Advantages And Disadvantages Of Overfeed Stoker

In this article, I will share the advantages and disadvantages of using different types of overfeed stokers.


If you want to know more about the working principle of different types of overfeed stokers you should read the article below.


You might like this: Overfeed & Underfeed Stokers: Classification and Working Principles


It’s important to know the advantages and disadvantages of different types of overfeed stokers before you decide to use them in a combustion system.


Let me start with the travelling grate overfeed stokers.


Advantages of travelling chain grate stoker

1. Simple in construction.

The travelling chain grate stoker has simple construction simply because of the few parts that make it up.


The main parts of the chain grate stoker are the sprocket and the chain and the hopper.


And that is why its construction is simple.


2. No formation of clinkers.

Clinker is a hard deposit of waste on the chain that is resulted from the combustion of fuel.


Especially, if the fuel being used has high sulphur content then clinker formation is going to happen.


The clicker formation will result in the fire produce being dirty, growing thick, and burning evenly on the grate, a lot of smoke will be produced making it hard to produce quality heat for steam generation.


When a chain grate is in use this problem of the formation of clinkers is not experienced because it’s self-cleaning and the air is sufficiently distributed in the grate.


This is one of the advantages that makes chain grate stoker makes it preferable over other types of stokers.


3. Heat production rate can be controlled.

The aspect of heat production control is very significant when it comes to steam generation.


The amount of heat produced by a stoker has a great influence on the pressure of steam that will be produced.


If higher pressure steam is needed, the energy produced by the fuel will have to be increased too and vice versa.


With the travelling chain grate stoker, the heat produced can be controlled by either increasing the speed of the chain or reducing it.


4. Low purchase cost and maintenance.

The cost of the initial purchase of a chain grate stoker is cheaper and this makes it economical.


Maintaining a chain grate stoker is cheaper and easier since it has self-cleaning mechanisms which most stokers don’t.


The only main maintenance it requires is the oiling of the chain and inspecting and replacing the wheels if they aren’t in good working condition.


5. Heat production at a high rate.

The heat production rate is important when it comes to the generation of heat.


The quality of steam produced is directly proportional to the rate of heat produced.


With the complete combustion that is offered by the chain grate stoker heat production is of a high rate.


A maximum burning rate of about 1.4 to 1.5MW/m2 can be obtained from the chain grate stoker.


Disadvantages of travelling chain grate stoker

1. Not suitable for boilers of higher capacity.

This is the first disadvantage of travelling chain grate stoker. The chain grate stoker is not suitable for boilers with higher capacity.


The main reason why it’s not suitable for higher-capacity boilers it’s because the amount of coal it burns is lower.


If the amount of coal that the chain grate can burn is little then the amount of heat produced is going to be lower.


Lower production of heat will only result in the production of poor-quality steam.


And that is why the chain grate stoker is not suitable for boilers of higher capacity.


2. Fuel lost with ashes is experienced.

The loss of fuel is usually experienced in chain grate stoker since it involves travelling of chain with the coal on top of it.


Some particles of the coal will be disposed of together with ashes especially when the chain is moving so fast and some coal is not burnt on the grate.


3. Limitation on preheated air.

Preheated air is essential when it comes to combustion. Significantly, the air that is used in combustion is preheated.


When air is preheated before being supplied to the furnace it increases combustion stability and proper combustion of poor-quality fuel is noticed.


You can learn more about air preheaters in the article below.


You might like this: Air Preheaters in Steam Boilers: Function, Types and Working Principles


On the chain grate stoker, the maximum temperature that the preheated air can attain is 1800C, which means that the thermal energy of the heat produced will also be limited.


The higher the temperature of the preheated air the higher the rate of combustion and improved stability of the combustion system.


Advantages of spreader stoker

1. A variety of coal can be used.

A variety of coal can be burnt in this type of stoker because of the spreading action that allows a sufficient mixture of air and coal.


This ensures that the spreader stoker doesn’t require specific and expensive fuel.


2. Clinker formation is reduced.

Clinkers tend to lower the quality of heat produced by the stokers.


In spreader stoker, the formation of clinkers is reduced because the fuel is spread.


Most of it is burnt in the air, while only a small volume falls on the grate.


You should know that large amounts of fuel being on the grate is what contributes to clinker formation apart from the sulphur content in the coal.


3. Flexible to load changes.

There is flexibility in the amount of coal that can be burnt in the spreader stoker.


Most fuel is burnt when it’s in the air, which means another volume of coal can be used on the grate.


Let us say, the spreader stoker grate can hold 95% of the coal, and 60% is burnt in the air only 35% of the coal can fall on the grate.


This means there is another room for about 60% coal on the grate.


It’s not like with chain grate stoker where the calculated load is supposed to be fed on the grate since overloading can bring wear issues on the chain.


And this is one of the advantages that spreader stoker has over other stokers.


4. Rapid combustion of the fuel.

Rapid combustion of the fuel is one of the advantages that the spreader stoker has.


This is possible because of the proper mixing of the coal and sufficient air flowing through the coal.


The addition of air from the bottom of the grate facilitates rapid combustion which leads to a high rate of heat production.


Disadvantages of spreader stoker

1. Sufficient collection and control of ashes are needed.

When it comes to ash control this is a problem that is experienced with spreader stoker.


Since most of the coal is burned while suspended in air, the ash problem is going to be chronic.


You have to remember that the air coming from the bottom of the grate to is going to keep on dispersing the ash produced.


That is why sufficient control of the ash produced is going to be needed.


When we talk about the collection of ash, a big pit is going to be needed because the production of ash happens on the grate and from the coal burnt while suspended in the air.


2. It needs a particular size of coal.

The size of coal needed in the spreader stoker has to be able to pass through the feeder and spreader.


If the coal is too big, then passing through the feeder and spreader is going to be an issue.


Big chunks of coal will block the feeder since the blades won’t be able to move the coal.


This will prevent combustion from taking place which is a huge issue when it comes to steam generation.


The Spreader stoker needs a particular size of coals to be used. The coal has to be checked and verified that it can work in the spreader stoker.


Final thoughts


Now you know which stoker you should go for by the points I have explained in this article.


Before you choose a stoker you have to know its advantages and disadvantages.


Purchasing the wrong stoker is going to cost you in so many ways.


If you have any questions leave a comment.


See you in my next article.


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