In this article, I will share a central system of pulverized coal firing overview, its components, the working principle and the advantages and disadvantages of using this coal firing system.
In my previous article, I talked about the unit system or direct system method of firing pulverized coal.
You might like this: Pulverized Coal Firing: Unit or Direct System, Components, Working Principle & Advantages
When it comes to the operation of these two systems; the unit and central are almost similar except for the fact that the central has more components and the route of coal transportation isn’t direct.
Another name for the central system that is used to fire the pulverized coal to the furnace is called Bin.
So, if you come across bin pulverized coal firing don’t be surprised by that term at all.
Without wasting time, let me share what you should know about the central system pulverized coal firing.
Main Components Of Bin Or Central System
The main components of the bin or central firing system are as follows;
Raw coal bunker; it’s where the fresh coal is fed to the system. The coal that is fed here is not yet dried or pulverized.
Dryer; it’s where the coal that is to be grinded is dried up using hot air. The hot air used in drying the coal can be either from the flue gases, air preheaters or bleeder steam.
Fan; it’s used to drive the coal away from the dryer after it has been used to dry up the coal.
Removal of the cool air from the dryer by the fan creates a vacuum giving room for another hot air to occupy the place and dry up the new volume of raw coal from the bunker.
Pulverizing mill; it’s used to crush and grind the dried coal from the dryer.
Exhaust fan; it’s used to remove the pulverized coal from the pulverized mill to the cyclone separator.
Cyclone separator; it’s used to remove the transporting air from the coal.
When the exhaust fan is used to extract the pulverized coal from the pulverizing mill, additional air is added to the coal.
The air has to be removed to allow a fresh volume of air to occupy the pulverized coal.
It’s the work of the cyclone separator to do that.
After the transporting air has been removed from the pulverized coal in the cyclone separator, the air returned to the pulverizing mill to keep on transporting the rest coal that will be produced back to the cyclone separator.
Conveyor; it’s used to convey the coal from the cyclone separator to the pulverized coal bunker (bin).
Feeder; it’s used to feed the pulverized coal to the burner from the pulverized coal bunker (bin).
Burner; it’s used to eject the pulverized coal to the furnace.
Furnace; it’s where the pulverized coal is burnt after being ejected by the burner under high pressure.
Now that you know the main components of the central system or bin, you can easily have an idea of the working principle of the entire system.
Nevertheless, let me share the working principle so that you can know how each unit performs its work and how they are connected.
Working Principle Of Central System Or Bin Of Firing Pulverized Coal
This is how the central system works; the raw coal is fed in the raw coal bunker where it’s then directed to the dryer by gravity. In the dryer, the coal is dried up by the hot air coming from the air preheater, bled steam or flue gasses.
As long as the air has enough heat energy to dry up the coal, it can be used as a drying agent.
After the hot air dries up the coal, it’s cooled. It is then taken out of the dryer via an exhaust fan which directs the cold air out through the vent.
This is to allow another volume of hot air to occupy the place and dry up another raw volume of coal that will be fed to the dryer.
The dried coal is sent to the pulverizing mill where it’s crashed and grinded.
The pulverized coal is sent out of the pulverizing mill by the exhaust fan connected to the outlet of the pulverizing mill. The exhaust fan takes the pulverized coal to the cyclone separator.
The cyclone separator separates the transport air from the powdered coal and passes the pulverized coal to a conveyor. The transport air removed from the coal is then returned back to the pulverizing mill via a piping system.
The conveyor sends the pulverized coal to the pulverized coal bunker (bin) where the coal is fed into the feeder.
It’s in the feeder where the coal is mixed with primary air via a fan. The feeder then takes the coal to the burner using the air pressure from the fan.
In the burner, secondary air is added and then it’s ejected to the furnace under high pressure and burns while suspended in the air.
This is the detailed working principle of the central system or bin.
It’s kinda similar to the unit system or direct, the only difference is the addition of a cyclone separator, conveyor and pulverized coal bunker (bin).
Also, the connection of the components differs from the unit system.
Advantages Of Using Central System Pulverized Coal Firing
1. The coal is grinded at a steady rate.
The coal is grinded at a steady rate without considering the boiler feed.
This means that the boiler feed doesn’t affect pulverizing of the coal in the system.
The main reason why this happens is simply because the connection of pulverizing mill is not directly to the burner.
So, if the boiler feed rate increases or decreases, the process of pulverizing the coal is not affected by any chance.
2. The system reserves some of the pulverized coal.
The pulverized coal from the conveyor is first fed into the pulverized coal bunker (bin) before it’s fed into the furnace.
The feeder controls the feeding rate of the pulverized coal into the furnace.
Some pulverized coal will always remain in the bin which is essential in case the entire system stops running.
If the system breaks, there will be some pulverized coal left in the bin that can be used as the system is being repaired.
This system ensures that the processes in the power plant go on no matter what happens with the pulverizing mill.
This is different when you compare it to the direct or unit system.
In a direct system or unit, if the pulverizing mill fails to work, so is the furnace because there is a direct connection and there is no bin to store some of the pulverized coal.
3. Any capacity of the pulverizing mill can be used.
A boiler of any capacity can use a small pulverizing mill if it’s the central system in use.
One of the reasons that make the central system applicable to any given boiler capacity; is that the rise in demand for pulverized coal is always met by the reserved coal in the bin.
So, even if the capacity of the central system is lower, it can still be used with a boiler of larger capacity because of the bin.
The trick is to start the pulverizing mill before the boiler is started. This is to ensure that there is plenty of reserved pulverized coal in the bin.
Once the bin is full of reserved coal, the boiler can be started as the pulverizing mill keeps on working and adding up the pulverized coal into the bin to keep the bin full.
Disadvantages Of Using Central System Pulverized Coal Firing
1. The initial cost is higher.
The central system is amazing for use because of how it’s designed but the issue is that it has a higher initial cost.
The power plant will have to invest so much money in purchasing the entire system.
If it’s to be designed, it has many components compared to the direct system, which will add to the cost of operation.
So, if the budget in the power plant is tight, it will be hard to install a central system pulverized coal firing.
2. It has complicated coal transportation.
The transportation of coal in the central system is complicated. This will be a problem when the system is clogged.
It will be hard to figure out where the system is blocked. It will force operators to destroy the entire system to find out the fault in the transportation system.
With the direct system, it will be easier to find faults in transportation because it’s only one route.
3. It requires more space for installation.
The number of units in the central systems is more compared to the unit system.
This means that it will require more space to be installed.
So, if the space in the power plant is limited, the installation of the central pulverized coal firing system will be hard.
And there is no way you can eliminate some of the units because they contribute to the efficiency of the system.
Lastly…
I have shared the summary of the central system pulverized coal firing but I am sure there is so much more to learn about this system.
Do your research if you want to use this content for business purposes or a research project.
Thanks for reading, if you have any questions, recommendations or any additional points leave a comment.
Thanks for reading, see you in my next article.
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