Clinker Coolers

Functions

• Hot clinker is to be cooled rapidly to secure a phase composition that imparts adequate cementitious properties.

• Heat exchange between clinker and air has to be efficient to ensure proper cooling and, at the same time, maximizing the recovery of heat to secondary and tertiary air.

A cooler has to accomplish these tasks efficiently and simultaneously. At the discharge end of the kiln the red hot clinker contains around 1.0 million Btu per short ton thermal energy.

Types of Coolers

• Rotary Coolers• Planetary Cooler• Shaft Coolers• Grate Coolers• Cross bar Coolers

Rotary Coolers

• Appears like another rotary kiln after rotary kiln. The cooler is inclined at 2.5o and speed of rotation is 3 rpm. The drive power consumption is about 3.5 kWh/ton. The clinker temperature after cooling is 200oC to 250oC.

Planetary Cooler

• A planetary cooler consists of a no. of cooling tubes mounted around the circumference of the kiln shell. It requires no excess air to handle, no fans or motor and no instrument. The power consumption is only about 0.5 to 1.0 kWh/ton of clinker, added to the kiln drive and exhaust fan, making it lowest for any kind of kiln.

• These coolers were popular in 1960 and 1970, when no. of cement plants came up with 4 stage pre-heaters.

Shaft Coolers

• This type of cooler has fairly even size distribution. The upper part is used as a fluidized bed in order to avoid agglomeration.

• Power requirement is 10-12 kWh/ton • With minimum air clinker discharge

temperature: 300 oC- 350 oC, but is reduced by water injection.

Grate Coolers• Cooling air moves cross current to the direction of clinker movement.• Clinker discharge temperature can be achieved up to 80oC, however, it needs more air,

which is to be recovered and de-dusted. Amount of air required is between 2.3 to 3.3 kg/kg of clinker but cooling air fans capacity is designed to allow the introduction of 4.5 kg of air per kg of clinker.

• Specific load on grate cooler built after 1975 is 30-40 Metric ton per dat per sq. meter grate area, which was 20 Metric ton earlier.

• Cooler consists of one or several grate. These grates can be named as grate-1, grate -2, grate -3 etc. Each grate consists certain no. of rows of grate plates.

• The air to the grates is supplied in various ways through air blower in to compartments under the grates or blown into ducts (called as air beam) connected directly to a limited no. of grates.

• The grate may be horizontal or inclined.• Normal clinker bed thickness is 600 mm on the grate.• More air is used in the hotter part of grate, which may be up to 200 kg/min/m2 and less in

the colder part 40 kg/min/m2.• The width of the grate is reduced at the inlet in order to spread the clinker more evenly.• With high air flow and thick layer of clinker, it provides uniform bed thickness.

Cross bar Coolers

• Developed in 1990s.• Clinker is conveyed by wedge-shaped bars suspended above

the grates.• Grate plates are all stationary.• Since the plates no longer moves, they have been made larger.• The traditional size of grate plates is 30x30 cm, whereas cross

bar cooler plats are 1x1 meter in size.• The air is supplied to each plate individually.• The amount of cooling air in reduced from 2.8 to 1.9 kg air per

kg of clinker, resulting in low power consumption of 4.0 kWh/ton clinker cooled.

Typical operational data of different cooler used in dry process kiln

Parameters units Planetary Rotary Shaft Grate Cross-Bar

Cooling Air requirement Total Cooling air Kg of air/ kg

clinker 1.1 1.1 1.3 2.8 1.9

Excess air to vent Kg of air/ kg clinker

0 0 0 1.7 0.8

Clinker Discharge Temperature After Cooler oC 160 220 360 80 100 After Cooler with water oC 120 160 150 NA NA Power Consumption kWh/Ton of

Clinker 0.8 3.5 12 7 4

Thermal Efficiency* % 67 70 74 60 71

*Thermal Efficiency of the cooler can be given as:

Control of Grate Coolers• Constant air through the clinker bed in terms of air per unit area

of cooler and per unit mass of clinker.• Negative pressure in the kiln hood to ensure proper supply of

secondary and tertiary air for fuel consumption in kiln and pre-calciner.

• Under grate air pressure • Grate speed for proper movement and retention of clinker in

cooler.• Clinker bed height

Optimization of grate cooler operation:• Optimizing the amount and temperature of Secondary air.• Maximizing the uniformity of operation

Undesirables

• Snow man formation• Red river formation

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