Open-Circuit and Closed-Circuit Grinding - Size Reduction Operations - Mechanical Operations - Chemo Concept

Most of the size reduction equipment produces products of various sizes. This means from grinding we get products of a size range.

According to equipment and size reduction techniques used, product size range varies.

Now to get products with low size differences, a screen can be used which separates bigger size particles from smaller or desired particles so we can send that bigger particle back to the crushing machine.

From this idea, Two different types of crushing techniques are developed and utilized in industries called Open-Circuit Grinding and Closed-Circuit Grinding, which we will learn in this article.

So let's define both mechanisms of grinding.

Open-Circuit Grinding

In the open-circuit grinding mechanism, Feed is introduced to the size reduction equipment. After size reduction, products are directly sent to another unit without any return of oversize particles back to size reduction equipment.

The open-circuit crushing mechanism is also called once though the type of crushing machine which means material passes only once through the machine will never be returned after it leaves the machine.

This type of crushing mechanism is mostly used with size reduction equipment which provides products with satisfactory size.

Open-Circuit Grinding can also be used for more than one grinding equipment arranged in series or parallel without the use of any classification equipment.

In short, the final product of this type of grinding never returns back to the mill.

Advantages of Open-Circuit Grinding

• Simple operation: As the product leaves the mill is not returned back to the mill or any type of classification is done on the product. This makes the operation very simple.
• Minimum Equipment Requirement: This type of grinding mechanism doesn't require a classifier to separate oversize and arrangement, sending oversize back to the mill so a lower amount of equipment is required. 

Disadvantages of Open-Circuit Grinding

• Wide range of product sizes: Products of Open-Circuit grinding are non-uniform and may contain a wide range of product sizes.

Closed-Circuit Grinding

In a closed-circuit grinding mechanism, Feed is introduced to the size reduction equipment. After size reduction, products are sent to classifying equipment that separates oversize particles from desired size particles, and oversize particles are sent back to crushing equipment for further size reduction.

This type of crushing machine is used when uniform size particles are required in a product.

For more than one crushers arranged in series or parallel can also operate in the closed-circuit grinding mechanism by providing classifying equipment after the product stream of last crushing equipment or intermediate classification can also be done to remove undersize particles.

In short, the final product of this type of grinding is screened to remove oversize particles from fines so oversize particles are recycle back to the crusher.  

There are many advantages and drawbacks to this type of grinding scheme.

Advantages Closed-Circuit Grinding

• Higher Capacity, lower power requirement per unit amount of material, and no over-grinding of fine particles: As undersize particles can be removed intermittently after any stage, more amount of feed can be fed to the machine. Also, this reduces power requirements for crushing in further stages. And as fines are removed from feed which prevents fines from over-grinding.
• No coarse particle in the product: As all the coarse particles are sent back, there is very little chance of getting coarse particles in the product.

Disadvantages Closed-Circuit Grinding

• More equipment is required for the operation which means higher capital investment is required to install this arrangement.

Open-Circuit Grinding vs Closed-Circuit Grinding

Open-Circuit Grinding	Closed-Circuit Grinding
The final discharge of the product is sent to the next unit directly, coarse particles are not sent back for further size reduction.	The final discharge of particles is classified and coarse particles are sent back for further size reduction.
No need for classification equipment, less equipment is required.	Classification equipment required, more equipment required.
Suitable for smaller reduction ratio	Suitable for large reduction ratio
May encounter over-grinding of fines	No over-grinding of fines because they can be separated early.
Higher power requirement per unit amount of material fed	Lower power requirement per unit of material fed
Simple operation	Relatively Complex Operation
Relatively low capacity	Relatively high capacity
More energy is required for crushing if more than one crushing stages are there.	Less energy is required for crushing.
Wide product sizes (Non-uniform product size)	Narrow product sizes (Uniform product size)
Chances of having coarse particles in the product stream	Very fewer chances of having coarse particles in the product stream