Pulverized
coal storage in Bunker
Periodically a power plant may encounter the situation
where coal must be stored for sometimes in a bunker, for instance during a
plant shut down. The bunker, fires can occur in dormant pulverized coal from
spontaneous heating within 6 day of loading. This time can be extended to 13
days when a blanket of CO2 is piped into the top of the bunker. The perfect
sealing of the bunker from air leakage can extend the storage time as two months
or more. The coal in the bunker can be stored as long as six months by
expelling air from above the coal with the use of CO2 and then blanketing of
all sources of air. A control system used for storing the pulverized fuel in
bunker is shown in figure.
Figure : Control system used for
storing the pulverized coal with the use of CO.
pulverized
coal handing system and Pulverized Fuel
Handling
System:
Two methods are in general use to feed the pulverized fuel
to the combustion chamber of the power plant. First is ‘Unit System’ secoand is
‘Centralor Bin System ‘.
In unit system, each burner of the plant is fired by one
or more pulverizers connected to the burners, while in the central system, the
fuel is pulverized in the central plant and then disturbed to each furnace with
the help of high pressure air current. Each type of fuel handling system
consists of crushers, magnetic separators, driers, pulverizing mills, storage
bins, conveyors and feeders.
Figure: Pulverized coal handling plant showing all
required equipment for unit and central system.
The arrangement of different equipment required in both
systems is shown in figure. With the help of a block diagram.
The coal received by the plant from the mine may vary
widely in sizes. It is necessary to make the coal of uniform size before
passing the pulverizer for efficient grinding. The coal received from the mine
is passed through a preliminary crusher to reduce the size to allowable limit
(30 mm). The crushed coal is further passed over magnetic separator which
removes pyrites and tramp iron. The further equipment through which coal is
passed before passing to pulverizer are already shown in figure.
a) Ball mill pulverizing
Ball and Race mill pulverizing
a)
Ball Mill
A line diagram of ball mill using two classifiers is shown
in figure. It consists of a slowly rotating drum which is partly filled with
steel balls. Raw coal from feeders is supplied to the classifiers from where it
moves to the drum by means of a screw conveyor. As the drum rotates the coal
get pulverized due to the combine impact between coal and steel balls. Hot air
is introduced into the drum. The powdered coal is picked up by the air and the
coal air mixture enters the classifiers, where sharp changes in the direction
of the mixture throw out the oversized coal particles. The over-sized particles
are returned to the drum. The coal air mixture from the classifier moves to the
exhauster fan and then it is supplied to the burners.
Ball
and Race Mills
Figure: shows a ball and race mill
In this mill the coal passes between the rotating elements
again and again until it has been pulverized to desired degree of fineness. The
coal is crushed between two moving surfaces, namely, balls and races. The upper
stationary race and lower rotating race driven by a worm and gear hold the
balls between them. The raw coal supplied falls on the inner side of the races.
The moving balls and races catch coal between them to crush it to a powder. The
necessary force needed for crushing is applied with the help of springs. The
hot air supplied picks up the coal dust as it flows between the balls and races
and then enters the classifier. Where oversized coal particles are returned for
further grinding. Where as the coal particles of required size are discharged
from the top of classifier.
Advantages:
i) Lower capital cost
ii) Lower power consumption
iii)
Less
space required.
iv) Less weight
Related Topics
Privacy Policy, Terms and Conditions, DMCA Policy and Compliant
Copyright © 2018-2023 BrainKart.com; All Rights Reserved. Developed by Therithal info, Chennai.