The process of heat regeneration significantly increases the thermal efficiency of steam turbine by reducing the amount of fuel
that must be added in the boiler. This process is known as heat regeneration
and a variety of heat regenerators
can be used for this purpose. Sometimes engineers use the term economiser
that are heat exchangers intended to reduce energy consumption, especially in case of preheating of a fluid
. On the other hand, the process of draining steam from the turbine at certain point of its expansion and using this steam for heating the feedwater supplied to the boiler is known as bleeding
and it must be noted, a small amount of work, WT
, is lost by the turbine.
As can be seen in the article “Steam Generator”, the feedwater (secondary circuit) at the inlet of the steam generator may have about ~230°C (446°F) and then is heated to the boiling point of that fluid (280°C; 536°F; 6,5MPa) and evaporated. But the condensate at the condenser outlet may have about 40°C, so the heat regeneration in typical PWR is significant and very important:
- Heat regeneration increases the thermal efficiency, since more of the heat flow into the cycle occurs at higher temperature.
- Heat regeneration causes a decrease in the mass flow rate especially through low-pressure stages of the steam turbine, hence the LP Isentropic Turbine Efficiency increases. Note that at the last stage of expansion the steam has very high specific volume, which requires large blades of the last stage.
- Heat regeneration causes an increases in working steam quality, since the drains are situated at the periphery of turbine casing, where is higher concentration of water droplets. Improved turbine drainage implies less problems with erosion of blades.