Types of Conveyors in Thermal Power Plant

Transfer of coal in thermal power plant including carrying of coal from unloading point to the storage site. It may require one equipment or several depending on the site of the thermal power plant. The type of conveyors used for transferring the coal are listed below:

1. Belt Conveyor
2. Screw Conveyor
3. Bucket Conveyor
4. Grab Bucket Conveyor
5. Skip Hoists
6. Flight Conveyors

Belt Conveyors in Thermal Power Plant:

Belt Conveyors are very suitable means of transporting large quantities of coal over large distances. Belt Conveyors consists of endless belt made of rubber, canvas or balata running over a pair of end drums or pulleys and supported by series of rollers (known as idlers) provided at regular intervals. The return idlers which support the empty belt are plain rollers and are space wide apart.

The initial cost of this coal carrying system is not high and power consumption is also low. The belt conveyors are successfully used on inclination up to 20^o to the horizontal. The load carrying capacity of the belt conveyors may vary from 50 to 100 tonnes/hr and it can be easily transferred through 400 meters

Some of the advantages and disadvantages of belt conveyors are discussed below:

Advantages of Belt Conveyors:

• This is most economical method of coal transfer in medium as well as large capacity thermal power plants
• Using Belt Conveyors the rate of coal transfer can be easily varied by just varying the speed of the belt.
• The repair and maintenance of belt conveyors are minimum
• The coal over the belt can be easily protected from the wind and rain just by providing over-head covers
• The power consumption to carry the coal is minimum compared with other conveyors in steam power plant

Disadvantages of Belt Conveyors:

• It is not suitable for short distances and greater heights
• It cannot be able to carry the coal at greater heights and inclination is limited to 20^o.

Screw Conveyors in thermal power plant:

It consists of an endless helicoid screw fitted and driving mechanism is connected to one end of the shaft. Other end of the shaft is supposed in an enclosed ball bearing. The screw while rotating is through transfers coal from one end to the other. The diameter of screw varies from 15cm to 50cm and its speed varies from 70 r.p.m to 120 r.p.m as per the capacity required.

Some of the advantages and disadvantages of screw conveyor are given below:

Advantages of Screw Conveyors:

• It requires maximum space and is cheap in the first cost
• Screw Conveyor is most simple and compact
• It can be made dust tight

Disadvantages of Screw Conveyors:

• The power consumption per unit weight transferred in considerably high
• The length of feed hardly exceeds 30 meters due to torsional strain of the shaft
• The wear and tear is very high and therefore the life of the conveyor is considerably short compared with belt conveyors

Bucket Conveyors in Thermal Power Plant:

The conveyor is extremely used for vertical lifts. It consists of buckets fixed to a chain which moves over two wheels. The coal is carried by the buckets from the bottom and discharged at the top. The maximum height of elevator is limited to 30m and maximum inclination to the horizontal is limited to 60^o.

Grab Bucket Conveyor in Thermal Power Plant:

A Grab bucket conveyor lifts as well as transfers the coal from one point to the other. The grab conveyor uses a crane or tower to transfer the coal with a bucket. 3 cu meter bucket operating over a distance of 60 m transfers nearly 100 tonnes of the coal per hour

The initial cost of the machine is high but the operating cost is less. Its use of the transfer the coal is justified when other arrangements or other type of conveyors are not available

Flight Conveyor in Thermal Power Plant:

This type of conveyor is generally used for the transfer of coal when fitting of number of storage bins situated under the conveyors is required. It consists of one or two strands of chain, to which steel scrapers are attached. The scraper scraps the coal through a trough and the coal is discharged in the bottom of the trough

The advantages and disadvantages of Flight Conveyors are given below:

Advantages of Flight Conveyors:

• It requires small head room
• The speed of the conveyor can be regulated easily to suit the requirements
• It can be used for coal as well as ash transfer 

Disadvantages of Flight Conveyors:

• There will be excessive wear and tear due to scrapping action and therefore the life will be short
• The repair and maintenance charges are high
• Power consumption per unit of coal or ash transfer is considerably high due to dragging action