According to the flow power, circulation mode and characteristics of the working fluid circulating through the evaporative heating surface, the water circulation mode of the boiler can be divided into: (1) Boiler with natural circulation.
The flow power of the working fluid in the evaporative heating surface of a natural circulation boiler is the density difference between the unheated downflow and the heated upflow. A natural circulation boiler is characterized by a drum, which constitutes a fixed separation point between the evaporative heating surface and the superheater. Its main features are a simple flow pattern, stable hydrodynamic characteristics and reliable operation. It has been widely used in the past in subcritical pressure boilers.
(2) Multiple forced circulation boilers
In the heating surfaceby evaporation of multiple forced circulation boilers, the flow power of the working fluid mainly depends on the density difference between steam and water. mixture and water. It depends on the pressure height of the circulation pump installed downstream of the boiler circulation loop. The circulation pump on the descent constitutes the main difference with natural circulation. Multiple forced circulation boilers are mainly used in subcritical pressure boilers.
(3) Single-pass boiler
The flow power of the working fluid in the evaporative heating surface of the single-pass boiler is the pressure head of the boiler feed water pump. A once-through boiler has no drum and the working fluid in the evaporative heating surface is forced to flow only once. This is the main difference with anatural circulation boiler. The applicable pressure range is very wide, especially for boilers with supercritical parameters.
(4) Compound circulation boiler
The basic feature of compound circulation boiler is that a circulation pump is also installed in the middle. The circulation pump only operates at low load, which allows. Part of the water to pass through The recirculation pipeline recirculates into the evaporative heating surface to completely cool the evaporative heating surface and stops working when the load is high, automatically switching to a boiler working state at single pass. Compound cycle boilers are mainly used in boilers with supercritical parameters.