In the opinion of Celson Calmon Ribeiro, Production Consultant at Suzano, eliminating the human variable from the system resulted in greater operational stability. “We have eleven operators. Each one thinks differently. This is the richness of human beings. When you switch to artificial intelligence, you balance those differences. In that sense, the project was very positive because it provided operational stability, continuity, and financial return,” he explains.
Implementation of advanced controls for the lime kiln to reduce gas consumption
A partnership between ANDRITZ and Suzano Aracruz reduces the specific consumption of Natural Gas (NG) through the implementation of advanced controls for the lime kiln.
Optimizing costs and processes is an ongoing challenge for Suzano Aracruz, a global leader in the manufacturing of bioproducts developed from the cultivation of eucalyptus. According to the company's quarterly report, Suzano sold 3.1 million tons of pulp and various papers during the third quarter of 2022—a four percent higher volume than was sold the previous year and a new third-quarter record for the company.
The use of Natural Gas (NG) is one of Suzano’s major drivers for production costs, and its lime kilns were the greatest consumers of NG. In order to reduce this cost and improve lime kiln efficiency, Suzano partnered with ANDRITZ to implement four advanced controls in one of three lime kilns (lime kiln A). Between March and November of 2021, the new controls resulted in a 2.61% reduction in NG consumption and a 3.37% reduction in total energy consumption.
For Aledio Moura, Panel Operator at Suzano, participating in the project was an important opportunity to exchange know-how and get to know another process control solution. In his opinion, there were three key operational stages that contributed to the results seen. The first was Suzano operators and ANDRITZ coming together to understand and discuss the modes and forms of operation of Suzano’s lime kiln. That initial stage was followed by the definition of limits for the control variables and, finally, monitoring and feedback of the operation with the ANDRITZ team.
Lime kiln operating modes and definition of control variables
The kiln area is responsible for recovering lime used in the causticizing process. “A precise recovery is especially important to avoid the necessity of adding lime to the system,” explains Rudson Venturim, OPP Analyst at Sindus ANDRITZ. “Of course, some lime will always be needed to keep the system performing optimally. And the lime used must be high-quality with a low carbonate residual so that it does not compromise the causticizing process.”
The goal of the work, therefore, was to study the characteristics of the kiln and optimize controls so that the equipment could produce the same amount and quality of lime while consuming less gas. Suzano’s main kiln controls have been completely manual, which significantly slowed down the operation. This resulted in higher NG consumption costs as NG was used to heat the lime mud inside the kiln. (Not all pulp mills use gas. The advanced controls used in this project would also apply to mills using oil for heating).
The main control variables impacting the process were oxygen, furnace rotation, production control, and gas flow, which together make up the kiln’s temperature profile. The team automated these controls to optimize the kiln operation.
Monitoring the operation and teamwork
Manual controls influence process stability, as well as the plant's chemical and energy consumption. “The controls - when operated manually - have a delayed response to process variations and fail to optimize resources such as chemical and energy consumption,” explains Cláudio Beiruth Xavier, Process Consultant at Suzano. “Once the advanced controls have been implemented, the standard deviation was reduced, which made it possible to approach the optimum operating point and respond faster to common and special process variations.”
The operational experience and knowledge of lime kiln operators was indispensable to the implementation process. When designing and implementing the system and running tests, operators discussed methods with the ANDRITZ team, reported difficulties, suggested points for improvement, and flagged occasions where the control needed an adjustment, all of which Aledio Moura says was fundamental for the success of the work.
Process specialists also actively participated, helping the team to model the controls and adjust the parameters. “With the experience of the plant, they talked about the regions where the kiln operates best and we adjusted until we found the optimal point together with them,” shares Alex Ribeiro, OPP Specialist at ANDRITZ.
An important step towards digital transformation
Digital transformation strategies are an important focus for the Suzano Group. In the opinion of Cláudio Beiruth Xavier, one of the aims of digital transformation is to generate a model that can simulate every variable in a process environment to better understand and control that process.
“The control and optimization of combustion in the lime kiln involves seeing how the calcination process takes place and how the human interface interacts with this process via Distributed Control Systems (DCS),” he says. The implemented fuzzy logic incorporates control blocks in a very adequate way. Therefore, digital transformation comes to explore the maximum optimization of processes”, he considers.
With the success of the lime kiln A project, Suzano Aracruz now plans to carry out the same work in their other kilns B and C.