Compare the convective and radiant superheaterreheater in te

Compare the convective and radiant superheater/reheater in terms of steam temperature as a function of steam flow rate.

Solution

Superheaters are one of the most important accessories of boiler that improves the thermal efficiency.

In super heaters there should not be any fins as it increases the thermal stresses and carful should be taken when choosing the super-heater material that is stand for high temp and corrosion resistance.

Super-heater types:

1) Convection super-heater: it is the earliest type of super-heater and it is located above or behind banks of water tubes to protect them from direct flam or fire.

Parameters that increase the convection

a. Increasing the fuel-and air flow (combustion gas flow).

b. Increasing the mass flow rate of the steam. Convection super-heaters are used for low temperature

2) Radiant Super heater:

They are placed exposed to the heat source which requires the improvement of metal temperatures.

Radiation is proportional to T_f⁴ -T_w⁴ where Tf and Tw are the flame and tube wall absolute temperature. Tf is greater than Tw so radiation is mainly dependent on the flam temperature. As the steam flow rate increases the exit temperature become lower as Tw goes up. Radiant and convective super-heaters and re-heaters are used for high-temperature steam.