Identifying chimney tower faults with the elios 3 at a cement plant

Benefits in a nutshell

Introduction 

In 2022 alone, 4.1 billion tons of cement were produced. This material has become one of the most critical construction materials and is in high demand. Any delay in the supply could have disastrous consequences and a widespread impact. 

For this reason, chimney plants have to balance two very important factors: there is high demand for their outputs, but they are working with complex machinery that needs careful maintenance. Thus, cement factories require careful planning to ensure maintenance requirements do not interfere with cement production. 

A major part of the production of cement involves putting limestone inside a kiln where it is broken down into a calcium oxide, one of the base elements of cement. These kilns burn at 1300 to 1450 degrees Celsius. The hot gases and waste from this process are partially let out via industrial chimney stacks. The chimney stacks on cement plants are critical to the infrastructure - they are one of the few parts of the cement production workflow that do not require regular maintenance. However, unexpected maintenance of these structures would potentially grind all cement production to a halt.

So when on cement plant engineer noticed that the chimney stack on their site looked a little bit tilted, they knew that fast action would be critical to ensuring the safety of the site and continuation of production. 

How a chimney stack works and what the customer needed

The chimney stack on this site was connected to two separate kilns. Typically, maintenance for each kiln takes place once a year (one kiln in winter, and the other in summer). This prevents both kilns from being offline at the same time and leaves space between their maintenance windows to complete projects and properly plan the next kiln’s work requirements. 

The cement stack on this site measured 120 meters tall with a diameter of 4 meters. Throughout production, it handles gases as hot as 150 degrees Celsius escaping through the concrete tunnel. To protect the structure, it is comprised of an inner and outer sleeve of concrete. Both support each other and withstand the extreme temperatures from gases escaping the 200-meter-long kilns. 

The interior of the chimney stack visualized with the Elios 3's LiDAR scan

In February 2023, an engineer noticed a slight angle seemed off at the top of the chimney stack. Immediately, an inspection was ordered as a fault with this structure could be expensive to not only inspect and maintain but cause increased costs due to halted production. Although each kiln connected to the stack can be shut down regularly, for an inspection to be done of the chimney, all production must temporarily be halted until more information is available. 

Solution: inspecting a cement chimney stack with the Elios 3

This cement production site has a specialized drone pilot on its staff who quickly went to the chimney to begin an inspection. An external view did not provide any clear information, which meant that the drone inspection of the chimney stack would have to be done with an enclosed-space drone capable of flying out of the line of sight - the Elios 3. The aim was to use the drone to gather visual and LiDAR data, which the drone gathers simultaneously, to do a photo-based inspection in addition to creating a 3D model of the chimney’s status. 

The cage structure of the Elios 3 in addition to its combined visual inspection and LiDAR scanning payload would be able to gather data about the condition of the stack which would be used to create a 3D model and plan the next steps. In the past, this would have to be done with a specialized crane that takes at least 1 - 2 days to set up and up to an entire extra day to complete the inspection. The crane is also very costly, with the process of setting up and dismantling it easily reaching 30,000 euros. 

However, the drone pilot completed the inspection within 1 hour. In addition, the cooldown time for the chimney is only 1-2 hours before it is safe to complete the flight, meaning that within 3 hours, the chimney was ready for use again - depending on the results of the drone’s flight. 

The internal space in the steel girder was small and hard to access, which is why the Elios 3 was used. 

Results of a cement stack inspection with a drone

After the flight, the raw LiDAR data was processed with GeoSLAM Connect 2.3, with the aim of creating a high-density point cloud while globally optimizing the data to account for any drift that may have occurred 

A single LAS file was then exported from GeoSLAM to CloudCompare where the point cloud was cross-sectioned and analyzed to visualize the chimney and determine the scale of damage. This was how the cement plant team was able to see that the drone inspection had unveiled a worrying problem: the inner sleeve of the stack was subsiding in the top 7 - 10 meters of the tower. Part of the concrete had collapsed and shifted 150mm to the East, causing the entire top 7.5 meters of the chimney to lean at a 4-degree angle. Failure to identify and fix this issue could have caused major problems ranging from further damage to the stack to partial collapse of some of the elements, in addition to safety risks with parts of the stack falling onto other equipment or even near people. 

The chimney stack was visualized in CloudCompare with the crack causing the upper part of the stack to lean to the side. 

Once the drone pilot had their results, they were able to quickly share the 3D model with decision-makers on the site. The maintenance plan was straightforward: the inner tube of the concrete chimney would have to be replaced at the top section. 

The maintenance and repair system was quick to respond: 

1. The cement plant managers informed a contractor of the dimensions and size of the cement tube they would need. The 3D model provided extensive information on the exact location, size, and dimensions of the areas needing to be replaced 
2. Engineers were simultaneously planning the best ways to remove the old part of the tube in a safe and timely manner. With full visualization of the asset, they could make a more detailed plan than is typically possible, leaving little to no planning to guesswork. 
3. The timeline was set for repairs, which would involve removing, cleaning, and then replacing the top of the stack in a safe and timely manner. 

When the maintenance team arrived, they were able to quickly remove the old part of the inner tube that was damaged. Although it was only the top 7-10 meters of the stack, it weighed 7 tons and naturally had to be carefully moved away. This removal took 5 days to safely remove. Next, the team set about cleaning and inspecting the outer tube’s interior where it had been hidden by the crumbling inner tube, which took another day. Finally, the new piece of concrete was brought in and installed, and completed within 4 days. The entire process was completed within 2 weeks and saved a lot of money and time just through the sheer efficiency of the inspection workflow and enhanced site awareness provided by the visual inspection and 3D model. 

Being able to fully visualize the status of the stack helped maintenance teams plan the best way to fix it. 

Drone programs in cement plants 

The use of a specialized drone like the Elios 3 on this site ended up saving the cement plant significant quantities of money almost immediately - including the 30,000 euros saved on bringing in a crane. Just the easy deployment and use of the Elios 3, rather than waiting for a crane to be installed, set the team at least 2 days ahead of typical workflows. 

The drone pilot commented that the Elios 3 flight was incredibly smooth, and they benefited from using the LiDAR SLAM system to help them navigate from inside the stack. Even though the drone was conducting a detailed inspection 110 meters above the pilot, the results were clear and the drone had no issues with signal. 

Moving forwards, this project will serve as an internal case study to warn other cement industry professionals about the danger and risk of a cement chimney stack being damaged and how to respond to the challenge as quickly as possible. The Elios 3 cut this workflow down by almost 3 whole days compared to traditional methods and gathered more information than is usually available. Thanks to the skill of this pilot and the speed of planning, no problems arose from this chimney’s degradation and the team was able to go back to cement production within 2 weeks of the chimney’s shutdown, reducing the impact on the factor’s overall cement production levels. 

Discover more about the Elios 3 and its applications