Control Technique Practical Work: Complete Technical Guide

Control technique practical work is the discipline that keeps the cement plant alive: the art of reading the signals, comparing them with the target and commanding the equipment: the temperature of the burning zone, the draft of the kiln, the load of the ball mill, the chemistry of the raw meal: every hour of the plant is a series of decisions taken by the instruments and the control room: the practical work of the control technique is not the theory of the page but the skill of the panel: the engineer who masters it turns the process data into the steady production and the low consumption: this file is the workbook of that discipline.

The Complete Cement Technical Package (931 files including the books, the courses, the Excel tools and the presentations: $249.99 one-time: instant download via the PayPal payment) includes this control workbook with its exercises, its diagrams and its charts: the one purchase that brings the library of the plant together: the engineer follows this article with the file in hand, section by section, and leaves with the practical frame of the loops of his own plant.

The page is organized like the workbook: the loop first, the instruments second, the controllers third, the kiln, the mills and the quality last, and the exercises in the end: the same order of the file: the reader goes from the definition of the controlled variable to the finished correction of the process, the path of every operator and every commissioning engineer of the cement industry.

1. The Control Loop: The Foundations of the Practical Work

The loop is the smallest unit of the control: every loop reads a process value, compares it to a target, and commands an actuator: the elements are always the same:

• The process variable (PV): the measured value of the process: the temperature, the pressure, the flow, the level, the speed: the true state of the plant at the moment of the measurement;
• The set point (SP): the target that the operator or the supervisor gives to the loop: the value the process must reach and hold: the operational target;
• The error (E): the difference between the set point and the measured value: E = SP − PV: the departure of the process from its target, the input of the controller;
• The controller: the brain of the loop: it reads the error and decides the correction: the proportional band, the integral and the derivative actions: the decision engine;
• The final element: the actuator: the damper, the valve, the feeder, the variable speed drive: the muscle of the loop: the physical action that moves the process;
• The process: the equipment in between: the kiln, the mill, the fan, the grinding: the dynamics of the heat, the mass and the inertia: the world that the loop must master;

THE CONCEPT OF THE FEEDBACK: the loop closes when the measurement returns to the controller after every action: the feedback is the faculty that corrects the drift without the human in the middle: the closed loop corrects itself against the disturbances, the open loop trusts the calibration: the practical work begins the day the engineer can draw the loop of each machine in his plant: the simple diagram explains most of the failures: the skill is transferable.

2. The Physical Variables of the Cement Plant: The Inventory of the Loops

The plant operates on a handful of physical variables: the complete list of the loops of the plant:

• The temperature: the burning zone at 1400 deg, the exit gas at 200 to 350 degC, the mill feed the grinding compartment: the most repeated measurement of the process;
• The pressure and the draft: the kiln hood, the preheater cyclones, the mill inlet: the negative pressure that moves the gas through the plant: the fan control;
• The flows: the fuel, the raw feed, the mill feed, the gas flow: the mass that runs the plant: the feeding rate of every bin and every scale;
• The levels: the silo levels, the bin levels, the tank levels: the inventory of the plant: the level controls the feeding process and the storage policy;
• The speeds: the kiln speed, the mill speed, the fan speeds, the separator speeds: the speed controls the residence time and the production;
• The compositions: the O2 of the kiln, the CO, the NOx, the chemistry of the raw meal and the cement: the analysers at the extremes of the process;

The inventory shows the rule of thumb of the plant: the loops are relatively few but they are everywhere: the discipline collects the variables in the central control room: the graphics of the DCS present them all: the engineer who knows the variables knows the plant: the practical work of the control is the work of observing these values with the knowledge of what they mean.

3. The Measuring Devices: The Eyes of the Loop

The loop is only as good as its measurement: the practical work starts with the selection and the care of the instruments:

• The thermocouples: the classic instruments of the cement plant: the range from the ambient to the 1400 degC of the material: installed in the bearings, the gas ducts, the preheater stages: the response time correct for the slow processes;
• The pyrometers: the radiation measurement of the burning zone: contactless, the measurement of the glowing clinker through the optics: the safeguard of the kiln temperature when the thermocouple dies;
• The resistance thermometers (Pt100): the precision of the lower ranges: the bearing temperatures, the mill temperatures: the stable and the accurate;
• The pressure transmitters: the draft measurement of the preheater and the grinding system: the differential pressures across the cyclones and the mill: the differential pressure of the mill as the load indicator;
• The flow meters: the feed of the material, the fuel flows, the water flows: the solid flow is also weighed: the belt scales and the rotor weigh: the mass of the feed;
• The gas analysers: the O2, the CO and the NOx of the kiln exit: the “chemist’s eye” of the combustion: the O2 as the index of the excess air: the CO as the index of the carbon monoxide that signals the loss of combustion;
• The level instruments: the ultrasonics, the pressure, the radar: the bins of the plant: the level signal drives the feeding logic above the low level.

The islands of the plant teach the lesson: the good instrument placed on the good spot is worth a thousand of the theories: THE MEASUREMENT IS THE FIRST LOOP: the plant cannot control what it cannot measure, and the maintenance of the measuring chain is the first practical work of every control engineer: the calibration log, the spare sensors and the weekly check of the basis.

4. The Controllers: The PID and Its Completers

The controller of the classic loop is the PID: the proportional, the integral, the derivative; the files and the engineers of the package call it the PID, the workhorse of all the industry:

• The proportional action (P): the output is proportional to the error: the bigger the error, the stronger the correction: the proportional gain (Kp): the gain too low, the loop too slow: the gain too high, the loop oscillates: the middle is found by the trial;
• The integral action (I): the accumulation of the error over the time: the removal of the steady state offset: the reset: the integral eliminates the error at the end, but too much integral gives the overshoot and the windup;
• The derivative action (D): the reaction to the rate of change of the error: the anticipation: the dampening: the derivative is dangerous in the noisy signals: it amplifies the ripple: used in restraint: the scheduled temperature loops of the mill receive it with care;
• The combination: the practical forms: the PI is the most used of the industry: the P only for the level, the PID for the quality: formulas of the allocation at the hand of the tuner;

The tuning of the controller is the born of the manual: the Ziegler-Nichols of the classic procedure: the step test or the oscillation test: the reactors give the values of the Kp, the Ti, the Td: the engineer of the package uses the time-tested values and then polishes by the trial on the running plant: the loops of the draft control work best with the PI, the temperature loops accept the gentle derivative: THE MANUAL: the section of the tuning with the example recipes is one of the most used pages of the workbook.

5. The Final Control Elements: The Hands of the Loop

The loop acts through the final elements: the list of the actuators of the plant:

• The dampers and the louvres: the draft control of the kiln and the mill: the position of the damper changes the flow and the pressure drop: the response fast and the simple;
• The control valves: the fluid’s fuel, the water, the auxiliary: the positioner converts the signal to the position: the characteristic of the valve (the linear, the equal percentage) shapes the loop;
• The variable speed drives (VSD/VFD): the fans, the mill mitters, the feeders, the pumps: the frequency control of the speed from 0 to the nominal: the modern control: the energy saving of the VFD on the fans is legendary: the law of the affinity: the flow by the speed, the power by the cube;
• The weigh feeders: the belt, the screw: the mass flow of the solid material: the weighing of the raw feed and the clinker: the accuracy of the feeding
• The rotary feeders and the screw feeders: the material transfer under the bin: the speed control of the feeder the flow to the process;
• The relay and the starter themes: the on-off actions: the pump start, the valve open, the air purge: the binary control of the plant;

The selection of the actuator depends on the process: the quick loops need the valves and the VFD; the mixing loops (the kiln feed) use the feeders: the actuator adds its own dynamics: the dead time and the nonlinearity: the practical work considers the hand element as part of the loop: the technician thinks of the delay of the actuator and the model of the lnP: the actuator is the muscle: the loop is only as strong as its muscle.

6. The Control of the Kiln Process: The Bureau of the Burning Zone

The rotary kiln is the hottest regulation problem of the plant: the practical work of the kiln loops:

• The burning zone temperature: the measured by the pyrometers: the control of the fuel: the temperature rises: the fuel reduces: the response very hot with the long lags: the base of the kiln control;
• The kiln speed and the feed: the ratio kept by the operator: as the feed rises, the speed rises, the degree of the filling stays constant: the `speed ratio` regulates the retention;
• The draft and the secondary air: the hood pressure kept slightly negative: the damper of the kiln: the pressure of the kiln must hold the flames and the bed: the controller of the pressure: the vigorous loops;
• The O2 of the exit gas: the combustion optimizes between 1% and 3% O2: the low O2 the fuel saving: the high CO the risk of the explosion: the O2 loop on the fan draft:
• The exit gas temperature: the flow of the material and the feed: the protection of the cyclones: the cold limits the control of the kiln;
• The feed rate of the material: the kiln feed set by the raw mill, the kiln itself takes what the silo sends: the feed enters the kiln through the planetary gates;

The kiln is the TALL ARENA OF THE PROCESS: the loops of the kiln interact: the draft changes the O2, the O2 changes the temperature, the temperature changes the feed: the kiln control is the coordination: the modern plants use the expert systems and the fuzzy logic that copy the operator: the manual presents the classic loops, the layer of the logic above, and the “heat & soak” strategy of the experienced.

7. The Control of the Preheater and the Calciner

The preheater tower is the heat exchanger of the plant: the loops of the tower:

• The stage temperatures: the temperatures of the cyclones from the top to the bottom: the 350, the 650, the 850: the controller keeps the profile: the deviations tell the blockages and the ragging:
• The differential pressures of the cyclones: the DP of each cyclone: the pressure rises with the internal circulation of the material: the cyclone blockage is seen in the DP before the temperature: the DP is the health card of the tower;
• The calciner temperature: the calcination at 850 to 900 plus the fuel of the calciner: the temperature and the O2 of the riser duct: the control of the secondary fuel of the calciner;
• The CO monitoring of the stage: the detection of the pockets of the incomplete combustion: the safety of the fuel of the aftersoft: the CO interlocks of the fuel injection;

The preheater loops are slower than the kiln, but the explosions never forgive: the practical work of the tower: the reading of the DPs, the early warning of the blockages and the blowout: the workbook gives the table of the normal DPs and the symptoms: the diagnosis of the tower is a daily performance of the operator.

8. The Control of the Raw Mill: The Load and the Drying

The raw mill grinds the mix of the limestone and the additives, and usually dries by the kiln gas: the loops of the raw mill:

• The mill load (the differential pressure): the DP across the mill: the load index: the DP rises with the material inside: the feed controller adjusts the rate to hold the DP: the tornado quality: the inside the bed state:
• The outlet temperature: the drying limit and the safety: the outlet temperature of the mill controls the hot gas damper: the cold gas and the air mix: the grinding and the drying must balance;
• The separator speed: the fineness of the product: the higher the speed, the finer: the control of the classifier: the quality parameter of the raw meal:
• The feed proportions: the limestone, the clay, the sand, the laterite: the proportioning feeders: the quality and the LSF: the ratio control of the feeders: the chemical loop in the EXO:
• The fan speed: the flow through the mill: the transport of the products: the fan the curve: the pressure control at the mill outlet;

The raw mill shows the MULTI-LOOP TYPICAL: the load loop, the dell temperature loop, the separator loop, the proportions: the corners of the plant: the classic failure: the loops pull in the opposite direction when the tuning is wrong: the practical work: first the master load loop, then the drying loop, and never change the two gains in the same day: the manual sequence of the commissioning.

9. The Control of the Finish Mill: The Quality of the Powder

The finish ball mill loop is the finishing language of the cement quality:

• The load control by the DP: the cement mill runs the full condition of the load: the DP, the “almost-full” philosophy: the feed as the high as the mill accepts: the bed: the vignettes;
• The curle and the ear measurement: the “noise” of the mill head: the direct indicator of the load: the full mill: the muted noise: the empty mill: the ringing: the acoustic mills of the optimizer:
• The product fineness: the Blaine and the residue of the 45 micron: the separator speed and the air: the closed circuit: the foal the classifier returns: the harder the material, the more the internal circulation;
• The temperature of the cement: the discharge temperature max of the 110 to 120  the protection of the gypsum: the temperature control and the water injection:
• The water injection: the cooling of the mill and the control of the soak: the water evaporates in the mill: the temperature stability and the cement performance:

The finish mill is the PRODUCTION MACHINE: the mass of the production: the quality that the plant ships: the tuning of these loops decides the tons per hour and the kWh/t: the workbook gives the complete session: the identification, the step test, the tuning of the DP loop, and the daily report sheet: the control of the cement mill the engineer of the future: the classic role.

10. The Control of the Quality: The Laboratory in the Loop

The quality of the cement is not measured only in the control room: the chemistry:

• The XRF analyser: the X-ray fluorescence of the raw meal and the cement: the elemental analysis: the CaO, the SiO2, the Al2O3, the Fe2O3: the minutes of the XRF: the fast information of the true loop:
• The blending control: the ratios of the raw mix: from the XRF to the LSF: the target of the feed: the controller computes the new proportions: the classic loop: the laboratory to the feeders: the closed loop of the quality:
• The on-line analysers: the cross-belt analysers of the quarry: the PGNAA: the spectrometry: the feed forward to the raw mill: the anticipatory loop: the response before the mill:
• The manual laboratory: the classic titrations, the Blaine, the sound: the back-up loop and the calibration: the correlation between the laboratory and the process analysers:

THE QUALITY LOOP: the chemistry is a control loop with a slow period: the sample, the analysis, the adjustment of the setpoint: the hour-scale loop: the practical work of the quality: the reconciliation of the online and the laboratory, the bias management, the statistics of the wasted: the workbook: the Excel calculator of the module, the LSF, the SM, the AM: the calculation engine of the mix.

11. The Safety Interlocks: The Hard-Wired Fourth Layer

Above the control loops, the safety layer:

• The interlocks of the start/stop: the sequence of the plant: the mills start after the fan, the kiln stops before the ID fan: the permissive of the interlock: the logical AND/OR of the plant:
• The low limits and the protection: the high temperature of the bearings, the low flow of the lubrication, the high vibration: the automatic trip: the protection of the equipment: the trip thresholds versus the alarm: the discipline of the reset:
• The CO and the fire: the CO of the filter ducts, the mill outlet: the CO2 inerting: the blast the bag filters: the trip of the hot gas path:
• The electrical interlocks: the motor isolation before and after, the sequence of the KV breaker: the safety of the energy isolation: the disconnector chain of the start:

The safety loops are the NON-BYPASS: the practical work the night: the bypass of the interlock is the worst enemy of the operation: the manual: the strict process of the interlock bypass, the registry, the reason, the time limit, the signature: the interlock is the last line between the abnormal and the damage: the engineer of the control treats the interlocks like the law of the plant.

12. The Practical Exercises of the Workbook: The Seven Sessions

The manual is a workbook: the seven exercises of the practice:

• Exercise 1: the identification of the loop. The training sheet of your plant: the PV, the SP, the actuator, the process for ten loops: the wheel: the 30 minutes of the identification: the basis of every session;
• Exercise 2: the dry tuning of the draft loop. The draft of the preheater: the step test: the response curve: the Ziegler-Nichols values: the simulation session of the workbook: the tuning numbers of your system;
• Exercise 3: the kiln temperatures incident. The worksheet of the burning zone: the pyrometer reading, the thermocouple, the sample: the diagnosis: the mismatch of the instruments: the corrective plan: the case study of the course;
• Exercise 4: the mill DP trip. The feed excursion: the DP curve of the last hour: the dead time: the reasons: the feed cut, the air change, the moisture change: the report:
• Exercise 5: the calciner dilemma. The CO irregularity: the fuel rich in the calciner: the temperature of the stage: the vortex: the safety schedule: the alarm response:
• Exercise 6: the quality loop failure. On the XRF drift: the series of the measurements: the bias discovered: the correction: the laboratory to the control: the case of the blending;
• Exercise 7: the commissioning day. The new mill: the sequence: the limit of the interlocks: the first start: the event log: the final tuning session: the handover report:

Each session carries the DATA TABLES and the empty worksheets of the plausibility: the practical specialty that the file: the engineer of the package works the sessions like the field training of the plant: and the answers, the lessons of the sessions: the appendix: the knowledge of the seven real cases.

13. The Tuning Practice: The Step-by-Step of a Real Loop

The tuning: the numbers of the controller: the methodical walk:

• Step 1: the manual mode. The loop runs the hand: the operator does the changes: the plant is safe and the comfortable;
• Step 2: the step test: a change of 5 to 10% of the output: the acquisition of the PV: the curve: the dead time, the time constant, the gain of the process: the identification of the FOPDT model;
• Step 3: the formulas: the Ziegler-Nichols and the Cohen-Coon: the parameters: the starting values of Kp, Ti, Td: the initial set:
• Step 4: the trial in automatic: the cut: the loop in the automatic: the response: the overshoot observation: the controller adapts: the gain increases and the oscillation appears: the Pareto of the response:
• Step 5: the fine-tuning: the last 10% adjustments: the response to the setpoint changes and the disturbances: the acceptance test: the loop logging 48 hours without the oscillations:

THE PRACTICE: the tuning of a dozen loops makes the technician: the loop of the first: the temperature of the mill, the pressure of the dust, the level of the bin: the same procedure: the manual has the plotting grid of the response curves, the blank strategy templates. The engineer trained on the 7 sessions of the manual arrives at his plant with the discovered blueprints of the loops ready for the field.

14. The Frontier: The Modem Control and the Future of the Control Room

The modern control of the cement: the same loops, the new tools:

• The DCS and the PLC: the distributed control system consolidates the loops: the PLCs and the bottom: the DCS of the plant: the redundancy and the diagnostics: the console of the operator; on the modern market the DCS/PAS (Process Automation System) is the standard control architecture of the cement industry;
• The advanced control (APC): the model-predictive control (MPC) of the mill and the kiln: the model of the process inside the controller: the predictions and the optimization: the advanced loops regulate the multivariable problem: the promise of the APC: the stable plant at the lower consumption: the honest view: the APC requires the good basic loops, the good measurements first:
• The expert and the fuzzy: the operator’s lessons in the fuzzy rules of the kiln: the classical: the implementation experience: the smiling: the rules are the knowledge of the mill; the expert shell tops the DCS; the plant keeps the human knowledge;
• The IoT and the analytics: the historians, the cloud: the trends: the big data: the maintenance of the machine learning: the prediction: the control of the future: the practical path: the historian of today:

The plant of the future is still the plant of the loops and the interlocks: the APC and the analytics are the layers of the same structure: the manuals of the package and the discipline of the fundamentals: the engineer controls the foundation, the advances: the career of the future: the control engineer: the bridge between the process and the computer: the work of the control was never more.

15. Frequent Questions on the Control Technique Work

Where do I start with the practical training?

With the identification of the loops of your plant: the exercise 1 of the workbook: the list, the diagram: one month with the identification, the loops of the own section: the training the loops: the graph: the two weeks of the curve watching: the loops of the priority: the damage of the draft and of the kiln: the start: the sessions of the workbook.

How much time does the PID tuning take?

A loop: from the half hour for the draft at the 8 hours: for the kiln: the time depends on the dynamics of the long: the plant: the safe tuning: the FOPDT of the step test: the formulas of the first numbers and the manual refinement: the time is the friend: the reviewer never stops the plant for the tuning: the session the small steps: the report of each campaign.

Is the PI or the PID?

Most of the cement loops serve the PI: the P for the flow and the draft, the PID for the temperature of the slow: the derivative is the amplifier of the noise: a dirty PID is worse than the P: the rule: the PI default, the D criminals: the practice of the reference: the manual the decision of the three: the logic of the tuning.

Do we really need the APC?

The classical loops first: the manual teaches the fundamentals: the APC multiplies the good fundamentals: the energy of the APC is between 2 and 6%: the benefits of the reported: the APC of the candidates: the plant: the accurate measurement and the stable loops: the first: the basic quality: the foundation: the APC: then it pays: the sequence of the implementation is the sequence of the benefits — never the reverse.

Where does the man sit in the control of the future?

In the supervision: the observer hierarchy: he sets the targets, the quality, the maintenance: he watches the advanced loops and detects the deterioration: the escalation of the abnormal: the human: the skills the shifts: the manual: the DCS, the ICM of the operator: the plant of 2030 still starts its people: the control engineer: the same basic, the new toys: the border of the profession is the knowledge of the foundation: the package: your library of the foundation.

16. Conclusion: The Control of the Plant is the Practical Work of the Engineer

The control technique: the engineering practice of the plant: the loop, the instruments, the controllers, the interlocks, and the people: from the draft of the kiln to the quality of the cement floor, the whole process is one network of the loops: the manual/workbook of the file: the exercises, the data tables, the worksheets, the sessions: the practical: the learning: the same structure: the completeness of the 931 files: the instrument of the control and the management of the plant in one.

The Complete Cement Technical Package (931 files: $249.99 one-time: instant download: the PayPal link) contains the whole of the control workbook: the sessions, the Excel engine, and the accompanying references: the one-time price: the lifetime of the practice: the engineer who masters the practical control of his plant shapes the performance, the energy and the quality of the plant: the control work: the science of the plant: the practice of the engineer: openly two one license: the handbook of the cement professional.

This file is part of the Complete Cement Technical Package (931 files) available from cementequipment.org. Respective rights holders; library copy for the licensed single user.