Steam crackers are the heart of modern petrochemistry. They represent the most important source of petrochemical raw materials. With the help of steam, naphtha, which consists of longer hydrocarbon chains, is cracked. The process consists of several steps: first, the raw gasoline is mixed with steam and evaporated. It is then briefly heated to over 800 °C in large furnaces causing the naphtha to decompose into smaller building blocks such as ethylene and propylene, which are central building blocks for many more processes. The reaction mixture is then separated in several steps and the products are further processed using a variety of chemical processes.
After several weeks of operation, more and more of the coke produced as a by-product during the process has deposited in the pipes in which the cracking process is taking place. These must be "decoked" every 40 to 90 days. For this purpose, the pipes are normally regenerated by introducing a preheated air-vapour mixture into them. In the process, the coke is burned off or "gassed-off" revealing the metallic surface of the tubes, which is also catalytically active for the cracking process.
This process is accelerated by the use of oxygen-enriched air and results in a much more thorough removal of the coke than when using non-enriched air. The use of oxygen in de-coking has the following advantages compared to pure air operation:
- High quality decoking and associated energy savings
- Shorter downtimes
- Greater flexibility in operation