The S riser pipes are heated. Due to the fluctuating water pressure in the downcomer F and the mixture of water and steam in the S riser pipe, the entire water and steam mass is accelerated. Inside the drum, there is a substantial decrease in the velocity of the mixture due to the large flow cross-section and as a result, the steam and water are separated. The water flows from the drum into the downcomers and back to the riser pipes. The amount of water lost through evaporation is compensated by the water being fed into the drum.
Corner tube boilers
With the corner tube boiler, the acceleration effect described above is also achieved through heating. However, steam is already separated from the water in header Z and some of the water runs through unheated return pipes R to the distributor V. The steam separated here is fed through overflow pipe U to the steam chamber of the drum. The remaining water reaches the drum via riser G, which produces the same result as in conventional boilers (see above). The rear downcomers considerably shorten the distance the water has to travel and so the water circulation rate increases. This means that it is possible to enlarge distance A between the heating surfaces and the drum.