practical advanced process control

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Practical AdvancedProcess Control for

Engineers & Technicians





Advanced Process Control (APC)

Advanced control is one of

the most important ways in

which the production

situation can be improved,

and model-based control

offers a very direct and

feasible solution for an

appropriate operation.






Advance Process Control system consist of threecomponents :•a computer-simulation model that integrates

process knowledge and historical data,

•control and optimization algorithms, and•current, real-time process information.

APC relates manipulated variables and control

variables, provides multivariate control, and also

provides adaptive tuning and predictiveprocess

diagnostics.






APC is often used for solving multivariable control

problems or discrete control problem. APC is composed

of different process control tools like :•

!odel Predictive Control "!PC#• $tatistical Process Control "$PC# techni%ues• &ault detection and classification• $ensor control

• &eedback $ystems






• 'ormally an APC system is connected to a (C$. )heAPC application calculates moves that are send to

regulatory controllers.

• *istorically the interfaces between (C$ and APCsystems were dedicated software interfaces.

• 'owadays the communication protocol between these

system is managed via the industry standard +PC

protocol.



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APC vs Classical Control•

APC is an intelligent and active software layer thatsits above the classical regulatory control layer or

the (C$ in a traditional automation hierarchy.

• egulatory control primarily maintains desired unitmeasurements such as mass and heat balances. t

does not continuously improve the process, but

rather ensures that the hardware components

within the system are not eceeding known process, e%uipment and safety limits.




APC vs Classical Control

• n contrast, APC is designed to reducechangeabilityof key variables and continuously ad/ust the

process to guarantee the desired end result.

• APC software solutions are developed by building amathematical model of the process. $ince many

variables can affect a single process, a key part of

developing an APC model is identifying and

understanding the multiple critical variables thataffect the desired end result.




APC vs Classical Control• )he model is built using all available knowledge of

the process including human operators0 knowledge,

operating data, and any known scientific principles,

such as &irst Principle e%uations.

• )he same process also identifies and eplains thecritical sources of variability. As described, the

basic procedure of creating an APC solution

delivers fundamental Process understanding.

• )he process model itself can be used in an off-line

supervisory mode or an on-line measurement and

control mode.




APC vs Classical Control• n an off-line mode, a model-based APC solution

can identify the best operating parameters to

achieve desired outcomes.

• t can also be used on-line as a software-based

analyzer to help provide and predict online %ualityor performance measurements.

• $oftware process analyzers provide more fre%uent,

robust and often more cost effective measurementsthan are available from traditional laboratory

nformation systems.




APC vs Classical Control)his software analyzer allows an operator to

monitor the real-time feedback and predictions of

future process performance, and make manualad/ustments to ensure desired end %uality.

)he same model-based solution can be deployed

online to provide real-time control and optimization.

)he APC solution continuously monitors key process

variables, predicts outcomes based on the established

model of the process, feeds the real-time and pre-

dicted data back into the model, simulates the impacton the plant0s ob/ectives and then issues commands

back to the (C$ to make changes to key variables that

are driving results.




APC vs Classical ControlAPC improves management and the optimization of

a plant operation in four main areas:"1#2nhanced ability to determine product %uality in

real-time, on-site without waiting for a lab sample or an end-

of-the-run analysis.

"3#mproved operations stability and consistency."4#Ability to push process constraints.

"5#ncreased operational efficiency.

APC0s value and effectiveness have been demonstrated in petroleum, refinining food, paper and other sectors.




APCs ! "enefits

APCs are recogni#ed as best practices and proven investment

opportunity typically offering $ to % month payback and

operational benefits !

•ncreased capacity and increased production of

preferredprofitable products by 46 to 76.

•)ighter control of important product %uality or operationalvariables "8796 reduction in variance#.•ncreased recovery or operational efficiency, process

optimization by 36 to 56 or more.•educed energy per unit feed or product "846#.•mproved stability and increased operating reliability in response

to process upsets.




ustification of Advanced Process

Controls (APCs)• ustification for implementing APCs comes from

improved performance, because they stabilize

operations.• APCs remember different operating scenarios, resulting

in no operator errors.• ;ith adaptive control, eisting control model can be

updated. 2.g., if you0re are using P( tuner, then you

could develop new tuning parameters.• ;ith predictive control, time delays can be handled more

effectively to optimize throughput and reduce waste.




ustification of Advanced Process

Controls (APCs)

• APC is a software layer in a plant automation system

above the primary controls that is responsible for

maintaining operations within the desired limits or at

desired targets, stable operations after process upsets,

coordination of operating changes, and with a

continuous drive for improved basic economics.




E'ample ! Application of APC in istillation Process




E'ample ! Application of APC in istillation Process

• )he distillation process is a classic multivariable problem with control

variables, manipulated variables and constraint variables.• <sing model predictive control, the column can be controlled and operated

as a unit instead of a collection of loops.• n addition to reduced operator load, the process engineer identified 599

lbhour savings in steam on one of the columns and =99 lbhr on the column

where (istillation +ptimizer application was implemented.

• ;ith a cost for 147 psi steam of >7 per klb, this translates into energy

savings of more than >79,999 <$( for these particular columns.• )his savings adds up as all of the distillation columns on site are converted

over from multi-loop control to !PC-based control.• $team reductions are a result of lower reflu flows that have been reduced

by about 396. ;hile this change increases the average overhead impuritiesas is epected, it is well within specifications.

• ?eyond better performance and increased efficiency, the best measure of the

success to date has been operators leaving the !PC control on more than

=96 of the time.




E'ample*+ ! APC Application in ,ood industry

• &onterra Co-op. (airy ingredients @roup, implemented APC at its facilities

in 1==7, to improve processing efficiency for milk proteins, powders, cheeseand casein.

• )he company realized an + of over 96.• Production rates improve by 7 to 176.• ts product %uality by 796, energy efficiency by 7 to 136, while product

yields increased and variability fell, for all key control variables.• As a result of the performance gains, the company has installed APC at

many of its 34 'ew Bealand-based operations and &onterra0s ma/ority-

controlled overseas /oint ventures.• et us consider one specific implementation, a milk powder plant making

nutritional, whole milk and skim milk powders. )he plant has twoevaporators and one spray dryer with the two falling-film evaporators

feeding a 'iro atomizing spray dryer processing .7 to = tons per hour.





• )he evaporators concentrate the milk to approimately 796 total solids

")$#, with each evaporator using two effects.• )here is !echanical Dapor ecompression "!D# on the first effect and

)hermal Dapor ecompression ")D# on the second effect.• After passing through the evaporators, the concentrate is dried in the dryer

chamber and then in the static fluid bed "$&?# and the two vibrating fluid

beds "D&?0s#.

• )he final moisture specification limit is typically set between 3.7-4.76.• )he APC pro/ect was implemented in two phases.• n the first phase, &onterra0s on-line grading analysis system was installed to

allow n-Process )esting "P)# results to be measured and reported

statistically. )his allows operators to view product composition results

relative to product specifications and budget goals. )he on-line gradinganalysis system also provides a means to interface P) results to control

applications.





• n the second phase, an APC application was developed to minimize process

variability by compensating for disturbances, with the intention of creating a performance-driven, EobedientF plant. !ultivariable predictive control software

was used to implement the evaporator and dryer application.

• n addition, as part of the implementation, a software-based analyzer was

deployed to predict moisture for continuous feedback to the control application.A wealth of historical data for dryer0s wide product mi allowed a model to be

created that reflected moisture ranges for a variety of products with a high

degree of accuracy. )he analyzer was enhanced by installing an application that

biased the prediction hourly with P) data from the online grading analysis

system.





Control applications were developed for each evaporator feeding the dryer

with the goal of reducing total solids ")$# variability by 796. An auditconducted that demonstrated that the APC solution had eceeded this

ob/ective, reducing the variation by approimately G46 for 2vaporator 1 and

H6 for 2vaporator 3.

)he reduction in standard deviation of evaporator total solids will allowoperations to increase total solids targets in the evaporators without violating

viscosity limits. )his allows increased water removal in the more thermally

efficient evaporators. A higher concentrate total solids additionally allows

increased dryer throughput. A 9.76 increase in total solids from the

evaporators could lead to a 36 increase in dryer throughput.





• Control applications were developed for each evaporator feeding the dryer

with the goal of reducing total solids ")$# variability by 796. An auditconducted that demonstrated that the APC solution had eceeded this

ob/ective, reducing the variation by approimately G46 for 2vaporator 1

and H6 for 2vaporator 3.

• )he reduction in standard deviation of evaporator total solids will allowoperations to increase total solids targets in the evaporators without

violating viscosity limits. )his allows increased water removal in the more

thermally efficient evaporators. A higher concentrate total solids additionally

allows increased dryer throughput. A 9.76 increase in total solids from the

evaporators could lead to a 36 increase in dryer throughput.




E'ample +! APC Application in ,ood industry -

reduction in oisture /ariability




0 102 3A4T T0 5403 06E7

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