Kromschroder's Gene Bendien inspects control system prior to furnace start-up.

TC Industries (TCI) Crystal Lake, Ill., is a family owned and operated company that has been in the heat processing business for over 50 years. The company has two divisions. The processed steel division fabricates and heat treats steel components, mainly for earth moving equipment and tractor components. The mill products division performs specialty heat treat processing for steel mills.

The mill products division currently operates three furnaces to fulfill its heat treating requirements. The three quench and temper lines consist of roller hearth furnaces that have 55, 85, and 90 ft. long high heat work zones and can quench material up to 50 ft. in length.

Mechanically, the #1 furnace was in fair shape; the quench and other systems had been upgraded earlier in the year and the lining was in good shape. However, the furnace had become unreliable, and the maintenance requirements were getting steadily greater. This meant downtime was increasing. Among the more persistent problems were various combustion and control problems, burner failures, and mechanical drive failures. The resulting down time put a burden on production, on time deliveries and product quality.

TCI, being a leading manufacturer, is very sensitive to product quality and the delivery needs of their customers. In order to meet their demands and continue to provide the quality of products and service that they are known for, they were going to have to address these problems. TCI decided to upgrade their #1 furnace.

Hot face of the furnace shows burner nozzle (at center of circle), outward through the layer of silicon carbide burner tile, and finally through refractory fiber sleeve.

Planning and Executing the Upgrade

The first step in executing the upgrade was to determine the primary objectives of the project. Then, a detailed plan was developed for the retrofit operation. This had to be a well-coordinated effort, because once the furnace was taken off-line it had to be re-assembled and back in production within three weeks. This was a challenging goal that required everyone's support to meet.

To reduce the project cost, it was decided to re-use some ancillary components that were still in good working condition and could be cleaned. It was agreed that the new design would employ a pulse fired combustion and control system to replace the existing cross-connected ratio control system. A plan was devised and a schedule developed that minimized effort, cost, and downtime.

But much had to be done before the equipment arrived and the demolition and reconstruction took place. The control system was converted from relay logic to a PLC, into which the PID and pulse-firing algorithm would be imbedded. Once the equipment arrived, the furnace was taken out of production, and the renovation process began. The existing burner system was replaced with the following equipment:

• A new fuel train.
• Forty BIC 80 TLB burners rated at 250,000 Btu/hr.
• Forty VR 50 high cycle pulse air valves.
• Forty GIK TN02-5B pulse regulators.
• Eighty VG 15 gas solenoid valves
• Forty BCU 460 T 10/2LR3B1/1 burner control units with air valve control and Profibus communications.

The crews from TCI and Thomas Industrial Services Inc. (Milwaukee, WI), a manufacturer, distributor and installer of combustion systems and controls, made short work of the demolition, gutting the furnace in little more than a day. Pre-fabricated air and gas headers that were mounted on the furnace and all the new combustion components were installed and piped. Concurrently, the electricians were mounting the BCU burner control units and running the Profibus cabling. When using Profibus, installation time and installed cost are reduced because it eliminates all the interconnection wiring, with the exception of that for the limits circuit and power. The complete process took eleven days from start to finish. Within two weeks, the furnace was back into production.

Rich Albright, TCI's plant engineer, says that since then overhaul the furnace has performed beautifully. TCI's production has increased 20 to 25 percent primarily because of down time reductions. They have had no down time or maintenance issues since the renovation was completed.

Why Pulse Firing?

Of the many modifications made to the furnace during the re-build process, the installation of pulse firing technology was among the most important. Products processed in TCI's #1 furnace range from thin strip stock to bars of thick cross section, with lengths varying from 20 to 50 ft. Before the overhaul, furnace operators had to manually adjust burners to process the variety of parts being processed. Pulse firing provides the ability to operate the burners in an on/off or high/low operation, increasing the system turndown and eliminating the need to manually adjust burners.

Achieving uniform microstructures in steel requires consistent control of the process temperature and thermal gradients. Pulse firing improves uniformity by increasing the internal furnace convective currents over a standard modulating control system, and eliminates system overshoot.

Pulse firing requires equipment with high duty cycles and reliability. The installed valve components are rated for millions of cycles and provide maintenance-free operation for years, and ignition reliability of the burners used is much better.

Although saving fuel is always a good reason to upgrade a furnace, other benefits such as improved reliability, increased throughput, reduced maintenance cost, operating flexibility and improved product quality can sometimes be more beneficial than fuel savings alone. Since the rebuild of this furnace, TCI has decided to upgrade two more.

On-site de-bugging of PLC program and wiring.

Project Re-Cap

A project of this nature requires a lot of time and planning. Here is a detailed review of the work that had to be done to re-build TCI's furnace and get it back into production.

• Replace the outdated, modulating control system with a state-of the art pulse-fired control system using an Allen-Bradley PLC and Profibus.
• Install BCU burner control units that combine flame management with micro-processor control, two-way bus communications, and local and networked diagnostics. The advantage of this is the BCUs become local wiring junction boxes at each burner, which slashes installation time since all burner components are wired directly to the BCUs and not to the main panel. This reduces check-out time and eliminates a significant number of interconnection wires.
• Install forty BIC 80 TLB burners, which provide reliable ignition and flame sensing capability, increasing system reliability and up time. Flame rods, which are less costly and more reliable than UV scanners, were used for flame sensing. The installed cost of the burner is also reduced because of the integrated air and gas metering orifices and built-in limiting orifice valve.
• Install individual air and gas control valves at each burner to maximize combustion efficiency and reliability. The system turns both air and gas off and on at each burner.
• Remove the old gas safety devices and installed a new system compliant with current National Fire Protection Association requirements.
• Increase the number of control zones from four to five for improved uniformity. The burners are all equipped with identical air and control equipment, and only the software determines the zoning. Pulse firing provides the flexibility to add zones or modify zone sizes without mechanical system modifications.
• Install new flame management system, which implements unison light-off, meaning each burner is managed individually. Thus, if there is a burner failure, only that burner is affected, and the rest will continue operation without disruption to production. The failed burner can be re-started at any time during operation. With the furnace's original flame control, if one burner failed all burners in that zone would shut down. This required the zone to be re-started every time there was a burner failure. Therefore, production time was lost while waiting for the furnace to come back to operating temperature.
• Replace push buttons and panel indicator lights with a new control unit to allow the operators access to the process and its controls.
• Replace relays and timers with an Allen-Bradley SLC 500 PLC, as well as the zone temperature controllers.

Side view of roller hearth furnace showing burner piping, individual air valve controls and gas ventilation.

Who Did What?

This project required close work and a coordinated effort between three companies and their representatives: Albright of TCI, Gene Bendien of Kromschroder Inc. (Hudson, OH), and Jim Thomas, president of Thomas Industrial Services Inc. Together, they devised a detailed plan to complete this project.

TC Industries rebuilt the drive system, changed some rollers, and did about half the tear-out. They pulled a new electrical service and tied in new electrical drive components. They fabricated adapter plates for the new burner mount configuration, installed a gas meter, and programmed the PLC for drive control.

Kromschroder Inc. calculated the heat required to operate the furnace, selected the burners and supporting equipment, and reviewed the proposed piping and electrical drawings. It participated in software logic development, and reviewed the final software package prior to installation. At start-up it assisted with lighting the burners, air and gas set-up at each burner, and the burner control interface. It also oversaw modification of the software to make the burner perform properly and provided training for TCI personnel in burner set-up and maintenance.

TISI assembled burner modules to shorten installation down time and designed and built a combustion and control panel with PLC, and temperature recorder. At the project's outset they made all electrical drawings, burner and gas train general arrangement drawings, and PLC documentation. They wrote a PLC program for pulse fire control, programmed a PanelView 1000 MMI to work with the A-B SLC 500 PLC, and provided and configured a Yokogawa recorder for future Ethernet communication to a central data gathering system. The company installed combustion gas and air headers; new electrical wiring and cable; new pre-piped gas safety valve manifold; BCU burner control units; new burners and control devices, and new thermocouples and production tubes. Additionally, they started and tuned the burner system, tested safety devices, tuned in the control loops, and helped trained TCI personnel to operate the furnace.

Conclusion

TCI's Albright, when talking about the rebuilding of the # 1 furnace, cannot stress enough how much the rebuild has benefited operations. The renovation of the furnace has decreased its downtime, increased production, improved temperature uniformity, and increased fuel efficiency. IH