Metals are typically found in Nature in the form of ores comprising of a chemical compound of the metal with other elements, such as oxygen (as an oxide), sulfur (as a sulfide) or carbon and oxygen together (as a carbonate). In the case of carbonates and sulfides, a process called “roasting” drives out the unwanted carbon or sulfur, leaving an oxide, which can be directly reduced. Roasting is usually carried out in an oxidizing environment. The metal oxide is then “smelted” into the metal.
Any sulfide metal ore upon roasting produces metal oxide and SO2. The SO2 then further oxidizes to SO3. See example below:
2 CuS + 3 O2 → 2 CuO + 2 SO2
CuS + O2 → Cu + SO2
2SO2 + O2 → 2SO3
The SO3 in the flue gas after the roasting/smelting process combines with moisture to form weak Sulfuric Acid which causes corrosion and wastage in ductwork and equipment. In some processes, some level of SO3 is desirable to enable particulate collection in a Hot Electrostatic Precipitator. However excessive weak acid increases the corrosion potential. Any remaining weak acid in the flue gas must be treated in a scrubber before the stack, which is a financial burden.
The Breen AbSensor-ADM, Acid Dewpoint Monitoring system, is ideally suited for these applications to measure the dewpoint of weak acid in the process. This measurement can then be utilized to modify operating conditions such as sulfation air or process temperatures to avoid excessive formation or condensation of weak acid. See below an application of the AbSensor-ADM to control sulfation air in the waste heat boiler in a copper smelting process.