The burner system is an important and integral component of a rotary kiln system to optimize the combustion of fuels to release heat in the kiln. Safety considerations, ease and flexibility of operation, product quality, energy efficiency, maintenance costs, and the environmental impact of the products of combustion are some of the most critical areas that a kiln operator must evaluate in selecting a kiln burner.
Metso, with over half a century of experience in designing and manufacturing rotary kiln-based thermal processing systems, has the technical expertise and capability to provide rotary kiln operators with a kiln burner system that best meets their requirements. Since 1950 Metso has successfully engineered and supplied more than 300 burner systems.
At Metso we have experience with many different fuels, including conventional fuels such as coal, coke, gas and oil, and unconventional fuels such as, COG (coke oven gas), saw dust, tires, biofuels and other alternative fuels. Different types and qualities of fuels can cause different temperature profiles within a rotary kiln, which will cause changes in operations.
The burner and process system oxygen content can affect product quality and energy consumption; controlling it, therefore, has great economic advantages. Air is typically used as the oxidizing agent, but in some applications purified oxygen is introduced to reduce gas flows, reduce nitrogen oxide generation and/or obtain higher temperatures. When the exact amount of air is mixed with a fuel to completely oxidize the hydrocarbon species present, it is calledstoichiometric combustion. Most plants that burn fuel target an excess air rate of 0.5% to up to 5% above stoichiometric conditions. The lower the excess oxygen content, the less gases are being sent through the system and therefore downstream gas handling equipment will be more efficient. Unfortunately, not all fuels may be combusted at such a low oxygen level, and in some applications having excess air can act as a benefit to the overall system.
When designing a burner system, Metsos engineers consider: the process, primary and secondary air momentum, system temperature profile requirements, and emissions requirements. Reduced NOx emissions and optimum flame shape is achieved with the use of two primary air chambers.
Designed for maximum flexibility of fuel type and flame shape. The primary fuel is typically pulverized coal or coal+coke, with the option to burn natural gas or fuel oil. Either natural gas or fuel oil can be ignited directly by the integral ignition system. Typically, natural gas or fuel oil is be used to heat up the rotary kiln and then ignite the coal flame, but either may be used to fire the kiln up to full operating capacity if desired.
Burner design features include single or dual primary air path, dual (axial and radial) natural gas paths, easily changeable fuel oil nozzle, adjustable fuel nozzle to primary air nozzle relationship, and easily adjustable burner mount and primary air flow.
A simple and elegant design that uses well established and proven changes in fuel/air mixing intensity to provide flame control. The Metso KFS designs avoid the complex mechanical adjustment mechanisms which are essential in the standard burner one-size-fits-all approach and avoids potential for local operations or maintenance to adjust incorrectly.
The primary air is split between axial air, for flame length and heat flux control, and swirl air for flame anchoring. A highly efficient aerodynamic swirler provides excellent flame stability. Each OptiMix burner is supplied with an integral pilot, including the extremely reliable natural gas or propane model.
For a wide range of gaseous fuels. Dual gas discharge locations ensure fine control on gas firing applications and turndown of over 20:1 ensuring the burner can be used in cold starts for refractory curing.
For conventional liquid fuels, such as #2 to #6 oils and including waste and re-refined oils. Using the proprietary CM atomiser offers at least 8:1 turndown using either steam or air atomisation. The PJ atomiser is specific for pressure jet applications. For alternative liquid fuels Metso KFS offer the WS Atomiser with air/steam-assist atomisation.
For pulverised coal and petcoke. Already a world leader in the pulp and paper industry where Metso KFS have burners firing natural gas, petcoke, methanol, and turpentine simultaneously. OptiMix S can also be designed to accommodate all types of solid alternative fuels such as lignin.
Developed using CFD Modelling, the DFN (direct-fired nozzle) burner has been proven across many projects to provide outstanding improvements in areas such as production, fuel consumption, NOx emissions, and ash ring formation.
Each DFN burner is custom-designed for the kiln both in terms of process performance and mechanical installation. High levels of performance are provided by careful use of bluff-body and swirl techniques to enhance fuel/air mixing combined with far greater flexibility than traditional straight-pipe.
The Metso KFS warm-up combustion system provides a safe and effective method to heat a rotary kiln from cold start through to main fuel firing. The Metso KFS system is ideal for existing rotary kiln operations based on straight pipe burner technology.
A key to a safe kiln warm-up is the ability to provide a stable flame for an effective and controlled heat release profile. The Metso KFS HeatSafe Burner (HSB) design is based on the proven Metso KFS OptiMixintegrated kiln burner design operating in over 100 rotary kilns.
The HSB can be gas or oil fired and incorporates a dependable source of ignition with a proprietary design fuel nozzle and high efficiency air swirler to provide easy light-off and a stable flame under variable kiln conditions.
Supporting the burners dependable flame stability are the associated fuel and primary air systems. Supervision of start-up, shutdown and operation of the HSB burner is provided by a Burner Managements System (BMS), which is fully compliant with the latest applicable standards.
As part of system design, Metso KFS offers a number of ancillary equipment items which enhance or complete the combustion system upgrade. Options are available for process and detailed design only, or full equipment supply:
Maintaining the proper heat profile of a rotary kiln is of the utmost importance in realizing the lowest Btu per ton of production as well as the highest quality product. To achieve the optimum burner flame shape and the most efficient combustion possible, the rate of mixing of both the air and fuel through the burner is paramount. NorthStar ProflameTMRotary Kiln Burners are capable of adjusting the flame shape and intensity while in continuous operation with no shutdown necessary. This has the effect of eliminating costly downtime and process temperature fluctuations that may otherwise affect your kilns heat profile and overall efficiency. In other words, although the rotary kiln burner is custom engineered for your specific target burning rate an operator may reconfigure the burner with simple, easy to perform adjustments should production parameters dictate a change in fuel consumption or flame shape. ProflameTMrotary kiln burners are capable of 10:1 turndown and can operate as much as 50% over the target design firing rate.