flue gases pass through tubes and water around it

water passes through the tubes and flue gases around it

forced circulation takes place

tubes are laid vertically

ash

volatile matter

moisture

hydrogen

zero

one

two

four

locomotive boiler

Babcock and Wilcox boiler

Stirling boiler.

all of the above

locomotive boiler

Cochran boiler

Cornish boiler

Babcock and Wilcox boiler