Pulverized Coal Firing: Unit or Direct System, Components, Working Principle & Advantages

In this article, I will share the unit system that is used in the firing of pulverized coal, its components, working principle and its advantage.


Another name for the unit system is the direct system; this is just a system that is used in feeding the pulverized coal to the furnace.


It’s just like the hand and mechanical firing when you don’t use pulverized coal.


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Different firing methods have to be used to feed the pulverized fuel to the furnace because the normal mechanical and hand firing won’t work.


And that is why it’s important to know how the unit system firing of pulverized coal works.


Now that you know what unit system/direct system is, it’s time to go deeper for you to understand how it works.


Before you know how it works, there are components that you need to know for you to connect how this machine works.


Main Components Of Unit System or Direct System

For the unit system or direct system to be functional these are the main components that should be used;


Raw coal bunker; It’s the place where the coal that is not grinded is fed before it’s taken to the feeder.


The raw coal bunker should be bigger enough to handle the bigger chunks of coal.


The feeder; it’s where the coal to be pulverized is fed to be dried up before being taken to the pulverizing mill.


For the coal to be grinded, it has to be completely dried. In the feeder, hot air is supplied to dry up the coal.


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The hot air can be from air preheaters, bled steam or the hot air recovered from the furnace due to the initial burning processes.


Heat can be recovered from the furnace and be used in drying up the raw coal from the bunker.


Pulverizing mill; it’s used to crush and grind the raw coal from the feeder.


Fan; it’s connected to the pulverizing mill, and its main function is to blow the pulverized coal away from the mill to the burner.


This helps to move the pulverized coal to the burner and creates room for raw coal to be fed into the pulverizing mill.


The burner; It’s where the pulverized coal is mixed with secondary air. The burner then ejects the pulverized coal with pressure to the furnace where it’s burnt.


The furnace; it’s where the pulverized coal is burnt producing heat energy needed for the processes in the power plant.


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Working Principle Of Unit System Or Direct System Of Firing Pulverized Coal

This is how the unit system of firing pulverized coal works; the raw coal is fed into the bunker where it drops directly to the feeder by gravity. In the feeder, the raw coal is dried up and prepared to be crushed and grinded.


The coal is dried up by hot air that can be from the air preheater, flue gasses or the hot air recovered from the furnace.


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After the raw coal has been dried up it’s directed to the pulverizing mill via a conveying system.


In the pulverizing mill, the coal is crushed and grinded, and primary air is added by the fan connected to the pulverizing mill while the grinding and crashing are ongoing.


When the grinding and mixing of the pulverized coal with primary air is done, it’s then blown to the burner where secondary air is added.


This is to ensure that the coal is correctly mixed with sufficient air to facilitate complete combustion and it also creates proper turbulence.


This also helps the burner to eject the pulverized coal into the furnace with considerable pressure.


The pulverized coal is then ejected to the furnace like a gas and it burns while suspended in the air.


Preheated air is also supplied to the furnace to ignite the incoming pulverized coal.


That is how simple the working principle of the unit system is. It’s called a unit system because the entire firing system constitutes of individual components that help fire the pulverized coal.


Advantages Of Using Unit System Pulverized Coal Firing

There are several benefits of unit direct system or unit system pulverized coal firing.

These are the advantages of using unit system pulverized coal firing;

1. The system is cheaper.

The unit system or direct system is cheaper compared to the central system pulverized coal firing.


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This is advantageous because it reduces the cost of operation in the power plant.


It’s cheaper to run a cheaper system since it doesn’t need complex maintenance or repairs.


2. The system is simpler in design and construction.

The system of firing pulverized coal is simple in design and construction and that is why it’s more advantageous than any other system.


It only constitutes of several components that are installed in certain order thus the name unit system.


A machine which is simpler in design and construction offers an easier way when it comes to maintaining and running it.


This means that experts are not needed to operate this system of firing pulverized coal.


This saves the power plant money and time.


3. There is direct control of combustion.

There is direct control of combustion since the pulverized coal is fired directly from the pulverizing mill and then to the burner.


If there is a need to reduce the temperature of the furnace, the only thing that can be done is to reduce the amount of pulverized coal that is supplied to the burner.


Also, the feeding rate can be easily controlled because of the direct connection.


This is essential for the safety of the personnel, controls the usage of pulverized coal and keeps the operation smooth.


If there is a decrease in the amount of heat energy produced from the furnace that issue can be easily be traced because the system is direct.


4. The coal transportation system is simple

The coal transportation system is simple because it moves from one unit to another within the system.


There is no complicated piping system needed to convey the pulverized coal from one point to another.


This saves time when it comes to construction and maintaining the entire system.


The coal transportation system being simple also reduces the chances of the piping system being clogged.




What I have shared with you in this article is just a summary of the unit system pulverized coal firing.


If you want to learn more about the factors that influence its efficiency you will have to do some research on that.


With this piece of information, you have an idea of how these systems work, I hope you enjoy reading it.


Thanks for reading, see you in my next article. If you have any requests or suggestions consider leaving your comment.


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  3. Advantages Of Cleaning Coal (Dewatering)
  4. Conditions For Proper Burning (Combustion) Of Fuel
  5. Steam Power Plant: Introduction, Components And Working Principle

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