Draught production in boilers and furnaces: Which of the following methods can be used to produce draught (the driving pressure difference) in a combustion system?

Introduction / Context:
Draught (draft) is the small pressure difference that draws air through the grate and carries flue gases through the passes to the stack. Knowing how draught can be created is a key aspect of boiler operation and design.

Given Data / Assumptions:

• Combustion needs steady airflow through fuel bed or burners.
• Pressure differences are small (commonly a few mm to a few tens of mm of water column).
• Multiple technologies exist to generate this pressure difference.

Concept / Approach:
Natural draught is created by a chimney due to density differences between hot gases and ambient air. Mechanical draught is provided by fans (forced-draught, induced-draught, or balanced-draught arrangements). Ejector (steam-jet) draught uses a high-velocity steam jet to entrain flue gases and create suction, historically important in locomotives and small boilers.

Step-by-Step Solution:
List available methods: chimney, fans, steam jet.Recognize all three produce a pressure difference across the furnace/grate.Select the combined option that includes all methods.Therefore, answer: all of these.

Verification / Alternative check:
Practical plants may use tall chimneys or FD/ID fans; steam jet ejectors are integral to locomotive boiler exhaust systems.

Why Other Options Are Wrong:
Each single-method option is incomplete; air preheater only recovers heat and does not generate draught.

Common Pitfalls:
Confusing air heating with pressure generation; ignoring ejector-based draught in historical designs.

Final Answer:
all of these