Fired equipment is the core of oil and gas, petrochemical, refining, manufacturing and numerous other industries. Although safety is a hot topic, it is only one of many considerations when designing a burner management system (BMS). So what do you need to pay attention to? What are priorities?
This post offers a basic understanding of how to begin to think broadly about your burner management system to ensure you are able to operate it safely, within compliance, achieving a high level of reliability while keeping it simple for operations to run and maintenance to maintain.
After the safety requirements and codes are established, it is imperative that those requirements are followed in all aspects of the BMS. Purpose-built and safety rated controllers have built-in functionality that cannot be altered which allows it to comply with most safety related applications. General purpose PLCs with non-built in features can include implementing logic for input/output checking, watchdog timing features, proper sequence of BMS operations and hardwired master fuel trip circuits that ensure the controllers are meeting the safety intent. Along with the BMS controllers, it is safety critical that all field devices being used are rated for its service and installed with safety guidelines in mind. Additionally, there are new technologies to enhance the safety of your BMS. For example some manufactures now offer safety valves that preform partial stroke test to insure the safety valve on the BMS will close when its needed.
NFPA, API, internal specifications and insurance requirements are a few of the considerations when designing a code compliant BMS. Code compliance addresses aspects of the system from the field devices to the BMS controller. To easily obtain a code compliant system, follow the code that has been decided or that is required to adhere to. The code compliance may include field devices designed and rated for the services that they are being installed for, the system components installed per the code requirements, and all components meeting SIL requirements (if applicable). One area we often find BMS out of compliance is were a customer is using a general purpose PLC for the high level and low level stack temperature trips. Per code the high and low stack temperature loops must be controlled from an FM approved device. General purpose PLC’s are not FM approved, so we use an FM approved controller to perform that function.
Fired equipment tends to get attention when it shuts down unexpectedly. Taking steps to understand the common causes of failure and designing accordingly helps your system run reliably with uninterrupted service. Most reliability concerns are raised by the field instrumentation of a BMS. Once a burner controller or PLC-based system is verified and commissioned, the failure of this hardware makes up a very small percentage of the causes of shutdown. One key component of reliability is the use of proper flame detectors for the application or service. Understanding the combustion characteristics assists in the determination of the proper flame detector that would positively identify combustion across all process conditions. This helps mitigate any nuisance trips that may occur when process conditions change.
Field instrumentation on the fuel delivery system, fuel skid, can impact the long-term reliability of the system. Because these systems tend to run for an extended period of time between maintenance periods, it is essential that the instruments, valving and all other important specifications are rated for the service they are intended for as well as having industrial leading MTBF data. In addition you need to look for instrumentation that has a high level stability over several years with high level of accuracy to insure you are providing the right gas pressure to your burners.
Ease of operation & maintenance
Maintenance personnel are responsible for the startup and shutdown of these systems, expected or not. Interfaces and lights should be intuitive to the operator concerning the sequence and operation of the BMS. If a piece of fired equipment unexpectedly shuts down, it is imperative that maintenance personnel act quickly to identify what went wrong and get the unit back up and running immediately. One of the common methods of alerts is a “first out” alarm. Whatever critical limit was lost and shut down, will be captured in the BMS controller and displayed. Designing a system that ensures a quick and reliable way to identify shutdowns is essential to increase the uptime of the fired equipment. This helps ensure that at any given moment, operators know the status of the system allowing them to safely startup and shutdown the system.
When selecting equipment, keep in mind that it needs to be easily maintained in the field to avoid headaches in the future. We therefore prefer using devices with modularity that allow you to fix a problem easily and quickly. One good example is the regulator that you select. Over time dirty gas passing through the regulator can cause the regulator to stick and not provide a reliable pressure to the burner(s). Regulators with top entry have a clear advantage over other regulators: you can open them up and clean them in place instead of having to bring them back to a bench. Top entry allows you to safely repair the issue and to get the system back up and running with minimal down time.
If you consider these points when designing your burner management system, you are a step ahead of the curve. However, make sure you research the latest codes periodically as NFPA and API codes do change over time and your system could be out of compliance without you knowing it. Also keep up with new developments in technology which can increase the safety and reliability of your system and allow you to build a system that’s easier to operate and maintain in the future.