Mar 15, 2022
Dryers and steam & condensate systems involve a complicated set of interdependent process values. Changes to one variable cascade to other variable changes. The following are some notes on overall troubleshooting and operations of steam and condensate systems in the mill. A previous Up & Running article presented tips for troubleshooting your dryer section.
The temperature of dryer can surfaces is a key measure of overall system efficiency. Trend the steam and dryer can surface temperatures down the machine to find where there is inefficient transfer of energy from steam to the dryer can surface. This can indicate condensate removal problems at high differential temperature. The temperature difference should not be greater than 40-50 °F. Can-to-can temperature differences should not be greater than 5-10 °F. Can cause sheet flutter due to inefficient drying.
Sheet temperatures define the drying curve of the machine. The sheet temperature should increase slowly to reduce picking and cockling in the early cans and sheet flutter later. High sheet temperature early in the section can indicate high pocket humidities (less evaporation and higher temps). Low sheet moistures going into early in the section can also indicate high pocket humidities (less evaporation and higher temps). Low sheet moistures going into the size press are caused by too many cans operating in the "falling drying rate zone", resulting in high can and sheet temperatures.
Vent valves to the condenser or atmosphere should normally be closed. Open valves are an indication of operating problems.
Condensing load in a section can be calculated by measuring the production rate, inlet and outlet sheet moisture, and heat added by dryers:
Condensing load and blowthough determine siphon and condensate line size. Blowthough about 15-20% of condensing load and enough to guarantee removal of condensate from the can. The amount of blowthrough is affected by:
A flooded dryer will stay flooded until the dryer section is shutdown and cleared.
For assistance troubleshooting your dryer section and steam & condensate sytems, contact your Valmet representative.