Water tube boiler

Direct-flow boiler, as a rule, is a coil placed in the furnace. Water (or other coolant ) is pumped through it using a pump.

Direct-flow boilers do not have a drum. Water passes through evaporation tubes once, gradually turning into steam. The zone where vaporization ends is called transitional. After the evaporation pipes, the steam-water mixture (steam) enters the superheater. The direct-flow boiler is an open hydraulic system. Such boilers operate not only at subcritical, but also at supercritical pressure .

In addition to heating screens from boiling tubes, heating screens are made from flat boiling surfaces. The fact is that heating screens from pipes welded into the grates cannot be made continuous for technological reasons, and the screening coefficient of the furnace for such gratings from boiling pipes is from 0.6 to 0.7, that is, to completely shield the furnace and trap all the radiant energy of combustion, you have to put two screens of pipes one after another. However, in once-through boilers, it is very difficult to combine 8-10 lattice boiling screens into one serial circuit, and sequential pumping of water in it is extremely difficult. Therefore not so long ago ^{[ when? ]} for the screening of furnaces in once-through boilers, flat boiling panels began to be used, which completely shield the entire perimeter of the furnace with their surface and fully capture all the radiant energy of fuel combustion. Such boilers have a higher heat output with moderate weight and volume.

The water in this boiler, having passed the economizer , enters the drum (located at the top of the boiler), from which, under the influence of gravity (in boilers with natural circulation), it enters the lowering unheated pipes, and then into the raised heated pipes, where vaporization occurs (lifting and lowering pipes form a circulation loop). Due to the difference in temperature, and therefore the density of the medium, in the lowering and lifting pipes, the water rises back into the drum. In it, the steam-water mixture is divided into steam and water. Water again goes to the downpipes, and saturated steam goes to the superheater. In boilers with natural circulation, the multiplicity of water circulation along the circulation circuit is from 5 to 30 times. Forced circulation boilers are equipped with a pump that creates a pressure in the circulation circuit. The multiplicity of circulation is 3-10 times. Boilers with forced circulation in the territory of the post-Soviet space are not widespread. Drum boilers operate at less than critical pressure.

• Gas-tube boiler
• Heating boiler
• Steam boiler

• Ship steam boilers - Article from the Technical Encyclopedia of 1927-34.
• Wikisource Vototrubny_kotel .