AN ARRANGEMENT FOR INSTALLATION OF MONITORING SENSORS OF A TREATMENT VESSEL FOR LIGNOCELLULOSIC MATERIAL

Abstract

An arrangement for installations of monitoring sensors of a vessel for treatment of lignocellulosic material, which vessel (1) has a central pipe (2) including at least one concentric pipe (3), mounted coaxially within the vessel (1). At least one sensor channel (4) is arranged along the outermost wall of the concentric pipe (3) of the central pipe (2) and that the at least one sensor channel (4) is connected to a cable conduit (5), which cable conduit (5) connects the exterior of the vessel (1) to the at least one sensor channel (4)) and the sensor channel (4) is several meters long and has plurality of holders (13) for sensors (11) and/or is configured to contain plurality of thermal sensors (11) with their cables (8).

Claims

1. An arrangement for installations of monitoring sensors of a vessel configured to treat lignocellulosic material, wherein the vessel includes a central pipe comprising at least one concentric pipe mounted coaxially within the vessel, the arrangement comprising: at least one sensor channel arranged along an outermost wall of the at least one concentric pipe of the central pipe, and a cable conduit connected to the at least one sensor channel and connected to an exterior of the vessel, wherein the at least one sensor channel is at least one meter long and includes at least one of: (i) a plurality of sensor holders configured to hold sensors is and (ii) a plurality of thermal sensors with cables for the thermal sensors.

2. The arrangement of claim 1, wherein an interior of an outer wall of the at least one sensor channel is longitudinally divided into at least two sensor channels, and the outer wall is a concentric pipe attached to an outer wall of the central pipe.

3. The arrangement of claim 1, wherein an outer wall of the at least one sensor channel is welded along opposite sides of the outer wall to the central pipe.

4. The arrangement of claim 1, wherein the at least one sensor channel includes at least one subchannel.

5. The arrangement of claim 4, wherein the at least one subchannel is entirely supported by the outer wall of the at least one sensor channel.

6. The arrangement of claim 1, wherein the at least one sensor channel includes a sealed channel connected to a source of pressurized fluid.

7. The arrangement of claim 6, wherein the source of the pressurized fluid is connected to a controller configured to determine a leak in the sealed channel.

8. The arrangement of claim 1, wherein the at least one sensor channel is at least one of: (i) extends vertically beyond the concentric pipes of the central pipe, and (ii) extends proximate an outlet of an outermost concentric pipe of the at least one concentric pipe.

9. The arrangement of claim 1, wherein the cable conduit connects to at least one of a top end and a lower end of the at least one sensor channel.

10. The arrangement of claim 1, wherein the cable conduit includes at least one of: (i) a cable tube extending through the cable conduit and into the at least one sensor channel, and (ii) an evacuation tube extending through the cable conduit and to a bottom of the at least one sensor channel.

11. The arrangement of claim 1, wherein the sensors include at least one of a temperature sensor, a chip level sensor, a liquid interface sensor, a liquid level sensor, and a residual alkali concentration sensor.

12. The arrangement of claim 1, wherein the at least one sensor channel is insulated against thermal conductivity from an outermost wall of the at least one concentric pipe of the central pipe.

13. The arrangement of claim 11, wherein the at least one sensor channel is insulated against thermal conductivity from an outermost concentric pipe of the at least one concentric pipe, and the at least one sensor channel includes the thermal sensors which, do not extend out of the at least one sensor channel into an interior of the vessel.

14. The arrangement of claim 1, further comprising at least one of: (i) a plurality of sensors of the same type at a same elevation level in the at least one sensor channel, and (ii) at least two sensors of the same type arranged at different elevations in the at least one sensor channel.

15. A digester vessel oriented vertically and configured to continuously treat a lignocellulosic material, the digester vessel comprising: an outer wall defining an interior chamber configured to treat the lignocellulosic material flowing continuously down through the digester vessel from an upper inlet to a lower outlet for the material; a central pipe coaxial with the outer vessel and extending at least ten meters within the interior chamber, wherein the central pipe is configured to deliver liquor to the lignocellulosic material in the interior chamber; a sensor channel mounted to an outermost wall of the central pipe and extending at least ten meters in the interior chamber, wherein the sensor channel supports sensors arranged at various elevations within the digester vessel; a cable conduit extending from the sensor channel, through the interior chamber and to an outlet at or external to the outer wall; and at least one sensor cable connected to a respective one of the sensors and extending through the sensor channel and through the cable conduit, wherein the at least one sensor cable is configured to transmit signals generated by the sensors to a processor external to the digester vessel.

16. The digester vessel of claim 15, further comprising an sealed channel extending through the cable conduit and the sensor channel, wherein the sealed channel is configured to be pressurized.

17. The digester vessel of claim 15, wherein the sensor channel has an outer wall exposed to the lignocellulosic material and is configured to shield the sensors from the lignocellulosic material.

18. The digester vessel of claim 15, further comprising an evacuation tube extending from an outlet external to the outer wall and the interior chamber, and extending to at least a bottom of the sensor channel, wherein the evacuation tube is configured to evacuate liquid from the sensor channel and out of the digester vessel.

19. The digester vessel of claim 15, wherein the cable conduit and the sensor channel are sealed and configured to isolate an interior channel through the cable conduit and the sensor channel from the lignocellulosic material.

20. The digester vessel of claim 15, wherein the sensor channel is concentric with the central pipe and extends around an outermost wall of the central pipe.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0032] FIG. 1 shows a pressurized vessel with a central pipe arranged in the center area of the vessel and a sensor channel arranged on it.

[0033] FIG. 2 shows a cut view of embodiments of the sensor channel arrangement.

[0034] FIG. 3 shows a cut view of an embodiment of the sensor channel arrangement.

[0035] FIG. 4 shows an embodiment of top part of the sensor channel arrangement on the central pipe.

[0036] FIG. 5 shows a preferred cable conduit arrangement at the top of the sensor channel.

DETAILED DESCRIPTION OF THE INVENTION

[0037] WO2016112203 describes process conditions within a digester vessel and types of sensors, which can be used for monitoring the conditions. The disclosed arrangements measure the conditions within the outer area of the vessel well, but having the monitoring sensors inside the center area of the vessel is more beneficial as they represent better the general conditions. Representative measurements can be obtained by far fewer sensors from the center area. In most cases, only one sensor at one elevation is needed for the monitoring task of the condition. The installations like the WO2016112203 discloses can initially or later be arranged with the current invention for further and/or comparative information needs and also for backup replacement of faulty sensors, but preferably with a limited number of sensors.

[0038] FIG. 1 shows main parts of a digester for chemical treatment of lignocellulosic material. The central pipe 2 comprises concentric pipes 3. It is mounted coaxially within the digester vessel 1. It is used for adding liquor or other fluids to the center of the chip column inside the digester, in a specific elevation. Their discharge elevations are engineered according to the purpose of the fluid and the specific process zone.

[0039] The central pipe 2 may extend from the top part of the digester to the bottom part of it. Monitoring sensors 11 (FIG. 3) are placed at multiple points on an outer wall 6 of sensor channel 4 along the entire height of the central pipe 2. Thus they can obtain data about the process conditions at multiple elevations within the center part of the digester 1. Only the most active areas of the treating process may need to be monitored and the outer wall 6 of the sensor channel 4 thus may cover even less than half of the height of the central pipe 2. Typically the sensor channel 4 will still be at least 10 meters long. The more length and more sensors are installed the more economical the inventive solution economically is.

[0040] Four sensors or meters might be a minimum amount for meters and sensors for reaching enough benefits. At least one cable channel 5 is provided for leading cables 8 (FIG. 2) out from inside the sensor channel 4 out to the exterior of the digester. If the cable channel 5 is on top of the sensor channel 4, it is easier to feed and replace the cables 8. Another suitable or optional position for the cable channel 5 is at the bottom of the sensor channel 4 for leading leaked liquid out and for getting the operation period of the digester extended if the leak has a small enough volume. Flanged joint may exist between the sensor channel 4 and the cable channel 5 for easier installation and service, but for avoiding any leaks and extra flow resistance, it is not preferred.

[0041] The sensors 11 provide information for allowing monitoring of operating conditions and liquor composition, such as residual alkali, within the digester. With liquor composition information at various heights along the digester, a profile of the reaction characteristics within the digester can be developed. Once developed, the profile of the reaction characteristics can be used to adjust the concentration and rate of circulated or fresh liquid being added to digester between the various process zones, such as impregnation zone, cooking zone and washing zone, or even within a process zone thereby allowing for improved reaction characteristics within the digester.

[0042] Placing electrochemical residual alkali sensors 11 at multiple heights along the central pipe 2 allows operators to collect comprehensive, real-time data on the process occurring within the digester vessel 1. In addition to this data, residual alkali concentrations are preferably measured also by taking samples from the digester in a way known per se. The sensors 11 are desirably electrochemical sensors. Digitized measurement values from the electrochemical and other process monitoring sensors 11 are compared by control algorithms to desired parameters via an analyzer such as an “AIC” (analyzing indicating controller). The AIC may then send adjustment signals to various controllers to control the liquor flow rate, liquor strength, temperature and extraction and addition rates of various liquors to the pressurized vessel. The use of such electrochemical sensors 11 to gather the necessary process information allows for a short time between measurement and reaction to the measurements. The controlling tasks are preferably based on adaptive artificial intelligence and/or machine learning algorithms, which are also able to automatically react to faulted and/or contaminated sensors 11 and can adjust control parameters.

[0043] FIG. 2 shows an outer wall 6 of a sensor channel 4 welded from both sides to the outermost concentric pipe 3 of the central pipe 2. The interior of the wall 6 may be divided by partition walls, tubes and/or gutters to subchannels 7. The tubes and gutters should only be joined to the outer wall 6 of a sensor channel 4. More than one such outer wall 6 of the sensor channel 4 with optional sets of subchannels 7 may be arranged aside the central pipe 2. The width of subchannels 7 or the wall 6 of the sensor channel 4 should be limited to be below 250 mm so that cables and connectors of the sensors 11 can easily be reached through the opening of sensor holders 13. Still the wall 6 of the sensor channel 4 should be smoothly joined to the central pipe 2 for not hindering the flow of treated material around the central pipe 2. Thus the outer wall 6 is preferably always divided by partition walls to a narrower subchannels 7 to accomplish a narrow enough channeling. An example, which uses a profiled tube a sensor channel 4 is illustrated at right side of the central tube 2. Temperature profile can be measured with several temperature sensors 11 installed along the central pipe 2. The cables 8 of the sensors 11 are preferably bundled to cable bundles. A sensor channel 4 may be insulated against thermal conductivity from the coaxial liquid pipes 3. As the temperatures within coaxial pipes 3 are at quite the same level, the insulation should be sufficient even without additional insulating material 12 when an insulated subchannel 7 is only joined to the outer wall 6 and it is not connected to the outermost coaxial channel 3. Then the temperature of the outer wall 6 is conducted also to the gutter or tube of the subchannel 7, which enables fulfilling the thermal measuring purpose. Vertical temperature profile can be measured by thermal sensors 11, which are positioned at different elevations inside the insulated subchannel 7. The temperature outside of the outer wall 6 should then be the same as or highly relative to the temperature of the thermal sensors inside the subchannel 7. The bundle of cables 8 for thermal sensors 11 may also be provided with preferably profiled insulating material 12, which suit to the subchannel 7 and restrict horizontal and/or vertical movement of air and heat within the subchannel 7. The bundle of thermal sensors 11 or a distributed sensing cable preferably is installed to an as narrow as possible subchannel 7 joined only to the outer wall 6.

[0044] The sensor channel 4 may also be formed from a suitably profiled tube attached on the coaxial pipe 3. Preferably is attached by continuous welds along the coaxial pipe 3, as the sensor channel 4 must not be able to separate from the central pipe during operation of the digester. A round tube is not a preferred profile as there should not be any sharp corners nor space or discontinuities between the outer wall of the sensor channel and the coaxial pipe 3. Otherwise treated material may build up around the central pipe 2 and the sensor channel 4. More preferably the corner a should be more than 120 degrees.

[0045] FIG. 3 shows a cut view of another embodiment of the sensor channel 4 arrangement. Detailed embodiments of arrangements presented in connection with FIG. 2 can be used similarly with arrangements of FIG. 3 and vice versa except the design of the outer wall 6. The outer wall 6 of the sensor channel 4 is now coaxial with the central pipe 2. The structure is stiffer than the arrangement of FIG. 2 and symmetric, which is beneficial in keeping the central pipe coaxially centered within the digester vessel 1. The interior of the outer wall 6 should be spaced apart from the coaxial pipe 3 by at least two partition walls, which will form at least two sensor channels 4.

[0046] Sensors 11 may be installed within a holder 13. The holder 13 is mounted on the outer wall 6 of the sensor channel 4 and it is configured to hold the sensor 11. Cables 8 of the sensors 11 are preferably bundled together and led via the sensor channel 4 to the top part and out through a lead-through flange from the vessel 1 of the digester. An electronic unit, which digitizes and/or transmits the measurement data from cables 8 to a process controller 16 (FIG. 4), is preferably located outside the digester.

[0047] FIG. 4 shows an embodiment of a cable conduit 5 arrangement on top of the sensor channel 4. A sensor channel 4 extends to a cable channel 5 higher than the coaxial pipes 3 in this embodiment. This is best achieved by the embodiment of FIG. 2, as it is costly to extend a coaxial outer wall 6 of the sensor channel 4 over the inlet tubes of coaxial pipes 3. Similarly, the arrangement of FIG. 2 can be extended below the central pipe 2 where the wall thickness of the digester 1 vessel will be much thicker and pressure higher than in the upper part and making openings is thus more critical and should be avoided. By the extensions, the sensors 11, which need to be installed to the digester at those higher and lower elevations can be installed on the sensor channel 4. Preferably every sensor channel 4 and their subchannels 7 are connected to the same cable conduit 5. Otherwise the cable conduits 5 hinder and divert downflow of the treated material, which may cause uneven treatment results. From the sensor channels cables 8 are connected to a process controller 16 maybe via electronic subcontrollers. Preferably, the cable conduit 5 is opposite to inlets of coaxial pipes 3 for balancing the downflow.

[0048] The installation of sensors 11 on the sensor channel 4 allows utilizing new kind of measuring devices within the digester. One such measuring device is a guided wave radar (GWR) for measuring and controlling liquor level and/or chip level within the top part of the digester. A GWR transmitter and receiver unit sends electromagnetic pulses toward a measured level and use the reflected signal to calculate the level in the tank. With GWR, the measured signal pulse travels along the waveguide 10 of the GWR. When the pulse hits the liquid, an indicative proportion of the energy is reflected back up to the transmitter and receiver unit, which then calculates the levels of the materials from the time difference between the pulse sent and the pulse reflected.

[0049] GWR technology has the ability to measure any interface level. Because a proportion of the emitted pulse will continue along the waveguide 10, the liquid interface can be detected. The GWR has the ability to detect the top liquid level of the media as well as any “interface level” or level of the media that is below the liquid level, which contains a different property than the top liquid level being measured. Thus it is possible to measure a chip level if it is lower than the liquor level, or vice versa.

[0050] The waveguide 10 can be made of a stiff metallic rod, flexible wire or a coaxial construction. The transmitter, to which the sensor is connected, can be located outside the digester. The GWR's waveguide can be installed easily through a relatively small lead-trough mounted on the outer wall 6 of the sensor channel 4 and so be led to the central interior of the digester, where the waveguide 10 is attached on the wall 6 of the sensor channel 4 or on the central pipe 2.

[0051] If the sensor channel 4 is closed i.e. also the connectors and/or leadthroughs of the cables 8 are leakproof. Then the sensor channel 4 can be pressurized by a source 15 of pressurized fluid connected to the sensor channel 4, preferably via cable channel 5. The sensor channel 4 is preferably pressurized by a gas and more preferably by an inert gas like nitrogen. The pressure is preferably up to 1 bar higher that pressure outside the sensor channel 4 at any elevation, where holders 11 for the sensors 11 exist. A suitable liquid like clean water may also be used as a pressurizing fluid, if all wirings, sensors 11 and connectors are leakproof. If a leak occurs, it can be detected by a pressure drop and/or by a need to fill up the pressurizing fluid from the source 15 of pressurized fluid to the sensor channel 4. If a pressurized sensor channel 4 or subchannel 7 is separated from other sensor channels 4, the leaking channel can be identified. Sensors, valves and/or pumps of the source 15 of pressurized fluid are preferably connected to the process controller 16 or another controller for controlling the pressure within the sensor channel 4. The process controller 16 may be configured for determination and/or indication of any leaks a leak out of the sensor channel 4 and/or the subchannel 7 and/or the cable conduit 5.

[0052] In certain embodiments, the GWR or other sensors 11 may provide information regarding the density of the column of chips. The information relating to the density of the column of chips can be monitored to develop a profile along the height of the digester. Inconsistencies, variations or fluctuations in the profile of the density of the column of chips may indicate channeling (i.e. areas within the column of chips with varying densities where streams of liquor may form and result in inconsistent reaction characteristics or other process upset condition within the column of chips). By monitoring the density of the column of chips directly and in real-time, undesirable operations of the digester are quickly recognized and addressed to minimize or eliminate unfavorable operating conditions.

[0053] FIG. 5 shows a cut view A-A of a preferred cable conduit 5 arrangement at the end of the cable channel 4. Subchannels 7 preferably extend over the bottom level of the cable conduit 5. Then it is easy to install cable tubes 9, which will lead the cables 8 to the subchannels 7 through the cable channel 5 when cables are installed. Preferably an evacuation tube 14 leads to the bottom of the cable channel 4 for discharging leaked liquids from the bottom of the cable channel 4. A level switch and preferably a pump should be mounted on the bottom end of the tube 14. If the cable channel 5 or another channel is mounted on the bottom of the sensor channel 4, the tube 14 and the pump can be omitted.

[0054] Pressurizing the sensor channel 4 can also be used for exhausting leaked liquid.