How to optimize vacuum for paper machine wire part

1. Process Energy
Conservation by
Optimization of Wire
Vacuum
By:
D K Singhal
deveshksinghal@gmail.com

2. Key Points Revision:

Role of furnish.

Diminishing gains of dryness with increase in
vacuum.

Diminishing gains of dryness with increase in
dwell time.

Web dryness as a function of basis weight.

3. Air Flow Increases With:

Increase in vacuum

Increase in open area or dwell time.

Increase in web dryness.

4. General Thumb Rules:
In the suction boxes of wire part, the
vacuum must be in increasing order.
 More vacuum: higher dryness
 More dwell time: higher dryness


5. Can I Reduce Energy Required
for Vacuum?
Dryness achieved (x) and energy required (y) follow a pattern
like this graph. (Please omit the values)

6. Strategies:
Apply vacuum in increasing order.
 Last suction box operates at maximum
vacuum.
 Reduction of its open area reduces air
flow requirements, hence vacuum power
consumption will reduce.


7. Strategies:
We generally apply less than 7” vacuum.
 For such a lower level, water ring vacuum
pump is not really required.
 Consider twin/three lobe blower or similar
equipment.


8. In-Plant Experimentation:
Start with vacuum in increasing order.
 Typical values could be
Reduction Box 6
Factor
Box 4
Box 3
Box 2
Box 1
60%
150
90
54
32
19
11mmHg
70%

Box 5
150
105
73
51
35
24mmHg
Check dryness after last box versus peak
vacuum, and the effect of peak vacuum in
last box on dryness.

9. Effect of Peak Vacuum:
Quite possibly, you may get a peak
vacuum level after which increase in
dryness is almost negligible.
 Initially, the same exercise may be done
by throttling the valves.
 Consider using a VFD to get desired peak
vacuum.


10. Effect of Peak Vacuum:

Remember◦ Reduction of peak vacuum will also help in
getting increased wire life.
◦ Furthermore, drag load on wire will also
decrease in addition to the possibility of
energy saving in vacuum pump.

11. Dwell Time:
For most furnishes and basis weight range
of 50-100gsm, 10-15ms is sufficient.
 Many mills operate at 50-150ms.
 Bagalley Box normally works at 2-3ms.
 A couple of graphs on coming slides
indicate effect of dwell time.


12. Effect of Dwell Time
For 48gsm newsprint

13. Effect of Dwell Time
127gsm (experimental data)

14. Dwell Time:

As clear from earlier graphs-
Even a single slot suitable for 15-20ms
can increase web solids from 5-6% to
practically maximum achievable.
 Multiple slots, with increasing vacuum help
maintain fiber network with lesser open
area in higher vacuum zone.


15. Roots Blower:
Many mills have installed roots blower and
are saving energy.
 Some faced problems of pulsation and
hammering. Proper layout and piping
design is a must to get results from roots
blower.


16. Typical Savings:



In a small paper mill (40 TPD), wire part
vacuum was reduced from 72m3/min(110kW
motor) to just 28m3/min(55kW motor) after
dwell time was reduced from 150ms to
100ms.
A significant improvement in wire life (nearly
double) was observed after modification.
Further reduction in dwell time is under
planning.

17. How to Achieve this?
Just check your table, and calculate
total open area.
 Find out total dwell time. Explore
possibilities to reduce if it is too
high, by shutting vacuum in one or two
boxes.
 Recheck web dryness after the same.
If everything is fine, replace boxes
with lesser open area ones.
 Or, discuss with some expert.


18. Conclusion:
There exists tremendous scope for energy
conservation in paper machine wire part.
 Proper designing of wire table and
optimization of vacuum play important role
in energy conservation and wire life
improvement.


19. THANK YOU
D K Singhal
deveshksinghal@gmail.com