3. high pressure boilers

High Pressure Boilers

• Fire tube boilers are cheaper and easier to transport at low operating pressures (<30bar) and steam generation rates less than 30000kg/hr.

• Above these parameters, the size of the shell becomes unwieldy to transport.

• The pressure vessel of the water tube boilers is of much smaller diameter.

• Water Tube Boiler can be site erected.

• Shape of the water tube is not limited to cylindrical.

• Water tube boilers are preferred for high operating pressures and outputs.

• Fire tube boilers are preferred for lower operating pressures and outputs.

Unique Features of H.P Boilers

• Method of circulation

• Type of tubing and drum arrangement

• Improved method of heating

Method of circulation of water and steam

• Water circulation is maintained using a centrifugal pump.

• Forced circulation is preferred above 160 bar.

• In boilers of critical importance forced is always used.

Type of tubing and drum arrangement

• The drum size is small or eliminated all together.

• The water tube is exposed to flue gases almost continuously to facilitate evaporation.

• The pressure drop is large if only one tube is used to get all the steam. Hence a parallel series of tubes is used.

• This helps reduce pressure loss, and also the steam quality can be controlled much better.

Improved method of heating

• Large heating devices are used.

• The velocity of the water in the tubes is made sonic.

• Evaporation at above critical pressure of steam.

• Mixing with superheated steam.

Advantages of H.P Boilers

1. Efficiency and capacity of the plant can be increased.

2. Forced circulation reduces scale formation.

3. Forced circulation increases the evaporative capacity of the boiler.

4. Forced circulation reduces the number of drums required.

5. Heat from the flue gases is used much more efficiently due to presence of smaller diameter tubes.

6. Pressurised combustion increases the rate of firing of fuels.

Advantages of H.P Boilers7. Flexibility in design of furnace and tubing.

8. Parts are uniformly heated, reducing overheating and chances of leakages.

9. Extreme compactness and light for a given output.

10. Meets rapid fluctuations in loads.

11. Components can be placed at a lower head due to forced circulation.

12. Efficiency can be increased by 40 to 45 percent.

13. Economical.

Disadvantages of H.P Boilers

• Require extremely sensitive controls.

• Water should be free from contaminants.

LaMont Boiler

45 to 50 t

130 bar

500 C

Benson Boiler