DIY guidelines for optimization of wire vacuum

DIY GUIDELINES FOR
OPTIMIZATION OF WIRE
VACUUMVACUUM
By: D K Singhal

Wire Part Vacuum
Why it is important to understand?
What are the energy saving potentials?
2
What are the energy saving potentials?
Is it being ignored?
Should we compare with other mills?
&
DIY Guidelines for Optimization of Wire Vacuum, September 2015
Who can guide us for this?

Is It Important?
Vacuum is the most power consuming section in a
paper machine.
3
paper machine.
Wire part vacuum not only affects the energy
consumption, but has a significant influence on wire
life, drag load etc.

Energy Saving Potential
It has been found out that vacuum pumps consume
more than 15-30% of total electrical energy
4
more than 15-30% of total electrical energy
consumed by a paper machine.

Have We Ignored Wire Part Vacuum?
To a certain extent, YES!.
If you are running a fourdrinier paper machine, and
5
If you are running a fourdrinier paper machine, and
want to know what capacity of vacuum pump you
need to install, all you have to depend on thumb
rules. Many a times, these are not accurate enough.
It has been observed that two or more mills making
same quality and product operate at different
same quality and product operate at different
vacuum levels, which shows ignorance about this
important topic.

Have We Ignored Wire Part Vacuum
Check any few machines making almost same
grade of paper, operating at almost same speed,
6
grade of paper, operating at almost same speed,
using almost the same furnish etc. If there is a
significant difference in vacuum pump power
consumption, that would be a clear proof that we
did not give proper attention to wire part vacuum.

Have We Ignored Wire Part Vacuum
I must indicate that many kraft paper mills in India,
using recycled fibers have initiated to reduce
7
using recycled fibers have initiated to reduce
vacuum in wire part, they shared information with
one another, they made various trials, made
investments to replace the existing system with
whatever they thought right, lost a lot of production
for trials etc., but now are operating with
for trials etc., but now are operating with
unbelievingly low vacuum power consumption levels.

Are There Some Standards?
Yes. TAPPI TIP 0502-01 (2013), “Paper Machine
Vacuum Selection Factors” deal with the issue, and
8
Vacuum Selection Factors” deal with the issue, and
presents some guidelines.
Let us consider present standards for press section.
TAPPI TIS 0505-01 recommends a minimum 660
m3/min/m2 open slot area. Furthermore, it is stated
that factors have ranged from 750 to 970
m3/min/m2.
m3/min/m2.
Furthermore, dwell time has been suggested to be
2-4 milliseconds.

Standards!
Quite obviously, if you choose minimum dwell time
with lower value of airflow required, you may get a
9
with lower value of airflow required, you may get a
particular capacity of desired vacuum pump.
But, if you choose to use higher value of dwell time
with higher value of airflow required, you may
select a vacuum pump having capacity up to 3 times
than that you chose earlier.
than that you chose earlier.
That is why, many papermakers are not comfortable
with the present standards.

We are Better than Other Mills!
This is again a good excuse, but, being better does
not mean there is no potential at all.
10
not mean there is no potential at all.
Maybe you are losing something, and other mill
losing much more.

Who Can Guide Us?
Machinery suppliers know a lot, but their prime
focus is selling machines. Except for a few, many
11
focus is selling machines. Except for a few, many
may not be interested in a non-profitable work.
On the other hand, most vacuum pump suppliers are
not that good in papermaking.
Maybe none. Because, nobody knows your machine
better than you. Selecting a good vacuum
better than you. Selecting a good vacuum
optimization method best suited for you is difficult.

The Complexities Within…
Air flow is a function of dwell time, vacuum level,
web GSM, pulp properties, web dryness, wire
12
web GSM, pulp properties, web dryness, wire
characteristics, piping resistance to air flow etc.
At higher vacuum levels, a part of drained water
gets evaporated thus requiring more volume (water
vapor included) for evacuation.
Unfortunately, the peak vacuum level is a function of
Unfortunately, the peak vacuum level is a function of
total air flow.

Complexities…
You apply more vacuum power (bigger vacuum
pump), and web dryness increases resulting in more
13
pump), and web dryness increases resulting in more
air flow, thus reducing peak vacuum, thus slightly
reducing air flow, thus reducing resistance to air
flow, thus reducing piping resistance thus increasing
air flow…..#$%@&%$#.

Finally….
Finally, you get…
14
HEADACHE

We are Better than XYZ Mill!
Yes. Noted again. ☺
Many a times we compare with a nearby mill and
15
Many a times we compare with a nearby mill and
feel happier. But, maybe the other mill needs to
work on its process more.
Should we not think of a method to evaluate
ourselves?

We! Ourselves?
Why not us?
Yes. We shall try to solve this riddle by ourselves.
16
Yes. We shall try to solve this riddle by ourselves.
Why not try ourselves?

Review
There are many variables.
Type of Wire
17
Type of Wire
Furnish
GSM
Dryness
Vacuum Level
Dwell Time
Dwell Time

Review
Type of Wire: We cannot change it. For Now.
Furnish: We cannot change it. For Now.
18
Furnish: We cannot change it. For Now.
GSM: We cannot change it. For Now.
Dryness: We want it to be maximum.
Vacuum Level: We want to optimize it.
Dwell Time: We should think of it.
Dwell Time: We should think of it.

Normalization of Fixed Parameters
We have seen some of the variables are fixed by
the process, like wire type, furnish, gsm etc.
19
the process, like wire type, furnish, gsm etc.
In fact, as indicated earlier, much work has not been
done to quantify the effect of these as a single
variable.
If we can develop a constant “X” to represent all
these variables, it would be much easier to evaluate
these variables, it would be much easier to evaluate
and predict the effect of applied vacuum.

Normalization of Fixed Parameters
In absence of any documented information on effect
of wire type, furnish, gsm etc., we need to develop
20
of wire type, furnish, gsm etc., we need to develop
such constants ourselves.
As the mills have different fiberlines, different pulp
processing parameters, different headbox
consistency, FPR, ash content etc., any such
development will help the individual mill the most,
development will help the individual mill the most,
compared to the one which has copied the value
from other mill.

Proceeding towards Normalization
The methodology is simple. As a machine is running,
we document vacuum levels and consistencies at
21
we document vacuum levels and consistencies at
different positions, collect design data, collect
airflow information and compile all these to achieve
a constant ‘X’, which is similar to say ‘porosity’.

Understanding the System
22

Basically, for any set of pulp furnish, quality, gsm,
type of wire etc., the air flow at point 1 depends
23
type of wire etc., the air flow at point 1 depends
upon the applied vacuum, web dryness and of
course the open area.
It has been found that for a particular vacuum level
and open area, the airflow increases in direct
proportion to the web dryness.
proportion to the web dryness.

In the similar way, in case web dryness is same, the
inlet airflow increases with applied vacuum.
24
inlet airflow increases with applied vacuum.
We must keep in mind that the here, the inlet
airflow means volume of air passing through the
web at the inlet condition.

Now, suppose, we develop a formula that airflow
(per unit meter of machine width) is denoted by the
25
(per unit meter of machine width) is denoted by the
multiplication of web dryness (consistency, %),
applied vacuum (mmHg or “Hg), open area
(represented by the dwell time for ease) multiplied
by a constant, say “X”.
We know applied vacuum in a box, we can
We know applied vacuum in a box, we can
calculate dwell time, we can check web dryness by
taking samples and checking.

This way, we can find out the airflow through a box
as a function of “X”.
26
as a function of “X”.
We might get values like 20X, 47X or 95X.
This way, we get inlet airflow for any suction box.

As we have calculated inlet airflow, it is easy to find
out airflow passing past the suction box.
27
out airflow passing past the suction box.
It can be calculated as the multiplication of
atmospheric pressure and air flow divided by the
absolute pressure in a suction box.

As the vacuum in the box is controlled by the valve
(indicated in red color), the vacuum level in the
28
(indicated in red color), the vacuum level in the
header must be higher than that in vacuum box,
airflow for which can be calculated as done earlier.

Net Airflow
Proceeding in the same way, airflow can be
calculated at the vacuum pump inlet.
29
calculated at the vacuum pump inlet.
If we add airflow for all the suction boxes, the sum
would be equal to vacuum pump capacity.
If you have noticed a typical characteristic curve of
a water ring vacuum pump, this remains almost a
straight horizontal line at a wide vacuum range.
straight horizontal line at a wide vacuum range.
It is easy to find out vacuum pump inlet flow rate by
that curve.

Finding ‘X’
This way, we’d get an equation something like this-
30
10X + 20X + 30X + 40X = 4000
Or, 100X = 4000
Or, X = 40
This way, we can find out our constant ‘X’, which
This way, we can find out our constant ‘X’, which
represents the nature of our furnish, quality of
paper, gsm etc. for the purpose of vacuum
optimization.

What is ‘X’
‘X’ is a constant depending on your raw material,
fiberline (refining etc.), chemical treatment (use of
31
fiberline (refining etc.), chemical treatment (use of
retention aids, other chemicals etc.), effect of paper
basis weight etc.
When you make lower GSM paper, ‘X’ will be
higher, when the paper is less porous, ‘X’ will be
high.
high.

Using ‘X’ for Optimization.
We shall not go in much detail with ‘X’. That is the
job of scientists.
32
job of scientists.
Once we have found ‘X’ for a particular basis
weight and mill operating parameters, we’ll use it
for vacuum optimization only.

Optimization Starts
We’ll start with making an Excel worksheet, giving
details about the existing wire part vacuum boxes,
33
details about the existing wire part vacuum boxes,
fill all the existing values and obtain the desired
vacuum pump inlet flow rate, in other words,
capacity.

Make an Excel Worksheet
34

Name the Boxes and Zones
35

Indicate Web Consistency
36

Consistency
37

Web Consistency
In case, dwell time is more than10-15ms, most
dewatering is confined to the initial part of suction
38
dewatering is confined to the initial part of suction
box. Hence, it is generally advisable to use
“consistency after the suction box”, in this column.

Vacuum Level
39

Units of Vacuum
Many mills are comfortable using ‘mmHg’ vacuum,
or ‘Pa’, while some prefer ‘inches of Hg’.
40
or ‘Pa’, while some prefer ‘inches of Hg’.
Here, we have taken vacuum in “inches of Hg”.
However, as the finally derived value ‘X’ is your
own, you may use any unit for vacuum you like. Only
the numerical value of ‘X’ will be different.

Open Area
41

Open Area
Open area can be calculated as the multiplication
of ‘% open area’ and ‘box width’
42
of ‘% open area’ and ‘box width’
Or
Total cumulative length of paper that passes over
vacuum.
In fact, it is not ‘area’, it is just length, hence
indicated in mm.

Airflow
Airflow is calculated a multiplication of these four
variables-
43
variables-
Constant ‘X’
Consistency
Vacuum Level
Open Area
To initiate, you may put any non zero value for ‘X’.
To initiate, you may put any non zero value for ‘X’.

Airflow
44

Airflow
45

Adjusting ‘X’
After you complete the table,
you get total airflow.
46
you get total airflow.
Target airflow value is the
vacuum pump actual capacity
at the operating peak vacuum
level.
You may try different values of
You may try different values of
‘X’ so that the Total and target
airflows are same.

Adjusting ‘X’
47

Compensation for Piping Losses
As discussed earlier, the vacuum level in header as
well as at vacuum pump inlet would be much higher
48
well as at vacuum pump inlet would be much higher
than in different suction boxes.
Obviously, one must calculate the airflow at vacuum
pump inlet, which has not been done in the previous
slides.
Well, to avoid the sheet become difficult to
Well, to avoid the sheet become difficult to
understand that part had been intentionally omitted
so far.

Experimentations with ‘X’
Once you get ‘X’, initiate trying with reducing open
area.
49
area.
On the same excel sheet you had developed,
reduce the open area of last suction box.
You will notice that the total airflow is reduced.
Now adjust this to the target airflow by increasing
the vacuum level in the last suction box.

Experimentations with ‘X’
You will notice that you are able to achieve much
higher vacuum levels in last suction box.
50
higher vacuum levels in last suction box.
Well, with increased vacuum level in a box, you
expect to get higher dryness (cy.) also.
Increase consistency also in the same excel sheet.
Finally, you’ll reach to a comfortably better set of
parameters.

Back to Paper Machine
After the experimentations on the excel sheet, we
need to actually implement the findings.
51
need to actually implement the findings.
In case, you reduced the open area, you may need
to replace the existing suction box top.
After the modifications are done, repeat the same
exercise to see if further improvements are possible.
You might find a minor change in the value of ‘X’, or
there is a slight difference between target and total
airflow of vacuum, but don’t worry.

Different Grades on a Single Machine
You may ask, if we have done the whole exercise
for a particular grade and basis weight, what
52
for a particular grade and basis weight, what
would be the result for the other one.
Normally, you’d do the exercise for lighter grades,
while the dwell time for higher basis weight will
automatically be higher (due to relatively slower
machine speed).
machine speed).

Properties of ‘X’
You might be interested to know more about ‘X’.
So, ‘X’ is strongly dependent on basis weight and
53
So, ‘X’ is strongly dependent on basis weight and
decreases with increase in basis weight.
‘X’ also decreases with increased web consolidation,
increased formation, increased refining etc.
‘X’ increases with increase in stock temperature,
machine speed, and peak vacuum level.

Oh! I Thought ‘X’ as Constant
For most practical cases, ‘X’ is almost a constant,
except for a minor changes. If you are going to
54
except for a minor changes. If you are going to
increase machine speed marginally, change grade
that needs refining or furnish alterations etc., you
should not worry much.
In case you increase machine speed significantly,
repeat the exercise.
repeat the exercise.

A Sample Excel Sheet
Now, having understood the concept, it would be
easier for you to go ahead with optimization.
55
easier for you to go ahead with optimization.
However, it would be better if we look at dwell time
in detail.

Dwell Time
56
The graph on the following sheet shows the effect of
dwell time and peak vacuum for 127gsm chemical
pulp.

Dwell Time
57

Dwell Time
58
We may observe the following points in the graph-
Peak dryness possible is more at higher vacuum level.
Dwell time to reach near to peak dryness is lower at
higher vacuum levels.

Dwell Time Some findings
59

Dwell Time
These data were obtained for mechanical pulp by
60
These data were obtained for mechanical pulp by
Xiao Zhang at STFI, Sweden, 2006.
We may see that for 50 gsm mechanical pulp
furnish, no significant improvement is visible after
50ms dwell time.
Furthermore, we might even consider reducing dwell
time to less than 50ms.

Dwell Time
61

Dwell Time
62
On the other hand, for higher gsm, longer dwell
time is really useful.
So, you really need to determine suitable dwell time
for your quality and basis weight.

Optimization of Dwell Time
The question is, “are you providing sufficient or
more than enough dwell time to your paper?”
63
more than enough dwell time to your paper?”
Well, this is a tricky question. In case you reduce
dwell time for a particular box, and you do not find
any decrease in consistency after that box, the
dwell time may be considered to be higher than
desired.
desired.

Optimization of Dwell Time
As we have already seen in our experiments, most
airflow is from the last suction boxes.
64
airflow is from the last suction boxes.
To begin with, we may reduce the open area of last
suction boxes.
In the following sheets, some more detailed sheets
are shown to explain this.

Checking Airflow at Pump
65

The Values We Got….
66

Airflow
Did you notice the airflows (values of 3564 at box,
and 4115 at vacuum pump inlet) have a difference
67
and 4115 at vacuum pump inlet) have a difference
of nearly 13%.
So, by adding last two columns, our calculations are
going to be nearer to actuals.

Reducing Dwell Time
68

Reducing Dwell Time
You may notice a steep reduction in airflow at
vacuum pump (4115 to 2935 m3/hr).
69
vacuum pump (4115 to 2935 m3/hr).
Now, you have two possibilities-
Reduce vacuum pump power consumption, or
Increase vacuum level in last suction box to get more
web dryness.
Get both the benefits.
Get both the benefits.

Reducing Dwell Time
Have you ever thought bagalley box has a very
narrow slot, in other words, a little dwell time, at
70
narrow slot, in other words, a little dwell time, at
much higher vacuum.
Many papermakers appreciate the benefits
achieved with bagalley box.

Dewatering
As the web dryness increases, the amount of water
removal for each unit percent of dryness increase;
71
removal for each unit percent of dryness increase;
decreases.
Hence, in later stages of suction boxes, very little water
is removed. Yet, more dewatering can be achieved with
application of high vacuum for smaller time.
The success of bagalley box is a good proof for this.
The success of bagalley box is a good proof for this.
May we think of replacing the last suction box with
bagalley?

Replacing Last Suction Box
Replacing the last suction box with bagalley seems
logical, particularly for machines operating below
72
logical, particularly for machines operating below
400-450mpm.
For 420mpm, a 14mm wide box will result in 2ms
dwell time, which should be sufficient to give good
results.
On a 75TPD machine, if dryness is increased from
On a 75TPD machine, if dryness is increased from
18% to 19%, the water removed will be in the tune
of just 850-900 lit. per hour.

Replacing Last Suction Box
Due to low dwell time, we need a smaller vacuum
capacity for this, and on the same time as little
73
capacity for this, and on the same time as little
water has to be removed from this, the water
removal line as well as the box size will be much
smaller than the conventional boxes.

High Vacuum at Pump Inlet
A higher vacuum level at pump inlet results in more
energy required.
74
energy required.
In the following example, we may see that we
require around 13% more airflow to be handled by
the vacuum pump due to just this reason.

75

In case, vacuum at pump inlet is higher than desired,
this means you are wasting power.
76
this means you are wasting power.
Ideally, there should be minimal gap between
vacuum levels at pump inlet and that at last suction
box.

Future Scope
Many scientists and researchers have done great
work in the area of wire part vacuum. However, I,
77
work in the area of wire part vacuum. However, I,
personally feel we need to focus more on this topic
and compile all information to develop
methodology for designing a good vacuum system
for new machines.
Action line for the same is presented in the next
Action line for the same is presented in the next
slides.

Standardization of ‘X’
We need to standardize ‘X’, by accepting agreed
units of vacuum, air flow rate, dryness etc.
78
units of vacuum, air flow rate, dryness etc.

Developing ‘X’ Database
In the next phase, ‘X’ need to be determined for
different machines, furnishes, basis weight etc.
79
different machines, furnishes, basis weight etc.
Simultaneously, effect of retention and drainage
aids, degree of refining etc. should be evaluated.

Development of ‘X’ References
Finally, we should develop reference values of ‘X’,
for different sets of furnish, product and basis
80
for different sets of furnish, product and basis
weight ranges.
This will help designers to design a vacuum system
with ease.

Achieved Dryness
Simultaneously, we should combine the theoretical
dryness gain in the developed excel table.
81
dryness gain in the developed excel table.
For the same, we need to compile a lot of
information, and come out with a single excel sheet
or a program that gives the desired output.

I Wish….
I wish some industry association or research
association comes forward, considers this a need of
82
association comes forward, considers this a need of
the time to develop standards for wire part vacuum
and help the paper industry.

83
Thank You.

About the Author:
Born in 1968, D K Singhal is B.E., M.E. (Pulp & Paper, 1993) from Deptt. of Paper Technology,
University of Roorkee (now IIT, Roorkee). He is a Certified Energy Auditor and Chartered Engineer
also.
84
also.
With more than 7 dozen publications, he has emphasized on development of low cost technologies
and management practices for quality and profitability improvement. With publications on
slideshare.net, energymanagertraining.com and paperonweb.com, he has been constantly
contributing to IPPTA (Indian Pulp & Paper Technical Association). He is also serving IPPTA as a
member of Editorial Board.
An initiative by D K Singhal, a cyber campaign initiated against unjustified targeting of paper
industry by “Idea” mobile, in their “Sirjee” advertisement campaign, after which this advertisement
industry by “Idea” mobile, in their “Sirjee” advertisement campaign, after which this advertisement
was taken off air.
He is also moderating a facebook group, “PAPERTECHNOLOGY” with nearly 1750 members from
India and abroad to discuss problems related to pulp & paper making.
He can be contacted at deveshksinghal@gmail.com

DIY guidelines for optimization of wire vacuum

Recomendados

Recomendados

Más contenido relacionado

La actualidad más candente

La actualidad más candente (20)

Destacado

Destacado (10)

Similar a DIY guidelines for optimization of wire vacuum

Similar a DIY guidelines for optimization of wire vacuum (20)

Más de Devesh Singhal

Más de Devesh Singhal (20)

Último

Último (20)

DIY guidelines for optimization of wire vacuum