Tail Gas Analyzer is used with feedback control of the air to the plant in large sulfur plants to optimize sulfur recovery. They are applied in Claus sulfur recovery process control. The tail gas analysis is an important tool for controlling the carbon black production process. A carbon balance permits the amounts of carbon black produced to be monitored continuously. This provides important data permitting control of the reactor including the steam boilers as well as optimization of the process. The primary method for setting the combustion airflow rate is done through the specification of tail gas analyzer. This unit is placed in the plant downstream of the reaction furnace and determines the correct airflow based on the user specified air demand condition. The furnace model also allows for direct user specification of the total airflow to the reaction, which will over-ride the requirement for a tail gas analyzer and air flow controller.