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Today’s pulp and paper manufacturers must deliver ever-increasing production capacities to combat the fierce international competition, characterizing their industry. In turn, this creates a growing demand for increasingly efficient maintenance methods. John Crane pulp and paper specialist Gary Webb outlines the role of lubrication within the maintenance schedule, looks at the financial case for installing mill-wide systems and examines the experiences of one leading paper mill in the United Kingdom.
In recent years, the increasing need for efficient maintenance methods has had a direct bearing on the topic of lubrication, and has prompted a reduction in manual lubrication activities. This is partly due to the cost of employing workers, but also because modern production technology can no longer be managed efficiently by hand. Regardless of the cause, the effect has been and will continue to be an increasing emphasis on the use of automated lubrication systems.
In addition to the demands for greater reliability and reduced downtime, the environmental and safety issues that influence maintenance and lubrication will also increase the future use of automation. Over the last 10 years, mill-wide grease lubrication systems have become accepted in Scandinavia as an essential part of the pulp or paper making process. This has helped redress the traditional idea that lubrication is just one individual cost within an overall maintenance budget. Today, lubrication is seen as an essential and integral element of a total maintenance solution where all component parts are interrelated.
Figure 1. Main Components of an
Automatic Grease Lubrication System
The Principle of an Automatic System
As this approach becomes more widely adopted, automatic grease lubrication systems are replacing manual greasing. Although a smaller automatic system may lubricate only a few bearings, increasingly larger examples are typically being used to serve entire items of equipment, and can often be found lubricating bearings on paper machines as well as related pumps, agitators, mixers, screens and filters. Larger systems often incorporate up to a thousand lubrication points and are capable of handling the lubrication requirements of an entire mill.
Generally, such a system is regulated by an electronic control unit which pumps grease from the lubrication center along the main supply lines to the dosing modules. Located near the lubrication points, these dosing modules feed a measured quantity of lubricant to individual bearings. A system of pressure switches monitors the operation of the overall system, and optical indicators check the action of each dosing module.
Mill-wide Grease Lubrication Systems
A mill-wide system featuring a large, automated central pumping system typically lubricates:
For the UPM-Kymmene mill at Shotton in North Wales, this mill-wide lubrication system represents the way of the future. UPM is currently investing 159 million USD (127 million Euros) in new pulp equipment which will help convert one of the UK’s largest newsprint mills to using 100 percent recycled fiber in its PM1 and PM2 machines. Installed in 1985, PM1 came with a Safematic grease lubrication system. Because of the growing move toward automatic mill-wide systems and their benefits, other critical equipment in the production line such as the rewinders, roll conveyors and the process equipment in the basement were fitted with automatic greasing systems.
The same process was adopted for PM2. In 2002, 140 additional lubrication points were automated in the stock preparation area, increasing the number of automated lubrication points in PM2 production line to more than 700, which is about 60 percent of all the rotating bearings.
The last project was for the RCF 3 unit with approximately 300 points being fitted with automatic grease lubrication in 2003.
A mill-wide lubrication system like Shotton’s often meets the growing demand for efficient and reliable production processes. And although switching from a manual to an automated system as UPM is doing can generate savings in labor costs, these are usually far outstripped by the financial benefits which result from reducing bearing failures and increasing plant runnability. For this reason, the payback time, even for a large mill-wide lubrication system, may be less than one year.
Lubrication Investments – Life Cycle Cost vs. Profit
Compared with normal maintenance investments, the cost of a typical mill-wide lubrication system can appear too expensive to be financed from a normal maintenance budget. Yet if the system is viewed as a production investment, the cost suddenly appears far more reasonable and makes it a viable proposition, as the following scenario demonstrates.
In general, there are only two principal ways to increase a plant’s production capacity: install new, higher efficiency production machinery, or increase runnability by adding a mill-wide lubrication system.
The Finnish pulp and paper industry has many examples of manufacturers who have opted for mill-wide systems. Studies of their experiences by both the Technical Research Centre of Finland (manufacturing department) and John Crane Safematic have shown that this alternative offers a far more profitable path than installing new equipment. The studies looked at both the life cycle costs (LCC) and the life cycle profits (LCP) generated by the mill-wide systems.
Figure 4. Reasons for Bearing Failures
Life Cycle Costs
The results from analyzing the LCC and LCP data help pulp and paper mills both justify the initial investment costs and identify all other costs and profits associated with a mill-wide lubrication system during its expected life cycle.
Begin by calculating the investment costs of a mill-wide system and estimate the main part of the LCC. This is achieved by assessing the following elements:
The Purchase Price
The capital cost of a lubrication system typically includes:
The piping, engineering and installation work represent significant parts of the investment, as each can have an enormous impact on the system’s overall LCC. For example, a poor choice of materials at the time of purchase may generate significantly higher operating and maintenance costs in the future.
Figure 5. Multilube Compact Automatic Lubrication System
for Single Machines in Remote Locations
System’s Operating Costs
Lubricant costs - Although the lubricant itself represents an essential cost, this can usually be reduced by the installation of an automated system.
Maintenance of the system - An automatic system will usually have minimal maintenance requirements because its individual components are self-lubricated thereby suffering minimum wear, even during long-term use. In some cases, the need for maintenance can increase dramatically after a few years of operation due to imperfections in the design and engineering of the system, or an inappropriate choice of component and piping materials.
Steve Dickinson at UPM confirms that experience has shown that these elements are particularly important for a mill-wide system, especially as a well-specified and well-implemented system can provide other long-term benefits.
“For example, a good standard of piping and the use of high-quality compression fittings will not only promote better reliability, but will make it far easier to modify the plant as requirements change over time,” he said.
There are other advantages too, Steve added. “We’ve found that most grease system maintenance tasks can be carried out while the machines are running, which obviously reduces downtime. Because a mill-wide system introduces a high degree of component standardization, it makes it easier to contract out the system’s own maintenance requirements which can also help reduce costs.”
Life Cycle Profits
Estimating profits is a more complex exercise, simply because a lubrication system itself has no convenient production capacities which contribute directly to the mill’s overall turnover and profit. However, listing those areas that can be improved by better lubrication reveals many items whose direct contribution to turnover and profit can be calculated. These include the following:
Fewer Bearing Failures
According to the SKF Bearing Failure Analysis and the New Life Time Theory, approximately 75 percent of bearing failures are either entirely preventable, or ones whose risk can be effectively reduced by automatic lubrication. Academic studies and practical experience show that this risk reduction can be greater than 50 percent depending on individual circumstances.
Fewer Bearing Failures and Reduced Mechanical Damage
Although bearings are just one component of rotating machinery, a bearing failure usually prompts other mechanical failures in seals, impellers and shafts. The resulting financial costs of these indirect failures are often much higher than that of the bearing failure itself – something which can often be avoided by the use of an automatic lubrication system.
However, Steve Dickinson points out that like the Shotton plant, any mill will have some lubrication points which would be impractical to include in a genuine mill-wide automatic system.
“These might be points which are typically located well away from the main plant or that need greasing only infrequently,” he said. “Given the potential consequences of a failure, there’s obviously a great need to maintain a reliable lubrication schedule. While this can be performed manually, there is an option to use a small, self-contained system that will lubricate a discrete area of the plant or equipment.”
Lower Production Losses
Thanks to improved condition monitoring techniques, bearing failures now seldom cause production losses. Despite this, some 10 percent of all failures are still unpredictable and if one causes a shutdown, even just a minor shutdown in a critical part of the system, it could quickly lead to closing the entire plant. The cost of just one or two such shutdowns can exceed the cost of installing the mill-wide lubrication system which would have prevented the shutdowns from occurring.
Reducing the occurrence of shutdowns will result in greater productivity from the process, yet the specific value of this extra productivity is often difficult to measure.
In general, an automatic system will need far fewer staff to run it than would be needed to carry out manual lubrication, allowing a proportion of the mill’s personnel to be diverted to more productive work.
“There’s still a definite need for skilled people even with an automatic system,” Dickinson said. “Although the system’s user interface is easy to use and understand, problems can still occur. When they do, you need the skills on hand to resolve such issues. However, you must remember that far fewer skilled people are needed than with a manual system, because the automatic systems are generally very reliable.”
Reduced Lubricant Consumption
The basic volumes of lubricant used in automatic and manual lubrication are broadly similar. However, the shorter lubrication intervals and ease of adjustment offered by an automatic system permit grease quantities to be standardized. This results in less waste, lower overall consumption and consequent cost savings.
Environmental and Safety Issues
The environmental and safety benefits of an automated system are difficult to precisely quantify, yet they do exist. The savings from recycling lubricants are an obvious example, along with reductions in the need to carry out any difficult manual lubrication tasks, and these benefits can often be of particular importance to the mill’s customers.
Lower Inventory Value
If the efficiency of the overall maintenance work can be improved by the use of automated lubrication, it will reduce both equipment failures and the need to maintain a large spares inventory.
“That has certainly been our experience with automated systems,” Dickinson said. “Reliability has improved and our spares inventory has been reduced – improvements which translate into cost savings.”
These types of savings are especially important in today’s climate where many mills run without spare or standby machinery on hand, yet must still provide consistently reliable production.
A Field Survey of Life Cycle Profit
In examining mill-wide lubrication systems, one section of the studies looked at the life cycle profits (LCP) of one particular mill whose detailed maintenance history made it possible to identify developments over a 10-year period.
The mill, which has a capacity of 450,000 metric tons/year (t/a) of bleached market pulp, began operating in 1985. (Both paper and pulp mills usually specify the production capacity in metric tons/year; tons per annum = t/a.) The mill’s original bearings were manually lubricated, but a project to automate its lubrication was begun in 1994. The project was completed four years later, by which time 90 percent of the mill’s bearings were lubricated automatically.
Analyzing the Results
At the start of the field survey, it was obvious that the greatest increases in life cycle profits were made by improving runnability and boosting production capacity. Upon examination, the development of these figures could be traced over a longer period, showing that production capacity had increased by more than 15 percent over a seven-year period. (The temporary decrease during 1996 was due to an additional four weeks of planned shutdown.)
The main reason for the overall capacity increase was the drop in the number of shutdowns caused by mechanical problems.
Since 1994, the mill has had no shutdowns caused by bearing failures, and the figures show that the frequency of other maintenance shutdowns is closely related to the incidence of bearing failures.
Typically, the best reductions in bearing failure frequency have been achieved in the most difficult locations, where the number of bearing failures had previously been highest with manual lubrication.
Calculation Model for LCP
Based on the figures revealed by the field study, the LCP in this case can be calculated as follows:
|Shutdowns (2 yearly)||$222,720|
* converted from British Pound figures
Table 1. LCP Calculation (One-year Amortization)
Investment (automation of 332 lubrication points) – $133,000
Operation and maintenance costs - $4,000
A 36 percent reduction in bearing failures (down on average from 25 to 16 each year). The average cost of a bearing failure, including other related costs, was $57,600.
A significant reduction in the number of shutdowns. Before 1994, there were usually two shutdowns per year, each lasting an average of six hours and costing $600/ton in lost production. Since 1994 there has been none. The variable costs have been estimated up to $280/ton. (Pulp production of this mill is 58 tons/hour, two shutdowns make 12 hours, lost sales margin of production is $320/ton (600 – 280 USD), total loss 222,720 USD.)
A reduction in labor costs. The time to lubricate the 332 points is 430 hours each year (three minutes per bearing, at two-week intervals). This has produced total annual savings of $15,500 (pricing manpower at $36 per hour).
Lower lubricant consumption. The annual lubricant consumption of approximately 3,000 kilograms per year has been cut by an average of 31.4 percent. Given a lubricant price of $6 per kilogram, this has generated a yearly savings of $5,600.
A saving in lubricant waste-handling fees. With an average fee of $12 per kilogram, the total cost was $11,200 per year.
Simplifying the calculation by using one year’s time of amortization (to write-off the cost), the LCP calculation for the first year is shown in Table 1.
In this case, the investment payback time is less than one year. Extending the LCP calculation over the next 10 years clearly illustrates the profitable nature of the investment.
Using the same calculation, the sensitive analysis for investment also becomes quite simple. By substituting the various calculation figures, the critical limit of investment can be determined, although the importance of shutdowns will always remain a dominating factor.
LCP calculations for automated lubrication will always be a specific tool for the pulp and paper industry. Nevertheless, the field survey results clearly show that the calculations can be simplified and still yield reliable and useful results.
Until now, most maintenance investments have been justified simply by the need to keep machinery or equipment systems operating. Yet if these investments are valued as part of the production investment procedure, LCP calculation offers the best tool to evaluate the decision. Such evaluations provide today’s forward-thinking pulp and paper operators with a pathway toward improved international competitiveness.
As the pressure mounts on North American pulp and paper producers to be more competitive globally, such mills are investing in projects which have the biggest return on their investment within the shortest payback time. Automated bearing lubrication systems are proving that they belong at the top of the investment list based on their dramatic cost savings over typically short periods of time (many within six months or less).
Currency figures used in this article are based on exchange rates at the time of publication.
The title “Life Cycle Calculation” more appropriately represents “Payback Time Calculation”. The reason is that for relatively small investments, paper and pulp mills are mainly interested in payback time of the investment. In Scandinavian mills, it is commonly agreed that a lubrication system investment with a payback time shorter than one or 1.5 years is acceptable. Therefore, the example with less than six months payback could be considered very profitable.
It is possible to calculate the Life Cycle Profit for five or 10 years depreciation time, which is typical in smaller investments. However, because the yearly maintenance and operation costs in automatic grease lubrication systems are relatively low and they remain stable through the whole lifetime, the cumulative figure is a slightly dull straight line (although big money anyway). The situation is quite different in oil circulation systems where the oil costs, water costs, filtration costs, etc. have a great impact on the total Life Cycle Profit.