Infrared temperature measurement in the modified Claus sulphur reactor
July 7, 2017
LumaSense Technologies’ E2T product manager, David Ducharme, explains why accurate temperature measurement is critical in a modified Claus sulphur reactor
There are two critical temperatures required for the safe and efficient operation of a sulphur furnace. The first is the refractory temperature, which is critical for high-temperature alarms and automated shutdown systems in the furnace. This measurement represents the infrastructure temperature, for which high temperature limits are specified by the engineering design. However, using only refractory measurements for furnace control offers no early warning of high-temperature excursions.
The second is the gas temperature, aka the combustion or flame temperatures. Measurement of this temperature offers the operator process temperature information and an early warning of temperature excursions before they are absorbed by the refractory and trigger alarms or shutdowns. The ability to measure combustion temperature accurately provides an early warning of critical temperature events that are crucial for controlling the furnace in the higher operating temperatures found in an oxygen-enriched environment.
Thermal event timeline High-temperature thermal events begin with a rise in the flame or gas temperature. The energy from the flame is absorbed by the refractory, causing an increase in its temperature over time and eventually reaching the high-temperature alarm or system-shutdown limits. It is therefore best practice to use gas or flame temperature measurements for process control together with a refractory measurement for safety systems. Yet typical industrial pyrometers only measure single temperatures and are subject to flame transparency changes in the furnace as feed changes accrue. Operators can therefore spend considerable capital on multiple units, yet fail to guarantee an accurate reading for their asset.
Flame transparency Single wavelength measurements are more prone to errors when measuring flame (Gas) or thru-flame (refractory). When clean burning, the flame can become partially transparent to the gas wavelength being used. This transparency will allow some of the cooler refractory to be seen and the refractory temperature to be included into the pyrometer measurement, resulting in a lower measurement for the gas temperature than is actually occurring. In the case of a dirty or larger flame, the refractory wavelength measurement will pick up elements of the flame temperature as a result of low flame transparency. In this case, this will add components of the flame temperature to the refractory measurement, producing a higher refractory measurement than is actually occurring. The issue is exacerbated by the changing flame transparency as feedstocks change over time, creating a variable error in a typical single wavelength pyrometer.
Both of the above errors can be eliminated by using a single two-wavelength pyrometer that contains separate refractory and gas (flame/combustion) detectors and filters.
Two measurements, one system
The LumaSense Pulsar 4 combines the two wavelengths for refractory and gas measurements in a single pyrometer, reducing the cost of installation and maintenance. The benefit of having a single pyrometer with two separate detectors filtered for refractory and gas measurements is the ability to apply flame transparency algorithms to the output to reduce flame impingement on refractory measurements and flame transparency in the gas combustion measurements. Using the information obtained from the refractory measurement and the gas flame/combustion measurement, and then applying the proprietary LumaSense Flame Measurement Algorithm (FMA), flame transparency errors can be removed and corrected in the refractory and gas measurement outputs of the pyrometer.
In practice, this results in more accurate measurement for furnace operations, greater advanced warning of any high-temperature events and reduced maintenance and installation costs.