Pellet mill

A pellet mill, also known as a pellet press, is a type of mill or machine press used to create pellets from powdered material. Pellet mills are unlike grinding mills, in that they combine small materials into a larger, homogeneous mass, rather than break large materials into smaller pieces.

Pellet mill is a device for granulation (pelletizing, pelletization, ozernenie, agglomeration) of finely ground materials, contributing to an increase in productivity of sintering machines, or the production of raw pellets. Can be used to obtain fuel pellets (pellets) from shredded wood waste; for pelleting feed for livestock, etc.

There are many types of pellet mills that can be generally grouped into large-scale and small-scale types. According to the production capacity, pellet mills also can be divided into flat die pellet mill and ring die pellet mill.

There are two common types of large-scale pellet mills: flat die mills and ring die mills. Flat die mills use a flat die with slots. The powder is introduced to the top of the die and as the die rotates a roller presses the powder through the holes in the die. A cutter on the other side of the die cuts the exposed pellet free from the die. In the ring die there are radial slot throughout the die. Powder is fed into the inside of the die and spreaders evenly distribute the powder. Two rollers then compress the powder through the die holes. Two cutters are used to cut the pellets free from the outside of the die.

Large scale pellet mills are usually used to produce animal feed, wood pellets, and fuel pellets for use in a pellet stove.

Small-scale mills are usually variations of screw presses or hydraulic presses. The same basic process is used for both types. A die, also known as a mold, holds the uncompressed powder in a shaped pocket. The pocket shape defined the final pellet shape. A platen is attached to the end of the screw (in a screw press) or the ram (in a hydraulic press) which compresses the powder.

Some platens are heated to speed up the time it takes and improve the overall structure of the pellet. They may also have water ports for quick cooling between uses.

Characteristics of granulators
drum pelletizer

drum length – from 8 m
diameter of the finished product – from 10 mm
drum slope – from 2 °
drum rotation speed – from 7 rpm
productivity – from 40 t / h
peripheral speed – from 25 m / min
diameter of the granulator – from 2.8 m
granulator length – from 11 m

dish-shaped (cup) granulator

Bowl angle – 40 – 60 °
productivity – from 30 t / h
diameter of the plate – from 3 m
plate height – from 0.8 m
plate rotation speed – from 3 rpm
tilt angle – from 45º

The use of granulators
In industry, granulators are used to produce raw pellets from finely divided iron ore concentrates in the pelletizing plants .

Drum pelletizer for pellets set in a closed loop with a roar and the undersize product (fines) is sent back to the drum in recycling, which accelerates the formation of pellets. The optimum amount of circulation load is 100-150% of the performance of the pelletizer.

Bowl pellets are used for pelletizing of one-component well-combining charges with constant physicochemical and mineralogical properties. In this case, pan-type pelletizers can produce pellets classified by size, which makes it possible to conduct the process without circulation load and screening. This simplifies the circuit diagram of the apparatus and the layout and technological design solutions for the building of the pelletizing workshop.

Pelletizing tools
Drum granulator
conical screen
ring gear
belt conveyor
console feeder
cleaning knives
spiral scraper for sticking

Dish-shaped (cup) granulator
cleaning knives

Classification of granulators
Granulators can be classified according to the device and principle of action into the following types:

drum granulators
dish-shaped (cup) granulators
cone granulators
multi-cone granulators
belt granulators
vibration granulators

One of the more common applications is to produce KBr pellets which are used in infrared spectroscopy applications.

Animal feed pellets are usually a mixture of dry powdered feedstock, such as flour, sawdust, or grass, and a wet ingredient, such as molasses or steam. Feedstocks for pellet mills can sometimes break down and then re-form, or polymerize, under the extreme heat and pressure of the pellet mill.

Source from Wikipedia