People think that the draft system is one of the most important parts of a boiler, but they don’t pay enough attention to it. The draft system makes sure that the right amount of air flows through the boiler and gets rid of the flue gases. This makes it possible for both small commercial boilers and big power plants to work efficiently. But what is a draft system, and why is it so important for a boiler to work well? The specifics will now be looked into. First, let us talk about why a steam plant needs a draft system.
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How does a thermal power plant work?
The energy in fuel, like coal or gas, is turned into heat when it burns. The water is then heated with this heat. There is a machine called a steam generator that turns water into very high-energy steam. The steam is then used to turn a turbine, which is a big fan, and make power.
Some important parts of this process work like this:
- Draft System: This system controls the air that helps the fuel burn.
- Water and Steam Circuit: This moves the water and steam around and moves heat around.
- Furnace: This is where the fuel is burnt to make heat.
- Fuel-burning System: This system gets the fuel ready to burn.
- Heat Recovery System: This system reuses heat that is wasted so that no energy is lost.
To put it simply, fuel burns to make heat, which turns water into steam. The steam turns the turbine, which makes power.
For now, this topic will talk about the draft system. In the next topics, the whole process will be slowly covered. The only goal is to make everything clearest, simplest, and most helpful way possible. There will be an effort to make sure that each idea is understood as completely as possible.
What is a draft system in a thermal boiler?
One way to control the flow of air inside a boiler is with the draft system. Its job is to move air into the furnace and take out the smoke and waste gases that are made when things burn. If the draft system isn’t working right, the fuel won’t be able to burn all the way, which wastes energy, uses more fuel, and makes more pollution.In natural draft, a chimney that is 200 feet (60 meters) tall and has a gas temperature of 490°F (250°C) can only make 1.15 inches of water. But the boiler and burning system can have as much resistance to gas and air flow as 50 inches of water, so natural draft alone can’t meet this need. Because of this, systems with a high draft loss need mechanical draft tools, like fans. There are different types and styles of fans that can meet these needs and keep the airflow and draft at a good level.
Types of Draft Systems
- Natural Draft: Air flows into the furnace spontaneously, without any help from a machine.
- Mechanical Draft: To control the flow of gases and air, fans or tools are used.
To sum up, without the draft system, fuel does not burn properly so efficiently, energy is wasted, and pollution increases.
- Natural Draft: With this method, air flows into the furnace without the need for a machine or fan. This process is based on gravity and how the oven is built.
- Mechanical Draft: Fans and tools control the flow of air and gases in this system. This kind of draft comes in three different types:
- Balanced Draft: There are both forced and induced fans in this type, which keeps the flow of air and waste gases even and under control.
- Induced Draft: When this type is used, the fan is put in after the heater and pulls out the exhaust gases (smoke).
- Forced Draft: When this type of furnace is used, the fan is placed outside the furnace and forces fresh air into it.
In mechanical draft systems, different fans are used to manage the flow of smoke and air, which makes the boiler work well.
Thermal Power Plant Draft System: An Easy-to-Understand Guide
Thermal power plants, which use coal as fuel to make electricity, are a major source of energy around the world. The draft system is an important part of a thermal power plant for keeping the combustion, heat movement, and pollution under control. Let’s take this step by step.
This is a simple guide to the thermal power plant draft system. Thermal power plants, which use coal as fuel to make electricity, are a major source of energy around the world. The draft system is an important part of a thermal power plant for keeping the combustion, heat movement, and pollution under control. Let’s take this step by step.
1. Pulverising Coal: The First Step
The first step is to break up the coal. The first thing that a thermal power plant does is grind up coal. A Pulverizer is a machine that breaks down coal into fine dust or powder. This makes it easier to burn and more efficient. The coal from the Coal Feeder goes into the crusher, which turns it into powder. This makes sure that the coal goes all the way through and makes the most energy possible.
2. The main source of air flow (PA fan)
Pulverized coal needs to be moved to the oven by air. This is where the PA Fan (Primary Air Fan) comes in. It provides the main air that moves the finely ground coal into the oven through pipes. The PA Fan keeps the coal in the air, which makes it simple to get to the stove.
3. What Forced Draft Air (FD Fan) Does
In the burning process, more air is needed to keep the flame stable and make it stronger. As the FD Fan (Forced Draft Fan)** blows fresh air into the furnace, it burns fuel more efficiently. This fan sends extra air into the furnace, which keeps the burning process steady.
4. The combustion process: putting fuel on fire in the furnace
The Furnace is where the coal is burned. In the burner, finely ground coal and air mix, making very hot gases called flue gases. After that, these gases go through the machine that moves heat. Heat from the boiler powers the whole plant because of its high combustion temperature.
5. Heat Transfer Stages: Reheater, Superheater, and Economizer
Reheater, superheater, and Economizer are the heat transfer stages. We’ll talk about each topic in more depth in upcoming topics. The furnace’s flue gases go through a series of heat exchanges to get the most heat out of them:
- Reheater: This part raises the temperature of the waste gases, which keeps the steam hot.
- Superheater (SH): The superheater’s job is to heat the steam even more. The temperature and pressure of the steam rise as it goes through the Primary Superheater (Pri. SH) and then the Secondary Superheater (Sec. SH).
- Economizer (Eco): The economizer warms up water with the heat that is left over from the waste gases. This water that has already been hot helps make steam and saves energy.
6. Air Heater (AH): The Process of Pre-Heating
Fumes go to the Air Heater (AH) after going through the economizer. The air heater takes the heat that is still in the waste gases and moves it to the fresh air, heating it up first. This air is already hot, and the FD and PA fans send it back into the furnace. This makes the burning process even more efficient.
7. Ash Handling System: Fly Ash and Bottom Ash
After being burnt, ash stays in the oven and is split into two groups:
- Bottom Ash: This stuff settles at the bottom of the furnace and is taken out from there.
- Fly Ash: These small pieces of ash come out of the furnace with the flue gases and go through the Air Quality Control (AQC) system, where they are cleaned out and taken away.
The ash handling method separates the ash and makes it easier to deal with waste.
9. Getting rid of flue gases (ID Fan and Stack)
The ID Fan (Induced Draft Fan) pulls the flue gases that are still in the pipe after the fire. The stack safely releases these gases into the air. The height of the stack helps keep pollution down and lets gases spread out well.
Final Thoughts: A thermal power plant’s draft system is a well-organized and effective system that handles every step of the process, from burning coal to getting rid of ash and waste gas. The purpose of each fan and part is to improve combustion and heat movement while lowering pollution. This method makes it safe and easy to make electricity. This process gives you a good idea of how thermal power plants work and how they make energy. This method is very important for making electricity, which is needed in today’s industrial world.
Let’s talk about what the ID, PA, and FD fans do.
- PA Fan (Primary Air Fan)
- Role: The PA fan’s job is to move finely ground coal to the furnace. It brings in main air to move the finely ground coal and start the combustion process.
- Location: The PA fan is placed between the crusher and the furnace, which lets it send the coal-air mix straight into the furnace.
- Use: The PA fan brings coal pieces into the furnace to start the combustion process. It is the first source of air.
- FD Fan (Forced Draft Fan)
- Role: The FD fan brings in new secondary air, which makes the burning process more stable and effective. It brings air into the furnace under positive pressure, which keeps the burning process going smoothly.
- Location: The FD fan is outside the furnace and blows air straight into it. It is the main source of air for forced draft.
- Use: The FD fan improves the combustion process by supporting high-temperature combustion, which makes coal burn better.
- ID Fan (Induced Draft Fan)
- Role: The ID fan’s job is to move waste gases from the furnace to the stack (chimney). The exhaust system draws these fumes in and lets them out through the chimney.
- Location: The ID fan is located between the air heater and the stack. It moves combustion products through the system, which includes the air heater, economizer, and AQC system, so they can reach the stacks.
- Use: The ID fan makes the furnace’s pressure drop, which moves flue gases out of the house easily through the chimney and helps reduce pollution.
A List of Roles and Locations
- The PA Fan, or Primary Air Fan, is placed between the crusher and the furnace. It sends primary air with the coal that has been ground up to the furnace.
- The FD Fan, or Forced Draft Fan, is outside the heater and brings in fresh secondary air.
- ID Fan (Induced Draft Fan): This is placed between the air heater and the stack and pulls waste gases out to the stack to keep the pressure low.
Together, these three fans control the flow of gases and air in the furnace. This makes the burning process more efficient and less harmful to the environment.
What you need to know about the draft system is what I’m going to talk about.
Schedule for the vibration meter:
- Schedule for 10 to 15 days: Set the sound metre to go off every 10 to 15 days. This regular check shows how the fan’s bearings and blade are doing. Keeping an eye on changes in vibration helps find early signs of wear, so repair can be done on time and breakdowns can be avoided.
- Bearing and Impeller Monitoring: The shaking metre shows how healthy the bearings and impeller are, which makes sure the motor runs smoothly and safely. Any sound patterns that don’t seem normal can be early warning signs of failure.
PA Link (Primary Air Link):
- Role of the PA Link: The PA link sends main air to the fan and controls the flow of air and combustion. It keeps the air pressure and flow in the system steady, which is important for the fan to work well.
- Maintenance and Inspection: The PA link needs to be checked regularly to keep the airflow and pressure steady and to stop leaks in the system.
Understanding Fan Safety Factors
- Safety Margin: Fans are made with extra space to make sure the boiler’s performance stays steady. This extra space is very helpful in emergencies or other odd situations, like when the boiler needs more airflow or draft.
- Operational Conditions: Ash from fuels like coal can build up on heated surfaces, which makes more air flow necessary. With these safety gaps, fans can handle this extra demand when it comes up.
- Load Increase and Emergency Use: This extra fan capacity is used to meet the higher demand when there is a quick rise in the boiler’s load or an emergency need for more power.
- Additional Margins:
- Air/Gas Flow: Fans can handle an extra 15 to 20 percent more air or gas flow.
- Pressure Increase: They can handle a rise in pressure of up to 15% to 20%.
- Temperature Rise: They can also handle an extra rise in input temperature of up to 25°F.
These fan safety factors make sure that the boiler works well even when things go wrong, so the system doesn’t get interrupted.
What is a brush coupling?
- Role of Brush Coupling: The brush coupling links the motor to the fan shaft and helps move torque. It handles misalignments and absorbs shocks, which are important for the fan to work smoothly.
- Usage Area: Brush coupling is used in high-torque situations, like industrial fans and blowers, where there are a lot of shocks and misalignments.
Roller Bearing with Two Rows:
- Function of Double Row Roller Bearing: This bearing can handle heavy axial and radial loads and is effective for use in high-load situations.
- Usage Area: Industrial fans, blowers, and heavy-duty tools that need to handle a lot of weight and keep vibrations to a minimum use double-row roller bearings.
Each of these parts is very important to how the fan works, and they need to be inspected and fixed on a regular basis to make sure the fan works well and lasts a long time.
- NOTE: A VFD (variable frequency drive) is best for a 10 HP fan because it adjusts the fan’s speed according to the load, saving energy and reducing operational costs. The VFD provides a smooth start-stop function, which reduces stress on the fan’s mechanical parts and lowers maintenance costs.
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