Metals Processing

Success Story: Nickel Mine Oxygen Compressor Inlet Guide Vanes A large nickel mine in Ontario, Canada produces nickel metal, which is used in the manufacturing of smartphones and rechargeable batteries that power electric cars. Sulfur dioxide (SO2) is a major air pollutant emitted in the roasting, smelting, and converting of sulfide ores. Fortunately, the SO2 is recovered and utilized to make sulfuric acid (H2SO4), an important coproduct that contributes to the mine’s operational revenue. This high-grade sulfuric acid is used to make recyclable fertilizers and paper products.  Oxygen gas is an important precursor compound required in the expanded process to make sulfuric acid. The gas is generated on site and supplied to the nickel smelter where it is used in flash furnaces that produce iron oxides, sulfur dioxide (SO2), and nickel matte. The sulfur dioxide produced by flash smelting is used to make sulfuric acid,removing the major environmental effect of smelting. Pressurized oxygen must be available to the nickel smelter, or the acid plant will need to halt operations – potentially costing up to $60,000USD per day in revenue. This very scenario worried the nickel mine’s acid plant operations management team since a legacy oxygen plant was beingdecommissioned. This meant there was no longer a backup supply.  The plant has two multistage centrifugal compressors, each powered by a large electric motor. Accurate positioning of the compressor inlet guide vanes (IGVs) is necessary to precisely control the gas throughout the compressor. Doing this effectively ensures the most efficient gas flow through the compressor. The plant operations group grew increasingly frustrated with the pneumatic actuators’ poor performance in positioning the IGVs. The mechanical position switches would drift—requiring recalibration every 6–8 weeks. Due to the compressibility of air, the compressor turndown increased to safely operate without surging, at the cost of compressor efficiency. In 2016, both compressor IGVs were upgraded with six REXA Electraulic™ Linear Actuators. Plant personnel immediately noticed improved accuracy—repeatable to 0.1% of span, regardless of process conditions.  The plant also noticed significant energy savings, since the Electraulic™ Actuators accurately controlled at a higher maximum capacity flow within turndown range. Each compressor had a 0.5 MW power reduction due to the improved air flow and higher compressor efficiency. The annual savings in electricity are calculated to be $1,092,000 USD per year. Literature Read the full Success Story by downloading here!  Download

Success Story: Steel Making Reheat Furnace Pressure Steel companies around the world continuously introduce and enhance processes that emphasize sustainable development. Key sustainable targets include minimizing the environmental footprint and increasing energy efficiency. These companies proactively develop actions to decrease fossil fuel consumption, thus reducinggreenhouse gas emissions. Through all these initiatives, companies proves it is possible to be socially responsible while reducing operational cost to produce quality steel. Modern continuous rolling mills produce large quantities of thin sheet metal but consume significant amounts of energy—particularly with reheat furnaces. These furnaces are gas fuel energy intensive, second only to blast furnaces.  The reheat furnace is located at the hot strip mill and is the process step before hot rolling. In this step, steel billets, plates, or blocks are usually heated from room temperature to ~1,200 C°. At this temperature, the billet can be hot rolled and achieve the desired metallurgical, mechanical and dimensional properties of hot rolled products. Optimal operations require the minimization of fuel consumption, while maintaining a controlled steel billet thermal soak.  From economic, production, and environmental standpoints, the operation of reheating furnaces is of great importance to the steel making process. Economically, the consumption of fuel needed for reheating can represent up to 15% of the operational cost of a rolling process. With respect to productivity, a reheat furnace capacity often dictates the production rate for the rollers, which means that reheating is usually the bottleneck in achieving the maximum production volume. The furnace operation must be reliable, as any downtime will cost the average sized mini mill nearly $45,000 per hour in lost product revenue.  Maintaining a controlled ramp up and holding soak temperature is not a straightforward task. Heat transfer to the steel billets is influenced by internal temperature setpoint of the furnace, flow rate of fuels and flow rate of air. Maintaining furnace pressure is very important. If the furnace pressure is too low, air will ingress in the furnace with oxygen, potentially causing scale formation, impacting quality and productivity. If the furnace operates too high, then the fuel consumption will increase operational cost.  At a steel mill in northeast Pennsylvania, the rolling mill team was frustrated by the furnace pressure control. The stack damper position used a pneumatic actuator and was responsible for the amount of flue gas exiting the stack. Control was poor, and the actuator was not reliable. The unit required maintenance to recalibrate the position switches. In winter, water in the air lines would freeze, making the actuator inoperable. Literature Download the full Success Story here!  Download

Furnace Fuel Gas Pressure Control Producing steel is an energy intensive process. Utilizing byproduct gases as a fuel source is vital to the plant’s operational efficiency. These byproduct gases, which are recovered from blast furnaces and coke ovens, are commonly used as a mixed gas fuel source throughout the plant. Reheat furnaces can use mixed gas as the primary fuel source. Mixed gas feed lines can have variable incoming pressure and constantly changing gas demand due to heating cycles and exit door losses. This creates challenges in regulating air/fuel mixture and temperature within the reheat furnace. Reheat furnace operation directly impacts steel properties. Austenite grain structure, which is sensitive to time and temperature, directly effects the strength and mechanical properties of steel.  Minimal variation of incoming mixed gas pressure feeding the reheat furnace is critical to producing high quality steel. Accurate and responsive mixed gas pressure control enables efficient combustion for a controllable temperature profile within the furnace. Efficient combustion will reduce SOx emissions and gas consumption. This leads to stable slab heat up and soak, resulting in a more efficient furnace producing a higher quality finished product with fewer slab defects.  Literature Download the Furnace Fuel Gas Pressure Control Application Spotlight! Webinar Download

Coke Oven Cross Over Valve Pressure Control Coke ovens process coal into coke that is used as a fuel source in blast furnaces. Coke ovens run continuously and do not use air as a combustion source. The co-product gas exiting the coke oven is tightly pressure controlled to +/- 1 millibar. Excess pressure may cause the gas to be diverted from the co-product plant to atmosphere. Insufficient pressure may cause air to enter the oven, ruining the coke.  REXA  Linear  and  Rotary  Actuator’s 100% duty cycle capability is used to precisely control the coke oven collection line gas pressure.  Benefits: Precise Modulating Control  Reliability  90 degree normal, 355 degree maintenance rotation  Literature Download the Coke Oven Collection Control Application Spotlight! Webinar Download

Coke Plant Quenching Flow Control The coking process takes place over a span of 12-36 hours in a coke oven. Once pushed out of the vessel, the hot coke is often quenched with water to cool it before storage.  After the coke has been cooled, it is transferred to the blast furnace for use in iron making. REXA  Linear  and  Rotary  Actuators are used to effectively deliver quenching water to cool the coke by controlling the header pressure. Benefits: Precise modulating control  Reliability 

BF Steam Turbine RPM Control What is a Blast Furnace? The mining industry uses blast furnaces for smelting to produce industrial metals, such as pig iron. It is top-charged with iron ore, coke and limestone while huge quantities of air blast enter the bottom of the furnace from the blower. Oxygen within this air first reacts with the coke to produce carbon monoxide, which then reacts with the iron ore in a reduction reaction. Molten slag and iron leave the bottom of the furnace, while carbon monoxide, carbon dioxide and nitrogen leave the top. This is a continuous process, which if interrupted by unscheduled downtime, leads to increased costs.  Steam Turbine Control Solution Steam turbine speed control is a critical application requiring superior reliability. REXA Electraulic™ Actuators enable a smooth and reliable supply of cold blast “wind” flow to your blast furnaces.  The consequences of an actuator fail are devastating to plant iron making operations.  Loss of “wind” causes the molten burden in the furnace to drop, therefore resulting in damage to the furnace and an interruption of production.  Our self-contained Electraulic™ actuators require zero oil maintenance, making them virtually maintenance-free.  Benefits: Reliable Operation in Tough and Demanding Environments  Accurate (0.1%) and Repeatable Positioning  Smart Communications for Reviewing Actuator Health/History  The BF Turbo Blower has many applications that REXA can provide an immediate solution for including:  Inlet Guide Vane Control  Anti-choke Control  Blower Anti-Surge Control 

Blast Furnace Gas Pressure Control Background Steel making is an energy-intensive process. At a tier one integrated steel mill in Jamshedpur, India, the mill energy consumption required for steel production meets with power generation produced at the power houses on site. As their primary fuel sources, this steel mill uses by-product gases from blast furnaces and coke ovens.  What is Blast Furnace Gas? Blast Furnace Gas (BFG) is the key fuel source used at the combustion boiler to generate steam. This steam is used in various plant processes, as well as the steam generator, to produce electrical power. There are three power houses in the plant, each with five to seven boilers. BFG feed has two issues: a variable incoming flow rate and a low, fluctuating calorific energy constant.  Problem The key in producing high quality steam is to have minimal process variation of incoming BFG entering the boiler. Furthermore, greater process control enables efficient combustion and boiler product steam pressure – leading to stable-pressured steam.  Unfortunately, even with the use of smart positioners, pneumatic actuators lack precision due to the compressibility of air. REXA Electraulic™ Actuators, however, are able to work through this and provide more precise and accurate performance than pneumatic and traditional hydraulic technologies.  Solution Check out the full Blast Furnace Gas Pressure Control Application Spotlight below! Be sure to also view our webinar showcasing how our actuation technology can enhance this application’s efficiency.  Literature Download our Steel Mill Blast Furnace Gas Pressure Control Application Spotlight! Download

Gas Pressure Control – Baghouse A baghouse is an air pollution control device commonly used in steel mills. Baghouses remove particulates out of hot gases from various steelmaking processes.  The use of air dampers controls the gas pressure to optimize particulate recovery and process availability. Rexa actuators are used to precisely maintain vacuum pressure; even a slight positive pressure inside the bags can result in reduced cleaning efficiency.  Benefits: Precise modulating control  Reliability