AUXILIARY PROCESS COMPONENTS(OF BOILER)

Auxiliary components are the components or parts that will be added in the system for additional help and support.

Boiler is a device which generate steam at predefined temperature and pressure which may be used for power generation. It is designed to transmit heat produced by burning of fuel to water and thus generate steam.

Auxiliary components are the devices incorporated in the boiler circuit to boost up the efficiency and performance of the steam generation plant and assist in the systematic and adequate operation of the boiler unit for prolonged periods safely. They are:

· Feedwater pump

It’s Function is to supply demi-water to boiler drum to produce continuous steam in the boiler.

· Superheater

It is an integral part of boiler and is placed in the path of hot flue gases from the furnace. The heat recovered from the flue gases is used in superheating the steam before entering into the turbine (i.e., prime mover). Its main purpose is to increase the temperature of saturated steam without raising its pressure.

· Economizer

It is used for feed water heating, for adding heat at higher temperature, use waste heat and increase efficiency.

· Air preheater/ Air heater

Air pre-heater transfer heat from flue gases to cold primary and/ or secondary air by means of rotating heating surface elements. Beneath this regenerative
type air pre-heaters, there exists a steam coil air pre-heater. These are located in the secondary pass of the furnace at a height of around ‘16’ M level. Each 200 MW unit is provided with two such air pre-heaters.

· PA Fan

The primary air fans (2 per unit — 50% capacity each) are designed for
handling atmospheric air upto a temperature of 50 deg C. These fans are located at *0'
M level near the boiler.

· FD Fan

The forced draft fans (2 per unit — 50% capacity each) are designed for
handling secondary air for the boiler. These fans are located at ‘0’ M level near the PA
Fan.

· ID Fan

There are two induced Draft fans per boiler located between the Electrostatic
precipitator and the chimney. These fans are used for sucking flue gas from furnace. Chimney : These are tall RCC structures with single/multiple flues (one flue per 200MW Unit). The height of these chimneys vary depending on the location considerations; anywhere between 150 m. to 220 m.

· Fuel Supply System

· Reheater

· Boiler condenser

· Deaerator

Dissolved oxygen from water is removed by deaerated. To remove oxygen and other harmful gases, hydrazine is dozed in deaerator. During operation condensate comes to Feed water tank through deaerator and also make-up water added to Feed water tank from demi-water tank.

· Coal feeders

Each mill is provided with a drag link chain/rotary/gravametric feeder to
transport raw coal from the bunker to the inlet chute, leading to mill at a desired rate. Mills : There are six mill (25% capacity each), for every 200 MW unit, located adjacent to the furnace at ‘0’ M level. These mills pulverise coal to the desired fineness to be fed to the furnace for combustion.

· Coal bunker

These are in’process storage silos used for storing crushed coal from the
coal handling system. Generally, these are made up of welded steel plates.’ Normally, there are six such bunkers supplying coal of the corresponding mills. These are located on top of the mills so as to aid in gravity feeding of coal.

· Burner

As evident from the name itself, these are used for burning pulverised coal or
oil. Every unit has a set of such burners located at different elevations of the furnace.

· Wind box

These act as distributing media for supplying secondary/excess air to the
furnace for combustion. These are generally located on the left and right sides of the
furnace while facing the chimney.

· Scanner fan

These fans, two per boiler, supply requisite air for scanner cooling.

· Soot blowers

Following three types of soot blowers, in requisite numbers, are
provided :
i Long retractable soot blowers
ii Wall blower
iii Air heater blower Superheated steam is tapped from superheater for the
purpose of soot blowing.
The pressure is reduced to 31 Kg/cm2 at 330 deg C by means of pressure reducing
valve. The soot blowers are used for efficient on-load cleaning of furnace,
superheaters, reheaters and regenerative air heaters.

There are some other fittings used in boiler for safe and proper operation:

· Water level indicator

· Pressure guage

· Safety valve

· Stop valve

· Temperature guage

And many more, that ease the working of a system and work efficiently.