JP7680667B2 - Method for measuring and managing the level of mixed raw materials in the mixing section of a mixing and molding machine, and mixing and molding machine - Google Patents

Description

The present invention relates to a method for measuring and managing the level of mixed raw materials in the mixing section of a mixing and molding machine used to manufacture unbaked carbon-containing agglomerates in steelmaking, and to technology related to the mixing and molding machine.

In a blast furnace, raw ore and lump coke are fed into the top of the furnace while air is blown in from the bottom. The reducing gas generated from the lump coke and the blown air is blown from the bottom to the top of the furnace, reducing and dissolving the iron oxide in the raw ore. To ensure the ventilation of the reducing gas in the furnace, the raw ore must be strong enough not to be pulverized in the furnace. For this reason, blast furnaces usually use raw materials that have been fired at high temperatures in advance, such as sintered ore or fired pellets.

In response to this, non-calcined carbonaceous agglomerates have been developed that use hydraulic binders such as cement to reduce the energy consumption required for calcination and thus the amount of carbon dioxide, a greenhouse gas, generated. As the raw material for this non-calcined carbonaceous agglomerates, it may be possible to use inferior fine ores that have been considered difficult to sinter and mold into agglomerates.

As described in Patent Document 1, it is possible to incorporate fine coke, which has a small particle size and is difficult to directly charge into a blast furnace, and anthracite, which is inexpensive but has low caking properties and is difficult to turn into coke, as reducing agents into unsintered carbon-containing agglomerates, and it is expected that the reducing agent ratio in the blast furnace can be reduced. According to the latest knowledge, it is clear that the effect of reducing the reducing agent ratio in the blast furnace can be maximized by setting the carbon content (T.C.) incorporated in unsintered carbon-containing agglomerates to 120 to 200 mass% (equivalent to 15 to 25 mass% in T.C.) of the theoretical amount of carbon required to reduce iron oxide to metallic iron.

Hydrates in unsintered carbonaceous agglomerates formed by the hardening reaction of hydraulic binders are decomposed by endothermic reactions when heated to approximately 400°C or higher in a blast furnace. This causes a significant decrease in the strength of unsintered carbonaceous agglomerates in the furnace, and there is concern that they may be pulverized. If unsintered carbonaceous agglomerates are pulverized in a blast furnace, it will worsen the air permeability inside the furnace, so a certain level of hot strength is required for unsintered carbonaceous agglomerates for blast furnaces. On the other hand, if a large amount of hydraulic binder is used to ensure hot strength, the amount of reducing material input to the blast furnace will increase to compensate for the heat lost by the endothermic reaction, and the cost of molten pig iron will increase. Therefore, there is a demand for a method of manufacturing unsintered carbonaceous agglomerates that can achieve the hot strength required for blast furnace use with as little hydraulic binder as possible.

Recently, a manufacturing method that can achieve the hot strength required for blast furnace use has been developed that uses vacuum extrusion to produce unbaked carbon-containing agglomerates for blast furnaces.

The vacuum extrusion molding machine for non-sintered carbon-containing agglomerates is composed of a first extrusion section (mixing section) and a second extrusion section (extrusion molding section) as shown in the example of FIG. 1. The section from the outlet of the first extrusion section (mixing section) to the second extrusion section (extrusion molding section) is vacuum degassed to -40 kPaG or less in order to ensure the necessary strength of the molded body, and in order to stably continue the vacuum extrusion molding, it is necessary to maintain the mixing raw material filling rate inside the mixing section and the extrusion molding section within an appropriate range. The appropriate value of the mixing raw material filling rate of the kneading section is 50 volume % or more and 90 volume % or less, and optimally, 50 volume % or more and 65 volume % or less. The appropriate value of the mixing raw material filling rate of the extrusion section is 50 volume % or more and 95 volume % or less, and optimally, 50 volume % or more and 60 volume % or less.

In an apparatus for kneading and molding wet powder like this process, it is rare for the mixed raw material level in the container to fluctuate uniformly, and localized fluctuations in the mixed raw material level often lead to fluctuations in the mixed raw material level throughout the entire apparatus. Therefore, in order to effectively suppress fluctuations in the mixed raw material filling rate within the apparatus and manage it within an optimal range, it is important to quickly detect the fluctuations in the mixed raw material level at the location where the fluctuations originate and take operational action.

However, in the prior art, as described in Patent Documents 2 and 3, there are many techniques for detecting the internal liquid level in a vertical mixer or kneader, but there are few techniques for detecting the raw material level in a kneading section that continuously mixes and kneads the raw materials while transporting them horizontally, as is used in non-calcined carbon-containing agglomerate manufacturing equipment. Also, as described in Patent Document 4, there is a prior invention that detects and manages the raw material level inside a device (screw pump) that transports raw materials horizontally, similar to this process, but the raw material level inside the device is considered to be uniform, and it is not a technology that assumes a local rise in the raw material level inside the device, as in this process.

The kneading and molding of non-calcined carbon-containing agglomerates will now be described in detail. In powder kneading and molding, the raw materials to be kneaded and, if necessary, water are put into a kneader, and the powder raw materials are kneaded with the kneading blades and screws in the device. The raw materials are then extruded and molded in a post-process extruder. There are various types of kneading and molding devices, but when kneading and molding raw materials continuously and in large quantities (for example, several tons/h or more), generally, as shown in the example of Figure 1, a kneading section 4 that uses kneading blades 4c (sometimes screws) attached to a horizontally installed single-shaft or multi-shaft shaft 4b to knead the raw materials while continuously transporting them horizontally, and an extrusion molding section 7 that extrudes the raw materials to be kneaded from an extrusion molding dam 7d with extrusion molding blades 7c (sometimes screws) to mold them, is often used. In the example shown in FIG. 1, the extrusion molding unit 7 transports the mixed raw material inside the casing 7a by extrusion molding blades 7c, which are attached to the rotatable extrusion molding unit shaft 7b.

In the kneading section 4 as shown in the example of FIG. 1, water is added to the raw material by using one or more water-adding nozzles 5 of any shape installed at any position on the upper part of the kneading section 4 (including the inside of the connecting pipe 3). In addition, weirs 4d of various shapes (any shape is acceptable as long as it provides discharge resistance, such as a perforated plate) are installed on the outlet side of the kneading section 4 to consolidate the raw material. In front of the weir 4d, a raw material consolidation section 4e with a narrower inner diameter than the kneading section 4 is installed so that the raw material is tightly packed and adheres closely to the weir 4d. The raw material is consolidated in the weir 4d and the raw material consolidation section 4e, and kneading is promoted by receiving a particularly large shear force from the kneading blades 4c.

1, when the extrusion molding section 7 is configured with the outlet side of the kneading section 4 vacuum degassed, the raw material compacted in the raw material compacting section 4e with its inner diameter narrowed also serves as a material seal to maintain the vacuum degassing conditions. Note that the weir 4d and raw material compacting section 4e have various shapes (for example, the raw material compacting section 4e may be tapered so as to narrow from the inlet side to the outlet side, and the weir 4d may be a perforated plate), but their basic roles are the same.

In a kneading and molding device of the type consisting of a kneading section 4 and an extrusion molding section 7 as shown in Figure 1, it is necessary to manage the level of the mixed raw material inside the device in both the kneading section 4 and the extrusion molding section 7. In either the kneading section 4 or the extrusion molding section 7, if the level of the mixed raw material is too high, the filling rate of the mixed raw material inside the device will be too high, causing the mixed raw material to overflow from the device or overloading the device, making it impossible to continue operating. On the other hand, in either the kneading section 4 or the extrusion molding section 7, if the level of the mixed raw material is too low, the filling rate of the mixed raw material inside the device will be too low, making it impossible to maintain a material seal and maintaining the necessary vacuum degassing conditions.

Next, we will explain the structural differences between the kneading section 4 and the extrusion molding section 7, which are important in managing the level of the mixed raw materials. The kneading section 4, except for the mixed raw material compaction section 4e that compacts the mixed raw materials, has a structure that allows the top to be opened and the inside to be observed from the top (open, grating, observation window, easily opened and closed lid, etc.). Therefore, the mixed raw material level inside the kneading section 4 can be easily observed from the top of the device. On the other hand, in the extrusion molding section 7, in order to maintain the mixed raw material compaction and vacuum degassing conditions, the entire area except for the vacuum chamber 6 is surrounded by strong liners on all sides, above, below, left and right, and the inside of the device cannot be observed from the top of the device.

Furthermore, even if an attempt is made to measure the level of the mixed raw material inside the extrusion molding section 7 by installing a sight glass at the top of the vacuum chamber 6, the mixed raw material falling inside the vacuum chamber from the outlet side of the kneading section 4 to the extrusion molding section 7 will interfere with the measurement. For example, if an attempt is made to measure the level of the mixed raw material in the extrusion molding section 7 using a level meter through a sight glass installed at the top of the vacuum chamber, the level meter will frequently pick up the distance from the sight glass to the falling mixed raw material, making it impossible to continue to quantitatively measure the level of the mixed raw material. For this reason, a method different from that used for the kneading section 4 is required to stably measure the level of the mixed raw material inside the extrusion molding section 7.

<Key points for stable operation of kneader>
1) Management of the raw material level Generally, in order to continue the kneading stably, it is important to maintain and manage the raw material level in the kneading section 4 within an appropriate range. For example, if the raw material level is too high, the raw material overflows from the top of the kneading section 4, making it impossible to continue the operation, or the kneading section 4 is overloaded and the operation is stopped. On the other hand, if the raw material level is too low, the water sprayed from the water-adding nozzle hits the shaft or the tip of the kneading blade 4c, making it impossible to add water evenly to the raw material, or it becomes difficult for the kneading blade 4c to apply force to the raw material, making it impossible to knead the raw material stably. In such cases, the raw material is supplied to the subsequent process with insufficient mixing, which may reduce the product yield or cause the operation to be stopped.

In a kneading and molding machine such as the example shown in Figure 1, large amounts of powdered raw material are continuously supplied and discharged, so if the balance between the supply and discharge of the raw material is lost, the raw material level of the entire kneading and molding machine or a specific location will fluctuate in a relatively short time (several tens of seconds to a few minutes), making it difficult to manage the raw material level. In addition, when mixing raw material whose properties are such that the flowability changes significantly with even a small change in the operating conditions (raw material particle size, raw material moisture, change in the number of rotations of shaft 4b, etc.), fluctuations in the raw material level are particularly likely to occur.

The reason for this is that changes in the fluidity of the raw material significantly affect the discharge resistance applied to the raw material by the weir 4d and the conveying force of the raw material by the kneading blades 4c. Furthermore, in the case of raw materials with relatively low fluidity (raw materials with a high angle of repose), localized fluctuations in the raw material level are likely to occur, which may then become the starting point for fluctuations in the overall raw material level.

Therefore, in order to continuously maintain stable mixing processing using a non-calcined carbon-containing agglomerate mixer such as that shown in the example of Figure 1, it is necessary to monitor the fluctuations in the mixing raw material level in the mixing section 4 and maintain the mixing raw material level within an appropriate range. In particular, when using mixing raw materials whose mixing raw material level is prone to fluctuations as described above, it is necessary to manage the mixing raw material level with even greater care.

2) Method of Adjusting the Raw Material Level As described above, the raw material level in the kneader can be adjusted by changing conditions such as the amount of raw material fed to the kneading section 4, the rotation speed of the shaft 4b, and the amount of water added from the water-adding nozzle 5, as shown in the example of Fig. 1. For example, increasing the amount of raw material fed to the kneading section 4 increases the raw material level, whereas decreasing the amount of raw material fed to the kneading section 4 decreases the raw material level.

In addition, increasing the rotation speed of the shaft 4b increases the ability of the kneading blades 4c to transport the raw material, so the raw material level decreases. On the other hand, decreasing the rotation speed increases the raw material level. In addition, increasing the amount of water added increases the fluidity of the raw material, making it easier for the raw material to slip when it comes into contact with the kneading blades 4c and making it difficult to transport, so the raw material level tends to increase. On the other hand, decreasing the amount of water added reduces the slippage between the raw material and the kneading blades 4c, making it easier to transport the raw material, so the raw material level tends to decrease. However, if the moisture content of the raw material is too low, the raw material loses its fluidity, making it difficult to transport, and the raw material level increases.

As for hardware conditions, thinning due to wear on the kneading blades 4c and the weir 4d reduces the raw material conveying capacity and discharge resistance, respectively, and causes fluctuations in the raw material level. The effects of wear on these hardware can be covered to a certain extent by adjusting the rotation of the shaft 4b, but if the wear progresses beyond a certain level, the hardware must be replaced. Also, adhesion of raw material to the casing 4a, shaft 4b, and kneading blades 4c of the kneading section 4 reduces the raw material conveying force and causes the raw material level to rise, but this can be prevented and eliminated by performing regular cleaning.

<Current method for monitoring raw material levels and issues>
In the kneading and molding machine for non-calcined carbon-containing agglomerates as shown in the example of FIG. 1, the worker often periodically monitors the mixed raw material level visually through a grating, window, opening, etc. 4f installed on the upper surface of the kneading section 4. However, periodic visual monitoring by the worker is prone to overlooking fluctuations in the mixed raw material level that occur in a short period of time and to variations in judgment between workers, and is not necessarily a means for quickly detecting fluctuations in the mixed raw material level. Furthermore, visual monitoring by the worker requires that a worker engaged in monitoring the mixed raw material level must always be located near the kneading and molding machine, which is also a factor in increasing production costs. The difficulty of visual management by the worker is particularly problematic when multiple systems of kneading and molding machines are operated in parallel.

Up until now, technologies for monitoring the level of raw materials using level gauges and level switches have been developed, but with conventional technology, the targets for automatic monitoring of the raw material level are limited to vertical mixers and molding machines, mixing sections, or screw feeders attached to hoppers, and there are no technologies aimed at mixers and molding machines that transport raw materials horizontally, as shown in the example in Figure 1. Furthermore, because these technologies consider the raw material level to be constant within the device, they are not necessarily able to quickly detect local fluctuations in the raw material level within the container.

In light of the above situation, there is a strong demand for the development of technology that can automatically and quantitatively monitor the internal raw material level in a non-calcined carbon agglomerate mixer such as the example shown in Figure 1, and detect fluctuations in the raw material level at an early stage.

Patent No. 5000402 Japanese Patent Application Laid-Open No. 61-216749 JP 2003-200414 A Japanese Patent Application Publication No. 10-319694

The present invention provides a device for measuring the raw material level in a continuous kneading section and a method for managing the raw material level in the kneading section, in order to operate stably and continuously, in a continuous kneading section that uses kneading blades or screws attached to a single or multiple horizontally installed shaft to transport and knead the raw materials in a horizontal direction, such as the kneading section used in a non-calcined carbon-containing agglomerate kneading and molding machine.

In order to solve the above problems,
(1) A method for measuring and managing the level of a mixed raw material in a kneading section of a kneading and molding machine, characterized in that a mixed raw material inlet, a connecting pipe that leads the mixed raw material to the kneading section, a kneader on which a shaft equipped with an impeller is disposed, and a weir from which the mixed raw material is pushed out are arranged in that order, and the level of the mixed raw material is measured at the entrance side of the mixed raw material consolidation section just before the weir and/or at the position where a water adding nozzle is installed.

Also,
(2) It is also preferable that the method for measuring and managing the level of the mixed raw material in the kneading section of the kneading and molding machine described in (1) is characterized in that the level of the mixed raw material is maintained at 50% to 90% of the height of the kneading section.

Also,
(3) When the hydration nozzle is disposed in a connecting pipe that leads the raw material to the kneading section, it is also preferable to use a method for measuring and managing the level of the raw material in the kneading section of a kneading molding machine as described in claim 1 or 2, characterized in that the level of the raw material in the kneading section at the position where the hydration nozzle is installed is measured at the inlet side of the kneading section.

moreover,
(4) A kneading and molding machine characterized in that it comprises an inlet for the raw material to be kneaded, a connecting pipe for leading the raw material to the kneading section, a kneader having a shaft equipped with an impeller, and a weir through which the raw material is pushed out, arranged in that order, and is equipped with a device for measuring the level of the raw material to be kneaded at the entrance side of the raw material consolidation section just before the weir and/or at the position where the water adding nozzle is installed.

moreover,
(5) It is also preferable that the kneading molding machine described in (4) is characterized in that the hydration nozzle is disposed in a connecting pipe that leads the raw material to the kneading section, and the raw material level measurement position at the installation position of the hydration nozzle is the inlet side of the kneading section.

The present invention provides a method for stably managing the level of mixed raw materials in the mixing section of a mixer and a mixer that can do so, and is of great technical significance.

FIG. 2 is a diagram showing a kneading and molding machine comprising a first extrusion section (kneading section) and a second extrusion section (extrusion molding section). This figure shows a situation in which the raw material gradually accumulates in a kneading and molding machine from just before the raw material compaction section 4e back to the inlet side of the kneading section 4, and the raw material level in the entire kneading section 4 gradually rises. FIG. 1 is a diagram showing a system in which a water-adding nozzle 5 is installed above the horizontal portion of a kneading section 4 in a kneading molding machine, and water is added from above to the raw material being kneaded and transported horizontally. FIG. 1 is a diagram showing an example of an application of the present invention. 13 is a diagram showing actual measurement data of the level of the mixed raw material measured by a microwave level meter installed at a position 150 mm before the mixed raw material compaction section 4e.

The following is an embodiment of the invention. In order to continuously maintain stable mixing processing using a mixing and molding machine such as that shown in the example of Figure 1, it is necessary to monitor the fluctuations in the mixing raw material level in the mixing section 4 and maintain the mixing raw material level within an appropriate range. In particular, when using mixing raw materials whose mixing raw material level is prone to fluctuations as described above, it is necessary to manage the raw material level with even greater care.

The reason is that in the kneading section 4, water is added to the raw material, so the raw material level is easily changed depending on the mixed state of the raw material and the added water, and the upper limit of the raw material filling rate allowed in the kneading section 4 is smaller than that in the extrusion molding section 7 (upper limit in the extrusion molding section 7: 95%, upper limit in the kneading section 4: 90%), so more precise raw material level management is required than in the extrusion molding section 7. Generally, even in actual operation, the frequency of problems caused by fluctuations in the raw material level in the kneading section 4 (overload, material seal collapse, etc.) is higher than that caused by fluctuations in the raw material level in the extrusion molding section 7. For these reasons, the present invention targets the kneading section 4.

<Key points and mechanisms of the present invention>
As a result of the investigation, it was found that the fluctuation in the raw material level in the kneading section 4 as shown in the example of Fig. 1 often originates from local raw material level fluctuations occurring in two locations: before the raw material compacting section 4e and at the installation position of the water adding nozzle 5. It was also found that the raw material level of the entire kneading section 4 can be stably controlled by installing instruments to measure the raw material level in these two locations. Below, the details of the investigation results will be described for each of the above two locations, including the mechanism that is the origin of the raw material level fluctuation and the raw material level control range for stable operation of the kneading section 4.

Here, the range of the raw material compaction section 4e may be the entire range from 0 to 100% of the range from the weir 4d to the inlet end of the kneading section 4, assuming that the length from the weir 4d to the inlet end of the kneading section 4 is 100%, or only a part of the range from the weir 4d to the inlet end of the kneading section 4. In the present invention, the latter is used, and it is preferable that the range from the weir 4d to the inlet end of the kneading section 4 is greater than 0% and less than 25%. As mentioned above, the raw material compaction section 4e has a narrower inner diameter than the kneader 4, so the raw material is densely packed toward the weir 4d, but if the material seal is 0% from the weir 4d toward the inlet end of the kneading section 4, it is often not possible to form a material seal, and if it exceeds 25%, the amount of densely packed raw material increases, which puts too much strain on the kneading root 4c, shaft 4b, and the driving sources such as the electric motors that drive them, leading to damage to the equipment and an increase in size, which is undesirable. In the present invention, a raw material level is placed just before or upstream of the inlet side of the raw material compaction section 4e, so that the raw material is densely packed in the raw material compaction section 4e and a material seal is formed at the weir 4d.

In the vacuum extrusion molding method, the raw material is compressed in the raw material compression section 4e to form a material seal, and the vacuum degassing conditions between the vacuum chamber 6 and the extrusion molding gate 7d are kept at -40 kPaG or less, which is necessary to ensure the strength of the molded product. In order to compress the raw material, the raw material compression section 4e has a narrower diameter than the previous section (25-100% from the gate 4d toward the inlet end of the kneading section 4), as mentioned above, and is covered on all sides by a strong casing 4a, so that the raw material is subjected to resistance from the gate 4d installed on the outlet side.

This structure allows a raw material level of 100% in the raw material compaction section 4e (100% raw material level is required at the weir 4d). On the other hand, the portion from the inlet end of the raw material compaction section 4e to the inlet end of the kneading section 4 is not expected to have a raw material level of 100% (appropriate range 50 to 90%), and the upper surface is provided with a grating, a steel plate with a sight window, or a steel plate that can be easily opened and closed as an internal observation section 4f on the upper surface of the kneading section 4 to monitor the raw material level inside. For this reason, as described above, it is preferable that the range of the raw material compaction section 4e is specified to be approximately 0% to 25% from the weir 4d toward the inlet end of the kneading section 4.

In this study, raw steel pellets (with an average moisture content of 9% to 14% by mass during normal operation) were used as the raw material to be mixed. Raw steel pellets are generally stored in outdoor raw material yards, and the moisture content is prone to change due to temperature and precipitation. This means that the moisture content of the raw material fed into the mixing section 4 can change unintentionally, and even slight changes in moisture conditions can easily cause the fluidity to change.

Furthermore, since variations in particle size conditions are likely to occur, the mixed raw material level is likely to fluctuate. In this study, granulation was performed from the outlet side of the kneading section 4 onwards under vacuum degassing conditions of ≦-40 kPa, and in order to maintain this, vacuum degassing was performed using the vacuum pump 8 in Figure 1, and the weir 4d and extrusion molding weir 7d must be material sealed with the mixed raw material. In the example shown in Figure 1, the vacuum pump 8 is connected to the vacuum chamber 6 via the vacuum pump connection pipe 9.

<Management of the level of the kneaded raw material before the kneaded raw material consolidation section 4e>
In the raw material compacting section 4e, the raw material conveyed from the inlet side of the kneading section 4 is resisted by the weir 4d, so that the raw material is compacted in the casing 4a. During normal operation, the discharge resistance of the raw material by the weir 4d and the conveying force of the raw material by the kneading blade 4c are balanced, and the raw material level is high only in the raw material compacting section 4e. However, if the extrusion force of the raw material is reduced or the fluidity of the raw material is reduced due to some reason, the discharge resistance by the weir 4d temporarily exceeds the extrusion force of the kneading blade 4c, and the discharge speed of the raw material from the weir 4d to the subsequent process is reduced. At this time, as shown in FIG. 2, the raw material gradually accumulates from just before the raw material compacting section 4e back to the inlet side of the kneading section 4, and the raw material level of the entire kneading section 4 gradually rises.

If the amount of raw material supplied from the inlet side of the kneading section 4 increases for some reason, the raw material level will also rise, and if the discharge resistance of the raw material decreases or the fluidity of the raw material increases, the raw material level will decrease starting from just before the raw material compaction section 4e. The raw material level will also decrease if the amount of raw material supplied from the inlet side of the kneading section 4 decreases for some reason. For these phenomena, if a means for measuring the raw material level is installed near just before the raw material compaction section 4e, fluctuations in the raw material level can be detected early and stable kneading can be continued.

Here, we investigated the conditions for the level of the raw material at the start of the raw material compaction section 4e that allows stable mixing to continue. The results of this investigation are shown in Table 1. From the investigation results, it was found that when the height of the kneading section 4 (height from the bottom to the top of the casing 4a) is taken as 100%, if the level of the raw material at a position just before the start of the raw material compaction section 4e (for example, a position about 100 mm to 300 mm from the start of the raw material compaction section 4e toward the inlet side of the kneading section 4) is controlled within a range of 50% to 90%, the raw material is compacted in the raw material compaction section 4e, the raw material level becomes 100% at least at the weir 4d, a material seal is formed, and stable mixing can be continuously maintained. If the raw material level exceeds 90% at a position 100 mm to 300 mm from the start of the raw material compaction section 4e toward the entry side of the kneading section 4, the raw material level will exceed 100% in about 5 to 30 minutes, making operation impossible. On the other hand, if the raw material level at a position 100 mm to 300 mm from the start of the raw material compaction section 4e toward the entry side of the kneading section 4 falls below 50%, the raw material is not compacted in the raw material compaction section 4e, so the raw material cannot be sufficiently mixed, and the insufficiently mixed raw material is sent to the subsequent process, resulting in unstable granulation in the subsequent process.

In the above investigation, a microwave level meter was used as a means for measuring the raw material level, which was installed at the top of the kneading section 4 at a position about 150 mm from the start point of the raw material compaction section 4e toward the inlet side of the kneading section 4. The raw material level can also be measured visually by an operator if a standard is set in advance. The measuring means of the level meter is not limited to a microwave level meter, and any type (laser distance meter, millimeter wave level meter, proximity sensor, various level switches, etc.) is acceptable as long as it can measure the raw material level in the kneading section. However, non-contact level meters such as laser distance meter and microwave level meter are preferable to prevent damage to the sensor and kneading section 4 due to contact with the raw material or kneading blades 4c, etc., and to prevent a decrease in measurement accuracy due to raw material adhesion to the sensor. Furthermore, since dust and water vapor derived from the raw material may be generated from inside the kneading section 4, microwave level meter and millimeter wave level meter, which can perform relatively stable measurement even in the presence of dust and water vapor, are more preferable.

The kneading state was judged based on the operating state of the extruder using the kneading section 4 as the first extrusion section. Problems with the operating state are, specifically, when the raw material cannot be consolidated in the raw material consolidation section 4e of the kneading section 4, or when water cannot be added evenly, resulting in an inability to maintain a material seal or insufficient kneading of the raw material, which leads to a decrease in pellet yield or strength. A kneading state in which pellet production can continue for 1 hour or more while satisfying the vacuum degassing condition of ≦-40 kPa was rated as ◯, and a state in which stable product production is not possible due to a decrease in yield or strength was rated as ×.

In this way, the control range of the raw material level just before the raw material compaction section 4e is 50% to 90% for continuous stable operation, 50% to 70% is better, and 50% to 60% is optimal. The reason for this is that by controlling the raw material level (the filling rate of the raw material) to a constant level, the force with which the raw material is pressed by the raw material blades 4c against the weir 4d is stabilized, and the variation in the properties of the raw material discharged is reduced.

Here, the level of the raw material to be mixed just before the raw material compaction section 4e can be adjusted by adjusting the amount of raw material input, the rotation speed of the shaft 4b, and the amount of water added from the water adding nozzle 5, as described above. If the above methods do not allow adjustment, there is a high possibility that the hardware is worn out or the raw material is adhering to the hardware, so the fluctuation in the raw material to be mixed can be suppressed by replacing or cleaning the parts.

<Management of the mixing raw material level at the water adding position in the mixing section 4>
The kneading section 4 may be provided with a water-adding nozzle 5 for adding moisture necessary for kneading. At the position of the water-adding nozzle 5 (water-adding position), the moisture content of the raw material is relatively high compared to the raw material before and after it, so the fluidity is likely to be high. For this reason, at the water-adding position, the moisture content of the raw material may become excessive (excessive fluidity) for some reason, and the raw material may easily slip when it comes into contact with the kneading blade 4c. At this time, the conveying speed of the raw material decreases, and the level of the raw material increases from the water-adding position to the inlet side of the kneading section 4. On the other hand, at this time, the raw material conveying speed decreases after the water-adding section, so the raw material supply is insufficient, and the level of the raw material decreases.

Here, we investigated the conditions for the level of the raw material at the water-adding position that allows stable mixing to continue. The investigation method was the same as that of the raw material compaction section 4e described above, but the raw material level was measured visually by an operator according to a preset standard. The results of this investigation are shown in Table 2. From the investigation results, it was found that when the raw material level at the water-adding position exceeds 90%, the raw material level at the same position exceeds 100% in about 5 to 30 minutes, overflows from the internal observation section 4f on the top surface of the kneader, and operation becomes impossible. On the other hand, when the raw material level at the same position falls below 50%, the water sprayed from the water-adding nozzle hits the shaft 4b or the kneading blade 4c before hitting the powder raw material. In this case, it was found that the raw material cannot be sprayed evenly, the moisture of the raw material is dispersed, the material seal collapses, and granulation cannot be continued stably in the subsequent process.

In this way, the control range of the raw material level at the water addition position allows for continuous and stable operation if it is between 50% and 90%, but between 50% and 70% is even better, and between 50% and 60% is optimal. The reason for this is that by controlling the raw material level (the filling rate of the raw material) to a constant level, the amount of water sprayed from the water addition nozzle onto the raw material is constant, which reduces the variation in the properties of the raw material discharged from the kneading section 4.

As described above, the level of the raw material to be mixed can be adjusted by adjusting the amount of raw material input, the rotation speed of the shaft 4b, and the amount of water added from the water-adding nozzle 5. If the above methods do not allow adjustment, there is a high possibility that the hardware is worn out or the raw material is adhering to the raw material, so the fluctuation in the raw material can be suppressed by replacing or cleaning the parts. In particular, since the rise in the raw material level starting from the water-adding position mostly occurs when the raw material at the water-adding position has too much moisture, reducing the amount of water added is often effective. The possibility of reducing the amount of water added can be determined by comparing the actual moisture value of the discharged raw material to the moisture value set in advance (for example, in the case of the pellet raw material in this study, if the moisture value exceeds the usual upper limit of 14 mass%, it is determined that there is too much moisture, and the amount of water added is reduced).

Next, the installation position of the water-adding nozzle 5 will be explained. There are two ways to install the water-adding nozzle 5: one is to install the water-adding nozzle 5 inside the connecting pipe 3 and spray water onto the raw material falling inside the connecting pipe 3, and the other is to install the water-adding nozzle 5 on the top of the horizontal part of the kneading section 4 (the part corresponding to the internal observation part 4f on the top of the kneader in Figure 3) and add water from above to the raw material being transported horizontally (in this case, the tip of the water-adding nozzle 5 can be above or below the surface of the internal observation part 4f on the top of the kneader). In the case of the latter installation method, the water-adding nozzle 5 is generally preferably installed within about 50% of the machine length of the kneading section 4, starting from the outlet end of the connecting pipe 3 (i.e., the starting point of the internal observation part 4f on the top of the kneading section 4), in order to ensure sufficient kneading time for the raw material after water addition.

The present invention is applicable to both the former and latter cases, as described later. The installation position of the level gauge will be described. The raw material level is measured at the inlet side and the outlet side of the kneading section 4. The level gauge is installed at the inlet side of the kneading section 4, which measures the raw material level in the range where the water-adding nozzle 5 is installed, and at the outlet side of the kneading section 4, which measures the raw material level just before the raw material compaction section 4e. In particular, the position of the inlet side level gauge 10 is a position where the raw material level at the place where the local raw material moisture content can be estimated to be the highest can be measured. The reason is that at such a position, the raw material is likely to slip when it comes into contact with the kneading blade 4c, and the raw material is likely to remain and the level is likely to rise.

Specifically, if the water-adding nozzle is installed inside the connecting pipe 3, it is preferable to install it at the start of the horizontal part (grating 4f) of the kneading section 4. On the other hand, if the water-adding nozzle is installed in the horizontal part (grating 4f) of the kneading section 4, it is preferable to install it immediately after the water-adding nozzle (exit side of the kneader). In the latter case, particularly when there are multiple water-adding nozzles, it is preferable to install them immediately after the water-adding nozzle position closest to the exit side of the kneading section 4, because it can be assumed that the moisture content of the kneaded raw materials is highest at such a position.

In the kneading section 4 as shown in the example of Figure 1, the level of the raw material is measured just before the raw material compaction section 4e (preferably 100 to 300 mm from the start of the raw material compaction section 4e toward the inlet side of the kneading section 4), at the installation position of the water-adding nozzle 5 (preferably within about 50% of the length of the kneader 4, starting from the outlet end of the connecting pipe 3 (i.e. the start point of the internal observation section 4f on the top surface of the kneader)), and the raw material level in the kneading section 4 is maintained at 50% to 90% of the height of the kneading section 4, allowing stable kneading to be continued.

The following describes the adjustment method when the detected mixed raw material level is outside the specified range. Since the mixed raw material level is generally operated at a constant production volume, the mixed raw material level is adjusted using two means: the number of rotations of shaft 4b and the amount of water added from water adding nozzle 5. An example of the adjustment method is shown below.

For example, when the raw material level before the raw material compaction section 4e is on the rise, the rotation speed of the shaft 4b is increased to promote the discharge of the raw material from the weir 4d, thereby lowering the raw material level. On the other hand, when the raw material level at the raw material compaction section 4e is on the decline, the rotation speed of the shaft 4b is decreased to raise the raw material level.

When the level of the raw material being kneaded at the water addition position is rising, this is most likely due to an excess of moisture in the raw material being kneaded, so the moisture content of the raw material being kneaded discharged from the kneading section 4 is measured, and if the raw material being kneaded has excess moisture, the amount of water being added from the water addition nozzle 5 is reduced to an appropriate range to lower the raw material being kneaded.

In addition, if the raw material moisture content is within the appropriate range but the raw material level is on the rise, the rotation speed of shaft 4b is increased to lower the raw material level, and if the raw material level is falling, the rotation speed of shaft 4b is decreased to raise the raw material level. When the amount of added water is not excessive, the raw material level fluctuates up and down in many cases in conjunction with the raw material level just before the raw material compaction section 4e and the raw material level at the water addition position. In other words, when one raw material level is rising, the other also rises, and when one raw material level is falling, the other also tends to fall.

Therefore, if the moisture content at the outlet of the kneading section 4 is measured and it is confirmed that the moisture content of the raw material is not excessive, in most cases it is acceptable to uniformly adjust the raw material level in the kneading section 4 by adjusting the rotation speed of the shaft 4b. If the raw material level cannot be adjusted by the rotation speed of the shaft 4b or the amount of water added from the water adding nozzle 5, the raw material level is adjusted by the amount of raw material supplied to the kneading section 4. Reducing the amount of raw material supplied will decrease the raw material level, and increasing the amount of raw material supplied will increase the raw material level.

An application example of this technology is as shown in FIG. 4, where the raw material sent from the mixer 1 is fed into the raw material inlet 2. The raw material fed into the raw material inlet 2 is led to the kneading section 4 through the connecting pipe 3, and is kneaded using the kneading blades 4c provided on the shaft 4b. A raw material compaction section 4e is provided in front of the weir 4d from which the raw material is pushed out, and a level meter is installed in front of the raw material compaction section 4e to ensure that the kneading material can be appropriately transported to the raw material compaction section 4e. In this embodiment, the level meter in front of the raw material compaction section 4e is installed at a position about 150 mm from the start point of the raw material compaction section 4e to the entry side of the kneading section. In addition, the water-adding nozzle 5 is installed at a position between 0 and 25% of the length from the start of the grating 4f (the boundary between the connecting pipe 3 and the grating 4f) to the weir 4d, assuming that the length is 100%, and the mixed raw material level is determined at around the 25% position.

Fig. 5 shows the actual data of the raw material level measured by a microwave level meter installed at a position 150 mm before the raw material compaction section 4e. It can be seen that the raw material level can be controlled within a range of about 50 to 80% by adjusting the rotation speed of the shaft 4b and the amount of water added from the water adding nozzle 5 through monitoring by the inlet level meter 10 and the outlet level meter 11. Note that the raw material level in Fig. 5 uses a moving average value (a moving average value over 5 s in this embodiment) in order to ignore periodic fluctuations accompanying the rotation of the shaft 4b, as is commonly done.

Table 3 shows examples of the present invention and comparative examples. Examples 1 to 5 in Table 3 are examples in which the raw material levels in front of the raw material compaction section 4e and at the water-adding nozzle 5 are in the range of 50 to 90%, respectively, and stable operation is possible. Comparative Example 1 is an example in which the raw material level in front of the raw material compaction section 4e exceeds 90%, and Comparative Example 2 is an example in which the raw material level at the raw material compaction section 4e is less than 50%, so neither is stable operation possible. Comparative Example 3 is an example in which the raw material level at the water-adding nozzle 5 exceeds 90%, and Comparative Example 4 is an example in which the raw material level at the water-adding nozzle 5 is less than 50%, so neither is stable operation possible.

The present invention can be applied to any type of kneading section 4, for example, as shown in the examples of Figures 1 to 4, regardless of the number, installation position, or shape of the water-adding nozzles 5, the size and shape of the weir 4d and the raw material compaction section 4e, or the size, shape, or number of the kneading blades 4c.

REFERENCE SIGNS LIST 1 Mixer 2 Feeding port 3 Connecting pipe 4 Kneading section 4a Casing 4b Shaft 4c Kneading blade 4d Weir 4e Kneading raw material consolidation section (a place where the kneading raw material is consolidated before the weir and kneading is particularly performed)
4f Internal observation section on the top of the kneader (grating, glass window, opening, etc.)
5 Water adding nozzle 6 Vacuum chamber 7 Extrusion molding section 7a Casing 7b Extrusion molding section shaft 7c Extrusion molding blade 7d Extrusion molding gate 8 Vacuum pump 9 Vacuum pump connection pipe

Claims (4)

A raw material inlet, a connecting pipe for introducing the raw material to the kneading section, a kneader having a shaft equipped with an impeller, and a weir through which the raw material is pushed out are arranged in this order.
A method for measuring and managing a level of a mixed raw material in a kneading section of a kneading and molding machine, in which an outlet side of the kneading section is vacuum degassed to -40 kPaG or less, comprising:
A method for measuring and managing the level of mixed raw material in the kneading section of a kneading and molding machine, characterized in that the level of the mixed raw material is measured using a microwave level meter or a millimeter wave level meter at the inlet side of the mixed raw material consolidation section before the dam and/or at the location where the water adding nozzle is installed, and the level of the mixed raw material is maintained at 50% to 90% of the height of the kneading section. The method for measuring and managing the level of the raw material in the kneading section of a kneading and molding machine according to claim 1, characterized in that when the water-adding nozzle is disposed in a connecting pipe that leads the raw material to the kneading section, the raw material level measurement at the water-adding nozzle installation position is performed on the inlet side of the kneading section. A kneading and molding machine comprising a raw material inlet, a connecting pipe for introducing the raw material into a kneading section, a kneader having a shaft equipped with an impeller, and a weir through which the raw material is pushed out, which are arranged in this order, and which is equipped with a device for measuring the raw material level at the inlet side of the raw material consolidation section just before the weir and/or at a position where a water adding nozzle is installed, and which is vacuum degassed to -40 kPaG or less at the outlet side of the kneading section,
A microwave level meter or a millimeter wave level meter is arranged on the inlet side of the mixed raw material consolidation section before the weir and/or at the installation position of the water adding nozzle,
A compounder operated so that the continuous mixed feed level is maintained at 50% to 90% of the mixing section height. The kneading and molding machine according to claim 3, characterized in that the water-adding nozzle is disposed in a connecting pipe that leads the raw material to the kneading section, and the raw material level measurement position at the water-adding nozzle installation position is at the entrance side of the kneading section.