Coker Heater Health Monitoring for Maximum Throughput and Reliability

Delayed coker process units are a unique and fun challenge. The integration of a batch process with a continuous process never ceases to entertain, and at the center of it all is a large and complex heater. As a bright-eyed and bushy-tailed process engineer many years ago, I was amazed that these things worked at all.

Modern delayed coker heaters provide the energy to drive the coking process with challenging feeds, wide temperature cycles, and operating constraints. The balancing act maintained by the operations team to hit the correct coil outlet temperature, maintain an even heat flux, manage drum swaps, and remain vigilant to comply with decoke timing can be quite challenging.

Fired heaters in coking units can be single or double-fired configurations, typically with multiple cells and many burners. Most recent designs favor the dual-fired approach, in which -burners are configured on each side of the process tubes. Keeping the heater radiant tubes healthy is critical to maintaining safe and reliable operations of the full coker unit. Three key enemies of the tubes are time, pressure, and temperature. Each should have properly specified parameters identified for corrosion, velocity, etc. Time and pressure are readily quantifiable parameters that allow for accurate and repeatable direct measurement possible. Temperature, however, can be tricky due to the possibility of internal tube fouling. I will generally refer to this fouling as “coke,” but please be aware that it is not always an organic formation. While coke is typically an organic formation, it can also be present as a non-organic compound. Our enemy, tube temperature, is critical to how long tubes will last and the economic considerations that should be considered. Figure 1 shows shift case examples of tube life for a given coker radiant tube. For instance, in a 9-chrome design, these heaters routinely operate with radiant tube temperatures between 1,000 and 1,250°F.

Over the course of many years, a 50°F difference in operating temperature can reduce tube life by decades. Put another way, a 4-5% change in a tube’s maximum operating temperature can significantly change how long it can survive its environment. As delayed coker operators and support teams, how do we manage this risk reasonably while providing as much flexibility to push unit rate and severity?