Benchmarking of PM vacuum system energy consumption

 

1. Background 

So far about one hundred PM vacuum system deskstop studies have been carried out. Conclusion has been, that more than 50 % of the systems suffer of poor efficiency. 

Is has been diffucult to specify, what are the machines that need improvement, and which do not. This article gives simple quidelines for the bencmarking.

2. Benchmarking of PM vacuum system energy consumption

PM vacuum system Speficic Energy Consumption ( SEC, kWh/tn) is one simple way to estimate the state of the existing system.

At the following is presented some typical energy consumption levels for different paper grades ( see pictures 1 and 2  ). This data is collected from the vacuum system studies during 2007 - 2011.

More detail data is available today, but for benchmarking purposes attached pictures give a good starting point.

                               Picture 1: PM vacuum system SEC as a function of PM speed.

                                Picture 2: PM vacuum system SEC as a function of basis weight.

3. Variation between the machines

There exists large variation based on paper grade and machine consept, which makes it difficult give exact conclusions. However, if SEC of PM vacuum system is lower than average, most probably savaing potential is small. For example 40 kWh/tn is good level for heavy board grades, but for low grammage fine papers 70 kWh/tn can be acceptable. 

Also in case the electric energy consumption is over 80 kWh/tn, most probably improvement potential always exists.

Vary many machines fall in the middle area, and in these cases the only way to find out the energy saving potential is to make a more detail study.

In many cases it is possible to improve the efficiency ( = decrease energy consumption) with relatively simple improvements without installation of expensive new equipment. If the pay-out time of 4 years could be accepted, improvement potential can be found from most of the machines.

4. Desktop study

Energy analysis should always be started by doing a desktop study. In order to do it, normally the PI diagram and DCS prints ot the vacuum system operation conditions already give a good starting point.

Further actions can be decided based on this desktop study. If energy saving potential exists, a more detail engineering including field measurements is needed to specify the required actions and pay-out time of the required investments.

5. Summary

Please, do the benchmarking first. It is atways the first step.
      - When it has been done, further actions can be started.


                                                                                                                            Kari U

Carbon diokside emissions reduced by 56.000 tn/year

1. Summary

Total energy savings achieved by vacuum system improvements at paper machines
has reached the level of 10 MW, which equals the carbon diokside emission of
about 56.000 tn/year.

2.  Screening results ( desk top study)

A desktop study of PM vacuum system eficiency has been done for about 90 paper
machines.Conclusion has been, that efficiency losses take place at 70 % of them.

Estimated total energy savings potential is over 30 MW ( see also picture 1).

In a typical case energy savings can be achieved with relatively small modifications, by improving the automation and pump connections ( = without installation of expensive  new equipment, new pumps, fans or blowers).


Picture 1: Cumulative energy savings at PM vacuum systems

3. Pre-Engineering

Pre engineering has been carried out for 30 paper mills, and the total verified
energy saving potential is about 15 MW. 

Pre engineering includes typically process synthesis ( = red pen version of the
vacuum system PI diagram), reliable estimates for energy saving and pay-out 
time of the required improvement.

4. System improvements and achieved results

Total energy savings at the end of 2012 are about 10 MW, which equals to about
56.000 ton CO2 emissions per year.

Biggest savings have been nearly 900 kW, and in average savings have been at 
the level of 400 .. 500 kW per machine. Pay-out time of improvements have often
been less than one year.

In some cases the required vacuum system modifications have been so small, 
that mills have done the improvements inmediatelly. More typically improvements 
and modifications of automation and piping are needed, and they have been 
done during a two day shut down. 

5. When to react

It seems to us, that vacuum system should always be cheked, when a rebuild
of PM is done. "Stand alone" vacuum system improvements  can also be very 
profitable, and not necessarily very expensive.

Improvement of the existing system should always be checked first ( = before 
installation of expensive new equipment ).
    
                                                                                                                        Kari U
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