clinker coolers

CLINKER COOLERS

By: Oliver Christian D. DeyparineIndustrial Processes – Cement Making

04/11/2023 08:16 AMOliver Christian Deyparine™ All Rights Reserved. © 2010

THE PURPOSE OF A COOLER IS, OBVIOUSLY, TO COOL THE CLINKER. THIS IS IMPORTANT FOR SEVERAL REASONS:

From an engineering viewpoint, cooling is necessary to prevent damage to clinker handling equipment such as conveyors.

From both a process and chemical viewpoint, it is beneficial to minimise clinker temperature as it enters the clinker mill. The clinker gets hot in the mill and excessive mill temperatures are undesirable. It is clearly helpful, therefore, if the clinker is cool as it enters the mill.

From an environmental and a cost viewpoint, the cooler reduces energy consumption by extracting heat from the clinker, enabling it to be used to heat the raw materials.

From a cement performance viewpoint, faster cooling of the clinker enhances silicate reactivity.

The cooled clinker is then conveyed either to the clinker store or directly to the clinker mill. The clinker store is usually capable of holding several weeks' supply of clinker, so that deliveries to customers can be maintained when the kiln is not operating.


WHAT IS CLINKER COOLER?

The clinker cooler is an integral part of the kiln system and has a decisive influence on performance and economy of the pyroprocessing plant. The cooler has two tasks: to recover as much heat as possible from the hot (1450 °C) clinker so as to return it to the process; and to reduce the clinker temperature to a level suitable for the equipment downstream.


PYROPROCESSINGSYSTEM


CLINKER COOLER

Heat is recovered by preheating the air used for combustion in main and secondary firing as close to the thermodynamic limit as possible. However, this is hindered by high temperatures, the extreme abrasiveness of the clinker and its wide granulometric range. Rapid cooling fixes the mineralogical composition of the clinker to improves the grindability and optimise cement reactivity.


Cooler - red-hot clinker falls onto the grate, cooled by air blown from beneath. The clinker is moving towards the

front of the picture. (Picture courtesy Cemex UK Cement)


The clinker cooling operation recovers up to 30% of kiln system heat, preserves the ideal product qualities, and enables the cooled clinker to be maneuvered by conveyors. The most common types of clinker coolers are reciprocating grate, planetary, and rotary. Air sent through the clinker to cool it is directed to the rotary kiln where it nourishes fuel combustion. The fairly coarse dust collected from clinker coolers is comprised of cement minerals and is restored to the operation. Based on the cooling efficiency and desired cooled temperature, the amount of air used in this cooling process is approximately 1-2 kg/kg of clinker. The amount of gas to be cleaned following the cooling process is decreased when a portion of the gas is used for other processes such as coal drying.


Typical problems with clinker coolers are thermal expansion, wear, incorrect air flows and poor availability, which work against the above requirements.

There are two main types of coolers: Rotary Grate.


ROTARY COOLERS

TYPES:

The Tube Cooler The Planetary Cooler


THE TUBE COOLER

The tube cooler uses the same principle as the rotary kiln, but for reversed heat exchange. Arranged at the outlet of the kiln, often in reverse configuration, i.e. underneath the kiln, a second rotary tube with its own drive is installed. After kiln discharge, the clinker passes a transition hood before it enters the cooler, which is equipped with lifters to disperse the product into the air flow. Cooling air flow is determined by the air required for fuel combustion. Apart from the speed, only the internals can influence the performance of the cooler. Optimisation of lifters must consider heat exchange (dispersion pattern) versus dust cycle back to the kiln.


THE PLANETARY (OR SATELLITE) COOLER

The planetary (or satellite) cooler is a special type of rotary cooler. Several cooler tubes, typically 9 to 11, are attached to the rotary kiln at the discharge end. The hot clinker enters through openings in the kiln shell arranged in a circle at each point where a cooler tube is attached. The quantity of cooling air is determined by the air required for fuel combustion and enters each tube from the discharge end, allowing counter-current heat exchange. As for the tube cooler, internals for lifting and dispersing the clinker are essential. There are no variable operating parameter. High wear and thermal shock, in conjunction with dust cycles, mean high clinker exit temperatures and sub-optimum heat recovery are not unusual. Clinker exit temperature can only be further reduced by water injection into the cooler tubes or onto the shell.

Because it is practically impossible to extract tertiary air, the planetary cooler is not suitable for precalcination. Secondary firing with up to 25% fuel in the kiln riser area is possible, however.


GRATE COOLERS

TYPES:

Travelling Grate Cooler Reciprocating Grate Cooler,

Conventional Reciprocating Grate Cooler, Modern


Cooling in grate coolers is achieved by passing a current of air upwards through a layer of clinker (clinker bed) lying on an air-permeable grate. Two ways of transporting the clinker are applied: travelling grate and reciprocating grate (steps with pushing edges).

Since the hot air from the aftercooling zone is not used for combustion, it is available for drying purposes, e.g. raw materials, cement additives or coal. If not used for drying, this cooler waste air must be properly dedusted.


TRAVELLING GRATE COOLERS

In this type of cooler, clinker is transported by a travelling grate. This grate has the same design features as the preheater grate. Cooling air is blown by fans into compartments underneath the grate. Advantages of this design are an undisturbed clinker layer (no steps) and the possibility of exchanging plates without a kiln stop. Due to its mechanical complexity and poor recovery resulting from limited bed thickness (caused by the difficulty of achieving an effective seal between the grate and walls), this design ceased to be used in new installations around 1980.


RECIPROCATING GRATE COOLER, CONVENTIONAL

Clinker transport in the reciprocating grate cooler is effected by stepwise pushing of the clinker bed by the front edges of alternate rows of plates. Relative movement of front edges is generated by hydraulic or mechanical (crankshaft) drives connected to every second row. Only the clinker travels from feed end to discharge end, but not the grate.

The grate plates are made from heat resistant cast steel and are typically 300 mm wide and have holes for the air to pass through them.



Cooling air is insufflated from fans at 300-1000 mmWG via compartments located underneath the grate. These compartments are partitioned from one another in order to maintain the pressure profile. Two cooling zones can be distinguished:

- the recuperation zone, from which the hot cooling air is used for combustion of the main burner fuel (secondary air) and the precalciner fuel (tertiary air);

- the aftercooling zone, where additional cooling air cools the clinker to lower temperatures.



The largest units in operation have an active surface of about 280 m2 and cool 10000 tonnes/day of clinker. Typical problems with these coolers are segregation and uneven clinker distribution leading to air-clinker imbalance, fluidisation of fine clinker (red river) and also build ups (snowmen) and less than ideal life of plates.


RECIPROCATING GRATE COOLER, MODERN

Introduction and development of modern technology reciprocating grate coolers started around 1983. The design aimed to eliminate the problems with conventional coolers thus coming a step closer to optimum heat exchange and also more compact coolers using less cooling air and smaller dedusting systems.



Key features of modern cooler technology are (depending on supplier):

- modern plates with built-in, variable or permanent, pressure drop, permeable to air but not clinker;

- forced plate aeration via ducts and beams;- individually adjustable aeration zones ;- fixed inlet;- fewer and wider grates;- roller crusher;- heat shields.


GRAND COULEE DAMGrand Coulee Dam, which used nearly 10 million cubic yards of concrete, making it one of the largest portland cement concrete projects in history

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clinker coolers

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