The challenge
A Yankee is one large steam-heated cylinder. Unlike a dryer section, it has no lower group to take its blow-through: all the steam that passes the cylinder with the condensate has to come back to it, or it is lost. When it cannot all come back, the Yankee floods and the sheet dries unevenly.
The solution
The mill put a variable-nozzle Jetomat® (Baelz 590) on the Yankee’s steam supply:
- Motive steam at 14 barg enters the Jetomat’s nozzle and does the pumping.
- The Yankee’s condensate goes to a condensate separator. The blow-through steam from the separator is drawn back by the Jetomat and mixed with the motive steam: the recirculation of the Yankee’s own steam.
- The mixed steam goes back into the Yankee at the pressure the machine needs.
- A pneumatic actuator (Baelz 373-P22) with an I/P positioner moves the nozzle spindle, so the motive-steam flow follows the load instead of throttling it.
The hardware
| Item | Detail |
|---|---|
| Thermocompressor | Baelz 590, DN 100, PN 25, variable nozzle |
| Nozzle and diffuser | 33 mm special nozzle, special diffuser sized for the Yankee duty |
| Body and diffuser | Ductile cast iron (GJS-400-18-LT); plug, spindle and nozzle in stainless steel |
| Actuator | Baelz 373-P22 linear pneumatic actuator, 40 mm stroke |
| Positioner | Baelz 86/IP8000, 4–20 mA, explosion-proof |
| Motive steam | 14 barg |
A long service life
- 1998: the Jetomat goes into service on the Yankee.
- 2009: Baelz issues the unit’s rating table across the Yankee’s working pressures.
- 2017: after nearly two decades, the mill orders a like-for-like Jetomat, built to the existing flange dimensions so it drops straight into the same line.
Why it works
The Jetomat is a steam jet thermocompressor: high-pressure motive steam expands through the nozzle, draws in the low-pressure blow-through steam and recompresses the mixture in the diffuser. Because the nozzle is variable, one unit follows the Yankee from warm-up to full speed and back down on a sheet break.
Takeaway
On a Yankee or an MG cylinder, the blow-through has nowhere else to go. A variable-nozzle Jetomat brings it back under control and keeps the cylinder draining at speed, and on this tissue machine it has done so for more than 25 years.
