Back-pressure turbines: Application of Saturated steam

While superheated steam is the preferred choice for a power plant with condensing turbines, saturated steam is also used in the industry and is generally known as combined heat and power (CHP) systems. In a cogeneration system, a back-pressure turbine is used to generate electricity while also capturing and utilizing the waste heat produced in the process.

Back-pressure turbines are commonly used when saturated steam is utilized for power generation. In this context, the back pressure turbine is designed to generate electricity by expanding the high-pressure saturated steam and extracting useful work from it. Unlike condensing turbines, which are primarily used with superheated steam and operate at lower pressures, back-pressure turbines are specifically designed to accommodate the relatively high pressure of saturated steam. When the saturated steam is exhausted from the back pressure turbine, it retains a significant amount of energy in the form of heat. This can be utilized for various industrial processes, heating applications, or as part of a cogeneration system to maximize the overall efficiency of the power generation process.

Back-pressure turbine details

A back-pressure turbine is a type of steam turbine that is designed to operate with a certain amount of back pressure in the steam exhaust system. The back pressure is maintained to meet the heating or process requirements of a facility.

How a back pressure turbine works:

1. Steam is produced in a boiler and then directed to the back pressure turbine.

2. The steam enters the turbine at high pressure and high temperature, causing the turbine rotor to spin.

3. As the steam flows through the turbine blades, it loses pressure and temperature, while simultaneously transferring some of its energy to the turbine rotor. This energy transfer causes the rotor to rotate at a high speed.

4. The rotating rotor is connected to a generator, which converts the mechanical energy of the rotor into electrical energy.

5. After passing through the turbine, the steam is exhausted at a certain pressure, referred to as the back pressure, and is then used for various heating or process applications within the facility.

6. The exhaust steam may also be condensed and returned to the boiler to be used again in the steam cycle.

Thermodynamics

It is interesting. H = U + PdV, H is enthalpy, U is internal energy, P is pressure and V is volume. The internal energy U of the steam is used for power generation, typically by adiabatic expansion in a turbine. The PdV work is not typically used for turning the turbine in the case of saturated steam as it would precipitate condensation. However, the PdV work is utilized for heating purposes, where the steam releases latent heat through condensation (dV).