How does the Steam Dryer work?
The pulp is fed through the inlet rotary valve (1) to the screw conveyor (2) bringing the pulp into the pressure vessel (3) which is pressurized with super heated steam of up to 3 bar g.
The only moving part in the dryer is the fan (4) circulating the steam through the heat exchanger (12), up through the perforated curved bottom (5), and into the low ring shaped fluid bed (6). In the fluid bed the pulp is kept “fluid” swirling around, as the arrows indicate. Guiding plates force the pulp to move forward in the fluid bed, until it arrives at the outlet conveyor (8), and leaves the dryer as dried pulp through the outlet rotary valve (9).
Due to the reduced velocity of the super heated steam in the conical part of the pressure vessel, the lighter particles suspended in the steam fall down onto the forward inclined plates and slide forward in the pressure vessel. In this way also the lighter particles pass forward in the dryer, and are discharged through the outlet rotary valve.
The circulating steam passes through the upper cylindrical part into the main cyclone (10), where fine dust still suspended in the steam is separated from the steam. The dust is by means of an ejector led through a pipe (11) into the outlet conveyor. From here the dust is carried out of the pressure vessel together with the dried pulp.
From the cyclone the dust free steam passes down through the tubes in the heat exchanger (12), where it is reheated by steam of a higher pressure supplied through the pipe (13) to the primary side of the heat exchanger. The supply steam is condensed in the heat exchanger and leave the dryer through the condensate outlet (14). A higher supply steam pressure will heat the circulating steam to a higher temperature which again will increase the capacity of the dryer. The capacity as a function of supply steam pressure can be seen under the menu “Dryer Capacities”.
The steam evaporated from the pulp leaves the dryer through pipe (15), and is used as supply steam for evaporator 1A.