Trinidad Cement Ltd (TCL) reports on a recent burner upgrade project at Claxton Bay...
CEMEX continues to execute its long-term investment strategy in TCL, its Trinidad & Tobago-based subsidiary. TCL is the nation’s sole cement manufacturer and has been steadily improving its quality, safety and efficiency to align to international standards. TCL is located in Claxton Bay, Trinidad & Tobago. It operates two wet process kilns, kilns 3 and 4, both of which are fueled by natural gas. Kiln 3 (1100t/day, L = 145m, Ø = 5.2m) was commissioned in the mid 1980s. It has a specific heat consumption of 1730kCal/kg of clinker. The burner in kiln 3 was essentially a pipe that did not facilitate any flame control, leading to frequent refractory failures, low clinker quality control and excessive fuel use. The burner was also floor-mounted, which limited the space available during shutdowns, leading to poor safety conditions during shutdown and maintenance.
Selecting a new burner
A decision was made to upgrade the burner as it would allow the plant to improve product and quality consistency, its equipment as well as use alternative fuels. A higher kiln reliability results in higher clinker production capability, well beyond market demand. Tenders to replace the burner in kiln 3 were invited at the end of 2018. Proposals were evaluated in early 2019 and all components were received in the fourth quarter of 2019. The project, executed at the beginning of 2020, comprised two main parts:
- Procuring and installing the burner;
- Re-engineering the burner support system.
The new burner selected was supplied by Unitherm, which has produced over 400 burners for rotary kilns and has over 60 years’ experience in the industry. The burner utilises the Mono Airduct System (MAS®) concept. This uses the whole primary air to cool the burner pipe and bring the whole primary air flow into a swirl intensity as required. This permits continuous swirl adjustment, reproducibility of flame shape, constant burner momentum and a single air jet penetration into the flame/kiln. The MAS® burner also has a channel that offers the option to burn liquid fuels in the future and the capability to support a second burner for the use of solid fuels.
The main benefits of the burner are lower required burner momentum for optimum burning of traditional and secondary fuels, lower pressure drop through the primary air nozzles and air channel and continuous flame shape control by the patented flame setting device to achieve optimum clinker quality. Only one high pressure fan is required, without a variable speed drive. This is independent from the number and kinds of fuels. In addition, the MAS® burner allows constant burner momentum along the entire flame setting range. The flame shape is easy to control and reproduce, with easy maintenance and service.
The new MAS® burner was purchased as a complete system with a flame monitoring detection device, gas electric ignition device, new primary air fan, a new protection (cooling) air fan, a kiln burner trolley and components and burner management system.
Optimising local and international engineering support
The new burner is considerably heavier than the old burner, so a new burner trolley was required. For this, support was provided by CEMEX’s regional office, which engaged Colombia-based Alfering to execute the detailed engineering and manufacturing of a new trolley after positive experience at the CEMEX Caracolito facility in Colombia. The manufacture of the trolley components was divided between Unitherm’s location in Austria and Alfering. Supervision and sign off on the quality of the trolley in Colombia was provided by CEMEX Caracolito and the unit was then shipped to TCL. The burner and fans were shipped directly to TCL from Austria.
The new, larger burner also reduced the already limited floor space on the burner platform at TCL. This meant that a clearance of only 1000mm would exist between the burner tip and the kiln access. To correct this issue, TCL suspended the new burner, including the old trolley, from the existing roof while the new trolley was manufactured. This resulted in a second equally large project that required significant additional capital expenditure. For this part of the project, design engineering was carried out by Trinidad-based RM Engineering. The execution was carried out by Amalgamated Engineering Services Ltd, also based in Trinidad & Tobago. This part of the project, which included various duct modifications, allowed the burner to be moved to the extreme north of the burner platform to provide significant extra space between the burner tip and kiln access.
The design engineering included interpretation of the OEM drawings and their dimensional requirements, assessment of the site conditions to ensure that the OEM requirements could be physically accommodated, including the burner/trolley having to traverse the length of the burner platform along the north-south axis.
The design also had to incorporate the gravity loads specified by the OEM in the structural design. Loads used in the analysis of the new support arrangement included gravity and generated seismic loads, together with the relevant load combinations (factor of safety) applied. This part of the project also incorporated design of the new burner/trolley suspended support system based on the analysis of the existing structure to ensure that the new burner/trolley and support structures could be safely suspended.
After the assessment of the existing structure, plate sections were added to stiffen the existing tapered rafters at vertical supports. Existing ducting was also modified as it obstructed the path of the trolley. The incoming gas line was also relocated to accommodate the new structure.
Project execution
The modifications to the burner platform and installation of the new kiln 3 burner started in January 2020 and took 35 days during a kiln outage at a time of high clinker inventory. There were no major issues in the execution phase of the project. The initial startup of the new burner on 26 February 2020 was seamless, with commissioning support provided by a Unitherm representative.
A number of simulations were done for the start-up of the new burner. The flame sensors indicated the presence of the flame to the operator. The operator was able to effectively control the gas and air flows to establish the stable minimum heating flame. The ignition flame is independent to the main burner, allowing for easier lighting and troubleshooting, which was also helped by new gas and air pressure sensors. The new burner takes approximately 1 minute to light. The old burner took about 20 minutes. This project was executed by a talented and well-trained cross-functional team of local engineers with the support of counterparts from CEMEX.
Fine-tuning continues
Fine-tuning of the new burner is still in progress at the time of going to press, so it is premature to evaluate the full operational benefits, as the kiln has not yet stabilised at full production. Initial observations include the fact that the new flame is narrower than the old flame and there is tight and consistent control of the flame shape.
