Title of Invention	"CLEANING METHOD FOR VACUUM FILTRATION APPARATUS AND VACUUM FILTRATION APPARATUS"
Abstract	A cleaning method for a vacuum filtration apparatus including: a filtering cloth for carrying a slurry and running in a substantially horizontal direction; a vacuum tray disposed under the filtering cloth; a vacuum line connected to the vacuum tray; a vacuum suction device for performing vacuum suction of the slurry via the vacuum line, the vacuum tray, and the filtering cloth; and a cleaning liquid supply device for supplying a cleaning liquid to the vacuum tray.  The cleaning method includes measuring a vacuum pressure in the vacuum line, and cleaning the vacuum tray based on the vacuum pressure.

Title of Invention

"CLEANING METHOD FOR VACUUM FILTRATION APPARATUS AND VACUUM FILTRATION APPARATUS"

Abstract

A cleaning method for a vacuum filtration apparatus including: a filtering cloth for carrying a slurry and running in a substantially horizontal direction; a vacuum tray disposed under the filtering cloth; a vacuum line connected to the vacuum tray; a vacuum suction device for performing vacuum suction of the slurry via the vacuum line, the vacuum tray, and the filtering cloth; and a cleaning liquid supply device for supplying a cleaning liquid to the vacuum tray.  The cleaning method includes measuring a vacuum pressure in the vacuum line, and cleaning the vacuum tray based on the vacuum pressure.

Full Text	CLEANING METHOD FOR VACUUM FILTRATION APPARATUS AND VACUUM FILTRATION APPARATUS BACKGROUND OF THE INVENTION Priority is claimed on Japanese Patent Application No 2004-275815, filed September 22,2004, the contents of which are incorporated herem by reference Field of the Invention The present invention relates to a cleaning method for a vacuum filtration apparatus and a vacuum filtration apparatus which filters slurry provided on a filtering cloth running m a substantially honzontal direction, by performing vacuum suction of the slurry using a vacuum tray disposed under the filtenng cloth Description of Related Art Refinement operations have been performed which, by performing filtenng operations, separate mother liquor from slurry and extract crystal components, or punfy the crystal components For example, when extracting crystal components of an organic matter dissolved in a solvent by separating the crystal components from the mother liquor, conventionally, such extraction has been performed using a centnfuge, a contmuous-type filtering machine, or honzontal tray filters, etc In such a case, liquid is cooled when contacting and passing through a cake layer and a filtenng cloth, due to reasons such as (l) the liquid contaimng the crystal components being a saturated solution, and (n) at the beginning of the filtenng operations, the filtering cloth and an upper surface section (a grid plate) of a vacuum tray both being m a room temperature condition which is generally lower than operating temperatures, and the upper surface section having large heat capacity influences the thermal condition of the slurry As a result, crystal components are recrystallized and adhere, in particular, to through holes of the filtering cloth, and through holes and leg portions of the grid plate, thereby causing clogging of the through holes and blockage of a flow path of the filtered liquid This kind of problem occurs regardless of the type of the machine (1 e, a batch operation type or a contmuous operation type) and remarkably lowers filtering performance As a result, crystal components having higher purity cannot be obtained and yield is lowered For these reasons, periodical cleaning of the filtering cloth and the grid plate is required, thereby causing lowered availability of the machine This land of problem also anses in the case in which the above-mentioned mechanical filtering operations are performed for purifying eutectic slurries or crystal components of solid solutions In the case in which the temperature difference between the dissolution temperature of the crystals of organic matter dissolved in the solvent and the crystal extraction temperature is less than 10 C, or in the case in which crystal components having a dissolution temperature of equal to or less than 30 C are recrystallized by separating it from mother liquor, the above-mentioned problem can be solved by utilizmg a special filtering apparatus such as the one disclosed m Japanese Unexamined Patent Application, First Publication No H02-126902 However, in order to extract crystal components having temperature conditions beyond the above using the above-mentioned apparatus, the apparatus needs to be modified correspondingly As a result, problems arise, in which the structure of the apparatus becomes complex and thereby the construction cost thereof increases In order to solve the problems explained above, for example, Japanese Patent No 3,497,206 discloses a cleaning method for a vacuum filtration apparatus, in which liquid containing crystal components is separated via a filtering cloth into the crystal components and mother liquor by vacuum trays disposed under the filtering cloth In this cleaning method, in some of the vacuum trays, crystals adhered to the underside of the filtering cloth are collected by dissolving them by supplying a tray cleaning liquid on the underside of the filtering cloth and filling the vacuum trays with it On the other hand, the other vacuum trays are operated as a vacuum tray for forming a cake, a vacuum tray for washing a cake, and vacuum tray for drying a cake, and the same kind of cleaning operations are performed for each of these vacuum trays However, when extracting the crystal components of the organic matter dissolved in the solvent by separating it from the mother liquor as explained above m the above-mentioned vacuum filtration apparatus, all of the plural vacuum trays are normally accommodated in a gastight room and are thus shielded from the outside In this case, smce the vacuum trays are enclosed in the gastight room, it is difficult to confirm the status of the crystals adhered onto the grid plate and the filtering cloth Therefore, timing for supplying the tray cleaning liquid to the underside of the filtering cloth has to be set to the time after which operating time determined in advance has passed However, in this case, although the tray cleaning liquid is supplied every time at the same timing, there are cases in which the amounts of crystals adhered onto the filtering cloth change dependmg on, for example, fluctuations of operating status etc of the vacuum filtration apparatus Accordingly, there are cases m which the grid plate is cleaned although it does not need cleaning, or conversely, the grid plate is not cleaned although it needs cleaning That is, there is a problem in that it is difficult to perform cleaning at a good timing If the timing for the cleaning is late, then filtering performance of the vacuum filtration apparatus will be lowered and inadequate cleaning or inadequate drying will happen, thereby causing deterioration in the product quality On the other hand, if the timing for the cleaning is too early, then the tray cleaning liquid will be wasted The present invention was made in view of the above circumstances and an object thereof is to provide a cleaning method for a vacuum filtration apparatus, and a vacuum filtration apparatus, both of which can smoothly remove crystals deposited on and adhered to a filtenng cloth and a grid plate at a good timing, thereby preventing cloggmg of through holes and blockage of a flow path for the filtered liquid SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a cleaning method for a vacuum filtration apparatus including a filtering cloth for carrymg a slurry and running m a substantially horizontal direction, a vacuum tray disposed under the filtenng cloth, a vacuum line connected to the vacuum tray, a vacuum suction device for performing vacuum suction of the slurry via the vacuum line, the vacuum tray, and the filtenng cloth, and a cleaning liquid supply device for supplymg a cleaning liquid to the vacuum tray The cleaning method mcludes measuring a vacuum pressure m the vacuum line, and cleaning the vacuum tray based on the vacuum pressure In addition, in order to achieve the above object, the present invention also provides a vacuum filtration apparatus including a filtenng cloth for carrying a slurry and running m a substantially honzontal direction, a vacuum tray disposed under the filtenng cloth, a vacuum line connected to the vacuum tray, a vacuum suction device for performing vacuum suction of the slurry via the vacuum line, the vacuum tray, and the filtenng cloth, a cleaning liquid supply device for supplying a cleaning liquid to the vacuum tray, a vacuum pressure measunng device for measunng a vacuum pressure m the vacuum line, and a control device for making the cleaning liquid supply device supply the cleamng liquid to the vacuum tray for cleaning the vacuum tray based on the vacuum pressure According to either one of the cleaning method for a vacuum filtration apparatus and the vacuum filtration apparatus of the present invention, timmg for supplymg cleaning liquid to the vacuum tray is determined based on the vacuum pressure in the vacuum line Thus, it becomes possible to confirm the amount of the crystal components of the slurry deposited and adhered onto a grid plate of the vacuum tray etc, regardless of fluctuations of operating status etc, of the vacuum filtration apparatus, and therefore, cleamng of the grid plate etc, can be performed at a good timing That is, the vacuum pressure will mcrease if the amount of the crystal components deposited on the grid plate etc, is large, while the vacuum pressure will decrease if the amount of the crystal components deposited on the grid plate etc, is small Thus, it can be arranged such that cleamng for the vacuum tray is performed when the vacuum pressure becomes higher than a predetermined value such as -40 kPaG By domg this, deterioration of product quality caused by insufficient cleaning or insufficient drying, and wasting of the cleamng liquid can be prevented Accordingly, since crystals deposited on the filtering cloth and the grid plate etc, can smoothly be removed at a good timing, clogging of through holes and blockage of a flow path of the filtered liquid can be prevented A plurality of the vacuum trays and corresponding vacuum lines may be provided along a running direction of the filtering cloth, and referring to the vacuum pressure in at least one of the vacuum lines, cleamng of the vacuum tray connected to the vacuum line to whose vacuum pressure referral is made may be performed Alternatively, a plurality of said vacuum trays and corresponding vacuum lines may be provided along a running direction of the filtering cloth, the vacuum pressures in each of the vacuum lines may be measured, and only the vacuum tray in which the vacuum pressure exceeds a predetermined value may be cleaned In these cases, it becomes possible to avoid cleaning of vacuum tray which does not need cleaning at the time, thereby preventing waste of cleaning liquid Accordingly, high-efficiency cleaning can be realized It may be arranged such that the vacuum tray is cleaned while the cleaning liquid is supplied such that the cleaning liquid overflows from the vacuum tray For example, if the cleaning liquid does not overflow from the vacuum tray and maintains a liquid-level of a predetermined height m the vacuum tray, there is a possibility that a liquid-surface portion of the cleaning liquid will cool through the cleaning processes, thereby resulting in temperature drop Therefore, there is a possibility that crystal components dissolved in the liquid-surface portion of the cleaning liquid will be recrystalhzed and deposited onto a wall surface of the vacuum tray contacting the liquid-surface portion In contrast, according to the present mvention, since the cleaning liquid is supplied such that it overflows from the vacuum tray, a standing fluid body will not be formed Accordingly, it becomes possible (1) to prevent recrystalhzation of the crystal components on the wall of the vacuum tray, (u) to prevent temperature drop of the cleaning liquid in the vacuum tray, and (in) to accelerate dissolution of the crystal components deposited onto the grid plate etc , into the cleaning liquid As a result, insufficient cleaning can be prevented Furthermore, by raising the height of the liquid surface of the cleaning liquid by making it overflow from the vacuum tray, close to the underside of the filtering cloth, not only the gnd plate but also the lower surface of the filtenng cloth can be immersed in the cleaning liquid As a result, the crystal components of the slurry deposited onto the ower surface of the cleaning cloth can be cleaned and removed The cleaning method for a vacuum filtration apparatus may further include maintaining a temperature of the cleamng liquid higher than a recrystallization temperature of a crystal component contained in the slurry Alternatively, the vacuum tray may include a vacuum tray for forming a cake, a vacuum tray for washing a cake, and a vacuum tray for drying a cake, each arranged along a running direction of the filtenng cloth, and the vacuum pressure measunng device and the cleamng liquid supply device may be provided at least for the vacuum line connected to the vacuum tray for drying a cake At the vacuum tray for drying a cake, since the amount of mother liquor contained m the slurry is small and since the amount of a gas to be sucked is large, temperature of the filtered liquid easily drops, thereby resulting m the recrystallization of the crystal components especially onto the grid plate etc In contrast, according to the present invention, since the vacuum tray for drying a cake m which the crystal components are easily deposited is provided with the vacuum pressure measunng device and the cleamng liquid supply device, the recrystalhzed crystal components can be effectively dissolved and removed Especially, if a plurality of vacuum trays for drying a cake and corresponding vacuum lines are provided, and if a vacuum pressure measunng device and the cleamng liquid supply device are provided to each of the vacuum lines, it becomes possible to continue drying processes of the vacuum trays for drying a cake while one of the vacuum tray for drying a cake is in cleaning As a result, it becomes possible to perform cleamng without stopping suction filtrations of the filter liquid in the vacuum filtration apparatus, thereby realizing high-efficiency cleamng operations BRIEF DESCRIPTION OF THE DRAWINGS FIG 1 is a general arrangement diagram showing one embodiment of a vacuum filtration apparatus according to the present invention FIG 2 is a side view of the vacuum filtration apparatus FIG 3 is a partially-enlarged cross sectional view of a vacuum tray shown in FIG 2 along the line A-A shown in FIG 2 DETAILED DESCRIPTION OF THE INVENTION Hereinafter, one embodiment of a cleaning method for a vacuum filtration apparatus and of a vacuum filtration apparatus of the present invention will be explained with reference to FIGS 1 to 3 As shown in FIG 1, the vacuum filtration apparatus of the present embodiment is provided with an apparatus main body 10, a vacuum line 20, a vacuum suction device 30, and a room temperature control lme 50 Detailed explanations for each of the apparatus main body 10, the vacuum line 20, the vacuum suction device 30, and the room temperature control line 50 will be made in the following As shown in FIG 2, the apparatus main body 10 includes a plurality of rollers 12 and an endless-belt-shaped filtermg cloth 11 wrapped around the rollers 12 An upper side portion of the filtering cloth 11 forms a filtering section 11A arranged such that it extends towards horizontally A roller 12A disposed on one side of the filtering section 11A and wrapped by the filtering cloth 11, is connected to a dnving device (not shown in the figures) The roller 12A is rotationally driven in the clockwise direction in FIG 2 by the driving device, thereby rotationally dnving the filtermg cloth 11 around the rollers 12 Along with the rotation of the filtenng cloth 11, the filtering section 11A of the filtenng cloth 11 continuously runs in the running direction of an anow F shown in FIG 2 A plurality (five m the present embodiment) of vacuum trays 16 each connected to a vacuum suction device 30 are provided under the filtering section 11A from a position just under a slurry supply device 13 (to be explained later) along the running direction F of the filtering section 11A Among these vacuum trays 16, a vacuum tray 16A disposed at the beginning side in the running direction F and just under the slurry supply device 13 is used for forming a cake (hereinafter "a tray 16A for forming a cake"), a vacuum tray 16B disposed adjacent to the tray 16A for forming a cake and substantially just under a cake washing device 21 (to be explained later) is used for washing the cake (hereinafter "a tray 16B for washing a cake"), and a plurality of vacuum trays 16C, 16D, and 16E disposed adjacent to the tray 16B for washing a cake and also disposed along the running direction F are used for drying (hereinafter, the vacuum trays 16C to 16E each referred as "a first tray 16C for drying a cake ", "a second tray 16D for drying a cake", and "a third tray 16E for drying a cake") The vacuum trays 16 adjacent to each other along the running direction F are jomed to each other As shown m FIG 2, a driving cylinder 18 such as an air cylinder attached to a frame 10A of the apparatus main body 10 and extendable towards the runnmg direction F is joined to the vacuum tray 16 disposed at the beginning side in the running direction F (I e, the tray 16A for forming a cake) among the vacuum trays 16A With this driving cylinder 18, all of the vacuum trays 16 are able to move as one unit forwards and backwards along the runnmg direction F at a predetermined stroke That is, all of the vacuum trays 16 can move forwards and backwards along the running direction F As shown in FIG 2, the apparatus mam body 10 is provided with a pair of rails 22 provided at both sides in the width and at the bottom side of the vacuum trays 16 and extending along the running direction F, and a plurality of rotatable support wheels 19 each contacting the corresponding vacuum trays 16 from the lower side thereof thereby supporting the vacuum trays 16, and having spaces therebetween along the width of the filtering cloth 11 The vacuum trays 16 are able to move forwards and backwards on the rotatable support wheels 19 On the other hand, each of the support wheels 19 is driven to rotate along with the forwards and backwards movements of the vacuum trays 16 driven by the driving cylmder 18 Each of the support wheels 19 has the same size and the same shape, and is attached onto the frame 10A of the apparatus main body 10 via brackets and the like, facing upwards, such that each of the wheels 19 can freely rotate around a rotational axis extendmg horizontally along the width direction of the vacuum trays 16 Each or the support wheels 19 has either one of a disc shape having the rotational axis in the center and a high thickness, or a cylindrical shape having a short axis Furthermore, these support wheels 19 are arranged along edges on both sides in the width of the bottom faces of the vacuum trays 16, such that the support wheels 19 form two rows extending parallel to the running direction F Each of the support wheels 19 in each row is arranged such that they form constant gaps therebetween along the runmng direction F, each of the support wheels 19 adjacent to each other in the width direction between the rows forms a pair, and each member of each pair of the support wheels 19 has the same height, and the same honzontal position in the runmng direction F The slurry supply device 13 for supplying slurry S onto the filtering cloth 11 is provided above another end side (the left side in FIGS 1 and 2) of the filtering section 11A of the filtering cloth 11 (l e , above the beginning side in the running direction F) The slurry S supplied from the slurry supply device 13 onto the filtering cloth 11 moves m the runmng direction F m accordance with the movement of the filtering section 11 A, and at the same time, vacuum suction of the slurry S is performed by each of the vacuum trays 16 via the filtenng cloth 11, thereby filtenng The cake washing device 21 for supplying a cake washing liquid L onto the filtenng cloth 11 is provided above the position on the filtenng cloth 11 where is on the forward side than the slurry supply device 13 in the running direction F The cake washing device 21 supplies the cake washing liquid L to a cake layer made by performing vacuum suction of the slurry S A knife 14 is provided next to the filtering cloth 11 in order to scratch and remove a dned cake which has been filtered and dned from the filtering cloth 11 Furthermore, a filter-cleaning device 15 for cleaning the filtering cloth 11 from which the slurry S is removed by the knife 14 is provided at a position at one end side of the filtering section 11A of the filtenng cloth 11 (I e , on the nght side m FIG 1, or the end side m the running direction F and under the filtenng section 11 A) In the present embodiment, as shown in FIG 1, the above-mentioned apparatus 10, slurry supply device 13, and cake washing device 21 are accommodated m a gastight room R, and are shielded from the outside As shown in FIG 3, each of the vacuum trays 16 has a flat face portion 16F extending along a lower surface of the filtenng section 11A and contacting the lower surface of the filtenng section 11A at an upper surface thereof, and a pair of wall portions 16G each extending upwards and outwards from both ends in the width of the fiat face portion 16F such that a gap therebetween in the width becomes wider moving upwards The flat face portion 16F is a stacked member in which a gnd plate 161 having through holes 16J formed thereon is stacked on a plate 16H The upper surface side of the gnd plate 161 contacts the lower face of the filtenng section 11 A, while the lower surface side of the grid plate 161 is joined to the vacuum line 20 connected to the vacuum suction device 30 As shown in FIG 1, the vacuum suction device 30 is equipped with gas-and-liquid separation tanks 31 to 33 for separating filtered liquid recovered from the vacuum trays 16 into gas and liquid, a vacuum pump 34 connected to the gas-and-liquid separation tanks 31 to 33 and applying vacuum suction to the slurry S on the filtering section 11A through the gas-and-liquid separation tanks 31 to 33, and a cooler 35 which is connected between the gas-and-liquid separation tanks 31 to 33 and the vacuum pump 34, and cools gases exhausted from the gas-and-liquid separation tanks 31 to 33 m advance of passmg then through the vacuum pump 34 The first gas-and-liquid separation tank 31 is connected to the tray 16A for forming a cake, the second gas-and-liquid separation tank 32 is connected to the tray 16B for washing a cake, and the third gas-and-liquid separation tank 33 is connected to the first tray 16C for drying a cake, the second tray 16D for drying a cake, and the third tray 16E for drying a cake Each of the gas-and-liquid separation tanks 31 to 33 is provided with liquid level measuring devices 36 to 38 for measuring the amount of the filtered liquid recovered from the gas-and-liquid separation tanks 31 to 33, pumps 39 to 41 for filtered liquid for exhausting the filtered liquid from the gas-and-liquid separation tanks 31 to 33, and automatic valves SV1 to SV3 which open and close filtered-hquid exhaust ports of the gas-and-liquid separation tanks 31 to 33 based on measurement results of the liquid level measuring devices 36 to 38 A first temperature measuring device 42 for measuring the temperature of the gas is provided between the gas-and-liquid separation tanks 31 to 33 and the cooler 35 The cooler 35 is controlled by operating the opemng degree of a control valve CVl based on the measurement results of the first temperature measuring device 42, and as a result, the temperature of the gas is controlled The vacuum filtration apparatus of the present invention is equipped with the room temperature control line 50 connected to the vacuum pump 34 The room temperature control line 50 controls the temperature in the gastight room R by receivmg the gas cooled by the cooler 35 and by supplying the gas into the gastight room R after controlling the temperature of the gas The room temperature control Ime 50 includes a first heater 51 for heatmg the gas supplied from the vacuum pump 34, a second temperature measuring device 52 for measuring the temperature in the gastight room R, and a flow rate measuring device 53 for measuring a flow rate of the gas heated by the first heater 51 and flowing mto the gastight room R The vacuum filtration apparatus of the present invention is further equipped with a control valve CV2 for controlling the first heater 51 based on the measurement results of the second temperature measuring device 52, and a control valve CV3 for controlling the flow rate of the gas supplied into the gastight room R based on the measurement results of the flow rate measuring device 53 The gas of which the temperature and the flow rate are controlled by the above-mentioned devices flows into the gastight room R through an automatic valve V4 As shown in FIG 1, the vacuum line 20 includes a first vacuum Ime 20A connecting between a bottom face of the tray 16A for forming a cake and the first gas-and-hquid separation tank 31, a second vacuum line 20B connecting between a bottom face of the tray 16B for washing a cake and the second gas-and-hquid separation tank 32, and a third vacuum line 20C connecting between (l) the first tray 16C for drying a cake, the second tray 16D for drying a cake, and the third tray 16E for drying a cake, and (u) the gas-and-hquid separation tank 33 The first vacuum line 20A has a first header pipe 22, the second vacuum Ime 20B has a second header pipe 23, and the third vacuum Ime 20C has a third header pipe 24 The internal space of the third header pipe 24 connected to the first tray 16C for drying a cake through the third tray 16E for drying a cake, is divided by two partitioning plates 25 into three spaces each having substantially the same volume And each of these spaces is connected to one of the first tray 16C for drying a cake through the third tray 16E for drying a cake correspondingly In the following explanation, among the divided internal spaces in the third header pipe 24, the space connected to the first tray 16C for drying a cake is referred as "third header pipe 24A", the other space connected the second tray 16D for drying a cake is referred as "third header pipe 24B", and the other space connected the third tray 16E for drying a cake is referred as "third header pipe 24C" A tray cleaning liquid supply device 26 for supplying a tray cleaning liquid which can dissolve crystal components of the slurry S to the first tray 16C for drying a cake through the third tray 16E for drymg a cake, is provided between (l) the first tray 16C for drymg a cake through the third tray 16E for drying a cake and (u) the third header pipe 24A through the third header pipe 24C An automatic valve SV5 is provided between the third header pipe 24A and the tray cleaning liquid supply device 26, an automatic valve SV6 is provided between the third header pipe 24B and the tray cleaning liquid supply device 26, and an automatic valve SV7 is provided between the third header pipe 24C and the tray cleaning liquid supply device 26 A first vacuum pressure measuring device 27A for measuring vacuum pressure within a range from the vacuum suction device 30 to the part of the lower face of the filtering section 11A which an upper face of the first tray 16C for drying a cake faces, is provided to the third header pipe 24A A second vacuum pressure measuring device 27B for measuring vacuum pressure within a range from the vacuum suction device 30 to the part of the lower face of the filtenng section 11A where an upper face of the second tray 16D for drymg a cake faces, is provided to the third header pipe 24B A third vacuum pressure measuring device 27C for measuring vacuum pressure within a range from the vacuum suction device 30 to the part of the lower face of the filtermg section 11A which an upper face of the first tray 16E for drying a cake faces, is provided to the third header pipe 24C As shown in FIG 1, the tray cleaning liquid supply device 26 is provided with an automatic valve SV8 connected to the first tray 16C for drying a cake, an automatic valve SV9 connected to the second tray 16D for drying a cake, an automatic valve SVIO connected to the first tray 16E for drying a cake, a third temperature measuring device 26 A for measuring the temperature of the tray cleaning liquid before it is supplied into the first tray 16C for drying a cake through the third tray 16E for drying a cake, a second heater 26B for heating the tray cleaning liquid, a control valve CV4 for controlling the flow rate of a heating medium supplied to the second heater 26B based on the measurement results of the third temperature measuring device 26 A, and a pump (not shown in the figures) for supplying the tray cleaning liquid to the first tray 16C for drying a cake through the third tray 16E for drying a cake, via the automatic valves SV8 to SVIO By adopting this configuration, temperature of the tray cleaning liquid supplied to the first tray 16C for drying a cake through the third tray 16E for drying a cake via the automatic valves SV8 to SVIO, is controlled such that the temperature becomes 5 C to 10 C higher than the temperature at which crystallization of the mother liquor begins The vacuum filtration apparatus of the present embodiment is equipped with a controller which is not shown in the figures The vacuum pressure measuring devices 27A to 27C, the automatic valves SV5 to SV7 and SV8 to SVIO, and the above-mentioned pump of the tray cleaning device 26, are connected to the controller Output signals output from the vacuum pressure measuring devices 27A to 27C are transmitted through the controller to the pump and the automatic valves SV5 to SV7 and SV8 to SVIO That is, when the vacuum pressures measured by the vacuum measuring devices 27A to 27C are lower than a predetermined value (for example, -40 kPaG), the controller closes the automatic valves SV8 to SV10, opens the automatic valves SV5 to SV7, stops supplying the tray cleaning liquid into the first tray 16C for drying a cake to the third tray 16E for drying a cake, and supplies the filtered liquid recovered from the slurry S through the filtering section 11A into the third header pipe 24 On the other hand, when the vacuum pressures are higher than the predetermined value, the controller opens the automatic valves SV8 to SV10, closes the automatic valves SV5 to SV7, stops supplying the filtered liquid mto the third header pipe 24, and supplies the tray cleaning liquid mto the first tray 16C for drying a cake to the third tray 16E for drying a cake Based on the measurement results of the vacuum pressure measuring devices 27A to 27C, the controller opens and closes the automatic valves SV5 to SV7 and SV8 to SV10 respectively, thereby cleaning the first tray 16C for drying a cake to the third tray 16E for drying a cake respectively That is, the automatic valve SV5 and SV8 are opened and closed based on the measurement results of the first vacuum pressure measuring device 28A, the automatic valves SV6 and SV9 are opened and closed based on the measurement results of the second vacuum pressure measuring device 28B, and the automatic valves SV7 and SV10 are opened and closed based on the measurement results of the third vacuum pressure measuring device 28C Next, the way to use the vacuum filtration apparatus having the above-mentioned configuration will be explained Firstly, in normal operation, the same as in conventional apparatuses, the slurry supply device 13 supplies the slurry S onto a position of the filtering section 11A which is above the tray 16A for forming a cake, and vacuum pressure applied onto the tray 16A for forming a cake will suck and filter the liquid in the slurry S, and thereby form a cake Subsequently, the cake layer is moved and disposed above the tray 16B for washing a cake by the filtering section 11A Then, the cake washing device 21 will provide the cake washing liquid L onto the cake layer, thereby washing the cake Furthermore, this cake layer is dned by carrying it sequentially from the first tray 16C for drying a cake to the third tray 16E for drying a cake Meanwhile, the filtered liquids recovered by each of the vacuum trays 16 will pass through the header pipes 22 to 24, and will be introduced into the corresponding gas-and-hquid separation tanks 31 to 33, and thereby separated into gas and liquid Liquid levels of the filtered liquids in the gas-and-hquid separation tanks 31 to 33 are continuously measured by the corresponding liquid level measurmg devices 36 to 38, and based on the measurement results, the filtered liquids in the gas-and-hquid separation tanks 31 to 33 are transferred to the arbitrary processes through the pumps 39 to 41 for filtered liquid and the automatic valves SV1 to SV3 On the other hand, since each of the gasses exhausted from the gas-and-hquid separation tanks 31 to 33 contains a little solution, the solution is thermally condensed and is removed by making the gasses pass through the cooler 35, and is subsequently returned into the second gas-and-hquid separation tanks 32 By performing this process, the gas sucked by the vacuum pump 34 is made to be in a dried condition, and is subsequently returned into the gastight room R through the room temperature control line 50 At this time, since temperature of the gas needs to be maintained higher than the crystal-depositing temperature of the mother liquor, temperature in the gastight room R is regularly measured by the second temperature measuring device 52 And, corresponding to an output from the second temperature measuring device 52, the temperature of the gas is controlled by the first heater 51 and the control calve CV2, such that the temperature becomes 5°C to 20°C higher than the temperature at which the mother liquor begins crystallization By performing this process, the temperature in the gastight room R is maintained in a constant temperature condition having a predetermined temperature In the temperature of the cake washing liquid L is also regularly measured by a fourth temperature measuring device (not shown in the figures) In addition, corresponding to the measurement results of the fourth temperature measuring device, the temperature of the cake washing liquid L is controlled such that the temperature becomes 5°C to 10 C higher than the temperature at which the mother liquor begins crystallization By performing this process, the temperatures of the mother liquor and the filtered liquid are maintained higher the temperature at which the mother liquor begins crystallization As a result, it becomes possible to prevent deposition of the crystals and to obtain stable operation for many hours However, even when the vacuum filtration apparatus is operated with the above-mentioned countermeasures in order to prevent deposition of the crystals, there is a possibility that the crystal components of the slurry S will adhered to the lower surface of the filtering section 11 A, and to the grid plates 161 of the first tray 16C for drying a cake through the third tray 16E for drying a cake Hereinafter, a case in which the crystal components are stacked and adhered onto the first tray 16C for drying a cake will be explained In this case, vacuum pressure between (l) the part of the lower face of the filtering section 11A which corresponds to the first tray 16C for drying a cake and (u) the vacuum suction device 30 rises And, if the first vacuum pressure measuring device 27A provided on the third header pipe 24A detects that the vacuum pressure becomes higher than the predeterrmned value, then an output signal from the first vacuum pressure measuring device 27A is transmitted to the automatic valves SV8 and SV5 and the pump through the controller As a result, the automatic valve SV8 will open and the automatic valve SV5 will close Then, while vacuum suction by the first tray 16C for drying a cake is stopped, the tray cleaning liquid in which the flow rate and the temperature are controlled m advance by the tray cleaning liquid supply device 26 will be supplied into the first tray 16C for drying a cake On the other hand, although the vacuum suction of the first tray 16C for drying a cake is stopped, vacuum suction operations by the other vacuum trays 16 (l e , the tray 16A for forming a cake, the tray 16B for washing a cake, the first tray 16C for drying a cake, the second tray 16D for drying a cake, and the third tray 16E for drying a cake) will be continued Filtering operation is continued for a predetermined time while the tray cleaning liquid introduced mto the first tray 16C for drying a cake overflows therefrom such that the grid plate 161 is immersed in the tray cleaning liquid and such that the lower surface of the filtering section 11A is dipped in the tray cleaning liquid Meanwhile, m accordance with the back-and-forth motions of each of the vacuum trays 16, the tray cleaning liquid will be automatically shaken, thereby performing an effective cleaning operation Especially, smce the tray cleaning liquid is supplied such that a little of the tray cleaning liquid overflows from the first tray 16C for drying a cake, the cleaning liquid contaimng the crystal components will not keep touchmg an inner wall of the first tray 16C for drying a cake and will not be cooled Therefore, recrystallization of the crystal components onto the inner wall can be prevented After a predetermined time has been passed, supply of the tray cleaning liquid is stopped by closmg the automatic valve SV8, and the tray cleaning liquid is recovered as a filtered liquid by opemng the automatic valve SV5 In order to clean the second tray 16D for drying a cake, the automatic valve SV6 is closed and the automatic valve S V9 is opened, and thereby a cleaning operation the same as the one mentioned above is performed Also, in order to clean the third tray 16E for drying a cake, the automatic valve SV7 is closed and the automatic valve SV10 is opened, and thereby a cleaning operation the same as the one mentioned above will be performed As explained above, according to the vacuum filtration apparatus of the present embodiment, since timing for supplying the tray cleamng liquid into the vacuum trays 16 is determined based on the vacuum pressure in the vacuum lme 20, it becomes possible to confirm the status of the crystal components deposited and adhered onto the grid plate 161 etc, regardless of fluctuations of operating status etc, of the vacuum filtration apparatus Accordingly, cleamng of the grid plate 161 etc, can be performed at a good timing That is, the vacuum pressure will increase if the amount of the crystal components deposited on the grid plate 161 etc , is large, while the vacuum pressure will decrease if the amount of the crystal components deposited on the grid plate 161 etc , is small Thus, it can be arranged such that the vacuum trays 16 are cleaned when the vacuum pressure becomes higher than a predetermined value such as -40 kPaG By doing this, deterioration of product quality caused by insufficient cleamng or insufficient drying, and wasting of the cleaning liquid can be prevented In addition, smce the vacuum pressure in the vacuum line 20 is measured for each of the first tray 16C for drying a cake through the third tray 16E for drying a cake, and since only a vacuum tray in which the vacuum pressure exceeds the predetermined value is cleaned, it becomes possible to prevent waste of cleamng liquid and to realize high-efficiency cleamng In addition, while cleaning the first tray 16C for drying a cake, by continuing drying processes of the second tray 16D for drying a cake and the third tray 16E for drying a cake, it becomes possible to continue cleamng operations without stopping suction filtrations of the filtered liquid in the vacuum filtration apparatus, thereby realizing high-efficiency cleamng operations Furthermore, smce suction filtration by the vacuum filtration apparatus is continued while the grid plate 161 is immersed in the tray cleamng liquid, the tray cleaning liquid will be automatically shaken, thereby realizing high-efficiency cleaning operations Furthermore, since the tray cleamng liquid is supplied into the vacuum trays 16 such that the tray cleamng liquid overflows from the vacuum trays 16, not only the grid plate 161 but also the lower face of the filtering section 11A can be dipped mto the tray cleamng liquid As a result, the crystal components deposited and adhered both to the grid plate 161 and to the filtering section 11A can be dissolved and removed satisfactorily That is, if each of the cleamng liquids does not overflow from the vacuum trays 16 and maintains a liquid-level of a predetermined height in the vacuum trays 16, there is a possibility that each of liquid-surface portions of the cleamng liquids will be cooled through the cleamng process, thereby resultmg in temperature drop thereof Therefore, there is a possibility that crystal components dissolved in the liquid-surface portions of the cleamng liquids will be recrystallized and deposited onto wall surfaces of the vacuum trays 16 contacting the liquid-surface portions In contrast, accordmg to the vacuum filtration apparatus of the present embodiment, smce the cleamng liquid is supplied such that it overflows from the vacuum trays 16, standing fluid body will not be formed Accordingly, it becomes possible (I) to prevent recrystalhzation of the crystal components on the walls of the vacuum trays 16, and (u) to prevent temperature drop of the cleamng liquids in the vacuum trays 16 As a result, dissolution of the crystal components deposited on the grid plate etc , into the cleamng liquid is accelerated, and thereby insufficient cleamng can be prevented Furthermore, by raismg the height of the liquid surface of the cleamng liquid so that it overflows from the vacuum trays 16, close to the underside of the filtering section 11 A, not only the grid plate 161 but also the lower surface of the filtering section 11A can be immersed in the cleaning liquid As a result, the crystal components of the slurry S deposited onto the lower surface of the filtering section 11A can be cleaned and removed Especially, according to the vacuum filtration apparatus of the present embodiment, since the temperature of the cleaning liquid is maintained higher than a recrystalhzation temperature of the crystal components, dissolution of the crystal components into the tray cleaning liquid can be further accelerated At the first tray 16C for drying a cake through the third tray 16E for drying a cake, since the amount of mother liquor contained in the slurry S is small and since the amount of gas to be sucked is large, the temperature of filtered liquid easily drops, thereby resultmg m the recrystalhzation of the crystal components especially onto the gnd plate 16 etc In contrast, according to the vacuum filtration apparatus of the present mvention, since the vacuum trays 16 in which the crystal components are easily deposited are provided with the vacuum pressure measuring devices 27A to 27C and the cleaning liquid supply device 26, the recrystalhzed crystal components deposited in the vacuum filtration apparatus can be effectively dissolved and removed In addition, according to the vacuum filtration apparatus of the present embodiment, even when one of the plurality of the first tray 16C for drying a cake through the third tray 16E for drying a cake is in cleaning, it is possible to contmue drying processes of the others, thereby enablmg realization of high-efficiency cleaning operations While a preferred embodiment of the invention has been described and illustrated above, it should be understood that this is exemplary of the invention and is not to be considered as limiting Additions, omissions, substitutions, and other modifications can be made without departing from the spirit or scope of the present mvention Accordingly, the invention is not to be considered as being limited by the foregoing description, and is only limited by the scope of the appended claims In the present embodiment, the first vacuum pressure measunng device 27A through the third vacuum pressure measunng device 27C and the cleaning liquid supply device 26 are provided to each of the vacuum lines 20 connected to the first tray 16C for drying a cake through the third tray 16E for drying a cake However, the configuration of the vacuum filtration apparatus of the present invention is not limited to this, but it is also possible to provide the first vacuum pressure measuring device 27A through the third vacuum pressure measunng device 27C and the cleaning liquid supply device 26, to one of the vacuum lmes 20 connected between the vacuum suction device 30 and one of the first tray 16C for drying a cake through the third tray 16E for drying a cake That is, for example, the vacuum pressure measunng device 27 and the cleaning liquid supply device 26 may be provided to only one of, or all of the first vacuum line 20A, the second vacuum lme 20B, and the third vacuum line 20C In addition, in the present embodiment, the tray cleaning liquid is automatically supplied into the vacuum trays 16, however, it may be possible to dispose the first vacuum pressure measunng device 27A through the third vacuum pressure measunng device 27C to the external of the gastight room R such that the vacuum pressures measured thereby can be viewed by an operator, and to allow manual control of the cleaning liquid supply device 26 etc, by an operator What is claimed is: 1. A cleaning method for a vacuum filtration apparatus including: a filtering cloth for carrying a slurry and running in a substantially horizontal direction; a vacuum tray disposed under the filtering cloth; a vacuum line connected to the vacuum tray; a vacuum suction device for performing vacuum suction of the slurry via the vacuum line, the vacuum tray, and the filtering cloth; and a cleaning liquid supply device for supplying a cleaning liquid to the vacuum tray, the cleaning method comprising: measuring a vacuum pressure in the vacuum line; and cleaning the vacuum tray based on the vacuum pressure. 2. The cleaning method for a vacuum filtration apparatus according to claim 1, wherein: a plurality of said vacuum trays and corresponding vacuum lines are provided along a running direction of the filtering cloth; and referring to the vacuum pressure in at least one of the vacuum lines, cleaning of the vacuum tray connected to the vacuum line to whose vacuum pressure is referral is made is performed. 3. The cleaning method for a vacuum filtration apparatus according to claim 1, wherein: a plurality of said vacuum trays and corresponding vacuum lines are provided along a running direction of the filtering cloth; the vacuum pressures in each of the vacuum lines are measured; and only a vacuum tray in which the vacuum pressure exceeds a predetermined value is cleaned. 4. The cleaning method for a vacuum filtration apparatus according to claim 1, wherein: the vacuum tray is cleaned while the cleaning liquid is supplied such that the cleaning liquid overflows from the vacuum tray. 5. The cleaning method for a vacuum filtration apparatus according to claim 1, further comprising maintaining a temperature of the cleaning liquid higher than a recrystallization temperature of a crystal component contained in the slurry. 6. A vacuum filtration apparatus comprising: a filtering cloth for carrying a slurry and running in a substantially horizontal direction; a vacuum tray disposed under the filtering cloth; a vacuum line connected to the vacuum tray; a vacuum suction device for performing vacuum suction of the slurry via the vacuum line, the vacuum tray, and the filtering cloth; a cleaning liquid supply device for supplying a cleaning liquid to the vacuum tray; a vacuum pressure measuring device for measuring a vacuum pressure in the vacuum line; and a control device for making the cleaning liquid supply device supply the cleaning liquid to the vacuum tray for cleaning the vacuum tray based on the vacuum pressure. 7. The vacuum filtration apparatus according to claim 6, wherein: the vacuum tray comprises a vacuum tray for forming a cake, a vacuum tray for washing a cake, and a vacuum tray for drying a cake, each arranged along a running direction of the filtering cloth; and a vacuum pressure measuring device and the cleaning liquid supply device are provided at least for the vacuum line connected to the vacuum tray for drying a cake.

Full Text

CLEANING METHOD FOR VACUUM FILTRATION APPARATUS AND VACUUM FILTRATION APPARATUS
BACKGROUND OF THE INVENTION
Priority is claimed on Japanese Patent Application No 2004-275815, filed September 22,2004, the contents of which are incorporated herem by reference
Field of the Invention
The present invention relates to a cleaning method for a vacuum filtration apparatus and a vacuum filtration apparatus which filters slurry provided on a filtering cloth running m a substantially honzontal direction, by performing vacuum suction of the slurry using a vacuum tray disposed under the filtenng cloth
Description of Related Art
Refinement operations have been performed which, by performing filtenng operations, separate mother liquor from slurry and extract crystal components, or punfy the crystal components For example, when extracting crystal components of an organic matter dissolved in a solvent by separating the crystal components from the mother liquor, conventionally, such extraction has been performed using a centnfuge, a contmuous-type filtering machine, or honzontal tray filters, etc In such a case, liquid is cooled when contacting and passing through a cake layer and a filtenng cloth, due to reasons such as (l) the liquid contaimng the crystal components being a saturated solution, and (n) at the beginning of the filtenng operations, the filtering cloth and an upper surface section (a grid plate) of a vacuum tray both being m a room temperature
condition which is generally lower than operating temperatures, and the upper surface
section having large heat capacity influences the thermal condition of the slurry As a
result, crystal components are recrystallized and adhere, in particular, to through holes of
the filtering cloth, and through holes and leg portions of the grid plate, thereby causing
clogging of the through holes and blockage of a flow path of the filtered liquid This
kind of problem occurs regardless of the type of the machine (1 e, a batch operation type
or a contmuous operation type) and remarkably lowers filtering performance As a
result, crystal components having higher purity cannot be obtained and yield is lowered
For these reasons, periodical cleaning of the filtering cloth and the grid plate is required,
thereby causing lowered availability of the machine This land of problem also anses in
the case in which the above-mentioned mechanical filtering operations are performed for
purifying eutectic slurries or crystal components of solid solutions
In the case in which the temperature difference between the dissolution temperature of the crystals of organic matter dissolved in the solvent and the crystal extraction temperature is less than 10 C, or in the case in which crystal components having a dissolution temperature of equal to or less than 30 C are recrystallized by separating it from mother liquor, the above-mentioned problem can be solved by utilizmg a special filtering apparatus such as the one disclosed m Japanese Unexamined Patent Application, First Publication No H02-126902 However, in order to extract crystal components having temperature conditions beyond the above using the above-mentioned apparatus, the apparatus needs to be modified correspondingly As a result, problems arise, in which the structure of the apparatus becomes complex and thereby the construction cost thereof increases
In order to solve the problems explained above, for example, Japanese Patent No 3,497,206 discloses a cleaning method for a vacuum filtration apparatus, in which liquid
containing crystal components is separated via a filtering cloth into the crystal
components and mother liquor by vacuum trays disposed under the filtering cloth In
this cleaning method, in some of the vacuum trays, crystals adhered to the underside of
the filtering cloth are collected by dissolving them by supplying a tray cleaning liquid on
the underside of the filtering cloth and filling the vacuum trays with it On the other
hand, the other vacuum trays are operated as a vacuum tray for forming a cake, a vacuum
tray for washing a cake, and vacuum tray for drying a cake, and the same kind of
cleaning operations are performed for each of these vacuum trays
However, when extracting the crystal components of the organic matter
dissolved in the solvent by separating it from the mother liquor as explained above m the
above-mentioned vacuum filtration apparatus, all of the plural vacuum trays are normally
accommodated in a gastight room and are thus shielded from the outside In this case,
smce the vacuum trays are enclosed in the gastight room, it is difficult to confirm the
status of the crystals adhered onto the grid plate and the filtering cloth Therefore,
timing for supplying the tray cleaning liquid to the underside of the filtering cloth has to
be set to the time after which operating time determined in advance has passed
However, in this case, although the tray cleaning liquid is supplied every time at the same
timing, there are cases in which the amounts of crystals adhered onto the filtering cloth
change dependmg on, for example, fluctuations of operating status etc of the vacuum
filtration apparatus Accordingly, there are cases m which the grid plate is cleaned
although it does not need cleaning, or conversely, the grid plate is not cleaned although it
needs cleaning That is, there is a problem in that it is difficult to perform cleaning at a
good timing If the timing for the cleaning is late, then filtering performance of the
vacuum filtration apparatus will be lowered and inadequate cleaning or inadequate
drying will happen, thereby causing deterioration in the product quality On the other
hand, if the timing for the cleaning is too early, then the tray cleaning liquid will be
wasted
The present invention was made in view of the above circumstances and an
object thereof is to provide a cleaning method for a vacuum filtration apparatus, and a
vacuum filtration apparatus, both of which can smoothly remove crystals deposited on
and adhered to a filtenng cloth and a grid plate at a good timing, thereby preventing
cloggmg of through holes and blockage of a flow path for the filtered liquid
SUMMARY OF THE INVENTION
In order to achieve the above object, the present invention provides a cleaning method for a vacuum filtration apparatus including a filtering cloth for carrymg a slurry and running m a substantially horizontal direction, a vacuum tray disposed under the filtenng cloth, a vacuum line connected to the vacuum tray, a vacuum suction device for performing vacuum suction of the slurry via the vacuum line, the vacuum tray, and the filtenng cloth, and a cleaning liquid supply device for supplymg a cleaning liquid to the vacuum tray The cleaning method mcludes measuring a vacuum pressure m the vacuum line, and cleaning the vacuum tray based on the vacuum pressure
In addition, in order to achieve the above object, the present invention also provides a vacuum filtration apparatus including a filtenng cloth for carrying a slurry and running m a substantially honzontal direction, a vacuum tray disposed under the filtenng cloth, a vacuum line connected to the vacuum tray, a vacuum suction device for performing vacuum suction of the slurry via the vacuum line, the vacuum tray, and the filtenng cloth, a cleaning liquid supply device for supplying a cleaning liquid to the vacuum tray, a vacuum pressure measunng device for measunng a vacuum pressure m the vacuum line, and a control device for making the cleaning liquid supply device

supply the cleamng liquid to the vacuum tray for cleaning the vacuum tray based on the
vacuum pressure
According to either one of the cleaning method for a vacuum filtration apparatus and the vacuum filtration apparatus of the present invention, timmg for supplymg cleaning liquid to the vacuum tray is determined based on the vacuum pressure in the vacuum line Thus, it becomes possible to confirm the amount of the crystal components of the slurry deposited and adhered onto a grid plate of the vacuum tray etc, regardless of fluctuations of operating status etc, of the vacuum filtration apparatus, and therefore, cleamng of the grid plate etc, can be performed at a good timing That is, the vacuum pressure will mcrease if the amount of the crystal components deposited on the grid plate etc, is large, while the vacuum pressure will decrease if the amount of the crystal components deposited on the grid plate etc, is small Thus, it can be arranged such that cleamng for the vacuum tray is performed when the vacuum pressure becomes higher than a predetermined value such as -40 kPaG By domg this, deterioration of product quality caused by insufficient cleaning or insufficient drying, and wasting of the cleamng liquid can be prevented
Accordingly, since crystals deposited on the filtering cloth and the grid plate etc, can smoothly be removed at a good timing, clogging of through holes and blockage of a flow path of the filtered liquid can be prevented
A plurality of the vacuum trays and corresponding vacuum lines may be provided along a running direction of the filtering cloth, and referring to the vacuum pressure in at least one of the vacuum lines, cleamng of the vacuum tray connected to the vacuum line to whose vacuum pressure referral is made may be performed Alternatively, a plurality of said vacuum trays and corresponding vacuum lines may be provided along a running direction of the filtering cloth, the vacuum pressures in each of
the vacuum lines may be measured, and only the vacuum tray in which the vacuum
pressure exceeds a predetermined value may be cleaned
In these cases, it becomes possible to avoid cleaning of vacuum tray which does not need cleaning at the time, thereby preventing waste of cleaning liquid Accordingly, high-efficiency cleaning can be realized
It may be arranged such that the vacuum tray is cleaned while the cleaning liquid is supplied such that the cleaning liquid overflows from the vacuum tray
For example, if the cleaning liquid does not overflow from the vacuum tray and maintains a liquid-level of a predetermined height m the vacuum tray, there is a possibility that a liquid-surface portion of the cleaning liquid will cool through the cleaning processes, thereby resulting in temperature drop Therefore, there is a possibility that crystal components dissolved in the liquid-surface portion of the cleaning liquid will be recrystalhzed and deposited onto a wall surface of the vacuum tray contacting the liquid-surface portion
In contrast, according to the present mvention, since the cleaning liquid is supplied such that it overflows from the vacuum tray, a standing fluid body will not be formed Accordingly, it becomes possible (1) to prevent recrystalhzation of the crystal components on the wall of the vacuum tray, (u) to prevent temperature drop of the cleaning liquid in the vacuum tray, and (in) to accelerate dissolution of the crystal components deposited onto the grid plate etc , into the cleaning liquid As a result, insufficient cleaning can be prevented
Furthermore, by raising the height of the liquid surface of the cleaning liquid by making it overflow from the vacuum tray, close to the underside of the filtering cloth, not only the gnd plate but also the lower surface of the filtenng cloth can be immersed in the cleaning liquid As a result, the crystal components of the slurry deposited onto the
ower surface of the cleaning cloth can be cleaned and removed
The cleaning method for a vacuum filtration apparatus may further include maintaining a temperature of the cleamng liquid higher than a recrystallization temperature of a crystal component contained in the slurry Alternatively, the vacuum tray may include a vacuum tray for forming a cake, a vacuum tray for washing a cake, and a vacuum tray for drying a cake, each arranged along a running direction of the filtenng cloth, and the vacuum pressure measunng device and the cleamng liquid supply device may be provided at least for the vacuum line connected to the vacuum tray for drying a cake
At the vacuum tray for drying a cake, since the amount of mother liquor contained m the slurry is small and since the amount of a gas to be sucked is large, temperature of the filtered liquid easily drops, thereby resulting m the recrystallization of the crystal components especially onto the grid plate etc
In contrast, according to the present invention, since the vacuum tray for drying a cake m which the crystal components are easily deposited is provided with the vacuum pressure measunng device and the cleamng liquid supply device, the recrystalhzed crystal components can be effectively dissolved and removed
Especially, if a plurality of vacuum trays for drying a cake and corresponding vacuum lines are provided, and if a vacuum pressure measunng device and the cleamng liquid supply device are provided to each of the vacuum lines, it becomes possible to continue drying processes of the vacuum trays for drying a cake while one of the vacuum tray for drying a cake is in cleaning As a result, it becomes possible to perform cleamng without stopping suction filtrations of the filter liquid in the vacuum filtration apparatus, thereby realizing high-efficiency cleamng operations
BRIEF DESCRIPTION OF THE DRAWINGS
FIG 1 is a general arrangement diagram showing one embodiment of a vacuum
filtration apparatus according to the present invention
FIG 2 is a side view of the vacuum filtration apparatus
FIG 3 is a partially-enlarged cross sectional view of a vacuum tray shown in
FIG 2 along the line A-A shown in FIG 2
DETAILED DESCRIPTION OF THE INVENTION Hereinafter, one embodiment of a cleaning method for a vacuum filtration apparatus and of a vacuum filtration apparatus of the present invention will be explained with reference to FIGS 1 to 3
As shown in FIG 1, the vacuum filtration apparatus of the present embodiment is provided with an apparatus main body 10, a vacuum line 20, a vacuum suction device 30, and a room temperature control lme 50 Detailed explanations for each of the apparatus main body 10, the vacuum line 20, the vacuum suction device 30, and the room temperature control line 50 will be made in the following
As shown in FIG 2, the apparatus main body 10 includes a plurality of rollers 12 and an endless-belt-shaped filtermg cloth 11 wrapped around the rollers 12 An upper side portion of the filtering cloth 11 forms a filtering section 11A arranged such that it extends towards horizontally A roller 12A disposed on one side of the filtering section 11A and wrapped by the filtering cloth 11, is connected to a dnving device (not shown in the figures) The roller 12A is rotationally driven in the clockwise direction in FIG 2 by the driving device, thereby rotationally dnving the filtermg cloth 11 around the rollers 12 Along with the rotation of the filtenng cloth 11, the filtering section 11A of the filtenng cloth 11 continuously runs in the running direction of an anow F shown in
FIG 2
A plurality (five m the present embodiment) of vacuum trays 16 each connected to a vacuum suction device 30 are provided under the filtering section 11A from a position just under a slurry supply device 13 (to be explained later) along the running direction F of the filtering section 11A Among these vacuum trays 16, a vacuum tray 16A disposed at the beginning side in the running direction F and just under the slurry supply device 13 is used for forming a cake (hereinafter "a tray 16A for forming a cake"), a vacuum tray 16B disposed adjacent to the tray 16A for forming a cake and substantially just under a cake washing device 21 (to be explained later) is used for washing the cake (hereinafter "a tray 16B for washing a cake"), and a plurality of vacuum trays 16C, 16D, and 16E disposed adjacent to the tray 16B for washing a cake and also disposed along the running direction F are used for drying (hereinafter, the vacuum trays 16C to 16E each referred as "a first tray 16C for drying a cake ", "a second tray 16D for drying a cake", and "a third tray 16E for drying a cake")
The vacuum trays 16 adjacent to each other along the running direction F are jomed to each other As shown m FIG 2, a driving cylinder 18 such as an air cylinder attached to a frame 10A of the apparatus main body 10 and extendable towards the runnmg direction F is joined to the vacuum tray 16 disposed at the beginning side in the running direction F (I e, the tray 16A for forming a cake) among the vacuum trays 16A With this driving cylinder 18, all of the vacuum trays 16 are able to move as one unit forwards and backwards along the runnmg direction F at a predetermined stroke That is, all of the vacuum trays 16 can move forwards and backwards along the running direction F
As shown in FIG 2, the apparatus mam body 10 is provided with a pair of rails 22 provided at both sides in the width and at the bottom side of the vacuum trays 16 and
extending along the running direction F, and a plurality of rotatable support wheels 19
each contacting the corresponding vacuum trays 16 from the lower side thereof thereby
supporting the vacuum trays 16, and having spaces therebetween along the width of the
filtering cloth 11 The vacuum trays 16 are able to move forwards and backwards on
the rotatable support wheels 19 On the other hand, each of the support wheels 19 is
driven to rotate along with the forwards and backwards movements of the vacuum trays
16 driven by the driving cylmder 18 Each of the support wheels 19 has the same size
and the same shape, and is attached onto the frame 10A of the apparatus main body 10
via brackets and the like, facing upwards, such that each of the wheels 19 can freely
rotate around a rotational axis extendmg horizontally along the width direction of the
vacuum trays 16 Each or the support wheels 19 has either one of a disc shape having
the rotational axis in the center and a high thickness, or a cylindrical shape having a short
axis Furthermore, these support wheels 19 are arranged along edges on both sides in
the width of the bottom faces of the vacuum trays 16, such that the support wheels 19
form two rows extending parallel to the running direction F Each of the support wheels
19 in each row is arranged such that they form constant gaps therebetween along the
runmng direction F, each of the support wheels 19 adjacent to each other in the width
direction between the rows forms a pair, and each member of each pair of the support
wheels 19 has the same height, and the same honzontal position in the runmng direction
F
The slurry supply device 13 for supplying slurry S onto the filtering cloth 11 is
provided above another end side (the left side in FIGS 1 and 2) of the filtering section
11A of the filtering cloth 11 (l e , above the beginning side in the running direction F)
The slurry S supplied from the slurry supply device 13 onto the filtering cloth 11 moves
m the runmng direction F m accordance with the movement of the filtering section 11 A,
and at the same time, vacuum suction of the slurry S is performed by each of the vacuum trays 16 via the filtenng cloth 11, thereby filtenng The cake washing device 21 for supplying a cake washing liquid L onto the filtenng cloth 11 is provided above the position on the filtenng cloth 11 where is on the forward side than the slurry supply device 13 in the running direction F The cake washing device 21 supplies the cake washing liquid L to a cake layer made by performing vacuum suction of the slurry S A knife 14 is provided next to the filtering cloth 11 in order to scratch and remove a dned cake which has been filtered and dned from the filtering cloth 11 Furthermore, a filter-cleaning device 15 for cleaning the filtering cloth 11 from which the slurry S is removed by the knife 14 is provided at a position at one end side of the filtering section 11A of the filtenng cloth 11 (I e , on the nght side m FIG 1, or the end side m the running direction F and under the filtenng section 11 A)
In the present embodiment, as shown in FIG 1, the above-mentioned apparatus 10, slurry supply device 13, and cake washing device 21 are accommodated m a gastight room R, and are shielded from the outside
As shown in FIG 3, each of the vacuum trays 16 has a flat face portion 16F extending along a lower surface of the filtenng section 11A and contacting the lower surface of the filtenng section 11A at an upper surface thereof, and a pair of wall portions 16G each extending upwards and outwards from both ends in the width of the fiat face portion 16F such that a gap therebetween in the width becomes wider moving upwards The flat face portion 16F is a stacked member in which a gnd plate 161 having through holes 16J formed thereon is stacked on a plate 16H
The upper surface side of the gnd plate 161 contacts the lower face of the filtenng section 11 A, while the lower surface side of the grid plate 161 is joined to the vacuum line 20 connected to the vacuum suction device 30
As shown in FIG 1, the vacuum suction device 30 is equipped with
gas-and-liquid separation tanks 31 to 33 for separating filtered liquid recovered from the
vacuum trays 16 into gas and liquid, a vacuum pump 34 connected to the gas-and-liquid
separation tanks 31 to 33 and applying vacuum suction to the slurry S on the filtering
section 11A through the gas-and-liquid separation tanks 31 to 33, and a cooler 35 which
is connected between the gas-and-liquid separation tanks 31 to 33 and the vacuum pump
34, and cools gases exhausted from the gas-and-liquid separation tanks 31 to 33 m
advance of passmg then through the vacuum pump 34
The first gas-and-liquid separation tank 31 is connected to the tray 16A for forming a cake, the second gas-and-liquid separation tank 32 is connected to the tray 16B for washing a cake, and the third gas-and-liquid separation tank 33 is connected to the first tray 16C for drying a cake, the second tray 16D for drying a cake, and the third tray 16E for drying a cake Each of the gas-and-liquid separation tanks 31 to 33 is provided with liquid level measuring devices 36 to 38 for measuring the amount of the filtered liquid recovered from the gas-and-liquid separation tanks 31 to 33, pumps 39 to 41 for filtered liquid for exhausting the filtered liquid from the gas-and-liquid separation tanks 31 to 33, and automatic valves SV1 to SV3 which open and close filtered-hquid exhaust ports of the gas-and-liquid separation tanks 31 to 33 based on measurement results of the liquid level measuring devices 36 to 38
A first temperature measuring device 42 for measuring the temperature of the gas is provided between the gas-and-liquid separation tanks 31 to 33 and the cooler 35 The cooler 35 is controlled by operating the opemng degree of a control valve CVl based on the measurement results of the first temperature measuring device 42, and as a result, the temperature of the gas is controlled
The vacuum filtration apparatus of the present invention is equipped with the
room temperature control line 50 connected to the vacuum pump 34 The room
temperature control line 50 controls the temperature in the gastight room R by receivmg
the gas cooled by the cooler 35 and by supplying the gas into the gastight room R after
controlling the temperature of the gas The room temperature control Ime 50 includes a
first heater 51 for heatmg the gas supplied from the vacuum pump 34, a second
temperature measuring device 52 for measuring the temperature in the gastight room R,
and a flow rate measuring device 53 for measuring a flow rate of the gas heated by the
first heater 51 and flowing mto the gastight room R The vacuum filtration apparatus of
the present invention is further equipped with a control valve CV2 for controlling the
first heater 51 based on the measurement results of the second temperature measuring
device 52, and a control valve CV3 for controlling the flow rate of the gas supplied into
the gastight room R based on the measurement results of the flow rate measuring device
53 The gas of which the temperature and the flow rate are controlled by the
above-mentioned devices flows into the gastight room R through an automatic valve V4
As shown in FIG 1, the vacuum line 20 includes a first vacuum Ime 20A
connecting between a bottom face of the tray 16A for forming a cake and the first
gas-and-hquid separation tank 31, a second vacuum line 20B connecting between a
bottom face of the tray 16B for washing a cake and the second gas-and-hquid separation
tank 32, and a third vacuum line 20C connecting between (l) the first tray 16C for drying
a cake, the second tray 16D for drying a cake, and the third tray 16E for drying a cake,
and (u) the gas-and-hquid separation tank 33 The first vacuum line 20A has a first
header pipe 22, the second vacuum Ime 20B has a second header pipe 23, and the third
vacuum Ime 20C has a third header pipe 24 The internal space of the third header pipe
24 connected to the first tray 16C for drying a cake through the third tray 16E for drying
a cake, is divided by two partitioning plates 25 into three spaces each having
substantially the same volume And each of these spaces is connected to one of the first
tray 16C for drying a cake through the third tray 16E for drying a cake correspondingly
In the following explanation, among the divided internal spaces in the third
header pipe 24, the space connected to the first tray 16C for drying a cake is referred as
"third header pipe 24A", the other space connected the second tray 16D for drying a cake
is referred as "third header pipe 24B", and the other space connected the third tray 16E
for drying a cake is referred as "third header pipe 24C"
A tray cleaning liquid supply device 26 for supplying a tray cleaning liquid
which can dissolve crystal components of the slurry S to the first tray 16C for drying a
cake through the third tray 16E for drymg a cake, is provided between (l) the first tray
16C for drymg a cake through the third tray 16E for drying a cake and (u) the third
header pipe 24A through the third header pipe 24C An automatic valve SV5 is
provided between the third header pipe 24A and the tray cleaning liquid supply device
26, an automatic valve SV6 is provided between the third header pipe 24B and the tray
cleaning liquid supply device 26, and an automatic valve SV7 is provided between the
third header pipe 24C and the tray cleaning liquid supply device 26 A first vacuum
pressure measuring device 27A for measuring vacuum pressure within a range from the
vacuum suction device 30 to the part of the lower face of the filtering section 11A which
an upper face of the first tray 16C for drying a cake faces, is provided to the third header
pipe 24A A second vacuum pressure measuring device 27B for measuring vacuum
pressure within a range from the vacuum suction device 30 to the part of the lower face
of the filtenng section 11A where an upper face of the second tray 16D for drymg a cake
faces, is provided to the third header pipe 24B A third vacuum pressure measuring
device 27C for measuring vacuum pressure within a range from the vacuum suction
device 30 to the part of the lower face of the filtermg section 11A which an upper face of
the first tray 16E for drying a cake faces, is provided to the third header pipe 24C
As shown in FIG 1, the tray cleaning liquid supply device 26 is provided with an automatic valve SV8 connected to the first tray 16C for drying a cake, an automatic valve SV9 connected to the second tray 16D for drying a cake, an automatic valve SVIO connected to the first tray 16E for drying a cake, a third temperature measuring device 26 A for measuring the temperature of the tray cleaning liquid before it is supplied into the first tray 16C for drying a cake through the third tray 16E for drying a cake, a second heater 26B for heating the tray cleaning liquid, a control valve CV4 for controlling the flow rate of a heating medium supplied to the second heater 26B based on the measurement results of the third temperature measuring device 26 A, and a pump (not shown in the figures) for supplying the tray cleaning liquid to the first tray 16C for drying a cake through the third tray 16E for drying a cake, via the automatic valves SV8 to SVIO By adopting this configuration, temperature of the tray cleaning liquid supplied to the first tray 16C for drying a cake through the third tray 16E for drying a cake via the automatic valves SV8 to SVIO, is controlled such that the temperature becomes 5 C to 10 C higher than the temperature at which crystallization of the mother liquor begins
The vacuum filtration apparatus of the present embodiment is equipped with a controller which is not shown in the figures The vacuum pressure measuring devices 27A to 27C, the automatic valves SV5 to SV7 and SV8 to SVIO, and the above-mentioned pump of the tray cleaning device 26, are connected to the controller Output signals output from the vacuum pressure measuring devices 27A to 27C are transmitted through the controller to the pump and the automatic valves SV5 to SV7 and SV8 to SVIO That is, when the vacuum pressures measured by the vacuum measuring devices 27A to 27C are lower than a predetermined value (for example, -40 kPaG), the
controller closes the automatic valves SV8 to SV10, opens the automatic valves SV5 to
SV7, stops supplying the tray cleaning liquid into the first tray 16C for drying a cake to
the third tray 16E for drying a cake, and supplies the filtered liquid recovered from the
slurry S through the filtering section 11A into the third header pipe 24 On the other
hand, when the vacuum pressures are higher than the predetermined value, the controller
opens the automatic valves SV8 to SV10, closes the automatic valves SV5 to SV7, stops
supplying the filtered liquid mto the third header pipe 24, and supplies the tray cleaning
liquid mto the first tray 16C for drying a cake to the third tray 16E for drying a cake
Based on the measurement results of the vacuum pressure measuring devices 27A to 27C, the controller opens and closes the automatic valves SV5 to SV7 and SV8 to SV10 respectively, thereby cleaning the first tray 16C for drying a cake to the third tray 16E for drying a cake respectively That is, the automatic valve SV5 and SV8 are opened and closed based on the measurement results of the first vacuum pressure measuring device 28A, the automatic valves SV6 and SV9 are opened and closed based on the measurement results of the second vacuum pressure measuring device 28B, and the automatic valves SV7 and SV10 are opened and closed based on the measurement results of the third vacuum pressure measuring device 28C
Next, the way to use the vacuum filtration apparatus having the above-mentioned configuration will be explained
Firstly, in normal operation, the same as in conventional apparatuses, the slurry supply device 13 supplies the slurry S onto a position of the filtering section 11A which is above the tray 16A for forming a cake, and vacuum pressure applied onto the tray 16A for forming a cake will suck and filter the liquid in the slurry S, and thereby form a cake Subsequently, the cake layer is moved and disposed above the tray 16B for washing a cake by the filtering section 11A Then, the cake washing device 21 will provide the
cake washing liquid L onto the cake layer, thereby washing the cake Furthermore, this
cake layer is dned by carrying it sequentially from the first tray 16C for drying a cake to
the third tray 16E for drying a cake Meanwhile, the filtered liquids recovered by each
of the vacuum trays 16 will pass through the header pipes 22 to 24, and will be
introduced into the corresponding gas-and-hquid separation tanks 31 to 33, and thereby
separated into gas and liquid
Liquid levels of the filtered liquids in the gas-and-hquid separation tanks 31 to
33 are continuously measured by the corresponding liquid level measurmg devices 36 to 38, and based on the measurement results, the filtered liquids in the gas-and-hquid separation tanks 31 to 33 are transferred to the arbitrary processes through the pumps 39 to 41 for filtered liquid and the automatic valves SV1 to SV3 On the other hand, since each of the gasses exhausted from the gas-and-hquid separation tanks 31 to 33 contains a little solution, the solution is thermally condensed and is removed by making the gasses pass through the cooler 35, and is subsequently returned into the second gas-and-hquid separation tanks 32 By performing this process, the gas sucked by the vacuum pump
34 is made to be in a dried condition, and is subsequently returned into the gastight room R through the room temperature control line 50 At this time, since temperature of the gas needs to be maintained higher than the crystal-depositing temperature of the mother liquor, temperature in the gastight room R is regularly measured by the second temperature measuring device 52 And, corresponding to an output from the second temperature measuring device 52, the temperature of the gas is controlled by the first heater 51 and the control calve CV2, such that the temperature becomes 5°C to 20°C higher than the temperature at which the mother liquor begins crystallization By performing this process, the temperature in the gastight room R is maintained in a constant temperature condition having a predetermined temperature
In the temperature of the cake washing liquid L is also regularly measured by a
fourth temperature measuring device (not shown in the figures) In addition,
corresponding to the measurement results of the fourth temperature measuring device,
the temperature of the cake washing liquid L is controlled such that the temperature
becomes 5°C to 10 C higher than the temperature at which the mother liquor begins
crystallization By performing this process, the temperatures of the mother liquor and
the filtered liquid are maintained higher the temperature at which the mother liquor
begins crystallization As a result, it becomes possible to prevent deposition of the
crystals and to obtain stable operation for many hours
However, even when the vacuum filtration apparatus is operated with the above-mentioned countermeasures in order to prevent deposition of the crystals, there is a possibility that the crystal components of the slurry S will adhered to the lower surface of the filtering section 11 A, and to the grid plates 161 of the first tray 16C for drying a cake through the third tray 16E for drying a cake
Hereinafter, a case in which the crystal components are stacked and adhered onto the first tray 16C for drying a cake will be explained In this case, vacuum pressure between (l) the part of the lower face of the filtering section 11A which corresponds to the first tray 16C for drying a cake and (u) the vacuum suction device 30 rises And, if the first vacuum pressure measuring device 27A provided on the third header pipe 24A detects that the vacuum pressure becomes higher than the predeterrmned value, then an output signal from the first vacuum pressure measuring device 27A is transmitted to the automatic valves SV8 and SV5 and the pump through the controller As a result, the automatic valve SV8 will open and the automatic valve SV5 will close Then, while vacuum suction by the first tray 16C for drying a cake is stopped, the tray cleaning liquid in which the flow rate and the temperature are controlled m advance by
the tray cleaning liquid supply device 26 will be supplied into the first tray 16C for
drying a cake On the other hand, although the vacuum suction of the first tray 16C for
drying a cake is stopped, vacuum suction operations by the other vacuum trays 16 (l e ,
the tray 16A for forming a cake, the tray 16B for washing a cake, the first tray 16C for
drying a cake, the second tray 16D for drying a cake, and the third tray 16E for drying a
cake) will be continued
Filtering operation is continued for a predetermined time while the tray cleaning liquid introduced mto the first tray 16C for drying a cake overflows therefrom such that the grid plate 161 is immersed in the tray cleaning liquid and such that the lower surface of the filtering section 11A is dipped in the tray cleaning liquid Meanwhile, m accordance with the back-and-forth motions of each of the vacuum trays 16, the tray cleaning liquid will be automatically shaken, thereby performing an effective cleaning operation Especially, smce the tray cleaning liquid is supplied such that a little of the tray cleaning liquid overflows from the first tray 16C for drying a cake, the cleaning liquid contaimng the crystal components will not keep touchmg an inner wall of the first tray 16C for drying a cake and will not be cooled Therefore, recrystallization of the crystal components onto the inner wall can be prevented After a predetermined time has been passed, supply of the tray cleaning liquid is stopped by closmg the automatic valve SV8, and the tray cleaning liquid is recovered as a filtered liquid by opemng the automatic valve SV5
In order to clean the second tray 16D for drying a cake, the automatic valve SV6 is closed and the automatic valve S V9 is opened, and thereby a cleaning operation the same as the one mentioned above is performed Also, in order to clean the third tray 16E for drying a cake, the automatic valve SV7 is closed and the automatic valve SV10 is opened, and thereby a cleaning operation the same as the one mentioned above will be
performed
As explained above, according to the vacuum filtration apparatus of the present embodiment, since timing for supplying the tray cleamng liquid into the vacuum trays 16 is determined based on the vacuum pressure in the vacuum lme 20, it becomes possible to confirm the status of the crystal components deposited and adhered onto the grid plate 161 etc, regardless of fluctuations of operating status etc, of the vacuum filtration apparatus Accordingly, cleamng of the grid plate 161 etc, can be performed at a good timing That is, the vacuum pressure will increase if the amount of the crystal components deposited on the grid plate 161 etc , is large, while the vacuum pressure will decrease if the amount of the crystal components deposited on the grid plate 161 etc , is small Thus, it can be arranged such that the vacuum trays 16 are cleaned when the vacuum pressure becomes higher than a predetermined value such as -40 kPaG By doing this, deterioration of product quality caused by insufficient cleamng or insufficient drying, and wasting of the cleaning liquid can be prevented
In addition, smce the vacuum pressure in the vacuum line 20 is measured for each of the first tray 16C for drying a cake through the third tray 16E for drying a cake, and since only a vacuum tray in which the vacuum pressure exceeds the predetermined value is cleaned, it becomes possible to prevent waste of cleamng liquid and to realize high-efficiency cleamng
In addition, while cleaning the first tray 16C for drying a cake, by continuing drying processes of the second tray 16D for drying a cake and the third tray 16E for drying a cake, it becomes possible to continue cleamng operations without stopping suction filtrations of the filtered liquid in the vacuum filtration apparatus, thereby realizing high-efficiency cleamng operations Furthermore, smce suction filtration by the vacuum filtration apparatus is continued while the grid plate 161 is immersed in the
tray cleamng liquid, the tray cleaning liquid will be automatically shaken, thereby
realizing high-efficiency cleaning operations
Furthermore, since the tray cleamng liquid is supplied into the vacuum trays 16 such that the tray cleamng liquid overflows from the vacuum trays 16, not only the grid plate 161 but also the lower face of the filtering section 11A can be dipped mto the tray cleamng liquid As a result, the crystal components deposited and adhered both to the grid plate 161 and to the filtering section 11A can be dissolved and removed satisfactorily
That is, if each of the cleamng liquids does not overflow from the vacuum trays 16 and maintains a liquid-level of a predetermined height in the vacuum trays 16, there is a possibility that each of liquid-surface portions of the cleamng liquids will be cooled through the cleamng process, thereby resultmg in temperature drop thereof Therefore, there is a possibility that crystal components dissolved in the liquid-surface portions of the cleamng liquids will be recrystallized and deposited onto wall surfaces of the vacuum trays 16 contacting the liquid-surface portions
In contrast, accordmg to the vacuum filtration apparatus of the present embodiment, smce the cleamng liquid is supplied such that it overflows from the vacuum trays 16, standing fluid body will not be formed Accordingly, it becomes possible (I) to prevent recrystalhzation of the crystal components on the walls of the vacuum trays 16, and (u) to prevent temperature drop of the cleamng liquids in the vacuum trays 16 As a result, dissolution of the crystal components deposited on the grid plate etc , into the cleamng liquid is accelerated, and thereby insufficient cleamng can be prevented
Furthermore, by raismg the height of the liquid surface of the cleamng liquid so that it overflows from the vacuum trays 16, close to the underside of the filtering section 11 A, not only the grid plate 161 but also the lower surface of the filtering section 11A can
be immersed in the cleaning liquid As a result, the crystal components of the slurry S
deposited onto the lower surface of the filtering section 11A can be cleaned and removed
Especially, according to the vacuum filtration apparatus of the present embodiment, since
the temperature of the cleaning liquid is maintained higher than a recrystalhzation
temperature of the crystal components, dissolution of the crystal components into the tray
cleaning liquid can be further accelerated
At the first tray 16C for drying a cake through the third tray 16E for drying a cake, since the amount of mother liquor contained in the slurry S is small and since the amount of gas to be sucked is large, the temperature of filtered liquid easily drops, thereby resultmg m the recrystalhzation of the crystal components especially onto the gnd plate 16 etc In contrast, according to the vacuum filtration apparatus of the present mvention, since the vacuum trays 16 in which the crystal components are easily deposited are provided with the vacuum pressure measuring devices 27A to 27C and the cleaning liquid supply device 26, the recrystalhzed crystal components deposited in the vacuum filtration apparatus can be effectively dissolved and removed In addition, according to the vacuum filtration apparatus of the present embodiment, even when one of the plurality of the first tray 16C for drying a cake through the third tray 16E for drying a cake is in cleaning, it is possible to contmue drying processes of the others, thereby enablmg realization of high-efficiency cleaning operations
While a preferred embodiment of the invention has been described and illustrated above, it should be understood that this is exemplary of the invention and is not to be considered as limiting Additions, omissions, substitutions, and other modifications can be made without departing from the spirit or scope of the present mvention Accordingly, the invention is not to be considered as being limited by the foregoing description, and is only limited by the scope of the appended claims
In the present embodiment, the first vacuum pressure measunng device 27A
through the third vacuum pressure measunng device 27C and the cleaning liquid supply
device 26 are provided to each of the vacuum lines 20 connected to the first tray 16C for
drying a cake through the third tray 16E for drying a cake However, the configuration
of the vacuum filtration apparatus of the present invention is not limited to this, but it is
also possible to provide the first vacuum pressure measuring device 27A through the
third vacuum pressure measunng device 27C and the cleaning liquid supply device 26, to
one of the vacuum lmes 20 connected between the vacuum suction device 30 and one of
the first tray 16C for drying a cake through the third tray 16E for drying a cake That is,
for example, the vacuum pressure measunng device 27 and the cleaning liquid supply
device 26 may be provided to only one of, or all of the first vacuum line 20A, the second
vacuum lme 20B, and the third vacuum line 20C
In addition, in the present embodiment, the tray cleaning liquid is automatically
supplied into the vacuum trays 16, however, it may be possible to dispose the first
vacuum pressure measunng device 27A through the third vacuum pressure measunng
device 27C to the external of the gastight room R such that the vacuum pressures
measured thereby can be viewed by an operator, and to allow manual control of the
cleaning liquid supply device 26 etc, by an operator

What is claimed is:
1. A cleaning method for a vacuum filtration apparatus including: a filtering cloth
for carrying a slurry and running in a substantially horizontal direction; a vacuum tray
disposed under the filtering cloth; a vacuum line connected to the vacuum tray; a vacuum
suction device for performing vacuum suction of the slurry via the vacuum line, the
vacuum tray, and the filtering cloth; and a cleaning liquid supply device for supplying a
cleaning liquid to the vacuum tray, the cleaning method comprising:
measuring a vacuum pressure in the vacuum line; and cleaning the vacuum tray based on the vacuum pressure.
2. The cleaning method for a vacuum filtration apparatus according to claim 1,
wherein:
a plurality of said vacuum trays and corresponding vacuum lines are provided along a running direction of the filtering cloth; and
referring to the vacuum pressure in at least one of the vacuum lines, cleaning of the vacuum tray connected to the vacuum line to whose vacuum pressure is referral is made is performed.
3. The cleaning method for a vacuum filtration apparatus according to claim 1,
wherein:
a plurality of said vacuum trays and corresponding vacuum lines are provided along a running direction of the filtering cloth;
the vacuum pressures in each of the vacuum lines are measured; and only a vacuum tray in which the vacuum pressure exceeds a predetermined

value is cleaned.
4. The cleaning method for a vacuum filtration apparatus according to claim 1,
wherein:
the vacuum tray is cleaned while the cleaning liquid is supplied such that the cleaning liquid overflows from the vacuum tray.
5. The cleaning method for a vacuum filtration apparatus according to claim 1,
further comprising
maintaining a temperature of the cleaning liquid higher than a recrystallization temperature of a crystal component contained in the slurry.
6. A vacuum filtration apparatus comprising:
a filtering cloth for carrying a slurry and running in a substantially horizontal direction;
a vacuum tray disposed under the filtering cloth;
a vacuum line connected to the vacuum tray;
a vacuum suction device for performing vacuum suction of the slurry via the vacuum line, the vacuum tray, and the filtering cloth;
a cleaning liquid supply device for supplying a cleaning liquid to the vacuum tray;
a vacuum pressure measuring device for measuring a vacuum pressure in the vacuum line; and
a control device for making the cleaning liquid supply device supply the cleaning liquid to the vacuum tray for cleaning the vacuum tray based on the vacuum

pressure.
7. The vacuum filtration apparatus according to claim 6, wherein:
the vacuum tray comprises a vacuum tray for forming a cake, a vacuum tray for
washing a cake, and a vacuum tray for drying a cake, each arranged along a running
direction of the filtering cloth; and
a vacuum pressure measuring device and the cleaning liquid supply device are
provided at least for the vacuum line connected to the vacuum tray for drying a cake.

Documents:

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Patent Number

279472

Indian Patent Application Number

2538/DEL/2005

PG Journal Number

04/2017

Publication Date

27-Jan-2017

Grant Date

23-Jan-2017

Date of Filing

20-Sep-2005

Name of Patentee

TSUKISHIMA KIKAI CO., LTD

Applicant Address

17-15, TSUKUDA 2-CHOME, CHUO-KU, TOKYO, JAPAN.

Inventors:

#	Inventor's Name	Inventor's Address
1	TOMOKI HONMA	C/O TSUKISHIMA KIKAI CO., LTD., 17-15, TSUKUDA 2-CHOME, CHUO-KU, TOKYO, JAPAN.

PCT International Classification Number

A47L 9/16

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	2004-275815	2004-09-22	Japan