These days, every well-equipped boiler system is sporting a deaerator. They serve several crucial functions on the boiler’s water side, the most obvious of which is storage of the feedwater supply. In this role, the deaerator makes sure the boiler has all the feedwater it needs to keep running. But it’s doing more than you might realize behind the scenes.
You’ll Warm Up to It
The first function the deaerator performs is elevating the temperature of the water before it enters the feedwater supply. By pre-heating the water, the deaerator prevents thermal shock, which is a potentially damaging condition that can occur when cold water enters a boiler running at full or near-full capacity. When the cooler water hits the very hot water and steam inside, it can cause a rapid contraction of hotter surfaces that can damage the boiler shell and tubes.
No Thank You, O2
The next important function a deaerator performs is the removal of excess oxygen from the feedwater. By removing this oxygen, the deaerator helps reduce the need for chemical additives and treatments that are otherwise required to prevent internal pitting in the boiler. If it’s not removed, it will react with the components in the boiler’s water side, and cause corrosion.
The deaerator gets rid of oxygen by basically pushing it out of the system through a vent. It does this by heating the water it contains past the normal boiling temperature of 212⁰ F, keeping it under constant pressure to prevent it from actually boiling.
Dial It In
Typically, a deaerator will be set to heat the water to 225-227⁰ F, and maintain it at a pressure of 5-7 psi above ambient pressure. This combination creates ideal conditions for the removal of oxygen, and the prevention of thermal shock. To make sure a deaerator is doing its job correctly, it’s important to check its gauges frequently. A drop in either temperature or pressure means something is wrong, and there are several common culprits to check.
- The Pressure Reducing Valve - This valve directs steam into the deaerator, while keeping it under enough pressure to allow the proper heating to occur. A malfunctioning pressure reducing valve, often indicated by an intermittent drop in pressure, means the deaerator isn’t getting enough steam to do its job. That will cause a subsequent drop in deaerator temperature and pressure. In some instances, the valve may simply be sized too small to let enough steam through to do the job. In either case, the valve should be inspected and serviced or replaced by a qualified WARE technician.
- The Nozzle - Another potential problem that can arise in deaerator operation is a malfunctioning spray nozzle. To maximize the surface area of the water as it enters the deaerator -- thereby increasing its ability to absorb heat -- the water is actually introduced as a spray. If that spray nozzle can’t distribute the water evenly and finely enough, the water won’t absorb enough heat from the incoming steam, and it won’t ever get hot enough. Common nozzle problems can include blockage from contaminants, a worn aperture, or a broken spring, all of which can cause uneven spray distribution and insufficient heat transfer.
- Up, Up, and Away - One of the most overlooked issues with a deaerator involves the vent, which provides the excess oxygen with a path to escape. If the vent is closed or otherwise blocked for any reason, the oxygen will remain trapped inside the deaerator, where it will displace useful steam. It will also allow the deaerator to maintain the proper pressure, but not the correct temperature. Therefore, one of the telltale signs of a blocked vent is a loss of temperature, but not pressure. If the pressure is within spec but the temperature is too low, the vent is a good place to start troubleshooting.
Remember to check your deaerator temperature and pressure at least daily. It also helps to make sure your gauges and sensors are up to date, and functioning properly. If your deaerator isn’t operating up to spec, or you need a new one installed, the skilled, professional technicians at WARE are standing by to help. Contact us today, and we’ll get your aerator back on the job and working like it should.