System and method for assessing dredging product in a dredgeline

Abstract

The invention relates to a system for assessing dredging product, comprising a transport conduit for transporting dredging product, wherein said transport conduit is provided with a gamma-ray sensor. The invention further relates to a method for assessment of particles in a flow of dredging product, wherein the flow of dredging product is provided through a transport conduit, wherein the method comprises the step of measuring natural radiation, especially gamma (γ) radiation from radionuclides in particles contained in said flow of dredging product, using radiation sensor, preferably a gamma-ray sensor, more preferably a gamma-ray spectrometer, while the flow progresses through the transport conduit.

Description

[0001]P136313PC00 Title: System and method for assessing dredging product in a dredgeline The invention relates to a method for assessing dredging product in a dredger. The invention further relates to a system for assessment of dredging product in a dredger. When dredging from a bedding of a body of water dredged product is transported through a transport conduit from a dredging head to a transport line for further transport, or for example to a hopper or a barge. Especially when using a suction dredger the dredging product contains a relatively high volume of water, such that a flow of dredging product is obtained through the transport conduit. During dredging data is gathered concerning the flow of dredging product, such as volumetric data, concentration data, average speed and the like, which data may be used for controlling the dredging process. The data gathered presently does not allow proper assessment of the constitution of the dredging product, especially not of the solid particles enclosed therein. In order to perform such assessment a sample is to be taken from the content of the hopper or barge, to be analyzed dry in a laboratory. This is time consuming, laborious and costly. Moreover a sample only provides information concerning material in the hopper or barge locally. There is no link between the sample and the original location of the soil prior to dredging. There is a need for an alternative method for assessing dredging product resulting from dredging. There is a need for a method for assessing dredging product providing data quicker, easier and / or cheaper. There is a need for an alternative system for assessing dredging product. There is a need for a system for assessing dredging product during dredging. At least one of these or other needs is at least partly fulfilled and / or at least one of the problems of the prior art is at least partly mitigated by a method or system according to the disclosure. In an aspect of the disclosure a system is provided for assessing dredging product, comprising a transport conduit for transporting dredging product, wherein said transport conduit is provided with a gamma-ray meter. It has been found that with a gamma-ray meter radiation of particles in a flow of dredging product flowing through the transport conduit can be detected, even when the flow has relatively high speeds inside the conduit and the flow of dredging product comprises a high water content, such as for example 80 percent or more in volume. In a system of the disclosure preferably the gamma-ray meter is designed for detecting radiation of solid particles of a flow of dredging product flowing through said transport conduit, more preferably the gamma-ray meter is designed for real time measuring natural radioactivity of particles in the dredging product, especially of atoms in said particles. In advantageous embodiments the gamma-ray meter is provided in and / or on an outer surface of said transport conduit, preferably on, such as close to or against an outer surface. The conduit can have a wall thickness of for example 15 mm of steel or more, for example 20 mm or more, such as 30 mm or more. Surprisingly it has been found that even with such relatively thick steel walls of the conduit natural radiation of radionuclides of solid particles in the flow of dredging product can be detected, wherein based on at least data thus obtained the particles can be assessed during flow. Preferably the gamma-ray sensor is a gamma-ray spectrometer, which is preferably designed for detecting gamma-ray from at least one of Potassium (K), Uranium (U) and Thorium (Th), preferably at least two, more preferably all three. The Gamma-ray results from the radio nuclides of said at least one of Potassium (K), Uranium (U) and Thorium (Th). It has been found that a lower level of gamma radiation of particles in dredging product is an indication of predominantly larger particles, such as in sand or gravel, whereas a higher level of gamma radiation in dredging products is an indication of predominantly smaller particles, such as silt. It has further been found that the gamma-radiation detected of Potassium (K) is a good predictor for particle size, wherein a lower level of gamma radiation of Potassium in the particles points to larger particles and vice versa. In embodiments the gamma-radiation is measured of the combination of the natural radiation from radionuclides of Potassium (K), Uranium (U) and Thorium (Th), such that enough radiation can be detected, even when the flow of dredging product only contains a relatively low amount of particles, such as for example up to 10% or 15% or more in volume of solid particles, contained in water. In further elaboration a system of the disclosure preferably the transport conduit is further provided with a density meter for measuring density of dredging product flowing through said conduit. For assessment of the dredging product flowing through the transport conduit then preferably data obtained by the gamma detector and data obtained by the density meter is combined. To this end in preferred embodiments the density meter and the gamma-ray meter are connected to a data processing system for processing radiation-data concerning gamma-ray detected from a flow of dredging product and processing density data of said flow of dredging product, wherein the data processing system is designed for assessing particles in said flow of dredging products based on combined processing of said radiation-data and said density data. Preferably the density meter is provided upstream or downstream of the gamma-ray spectrometer, if a nuclear density meter is used. If a non- nuclear density meter is used it is preferably positioned opposite the gamma ray sensor, for providing an optimal correlation between the density measured and the gamma ray measured. Preferably the gamma-ray meter is and more preferably the gamma-ray meter and the density meter are provided at a conduit at a position or positions where the transport conduit extends at an angle relative to a horizontal plane, especially a substantially vertical part of the transport conduit. In such embodiments the density meter can be positioned at a level above or below a position at which the gamma-ray meter is provided. Said level can be spaced apart from the gamma-ray meter, measured along the transport conduit. This is especially advantageous when the density meter is radioactive radiation based. It has been found that during use influence of a radioactive density meter on radiation measured by the gamma ray detector is largely mitigated by the water or mixture of water and soil flowing through the conduit. If a non- nuclear density meter is used the density meter and the gamma ray detector can be provided at the same level, opposite each other. In a system according to the disclosure preferably a database of gamma-radiation profiles of soil types is provided. Such database can for example be established by uploading data of samples of soil, especially gamma-radiation data of such samples of soil, such that data obtained by the gamma-radiation meter can be compared with such data of samples, allowing assessment of the particles in the flow. Thus for example it can be assessed whether the dredging product for example comprises predominantly silt, a combination of silt and sand, predominantly sand, a combination of sand and gravel or predominantly gravel. In an aspect a method is disclosed for assessment of particles in a flow of dredging product, wherein the flow of dredging product is provided through a transport conduit. The method comprises the step of measuring natural radiation, especially gamma (γ) radiation from radionuclides in particles contained in said flow of dredging product, using a radiation sensor, preferably a gamma-ray meter, more preferably a gamma-ray spectrometer, while the flow progresses through the transport conduit. In a method of the disclosure preferably the radiation is measured through a wall of said transport conduit. Thus the detector can be kept accessible and be kept out of contact with the product flowing through the conduit to be measured. Preferably at least radiation of Potassium (K) is measured, or at least radiation of gamma-ray from Potassium (K) and at least one of Uranium (U) and Thorium (Th), preferably at least two, more preferably all three. In preferred embodiments during use additionally density of said flow inside the transport conduit is measured. For example this is measured downstream of an area in which said natural radiation is measured. In embodiments of a method of the disclosure data concerning said natural radiation is combined with data concerning density, forming combined a combined data set, wherein based on said combined data set the particles in said flow are assessed. Preferably in such embodiments for assessing the said particles the combined data set is compared with data concerning soil stored in a database. In embodiments of a method of the disclosure location data concerning a location at which the dredged product flowing through the transport conduit has been dredged is stored in a database, associated with data concerning the particles in said flow. Thus easily for example a map can be formed disclosing a relation between particles, especially particle properties, and location. Such a map can then for example be displayed showing information based on said location data and said data concerning said particles, for example during dredging. The disclosure is further directed to the use of a gamma-ray spectrometer in assessing dredging product, especially solid particles, in a flow of dredging product flowing through a transport conduit of a dredger. The disclosure is further directed to a dredger, comprising a system according to the disclosure or equipped for a method according to the disclosure. For a better understanding of the disclosure embodiments of a method and system according to the disclosure will hereafter be described, by way of example only, with reference to the drawings. Therein shows schematically: Fig.1 in side view part of a dredging vessel, showing at least a transport conduit for transporting dredging product; Fig.2 a system for assessing dredging product; Fig.3 alternative embodiments of a system for assessing dredging product; Fig.4 a graph showing the radiation spectrum of particles, showing peaks in counts per second (cps) at energy (keV) for K, U and Th; Fig.5 fingerprints of four soil samples, defined by concentration in Becquerel per kilogram (Bq / kg); Fig.6 an example of a sample concentration of K, Th and U, for dredged soil, and background radiation; Fig.7 a graph showing the relation between particle size (micrometers) and gamma radiation of40K (Bq / kg); Fig.8 a graph showing PSI’s (Particle Size Indicator) for three dredging areas, showing the relation between total counts (Bq) measured and the density of the dredging product; Fig.9 a map showing results of gamma radiation measured during dredging in three area’s; and Fig.10 an alternative embodiment of a system according to the disclosure. It should be noted that these drawings are schematic, not necessarily to scale and are provided for a better understanding of the disclosure. The embodiments shown in the drawings and described hereafter are shown only by way of example and should not be considered limiting the scope of the disclosure. In the description the same or similar reference signs will refer to the same or similar features. In this description reference is made to dredging product, which should be understood as meaning at least a mixture of a liquid fraction and a solid fraction, and / or a mixture of at least water and soil, the soil comprising at least one or more of sand, sludge, silt and / or gravel. In this description a method and system are described, as well as parts thereof, wherein natural radiation, especially gamma (γ) radiation from radionuclides in particles contained in a flow of dredging product is measured, using a radiation sensor, preferably a gamma-ray meter, more preferably a gamma-ray spectrometer, while the flow progresses through a transport conduit. This should be understood as meaning that the said natural radiation is measured of said radionuclides in the particles while the particles move with the flow of dredging material through the transport conduit. In a method according to the disclosure for assessment of particles in a flow of dredging product, the flow of dredging product is provided through a transport conduit, wherein the method comprises the step of measuring natural radiation, especially gamma (γ) radiation from radionuclides in particles contained in said flow of dredging product, using radiation sensor, preferably a gamma-ray sensor, more preferably a gamma- ray spectrometer, while the flow progresses through the transport conduit, which is to be understood as meaning that the particles of which said radiation is measured progress through the conduit with the flow while said assessment is made. Fig.1 and 2 schematically show a system 1 for assessing dredging product 2, during dredging. In fig.1 and 2 the system 1 is shown as provided on a dredging vessel 3, here by way of example shown as a Cutter Suction Dredger (CSD) of which only a relevant part is shown and discussed. In a system 1 of the disclosure a transport conduit 4 is provided for transporting dredging product 2 from a dredging head 5 to for example a further transport line, for transporting the dredging product to a use location, or to a transport and / or storage provision, like for example but not limited to a separate barge, or to for example a further transport system, such as for example but not limited to known pressure transport systems for transporting the product through piping 4A, as schematically shown in fig. 1. Alternatively dredged product can be stored in a hopper, in a known manner (not shown). In fig.1 and 2 the transport conduit 4 is connected to or comprises a dredging pump 6, for suction of dredging product from the dredging head 5 through the transport conduit 4. As will be discussed further on, the dredging product will normally be a suspension or mixture of for example sludge and / or silt and / or sand and / or gravel and / or clay, and water. The system 1 is further provided with a gamma-ray sensor 7, also referred to as gamma-ray detector system or similar wording. An example of a gamma-ray detection system 7 suitable for use in a system or method of the disclosure is known in the art and is for example described in EP0754306. The gamma-ray detector 7 is designed for detecting radiation of solid particles Px of a flow of dredging product 2 flowing through said transport conduit 4. The solid particles Pxcan for example be sand, sludge, silt and / or gravel. The solid particles Pxhave a natural radioactive activity, transmitting radiation, formed by or including gamma radiation (γ- radiation). In the present disclosure preferably a gamma-ray sensor 7 is provided which is at least sensible for natural radiation from radionuclides of at least one of, and preferably a number of and more preferably all of Potassium (K), Uranium (U) and Thorium (Th) and their decay products. The nuclides can for example be instable isotopes, such as40K,232Th and235U,238U. It is noted that these nuclides have a very long life, with a half- time which can be up to or more than 109years. These nuclides decay over their lifetime to stable isotopes, through a long sequence of intermediate products, also referred to as their decay products, while emitting at least gamma radiation. Because the energy of each photon of Electromagnetic (EM) radiation is proportional to its frequency, gamma rays have sufficient energy such that they are typically observed by counting individual photons. Since each of the said radionuclides has its own, specific radiation pattern, the presence of each of these nuclides can be detected from a profile obtained with the gamma-ray sensor 7. In preferred embodiments a data processing system 11 is provided for processing at least data obtained by the gamma-ray sensor 7. The data processing system 11 can be provided with a database 12 or can be connected to a database 12, the database 12 comprising reference profiles for various dredging materials, such as of components of soil. The processing system 11 furthermore preferably comprises an algorithm for comparing a gamma-ray profile obtained with the gamma-ray sensor 7 with known profiles stored in said database 12, for assessing components of the dredged product. As is shown in fig.2, the gamma-ray sensor can be provided in and / or on an outer surface 8 of said transport conduit 4. The gamma-ray sensor 7 is preferably mounted such that there is no contact between the flow of dredging product 2 flowing through the conduit 4 and the sensor 7, thus protecting the sensor 7 at least from abrasion by the flow of dredging product 2. Moreover this allows for easy placing, removing, maintenance and repair of the sensor 7. The wall 9 of the conduit 4 is preferably made of metal and has a relatively large thickness. For example the wall 9 can have a thickness t of more than 2 centimeters, for example 3 centimeter or more. Surprisingly it has been found that nevertheless in real time said natural gamma radiation of the said solid particles Px can be measured by the gamma-ray sensor 7, through said wall 9. Fig.3 shows an embodiment in which the transport conduit 4 is further provided with a density meter 10 for measuring density of dredging product 2 flowing through said conduit 4. By measuring the density of the dredging product 2 flowing through the conduit 4, it can easily be assessed what percentage of the volume of dredging material 2 flowing through the conduit is formed by solid particles Px. The density meter 10 and the gamma-ray sensor 7 are connected to the data processing system 11 for processing radiation-data concerning gamma-ray detected from the flow of dredging product 2 and processing density data of said flow of dredging product 2. The data processing system 11 is preferably designed for assessing particles Pxin said flow of dredging product 2 based on combined processing of said radiation-data and said density data. Density meters 10, also referred to as density measurement system 10 as such for measuring density of a flow of dredging product 2 are known in the art. In embodiments the density meter 10 can be based on a nuclear source 13, and a detector 14 for detecting radiation emitted by said nuclear source 14. In embodiments the density measurement system can be based on a gamma radiation source 13 and a receptor or detector 14 for such gamma radiation, as is for example, but not limited to, provided by Berthold Technologies GmbH, Germany, or a nuclear meter as provided by Smar Technology Company, Brazil. In alternative embodiments a density measurement system or density meter 10 can be based on non-nuclear technology, such as for example provided by Alia Instruments, The Netherlands, or by Industrial Tomography Systems, (ITS), UK. With a density meter 10 the density of the flow of dredging product 2 can be measured in real time, while flowing through the conduit 4, in the flow direction F. In the embodiments shown the gamma-ray sensor 7 and, if provided for, the density meter 10 is / are provided preferably in a conduit having a substantially vertical direction of flow F. The substantially vertical direction of flow F can provide the advantage that stratification in the flow can be avoided as much as possible. In such vertical flow the risk is mitigated or at least significantly reduced that for example solid material within the flow of dredging product 2 will have the tendency to transit towards a wall 9 of the conduit, for example because of gravity and / or friction between the solid particles Px and the wall 9. With a substantially vertical flow F it can be ensured to a very high degree that the flow will be substantially homogenous across a cross section of the conduit 4. In the embodiment of fig.3 the density meter 10 is positioned spaced apart over a distance Z from the gamma ray sensor 7, seen in a direction of flow F of the conduit 4. In fig.3 by way of example the density meter 10 is positioned at a level above a position at which the gamma-ray meter 7 is provided. Said level spaced apart from the gamma-ray meter, measured along the transport conduit 4. In preferred embodiments the said level at which the density meter 10 is positioned is spaced apart over a distance Z, for example but not limited to at least half the largest inside cross measure, especially diameter D of the transport conduit 4, measured at the position of the gamma-ray meter 7. Said distance can for example be at least once the said largest inside cross measure D of the transport conduit 4. This is especially relevant when using a nuclear based, such as gamma ray based density meter 10, since otherwise the radiation emitted by the density meter source 13 may undesirably influence the reading obtained by the gamma-ray sensor 7. More generally the density meter 10 is in such embodiments preferably spaced apart from the gamma-ray sensor 7 over such distance Z that the reading of the gamma-ray sensor 7 is not significantly influenced by the radiation emitted by the source 13.at least when flow is present in said conduit 4. It has been found that such influence is mitigated to a high degree during use, when water or a mixture of dredged soil and water is pumped through the conduit 4. Hence in embodiments said distance Z can be relatively small, for example less than said diameter or less than half said diameter D. It will be clear that a density meter 10 can also be positioned differently relative to the gamma-ray sensor 7, for example upstream from the gamma-ray sensor 7 instead of or in addition to downstream thereof. When using a density meter based on non-nuclear technology, also referred to as non-nuclear density meter, the density meter 10 can be positioned directly opposite the gamma ray sensor 7, such that the distance Z as for example shown in fig.3 or fig.10 is about zero or at least as small as allowable based on the sensor 7 and density meter 10 used. This can further optimize the correlation between the density and the gamma radiation measured. With a system 1, comprising a gamma ray sensor 7 and preferably a density meter 10 as disclosed, on a dredging vessel 3, a method for assessment of particles Pxin a flow of dredging product 2 can be performed, especially for real time assessment of the composition of the dredging product 2, more specifically of the particles Px in the soil contained therein, such as type and distribution of particles Px. In such method a flow of dredging product 2 is provided through a transport conduit 4, wherein the method comprises the step of measuring natural radiation, especially gamma (γ) radiation from radionuclides in particles Pxcontained in said flow of dredging product 2, using radiation sensor 7. The radiation sensor 7 preferably is or at least comprises a gamma-ray sensor 7. The gamma-ray sensor 7 preferably is a gamma-ray spectrometer. The radiation is measured while the flow progresses through the transport conduit 4, preferably real time. By assessing the composition of the flow of dredging material 2, especially of the solid particles Px of the soil, the quality of the dredging product 2 can be assessed. For example it can be assessed whether the solid particles Px contained therein are predominantly sand or silt, and / or what the size distribution of the solid particles Pxis. Also during dredging it can be established whether the composition of the dredging product forwarded through the conduit 4 changes, for example but not exclusively in water content or particle Pxdistribution. As discussed, the radiation is preferably measured through a wall 9 of said transport conduit 4, such that the or any sensor 7 need not be in contact with the flow of dredging product 2. Thus the sensor 7 is better protected against for example abrasion, and can be more easily be reached for maintenance or repair. Gamma radiation has the advantage that it passes easily through relatively thick metal walls 9, such as a wall 9 of a transport conduit 4 of a dredging vessel 3. In embodiments of a method according to the disclosure natural gamma radiation is measured, emitted by particles Pxin the soil in the dredging product 2. Preferably at least radiation of Potassium (K) is measured, more preferably at least radiation of gamma-ray from Potassium (K) and at least one of Uranium (U) and Thorium (Th), preferably at least two, more preferably all three. Radiation of Potassium should be understood as including radiation from decay products of Potassium. Similarly radiation of Uranium and Thorium should be understood as including radiation of decay products thereof. It is known that different nuclides emit gamma radiation (photons) with different intensities. Fig.4 shows a graph taken from EP0754306, showing the intensity of radiation at different energy levels, with an indication of the positioning of K, U and Th in such spectrum. Based on the energy (keV) of radiation detected the nuclides can be assessed. Different types of soil particles Pxhave different nuclides and / or different concentrations of nuclides. Fig.5 by way of example shows a graph of concentrations of nuclides in different types of soil tested, for reference, also referred to as “fingerprints” for the relevant soil types. The nuclides measures are40K,238U and232Th. In the graph of fig.5:- at the left hand side the concentrations are shown for “whitesand” (“wit zand”; WZ), showing 2.1 Bq / kg from40K, 2.5 Bq / Kg of238U and 1.3 Bq / kg of232Th; -in the group of three columns second from the left theconcentrations are shown for “Wester Gouw soil” (“Wester Gouwe”; WG), showing 29 Bq / kg from40K, 12 Bq / Kg of238U and 16 Bq / kg of232Th; -in the group of three columns third from the left theconcentrations are shown for “Markerwadden soil” (Markerwadden”; MW), showing 53 Bq / kg from40K, 27 Bq / Kg of 238U and 35 Bq / kg of232Th; and -in the group of three columns fourth from the left theconcentrations are shown for “Clay Rijperij” (“Klei Rijperij”; KR), showing 62 Bq / kg from40K, 23 Bq / Kg of238U and 37 Bq / kg of232Th. The “White Sand”, “Wester Gouwe soil”, “Markerwadden soil” and “Klei Rijperij” (WZ, WG, MW, KR) are samples of soil retrieved from different locations, which were measured after drying. In fig.5 for each type of soil also the color is shown, which allows for visual inspection also. Fig.6 shows a similar graph, showing radiation measured for a soil sample dredged at one position, in which graph the concentration of K (in percentage), U (in ppm) and Th (in ppm) is shown. In this graph for the sample the total radiation is shown in the green column (left hand of each set of columns), whereas background radiation is shown for each of the three nuclides in the blue column of each set (right hand of each set of columns). The background radiation is measured in a sample comprising no soil. The radiation from the three types of nuclides is therefor calculated by subtracting the background radiation from the total radiation measured. The total radiation of a sample is measured in a lab by placing the sample on top of a gamma sensor in a lead box. Background radiation is then measured by removing the sample from the sensor. The remaining radiation is thus ‘environmental’ radiation or background radiation not originating from the sample and can be distracted from the total radiation measured. It has further been found that a correlation exists between size of particles Pxin soil and the gamma radiation measured from40K contained in said soil cq particles Px. In fig.7 this is shown in a graph for soil dredged from one location, as samples, wherein the radiation was measured by dragging a gamma sensor over the sea bed and the particle size assessed from the samples. As is shown in the graph of fig. 7 the radiation measure in Bq / kg (Activityconcentration K) is directly and proportionally related to the average particle size, wherein the larger the particles Px, the smaller the radiation measured. By measuring the gamma radiation from40K in dredged soil thus the average particle size can be assessed. In such samples D50 should be understood as a particle size wherein 50% of the particles in the sample is larger, and 50% is smaller dan said D50. In embodiments of a method of the disclosure for assessment of particles in a flow of dredging product 2, the flow of dredging product 2 is provided through the transport conduit 4, wherein natural radiation is measured, especially gamma (γ) radiation from radionuclides in particles Pxcontained in said flow of dredging product 2, using the radiation sensor 7. As discussed the sensor 7 preferably is a gamma-ray sensor, more preferably a gamma-ray spectrometer. The radiation is measured while the flow progresses through the transport conduit 4. In embodiments at least radiation of Potassium (K) is measured. In embodiments at least radiation of gamma-ray from Potassium (K) and at least one of Uranium (U) and Thorium (Th). Preferably radiation from both of Uranium (U) and Thorium (Th) is measured, preferably in combination with Potassium. In advantageous embodiments the combined gamma radiation of all nuclides in the particles emitting gamma radiation is measured, such that even with a relatively low concentration solid particles in the flow or product 2 and relatively high speed of flow, a significant reading is obtained. In the database 12 preferably a fingerprint for soil or for components of said soil at a dredging location is stored, especially radiation of the different nuclides in said soil, as for example is shown for different types of soil in fig.5 and 6. The fingerprints can be obtained prior to dredging, for example in prior sessions, and stored in the database 12, or can be obtained during dredging, by sampling, which sample can be dried and assessed, obtaining the fingerprints for the soil and / or individual nuclides. The samples can for example be dried, for example in an oven, to a water content of less than 10% in volume, for example less than 5%, more preferably less than 3% in volume, or even further, to about 0%. By having little to no water in the samples the advantage is obtained that a direct relation is obtained between the dry weight of the sample, the volume of the sample and the radiation measured from the sample. During dredging preferably the density of the dredging product flowing through the conduit 4 is measured using a density measurement system 10 as for example shown in fig.3. Preferably the density is measured constantly during dredging, or at regular intervals. Data concerning the natural radiation obtained during dredging is preferably combined in the data processing system 11 with data concerning the density, at least during the period the natural radiation is measured, such that for the flow of dredging product 2 the constitution can be assessed based on the fingerprint or fingerprints stored in the database 12. Data concerning said natural radiation is combined with data concerning said density, forming a combined data set, wherein based on said combined data set the particles Pxin said flow are assessed. For assessing the said particles the combined data set is preferably compared with data concerning soil stored in the database. By obtaining the relevant data periodically or continuously for the dredging product 2 dredged as a load, for example dumped into a hopper or barge, the particle distribution can be assessed and recorded for such load, or at least an assessment can be made of sand and silt or clay dredged in said load. This allows for assessment and registration of the quality of the load. Moreover, if a change in the particles contained in the flow of product is detected, for example by a change in the radiation measured and / or the fingerprint assessed, the dredge master controlling the dredging can be informed of such change, such that for example the dredging can be stopped, if the change is undesirable, or can be intensified if the change is assessed as positive for the dredged product. In embodiments location data concerning a location at which the dredged product 2 flowing through the transport conduit 4 has been dredged is stored in a database, associated with data concerning the particles Px in said flow of product 2. The location data can for example be obtained using a GPS system. Similarly fingerprints for samples taken at locations can be stored in the database with the relevant location data. Preferably the combined data on the assessed particle distribution and location data are displayed for observation for a dredger, such as a dredge master. The information can be displayed as a map 100 showing information based on said location data and said data concerning said particles Px, as is shown by way of example in fig.9 for locations near a coast. By way of example positions are indicated by longitude (horizontal axis, indicated by letters A – J) and latitude (vertical axis, indicated by numbers 1 – 6). Fig.8 shows a graph in which the total count in becquerel (Bq) is shown (vertical axis) for different densities of soil dredged (horizontal axis), at different locations in different areas. Total count should be understood as at least meaning the sum of gamma radiation measured of at least K, Th and U. In the graph PSI’s can be read for different locations, wherein the PSI is a Particle Size Indicator, and is calculated as the density (rhomix; kg / m3) divided by the count in Bq of natural radiation (Bq). In practice the graph of fig.8 and / or map of fig.9 can be presented in colour, for an even better understanding. In fig.9 at the right hand side a legend is shown indicating the PSI by grey scale. The PSI indicated in this legend, as example, runs from 30 (darkest) to 38 (lightest). In fig.8 for three different areas radiation counts (Bq) versus densities (kg / m3) during dredging are shown, which areas are shown in fig.9. In fig.8 line L1is an indication of an average PSI for area A1in fig.9, located at about 2 (latitude) and I and J (Longitude) showing different levels of radiation. Line L2 is an indication of an average PSI for area A2in fig.9, located at about 3 and 4 (latitude) and F (longitude). Line L3 is an indication of an average PSI for area A3 in fig.9, located at about 5 (latitude) and D and E (longitude) As can be ascertained from fig.8 in area A1predominantly sand was dredged, in area A3 predominantly mud or silt was dredged, and in area A2a mixture of silt and sand was dredged. In this example this was defined by taking samples from the dredged materials and testing them in a lab, similar to samples as shown by way of example in fig 5. In area A1 by way of example positions at which samples were taken are indicated by dots 101. As can be seen in fig.8 the angle of inclination α3 of line L3 is steeper than the angle α2 of line L2, which is again steeper than said angle α1 of line L1. The angle α is an indication of the relation between density and the related radiation count and thus of the PSI. As can be seen in fig.8 the radiation count increases quicker with an increase of density for silt than for sand. The density was measured using the density sensing system 10, wherein tests were performed with increasing densities, meaning less water per cubic meter (m3) dredging product. It is clear from fig.8 that the radiation emitted by the silt is higher or at least increasing more quickly for silt than for sand. For the mixture of water, sand and silt as dredged in area A2 the radiation emitted is between that of the sand / water mixture and the water / silt mixture. By way of example, in a method of the disclosure a dredger dredged in area A1, wherein during dredging the total gamma radiation and density were measured of the flow of dredging product 2 through the conduit 4, the data obtained processed and stored in the system 11 and database 12, together with the relevant location data. The obtained data was used for developing the graph as shown in fig.8, line L1, and the map as shown in fig.9. The dredger registered said data during multiple dredging cycles, in between which dredged loads were delivered at a delivery location. In each subsequent dredging cycle again said data was obtained. Similarly dredging cycles were performed in areas A2and A3, again registering the relevant data. By plotting the data as for example shown in fig.8, it can be assessed, for example by the inclination angle α of the PSI-line L, what the consistency of the dredged product 2 is, at least predominantly. The steeper the angle α, the lower the content of sand in the dredged product 2. A line L with a small angle will be an indication of more sand in said dredged product 2. By providing a map 100 as shown, by way of example, in fig.9, it is possible for the dredger to decide where in the relevant area a next dredging run dredging is preferred. In this disclosure sand should be understood as a material or mixture of materials having a granular size of between 0.06 and 2 mm, wherein sand may also comprise a limited volume percentage of gravel, having a granular size of between 2 and 60 mm, and particles smaller than 0.06 mm. In this disclosure dry sand should be understood as sand having a low moisture content, especially a moisture content significantly lower than when hydraulically loading sludge comprising said sand. Dry sand can for example have a moisture content of 15% by weight or less, for example a moisture content of 10% or less, and can have upward from 80% in volume material with a granular size between 0.06 and 2 mm. In this disclosure silt (slib) should be understood as a predominantly granular material or mixture of materials having a granular size of between 0.002 and 0.06 mm, wherein silt may also comprise a limited volume percentage of material having a granular size of between 0.06 and 2 mm, and particles smaller than 0.002 mm. In this disclosure dry silt should be understood as silt having a low moisture content, especially a moisture content significantly lower than when hydraulically loading sludge comprising said silt. Dry silt can for example have a moisture content of 15% by weight or less, for example a moisture content of 10% or less, and can have upward from 80% in volume material with a granular size between 0.002 and 0.06 mm. Clay will predominantly have a granular size of below 0.002 mm. Sand and silt or a mixture thereof can also be referred to as soil. Sludge is to be understood in this disclosure as dredged product, comprising water and soil, the soil containing or consisting predominantly of at least one of sand and silt, clay, rock. During dredging the sludge can for example have about 50 – 99% in volume of soil and 1 – 50% of water. As can be discerned from for example fig.8, the density of the dredged product will be about 1000 kg / m3when the flow contains substantially no soil and is hence substantially only water. Any gamma radiation in such flow will be the result of background radiation. In this disclosure sludge should at least be understood as meaning a mixture of water, especially sea water, and soil, which mixture can be dredged by suction and can be hydraulically loaded into a vessel, especially by pumping. The density of the dredged product can for example be between about 1000 kg / m3and 1400 kg / m3or more. Gamma radiation is preferably measured constantly, averaged in time intervals, for example time intervals of for example between 5 and 60 seconds, such that enough gamma radiation is received by the gamma sensor. Preferably the time intervals are short, for example about 30 seconds, wherein with lower radiation longer time intervals may be used, and with higher radiation shorter time intervals can be used. Preferably the gamma radiation of40K is registered separately too, such that the particle size can be assessed too, as shown by way of example in fig.7. Thus in the system the consistency of the dredged load can be assessed, both in sand and silt and in particle size, preferably both in average size and in size distribution. Fig.10 schematically shows an alternative embodiment, in which a system 200 of fig.2 or 3 with a gamma radiation sensor 7 is connected to a downstream side of a transport line or piping 4A, for example a transport piping 4A coming from a dredging vessel 1 or another source of dredging product 2. In such embodiment the system 200 can be placed on shore, i.e. not on a vessel, or at least not on a dredger. In fig.10 a pump 6 is shown in broken lines. Such pump 6 can also be positioned differently, for example upstream of the transport piping 4A, such as for example on the vessel 1 providing the dredging material 2. The invention is not limited to the specific embodiments as shown and discussed by way of example. Many variations are possible within the invention as defined by the claims. For example, a dredger for use in a system or method of the disclosure can be a different type of dredger, and can have a hopper in stead of or in addition to piping 4A. A gamma sensor according to the disclosure can also be provided on a different conduit, such as a transport conduit like piping 4A or a conduit for discharging sand and / or silt from a dredger, like by rainbowing. The gamma radiation sensor can be provided in a different position, like in an inclined or horizontal conduit, and can for example be provided in a wall of the conduit or inside the conduit. The gamma sensor and density sensor can be combined, especially when a non-nuclear density sensor is used.

Claims

Claims 1. System for assessing dredging product, comprising a transport conduit for transporting dredging product, wherein said transport conduit is provided with a gamma-ray sensor.

2. System according to claim 1, wherein the gamma-ray sensor is designed for detecting radiation of solid particles of a flow of dredging product flowing through said transport conduit, while the particles are moving with the flow through the transport conduit.

3. System according to claim 1 or 2, wherein the gamma-ray sensor is provided in and / or on an outer surface of said transport conduit.

4. System according to any one of the preceding claims, wherein the gamma-ray sensor is designed for real time measuring natural radioactivity of particles in the dredging product, especially of atoms in said particles.

5. System according to any one of the preceding claims, wherein the gamma-ray sensor is a gamma-ray spectrometer, which is preferably designed for detecting gamma-ray from at least one of Potassium (K), Uranium (U) and Thorium (Th), preferably at least two, more preferably all three.

6. System according to any one of the preceding claims, wherein the transport conduit is further provided with a density meter for measuring density of dredging product flowing through said conduit.

7. System according to claim 6, wherein the density meter and the gamma-ray meter are connected to a data processing system for processing radiation-data concerning gamma-ray detected from a flow of dredging product and processing density data of said flow of dredging product, wherein the data processing system is designed for assessing particles in said flow of dredging products based on combined processing of said radiation-data and said density data.

8. System according to any one of claims 6 or 7, wherein: - the density meter is provided upstream or downstream of the gamma-ray sensor when the density meter is based on nuclear technology; or - the density meter is positioned opposite the gamma-ray sensor when the density meter is based on non-nuclear technology.

9. System according to any one of claims 1 – 5 and any one of claims 6 – 8, wherein: - the density meter is positioned at a level above a position at which the gamma-ray sensor is provided, said level spaced apart from the gamma-ray sensor, measured along the transport conduit when the density meter is based on nuclear technology; or - the density meter is positioned at a same level as the gamma-ray sensor, such as opposite the gamma-ray sensor when the density meter is based on non-nuclear technology.

10. System according to any one of the preceding claims, wherein the system further comprises a database of radiation profiles of soil types.

11. System according to any one of the preceding claims, wherein the gamma-ray sensor is positioned at an inclined and preferably vertical section of the transport conduit.

12. Method for assessment of particles in a flow of dredging product, wherein the flow of dredging product is provided through a transport conduit, wherein the method comprises the step of measuring natural radiation, especially gamma (γ) radiation from radionuclides in particles contained in said flow of dredging product, using radiation sensor, preferably a gamma-ray sensor, more preferably a gamma-ray spectrometer, while the flow progresses through the transport conduit.

13. Method according to claim 12, wherein the radiation is measured through a wall of said transport conduit.

14. Method according to claim 12 or 13, wherein at least radiation of Potassium (K) is measured or at least radiation of gamma-ray from at least two of Potassium (K) least one of Uranium (U) and Thorium (Th), preferably at least all three.

15. Method according to any one of claims 12 – 14, wherein density of said flow inside the transport conduit is measured.

16. Method according to claim 15, wherein said density is measured upstream or downstream of an area in which said natural radiation is measured.

17. Method according to any one of claims 12 – 14 and claim 15 or 16, wherein data concerning said natural radiation is combined with data concerning said density, forming a combined data set, wherein based on said combined data set the particles in said flow are assessed.

18. Method according to claim 17, wherein for assessing the said particles the combined data set is compared with data concerning soil stored in a database.

19. Method according to any one of claims 12 – 18, wherein location data concerning a location at which the dredged product flowing through the transport conduit has been dredged is stored in a database, associated with data concerning the particles in said flow.

20. Method according to claim 19, wherein a map is displayed showing information based on said location data and said data concerning said particles.

21. Use of a gamma-ray meter in assessing dredging product, especially solid particles, in a flow of dredging product flowing through a transport conduit of a dredger.

22. Dredger, comprising a system according to any one of claims 1 – 11 or equipped for a method according to any one of claims 12 – 20.

23. Method of dredging, wherein dredging product is dredged from a water bedding and transported through a transport conduit towards a collecting provisionfor said product, wherein during dredging a method of any one of claims 12 – 20 is applied, wherein data is stored concerning the product collected, based on said assessment.

24. Method according to claim 23, wherein said data includes at least information concerning particle size of the collected product.

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