Steam boilers are integral to the operation of countless industrial and commercial facilities. That's why it's important boilers be provided with the utmost of attention and care so they will operate efficiently and without the need for continual repair or rebuilding. Preventative measures are vital for keeping a steam boiler up and running. One such important measure is the use of deaerators for treating boiler feedwater. Below is why deaerators are so critical and what you should know about their use with your steam boilers:
Boiler deaerators – their purpose and how they work
Deaerators remove oxygen from boiler feedwater, and that makes them indispensable to the operation of steam boilers. When feedwater is heated, the dissolved oxygen molecules in water becomes highly corrosive to metal, including the internal components of boilers. Corrosion causes boilers to function poorly and reduces their lifespans; in some instances, corrosion can weaken a boiler enough to even cause a rupture or explosion.
Boiler deaerators function using a simple, but elegant, principle of physics known as Henry's Law. This principle postulates that as the pressure of the atmosphere above a fluid decreases, the fluid's ability to carry gases also decreases. This can be demonstrated vividly with a bottle of carbonated soda. When the bottle is sealed tight, the carbon dioxide inside the soda is unable to escape due to the pressurized atmosphere. Once the lid is removed, however, the pressure lessens, and the soda is unable to contain the carbon dioxide.
With a boiler deaerator, the feedwater is sprayed into a heated, pressurized holding tank; as steam rises from the heated water and releases its oxygen, the water spray is heated and "scrubbed" of its oxygen. The oxygen is then permitted to vent into the outside atmosphere. This process is not complex, but all parameters must be properly aligned for it to work well. Below are some important guidelines to keep in mind when using boiler deaerators:
Boiler deaerators – guidelines for proper and optimal operations
Since boiler deaerators use steam to vent the oxygen to the atmosphere, there is a fine line between failing to eliminate oxygen and venting too much steam. The first problem will hamper the operation of deaerators, and the second will ultimately result in a waste of feedwater and a loss of heating efficiency. These potential issues must be analyzed by the engineering department, and they will need to adjust vent diameters and other parameters to keep deaerators operating at their intended levels.
Another potential problem that occurs with deaerators is a failure to properly heat the feedwater. Feedwater that is kept at too low of a temperature will not release its oxygen, and this will result in corrosive byproducts that damage boilers. At the other end of the spectrum, water that is heated too much will boil, and this will cause volatility in the operation. The feedwater must be kept at a steady, optimal temperature for the deaeration process to work as intended.
Most physical deaerators are unable to remove all of the dissolved oxygen gases in the feedwater, so there will be a need for supplemental deaeration. Chemicals in the form of oxygen scavengers are an excellent choice for cleaning up the remaining molecules within feedwater. However, any chemical must be considered in light of its overall effect on the boiler and its operations. A couple of commonly-used oxygen scavengers are:
Hydrazine is an effective oxygen-reduction agent; however, it is a volatile, toxic chemical if handled without caution, as it is capable of causing death by overexposure and is a potential explosion hazard.
Sodium sulfite is also used as an oxygen scavenging agent in boiler feedwater. It is significantly less hazardous than hydrazine products.
Keeping this information in mind will help you keep your boilers in good condition. If the any of the deaerators on your boilers aren't working correctly, it's important to get them fixed. Even if that means using a rental boiler while the repairs are made. You can go to sites of local industrial equipment suppliers to learn more.