Field of the disclosure The disclosure relates generally to liquid removal, e.g. dewatering. More particularly, the disclosure relates to a method, to a system, and to a computer program for estimating residual liquid content of material, e.g. slurry, discharged from a liquid removal process. Furthermore, the disclosure relates to a method and to a liquid separation device for removing liquid from material. Furthermore, the disclosure relates to a computer program for controlling a liquid removal process.

Background

In many cases, a liquid separation device for removing liquid from material such as e.g. slurry comprises a carrier for carrying the material and a pump system for effecting a pressure difference over the carrier and the material carried by the carrier. In many implementations, the carrier is moving and material having a high liquid-content is supplied onto a surface of the carrier. The above-mentioned pressure difference causes a gas flow which removes liquid from the material through the carrier when the material travels through a liquid removal area affected by the pressure difference. Material from which at least a part of liquid has been removed in the above-described way is peeled off from the surface of the carrier and delivered to further processing and/or storing. A liquid separation device can be for example a rotary vacuum drum-filter, a rotary vacuum disc-filter, or a vacuum belt-filter where the gas flow, e.g. an air flow, for removing liquid is based on vacuum. It is however also possible that the liquid-removing gas flow is based on gas pressure higher than the atmospheric pressure. Furthermore, it is also possible that the liquid-removing gas flow is based on gas pressure higher than the atmospheric pressure on one side of the carrier and on vacuum on the other side of the carrier.

The residual liquid content of material which is discharged from a liquid removal process of the kind described above can be controlled by changing the speed of the carrier, the supply rate of the material onto the carrier, and/or the pressure difference. The residual liquid content can be reduced by increasing the pressure difference, by decreasing the speed of the carrier, and/or by reducing the supply rate of the material onto the carrier. Correspondingly, the residual liquid content can be increased by decreasing the pressure difference, by increasing the speed of the carrier, and/or by increasing the supply rate of the material onto the carrier. Concerning the control of a liquid removal process of the kind mentioned above, it is advantageous to have an estimate of the residual liquid content of material that is discharged from the liquid removal process. Thus, there is a need for technical solutions for estimating the residual liquid content with a sufficient accuracy and with a sufficiently small estimation delay, too.

Summary

The following presents a simplified summary in order to provide a basic understanding of some embodiments of the invention. The summary is not an extensive overview of the invention. It is neither intended to identify key or critical elements of the invention nor to delineate the scope of the invention. The following summary merely presents some concepts of the invention in a simplified form as a prelude to a more detailed description of exemplifying embodiments of the invention.

In accordance with the invention, there is provided a new estimator system for producing an estimate value indicative of residual liquid content of material discharged from a liquid removal process based on a gas flow directed to the material. The material can be for example slurry from which liquid, e.g. water, is to be removed. An estimator system according to the invention comprises:

- humidity indicator equipment for obtaining humidity data indicative of a change of humidity of the gas, the change of the humidity having occurred during the liquid removal process, and

- data processing equipment comprising:

- one or more memory circuits containing pre-stored data expressing a correlation between a decrease of the liquid content of the material during the liquid removal process and the change of the humidity of the gas, the change of the humidity being caused by evaporation of liquid from the material during the liquid removal process, and

- one or more data processing circuits for reading the pre-stored data from the one or more memory circuits, for producing the estimate value based on the humidity data and on the pre-stored data, and for outputting the produced estimate value.

The above-described estimator system is based on the fact that evaporation of liquid from wet or moist solid material increases the humidity of the gas, e.g. air, which is used for removing liquid from the material. Therefore, there is the above-mentioned correlation between the humidity change and the residual liquid content of the material. The indication of the humidity change can be based on, for example but not necessarily, a change of one or more of the following quantities: relative humidity, absolute humidity, dewpoint temperature, frostpoint temperature, a mixing ratio, wetbulb temperature, a ratio of humid air volume to dry air volume, water vapor pressure, water vapor saturation pressure, and enthalpy i.e. Specific Enthalpy of Moist Air.

In accordance with the invention, there is provided also a new liquid separation device for removing liquid from material e.g. slurry. A liquid separation device according to the invention comprises: - a pump for generating a pressure difference,

- a carrier for conveying the material through a liquid removal area affected by the pressure difference so that there is a gas flow through the carrier and the material carried by the carrier,

- an estimator system according to the invention for producing an estimate value indicative of residual liquid content of the material coming out from the liquid removal area, and

- a controller for controlling at least one of the following in accordance with the estimate value: the speed of the carrier, the supply rate of the material onto the carrier, the pressure difference. In accordance with the invention, there is provided also a new estimation method for producing an estimate value indicative of residual liquid content of material discharged from a liquid removal process based on a gas flow directed to the material. An estimation method according to the invention comprises: - obtaining, by humidity indicator equipment, humidity data indicative of a change of humidity of the gas, the change of the humidity having occurred during the liquid removal process, and

- reading, by data processing equipment from one or more memory circuits, pre-stored data expressing a correlation between a decrease of the liquid content of the material during the liquid removal process and the change of the humidity of the gas, the change of the humidity being caused by evaporation of liquid from the material during the liquid removal process,

- producing, by the data processing equipment, the estimate value based on the humidity data and on the pre-stored data, and - outputting, by the data processing equipment, the produced estimate value.

In accordance with the invention, there is provided also a new method for removing liquid from material. The method comprises:

- generating a pressure difference,

- conveying, with a carrier, the material through a liquid removal area affected by the pressure difference so that there is a gas flow through the carrier and the material carried by the carrier,

- producing, by data processing equipment, an estimate value indicative of residual liquid content of the material coming out from the liquid removal area by carrying out an estimation method according to the invention, and - controlling, by a controller, at least one of the following in accordance with the estimate value: the speed of the carrier, the supply rate of the material onto the carrier, the pressure difference. In accordance with the invention, there is provided also a new computer program for producing an estimate value indicative of residual liquid content of material discharged from a liquid removal process based on a gas flow directed to the material. The computer program comprises computer executable instructions for controlling a programmable processor to:

- receive humidity data indicative of a change of humidity of the gas, the change of the humidity having occurred during the liquid removal process, and

- read, from one or more memory circuits, pre-stored data expressing a correlation between a decrease of the liquid content of the material during the liquid removal process and the change of the humidity of the gas, the change of the humidity being caused by evaporation of liquid from the material during the liquid removal process,

- produce the estimate value based on the humidity data and on the pre-stored data, and

- output the produced estimate value.

In accordance with the invention, there is provided also a new computer program for controlling a liquid removal process that comprises conveying, with carrier, material through a liquid removal area affected by a pressure difference so that there is a gas flow through the carrier and the material carried by the carrier, wherein the computer program comprises:

- computer executable instructions according to the invention for controlling a programmable processor system to produce an estimate value indicative of residual liquid content of the material coming out from the liquid removal area, and

- computer executable instructions for controlling the programmable processor system to control at least one of the following in accordance with the estimate value: speed of the carrier, supply rate of the material onto the carrier, the pressure difference. In accordance with the invention, there is provided also a new computer program product. The computer program product comprises a non-volatile computer readable medium, e.g. a compact disc "CD", encoded with a computer program according to the invention. Exemplifying and non-limiting embodiments of the invention are described in accompanied dependent claims.

Various exemplifying and non-limiting embodiments of the invention both as to constructions and to methods of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific exemplifying embodiments when read in conjunction with the accompanying drawings.

The verbs "to comprise" and "to include" are used in this document as open limitations that neither exclude nor require the existence of also un-recited features. The features recited in the accompanied dependent claims are mutually freely combinable unless otherwise explicitly stated. Furthermore, it is to be understood that the use of "a" or "an", i.e. a singular form, throughout this document does as such not exclude a plurality.

Brief description of the figures

Exemplifying and non-limiting embodiments of the invention and their advantages are explained in greater details below in the sense of examples and with reference to the accompanying drawings, in which: figure 1 illustrates a liquid separation device according to an exemplifying and non- limiting embodiment of the invention for removing liquid from material e.g. slurry, figure 2 shows a flowchart of an estimation method according to an exemplifying and non-limiting embodiment of the invention for estimating residual liquid content of material discharged from a liquid removal process, figure 3 shows a flowchart of a method according to an exemplifying and non-limiting embodiment of the invention for removing liquid from material e.g. slurry, figure 4 illustrates a liquid separation device according to an exemplifying and non- limiting embodiment of the invention for removing liquid from material e.g. slurry, and figure 5 illustrates a liquid separation device according to an exemplifying and non- limiting embodiment of the invention for removing liquid from material e.g. slurry.

Description of exemplifying embodiments

The specific examples provided in the description below should not be construed as limiting the scope and/or the applicability of the accompanied claims. Lists and groups of examples provided in the description are not exhaustive unless otherwise explicitly stated.

Figure 1 illustrates a liquid separation device according to an exemplifying and non- limiting embodiment of the invention for removing liquid from material 1 10 that can be for example slurry. In this exemplifying case, the liquid separation device is a vacuum belt-filter that comprises a carrier 107 configured to convey the material 1 10, e.g. a cake of slurry, in the positive x-direction of a coordinate system 199. It is also possible that a liquid separation device according to an exemplifying and non- limiting embodiment of the invention is a rotary vacuum drum-filter, a rotary vacuum disc-filter, or another liquid separation device that is based on gas flow through material from which liquid is removed. The liquid being removed from the material 1 10 can be for example water.

The liquid separation device comprises a pump 106, a piping system, and other structures configured to maintain a pressure difference Δρ over the carrier 107 and the material 1 10 carried by the carrier. The material 1 10 is supplied on the carrier 107 so that the carrier 107 conveys the material through a liquid removal area 109 affected by the pressure difference Δρ. The pressure difference Δρ maintains a gas flow through the carrier 107 and the material 1 10 carried by the carrier, and thereby the pressure difference Δρ sucks liquid from the material 1 10 through the carrier 107. In typical cases where the material 1 10 is porous, some of the pores of the material 1 10 become empty of liquid due to the influence of the gas flow maintained by the pressure difference Δρ. The process of emptying the pores is called desaturation or deliquoring. The above-mentioned gas can be e.g. air.

The liquid separation device further comprises an estimator system according to an exemplifying and non-limiting embodiment of the invention for producing an estimate value LC _e which is indicative of residual liquid content of the material 1 10 coming out from the liquid removal area 109. The estimator system comprises humidity indicator equipment 101 for obtaining humidity data which expresses how much the humidity of the gas changes during the liquid removal process, i.e. when the gas flows through the material 1 10 and the carrier 107. The humidity indicator equipment 101 may comprise for example a first gas humidity sensor 103 for measuring a first gas humidity value HIG from the gas flow directed to the material 1 10 and a second gas humidity sensor 104 for measuring a second gas humidity value H2G from the gas flow leaving the material 1 10. In this exemplifying case, the difference between the second and first gas humidity values htas - HIG expresses how much the humidity of the gas changes when the gas flows through the material 1 10 and the carrier 107. In order to improve the accuracy of the humidity data, it is possible to use more than one first gas humidity sensor and/or more than one second gas humidity sensor e.g. in the vacuum box below the carrier 107. The gas humidity sensor 103 can be for example a commercially available device such as e.g. Vaisala HUMICAP® HMW90-series humidity sensor. Correspondingly, the gas humidity sensor 104 can be for example a commercially available device such as e.g. Vaisala HUMICAP® HMT330 -series humidity sensor.

The above-mentioned estimator system further comprises data processing equipment 102 for forming the estimate value LC _e indicative of the residual liquid content based on the above-mentioned humidity data and on pre-stored data expressing a correlation between a decrease of the liquid content of the material 1 10 during the liquid removal process and the change of the humidity of the gas. The change of the humidity of the gas is caused by evaporation of liquid from the material during the liquid removal process. Therefore, there is the correlation between the residual liquid content of the material 1 10 and the above-discussed humidity difference H2G - HIG. The above-mentioned pre-stored data expressing the above-mentioned correlation can be obtained for example with a procedure comprising the following actions:

1 ) Measurement of the humidity difference H2G - HIG within a range of conditions, such as e.g. different solid loadings per filtration area, kg _S oiids/m ² , and different pressure differences Δρ, and taking corresponding samples of material discharged from the liquid removal process. The aim is to produce material samples with different residual liquid contents to cover the whole range from saturated material samples to material samples from which more liquid cannot be removed mechanically by a gas flow. 2) Determination of the residual liquid contents of the material samples e.g. by drying them to obtain the equilibrium dryness, and by calculating the mass fraction of liquid in them. The standard temperature of 1 05°C is applicable for most inorganic materials, and the applied temperature can be higher or lower than 1 05 °C if the material requires this. 3) Forming the correlation between the humidity difference H2G - HIG and the residual liquid content for example by presenting corresponding values of the residual liquid content and of the humidity difference under consideration as points on a coordinate plane and fitting a curve, typically a straight line, to the data by an adequate mathematical method. An estimator system according to an exemplifying and non-limiting embodiment of the invention further comprises temperature sensor equipment 1 21 for obtaining temperature data which expresses the difference between the temperature of the gas leaving the material 1 10 and the temperature of the gas arriving at the material 1 1 0. The expression "temperature sensor equipment" is to be understood in a broad sense so that the temperature sensor equipment can be any suitable temperature indication equipment for obtaining the temperature data directly or indirectly based on any suitable phenomenon/phenomena directly or indirectly related to temperature. The temperature sensor equipment 1 01 may comprise for example a first gas temperature sensor 1 22 for measuring a first gas temperature value TIG from the gas flow directed to the material 1 1 0 and a second gas temperature sensor 1 23 for measuring a second gas temperature value T2G from the gas flow leaving the material 1 10. In this exemplifying case, the difference between the second and first gas temperature values T2G - TI G expresses how much the temperature of the gas changes when the gas flows through the material 1 10 and the carrier 107. In order to improve the accuracy of the temperature data, it is possible to use more than one first gas temperature sensor and/or more than one second gas temperature sensor e.g. in the vacuum box below the carrier 107. In the estimator system according to this exemplifying and non-limiting embodiment, the data processing equipment 102 can be configured to form another estimate for the residual liquid content based on the above-mentioned temperature data and on pre- stored data expressing a correlation between a decrease of the liquid content of the material 1 10 and the change of the gas temperature due to the cooling effect caused by evaporation of liquid from the material during the liquid removal process. The heat energy required for evaporation of the liquid is provided partly by the gas flow directed to the material 1 10 and partly by the material 1 10 which in turn cools the gas. Therefore, there is the correlation between the residual liquid content of the material 1 10 and the above-discussed temperature difference T2G - TI G. The data expressing the correlation related to the gas temperature can be obtained for example with a procedure that is similar to the above-described procedure for obtaining the data expressing the correlation related to the gas humidity, i.e. the temperature difference T2G - TI G is used instead of the humidity difference H2G - H I G in a procedure of the kind described above. The reliability of the estimate value LC _e of the residual liquid content can be improved by using both the estimation method based on the change of the gas humidity and the estimation method based on the change of the gas temperature. In an estimator system according to an exemplifying and non-limiting embodiment, the temperature sensor equipment 101 comprises a material temperature sensor instead of or in addition to the first gas temperature sensor 122. The material temperature sensor is configured to measure a material temperature value from the material 1 10 at an area where the material 1 10 arrives at the liquid removal process. The material temperature value can be used instead of or in addition to the first gas temperature value TI G. The material temperature sensor is not shown in figure 1 . The reliability of the estimate value LC _e of the residual liquid content can be further improved by using the material temperature value in addition to the first gas temperature value TI G. The liquid separation device comprises a controller 1 08 for controlling the operation of the liquid separation device at least partly in accordance with the above- mentioned estimate value LC _e so as to keep the residual liquid content within desired limits. The controller 1 08 can be configured to control for example the pressure difference Δρ, the speed v of the carrier 1 07, and /or the supply rate s of the material 1 10 onto the carrier. The residual liquid content of the material 1 10 coming out from the liquid removal area 1 09 can be reduced by increasing the pressure difference Δρ, by decreasing the speed v of the carrier, and/or by reducing the supply rate s of the material onto the carrier. Correspondingly, the residual liquid content can be increased by decreasing the pressure difference Δρ, by increasing the speed v of the carrier, and/or by increasing the supply rate s of the material onto the carrier. As the estimate value LC _e is based on the measured humidity data and on the pre-stored data indicative of the corresponding correlation, the estimation delay can be small and thereby the estimate value LC _e represents a real-time estimation of the residual liquid content. The estimate value LC _e is a real-time estimation of the residual liquid content also in cases where the estimate value LC _e is based, in addition to the humidity data, on the measured temperature data and on the pre-stored data indicative of the temperature-related correlation. It is worth noting that the estimate value LC _e used for controlling the liquid separation device can be for example the above-mentioned humidity difference H2G - HIG. In cases where the above-discussed correlation is assumed to be linear, the humidity difference h c - HIG can be assumed to be directly proportional to the residual liquid content, i.e. the ratio '(H2G - HIG) / residual liquid content' is assumed to be constant. The gain of the control loop can be tuned to be in harmony with the ratio: '(H2G - HIG) / residual liquid content'.

The implementation of the data processing equipment 102 can be based on one or more analogue circuits, one or more digital processing circuits, or a combination thereof. Each digital processing circuit can be a programmable processor circuit provided with appropriate software, a dedicated hardware processor such as for example an application specific integrated circuit "ASIC", or a configurable hardware processor such as for example a field programmable gate array "FPGA". Furthermore, the data processing equipment 1 02 may comprise one or more memory circuits each of which can be for example a Random-Access Memory "RAM" circuit. Correspondingly, the implementation of the controller 108 can be based on one or more analogue circuits, one or more digital processing circuits, or a combination thereof. Furthermore, the controller 108 may comprise one or more memory circuits.

Figure 2 shows a flowchart of an estimation method according to an exemplifying and non-limiting embodiment of the invention for producing an estimate value indicative of residual liquid content of material discharged from a liquid removal process based on a gas flow directed to the material. The estimation method comprises the following actions:

- action 201 : obtaining humidity data indicative of a change of humidity of the gas, the change of the humidity having occurred during the liquid removal process, and

- action 202: producing the estimate value at least partly based on the humidity data and on pre-stored data expressing a correlation between a decrease of the liquid content of the material during the liquid removal process and the change of the humidity of the gas, the change of the humidity being caused by evaporation of liquid from the material during the liquid removal process.

An estimation method according to an exemplifying and non-limiting embodiment of the invention further comprises:

- obtaining temperature data indicative of temperature of the gas leaving the material and temperature of the gas arriving at the material, and

- producing the estimate value at least partly based on the temperature data and on other pre-stored data expressing a correlation between the decrease of the liquid content of the material and a temperature difference between the gas leaving the material and the gas arriving at the material, the temperature difference being a corollary of a cooling effect caused by the evaporation of liquid from the material during the liquid removal process. The method may comprise for example the following actions for obtaining the temperature difference between the gas leaving the material and the gas arriving at the material:

- measuring at least one first gas temperature value TIG from the gas flow directed to the material, and

- measuring at least one second gas temperature value T2G from a gas flow leaving the material, where a difference between the second and first gas temperature values is indicative of the temperature difference between the gas leaving the material and the gas arriving at the material. Figure 3 shows a flowchart of a method according to an exemplifying and non- limiting embodiment of the invention for removing liquid from material e.g. slurry. The method comprises the following actions:

- action 301 : generating a pressure difference,

- action 302: conveying, with a carrier, the material through a liquid removal area affected by the pressure difference so that there is a gas flow through the carrier and the material carried by the carrier,

- action 303: producing an estimate value indicative of residual liquid content of the material coming out from the liquid removal area by carrying out an estimation method according to an embodiment of the invention, and - action 304: controlling at least one of the following in accordance with the estimate of the residual liquid content: the speed of the carrier, the supply rate of the material onto the carrier, the pressure difference.

In a method according to an exemplifying and non-limiting embodiment of the invention, the pressure difference is increased in response to a situation in which the estimate value is greater than a target value and the pressure difference is decreased in response to a situation in which the estimate value is less than the target value. In a method according to an exemplifying and non-limiting embodiment of the invention, the speed of the carrier is decreased in response to a situation in which the estimate value is greater than a target value and the speed of the carrier is increased in response to a situation in which the estimate value is less than the target value.

In a method according to an exemplifying and non-limiting embodiment of the invention, the supply rate of the material onto the carrier is decreased in response to a situation in which the estimate value is greater than a target value and the supply rate of the material onto the carrier is increased in response to a situation in which the estimate value is less than a target value.

A computer program according to an exemplifying and non-limiting embodiment of the invention comprises computer executable instructions for controlling a programmable processing system to carry out actions related to a method according to any of the above-described exemplifying embodiments of the invention. A computer program according to an exemplifying and non-limiting embodiment of the invention comprises software modules for producing an estimate value indicative of residual liquid content of material discharged from a liquid removal process based on a gas flow directed to the material. The software modules comprise computer executable instructions for controlling a programmable processor to: - receive humidity data indicative of a change of humidity of the gas, the change of the humidity having occurred during the liquid removal process, and

- produce the estimate value based on the humidity data and on pre-stored data expressing a correlation between a decrease of the liquid content of the material during the liquid removal process and the change of the humidity of the gas, the change of the humidity being caused by evaporation of liquid from the material during the liquid removal process.

A computer program according to an exemplifying and non-limiting embodiment of the invention comprises software modules for controlling a liquid removal process that comprises conveying, with carrier, material through a liquid removal area affected by a pressure difference so that there is a gas flow through the carrier and the material carried by the carrier. The software modules comprise:

- computer executable instructions according to an exemplifying and non- limiting embodiment of the invention for controlling a programmable processor system to produce an estimate value indicative of residual liquid content of the material coming out from the liquid removal area, and

- computer executable instructions for controlling the programmable processor system to control at least one of the following in accordance with the estimate value: the speed of the carrier, the supply rate of the material onto the carrier, the pressure difference.

The above-mentioned software modules can be e.g. subroutines or functions implemented with a suitable programming language.

A computer program product according to an exemplifying and non-limiting embodiment of the invention comprises a computer readable medium, e.g. a compact disc "CD", encoded with a computer program according to an exemplifying embodiment of invention.

A signal according to an exemplifying and non-limiting embodiment of the invention is encoded to carry information defining a computer program according to an exemplifying embodiment of invention. Figure 4 shows a schematic top-view of a liquid separation device according to an exemplifying and non-limiting embodiment of the invention for removing liquid from material 410 that can be for example slurry. In this exemplifying case, the liquid separation device is a rotary vacuum disc-filter. The liquid separation device comprises an estimator system according to an exemplifying embodiment of the invention for producing an estimate value indicative of the residual liquid content of the material 410 after the liquid removal process. The estimator system can be similar to that explained with reference to figure 1 .

Figure 5 shows a schematic side-view of a liquid separation device according to an exemplifying and non-limiting embodiment of the invention for removing liquid from material 510 that can be for example slurry. In this exemplifying case, the liquid separation device is a rotary vacuum drum-filter. The liquid separation device comprises an estimator system according to an exemplifying embodiment of the invention for producing an estimate value indicative of the residual liquid content of the material 510 after the liquid removal process. The estimator system can be similar to that explained with reference to figure 1 .

The above-presented examples relate to continuous liquid removal processes where material, e.g. slurry, under liquid removal is transferred as a continuous flow through an area affected by a pressure difference. It is, however, worth noting that the above-described principle for estimating the residual liquid content is applicable also on a batch process where a batch of material is subject to liquid removal so that the liquid removal process starts at a first moment of time for the whole batch and, correspondingly, the liquid removal process ends for the whole batch at a second moment of time. The specific examples provided in the description given above should not be construed as limiting. Therefore, the invention is not limited merely to the exemplifying and non-limiting embodiments described above. Lists and groups of examples provided in the description are not exhaustive unless otherwise explicitly stated.