PTQ Q3 2026 Issue

Pressure drop in kg/cm

Impact of steam injection location

10 8 12

300

Complete heater Radiant section only

240

250

200

150

134

135

2 4

127

100

50% crossover + 50% at 8” tube

At crossover

Convection inlet

At 8” tube

21.2

Convection inlet

50% crossover + 50% at 8” tube

At crossover

At 8” tube

Figure 6 Impact on pressure drop

Figure 5 Impact of steam injection location

provision has been adopted primarily based on prevailing practices and, in some cases, on thumb rules alone. Through this article, various scenarios have been eval - uated, and it is observed that injecting steam at approx - imately 1.0 wt% of the RCO flow rate can yield effective results. However, it must be evaluated in detail on a case- by-case basis and through detailed simulation, utilising commercially proven tools. Further, the location of steam injection can also play a major role, especially if the vacuum heater is limited by pressure drop. To conclude, it is recommended that the vacuum heater prone to coking is evaluated in detail, with multiple factors such as film temperature and residence time taken into account. Additionally, practical considerations such as nozzle chocking should be given due importance when determining the best solutions for that particular vacuum heater. A comprehen - sive evaluation of the steam injection rate and its location can significantly improve furnace run length and prevent further accelerated coking, which calls for frequent shutdowns. The authors would like to wholeheartedly thank the management of EIL for their support and encouragement in the publication of this work. Further reading 1 Barletta, T., Why vacuum unit fired heaters coke, PTQ Autumn 2002. 2 Barletta, T., Conditions influencing coke formation, PTQ Revamps and Operations . 3 Golden, S, et al, Deep-cut vacuum unit design, PTQ Q4 2005 . 4 Jinyu, et al, Controlling film temperature in fired heaters, PTQ Q1 2013. 5 Al-Barrak, et al, Vacuum heater operational cycle improvement study, PTQ Revamps 2024 . Ankur Saini is Senior Manager in Engineers India Limited’s heat transfer department having more than 13 years of experience. His area of work includes design, revamp assessments, and troubleshooting of oil refin - ery fired heaters. He holds a Bachelor’s degree in chemical engineering from BIET Jhansi. Email: ankur.saini@eil.co.in Rupam Mukherjee is Assistant General Manager in Engineers India Limited’s heat transfer department. He has more than 17 years of experience in design and engineering, performance improvement, and troubleshooting of fired heater systems. He is a chemical engineer with a post-graduate degree in energy and environment management from I.I.T. Delhi. He is a Certified Energy Auditor (CEA) with the Bureau of Energy Efficiency, India. Email: rupam.mukherjee@eil.co.in Shilpa Singh is General Manager in Engineers India Limited’s heat transfer department, with more than 28 years of experience in this field. She leads a team of chemical engineers involved in grassroots designs, revamp studies, and capacity and efficiency improvement projects for fired heater systems. She holds a Bachelor’s degree in chemical engi - neering from I.I.T. Delhi. Email: shilpa@eil.co.in

From these observations, the benefits of steam injection can be seen for improving furnace run length in services prone to coking. However, at this juncture, it is important to note that this steam injection provision comes with a price other than the direct cost of steam. The major restriction when injecting steam in RCO is generally the fluid pressure drop across the vacuum heater. With continued operation and formation of a coke layer over time, the pressure drop can increase, and in such a scenario, the vacuum heater can be limited by throughput. However, an increase in pressure drop due to steam injec - tion can be minimised by carefully choosing the injection location. The impact of steam injection location on pressure drop is depicted in Figure 6 . As shown in Figure 6, the pressure drop increases as the steam is injected as far upstream as possible from the radi - ant outlet. Thus, in cases where the vacuum heater pres - sure drop becomes limiting, the steam injection location can be further optimised. Injecting the steam at the crossover instead of the convection inlet tube can reduce the overall pressure drop without any adverse rate of coking, provided coking does not initiate in the convection coil itself. This has to be carefully evaluated by a competent heater designer based on the type of crude being processed in the unit and the RCO preheat, and should not be considered as a gener - alised conclusion. In the aberration scenario, the refinery operator may be unaware that the crossover steam injection nozzle may be choked by debris or coke deposition, although the common steam injection flowmeter may show a flow rate within design requirements. In such cases, the refiner may experience a very high rate of coking as the fluid residence time increases multifold, even with the entire quantity of steam injection. Thus, the vacuum heater may initially see a very low pressure drop; however, the pressure drop may increase exponentially once heavy coking initiates inside the heater tube. Conclusion Vacuum heaters process RCO, which is prone to coking. Even with the latest design features, coking cannot be com - pletely avoided. However, with certain strategies, it can cer - tainly be minimised. One such proven and effective strategy is to inject velocity steam into the RCO. Traditionally, this

PTQ Q3 2026