Every operating boiler is a well-tuned symphony of purpose, with different pieces of equipment working together to turn water into steam. Have you ever stopped to wonder, though, how a boiler operator can keep track of what’s going on as the system operates? Or how they make adjustments to keep everything working as it should? It has to do with a series of controls that monitor and adjust different parameters of the boiler as it operates. Together, they keep every boiler working safely and efficiently.
WATER LEVEL CONTROLS
You can’t make steam without water, and keeping the boiler supplied is absolutely crucial to safe, efficient operation. If the water level gets too high, the steam will carry excess moisture or even slugs of water into the steam system, resulting in condensate flooding of processes, or hazardous water hammer events. If the water level gets too low, the boiler will become overheated. That leads to damage as the metal becomes stressed and starts to lose its structure on a molecular level. That’s why Water Level Controls are so crucial.
The most basic way to monitor the water level is with your own eyes, using a sight glass. A properly operating sight glass will tell you the water level just by looking. But for automated control systems that need a way to monitor the water level, there’s the float switch. As the name implies, a float switch has a hollow bulb that floats on top of the water inside the pressure vessel. As the level of water goes up and down, the float moves up and down as well. This is generally used as a signal for the feed pump or level control valve to respond. If the water level gets too low, the float will trigger the burner cut-out and low water alarm switches, shutting the boiler down to keep it from overheating.
Electronic probes can also be used to verify safe water levels, as well. If the probe detects that there is no water around it, it will likewise trigger an alert or shut the boiler down.
STEAM CONTROLS
Once that water has been turned into steam, the steam has to be controlled and routed to the end work processes. To do that, your boiler uses a series of Valves. But there’s more than one type of valve in your boiler, because routing that steam requires different capabilities. Each of these valves can be controlled by hand, or by an actuator in an automated system.
Ball valves use a solid ball with a hole through it, mounted inside a housing that rotates 90 degrees. They can be used as isolation valves because they can seal off the flow entirely. You’ll find them typically used in blowdown lines, fuel lines, and of course water supply lines.
Gate valves operate by raising and lowering a metal gate inside a housing, sort of like the door on your garage. Since they do not offer a great deal of flow control, they are generally used to enable or isolate the flow of water into the boiler.
Globe valves operate by raising and lowering a metal sphere onto a concave seat, restricting or permitting the flow of water through them. Since they offer precise control, they’re used to modulate the flow of water, steam, and fuel. Some globe valves will even have calibration marks that indicate how far the handle is turned.
PRESSURE CONTROLS
Since physics follows rules, you can tell what one part of the boiler is doing by monitoring other parts. This comes into play with Boiler Pressure Controls. By monitoring the pressure of the boiler, the operator (or monitoring system) is able to gauge how the boiler is operating, and what adjustments need to be made to keep the steam flowing properly. If the pressure is too low, steam production has to be increased. If the pressure is too high, the firing rate needs to be lowered. If the boiler pressure is excessive, the boiler will shut down automatically for safety.
3-ELEMENT STEAM DRUM LEVEL CONTROL
Achieving optimal steam flow to the work processes is crucial to any boiler operation, and it’s easier today than it’s ever been thanks to the advent of 3-Element Steam Drum Level Controls. While simpler systems simply monitor the water level to know if the boiler is operating efficiently and safely, the 3-Element Steam Drum Level Control actually monitors three different parameters. Depending on the system design, that may be water flow, steam flow, and water level, or in other cases: firing rate, steam pressure, and water level. By checking multiple factors, a boiler control system is able to determine with greater accuracy how the boiler is firing, and how much steam it’s producing. The control can then adjust the amount of water entering the boiler to precisely match the steam coming out of the steam drum to keep the system operating in equilibrium.
BAROMETRIC DRAFT CONTROLLERS
As a boiler operates, it vents exhaust gases through the stack into the atmosphere. But the pressure inside the stack has to be carefully monitored to make sure the boiler is operating safely. Ideally, stack pressure should be slightly lower than ambient air pressure to help draw combustion gases out of the fire side and up into the stack. This slightly negative pressure is called “draft”. If the pressure in the stack is too high or low, the volume of air being supplied for combustion could be negatively affected. That’s where Barometric Draft Controls come into play. They monitor stack draft and alert the operator (or control system) if stack pressures get too high. If the pressure is too high, the operator (or control system) can respond and adjust to maintain the proper draft.
FLAME SAFEGUARD CONTROLS
One primary device on every boiler has the job of monitoring all of these safeties: the Flame Safeguard Control. The flame safeguard control monitors the safety interlock systems, sequences the lightoff process, and also verifies that flame is present (or not) according to the sequence stage. This control supervises the light-off sequence when there is demand, including the steps of purging, lightoff, and modulation. When a boiler is first started, the combustion chamber has to be cleared of any residual fuel or combustion gases. To make sure the coast is clear, the purge controller will open up the air dampers and turn on the purge fan, blowing fresh air through the combustion chamber to make sure everything is out of it before the boiler starts up. During lightoff the pilot and main fuel valves are staged according to strict safety timings, with flame status verified at all times, and the unit will shut down if flame signals are not above minimum thresholds at specific checkpoints. Once lit, the safeguard releases modulation control to the firing rate system.
When the boiler is shut down, whether done intentionally or by the triggering of an emergency shutdown, the purge controller goes to work again. As in a startup purge, the dampers are opened and the purge fan is activated to clear out any residual fuel or gases from the combustion chamber.
AUTOMATED PERFECTION
With all these different sensors to monitor and controls to operate, a boiler operator will have a lot to do. Thankfully, modern technology is here to help. Automated boiler control systems are remarkably advanced these days, taking hundreds of readings every minute and making minute adjustments to optimize performance on a continual basis. As far as WARE is concerned, nobody does a better job of automated boiler control than AUTOFLAME. Using state-of-the-art sensors and precise servos, the sophisticated brain of an AUTOFLAME system can squeeze every last energy dollar out of a boiler, while making sure it operates safely and reliably.
If you’d like to learn more about how all of your boiler’s controls work together, consider taking a class at WARE’s Boiler University. Our classes are taught by seasoned experts who know everything about safe, efficient boiler operation. If you think your boiler controls may be operating incorrectly, or if they need service or maintenance, the professional technicians at WARE have the expertise and skill to help. If you’re looking for parts and supplied to keep your boiler operating, WARE’s BoilerWAREhouse.com is just a click away, with the nation’s largest selection available with fast shipping. Whatever you need, we’re here to help.