In a pirotubular industrial boiler, the primary fluid is in a liquid state and in a container that is crossed by tubes. It is through these tubes that gases circulate at an elevated temperature as a result of the combustion process that occurs. The fluid, i.e. water, evaporates when it comes into contact with hot tubes and creates steam.
On the other hand, the fluid in a water tube boiler travels through the tubes of the boiler during the heating process and reaches high outlet pressures. This type of boilers is widely used in thermoelectric power plants due to their enormous capacity for steam production.