Abstract
Due to environmental issues and profitability of paper production, energy consumtion of the PM line is normally followed carefully during production. However, what consumption level is high or low, can be find out only by comparing the consumption to other machines, favourably producing similar grades.A new tool for the comparison ( benchmarking) of electric energy consumption on-line is now available at www.kgu.fi . Basis of this new on-line benchmarking method is summarized in this article.
This new on-line benchmaring can always be executed free of charge, and the target has been to make it as simple as possible, thus everyone interested in energy costs of the paper production line can easily execute it.
1. Required data for the on-line benchmarking
1.1 Mill data
Mill name, location and machine number can be stored in the database, but it is optional, and benchmaring can also be done anonymos. However, if a more detail study or comparion is needed at a later stage, it is not possible, if the machine can not be identified.1.2 PM line production
Calculation of electric energy consumption is based on 100 % efficiency of the line. Thus the production is simply calculated based on the machine basis weigh, speed and width, which must be given to calculate the production ( @ 100 % efficiency).Prod (t/h) = Basis weight(g/m2) * Reel trim (mm) * Speed ( m/min) * K (1)
1.3 Energy energy consumption ( SEC)
Energy consumption is calculated based on the normal running load (NRL) of the line during production, which is thus needed for the benchmaking. Specific energy consumption is the ratio of NRL-load and production.SEC ( kWh/tn) = NRL-Load ( MW) / prod (t/h) (2)
The price of enercy ( €/MWh) is also needed for the estimation, compare also to statistics of electric energy prices in Europe /1/.
1.4 Production line efficiency and operation time
At the end, the energy costs of packed production and annual energy costs are of cause important. Thus production line efficiency and annual operation time are needed.
Picture 1: Parameters of the PM line efficiency
2. Calculation results of PM line energy consumption
Based on the data given above, several specific consumption and cost figures can already be calaculated, such as:- Line Specific energy Consumption ( SEC, kWh/tn),
- Specific energy costs ( €/tn),
- Annual electric energy costs ( M€/a),
- etc...
These figures are calculated, by clicking the "Calaculate PM line SEC" button ( see example 2)
Picture 2: Example of PM SEC calculation
3. Benchmarking of energy consumption
3.1 Standard deviation
Standard deviation is defined according to the formula shown at the picture 3.
Picture 3: Standard deviaton
3.2 PM line categories ( based on SEC of the line)
Production lines are divided into four (4) categores, based on the specific energy consumption according to the table 1.Table 1: Production line categories based on SEC
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Category SEC (kWh/tn) Comment
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1 SEC < Average - Deviation Low consumption
2 SEC < Average Lower than average
3 SEC > Average Higher than average
4 SEC > Average + Deviaton High consumption
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The distiribution ( of SEC) can be described according to picture 4. Thus for example, about one third of production lines will land to categories 2 or 3 ( production lines, where SEC is near to the average). Thre rest of the lines will belong to the categories 1 or 4 ( relatively high, or low electric energy consmption).
Picture 4: Standard deviaton
Our database is "live", which means that the average and distribution levels will develop during the time when new data is enetered to the database.
4. Benchmarking of electric energy consumption of PM lines
The average electric energy consumption of all PM lines at our database is about 550 kWh/tn ( May, 2014), which equals to the energy cost of about 38 €/tn ( energy price 70 €/MWh). Differences between paper grades are relatively high ( see table 2 ).Of cause we hope these figures will slowly decrease in the future, and up to date average and deviation figures can be seen, when the benchmarking is executed on-line ( http://www.kgu.fi/benchmark_pm_sec.php )
Table 2: Average SEC levels at the database ( Compare also /2/ and /3/ )
| Grade | Ave SEC | StdDev. | Ave cost |
| kWh/tn | kWh/tn | €/tn | |
| Newsprint | 534 | 60 | 35,2 |
| SC (magazine) | 607 | 78 | 42,5 |
| LWC / MWC | 562 | 83 | 39,3 |
| WFC ( Coated Fine) | 567 | 78 | 39,7 |
| WFU ( Uncoated fine, Copy) | 552 | 79 | 38,7 |
| Liner/Fluting < 150 g/m2 | 455 | 86 | 31,8 |
| Board_over > 150 g/m2 | 460 | 100 | 32,2 |
| Averages | 546 | 77 | 37,9 |
5. Artifical intelligece
On-line benchmarking includes also verbal analysis. Several comments are given in this "artificil intelligence" section of the program. Energy consumption and annual energy costs area compared to average, and good ( =average-deviation) levels. Comments are displayded depending on the theoretical energy saving potential compared to the other machines based on four (4) different parameters:1. What category PM line belongs to ( 1-4),
2. SEC ( kWh/tn) compared to the other machines,
3. Annual energy consumption ( MWh/a), and
4. Annual energy cost of the PM line ( M€/a).
All parameters are further divided into several subcategries, thus there exists theoretically more than one hundred variations of different comments that can be given for the user.
Picture 5: PM line categories based on SEC.
6. Comments and conclusions
Benchmarking alone can of cause not give detail solutions for possible improvements, but it can indicate overall saving potential compared to other lines ( producing similar grades). The only way to find out the feasible improvement positions is to study in more detail the consumption of various sub systems.Typically there does not exist only one single solution to achieve a good, low level of energy cnsumption. Low SEC can only be achieved by studying process systems one by one and make the improvements where needed.
We will discuss the feasible improvement possibilities of PM subprocesses in the future articles in more detail. We hope this PM line total electric energy benchmarking will help to assess the importance of the energy saving improvements of various sub systems at the mill.
References
1. Energy price statistics by Eurostat / European Commissionhttp://epp.eurostat.ec.europa.eu/statistics_explained/index.php/Energy_price_statistics
2. Pulp and paper industry, energy bandwidth study - jacobs / IPST
http://energy.gov/sites/prod/files/2013/11/f4/doe_bandwidth.pdf
3. Energy efficiency in U.S, manufacturing / The Case of Midwest Pulp and paper Mills
http://www.wri.org/sites/default/files/energy-efficiency-in-us-manufacturing-midwest-pulp-and-paper_0.pdf
