COOLER
FUNCTION
a) The main function of the cooler is to recuperate the heat contained in the clinker coming from the kiln as heat recovery from secondary, tertiary and to coal mill air is important for kiln efficiency and fuel saving.
b) The cooler must also lower the temperature of the clinker before it leaves so it can be safely transported to the storage area
c) The clinker breaker at the cooler outlet reduce the clinker size so it can be transported on the conveyor system
COOLER OPERATION
Cooling of the clinker material is accomplished by forcing ambient air upward through the material as it is being conveyed through the length of the cooler by reciprocating action of the grates.
The clinker cooler is divided into two major areas, which are separated by the grate line. They are the over grate area where the clinker is cooled down and where the hot gases are handled and the under grate compartment where cooling air is blown into the system.
The grate line consists of many perforated grate plates arranged in overlapping rows. The alternate rows are movable and are connected to a wheel mounted frame which is moved back and forth on its tracks by a crank type drive that drives the grates their reciprocating motion. See figures 2 to 6.
In normal operation, the cooler is running in auto to keep a constant under grate pressure and air flow under the second compartment in order to control the secondary air temperature.
However under upset conditions, the cooler must be switched on manual.
COOLER CONTROLLERS In normal operation:
The speed of the grate change the residence time of the clinker inside the cooler (to control the cooling rate of the clinker and to protect the grate to get overheated)
The air flow distribution under each compartment to maintain good heat recuperation and good cooling of the clinker
In case of emergency: (such as a badly overheated cooler condition, the operator must always)
Decrease the kiln speed in order to reduce the clinker input to the cooler and control the heat input
OPERATION OBJECTIVES
To keep as much as possible:
The clinker temperature at the cooler discharge as low as possible (high temperature could damage the clinker transport system)
The secondary air temperature as stable and as high as possible to get the best recuperation from the clinker and improve the fuel efficiency of the kiln
To keep the depth of the clinker bed near 15” water gage inorder to get good heat recuperation from the clinker in cooler (according to fan capacity)
To keep the hood pressure always slightly negative
To set the cooler fans flow in such away to have enough capacity to get air through the clinker bed and to insure proper cooling of the grates and the clinker load inside the cooler
Cooler settings should be such that bed grates, cooler drive unit, clinker crusher, cooler wall and clinker conveyors system cannot become overheated.
RULE IN COOLER OPERATION
A fundamental rule on grate cooler is to never permit raw feed or extremely fine clinker to enter the cooler as the cooler can become overheated and damage.
During kiln pushes, lower the kiln speed in order to reduce fine clinker input in the cooler.
Never run the kiln with positive pressure as this result in troubled kiln operating conditions as:
Fine clinker in nose ring resulting to wear of kiln seal Viewing in kiln is unpleasant and unsafe
Could damage the optical equipment and the TV camera
Formation of rings and “snowmen” in cooler inlet can be attributed to positive pressure
Exception: One exception to this rule if ever very high temperature in cooler and if needed to introduce sufficient air in cooler.
MAIN SENSORS
The Main Sensors to Control the Cooler Operations are:
The fans flow for each compartment
The under grate pressures under grate #1 and #2 The secondary air temperature
The grate speed under grate #1 and #2
The clinker discharge temperature at the cooler outlet
Also Secondary Sensors as:
Grate temperature in #1 and #2 compartments TV camera showing the cooler interior
Hood Draft
Control by regulation the excess air inside the cooler by the cooler exhaust fan damper It maintains a constant pressure in front of the kiln
A good hood pressure regulation is important for the burning zone stability
Assuming other Factors Remain Constant:
An increase in the ID fan speed will lower the hood pressure A decrease in the ID fan speed will increase the hood pressure
Also increasing the amount of air in cooler results in higher hood pressure
Under Grate Pressures and Air Flow Rates
The under grate pressure is govern by the following factors:
Depth of the clinker bed over the grate Average particle size of clinker in the cooler Amount of air flow into the cooler
Should be at 15” water gage (under 2nd compartment) to get good heat recuperation
Clinker Bed Depth
The depth of the clinker bed is controlled by the speed of the cooler grate
The faster the grate, the thinner becomes the bed and lower is the under grate pressure
Because of the relation between the grate speed, bed depth and under grate pressure, it is possible to maintain a constant under grate pressure by regulating the grate speed
It is usually done under the second compartment of the cooler because it is that location at the cooler inlet where the clinker bed is more stable and give an early and good under grate pressure signal for the automatic cooler control.
PARTICLE SIZE OF CLINKER
A critical factor in under grate reaction is the average particle size of the clinker in the cooler.
A fine clinker bed impose more resistance against air flow, when the under grate pressure increase, the fan has to use more force to push the air through this kind o f bed
Then the under grate pressure increase when the clinker gets finer because the smaller particles impede the air flow through the bed
Therefore, the airflow rate is increased to restore the normal flow through the bed and the clinker bed can become fluidized
A fluidized clinker bed is highly undesirable and dangerous, because the bed in such a state does not move along properly in the cooler
On horizontal grate, the clinker tend to remain stationary and tend to build on top of the grates and when sufficient weight has been acquired by the bed, it starts to move again
So the clinker cannot be properly cooled down and could choke off the airflow through the bed
OPERATION OF COOLER FANS
The air volume for cooler fans is most commonly carried out by means of fan outlet damper.
The fan speed is constant so it is necessary to change the position of the damper to reduce or to increase the air moved by the fan.
Fan damper is normally open at 60% as necessary leeway is required to increase air flow.
Maximum air flow is when the fan damper reached about 88% open.
The air volume output is directly related to the under grate pressure.
The fan must have sufficient capacity to provide necessary amount of air at maximum under grate pressure.
The maximum operating under grate pressure needs to take into account the cooler fans capacity.
Flow rate for each fan and under grate pressure set point need to be set on for a good cooler operation.
The fan manufacturers provide performance curve for each compartment fan.
Fan Static Pressure
Fan static pressure is the total pressure developed by the fan, less the velocity pressure in the fan discharge duct.
For practical purposes, fan static pressure in a cooler system is equal to the under grate pressure, and the air flow is a function of this static pressure and the power applied to the fan. (Figure 7)
Whenever the under grate pressure exceed the limit of the fan, the flow decreases and less cooling is taking place then the cooler could be damaged.
CLINKER AND AIR DISTRIBUTION
For proper cooling, it is essential that clinker is evenly spread over the width of the cooler so that the bed offers a uniform resistance of the air passage through its width.
When clinker passes to one side of the cooler leaving a thinner bed on the other side, the air will naturally seek a passage through the bed where it offers the least resistance.
So air passes through bed where it is least needed and little air passes where it is needed most.
Formation of “snowmen” at the cooler inlet is the prime cause of this condition.
Various devices as dead grate, spreaders or grate with their own air supply to spread the clinker rapidly over the width of the cooler inlet are used to fight “snowmen” formation.
For proper air distribution and good cooler regulation, no air should freely pass from one cooler compartment to another through leaks or other opening on the compartment walls.
The under grate pressure is usually set that the highest pressure is found in the first compartment, and the lowest in the last compartment.
Emergency High Clinker Temperature
Installed on the drag conveyor is this sensor to measure the clinker temperature at the cooler discharge.
If the clinker temperature is above 300oF (150oC), it will transfer the clinker to the emergency bin automatically and will stay there until the desired temperature will come back. High clinker temperature is caused by inadequate cooling of clinker in cooler.
Guideline:
In cooler normal operation, no red clinker should be seen passing the third compartment.