Patent Publication Number: US-2003230009-A1

Title: Marine-based platform for dredged solids management

Description:
RELATED APPLICATIONS  
     [0001] This application is based upon Provisional Application No. 60/388,701, filed Jun. 14, 2002 entitled “Marine-Based Platform for Dredged Solids Management.” 
    
    
     
       TECHNICAL FIELD OF THE INVENTION  
       [0002] This application relates to a system and method for processing and transporting contaminated sediments collected from the marine environment.  
       BACKGROUND OF THE INVENTION  
       [0003] Routine removal of sediments that accumulate on the bottom of natural and artificial water bodies is commonly practiced to permit navigation of ships and/or to maintain designated water depths. Sediments are sometimes removed to clean up the bottom of these water bodies when such sediments are found to be contaminated and a threat to public health and/or the ecosystem. Such cleanup dredging is commonly referred to as environmental dredging.  
       [0004] Current methods of dredging can be divided into two general categories. They include mechanical dredging and hydraulic dredging. The fundamental difference between these categories is the equipment used and the form in which the sediments are removed. Mechanical dredges remove the sediments directly with clamshell buckets at a relatively low liquid to solids ratio (i.e., relatively little water is entrained in the sediments compared to hydraulic dredging operations). Hydraulic (or vacuum type) dredges loosen sediments at the bottom of a waterway with an auger or cutterblade and vacuum a sediment-water mixture resulting in the removal of a slurry at a high liquid to solids ratio. One of the more difficult problems associated with environmental dredging operations is the handling and management of mechanically or hydraulically dredged sediments after they are removed from the waterway.  
       [0005] During mechanical dredging operations, sediment removed from the bottom of the waterway is typically deposited into hopper barges, and subsequently transported to a shoreside unloading facility where the sediment is removed, processed to reduce the moisture content (i.e., dewatered), reloaded onto secondary transport facilities (rail, truck or barge), and transported to a final disposal site.  
       [0006] During hydraulic or vacuum dredging operations the sediment is extracted and pumped in a slurry form, typically through pipelines, to processing facilities that must store, separate (settle), and dewater the sediments. The dewatered sediments must subsequently be loaded onto secondary transport facilities (rail, truck, or barge) for transport to the final disposal location. Alternatively, the sediments might be permanently retained at the processing location in a storage lagoon or impoundment.  
       [0007] When the dredged sediments are contaminated, their handling and management after extraction is particularly problematic. This is due to the difficulty in finding suitable shoreside locations for an off-loading and processing facility, and the extra care that must be provided to ensure that the sediments are contained, all free water is treated to remove contaminants, and exposure to the sediments or spills do not occur in handling.  
       [0008] Depending on the size and extent of the dredging project, one or more of these land-based facilities may be needed. The construction of such facilities can be expected to result in significant community resistance and permitting problems, which will be compounded when the sediments in question are contaminated. In addition, the cost of constructing facilities for managing contaminated sediments will be extremely high, and in most cases such facilities will be temporary in nature and will only operate during the term of the dredging or cleanup operation.  
       [0009] The present invention relates to a system and method that provides an alternative to the construction of new land-based facilities for managing contaminated dredge materials. The system incorporates a marine platform that contains processing equipment and operations to receive the dredged sediment and convert it into a material that can be conveyed and deposited into containers located on a separate container vessel. The container vessel subsequently transports said containers to an existing cargo port facility, where the containers can be off-loaded and transported to a final disposal site. At this disposal site, the sediments can be removed from the containers and landfilled, and the containers can be returned to the container vessel for reuse.  
       [0010] To convert the extracted sediment into a material suitable for containerization, processing is required. This processing includes oversize material separation and partial dewatering followed by sediment dehydration. Oversize material separation involves the use of grizzly screens. These are coarse screens constructed to separate materials that are greater than approximately 4 to 8 inches in size (oversize material) from materials that are less than said size (undersize material).  
       [0011] The oversize material collected in this process is discharged to a separate container for storage and subsequent disposal. The undersize material, which is the sediment that falls through the grizzly, is deposited into a sediment sump in which a conveyor (preferably a drag flight type) lifts the undersize material up an inclined slope. A drag flight conveyor is a conveying system that drags the material through a fixed flat bottom conveyor trough (preferably enclosed) by means of conveyor flights (rectangular plates) that are located at fixed intervals (e.g., 48 inches on center) within the trough. The conveyor flights are attached to conveyor chains that are connected to sprockets and motors that drive the system. Such conveying systems are commonly used in the power industry to convey power plant residues and can be employed in a submerged environment.  
       [0012] Conveying the sediment up an inclined slope permits free water to drain back down the slope into the sediment sump. From the sump this water is pumped to either an on-board or on-shore water treatment plant. The sediment, which is dragged up the incline, is deposited into a hopper that feeds a mixing device where one or more dehydrating reagents, such as Portland cement, lime, quicklime, cement kiln dust, lime kiln dust, coal fly ash, or a combination of reagents, that will absorb or react with the moisture in the sediment, is introduced and mixed with the sediment. The mixed sediment is subsequently discharged from the mixer where it is conveyed using a conveying system (preferably drag flight) down a horizontal conveyor run where an opening in the bottom of the conveyor trough directs the sediment into hoppers that divert the sediment by gravity into containers located on a container vessel situated below the horizontal conveyor. Vibrating hoppers can assist in moving the sediment through the hoppers.  
       [0013] The container vessel location is critical to enable the processed sediment to drop into the containers that are on-board its deck. Container vessel location is determined by docking the container vessel inside a floating slip that is part of the marine platform system. The container vessel remains in this docked position until its containers are filled with sediment, at which time the containers are covered, the vessel leaves the platform docking slip, and a new container vessel (with unfilled containers) enters the slip. The container vessel and its cargo (processed sediment) after leaving the platform docking slip is transported to an existing port facility where the containers can be off-loaded (similar to cargo) and subsequently stored and transferred onto a secondary transportation system for transport to a final disposal site.  
       [0014] The free water that drains from the sediment into the sediment sump under the grizzly screen will require treatment to remove any contaminants present prior to discharge back to the receiving water. This is accomplished by transporting the water to a water treatment plant. The water treatment plant may be located on a separate or contiguous marine platform or may be located shoreside. In a mechanical dredging operation, the relatively low liquid to solid ratio associated with the extracted sediment may be such that the free water available is of such volume that a water treatment facility could be located on a separate or contiguous marine platform. Alternatively, if hydraulic dredging is employed, the higher liquid to solid ratios associated with the extracted sediment may be such that the volume of water available is too great for a water treatment plant to be practically employed on a marine platform, whether separate or contiguous. In this case the free water generated will need to be pumped to an on-shore location. While the pumping of water to an on-shore treatment facility will necessitate the construction of an on-shore facility, such a facility will be much smaller and less burdensome to a local jurisdiction than a sediment processing facility since it need only process the liquid fraction of the sediment and not the bulk of the sediment collected. In addition, such a plant can be made portable and mobile and more readily assembled and disassembled, resulting in less impact to the host community.  
       [0015] The marine platform upon which the referenced processing activity occurs will need to be an adaptable unit capable of operating in various environments, will need to be a mobile, transportable system, and will need to be easily deployable. This is because dredging in most locations is not a continuous year-round operation and the physical dimensions (width and depth) of waterways and specific reaches within a waterway can be expected to vary. A marine platform constructed using sectional barges (barges that can be connected or interlocked in the field to produce different-sized platforms, and readily transportable by truck to a job site) meets these requirements. Such barges are in commercial use in many marine operations and can be used to construct that platform upon which the processing equipment is located, the platform docking slip for the container vessels and the container vessels.  
       [0016] Processing equipment that will be located on said platform will include a grizzly screen, a sediment sump, inclined conveyors, horizontal drag conveyors, reagent storage silos or tanks, mixers, hoppers, and supporting structures for all equipment, and in particular the horizontal conveyor. The horizontal conveyor, spanning the length of the platform docking slip, is supported by an overhead structure (truss) that extends over the docking slip.  
       SUMMARY OF PRIOR ART  
       [0017] Processing of dredged sediments to convert such sediments into a usable product or to dewater the sediments prior to disposal is not a new concept. Dredged sediments are mined in many locations from the bottom of waterways for use as an aggregate material in fill or construction applications. There are numerous applications where the properties of the collected dredged materials or sediments are modified so that the material can be applied in a fashion coincident with the design objectives of the final product. While most of these processing schemes have included equipment located shoreside, some have included processing on the dredge vessel or ships adjacent to the dredge vessel. These operations typically involve screening, dewatering, or reagent mixing processes to render the dredged material suitable for the desired application.  
       [0018] Studler, U.S. Pat. No. 5,293,731 B1, describes a method for treating dredged materials to form a sediment product suitable for use as structural fill material. Studler describes in his patent a process in which dredged sediment, extracted from the bottom of the waterway, is placed in a barge (referred to as a treatment vessel). From this treatment vessel free water that accumulates on top of the sediment is pumped to a water treatment facility. Large pieces of debris are removed from the sediment either by using a specialized debris rake to remove the debris from the sediment after it is placed in the treatment vessel, or by direct loading of the sediment onto vibrating or non-vibrating screens prior to entering the treatment vessel. These screens separate oversize materials (debris) from the remainder of the dredged sediment. The dredged sediment that remains in the treatment vessel is subsequently mixed with a dehydrating reagent (such as Portland cement) and transferred to shore where the material is stored and cured prior to use. Studler&#39;s objective is to provide a processing system to prepare the sediment so that the sediment will have suitable engineering properties for use as a fill material.  
       [0019] Pal and Yost, U.S. Pat. No. 6,139,485, describe a land-based system for stabilizing contaminated soils, which incorporates the use of crushers, grizzly screens, and pugmill mixers to mix selected reagents with processed sediment. The primary purpose of this application is to convert leachable lead in the sediments into a non-leachable form.  
       [0020] Gurfinkel and Shepsis, U.S. Pat. No. 5,240,608, describe a system that incorporates the processing of dredged sediment on a marine platform to produce either a molded brick or a lightweight aggregate material. Gurfinkel claims an invention capable of separating the sediment into different size fractions for use in either aggregate or brick-making process lines. His invention is intended to separate and treat all the water contained in the sediment and produce no waste. Gurfinkel outlines multiple processing embodiments that could be incorporated into his operation.  
       [0021] Hodges, et al, U.S. Pat. No. 6,149,811, describe an invention in which a dredged slurry from a hydraulic dredging operation is introduced into a solids/liquid separation system to separate the solid and liquid fractions of the sediment. The invention includes a water treatment system to treat the separated water prior to discharge back into the environment. Hodges describes a screening system, the addition of flocculants to agglomerate and densify the sediment and the separation of the flocculated sediment from the slurry by means of a specially designed screening system. Hodges claims that his system has numerous advantages over other more complex systems proposed for dewatering hydraulically dredged sediments, in particular Breidenbaugh, U.S. Pat. No. 4,541,927.  
       [0022] Breidenbaugh. U.S. Pat. No. 4,541,927, describes a processing system, situated on a marine platform that collects and processes sediments from hydraulic dredging operations which centrifuges, screens, aerates, dries, and bags the processed or dried spoils to avoid the need for shoreside processing and to permit the processed or bagged materials to be directly marketed as an aggregate material or shipped (bagged) to a landfill for disposal. Breidenbaugh does not add any reagent to his process and relies on energy-intensive centrifuges, screening, aeration and heat drying to produce a suitable end product.  
       [0023] Dutra, U.S. Pat. No. 5,042,178, proposes a process, the objective of which is to produce a densified slurry for disposal of the sediment at a marine aquatic disposal site. Dutra proposes the use of a hopper into which mechanically dredged sediments are deposited. The hopper contains a bottom grate through which the dredge material falls. This bottom grate provides for the breaking up of the sediment and the separation of large oversize debris from undersize debris. The invention incorporates a series of water jets directed at the sediment that falls through the grate to further break up the sediment and assist in producing a slurry that is discharged to an open-bottom hopper barge. Dutra claims that the slurry will segregate in the hopper barge, where the free water will come to the top and the heavier sediment will sink to the bottom of the barge, producing a more densified slurry than slurries generated during conventional hydraulic dredging operations. This more densified slurry will, according to Dutra, more readily sink to the bottom of a marine aquatic disposal site, when discharged from an open hopper barge, resulting in less dispersal of the sediment as it falls through the water column.  
       [0024] The use of marine based water treatment plant platforms for treating waters removed from contaminated dredge sediments has been proposed by Chesner and Melrose in U.S. Pat. No. 6,432,303 B1, and U.S. patent applications Ser. Nos. 10/094,064 and 10/151,762.  
       [0025] The use of docking slips that incorporate cranes, conveyors, and gantries for loading and off-loading cargo at a ship-port interface is a common practice at most major port facilities.  
       [0026] Arntzen, U.S. Pat. No. 6,524,051 B1, describes a special terminal system for unloading containerized cargo from container ships. Amtzen&#39;s system makes use of a specially constructed terminal building that contains docking slips constructed inside the building and an overhead beam support system to lift containers from the vessels.  
       OBJECTS OF THE INVENTION  
       [0027] The invention disclosed in this application is intended to establish an alternative processing and transport system that provides for the processing and transportation of the dredged sediment on a marine-based platform. The purpose of such a system is to provide a cost-effective solids management system with minimal impact to on-shore communities in the vicinity of the dredge cleanup area.  
       SUMMARY OF THE INVENTION  
       [0028] The invention involves the deployment of marine-based solids processing and transportation vessels in which sediment collected from the waterways are processed, deposited into containers, and transported to off-loading facilities where the sediments can be securely transported to a final disposal site.  
       [0029] While various processing systems, which include screens, mixers, chemical reagents and dewatering systems have been used or have been proposed for use in both marine and shoreside operations, and while marine-based water treatment systems have been proposed and docking slips are common in ship-port cargo unloading operations, the invention proposed herein is unique in its system and method of operation. It includes a simple system capable of managing either mechanical or hydraulically dredged sediments. It provides a unique marine-based platform that not only processes the sediment to make it suitable for containerization, but also provides for a special handling system to convey and fill containers, located on a separate container transport vessel. It provides for collecting and pumping water to a water treatment to ensure that free water is properly managed and ensures that the sediment placed in containers can be easily managed at existing cargo ports where the containers can be readily off-loaded for transport to a disposal site. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0030]FIG. 1 is an isometric view of the marine-based platform of the present invention. 
    
    
     DESCRIPTION OF THE SYSTEM  
     [0031] The system developed by the inventors includes two marine-based platforms to manage sediments extracted from the bottom of a waterway using either mechanical or hydraulic dredging operations. These two platforms are described herein as a marine-based solids processing vessel and a container transport vessel.  
     [0032]FIG. 1 depicts in an isometric view the two marine-based platforms used in the system. The marine-based solids processing vessel  10 , shown in FIG. 1, is a vessel equipped with specialized solids processing equipment designed to screen, stabilize, and distribute sediment into containers located on the container transport vessel  20 . The marine-based solids processing vessel  10  is further designed with a slip that can accommodate and dock a container transport vessel  20 , which can be directed into the slip to receive processed dredge materials for transport. Alternatively, transport vessel  20  can be connected and docked adjacent to solids processing vessel  10  by a connector, such as with ties, ropes, cables, clamps, and the like, in a side-by-side or end-to-end rafting up relationship.  
     [0033] The marine-based processing vessel, as shown in FIG. 1, contains a sediment feed hopper  30  that is used to receive sediment that is collected in the dredging operation and deposited directly into said hopper. At the bottom of the hopper is a grizzly screen  40  (with openings between approximately 4 inches and 8 inches) used to segregate oversize (plus approximately 4-inch sediment materials) from the undersize materials. The oversize sediment materials are deposited into an oversize materials storage container  50  and the undersize sediment materials are deposited into a sediment sump tank  60 , located below the screen. The undersize sediment materials are subsequently transported using an inclined drag flight conveyor in an enclosed trough  70  to an input hopper that feeds the sediment into a mixing device  80 , such as a rotating paddle drum or pugmill.  
     [0034] The mixing device provides the means to blend the undersize dredged materials with cementitious reagents, such as Portland cement, quicklime, kiln dusts, or other dehydrating agents, which are stored in a silo  90  on the processing vessel  10 . The dehydrating agent can be introduced to said mixer  80  mechanically (by conveyor) or pneumatically (blown into) through a feed line  140 . The purpose of blending the dredge materials with cementitious reagents is to induce hydration reactions in order to reduce the moisture content of the blended mix. Free water that drains from the dredge mud during its travel up the inclined conveyor  70  is collected in the sediment sump tank  60  and pumped via a pipeline  150  to a water containment or treatment system (not shown) for processing. From the mixing device  80 , the blended-stabilized mix is conveyed down an enclosed horizontal conveyor trough  100  supported by an overhead truss  110  to permit the conveyor to extend over the slip area into which a container transport vessel  20  can be docked.  
     [0035] The stabilized dredge material conveyed down the horizontal drag flight feed conveyor trough  100  is distributed into containers  120 , located on the container transport vessel  20 , by solid gates located under the conveyor trough  100  that can open to discharge the sediment material into distribution hoppers  130 . Said distribution hoppers  130 , which route the sediment materials to selected containers  120  located on the container vessel  20 , can consist of bifurcated hoppers, capable of distributing the stabilized dredge material to parallel rows of containers, or rotating extendable chutes, capable of directing the dredge material, collected from the feed conveyor  100 , to designated storage containers.  
     [0036] The primary advantage of the proposed system over existing methods for managing dredged sediments, described above, is that all processing activities are handled on the water. No land-based sediment processing facilities are needed. If a port facility is nearby, the containerized and covered sediment can be off-loaded like any containerized commercial product in a secure manner. The existing port transportation infrastructure can be used for handling and transporting the stabilized and containerized material, ultimately reducing the cost of dredge management.  
     [0037] While FIG. 1 depicts one container transport vessel docked in one slip, where the containers are fed by one processing and conveying train, the scope of the invention can include multiple container vessels docked within one or more slips, fed by one or more processing and conveying trains. The exact number of slips, trains, etc. will be dependent on the desired sediment removal rates and the spatial-navigational requirements of the waterway. In addition, the excavator, crane, or hydraulic dredge used to excavate the sediment, while not shown in FIG. 1, can be situated on a separate vessel or be situated directly on a portion of the marine-based solids processing vessel, without modifying the scope of the invention.  
     [0038] In the foregoing description, certain terms and visual depictions are used to illustrate the preferred embodiment.  
     [0039] However, no unnecessary limitations are to be construed by the terms used or illustrations depicted, beyond what is shown in the prior art, since the terms and illustrations are exemplary only, and are not meant to limit the scope of the present invention.  
     [0040] It is further known that other modifications may be made to the present invention, without departing from the scope of the invention, as noted in the appended Claims.