SO2 gas is used in various processes of mining and pulp and paper industry.
Sulfur dioxide has many commercial and industrial uses such as; cooking liquor and SO2 water in the paper pulp industry, sulfuric acid production, ore and metal refining, solvent extraction of lubricating oils, disinfecting and fumigating, oxidizing agent, reducing agent, and antioxidant.

Burning sulfur in air causes two different reactions:

S + O2 → SO2 + heat

SO2 + 1/2 O2 → SO3 + heat

The second reaction is undesirable. It can be suppressed in favor of the first:

1. Keep SO2 concentration high
2. Keep combustion temperature high

There are two traditional methods for monitoring the temperature in reaction vessels:

• Pyrometer
• Thermocouples

Pyrometer Solution – E²T Pulsar III – The E²T Pulsar III is traditionally used in measuring the reaction temperatures within sulfur recover units (SRUs) to control temperatures and increase the efficiency of removing sulfur from natural gas.  This is essentially the opposite procedure of the application we are interested in, but both processes require the same temperature monitoring.

The pyrometer has several unique features:

• Simultaneous measurement of refractory and gas temperatures.
  • Measures 2 wavelengths for continuous and instantaneous measurement of
    • Refractory Temp (RT)
    • Gas Temp (GT)
    • Integrated Temp (FF)
• Instant or average readings

Challenges in employing the pyrometer:

• Where to install the pyrometer?
• Will system withstand 2000C temperature and 100KPAG atmosphere within combustion chamber?
• Backups recommended?

Solutions:

• Short vessel (35”) – locate Pulsar as far away as possible from the mister – best to get gas temp at point having least amount of sulfur particulate and highest acid gas concentration
• Arrange viewport to target a critical refractory point so the pyrometer can measure both gas and refractory
• Pyrex window when installed with recommended purging requirements (N2 or combustion air) will never see the 2000C gas temperatures of the process and will easily handle the 100KPAG pressures of the vessel.
• Thermocouple used for backup.

Thermocouple Backup Solution:

• In this application, we employed a duplex type B thermocouple (platinum-30% rhodium/platinum-6% rhodium which is good up to 1800C) with an alumina inner tube and a Hexoloy outer tube.  The alumina provides protection of the platinum from contamination, and the Hexoloy provides physical protection for the alumina. This thermocouple measures the outer sulfur burner shell which is at approximately 200C.