Russian Marine Steam Turbine Propulsion

Each type of marine propulsion system has its own advantages and disadvantages. So, reciprocating steam plants, along with their ease of maintenance and reliability in operation, have a low coefficient of performance lying in the range of 10-15%. On new-built ships, almost no steam pistons are installed. Steam turbine plants have significant advantages, consisting in the small dimensions and low weight of the unit with its large capacities (reaching 70,000 hp) and virtually unlimited possibilities for further capacity growth.

Marine steam boiler plants produce the steam necessary for the operation of the main machines, as well as for other auxiliary purposes, on ships with steam piston or steam turbine power plants. Depending on the consumers of steam, ship's boilers are divided into main ones, which provide steam to the main machines, and auxiliary, feeding auxiliary mechanisms and supplying steam for other needs. The main ship's steam boilers must have a high degree of reliability in operation, withstanding a rapid change in operating mode, and temporarily increase steam production in excess of the normal amount to ensure a forced course of the vessel.

On ships, in most cases water tube boilers are used as the main steam boilers. The heating surface of water tube boilers consists of pipes filled with water and washed from the outside with hot gases resulting from the combustion of fuel. In contrast to pipes of water tube boilers, pipes of fire tube boilers, on the contrary, are washed by hot gases from the inside, and outside there is water to be evaporated. Combined boilers are also used on ships, which are similar in design to fire tube boilers, but with elements of water tube boilers.

Marine turbines are used to convert the thermal energy of steam or gas into mechanical work. The method of converting energy in a turbine is independent of the working fluid used in the turbine. Therefore, the working processes taking place in steam turbines do not differ significantly from the working processes taking place in gas turbines, and the basic principles for designing steam and gas turbines are the same.

Fresh steam or gas entering the nozzle, which is the directing apparatus, expands, the potential energy turns into kinetic, and the steam or gas acquires a significant speed. Upon exit from the nozzle, steam or gas enters the channels of the working blades mounted on the rim of the turbine disk sitting on the turbine shaft. The working fluid presses on the curved surfaces of the working blades, causing the disk with the shaft to rotate. The combination of such guide vanes (nozzles) and rotor blades on a turbine disk under consideration is called a turbine stage . Turbines having only one stage are called single-stage , unlike multi-stage turbines.

Turbines are divided into two main groups according to the working principle of a working fluid (steam or gas). Turbines in which expansion, steam or gas occurs only in stationary guiding devices, and only their kinetic energy is used on the working blades, are called active . Turbines in which the expansion of steam or gas also occurs during the movement of the working fluid in the channels of the working blades are calledreactive. Turbines rotate only in one direction and are non-reversible, that is, they cannot change the direction of rotation. Therefore, reverse turbines are usually provided on the same shaft as the main forward turbines. The power of marine reverse turbines does not exceed 40-50% of the power of forward turbines. Since these turbines should not provide high efficiency in operation, the number of stages in them is small.

Ship steam turbine units operating at an initial steam pressure of 40-50 atm and a steam temperature of 450-480°C have an economic efficiency of 24-27%. Economic (effective) efficiency is the ratio of heat converted into useful work to heat that develops with the complete combustion of the spent fuel. Effective efficiency characterizes the efficiency of the engine. With an increase in pressure to 70–80 atm and vapor temperature to 500–550 ° ?, the economic efficiency increases to 29–31%. A further increase in the initial vapor pressure and the improvement of the plants will make it possible to increase the efficiency of the ship steam turbine plant to approximately 35%.

On modern steam vessels, feed water from condensers to heaters is supplied through several heating stages. Heating is due to the heat of the working fluid of the turbine and exhaust flue gases flowing around the economizer. Almost all accessories are electrically driven. Steam turbine driven generators typically produce a constant current voltage of 250 V. Alternating current is also used. If power is transferred from the turbine to the screw through a gearbox, an additional small turbine is used to provide reverse gear (reverse rotation of the screw). The power on the shaft during reverse rotation is 20–40% of the main power.

The electric drive from the turbine to the propeller was very popular in the 1930s. In this case, the turbine rotates a high-speed generator, and the generated electricity is transmitted to low-speed electric motors that rotate the propeller shaft. The efficiency of the gear transmission (gearbox) is approximately 97.5%, of the electric drive is about 90%. In the case of an electric drive, reverse rotation is achieved simply by switching polarity. In Russia, the first turbine ship was the destroyer "Swallow" (1904). This former British experimental vessel Carolina, built in 1904-1905, was purchased by Morved for staff training and experiments with turbine units. The ship had two power plants of 1000 hp. each with a displacement of 140 tons developed a maximum speed of 18.5 knots. Sevastopol, the battleship of the Russian and Soviet fleets , had ten Parsons turbines with a total capacity of 32,000 hp, which provided the ship with a speed of about 22 knots.

Currently, steam turbines have faded into the background. But their operation on some ships continues. For example, on a heavy aircraft carrier cruiser “Admiral of the Fleet of the Soviet Union Kuznetsov” there are 4 steam turbines of 50 thousand hp each. The maximum allowable speed was 29 knots. The long start-up time of a steam turbine is explained by the need to warm up both the turbine itself and the steam generator with all the necessary steam pipelines. All this takes a lot of time. The operation of a gas turbine is much simpler than steam, as water is not used as the working fluid of the cycle. Therefore, there is no need for a capacitor, feed, condensate and circulation pumps, pipelines.