On the circulation system of fire-tube boilers

Boilers can be classified into three types based on their water circulation method: natural circulation, forced circulation, and once-through boilers. In a natural circulation boiler, the water or steam in the heating pipes circulates due to the density difference between water and steam within those pipes, without the need for any external power. The cyclic flow of the working fluid driven by the head of a water pump is called forced circulation. Formation of natural circulation: The drum, downcomer, lower header, and upcomer (i.e., the water wall) form a circulation loop. As the water in the rising pipe is heated inside the furnace and turns into steam, the density of the steam-water mixture is low. In contrast, the descending pipe is not heated outside the furnace; it contains water with a high density. The difference in density between these two creates a driving force that causes the water to flow downward along the descending pipe, while the steam-water mixture flows upward along the rising pipe. This results in a natural circulation of water. The structure of a forced-circulation boiler is basically the same as that of a natural-circulation boiler; it also has a steam drum. The difference lies in the addition of a circulation pump in the downcomer, which serves to enhance the force driving the steam-water circulation. The structure of a DC furnace differs from that of a natural circulation boiler; it lacks a steam drum. Instead, it relies on the pressure from the feed water pump to force the working fluid through the tubes in the boiler’s heating surfaces, passing through the economizer, the evaporation surface, and the superheater, thereby heating the water completely into superheated steam. It is now generally suitable only for subcritical and supercritical pressure boilers. Comparison between forced-circulation boilers and natural-circulation boilers: Advantages: Suitable for subcritical and supercritical pressures; since the working fluid flows forcibly through the heating surfaces, the arrangement of these surfaces can be more flexible, resulting in uniform heating and good water circulation; rapid start-up and shutdown; the water wall allows for smaller tube diameters and thinner tube walls (as permitted by the pressure conditions), which reduces the volume of the steam drum and saves steel. Disadvantages: The addition of a circulation pump makes the system complex, increases costs, and makes maintenance difficult.

Those upstairs, please don’t just look up basic information; what I need is actual analysis. Also, could someone provide some articles on the water circulation in fire-tube and water-tube boilers?

It belongs to natural circulation. The circulation pump mentioned by the poster is part of the circulation system; the entire system operates on a forced circulation basis, while the boiler itself uses natural circulation.

What was said upstairs is correct; however, by installing nozzles at the inlet of the collection tank, an impelling force is generated, and the water circulation improves significantly compared to natural circulation alone.