When natural gas and crude oil is extracted from the ground it contains some percentage of sulfur. Gas or oil with a high level of sulfur is said to be sour. Gas or oil with a low level of sulfur is said to be sweet. This sulfur is removed from the gas stream by a chemical reaction. After this process, the sulfur is removed from the gas or oil and is instead contained in amine gas and sour water gas. The sulfur is then removed from the amine gas and sour water gas in a thermal reactor called an SRU (Sulfur Reactor Unit). This process is known as the Claus process. The Claus reaction that removes these gasses from the process stream is exothermal, meaning that it creates heat once the process has begun. As a result, there are several reasons to monitor the temperature of the thermal reaction.
The thermal reaction is more efficient when run at higher temperatures, and the gas stream may be run through more quickly; therefore, there is tremendous incentive to run the process hot. Many plants inject oxygen in an effort to raise operating temperatures and to increase process capacity. However, the refractory walls of the vessel degrade at excessive temperatures, making it essential that the process temperature be closely monitored to balance the need to be efficient at extracting the sulfur while at the same time extending the life of the refractory. These gasses are highly toxic, and the safe operation of the process is highly critical.
So while temperature is a critical process control parameter in the sulfur recovery process, there can be a number of complications when trying to get an accurate measurement. There are two generally accepted methods of measuring temperature inside of a Claus reactor - thermocouples and infrared pyrometers. This article gives a very comprehensive overview of the benefits and drawbacks of each measurement technique. However, the following are the most common issues and difficulties associated with the SRU temperature measurement and how to address them.
1. Constant replacement of thermocouples
One of the most common ways to measure the temperature inside the furnace is with a contact thermocouple device. However, the inside of the reactor is a hot, nasty, and corrosive environment and thermocouples will often fail and need to be replaced. Thermocouples tend to be troublesome because of their unreliability and require a lot of maintenance work to replace them. It can be difficult to consistently run a process to the same temperature off of thermocouples alone and another means of measurement is typically required. Not to mention, that the constant replacement of these thermocouple devices can be expensive over time.
Solution: Non-contact temperature devices are often used instead or in addition to thermocouple measurements. Non-contact measurement