diy guidelines for optimization of wire vacuum · web gsm, pulp properties, web dryness, wire 12...

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?

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� 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.

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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

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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

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� 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,

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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

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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

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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

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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.

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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

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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

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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

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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…

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HEADACHE �


We are Better than XYZ Mill!

� Yes. Noted again. ☺

Many a times we compare with a nearby mill and

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� 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.

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� Yes. We shall try to solve this riddle by ourselves.

� Why not try ourselves?


Review

� There are many variables.

� Type of Wire

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� 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.

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� 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.

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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

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of wire type, furnish, gsm etc., we need to develop such constants ourselves.

� As the mills have different fiberlines, different pulp processing parameters, different headboxconsistency, 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

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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 System22


Understanding the System

� Basically, for any set of pulp furnish, quality, gsm, type of wire etc., the air flow at point 1 depends

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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.

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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

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(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”.

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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.

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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

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(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.

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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-

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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

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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.

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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,

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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 Worksheet34


Name the Boxes and Zones35


Indicate Web Consistency36


Consistency37


Web Consistency

� In case, dwell time is more than10-15ms, most dewatering is confined to the initial part of suction

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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 Level39


Units of Vacuum

� Many mills are comfortable using ‘mmHg’ vacuum, or ‘Pa’, while some prefer ‘inches of Hg’.

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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 Area41


Open Area

� Open area can be calculated as the multiplication of ‘% open area’ and ‘box width’

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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-

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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


Airflow45


Adjusting ‘X’

� After you complete the table, you get total airflow.

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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

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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.

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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.

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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.

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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

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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

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� 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

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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.

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easier for you to go ahead with optimization.

� However, it would be better if we look at dwell time in detail.


Dwell Time56

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


Dwell Time57


Dwell Time58

� 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 findings59


Dwell Time

These data were obtained for mechanical pulp by

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� 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 Time61


Dwell Time62

� 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?”

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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.

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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 Pump65


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

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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 Time68


Reducing Dwell Time

� You may notice a steep reduction in airflow at vacuum pump (4115 to 2935 m3/hr).

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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

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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;

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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

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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

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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.

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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.


High Vacuum at Pump Inlet75


High Vacuum at Pump Inlet

� In case, vacuum at pump inlet is higher than desired, this means you are wasting power.

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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,

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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.

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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.

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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

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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.

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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

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association comes forward, considers this a need of the time to develop standards for wire part vacuum and help the paper industry.


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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.

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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 [email protected]

diy guidelines for optimization of wire vacuum · web gsm, pulp properties, web dryness, wire 12...

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