General
Spray drying absorbers normally operate at flue gas temperatures close to the water dew point at the flue gas outlet. Changes in the flue gas inlet conditions could lead to creation of moist and sticky product unless these changes are caught by the flue gas outlet temperature control system. Careful control of SDA (absorber) exit flue gas temperature is essential.
Operating close to the temperature limit for safe operation, a reliable temperature control loop for the flue gas exit temperature is essential. Often such loops are made as cascade loops using flue gas flow rate and even absorber flue gas inlet temperature as feed forward signal.
Demands on the absorber exit flue gas temperature measurement exist, as the time constant for the temperature transmitter is important.
Time constants for selected temperature measurements at gas velocities of ca 5 to 20 m / sec shall be according to: