Classification of boiler

Boilers can be classified based on:

1. Mode of circulation of working fluid
   – Natural circulation, forced circulation, etc.

2. Type of fuel
   – Coal, oil, gas, biomass, electricity, etc.

3. Mode of firing
   – Pulverized fuel firing, stoker firing, fluidized bed firing, etc.

4. Nature of heat source
   – Combustion, nuclear, waste heat recovery, electric resistance, etc.

5. Nature of working fluid
   – Water, thermal oil, molten salt, etc.

6. Position of the furnace
   – Externally fired or internally fired

7. Type of furnace
   – Horizontal, vertical, or inclined furnace arrangements

8. Boiler size
   – Small, medium, large capacity (by steam generation rate or heat transfer area)

9. Materials of construction
   – Cast iron, steel, alloy steel, etc.

10. Shape of tubes and their spatial position
    – Straight or bent tubes; horizontal, vertical, or inclined

11. Content of the tubes
    – Water-tube boilers (water inside tubes) or fire-tube boilers (hot gases inside tubes)

12. Steam pressure
    – Low pressure, medium pressure, high pressure, supercritical, ultra-supercritical

13. Specific purpose of utilization
    – Power generation, process heating, waste heat recovery, marine use, locomotive, etc.

14. General shape
    – Cylindrical, rectangular, etc.

15. Manufacturer’s trade name
    – Specific design names or patented models by different manufacturers

16. Special features
    – Once-through design, superheater, economizer, reheater, modular design, etc.