NL9201853A - METHOD AND APPARATUS FOR SELECTIVE REMOVAL OF INSULATED AND UNSAFEED DREDGING SPECIES - Google Patents

Description

"Method and device for the selective removal of contaminated and non-contaminated dredged material"

The present invention relates to a method for selectively removing contaminated and non-contaminated or at least little contaminated dredged material from a hopper dredger, while the latter cannot be selectively separated or dredged separately with a hopper dredger due to their manner of excavation, respectively. be loaded in cargo hold.

When dredging in certain fairways, estuaries, etc., significant amounts of contaminated sludge are found under certain circumstances. In many cases these contaminated sediments are found together with not or considerably less contaminated sandy materials in a locally mutually strong and frequently varying mixing form.

Various reasons, mainly of an ecological nature, call for a separation of sand and silt. On the one hand, the need arises to separate the contaminated materials from the non-contaminated materials by means of a treatment (whereby, of course, in this case, emphasis must be placed on the need that the separation system must also have a separation efficiency in addition to an important production capacity. which remains independent of the strongly varying supply modalities). On the other hand, the areas on land provided for discharging dredged materials are becoming increasingly limited, so that it can no longer be tolerated that important surfaces would be permanently covered with contaminated dredging sludge. In addition, it can no longer be tolerated that contaminated sludge would be permanently discharged under water elsewhere in the water basin.

The inventive idea now rests on the result of a combination of two basic findings. These two basic findings mean that: 1) the spoil to be dredged or to be extracted (occurring in excavation as described above), for sedimentological reasons, after extraction by hydraulic transport, i.e. dredging, resulting in the maximum breaking of potential in situ grain cohesion of the spoil and after loading, if necessary overflow, in a cargo hold of a hopper dredger or a vessel equipped for that purpose, will deposit in a cargo hold in the form of a settled heavier "coarse" -grained sand fraction with on top of a longer-term non-settled lighter fine-grained sludge fraction.

2) many pollutants, for other than sedimentological reasons, prefer to adhere largely (via adsorption) to finer silt granules and little or no negligible to the coarser sand grains.

The result of the combination of the two basic determinations is that, after the hydraulic loading process has ended, a sufficiently long-term stable two-layer structure can form in the cargo hold, consisting of an underlying sedimented, grain-free stacked, practically unsullied sand layer. and, on the other hand, an overhead floating-liquid grain contactless contaminated sludge layer.

On the basis of this last determination, a method has been developed according to the invention and, within the framework of this method, an apparatus has been developed which is technically feasible (including separation principle and materialization of it) to the problem posed and from an economic point of view (including separation capacity, separation efficiency, system and method) due to cycle construction hopper piston) defensible solution provided.

In order to make this possible according to the invention, after a loading cycle, during which the loading space of the hopper dredger is filled to a maximum, if necessary to overflow, a separation (for example, sludge contaminated during dredging extraction zone to discharge point) is allowed between the heavy fraction. (sand), which, as is known, can be regarded as a pure fraction, and the light fraction (sludge), which, as also known, must be regarded as a contaminated fraction, after which the light fraction is pressed on land from a hopper dredger, or, for temporary storage, dissolved under water. This form of unloading is dumping via the overflow chutes and is in principle non-valves. The heavy fraction is then pressed ashore elsewhere or cleaved under water. If necessary, if the heavy fraction, after removing the light fraction, is considered too limited in size, the above operation is repeated (several times if necessary).

According to a preferred embodiment, the above-mentioned light fraction is pressed to land and the above-mentioned heavy fraction is pressed into the water basin.

As stated above, the invention also relates to the device for performing the method as just explained.

Other details and advantages of the invention will become apparent from the following description of a method and an apparatus for selectively removing contaminated and uncontaminated or at least little contaminated dredged material from a hopper piston, according to the invention. This description is given by way of example only and does not limit the invention. The reference numbers refer to the attached figures.

Figure 1 is a schematic cross-sectional view, at the level of the cargo hold, over a hopper dredger, equipped with a device according to the preferred embodiment of the invention.

Figures 2 (a-g), 3 (a-g) and 4 (a-g) are schematically depicted different dredging cycles representing the sequence of possible hopper piston cargo space filling configurations.

Figure 5 (into which Figures 2, 3 and 4 can be integrated) provides a schematic representation of the method of the invention in the case where, for example, only three dredging loading cycles are required.

The method elucidated by these different figures is based on the observation that the pollutants, for example the heavy metals, bind practically 100% on very fine-grained materials. The latter refers mainly to materials with dimensions not exceeding 63 μπι.

Now when, as in many streams, sea mouths and other water basins, an important local and frequent diversity in dredging sludge is encountered, the finding outlined above is particularly attractive from a technical and economic point of view. When it is also established that the sedimentation of the heavy (sand) fraction, present in the mass of the dredged spoil, occurs relatively quickly, this can be used in the context of the method according to the invention.

In the following, by way of non-limiting example, the method will be described in its application in dredging a water basin by switching on a so-called hopper dredger.

In Figure 1, the ship's cross section, at the cargo hold of the hopper dredger, is indicated by the general reference 1. The bottom flaps of the useful cargo hold 2 are not proposed because they can have any shape and work according to different principles. The dredging materials are poured into the cargo hold 2 through the supply pipe 3 and the spreader 4. The height of the spreader 4 is adjustable in the usual manner.

The adjustable overflow (sleeve) 5 shown in figure 1 (of which several may be present) is (under its conventional embodiment, ie in open connection with the water basin) inherently part of a hopper dredger for the purpose of conventional / traditional use / deployment of the hopper dredger, ie when loading cargo space with overflow losses via the overflow or overflow duct. A first facet in connection with the device to be provided for making the method according to the invention possible occurs here: the overflow or overflow sleeve can, at will, by means of sealing systems, or remain in open connection with the water basin (traditionally loading with overflow losses). or be connected exclusively to a conventional empty suction channel or empty suction pipe to enable suction and pressing of the overlying liquid contaminated sludge layer present in the cargo hold, without additional water supply ex water basin.

In view of the adjustment range of the conventional overflow or overflow shaft 5, in many cases (depending on the sludge / sand composition in the dredging zone and possibly during the first loading cycles) the upper level of the unsullied sedimented sand layer will fall below the minimum adjustable level of overflow or overflow shaft 5. In these cases, to enable suction and pressing of the liquid-contaminated sludge layer present between the two levels, (and this is a second facet of the device to be provided) at least one additional two- or multi-part telescopic overflow (shaft) 6 is installed and connected to the conventional empty suction channel 7. Of course, overflow (tube) 6 is, for two obvious reasons, provided with a shut-off valve that can be operated hydraulically or mechanically.

After the cargo hold 2 of the (trailing) hopper dredger has been completely emptied to remove residual water, this cargo hold is filled with a mixture of water and dredged materials. These materials consist partly of a heavy fraction that will settle and of a light, non-settled fraction that will be found in the cargo hold above the heavy fraction.

The settling time for the heavy fraction (little or no contaminated sand) depends to a certain extent on certain parameters, for instance on the grain size of the sand, the viscosity of the liquid phase in which to settle and the settling height. The height of what can be regarded as the top surface of the settled heavy fraction can be determined by various techniques (whether continuous or remote). One of these is the simple use of a sounding rod.

It is expected and in function of a number of interdependent parameters that the sedimentation, ie the separation between the heavy and light fraction, will have been fully completed, mainly in the period of time that the hopper dredger needs to move from the dredging site to the light fraction (contaminated sludge) is pressed ashore to sail. Depending on the intended further processing, the light fraction thus pressed on land can, after a temporary stay at the unloading location, be transported in the usual way to a site provided for this purpose or to a processing facility whose principle and operation are not the essence of the invention and will therefore not be described.

If the size of the sedimented pure sand that remains in the cargo hold after pressing or otherwise removing the contaminated fraction from the cargo hold, the hopper dredger can sail to the place where in the river (or more generally the water basin) may be flapped (or to the place where land may be pressed).

However, if, for certain reasons, the size is considered insufficient, it will be sailed again to the dredging / recovery zone where the previously described dredging operations with subsequent sedimentation phase are repeated. These sub-cycles (meaning dredging and loading cycles) can, for certain reasons, be repeated several times (see figure 5 for three dredging loading cycles, for example) before the thus accumulated pure sand size in the cargo hold is considered sufficient to be flapped (or sprayed). at the designated location.

Pressing the tarnished light fraction onto land can be carried out in a very advantageous embodiment according to the invention by using a device mainly consisting of a telescopic and height-adjustable overflow sleeves 5 and 6 arranged in the cargo hold 2. these overflow ducts 5 and 6 are connected to a conventional empty suction channel 7 along which, via the conventional dredge pump or pumps connected to empty suction channel 7, the contaminated light fraction is sucked out of cargo hold 2 and pressed ashore. The overflow sleeves 5 and 6 are only a possible embodiment of the parts referred to by the general term overflow.

The overflow sleeve 6 can be closed at the top by a valve 8, which can be operated either mechanically or hydraulically.

Ultimately it will be emphasized that, due to the nature of the earthmoving used (dredging hydraulic / wet earthmoving), the potential in situ grain cohesion of the sludge-sand mortar due to the wet turbulent transport (via drag or cutting head, suction pipe, centrifugal pump , cargo hold supply line and spreaders) is broken to the maximum, allowing discrete settling of "any" silt sand grain.

As discrete grain settling becomes possible as a result of the recently explained discrete settling, after the end of the charging process, due to the difference in settling modality between fine (er) (sludge) grains and coarse (er) (sand) grains, In the cargo hold, within the usual available settling time during navigation, a stable two-layer structure quickly emerges consisting of an underlying settled grain-contact-resistant heavier sand fraction and an overhead floating liquid grain-contactless lighter sludge fraction.

For a clear understanding of the various dredging cycles to which Figures 2-4, on the one hand, and 5, on the other hand, the following explanation of the reference numbers used is given.

In Figures 2-4, 1 obviously refers to schematically depicted hopper dredgers, the payload space is clarified by 2, while 5, 6 and 7 respectively are meant; an overflow duct 5, an additional multi-part overflow duct 6 and an empty suction channel 7 to which both overflow ducts are connected.

The surrounding water and in certain circumstances the water that partially fills the overflow chutes is usually represented by a horizontal hatching.

The heavier and settled sand carries the reference 13, while the phase consisting of silt and sand and where the settling stage of the heavier sand phase has not yet been reached carries the reference 14.

15 then refers to the lighter sludge fraction that is always found above the settled heavier fraction 13, which consists of sand, or above a fraction 14, which consists of sludge and sand and in which the heavy fraction 13 has not yet settled. The settling time can correspond to the sailing time between the dredging location and the place where the sludge will be removed or correspond only to a fraction of this time.

A sequence of multiple dredging and unloading or valve operations is shown in Figure 5. In this figure, reference numerals 9, 10 and 11 respectively denote a) the dredging or recovery zone (reference 9); b) the place of discharge of the contaminated sludge (reference 10); c) the place of unloading of the unsullied sand (reference 11)

By 9 'and 9 "are meant respectively: a) load space filling configuration at start of loading (reference 9"); b) load space filling configuration at end of loading (reference 9 ");

By 10 'and 10 "are meant respectively: a) cargo hold filling configuration at the beginning of sludge discharge (reference 10'); b) cargo hold filling configuration at the end of sludge discharge (reference 10");

Finally, 11 'and 11 "respectively indicate: a) cargo hold filling configuration at start of sand unloading (reference 11"); b) cargo hold filling configuration at end of sand unloading (reference 11 ").

Once the heavy fraction, which is not or slightly contaminated, has finally been completely removed in the phase indicated by 11 "by valves or presses, the hopper piston can be switched on again for the phase indicated by 9".

The amounts of sand and silt indicated in the schematic figure 5 are only approximate for an understanding of a fully multi-stage cycle. The arrows of course clarify the movement of the dredging gear.

The term "hopper dredger" means trailing suction hopper dredger, hopper dredger and point-fixe or stationary hopper dredger.

Claims (7)

1. Method, ideally applicable in water basins where, at the location of the dredging zones, the dredging sludge under such a locally strong and frequently varying mixture of unsullied heavy sand fraction and contaminated light sludge fraction prevents selective / separate dredging or extraction of both in excavation fractions by means of a hopper dredger is impossible for the selective removal from a hopper dredger of dredged and mixed dredged material into the cargo hold, contaminated and not or at least little contaminated dredged material, characterized in that after a dredging operation in which the cargo hold of the hopper dredger is is filled to the maximum and without blending losses, a separation takes place between the heavy fraction (sand), which, as is known, can be regarded as a pure fraction, and the light fraction (sludge), which, as also known, must be regarded as a contaminated fraction, after which, from the hopper dredger, the light fraction at one unloading point from cargo hold 2 far and the heavy fraction at another unloading site, and if necessary, if the heavy fraction, after removing the light fraction in the cargo hold, is considered too limited in size, repeat the above operations. 2. Process according to claim 1, characterized in that the above-mentioned light fraction is pressed to land. Method according to claim 1, characterized in that the above-mentioned light fraction is discharged in a vessel equipped for that purpose. Method according to claim 1, characterized in that the above-mentioned light fraction is poured under water for temporary storage. Process according to any one of claims 1 to 4, characterized in that the above-mentioned heavy fraction is valveed or dumped into the water basin. Process according to one of Claims 1 to 4, characterized in that the above-mentioned heavy fraction is pressed to land. Device for carrying out the method according to any one of claims 1-6, wherein, after a dredging operation in which the cargo hold of the hopper dredger is filled to a maximum and without overflow losses, a separation is carried out between the heavy fraction (sand), which as is known, can be regarded as an unsullied fraction and the light fraction (sludge) which, as is also known, must be regarded as contaminated fraction, after which the light fraction is removed from the cargo hold at one unloading point and the heavy fraction at a other unloading point presses or flaps, and if necessary, if the heavy fraction, after removing the light fraction, is considered too limited in size in the cargo hold, repeat the above-mentioned operations, characterized in that in the cargo hold (2) of the hopper dredger has at least one traditional overflow duct (5) connected to a conventional empty suction channel (7) and additionally at least one height-adjustable one- or more-membered telescopic overflow tube (6) is mounted which is connected to a conventional suction channel (7), which in turn is connected to conventional mud pumps, and means are provided for conversion of said overflow tube (6) to be set on the separation planes, i.e., the interfaces are defined as the dividers in a cargo hold (2) between the heavy and light fractions, located below the minimum adjustment level of the overflow duct (5).