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Dredges

China has created six islands in the South China Sea. The island area has rapidly expanded. It took only 18 months to build nearly 3,000 acres of land, Vietnam took 5 years and Malaysia took 30 years to build A piece of 60 acres of land. China reclamation land capacity is called the first in the world, the PLA Navy dredgers are more and more bulky.

Though the dredging industry is not something on most peoples minds, it is closely related with the national economy and the daily life of every citizen. Hong Kong is the only natural deepwater port among Chinas 1,400 ports. If it was not for the dredging industry, a total of 90% of Chinas shipping lanes with overseas countries would be blocked.

The industry has also made remarkable contributions in island-making in recent years. With the help of the industry, the famous tourist attraction West Lake in eastern Chinas Zhejiang province has completed comprehensive water treatment. At present, China has more than 1,000 types of dredging dredging vessels, ranking the third in the world, which can be described as a large dredging country. However, dredging vessels are small in size.

By 2006, the vast majority of dredgers in the dredging industry in China were imported from abroad. Zhong Wenwei, chairman of Tianjin Communications Bureau of China Communications, said that the dredging vessels in China have gone through the process of importing whole ships, designing domestically from overseas and designing domestically and domestically.

According to the newly formulated grading standards for trailing suction hopper dredgers in 2012, trailing suction hoppers dredges of more than 30,000 m3 belong to Mega TSHD. At present, the world's giant trailing suction hopper dredger is dominated by Jan de Nul, Van Oord, DEME, Boskalis.

The super-giant trailing suction hopper dredger belongs to a high-tech, difficult and high value-added ship. The cost of a 30,000-ton super-giant trailing suction hopper dredger was 220 million euros, 10 times the price of bulk carriers, exceeding the cost of two 300,000-tonne VLCC tankers.

For international comparison, in 2015 a self-propelled cutter suction dredge ordered at Croatian shipbuilder Uljanik Brodogradiliste by Jan de Nul would have a total installed diesel power of over 40,000 kW, making it some 50% more powerful than the group's J.F.J. De Nul, currently the largest cutter suction dredge in the world. The cutter power will be 8,500 kW and the cutter ladder will weigh around 2,000 tonnes. These figures are unrivaled and make the vessel the ultimate tool for dredging hard rock. The vessel, initially designated JDN8069, featured one MAN 14V48/60CR and two MAN 9L48/60CR engines plus three step-up Renk Rheine gearboxes for a diesel-electric plant.

The design of previous seven large self-propelled cutter suction dredgers served as a basis for the new CSD concept. The new vessel will offer approximately 50% more power than J F J De Nul, which is the worlds biggest cutter suction dredger currently operational. JDN8069 will have an overall length of 151.3m, breadth of 36m, draught of 5.75m and dredging depth of 45m. It will be outfitted with accommodation facilities for carrying 67 personnel.

A dredge is a ship, boat, barge or other floating platform equipped with a pump-type excavation system. The excavation system removes material (e.g., debris, aggregate, ore, contaminates, etc.) from a lake, canal, harbor, river, ocean, pond, or stream bed by digging through the material, agitating the material and/or simply drawing suspended material to create a slurry from a mixture of collected material and water, and pumping the slurry through conduits to a desired location onboard the vessel, in the water, or on land. Dredging can be associated with many different industries, including conservation, construction, mining, and transportation.

There are several types of dredges that are commonly classified as mechanical, hydraulic, hybrid, or pneumatic. Mechanical dredges use digging buckets such as a clamshell suspended by a cable from a crane, an excavator on a fixed arm, or dragline buckets suspended by a cable from a crane. Hydraulic dredges add water to sediment to create a slurry that can be pumped by pipeline to the dewatering site or to a hopper dredge. Hybrid dredges use mechanical devices to remove the sediment and then to mix it with water to create a slurry that is then pumped to a dewatering site. The hybrid process option includes various pumps that can move slurries with higher solid content than traditional hydraulic dredges, so that much less water is added to make the slurry. Pneumatic dredges are similar to hydraulic dredges, except that they use pneumatic systems to move the dredged material.

Dredging generally involves the enhancement or preservation of navigability of waterways or the protection of shorelines through the removal or replenishment of soil, sand or rock. Dredging is the removal of sediments and debris from the bottom of lakes, rivers, harbors, and other water bodies. It is a routine necessity in waterways around the world because sedimentationthe natural process of sand and silt washing downstreamgradually fills channels and harbors. Dredging often is focused on maintaining or increasing the depth of navigation channels, anchorages, or berthing areas to ensure the safe passage of boats and ships. Vessels require a certain amount of water in order to float and not touch bottom. This water depth continues to increase over time as larger and larger ships are deployed. Since massive ships carry the bulk of the goods imported into the country, dredging plays a vital role in the economy.

Several types of mechanical dredges are used. Dipper dredges and clam shell dredges are the two most common. Mechanical dredges are rugged and capable of removing hard-packed materials or debris. They can be worked in tight areas and are efficient when large barges are used for long-haul disposal. Mechanical dredges have difficulty retaining loose, fine materials in buckets, do not dredge continuously like pipeline dredges, and may need added controls when handling contaminated sediments. Mechanical dredges place the material into barges for transport to the placement location.

The two primary types of hydraulic dredges are the cutterhead pipeline dredge and the self-propelled hopper dredge. Advantages of cutterhead pipeline dredges include their ability to excavate most materials, to pump directly to a disposal site, to dredge almost continuously, and to dredge some types of rock without blasting. However, cutterhead pipeline dredges have limited capability in rough weather; have difficulty with coarse sand in swift currents; and, for the most part, are not self-propelled. In addition, the necessary pipeline can be an obstruction to navigation and, when handling debris in sediment, the removal efficiency is diminished.

Self-propelled hopper dredges can operate in rough water and move quickly to a jobsite under their own power. The dredging operation does not interfere with other traffic. Work progresses quickly and is economical for long haul distances. Hopper dredges are limited to work in deep waters, but they cannot dredge continuously. Excavation is less precise than with other dredges, and this dredge type has difficulty dredging steep banks and consolidated materials. Specialty dredges such as the dustpan dredge and sidecaster dredge are used to remove loosely compacted coarse-grained material at rapid shoaling sites or in areas where the sediment is needed.

Hydraulic dredges remove and transport sediments in a slurry through a pipeline for placement at an upland or in-water location. If placed in an upland location, the dredged material is settled out. The percent of solids in the slurry is dependent on the dredge, the operator, and the type of material. Most hydraulic dredges are not self-propelled, but instead use spuds and swing winches (a type of walking mechanism) to move through a sediment removal area. Some hydraulic dredges rely solely on suction to remove sediments and are effective at preventing resuspension of sediments. Other dredges have a cutter head, high-pressure water jets, or a rotating auger to loosen sediment for subsequent suction into the hydraulic portion of the dredge. The selection of these dredges will be dependent on the consolidation of the sediments and contractor preference.

Compared to other types of dredges, hydraulic dredges can remove large volumes of material and offer advantages of flexibility, high production rates, and low cost. However, the amount of water that is generated with the spoil material must be managed, and disposal storage cells of adequate size to allow for necessary detention times to separate the solids must be available. Discharge of return water from the storage cells will likely require special permitting and water quality compliance. In those instances where the sediment particles are extremely fine, managing the dredged water and settling of solids could require a substantial effort.

Pipeline conveyance might require the use of booster pump(s), depending on the distance to the disposal location. Disposal locations that are less than approximately 1 mile will not likely require a booster pump. Typically, the water content of the slurry ranges from seventy percent (70%) to one hundred percent (100%), with pipe line velocities maintained at between seven (7) feet to fifteen (15) feet per second in order to achieve adequate particulate suspension. Because of the high water content of the slurry and high pump velocities, disposal of the slurry is a problem. A common method of dealing with the disposal problem is to pump the slurry into a lagoon or settling basin and let the excess water run-off.

A suction dredger is one of the oldest type of suction dredgers that utilizes a mud pump to suck unbreakable dredged soil. When dredging soil needs to be broken, the method of high pressure water jetting is often used. Suction dredgers are somewhat similar to barges, with cable systems such as bucket dredgers. In the hull is equipped with a cabin and a mud pump chamber, the use of centrifugal pump, suction pipe through the cabin into the hull open file. With a tower crane or winged crane and winch can be put into the water pipe along the pipette is installed with one or more nozzles jet pipe nozzle is installed near the mouth of the suction inlet with a grille to prevent the pebbles , Stones or other debris into the straw and mud pump. As the straw is lowered into the bottom of the mud, a mixture of water and sand (mud) is sucked and the dense, dredged soil is crushed and mixed with water to form a slurry or suspension, with the help of a high-pressure water jet system, for suction. During dredging, a deep pit is formed in the dug area, and silt flows along the slope to the mouth to suck up the sediment. Controlling the cable moves the dredger.

Dredging with this type the dredging depth accuracy is very low, but its performance of digging sand and low-density soil is very good. Some suction dredgers are equipped with a submersible mud pump or a submersible mud pump combined with an inboard mud pump. Working offshore (offshore) requires the installation of a dedicated wave compensator on the drawworks winch. The mud sucked up by the dredger is drained to the mud barb bound by the dredging vessel via the mud pipe. In the mud barge, sediment settles and the water is forced to overflow out of the mud barge hatch, sometimes using a float pipe connected to a relay pump to direct the aspirated dirt to the dumping area. The cutter suction dredger is also a type of open-end vessel, with two heavy-duty positioning steel piles at the stern. During the construction dredging, the positioning steel piles are used to keep the ship's position. One of the steel piles is always lowered into the mud to keep the position. Some cutter suction dredgers, near the stern of the middle, is equipped with a positioning pile trolley, the positioning of the steel pile on the dredging of the main positioning pile. The truck can be dredged forward without moving the main stake. In a short period of time, another auxiliary positioning stake may be placed in place of the main positioning stake.

Artificial islands have various uses, for example in supporting drilling platforms in oil-exploration and extraction, as foundations for lighthouses, and as copperdams or breakwaters. However, the cost of constructing such islands by depositing naturally-occurring materials can be extremely high because of the massive quantities of material which are required. The underwater angle of repose of most natural materials is extremely low, and there is also the problem of the scouring action of water which may not only erode the island but also lead to silting in nearby areas. Thus, it can be unacceptably costly to construct artificial islands except in areas of shallow and still water and, of course, islands are usually required in other locations.

Such artificial islands are constructed by conveying an amount of material obtained elsewhere, for example, with the aid of a dredger by transport means and by depositing it on the bottom of the sea. The inhibiting means for reducing the rate of effluence along the sea bottom, for example, embankments, artificial sea-weed and the like prevent the quantity of material from settling far away from the building site on the bottom due to kinetic energy.

These new land areas rely on a huge Chinese "dredging team." Interestingly, these vessels did not exist 15 years ago. Since 2001, China intends to expand and improve the then poor quality dredger fleet in order to meet the growing domestic demand for deeper waterways and harbors. This investment was successful. The dredging capacity of China has increased from 300 million cubic meters in 2001 to over 1 billion cubic meters in 2009, making it the number one dredging power in the world.

The number of dredgers in China is the largest in the world. Together with the large and advanced dredging vessels in China, the Chinese dredger team boarded the championship. Between 2005 and 2012, China built 20 trailing suction hoppers dredgers with a capacity of 9,000 cubic meters or more. From 2004 to 2011, at least 44 cutter suction dredgers were built in China, including those built in 2010 The world's third-largest self-propelled cutter suction dredger "Whale".



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