CVA 002 aircraft carrier - Propulsion
As is well known, China is deficient in marine propulsion technology, and has not produced significant steam turbine or gas turbine marine propulsion plants. Only a few PLAN warships are equipped with such propulsion plants, which are standard in navies around the world, and the few Chinese installations involve plants of foreign manufacture. China's commercial and military surface vessels are uniformly outfitted with marine diesel engines.
The full integrated electric propulsion for the new aircraft carrier might use gas turbine, diesel engine and the like for flexible power distribution and advanced propulsion. Three main prime movers exist; internal combustion engines, gas turbines and steam turbines. Nuclear powered or oil fired boiler powered steam cycles are used with steam turbines according to the vessel type.
The marine power plant is that part of the ship responsible for generating both mechanical and electrical power for the ship propulsion and various electric consumers. Usually, these two operations are achieved separately, but in some configurations both are performed together. The power plant may be of the electric type, where propulsion is done via electric motors, or the conventional type, where mechanical power from the prime mover drives the propulsion either directly or through a gearbox.
The diesel engines give good flexibility for the naval architect to achieve the required speed for a given ship with the best fuel economy. A ship propulsion system can consist of only one diesel engine and in some cases up to 12 engines - only for propulsion - especially in naval vessels requiring large propulsion flexibility and high redundancy. For the electric generation, the diesel engine is almost the only engine type used, even with other types of prime movers used for propulsion. Also the diesel engines have the best efficiency levels of all other means of propulsion with a range of 35% to 55%.
Since the year 2000, many vessels around the world were powered by gas turbines, but most of them use the gas turbine in a combined configuration to achieve a more feasible and flexible propulsion solution due to the high fuel consumption of gas turbines, these combined configurations include the combined diesel and gas (CODAG) where the required power is produced by both diesel engines and gas turbines at the same time and at part load only one type of engines is operated according to the required power. In the combined gas and steam (COGAS), the exhaust of the gas turbine is used to provide enough heat for steam generation.
The Party Committee of Harbin Electric Group Steam Turbine Company has conscientiously implemented General Secretary Xi Jinping's important expositions on the reform, development and party building of state-owned enterprises, and resolutely implemented the decisions and arrangements of the Party Central Committee and the State Council. With the confidence and determination to dare to wade through dangerous shoals and tackle tough problems, it has steadily promoted the high-quality conclusion of the three-year action plan for state-owned enterprise reform.
China Shipbuilding Industry Corp said its Wuhan Institute of Marine Electric Propulsion finalized its Integrated Electric Propulsion technology in mid-July 2013. It said the in-house development will help the nation wean itself off the longstanding dependence on imported parts in manufacturing ships. Most surface vessels in China use mechanical transmissions and are propelled by a motor or an engine spinning a propeller. Many Western countries have adopted integrated electric propulsion, in which gas turbines or diesel generators produce electricity that powers electric motors.
The development of integrated electric propulsion may resolve engine problems that have long haunted the nation and its navy. One of the major issues has been a lack of domestic companies who can make gas turbine engines to support long distance voyages. Without domestically developed gas turbine engines, the Chinese navy had been forced to import foreign engines for its ships.
The main advantage of a steam-powered aircraft carrier is that it can stay on the sea for a long time without having to go ashore to refuel or refill water. This advantage is very important because it allows aircraft carriers to maintain complex military operations for a long time, such as fleet operations, rotation of forces, etc. In addition, compared with other types of ships, the take-off and landing of aircraft on steam-powered aircraft carriers is very simple.
The process of taking off and landing is relatively easy for pilots on such a carrier, even in moving sea conditions. Compared with traditional warships, carriers can allow aircraft to operate from a long distance, greatly increasing the long-range capability of munitions delivery. This capability is important because it allows carriers to participate in deep ocean-guided operations and support advanced land-based combat.
For example the Mitsubishi marine propulsion steam turbines MS-2 series and MR-? series are widely used in various ship types. The high-pressure/high-medium-pressure turbines, low-pressure turbines, reduction gears, main thrust bearings, and main rehydration devices that constitute these marine propulsion steam turbines have been standardized. By selecting the appropriate combination, each unit can meet the maximum propulsion power conditions of 45MW, whiel the Fujian would require about 185 MW, or four such unites.
The reason why China chose steam power for the launch of its aircraft carrier is mainly due to economic and technical considerations. Steam power itself is mature and stable, and the installation cost is relatively low. It can quickly launch an aircraft carrier in a short period of time, which meets actual needs. However, technologies such as electric power and gas turbines are relatively new, and the installation cost is relatively high. They require a certain amount of research results and capital investment to be gradually realized. Although these technologies have broad development prospects, they require time and financial support.
The steam turbine on the aircraft carrier and the steam engine on the steam locomotive are not products of the same era at all. The steam turbine is a very advanced rotary power system with the advantages of high output power, small size, light weight and low vibration. The maximum power of a single ship steam turbine exceeds 70,000 horsepower, and it is still the preferred power for large surface ships such as aircraft carriers.
When it comes to nuclear power, its mechanical output part also uses steam turbines, but it uses nuclear reactors instead of ordinary fuel boilers to generate steam, driving the steam turbine to output mechanical energy. In principle, it is the same as the power system of the 002 aircraft carrier. The difference between them is that one produces saturated steam and the other produces superheated steam. In this regard, conventional steam turbines have more advantages, as they use more suitable superheated steam.
Conventional-powered aircraft carriers can have no problem making 100,000 tons or even larger. For example, the full load displacement of the Kitty Hawk, the last conventional-powered aircraft carrier of the United States, is as high as 86,000 tons. It is powered by 8 oil-fired boilers and 4 steam turbines. The maximum output power reaches 280,000 horsepower and the maximum speed is as high as 32 knots.
Fujian takes a long time to start up, but the same problem still exists for US aircraft carriers. Because the Liaoning, Shandong, and Fujian aircraft carriers use steam turbines as their powerplant, some have criticized their long startup times. This is true! This is due to the nature of steam turbines. To prevent significant thermal stress, deformation, or damage to metal equipment (boilers, piping, and turbines) caused by large temperature differences, a slow and uniform preheating process—the warm-up process—is essential.
However, this problem also exists on US nuclear-powered aircraft carriers. US nuclear- powered aircraft carriers do not rely directly on nuclear propulsion. Instead, they derive their propulsion from steam turbines . The nuclear reactor generates heat, heating water into high-pressure steam. This high-pressure steam is then fed to the ship's four large steam turbine engines (steam turbines), which drive shafts that propel the propellers, providing the necessary propulsion power. Consequently, US nuclear-powered aircraft carriers also experience lengthy startup times.
So is there a way to reduce the startup time of steam turbine ships? Yes! By keeping the ship in a "hot and warm standby" state, you can significantly shorten the sailing time!
Hot Standby (Banking): This is the highest level of alert. The boiler remains ignited, but combustion is very weak, maintaining only a relatively high temperature and pressure (e.g., below operating pressure but significantly above ambient pressure) within the boiler. From this state, waking up the boiler and bringing it up to a steam pressure suitable for turbine operation can be shortened to tens of minutes to one or two hours. Warm Standby (Cold Iron): When no sailing is expected for an extended period, the boilers may be shut down without completely draining the system. The system cools very slowly, utilizing the boiler's insulation. Starting up from Warm Standby is faster than starting from a completely cold state, but slower than starting from Hot Standby. This can take several hours.
The advantage of nuclear-powered aircraft carriers lies in their ability to operate continuously for decades. By maintaining the reactors at low power while docked in port, they can be physically kept in a constant state of hot standby. Conventional aircraft carriers like the Liaoning and Shandong, however, typically operate in warm standby mode or keep only one of their boilers in hot standby mode while the others are completely shut down, due to the increased fuel consumption associated with maintaining hot standby. The Fujian, however, features an integrated power system not found on the Liaoning and Shandong. While it still utilizes steam boilers, the concept and implementation of its "hot/warm standby system" represent a revolutionary change compared to the Liaoning and Shandong.
Simply put, the Fujian's integrated power system replaces the traditional mechanical propulsion chain with an electric propulsion chain (boiler-steam turbine-main generator/diesel generator-grid-propulsion motor-propeller). Therefore, if an emergency departure is required, the Fujian no longer needs to wait for the main boiler steam pressure to reach a sufficient level before starting the main engine and performing departure operations like the Liaoning and Shandong.
Instead, it can directly start the backup diesel generator to provide basic power for the entire ship within a few minutes. Combined with the fact that the Fujian drives the propeller through an electric propulsion motor as mentioned earlier, as long as there is electricity in the grid (from the auxiliary generator or the main generator), it can immediately power the propulsion motor and leave the port by low-speed maneuvering (should be around 5-10 knots), realizing "warming up the car and walking at the same time". After the main boiler is heated, the main generator will be connected to the grid and switched to full-speed navigation.
Therefore, in theory, the Fujian ship relies on the fundamental changes in its propulsion mode brought about by the ship's integrated power system. If it receives an emergency task, the Fujian ship can respond quickly and leave the port without having to wait for a long time like the Liaoning and Shandong ships in the past.
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