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Digital Re-print - September | October 2011 The Virtual Mill at the DMSB: Simulation of a 200-tonne wheat mill under professional conditions

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The educational and training programme offered at the Deutsche Müllerschule Braunschweig

(DMSB) is unique in Germany, Austria and Switzerland. Graduates of the DMSB work in leading positions in grain and feed mills and in mill construction firms.

To make teaching more practically ori-entated, the building of a school mill was discussed, like the one that is in use at the ENSMIC, our partner school in France.

In 2008, an exam paper dealt with the requirements in space, buildings and machin-ery on the premises of our school on the Salzdahlumer Strasse in Braunschweig.

Besides the costs, which could not have been covered by the Supporters’ Society of the DMSB and supporting com-panies, another argument for not building the mill was

the problem of disposing the products of the grinding process.

So, emphasis was put on the modernisa-tion of the existing laboratory equipment and the installation of new equipment for testing and training, instead.

This included the new centre for convey-

ing equipment (see picture 1), the installation and modernisation of several training stands, for example, machines for pneumatic con-veying, a roller mill with plansifter and the updating of hardware and software in the automation laboratory.

The co-operation of the teachers at our school with partners in the industry resulted in the idea to visualise the grinding process in a flour mill on a personal computer. This would give the DMSB students an oppor-tunity ‘to run a mill’ under conditions similar to those in a real mill. We call this system a ‘Virtual Mill’.

The company Keller-HCW/Laggenbeck has years of expe-rience in process visualisation and the programming of mill controls and was available as a partner. Mr Hartmann, Mr Sparenberg and Mr Stallmeyer were engaged in transforming the project into reality. Mr Klabunde, who has been a senior expert for our school for many years and has always been ready to give his profes-sional advice, took part in the

development of the principal structure of the simulated mill.

He also set up a PC programme that is able to communicate with the process control and process visualisation. This allows us to show how the mill reacts to changes of the grinding parameters (like the grinding gap or the mesh size of the sieves in the various passages) very similar to the reactions that occur in a real mill.

Siemens AG offer with their programme

by Uwe Schulz and Hasso Klabunde, Deutsche Müllerschule braunschweig, Germany

The virtual Mill at the DMSb: Simulation of a 200-tonne wheat mill under professional conditions

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Principal structure of the Virtual Mill

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„Siemens Automation Cooperates with Education (SCE)“ educational institutions the opportunity to acquire professional software for process visualisation and process control at low cost. This enabled us to configure the Virtual Mill using hardware and software with industry standard and to combine them with real measuring, protecting and controlling devices. Mr Schulz, teacher for automation at our school, set up a PLC programme, which allows to simulate faults and their consequences close to reality.

Hardware and software cost about €60,000.

The sum was paid by the Supporters’ Society of the DMSB between 2008 and 2010.

The actual stateWhile developing the Virtual Mill, various

earlier projects on the basis of PLC and operator panels were realised. These are now available for student experiments and training during their automation lessons.

The experience that was gained during this work and a lot of further ideas and suggestions made by DMSB teachers and specialists, led to the realisation of the Virtual Mill, which

today consists of the follow-ing hardware and software components (see picture 2):

Dell PC with Windows XP-Profession operating systemProduction Management System ‘CellaTrace’ by Keller-HCWProcess Visualisation Software ‘CellaControl’ for grain mills by Keller-HCW, based on Simatic-WinCC by SiemensPLC system (in form of a software PLC), Simatic-WinAC/LC in

the programming environment Simatic Step7

Network intercommunication via Ethernet and PROFIBUS DP with connection to two systems Simatic S7 CPU 315 2 DP/PN via DP/DP couplers

Hardware components, such as level indicators by VEGA or elevator monitoring by Agromatic.

Calculation software based on ‘Visual-Basic’

Fault simulation programmed in Step7-S7 GraphThe mill’s flow chart (see picture 3)

depicts a real 200-tonne wheat mill. It forms the basis for calculations of machinery and the determination of grinding parameters for the teaching in subjects related to grain milling.

Short description of the simulated milling process

The job management in the Virtual Mill is done by the production management system CellaTrace.

Here, raw materials, finished products, bin data and laboratory data are generated.

Jobs are automatically transferred to the process control system CellaControl and ful-filled by the simulated mill. The user will also receive circulation reports (see picture 5).

The mill that is realised and simulated

CellaTrace

CellaTrace circulation report

Flow chart of the Virtual Mill

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In the last column the individual percents are converted into the feed from the first break. The graph below gives the numbers in form of a sieve analysis. The three-column table on the right shows the actual feeds from the first break, as well as, on the right, the feeds before changing the roll settings.

In the small table below the yields of flour one and two, and of germ and bran which can also be seen before and after changing the mill settings.

Changes of the grinding moisture and the relative air humidity can be entered in the spaces in the bottom left corner. If for example, the moisture is set higher, the tailings from the plansifters is not sifted so well, the quantities change, more bran and less flour is produced. The changes are small, but noticeable.

The same will happen when the mill capacity is increased or the relative air humidity is set higher. This influences all pas-sages and, consequently, the flour yield.

The calculation is simply a mathematical com-putation of the feeds on the basis of the sifter fractions in percents. Details like the moisture loss and the losses of flour in filters are neglected.

On this basis, the feed on the following passages and the yield of final prod-ucts is calculated. The basic adjustment also pre-sets the power input of the drive motors in the roller mills, the moisture content at which the wheat is ground and the relative air humidity.

The following settings can be changed: Mill capacity, roll settings, sieve meshes in the plansifter, conveying of final products, grinding moisture and relative air humidity. The resulting changes in the plan-sifter tailings are calculated and the feeds on the follow-ing passages and the yield are determined. The power input of the drive motors is also calculated, and it is tested if the maximal power input is already reached.

Roller mill setting, sieve analysis and feeds on passages

The setting of the roller mills in the first passages is of great importance.

These product streams are the largest in a mill, and even a slight maladjustment will result in significant changes in the feeds. An example screenshot is shown in picture 11.

The rollers of the break passages I and II have been set two percent higher than the original setting. This results in smaller feeds of the front passages and larger feeds on the back passages. The flour yield of quality one is reduced by two percent.

This is partly compensated by 1.1 percent due to larger feeds in the following passages, but the overall flour yield will be reduced from 80.1% to 79.2 percent.

The column on the left of picture 11 shows a list of the passages. Break passage II is highlighted. The roll setting can be changed using the sliding button on the right of the column. The result is shown in the next col-umn in form of a table.

In the picture, all pas-sages are set to normal (= 0), only break pas-sage I is set seven points higher, break passage II four points higher.

The table in the top centre shows the quan-tities of the individual fractions of the break sifter II, which has been selected here.

On the left are the sieve meshes and the yields in individual and total percents. The column ‘to’ (‘nach’) gives the passage were the tailings are sent to.

within the software-based PLC system (see picture 6) is visualised on the basis of Simatic Win-CC using CellaControl, which has already been adopted in numerous real mills.

The Virtual Mill includes the following main plant components:• Grain silo with truck reception, pre-

cleaning and storage• Cleaning section with screen room and

dampening (see picture 7)• Milling section with first-break scales,

roller mills and sifters (see pictures 8 and 9)

• Flour silo with bins, blending and loading-out (see picture 9)The components of the plant can be run

automatically as well as hand-operated. It is possible to address all indicators and protec-tion devices to find out how the plant reacts.

By setting the roll gap in the roller mills and by changing the sieve mesh in the plan-sifters it is possible to influence the actual grinding process. After the calculation has been started, the resulting parameters, for example, the feed on the individual passages or the current and power input of the drive motors, can be visualised in the respective process displays. This will be explained in more detail in following part of this article.

How the running of the mill is ‘visualised’

There is pre-set basic adjustment of the mill with a certain capacity, certain roll gap settings, plansifter sections with respective meshes and certain percentages of product tailings.

Software-based PLC WinLC RTX

Visualisation of the process, screen room

oller mills with specification and possible roll gap setting

Grain&feed millinG technoloGy14 | September - october 2011

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Grain&feed millinG technoloGy September - october 2011 | 15

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the correlation of roll setting and power con-sumption of the roller mills.

Finally, it is possible to examine how mill capacity, grinding moisture and relative air humidity are correlated and how countermeas-ures can be taken by changing the adjustment of the mill.

In a real training mill, many of these facts could not be imparted, because the necessary amount of data would not be readily available.

So, the miller will learn how to run a mill in a surrounding that is close to his practical work, and the future millwright will become acquainted with circuit, interlocking and moni-toring devices of the plant.

Summary and outlookThe Virtual Mill provides teachers and stu-

dents at the Deutsche Müllerschule and other interested persons with a complex system for training and study.

It visualises machinery and automation in modern mills and it simulates the results of changes in milling parameters in a realistic environment.

In the worst case production will be stopped because due to an overload in the roller mills the motor protection devices respond and the respective passage comes to a standstill. But this will have no actual consequences, as it would have in a real mill.

In future, the Virtual Mill will become part of lectures and practice in the subjects Process Engineering, Milling Machines and Business Economics. It can also be used in other sub-jects, for example, data from laboratory training can be entered into the production control system to ‘produce’ appropriate mixtures of milling products.

The subject Process Construction will use the given machinery equipment as a basis for planning other mills, in the subject Mill Construction these plans will be checked for statics and conformance with building regula-tions. More teaching concepts making use of the Virtual Mill will follow.

before and after the rolls. When the maximal value is exceeded, an ‘!’ is added in the column ‘maximal A’, the transgression is signalled to the PLC, the motor stops work and the interlock-ing is triggered.

If the roll settings remain within the permit-ted limits, a new calculation can be carried out using the command ‘New calculation’ (‘Neu rechnen’). The new feeds, yields, power inputs and milling factors, caused by the changes, is transferred to all following passages. At the same time, the outputs of all roller mill drive motors are summarised and indicated in the lower right corner as kW and kW/t.

What can DMSB students learn when using the Virtual Mill?

The Virtual Mill can simulate all processes that occur in a real mill: Starting with grain reception and storage in silo bins, then convey-ing and blending in the silo, cleaning and pre-paring the grain in the grinding bins, the actual grinding, the conveying to finished product bins and finally the loading into bulk trucks.

Just as in a real mill, the PLC equipment is given a ‘job’ for every procedure, and

the fulfilment of this job is monitored in detail. In case of faults, for example, the complete filling of a bin an alarm is set off and the interlocking system is actuated. Then, the job has to be started again from the beginning.

In the grinding equip-ment itself, the interde-pendencies between roll setting and plansifter meshes or between feed to passages and flour yield can be analysed, as well as the results in the follow-ing passages when these parameters are changed. It is also possible to study

Consequently, the figures differ slightly from reality, but nevertheless they show the ranges and the correlations, because the differences are minimal and do not affect the training purpose.

The percental feeds to the passages and the yields are transferred to the PLC, where they are compared with limit values. If the limit values are exceeded, the system is alarmed and the interlocking reacts.

Roll settings and power input at the roll drives

The operator in a real mill has an ammeter on each roller mill, which has a red marking indicating the maximal value.

This shows him the scope within which he may set the rolls. In our Virtual Mill we also have an ‘ammeter’ which is represented by the column ‘actual A’ (‘A ist’) in picture 11 next to the roll setting.

When the roll setting is changed with the sliding button on the left, the ampere value in the column pactual Ap also changes. The calculation also takes into account the feed and a milling factor based on the sieve analysis

Roller mills with overview of specifications Picture 10: Flour silo with loading-out section

Display of the programme that sets the mill

Grain&feed millinG technoloGy16 | September - october 2011

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