Chemical Engineering March 2014 - 54

light and alarm. If the feed is continued,
the bin will overfill and the
solids will back up into the conveying
line, causing pluggage.
If a conveying line has diverter
valves, the position of the diverter
valves must be set up in a " through "
mode or in a " divert " mode before
starting the blower and the solids
feed. If the destination bin or silo
is changed for the next conveying
cycle, the diverter valves position
must be changed before the conveying
blower and the rotary valve
are started.
Graphic control panel. In the
central control room, a graphic
panel (Figure 1) should be provided
to show a schematic diagram
of the conveying system, starting
from the air supply blower
to the receiving bins or silos.
This panel should have the following
lights:
* Run lights to indicate the operaing
status of the blower motor and
the rotary-valve motor
* Position lights to indicate the divert
or through position of the diverter
valves
* Position lights to indicate the low
and high levels in the receiving
bin or silos
* Run lights to show the operating
status of the bin vent filters/dust
collectors
Figure 1 shows in one glance how
the conveying system has been set
up, and the operating status of all
components of the system.
Monitoring conveying air pressure.
Conveying pressure is a key
parameter in pneumatic conveying
systems. It must be regularly
monitored from the control room
as well as locally at the blower.
For measurement of the conveying
pressure, a locally mounted pressure
indicator should be provided at
the blower discharge. If the blower
is located far away from the rotary
valve, a second pressure indicator
should be provided just upstream of
the rotary valve.
These two measurements will
show the overall pressure being
provided by the blower, and the
pressure drop in the conveying line.
In addition to local pressure indicators,
these pressure measurements
should also be provided in the
control room using pressure
transmitters.
Digital pressure indicators are
better than the analog type, because
they can show the pressure much
more accurately, up to two decimal
points. These pressure measurements
should be archived on the
computer so that historical data are
available if needed in the future.
An alarm for high blower-discharge
pressure should also be provided in
the control room.
Monitoring blower discharge air
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ChemiCal engineering www.Che.Com marCh 2014 55
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Chemical Engineering March 2014

Table of Contents for the Digital Edition of Chemical Engineering March 2014
