An economiser is a very important part of boiler systems, which are used to make factories and power plants more efficient. By using waste heat in the boiler system, an economiser helps cut down on energy use and improve performance. The word economizer comes from the word economics. Let’s talk about what an economizer is and how it helps heaters in more detail.

What is a boiler economiser?

Economisers are made to do more than just exchange heat. They can also be used to treat boiler tubes with heat. The waste heat from the boiler is collected and moved to the feedwater. This lowers the amount of energy needed to heat the water, which in turn lowers the amount of fuel used. Through the economiser, up to 70% of the hot waste gas heat can be used again, but about 30% is not used because of some restrictions. To fix this, a 30% more efficient economiser based on the Rankine cycle has been created to take in more heat. This cycle is necessary for a power plant to work and includes steps that make the plant more efficient as a whole. In later parts, we’ll talk more about the Rankine cycle’s role in thermal power plants to help you understand these processes better.

How do boiler economists work to prevent process failures?

In vertical tube economiser. The flue fumes that come out of the boiler go into the economiser from the bottom. These gases carry heat that would have been lost otherwise. It has lines inside that let the feed water flow through it. Hot fumes from the flue pass over these pipes and heat the water around them. This process of moving heat around helps warm the water up before it goes into the boiler. As the waste gases cool down, they leave the top of the economiser. This is after giving most of their heat to the water. The economiser uses the leftover heat from the flue gases in this way, which saves fuel and makes the boiler work better.

The flue gas will flow from the top to the bottom if the tubes are flat. The temperature where the gas arrives will always be at least 140 degrees Celsius.

Problem of Condensation Below 140°C

Flue gases start to condense when their temperature goes below 140°C. This is because they contain water vapour. This mist is bad because it can cause corrosion and damage to the equipment. Let’s get a better sense of this occurrence.

Condensation and Acid Formation

In flue gases, oxides of sulfur and nitrogen are commonly found. These compounds are produced during combustion processes. As soon as these gases cool below 140°C, they mix with water to make sulphuric acid and nitric acid. These acids eat away at metals very quickly and can build up on boiler tubes, economisers, and chimneys, damaging their structure.

Impact of Horizontal Tube Configuration

The waste gas moves from the top to the bottom of the economiser or heat exchanger if it has tubes that are flat on the bottom. The chances of condensation go up if the temperature of the arriving flue gas drops below 140°C. This is because the gases flow horizontally and can cool down more easily. This causes the water in the waste gases to condense and settle inside the tubes.

Importance of Avoiding Condensation

1. Corrosion Prevention: Corrosion in the tubes or economiser can get worse when there is acidic condensation. This can raise upkeep costs and shorten the boiler’s life.
2. Heat Transfer Efficiency: A layer of condensation builds on the heat exchanger’s surface, making it less effective at moving heat.
3. Safety: Too much moisture can be dangerous because it can cause the boiler to build up pressure and damage its structure.

What should be done?

1. Temperature Control: To keep condensation from happening, make sure that the waste gas doesn’t start out at a temperature below 140°C.
2. Water Drainage System: Some economiser systems have draining systems that get rid of condensation and keep the system from rusting.
3. Material Selection: Materials that don’t react with acids can also be used to stop rusting from condensation.

By following these steps, you can keep the waste gases above 140°C, which will help the boiler and economiser systems work well and last longer.The economiser is a closed feedwater heater because the flue gas and water flow through different tubes, and heat is only transferred through conduction.

Advantages of Economiser in Boiler?

1. Improved Boiler Efficiency:

For every 6°C rise in temperature in the economiser, the boiler works better by 1°C. This improvement is pretty useful because with each one, total energy use and fuel costs go down.

Let’s take one example to show you the calculation to determine the increase in boiler efficiency when the feedwater temperature rises from 100°C at the inlet to 172°C at the outlet of the economizer.

Step-by-Step Calculation

1. Total Temperature Increase:
   The feedwater temperature increases from 100°C to 172°C.
   Total increase = 172−100=72°C
2. Efficiency Gain per 6°C Increase:
   Boiler efficiency increases by 1% for every 6°C rise in temperature.
3. Total Efficiency Increase Calculation:
   Efficiency increase = Efficiency increase = 72°C/6°C.×1%=12%

Result:

The boiler will work about 12% better if the temperature of the feedwater goes from 100°C to 172°C. When the temperature of the flue gas drops by 16 °C, less heat is lost. This lets the economiser take in more heat, which helps warm up the feedwater. This makes the boiler 1% more efficient and cuts down on the amount of fuel it uses.

2. Fuel Cost Savings:

It is possible to save up to 5% on fuel costs and 1% on heat energy by raising the temperature of the feedwater in the economiser by 10 °C. This is better because the stove uses less fuel and wastes less energy because the water is already heated before it goes in. The boiler can work more quickly because of this process, which saves money and energy overall. We can save 15% to 25% this way. By using an economiser, you can cut your pollution by 10–12%. CO₂ and other harmful gas pollution go down when people use less fuel. This is necessary to follow rules for the climate and the business world.Maintenance costs can be cut by 10-15% by using an economiser. It makes the heating surfaces of the boiler less stressed, which means they last longer and don’t need to be fixed as often.

3. Extended Boiler Life and Reduced Wear:

Using an economiser can add 15 to 20 percent more years to the life of the boiler. Preheated water makes the boiler less stressed, which is good for its tubes and structure as a whole. This keeps the boiler system working well for longer and cuts down on the cost of repairs. Things like calcium sulphate and magnesium sulphate that form hard scales build up in the economizer’s pipes. These deposits don’t get into the boiler lines, which keeps the boiler from getting clogged or rusty and, in the end, makes it last longer. A Soot blower is used to keep the economiser lines clean of buildup. Every 8 to 10 hours, high-pressure air or steam is used to clean the lines. This gets rid of fly ash and deposits, which helps the heat transfer work better.

The heating surface area of an economizer is only about 25% to 40% of the total surface area of the boiler. This means the economizer is smaller than the boiler, but it is still large enough to capture maximum heat from the flue gases.

TYPE OF ECONOMIZER IN BOILER

Boilers have heat exchanges called economisers that use waste heat from flue gases to warm up the boiler feedwater. This makes the boiler more energy efficient and uses less fuel. There are different kinds of economisers that can be grouped by how they are built, what they do, and how well they work.

1. Based on Heat Recovery

• Condensing Economizers: Are the best type of boiler economiser because they get back both obvious and latent heat. They lower the temperature of the waste gases below the point at which water vapour condenses. This lets the heat that was stored in the gases escape. This lets the condenser economisers take in as much heat as possible, which can make the system 10-15% more efficient. Most of the time, these economisers are used in stoves that burn natural gas because natural gas has little sulphur, which lowers the risk of corrosion.
• Non-Condensing Economizers: Recover only sensible heat without cooling the flue gases below their condensation temperature. This design only heats things up in a reasonable way; the water doesn’t change phases. This kind isn’t as good as condensing economisers, but a lot of coal-fired power plants use them because condensation can cause rusting when sulphur is present. This type is mostly used in industrial power plants where long-lasting and low-maintenance parts are needed because it heats in a reasonable way.

2. Based on Construction:

1. Plain Tube-Type Economizers: Water runs through simple tubes that are left bare. Their design is simple, and soot scrapers are used to keep the outside clean so that heat can still move through them effectively. These economizers are typically low-cost and easy to maintain, though their heat transfer efficiency is somewhat limited.
2. Gilled ya Finned Tube-Type Economizers: Extended surfaces, such as gills or fins, are added to the tubes to increase the heat transfer surface area. This design improves efficiency, as fins can capture more heat from flue gases. In finned economizers, the fin density is adjusted based on the type of fuel used:

(a) 150 to 200 fins per metre (clean fuels): 150 to 200 fins per metre are added when clean fuels like natural gas are used. This makes sure that the most heat is recovered and that the system works as efficiently as possible since clean fuels leave behind very little ash and soot.

b) 120 fins per metre (oil fuels): It is best to have 120 fins per metre when using oil fuels because burning oil leaves behind some ash and waste that needs to be cleaned up.

C) 80 to 100 fins per metre If the fuel is dry: That’s how many fins are used for dry fuels like coal or biofuel. Because dry fuels make more ash and soot, a smaller fin density is better for cleaning and maintaining.

To keep a balance between economy and durability, finned economisers are made with the type of fuel and deposit risk in mind.

3. Based on Steam Generation

• Steaming Type Economizers: As the feedwater goes through the economiser, it turns a small amount of it (about 5–7%) into steam. These economisers can be used in high-temperature situations that need to pre-heat and evaporate some water. The benefit is that they help make steam, which makes the system more efficient and reduces the load on the engine.
• Non-Steaming Type Economizers: Warm up the feedwater without turning any of it into steam. Before putting the water into the boiler, they heat it to about 75% of its boiling temperature to keep it stable. For normal heating, these economisers work well because they safely and efficiently heat up the system without changing the phase.

4.  Based on Flow Direction:

• Co-current Flow: use tubes that go up and down, and they’re best when floor room is limited. Because these economisers are small and can be stacked vertically, they can be used in places where room is limited. Both the flue gases and the feedwater flow vertically in this form, which makes the installation footprint smaller overall.

• Counter-current Flow Economizers: having tubes that are laid out horizontally makes them easy to clean and maintain. The tubes in the horizontal form are straight down, which makes it easy to use soot blowers and other maintenance tools. This type is usually chosen when there is a lot of floor room and regular upkeep is needed.

5. Additional Types

• Vertical Economizers: use tubes that go up and down, and they’re best when floor room is limited. Because these economisers are small and can be stacked vertically, they can be used in places where room is limited. Both the flue gases and the feedwater flow vertically in this form, which makes the installation footprint smaller overall.

• Horizontal Economizers: having tubes that are laid out horizontally makes them easy to clean and maintain. The tubes in the horizontal form are straight down, which makes it easy to use soot blowers and other maintenance tools. This type is usually chosen when there is a lot of floor room and regular upkeep is needed.

WHAT IS SOOT BLOWER

The soot fan is an important part of the boiler and economiser that helps keep the tubes clean. Its main job is to regularly clean the tubes of soot, ash, and other deposits that build up on them. This keeps the heat movement and boiler performance at their best. These buildups move with the waste gases and slowly stick to the tube surfaces. Over time, this can make the boiler less efficient.

How a Soot Blower Works:

Jets of high-pressure air or steam are used by a soot blower to clean the sides of tubes of soot and ash. When these jets hit the tube surfaces, they move deposits out of the way and remove them. The deposits then leave with the waste gases through the chimney. The soot blower is turned on and off at regular times to keep deposits from building up. This keeps the system clean and running at its best. Powerful air or steam is used to clean the lines every 8 to 10 hours.

Different kinds of soot blowers

1. Long Retractable Soot Blower (LRSB): The long lance on these soot fans goes into the boiler and blows steam or air. They are usually found in bigger boilers.

2. Soot blower that turns: Sprayers with spinning tips that work great on surfaces like superheaters and economisers. The turn lets the nozzle spread air or steam evenly over the tubes, which helps clean them completely.
3. Soot blower with a fixed mount: These are fixed in certain places and are used for cleaning particular areas. They work best in smaller areas or tight passageways, getting rid of deposits effectively in those areas.

Why Soot Blowers Are Important

• Improving the Efficient Transfer of Heat: Clean tubes and surfaces make it easier for heat to move, which cuts down on fuel use and keeps the boiler running efficiently.
• Cutting down on repair and maintenance costs: By getting rid of deposits, you lower the chance that boiler and economiser tubes will get clogged or damaged. This lowers the cost of upkeep and keeps breakdowns to a minimum.
• Making sure safety: Deposit-free tubes make burner operation safer because soot and ash buildups can cause overheating and fire risks.

Soot blowers are important parts of boiler systems because they keep the system clean and efficient, which is good for the boiler’s health and performance in the long run. Click on this link to learn more about you. https://www.coalhandlingplants.com/soot-blower-in-boiler/

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