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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 somewhat small, and often works as something of a filter that can trap 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 rust and degradation of the boiler machine, which can cause a range of problems both in terms of maintenance and efficiency. There are two primary types, namely tray-type and spray-type; both have similar functions, but work slightly differently. Choosing one over the other is usually a question of how much water there is, as well as the overall size and capacity of the boiler.
Even the best deareators can’t usually capture all loose gas, particularly not in large machines. In these cases, using what’s known as a “scavenger” chemical — sodium sulfite, for instance, or a range of organic and natural compounds — can work alongside the device to finish the process. Owners usually also have to keep an eye on the deaerator and check it regularly for service and cleaning in order to keep it in good working order. This can be time consuming, but is usually better than the alternative should it stop functioning properly.
Many machines and heavy equipment use boilers as a way of producing energy and powering things like motor rotation. They work by heating water and then harnessing the pressure and heat energy produced. Water, of course, is made of hydrogen and oxygen, but as water boils, particularly as 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 presents itself in gas form, and as a gas, it can stick very easily to the interior walls of the machinery where it can cause corrosion. When the gas particles attach to metal they typically form rust, for instance, which over time can both clog the systems and pollute them. Deaerators usually aim to capture and isolate these gas bubbles before they have a chance to interact with the metal and cause harm.
In a tray-type deaerator, feedwater enters at the top through a distribution pipe. The water cascades down through layers of perforated trays. At the bottom, low-pressure steam is produced, which moves up through the perforated trays. The steam comes into contact with the feedwater and heats it to its saturating temperature, which causes oxygen and other corrosive gases to separate out. 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 be removed later by a technician.
Spray-type models work a little bit differently. Rather than dripping the water through trays, these spray the feedwater in a fine mist. In many cases, the spray is introduced first into a preheated section, which raises the temperature to help release oxygen and other gasses. Steam is produced at the bottom, and it rises to meet the heated feedwater and scrub the gasses from it. These gases are released through a vent at the top. A storage tank is positioned underneath the device to receive the processed feedwater.
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 that is what is known as a “scavenger” of oxygen. Sodium sulfite is the most popular oxygen scavenger; however it can break down into acidic gases at high temperature, and this can actually increase corrosion in certain settings. Steam systems using high pressure should typically use organic oxygen scavengers instead.
A deaerator, just like other equipment in a plant, will experience wear and tear and should therefore be regularly checked and maintained. It is a good practice for operators to conduct regular off-line check-ups to keep the device in good running condition. A checklist is often really useful in the performance of routine checks to avoid missing any steps in the maintenance procedure.