Ship steam power plant

There are two types of steam power plants: reciprocating steam engines and steam turbines. The reciprocating steam engine was first used in sea-going ships. Because of its simple structure, reliable operation, convenient management and low noise, it occupied a dominant position for a long time in the past. However, due to its poor economy, large volume and mass, it has now been basically replaced by other marine engines. Since the steam turbine was installed on the ship, it has been developing slowly due to the challenge of the diesel engine. Although the main steam turbine has high single-unit power, stable operation, less friction and wear, light vibration and low noise, the thermal efficiency of its device is low. Its total mass and volume are large, which limits its use in small and medium ships. However, in recent decades, due to the improvement of the efficiency of steam turbines and boilers; the serialization, generalization and simplification of manufacturing, the cost of the device has been reduced; the use of multi-stage heating, intermediate reheating and waste heat recovery systems has greatly reduced the cost of The fuel consumption rate of the device and the adoption of low propeller speed have expanded its application range. Many data show that when the power exceeds 22000kW and the speed exceeds 20kn, the superiority of the steam turbine power plant is more prominent.

The full name of a steam turbine is a steam turbine engine, which is a machine that converts the kinetic energy of water vapor (formed by heating water) into kinetic energy that rotates the turbine. Compared with the single-stage reciprocating steam engine originally invented by James Watt, the turbo steam engine has greatly improved the thermal efficiency, is closer to the ideal reversible process in thermodynamics, and can provide greater power, and it has almost completely replaced the reciprocating steam engine. Turbine steam engines are especially suitable for thermal power generation and nuclear power generation. About 80% of the world’s electricity is generated by turbine steam engines. It is also used in many old ships, but has been almost completely replaced by gas turbine engines in modern ships.

The steam-gas turbine combined cycle is a device cycle that combines two heat engines, a steam turbine and a gas turbine, which work according to different thermodynamic cycles, and is sometimes referred to as a combined cycle. The theoretical basis of the combined cycle has been established long ago. Carnot, one of the founders of thermodynamics, once proposed the concept of the combined cycle. But it wasn’t until the mid-20th century that practical combined-cycle power plants began to be invented. The key to developing the combined cycle is to develop a gas turbine with high temperature, high performance and high power. In order to adapt to the situation of oil shortage, the efficient burning of coal in gas turbines is also a key technology. At present, all the advanced industrial countries in the world have the products of stereotyped combined cycle units. Among them, the highest power has exceeded 6x105kw, and the highest thermal efficiency has reached more than 47%. It is used as heat and power for the unit, and the fuel utilization rate can be as high as about 80%. The longest running time of a single unit has exceeded 1x105h. It is very difficult to increase the thermal efficiency of the heat engine by 1%. Combined, significant energy savings can be achieved.

In order to improve the efficiency of the heat engine, the heating temperature in the heat engine should be increased as much as possible and the heat rejection temperature should be reduced. However, the thermodynamic cycles of steam turbines and gas turbines cannot well meet the above requirements. If they are combined to heat the steam with the exhaust heat of the gas turbine, the dual advantages of higher heating temperature of the gas turbine and lower exhaust heat temperature of the steam turbine can be obtained at the same time. Due to the advantages of high power, steam turbines are still widely used in modern large warships. For example, large aircraft carriers and nuclear submarines use steam turbines as power.