DESIGN FEATURES OF  BOILER

General description of boiler

boiler is a device used to generate hot water or steam using chemical heat of fuel.

-fuels could be coal, oil, gas or any other biomass fuels like rice husk, bagasse, cane trash etc.  the mixed  composition of oil / gas fuel is also possible

-conversion of water to steam takes place by three heat addition

Function of Drum:
-to produce water-free steam and steam-free water
-to remove steam bubble from water volume entering down comer to improve circulation
-mixing and distributing feed water
-adding chemicals
-facilitating blow down

drum internals:
-turbo separators
-primary drier
-secondary separator

Furnace:

-to provide enclosure for combustion of fuels

acts as evaporator by absorbing high temperature radiant heat by means of water cooled wall construction

-furnace design is governed by
*type of fuel
*allowable heat loadings
*burner arrangement

Boiler bank:
acts as evaporator by absorbing heat from flue gas by convective mode

necessary for low pressure boiler where large amount of latent heat is to be supplied to water to convert into steam

Superheaters :

Superheaters are designed to provide required degree superheat to steam.

they are designed to give designed performance with optimum material selection.

-superheater arrangement is finalised taking proper care of :

*spacing of tube
*steam velocity
*gas velocity
*temperature control 

Variable type desuperheater:

desuperheaters are provided for effectively controlling superheater outlet temperature.

type of desuperheater provided is water spray type.

provided between primary & secondary superheater

Economiser:
economiser is used to provide sensible heat to feed water
this is a convection heat transfer section located after boiler bank

• designed considering factors like :
  • cold end corrosion
  • non steaming
  • erosion

Air heater:

air heaters are heat recovery section which absorbs the low temperature leaving boiler

they are located down stream of economiser

air heating helps combustion efficiency

-air heater help to improve boiler efficiency by optimally reducing gas temperature leaving boiler

Boiler auxiliaries :
fans :
for combustion of fuel air has to be supplied into the furnace and the gas generated in the furnace has to be thrown into stack continuously.
forced draft fan: air supplied for combustion through grate
secondary air fan: secondary air for spreader, & sa nozzle
induced draft fan : to evacuate the gases through chimney

Boiler feed pumps :
-boiler feed pumps are designed to give required feed water flow to boiler drum at desired pressure.
-they are multistage centrifugal pumps
-pumps are provided with auto recirculation valve for their low load projection

Soot blowers:

during the operation of boiler there is possibility of fouling or slag build up on heating surfaces of boiler depending on the fuel/ash characteristic

-such fouling will affect the performance of boiler like:
*boiler may not give required generation
*desired superheat temperature may not
be achieved
*draft loss will increase

-to take care of such eventuality, soot blowers are provided as on load cleaning device which are to be regularly used to over come slagging problem

-frequency of soot blowing shall be decided by studying the fuel characteristic

you can also check Troubleshooting of Boiler

Deaerator :
deaerators are provided to remove the dissolved oxygen in boiler feed water.

-oxygen in feed water is harm full for pressure part as they cause corrosion and pitting of pressure parts.

boiler shall never be operated for long time with deaerator out of service.

feed water temperature at the outlet of deaerator shall be 135°c.

Valve and Fittings:
-boiler is provided the valves for :
*controlling and regulating
steam/water flow
*isolating the lines
*prevent excess pressure build up
*to prevent back flow of fluid into
upstream side
valves plays vital roll in fluid
flow control and are to be maintained in good condition to get good availability of plant.

      TIPS FOR EFFICIENT OPERATION OF THE BOILER:

–Operation of the boiler with higher excess air than recommended means, higher dry gas loss and lower efficiency and higher power consumption.  Hence, it recommended to operate the  boiler at indicated values.

–Keep the gas temperature leaving closer to predicted value indicated.  Higher the gas temperature, lower would be the efficiency.

–Adjust the secondary air to get lower unburnt in ash.  Reduction in unburnt will improve the boiler efficiency.

–Prevent any leakage in furnace, ducting etc.  Ingress of air into the furnace will reduce efficiency and increase power consumption.

–Always ensure minimum 30% MCR flow through superheater   

we also supply Boiler spare parts you can check that on our website