located in the north of yangtze river delta, rudong county in nantong, jiangsu province borders on the south yellow sea at its eastern and northern sides. it is featured by such favorable weather conditions as four distinctive seasons, sufficient sunshine and marked monsoonal climate, thus mild and humid. china longyuan power has become the domestic “offshore wind power leader” since longyuan jiangsu rudong offshore wind power project, the largest offshore wind power project of its kind in china, was successfully put into operation.
recently, the “design for new-type single pile foundation of wind turbine in intertidal zone and the key technology of construction, equipment r&d and engineering application” of china longyuan power won the first prize for 2013 china power technology, marking that the offshore wind power development technology of the company has reached a high level. the leading exploration made by the project in design for foundation of offshore wind turbine and construction equipment r&d is producing active demonstration effect, which will continue in wind power industry nationwide and even worldwide.
single pile foundation supported by state-of-the-art technology
the difficulty for offshore wind power development is wind turbine foundation, i.e. piling technology. single pile driving acts as an essential factor for developing offshore wind power in a large scale.
“offshore wind power amounts to constructing a piece of ‘land’ on the sea for erecting wind turbine, and such piece of ‘land’ needs a solid and steady pile. however, piling on the sea is similar to hole drilling on tofu”, said zhang gang, president of longyuan offshore company, which indicates the difficulty of piling on the sea.
single pile foundation is common on an international basis. to guarantee the verticality of the single pile foundation, other nations often use the with transition section to adjust the deviation brought about by piling. the transition section and single pile are connected with high-strength grouting materials. this increases construction cost and cycle, in addition, microcracks have been found in the connection part made by grouting materials of a number of single pile foundations abroad, leading to sliding of the transition section. given that high-strength cannot be produced domestically at present, together with the high cost of importing grouting materials, technicians in longyuan offshore company made technological innovations on the single pile foundation and canceled the transition section on the traditional piles.
“canceling the transitional section requires high precision for the verticality of single pile foundation. to this end, we optimize top flange structure, developed a large , and realized the effective single pile guiding and rectification in the process of piling through monitoring and rectification techniques on the verticality in pile driving. in this way, the error of perpendicularity reaches 2‰, which is far lower than the 4‰ required by the international rule”, gao hongbiao, vice-president of longyuan offshore company explained the process of piling to the interviewer with patience. “it is not so easy to drive a single pile foundation with length of over 50 meters, diameter of 5 meters and weight of several tons to the position more than 40 meters in depth, and control the error rate of the final verticality within 2‰.”
gao hongbiao said that single pile driving technology and the application of large specialized construction equipment largely reduce the cost for the wind power engineering in intertidal zone. without transitional section, steel decreases by 40-60 tons and the cost for grounting materials drops nearly 700,000 yuan for each set. furthermore, the time for construction falls from 8 days to only half a day on average, which greatly improves construction efficiency.
“we now developed trial or demonstration wind power plant, thus the cost also contains experiment and associated research and development in early stages and other expenditures. without considering this part of cost, the cost for the project totals 16,000 yuan/kw, compared to that between 25,000 yuan/kw and 30,000 yuan of the offshore wind power project in europe,” said fan zichao in the planning and development department of china longyuan power.
a technical evaluation expert in chinese society for electric engineering holds that this technology promotes the progress of offshore wind power single pile foundation design and construction technology, produces remarkable economic and social benefits, and thus has high practical value and popularization and application prospects. the technical achievements has reached international advanced level as a whole, among which, the technology and equipment of pile driving and control in intertidal zone have attained world leading level. with the single pile without transitional section but in large diameter which is firstly adopted and put into practice, overseas peers look at us with new eyes, providing demonstration and reference for the development of offshore wind power in a large scale in the future.
the workmanship of the new-type single pile is also an important technical innovation. the section coming out of the beach face of the single pile foundation, the most sensitive part of whole foundation, is easily to be corroded as it exposes to either the air or the sea water from time to time with the rising and falling tides. therefore, longyuan people wear a pair of orange “rain boots” specially for the wind turbine. this is the anti-corrosion solution of “metal thermal spraying + marine paint coating + sacrificial anode” china longyuan power and applied in offshore wind turbine foundation for the first time, greatly reducing corrosion on the wind turbine foundation by the sea water.
“never belittle such a simple application. it is of great importance to protecting wind turbine foundation,” said jiang jianjun, director of the safety supervision department of longyuan offshore company. base, foundation, tower, engine room, hubs and vanes constitute the system for the normal operation of the wind turbine. it guarantees the above elements to be combined in a safe and effective manner.
first-class equipment ushers in development boom
the depth of water in the intertidal area is only 5 meters, which requires that the vessel should not be too heavy, or it may crash the keel of the vessel. in addition, with the steel-structure polygonal frame for application, large-diameter single pile base for wind turbines, single pile weighed in over 400 tons and fan blade reaching a hundred meter in diameter, the strength of the vessel should not be small. “hercules working firmly in the intertidal zone” is the kindly salutation of the offshore staffs of china longyuan power for longyuan zhenhua no.1 workboat.
therefore, china longyuan power and shanghai zhenhua heavy industries co., ltd. have jointly set up jiangsu longyuan zhenhua marine engineering co., ltd., a company specialized in offshore wind power construction, and bought a large s-800 hydraulic impact hammer from ihc company (netherland), as well as customized more than 20 vessels for special purposes, including cable vessel, anchor vessel, lifting vessel and transport vessel. on may 18, 2011, longyuan zhenhua no.1 workboat，the first offshore wind power 800 tons full circle crane vessel, was put into service, reducing the cost of offshore wind power by around 25%. the launched longyuan zhenhua no.2 workboat, a jack-up platform suitable for offshore wind power, is the first rack and pinion offshore wind installation vessel in china with the capacity of preventing from 12-grade storm. at present, there are only 3 installation vessels in china and the maximum lifting capacity of its double hooks is 800 tons. with the largest lifting capacity and most advanced functions, the installation vessel is applied to the development of offshore wind power farther away the shore. with current construction equipments, china longyuan power can start three offshore working planes at the same time and its annual construction capacity reaches up to 300,000 to 350,000 kw. so far, china longyuan power has possessed a large-scale wind power construction capacity in intertidal and offshore zones.
currently, china longyuan power has won a number of patents on offshore wind power construction, such as “construction equipment for wind power in offshore intertidal zones” and “steel-pipe pile driving equipment”. even experts who were doubtful about it initially have to give thumbs-up and praise china longyuan power for its spirit of “pioneer”.
“the longyuan jiangsu rudong offshore wind power demonstration project is of great significance. it developed and manufactured a new non-transitional single pile base for wind turbines with independent intellectual property rights, which can be applied to offshore wind power development in intertidal and offshore zones. technicians developed supporting construction technologies and special equipments that are used in jiangsu rudong intertidal (offshore) wind farm. thanks to considerable experiences in development, construction, operation and maintenance accumulated by nearly a hundred of wind turbines in offshore intertidal zone, we have made a positive exploration for offshore wind power nationwide, which can be expanded to the wind farm construction project in other intertidal zone and offshore zones throughout the country”, zhang gang proudly said.