At the end of this module, you will be able to:
- List the main objectives of a paper or board machine dryer section
- Identify and describe the purpose of dryer cans, dryer felts, dryer hoods, drive sections, and steam groups in a dryer section
- Explain how thermocompressor steam systems and cascade steam systems allow steam to be reused in dryer sections
- Identify and describe the components of a thermocompressor
- Identify and describe steam and condensate flows in a typical thermocompressor steam system
- Identify and describe safety hazards and safety guidelines related to paper machine thermocompressor steam systems
The following key questions are answered in this module:
What is a steam group on a paper or board machine?
A steam group is a set of dryer cans that are supplied steam at a controlled pressure from a single steam header, and typically discharge all of their condensate to a single common condensate header.
What is a thermocompressor?
A thermocompressor is a device that uses high pressure "motive" steam to pull in lower pressure steam in order to boost it to a more useful steam pressure so it can be re-used.
How does a thermocompressor like a valve?
Because the size of the nozzle opening can be changed by an actuator, which changes the flow of motive steam and therefore the amount of lower pressure steam that is pulled in, a thermocompressor basically acts like a valve.
Why is that thermocompressor steam systems can respond more quickly to production rate changes than cascade steam systems?
Thermocompressor systems allow for independent control of the steam pressures in the groups so the system response is faster.
How do thermocompressor steam systems account for the decrease in drying rate that occurs as the sheet dries on a paper or board machine?
Steam header pressures (and therefore temperatures) are often lower toward the wet end and higher toward the dry end to compensate for the decrease in drying rate.
Below is a transcript of the video sample provided for this module:
In a thermocompressor, the high pressure motive steam passes through the nozzle, which significantly increases its velocity and lowers the pressure at that point in the device. Steam from the condensate separator tank is pulled into this low pressure area. As the combined steam moves through the diffuser, the velocity decreases and the two steams come to thermodynamic equilibrium and an intermediate pressure steam emerges. The actuator moves the spindle toward or away from the nozzle opening to control the flow of motive steam through the thermocompressor nozzle. Therefore it controls the creation of the vacuum and the amount of flash and blow through steam that is pulled into the thermocompressor.
Use the additional resources and links below to learn more about this topic: