Reheaters

Reheaters

Figure A

• Reheaters are used in between the stages of turbine to reheat the steam so as improve overall efficiency of plant and to avoid low dryness fraction of steam in later stages of turbine.
• Therefore, the basic concept and design is similar to superheater except that these operate comparatively at lower pressures and temperatures.
• As a result the stress developed in reheaters are lower than superheaters. Due to this, lesser costly materials like lower grade steel alloys can be used for reheaters.
• Arrangement for reheating of steam in convective reheater in between the stage of high pressure (H.P.) and intermediate pressure (I.P.) turbines is shown in Figure A. Energy balance equation is :

m_s (h₂– h₁) = m_{g  .} C_pg x ₍t_g1 – t_g2) =  U_o A_o (△T)_m

• In modern boiler practice, a reheater is divided into two sections as convective section of reheater placed in convective zone and the remainder section is placed just at the furnace exit to receive radiant heat and hung from the top.
• The convective section is called primary section and radiant section is called secondary section of the reheater which is pendant type.