Remote burner optimization increases production by 14% at Graymont

Graymont’s plant is a major manufacturer of quicklime, supplying quality pulverized limestone. Since 2013, the plant has had two Metso Outotec kilns in operation. One of the kilns had a DFN burner while the other had a next generation burner, the DFN-X. At the time of installation, the DFN-X was an untested design with the inclusion of improved gas injection technology for enhanced heat flux manipulation when firing on natural gas. Since then, many DFN-X burners have been installed across the lime industry and, with appropriate tuning, significantly outperforms older generations of burner.

The challenge of optimizing from a distance

Each year, Graymont switches its kilns from solid fuel to natural gas which can cause a 28% derating of production. Historically, the main limitation of switching from solid fuel to natural gas is elevated feed-end temperatures as a result of the properties of the fuel. Preheater lime kilns can be susceptible to build-up in the preheater when temperatures are high and other conditions are met. The challenge was to increase production when transitioning to gas firing without exceeding the temperature limit through process and combustion optimization.

Due to COVID-19 restrictions, experts could not go to site and the customer requested that the work be performed remotely. This was an additional challenge as it is necessary to see the burner flame in real time when trying to improve performance. As with other pyro processes, pebble lime kilns are holistic systems in that a change in one area will lead to changes elsewhere. It is therefore crucial to have expertise in both combustion and the overall process to successfully optimize. Additionally, time must be allowed for the system to come to equilibrium.

A solution centered around customer needs and success

Metso Outotec was tasked to reduce derating and increase throughput through optimization services. Given the circumstances, Graymont and Metso Outotec worked very closely to create a constant flow of information. With great collaboration, the optimization process consisted of the following steps:

• Customer collected a full set of operating data when coal firing so that the team could "benchmark" the system and cross-validate/audit the inputs
• Transition from coal to natural gas according to Graymont Standard Operating Procedures
• Metso Outotec advised adjustments based on specific targets such as gas pressures, air flowrates and so on
• To continue the momentum, operational data was sent to the Metso Outotec specialist to review overnight and make the next round of recommended adjustments the following day
• Metso Outotec remotely guided Graymont to implement changes with Graymont providing essential feedback of the burner flame intensity/luminosity
• Other characteristics were analyzed and optimized such as instances of pulsing or other transient behavior, flame profile and location - overall flame envelope, any impingement on refractory, interaction with the bed, etc

Outstanding results achieved by collaboration and expertise

• Reduction of feed-end temperature around 5% after optimizing the gas injection, providing the headroom required to ramp up production.
• Approximately 14% overall production increase:
  • Roughly 9% tpd increase from the system with the DFN-X
  • Roughly 5% tpd increase from the system with the DFN
• Product quality improved or within specification (residual carbonate/reactivity)
• Minimal flame impingement on refractory and no signs of increased shell temperature

What's next: Further upgrades and continued optimization

In addition to the optimization work, both Graymont and Metso Outotec were interested in comparing the performance of the DFN-X and DFN burners to assess feasibility of a combustion system upgrade. Based on the findings, the DFN-X burner clearly outperformed DFN burner in every respect, prompting Graymont to move forward on:

• Upgrading the older generation DFN burner to DFN-X burner to significantly improve gas firing performance
• Upgrading the existing DFN-X with new gas pokers. Increase the size to further enhance gas injection

Additional opportunities being considered:

• Gas valve train upgrade to eliminate pressure limitations
• Upgrade the burner mounting to improve adjustability (burner aiming)
• Reinstatement of feed-end gas analysis equipment to improve the process control

More information on Graymont

Graymont is a global leader in lime and limestone solutions. Headquartered in Canada, Graymont serves markets throughout North America and Asia-Pacific. Graymont is also the strategic partner of Mexican-based Grupo Calidra, the largest lime producer in Latin America. Professionally managed and family owned, the Company has been in operation for over 70 years.

More information on Metso Outotec Pyro Processing Solutions

With over 100 years of designing, manufacturing and servicing kilns, dryers, coolers and similar trunnion-supported rotary equipment, our experts have seen it all. Our comprehensive service portfolio is supported by deep technical knowledge, experienced people, and specialized tools. From diagnostics, maintenance, and upgrades, to parts supply and specialized training, we got you covered. Get more information on our pyro processing solutions in the downloads below.