An on-line drying control method for powdered or granular materials and a system to execute the method

Abstract: An on-line drying control method for powdered or granular materials and a related system to execute the method. A fixed amount of materials stored and dried in a drying means ( A ) such as a hopper dryer is sampled, transported into a moisture measuring/operating station ( B ) wherein the sampled materials are heated in a heat treatment chamber (3) and the moisture content is calculated by an operation unit (10). The moisture content is sent to a temperature controller ( C ) to control the temperature of the drying means ( A ) so that the obtained moisture content corresponds to a predetermined moisture content while comparing both moisture contents.

Description: Field of the Invention The present invention relates to an on-line drying control method for powdered or granular materials including inorganic materials such as resin and ceramic wherein materials stored and dried in a drying means such as a hopper dryer are automatically sampled and the moisture content thereof measured, and the temperature of the drying means is controlled based on the obtained result. The invention also relates to an on-line drying control system for said materials. Prior Art Generally, controlling the moisture content of resin materials has been considered a most important problem to overcome in order to maintain good quality of resin products, because an inappropriate moisture content of resin materials to be supplied into a molding machine causes defects in the products such as silver line or void. Therefore, resin materials are usually dried by the use of a hopper dryer before being supplied into the molding machine. However, resin materials before being fed into the hopper dryer are apt to absorb moisture in the air while stored in a silo or tank for a period of time after a kraft bag or a flexible container which is used to carry the resin materials is opened. Accordingly a fixed heating temperature and a fixed heating time are settled for the hopper dryer based on an estimated moisture content of resin materials. But such a conventional method for drying resin materials by the use of hopper dryer leaves further room for improvement in saving labour to achieve the most appropriate drying method as the heating of materials is controlled based on an estimation without sufficiently understanding the conditions of resin materials before they are heated. An object of the present invention is to provide an on-line drying control method for powdered or granular materials wherein a fixed amount of materials is automatically sampled, the moisture content thereof is by feeding into a moisture measuring/operating station and the temperature of drying means is controlled based on the obtained moisture content, and to provide an on-line drying control system for materials to execute the method efficiently. The Invention According to one aspect of the present invention, there is provided an on-line drying control method for powdered or granular materials wherein the moisture content of the materials is detected and set at predetermined value by executing the following steps repetitively each time a fixed amount of materials is sampled, characterized by the steps of: directly transporting the materials into a heat treatment chamber having a gastight heating means after sampling and measuring a fixed volumetric amount of materials stored in a drying unit associated with a temperature controller for controlling heating means in the drying unit; heating the materials in said heat treatment chamber while supplying the chamber with a pressurized and dried inert gas; titrating and analysing moisture generated by heating the materials in said heat treatment chamber by supplying the moisture, together with inert gas, to a moisture measuring unit; measuring the weight of the heated materials discharged from the chamber into a receiver of a weight measuring unit provided under said heat treatment chamber; automatically calculating the moisture content of said sampled materials by feeding the moisture value detected in said moisture measuring unit and the weight value measured in said weight measuring unit to a calculating unit; comparing a target predetermined moisture content with the moisture content output from said calculating unit in said temperature controller, by reference to a preprepared temperature control table; and executing feedback control of said heating means so that the moisture content of the materials becomes the target predetermined moisture content set in said temperature controller. According to another aspect of the invention, there is provided an on-line drying control system for powdered or granular materials wherein materials stored in a drying unit having a heating means is controlled so as to have a predetermined value of moisture content by sampling a fixed volumetric amount of materials stored in said drying unit, characterized in that said system comprises: a valve for sampling and measuring a fixed amount of powdered or granular materials stored in said drying unit; a heat treatment chamber having a gastight heating means and having sufficient capacity to contain the fixed amount of sampled materials, said heat treatment chamber being disposed under said valve; a transport pipe be; ween said valve and said heat treatment chamber, said transport pipe having a control valve to control supply of materials from said valve and having a gas vent valve for opening to atmosphere; a moisture measuring unit connecting to an upper part of said heat treatment chamber via a branch pipe having a control valve; a control damper disposed under said heat treatment chamber to discharge the materials stored in said heat treatment chamber; an inert gas feeding means having a feed port at a lower part of said heat treatment chamber and having a feed pipe incorporating a control valve for controlling introduction of pressurized and dried inert gas into said heat treatment chamber; a weight measuring unit disposed under said control damper for measuring the weight of the heated materials; a calculating unit which calculates the moisture content of the materials utilising the weight value of the heated materials obtained from said weight measuring unit and the moisture value from said moisture measuring unit each time a fixed amount of materials is sampled; and a temperature controller connected with said calculating unit for feedback control of said heating means, the moisture content of materials to be controlled being set as a target value in said temperature controller in advance, and said controller comparing the predetermined moisture content with the moisture content output from said calculating unit, with reference to a preprepared temperature control table, and executing feedback control of said heating means so that the moisture content of the materials stored in said drying unit becomes the target value set in said controller. Preferably, the system further comprises a materials measuring chamber with a level detection sensor for detecting the stored amount of materials under said valve and a supplementary control damper disposed between said materials measuring chamber and said heat treatment chamber, wherein said materials stored in said drying unit are sampled and measured with said supplementary damper closed. Moreover, the system may include a pressurized transport means including a pressurized gas injection port connecting said material discharge port of said drying unit with said heat treatment chamber via said valve; the powdered or granular materials in said drying unit being sampled and pneumatically transported to said heat treatment chamber by pressurized transport means. Alternatively, the system may include a pressurized transport means connecting the materials discharge port of said drying unit with said materials measuring chamber having the level detection sensor via said valve, and a pressurized gas injection port in said pressurized transport means, and the powdered or granular materials in said drying unit are sampled and pneumatically transported to said measuring chamber by said pressurized transport means. A moisture measuring/operating station in accordance with the invention may use a moisture measuring unit which executes a coulometric titration, a volumetric titration or a simple absorptive photometric titration which has been disclosed in Japanese Patent Application 63-039291, Karl Fischer reagent being used for all those methods. Description of Embodiment In the accompanying drawings: Figure 1 is a schematic diagram showing one preferable embodiment according to the present invention; Figure 2 is a schematic diagram showing another preferable embodiment according to the present invention; Figure 3 is a schematic diagram showing still another preferable embodiment according to the present invention; and Figure 4 illustrates the partially enlarged sectional view of another preferable construction of moisture measuring/operating station of the system. The system shown in Figure 1 employs a transporting means wherein powdered or granular materials stored and dried in a hopper dryer A provided as a drying means are sampled by a rotary valve 8a constructing a material sampling means 8A and supplied by gravitational fall into a moisture measuring/operating station B . In this system the moisture measuring/operating station B is constructed such that a heat treatment chamber 3 made of a heat-resistant glass provided with a heating means 4 at its periphery is disposed under the rotary valve 8a and the valve 8a and the heat chamber 3 are connected by a transport pipe P1 having a control valve 7a to control the material supply and a vent valve 7b to open to atmosphere, the control valve 7a including a highly airtight valve disc to prevent the leakage of moisture produced when the materials are heated in the chamber 3. A material discharge port 3b provided under the chamber 3 is provided with a solenoid-operated control damper 5 which opens and closes the port 3b by reciprocating a valve disc 5a and a weight measuring unit 2 is provided under the damper 5. The weight measuring unit 2 is equipped with a receiver 21 which can open and close to receive the heated materials discharged from the port 3b of heat chamber 3. When the materials are received in the receiver 21, the weight is automatically measured and is converted into an electrical signal at a signal processor 2a of measuring unit 2, the converted data being sent to a calculating unit 10. The heat treatment chamber 3 has a capacity enough to contain one sample of powdered or granular materials measured by the rotary valve 8a and its upper part is connected with a branch pipe P2 having a control valve 1a and leading to a moisture measuring unit 1. Many kinds of trace moisture measuring unit, which use Karl Fischer reagent and the introduction port of which can be directly connected with the branch pipe P2, can be used as the moisture measuring unit 1. If such a unit is provided, a highly accurate coulometric or volumetric moisture measurement by means of Karl Fischer reagent can be achieved by supplying the moisture evaporated by heating the materials into the unit 1 together with an inert gas and by inputting the weight of materials before they are heated. The moisture measuring unit 1 in this embodiment executes a coulometric titration. The value titrated and analyzed by the unit 1 is converted into an electrical signal and sent to the calculating unit 10, as is the weight value measured by the weight measuring unit 2. Thus the value titrated and analyzed by the moisture measuring unit 1 and the weight value measured by the weight measuring unit 2 are input into the calculating unit 10, the moisture content being calculated and sent to a temperature controller C . The controller C is provided with a setting device 11 to set the most appropriate value for the moisture content of materials by a dial or push-button operation, whereby the moisture content of materials to be dried is controlled. After the moisture content of sampled materials is calculated in the calculating unit 10, the controller C compares the obtained moisture content with the moisture content settled by the settling device 11, reads a data table prepared in advance for controlling temperature and controls the temperature of drying means A such as a hopper dryer by sending a control signal into a heating part 12 so as to compensate for deviation of the measured moisture content from the required value. An inert gas feed port 6a is provided at the lower part of the heat chamber 3 in the moisture station B and connected through a control valve 6b to a gas source 6 which feeds an inert gas such as a dried nitrogen gas or helium gas. The heat treatment chamber 3 is equipped with a heating means 4 at its periphery constructed by Nesa electrodes or a well-known Nichrome wire. If the heating means is constructed by Nesa electrodes, the materials in the heat chamber 3 can be seen through and also the body of chamber 3 can be made thin and compact. The heat treatment chamber 3 is heated to and maintained at a temperature just below that at which the stored materials are vaporized in order to evaporate all the moisture contained in the materials. For this purpose, a temperature control unit 4a sets and controls the most appropriate temperature of the chamber 3 before containing materials depending on the materials to be heated therein. According to this system, when sampling is required, the damper 5 is shut and the control valve 1a is closed to close the branch pipe P2 leading to the moisture measuring unit 1. At the same time the control valve 7a and the vent valve 7b are opened and the rotary valve 8a is driven in rotation while an inert gas is introduced into the chamber 3 by opening the control valve 6b, samples thus being supplied into the chamber 3. At this time the vent valve 7b is opened to atmosphere to prevent air from entering into the chamber 3. After a fixed amount of powdered or granular materials dried in the drying means is thus contained in the chamber 3, the control valve 7a and the vent valve 7b are closed with the damper 5 still closed. The control valve 1a is opened to open the branch pipe P2 leading to the moisture measuring unit 1 while the control valve 6b is opened to introduce an inert gas from the lower part of chamber 3 into all over the inside thereof. Under these conditions, powdered or granular materials are heated in the chamber 3 and the moisture produced by the evaporation of heated materials is supplied into the moisture measuring unit 1 together with the introduced inert gas. The supply of inert gas continues until the measuring unit 1 detects the end of titration. When the unit 1 detects its end, a display 10a of calculating unit 10 shows a sign indicating the end of titration. After the heat treatment of powdered or granular materials is thus finished, the materials in the chamber 3 are supplied into the weight measuring unit 2 by opening the control damper 5. In the unit 2 the materials received at the receiver 21 are weighed and the value is converted into an electrical signal by the signal processor 2a then sent to the calculating unit 10, wherein data sent from the moisture measuring unit 1 and the weight measuring unit 2 are calculated and the obtained moisture content of the materials is monitored and shown on the display 10a of calculating unit 10. The moisture content of sampled materials thus calculated in the calculating unit 10 is sent to the temperature controller C in the form of electrical signal and compared with the moisture content settled by the setting device 11. A heat control signal to compensate the deviation of two moisture contents is sent to the heating part 12 of drying means A. Consequently, the materials in the drying means A are heated and dried so as to get the moisture content settled by the setting device 11. Figure 2 shows a schematic diagram showing another preferable embodiment according to the present invention. In this system a rotary valve 8b in a material supply means 8A of moisture measuring/operating station B does not work as a measuring device. A fixed amount of powdered or granular materials is weighed by a material measuring chamber 9 having a detection sensor S to detect the level of materials and provided between the material supply means 8A and a heat treatment chamber 3. Materials are supplied into the material measuring chamber 9 by opening a control valve 7a until the sensor S detects that supplied materials reach a determined level. After a fixed amount of materials is stored in the chamber 9, the materials are supplied into the heat chamber 3 by opening a first control damper 51 provided between the measuring chamber 9 and the heat chamber 3. A second control damper 52 to discharge the heated materials and a weight measuring unit 2 are provided under the heat treatment chamber 3, the heated materials to be titrated and analyzed being weighed by the measuring unit 2. A calculating unit 10 calculates data sent from a moisture measuring unit 1 and the weight measuring unit 2 and indicates the obtained moisture content of the materials on its display 10a. And other constructions are the same as the above-mentioned first system. Figure 3 is a schematic diagram showing still another preferable embodiment according to the present invention. This system is characterised by a pneumatic transporting means 81 having an injection nozzle equipped at a discharge port provided at the lower part of a hopper dryer A as a drying means. Powdered or granular materials are taken out of the hopper dryer A by feeding a pressurized gas into the transporting means 81 and supplied through a transport pipe line P4 by a pneumatic transportation into a moisture measuring/operating station B . The numeral 83 indicates a unit to dehumidify and dry a gas to be supplied into the hopper dryer A . The materials pneumatically transported by a pressurized gas by the use of such a transporting means 81 are separated from the gas by a filtering device 14 provided at the entrance of measuring chamber 9 of moisture measuring/operating station B . A capacitance level sensor S is provided with the measuring chamber 9 as a weight detection sensor, the sensor S controlling open and close operations of a control valve 7a to store a fixed amount of materials in the chamber 9. A fixed amount of materials stored in the chamber 9 falls into a heat treatment chamber 3 by opening a first control damper 51 to be stored therein. At this time an inert gas introduced from a feed port 6a provided at the lower part of the heat chamber 3 is bled to atmosphere from the filtering device 14 passing through the heat chamber 3 and the measuring chamber 9. Therefore, both chambers 3 and 9 are prevented from entering of outer air and can be kept under dried circumstances which are suitable for titrating and analysing moisture content. The pneumatic transporting means 81 according to this system includes the pressurized gas injection nozzle provided at the initial end side of discharge port of hopper dryer (gas source side) and materials are sucked by injecting a pressurized gas from the nozzle by operating the gas source (not illustrated), that is well known as an ejecting effect. Such a pneumatic transporting means 81 has been already disclosed in Japan by the present applicant. Materials stored in the hopper A are taken out into the transport pipe line P4 and transported pneumatically when a pressurized gas injected from the nozzle creates negative pressure at the discharge port side of hopper A by the effect of ejection. This transporting means 81 is free from clogging caused at the beginning of suction operation because the apparent area of suction port becomes larger than that of a conventional suction nozzle having the same calibre, whereby a small amount of materials can be pneumatically transported by the use of a thin transport pipe. The system in Figure 3 is also characterized by including a material storing chamber 13 to store at least more than one sample of materials provided under the heat treatment chamber 3 in the moisture measuring/operating station B . A layer of powdered or granular materials to be heated is piled on a layer of materials stored in the storing chamber 13 and heated in the chamber 3. After the materials of upper layer are heated in the chamber 3, the materials in the storing chamber 13 are discharged by gravitational fall when a valve disc 52a of control damper 52 is opened. A level sensor S1 is provided with the storing chamber 13 as a weight detection sensor in order to control the amount of discharge, whereby immediately after one sample of materials is discharged, the valve disc 52a of damper 52 is closed, control valves 7a and 6b are opened and an inert gas is introduced into the chamber 13. At the same time a fixed amount of materials newly sampled by the pneumatic transporting means 81 is supplied into the heat treatment chamber 3. According to this system in which the material storing chamber 13 is provided under the heat treatment chamber 3, powdered or granular materials which have been already heated are stored in the storing chamber 13. Therefore, the chamber 3 is prevented from losing the heat by the supply of materials, contrary, the retained heat of materials can be applied to the above layer of materials, whereby an energy-saving system and quick analysis can be achieved. Further according to this system, an inert gas is introduced into the heat chamber 3 by opening the control valve 6b when a new sample of materials is supplied. So, this system is more effective in bringing uniformity to the temperature in the heat chamber 3 because the inert gas works as a medium to transfer the heat of materials which have been already heated and also maintaining the temperature in the chamber 3. Furthermore according to this system, the weight of materials may be measured before heating by sampling a fixed amount of materials and feeding through the chamber 3 without executing heat treatment into the weight measuring unit 2. In this case, as the weight of the materials measured by the measuring unit 2 differs from that of heated materials, the average weight of sampled materials, which are not heated, taken out at a few times may be used as the weight data in order to consider the difference between both weights. Figure 4 illustrates the partially enlarged sectional view of another preferable construction of moisture measuring/operating station B . A pneumatic transporting means 81 is provided at a discharge port at the lower part of hopper dryer A constructing the drying means and the upstream end of a transport pipe line P4 extended from the transporting means 81 is connected to a feed port formed at the upper end of material measuring chamber 9 of material measuring/operating station B . The station B includes a heat treatment chamber 3 having a heating means 4 constructed by winding a Nichrome wire under the material measuring chamber 9 interposed by a first control damper 51, a material storing chamber 13, described heretofore, provided under the heat chamber 3, a second control damper 52 under the chamber 13, and a weight measuring unit 2 having a receiver 21 to receive powdered or granular materials discharged from a material discharge port 13b of the storing chamber 13 under the damper 52. Capacitance level sensors S and S1 are provided as a weight detection sensor for the measuring chamber 9 and the storing chamber 13 respectively. The transport pipe line P4 connected with the transporting means 81 at its downstream end is connected to the upper end of measuring chamber 9 and a filtering unit 14 to separate the transported materials from a pressurized gas is provided at the side of the chamber 9. The first control damper 51 provided between the measuring chamber 9 and the heat chamber 3 includes a solenoid-operated highly airtight valve disc 51a. The solenoid-operated second control damper 52 disposed under the storing chamber 13 is constructed so as to be able to introduce an inert gas by filling a breathable ceramic material 53 in a gas introduction pipe 54 even if a valve disc 52a is closed, as described hereinafter. The numeral 1a indicates a control valve interposed in the branch pipe P2 leading to a moisture measuring unit 1 (illustrated in Figure 3) from the upper part of heat treatment chamber 3. The temperature control of the drying means A is executed like the system shown in Figure 1. For this purpose the temperature controller C s provided with the setting device 11 for moisture content, receiving the signal from the calculating unit 10 of moisture measuring/operating station B and sending a control signal to the heating part 12 of drying means A . The valve disc 52a of control damper 52 is provided with a valve port 52b to discharge the materials and filled with the breathable ceramic material 53 so as to close a material discharge port 13b constructed under the heat chamber 3 when the valve disc 52a is at closed position. The gas introduction pipe 54 having one opened end is provided with the ceramic material 53 and the opening of the pipe 54 is connected with a gas feed pipe P3' leading to a pressurized and dried inert gas source 6'. According to such a construction, as the valve port 52b conforms to the discharge port 13b when the damper 52 is opened, powdered or granular materials contained in the chamber 13 are discharged by gravitational fall through the port 13b. When the damper 52 is closed, the ceramic material 53 closes the port 13b and prevents the discharge of materials. However, an inert gas entered from the gas introduction pipe 54 successively goes into the heat chamber 3 because the gas can pass through the ceramic material 53, thus the replacement by an inert gas, as described heretofore, and the supply of inert gas when materials are heated can be achieved. In the above-mentioned embodiments a construction in which sampled materials are weighed before heating or after heating by the weight measuring unit 2 is explained. However, such a weight measuring unit 2 may be removed and the apparent specific weight and the volume of sampled materials may be input into a calculating unit 10. Such a system can further simplify the construction thereof because of the removal of weight measuring unit 2 and is more effectively used for the moisture control of the same kind of powdered or granular materials. In this case, the system may be preferably constructed such that the volume of sampled materials is input into the calculating unit 10 automatically.

Claims: An on-line drying control method for powdered or granular materials wherein the moisture content of the materials is detected and set at predetermined value by executing the following steps repetitively each time a fixed amount of materials is sampled, characterized by the steps of: directly transporting the materials into a heat treatment chamber (3) having a gastight heating means (4) after sampling and measuring a fixed volumetric amount of materials stored in a drying unit (A) associated with a temperature controller (C) for controlling heating means (12) in the drying unit; heating the materials in said heat treatment chamber (3) while supplying the chamber with a pressurized and dried inert gas; titrating and analysing moisture generated by heating the materials in said heat treatment chamber (3) by supplying the moisture, together with inert gas, to a moisture measuring unit (1); measuring the weight of the heated materials discharged from the chamber (3) into a receiver (21) of a weight measuring unit (2) provided under said heat treatment chamber (3); automatically calculating the moisture content of said sampled materials by feeding the moisture value detected in said moisture measuring unit (1) and the weight value measured in said weight measuring unit (2) to a calculating unit (10); comparing a target predetermined moisture content with the moisture content output from said calculating unit (10) in said temperature controller (C), by reference to a preprepared temperature control table; and executing feedback control of said heating means (12) so that the moisture content of the materials becomes the target predetermined moisture content set in said temperature controller (C). An on-line drying control system for powdered or granular materials wherein materials stored in a drying unit (A) having a heating means (12) is controlled so as to have a predetermined value of moisture content by sampling a fixed volumetric amount of materials stored in said drying unit (A), characterized in that said system comprises: a valve (8a) for sampling and measuring a fixed amount of powdered or granular materials stored in said drying unit (A); a heat treatment chamber (3) having a gastight heating means (4) and having sufficient capacity to contain the fixed amount of sampled materials, said heat treatment chamber (3) being disposed under said valve (8a); a transport pipe (P1) between said valve (8a) and said heat treatment chamber (3), said transport pipe (P1) having a control valve (7a) to control supply of materials from said valve (8a) and having a gas vent valve (7b) for opening to atmosphere; a moisture measuring unit (1) connecting to an upper part of said heat treatment chamber (3) via a branch pipe (P2) having a control valve (1a); a control damper (5) disposed under said heat treatment chamber (3) to discharge the materials stored in said heat treatment chamber (3); an inert gas feeding means (6) having a feed port (6a) at a lower part of said heat treatment chamber (3) and having a feed pipe (P3) incorporating a control valve (6b) for controlling introduction of pressurized and dried inert gas into said heat treatment chamber (3); a weight measuring unit (2) disposed under said control damper (5) for measuring the weight of the heated materials; a calculating unit (10) which calculates the moisture content of the materials utilising the weight value of the heated materials obtained from said weight measuring unit (2) and the moisture value from said moisture measuring unit (1) each time a fixed amount of materials is sampled; and a temperature controller (C) connected with said calculating unit (10) for feedback control of said heating means (12), the moisture content of materials to be controlled being set as a target value in said temperature controller (C) in advance, and said controller (C) comparing the predetermined moisture content with the moisture content output from said calculating unit (10), with reference to a preprepared temperature control table, and executing feedback control of said heating means (12) so that the moisture content of the materials stored in said drying unit (A) becomes the target value set in said controller (C). An on-line drying control system for powdered or granular materials as set forth in claim 2, characterized in that said system further comprises a materials measuring chamber (9) with a level detection sensor (S) for detecting the stored amount of materials under said valve (8a) and a supplementary control damper (51) disposed between said materials measuring chamber (9) and said heat treatment chamber (3), wherein said materials stored in said drying unit (A) are sampled and measured with said supplementary damper (51) closed. An on-line drying control system for powdered or granular materials as set forth in claim 2, characterised by: a pressurized transport means (81) including a pressurized gas injection port connecting said material discharge port of said drying unit (A) with said heat treatment chamber (3) via said valve (8a); the powdered or granular materials in said drying unit (A) being sampled and pneumatically transported to said heat treatment chamber (3) by pressurized transport means (81). An on-line drying control system for powdered or granular materials as set forth in claim 3, characterized by: a pressurized transport means (81) connecting the materials discharge port of said drying unit (A) with said materials measuring chamber (9) having the level detection sensor (S) via said valve (7a), and a pressurized gas injection port in said pressurized transport means (81), and the powdered or granular materials in said drying unit (A) are sampled and pneumatically transported to said measuring chamber (9) by said pressurized transport means (81).

Inventors: HIROSHI OGIRI ROOM KURERU KIBO, KAZUE MURATA, SADAAKI TANAKA, HIROSHI, OGIRI,, KAZUE, MURATA, SADAAKI, TANAKA, HIROSHI, OGIRI, ROOM 706 KURERU KIBOUGAOKA
Applicants: MATSUI MFG CO, KABUSHIKI KAISHA MATSUI SEISAKUSHO
Application year: 1990
Main classification: G05D22
IPC codes: B29B13, G05D22, F26B25