Results of Gerdau Ameristeel Jackson EAF operation with PTI, Inc. LimeJet TM Injection System Tony Klippel, Ron Miller, John Counce Gerdau Ameristeel Jackson 801 Gerdau Ameristeel Road Jackson, Tennessee 38305 Tel: 704-596-0361 Email: tklippel@gerdauameristeel.com, rmiller@gerdauameristeel.com, jcounce@gerdauameristeel.com Val Shver, Dave Stanton, Jon Brown Process Technology International, Inc. 4950 south Royal Atlanta Drive, Suite A Tucker, GA 30084 Tel: 770-934-9502 Email: vshver@pticombustion.com, dstanton@pticombustion.com, jbrown@pticombustion.com ABSTRACT Gerdau Ameristeel Jackson has commissioned two Process Technology International Inc. (PTI) lime injection systems for their 120 ton EAF located in Jackson, TN. The lime systems convey hi-cal lime and dolo-lime approximately 120 feet from a pressurized vessel to PTI s LimeJET TM injection burners mounted in a PTI JetBOx TM on the side wall of the EAF. Lime was originally loaded in loose form with the scrap into the charge bucket. This method of loading resulted in loss of lime to the operation floor. The lost material increased the amount of lime consumed, caused a housekeeping mess and posed a safety hazard to the operators in the melt shop. In addition to housekeeping, another major goal of the project was to reduce the lime and dolo-lime consumption at the EAF. This can be achieved by directly injecting the lime to the slag during furnace power-on and thus giving greater control over the slag chemistry during melting. Lower lime consumption, improved housekeeping and safety in the melt shop are discussed. INTRODUCTION Gerdau Ameristeel is the fourth largest overall steel company and the second largest minimill steel producer in North America. The company has the capacity to manufacture over 12 million tons of mill finished steel products annually. The Jackson mill produces 0.70M tons (0.71 M Ton) per year of MBQ and SBQ bar grades. One of the biggest safety and housekeeping issues in the melt shop at Gerdau Ameristeel Jackson was the handling of lime. The methods used to transfer lime from the storage areas to the EAF resulted in lime spillage and loss to the dust evacuation system. Gerdau Ameristeel Jackson sought to eliminate this material spillage, while improving housekeeping and safety in the melt shop. The preferred solution was direct addition of the lime from the storage areas into the EAF DESCRIPTION OF PROBLEM Prior to August 2008, both lime and dolo-lime were delivered to the mill by truck and pneumatically transported from the trucks to the bulk storage silo. Both types of lime were then transferred from their respective bulk storage silos into a single secondary hopper. Once filled with the correct amounts of lime and dolo-lime, the hopper was transported by fork truck from the melt bay to the scrap bay. The hopper was then picked up by an overhead crane, lifted to the top of the scrap bucket and the lime mixture was poured onto the scrap in the bucket. The lime was then delivered to the EAF during the scrap charging process.
This method of adding lime to the scrap bucket resulted in significant lime spillage throughout all transfer points: during the hopper filling, hopper transport to the scrap bucket and when pouring the lime into the bucket. Whether spilled on the ground or lost to the air, fine lime dust became suspended in the melt shop atmosphere. This dust presented both a housekeeping and fugitive dust emission problem. Additionally, the lime particles would settle into every corner of the melt shop. This coating of lime on every exposed surface and piece of equipment in the melt shop resulted in additional maintenance and housekeeping. A better method of lime addition to the EAF was needed. DESIGN CRITERIA In early 2008, Gerdau Ameristeel Jackson started to redesign the method used to add scrap to the EAF. The melt shop wanted to move away from the typical method of adding scrap by overhead crane into the scrap bucket to a system that used trucks to dump scrap directly into a bucket set into a hole in the ground. The proposed new method of scrap bucket charging would make charging lime to the scrap bucket from a hopper suspended overhead from a crane impractical. It was evident that redesigning the scrap handling system would require an adjustment to the lime charging system. A simple, leaner process of adding lime to the EAF was needed that resulted in a safer, cleaner melt shop. The new lime handling system had to reduce the number of steps needed to get lime to the EAF and also contain the lime to reduce fugitive lime dust emissions to the melt shop and general mill environment. In addition, there was a desire to better equip the EAF operators to control slag chemistry and thereby improve slag conditions in the EAF. This required the operator to have better control of the amount of lime and dolo-lime added to each heat. In addition, automating the lime feed rate would insure the lime addition matched the melting process - 50 minute power on time and 70 minute tap to tap time. A list of the design criteria developed for this project is as follows: Table 1 - Design Criteria for the New Lime System Reduce lime spillage and waste Reduce lime consumption per ton of steel Reduce lime dust emissions to melt shop and mill environment Increase operator control over lime additions to the EAF System must automatically adjust feed rates to match EAF process Feed rates must fit within current and future EAF power on and tap to tap times 6,300 lbs (2,857 kg) of Hi-Cal and 2,700 lbs (1,225 kg) of Dolomite Lime Increase operator slag chemistry control and increase arc stability control The next step in the project was to select the method by which to add lime to the EAF. The selection process was broken into two areas - how to move the lime from the bulk silos to the EAF and the best method of adding lime into the furnace. Possible methods used to move the lime to the EAF and then add lime to the furnace are discussed in the following sections. Lime Conveying There are many methods available for moving lime from a silo to the EAF. This project considered both belt and pneumatic conveyors. Methods of bulk lime addition to the EAF, while requiring the least amount of capital, were already discounted because of prior experience with the amount of labor and mess involved. Belt and pneumatic conveyors each have characteristics that make them good choices. The pros and cons of each type of conveyor were considered for this project. Belt conveyors can easily move different size material at different flow rates over long distances. However, the capital cost of installing belt conveyors was considered too expensive. In addition, since the lime sits on top of the belt, this type of conveyor does not readily contain the lime. Fine lime dust can be blown off the conveyor and
material can spill at each drop point in the conveyor line thus adding to the housekeeping and environmental issues. Belt conveyors met some but not all of the design criteria for this project and were eliminated from consideration. Pneumatic conveyors were considered and chosen for this project. Since the material is moved from within a pipe, the pneumatic conveyors easily contain the lime thereby eliminating the lime spillage and dust emissions to the melt shop. Pneumatic conveying systems are limited by the type and size of material that can be easily moved through the pipes. The material for this project, lime powder, is easily fluidized and is an ideal candidate for pneumatic conveyance. A pneumatic conveyor system meets all of the design criteria for this project and was within the project budget. Lime Injection Once the lime is brought from the silo to the EAF, there must be a method of adding the lime to the furnace. Two methods of adding lime into the EAF were considered: roof addition and side wall addition. The first method considered was lime addition through the roof above the scrap. Since the lime is falling on top of the scrap, this method allows the lime to be fed to the furnace as soon as the roof is closed and an arc is struck. The possibility that a skull will form at the injection port is minimal since the scrap and lime melt away from the point of addition. However, adding lime on top of the scrap presents several problems. First, some of the lime is lost to the bag house due to proximity of the lime to the fourth hole and second, there is some lag time between when the lime is added to the EAF and when the lime goes into solution. The lime added on top of the scrap must travel down with the scrap into the molten slag and steel and then melt to become part of the slag. The loss of material to the bag house and the lag time of getting lime to the molten bath were the main reasons that roof addition was not considered for this project. The second method considered was injection of lime through the side wall of the EAF. Installing the lime port in this location puts the injected lime as close to the newly formed liquid bath as possible. Any lime injected should go directly into solution as it contacts the liquid pool. However, there can be several problems associated with this addition method. First, there is the tendency of skull formation when the lime is injected into the EAF with cold scrap present. After several heats, the lime port can be completely blocked by lime, scrap and slag. Fortunately, with the addition of a burner at the lime injection point, this problem is solved. Second, lime injection cannot be started until the burner has created a pocket into which the lime can be injected which may be several minutes after an arc is struck. While sidewall lime injection cannot be started as soon as an arc is struck, it is reasonable to expect that lime injection can be started after several minutes of burner firing. This allows the sidewall injection of lime to start adding lime to the EAF at approximately the same time as a roof feed system. The additional advantage of sidewall injection is that now the lime is being added under not on top of the scrap. Adding lime under the scrap allows for the lime to go into solution sooner, form a foamy slag earlier and reduce the lime lost to the bag house. SELECTION PROCESS Gerdau Ameristeel Jackson started a search for an equipment vendor who could provide a system that met all of the design criteria, used pneumatic conveying and injected the lime through a sidewall mounted burner. All vendors were evaluated for their suitability for the furnace and operation at Gerdau Amersteel Jackson. Spreadsheets were developed to compare the features and performance of the various lime injection systems. Criteria for the selection of the vendor were then finalized. A list of vendor selection criteria developed for this project is a follows: Table 2 - Vendor Selection Criteria Cost of Project Ability to deliver within the specified dates Compatibility with existing EAF equipment Ability to integrate Lime HMI into the current operator control system Ability to provide pneumatic lime injection into the EAF Ability to provide a lime port with burner and supersonic oxygen injection
The Gerdau Ameristeel Jackson team chose the PTI LimeJet TM system to control and convey lime from the silo to the EAF and the PTI QuadJet TM burner/injector to inject both lime and supersonic oxygen into the furnace. Gerdau Ameristeel Jackson chose PTI because of the system price, on time delivery, the ability to seamlessly integrate the new lime system into the existing operator HMI along with the technical experience and integrity that the PTI team demonstrated during the previous common project. In addition, the new QuadJet TM technology delivers a single piece of equipment which functions as a burner, lime injector and supersonic oxygen injector and requires no additional EAF modifications for lime injection. DESCRIPTION OF INSTALLATION The installed equipment consists of two new bulk silos, two injection units, two sets of injection lines and two new injection burner/lances. The bulk silos are sized for each type of lime. The lime silo is capable of holding 442,800 lbs (200 M ton) of lime and the dolo-lime silo is capable of holding 376,200 lbs (170 M ton) of dolo-lime. Each silo is filled by pneumatic truck. This requires receipt of 2 truckloads of lime and dolo lime each day the melt shop is in operation. Lime levels in the silos are monitored by ultrasonic level detection. In addition, the old transfer hopper system is available as a back up with lime from the silos if anything happens to the pressure vessels or lime conveying pipes. Each silo is equipped with a bypass lime that allows the hopper to be filled directly from each new silo. Figure 1 - Outside view of Lime Storage Silos Each silo has its own pressure vessel, conveying line and injector. Each pressure vessel is capable of holding 6,000 lbs (2,720 kg) of lime or dolo-lime and each operates independently. The pressure vessels hold enough lime or dolo lime for one heat. The pressure vessels are refilled automatically at the end of each heat from the silo that sits directly above the pressure vessel. The pressure vessel sits on load cells, which monitor the lime feed rate and total lime Figure 2 - Lime Pressure Vessel Located Under the Silo
consumption per heat. The LimeJet TM system is equipped with a lime flow and detection system. This flow detection system monitors the flow of lime to the EAF and automatically adjusts the system to avoid and clear any line blockage. Each pressure vessel is connected to the EAF with approximately 120 feet (36.5 m) of 2 ½ (63.5 mm) nominal diameter pipe. The pipe is a standard schedule 80 carbon steel pipe. The elbows used in the piping run are long radius, hardened carbon steel. The inside of each elbow is hardened to 600 Brinell. This type of elbow has held up well to both the high-cal and dolo lime. As of the writing of this paper, the system has been in service for over 6 months. In addition, all components in the silo, pressure vessel and injection lines are showing little or no sign of wear. Figure 3 - Lime Pipe Vertical Rise Figure 4 - Lime Piping Entering Melt Shop Figure 5 - Flex hose from hard pipe to EAF The transport lines have a vertical run of 17 feet (5.2 m) straight up as they leave the injector. The lines then run 100 feet (30.5 m) to the EAF. 30 feet (9.1 m) of metal flex hose connects each pipe to their respective burner/injection ports. The flex hose used to connect the hard pipe to the EAF is a 3 inch (76.2 mm) braided metal hose which connects directly to the back of the QuadJet TM injectors mounted within each PTI JetBOx TM. No modifications to the EAF or JetBOx TM were required to install the new QuadJet TM material burner/injector. Figure 6 - Flex Hose Attached to PTI QuadJet TM installed in a JetBOx TM
Installation Issues Material sizing and air quality were issues that affected the performance of the lime injection system after commissioning. At the start of this project, it was understood that both material sizing and air quality were critical to the optimal performance of this project. The material was specific to be ½ inch by down and air quality was specified to be 1 mg of liquids per 1 Nm 3 of air. While steps were taken to ensure that these issues would not impact the performance of the system, both material sizing and air quality caused minor performance problems. The first issue that caused a problem was the sizing of the lime. The lime sizing was specified as ½ inch (12.7 mm) by down to facilitate the optimum operation of the pneumatic conveying system. Unfortunately, the lime supplier allowed a handful of lime over 2 inches (50.8 mm) in diameter to be delivered in each truck load. Some of this oversized material made it all the way to the injector at the EAF. As the injector has a 2 injection pipe, these large chunks of lime became stuck in the injector and stopped the flow of lime. Fortunately, this problem was easily corrected. A box was constructed to sit just in front of the silo fill pipe. Inside this box was a ½ inch (12.7 mm) mesh screen that prevented any oversized material from entering the silo and stopping the flow of lime to the EAF. Since this screen was installed, no further clogging of the transport line or injectors has occurred. The final issue that affected the performance of the lime injection system was wet air. Gerdau Ameristeel Jackson did not install an additional air compressor or dryer for this project. After the initial installation, the flow rate of lime gradually decreased over several weeks. It was determined that enough moisture was contained in the system air to cause the lime to hydrate and start building up on the inside of the transport pipe. Once this build up was cleaned out, the flow rate returned to normal. Both material sizing and air dryness are critical issues when installing a pneumatic conveying system. Even with the precautions taken during the design of this project, these issues both contributed to minor lime flow issues. Fortunately, both problems were easily corrected and no further clogging problems were encountered. Summary of Installation The installation of the silo, transport lines and PTI LimeJet TM system went extremely well. The Silos and PTI equipment arrived on-time and ready to be installed. The installation of the LimeJet TM was seamless and on time. The system worked as planned from the first heat, with some adjustment needed on the first heat to set the flow rate. By the second heat the system was functioning as designed. PTI QuadJet TM Figure 7 - PTI QuadJet TM Gerdau Ameristeel Jackson installed PTI QuadJet TM injectors at both the high-cal and dolo lime injection sites. The QuadJet TM was designed to install directly into the existing JetBOx TM with no additional modifications. The existing water, oxygen and gas lines were reused. The only new hose was the flex hose for the lime. The QuadJet TM incorporates all of the functions of the supersonic injector that it replaced. These injectors can be operated as a 4.5 MW burner, at 1800 scfm (2,900 Nm 3 /hour) supersonic oxygen injector or 550 lb/min (250kg/min) lime injector.
The QuadJet TM is capable of injecting lime in burner mode or supersonic mode. Both modes perform equally well when lime is being injected. In addition, there is no loss of efficiency of the supersonic stream during lime injection. The QuadJet TM has allowed Gerdau Ameristeel Jackson to add lime injection capability without installing additional hardware or modify existing equipment on the EAF. SYSTEM RESULTS The installation of direct lime injection to the EAF was accomplished in two steps. Dolo lime was the first material injected to the EAF. Then, three weeks later, high-cal lime was added. The strategy of bringing each material on line separately was taken to allow proper adjustment of each system. It also allowed some time to assess the impact of injecting lime into the EAF. After the first few heats in operation, it was clear that the injection system functioned properly and lime injection into the EAF was not causing any issues. On August 8, 2008, lime was first injected through the PTI QuadJet TM into the furnace at Gerdau Ameristeel Jackson. The first heat into which lime was injected went smoothly. The initial flow rate attempted was 100 lb/min. (45.4 kg/min). The lime injection rate was held at 100 lb/min (45.4 kg/min) for 5 minutes for a total lime injection of 500 lbs (277 kg). However, with 6300 lbs (2857 kg) of high-cal and 2700 lbs (1225 kg) of dolo lime required each heat, higher flow rates would be required in order to inject the needed lime within the existing power on times. To achieve these lime injection requirements, the following schedule was developed. Table 3 - Initial Injection Schedule Charge Time (min) HI-Cal Lime (lbs) Dolo Lime (lbs) Total First Charge Last 8 minutes 2800 lbs (1269 kg) 1200 lbs (545 kg) Second charge Last 5 minutes 1750 lbs (794 kg) 750 lbs (340 kg) Refine First 5 minutes 1750 lbs (794 kg) 750 lbs (340 kg) Total 18 minutes 6300 lbs (2857 kg) 2700 lbs (1225 kg) 9000 lbs (4082 kg) This time schedule requires that the hi-cal lime be injected at a minimum flow rate of 350 lb/min (159 kg/min) and the dolo lime be injected at a minimum flow rate of 150 lb/min (68 kg/min). Gerdau Ameristeel Jackson started 100% lime injection on August 31, 2008. By this time, the lime injection schedule was changed to 5,000 lbs (2268 kg) of hi-cal and 2,800 lbs (1,270 kg) of dolo-lime. The hi-cal lime is injected at 450 lbs/min (204 kg/min) and the dolo-lime is injected at 300 lbs/min (136 kg/min). The new injection schedule that was developed over several weeks of trials is as follows. Table 4 - Current Injection Schedule Charge Time (min) HI-Cal Lime (lbs) Dolo Lime (lbs) Total First Charge Last 11 minutes 2500 lbs 2000 lbs Second charge First 9 minutes 2500 lbs 800 lbs Refine - 0 lbs 0 lbs Total 20 minutes 5000 lbs (2268 kg) 2800 lbs (1270 kg) 7800 lbs (3538 kg) While the total amount of lime added to the EAF was reduced, the slag volume processed by the mill service did not decline. In addition, the slag chemistry remained unchanged from before the start of 100% lime injection. The slag chemistry before and after this project was as follows: Table 5 - Slag Chemistry B3 ratio CaO% MgO% FeO% SiO 2 % 1.3 1.4 30-34% 10 12% 25 28% 15 16% It was determined that it was possible to start injecting lime into the furnace sooner than expected. The initial theory purported that lime injection could not be started until 5 or 6 minutes of burner time was completed. Instead, it was
found that lime injection through the QuadJet TM burner could be started after 2 or 3 minutes of burner time without any skull formation in front of the line injection burner. This allowed all of the high-cal lime to be injected during the first charge and all of the dolo lime to be injected during the second charge. All of the lime is injected while the burner is in burner mode. In addition, there is no disruption to the flow of lime with increasing burner power. Whether at 0.5 MW or 4.5 MW, the flow rate of lime remained stable. While not needed, trials were conducted to inject lime during supersonic oxygen injection. The flow rate of lime remained stable during supersonic oxygen injection as well. Conversely, the introduction of lime during supersonic injection did not affect the oxygen flow rate. Decarburization rates remained the same as the previous injectors with no material injection capability. Additional trials revealed that the system was capable of injecting lime up to 550 lbs/min (250 kgs/min) through the 2 ½ inch (63.5 mm) schedule 80 transport pipe. SYSTEM IMPACT The direct lime injection system achieved the main project goals of lime usage reduction and improved operator safety. Since switching to pneumatic injection, the lime usage has dropped from 9,000 lbs (4,082 kg) of total lime usage to a new lime usage amount of 8,500 lbs. This reduction in lime usage accounts for a 9% reduction in direct consumable material cost for each heat. Accompanying this lower specific EAF lime use is 500 lbs (227 kg) less lime being lost to the bag house or shop floor. This reduction in fugitive lime dust emissions to the melt shop has resulted in a less housekeeping labor (and cost) and dust sent to the bag house. The impact of the new direct lime injection system is summarized as follows: Improved Operator Safety - through elimination of fugitive lime dust emissions o Reduction in eye irritation Reduced Maintenance o Reduced fork truck damage 9% reduction in lime consumption o 4.2 lb/ton reduction in lime consumption Improved Housekeeping o Clean up on cranes and in melt shop virtually eliminated Increased control over slag chemistry o Operators are able to run slag samples every heat for real time changes to lime additions. CONCLUSIONS The PTI LimeJet TM and QuadJet TM system was a good choice for the direct injection of lime to the EAF. All of the design criteria set at the start of this project were achieved. Lime consumption was reduced by 9% and all fugitive lime emissions to the melt shop were eliminated thus improving the operator safety in the melt shop. The ROI for this project was less than one year with the direct cost reductions realized from a reduction in specific lime usage, housekeeping, vacuum trucks and reduced bag house dust volume (treatment). Other improvements in safety and environmental could not be quantified in dollar amount, but will result in long term cost reductions. The new system also increased the operator control over the lime injection to the EAF. With the fully integrated operator interface for the lime injection system, the operator can adjust the hi-cal and dolo lime amounts to achieve the best slag chemistry. Additionally, the system is fully automatic. Once the operator sets the lime amounts, the system adjusts the feed rates to match the process. The lime is injected automatically during the appropriate times in the melt down to achieve the best foamy slag and slag chemistry. The PTI LimeJet TM system proved to be a good choice for pneumatic EAF lime injection at Gerdau Ameristeel Jackson. The on time delivery, smooth start-up and low maintenance have made this installation a success. It is expected that with the enhanced control over slag chemistries, this new lime injection system will ultimately provide improvements in electrical energy usage and liquid steel yield. Gerdau Ameristeel Jackson and PTI Inc. would like to thank the operation, maintenance and engineering personnel in the melt shop for all their planning and hard work made this project a success.