06.10 automation

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Dairy Processing Handbook/Chapter 6.10 177

Automation

Getting the most out of a plant The nature of dairy operations has changed over the past few decades.Small, local dairies with manual operations have become outdated andbeen replaced by larger units with factory-style production.

This trend has caused many and far-reaching consequences. Processesin small dairies were supervised and controlled by a few skilled people, whocarried out most operations manually and also cleaned the equipment byhand at the end of each run. As dairies expanded, both the number andsize of the machines grew, as did the number of manual operationsrequired. Cleaning, in particular, was a laborious business – every machinethat had been in contact with the product had to be disassembled andcleaned by hand at least once a day.

Cleaning-In-Place (CIP), introduced in the mid-1950s, is used at most of today’s dairies. CIP means that equipment no longer needs to bedisassembled for cleaning. Machines are designed to be cleaned withdetergent solutions, which are circulated through the production linesaccording to a set cleaning program.

Extensive mechanisation of dairy operations gradually became a reality,with the result that more and more of the heavy manual labour was takenover by machines. Mechanisation, together with the rapid expansion of production capacity, also led to a substantial increase in the number of operations that had to be executed. More valves had to be operated, moremotors had to be started and stopped. The timing of individual operationsalso became critical. Operating a valve too soon or too late, for example,could lead to product losses. Every malfunction in the process, and everyoperator error, could have serious economic and qualitative consequences. Automation was the solution to handle these problems.

Process control Automation is a fast-moving field. Only a few decades ago, process controlsystems were based on electro-mechanical relays, wired together in alogical pattern. They were replaced by hardwired electronic control systems,which were faster and more reliable, as they contained no moving parts.

The next improvement was programmable control systems with the logicexpressed in data bits stored in an electronic memory, not in the physicalarrangement of the wiring. This not only made it easier to modify theprogram whenever necessary, but also reduced the cost of the hardware.

In modern control systems, the growing capability and reduced cost of computers and microprocessors has been utilised to distribute controlfunctions to local units. This gives the system as a whole more flexibility anda very high potential. The new processors can be used to control a single

machine, or build up a total control and management system to make anentire plant more productive.

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The most important advantagesof automation are:• Production safety

• Product quality• Reliability• Production economy• Flexible production• Production control• Tracability

selection of process equipment to satisfy external demands. Even if theprocessing units in a plant are chosen primarily to achieve the statedproduct quality, various compromises must be made, particularly if manydifferent products are to be manufactured.

Such considerations apply, for example, to the cleaning requirements of the equipment and its suitability for connection to the proposed cleaningsystem. Compromises must also be made on other matters, such as theconsumption of energy and service media, and the suitability of theequipment to be controlled. When selecting process equipment, it isimportant to remember that the process control solution should also beconsidered.

Correctly applied process control, in which a thorough knowledge of products, processes and process equipment guides the design, has manyadvantages. The most important are:• Safety• Product quality• Reliability• Production economy• Flexible production• Production control

Safety is secured by the control system through the continuous supervisionof equipment and processes. A malfunctioning machine will be brought to asafe status if a serious fault occurs, and a process fault will stop the relatedprocess. This system ensures the prevention of unwanted mixing of products, overfilling of tanks and other faults, which might cause productlosses and production disruptions.

The process is monitored in exactly the same way during eachproduction run, which means that the finished product will always have thesame high quality after fine-tuning of all processing variables for an optimumoutcome.

Precise control of the process means that product losses andconsumption of service media, cleaning solutions and energy are kept to aminimum. As a result, the production economy of a well-designed and

adapted control system is very good.Flexible production can be achieved by programming the control systemwith various production alternatives and production recipes. Changes inproduction can be implemented simply by altering a recipe, instead of modifying the actual program.

The control system can also provide relevant production data andinformation in the form of reports, statistics, analyses, etc. The databecomes a tool for more precise management decisions.

Control levels The following definitions have been adopted to describe the level of controlin the system:• Manual control• Unit control and supervision• Line control and supervision• Production management

Manual control All operations in the plant are carried out manually. Control modules aremanually operated, but normally they are started or stopped from panelswith push buttons, with no interlocking function. Some single valves, suchas the diversion valve in a manual pasteuriser, may be automaticallycontrolled, but the plant or line is still considered to be manual.

Unit control and supervisionEach process unit is operated from its specific operator panel. Each unithas a standardised way of communicating with other units and supervisory

A plant design is always acompromise between:

1 Product2 Process3 Economy4 External factors

Fig 6.10.2 Swing-bend is an example of a manual control system.

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Dairy Processing Handbook/Chapter 6.10180

systems. The units either communicate with a limited number of I/O-signalsor with a communication link. The complexity of the control systems is low,so the demands on the local service organisation are limited.

Line control and supervision The operator supervises the plant or line from one or more User Interfaces.Process units, with their own specific operator panel, are normally

supervised from central User Interfaces. Co-ordination of routings andoperation of units is done from one or more plant PLCs.

Line control and supervision gives an excellent plant overview andfacilitates increased plant functionality, i.e. operations can be carried out in asequence and losses can be minimised by optimisation of the processsequences. Changes in the process will require modification in the controlprogram, and therefore demands on the local service organisation are high.

Production management Production and cleaning can be executed in jobs or batches, using recipes. The Production Manager can schedule batches from an operator station,which can be situated in an office. The operator of the process supervisesthe execution of scheduled batches from one or more operator stations. Ina bigger plant, each operator station should encompass a dedicatedproduction area.

Control of process units that have their own specific operator panelsshould be included in the execution of batches. One or more plant PLCscontrol the routings, and the plant server co-ordinates all activities in theplant. The history of the batches is stored in a database. The use of advanced technology means the control system is highly complex.Changes in the process will result in modifications of the plant models,recipes and programs, and therefore the demands on the local serviceorganisation are high.

Operations can be carried out in sequences, and product losses can beminimised by sequence optimisation. The performance of the plant can beanalysed, and the way a specific end product was produced can be tracedback through production.

Requirements for a control systemReliability, flexibility and economy are the most important requirements for amodern process control system. This means that the control system should:• Be reliable and easy to maintain• Have a user interface that is logical, self-instructing and efficient• Be based on off-the-shelf hardware and software• Include software for diagnostic testing and modification• Be easy to extend

Extending a control systemOne of the most important requirements for a control system is thepossibility to extend the system when required. It should be possible tobuild a system of any size, step by step, by adding standard components. A small process controller installed to control a reception line could beextended later with more controllers of the same brand that control milk treatment, filling, etc. At the same time, management routines could beadded to existing controllers to feed data into management computers.

When extending a control system, it is very important that all controlsystem components, from the remote sensor to the user interface, are easyto connect to each other in order to create a smooth functioning control

system platform. Using products from a sole supplier will normallyguarantee this.

Fig 6.10.3 Unit control and supervision system.

Fig 6.10.4 Line control and supervision

system.

Fig 6.10.5 Production management system.

Tetra ak

TA FLEX

TT01

0 00- 4-13 21 7

21.0

21.0

0

FT20

TC44

21.0

TC64

21.0TC63

1

2

4

3

R

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How does the control system work?

Definitions Automation = Process Control and Production Management.

Automation means that all actions needed to control a process withoptimal efficiency are handled by a control system on the basis of instructions that have been programmed into it.

Process Control System = The system executing Process Control. Itnormally incorporates:• User Interfaces, which are used by the process operator to

communicate with the control system and the process.• Process Control, normally a PLC (Programmable Logic Controller),

which executes actual control of the process.• I/O-system interfaces with control modules and transmitters in the

process.Management Execution System (MES) = The system executing

Production Management.• It can also form a link to other company systems such as Enterprise

Resource Planning (ERP) systems.

LogicLogic is a fundamental concept in Process Control. It denotes the decision-making mechanism, making it possible to perform a given task according toa given model. The human mind is programmed by education andexperience to perform a task in a certain way.

Figure 6.10.7 shows in a manual system, how an operator uses logicto solve a control problem, which involves supplying a process linewith milk from a battery of tanks. He receives information from theprocess, e.g. that tank T1 will soon be empty, tank T2 iscurrently being cleaned, tank T3 is full of product, etc. Thisinformation is processed logically by the operator. The figureillustrates his train of thought – the questions and decisionshe has to formulate. Finally, he implements his decisions bypushing the correct buttons on his panel to actuate the rightvalves, pumps and other control modules.

The operator has no great difficulty in solving thisparticular control problem. Even so, the potential for errors isalways present. Detergent and milk could be mixed bymistake. The process line may run out of milk, resulting inburning-on at the heat transfer surfaces. Milk in the tanksmay be wasted when the tank is cleaned. The risk of sucherrors increases if the operator is responsible for several similarsections of the process at the same time. He may be rushed andunder stress, which heightens the risk of him making a mistake.

At first glance it is easy to assume that the operator is

constantly faced with choices between many alternative solutionsto control problems. A closer look reveals that this is not the case. After many hours of operation the dairy has verified the controlsequences, which results in optimum product quality, safety andeconomy. In other words, the operator has acquired a more or lesspermanent control logic. He selects tanks according to establishedroutines, uses a stopwatch to time milk drainage from atank, so that he knows exactly when toswitch to a full tank in order to minimiseproduct losses, and so on. Each process canbe analysed in this way and it is then possible, onthe basis of the analysis, to determine the control logicthat produces optimum results.

The control logic is stored in the form of a program in the specificprocess controller, which is normally a PLC.

Fig 6.10.6 Process Control is normally executed by a PLC (Programmable

Logic Controller).

R

C

TUNE

SET

PROG

R

C

TUNE

SET

PROG

T3? Yes, it´s OK.

T1? it´s empty now.Wait 10 seconds forthe line to the valve

cluster to drain

Shut V2, open V1,shut V4, open V3.

Which tank shall ichoose?

T2? No, it´sbeing cleaned.

How much milk isleft in T1?

I must switch tanksin 10 minutes

Fig 6.10.7 In a manual process theoperator uses his logic to solve the processing demands.

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Control system All the transmitters and control modules in the process (4) are connected tothe logic by the Input/Output (I/O) system (3). In this way, all the necessaryinformation regarding temperatures, flows, pressures, etc. is transmitted tothe logic of the control system. After processing of I/O-signals and operatorcommands, the logic sets the correct output signals to actuate the controlmodules involved in the process. This is done in a certain order to comply

with the logical conditions that apply to the process. The control modulessend back feedback signals confirming that the commands have beencarried out. These feedback signals are used by the logic as conditions,permitting the next step in the sequence to be actuated. The principallayout of a control system is shown in Figure 6.10.8.

If the output signal and the feedback signal do not match, an alarmsignal is generated, trying to bring the related process to a safe state. Thisassumes, of course, that the fault in question can be predicted. As a

SYSTEM

SYSTEM

1

2

3

4

Logic In/outLogic In/out

Fig. 6.10.8 Principle of a processcontrol system.

1 Operator VDU 2 Printer terminal 3 Input/Output units4 Process equipment

process becomes more complicated, and demands on operational securityand economy become stricter, the required control program (logic) has tobe extended accordingly.

All user interfaces (1) are connected to the logic as well as local operatorpanels.

Distributed intelligenceEfficient process control requires first-class electronic solutions in theprocess. The operation of the entire automatic process control system willbe jeopardised if transmitters and sensors do not work properly.

The valve control system shown in Figure 6.10.9 is an example of distributed intelligence. Running a dairy of any size involves keeping track of hundreds or thousands of valves and operating them in differentcombinations and sequences. PLCs are dedicated systems to solve thesecontrol tasks in the shortest possible time. To do this, the PLC needs achannel for instant communication with all the valves. This makes theinstallation expensive, but new valve control systems have been developedto provide an economical solution.

A modern system consists of a number of valve tops (1), one for eachvalve. The valve tops are connected to a common fieldbus cable and acommon compressed-air line. The fieldbus cable is connected to a gatewaycommunicating with the control system (2) and the power supply serving

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the valve tops. Several fieldbuses can be connected to theprocess controller to control the required number of valves.

Another important advantage of the system is that thevalve top unit reports the valve status back to the controlsystem. The modem scans the status of all valvescontinuously and instantly informs the process controller if amalfunction arises. This facilitates fault tracing andmaintenance, especially since it is possible to disconnectindividual valve units without disrupting theoperation of other parts of the control system.

The fieldbus concept is also starting to beapplied for transmitters and instrumentation asa whole – distributed temperature control andflow-metering are just two examples.

For the producer, the advantage is not only a significant reduction ininstallation and commissioning costs, but also the increased amount of useful information, which makes the total investment in a control systemlower than for a traditional system.

Batch control

Production in liquid food plants is becoming more complex as new andmore complicated recipes are introduced. Strict recipe procedures must befollowed to manage production and guarantee product quality.

The increased number of products demanded by producers meansshorter production runs. In order to stay competitive in this situation, theefficient planning and running of production is a necessity.

The manufacture of 50 tons of strawberry yoghurt, for example, is calleda batch. Instead of only executing conventional process operations, such astransfers to and from process units, the batch control system takes totalcontrol of production, from milk reception until the yoghurt cups are storedfor distribution. The major benefit of batch control is that the system helpswith all the necessary actions.

Recipe management Using recipe management, a producer will have full control whenintroducing new products. If no new process equipment is needed, there isno need to call in external assistance to reprogram the control system. Allprocedures are edited on site using easy-to-understand tools.

All previous recipes are automatically stored and ready to use wheneverneeded in the future. Any existing recipe can be easily modified on line andstored as a new version or a completely new recipe.

Flexibility is maximised, as all recipes are scalable.

Control of production The batch control system gives comprehensive on-line information aboutwhat is happening in production: production figures and totals to date, dataon products scheduled for runs later in the day, and current problemsrelated to production and lines. All this information can be displayed on anyuser interface connected to the network.

How does the data management system work?

Work Tracking

Logging production dataEverything that occurs in the control system can be logged automatically ina database and tagged with a specific identity. This means it is possible toautomatically compare parameters between production runs by producing

Fig. 6.10.9 Valve control system.

1 Valve control units 2 Control system (PLC)

1

2

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a report, which will probably reveal any quality problem that has occurred ina specific period. In this way, it is possible to solve problems concerninginconsistent quality or difficulties in running a particular product.

In addition, it is possible to automatically produce a report defining alltarget and actual values during production – all events and any errors thatoccurred during a particular production run. Laboratory data can be addedand connected directly to the tagged output.

Tracking production The producer must define the target level for tracking production. There aresystems and methods available to provide the required level. Alternativesare:1 Full traceability – production runs are separated with flush/CIP.2 Limited traceability – filling and emptying of tanks or process lines cannot

be done simultaneously.3 No traceability – filling and emptying is done simultaneously. The full traceability level provides all the data for any type of report, but thisalso imposes restrictions on how the plant can be run. The lowest level willgive a more flexible plant, but with minimal or no traceability.

Analysis The customer requirement trends regarding plant engineering have beenmore and more focused on lower production costs and minimising losses,rather than process components and simple transfer functions. Often therequirements set out in the contract propose “minimising losses” or“reducing losses to 1 %”, etc. There are hardly any proven tactics ormethods to deal with such demands, unless a certain methodology is usedwhen designing and commissioning the plant. There are many questionsthat need to be resolved. How do you:• Estimate theoretical product losses?• Design the plant process and automation to minimise, measure and

confirm product losses?• Commission while keeping the product loss paragraph in mind?

• Ensure that product loss reports during normal plant operation aremeaningful and lead to correct actions?

For day-to-day production, a report can be produced based on the optimalrunning scenarios decided during plant dimensioning, optimisation or atlater stages. The optimal running scenario for the given production daycould also be sourced from other programs. There could be several optimalscenarios in the plant, (generated during optimisation or later), dependingon time of the year, the day, etc. The manager or planner selects the correctoptimal scenario for the day.

The report shows unit by unit whether the plant is operating according tothe optimal dimensioning and production planning.

Certain figures are shown for each unit. These figures represent specificset values (taken from the optimal scenario) compared with the actual

figures. The figures/unit could be:Lines, pasteurisers, filling machines• Ratio of production hours/idle hours• Ratio of start/emptying/production run hours• Ratio of circulation (or, for lines or machines: transfer selected, but pump

idle) time/production time• Amount and type of cleaningTanks• Ratio of product in tank period/24 hr• Amount and type of cleaning The figures for optimal and actual running are compared. If the figures differby more than a certain value, they are highlighted. The reason could beoperator error, less than optimal planning or that the plant is not

dimensioned for that type of production. The deviation could also becaused by equipment faults (temporary problems). The findings and causescan be scrutinised later by the planning manager.

Pr oduct data

MILK

Silo tank S4 04°C

Time 14:23 – 20:04

Pasteur iser B2

Time 19:34 – 20:05

05– 65– 74 / 15 s– 14– 03 °C

Separ ation, standar disation

fat content 1,5 %

Par tial homogenisation

at 200 bar

Stor age tank T18 04 °C

Time 19:35 – 20.06

Filling machine TBA 12

Time 19:55 – 20.47

Packing line P4 04,5 °C

Time 19:55 – 20:58

Container E237 699

Stor age section LL76 03°C

Distr ibution lor r y D24

Dairy Farm

567Delivered

2003-02-10

at 14:22Qua

ntity22 000 l

Temperature

04 °CFat content

3,6 %Protein2,7 %

Fig. 6.10.10 The whole dairy process

can be traced.

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Planning and schedulingDevelopment of planning and scheduling systems within the industry hasonly just begun. The basic idea is to integrate the whole informationstructure of the plant or the entire company.

There are already tools available to produce an analysis of customerorders, available production resources and raw materials, and turn this intothe optimal production schedule for a specific period.

Fig. 6.10.11 Totally integrated system

including Management InformationSystem.

1 Process controllers 2 Operator VDU

3 Manufacturing Execution System

1

2

3

1

2

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06.10 automation

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