Designing a Burner Management System (BMS) requires careful consideration of various factors to ensure safety, reliability, and efficiency. Following these guidelines, you will be 100% sure designing burner management system.
Anyhow if you don’t know basics of ”What is a Burner Management System and Working?”.
BMS Design Considerations.
Burners, furnaces, and boilers are complex systems crucial for producing heat. The burner is where gas or fuel oil is burned to create heat, often located on the floor and pointing upwards. In large heaters, there are usually multiple burners. Combustion happens when fuel mixes with air and ignites. Perfect combustion occurs when fuel, temperature, and turbulence are controlled. Turbulence is important because it helps mix the fuel and air thoroughly. When fuel and air mix perfectly and burn completely, the flame is hot and combustion happens quickly.
Accidents in plants are often preventable, with many caused by inadequate monitoring of boiler functions. Issues like faulty interlocks, unmonitored conditions, and boiler or burner malfunctions can pose serious safety risks. The Burner Management System (BMS) is a complex safety system for thermal power plants that ensures the safe start-up, operation, and shutdown of boiler burners. It’s designed to work with various fuels like natural gas, oil, coal, and biomass to ensure reliability, flexibility, and safety.
The BMS initiates safety procedures to prevent explosions if unsafe conditions are detected, protecting equipment and people from harm. It’s essentially an on/off control system that allows firing the boiler when conditions are safe but shuts off fuel or puts the boiler in a safe state if there’s a problem. BMS designs meet national and international standards, enhancing overall plant efficiency and reducing maintenance costs.
BMS components are typically housed in a control cabinet and are fully integrated for automatic control of burner sequencing, including start-up, operation, and shutdown. An industrial-grade microprocessor-based BMS monitors safety features, actuator positions, and flame status, ensuring safe and efficient operation of the boiler.
1. How BMS Handle Fuel Types?
Many Burner Management Systems (BMS) are designed to handle multiple fuel types, with fuel selection determined either by hard-wired contact or through a Modbus link based on user configuration.
Key additional functions of a BMS typically include:
- Ensuring all recycle and shutdown interlocks are connected to separate, parallel 120 VAC inputs to prevent accidental shutdowns.
- Providing power for flame scanners and employing dual scanners wired to separate digital inputs to prevent false alarms.
- Implementing “assured low fire cutout” to reduce thermal stress on equipment by gradually reducing burner firing rate before shutdown.
- Monitoring flue gas temperature to prevent dry boiler operation, which can lead to explosions or meltdown.
- Offering adjustable time delays for low fuel pressure, low atomizing flow, and low draft interlocks to prevent unnecessary shutdowns.
- Accommodating automatic gas valve leak detection when necessary.
- Implementing logic for safe purging of oil guns to prevent unsafe conditions.
- Providing user-configurable auxiliary relays for alarms or to start auxiliary equipment like fans or pumps.
- Implementing optional in-situ oxygen analyzer functionality to alarm or shut down the burner based on oxygen levels.
- Offering individual annunciation for recycle and non-recycle limits for easier troubleshooting.
- Recording time/date stamps and status information for the last ten boiler shutdowns for troubleshooting purposes.
- Including Modbus communications for easy integration with other systems.
- Providing a common dry alarm contact output for Building Management Systems to receive fault or alarm notifications related to the BMS.
- Ensuring flame safeguard logic and associated software are recognized by Underwriters Laboratories for safety and reliability.
2. Boiler BMS Control Strategies.
In a boiler burner management system, there are two main control strategies: primary control and combustion control.
- Primary Control: This strategy ensures that fuel is allowed to flow only when all necessary conditions for safe ignition are met. It focuses on safety and prevents fuel from flowing if ignition conditions aren’t optimal.
- Combustion Control: This strategy regulates the ratio of fuel to air in the furnace within specified limits to maintain continuous combustion and a stable flame throughout the boiler’s operating range.
The major steps in the boiler burner management system include:
- Boiler Self-Protection Check for Startup: Ensuring that the boiler is safe to start and all necessary safety checks are completed.
- Pre-purging, Pilot Trial, and Ignition: Clearing out any residual gases from the furnace, conducting a trial ignition of the pilot flame, and igniting the main burner.
- Main Burner Trial and Ignition: Checking and igniting the main burner to start the combustion process.
- Maintaining Air/Fuel Ratio According to Load Demand: Adjusting the flow of fuel and air to maintain the optimal ratio for combustion as per the demand for heat from the boiler.
- Post-Purging After Burner Stop: Clearing out any remaining gases from the furnace after the burner has been shut down to ensure safety and prevent the buildup of hazardous conditions.
These steps ensure the safe and efficient operation of the boiler burner system throughout its startup, operation, and shutdown phases.
3. Combustion Systems Management.
A burner management system (BMS) is a safety solution designed to manage combustion systems, and it plays a critical role in:
- Start-up and Main Flame Detection: Ensuring the safe ignition of the burner and detecting the main flame once it’s established. This involves carefully monitoring ignition processes to prevent hazardous conditions.
- Control and Monitoring: Regulating the operation of the burner system by controlling fuel flow, air supply, and other parameters to maintain safe and efficient combustion. It continuously monitors various factors such as flame presence, temperature, and pressure to ensure optimal performance.
- Shutdown Sequences: Implementing safe shutdown procedures in response to various conditions, including emergencies or abnormal operating conditions. The BMS initiates shutdown sequences to safely extinguish the flame and stop fuel flow, mitigating risks and preventing accidents.
Overall, the BMS plays a crucial role in ensuring the safe and reliable operation of combustion systems by managing start-up, monitoring performance, and executing shutdown procedures as needed.
4. Main Purpose of BMS.
The Burner Management System (BMS) serves several important purposes as engineer point of view:
- Preventing Unsafe Startups: It ensures that the combustion system doesn’t start up if unsafe conditions are detected, preventing potential hazards.
- Safety Protection: The BMS protects against unsafe operating conditions and prevents the admission of improper amounts of fuel into the furnace, reducing the risk of accidents.
- Operator Assistance: It provides operators with status information, aiding them in monitoring and managing the combustion process effectively.
- Initiating Safety Procedures: If an unsafe condition is detected, the BMS initiates safety procedures or shutdown interlocks to maintain a safe operating environment and prevent accidents.
- Dedicated Furnace Safety Control: The BMS is specifically designed to ensure the safety of the boiler furnace, focusing on safety-related functions and providing assistance to operators in managing furnace operations.
5. How to Prevent Explosions in BMS?
Preventing furnace explosions requires addressing two critical factors: the presence of a flammable mixture and sufficient energy for ignition within the furnace. Since ignition requirements for an explosion are minimal, it’s nearly impossible to safeguard against all potential ignition sources like static electricity discharges, hot slag, or furnace surfaces. Thus, the primary method for averting furnace explosions is by preventing the accumulation of explosive fuel mixtures.
Explosive fuel accumulations typically form in the following ways:
- Loss of Ignition: This occurs when a flammable substance is introduced into the furnace atmosphere without ignition. Without ignition, the fuel accumulates and can reach explosive levels.
- Fuel Interruption: When a fuel-rich mixture is introduced into an air-rich atmosphere, and ignition fails to occur, a potentially explosive situation can develop due to the accumulation of unburned fuel.
- Air Interruption: Conversely, if an air-rich mixture is introduced into a fuel-rich atmosphere and ignition fails to occur, an explosive situation can arise due to the accumulation of unburned air.
Preventing these scenarios involves rigorous safety protocols, monitoring for potential hazards, and implementing measures to ensure proper fuel-air ratios and ignition. By addressing these factors, the risk of furnace explosions can be significantly reduced.
6. Safety Interlocking in a Burner Management System.
The safety interlocking in a Burner Management System (BMS) varies based on the characteristics of the firing system and the type of fuel used. However, all BMS systems typically address the following functions:
- Pre-firing Purge: Clearing the furnace of any residual gases or combustible materials before ignition to ensure a safe starting environment.
- Establishing Permissives for Ignition: Ensuring that conditions are appropriate for igniting the ignition fuel, such as completing the pre-firing purge and ensuring fuel pressure is within acceptable limits.
- Establishing Permissives for Main Fuel Firing: Once ignition is successful, verifying that conditions are suitable for firing the main (load-carrying) fuel, including obtaining ignition permissives.
- Continuous Monitoring: Monitoring firing conditions and other critical operating parameters to detect any abnormalities or unsafe conditions.
- Emergency Shutdown: Initiating emergency shutdown procedures for portions or all of the firing equipment in response to hazardous conditions or malfunctions.
- Post-firing Purge: After the firing process is complete, purging the furnace of any remaining gases or residues to ensure safety for subsequent operations.
These functions are essential for ensuring the safe and efficient operation of the firing system and are integral to the overall safety strategy of the BMS.
7. BMS and Safety.
The importance of compliance and safety in Burner Management Systems (BMS) cannot be overstated. Unfortunately, many existing BMS systems do not meet current standards, utilizing outdated relay-based control systems or non-approved standard PLCs. This poses significant risks to both personnel and equipment. Even non-dangerous sporadic failures can lead to costly downtime and difficult troubleshooting processes.
The decision to upgrade such BMS systems goes beyond safety concerns. Antiquated relay-based systems often reach a point in their lifecycle where reliability becomes a serious issue. While minor issues in small BMS setups can be addressed relatively easily, the lack of documentation for modifications made during critical situations complicates future repairs.
In essence, even small BMS applications with traditional relay control systems become increasingly challenging to maintain over time. Therefore, it is essential to prioritize compliance with safety standards and consider upgrading outdated BMS systems to ensure both safety and operational reliability.