Roasting Shutdown Services improve productivity and availability at Nyrstar, Clarksville

Nyrstar is the world’s 2nd biggest zinc producer operating five zinc smelters across 3 continents using Outotec fluidized bed roasting technology. The zinc roaster in Clarksville, Tennessee, USA started its operation in 1978.

The roaster is the starting point for metallurgical zinc production, a critical area for the operations. Over recent years, plant availability decreased, directly affecting the production of the site.

“Nyrstar Clarksville had been experiencing significant issues with the 65m2 roaster which led to the decision to replace internal refractory in 2018. Upon commencement of the project, inspections of the roaster revealed that its steel shell had been significantly compromised and required a new design and replacement,” said Robert Winton, General Manager of Nyrstar Clarksville in Tennessee, USA.

“I had dealt with Outotec shutdown services during my previous work experience on a furnace rebuild in 2006. Based on my previous experience I suggested that we contact Outotec to assist with the expanded shutdown scope,” added Mr. Winton.

In early 2019, Nyrstar awarded Outotec with a plant inspection for the roaster as well as with the planning and execution of the plant shutdown in summer 2019. Based on the inspection results, and the critical roaster steel shell condition, we advised the customer to replace the roaster furnace with a new nozzle grate up to the dome and to eliminate both the cleaning ports and the walkway around the upper vertical wall of the roaster, which was agreed as the final scope of work.

Excellent project execution despite the tight schedule

After approval in May 2019, there was a tight schedule of about 100 days for the planning/scheduling and fabrication of the new roaster furnace shell. We collaborated closely with Nyrstar to ensure the timely, efficient project execution, within a short period. Nyrstar assigned contractors, mobile equipment and the required team, and Outotec supported them in finding the appropriate demolition equipment and provided our demolition expertise personnel as well as with planning and scheduling.

Outotec scope:

• shutdown planning and scheduling
• shutdown construction management
• remote demolition of the roaster furnace
• engineering of the critical lift plan, lifting lift design and lifting frame for all critical lifts

The project in a nutshell:

• Outotec project management
• 8 contracting companies
• approx. 300 persons
• 227 ton of steel
• 191-ton single crane super lift
• 80 000 refractory bricks
• 510 000+ man-hours
• 0 Lost Time Injury /(LTI)

The Outotec team included 3 experts per day shift, 2 shift superintendents, 1 construction/project manager, 1 safety advisor and 12 experts for demolition work from Outotec competence centers.

The equipment used in the project execution:

• 4 remote-controlled demolition machines
• 2 remote-controlled payloaders
• 1 Outotec remote demolition platform, which was transported from Nyrstar Hobart in Australia
• Outotec patented Versa XO2® thermic lance system – lance bars and lancing equipment including specialized PPE

The feed stopped on 2nd September and started on 27th October 2019 after four days of preheating. Despite the remarkably tight schedule of the project, the replacement of the new roaster furnace was accomplished within 56 days. The plant age and lack of documentation caused a seven-day delay, required to remove the unforeseen asbestos material and to confirm the exact weight of the furnace sections. The professional Outotec construction management and the positive working spirit among all the involved teams on site helped to minimize downtime and ensure a safe solution for the removal of the steel roaster sections.

The roaster furnace was disassembled in large sections, including the dome, upper vertical wall, conical section and lower vertical wall with nozzle grate.  Additional work was carried out on the ground to ensure the highest level of safety. A 400-ton mobile crane (191-ton single lift) was used to remove and install the old and new roaster sections respectively.

Throughout the project, we prioritized safety, especially in the areas containing asbestos and personnel exposure, and delivered a safe plant with no LTI’s.

“Time was the challenge for Nyrstar: we had a limited period to assemble a team and execute a critically important project for Clarksville. Our team was a dedicated and competent group of experts who managed and completed a challenging project to deliver a roaster that performed efficiently since commissioning in October 2019,” added Nyrstar’s Robert Winton.

Remote refractory demolition

Our proven 12-point shutdown planning system and remote refractory demolition services assure safety using remote demolition machines, eliminating the need for human intervention within the roaster, reducing labor resources and speeding project execution up.

The refractory demolition was carried out within 11 days. Our proprietary Outotec® Roasting Demolition Platform was operated remotely to demolish the dome and upper vertical wall within 7 days. The platform was previously designed and delivered by Outotec for Nyrstar’s Australian zinc plant in Hobart and had been used for ongoing refractory demolition service jobs. The platform was shipped to Clarksville using two securely mounted, remote-controlled robotic machines, which were hoisted lifted inside the roaster utilizing a mobile crane.

Steel sections of the dome and parts of the upper vertical wall were cut using Outotec Versa X02 patented temperature thermic lance rods which were lowered to the ground, to further ensure safety, considering the condition of the roaster shell.

*This case study has been written prior to the merger of Metso and Outotec.