Eliminate Heater Draft Problems on the Fly

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By Erwin Platvoet

The Problem

A refinery heater experienced substantial draft problems resulting in several instances with positive pressure at the arch with excursions of up to 0.25 inH2O (6.3 mmH2O). Adding a steam eductor to the stack is often the simplest solution to create additional draft. Its principle of operation is simple and straightforward: inject steam into the flue gas through one or multiple injection ports and use momentum of the high-velocity steam jets to entrain the surrounding flue gas. However, what is normally a straightforward job became complex due to constraints at site:

  • The heater would not be shut down to add a steam eductor or make any modifications.
    • There were only two small connections (1½ in. DN40) in the offtakes to the stack that could be used to add lances while the heater is in operation.
    • There were no connections on the opposite side of the duct, so the design would only be supported from one side.
  • The small diameter lance would need to be robust and resist bending and vibration due to the steam thrust.
  • The internal steam velocity could not exceed sonic velocity, and the steam distribution along the length of the lance would need to be uniform.

The Solution

The draft deficiency sets the required amount of steam, which is then used to design a basic steam eductor using empirical formulas for jet pumps. Initial results showed that the internal velocity of the steam lance would approach sonic velocity, and the distribution of steam into flue gas would be challenging. Therefore, CFD modeling was used to design and check the final details of the eductor.

The only way to achieve high steam flow rates with a small diameter lance is by using higher steam pressures. The high ratio of pressures over the injection port results in injection velocities exceeding Mach 4, which creates “barrel shock” regions. To accurately capture high-velocity flow fields inside the lance and across the supersonic regions requires careful meshing and modeling of turbulence.

 

Plot of Mach contours at the steam injection port - Heater draft problems - CFD Modeling

     Figure 1 – Plot of Mach contours at the steam injection port

 

After several iterations, a steam lance design was found that could entrain sufficient flue gas and reduce the inlet static pressure by 0.25 inH2O.

flue gas - Velocity contours (ft/s) - Heater draft problems

               Figure 2 – Velocity contours (ft/s)

 

To connect to the existing 1.5-inch offtake duct connections without altering the original steelwork, mechanical grip tube fittings and a reducer were utilized in the design. A structural analysis was conducted to verify that the existing connection, shell plate, and nearby stiffeners could safely accommodate the steam thrust forces generated by the lance.

Steam Lance Fittings - Heater draft problems

               Figure 3 – Steam Lance Fittings

 

Conclusions

Designing a steam lance can be difficult and requires careful consideration of both the internal and external flow fields, as well as the mechanical robustness. But if the homework is done right, a lance can be designed for the most complicated situations.

Learn more about how our engineering experts can make fired heaters more efficient by reaching out to us at info@xrgtechnologies.com.

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ERWIN PLATVOET
As CTO of XRG, Erwin is a true innovator, whose career spans more than three decades in heat transfer and combustion industries. Erwin is a graduate of Twente University in the Netherlands with a MS in Chemical Engineering. Erwin has served the industry around the globe in a variety of roles including Research and Development Engineer, Cracking Furnace Specialist, and Director of Engineering, and now CTO. Erwin holds eight patents in fired heat transfer and emissions control technology, has published numerous papers, and co-authored the John Zink Combustion handbook and Industrial Combustion Testing book. Erwin has been an active member of the API 560 and API 535 subcommittees and taken an active role in revising these standards.
BAILEY HENDRIX
Bailey graduated from Oklahoma State University with a Bachelor of Science in Mechanical Engineering. Upon graduation, she joined the private sector as an Applications Engineer in Tulsa, OK at a local combustion company where she managed the sales activities for the process burner refining market. She quickly accelerated her career, becoming the Refining Account Manager responsible for all business development and sales of process burners in North and South America. Her strong leadership skills and interpersonal qualities led her to a position as the Western Hemisphere Sales Director for the process burner business, leading a group of sales engineers in the areas of new equipment, retrofits and burner management systems. Her financial and commercial acumen drives the success of XRG Technologies’ business development.
ALLEN BURRIS
Allen’s background includes 10 years of experience in designing and selling process burners. Allen is a graduate of Oklahoma State University with a BS in Mechanical Engineering and is a licensed professional mechanical engineer in the State of Oklahoma. His knowledge and superior customer focus led him to a career change to process design, custom-engineered fired heater sales, and associated sub-systems for the petrochemical, refining and NGL industries. With more than two decades of experience in the combustion and fired heater industry, Allen has what it takes to overcome challenges associated with complex projects and possesses.
TIM WEBSTER
With over 25 years of experience in the combustion industry, Tim brings a wealth of industry experience and technical expertise to XRG. Tim graduated with a Bachelor of Science in Mechanical Engineering from San Jose State University and received a Master of Engineering from the University of Wisconsin. Tim began his career engineering custom combustion systems for a wide range of applications including boilers, heaters, furnaces, kilns, and incinerators. Tim is a licensed professional mechanical engineer in the states of California, Texas, Louisiana and Oklahoma, has authored numerous articles and papers, and has co-authored several combustion handbooks.
matt martin
As the Lead Scientist at XRG, Matt has over 30 years of experience in the combustion industry. He specializes in CFD of fired equipment, including UOP platforming heaters, burners in process heaters, thermal oxidizers and flares with over 300 simulations of installed, field-proven equipment. Matt received a Bachelor of Science in Computer Science with a minor in Mathematics from the University of Tulsa. He has written numerous publications, is listed as inventor or co-inventor on 27 patents and was awarded the title of Honeywell Fellow in 2011 for technical excellence and leadership.
gina briggs
Gina is a native Oklahoman and attended the University of Tulsa, graduating with a BSBA in Accounting. She is a Certified Public Accountant and Chartered Global Management Accountant. Gina began her career with the Tulsa office of Deloitte Haskins and Sells, providing audit and tax services. Since leaving Deloitte, she has held CFO positions with privately held companies in the manufacturing, construction and distribution industries. In 2013, she began a consulting practice providing contract CFO services to companies, one of which was XRG and joined XRG as CFO in 2019. Gina has always enjoyed working in the small business arena, helping business owners to profitably grow and manage their businesses.