C04_Automation of Sugar Boiling Process in Batch Vacuum Pans Using ABB

7/29/2019 C04_Automation of Sugar Boiling Process in Batch Vacuum Pans Using ABB

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2004 EEE International C onferen ce on Industrial Technolo gy (ICIT)

Automation of Sugar Boiling Pro cess in Batch Vacuum Pans usingABB-FreelancePLC (A C 800F) and Conductor NT SCADAMaheshwarnath Behary, Robert T.F. Ah King an d Harry C. S. RughooputhFaculty of Engineering

University ofMauritiusReduit, M [email protected] In this paper, the design and implementationof the sugar boiling process in batch vacuum pans usingthe ABB-Freelance PLC and the Conductor N T isproposed. With a wei-designed automated system, theneed for operators supervision is greatly minimisedand hence permits the labour cost to be reduced andoptimising the repeatability and efficiency of th eprocess done by the system. Thus, the operator mayreadily and effcientty take real time action on the flowof the process permitting the latter to have an upperhand on the system as the latter may decide his owndesirable set points at critical intervals during thesugar boiling process. Using Function Block Diagrams(FBD) and Sequential Function Chart (SFC) as themain programming languages for the PL C and with theappropriate interfacing of the designed system on theSCADA as per the Conductor NT manual, a completecentralised control of the automated system for batchvacuum pans is proposed.Keywords: Automation, control, PL C, SCADA, sugarboiling process.1 IntroductionNowadays to maximise profit we need to minimise the costof production. The sugar industry [1,2] will definitely needdecrease the cost of production, which can be achieved byreducing labour or by displacing labour into ano ther sector.Furthermore, energy consumption will have to be used inan optimum way without any unnecessary wastage.Centralisation will be the next target, that is, smallindustries might have to close down and their activitiestaken up by major industries. After considering thesesuggestions, the best way to sustain these ideas isautomation. In fact, through innovation and upgrading themachineries, the costs of production, as w ell as the harvestwill be more promising to back the above ideas.The aim of this project is the automation of type batchvacuum pans. The boiling process that is undergone in thebatch vacuum pans is very compkx and lengthy. Todevelop the control statement the modular technique hasbeen used and this is enhanced by the use of the SequentialFunction Chart. The compIete automation design isproposed for the batch vacuum pans.

2 Overview of Cane Sugar ManufactureThe different processes involved wth the cane stalks arediscussed. Prior to extraction, the cane should be convertedto strands of thread-like fibre with pith (ffufTy in form), foran optimum juice extraction. Afier juice is extracted it isscreened, heated, defecated, decanted, filtered to removedirt and clay. After filtration, the juice passes through aseries of evaporators in order to remove maximum water.As water is removed, the juice becomes more viscous andthe brix (dissolved substance in solution) rises rapidly andthis viscous liquid is called syrup. Th e syrup is hrtherheated in a vacuum pan until it reaches the point ofsaturation, then s eedling can be initiated by the addition ofslurry (mixture of ethanol and icing sugar). The boilingprocess continues and the icing sugar c rystal grows and themixture becomes more viscous. The resulting viscousmother liquor is termed as massecuita. Finally, themassecuite is sent to centrifugal where the sugar crystalsand the moIasses are separated. The process continuesuntil sugar of type A, B and C are manufactured. Furtherprocessing is done to the crystals and stored in silos forease of transportation. The processed sugar is now readyfor domestic and commercial uses.2.1 Steps invok ed in a sugar boiling cycleThe flowchart in Fig. 1 shows the complete sequencesinvolved in a sugar boiling cycle. For ease of programmingthe sequences have been defined into discreet steps. All theactions that follows within a particular step have beenfiather defined in complete details so as to define the statesof all the input and output devices of the proposed systemin the control statement of th e system,3 Design for the New Automated System ofthe PansAfter considering the various requirements of the newsystem and considering its economic feasibility, aproposed design has been brought forward. It should benoted that the developed system should be very userfiiendly so as the operators can hlly interact with thesystem. To accomplish this an easily interpreted GUI(Graphical User interfa ce) should be developed.

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3.1 Functional Decom position of Proposed DesignFig. 2 shows the detailed design of the batch vacuum pans1 an d 2. Tags have been labelled in the design and aredefined completely in Table 3.1 and Table 3 .2 that follow.As it ca n be seen in the design, the lines in red show theinput signals from the transmitters namely the pressure,resistivity, vacuum and level transmitters. Lines in blueshow the processed output signals to actuate the regulationvalves to achieve desired conditions. Control is achievedby using PID (Proportional Integral And Derivative)Controller [6], which is a block function in the PLC that isthe algorithm of the PID ,exists in software in the PLCapplication program. In calandria of the pan, a pressuretransmitter is placed which will be used to sense pressureand send feedback to a PID block, which will regulate thepressure valve in order to reach the desired setpoint.Likewise, the other closed loops in the system performrespective control actions. -Moreover, the real-time valuesfrom the transmitters will be used for monitoring, hencethe need for these to be displayed with appropriate units onthe SCADA. The proposed system also contains ON/OFFvalves, which can operate in only two modes, which iseither opened or closed position. The states of these valvesalso need to be displayed on the SCADA for monitoringpurposes.< w I

Fig. 1 showing the various steps involv ed in a sugarboiling cycle

VC TD W

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UAVO297BATCHVACUUM PA N TWO

SLIAVO31

RSTO:- BAT C H VACUUM PAN ONEl lAVO13r

I S U A V K l B

Fig. 2: Detailed design of the batch vacuum pans

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3.2 Control Principtes Used to Control the Param etersin the New System 3.3 Identification of Inputs and Outputs for the BatchVacuum Pans1.

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Regulation of vacuum (0 inch mercury to 29.2 inchesof mercury) is achieved by controlling the entry offinely sprayed cold water in the barometric condenser,since vapour evolving kom the juice being heated inthe batch vacuum pans enters the barometriccondenser, which is a closed chamber. So this can beused to create vacuum by direct contact of cold waterwith the evolved vapour. Obviously, there will becondensation of the vapour and hence leading tovolume contraction in the condenser. This will lead tothe creation of vacuum.Regulation of pressure (- 1.0 bar to +0.6 bar) in thecaIandria can be achieved by varying flow of steaminto the calandria. To control the flow rate a regulationvalve can be used. By increasing the opening of thevalve, flow rate of steam can be increased and henceleading to an increase in pressure. Likewise, adecrease in pressure can be achieved by graduallyclosing the valve.Regulation of the hot water valve (0-100%) andsyrup/molasses valve (0-100%) will be used to controlthe desired slope (variation of concentration wthtime) set by the operator especially during the feedcrystal growth stage. Increasing the opening of thevalve will lead to increas e in flow rate and vice-versa.The water valves, syrup valves, pressure valves, coldwater inlet valve in the barometric condenser areexpected to be controlled automatically according tothe IeveUpercent opening of water valve,resistivity/percent opening of syrup valve, actualpressure in cahndridpercent opening of pressurevalve, actual vacuum in pansipercent opening of coldwater inlet valve in the barometric condenser. Thesecontrol valves are supposed to response according tothe instruction given by the controller.The remaining valves are the ON/OFF valves. Thesevalves have only two states, either they are opened orclosed. So, a signal from the Programmable LogicController is sufficient to either activate or deactivatethe solenoid of the valve .which turn opens or closesthe valves by positioning the controller of the valvesto allow f low of compressed air in the correctdirection.As it can be seen in Figure 2, lines in red shows inputanalogue signals kom the t ransmitters involved.However, lines in blue shows the controlled outputsignals from the controller to the correspondingrcgulation valves.It should be noted in the proposed design, an orcondition is defined for the inputs from the twovacuum transmitters. This is done so that each pan canwork independently of each other. Secondly, anaveraging function has also been used to average thetwo incoming signals from the two transmitters, so asto give priority to the pan with the lowest vacuum.

After analysing the proposed design (Figure 2) , first a listfor all the inputs and outputs were identified. Moreover, alltag5 used in the proposed design have been defined. Itshould be noted that the states of al l ONlOFF valves arebeing monitored; to accomphsh this feedback fiom theposition of the valves will be used. This signal will beobtained from the inbuilt limit switches in the valves.Moreover, the state of the discharge valve will not bemonitored, since this valve shall normally be closed in theprocess, hence no need to monitor its state. A visual alarmconsisting of a lamp will also be used. The lamp will beplaced near the pan, and will be used to signal for thesatisfaction of preset parameters (setpoint) set by theoperator. For example if the operator sets a setpoint for thebrix, the moment the setpoint has been attained the lampshall light up to catch the attention of the operator. Thelatter can then take appropriate Iocal action that is openingor closing valves. This will be used more frequently whenthe system will operate in the manual mode, or iscontroIled manually, that is, the operators intervention toconfirm that the next step can be started.4 Description of Equipment UsedA brief overview of the hardware and software that will beused for the realisation of the project is given. Then, thedetails and technical specification of the hardware usedwill be elaborated further. After the selection of thematerials, selected quotations for th e equipment will beanalysed in details for the selection of the cost-effectivecomponents.4.1 Understanding the Working Principles of the ABB-PL C (A C SOOF) [10,12]After considering the working principles of this PLC, forinstance a proper understanding of the communicationprotocols that have been used namely the Profibus DPprotocol and the Ethernet protocol. The input and.outputaddressing techniques of this PLC has been mastered, asthis will be useful in the control development,4.2 Ethernet ProtocolEthemet is quite a rapid medium of communicationespecially when dealing wth bulky softwares like theSCADA, which consists of synoptic views. That is whyEthemet has been used to communicate with the SCADAinstead of Profibus-DP. The use of Erhernet also permitsseveral computers to be connected to the network atdifferent locations in the plant for control and monitoring.It should be noted that Ethernet assign a unique address toeach hardware connected to the network, that is, it uses theTCP/IP protocol (Internet Protocol).

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4.3 Profibus DP Protocol maintainability, power supply requirements,ruggedness, availability, cost and so on.Profibus specifies the functional and technicalcharacteristics of a serial fieldbus. This bus interconnectsdigital and analogue field devices in the low(sensor/actuator level) up to medium (all level)performance range. The system contains master and slavedevices. Masters are called active stations. Slave devicesare simple devices such as valves, actuators and sensors.For the actual case, the PLC with the profibus module isthe master and the data logger modules are the slaves,which supply .data (serial form) to the PLC. One mainadvantage of using profibus-DP is to minimise the cost ofwiring, Instead of using many wires for taking signals fromisolated field devices, a single twisted pair cable, whichtransmits all the data into a serial communication [4] canbe used instcad to m inimise the cost of Wiring.4.4 The SCADA (Supervisory Control And DataAcquisition) SystemThe SCADA system communicates Wth specificcontrollers to retrieve data. S CAD A was traditionally usedfor data collection from PLCs and plant floor controllers.SCADA systems were also used for monitoring andsupervisory control of processes. The role of SCADAsystems has expanded. SCADA systems [3] are a vital partof many manufacturers information systems. Themanufacturing data, real-time values of parameters beingmonitored can also he used to program dynamic attributes(visual alarm like flashing and so on). Furthermore theycan also be used to program database for parameters ofinterest and collected data are clearly visible in th e form ofgraphs, this is normally known as historical trending. As awhole the SCADA is use to develop user-fiiendlygraphical intcrface. The main advantage of using SCADAis that graphical user interface (GUI) can be developed inan easiIy programmable way.4.5 Selectionof Sensors 171In selecting a sensor for a particular application, there are anumber of factors that need to be considered:

Identify the nature of the measurement requiredthat is factors like the variable to be measured, itsnominal value, the range of values formeasurements, the required speed ofmeasurement, the reliability required, theenvironmental conditions under which themeasurement is to be made.Identify the nature of the output required from thesensor; this determines the signal conditioningrequirements in order to give suitable outputsignals fkom the m easurement.Possible seiisors should be identified taking intoaccount factors like range of operation, accuracy,linearity, speed of response, reliability,

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4.6 Selection of ComponentsFor this project, the sensors were obtained from thesuppliers and they also have their inbuilt signalconditioning circuit. That is, standard output like 4-20 mAwas readily obtained from the ordered transmitters. Thevarious transmitters that were required for this project areas follows:

0 Pressure transmitters [9]Vacuum transmittersLevel transmitters

Resistivity transmitters (Radio frequency probe)P I

4.7 Criteria for th e Selection of ValvesControl valves are called to handle all kinds of fluids atbroad range of temperatures. So selection of a controlvalve body assembly requires particular consideration toprovide the best available Combination of valve body style,material and tr im construction design for the intendedservice. In order to select the control valve best suited forthe existing service conditions the following applicationguidelines should be considered.

Type of fluid to be controlled.Temperature range of fluid.Viscosity range of fluid.Minimum and maximum flow required.Minimum and maximum inlet pressure at thecontrol valve.Minimum and maximum outlet pressure at thecontrol valve.Pressure drop across the valve expected duringnormal flow conditions.lnlet and outlet pipeline size and schedule of pipe.

After considering the spec ifications of all the components,these components have been ordered so as to complete theproposed design.5 Understanding the Software for th eControl Statement IThe selected languages used are namely (1 ) The FunctionBlock Diagram (FBD) and (2 ) The Sequential FunctionChart (SFC). Some basic function blocks used for thesoftware development with th e FBD are discussed indetails. The rules of thumb of the SFC are also explainedas per the AC-800F manual. As per the requirements of thecontrol statements, approximately 20 function blocks wereused to develop the control statement. So, a deepunderstanding of these fbnction blocks is needed.

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5.1 Programming the PLCThe control statement was developed into different folderswith spe cific task that is using the modular technique. Thissimplifies our task in the testing stage. During theprogramming stage, some compulsory limits of thefunction blocks were not defined and these have to beentered by the operator. Hence, parameters for pan one wasdeveIoped so as to simplify the task of operator so that thelatter can easily enter the setpoint from the GUI. Thischaracteristic of the program enable the operator to havefull control on the boiling process and makes the systemflexible and adaptive in the cases of poor yielding fiom thesugar cane that is low purity syrup obtained. Theprogramming stage includes the development of theallocation list that is representing the hardware used wth acorresponding PLC address. The control statemen t that hasbeen developed should be tested to make sure that itcontains no bug.6 Graphical U ser Interface DevelopmentThe pan boiler operators should easily understand the GU Ideveloped so that they can interact fully with the system,which pcrmits full control on the sugar boiling process asper the operators choice.6.1 Real-Tim e Aspect of the SystemMost control rooms in industries require PC-based s ystemsthat automatically acquire data and display the parametersbeing monitored. The monitored parameters are relevant tothe current operating state of the plant, highlightingpotential problem areas to the control room staff andengineering staff. The displays must be informative andeasily interpreted at a glance by the operators. The mainemphasis concerns the real-time aspect of the system, that

is, the speed and capacity at which the data is gatheredfrom the system being monitored (Fig. 3).

L . .Fig. 3: Basic block diagram for the online data acquisitionsystem6.2 Developed Synoptic Views for this ProjectThe synoptic view shown in Fig. 4 has been developed inthe Conductor NT SCADA [l 11, the synoptic view is veryinformative as real time values and states of all the devicesused in this project is readily available by a simple glance.6.3 Synaptic view for the parameters of pansThis synoptic view shown in Fig. 5 has been developed tosimplify the task of the operator so that the latter can easilyenter the setpoint. This permits the operator to have fullcontrol on the process. The working principle of thissynoptic view is explained below.6.4 Developed synoptic view for historical trending ofpansA historical trending sub model was configured for eachpan respectively (Fig. 6) . This sub model was configuredsuch that the variation of the five main analogueparameters can be d isplayed with rea1 time fluctuations andcan store these fluctuations up to one week. The processmanager can thus have knowledge about these fluctuationsand the current yielding obtained from the sugar canebeing processed at the factory. A11 the synoptic views thathave been developed should be tested independently tomake sure that each sub models in the synoptic view hasbeen correctly interfaced on the SCADA.

Fig. 4: Combined synoptic view fo r pan one and pan two857


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Fig. 6: Historical display

Fig. 5: Synoptic view for the parameters of pan on e

of the SCADA6.5 Cost analysisThe idea behind this renovation was to reduce the cost ofproduction by decreasing energy consumption, labour andalso to optimise the sugar boiling process. We w ould haveto acknowledge the fact that large investments are neededin any re-engineering shift and competitiveness andincreased profitability should trail the way. In a standardeconomic analysis such as for this project, rough estimatesmust be made. Art economic analysis can be performed onthe system together wth an economic breakdown of themain categories concerned. This can guide the company oranybody in the assessment of the project feasibility interms of cost, selectivity and decision-making.7 ConclusionsThis automation project will definitely bring along wth itbenefits which will enable the factory to make maximumprofit at minimumcost. Examples of some of the benefitsthat will be witnessed after the implementation are(1) A decrease in production time,(2) Maximum sucrose yielding from the syrup, that

(3) A decrease in labour cost, and(4) An efficient energy consumption.is, lower purity of the final molasses,

Furthermore, the aims of increasing the profit, decreasingthe cost of production and optimising the productioncapacity will be attained. This system will clear the need ofoperators to be pennanently on site, next to the batchvacuum pans and actuating parameters manually as

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requested by the regulation process. This system willprovide the benefits of remote control and automaticregulation fiom a centralised control room action.References

J.V. PiIlay, Essential Sugar Technology by SugurMiIling Research Instjtute, University o f Natal, 4041Durban, South Africa.E. Hugot, Handbook Of Cane Sugar Engineering,Elsevier Publishing Co., 1960.John Stenerson, Fundumentals of ProgrammableLogic Controllers, Sensors, And Communications,Second Edition, Prentice Hall New Jersey, 1999. .Jerry FitzGerald and Alan Dennis, Business DataCo m m uni cd o ns and Nerworking, 6& Edition, WileyNew York, 1999.Douglas E. Comer, Internetworkingwith TCP/IP, 3rdEdition, Prentice-Hall New Jersey, 1995.W . Bolton, Electronic Conpol Systems in MechanicalEngineering, Addisoq Westley Longman Limited, 3dEdition, 1997.Katsuhiko Ogata, Modern Control Engineering,Prentice-Hall of India, New D elhi, 2000.The FS Duotrac Radio Frequency Probe UserManual.Operation and Maintenance Instruction Manual forIntelligent Pressure Transmitters (LD 300 series).(101 A C S6OF Documentation Version-6.2, PL C Manual.[l 11 Conductor NT (Version 4.0) Graphic Editor.

[12] hm://www.abb.com/control858

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C04_Automation of Sugar Boiling Process in Batch Vacuum Pans Using ABB