A deaerator is a device used in industrial boilers to remove dissolved oxygen gas from water supply. There are two types, tray and spray, which capture gas bubbles to prevent corrosion. Chemical scavengers may be used to complete the process. Regular maintenance is required to keep the device in good working order.
A deaerator is a mechanical device used in industrial boilers to remove dissolved oxygen gas from the internal water supply. In most cases the actual device is quite small and often functions as a sort of filter capable of trapping oxygen gas bubbles as they pass through the feedwater supply on their way to the main boiler chamber. Gas that is not captured can cause the boiler machine to rust and degrade, which can cause a variety of problems in both maintenance and efficiency. There are two main types, namely tray type and spray type; both have similar functions, but work a little differently. Choosing one over the other is usually a matter of how much water there is, as well as the overall size and capacity of the boiler.
Even the best deaerators usually fail to capture all of the dissolved gas, especially not in large machines. In these cases, the use of a chemical known as a “scavenger” — sodium sulfite, for example, or a range of organic and natural compounds — can work in conjunction with the device to complete the process. Owners also usually need to keep an eye on the deaerator and check it regularly for maintenance and cleaning to keep it in good working order. This can be time consuming, but is usually better than the alternative if it stops working properly.
Basic concept and fundamental importance
Many heavy machines and equipment use boilers to produce energy and power things like engine rotation. They work by heating the water and therefore exploiting the pressure and the thermal energy produced. Water, of course, is made up of hydrogen and oxygen, but when water boils, particularly when it boils for long periods of time, both of these elements tend to dissolve. There is nothing inherently wrong with dissolved oxygen, but it can and often does pose some pretty serious problems for pressurized machinery.
Most of the time, dissolved oxygen comes in the form of a gas and, as a gas, can adhere very easily to the internal walls of machinery where it can cause corrosion. When gas particles stick to metal, they typically form rust, for example, which over time can clog and pollute systems. Deaerators usually aim to capture and isolate these gas bubbles before they have a chance to interact with the metal and cause damage.
Examples of tray types
In a tray deaerator, the feed water enters the top through a distribution pipe. Water cascades through layers of perforated pans. In the lower part, low pressure steam is produced, which rises through the perforated trays. The steam contacts the feed water and heats it to its saturation temperature, which causes oxygen and other corrosive gases to separate. The dissolved gases exit through a vent at the top, while the deaerated feedwater falls to the bottom and into a storage tank where it can later be removed by a technician.
Spray patterns
Spray patterns work a little differently. Instead of dripping water through the trays, they spray the feed water in a fine mist. In many cases, the spray is first introduced into a preheated section, which raises the temperature to help release oxygen and other gases. Steam is produced at the bottom and rises to meet the heated feedwater and scavenge gases from it. These gases are released through a vent at the top. A storage tank is placed under the device to receive the treated feed water.
Process completion
Deaeration is one of the best ways to remove oxygen and other corrosive gases, but it may not remove them completely. In such cases, it may be necessary to apply a chemical known as an oxygen “scavenger”. Sodium sulfite is the most popular oxygen scavenger; however it can degrade into acidic gases at high temperatures, and this can actually increase corrosion in certain settings. Steam systems using high pressure should typically use organic oxygen scavengers instead.
Care and maintenance required
A deaerator, just like other equipment in a plant, will experience wear and tear and should therefore be regularly checked and maintained. It is good practice for operators to carry out regular offline checks to keep the device in good working order. A checklist is often really helpful in performing routine checks to avoid missing any step in the maintenance procedure.
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