduits 70a, 70b. The fluid container 110 or the fluid conduits 70, 70b may further comprise a valve 112 for regulating the flow of fluid. The pressure vessel 120 may comprise or be connected to a gas pipe 122 for delivering the super-atmospheric gas 6 to the valves 130a, 130b.

The system 100 so implemented can be used to manually, when a need for facilitating discharge and / or resolving blockages occur, admit the super- atmospheric gas 6 into the fluid conduits 70a, 70b to cause a fluid-gas- mixture to be injected into the treatment vessel 10 to resolve the blockage and/or facilitate discharge 8 of the lignocellulosic material.

For automatic use, the system 100 further comprises a detector 140 configured to detect at least a partial blockage of lignocellulosic material within the treatment vessel 10. The detector 140 is here shown positioned at the outlet opening 48 to detect the flow and/or composition of lignocellulosic material being discharged from the treatment vessel 10.

The system further comprises actuators 150a and 150b operationally interconnected with valves 130a and 130b for causing the super- atmospheric gas to selectively enter fluid conduits 70a, 70b when the actuators 150a, 150b are activated.

Finally, the system further comprises a control unit 160 operationally interconnected between the detector 140 and the actuators 150a, 150b and configured to activate the actuators 150a, 150b when the detector 140 detects a blockage.

The control unit 160 can additionally be configured to activate the actuators 130a, 130b in different order, with different timing, and/or with different gas pressures to obtain various patterns of injection of the fluid- gas-mixture.

FEASABLE MODIFICATIONS

The invention is not limited only to the embodiments described above and shown in the drawings, which primarily have an illustrative and exemplifying purpose. This patent application is intended to cover all adjustments and variants of the preferred embodiments described herein, thus the present invention is defined by the wording of the appended claims. Thus, the equipment may be modified in all kinds of ways within the scope of the appended claims.

It shall also be pointed out that all information about/ concerning terms such as above, under, upper, lower, etc., shall be interpreted/ read having the equipment oriented according to the figures, having the drawings oriented such that the references can be properly read. Thus, such terms only indicate mutual relations in the shown embodiments, which relations may be changed if the inventive equipment is provided with another structure / design.

It shall also be pointed out that even thus it is not explicitly stated that features from a specific embodiment may be combined with features from another embodiment, the combination shall be considered obvious, if the combination is possible.

Throughout this specification and the claims which follows, unless the context requires otherwise, the word “comprise”, and variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated integer or steps or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

Claims

1. A treatment vessel (10) for treating lignocellulosic material (2), the treatment vessel comprising: a main section (20) having an interior volume (22) for holding and treating lignocellulosic material, the main section having a first end (24) and a second end (26), an outlet section (40) having an interior volume (42) in fluid communication with the interior volume (22) of the main section, the outlet section (40) tapering from a first end (44) joined to the second end (26) of the main section (20) towards a second end (46) of the outlet section (40), wherein an outlet opening (48) for discharging lignocellulosic material from the treatment vessel (10) is provided at the second end (46) of the outlet section (40), at least one nozzle (60a) for injecting fluid (4), the fluid being a liquid, into the treatment vessel (10), the nozzle (60a) being arranged on the inner circumference of the treatment vessel (10) and being positioned within a perpendicular distance (dl, d2) from a transition plane (T) defined by the junction between the first end (44) of the outlet section (40) and the second end (26) of the main section (20), wherein the distance (dl, d2) is s of the diameter (D) of the main section (20) of the treatment vessel (10), a fluid conduit (70a) fluidly connected to the nozzle (60a) for providing the nozzle (60a) with a fluid to be injected into the treatment vessel (10), wherein the fluid conduit (70a) is provided with a gas inlet (80a) for admitting a super-atmospheric gas (6) having a super-atmospheric pressure into the fluid conduit (70a) in order for the gas to be mixed with the fluid.

2. The treatment vessel (10) according to claim 1, wherein the gas inlet (80a) is positioned at a position sufficiently upstream from the nozzle (60a) such that the gas (6) is mixed with the fluid before the fluid-gas-mixture is injected from the nozzle (60a) into the treatment vessel (10).

3. The treatment vessel (10) according to any preceding claim, wherein the gas inlet (80a) is positioned at least 1/ 16 of the diameter (D) of the main section (20) upstream of the nozzle (60a).

4. The treatment vessel (10) according to any preceding claim, wherein the gas inlet (80a) is positioned at the most 2 times the diameter (D) of the main section (20) upstream of the nozzle (60a).

5. The treatment vessel (10) according to any preceding claim, wherein the nozzle (60a) is arranged on the inner circumference of the outlet section (40).

6. The treatment vessel (10) according to any of the claims 1-4, wherein the nozzle (60b) is arranged on the inner circumference of the main section (20).

7. The treatment vessel (10) according to any of the preceding claims, wherein the nozzle (60a) is configured to inject the fluid (4) in a direction forming a positive angle (a) with the transition plane (T) .

8. The treatment vessel (10) according to any of the claims 1-6, wherein the nozzle (60b) is configured to inject the fluid (4) in a direction forming a negative angle (b) with the transition plane (T).

9. The treatment vessel (10) according to any preceding claim, comprising: a plurality of nozzles (60a) according to any of the preceding claims and, a plurality of fluid conduits (70a) according to any of the preceding claims.

10. The treatment vessel (10) according to claim 9, wherein the plurality of nozzles (60a) comprises: a first plurality of nozzles (60a) arranged on the inner circumference of the outlet section (40) and being configured to inject the fluid (4) in a direction forming a positive angle (a) with the transition plane (T), and a second plurality of nozzles (60b) arranged on the inner circumference of the main section (20) and being configured to inject the fluid (4) in a direction forming a negative angle (b) with the transition plane (T).

11. A system (100) for treating lignocellulosic material, the system comprising:

- a treatment vessel (10) according to any of the claims 1-10,

- a fluid container (110) connected to at least one of the fluid conduits (70a), and

- a source (120) of super-atmospheric gas (6) having a super- atmospheric pressure fluidly connected to the gas inlet (80a) of at least one fluid conduit (70a), the source being configured to selectively allow super-atmospheric gas to enter the at least one fluid conduit (70a).

12. The system according to claim 11, wherein the source (120) of super- atmospheric gas (6) comprises:

- a pressure vessel (120) for holding the super-atmospheric gas (6), and

- a valve (130) fluidly interconnected between the pressure vessel (120) and the gas inlet (80a), the valve being configured to selectively allow super-atmospheric gas to pass from the pressure vessel (120) into the at least one fluid conduit (70a).

13. The system (100) according to any of the claims 11-12, further comprising:

- a detector (140) configured to detect at least a partial blockage of lignocellulosic material within the treatment vessel (10),

- an actuator (150a) operationally interconnected with the source of super-atmospheric gas (120) for causing the super-atmospheric gas to selectively enter the at least one fluid conduit (70a) when the actuator (150a) is activated, and

- a control unit (160) operationally interconnected between the detector (140) and the actuator (150a) and configured to activate the actuator (150a) when the detector (140) detects a blockage.

14. The system (100) according to claim 13, wherein the detector (140) is configured to detect the flow and / or composition of lignocellulosic material being discharged (8) from the treatment vessel (10) through the outlet opening (48).

15. Use of one or more treatment vessels (10) according to any of the claims 1-10 or the system (100) according to any of the claims 11-14 for treating lignocellulosic material.

16. A method of facilitating discharge and/or removing blockage of lignocellulosic material treated in a treatment vessel (10) according to any of the claims 1-10 or in the system (100) according to any of the claims 11-14, the method comprising the step of: i) admitting super-atmospheric gas (6) having a super-atmospheric pressure into at least one fluid conduit (70a) through the gas inlet (80a).

17. The method according to claim 16, further comprising the step of: ii) determining a need to facilitate discharge and / or remove blockage of lignocellulosic material, and performing step (i) upon determining a need to facilitate discharge and / or remove blockage of lignocellulosic material in step (ii).

18. The method according to claim 17, wherein step (ii) comprises monitoring the flow and / or composition of treated lignocellulosic material discharged through the outlet opening (48).

19. The method according to any of claims 16-18, wherein the pressure of the super-atmospheric gas is at least 1 bar, such as 1-3 bar, above the pressure at the nozzle (60a) to which the at least one fluid conduit (70a) is fluidly connected.