Identifying Flooded Dryers in Papermaking
Flooded paper dryers exhibit a number of tell-tale signs which can be used to identify that the dryer is flooded. The following troubleshooting techniques can be used :
- Visually inspect the condensate sight glass on the condensate outlet if one is installed. This is the most reliable way to verify if flooding is evident. Unfortunately, not all dryer cylinders have sight glasses installed.
- Visually check for condensate leaking from the rotary joints, dryer doors, etc.
- Increase the section dP and monitor the separator tank level and the level control valve position. If both parameters increase and stay above the long term trend for several minutes, then flooding is most probably evident.
- Check the dryer drive loads in conjunction with the dryer draws for the operating conditions. If both are in accordance with the historical trends, and the drive load is high, flooding is most probably occurring. On some occasions, one section can be pulling the preceding section, causing a higher drive load than normal, hence drive loads cannot be interpreted in isolation as evidence of flooding.
- If dryer steam pressures are operating above the normal pressure range for the grade and speed under consideration. Refer to the table for the targeted steam temperature to shell temperature differences for various steam pressures for dryers with and without dryer bars installed. Alternatively, for a fixed dryer pressure, the paper machine is operating at a lower than normal speed for the targeted moisture set-point.
Steam Pressure (kPA) No Dryer Bars (°C) Dryer Bars (°C) 70 20 to 22 16 to 20 205 22 to 28 20 to 22 415 28 to 33 22 to 28 690 33 to 39 28 to 33
- Swaying of the dryer framework in the cross-machine direction.
- The dryer shell surface temperatures are lower than those previously measured for the same operating conditions, steam pressures, and dryer speed.
- The sheet temperatures, which tend to follow a similar pattern as the shell temperatures, are lower than normal for the same operating conditions, steam pressures, and dryer speed.