For better burner management, focus on the flame
Combustion equipment such as boilers, heaters and furnaces, found in almost all industries, are often overlooked as plant safety concern areas. Fortunately, a company can take steps to improve its burner management system (BMS), ensuring that critical combustion equipment operates safely and efficiently. Whether a plant is being built from the ground up, or an organization is looking to improve existing BMS equipment, plant decision-makers should consider five key issues to help ensure the combustion system fires reliably every time.
1. Ensure safe, productive operation
BMS performance and plant performance go together. A poorly designed system that regularly falls victim to spurious trips, light-off problems and difficult troubleshooting may still protect plant equipment and personnel, but the process interruptions these trips cause can significantly impact plant operability and performance.
A BMS provides critical combustion safety functionality. As the BMS manages safe light-off, startup and shutdown of the combustion unit, it monitors the process for unsafe conditions. To protect people and the plant, the system must be designed properly and perform well over the equipment’s lifecycle.
To avoid lost production when operations and maintenance troubleshoot BMS failures, the system should incorporate best practices in selecting and maintaining field equipment, leveraging safety-rated equipment, collecting and analyzing critical BMS data and using a sequenced approach to logic design. BMS best practices ensure safety conditions are identified and accounted for, allowing operators to identify upset causes quickly and reliably (see Figure 1).
2. Sequence-based approach
The oldest legacy systems use relay panels to perform safety logic sequences. These large, hardwired Boolean logic installations were relatively reliable, but difficult to troubleshoot or change. As technology progressed, hardwired relay panels were replaced by programmable logic controllers (PLCs) – specialized computers that emulate relay logic with software. This made safety sequence modification easier than with relay logic.
Sequence-based configuration changes the paradigm on BMS logic. The safety sequence is easily understood. Permissives and operator actions needed to move from one step to the next are documented. Outputs associated with each step are clearly defined. A burner’s BMS logic is defined and documented on a single small spreadsheet.
3. A holistic approach
Best-practice BMS practice starts with a holistic management approach encompassing external sensing devices, actuators and even the process piping associated with fuel delivery. Component maintenance is as critical as maintenance of BMS hardware and software. If the system backbone isn’t working properly, the BMS isn’t entirely effective.
Organizations striving to ensure BMS availability should take a holistic approach to maintenance, evaluating and maintaining all equipment connected to the combustion system. Whether a BMS enhancement is an update to a legacy system or a greenfield implementation, understanding the interconnectivity between the system and its equipment is essential.
Retrofitting an existing system. A comprehensive system assessment helps ensure BMSs meet current industry codes and recommended practices.
Bringing burner management up to present standards is necessary and increasingly required by law. As updates are completed, it’s beneficial to look for areas to simplify logic and improve data collection.
Retrofit projects often are a chance to eliminate series wiring of sensor devices and to replace switches with transmitters. When many a BMS was first installed, having multiple sensors wired in series to a single controller input saved money. Years later, this configuration increases troubleshooting complexity.
Similarly, in many cases, switches were inexpensive to buy during initial installation. Today, they no longer provide the diagnostic capability that lends itself to high system availability.
Another way to ensure a retrofit to an existing BMS installation incorporates best practices is to perform a comprehensive field survey. In legacy systems, it is common to find field issues that need correcting, including sensing devices that are missing, installed equipment not listed for safety service and vent pipe sizes that are insufficient, among others. A field survey helps the update team see the big picture, making it easier to ensure that the final product delivers benefits across the equipment’s lifecycle.
Greenfield implementations. When developing specifications for a BMS installation, pay attention to the field devices. Sensor or actuator problems cause BMS reliability issues. To avoid recurring problems, take care to choose the proper devices and ensure proper installation. The easiest way to be sure all devices follow best practices is to perform a comprehensive field survey.
Whether performing a retrofit upgrade or greenfield installation, a site survey helps the implementation team decrease unplanned outages and increase troubleshooting efficiency. A survey helps teams determine where to make improvements leveraging smart instrumentation, along with a smart BMS. The best instrumentation and toolsets not only walk a user through each sequence of a fired equipment startup, but, in the case of an upset, quickly identify the exact cause for it. Often, leveraging the assistance of a trusted expert partner can increase site survey benefits (see Figure 2).
4. SIL ratings and integrated systems
Although a safety integrity level (SIL) rating is not always applied to safety functions related to fire-heated equipment, standards and best practices today require use of control hardware that carries an SIL rating. Whether hardware is adopted with an SIL certification to meet company guidelines or to comply with legal requirements, taking advantage of the rating establishes whether the selected BMS meets organizational risk tolerance.
SIL-rated controllers include functionality and diagnostics that make them particularly well suited to safety applications. SIL equipment cost is typically offset by the savings generated in the safety solution design based on the benefits of built-in SIL hardware diagnostics. Some organizations that choose not to use SIL-rated controllers must take additional steps or even add components to prove the solution can safely fire equipment. Moreover, as SIL-rated devices significantly decrease failure probability, they correspondingly reduce safety equipment risk, meaning fewer problematic incidents and less downtime.
Additional savings can be found with integrated systems. When designing a BMS, as with any safety instrumented system (SIS), the safety function must be physically or logically separated from the control system. Taking advantage of logical separation allows the safety function to be separated per industry standards while keeping the system integrated with the overall process controls.
An integrated control architecture typically results in significantly reduced lifecycle operating and maintenance costs. Integrated systems simplify engineering, quickly generating front-end savings. After the system is put into production, the use of integrated hardware allows a plant to manage one system instead of two, with results that drive value across the lifecycle (see Figure 3). Modern automation systems can provide all the benefits of a single system while still maintaining the required separation for the logic solver.
5. The user interface is critical
A sequenced approach to safety logic design allows organizations to build an improved user interface, designed using best practices, to help personnel more quickly and effectively react to what they see happening in the BMS. The burner management sequence is presented using clear, intuitive graphics, clearly differentiating all possible states and highlighting the process’ active stage.
The sequenced approach also allows organizations to customize the BMS interface to fit their plants’ needs. Different sites may require operations interaction to start different parts of the process or may choose to automatically advance past individual steps. A sequenced approach makes such custom designs simple to implement.
Proper combustion equipment startup, shutdown and operation is critical to a plant’s safety and operation. Applying modern best practice strategies to build, update or maintain a BMS can deliver substantial dividends in the form of improved safety and increased uptime for critical processes. Whether installing a brand new BMS or searching for ways to improve availability of an existing system, taking advantage of technology advance delivers benefits to improve functionality and lower total cost of ownership across the equipment lifecycle.