Thinking Local

Mark Mutter and Lawrie Evans, JAMCEM Consulting, UK


Introduction

For a process engineer working within the cement industry, the challenges are becoming ever greater. The demands for higher profitability from the plant continue to grow and these demands are expected to be delivered with increasingly fewer resources. CAPEX is often limited to projects that will deliver a payback of less than two to three years; both maintenance and sustaining expenditure are squeezed to minimal levels; and many of the easier opportunities for improving profitability - the so-called low hanging fruit - have already been implemented.

For managers of cement plants, getting the right people to undertake these engineering roles has also become difficult. In many countries, fewer young people see engineering as an attractive career path, preferring to take degrees in areas such as finance and IT. This has led to a reduced pool of available engineers, with many of these seeing the cement industry as unglamorous, dirty and hot, and therefore preferring less challenging roles in other industries.

In addition, the drive for profitability and the implementation of 'synergy savings' when companies merge has resulted in a reduction in engineering resources both on the plants and in the corporate centre. Unfortunately, those that leave are often those with the most experience, taking with them years of knowledge of the plant. For those that are left behind, the learning curve is steep and little guidance or mentoring is available to develop the capabilities of younger engineers. To compound this problem for plant managers, any engineers that do come into the company that show promise for the future are frequently fast tracked into corporate roles. This interrupts the engineers' development at too early a stage for the learning process to be sufficiently completed.


Standardisation of process evaluation

One way in which many cement companies have tried to address the reduction in engineering resources on the plants — as well as the lack of experienced engineers to mentor and train the new intake of engineers — is through the standardisation of engineering practices and procedures. While it is common practice to develop standardisation within a company — especially as it grows — it is essential that this standardisation does not result in a lack of thinking on the cement plant by the engineers, such that all the engineer is doing is comparing the data from their own plant with that which is found in the in-house reference manual.

At no time is this practice more wasteful and unproductive when performing plant test work. Much effort goes into organising the team to complete a mill audit or pyroprocessing heat balance, taking the measurements, having the laboratory analyse the samples that are taken and completing the calculations from pitot traverses and other measurements. Engineers need to remember that plant test work is not just a tick box exercise to produce a series of numbers, but a way of identifying opportunities to improve performance on the plant.

With all this effort being invested, it is essential that the test work is completed in a manner such that the all the measurements are accurately taken and that correct conclusions are drawn from the measurements. As each plant is different, both in design and raw materials, the required test work on each plant will differ, and the standardised methods of plant testing will not always take into consideration the differences between cement plants. As an example, when completing a pyroprocessing audit, some areas that can be missed when following the standard procedures are as follows:

  • Not correctly calculating the heat losses from the volatiles bypass, which is made up of three components: the heat value in the hot gases leaving the system; the heat in the meal leaving in the system and the energy that has been input into the meal leaving the system to partially decarbonate it.

  • Not taking into consideration the losses from carbon monoxide emission or the heat value lost in unburnt fuel - especially important when using natural gas as a fuel - which can be obvious areas for process optimisation.

  • Not measuring the power consumption of the main fans to allow a cross-check to be made on the measured airflows.

  • Failing to take oxygen measurements all the way from the kiln exit to the final fan to understand both where inleak is occurring in the gas handling system and the impact that this may have on the pyroprocessing system.

Before any audit, the process engineer needs to consider their own specific plant and what needs to be measured, while taking reference from the standard examples given in the company reference manual.

Following completion of the audit and the calculation of the results, further thought is required as to how these results are going to be used for process improvement. For all this effort to end up in a report that simply compares the results of the work with the standards in the reference manual adds minimal value to the engineering effort, apart from indicating whether the numbers are in the correct range or not. Proper engineering needs to be applied to the results of any process test work with one of the following considerations applied:

  • If the results of the test work show that the equipment is operating within the expected range, is there any way in which the equipment could be further optimised to reduce costs or improve performance, and how does this result affect the overall performance of the system.

  • If the result falls outside of the expected range, why is this happening? What needs to be further investigated to bring the equipment back into the ideal operating range? Who needs to take actions to correct the situation?

Process engineers also need to consider the readership of the reports that are produced from this test work. For example, a process engineer presenting the results of the audit by simply comparing their results with a set of standards will not assist the production manager in knowing that he needs to plan to install new refractory in the annual repair due to high shell losses. It will also not help the mechanical engineer to identify areas of high inleaking air that are costing the plant additional fuel and power consumption, as well as lost production on the kiln. It is a key role for the process engineer to not only take the measurements and understand what these plant measurements mean, but to translate them into a form that the other disciplines on the plant can understand and from which action plans can be developed.


Standardisation of targets

In standardising the process engineering function down to the level where the process has defined operating parameters, it is necessary to take into account that there are a number of variants for a particular process type, as well as different process configurations for the same description. Examples of this are as follows:

  • When considering a four-stage calciner, we could be talking about a single string or twin string calciner. Even within the twin string calciner, we could be considering an in-line calciner or a separate line calciner.

  • When considering a closed-circuit ball mill, there are a number of different ways the mill could be vented, and the configuration of the separator can be different in terms of how the final product is collected.

All the subtle differences in the equipment type and configuration mean that instead of a specific target for each plant being developed (for example for fuel consumption or power consumption), ranges of values are supplied as acceptable results. While this may be satisfying for the process engineer to find out that they are within the acceptable range, it does not provide a great deal of motivation to find the true target of the individual piece of equipment and then identify the potential performance improvement gap.

For example, when considering a pyroprocessing system, the following factors need to be considered:

  • The chemical and physical composition of the kiln feed to the system - in particular the lime saturation factor (LSF) of the feed to the system. In countries where lower LSF clinker is produced, there will be lower kiln fuel consumption, and therefore this should be considered in the definition of the target. Without taking this into consideration, other process inefficiencies may be masked by the contribution that the lower LSF has for the whole system.

  • Carbon in the raw meal, which will normally result in a lower fuel consumption target compared to a plant without fuel in the raw materials. In plants that have carbon in the raw materials, consideration of the burn-out characteristics of the carbon is also required to determine the contribution to the fuel consumption reduction.

  • The use of a volatiles bypass, with the target being defined as the minimum level required for the removal of the necessary amount of chloride or sulphate, not the level at which the plant feels comfortable.

  • A reasonable number of stoppages for the line so that the monthly/annual average fuel consumption can be compared to the actual results, as opposed to the monthly/annual average being compared to the company standard, which is normally a steady-state fuel consumption.

Similar comments can be made when considering the power consumption of the plant. There is little value in having a standard figure for each process stage defined in a reference manual when a plant-specific target can be developed. This should be a bottom up approach, taking each process stage and breaking it down into the elemental parts. Examples of this approach are as follows:

  • For raw milling on a vertical mill, the mill motor power consumption should be calculated based on the target raw meal residue and mill throughput. The mill fan power should then be calculated based on the necessary airflow for the mill throughput. The separator power and auxiliaries can then be added to give a power consumption for that plant section.

  • For cement milling, the mill motor power target should be at the maximum addition rate of secondary cementitious materials (SCM) that is allowed under the local standard for the cement type, not the level that is currently produced. This then gives impetus to improve the quality of clinker used in the cement and the separator performance, and develop any necessary capital investment plans to increase the level of SCM addition. The power required for the separator and ancillaries can then be added to this target.

Even when targets for process stages have been developed in this way, it is still necessary to monitor the main drive's consumption level, compared to the target, to identify any drift in performance. For example, a steady upwards drift in the power consumption in the cooler exhaust fan could be a sign of increasing inleaking air across the cooler exhaust system, which would merit further investigation. Using a well-configured power monitoring system can greatly improve the overall control of power consumption of the plant.


Global standards for local plants

One of the most illogical issues that arises is the implementation of global targets that do not make either financial or business sense. An example of this would be the implementation of a global alternative fuels substitution rate, where all plants within a company must reach a certain substitution rate. While this may be done for the right reasons, to satisfy internal targets and external commitments to long-term sustainability, it does not make sense in the following situations:

  • When the local source of fuel is subsidised, making it so cheap that the implementation of the alternative fuel project will not give a return on the investment.

  • When alternative fuels are scarcely, or not reliably available, due to an inadequate collection structure or tax on the fuel's disposal, meaning that the cost of the alternative fuel is higher than the cost of the conventional fuel in use.

  • When alternative fuel suppliers increase the price of the fuel over time, which results in the cost of the fuel mix increasing to similar levels as the conventional fuel.

  • When the use of alternative fuels reduces the kiln output to a point where the market demand cannot be satisfied.

In each of these cases, it does not make sense to either implement or continue with certain alternative fuels simply for the sake of maintaining the company target.

A similar case also exists with a global cement-to-clinker ratio. Reducing the quantity of clinker in cement brings financial benefits, as well as reductions in CO2, emissions. It is also an effective method of increasing the cement production capacity for a fixed clinker output. However, the materials must be consistently available at a reasonable price and the plant must be capable of producing cement that is competitive and appropriate for the local market.


The way forward

The use of standardisation itself is not a bad thing and is required as companies get larger; however, this standardisation cannot be allowed to lead to a lack of analysis and implementation of engineering solutions. It is not surprising that some of the most innovative engineering solutions that are seen by JAMCEM Consulting are in small companies with fewer sites, that have minimal standardisation and less engineering resources at the head office. In these plants, engineers must be truly innovative and use the limited resources that they have. This does not mean to say that, where the opportunity exists within a large company, thought should not be given to how younger engineers should be trained - exposure to several plants with different processes and operational issues will give the engineers a much broader starting point from which to consider how their own plant can be optimised.

Just as many companies change their strategies to improve their performance, it is perhaps time that some of this standardisation is blended with a certain degree of localisation. Adapting the targets to the local conditions and raw materials, and the cement types that are required in the market should bring back some real engineering thinking into an industry that is already struggling to find the next generations of good process engineers.


The use of materials published on the site is allowed only with the reference to the source (the journal «Cement and its application») and a hyperlink to the quoted material.
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The use of materials published on the site is allowed only with reference to the source (the journal «Cement and its application») and a hyperlink to the quoted material.
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