Gas-gas heater protection system and method

A system for protecting a gas-gas heater made of a material, the heater for receiving hot, raw flue gas from an air heater and cooling same, the cooled raw flue gas being provided to a desulfurization plant for cleaning the flue gas and a cooled, clean flue gas being provided back to the gas-gas heater for heating after being cleaned in the desulfurization plant, the system comprising:

• a hot, raw flue gas path from the air heater to the gas-gas heater, the hot, raw flue gas having a gas temperature;
• quench means communicating with the hot, raw flue gas path at a location downstream of the air heater and upstream of the gas-gas heater for providing rapid cooling of the hot, raw flue gas entering the gas-gas heater;
• and
• control means communicating with the hot, raw flue gas path and the quench means, the control means having a variable, pre-set temperature value, the pre-set temperature value being a temperature value at which the material of the gas-gas heater can be damaged by the gas temperature of the hot, raw flue gas, the control means monitoring the hot, raw flue gas path at a location downstream of the air heater and upstream of the quench means for detecting when the gas temperature of the hot, raw flue gas leaving the air heater is greater than the pre-set temperature value and activating the quench means for rapidly cooling the hot, raw flue gas entering the gas-gas heater until the monitored gas temperature is less than the pre-set temperature value.