Application Guide

63-706243
Boiler Flue Gas-Induced Draught (ID) Fan (See Fig. 52)
Micronik 100
Boiler #3
M
T
Boiler #2
M
T
Boiler #1
M
T
PS
Common Flue
Inverter
Chimney/Stack
RST
PG
MONPARREFBTNS
RUNREADY FAULT
Honeywel
l
Fig. 52. Boiler flue gas ID fan application.
Application Description
Traditionally a damper in the common flue from all boilers is controlled by a static pressure sensor located before the ID fan.
Individual dampers for each boiler are located in their own flue, these dampers close when the boiler is off line to prevent
airflow through the boiler which can cause condensation and corrosion.
The common flue gas static pressure sensor detects the change in static pressure when the individual dampers close and
modulates the common damper to prevent the induction of too much air into the on-line boilers. Only when all the boilers are on
full load will the dampers be fully open.
Fitting a VFD to control the speed of the main ID fan will enable more precise control of the static pressure within the flue, thus
reducing losses and preventing excess air flow through the on-line boilers. Thereby, matching the fan speed to the exact static
pressure requirement, overcoming the need for the dampers, increasing the efficiency of the boiler and reducing electrical
energy used by the ID fan.
Other Applications
— Process furnaces (metal refining).
— Hospitals.
— Incinerators (waste burning).
Benefits
— Reduced electrical energy.
— Prevents too much air from passing through
on-line
boilers, thus improving combustion efficiency.
VFD Features Used
— Power fail recovery.
— Auto restart on trip.
IMPORTANT
Careful commissioning is required to ensure efficient combustion is maintained and that emissions are kept under
control.