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Cement Factory

I.Control method of common electric equipment in cement plant

1. Measurement points of general motors

Ready (RD): DI point, ready, whether starting conditions of equipmentare available;

Response (RN): DI point, response, whether equipment operates or not;

Drive (DR): DO point; drive, whether equipment is driven by DCS;

2. Basic control principle

Equipment can be driven after it is ready and can be operated after it’sdriven. Different interlock protections shall be provided.

Startup fault: the computer will automatically have faults, give outalarm and stop drive in case the driven equipment has no response withinspecified time;

Operation fault: the driven equipment will automatically have faults,give out alarm and stop drive in case the response is returned, self-protectionof drive is activated but the response is missing during operation and itexceeds the specified time;

Safety interlock: safety protection of motor: comprehensive faults;temperature switch; speed switch; misalignment switch; tear;

Upper interlock: also called startup interlock, which can ensure thatthe equipment starts according to process;

Lower interlock: also called operation interlock, which can ensure thatthe equipment operates according to process; it can have automatic interlockand stop the drive of equipment in case the lower equipment (which is involvedin sequential interlock) has abnormal faults;

Shutdowninterlock: it can ensure that the equipment stops according to the process andcan permit the effectiveness of shutdown command;

Vibration:the measurement point signals which enter computer system become abnormal dueto different reasons at site. It includes: instantaneous interruption and closeof measurement point signals and the measure value exceeding the normal range.

Delay protection: the safety interlock can beprovided with delay output protection; the delay time can be one second orwithin reasonable time; the vibration of measurement points within specifieddelay can be ignored and it’s not involved in interlock control; thecomputer system will execute the corresponding interlock control if thevibration exceeds the specified time. Similarly, the lower interlock can beprovided with delay disconnection protection.

3. Groupoperation

The related equipment shall be reasonablydivided into certain groups according to process requirements for groupcontrol, namely group startup and shutdown.

The nine forms of group are as follows:

Groupready; group startup command; group startup activated; group shutdown command;group shutdown activated; group fault; group operation; group interlock; group state.

For example, the powder grinding sectioncan be divided into certain groups according to the technological process:

Group 1: thin oil station group

Group 2: system fan group

Group 3: finished products delivery group

Group 4: powder selecting machine group

Group 5: hoister group

Group 6: group for water resistance ofgrinder main motor

Group 7: group for grinder main motor

Group 8: feeding group

4. Unlock

The unlocked motor can be separated fromgroup control and can control startup and shutdown independently

5.Forward/reverse rotation of motor

Forexample: electric hydraulic push rod and gate valve are equipment withforward/reverse rotation and their measurement points include:

Ready (RD); forward response (RNF);reverse response (RNR); forward drive (DRF); reverse drive (DRR); forward limit(LMF); reverse limit (LMR);

Forward/reverseselection (SEL) shall be provided for each motor which has forward/reverserotation.

Interlock protection:forward/reverse response is used to protect motor which has forward/reverserotation, that is to say, the forwardselection has interlock with forward response and reverse selection hasinterlock with reverse response; but the interlock for motors of electrichydraulic push rod and gate valve shall be considered differently since thelimit points in computer system cannot be timely and accurately measured whenmost of limit switches fail due to different reasons at site when forward orreverse limit is used as interlock; the forward/reverse selection, instead oflimit, shall be used as interlock to avoid unnecessary troubles; the time shallbe considered since the response will be missing firstly when drive arrives atlimit position and the limit will arrive in 2s and there shall be no operationfaults of equipment in this period.

Gate valve opens along with groupstartup and closes along with group shutdown;

6. Controlof high-voltage motor

High-voltage motor has similar control withlow-voltage motor, except that the high-voltage motor is provided withhigh-voltage control protection:

FT1 Accident trip

FT2 Integrated over-current relayhas faults

FT3 Power loss alarm

FT4 Disconnection of trip circuit

FT5 Thermal overload

Check ifthe high-voltage protection is activated through computer when high-voltagemotor has fault. The high-voltage motor is also provided with temperaturemonitoring of motor bearings, rotor and stator and can automatically cancel thedrive of high-voltage motor when temperature exceeds the specified value andthe computer protection is activated. The different protection values are asfollows:

Bearing protection temperature: 75℃

Temperature protection of stator: 120℃

Temperature protection of rotor: 120℃

The combination of high-pressure fanstartup and related valve shutdown limit interlock is the startup interlock

7. Controlof variable frequency motor

Thevariable-frequency and variable-speed motor is generally composed of rawmaterial and powder selecting machine and feeding belt motor, both of whichhave their own frequency conversion control devices and only the drive andspeed of computer system are given and the speed is reset before drive.

8. Controlof DC adjustable-speed motor

DCadjustable-speed motor can be selected by main motor, Section 1 and 2 motor ofgrate bed of grate cooler and high-temperature fan in kiln as an option. Thecircuit shall be driven and controlled following the drive of main lop, returnof response and time delay.

9. Valvecontrol

I. Valve with analog quantity: the preset andfeedback of analog quantity are provided;

II. Mixed control of valve: it has the feedback ofanalog quantity and open/close drive of valve;

III. Electric valve: only open/close drive isprovided for electric valve;

Most of hard servo amplifier and hardmanual controller can be canceled through software control; the control ofelectric valve is performed by actuator + hard servo amplifier + hard manualoperation and then (0~10MA) signals are outputted to hard manualcontroller by DCS 4~20MA. The hard servo and hard manual controller canbe totally replaced with soft servo + soft manual controller. Compare the setvalue with valve feedback and then compare the deviation with dead zone inorder to determine the open and close of valve and the deviation of feedbackvalue and set value shall be controlled within the range of dead zone.

Loop control panel can be used foractuator which has positioning accuracy no higher than 1% when travel time ismore than 30s or positioning accuracy higher than 1% when travel time is lessthan 30s.

II. Control plan of different sections

1.Grinding of raw materials

The adjustable-speed belt weigher of rawmaterials and ingredients and the quantitative feeding are provided withautomatic control. The scale controller near machine can be replaced with DCSto perform calibration and measurement.

Automatic closed-loop control of X fluorescence analyzer and proportion of raw materials.

Automaticclosed-loop control ofload and yield of raw material grinder.

Automaticclosed-loop control ofoutlet air temperature and inlet cold and hot air valve of raw materialsgrinder.

Unlock/interlock start/stop control andprotection of grouped equipment.

Start/stop control and protection of thinoil station.

2.Preparation of coal powder

Automatic flow stabilization of coalfeeding at kiln inlet and outlet.

Automaticclosed-loop control of outlet air temperature and inlet cold and hot air valveof coal grinder.

Automatic flow stabilization of coal powderweighing bin.

Unlock/interlockstart/stop control and protection of grouped equipment.

3. Calcining kiln outlet

Automatic control of timing inflation andunloading of raw material homogenization silo.

Automaticclosed-loop control of weight in weighing bin of raw materials and bottomdischarge in homogenizationsilo.

Interlock protection for CO content inelectric dust collector and Cyclone C1 (or C5).

Automaticclosed-loop control of outlet temperature and water injection capacity (orbackwater capacity) of conditioning tower.

Automaticclosed-loop control of outlet air pressure of Cyclone C1 and revolving speed ofhigh-temperature fan.

Automatic and timing block blowing andmaterial blocking pre-alarm for preheated at kiln outlet.

Automaticclosed-loop control of outlet temperature of decomposition furnace and coalfeeding capacity at kiln outlet.

Unlock/interlock start/stop control andprotection of grouped equipment.

4.Calcining kiln inlet

Automaticclosed-loop control of kiln hood pressure and revolving speed of exhaust fan(or openness of exhaust valve) kiln inlet.

Automatic closed-loopcontrol of grate pressure and speed in Chamber 1 of grate cooler.

Unlock/interlock start/stop control andprotection of grouped equipment.

Manual and automatic control of ash hopperunloading in grate cooler.

Unlock/interlock start/stop control andprotection of grouped equipment.

5. Cementgrinding

The adjustable-speed belt weigher ofcement and ingredients and the quantitative feeding are provided with automaticcontrol. The scale controller near machine can be replace with DCS to performcalibration and measurement.

Automaticclosed-loop control of cement grinder load (ball grinder) and yield.

Start/stop control and protection ofroller press

Unlock/interlock start/stop control andprotection of grouped equipment.

Start/stop control and protection of thinoil station