When we put water into the boiler that has oxygen in it, it starts to combine with the high temperature, which causes corrosion. Over time, this process breaks down the metal parts of the boiler, which leads to rust formation. Corrosion makes the boiler’s structure weaker, which makes it more likely to leak and break. This lowers its performance and safety. To stop these corrosive effects and make sure the boiler system lasts as long as possible, it is important to control the water quality properly.

Technically we can say that iron oxide (Fe2O3) is made when oxygen reacts with the metal. This is called an oxidation process. Over time, this process makes the walls and pipes of the boiler thinner, which weakens their structure.

The gas carbon dioxide causes another problem. This substance breaks down in water to make carbonic acid (H2CO3), which is a weak acid. This acid can lower the pH of the water, making it more acidic, which speeds up the rusting process even more. The oxidation from oxygen and the acidity from carbon dioxide can break down the boiler’s materials very quickly, which can make it less safe and less efficient. To stop these processes and keep the system working, it is important to keep an eye on and treat the water quality in boilers.

Carbon Dioxide and Carbonic Acid Formation

Carbon dioxide (CO2) turns into carbonic acid (H2CO3) when it mixes with water. The process of making carbonic acid is an equilibrium reaction.

CO₂ + H₂O → H₂CO₃

The pH of the water drops when carbonic acid is present, making it acidic. Acidic water reacts strongly with metals, which slowly eat away at the metal walls inside the boiler. The acidic air inside the boiler speeds up the rate of corrosion, which weakens the metal over time.

Carbonic acid can cause acidic rust that can make the boiler much less reliable. To make sure the heaters work right, it is important to keep the carbon dioxide levels low. If CO₂ is in the water, it is usually taken out with degasifies or chemical solutions to keep the boiler from breaking down permanently.

A Degasifiers is a piece of equipment used to get rid of gases that are trapped in water, mostly oxygen and carbon dioxide. This process’s main goal is to make sure that the water going into the boiler is clean and free of gases. This keeps rust and other problems from happening.

The way degasifiers work is pretty simple: they treat the water by using both heat and hoover. When you put water under a vacuum and heat it, the gases that are dissolved in it, like oxygen and carbon dioxide, separate from the water and evaporate, leaving the system. This gets rid of all the gases in the water, making it safe to use in the boiler.

By getting rid of these dissolved gases successfully, degasifies keep boiler systems working well and keeping them intact. They also lower the risk of corrosion and make the equipment last longer.

It is very important to clean the water before putting it into the boiler, and we already know why this is important. Getting rid of these impurities is called “water treatment,” and there are two main types of treatment: chemical and mechanical.

For the first time, a deaerator is used in a mechanical process. This process removes 90 to 95% of the impurities in the water. In other words, out of a million particles of water, only about 0.007% are still dirty after this process.

In the second way, the feed water is dosed at both low and high pressures. This is called the chemical process. Acids like sodium sulphate and hydrazine are used in this method to clean the water. The mechanical process gets rid of most of the impurities, but the chemical treatment makes the water even cleaner, so it can be used in the boiler. By using both mechanical and chemical water treatment methods, we can greatly improve the quality of the water that boilers use. This makes the boilers more efficient and lasts longer while lowering the risk of rust and other problems. The next blog post will talk about LP dosing and HP dosing. For now, we’ll talk about how the mechanical process in the deaerator works.

Let’s look at a deaerator in more detail. This machine takes dissolved gases like oxygen and carbon dioxide out of the water that will be used in the boiler. Each part does its own thing, which makes the whole process run smoothly and quickly. Let’s look at each method in more depth.

• Pressure-Reducing Valve: The pressure-lowering valve controls the pressure of the water and steam before they enter the deaerator. This keeps the deaerator safe to use. This stops too much pressure that could damage the machine or stop the deaerator from working.
• Raw (fresh) Make-up Water: The deaerator gets fresh water through this opening. The water has gases like oxygen and carbon dioxide mixed in it. This water that hasn’t been cleaned goes into the system to be degassed so that it can be used safely in the boiler.
• Continue Purge Vent: As the water heats up, dissolved gases like oxygen and carbon dioxide separate from it and are let out through the purge vent. It makes sure that these toxic gases leave the system, which keeps the boiler from rusting.
• Condensate Return Water: The water from the condensation return is pumped back into the deaerator. This water already doesn’t have any gases dissolved in it. This helps the plants get the water they need while reducing their need for fresh water.
• Safety Relief Valve: When the pressure gets too high, the safety escape valve opens to let the extra air out. It prevents too much pressure from harming the deaerator and other nearby components.
• Low Pressure Steam Supply: This steam source warms the water, which helps the process of degassing. Dissolved gases separate and escape as the water heats up. This makes sure that the water is safe for use in boilers.
• Pre-heater Section: Before full degassing, the pre-heater part warms the water a little. This helps break down dissolved gases so they are easier to remove. This step before degassing makes the process go more quickly.
• Overflow Trap: The overflow trap gets rid of extra water in the system so that the deaerator always has the right amount of water. It keeps the deaerator from spilling and makes sure it works correctly every time.
• Scrubber Section: The scrubber part improves the touch between the water and steam, which helps get rid of impurities. By helping the gas leave the water, it makes the degassing process work better overall.
• Deaerator Storage: This tank briefly stores cleaned water so that it can be fully degassed before being pumped to the boiler. It keeps the water flow steady and gives the system a backup so it can keep running smoothly. The holding tank is made to hold enough water to keep the whole plant running for 10 to 20 minutes. This keeps the flow of clean water steady while the plant is working. It is important for a deaerator to always have 50 to 60% of its water capacity full.
• Anti Vortex Baffles: Anti-vortex shields keep the flow of water steady and stop vortices from forming, which can make pumps harder. They make sure that the boiler feed pumps always get water.
• Boiler Feed Pumps: These pumps move cleaned water that doesn’t contain gas to the boiler. This keeps the boiler safe and working well. They keep the water supply steady and free of gases that break down things. avoid mistake in picture
• Inspection Man Way: The viewing way lets you get to the inside of the deaerator to clean and do repairs. Technicians can look at and fix parts inside the system to make sure it works well.

Types of Deaerators And There Operation

Spray and Tray types are the two main types of deaerators. Even though there are more than two kinds of deaerators, we will focus on these two.

Spray Type Deaerator

In a spray-type deaerator, water is injected in the form of a spray, helping to remove dissolved gases effectively. Spray-type deaerators work by adding water in the form of a spray, which helps get rid of dissolved gases effectively. Spray-Style There are deaerators that remove air from the system and also store water for the boiler’s feed.

A normal spray-type deaerator is a flat tank with a baffle separating the two main parts: the preheating section and the deaeration section.

In simpler terms, here’s what it means:

1. Heating the Water: The preheat area and feed water spray tip work together to get the boiler feed water to a temperature close to boiling point. The cooking process makes it easier to get rid of the gases that are dissolved in the water, such as oxygen and carbon dioxide.

2. Removing Gases (Deaeration): The hot water moves from the section that heats up to the section that removes gases. Here, a sparger lets low-pressure steam rise from the bottom and mix with the water. These gases help to leave the water through the steam.
3. Gas Exit: The gases that are taken out of the water leave through a vent at the top of the tank. This makes sure that the system only has water that doesn’t contain gases.
4. Supplying water to the boiler: A pump takes the dearated water from the bottom of the vessel and supplies it to the boiler system, where it is used to generate steam The purpose of this process is to supply gas-free water to the boiler, which helps prevent corrosion and damage, ultimately extending the boiler’s lifespan.

• Spray Nozzle: This nozzle sprays the feedwater into small droplets, increasing the surface area of the water and enhancing its interaction with steam.
• Spray Nozzle Shroud: The shroud’s purpose is to keep the spray droplets contained, ensuring they remain in proper contact with the steam for effective degasification.
• Baffle: The baffle controls the flow of water droplets and steam, maximizing their interaction. It channels the water in a specific direction, enhancing contact with steam.
• Steam Supply Pipe: The steam supply pipe distributes steam that interacts with the water droplets, assisting in the release of dissolved gases.
• Preheating Section: In this section, the water is initially heated, which weakens the gas molecules, making it easier for them to be removed.
• Deaeration Section: This section allows for the final interaction between water and steam, completely removing any remaining dissolved gases. The gas-free water is then ready to be fed into the boiler.

Additionally, an air vent plays a crucial role in providing a pathway for the removal of dissolved gases.

Tray-Type Deaerator

A tray-type deaerator consists of a vertical domed section mounted on top of a horizontal cylindrical vessel. Let’s break down how it works in a simple way:

1. Water Entry and Flow: The feedwater from the boiler comes in from the top and goes down the vertical part first. The water moves down over trays with holes in them, which are called perforated trays. The surface area of the water grows as it falls through these holes.
2. Entry of steam and removal of gas: Low-pressure steam comes in at the bottom and moves up through the trays’ holes. When steam meets water, it helps get rid of gases that are dissolved in the water. In some designs, a packed bed (small pieces that are tightly packed together) is used instead of perforated trays. This makes the contact between the steam and water better.
3. Gas Venting: The gases are let out of the system through a vent valve at the top of the dome-shaped part when the steam takes them from the water. This makes sure that the gases don’t stay in the water, so the water is gas-free.
4. Storage and supply of water: The gas-free water builds up in the horizontal storage tank below. It is pumped to the boiler from here to make steam. A sparger pipe lets low-pressure heating steam into the holding tank. This keeps the water warm and ready to be fed into the boiler.

In short, a tray-type deaerator uses open trays to mix and interact with water and steam. These trays effectively remove dissolved gases, providing safe, gas-free water for the burner.

Tray-Type Deaerator Explained

1. Trayed Section: This is the tall part of the deaerator where water and steam mix. It has trays with holes that help increase contact between the two.
2. Water Storage Section: Below the trayed section, this part holds the treated water that is free from gases.
3. Air Vent: This vent lets out any gases that are removed from the water, keeping it clean.
4. Boiler Feed Water: This is the water coming into the deaerator that needs to be cleaned.
5. Deaeration Steam: Low-pressure steam enters from the bottom and rises through the trays. It helps remove the dissolved gases from the water.
6. Heating Steam: Additional steam can come in to keep the water warm, making it easier to remove gases.
7. Pump: The pump takes the cleaned water from the storage section and sends it to the boiler to make steam.

How It Works

1. Water Flows In: Boiler feedwater enters from the top and flows down over the trays.
2. Steam Rises: Low-pressure steam comes in from the bottom and rises through the holes in the trays.
3. Gas Removal: The steam helps push out any dissolved gases, which escape through the air vent.
4. Clean Water: The water collects in the storage section below, now free of harmful gases.
5. Ready for the Boiler: The clean water is pumped to the boiler for steam generation.

In simple terms, the tray-type deaerator helps keep the water clean and safe for the boiler by using steam to remove unwanted gases.
The mechanical principle of the deaerator works based on Henry’s Law and inverse solubility. Let’s understand what they mean:

Henry’s Law

Henry’s Law says that if the temperature stays the same, the amount of gas that can dissolves in a liquid depends on how much pressure that gas has. In other words, if the pressure goes down, the gas will become less soluble, which will allow it to leave the liquid.

This rule is used in deaerators when gases are taken out of the water by venting. The partial pressure of the gases that are dissolved in water and steam goes down when they meet. Henry’s Law says that this makes the gases less soluble, which makes it easy for them to escape from the water and come out of the vent. This is good because it removes the gas from the water, making it safe to use in the stove. The pressure that each gas in a blend puts out on its own is called its partial pressure. For instance, if oxygen and carbon dioxide gases are mixed with water, each gas will have its own specific pressure in the water. The pressure of this one atom is called its partial pressure.

Inverse Solubility

The principle of inverse solubility states that the behavior of certain gases and solids is such that their solubility decreases as the temperature increases. This means that when we heat water, the solubility of dissolved gases decreases, allowing them to escape more easily.

In a deaerator, the water is initially preheated, which raises its temperature. At higher temperatures, dissolved gases like oxygen and carbon dioxide cannot remain dissolved in the water and are released upon contact with steam. This is why the preheating step is so important, as it helps to separate the gases and makes the water degassed.

In this way, both Henry’s Law and the principle of inverse solubility are used in a deaerator to efficiently remove dissolved gases.

principle hydrostatic pressure

This principle is based on hydrostatic pressure.

If you put the deaerator higher than the boiler feed pump (BFP), it will naturally add more pressure at the pump’s suction inlet. Around 1 kg/cm² (or 1 bar) of pressure is added for every 10 metres of water height.

This means that putting the deaerator 10 metres above the ground adds an extra 1 kg/cm² of pressure to the BFP’s suction.

The benefits of this extra pressure include:

1. Smoother Suction: This added pressure helps the pump pull water more easily, making the suction process smoother.
2. Reduced Cavitation Risk: Cavitation (formation of vapor bubbles that can damage the pump) is less likely because the higher suction pressure helps keep the water stable.

Therefore, placing the deaerator at a slight elevation is a practical design choice that makes the pump’s suction more stable and efficient.