STEAM GENERATION

BOILER

A ‘Boiler’ means a pressure vessel in which steam is generated for use external to itself by application of heat which is wholly or partly under pressure when steam is shut off but does not include a pressure vessel

(1) With Capacity less than 25 ltrs (such capacity being measured from the feed check valve to the main steam stop valve);

(2) With less than 1 kilogram per centimeter square design gauge pressure & working gauge pressure

(3) In which water is heated below one hundred degree centigrade

Fuel Used In Boiler

S.No Solid Liquid Gaseous AgroWaste 1 Coal HSD NGas Baggase 2 Lignite LDO Bio Gas Pith 3 Charcoal Fur.Oil Rice Husk 4 LSHS Paddy Straw 5 Coconut shell 6 Groundnutshell

MSW/RDF

Type Of Boiler

1. Fire Tube Boiler

2. Water Tube Boiler

3. Packaged Boiler

4. Stoker Fired Boiler

5. Pulverized Fuel Boiler

6. Waste Heat Boiler

1.Fire Tube Boiler

• Relatively small steam capacities (12,000 kg/hour)

• Low to medium steam pressures (18 kg/cm2)

• Operates with oil, gas or solid fuels

2.Water Tube Boiler

• Used for high steam demand and pressure requirements

• Capacity range of 4,500 – 120,000 kg/hour

• Combustion efficiency enhanced by induced draft provisions

• Lower tolerance for water quality and needs water treatment plant

3.Packaged Boiler• Comes in complete

package• Features

• High heat transfer• Faster evaporation • Good convective heat

transfer• Good combustion

efficiency• High thermal efficiency

• Classified based on number of passes

Oil Burner

To Chimney

4.Stoker Fired Boiler

Uses both suspension and grate burning

Coal fed continuously over burning coal bed

Coal fines burn in suspension and larger coal pieces burn on grate

Good flexibility to meet changing load requirements

Preferred over other type of stokers in industrial application

a) Spreader strokers

Uses both suspension and grate burning

Coal fed continuously over burning coal bed

Coal fines burn in suspension and larger coal pieces burn on grate

Good flexibility to meet changing load requirements

Preferred over other type of stokers in industrial application

b) Chain-grate or Travelling-grate stoker

5.Pulverized Fuel Boiler

Coal is pulverized to a fine powder, so that less than 2% is +300 microns, and 70-75% is below 75 microns.Coal is blown with part of the combustion air into the boiler plant through a series of burner nozzles.

Pulverized coal powder blown with combustion air into boiler through burner nozzles

Combustion temperature at 1300 -1700 °C

Benefits: varying coal quality coal, quick response to load changes and high pre-heat air temperatures

(contd…..)

Advantages

Its ability to burn all ranks of coal from anthracitic to lignitic, and it permits combination firing (i.e., can use coal, oil and gas in same burner). Because of these advantages, there is widespread use of pulverized coal furnaces.

Disadvantages

High power demand for pulverizing Requires more maintenance, flyash erosion and pollution

complicate unit operation

6.Waste Heat Boiler• Used when waste heat

available at medium/high temp

• Auxiliary fuel burners used if steam demand is more than the waste heat can generate

• Used in heat recovery from exhaust gases from gas turbines and diesel engines

Pricinple of Operation

Combustion of fuel produce heat, which is transferred to the container and makes the water evaporate. The vapor or steam can escape through a pipe that is connected to the container and be transported elsewhere . Another pipe brings water (called “feedwater”)to the container to replace the water that has evaporated and escaped. Since the pressure level in the boiler should bekept constant (in order to have equal to the mass of the water that is added. If steam leaves the boiler faster than water is added, the pressure in the boiler falls stable process values), the mass of the steam that escapes has to be. If water is added faster than it is evaporated, the pressure rises .If more fuel is combusted, more heat is generated and transferred to the water. Thus, more steam is generated and pressure rises inside the boiler. If less fuel is combusted, less steam is generated and the pressure sinks.

BURNERWATER

SOURCE

SOFTENERSCHEMICAL FEED

FUELBLOW DOWN SEPARATOR

VENT

STACK DEAERATOR

PUMPS

BOILER

ECO-NOMI-ZER

VENTEXHAUST GASSTEAM TO PROCESS

Pricinple of Operation

Deaerator

A deaerator is used to strip corrosive gases from boiler feed water by sparging with steam.

Safety Consideration Boiler firebox Main stop valve Safety valve Smoke Tube Gas Burner

Reference http://en.wikipedia.org/w/index.php?

search=steam+generation&title=Special%3ASearch&go=Go

http://www.ttboilers.dk/steamgenerator_steamboiler.htm