While human operators are sometimes required for boiler operation, and this provides some level of awareness and protection, safety equipment is designed to be a final safeguard against catastrophe. When water is boiled to steam, it expands 1400 times in size, which is perfectly fine in the controlled environment of a properly functioning boiler system.
However, if there is a malfunction and a large quantity of high pressure/high temperature water is released to the atmosphere, the expansion of that water to steam results in catastrophic damages. Safety equipment on boilers provides a safeguard against dangerous conditions that could arise.
Boilers and other pressure equipment are only designed to operate at maximum pressure and temperature, so exceeding the design conditions may result in premature failure and unsafe operation. Also, the system the boiler is connected to may be rated at a lower pressure than the boiler system and therefore, operating at elevated levels could pose a risk to downstream systems and components as well.
Burner Controllers / Flame Safeguards
Controllers that provide the proper sequencing for burner operation including ignition, flame monitoring, purging, cut-off, and typically include safety limit and operational limit circuits.
On the majority of boilers, a microprocessor-based controller is a component controlling the sequencing of operation of the burner. These controllers have limit circuits built into the programming that runs continuous safety checks to monitor the associated components for safe operation.
The limit circuits vary between recycling limits and safety limits. The main difference is really the requirement for operator intervention to confirm the correction of the fault that caused the limit to “trip.” These devices operate the burner and are the first line of defense for conditions that will cause unexpected operation or unsafe conditions.
Pressure or Temperature Controls
A set of controllers used to control the pressure or temperature of a boiler. Depending on the type of burner operation, different types of controllers will be utilized.
In a steam boiler system, the pressure in the boiler is maintained by the burner firing rate. Since temperature and pressure are proportional for saturated steam, the more heat that is added, the higher the temperature and pressure of the boiler will be. The pressure controls are set for the desired operating pressure and automatically adjust the burner to produce the expected conditions. Normally, there is redundancy in the pressure controls as well to turn off all systems in the event of a “high pressure.”
Pressure Relief Valves
A type of safety valve used to limit the pressure in a system and protect from over-pressurization.
These devices exist to prevent the over-pressurization of a system, whether it is a boiler, tank, heat exchanger, piping, or another associated component. There are several types of safety valves that differ in how they function, as well as the particular application, but the reasons for installation are all the same — system protection.
Depending on the local jurisdiction, these safety valves should be tested regularly to demonstrate the functionality and accuracy of settings. Only a certified company can make adjustments and perform testing on these valves.
Low Water Cutoff and Auxiliary Low Water Cutoff
A safety device used to protect equipment from the hazards of a low water condition. Typically when two “LWCO” are used, the first will control the flow of make-up water into the equipment and the second will have a manual reset that is tied into the safety limit circuit of the Burner Controller.
There are two main types of LWCO devices: probe/electrode and float.
There are two main functions that are performed with the LWCO devices:
- Level Control: This can be done with either type but typically done with a float type LWCO that has an automatic reset. The float contacts are connected to the feed water delivery system (either the feedwater valve or the feedwater pump motor) and control the flow of water to the boiler.
- Fuel Cutoff: This can be done with either type, but includes a manual reset, which requires operator input to undo this fault condition. This function cuts off the burner and renders the boiler “out of operation” until the condition is corrected.
In a system utilizing two LWCO (Primary and Auxiliary), the first controls the level and the second is a safety lockout for the burner. For that reason, the Auxiliary LWCO is set to a lower level than the Primary LWCO.
All in all, boilers, while very safe under normal circumstances, can be dangerous without the proper safety equipment and protocols. Understanding the purpose of the different types of safety equipment, as well as implementing and maintaining them properly, is crucial to the safety of your workers and the long-term health of your boiler.
