One of the most versatile and oldest mover technologies, steam turbines drive numerous machines and undergo the production of power in various plants across the world. For more than a hundred years, steam turbine services is underutilization. It is the modern form of reciprocating machines with greater cost-effectiveness and efficiency. The lowest capacity of a steam turbine is <0.75kw kilowatts and for large drivers, it can be even hundreds of megawatts.
Varied types of steam turbines depending on designs
Steam turbines are basically of two types depending on their designs. The first one is – Reaction design. Here, the operational principle of the turbine depends on the fact that the rotor extracts its rotational energy from the team immediately after it leaves the blade. The second one is – impulse design. In this design, the rotor moves as steam force power on the blades. The spinning component of a steam turbine is the rotor that consists of blades and wheels. These attached components are responsible for extracting the energy from the steam.
Usually, steam enters the turbine from one end and travels one directionally toward its other end, and then exits the system to enter the next section or to get adequately heated. However, in the case of a double-flow steam turbine, the steam enters in the middle of the casing and flows in two opposite directions towards the terminal point of the sections. Except for any specific circumstances, these turbines are not popularly used anymore.
Along with the above-mentioned two types, there are three major types of steam turbines depending on their working principles. These are as follows:
- Back-pressure steam turbine
This type of steam turbine is most suited for being applied to mechanical-drive appliances like drivers of pumps and compressors. The name “back-pressure turbine” implies that in these specific steam turbines, the pressure produced by the exhausted steam is always greater than the normal atmospheric pressure.
However, each plant has its specific sets of applications to establish the pressure of the discharged steam. The utilization of large and small LP or low-pressures, usually, occurs for low-pressure applications, like heating systems. However, higher pressures are often utilized for supplying steam for various industrial procedures.
- Condensing steam turbine
This is the primary variation of steam turbines. It has been utilized for huge drive applications above specific power rating limitations. The mechanism of this steam turbine is that here the exhausted energy directly goes to one or multiple condensers that maintain the conditions of the vacuums. The steam is condensed by cool water kept inside an array of water tubes and in the condenser, it transforms into liquefied form.
- Extraction steam turbine
The specialty of this steam turbine is that it can have one or multiple openings in the casing. These openings are used for the extraction of a specific portion of the steam by applying some amount of intermediate pressure. This extracted steam is later utilized for various procedure purposes. Whether the extraction pressure can be automatically regulated or not, entirely depends on the particular design of the steam turbine.
The basic functional principles of a steam turbine
The first step of the functioning of a steam turbine is the heating of the steam that occurs in waste recovery systems or boilers (commonly known as steam generation systems). Here through heating, the temperature of the steam is rose to 600°. Through the steam generation system, the first valve travels to the steam turbine. It is the major shutdown valve or stop valve or main trip. Staying fully closed or fully open, this valve controls the entire steam flow. Throttle valves are also used for the same purpose.
The heated steam hits the first row of the rotor’s blades at high pressure and produces a huge amount of torque. Due to this, the rotor starts running. Via the progression of the procedures, gradually the steam loses its energy and pressure; therefore, it needs very large surface areas to produce torque. Therefore, the size of the rotor’s blades is increased in each step. Nozzles make the steam hit the blades at a specific angle so that it can produce the maximum possible energy. In the last stage, the steam is guided by an exhaust hood to minimize the loss of pressure. After leaving the exhaust section, the steam directly enters into a condenser for liquefying. The liquefied water is returned to the steam generation system.
Major advantageous features of a steam turbine
A steam turbine is utilized to produce the highest amount of mechanical power. The specialty of the turbine is that to produce that large amount of power it uses a very low amount of steam. The entire procedure happens in a compact driver arrangement, and generally, the configuration that it uses is direct-drive.
The benefits of using these turbines are:
- The steam turbine is better than piston and reciprocating engines because it can produce power with the use of only a few parts.
- These turbines are incredibly efficient compared to other electricity-generating machines.
- Extremely suitable for huge thermal power plants as these turbines can be of up to 1.5 GW (2,000,000 hp) size.
The capabilities of speed adjustment and speed variation are also crucial for a steam turbine to function properly. These turbines are extensively used in various power generation units and driver applications to provide mechanical drives.
