ID,FD,PA FANS FOR BOILER IN THERMAL POWER PLANT PLAN AND BRIEF DESCRIPTION OF FANS

Till my last dispatch I completed the topics of Boiler  structure , Boiler Pressure Parts , Rotary air preheater as major equipment . I have discussed about the plans and erection sequence of the same . Now I will discuss about the fans ( ID , FD and PA) .I am receiving number of e-mails about my dispatches .The questions  are mainly about erection sequences ,clarification of the pictures , suitability of my erection sequence with their project and also about construction equipment. I

request all the readers to read relevant blogs of my 87 dispatches and he will certainly get the answer.

If there is any doubt I will be there to help you out.

Erection sequence of FANs differs with the layout of the plant. According to Mill position side ,rear
or front Fan erection  sequence differs. These are true for FD ,PA fans only. ID Fan is independent of
Boiler erection . An e-mail received from one of the reader about the commencement of civil work for foundations.

First of all we should not consider only fans in that area. There will foundations for Duct support
between Boiler Outlet Flange to ESP , Foundations for Transfer point structures , foundations for
Mill Reject System silos.If foundations require piling then piling and pile cap to be completed
with boiler foundations. If pile cap drawings are not available then pile cap can be  done afterwards.
But then pile cap to be carried out one by one. It has been seen that this type of job leads to delay
due to massive excavation for individual fans.This excavation can only be started when Boiler supporting structure erection completion ( ceiling Girder erection , rear structure erection and air heater  structure erection completion). There should be alternate route for feeding second Pass Pressure Part
material feeding . Civil works for other foundations are to completed with fan foundations . Minimum two heavy duty crane ( 250 MT) capacities will be placed in boiler rear to carry out erection work of Boiler and CHP.Individual fan erection time cycle is around three months to four months. During this time boiler 2nd pass erection ,ducting above air heater , air heaters , Eco handling structures , ESP side inlet nozzle , Gates and dampers of ducting will also be required for erection completion. Therefore this area is very important regarding interfaces are concern and close co-ordination and monitoring are required .

Besides ID ,FD and PA there are two important fans are there one is seal air fan and other is scanner fan. A brief description is given below.
                                                               FANS FOR POWER PLANT

-Supply air for combustion in the furnace and for evacuation of the flue gases formed from the combustion.

-Maintain Balanced Draft inside the furnace.

-Supply air for cooling of equipments working in hot zones.

-Supply air for sealing of gates, feeders & mills bearings etc.

-Air used for combustion is divided into 2 parts:

1.Primary Air

Portion of total air sent through mills to the furnace. This air dries the pulverized coal and transport it to the furnace for combustion.

2.Secondary Air

Large portion of total air sent to furnace to supply necessary oxygen for the combustion.

Types of Fans  :- 1. Axial Fan with two subgroup as i) Impulse ii) Reaction.

2. Radial fans or Centrifugal fan. ( Single suction or double suction).

                                                FD FANS

Supplies secondary air to the furnace through APH to assist in combustion.

Supply total air flow to the furnace except where an independent atmospheric P.A fan is used.

Provides air for sealing requirement and excess air requirement in the furnace.

Axial fan-reaction type with blade pitch control is use in the Pulverized fired boiler(210/250/500 MW).

                                                                    PA FANS

Supply high pressure primary air through APH needed to dry & transport coal directly from the coal mills to the furnace.

Primary air for mills is divided into cold & hot primary air.

Axial fan-double stage-reaction type with blade pitch control is use in the Pulverized fired boiler(210/250/500 MW).

                                                                    ID FANS 

Suck the gases out of the furnace and throw them into the stack by creating sufficient negative pressure in the furnace (5-10 mmwc) in the balanced draft units.

Located in between the ESP and Chimney in the flue gas path.

Radial Fans -double suction-backward curved vane with inlet guide vane(IGV)control and VFD control is use in all boilers

Handles large volume hot dust/ash laden flue gas (temp up to 150 deg C) from furnace and all leakages occurring in the system till the inlet of the fan.

Overcome the pressure drop inside the furnace, Super heater, Re -heater, Economiser, Gas ducting & ESP.

Consumes max. power in all boiler auxiliaries as it handles the large volume and heavy pressure drop of the flue gas.

                                                               SCANNER AIR FANS 

Scanner Air Fan is belong to Centrifugal Fan category.

Supply cooling air to all the flame scanners at different elevations housed in the furnace for sensing flame.

A.C scanner fan boost the pressure of cold secondary air from F.D fan discharge duct in normal operation.

D.C scanner operates only in case of a.c power failure and sucks air directly from the atmosphere.

                                                                     SEAL AIR FANS

Seal Air Fan is also belong to Centrifugal Fan category.

Supply seal air at a pressure higher than system or equipment pressure.

Supply seal air to raw coal feeders, mills bearings, gates etc

Seal fan either boost the pressure of cold secondary air from F.D fan discharge duct or takes air directly from the atmosphere in normal operation.

In my next part i will provide erection sequence of three major fans.

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