FIELD OF THE INVENTION

The invention relates to a method and an arrangement for regenerating sand to be cleaned.

BACKGROUND OF THE INVENTION

In prior art solutions, a heated rotating oven or a so-called fluidised-bed boiler is used for thermal recovery of sand.

A drawback with the solutions mentioned above may be varying quality of the cleaned sand because of many variables in the cleaning process. Also, sand to be cleaned may comprise many variables that affect the outcome of the cleaning process.

BRIEF DESCRIPTION OF THE INVENTION

An object of the present invention is to provide a novel method and arrangement for regenerating sand to be cleaned.

The invention is characterized by the features of the independent claims.

The invention is based on the idea of monitoring visually quality of the regenerated sand. Based on analysed quality of the regenerated sand, the regenerated sand is directed either to a further treatment process or back to a regeneration system.

An advantage of the solution is ensuring better quality of the regenerated sand. Quality of the regenerated sand is ensured because the regenerated sand is actively monitored. Better quality of the regenerated sand may also be achieved because the regenerated sand may be regenerated again if observed to be necessary.

Some embodiments of the invention are disclosed in the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following the invention will be described in greater detail by means of preferred embodiments with reference to the accompanying drawings, in which

Figure 1 shows schematically an arrangement for regenerating sand to be cleaned according to an embodiment, and Figure 2 shows schematically a process chart of regenerating sand to be cleaned according to an embodiment.

For the sake of clarity, the figures show some embodiments of the invention in a simplified manner. Like reference numerals identify like elements in the figures.

DETAILED DESCRIPTION OF THE INVENTION

Figure 1 shows schematically an arrangement for a regeneration, i.e., cleaning, of used sand, i.e., sand to be cleaned, such as foundry sand used at a foundry. Used foundry sand typically comprises on the surface of a grain of sand, a clay-based or resin-based binder film by means of which a mould made of sand may be hardened. Said binder film is typically of bentonite, but instead of bentonite said binder film may also be of another clay-based or resin-based binder, such as kaolinite. In the regeneration or cleaning of used foundry sand, the said clay-based or resin-based binder film is intended to be removed for the surface of the grains of sand.

The arrangement of Figure 1 comprises, among other things, a regeneration system 1 for the thermal regeneration of the sand to be cleaned, and a quality monitoring system 100 for monitoring quality of the regenerated sand. The regeneration system 1 of Figure 1 comprises a heated rotating oven 2 for the thermal regeneration of the sand. Additionally mechanical impacts could be subjected to the sand to be cleaned for improving a separation of the binder film from the sand, whereby the regeneration of sand would comprise both the thermal and mechanical cleaning of the sand to be cleaned. Alternatively, the regeneration system could comprise a so-called fluidised-bed boiler for thermally regenerating the sand, in which fluidised-bed boiler a powerful airstream is fed upwards from a bottom part of the boiler and the air stream causes the sand to be cleaned, ash, and fuel used for heating the boiler to float.

The regeneration system 1 of Figure 1 comprises a pre-processing stage 3 for pre-processing the sand to be cleaned, such as for crushing any lumps and cleaning the sand by magnetic separation for removing magnetic metallic particles from the sand to be cleaned.

The pre-processed sand passes through a dosing feeder 4 to a conveyor 5, the dosing feeder 4 feeding the sand to be cleaned to the conveyor 5, along which the sand moves to the oven 2 for the regeneration. Dust removal, as well as also magnetic separation, may be performed for the sand when the sand drops from the dosing feeder 4 and moves on the conveyor 5. The sand to be cleaned is fed into the oven 2 advantageously at a first end 2a of the oven 2, as shown schematically with an arrow indicated with a reference sign F-1N and the regenerated sand, i.e., the cleaned sand, may flow out of the oven 2 at a second end 2b thereof, as shown schematically with an arrow indicated with a reference sign F-OUT.

The regeneration system 1 further comprises a heat source 6 for producing heat to heat the oven 2. The heat source may for example be a liquid gas burner. In the embodiment of Figure 1, the heat energy is fed to the oven 2 at the first end 2 thereof, but the heat energy may be fed in the oven 2 at some another location of the oven 2 too, such as at the second end 2b of the oven 2 or the middle region of the oven 2. As concerns the feeding of the heat energy and the conveying of the sand, it is important that the sand moving into the oven 2 can be heated up fast. The oven 2 is in a thermal insulation material to reduce thermal losses. The temperature of the oven 2, a temperature of the sand to be cleaned, may be measured with one or more temperature sensors 7, positioned for example at the second end 2b of the oven 2.

The oven 2 is substantially supported by supports 8. The oven 2 is typically set slightly inclined so that the second end 2b of the oven 2 is lower than the first end 2a. There are means advantageously arranged to the supports 8 for adjusting an inclination of the oven 2 in response to a respective control signal. Additionally, there are rotating means 9 to rotate the oven 2 and to adjust a rotating speed of the oven 2 in response to a respective control signal.

Flue gasses are removed from the second end 2b of the oven 2 through a flue gas conduit 10. With the flue gasses, impurities removed from the sand are also discharged. The flue gasses are processed with appropriate filter arrangements and cooled down to recover heat.

The regenerated, i.e., cleaned, sand may flow out of the oven 2 at the second end 2b thereof, as shown schematically with the arrow indicated with the reference sign F-OUT, towards a quality monitoring system 100 for monitoring quality of the regenerated sand. Before the regenerated sand entering the quality monitoring, the sand may pass through an after-treatment stage 11, wherein the sand may be subjected to various processing phases, including, for example, dust removal, washing by spraying water to the sand, water removal, or cooling down sand to recover heat.

One or more actuators in the regeneration system 1 may be controlled by means of a regeneration system control unit 12. The control unit 12 also monitors values of different detectors and sensors in the regeneration system 1 and utilizes the information when controlling the actuators. The control unit 12 may also be provided with different kind of starting data, i.e., initial data. The control unit 12 may be part of a control room hooked up in connection with the regeneration system 1, from which the operation of the regeneration system 1 may be managed by means of user interface of different kind. Control room solutions of different kind are known per se, so for that reason they are not described in closer detail in this context.

Measured, and possible initial data of the sand to the cleaned, are fed to the regeneration system control unit 12. The control unit 12 notes these when it determines the most suitable parameters for the different actuators to regenerate, i.e., clean, the batch of sand or continuous flow of sand coming in to be processed at each time. As initial data may be given, among other things, the previous use of the sand, storage location or locations of the sand after the previous use, humidity content of the sand mass, or the temperature of the sand as measured by one or more sensors placed in the dosing feeder 4, for example. Previous use indicates what impurities there might be in the sand due to the previous use. The storage locations indicate what might have happened to the sand between the previous use and the cleaning carried out. The temperature before cleaning in turn helps the control unit 12 determine the sand temperature throughout the regeneration process.

In addition to the initial data, details on the future planned use of the sand, or the desired purity grade of the cleaned sand may be needed. A batch of sand may, for example, be recovered back to foundry use, so clean even that it replaces part of the virgin sand at the foundry, or even all the virgin sand, wherein the virgin sand is sand used as the casting sand. Mechanically recovered casting sand, or foundry sand, may be used as filler sand in casting, but it is not considered usable as the actual casting sand.

A batch of sand, or part of it, may also be cleaned somewhat more lightly, too, so that after cleaning the sand is no longer classified as waste but can be used for another use. Sand for further use at a foundry has specific limit values for, for example, the amount of dust. Of sand for another purpose, dust removal may be reduced, if so desired, or one or more dust removal stages left out altogether.

When for example foundry sand is cleaned, important in the adjustment of the heat source 6, in addition to monitoring the temperature of the oven 2, is at least an amount of sand fed in the oven 2, its advancing speed in the oven 2 and cleaning requirement, as well as what sort of impurities there are in the sand, and how clean the obtained sand must be. If the advancing speed increases, the amount of the heat energy fed in must be increased. By increasing the advancing speed when a substantially similar outcome is aimed at, the temperature of the oven 2 must be made higher, which speeds up thermal regeneration or cleaning. A higher temperature in the oven 2 possibly causes more heat losses, on the other hand the lead-time is accelerated. However, at too high a temperature sand begins to glaze what should be avoided. Consequently, there is reason to monitor thermal regeneration or cleaning by using automation as a help, which also means that sensors, regulators, and meters of different kind are needed, and all of the automation, or at least most of automation, is controlled by means of a user interface in the control room.

When for example foundry sand is cleaned, there must be enough air space for the discharge of impurities. The impurities are removed with the flue gasses, so the amount of sand in the oven 2 must be kept sufficiently low. In other words, the sand to air mixture ratio must also be monitored. The larger the amount of sand in the oven 2 is, the worse can the impurities from among the sand exit with the flue gasses. This being the case, in the case of sand recovered back to foundry use there may be 25 to 45% of sand out of the inner volume of the oven 2. Advantageously, the amount of sand maybe approximately 30 to 35% of the inner volume of the oven 2. When determining the amount of sand and the rotating speed of the oven 2, it is also important that the sand mass must not just flow along the bottom of the oven 2, which means that the rotating speed is too low in relation to the amount of sand being cleaned. If the rotating speed of the oven 2 is too high, the sand rotates on the inner circumference of the oven 2 with the oven 2. With a suitable rotating speed in relation to the sand mass being cleaned, the sand rises on the inner circumference of the oven 2 up to such an extent that at some stage the sand mass detaches from the inner circumference of the oven 2 and at least partly falls in the air. In such a case, the sand mass is regenerated or cleaned more evenly, because cleaning hot air is better mixed with the sand mass, that is, the sand being cleaned is better aerated and the impurities may better exit with the air.

According to an embodiment, an additive may be added to pre-processed sand after magnetic separation to improve the cleaning of certain impurities in thermal regeneration. The additives used must be very steadily mixed with the sand being cleaned. For such a purpose, mixers have been designed which are known per se and therefore not described in detail in this context. Mixing is important from the viewpoint of the outcome. The concentration of the additive should be constant as concerns the sand mass being cleaned. The recommended concentrations for kaoline-based additives, for example, are in the neighbourhood of 1 to 3% when fluidised-bed boilers are used, but it has been detected that when the disclosed rotating oven is used, similar results may be obtained with significantly smaller amounts of additives, such as with an additive amount of less than 0.8% and advantageously with an additive amount as low as 0 to 0.3%. The dosage of an additive is affected by the initial data measured and obtained from the sand to be cleaned.

According to an embodiment, the method for the regeneration of the sand to be cleaned comprises: feeding pre-processed sand into the rotating oven 2, feeding heat energy to the rotating oven 2, monitoring the temperature of the oven 2 with one or more temperature sensors 7, adjusting the temperature of the oven 2 at least partly on the basis of the monitored oven temperature by adjusting the amount of heat energy fed in, adjusting the amount of sand fed into the oven, adjusting an inclination and rotating speed of the oven 2 to adjust the advancing speed of the amount of sand in the oven 2 at least partly based on the amount of sand fed in or the monitored oven 2 temperature, or both, and letting the regenerated sand run out of the oven 2.

According to an embodiment, the temperature of the oven 2 is adjusted by taking into account an average temperature of the sand to be cleaned.

According to an embodiment, the temperature of the oven 2 is adjusted by substantially taking into account an average temperature of the sand and/or the oven 2 at the second end of the oven.

The average temperature of the sand need not be measured directly from the sand being cleaned, because it can be computationally determined in many ways. In determining the average temperature of the sand, the following information, for example, may be used, determined by the regeneration system control unit 12 from the sensors and actuators: 1) oven temperature at any one time, 2) amount of sand fed in the oven 2 per each time unit, 3) advancing speed of the sand in the oven 2, 4) temperature of the sand to be cleaned as it is being fed into the oven 2, 5) temperature of sand exiting from the oven 2, 6) amount of heat energy fed in the oven 2 at any one time, 7) heat losses in different parts of the regeneration system, and 8) temperature of flue gasses exiting from the oven 2.

According to an embodiment, the regeneration system control unit 12 uses the information it has received concerning each time instant on the oven 2 temperature at any one time, amount of sand fed in the oven 2, advancing speed of the sand, temperature of the sand to be cleaned as it is being fed into the oven 2, temperature of exiting sand, amount of heat energy fed in, heat losses in different parts of the apparatus, and temperature of exiting flue gasses as well as other possible measured values as return data to perform future controls and adjustments.

Therefore, the regeneration system control unit 12 can, by means of the return data, make corrective adjustment actions, for example, in the control room to reach the target settings given to the control unit 12. From the control room, it is possible to determine, for example, target values for the average temperature of the sand, the cleaned sand that is let run out of the oven 2, exiting flue gasses, or any combination of the above. It is also possible to set a target for the advancing speed of the sand, and by monitoring the realized values obtained as the return data the control unit 12 can determine whether the target was realized and carry out required changes if the realization calculated according to the return data does not correspond with the target.

There may be a loss of ignition while regenerating the sand to be cleaned in the regeneration system 1. While regenerating the sand to be cleaned, impurities are removed which affects to the colour of the sand to be regenerated. The more impurities are remaining after the regeneration, the higher the loss of ignition of the regenerated sand. The higher the loss of ignition of the regenerated sand, the greater is the degree of darkness of the regenerated sand. In more detail, the colour of the sand under regeneration is changed because of the regeneration. In the present solution the loss of ignition of the regenerated sand may be monitored by monitoring visually the regenerated sand.

Figure 2 is a schematic process chart for the method of regenerating sand to be cleaned. The method comprises a step of regenerating 201 sand to be cleaned. Sand is cleaned by the regeneration system 1. The method further comprises a step of visually monitoring 202 the regenerated sand. The regenerated sand is monitored by a monitoring system 100 described below. In monitoring 202 the regenerated sand is visually analysed for determining a quality of the regenerated sand. If quality of the regenerated sand is acceptable, the regenerated sand is directed forward 203 to a further treatment process. If the quality of the regenerated sand is not acceptable, the regenerated sand may be directed back 204 to the regeneration.

The arrangement shown in Figure 1 comprises a mesh 110 to filter the regenerated sand received from the regeneration system 1. The mesh 110 filters the regenerated sand based on a selected mesh size of the mesh 110. The regenerated sand with grain size less than the mesh size of the mesh 110 moves through the mentioned mesh 110. The mesh 110 may be inclined to an angle, so that the regenerated sand with the grain size more than the mesh size of the mesh 110 moves out 112 from the mesh 110 and may be directed back to the regeneration system 1. The mesh 110 may be shaken by a shaker, so that the regenerated sand with the grain size more than the mesh size of the mesh 110 moves easier out from the mesh 110.

The arrangement comprises a feed hopper 120 that is configured to receive 111 the regenerated sand from the regeneration system 1. In Figure 1 the feed hopper 120 receives 111 the fraction of the regenerated sand passing through the mesh 110. The feed hopper 120 has determined capacity to receive the regenerated sand.

The quality monitoring system 100 is configured to monitor visually quality of the regenerated sand. As in Figure 1, the quality monitoring system 100 comprises at least one detecting device 130 for visually monitoring substantially continuously the loss of ignition of the regenerated sand. In Figure 1 the detecting device 130 for visually detecting the loss of ignition of the regenerated sand is a colour sensor. The loss of ignition of the regenerated sand may be monitored by monitoring the regenerated sand in the feed hopper 120. The mentioned colour sensor detects the colour of the object it is configured to monitor to. The mentioned colour sensors cast light on the regenerated sand and the light reflected to the colour sensor may then be measured by the colour sensor. The colour sensor may be arranged in the feed hopper 120 or near the feed hopper 120 so that a surface of the regenerated sand in the feed hopper 120 or a flow of the regenerated sand may be monitored. The colour sensor may operate substantially continuously.

In addition, the quality monitoring system 100 comprises a quality monitoring system control unit 150 that is connected to the detecting device 130 for visually detecting. The quality monitoring system control unit 150 is configured to analyse quality of the regenerated sand based on the loss of ignition of the regenerated sand. The quality of the regenerated sand may be monitored by monitoring the loss of ignition of the regenerated sand. The loss of ignition of the regenerated sand may be analysed by monitoring colour of the regenerated sand. The loss of ignition of the regenerated sand is indicated by a degree of darkness of the regenerated sand. In the embodiment disclosed above, monitoring colour of the regenerated sand is implemented by monitoring colour of surface of the regenerated sand in the feed hopper 120.

Depending on a final product and its intended use, cleaning requirements of the regenerated sand may vary. Typically, light shades of the loss of ignition of the regenerated sand are better compared to darker shades of the loss of ignition of the regenerated sand. Darker shades of the loss of ignition of the regenerated sand indicate higher loss of ignition of the regenerated sand.

The quality monitoring system control unit 150 may comprise a predetermined limit value for the loss of ignition of the regenerated sand. The predetermined limit value is a predetermined limit value for the degree of darkness of the regenerated sand. The quality monitoring system control unit 150 is configured to compare value received from the detecting device 130 to the predetermined limit value for the loss of ignition of the regenerated sand. Monitored values of the regenerated sand from the detecting device 130 match to the predetermined limit value for the loss of ignition of the regenerated sand, or they may be over or below when compared to the predetermined limit value for the loss of ignition of the regenerated sand. The predetermined limit value may be changed if needed. With the predetermined limit value set for the loss of ignition of the regenerated sand it may be determined a criterion for an acceptable degree of darkness of the regenerated sand, i.e., a criterion indicating an acceptable quality of the regenerated sand to be directed forward to the further treatment process.

The arrangement comprises a flow switch valve 140 for directing, based on the monitored quality of the regenerated sand, the regenerated sand forward

141 to the further treatment process, or for directing the regenerated sand back

142 to the regeneration system 1. In Figure 1 the flow switch valve 140 is arranged at the lower end of the feed hopper 120 for receiving the regenerated sand from the feed hopper 120. The flow switch valve 140 is connected to the quality monitoring system control unit 150 that is connected to the detecting device 130. Based on information received from the detecting device for visually detecting 130, the quality monitoring system control unit 150 is configured to open or close ports of the flow switch valve 140. In Figure 1 the flow switch valve 140 comprises a first port for directing the regenerated sand forward 141 to the further treatment process and a second port for directing the regenerated sand back 142 to the regeneration system 1. The flow switch valve 140 is configured to direct the regenerated sand forward to the further treatment process in response to the degree of darkness of the regenerated sand fulfilling the predetermined criterion set for acceptable loss of ignition of the regenerated sand. Thus, according to an embodiment, the regenerated sand is directed forward to the further treatment process in response to the degree of darkness of the regenerated sand being smaller and/or equal to the predetermined limit value. The flow switch valve 140 is configured to direct the regenerated sand back to the regeneration system 1 in response to the degree of the darkness of the regenerated sand not fulfilling the predetermined criterion set for acceptable loss of ignition of the regenerated sand. Thus, according to an embodiment, the regenerated sand is directed back to the regeneration system 1 in response to the degree of the darkness of the regenerated sand exceeding the predetermined limit value.

The further treatment process comprises at least one of the following: bagging of the cleaned sand, intermediate storage of the cleaned sand, or process for manufacturing foundry sand. The regenerated sand, received from the flow switch valve 140 may be conveyed by a conveyor to the further treatment process. For the sake of clarity, the mentioned conveyor isn’t illustrated in Figure 1.

The arrangement comprises all equipment needed for directing the regenerated sand back 142 to the regeneration system 1 from the flow switch valve 140. As an example, the arrangement may comprise a conveyor of any kind from the flow switch valve 140 to the regeneration system 1. The regenerated sand may be conveyed to the dosing feeder 4. For the sake of clarity, the mentioned conveyor isn’t illustrated in Figure 1.

The regeneration system control unit 12 in Figure 1 may be connected to the quality monitoring system control unit 150 for the regeneration system control unit 12 for being able to control an operation of the regeneration system 1 based on the monitored quality of the regenerated sand. Based on the monitored quality of the regenerated sand, that is based on the monitoring of the loss of ignition of the regenerated sand, at least one of the following parameters may be adjusted in the regeneration system 1: amount of feeding sand to be cleaned into the rotating oven 2, amount of feeding heat energy to the rotating oven2, the inclination of the oven 2, or the rotating speed of the oven 2.

An advantage for the connection between the regeneration system control unit 12 and the quality monitoring system control unit 150 is that the quality of the regenerated sand may be turned from unacceptable to acceptable because of returning the unaccepted regenerated sand back to the regeneration and possibly adjusting an operation of the regeneration system 1 by means of the regeneration system control unit 12 based on information received from the quality monitoring system control unit 150. Anyway, the connection between the regeneration system control unit 12 and the quality monitoring system control unit 150 is not necessary. If the regenerated sand with unacceptable quality is directed back 142 to the regeneration system 1, newly regenerated and newly monitored sand may have acceptable quality even though adjustments are not made in the operation of the regeneration system 1.

One or more actuators in the flow switch valve 140 may be controlled by means of the quality system control unit 150. The quality system control unit 150 may also be connected to the shaker of the mesh 110, wherein the control unit 150 may adjust intensity of shaking of the shaker. The control unit 150 utilizes the information when controlling the actuators. The control unit 150 may also be provided with different kind of starting data, i.e., initial data, wherein the mentioned starting data may include plurality of predetermined criterion sets for the acceptable loss of ignition of the regenerated sand according to each different final product.

According to an embodiment, the feed hopper 120 may be a conveyor that is configured to receive the regenerated sand from the regeneration system 1. The conveyor may receive the regenerated sand through the mesh. For example, the conveyor may be a belt conveyor. The conveyor may be connected to the quality monitoring system control unit 150 with which line speed of the regenerated sand travelling on the conveyor may be adjusted. The detecting device 130 for visually detecting the regenerated sand may be arranged so that the regenerated sand may be monitored while traveling on the conveyor.

According to an embodiment, the detecting device 130 for visually detecting is a camera that is configured to capture at least one image of the regenerated sand travelling on the conveyor. For the sake of clarity, at least one image may be taken during the regenerated sand traveling on the conveyor. The camera may for example be a line scan camera, an analog area scan camera, a digital area scan camera or a FullHD resolution camera. A frequency of capturing at least one image may be fitted to the line speed of the conveyor or vice versa. The camera is directed towards the conveyor so that the regenerated sand traveling on the conveyor may be monitored by the mentioned camera. The regenerated sand travels through an area on the conveyor, in which the mentioned area is monitored by the at least one camera. In addition, the quality monitoring system 100 comprises an image analysing unit that is connected to the camera. The image analysing unit is intended to analyse the quality of the regenerated sand based on the at least one image. The image analysing unit may comprise a library wherein a set of reference images of regenerated sand of different colours or colour hues, or of different degrees of darkness of the regenerated sand, may have been stored. The reference images of regenerated sand of different colours or colour hues or different degrees of darkness may include many examples of acceptable and/or unacceptable colours or colour hues or degrees of darkness of the regenerated sand. The at least one image may be compared to the set of reference images. The at least one image may be compared to the set of reference images by using for example artificial intelligence Al in the image analysing unit. The Al may be taught which colour(s) or colour hue(s) or degree(s) of darkness are acceptable and/or unacceptable.

It will be obvious to a person skilled in the art that, as the technology advances, the inventive concept can be implemented in various ways. The invention and its embodiments are not limited to the examples described above but may vary within the scope of the claims.