Vividha Dhapte M. Pharm

Lecture 29

BOILERS

Lecture in Pharma EngineeringDept. of Pharmaceutics,

Marathwada Mitra Mandal’s COLLEGE OF PHARMACY, Pune

Contents1.Classification

Classification of Boilers

1. Fire Tube Boiler2. Water Tube Boiler3. Packaged Boiler4. Fluidized Bed (FBC) Boiler5. Stoker Fired Boiler6. Pulverized Fuel Boiler7. Waste Heat Boiler8. Thermic Fluid Heater (not a 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

Oil Burner

To Chimney

Comes in complete package

Features• High heat transfer• Faster evaporation • Good convective

heat transfer• Good combustion

efficiency• High thermal

efficiencyClassified based on

number of passes

4. Fluidized Bed Combustion (FBC) Boiler Particles (e.g. sand) are suspended in high

velocity air stream: bubbling fluidized bed Combustion at 840° – 950° C Capacity range 0,5 T/hr to 100 T/hr Fuels: coal, washery rejects, rice husk,

bagasse and agricultural wastes Benefits: compactness, fuel flexibility,

higher combustion efficiency, reduced SO2 & NO2

4a. Atmospheric Fluidized Bed Combustion (AFBC) Boiler

Most common FBC boiler that uses preheated atmospheric air as fluidization and combustion air

4b. Pressurized Fluidized Bed Combustion (PFBC) Boiler

Compressor supplies the forced draft and combustor is a pressure vessel

Used for cogeneration or combined cycle power generation

4c. Atmospheric Circulating Fluidized Bed Combustion (CFBC) Boiler

Solids lifted from bed, rise, return to bed

Steam generation in convection section

Benefits: more economical, better space utilization and efficient combustion

5. Stoke Fired Boilersa) Spreader stokers Coal is first burnt in suspension

then in coal bed Flexibility to meet load fluctuations Favored in many industrial

applications

5. Stoke Fired Boilersb) Chain-grate or traveling-grate stoker

Coal is burnt on moving steel grate

Coal gate controls coal feeding rate

Uniform coal size for complete combustion

6. Pulverized Fuel Boiler 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

7. 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

8. Thermic Fluid Heater Wide application for indirect process heating Thermic fluid (petroleum-based) is heat

transfer medium Benefits:

Closed cycle = minimal lossesNon-pressurized system operation at 250 °C

Automatic controls = operational flexibilityGood thermal efficiencies

8. Thermic Fluid Heater

Control panel

Blower motor unit

Fuel oil filter

Exhaust

Insulated outer wall

1. Thermic fluid heated in the heater

2. Circulated to user

equipment

User equipment

3. Heat transfer through heat exchanged

4. Fluid returned to

heater

Water tube boiler Fire tube boiler1. When water is contained inside thetubes (called water tube) which aresurrounded by flames and hot gasesfrom outside, then the boilers arenamed as water tube boilers.

1. When the flames and hot gases,produced by combustion of fuel, passthrough the tubes (called multitubes)which are surrounded by water, then the boilers are named as fire tube boilers

2. They are safe, quick steaming,flexible in construction and operation.

2. They have an advantage of low cost and compact design.

3. These boilers are extensively usedbecause they can be built for high pressure and large evaporative capacities.

3. They are used where steam pressure does not exceed about 10 bar and where moderate quantity of steam is required.

4. Examples: Babcock and Wilcox boiler, sterling boiler, Lamont boiler, Benson Boiler, loeffler boiler

4. Examples: simple vertical boiler, Lanchashire boiler, Cocharn boiler, Locomotive boiler.

References• en.wikipedia.org/wiki/Boiler • www.sazboilers.com

Questions

1. Give classification of Boilers.2. Compare between water tube and fire

tube boiler