Kiln Operation

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Absolute value is very important and must be held below the allowed “T” for the chain system. The trend is representative but has slow reactions with respect to the back end temperature. Very important to the kiln operation in order to make a good material preparation before it reached the burning zone.

Burning Zone Temperature

Importance of this instrument is often overestimated. Precise only when kiln conditions are clear.

The secondary air dust influence in the indication of the instrument and readings are in error when kiln gets hot and dusty.

It must be correlated with the kiln amps indication and the secondary air temperature to ensure the validity of the reading.

Shell Temperature (Scanner)

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It is often used only to detect hot spots on the kiln shell, an estimation of brick thickness, and coating in the kiln.

On bigger charts, it gives a good indication of the burning zone temperature profile. It is one of the fastest indications of a slowly moving ignition point in burning zone.

It is a very good indication of flame variations due to the burner pipe position, flame shape and direction. (Good indication when adjusting flame in kiln).

Absolute value is important to detect hot spots and rings.

Trend indicates changes in the burner system, kiln speed, ignition point movement and operating conditions which are affecting the temperature profile of the burning zone.

Kiln Drive Amps

It is the most important sensor used to evaluate the burning zone state. The running set point will change according to the raw material composition. Amperage value changes with ring formation.

Amperage value changes with the size of the clinker.

The absolute value is important only when amperage is high (fuse protection limitations). The trend is a very good indication of burning zone length and temperature; therefore the amps should be recorded in such a way to give a good indication in its variations.

A drastic increase of the amps trend, followed by a fast decrease is an indication of loss of coating or a broken ring inside the kiln.

A target amps range should be established (depending on raw mix and other factors) through which this variable can fluctuate safely.

A drastic increase in amps could indicate a possible mechanical condition problem.

NOx Analyzer

Essentially it is an indication of the flame temperature. Higher is the flame temperature, the higher will be the NOx concentration.

NOx content in the flue gases in the smoke stack originate partly from high temperature synthesis in flame from oxygen and nitrogen.

NOx level has been measured in the range between 500 and 2000 ppm in the Lafarge group. NOx increase with excess air and is strongly correlated to low excess air levels.

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At higher levels, i.e. 3% and greater, NOx is weakly dependent on excess air. Correlation between burning zone temperature and NOx level is good.

NOx is generally, but not systematically correlated with the kiln drive amps. NOx gives a truer picture of burning conditions. Kiln drive amps will change due to ring formation and degradation, whereas NOx signal will not.

NOx correlates better with clinker liter weight than free lime.

NOx is affected by fuel changes. Natural gas flames yield the highest NOx level.

All the factors having an impact on the flame temperature will affect the NOx signal like the following:

The secondary air temperature, The primary air temperature, The burning zone temperature,

Chemical composition and fineness of the fuel, The air and fuel ratio and

The flame environment (reduced or oxidized atmosphere).

A quick decrease in the NOx signal is an indication of the burning zone temperature dropping. A slow and even decrease on the NOx signal is an indication of a slow cooling of the burning zone and is related to a bad material preparation from the kiln back end.

On the automatic kiln control system developed by Lafarge, the program is giving 30% of it as evaluation of the burning zone state to the NOx signal, 55% to the kiln amps, and 15% to the clinker temperature at the kiln outlet.

Secondary Air Temperature

It should be kept as stable as possible by the automatic cooler control system (+/- 85oF or 39oC). Absolute value is not important because most indications are incorrect due to instrument inaccuracy.

Trend is very important as it shows variations of material from the kiln and the gas temperature variations to the kiln.

The secondary air temperature should be as high as possible in respect of the various refractory temperatures in front of the kiln.

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Hood Draft

Absolute value is important and is automatically controlled at a constant value (usually looped to cooler exhaust fan damper / fan).

It should be low as possible (to reduce in-leakage).

It is the separation between cooler and kiln and it should be always constant to avoid influences of changes in the cooler gas flow to the kiln operation.

A poor regulation of this signal will induce variations in the kiln gas flow and could bring the kiln into cycling.

Feed End Draft and ID Fan Draft

Trend and absolute value help to detect build-up in the kiln.

This is a very important sensor if many ring problems occur in a plant.

Cooler Exhaust Gas Temperature

Trend will give you information about the temperature profile in cooler gas flow variations and clinker temperature.

Absolute value is an important limitation for protection of the dust collection system.

The cooler exhaust temperature is a more reliable clinker discharge indication than the clinker temperature.

Clinker Discharge Temperature

Trend has no importance for cooler operation.

Absolute value is an important limitation for safety of the clinker transport system. Clinker temperature measurements are generally not very accurate.

Under Grate Pressure

The absolute value should be maintained constant with automatic control.

The value varies with the cooler bed depth and with clinker size. It must be held constant in order to achieve a constant secondary air temperature. Also, only a constant air flow can allow the relationship between under grate pressure, bed depth and secondary air temperature to be valid.

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Variations of the under grate pressures trend are reflected by variations in the cooler grate speed.

Under grate pressures together with cooler drive amps, should give an indication of the clinker size.

Under grate pressure set point should be at least 5 inches (H2O) in order to get good heat recuperation from the clinker bed in the cooler.

Oxygen Analyzer

Trend and set point value are very important. It should be maintained as constant as possible.

It can supply indications about general kiln conditions, burning zone and back end temperature. One of the best indications when the kiln is pushing to indicate if the push is still on or over (related with the amount of CaO in the kiln gases).

It should be kept as low as possible when the kiln is stable, without going into CO range.

However, when using coal or coke, set point should be increased to overcome the fuel quality variations.

MAIN PARAMETERS USED TO CONTROL AND EVALUATE KILN

Kiln Amps

It is a very good indication of the burning zone state, accurate at 80% of the time.

NOx Analyzer

Nitrogen Oxide level is related to the flame temperature than the burning zone temperature. NOx vary all the factors that has an effect on the flame.

It is a very good indication of the burning zone state.

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It should be related to the kiln feed rate.

It should be used as the main controller for the burning zone and the kiln back end temperature.

Kiln Speed

It should be related to feed rate.

It should be set with a constant feed ratio.

Small variations of the kiln speed (1 to 3 revs) could be used to control the burning zone state. However, kiln speed variations should be used only after the fuel flow rate has been used as the primary controller on long wet and dry kiln.

Often if over used, speed variations in the material loading of the kiln and will lead the kiln into a cycle.

On large temperature variations in burning zone like raw material pushes, the kiln speed must be used with wide variations (as example 30 revs or even a complete stop) to avoid raw materials to go in the cooler and to re-heat the burning zone.

Fan Draft

It should be related to the oxygen level, fuel flow rate and feed rate. It is the main controller to keep the temperature profile along the kiln. The rpm variations should be small during kiln normal operation +/- 15 rph.

During kiln pushes and kiln slow speed, large speed variations will be required to maintain the chain gas temperature under safe limit of the chain system.

Back End Temperature

It should be kept at constant level according to feed rate. It should be kept stable in auto by the water spray system. Good indication of the feed end “T”.

Indicate variations in the feed and dust variations to the kiln. When in auto, use water flow variations for indication.

Gas Temperature

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It should be kept inside a certain “T” range.

It is controlled by the ID fan speed variations and the fuel rate.

Oxygen level

It is related to the ID fan speed and fuel rate.

Minimum and maximum level limits need to be established, to control combustion efficiency. When kiln stability has been reached the O2 level should be set in auto with the ID fan speed to lock the temperature profile of the kiln.

Hood Pressure

Control of excess air by cooler exhaust fan Open during kiln pushes

Need to be kept stable to avoid variations in cooler to upset the burning zone

Secondary Air Temperature

Temperature of combustion carried back to kiln from the cooler Large variations during kiln pushes

Should be controlled in a very small range in auto during normal kiln operation with a good regulation of the clinker cooler (+/- 85oF or 39oC)

Cooler Exhaust Temperature

Varies with clinker input to cooler Will indicate variations during a push

Under Grate Pressure

Related to cooler grate speed

Set point controlled by the under grate pressure of second compartment to keep a constant clinker bed depth in order to get stable and high secondary air temperature

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Quality and characteristics of the raw materials

Quality of the fuel used as a example: heat value, ash content, volatile matter and moisture level Dust quality and quantity returned to the kiln

Accuracy of the feeders Chain system design

Accuracy and good response of all control loops and sensors of the kiln system

For these variables that he cannot control, the operator should be kept informed of any changes done and should make sure that those variables are kept inside an acceptable range to maintain a good kiln stabilization.

VARIABLES WHICH THE OPERATOR CAN CONTROL

Material feed to the kiln Fuel feed to the kiln Speed rotation of the kiln

Temperature profile along the kiln Draft at the feed end of the kiln Supply of combustion air

Retention time of the material in the kiln Temperature of the combustion air Flame shape

Observation of instruments, and correct reaction to their readings

Observation of the kiln burning zone, and correct reaction to this evaluation

However, some restrictions are sometimes given on the utilization of those variables and may vary from plant to plant due to local conditions and are usually the following:

Set point on the maximum speed of the kiln Set point on the maximum feed rate to the kiln

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Settings on the burner pipe and its position Primary air settings and fuel tip velocity Set point on cooler fans flow

Set point for the under grate pressure and the clinker bed depth in the cooler

KILN LIMITATION FACTORS

Dust Emission at Precipitator Stack (Local emission regulations)

Gas Chain Temperature

Maximum value depend on chain quality and position

Diameter of Kiln

Gas velocity in kiln (70 ft/sec in free section of kiln and 30 ft/sec in chain section maximum) Heat load in front of kiln, flame erosion on kiln walls

ID Fan Capacity

Maximum fan speed and low oxygen level

Cooler Capacity

No red clinker should be present after third compartment of cooler in normal operation Clinker discharge temperature not to exceed 170oF (80oC)

Cooler exit gas should be about 370oF (190oC)

Bed depth to allow good under grate pressure (15”) with sufficient fan capacity

KILN OPERATION TARGET

Highest clinker production with Good quality clinker

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Stable kiln operation

Oxygen level as low as possible Gas and fuel oil – 1.0 to 1.5%

Coal and coke around – 2.0% (depending on the variations in fuel mixture)

Kiln exit temperature as low as possible

Flame as short as possible (with respect of the burning zone refractory) Keep burning zone short in front of the kiln

Secondary air temperature as high as possible but stable

Temperature not above liquid phase temperature in front of kiln to protect refractory and coating

Run with an under grate pressure as high as possible Compatible with the cooler fans static pressure capacity

Primary air as low as possible

As combustion air to replace by hot air from cooler as much as possible

Clinker Temperature

Not to exceed 230oF (110oC) as it could promote quality problems (false set) during the grinding process

Gravel bed filter

Normal operation temperature is 350oF (180oC)

Maximum temperature for normal operation is 660oF (350oC) For 2 hours, up to 750o_{F (400}o_C)

For 20 minutes, up to 840oF (450oC)

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Operate the kiln:

With higher free lime

Reduce air leakages:

Around and near the nose ring area and seal Air in-leakage on kiln hood

Around blast pipe port holes and doors

Hood pressure set point as close as possible to zero Primary air should be kept as low as possible

Reduce length of pre-cooling zone by: Adjusting the burner position

Proper material load (kiln speed/feed ratio)

Increase clinker bed depth in cooler (near 15 inches) Oxygen to be maintained at minimum level

Good flame shape and temperature

Good chemical composition Good burnability factors Constant raw mix

TYPICAL KILN PROBLEMS

List of most frequent factors at work when kiln operation is unsatisfactory

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2) Faulty suspension results in high pre-heater outlet temperatures, thus reduces capacity (bleed air)

3) Poor operating practices (burning techniques) 4) Reducing conditions in kiln

5) Reducing conditions in burning zone due to flame impingement with load 6) Lack of momentum at burner tip leads to long, lazy flame

7) High primary air, (30%+) due to direct firing of coal, (critical in dry process kiln) 8) High level of volatile elements in raw feed particularly chlorine

9) Systematically hot burning 10) Inadequate chain system

11) Poor cooler heat recovery due to cooler fan design

12) Poor cooler heat recovery due to excessive air flows, insufficient pressure in under grate compartments

13) Chemically variable raw mix C3S, more than 10 points over a shift 14) Variable slurry moisture (more than 3 points)

15) Variable addition of hi-alkali or hi-volatile dust from precipitator (over a period of more than one-half hour)

16) Erratic feed rate

17) Erratic fuel rate (wet coal)

18) High leakage into hood seal (more than 10% of combustion air) 19) Inadequate or obsolete design of equipment or facilities 20) High leakage into pre-heater and down-comer duct

21) Flame erosion on lining could create premature brick failure

22) Kiln misalignment, excessive tire clearances and other factors of shell deflection 23) Bricking techniques lead to rings not tight enough

24) Low slurry moisture 25) High slurry moisture

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1) Heat consumption higher than normal Long dry: Higher than 3.4 MBtu/ton Long wet: Higher than 5.2 MBtu/ton

Four stage Pre-heater: Higher than 3.1 MBtu/ton 2) Output lower than nominal and / or standard

3) Kiln is unstable and requires frequent massive shutdowns 4) Kiln is cycling spontaneously without any action of operator 5) Kiln is out of draft with output below nominal

6) Stack stinks – SO2 emissions are high 7) Mud ring in chain section on wet kiln 8) Back-spills on wet kiln

9) Burning zone rings 10) Discharge end rings 11) Snowmen in cooler

12) Frequent burning zone burnouts (brick life is less than 3 months) 13) High dust return (above 20% of clinker) causes handling problems 14) Cyclones plug-ups (four stage pre-heater)

15) Build-ups in pre-heater feed box (four stage pre-heater) 16) Cooler exhaust system seems undersized/under-designed

- Hood frequently under pressure (during pushes) - Exhaust temperature is higher than normal - Bleed in damper is open very often

- Frequent bag burnouts in cooler bag house 17) Red grates in the cooler all the time. Frequent grates burnouts 18) Red rivers on side of cooler

19) Under pushes, cooler speed up to maximum, yet some fans stop blowing any air (pressure overload)

20) Kiln drive seems undersized, kicks out upon start-up after a short shutdown

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Viewing the kiln interior

This may sound somewhat elementary, but we should never forget that we are looking into an extremely luminous source. Although filtering glasses are used, the light source is so strong that focusing the eyes into it for too long a time could cause partial blindness. One should look no longer than one minute at a time into the fire. If longer viewing is required, look a side for few seconds occasionally to rest the eyes. Looking steadily too long at the flame results in the eye losing its ability to see details, hence the need for a short rest every minute or so.

The question of what type of colored filter glass to use must be left to the operators. Burning with a natural gas flame usually makes necessary a darker colored than oil fire would require, because of the greater luminosity of the flame. As a rule, one should always use a glass that enables him to see under and behind the flame. Once a certain glass has been chosen, the operators should stay with this glass at all times in order to properly judge the burning zone conditions. How frequently should one look into the burning zone? There is no set answer to this question. Experienced operators sometimes become over-confident and think that it would be perfectly safe to leave the kiln alone for periods in excess of 30 minutes. This action however, is against good burning practice. The secret of every good operator is his ability to recognize a change in kiln condition at the time a change takes place and not later. For this reason, a good operator will never leave a kiln too long a time unchecked. When things are going smoothly, the kiln should be checked every half hour, with more frequent checks if adjustments are being made. There is no such thing as operating a kiln by the instrument alone, as the instruments do not show, for example heavier and lighter loads entering the burning zone until it is almost too late to make the necessary adjustment.

The kiln condition can be estimated from the color observed in the hottest part of the flame.

Dark red cherry red orange-yellow white

Cold - - normal hot

Any deviations from the orange-yellow range should be investigated to determine the cause and when adjustments need to be made to the kiln operation to get back to normal kiln condition.

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Appearance of burning zone

Good or bad visibility

Bright white or dark red color

Good appearance is an orange-yellow color

The gas stream should be calm without great turbulence

Appearance of coating

Coating should begin approximately ½ diameter of kiln size from the nose ring

Color of coating tells a great deal about the condition in burning zone as coating acts as heat storage in burning zone

Overall thickness of coating should be between 9 and 12 inches and is dependent of the type of raw mix

Check for ring formation near lower or upper section of the kiln

If the surface of the coating appears smooth, then the burning zone in this area is hot If the coating appears “lumpy” then the burning zone is okay

A bare spot without coating could be due to flame erosion, thick brick or high flame temperature in this location

Appearance of the coating falling off from the top of the kiln shell: Large pieces: normal

Fine noodles dripping: too hot

The location where the coating pieces are falling from the top of the kiln wall, above the end of the flame is generally where the raw load is. So whenever the raw load cannot be seen in the bottom and behind the flame of the kiln, try to look at the top.

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Is clinker balling or fine? Is material sticky?

Is material heavy or light?

Is material movement fast or slow?

Is material climbing low or high in the wall? (material should climb up +/- to the 10 o’clock position in normal operation)

Appearance of material before falling in the cooler, fine or nodular

Upper burning zone section

Are rings building up or not? Is coating formation seem normal?

Try to evaluate the length of the coating (50 to 100 feet from burning zone to far up)

Raw feed location

Look behind the flame at the bottom of the kiln

Normal position is approximately ¼ diameter distance under the flame

Never allow raw feed to come ½ way under the flame as kiln speed will have to be reduced to control it (kiln low speed)

An advancing or receding dark feed is the earliest indication of a burning zone that is warming up or cooling down. So that is why it is important for the kiln operation to be able to see this load. Every effort should be done during normal operation to keep this load in sight.

Flame appearance

Should always be evaluated during stable kiln condition Long (100 ft) or short (30 ft)

Hard or lazy Bushy or narrow

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Bright or dark

White or orange yellow

Eroding the coating or the brick wall Aiming high, low or in the center Eroding the material load

If fuel is burning in suspension or in the material load Position of the ignition point when coal or coke is used

The flame temperature should be as hot as possible as long as it does not create problems with the coating and the kiln refractory. Whenever a change is made on the flame shape, a close monitoring of the shell temperature should be done.

Coal flames

Coal normally burns with longer flame than oil

A coal flame normally starts at 3 to 5 feet from the burner tip Coal fineness to be about 85% passing 200 mesh

Keep the coal system air flow at about 70 ft/sec to avoid coal deposit inside pipe, while keeping primary air to minimum (direct system and burner design)

On direct firing system, coal fan damper setting should be set at minimum value and the fuel rate changes made only by making changes with the coal feeder system in order to keep the flame shape short and as constant as possible.

Burner pipe appearance

Is the tip of the blast pipe in good condition? Is the burner cast-able in good condition? Is the burner pipe aimed correctly?

How is the pipe location relative to the nose ring? Are snowmen building up on top of burner pipe?

Whenever a bad condition deflecting the flame is observe, a quick evaluation should be done to evaluate if the kiln can continue its operation or if it needs to be shut down to fix the burner pipe.

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Nose ring appearance

 Check the condition of the cast-able or the refractory on the top of the nose ring if okay  Check the temperature aspect and the wear of the nose ring castings

 Check if the nose ring seal is in good condition

Secondary air

Calm or upset

Dusty if the clinker is fine Clear if clinker is balling

Foggy and white if temperature is hot

The secondary air temperature has a major influence on the flame and its shape.

Primary air

Should be as low as possible to obtain satisfactory heat recuperation from cooler Has an important influence on the shape of the flame (bushy or narrow)

Pressure should be as constant as possible

When good settings of the flame have been found, the primary air settings should not be changed in normal operation unless a high temperature condition in the kiln refractory has raised and required to change the flame.

When the kiln is down

Look for ball or ring formation at upper section of burning zone

Evaluate length of coating if okay, too long means we burned the kiln too far up Load level inside kiln if even and normal

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Appearance on load during kiln jacking (sticky or normal)

Look at the sealing efficiency of the kiln back end (no suction or gases movement inside of kiln should be observed).

When kiln is shutdown, the gases should be bottled inside of the kiln as fast as possible by closing the kiln back end damper or its equivalent and by adjusting the hood pressure set point, slightly positive. The procedure need to be done to avoid heat loss from the kiln to insure a slow cooling of the refractory and avoid thermal shocks on the bricks.

KILN UPSETS

Burning zone too hot

Too much liquid is formed and all temperatures are above the solid state temperature therefore no coating is formed. Coating will be lost and this could damage the refractory.

A) Appearance the kiln could be white and hazy in front end and the clinker will be balling. B) Appearance of the kiln could appear cold if burning is too far. The clinker could be fine (very

long burning zone).

A) Hot burning zone with high secondary air temperature

The front of kiln is very hot and white, often hazy The secondary air temperature is high

The clinker is balling and getting bigger Often the dark load is visible behind the flame

These conditions occurs when the burning zone length is moving down and concentrating the heat on a shorter burning zone length in front of kiln.

This situation can be overcome quite easily by reducing the fuel rate and the ID fan slowly step by step until the burning zone gets back to its normal condition.

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Can be caused by burning too far back into the kiln Flame too long and ignite too far

Pre-cooling zone is too long in front of the kiln

Long burning zone promotes very fine clinker formation which is sent back as dust into the kiln with the secondary air gas stream

Whenever dusty conditions prevail in front, corrective measures should be based on the clinkering conditions behind the flame rather than on the color of the front of the kiln.

Aspect of the clinker falling in cooler is very important at that time to evaluate the kiln condition.

Kiln amps, fuel flow rate, shell temperature and back-end temperature are usually above the normal operation settings during these conditions.

Get free lime done from clinker coming out of the kiln to see if OK

If operator is in doubt about the kiln being cold or hot, the kiln rotation could be stopped (out of the interlock for a few seconds) to allow condition of the burning zone to clear and to view inside the kiln

If doubt still persists, the kiln should be assumed to be hot and it should be cooled down by reducing the fuel and the ID fan speed until the burning zone get back normal or end up to be completely cold.

Except for very hot and emergency conditions, such as cooling should take as long as a full shift to be done, to avoid high heat concentration in front and quick losses of coating from the upper section of the burning zone which could upset the burning zone temperature.

KILN CYCLING

This is an unstable condition when the load in the kiln decreases, causing the temperature of the burning zone to rise and forcing the operator to reduce the fuel rate. Then, the burning zone starts to cool off in turn forcing the operator to increase the fuel rate. In severe cases, the temperature continue

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to drop, even though the fuel rate is at maximum and it become necessary to reduce the kiln speed to slow down the entry of the feed into the burning zone. Once a kiln gets into an upset such as this, the cycle will repeat.

Kiln cycling could be related to the following reasons; Variations in kiln feed: physical or chemical, Variations in dust re-introduction to kiln,

Variations in the water spray control system in kiln inlet (if any), Materials hold up in the chain system (for wet process kilns), Poor chain system design (for wet process kilns),

Variations in hood pressure control

Poor cooler settings and control which promote secondary air temperature variations, Operating the kiln above its production capacity,

Variations in the quality and the quantity of the fuel supply to the kiln, Bad operating practices, especially over reacting with the kiln speed and Volatile recirculation inside the kiln system especially chlorine

So all the above reasons should be investigated in order to find the cause of the cycling problem and corrected.

HOW TO BREAK A CYCLE IN A KILN

Reduce feed/speed ratio by approximately 10% in order to change the material load in the kiln (also mainly to change the material load in the chain system).

Increase the fuel flow rate by 5% above the normal setting of the current production level.

Keep the oxygen level above 2% and try to control the back end temperature variations as much as possible by using fuel rate and ID fan variations.

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Let the kiln amps vary and do not attempt to chase them by varying the kiln speed. Just try to control them if they get above or below the critical range by varying the fuel flow rate.

If the kiln speed need to be varied than it should be done with very small variations, in order to avoid upsetting the material in the kiln.

If the kiln speed needs to be increased to go back to normal production level, then it should be carried out more slowly than normal.

As you get to normal production level, fuel settings should be held above normal before returning to normal operation settings.

KILN EMERGENCY CONDITIONS SECTION

RED SPOT ON KILN SHELL

Indicators:

By visual observations

Shell scanner sharp and rapid shell temperature increase to level above 850oF (450oC)

Visual observations of loose refractory bricks in the material load of the kiln or in the clinker at the cooler discharge

Possible Effects and Danger

Severe warping and damage to kiln shell

Shell temperature between 900 and 1100o_{F (480 and 590}o_{C), deep red color on shell} Shell temperature over 1200oF (650oC), very bright red and shell bulges and warps

Recommended Actions to Take

A) For small red spot located in the upper transition or center of burning zone Continue normal operation of kiln but:

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Place shell cooling fans in the area of red spot

Shorten flame to bring black feed over area of red spot in attempt to form new coating Keep watching the shell temperature trend

Maintain normal burning zone temperature

Change kiln feed chemistry to obtain an easier burning mix

B) For large red spot located under or near a kiln tire or in areas were no coating is formed SHUT DOWN KILN IMMEDIATELY

Warning: Under no circumstances should a water spray be used on the red spot, as this

could result in severe kiln shell damage.

Possible Measures to Prevent Re-occurrence

Make sure flame configuration and characteristics are not causing localized coating erosion or continuous and excessive overheating

Employ proper refractory installation methods Minimize frequency of kiln shutdowns and upsets Minimize frequency of clinker type changes over

Avoid “hard” burning mixes (i.e. ensure sufficient percentage of liquid content in mix to promote coating formation)

RAW, UNBURNED FEED IN CLINKER COOLER

Indicators:

On rush of raw feed into and beyond burning zone

“Black feed” position advanced more than ½ way under the flame “Black-out” in burning zone

Red grates in cooler

Rapid rise in cooler grate and clinker discharge temperatures Cooler drag-chain amperage increases rapidly

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Thermal damage to cooler grates and grate drive mechanism Fire on clinker conveyor belts

Excessive high temperatures in coal mill air circuit

Warning: Watch for incomplete combustion when visibility in burning zone is severely restricted.

Actions to Take

First and foremost, do not wait until raw feed is in the cooler; act when the first signs of impending problems are visible in the burning zone.

Immediately reduce kiln speed to minimum (or turn on auxiliary drive)

Reduce fuel and ID fan speed in accordance with standard slowdown procedures to protect the kiln back end temperature

Reduce cooler grate drive speed (switch to manual control) to allow material in cooler more time for cooling

Adjust cooler air flow rates to obtain maximum cooling without the hood pressure going positive Advise all unauthorized personnel to stay clear of the firing floor, cooler and coal mill area

Preventive Measures to Avoid Re-occurrence

Accelerate frequency of visual observations of burning zone for early detection of impending cooler upsets

Evaluate kiln output rates vs. capabilities and kiln operating stability

LARGE RING BROKEN LOOSE IN KILN

Indicators

Visual observations of large junks in burning zone Sudden drop in kiln back end draft

Large drop in oxygen content of kiln exit gases Hood pressure tending towards positive side Sudden change in kiln drive amperage

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Possible Effects and Dangers

Overloading cooler with unburned feed

On rush of excessive amounts of feed into the burning zone Damage to cooler drives and grates

Large pieces jamming cooler hammer crusher Red hot clinker leaving cooler

Actions to Take

When amount of feed and ring fragments in burning zone are extremely large: Immediately reduce kiln speed to minimum

Reduce fuel and ID fan speed to keep back end temperature under control Switch cooler grate control to manual and reduce grate speed

Adjust cooler air flows to maximum flow possible, without the hood pressure going positive Have personnel on standby to watch the cooler and the hammer crusher for possible overloading, overheating and jamming

Possible Preventive Measures to Avoid Re-occurrence

Laboratory to reevaluate chemistry of kiln feed (including dust return rates) for possible elimination of ring formation if no solution in this area possible, then

Initiate regular schedule to remove rings and heavy build-up by means of special devices design for this purpose

Initiate regular procedures to displace the burning zone location on a daily basis

BURNING ZONE DANGEROUSLY HOT

Indicators

Clinker balling in burning zone Material load sausage-like Coating dripping off the wall

Sliding molten clinker bed in burning zone Burning zone recording temperature too high

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Cooler under grate pressure too high

Material load turning to liquid in burning zone Very brilliant and white burning zone

Loss of coating and thermal damage to refractory Red spot in the kiln shell

Thermal damage to cooler and kiln hood components

Possible Actions

Reduce fuel flow rate to minimum until sausaging stops

Increase kiln speed approximately 10 rph until sausage is broken Provide maximum air in cooler (without hood pressure going positive)

The kiln rotation to be adapted is the aspect of the material near to fall into the cooler. No liquid material in the cooler, stop kiln rotation if needed.

Reduced primary air flow, then as soon as the objective of breaking the agglomeration is accomplished,

Reduced the kiln and ID fan speed then increase fuel flow rate to normal operating conditions

Preventive Measures

If “sausaging” is frequent and result of easy-burning mix, have laboratory evaluate possibility of providing a mix with less percentage of liquid content

Make more frequent, vigilant observation of the burning zone conditions

Evaluate flame position and shape to determine if thinner, longer flame is possible

SUDDEN, SHARP RAISE IN BACK-END TEMPERATURE

Possible Reasons Feed shortage

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ID fan speed too high Kiln speed too low Chain fire

Chain fire on wet and dry kilns

Thermal damage to back end, dust collector and pre-heater tower equipment Delayed ignition of fuel in back end of kiln

Possible Actions

Immediately de-energize electrostatic precipitator

Immediately reduce fuel flow rate and ID fan speed to obtain less than 0.3% oxygen in exit gas Warning: Do not cut off fuel flow rate completely as this could trigger an explosion.

Increase kiln speed and feed rate

Warn personnel to stay clear of kiln back-end Do not open any doors in kiln back-end

Then as soon as the primary objective of bringing the kiln back-end temperature under control is accomplished:

Return kiln control variables to normal to restore operating conditions Check out back-end to determine if thermal damage had occurred

Preventive Measures

Do not operate kiln without feed for more than 10 minutes

Provide alarms and properly maintain kiln instrumentation to obtain warnings before the back-end temperature gets out of maximum range

Maintain close vigilance over combustion, back-end and flow conditions during kiln starts, shutdowns and upsets

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Indicators

Combustibles in exit gases Oxygen in exit gas too low

Flame extinguished for poor ignition conditions Burning zone temperature too low

Excessive fuel rates and/or insufficient kiln draft Possible Actions

Immediately de-energize electrostatic precipitator Immediately reduce fuel flow rate (do not shut off) Increase ID fan speed to obtain:

a) Zero combustible in exit gas

b) Oxygen between 0.2 and a maximum of 0.5% in exit gas

After black smoke has cleared, maintain the low oxygen/zero combustibles for at least 10 minutes before restoring kiln variables to normal

Preventive Measures

Improve control over flame and firing conditions

Make frequent, vigilant observation of fuel flow rates, gas analysis, flame and kiln draft conditions during kiln starts and upsets

DISTORTED FLAME SHAPE

Indicators

Irregular and unusual flame shape

Fragmented flame where part of flame impinges on lining near kiln discharge area

Inspect burner pipe for damage or plugged circuit

If flame is erratic and severely impinges upon lining near the kiln discharge area: Shutdown kiln immediately!

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If flame is only slightly distorted; adjust burner position and primary air flow Check shell temperature on kiln scanner

Schedule a burner pipe repairs for next kiln shutdown

Preventive Measures

Frequent visual inspection when looking inside the kiln

Regular inspection and maintenance of burner pipe during each prolonged kiln shutdown Improve protection (castables, air cooling) for burner pipe

Maintain primary air flow for at least 2 hours after a kiln has been shutdown or pull back the burner pipe immediately when kiln is being shutdown

LOSS OF SECTION OF REFRACTORY LINING

Indicators

Loose bricks in clinker bed of burning zone

Delineated (linear instead of round) red spot on kiln shell Rapid rise in kiln shell temperature

Thermal damage and distortion of kiln shell and tire

Further collapse of large sections of linings (especially in alumina brick sections)

Possible Actions

Immediately shutdown the kiln

Preventive Measures

Employ proper refractory installation methods and procedures Make annual checks of kiln alignment and shell ovality

Have refractory manufacturer provide uniform shapes and proper expansion allowance for each type of brick

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Avoid excessive turning when kiln is cold during shutdowns

COOLER DRIVES OR CLINKER BELT STOPPED

Indicators

Cooler overloaded

Large chunks of coating in cooler High under grate pressure

High cooler drive amps prior to drive stop Clinker transfer chutes plugged

Thermal damage to cooler components

Possible Actions

Immediately reduce kiln speed to minimum and attempt to restart clinker belt and/or cooler drive

If drives cannot be restarted within 5 minutes, shutdown the kiln

Note: After kiln has been shutdown, consider possibility of turning the kiln in less frequent intervals to prevent further overloading of cooler. (Kiln still had to be rotated periodically nevertheless)

Preventive Measures

Know at what amperage the cooler drive is likely to fail and provide alarm for overload

Adjust kiln parameters (namely kiln speed) before cooler can become overloaded at the times when heavier feed load is observed in the burning zone

RED CLINKER AT COOLER DISCHARGE

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High drag chain amps

Sudden drop in under grate pressure (grate out)

Excessively high under grate pressure (cooler overloaded) Cooler drive amps and clinker bed depth too high

Cooler loaded with coating and ring fragments Snowman formation at cooler inlet

Thermal damage to cooler components

Thermal damage to clinker transport equipment

Possible Actions

Immediately make a visual check of the cooler to determine reason for red-clinker discharge If cooler grate out, shutdown kiln

If cooler overloaded, reduce kiln speed to minimum and reduce cooler grate drive speed to allow more time for cooling

Increase air flow into cooler

Activate water spray at cooler discharge and reroute clinker to prevent damage to conveyor belts

Preventive Measures

a) On frequent grate failures

Investigate for possible faulty grate installation methods by maintenance department Investigate quality of grates and bolts used

b) On frequent one-sided loading of cooler bed Investigate possible cooler design changes

Investigate possibilities for elimination of stalagmite (snowmen) formation at cooler inlet

c) On frequent overloading of cooler due to upsets

Slow down kiln speed before raw feed enters cooler or cooler can become overloaded (make your corrective moves before things get out of control)

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RAPID RAISE OF TEMPERATURE IN COAL SYSTEM

Possible Effects and Dangers Explosion

Thermal damage to coal system

Possible Actions

Warning: Do not open any door in the system that could provide the oxygen for an explosion or a more serious fire.

Inject inert gas (CO2) into coal mill inlet Flood coal mill with kiln feed or excessive coal Warn all personnel to stay clear of system Stop or reduce air flow to coal mill to minimum

Preventive Measures for Re-occurrence

Provide coal mill inlet with magnetic device to extract metal fragments from coal feeder belt Keep paper, rags, etc. out of coal storage pile

Do not feed coal mill with coal that has undergone spontaneous ignition (smothering) while in storage

Keep coal mill de-tramp chute clear

Provide coal mill system with automatic fire-extinguishing devices

Do not operate coal mill above predetermined safe temperature for any given type of coal

POWER FAILURE

Possible Effects and Dangers Warping of kiln shell

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On coal-fired kilns, settlement of ground coal in coal system that could lead to a fire and/or explosion

Possible Actions

Immediately start auxiliary power generator and primary air fan (coal mill fan on direct fired kilns)

Retract burner pipe and protect TV monitor in kiln hood

Start ¼ turn on kiln not later than 10 minutes after the power failure

If available, close feed-end damper manually to prevent hot gases from escaping from kiln by natural draft

Power Failure Main Procedures

Start generator or auxiliary drive

If it is raining, carry out ¼ turn as described previously

Close kiln back-end, ID fan damper, or precipitator inlet damper if power failure is of long duration

Keep primary air fan running to cool down the burner pipe (and pre-calciner burners) or pull the burners out of the kiln

Try to restore power as soon as possible

The following should be connected on the auxiliary power system: Emergency light in control room

Emergency light in kiln platform Telephone system for outside calls Radio system inside the plant

ID fan louvers and precipitator inlet damper Kiln auxiliary drive

Primary air fan

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Instructions should be given to all members of the shift for specific responsibilities during a power failure as example:

Operator A:

Carry out safety procedures on kiln system Start the auxiliary power system

Close kiln back end (if on auxiliary system) Rotate the kiln

If it is raining continuously, rotate kiln as soon as possible Protection of burner pipe (pull out of kiln

Call the power company

Operator B:

Get to main power breaker and try to reset it

Go to kiln back-end and close ID fan louvers (if they are not connected on the auxiliary drive) If the auxiliary drive control is not remote, make kiln rotation in local

A CHAIN FIRE

Indicators

Rapid, sudden rise in intermediate and exit gas temperatures By visual observation

Melt-down and loss of chains

Damage to kiln shell in chain system area On wet process kilns; steam explosion Thermal damage to kiln back-end equipment

Possible Actions

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Immediately reduce fuel rate to minimum (but don’t shut fuel off completely)

At the same time, reduce ID fan speed to obtain zero combustibles and less than 0.3% oxygen Increase kiln speed and feed rate to maximum until the back end temperature is under control On wet process kilns, clear all personnel from firing floor

Preventive Measures

Avoid operating the kiln for more than 10 minutes when there is feed shortage

Establish and enforce maximum permissible operating limits for intermediate and/or exit gas temperatures

HEAVY RAIN OR THUNDERSTORMS

On kilns that are exposed to elements;

Loss of coating and collapse of refractory lining Thermal damage and warping of kiln shell Possibility of power failure

Possible Actions

If storm occurs shortly after a kiln shutdown;

Jack (turn) kiln more frequently or continuously on auxiliary drive

Start auxiliary power generator in preparation for a possible power failure

SUDDEN, HIGH POSITIVE HOOD PRESSURE

Possible Reasons ID fan failure

Large ring or build-up broken loose inside kiln

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Steam explosion on wet-process kilns

All personnel on firing floor is in danger

Thermal damage to equipment on firing floor and hood Danger of backfire in coal system

Possible Actions

Immediately clear all personnel from firing floor

Immediately reduce fuel rate to minimum and increase ID fan speed Reduce cooler air flow rates into under grate compartments

Open cooler excess air damper manually

OVERHEATED KILN BEARINGS

(Procedure needs to be approved by your Maintenance Department)

Slow down kiln speed near minimum 20 rph. Do not stop the kiln (bearing will seize) Open reset door on top of bearing and pour in sulfur until noise stops

You can add also “powdered graphite” to the bearing lubricating oil The sulfur must be poured on the shaft and not on the bearing casing Keep a bag of sulfur near the control room location

Call the Maintenance Supervisor

Check if the oil heating is on or not, and stop it if it is in operation (breaker location must be known to all)

Check if the water or glycol circulation is okay. If there is no circulation, open the water valve very slowly If you cannot reach the Maintenance Supervisor, call for an Oiler and a Maintenance man

Install a water hose to get cold water in the bearing (not a close circuit loop)

Drain the oil and add new oil until the new oil has reached its normal temperature (below 120oF/50oC you should have a temperature gauge showing the oil temperature on each bearing)

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Type of oil to use for the bearings to be confirmed by your maintenance department

KILN HAZARDOUS CONDITIONS

Shooting Rings with Gun

Do not allow any employees other than the gun crew on the firing hood during ring shooting Do not tamper with the ammunition

Keep all live ammunition locked up and away from the firing floor when not in use Permit only experienced and trained persons to operate the kiln gun

Use ear muffs when firing gun

Cotton stuffed in the ear is not adequate

Clean gun at frequent intervals and do not attempt to fire an apparent defective gun

If kiln has no chain section, keep all persons away from the kiln back end and rope this area off before shooting

Clinker, Fuel Oil and Coal Dust Spills Clean up spills immediately

Provide adequate clean-up cans and facilities for easy removal of spills Initiate repair action when spills are caused by leaks that can be repaired

Gas, Fuel Oil, Coal and Steam Leaks in Fuel System

Report any gas odor on the firing floor immediately to the shift supervisor

Provide for periodic inspection of fuel and steam lines and system to detect leaks and other defects as a preventive measure against major breaks in the system

Burner Hood, Porthole and Cooler Doors

Do not allow anyone to look into the burning zone while the kiln is on operation unless approved safety equipment for viewing is used

Use proper protective clothing when working near open burner hood and cooler doors while the kiln is in operation

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Instruct all persons to stay clear of the portholes whenever the hood pressure is temporarily on the positive side

Relining the Kiln with Refractory Bricks and Materials

Use protective screen when working under loose refractory and coating, if no alternate procedure is possible

Any employee working inside the kiln should have positive means, such as locking out the kiln drive with his own lock, to assure that the kiln cannot be started while he is inside

Have proper posture and steady footing when lifting bricks or scaling coating

Do not work underneath the burner hood bridge while material is being hauled in and out of the kiln

Do not test run cooler fans when workmen are inside the kiln Do not run ID fan when workmen are at kiln rear or in chain section

Working Near or on Dust Collecting Equipment

Wear extra protective clothing to guard against burns from hot dust Wash skin thoroughly with clear water after contact with alkaline dust

Have a second workman as safety man standing by whenever working under or in bins or hoppers containing material

Do not allow workmen to work inside hopper without being properly secured on safety lines and belts

When working on plugged flue hangers, be constantly on guard against potential dust flushes and cave in of overhanging materials

Backfire and explosion During Kiln Light-up

Open either one cooler or burner hood door before lighting fire in kiln Secure proper draft in kiln before fire is lighted (very important)

Do not allow unauthorized person to stand near the burner hood during light-up Stay clear of burner hood ports when igniting the fuel

Avoid excessive fuel flow on initial light-up of flame Start the primary air fan before opening the fuel valve

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When firing coal, make sure that no coal dust spills are present on firing floor, around coal feeder, or in the primary air pipe

Setting any Kiln Machinery into Motion During Start-up

Make sure all persons are clear of kiln equipment before each unit started Sound horn to signal startup

Inspect all circuit breakers before the startup to make sure that all safety tags and locks have been removed

Make sure all machine guards are in place before any equipment is started

Relining the Kiln with Refractory Bricks

Construct a proper bridge across the burner hood from firing floor to kiln nose Inspect coating and remove loose overhangs before passing underneath Keep all unauthorized personnel out of kiln interior

KILN OPERATION SECTION

KILN OPERATION TECHNIQUES

There are Three Common Techniques for Burning Clinker in a Rotary Kiln

Maintain a constant kiln speed, and vary the fuel rate to counteract the temperature changes in the burning zone

Maintain a constant fuel rate, and vary the kiln speed to hold the burning zone temperature at the desired label

Vary the kiln speed, the fuel rate or both to maintain the desired burning zone temperature

These techniques have one error in common. They show concern only for the burning zone temperature.

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Unfortunately, many kiln operators think that this is good enough, reasoning that, as long as good-clinkers are produced, what more is necessary? The fallacy of this reasoning lie in the fact that ideal stable kiln conditions can be obtain faster and more economically when equal consideration is given to all zones in the kiln and not the burning zone alone.

The process of clinker burning, therefore the process of rotary kiln control starts not at the place where the feed enters the burning zone but at the point where feed enters the kiln.

The Proper Operation Technique is:

Vary the kiln speed, the fuel rate and the induced draft fan in any combination to maintain the proper burning zone temperature and maintain a constant back-end temperature for a given rate of feed. This technique is called; “Burning a kiln from the rear”.

By doing so, you prevent the variations instead of reacting to them when they reached the burning zone.

If you stabilize the kiln back-end temperature you will be able most of the time to overcome the burning zone temperature variations mainly by using the fuel input to the kiln and the ID fan speed.

In long wet and dry kilns, kiln speed variations should be avoided as much as possible in normal operation as it create variations in the material loading of the kiln and eventually could lead to the kiln into an upset.

If kiln speed variations is to be used, then they should be small (1 to 3 rph) keeping in mind that the material load of the kiln will be more or less +/- 2 hours later as it will reach the burning zone, (kiln retention time).

However, speed variations must be used on pre-calciner kilns to control the burning zone temperature as the calcinations rate or the feed preparation is done by the fuel input on the pre-calciner burners.

The feed/speed ratio must remain constant all the time once the perfect loading of the kiln has been found. Speed/feed ratio should not be changed to control the kiln.

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BURNING ZONE EVALUATION

The burning zone condition can be estimated from the colors observed in the hottest part of the flame. An orange-yellow color is normal.

When looking into burning zone, one will observe a sharp color change of the lowest part of the feed bed under the flame from dark to bright.

This point in burning zone is of great importance to the operator as it is the earliest indication when the burning zone tends to warm up or to cool down.

In normal operation, the position of the dark feed remains stationary approximately one quarter of the distance into the flame. This point should be used at the main indicator for evaluation of the burning zone.

If the dark feed move further under the flame (towards the front of the kiln) the burning zone is cooling down.

If the dark feed shifts in the direction of the kiln rear the burning zone is warming up.

The position of the dark feed can feed can move because of changes in the flame shape, the feed loading of the kiln or if the feed to kiln is harder to burn. Any change in the position of the dark feed must be viewed in the light of all of these influences.

The operator must be able to see the dark feed whenever he looks inside the kiln and he must regulate the operation of the kiln so as to achieve this;

A slow shifting of the dark feed in either direction can usually be counteracted by a small change in the fuel input rate in order to keep the feed in its proper place.

Kiln Operation

TABLE OF CONTENTS

PAGE

GENERAL KILN SECTION

KILN EMERGENCY CONDITIONS SECTION

KILN OPERATION SECTION

KILN START-UP AND SHUTDOWN PROCEDURES

COOLER SECTION

COMBUSTION SECTION

BASIC PRINCIPLES SECTION

GENERAL KILN SECTION

DESCRIPTION OF MAIN KILN SYSTEMS

KILN OPERATION PRIORITIES

KILN SYSTEM STABILITY

MAIN PARAMETERS, TRENDS AND ABSOLUTE VALUES

MAIN PARAMETERS USED TO CONTROL AND EVALUATE KILN

VARIABLES WHICH THE OPERATOR CAN CONTROL

KILN LIMITATION FACTORS

KILN OPERATION TARGET

TYPICAL KILN PROBLEMS

List of most frequent factors at work when kiln operation is unsatisfactory

Viewing the kiln interior

KILN UPSETS

KILN CYCLING

HOW TO BREAK A CYCLE IN A KILN

KILN EMERGENCY CONDITIONS SECTION

RED SPOT ON KILN SHELL

RAW, UNBURNED FEED IN CLINKER COOLER

LARGE RING BROKEN LOOSE IN KILN

BURNING ZONE DANGEROUSLY HOT

SUDDEN, SHARP RAISE IN BACK-END TEMPERATURE

DISTORTED FLAME SHAPE

LOSS OF SECTION OF REFRACTORY LINING

COOLER DRIVES OR CLINKER BELT STOPPED

RED CLINKER AT COOLER DISCHARGE

RAPID RAISE OF TEMPERATURE IN COAL SYSTEM

POWER FAILURE

A CHAIN FIRE

HEAVY RAIN OR THUNDERSTORMS

SUDDEN, HIGH POSITIVE HOOD PRESSURE

OVERHEATED KILN BEARINGS

KILN HAZARDOUS CONDITIONS

KILN OPERATION SECTION

KILN OPERATION TECHNIQUES

BURNING ZONE EVALUATION